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Water is a suitable medium for the Petasis-borono-Mannich multicomponent reaction. Salicylaldehyde, glyoxalic acid, glycoaldehyde and glyoxal were reacted with several boronic acids and different amines affording alkylaminophenols, 2H-chromenes, α-amino acids, α-amino alcohols and 2-hydroxylmorpholines in good to high yields. An efficient new one-pot method for the assembly of boron-heterocycles based on amino-acids, boronic acids and salicylaldehyde using water as the reaction media is presented. The mechanisms of these reactions were studied by means of DFT calculations, and the effect of solvent on the calculated energy barriers was addressed, for different aldehydes.

Spiro[2,4]hepta-4,6-diene and spiro[4,4]nona-1,3-diene react with [Mo(CO) 2 Cp’(NCCH 3 ) 2 ][BF 4 ] (Cp’ = Cp, Ind; Ind = η 5 -C 9 H 7 ) to afford the corresponding diene complex [Mo(diene)(CO) 2 Cp′] + . When Cp’ = Ind, the reaction proceeded forward leading to ring opening in the case of the small spiro ring. Although this and another product resulting from migration of the side arm to the carbonyl were detected when Cp’ = Cp, they did not form from the diene complex. A DFT/PBE1PBE study was carried out and showed a kinetically controlled reaction pathway leading from the [Mo(diene)(CO) 2 Ind] + to the reaction product, with an activation barrier of 21.3 kcal mol −1 . The thermodynamic preferred species was the non-observed complex (insertion), and its formation required higher barriers. In the presence of Cp, all the barriers increased significantly, explaining the inertness of the initial diene complex. The interpretation of this behaviour is associated with the ease of the η 5 → η 3 haptotropic rearrangement of the indenyl, which helps to lower some relevant barriers. This route is not available for the Cp analogue.

Iminopyrrolyl complexes of sodium were prepared from the reaction of 2-arylformiminopyrrole ligand precursors (aryl = C(6)H(5) (I); 2,6-Me(2)C(6)H(3) (II); 2,4,6-Me(3)C(6)H(2) (III); 2,6-(i)Pr(2)C(6)H(3) (IV)) with one equivalent of sodium hydride. The resulting corresponding compounds 1-4, [{Na(mu(2):kappa(2)N,N'-iminopyrrolyl)}(2n)(OEt(2))(2x)] (nor = 1; x = 0 or 1), were obtained in moderate to high yields and were characterised by NMR spectroscopy, high resolution mass spectrometry and X-ray diffraction, when suitable crystals were obtained. The X-ray structure of compound 1 (n1; x = 0) reveals the formation of a coordination polymer with repeating units consisting of dimers that contain two iminopyrrolyl ligands chelating two sodium atoms, where both pyrrolyl rings exhibit bridging sigma + sigma coordination to the Na atoms within the dimer; the self-assembling of the polymer is established by additional pi-bonds (eta(5)-coordination) of each of the pyrrolyl rings to the sodium atoms of the adjacent dimer units. Conversely, the structure of complex D(IV) (n = x = 1) shows it as one of such dimers capped by two diethyl ether molecules, each coordinated to the sodium atoms (n = 2; x = 1). DFT calculations indicate that the differences between the structures 1-4 of arise from the increasing bulkiness imposed by the corresponding substituents of the iminic aryl groups.

Several new iron(II) complexes of the types [Fe(PNP)X2] (X = Cl, Br) containing tridentate PNP pincer-type ligands based on 2,6-diaminopyridine and 2,6-diaminopyrimidine have been prepared. They all exhibit intermolecular Fe−X···H−N hydrogen bonds, forming supramolecular networks in the solid state. In the case of X = Cl these compounds react readily with gaseous CO both in the solid state and in solution to give selectively the octahedral complexes cis- and trans-[Fe(PNP)(CO)(Cl)2], respectively, whereas with X = Br mixtures of cis and trans isomers are obtained. These transformations are accompanied by color and spin-state changes. CO binding is fully reversible in all cases, and heating solid samples of either cis- or trans-[Fe(PNP)(CO)(X)2] leads to complete regeneration of analytically pure [Fe(PNP)(X)2]. Mossbauer spectroscopy confirmed the high-spin nature of the parent five-coordinate Fe(II) complex (δ = 0.80(1) mm s−1) and the shift to two different low-spin octahedral species after reaction with...

The axial coordination of N-heterocyclic carbene ligands onto dirhodium(II) complexes was examined, together with its role in the intramolecular C-H insertion reactions of alpha-diazoacetamides. The formation of a decarbonylated product occurs by a free-carbene mechanism in which the structures of the catalyst and the acetamide play a decisive role.. - Fundacao para a Ciencia a Tecnologia [POCI 2010]; FEDER [PTDC/QUI/66695/2006, PTDC/QUI/66015/2006, SFH/BPD/46589/2008, SFRH/BD/30619/2006]. - We thank to Fundacao para a Ciencia a Tecnologia (POCI 2010) and FEDER (PTDC/QUI/66695/2006, PTDC/QUI/66015/2006, SFH/BPD/46589/2008 and SFRH/BD/30619/2006) for their financial support, and the Portuguese NMR Network (IST-UTL Center) for providing access to the NMR facility.

Pulsed gradient spin-echo (PGSE) diffusion characteristics for a) the new [brucinium][X] salts 6 a-f [a: X = BF(4)(-); b: X = PF(6)(-); c: X = MeSO(3)(-), d: X = CF(3)SO(3)(-); e: X = BArF(-); f: X = PtCl(3)(C(2)H(4))(-)], b) 4-tert-butyl-N-benzyl analogue, 7 and c) the aryl carbocations (p-R-C(6)H(4))(2)CH 9 a (R = CH(3)O) and 9 b (R = (CH(3))(2)N), (p-CH(3)O-C(6)H(4))(x)CPh(3-x)(+) 10 a-c (x = 1-3, respectively) and (p-R-C(6)H(4))(3)C(+) 11 (R = (CH(3))(2)N) and 12 (R = H) all in several different solvents, are reported. The solvent dependence suggests strong ion pairing in CDCl(3), intermediate ion pairing in CD(2)Cl(2) and little ion pairing in [D(6)]acetone. (1)H, (19)F HOESY NMR spectra (HOESY: heteronuclear Overhauser effect spectroscopy) for 6 and 7 reveal a specific approach of the anion with respect to the brucinium cation plus subtle changes, which are related to the anion itself. Further, for carbocations 9-12, (all as BF(4)(-) salts) based on the NOE results, one finds marked changes in the relative positions of the BF(4)(-) anion. In these aryl cationic species the anion can be located either a) very close to the carbonium ion carbon b) in an intermediate position or c) proximate to the N or O atom of the p-substituent and remote from the formally positive C atom. This represents the first example of such a positional dependence of an anion on the structure of the carbocation. DFT calculations support the experimental HOESY results. The solid-state structures for 6 c and the novel Zeise's salt derivative, [brucinium][PtCl(3)(C(2)H(4))], 6 f, are reported. Analysis of (195)Pt NMR and other NMR measurements suggest that the eta(2)-C(2)H(4) bonding to the platinum centre in 6 f is very similar to that found in K[PtCl(3)(C(2)H(4))]. Field dependent T(1) measurements on [brucinium][PtCl(3)(C(2)H(4))] and K[PtCl(3)(C(2)H(4))], are reported and suggested to be useful in recognizing aggregation effects.

