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Transition-metal indenyl complexes usually exhibit different reactivity compared with their cyclopentadienyl analogues. Up to now, at least 10 metal-indenyl bonding modes have been reported. Because of the “indenyl effect”, transition-metal indenyl complexes usually display elevated reactivity in substitution and related reactions. This review provides an overview on the use and impact of indenyl phosphines in the organometallic chemistry and transition-metal-catalysed reactions in recent two decades. Some cationic and zwitterionic metal complexes supported by P,N-substituted indene or indenide ligands are descibed. They have been reported to induce the cleavage of the E–H (E = H, Si and B) bonds and could be used as catalysts for addition of E–H bonds to unsaturated substrates. Moreover, 2-aryl indenyl phosphine ligands L3-L12 have proven to be a class of versatile ligands for palladium-catalysed C–C and C–N cross-coupling reactions.

Indenyl (Ind) rhodium N-heterocyclic carbene (NHC) complexes [Rh(η5 -Ind)(NHC)(L)] were synthesised for 1,3-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene (SIPr) with L=C2 H4 (1), CO (2 a) and cyclooctene (COE; 3), for 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene (SIMes) with L=CO (2 b) and COE (4), and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) with L=CO (2 c) and COE (5). Reaction of SIPr with [Rh(Cp*)(C2 H4 )2 ] did not give the desired SIPr complex, thus demonstrating the "indenyl effect" in the synthesis of 1. Oxidative addition of HSi(OEt)3 to 3 proceeded under mild conditions to give the Rh silyl hydride complex [Rh(Ind){Si(OEt)3 }(H)(SIPr)] (6) with loss of COE. Tethered-fluorenyl NHC rhodium complexes [Rh{(η5 -C13 H8 )C2 H4 N(C)C2 Hx NR}(L)] (x=4, R=Dipp, L=C2 H4 : 11; L=COE: 12; L=CO: 13; R=Mes, L=COE: 14; L=CO: 15; x=2, R=Me, L=COE: 16; L=CO: 17) were synthesised in low yields (5-31 %) in comparison to good yields for the monodentate complexes (49-79 %). Compounds 3 and 1, which contain labile alkene ligands, were successful catalysts for the catalytic borylation of benzene with B2 pin2 (Bpin=pinacolboronate, 97 and 93 % PhBpin respectively with 5 mol % catalyst, 24 h, 80 °C), with SIPr giving a more active catalyst than SIMes or IMes. Fluorenyl-tethered NHC complexes were much less active as borylation catalysts, and the carbonyl complexes were inactive. The borylation of toluene, biphenyl, anisole and diphenyl ether proceeded to give meta substitutions as the major product, with smaller amounts of para substitution and almost no ortho product. The borylation of octane and decane with B2 pin2 at 120 and 140 °C, respectively, was monitored by 11 B NMR spectroscopy, which showed high conversions into octyl and decylBpin over 4-7 days, thus demonstrating catalysed sp3 C-H borylation with new piano stool rhodium indenyl complexes. Irradiation of the monodentate complexes with 400 or 420 nm light confirmed the ready dissociation of C2 H4 and COE ligands, whereas CO complexes were inert. Evidence for C-H bond activation in the alkyl groups of the NHC ligands was obtained.

Constrained geometry, planar chiral, dichloro[η5:κS-indenyl-sulfanyl]rhodium complex (pS)-1 reacts with (E)-2-pentene in the presence of silver hexafluoroantimonate to afford syn,syn-1,3-dimethyl-π-allyl complex (pS)-2 in 88% yield. Reaction of (pS)-2 with the sodium or tetrabutylammonium salts of dimethyl malonate anion provided dimethyl 2-[(1R,2E)-1-methyl-2-buten-1-yl]-1,3-propanedioate ((R)-3) in 68–70% yield and 66–68% enantiomeric excess. NMR analysis and density functional theory calculations establish that asymmetric induction is substantially determined by the electronic asymmetry of the indenyl ligand polarizing the preferred site of nucleophilic attack on the π-allyl ligand toward the terminal carbon that is syn to the indenyl benzo-ring.

