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5 páginas, 2 figuras, 2 tablas, esquemas., A new method for the synthesis of cationic Pd(IV) complexes, based on the chemical oxidation of an anionic Pd(II) metallacycle in the presence of an additional ligand, is presented. Electrochemical analysis of these compounds reveals that the stability of the +4 oxidation state is sensitive to the electron-donor capability of the added co-ligand and to the steric features of the Tp‘ ligand., Financial support from the DGI (Project PPQ2003-00975), the Ministerio de Educación, Cultura y Deporte (research studentship, D.d.R.), and the Junta de Andalucía is gratefully acknowledged.

Reaction of the hydride complexes [M 2 Cp 2 (μ-H)(μ-PPh 2 )(CO) 4 ] (M = Mo, W; Cp = η 5 -C 5 H 5 ) with [FeCp 2 ]BF 4 proceeds in a 1:2 ratio to give the unsaturated tetracarbonyl salts [M 2 Cp 2 -(μ-PPh 2 )(CO) 4 ]BF 4 , which spontaneously (M = Mo) or in the presence of CO (M = W) transform into the corresponding electron-precise pentacarbonyls [M 2 Cp 2 (μ-PPh 2 )(μ-CO)-(CO) 4 ]BF 4 . In contrast, reaction of the above hydride complexes with [FeCp 2 ](BAr' 4 ) (Ar' = 3,5-C 6 H 3 (CF 3 ) 2 ) proceeds in a 1:1 ratio to give the paramagnetic salts [M 2 Cp 2 (μ-H)(μ-PPh 2 )-(CO) 4 ](BAr' 4 ). No further reaction takes place with [FeCp 2 ](BAr' 4 ) unless a proton acceptor such as water or tetrahydrofuran is present, in which case the corresponding salts [M 2 Cp 2 -(μ-PPh 2 )(CO) 4 ](BAr' 4 ) or [M 2 Cp 2 (μ-PPh 2 )(μ-CO)(CO) 4 ](BAr' 4 ) are rapidly formed. Reactions of the anions [M 2 Cp 2 (μ-PPh 2 )(CO) 4 ] - (as (H-DBU) + salts, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene) with [FeCp 2 ]BF 4 proceed stepwise to give first the 33-electron radicals [M 2 Cp 2 (μ-PPh 2 )(CO) 4 ], which can be isolated as very air-sensitive green solids, and then the unsaturated salts [M 2 Cp 2 (μ-PPh 2 )(CO) 4 ]BF 4 , which are identical to those formed from the neutral hydrides. The structure and dynamic behavior of the new compounds are analyzed on the basis of solution IR, 1 H, 3 1 P, and 1 3 C NMR or ESR spectroscopic data. In addition, the redox and other chemical transformations connecting all the new compounds are??

The complex trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2] is obtained in 91% yield by refluxing toluene solutions of [Fe2Cp2(CO)4] (Cp = η5-C5H5) and the secondary phosphine PPh2H. This compound isomerizes upon irradiation with visible−UV light under a CO atmosphere to yield cis-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2]. The above hydride complexes react under photochemical conditions with 1 equiv of secondary phosphines PR2H (R = Et, Ph) to give the corresponding monocarbonyl compounds [Fe2Cp2(μ-PPh2)(μ-PR2)(μ-CO)] via the hydride intermediates [Fe2Cp2(μ-H)(μ-PPh2)(CO)(PR2H)] (detected and isolated for R = Et). Deprotonation of trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2] with LiBu gives the binuclear anion [Fe2Cp2(μ-PPh2)(CO)2]-. This highly nucleophilic carbonylate reacts rapidly with [AuCl(PiPr3)] or MeI to give the corresponding gold diiron cluster [AuFe2Cp2(μ-PPh2)(CO)2(PiPr3)] or methyl derivative [Fe2Cp2(Me)(μ-PPh2)(μ-CO)(CO)2], respectively. Both hydrides cis- and trans-[Fe2Cp2(μ-H)(μ-PPh2)(CO)2] can be reversibly oxidized at low tempe...