Green and fast: Allylation of aromatic and aliphatic thiols, by using allyl alcohols as substrates, requires only minutes at ambient temperature with a Ru catalyst (see scheme). Quantitative conversion is normal and the catalyst possesses high functional-group tolerance.The allylation of aromatic and aliphatic thiols, by using allyl alcohols as substrates, requires only minutes at ambient temperature with either a Ru(IV) catalyst, [Ru(Cp*)(eta(3)-C(3)H(5))(CH(3)CN)(2)](PF(6))(2) (2; Cp*=pentamethylcyclopentadienyl) or a combination of [Ru(Cp*)(CH(3)CN)(3)](PF(6)) and camphor sulfonic acid. Quantitative conversion is normal and the catalyst possesses high functional-group tolerance. The use of [Ru(Cp*)(CH(3)CN)(3)](PF(6)) alone affords poor results. A comparison is made to the results from catalytic runs based on the use of carbonates rather than alcohols, by using 2 as the catalyst, and it is shown that the products from the alcohols are formed faster, so there is no advantage in using a carbonate substrate. The observed branched-to-linear (b/l) ratios when using substituted alcohols decrease with time suggesting that the catalysts isomerise the products. A new methodology from which one can select the desired isomeric product is proposed. DFT calculations and NMR spectroscopic measurements, by using an arene sulfonic acid as co-catalyst, suggest that eta(6)-complexes are not relevant for the catalytic system. Moreover, the DFT results indicate that 1) any eta(6)-complexes from the acids RC(6)H(4)SO(3)H result from deprotonation of the acid, 2) complexation of the thiol, via the deprotonated sulfur atom, is preferred over complexation of the O atom of the sulfonate, RC(6)H(4)SO(3) (-) and 3) a sulfonate O-atom complex will be difficult to detect.

The Ru-catalyzed allylation of differing indole compounds using ArCH(OH)CH═CH2 (Ar = Ph, 2-CH3C6H4, 2-CH3OC6H4 2-ClC6H4, and 1-naphthyl) is relatively fast (usually

Water was used as the solvent in the Petasis borono-Mannich reaction. With the use of salicylaldehyde, secondary amines and boronic acids, several alkylaminophenols were obtained in considerably high yields in water. By using the same methodology, 2H-chromenes were prepared with the use of vinyl boronic acids. The reaction mechanism was studied by DFT calculations, and the results obtained corroborate the solvent effect experimentally observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The reaction of two commercially available compounds, phenanthrenequinone and 2,6dialkylaniline (alkyl = Me, iPr), catalyzed by formic acid, in refluxing methanol, gave rise exclusively to 10-(2,6-dialkyl-phenylimino)-10H-phenanthren-9-one compounds (alkyl = Me (1), iPr (2)). In refluxing toluene, and when diisopropylaniline is employed, the heterocyclic compound 7-isopropyl-3,3-dimethyl-10'H-spiro(indoline-2,9'-phenanthren)-10'-one (3) was unexpectedly prepared as the major reaction product, in the presence of catalytic amounts of various Bronsted acids. DFT calculations indicate that the conversion of 2 into 3 involves a sigmatropic rearrangement as rate limiting step with a high energy barrier (25-28 kcal/mol), in agreement with the requirement of high reaction temperatures.

A study of the reactivity of [MoCpBz(CO)3H] (CpBz = pentabenzylcyclopentadienyl) as a catalyst precursor for the ionic hydrogenation of 3-pentanone is presented. The complexes [MCpBz(CO)3OTf] (M = Mo (3), W (4)), [MoCpBz(CO)3(O═CEt2)]BF4 (9), and [MoCpBz(CO)3(O═CMe2)]BF4 (12) are described. 9+ and [MoCpBz(CO)3(OHCHEt2)]+ (8+) were identified by NMR under catalytic conditions. The reaction of [WCpBz(CO)3H] with triflic acid led to [WCpBz(CO)3(H)2]+ (7+), which was identified by NMR as a dihydride complex. The influence of steric and electronic effects on the catalyst activity is discussed on the basis of experimental results and a mechanism proposal resulting from DFT calculations. The proposed mechanism includes facile protonation of the acetone O atom promoted by a dihydride Mo(IV) complex, followed by slower hydride transfer from the metal center to the carbonyl C atom. The results indicate strong coordination of both the product (isopropyl alcohol) and the reactant (acetone), leading to some blocking o...

The dicationic Ru(IV) salt [Ru(Cp*)(η3-C3H5)(CH3CN)2](PF6)2 is shown to be an excellent and rapid catalyst for the C-allylation of indole compounds using allyl alcohols as substrates. Selective, one-pot N,C-double allylation is also possible. Preliminary experiments suggest that vinyl epoxides may be used as an allyl source. Stoichiometric reactions of CH2═CHCH(OH)CH═CH2, CH2═CHCH(OAc)CH═CH2, and CH2═CHCH═CHCH2Br with [Ru(Cp*)(CH3CN)3](PF6) afford new Ru(IV) η3-vinyl-allyl salts, two of which, [Ru(Cp*)(κ2-OAc)(η3-vinyl-allyl)](PF6) (13) and [Ru(Cp*)Br(η3-vinyl-allyl)(CH3CN)](PF6) (14), have been studied by X-ray diffraction methods. In addition to the Ru(IV) η3-vinyl-allyl bonding mode, we also find an isomer of the bromo salt 14 possessing a dynamic Ru(IV) S (rather than U)-shaped η5-pentadienyl moiety, 20. DFT computational results for 20 indicate that the S-shaped rather than the U-shaped form is the most stable Ru(IV) species and that the stability difference between these two forms is mainly due to i...