A series of cyclopentadienyl and indenyl molybdenum(II) compounds with intramolecularly coordinated pyridine arm, including scorpionate-like species bearing two irreversibly coordinated arms on the indenyl core, was synthesized and characterized. All presented structural types were confirmed by X-ray diffraction analysis. Due to strong nucleophilicity of pyridine, the intramolecular interaction is considerably stronger than in case of analogous species bearing tertiary amines in the side chain. Although the starting compounds for syntheses are isostructural, the reaction outcomes differ considerably. The cyclopentadienyl precursor gives a pentacoordinated 5:N-compound while the indenyl analogue produces a hexacoordinated species with unprecedented 3:N-coordination mode of the indenyl ligand representing an unusual example of so-called indenyl effect. The unusually high stability of the 3:N-coordination compounds toward 3 to 5 haptotropic rearrangement was clarified by theoretical calculations. As the strong intramolecular interaction prevents rotation of the indenyl, it cannot reach the conformation suitable for the 3 to 5 rearrangement. As the result, the low hapticity is effectively locked.

Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)3IndRh] (Ind = (C9H7)&minus, indenyl anion) are investigated. A detailed exploration of the potential energy surfaces (PESs) was carried out to identify the intermediates and transition states, using a relativistic density functional theory (DFT) approach. For comparison, monometallic parent systems, i.e., CpRh (Cp = (C5H5)&minus, cyclopentadienyl anion) and IndRh, were included in the analysis. The active center is the rhodium nucleus, where the [2+2+2] cycloaddition occurs. The coordination of the Cr(CO)3 group, which may be in syn or anti conformation, affects the energetics of the catalytic cycle as well as the mechanism. The reaction and activation energies and the turnover frequency (TOF) of the catalytic cycles are rationalized, and, in agreement with the experimental findings, our computational analysis reveals that the presence of the second metal favors the catalysis.

The magnitude of the “kinetic indenyl effect” for the π-thiapentalenyl ligand, isoelectronic heteroanalogue of the indenyl ligand, has been tested using the reaction between complex, Rh(η5-th)(CO)2 3 (th = 2-ethyl-5-methyl-cyclopenta[b]thienyl or thiapentalenyl) and PPh3 as a model process. Only moderate “kinetic indenyl effect” of the thiapentalenyl ligand was observed. The rational for such behavior was also supported by DFT computational correlation of ground and transition states for the reaction of carbonyl group substitution by a phosphine in the corresponding indenyl and thiapentalenyl rhodium complexes.

The second-order rate constants for the insertion of cyclohexene into substituted bis(indenyl)zirconocene dihydrides, (η5-C9H5-1,3-R2)2ZrH2 (R = SiMe3, CHMe2), to yield the cyclohexyl hydride compl...

The complex [IndCpMo(NCMe) 2 ][BF 4 ] 2 provides a suitable entry to the synthesis of IndCpMoBr 2 and IndCpMoMe 2 . The latter, also available from IndCpMoX 2 (X = Cl, Br) and MeMgCl, reacts with HCl to give IndCpMoCl(Me) which, in turn reacts with NaSPh to yield IndCpMo(SPh)(Me). Cyclic voltammetry shows that these three alkyl complexes undergo a 1e reversible oxidation to 17 e Mo V cations. IndCpMoCl(Me) is oxidized by [Cp 2 Fe]BF 4 to afford [IndCpMoCl(Me)]BF 4 in 95% yield. Reaction of [IndCpMo(NCMe) 2 ][BF 4 ] 2 with KBPz 4 in CH 2 Cl 2 /NMF leads to [IndCpMo(κ 2 -BPz 4 )]BF 4 . Taken together with previous reports these results show that the indenyl ring slows down substitutional chemistry at the Cp 2 ′ Mo ( IV ) fragment (Cp′ = Cp, Ind) by steric reasons, overshadowing any acceleration due to a possible indenyl effect.

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.