Fast scan rate cyclic voltammetry has been used to elucidate the heterogeneous and homogeneous aspects of the redox chemistry of cis- and trans-[Mn(CN)(CO)2{P(OPh)3}(Ph2PCH2PPh2)]. The cis species, on oxidation, isomerizes to the trans conformation, and the various processes can be understood as components of a square reaction scheme. In solution phase, the homogeneous rate constant for isomeric conversion is found to be independent of solvent and concentration, with a value of 38 s-1 obtained by comparison with digitally simulated responses. The heterogeneous rate constants for the cis0/cis+ and trans0/trans+ couples in acetonitrile have values of 0.06 and 0.065 cm s-1 respectively. The cis or trans complex was readily immobilized on an electrode surface, either by mechanical attachment or by precipitation from solution. However, electrolysis in the solid state was strongly dependent on the identity of the supporting electrolyte anion. This dependence is similar to the Hofmeister series of anions with la...

Frozen solution electron paramagnetic resonance (EPR) spectra are reported for [(η 4 -cod)Rh(μ-RNNNR) 2 -Ir(CO) 2 ] + (cod = 1,5-cyclooctadiene), [(PPh 3 )(CO)Rh(μ-RNNNR) 2 Ir(CO)(PPh 3 )] + (R = p-tolyl) and [Tp'Ir-(CO)(PPh 3 ] + (Tp' = hydrotris(3,5-dimethylpyrazolyl)borate). In the first spectrum, the Rh hyperfine coupling dominates and there are no significant quadrupolar effects. In the second spectrum, the low-field (g x and g y ) features are 1:2:1 triplets rather than 1:1:1:1 quartets (I = 3/2 for 1 9 1 Ir and 1 9 3 Ir), and in the third, the x and y features appear to be doublets. These anomalies result from the very large quadrupole moment for the iridium isotopes. This can be partially understood from a perturbation theory treatment, but quantitative simulations require direct matrix diagonalization and careful treatment of the problem, with respect to the orientation of the electron spin and nuclear spin quantization axes. The theoretical aspects of the calculations are presented, together with an interpretation of the results in terms of the electronic structures of the complexes.

The complex [Mo(CO)(PhC≡CPh) 2 (η 5 -C 5 Me 5 )][BF 4 ] reacts with 3 equiv of CNBu t to yield the mixed alkyne-isocyanide complex [Mo(CNBu t ) 3 (PhC≡CPh)(η 5 -C 5 Me 5 )][BF 4 ], 1. Reaction of 1 with a fourth equivalent of CNBu t generates [Mo{=C(NHBu t )C(Ph)=C(Ph)CN}(CNBu t ) 2 -(η 5 -C 5 Me 5 )][BF 4 ], 2, containing an η 3 -vinylcarbene ligand formed from the coupling of two of the coordinated isocyanide ligands with the diphenylacetylene, with concomitant protonation of one of these isocyanide fragments and dealkylation of the other. Complex 2 may be deprotonated to give [Mo{C(=NBu t )C(Ph)=C(Ph)CN}(CNBut) 2 (η 5 -C 5 Me 5 )], 3. Protonation of 1 with HBF 4 .Et 2 O generates [Mo{=C(Ph)C(Ph)C=NHBu t }(CNBu t ) 2 (η 5 -C 5 Me 5 )][BF 4 ] 2 , 4, by inducing the coupling of a protonated isocyanide ligand with diphenylacetylene, and 4 reacts with CNBu t to give 2. A similar reaction of 4 with P(OMe) 3 generates [Mo{=C(NHBu t )C-(Ph)=C(Ph)CN}(CNBu t ){P(OMe) 3 }(η 5 -C 5 Me 5 )][BF 4 ], 5, involving the same coupling and elimination pattern. The diphenylacetylene and CNBu t ligands of 1 may also be reductively coupled. Thus, treatment of 1 with sodium-mercury amalgam and subsequent protonation with HBF 4 .Et 2 O gives the metallacyclopentatriene-like [Mo{=C(NHBut)C(Ph)=C(Ph)C-(NHBu t )}(CNBu t )(η 5 -C 5 Me 5 ][BF 4 ], 6, or [Mo{=C(NHBu t )C(Ph)C(Ph)CH-NHBu t }(CNBu t )(η 5 -C 5 Me 5 )][BF 4 ], 7, depending upon the solvent. Complex 7 contains an N-protonated η 4 -monoazadiene ligand with a pendant carbene functionality that is also coordinated to the metal. The crystal structures of 1, 2, 3, 6, and 7 have been determined.