Light from a mercury vapor high-pressure lamp was used to induce the photolytic decomposition of alpha-diazo acetamides in hexane and in nonconventional media such as water or a film. The corresponding beta- and/or gamma-lactams were obtained in reasonable yields and in some cases with good diastereoselectivities with no need to use a metallic catalyst. Experimental studies on chiral substrates demonstrated the occurrence of insertion with retention of configuration.

Exposure of a series of zirconocene amido and hydrazido hydride complexes, (η5-C5Me4H)2Zr(NHR)H (R = tBu, NMe2, Me, H), to 4 atm of D2 gas at 56 °C produced isotopic exchange in both the N−H and Zr...

The Bronsted acid-mediated reaction of unactivated alkynes with aryl sulfoxides leads to simultaneous hydration and intermolecular C-C bond formation. This solvent- and metal-free transformation directly delivers α-arylated carbonyl compounds as the products of a formal hydrative arylation in an atom-economical manner. The products bear useful synthetic handles for further functionalization.

Fe(II) hydrido carbonyl complexes supported by PNP pincer ligands based on the 2,6-diaminopyridine scaffold were found to promote the catalytic hydrogenation of CO2 and NaHCO3 to formate in protic solvents in the presence of bases, reaching quantitative yields and high TONs under mild reaction conditions, with pressures as low as 8.5 bar and temperatures as low as 25 °C. NMR and DFT studies highlighted the role of dihydrido and hydrido formate complexes in catalysis.

(Chemical Equation Presented) Efficient dinuclear catalysts: A complex of {Rh2(OAc)4} with two N-heterocyclic carbenes (NHCs) at the axial positions catalyzes the arylation of aldehydes (see picture; R = alkyl, aryl). DFT calculations reveal subtle stereoelectronic effects resulting from the NHC coordination to the dirhodium(II) complex and suggest that complexes with one axial NHC ligand are the catalytically active species. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

A series of 2-iminopyrrole ligand precursors with increasing bulkiness [HNC4H3C(R)=N-2,6-R'2C6H3] (R = R' = H, 1a; R = Me, R'= H, 1b; R = H, R' = Me, 1c; R = R' = Me, 1d; R = H, R' = iPr, 1e; R = Me, R' = iPr, 1f) were synthesized and deprotonated with NaH to give the corresponding iminopyrrolyl sodium salts 2a-f. A set of homoleptic bis-ligand Co(II) complexes of the type [Co(kappa2N,N'-NC4H3C(R)=N-2,6-R'2C6H3)2] (R = R'= H, 3a; R = Me, R'= H, 3b; R = H, R' = Me, 3c; R = R' = Me, 3d; R = H, R' = iPr, 3e; R = Me, R' = iPr, 3f) was prepared by reaction of CoCl2 with the corresponding iminopyrrolyl sodium salts 2a-f. The new complexes were characterized by elemental analysis, magnetic susceptibility measurements, in powder and in solution, UV/vis/NIR, and, in some cases, X-ray crystallography. According to X-ray diffraction and magnetic measurements, the Co complexes 3a-e proved to be tetrahedral, which is the preferred geometry for Co(II) compounds. However, a square planar geometry is observed in the case of 3f, as determined by several characterization techniques. In this case, DFT calculations suggest the square planar geometry is slightly more stable than the tetrahedral one probably due to a combination of steric and electronic reasons.

DFT calculations were used to study the mechanism of all fluxional processes of cyclopentadienyl ligands (Cp = C5H5) in a molybdenum bis(imido) complex, [Mo(η5-Cp)(η1-Cp)(NtBu)2]. Four dynamic processes could be identified: (1) rotation of η5-Cp in its plane, (2) rotation of η1-Cp around the Mo−C bond, (3) metallotropic migration along the ring carbons of η1-Cp, and (4) interchange between the two Cp ligands, η1-Cp and η5-Cp. The mechanism obtained for process 3 corresponds to a [1,2]-migration, in agreement with experimental NMR studies. The mechanism of process 4 corresponds to a single-step path, and the calculated activation energy (15 kcal mol-1) matches exactly the experimental value. No η3-Cp intermediates could be found in any process.

Five pure and four hybrid DFT functionals associated with VDZP, VTZP, and VQZP basis sets are tested (Gaussian 03) for their performance on the geometry optimization of [Ru(η(5)-C5H5)(η(3)-CH2CHCHC6H5)(CH3CN)2](2+). When the calculated geometries were compared with the X-ray structure determination for the analogous complex with permethylated cyclopentadienyl, it was found that in all cases the coordination mode of the η(3)-allyl was very poorly described, despite the functional used. The Ru-C bond distance corresponding to the substituted allyl carbon was overestimated by 0.23-0.50 Å, depending on the functional and the basis set used. These results were reproduced by further testing carried out with the ADF program and larger basis sets. MP2 leads to an acceptable value for the same Ru-C distance, with an underestimation of 0.07 Å, suggesting that, at least in the case of the functionals tested, DFT does not provide an accurate description of a weak Ru-C interaction.

3-Hydrazonocamphor, 3-(RR1NN)C10H14O (R = Me, R1 = H), undergoes intramolecular hydrogen bridging by coordination to platinum or palladium. This effect is evidenced by considerable decrease in the ν(C=O) frequency (compared to the free ligand) in the IR spectra of the complexes [MCl2L2] (M = Pd, Pt; L = 3-(RR1NN)C10H14O) as well as by the magnetic non- equivalence of the two ligands, as revealed by 13C NMR. DFT calculations indicate that coordination of 3-(Me(H)NN)C10H14O promotes E/Z isomerization of the hydrazono group of the ligand, inducing formation of intramolecular hydrogen bonding and corresponding stabilization of the complex. Characterization of the complexes [MCl2L2] (M = Pt; L: R, R1 = Me (1), R = Me, R1 = H (2) and M = Pd; L: R = Me, R1 = H (3)) was performed by analytical and spectroscopic techniques. Redox properties of the 3-hydazonocamphors and their complexes were studied by cyclic voltammetry. The structure of trans-[PtCl2{3-(Me2NN)C10H14O}2] was determined by single-crystal X-ray diffraction analysis. The complex has square-planar geometry and crystallizes in the tetragonal P43 space group.