The bis(indenyl) derivatives of Fe, Co, and Ni were studied by means of DFT calculations ( adf program). The calculated structures were compared with the experimental ones and a good agreement was observed. While bis(indenyl)iron is an 18-electron compound, exhibiting an almost perfect η 5 coordination of the indenyl ring, the cobalt complex is a paramagnetic species, owing to the presence of an extra electron and structural distortions start to be detected. More interesting is the nickel complex, where the ring exhibits a coordination between η 2 +η 3 and η 3 , and is definitely slipped and folded. On the other hand, nickelocene chooses a distorted η 5 coordination with long NiC bonds and two unpaired electrons. This different behavior is related to the tendency of the indenyl to slip, compared to cyclopentadienyl. The geometry of the indenyl ring in bis(indenyl)nickel is useful to compare with that of non-isolable intermediates and transition states.

Kinetic studies were performed for CO substitution reactions of (η 5 -C 5 H 5 )M(CO) 4 and (η 5 -C 9 H 7 )M(CO) 4 (where M=Nb, Ta) with phosphines and phosphites. Niobium derivatives were found to undergo ligand exchange at higher rates than tantalum, and indenyl derivatives exchanged faster than cyclopentadienyl derivatives. The cyclopentadienyl compounds were found to react by a dissociative or dissociative interchange mechanism as opposed to an associative mechanism as suggested by an earlier kinetic study. The indenyl compounds were found to predominantly react by an associative mechanism. Rate and thermodynamic data indicate that the indenyl effect is operative in these Group V compounds. The molecular structure of (η 5 -C 5 H 5 )Nb(CO) 3 [P(C 6 H 5 ) 3 ]·0.25CH 2 Cl 2 was determined: P 1, a =10.817(2), b =12.403(2), c =18.962(3) A, α =100.901(13), β =104.695(10), γ =103.52(2)°, V =2307.6(7) A 3 , Z =4, R F =3.36.

A review of some structural and reactivity aspects of the coordinated indenyl ligand, dealing mainly with the systems theoretically studied by the authors is presented. In the first section, the structural characterization of η5 and η3 indenyl is attempted, noticing that the nodal properties of the π orbitals of the indenyl prevent a totally symmetric coordination in a η5-indenyl. The two bonds to the hinge carbon atoms are always longer, and the distance becomes longer than a M–C bond in the η3-indenyl derivatives. Some intermediate distances are found in [(Ind)2Ni] where, formally, the ligand is halfway between η5 and η3. The ring slippage occurs when two electrons are added to the system, occupying a metal–indenyl antibonding orbital, which becomes more stable upon folding. We reviewed electrochemical and ligand addition driven slippage, in the second section. A comparison with the behavior of the cyclopentadienyl ligand was attempted in the end.

The triruthenium cluster with bridging ethanethiolato and indenyl ligands [( η 5 -C 9 H 7 )Ru( μ -SEt)] 3 ( 2 ) was synthesized by heating the mononuclear indenyl complex [( η 5 -C 9 H 7 )Ru(SEt)(PPh 3 ) 2 ] ( 1a ) in toluene. Cluster 2 reacted with MeI to afford the S-methylated cluster [( η 5 -C 9 H 7 ) 3 Ru 3 ( μ -SEt) 2 ( μ -SEtMe)]I·CH 2 Cl 2 ( 4a ) with high stereoselectivity through the attack of MeI on the axial SEt group from the equatorial side. The PF 6 − salt of the cationic cluster [( η 5 -C 9 H 7 ) 3 Ru 3 ( μ -SEt) 2 ( μ -SEtMe)][PF 6 ] was further converted into the cationic carbonyl complex [( η 5 -C 9 H 7 ) 2 Ru 2 ( μ -SEt)(CO) 4 ][PF 6 ] ( 5 ) by treatment with CO at 50°C. The crystal structures of 4a and 5 were determined by X-ray diffraction study. When a THF solution of 2 was allowed to contact with atmospheric pressure of CO at room temperature, the trinuclear carbonyl cluster [( η 5 -C 9 H 7 ) 3 Ru 3 ( μ -SEt) 3 ( μ -CO)(CO)] ( 6 ) and the dinuclear carbonyl complex [( η 5 -C 9 H 7 )Ru( μ -SEt)(CO)] 2 ( 7 ) were obtained. The structures of 6 and 7 were also crystallographically determined. Furthermore, cluster 2 was oxidized in refluxing CHCl 3 to give [( η 5 -C 9 H 7 )Ru(SEt)Cl] n ( 9 ). The Cp analogue of 2 , [CpRu( μ -SEt)] 3 , failed to react with CO and CHCl 3 , and the hapticity change of the indenyl ligand in 2 is considered to be crucial for the initial interaction of 2 with CO and CHCl 3 . These reactions provide rare examples of the indenyl ligand effect in a multinuclear complex.