The synthesis, electrochemistry, and structural characterization of the mononuclear complex [Pd{C6H4N(H)NC(CH3)C5H4N}(p-tolN−NNp-tol)] (1) containing the monodentate 1,3-di-p-tolyltriazenido ligand is described. Compound 1 is an example of a stable species containing a Pd−N amido bond cis to a Pd−C aryl bond. Kinetic parameters for the dynamic intramolecular N(1)−N(3) exchange of the monodentate ligand in complex 1 have been calculated. The cis and trans isomers of the orthometalated face-to-face complex [{Pd(C6H4NNC6H5)(μ-p-tolNNNp-tol)}2] (2) have also been prepared, and the crystal structure of the trans isomer is reported. There are noticeable differences in the electrochemical behavior of the mononuclear and binuclear species. From the electrochemical experiments on both isomers of 2 it is possible to recognize different redox sites, to calculate the electronic coupling between them, and to suggest where the reversible electron transfers occur. Each isomers of 2 undergoes two one-electron oxidations ...

The complexes [M(NCMe)(RC2R)2(η-C5R‘5)]+ (M = Mo or W, R = Me or Ph; R‘ = H or Me, C5R‘5 = C5HPh4) undergo one-electron reduction to [M(NCMe)(RC2R)2(η-C5R‘5)], which rapidly lose acetonitrile to give the 17-electron complexes [M(RC2R)2(η-C5R‘5)]. The stability of [M(RC2R)2(η-C5R‘5)] depends on R and R‘; for R = Ph, the radical is sufficiently stable so that its reduction to the 18-electron anion [M(RC2R)2(η-C5R‘5)]- is detected in the cyclic voltammogram. Chemical reduction of [Mo(NCMe)(PhC2Ph)2(η-C5HPh4)]+ with [Co(η-C5H5)2] gives the air-sensitive solid [Mo(PhC2Ph)2(η-C5HPh4)], characterized as an alkyne-based radical by ESR spectroscopy, which gives [Mo(NCMe)(PhC2Ph)2(η-C5HPh4)]+ when treated with [Fe(η-C5H5)2]+ in acetonitrile. The carbonyl cations [M(CO)(RC2R)2(η-C5R‘5)]+ (M = Mo, W) undergo two sequential one-electron reductions, the first of which is reversible and gives the 19-electron species [M(CO)(RC2R)2(η-C5R‘5)]. The 19-electron radical [Mo(CO)(PhC2Ph)2(η-C5Me5)] has been characterized in sol...

The preparation and characterization of [Cr(CO)2L(η-C6Me6)] (L = PEt3, PPh3, P(OEt)3 and P(OPh)3, are reported. One-electron oxidation affords unstable Cr(I) cations, [Cr(CO)2L(η-C6Me6)]+, EPR spectra of which are reported. Detailed analysis of the anisotropic 31P hyperfine interaction indicates that, in frozen CH2Cl2/THF, the phosphine and phosphite complexes have 2A‘ and 2A‘‘ ground states, respectively. The hyperfine anisotropy can be accounted for by dipolar interaction of the 31P nucleus with spin density on Cr and, in the case of the phosphite complexes, with ∼0.01 P 3py spin density resulting from π-backbonding. Line width anomalies observed in EPR spectra of these and other Cr(I) and Mn(II) “piano stool” complexes can be understood in terms of molecular distortions resulting from solvation in frozen solutions.