The synthesis and reactivity of a Co(I) pincer complex [Co(ϰ(3) P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) featuring an η(2)-C(aryl)-H agostic bond is described. This complex was obtained by protonation of the Co(I) complex [Co(PCP(NMe) -iPr)(CO)2]. The Co(III) hydride complex [Co(PCP(NMe) -iPr)(CNtBu)2(H)](+) was obtained upon protonation of [Co(PCP(NMe) -iPr)(CNtBu)2]. Three ways to cleave the agostic C-H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C-H bond cleavage) and reformation of [Co(PCP(NMe) -iPr)(CO)2]. Second, C-H bond cleavage is achieved upon exposure of [Co(ϰ(3)P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) to oxygen or TEMPO to yield the paramagnetic Co(II) PCP complex [Co(PCP(NMe) -iPr)(CO)2](+). Finally, replacement of one CO ligand in [Co(ϰ(3) P,CH,P-P(CH)P(NMe) -iPr)(CO)2](+) by CNtBu promotes the rapid oxidative addition of the agostic η(2) -C(aryl)-H bond to give two isomeric hydride complexes of the type [Co(PCP(NMe) -iPr)(CNtBu)(CO)(H)](+).

Treatment of anhydrous FeX2 (X = Cl, Br) with 1 equiv. of the asymmetric chiral PNP pincer ligands PNP-R,TAD (R = iPr, tBu) with an R,R-TADDOL (TAD) moiety afforded complexes of the general formula [Fe(PNP)X2]. In the solid state these complexes adopt a tetrahedral geometry with the PNP ligand coordinated in κ(2)P,N-fashion, as shown by X-ray crystallography and Mössbauer spectroscopy. Magnetization studies led to a magnetic moment very close to 4.9μB reflecting the expected four unpaired d-electrons (quintet ground state). In solution there are equilibria between [Fe(κ(3)P,N,P-PNP-R,TAD)X2] and [Fe(κ(2)P,N-PNP-R,TAD)X2] complexes, i.e., the PNP-R,TAD ligand is hemilabile. At -50 °C these equilibria are slow and signals of the non-coordinated P-TAD arm of the κ(2)P,N-PNP-R,TAD ligand can be detected by (31)P{(1)H} NMR spectroscopy. Addition of BH3 to a solution of [Fe(PNP-iPr,TAD)Cl2] leads to selective boronation of the pendant P-TAD arm shifting the equilibrium towards the four-coordinate complex [Fe(κ(2)P,N-PNP-iPr,TAD(BH3))Cl2]. DFT calculations corroborate the existence of equilibria between four- and five-coordinated complexes. Addition of CO to [Fe(PNP-iPr,TAD)X2] in solution yields the diamagnetic octahedral complexes trans-[Fe(κ(3)P,N,P-PNP-iPr,TAD)(CO)X2], which react further with Ag(+) salts in the presence of CO to give the cationic complexes trans-[Fe(κ(3)P,N,P-PNP-iPr,TAD)(CO)2X](+). CO addition most likely takes place at the five coordinate complex [Fe(κ(3)P,N,P-PNP-iPr,TAD)X2]. The mechanism for the CO addition was also investigated by DFT and the most favorable path obtained corresponds to the rearrangement of the pincer ligand first from a κ(2)P,N- to a κ(3)P,N,P-coordination mode followed by CO coordination to [Fe(κ(3)P,N,P-PNP-iPr,TAD)X2]. Complexes bearing tBu substituents do not react with CO. Moreover, in the solid state none of the tetrahedral complexes are able to bind CO.

Carbene intermediates are very useful species for a range of reactions including C-H insertions and cycloadditions. They are most commonly generated by metal-catalyzed release of nitrogen gas from diazo precursors. Herein, we present a novel C-H insertion of simple β-ketoamide substrates, through reaction with (diacetoxyiodo)benzene (DIB) in the presence of a base. This unprecedented transformation bypasses the use of either diazo precursors or metal catalysts and directly delivers β-lactam products by an iodonium ylide, in a single step under mild conditions. Mechanistic studies support the intermediacy of a free singlet carbene of unique reactivity and selectivity.

Cleavage of the [Ir(η 4 -COD)Cl] 2 dimer in the presence of the corresponding imidazolium salts and the strong base t BuO − leads to the formation of Ir(I) derivatives of N -heterocyclic carbenes. When halide is replaced by NaCp, a mixture of [Ir(η 4 -COD)(NHC R )(η 1 -Cp)] and [Ir(η 2 -COD)(NHC R )(η 5 -Cp)] is obtained. The latter is favored for R = Cy, while the former predominates for R = Me. Conversely, [Ir(η 4 -COD)(NHC R )(η 1 -Ind)] is the only product of the reaction with NaInd, despite the R substituent. DFT/B3LYP calculations confirmed that the η 1 coordination mode of the ring gives rise to the most stable structures, namely square planar complexes of 5d 8 Ir(I). The energy of the 18 electron species containing η 2 -COD and η 5 -Ind or Cp is higher by 13 and 5 kcal mol −1 , respectively. The fluxional behaviour of indenyl, detected by NMR in the solutions of [Ir(η 4 -COD)(NHC R )(η 1 -Ind)], is associated to the low energy of the η 3 -Ind species required in the conversion process, and is not easily observed in the cyclopentadienyl derivatives, where a similar intermediate is disfavored.

DFT/B3LYP calculations with a VDZP basis set were used to understand the structural preferences of the bis(indenyl) complexes [Zr(Ind)2L] (Ind = indenyl = C9H7-) as a function of the type of ligand...

PGSE diffusion, 1 H, 19 F Overhauser, and related 2-D NMR studies on several salts of the dications [Pd(H 2 O) 2 (BINAP)] 2+ , [Pd(μ-OH)(BINAP)] 2 2+ , and [Pd 2 (μ-OH)(μ-NH(p-RC 6 H 4 ))(BINAP) 2 ], R = Cl, CH 3 , MeO, and, in one case, [Pd(μ-O 2 PF 2 )(BINAP)] 2 (PF 6 ) 2 , are reported. These solution NMR results, together with DFT calculations, reflect on how the anion interacts with the cation, as well as the extent, and the solvent dependence of the ion pairing. The solid-state structure of [Pd 2 (μ-OH)(μ-{NH(p-Tol)})-(BINAP) 2 ](CF 3 SO 3 ) 2 has been determined.