(Methylcyclopentadienyl)Mn(CO)NO + (1 + ) undergoes a one-electron reduction at an electrode to give a 19-electron neutral radical that rapidly dissociates CO and dimerizes to yield [(MeCp)Mn(CO) 2 NO] 2 . In the presence of P-donor nucleophiles (L), the reduction of 1 + initiates a rapid electron transfer catalyzed (ETC) CO substitution to give a quantitative yield of (MeCp)Mn(CO)(L)NO + . The substitution reaction occurs via the 19-electron intermediate 1 , which dissociatcs CO in the rate limiting step with the following activation parameters: Δ H ≠ =60±6 kJ; δ S ≠=+ 37 ± 15 J K -1 . The 17-electron intermediate (MeCp)Mn(CO)NO is then trapped by the nucleophile to give the electron rich (MeCp)Mn(CO)(L)NO, which spontaneously transfers an electron to 1 + to afford the final product and regenerate 1 . A variety of electrochemical techniques, including low temperature voltammetry and steady-state voltammetry with microelectrodes, was employed to quantitatively define the details of the reaction mechanism. The indenyl analogue of 1 + , (indenyl)Mn(CO) 2 NO + (2 + ), was found to undergo ETC substitution reactions by the same dissociative mechanism and at approximately the same rate as 1 + . The conclusion is that the ‘indenyl effect’ does not operate in these 19-electron complexes. The rhenium complex CpRe(CO) 2 NO + is reduced by orte electron to give a relatively stable neutral radical that does not react with P-donor nucleophiles on the voltammetric time scale of 0.5 V s -1 . The conclusion is that CO dissociation from 19-electron complexes follows the reactivity order Mn ⪢ Re.

The potential energy surfaces of both neutral and dianionic SnC(2)P(2)R(2) (R=H, tBu) ring systems have been explored at the B3PW91/LANL2DZ (Sn) and 6-311 + G* (other atoms) level. In the neutral isomers the global minimum is a nido structure in which a 1,2-diphosphocyclobutadiene ring (1,2-DPCB) is capped by the Sn. Interestingly, the structure established by Xray diffraction analysis, for R=tBu, is a 1,3-DPCB ring capped by Sn and it is 2.4 kcal mol(-1) higher in energy than the 1,2-DPCB ring isomer. This is possibly related to the kinetic stability of the 1,3-DPCB ring, which might originate from the synthetic precursor ZrCp(2)tBu(2)C(2)P(2). In the case of the dianionic isomers we observe only a 6 pi-electron aromatic structure as the global minimum, similarly to the cases of our previously reported results with other types of heterodiphospholes.([1,4,19]) The existence of large numbers of cluster-type isomers in neutral and 6 pi-planar structures in the dianions SnC(2)P(2)R(2)(2-) (R=H, tBu) is due to 3D aromaticity in neutral clusters and to 2D pi aromaticity of the dianionic rings. Relative energies of positional isomers mainly depend on: 1) the valency and coordination number of the Sn centre, 2) individual bond strengths, and 3) the steric effect of tBu groups. A comparison of neutral stannadiphospholes with other structurally related C(5)H(5)(+) analogues indicates that Sn might be a better isolobal analogue to P(+) than to BH or CH(+). The variation in global minima in these C(5)H(5)(+) analogues is due to characteristic features such as 1) the different valencies of C, B, P and Sn, 2) the electron deficiency of B, 3) weaker p pi-p pi bonding by P and Sn atoms, and 4) the tendency of electropositive elements to donate electrons to nido clusters. Unlike the C5H5+ systems, all C(5)H(5)(-) analogues have 6 pi-planar aromatic structures as global minima. The differences in the relative ordering of the positional isomers and ligating properties are significant and depend on 1) the nature of the pi orbitals involved, and 2) effective overlap of orbitals.