The reaction of [Mo2(μ-C8Me8)(η-C5H5)2] (1) with 1 equiv of [Fe(η-C5H5)2][PF6] in CH2Cl2 gives [Mo2(μ-C8Me8)(η-C5H5)2][PF6] (1+[PF6]-), which reacts with a second 1 equiv of [Fe(η-C5H5)2][PF6] or 1 equiv of the trityl radical, •CPh3, to give [Mo2(μ-C8Me7CH2)(η-C5H5)2]+ (2+); depending on the oxidant the activation of one C−H bond of 1, with the formation of 2+, can occur by an EC or EEC mechanism. Complexes 1 and 1+ constitute the first isolable redox pair to show the structural effects of one-electron oxidation on a metal−alkene bond. An X-ray crystal structure analysis shows that the geometry of 1+ is similar to that of 1 and has approximate Cs symmetry. The Mo−Mo distance in 1+ is consistent with the presence of a MoMo double bond. The C8 chain acts as a double μ-allylidene ligand while binding to Mo(2) as an η-alkene through C(4) and C(5). The Mo−C distances for atoms C(1), C(2), C(3), C(6), C(7), and C(8) of the C8 chain are remarkably similar in 1 and 1+ while the Mo(2)−C(4) and Mo(2)−C(5) distances...

The X-ray crystal structure analyses of the three redox pairs [Rh 2 (CO) 2 LL'{μ-PhNC(Me)NPh)} 2 ] z [z=0,1; L=L'=PPh 3 (1, 1 + ); L=L'=P(OPh) 3 (1, 1 + ); L=PPh 3 , L'= P(OPh) 3 (3, 3 + )] are reported and the molecular structures compared with those of [Rh 2 (CO) 2 (PPh 3 ) 2 (μ-RNNNR) 2 ] z [z=0,1; R=p-tolyl (4, 4 + )]

Molecular orbital calculations at the extended Huckel level have been carried out on the model binuclear cyanobridgedcationiccomplexesofthe type [[Mn]-CN-[Mn]) + ,where [Mn]=cis- or trans-mer-Mn(CO) 2 (PH 3 ) 3 + . The results are consistent with a weak Mn- - -Mn interaction mediated by the CN bridge. The energy and composition of the highest occupied orbitals are determined by the stereochemistry and so is the Mn atom at which the HOMO is localized.

The η2(3e)-vinyl complex is oxidized by [FeCp2]+, [CPh3]+, or B(C6F5)3 to form the 17-electron cation which on warming loses H to form the cationic η2(4e)-alkyne complex [Mo(η2-PhC⋮CPh){P(OMe)3}2Cp]+. In the case of the borane there is evidence for a competing reaction between the η2-vinyl complex and the acid (H2O)B(C6F5)3, resulting in the formation of a labile trans-stilbene complex.

The geometry variations in the M-PA 3 units of 24 transition metal-phosphine and -phosphite complexes whose crystal structures are known for multiple oxidation states of the complex are tabulated and discussed. Conclusions are drawn with regard to the effect of oxidation at the metal on M-P π-back-bonding and the consequent structural effects on the PA 3 ligand

Les complexes pentaphenylcyclopentadienyl («η 5 »-C 5 Ph 5 ) M(CO) 2 avec M=Co ou Rh, sont reduits par un electron en leurs radicaux anioniques correspondants. Les potentiels E° (vs ecs), mesures par voltammetrie cyclique, sont de −1,57 V pour M=Co et de −1,70 V pour M=Rh, dans des solutions de THF. Les etudes de spectroscopie RPE montrent que l'anion avec Co est moins stable que celui avec Rh

Synthese des cations (cyclohexadienyl)Mn(CO)(NO)L + par traitement de (cyclohexadienyl)Mn(CO) 2 L (L=CO, PBu 3 ) avec NOPF 6 . Mecanisme des reactions de ces cations avec les nucleophiles

Etude RMN de 1 H et RX montrant que l'addition de BH 4 − aux cations cyclohexadienyl-Mn(CO) 2 (NO) donne des complexes de cyclohexadiene par une reaction stereospecifique