Neutral allylnickel complexes of the general formula [Ni(η3-C3H5)(Im)Br] (where Im = 1,3-di-tert-butylimidazol-2-ylidene (tBu2Im), 1,3,4,5-tetramethylimidazol-2-ylidene (Me4Im), 1,3-dimethylimidazol-2-ylidine (Me2Im)) were prepared from the reaction of the dimer [Ni(η3-C3H5)Br]2 with 2 equiv of the corresponding free N-heterocyclic carbene (NHC). The halide exchange of Br- by I- can be easily performed, giving rise to compounds of the type [Ni(η3-C3H5)(Im)I]. The new complexes [Ni(η3-C3H5) (tBu2Im)Br] (1), [Ni(η3-C3H5)(Me4Im)Br] (2), [Ni(η3-C3H5)(Me2Im)Br] (3), [Ni(η3-C3H5)(Me2Im)I] (4), and [Ni(η3-C3H5)(Me4Im)I] (5) were obtained in good yields and were fully characterized by elemental analysis and NMR spectroscopy. The X-ray crystal structures of 1, 2, 4, and 5 reveal a square-planar geometry at the nickel atom and a tilt angle of the NHC ring (in relation to the Ni square plane) dependent on the bulkiness of both the N substituents and the halogen bound to Ni. Variable-temperature NMR experiments in so...

DFT/B3LYP calculations with a VDZP basis set were used to study the mechanism of interchange between the two inequivalent indenyl ligands (Ind‘ = C6H5R2) in η5/η9 sandwich complexes, [Zr(η5-C6H5R2)(η9-C6H5R‘2)], as a function of the indenyl substituent (R, R‘ = H, CH3, SiH3; R and R‘ on the 1,3-indenyl carbons). The results indicate that haptotropic shifts and, consequently, the ligand interchange process are more favorable in complexes with silylated indenyls than in complexes with alkylated ligands. Both electronic and steric effects play an important role in the rearrangement process, determining the differences found for the two types of substituents. On one hand, alkylated indenyls show a preference for η9-coordination over their silylated counterparts, resulting in stronger metal−(η9-Ind‘) bonds, more stable complexes, and ground-state stabilization of the η5/η9 species. On the other hand, interligand steric repulsion is considerably higher for complexes with alkylated ligands than for silylated ana...

PGSE NMR diffusion, Overhauser and DFT studies on the salts [Pd(η3-CH3CHCHCHPh)(dppe)](anion) (dppe = 1,2-bis(diphenylphosphino)ethane, anion = BF4-, CF3SO3-, BArF-, PF6-) are reported. In dichloromethane solution there is little or no ion pairing for the BArF derivative, whereas the other three anions show intermediate degrees of ion pairing. In chloroform solution the CF3SO3- and BArF- salts show complete ion pairing. The 19F,1H HOESY studies reveal a selective approach of the CF3SO3- and PF6- anions with respect to the allyl ligand. The approach brings the anion somewhat closer to the allyl phenyl ring than to the allyl methyl group. Further, the anion approaches the Pd center from the side of the two terminal allyl protons. The anions are not attracted to the allyl ligand but rather are choosing both an electronically (allyl phenyl vs allyl methyl) and sterically (terminal allyl protons vs central allyl proton) preferred pathway toward the P and metal atoms. This result is partially rationalized via D...

The bonding of pyrrolyl ligands (pyr′) in group-4 metal complexes, [M(pyr′)Cl 3 ], is studied by means of DFT/B3LYP calculations with a VDZP basis set. Two metals (M = Ti, Hf) and two pyrrolyl ligands are addressed, pyr′ = pyrrolyl (pyr), and 2,5-dimethylpyrrolyl (dmp). The study allowed the characterization of the π-pyr′ complexes with a η 5 coordination of this ligand, the σ complexes with the pyr′ bonding established by the nitrogen lone pair, and the transition states for the interconversion between the two isomers. A comparative analysis of the pyr′ bonding to the metal in all the species is provided, as well as a detailed study of the mechanism for the interconversion between the two pyr′ coordination modes. This is a slippage process without significant folding of the pyr′ ring and the activation energies obtained ( E a –1 ) suggest the possible fluxionality between the two coordination modes, in solution. Calculated pyr′–M bond enthalpies show an increase in the bond strength going down the group, allowing a rationalization of the differences in stability of the two coordination modes observed for the various metals and, consequently, of the associated ring slippage process. To cite this article: A.R. Dias et al., C. R. Chimie 8 (2005) . Resume Les liaisons des ligands pyrrolyl dans les complexes metalliques du groupe 4, [M(pyr′)Cl 3 ], ont ete etudiees a l'aide de calculs de fonctionnelle de densite DFT/B3LYP avec une base VDZP. Les deux metaux (M = Ti, Hf) et deux ligands pyrroles pyr′ = pyrrolyl (pyr), et 2,5-dimethylpyrrolyl (dmp) ont ete etudies. L'etude a permis la caracterisation des complexes π-pyr′ avec une coordination η 5 du ligand, des complexes σ avec liaison pyr′ par la paire azote unique et de l'etat de transition pour l'interconversion entre ces deux isomeres. Une analyse comparative de la liaison pyr′–metal dans toutes les especes est donnee, ainsi qu'une etude detaillee du mecanisme de l'interconversion entre les deux modes de coordinaiton des pyr′. Il s'agit d'un processus de glissement sans effet sur le cycle pyr′ ; les energies d'activation ( E a –1 ) amenent a envisager une possible fluxionalite entre les deux modes de coordination en solution. Les enthalpies des liaisons pyr′–M calculees montre une augmentation de la force des liaisons a mesure que l'on descend dans la colonne, ce qui permet de rationaliser les differences de stabilite entre les deux modes de coordination observes pour des metaux varies et, par consequent, le processus de glissement de cycles associe. Pour citer cet article : A.R. Dias et al., C. R. Chimie 8 (2005) .

The mechanisms of three dination modes of the two indenyl li- one crucial step, followed by a smooth closely related reactions were studied gands (η 5 /η 9 , η 5 /η 5 and η 6 /η 9 ), and three transition of the Zr intermediateto the in detail by means of DFT/B3LYP cal- conformations for each isomer (syn, more stable η 5 /η 9 -species. The overall culations with a VDZP basis set. Those anti, and gauche). The fluxionality ob- activation energy calculated (E a = reactions correspond to 1) the reduc- served was found to occur in a mecha- 29 kcal mol - 1 ) compares well with extive elimination of methane from [Zr- nism involving bis(η 5 -Ind) intermedi- perimental values for related species. (η 5 -Ind) 2 (CH 3 )(H)] (Ind=C 9 H 7 - , in- ates, and the calculated activation The formation of the THF adduct foldenyl), 2) the formation of the THF energy (11-14 kcal mol - 1 ) compares lows a one step mechanism from the adduct, [Zr(η 5 -Ind)(η 6 -Ind)(thf)] and 3) very well with the experimental values. appropriate conformer of the [Zr(η 5 -the interconversion between the two Two alternative mechanisms were ex- Ind)(η 9 -Ind)] complex, producing easily indenyl ligands in the Zr sandwich plored for the reductive elimination of (E a =6.5 kcal mol - 1 ) the known prodcomplex, [Zr(η 5 -Ind)(η 9 -Ind)], which methane from the methyl/hydride com- uct, [Zr(η 5 -Ind)(η 6 -Ind)(thf)], a species forms the link between the two former plex. In the more favourable one, the previously characterised by X-ray crysreactions. An analysis of the electronic initial complex, [Zr(η 5 -Ind) 2 (CH 3 )(H)], tallography. This complex was found to structure of this species indicates a sat- yields [Zr(η 5 -Ind) 2 ] and methane in be trapped in a potential well that preurated 18-electron complex. A full un- vents it from evolving to the derstanding of the indenyl interchange 3.4 kcal mol - 1 more stable isomer, [Zr-process required the characterisation of (η 5 -Ind) 2 (thf)], with both indenyl liseveral isomers of the Zr-bis(indenyl) gands in a η 5 -coordination mode and a species, corresponding to different spin spin-triplet state (S=1). states (S=0 and S=1), different coor.