13-vertex indenyl cobaltacarboranes with 4,1,6-, 4,1,10- and 4,1,2-CoC(2)B(10) architectures have been synthesised by reduction of the corresponding closo carborane and metallation with an {(eta-C(9)H(7))Co} fragment. Variants of the 4,1,6-isomer were prepared with no, one and two methyl groups on cage C atoms, whilst 4,1,2-species were obtained both with two methyl groups and a trimethylene tether on the cage C atoms. Thermolysis of the 4,1,6-isomers yielded the corresponding 4,1,8-isomers, which in turn were converted to 4,1,12-isomers by thermolysis at higher temperatures. Alternatively relatively mild heating of the 4,1,10-isomer led to the 4,1,12-isomer directly. Products were characterised by mass spectrometry, (1)H and (11)B NMR spectroscopies and, in most cases, elemental analysis, and nine compounds were studied crystallographically. The 4,1,6-, 4,1,8-, 4,1,10- and 4,1,12- species have docosahedral cages whilst the 4,1,2-species are henicosahedral. In the structural studies attention focused on the orientation of the indenyl ligand with respect to the carborane ligand since this affords experimental information on the metal-cage bonding through the structural indenyl effect. There is a general tendency for the indenyl ligand to adopt orientations in which the ring junction C atoms lie trans to cage B atoms. In cases where the orientation is not compromised by the presence of a non-H substituent on the face of the carborane there is generally good agreement between the experimental orientation and that computed by DFT calculations for the related naphthalene ferracarboranes (eta-C(10)H(8))FeC(2)B(10)H(12). The presence of C-methyl substituents in the indenyl cobaltacarboranes tends to override this preference except in the case of 1,6-Me(2)-4-(eta-C(9)H(7))-4,1,6-closo-CoC(2)B(10)H(10) where the indenyl ligand instead is forced to incline away from the cage methyl groups. In DCM solution the 4,1,6-, 4,1,8-, 4,1,10- and 4,1,12- isomers of (eta-C(9)H(7))CoC(2)B(10)H(12) exhibit two, stepwise, 1-electron reductions assigned to Co(III)/Co(II)/Co(I) couples at less negative potentials than those of the corresponding Cp compounds. Moreover these reductions are easier for those isomers (4,1,6- and 4,1,10-) in which there are two cage C atoms in the carborane face to which the metal atom is bound. By spectroelectrochemical and EPR measurements it is concluded that the reductions of these indenyl cobaltacarboranes are largely metal-based.

The new iridium (I) ethylene complexes (η 5 -C 5 H 5 )Ir(η 2 -C 2 H 4 )CO and (η 5 -C 9 H 7 )Ir(η 2 -C 2 H 4 )CO have been prepared. For these complexes, as well as for (η 5 -C 5 H 5 )Ir(η 2 -C 2 H 4 ) 2 and (η 5 -C 9 H 7 )Ir(η 2 -C 2 H 4 ) 2 , the barrier to ethylene rotation about the iridium-ethylene bond axis has been determined by line-shape fitting of variable-temperature 1 H NMR spectra

The titanium methoxo complex Ti(η5-C9H7)Cl2OMe), prepared from the trichloro complex Ti(η5-C9H7)Cl3, was found to polymerize ϵ-caprolactone with ring opening significantly more efficiently than analogous cyclopentadienyl derivatives. The crystal structure of Ti(η5-C9H7)Cl2OMe) was determined and shows a Cs-symmetric piano-stool conformation with the strongly π-donating methoxo group trans to the six-membered ring.

The hetero-bimetallic Ind complexes (Ind=indenyl anion) with the formula (CO)3Cr(μ-Ind)RhL2 (L=CO, ethylene; L2=COD, COT, NBD) have two possible conformers, one with the metals at antipodal sides of the condensed bicyclic polyene (antarafacial, anti) and the other with both metals on the same side (cofacial, syn). These systems can be considered to contain 34 valence electrons by assuming that Ind is capable of donating all of its ten π electrons to the metals. A qualitative MO analysis, based on EHMO calculations, is presented. The anti conformer is compared to the homometallic 34e species, namely [CpRu(μ-Ind)RuCp]+. Here, the pseudo-symmetrical relationship between the two identical metal fragments strongly suggests that one Ind σ-bonding MO donates part of its electron density to each of the two metals, which thus become formally saturated (36e). This argument is extended to the anti CrRh derivative in which a critical role is played by an empty FMO of the (CO)2Rh(I) fragment with π‖ symmetry (i.e. lying in the molecular mirror plane). The latter, in spit the large π CO ∗ contributions, has good acceptor capabilities at the metal.The calculations suggest that the so-called indenyl effect, namely the increased rate of substitution of one CO ligand by another σ donor (e.g. a phosphine), although a structurally dynamic process, also depends on the electron density which accumulates on the aforementioned π‖ FMO. In the series (η5-C5H5)Rh(CO)2, (η5-C7H9Rh(CO)2 and {η5-[(CO)3CrC7H9]}-Rh(CO)2 the progressively reduced donor capabilities of the cyclic polyene toward the (CO)2Rh(I) fragment induce a larger electrophilicity in rhodium, in good agreement with the experimental data on substitution reactivity. Finally, the electronic features of the cofacial conformer (CO)3Cr(μ-Ind)Rh(CO)2 are examined. In spite of the long CrRh separation ( > 3 A ) the graphically illustrated MO analysis indicates a direct, heterodox, intermetallic linkage, which helps the metals to achieve a formal electronic saturation. In this case, the limited propensity of the complex toward any CO substitution reactions is likely attributable to the hindered mobility of the (CO)2Rh(I) fragment.

The mechanism of carbonyl substitution in [Fe(Ind)(CO)(2)I] (Ind = C(9)H(7)(-), indenyl) by P(OMe)(3) was investigated by means of DFT calculations. The most favourable path involves a spin crossover of the complex from the ground state singlet to the triplet potential energy surface (S = 1), followed by dissociative loss of CO, and phosphite addition to the coordinatively unsaturated intermediate, [Fe(Ind)(CO)I], with S = 1. In the final step, the system returns to the spin singlet surface, affording the product. This dissociative mechanism is in agreement with the experimental findings. Several pathways occurring exclusively along the singlet surface (S = 0) were explored, namely the expected associative mechanism, which is the most favourable among them, and the "pseudo" associative including the participation of solvent (n-octane). In all cases the corresponding energy barriers were significantly higher than the ones involved in the "spin forbidden" mechanism. The rate enhancement observed comparing the Ind complex with the cyclopentadienyl (Cp = C(5)H(5)(-)) analogue reflects the stability difference between the corresponding S = 0 and S = 1 species in the initial step. The larger number of π orbitals and the lower symmetry of the indenyl ligand, compared with Cp, results in a smaller HOMO-LUMO gap, in a more accessible triplet species, and in a smaller barrier for the spin crossover.