X-ray, 13C NMR, and DFT studies on the cationic Ru(IV) allyl complex Ru(Cp*)Cl(CH3CN)(η3-PhCHCHCH2), as a PF6 salt, have revealed a marked asymmetry in the bonding of the allyl ligand, which can be interpreted as arising from differences in π-bonding from the metal center to the two terminal allyl carbons. This asymmetry in the bonding is offered as an explanation for the observed control of regioselectivity in the Ru-catalyzed allylic alkylation reaction.

Metal–η 5 -cyclopentadienyl (M–Cp) and metal–η 5 -pyrrolyl (M–pyr) bond dissociation enthalpies in group 4 complexes were determined from DFT/B3LYP calculations with a VTZP basis set. Thermochemical cycles involving calculated enthalpies of ligand exchange reactions and experimental values of ligand electron affinities and M–Cl bond dissociation enthalpies were applied to [M(η 5 -X)Cl 3 ] piano stool complexes (M = Ti, Zr, Hf; X = pyr, Cp), allowing a comparative study of those metal–ligand bond strengths. The results indicate that both ligands establish weaker bonds with Ti than with the heavier elements, Zr and Hf. Very similar bond dissociation enthalpies were obtained for pyrrolyl and cyclopentadienyl (within 1 kcal mol −1 ), suggesting that the well known difference in reactivity between those families of complexes should derive from kinetic rather than thermodynamic causes.

The mechanism of formation of an eta4-cyclobutadiene complex from a metallacycle, generated by oxidative coupling of two acetylenes with the fragments CpRuCl, [CpRu(PH3)]+, CpCo, and CpRh, was investigated by means of DFT/B3LYP calculations. Two distinct pathways can be envisaged. 1) A multistep reaction, which can be denoted the Vollhardt mechanism, proceeding via a cyclopropenyl carbene and a tetrahedrane-type intermediate. 2) A one-step transformation involving the formation of a third M-C bond with rearrangement of the metallacyclic ring. Although path 2 is definitely favored over path 1, both pathways are energetically prohibitive unless substituents are present on the acetylene. For the CpRuCl system with HC triple bond CR the barrier varies with R in the series H approximately PhMeSiMe3. On going from H to SiMe3, the barrier for path 2 drops from 41.1 to 26.8 kcal mol(-1). This latter value is already reachable, in agreement with experiment. Whereas the reaction mechanisms involving the fragments CpCo, CpRh, and CpRuCl are very similar (but not identical owing to the additional ligand in CpRuCl), those of [CpRu(PH3)]+ reveal a modification with serious consequences. In both paths 1 and 2, the originally planar metallacycle experiences first a bending distortion induced by the sigma-donor strength of P (in contrast to Cl), which compensates the loss of electrons from the ring brought about by bending. The bent metallacycle is already electronically asymmetric and thus the further course of the reaction is facilitated.

The symmetric bis(iminophosphorano)methanes CH 2 [P{=NP(=O)(OR) 2 }Ph 2 ] 2 (R = Ph (2a), Et (2b)) have been obtained by treatment of bis(diphenylphosphino)methane with a 2-fold excess of phosphorylated azides (RO) 2 P(=O)N 3 . The asymmetric ligand CH 2 [P{=NP(=O)-(OPh) 2 }Ph 2 ][P{=NP(=O)(OEt) 2 }Ph 2 ] (2c) has been prepared by oxidation of Ph 2 PCH 2 P{=NP-(=O)(OEt) 2 }Ph 2 (1b) with (PhD) 2 P(=O)N 3 . Compounds 2a-c can be deprotonated with sodium hydride, affording the corresponding methanide anions NaCH[P{=NP(=O)(OR) 2 }-Ph 2 ] 2 (R = Ph (3a), Et (3b)) and NaCH[P{=NP(=O(OPh) 2 }Ph 2 ] [P{=NP(=O)(OEt) 2 }Ph 2 ] (3c). Treatment of [{Ru(η 6 -p-cymene)(μ-Cl)Cl} 2 ] with 3a-c results in the formation of the neutral complexes [RuCl(η 6 -p-cymene)(κ 2 (C,N)-CH[P{=NP(=O)(OR) 2 }Ph 2 ] 2 )] (R = Ph (4a), Et (4b)) and [RuCl(η 6 -p-cymene)(κ 2 (C,N)-CH[P{=NP(=O)(OPh) 2 }Ph 2 ][P{=NP(=O)(OEt) 2 }Ph 2 ])] (4c), via selective κ 2 (C,N) coordination of the bis(iminophosphorano)methanide anions to ruthenium. The cationic species [Ru(η 6 -p-cymene)(κ 3 (C,N,O)-CH[P{=NP(-O)(OR) 2 }Ph 2 ] 2 )][SbF 6 ] (R = Ph (5a), Et (5b)) and [Ru(η 6 -p-cymene)(κ 3 (C,N,O)-CH[P{=NP(=O)(OPh) 2 }Ph 2 ][P{=NP-(=O)(OEt) 2 }Ph 2 ])] [SbF6] (5c/5c') have been also prepared by reaction of 4a-c with AgSbF 6 . Deprotonation of complexes 4a-c or 5a-c' with NaH generates the unprecedented ruthenium carbenes [Ru(η 6 -p-cymene)(κ 2 (C,N)- [P{=NP(=O)(OR) 2 }Ph 2 ] 2 )] (R = Ph (6a), Et (6b)) and [Ru(η 6 -p-cymene)(κ 2 (C,N)-C[P{=NP(=O)(OPh) 2 }Ph 2 ][P{=NP(=O)(OEt) 2 }Ph 2 ])] (6c). The structures of compounds 2a, 5a, and 6a have been confirmed by X-ray crystallography. DFT calculations on a model for complexes 6a-c, [Ru(η 6 -C 6 H 6 )(κ 2 (C,N)-C[P{=NP(=O)-(OMe) 2 )Me 2 ] 2 )], suggest a nucleophilic character for the carbon atom in Ru=C. In agreement with this theoretical prediction, protonation of complexes 6a-c with HCl or HBF 4 takes place selectively on the carbenic carbon, regenerating 4a-c or 5a-c', respectively.

Te(II) forms binuclear complexes with bridging [{S=P(Ph)(2)}(2)N](-) ligands and axial aryl groups with very long (TeTe)-Te-... distances, while Te(I) analogues with [S2P(R)(2)](-) have no axial ligands and exhibit a Te-Te bond. No such selenium complexes have been found, although a square-planar mononuclear derivative of [{S=P(Ph)(2)}(2)N](-) is available for both Te and Se. In an attempt to study the nature of the (TeTe)-Te-... interaction, a variety of theoretical approaches and basis sets was used in order to find the best way to reproduce the (TeTe)-Te-... distance in the Te(II) derivatives. DFT calculations with the ADF program provided the best answer, since MP2 calculations are more computationally demanding. While the formal oxidation state of Te is a requirement for a Te-Te bond, the type of ligand strongly determines the geometry of the binuclear species. The smaller [S2P(R)(2)](-) leads to more asymmetric species, with Te forming a normal Te-S bond and a very weak one; with [{S=P(Ph)(2)}(2)N](-), both Te-S bonds have comparable lengths. Selenium analogues were found to behave similarly.

The synthesis of the first tungsten azametallocene complexes with pyrrolyl ligands, [W(NC4Me4)2L2], is reported. The dichloro complex (L=Cl) was obtained from the reaction of WCl4DME (DME=1,2-dimethoxyethane) with Li(NC4Me4) in poor yield (6.5%). A small amount (ca. 0.063 g, yield: 15.8%) of the dimethyl complex, [W(NC4Me4)2(CH3)2], resulted from the reaction of the dichloro species (L=Cl) with LiCH3. Both complexes were characterised by 1H, 13C{1H} NMR and mass spectroscopy. Molecular orbital studies based on B3LYP/DFT calculations were performed in order to study the complexes electronic structure, focusing the pyrrolyl coordination mode. Equivalent bond strengths were found for the two extreme coordination modes of that ligand: π coordination (η5) through the pyrrolyl π system, and N-σ coordination established by the nitrogen lone pair. The relative stability of the isomers originated by the different pyrrolyl coordination modes, results from a delicate balance between electronic and stereochemical factors, on each case. The calculations suggest the existence of a fluxional process in solution, involving the π/π and the σ/π isomers of [W(NC4Me4)2(CH3)2].

The bonding geometry of pyrrolyl ligands (pyr') in zirconium complexes was studied by means of DFT/Β3LYP calculations with a DZVP basis set. Monopyrrolyl complexes, [Zr-(pyr')L 3 ], and bispyrrolyl species, [Zr(pyr') 2 L 2 ], were addressed, with different pyrrolyl ligands, pyr' = pyrrolyl (pyr), 2,5-dimethylpyrrolyl (dmp), 2,4-dimethyl-3-ethylpyrrolyl (dmep), and ancillary ligands, L = chloride, methyl. Two coordination modes of pyr' were considered. The first is the π coordination of pyr', with the bonding to the metal established by means of the ring π orbitals. Slightly distorted η 5 coordination results, with the nitrogen tending to approach the metal. The second corresponds to a σ-pyr', with the nitrogen lone pair used to establish a a bond to the metal. The slippage from a π to a δ-pyr' produces an electronically poorer metal center and results, normally, in a less stable complex, although this effect is partially compensated by a strengthening of the Zr-N in the a coordination mode, when compared with the one existing in a π-pyr'. The σ-pyr' coordination and the π-σ slippage were found to be disfavored by substituents in the a carbon atoms of pyr', confirming a known empirical rule. The interconversion between the two coordination modes of the pyr' ligand was studied in all the complexes and determined to correspond to a slippage process without any significant ring folding. In the corresponding transition states the Zr-C bond breaking process is completed for the two β carbon atoms, and the slipping pyr' ring coordinates in a flat η 3 mode. The activation energies calculated for the slippage process in the various species (

The reactions of [Ti(η5-Ind)(NMe2)2Me], [Ti(η5-Ind)(NMe2)Cl2], and [Zr(η5-Ind)(NMe2)2Cl] with 2,6-dimethylphenyl isocyanide (CN(2,6-Me2Ph)) and tert-butyl isocyanide (CN-t-Bu) have been investigated. For the first complex, insertion occurs exclusively into the Ti−C bond to give [Ti(η5-Ind)(NMe2)2{C(Me)N-t-Bu}] (1), which, according to DFT results, is due to the weakness of the Ti−CH3 bond when compared to Ti−NR2. [Ti(η5-Ind)(NMe2)Cl2] was found to react with 1 equiv of CN(2,6-Me2Ph) to yield [Ti(η5-Ind){C(NMe2)N(2,6-Me2Ph)}Cl2] (2). Two equivalents of 2,6-dimethylphenyl isocyanide reacts with [Zr(η5-Ind)(NMe2)2Cl] to give the double insertion compound [Zr(η5-Ind){C(NMe2)N(2,6-Me2Ph)}2Cl] (3). The same reaction performed with CN-t-Bu proceeds slowly and enabled the characterization, by NMR, of [Zr(η5-Ind)(NMe2){C(NMe2)N-t-Bu}Cl] (4) and [Zr(η5-Ind){C(NMe2)N-t-Bu}2Cl] (5). The molecular structures of 2 and 3 have been determined by X-ray diffraction. DFT calculations of the insertion of CNH in the zirconium...

The formally ‘20-electron’ [M(Ind)2L2] complexes (M=Group 6) are studied by means of DFT/B3LYP calculations for L=CO, H, and Cl. The carbonyl derivatives behave similarly for all metals and the preferred conformation of the two indenyl rings is staggered, with one η5- and one η3-indenyl, with the rings oriented in order to maximize back donation to the carbonyls. The calculated structures could be compared with experimentally determined ones for Mo and W, the agreement being very good. When the π-acceptor carbonyls are replaced by hydrides, strong σ-donors, the metal is more electron rich and the rings become the only π-acceptors in the system. As a consequence, the slippage is increased in the most favored conformation, with one η3-indenyl and the other ring having a hapticity between η5 and η3. In the case of the chloride complexes, the situation for Mo and W is intermediate between CO and H, as Cl is a π-donor, but electronegative. Interestingly, the most stable Cr complexes are paramagnetic tetrahedral species with four unpaired electrons, with an energy 63 kcal mol−1 lower than that of the only converged diamagnetic structure.