The indenyl effect has been introduced to pentadienyl ("open cyclopentadienyl") chemistry by preparation of the phenylmethallyl ("open indenyl") ligand oInd(Me). The reaction of its potassium salt K(oInd(Me)) with [(η(5)-C(5)Me(5))RuCl](4) afforded the sandwich complex [(η(5)-C(5)Me(5))Ru(η(5)-oInd(Me))] (1), which, upon treatment with PMe(3), CO, and 2,6-dimethylphenyl isocyanide (CN-o-Xy), easily underwent η(5)-η(3) hapticity interconversion and formed the complexes [(η(5)-C(5)Me(5))Ru(η(3)-oInd(Me))(L)] (2, L = PMe(3); 3, L = CO; 4, L = CN-o-Xy). In these complexes, the η(3)-bound phenylmethallyl ligand adopts an anti-conformation with regard to the relative positions of the phenyl and methyl substituents. For the PMe(3) complex anti-2, slow conversion to the syn-isomer was observed, and this equilibrium reaction was monitored by NMR spectroscopy at 50 °C to determine a first order rate constant of k(323 K) = 6.57 × 10(-6) (± 0.02 × 10(-6)) s(-1) and an activation barrier of ΔG° = 26.8 kcal mol(-1). DFT calculations afforded a stabilization of syn-2 and syn-3 by ΔG(298) = -1.54 and -1.74 kcal mol(-1) over the respective anti-isomer.

Discussion des effets sur les parametres RMN. Etude RX de deux complexes: (η 5 -C 9 H 7 )Mo(CO) 2 (η 2 -CH 3 -1C 3 H 4 ] cristallise dans P2 1 /n avec Z=4 (R=0,033), [η 5 -C 9 H 7 )IrH{P(C 6 H 5 ) 3 } 2 ]BF 4 •CH 2 Cl 2 cristallise dans P2 1 /n avec Z=4 (R=0,046)

Deprotonation of indene–tricarbonylchromium with KH in tetrahydrofuran at –40 °C gives the η6-tricarbonylchromium–indenyl anion which reacts with [Rh(CI)COD]2(COD = cyclo-octa-1,5-diene) to form [η6-Cr(CO)3-indenyl-η3-rhodium-η4- COD]; the same bimetallic complex is obtained by reaction of the rhodium dimer with the isomeric η5-indenyl-tricarbonylchromium anion.

The compound (eta/sup 5/-C/sub 9/H/sub 7/)V(CO)/sub 4/ was prepared for the first time and its structure determined by X-ray crystallography. The structure closely resembles that of (eta/sup 5/-C/sub 5/H/sub 5/)V(CO)/sub 4/, with the V(CO)/sub 4/ moiety forming a square pyramid, and a planar indenyl group coordinating to the vanadium through the five-membered ring. The compound crystallizes in the space group Pna2/sub 1/ with a = 22.722 (6) A, b = 6.814 (1) A, c = 7.449 (2) A, and Z = 4. The reaction of (eta/sup 5/-C/sub 9/H/sub 7/)V(CO)/sub 4/ with P(n-Bu)/sub 3/ and with P(OEt)/sub 3/ to form (eta/sup 5/-C/sub 9/H/sub 7/)V(CO)/sub 3/PR/sub 3/ takes place by a dissociative (S/sub N/1) process with kinetic parameters of k(100/sup 0/C) = 3.7 x 10..sqrt../sub 4/ s/sup -1/, ..delta..H = 31.9 +/- 0.3 kcal/mol, and ..delta..S = 10.5 +/- 0.9 cal/(mol K). Again the indenyl effect on dissociative reactions is shown to be much smaller than on associative reactions when compared with the effect for corresponding cyclopentadienyl compounds. 18 references, 1 figure, 4 tables.

The addition of PH3 to [(η5-X)Mn(CO)3] was studied by means of molecular orbital calculations performed with the B3LYP HF/DFT hybrid functional. Five reactions, with different π ligands, were compa...

Carbonyl substitution by triphenylphosphine (PPh3) in the indenyl compounds Rh(η-C9H7)(CO)2 and Mn(η-C9H7)(CO)3 proceeds by a second order rate law which is first order in complex and first order in PPh3 and in both cases the rates are much faster than for the corresponding cyclopentadienyl complexes; for rhodium a rate enhancement of 108 is found for the indenyl compound over the corresponding cyclopentadienyl compound.