A gold-catalyzed methylenecyclopropanation of amino-substituted allenes using diphenylsulfonium ylides derived from activated methylene compounds as an interesting safe alternative to diazo compounds is presented.

The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C=O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations.

Three new mononuclear oxovanadium(IV) complexes [VO(acac)(R-BIAN)]Cl (BIAN = 1,2-bis{(R-phenyl)imino} acenaphthene, R = H, 1; CH3, 2; Cl, 3) were prepared and characterized. They promoted the catalytic oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex 3 with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by 2 with tbhp (248 mol mol(V)(-1) h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C=C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex [VO(acac)(H-BIAN)](+) (1(+)) was isolated in an FTICR cell after adding tbhp to 1. EPR studies provide evidence for the presence of a V(IV) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex 1. DFT calculations suggest that a [VO(H-BIAN)(MeOO)](+) complex is the likely active V(IV) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.

A series of allyl complexes of the general formula [Cp'Mo(eta(3)-C3H5)(CO)(2)], where Cp' = Cp, CpMe, Cp*, Ind, IndMe, IndMe2, Flu, and three tungsten analogues, has been prepared and characterized by H-1, C-13, and Mo-95 NMR, cyclic voltammetry, and the structure of [IndMo(eta(3)-C3H5)(CO)(2)] was determined by Xray single crystal analysis. Two conformers, corresponding to the two extreme orientations of the allyl ligand (endo and exo), have been identified in solution by H-1 and Mo-95 NMR for all the complexes, except for [FluMo(eta(3)-C3F15)(CO)(2)], which only presents an exo conformation in solution. A Mo-95 NMR investigation also shows the influence of electron donor capability of the Cp' ligands on the Mo-95 chemical shifts of the Mo center. He I and He II photoelectron spectra probe the electron richness of the metal center and the electronic structure of the complexes. Cyclic voltammetry studies show one oxidation process, which is only reversible for the Cp derivatives. DFT calculations provided a reliable way to determine ionization energies, and reflected very well the trends of the other properties, from the Mo-95 NMR chemical shifts, to vibration frequencies, and oxidation potentials. (1) 2015 Elsevier BY. All rights reserved.

The transferability of the IrI bond enthalpies in [Ir(μ-S t Bu)(I) 2 (CO) 2 ] 2 and trans -[Ir(X)(I) 2 (CO)(PPh 3 ) 2 ] (X=F, Cl, Br, I) complexes was investigated by theoretical calculations based on the B3LYP HF/DFT hybrid functional. It was concluded that the IrI bond snap enthalpy, E s (IrI), in [Ir(μ-S t Bu)(I) 2 (CO) 2 ] 2 was 35 kJ mol −1 smaller than in trans -[Ir(X)(I) 2 (CO)(PPh 3 ) 2 ] and, therefore, not transferable between both types of molecules. The relative magnitude of the obtained E s (IrI) values is in agreement with the slightly longer IrI distance and smaller Wiberg index found, on average, for [Ir(μ-S t Bu)(I) 2 (CO) 2 ] 2 . In this case, however, the computed d IrI and WI IrI do not seem to be sensitive indicators of ‘bond strength’, since a variation of 35 kJ mol −1 in the E s (IrI) values leads to changes of only 0.01 A in the bond distances and 0.005 in the Wiberg indexes. The calculations reproduce the experimental IrI mean bond dissociation enthalpies, 〈 DH °〉(IrI), in the binuclear and mononuclear systems with a maximum deviation of ca. 10 kJ mol −1 .

The eta(5)-to-eta(3) coordination shift of cyclopentadienyl (Cp=C(5)H(5)(-)) and indenyl (Ind=C(9)H(7)(-)) ligands in molybdenocene complexes, [(eta(5)-Cp')(eta(5)-Cp)Mo(CO)(2)](2+) (Cp'=Cp or Ind), driven by a two-electron reduction of those species, was studied and compared by means of molecular orbital calculations (B3LYP HF/DFT hybrid functional, DZP basis sets). The results obtained, in terms of optimized geometries, relative energies, and bond analysis parameters, compare well with the experimental data, and verify the well-known indenyl effect, that is, a significantly more facile eta(5)-to-eta(3) rearrangement for the indenyl ligand when compared to cyclopentadienyl. However, the study of the folding of free Cp and Ind, combined with the (eta(5/3)-Cp')-M bond analysis, shows that the observed difference is not the result of an intrinsic characteristic of the indenyl ligand, such as the traditionally accepted aromaticity gain in the benzene ring formed in eta(3)-Ind complexes. Instead, it is directly related to the Cp'-M bond strength. While the difference in the energy required to fold the two free ligands is negligible (< or =1 kcal mol(-1) for folding angles up to 20 degrees), the (eta(5)-Cp)-M bond is stronger than that of (eta(5)-Ind)-M; however, the opposite situation is found for the eta(3) coordination mode. The net result, for Cp'=Ind, is a destabilization of the eta(5) complexes and a stabilization of the eta(3) intermediates or transition states yielding smaller activation energies and faster reaction rates for processes in which that is the rate-determining step.

New Cu(I) and Ag(I) binuclear complexes were prepared by reaction of [M(NCCH3)4][PF6] (M = Ag, Cu) with the bidentate phosphine ligands Ph2PNHPPh2 (dppa) and Ph2PCH2PPh2 (dppm). In the reaction of Cu(I) with dppa the phosphine is easily oxidized to give the octahedral species of [Cu(dppaO2)3][PF6], 1. In an inert atmosphere, the binuclear complexes [Cu2(dppa)2(NCCH3)3][PF6]2, 2, [Cu2(dppa)2(NCCH3)4][PF6]2, 3, [Ag2(dppa)2(NCCH3)2][PF6]2, 4, and [Ag2(dppm)2][PF6]2, 5, were formed and structurally characterized by X-ray diffraction (except for 5). The electrochemical studies showed that the most relevant property of the binuclear species was the ease of forming the metal upon reduction. EH and DFT calculations were performed in order to try and understand the structural features of the [M2(dppa)2(NCCH3)x]n+ complexes, including the 0.47 A increase in M⋯M distance upon going from 2 to 3.