Luigi Garlaschelli

Hydroformylation of olefins under mild conditions: Part I: the Co4−nRhn(CO)12 + x L (n = 0, 2, 4 ; x = 0 - 9) system and preformed Rh4(CO)12−xLx clusters (x = 1 – 4)

Abstract The hydroformylation of cyclohexene, 1-pentene and styrene under mild conditions (25–50 °C, 1 atm equimolar mixture of CO and H 2 ) has been investigated using as catalyst precursor either the Co 4- n Rh n (CO) 12 + x L ( n = 0, 2, 4; x = 0 – 9) system or preformed Rh 4 CO) 12− x L x ( x = 1 – 4) substituted clusters, where L is a trisubstituted phosphine or phosphite. The activity of these systems increases as a function of x , and reaches a maximum for a L/Co 4− n Rh n (CO) 12 ( n = 2, 4) molar ratio of ca . 5 – 6. A further increase in this ratio corresponds to a smooth decrease in the activity. This ratio has apparently a negligible effect on the regioselectivity in the hydroformylation of both 1-pentene and styrene. In contrast, both the activity and the regioselectivity are significantly affected by the nature of the ligand employed as cocatalyst. When working with Rh 4 (CO) 12 as well as Rh 6 (CO) 16 , and trisubstituted phosphites as ligands, infrared spectroscopy and 31 P NMR invariably show the presence of Rh 4 (CO) 9 L 3 as the most substituted rhodium carbonyl species present in solution, and there is no evidence of fragmentation of the tetranuclear cluster during the catalytic process. In contrast, when using phosphine ligands such as PPh 3 , evidence of fragmentation to Rh 2 (CO) 6 (PPh 3 ) 2 or to Rh 2 (CO) 4 (PPh 3 ) 4 species has been obtained at the higher PPh 3 /Rh 4 (CO) 12 molar ratios. Degradation of the ligand employed as cocatalyst, particularly the arylsubstituted phosphines, is observed, and this is probably at the origin of the loss of catalytic activity of some of these systems with time.

Chemistry of tetrairidium carbonyl clusters. Part 1. Synthesis, chemical characterization, and nuclear magnetic resonance study of mono- and di-substituted phosphine derivatives. X-Ray crystal structure determination of the diaxial isomer of [Ir4(CO)7(µ-CO)3(Me2PCH2CH2PMe2)]

The reactions of the anionic cluster [NEt4][Ir4(CO)11Br] with uni- and bi-dentate phosphines and arsines have been investigated. The bromide ligand is quantitatively displaced by 1 mol equivalent of phosphine or arsine at low temperature, the only complexes being formed under these mild conditions being the monosubstituted products [Ir4(CO)11L](L = PPh3, PPh2Me, PPhMe2, or AsPh3), [Ir4(CO)11(L–L)](L–L =trans-Ph2PCHCHPPh2), and [(OC)11Ir4(L–L)Ir4(CO)11][L–L =trans-Ph2PCHCHPPh2 or Ph2P(CH2)nPPh2(n= 3 or 4)]. Similar reactions with higher than stoicheiometric amounts of phosphine (L = PPh3, PPh2Me, or PPhMe2) or diphosphine [L–L = Ph2P(CH2)nPPh2(n= 1–4), Me2P(CH2)2PMe2, cis-Ph2PCHCHPPh2, or o-Ph2PCH2C6H4CH2PPh2] give in good yields the disubstituted compounds [Ir4(CO)10(L–L)] respectively. The stereochemical arrangements of the phosphine ligands and the dynamic processes occurring in solutions of these complexes are discussed on the basis of i.r. and n.m.r, data. The structure of the diaxial isomer of [Ir4(CO)7(µ-CO)3(Me2PCH2CH2PMe2)] has been determined by X-ray diffraction. The complex crystallizes in the monoclinic space group P21/c, with cell constants a= 15.694(2), b= 10.403(2), c= 15.706(2)A, β= 92.63(2)°, and Z= 4. The structure has been solved from 2 289 diffraction intensities collected by counter methods, and refined by least-squares calculations to R= 0.087 (R′= 0.091). The four iridium atoms define a tetrahedron with three bridging CO ligands around a triangular face. All remaining carbonyls are terminally bonded and the two P atoms of the Me2PCH2CH2PMe2 ligand are found in axial positions, generating a six-membered ring.

New tetrahedral cluster compounds of iridium. Synthesis of the anions [Ir4(CO)11X]− (X = Cl, Br, I, CN, SCN) and x-ray structure of [PPh4] [Ir4(CO)11Br]

Abstract [Ir4(CO)11X]− anions are obtained by reaction of halide and pseudo-halide ions with Ir4(CO)12. X-ray determination of the structure of [Ir4(CO)11Br]− shows that the carbonyl arrangement differs from that of the parent Ir4(CO)12, and is similar to that known for Co4(CO)12; one terminal CO group in the basal M3(CO)9 moiety is replaced by the bromide ligand, and two of the bridging CO groups become markedly asymmetric.

Structural studies of Rh4(CO)12 derivatives in solution and in the solid state

Abstract The crystal structures of Rh4(CO)10(PPh3)2 and Rh4(CO)9P(OPh)33 are reported. 31P-1H NMR studies on Rh4(CO)12-x {P(OPh)3}x(X  1, 2 and 3) show that each derivative exists as only one isomer in solution whereas the analogous triphenylphosphine derivatives can exist as different isomers. A quantitative redistribution of triphenylphosphites occurs on mixing Rh4-(CO)12-xLx with Rh4(CO)12-yLy (L  P(OPh)3; x  0, 1, 2, y  x + 2; x  0, y  x + 4) to give Rh4(CO)12-zLz[z  1 2 (x + y)]; a related rapid intermolecular randomisation of carbonyls occurs on mixing Rh4(12CO)12 with Rh4(13CO)12.

Chemistry of iridium carbonyl : I. Chemical and structural characterization of the tetranuclear anions [Ir4(μ-CO)3(CO)8(COOR)]-

Abstract 1 The anions [Ir 4 (CO) 11 (COOR) - (R  Me, Et) have been prepared by reacting Ir 4 (CO) 12 with alkali alkoxides in dry alcohol and under an atmosphere of carbon monoxide. The reaction of [Ir 4 (CO) 11 (COOMe)] - with primary and secondary alcohols (EtOH, Pr i OH) gives rise to specific alcoholysis. The anions [Ir 4 (CO) 11 (COOR) - react with acids in THF solution to give quantitatively Ir 4 (CO) 12 . The chemical, spectroscopic and crystallographic characterization of the tetranuclear anions are reported.

Hydroformylation and hydrocarbonylation of dicyclopentadiene with cobalt—rhodium catalytic systems promoted by triphenylphosphine: Synthesis of monoformyltricyclodecenes, diformyltricyclodecanes and di(tricyclodecenyl)ketones

Abstract A carbonyl cobalt—rhodium mixed system, promoted by the triphenylphosphine ligand, catalyzes in mild conditions the selective hydroformylation of endo-dicyclopentadiene. In the pressure range of 20–40 atm of syngas and at a temperature of 70–110 °C, an isomeric mixture of diformyltricyclodecanes is obtained in high yields and with selectivity up to 95%, as a result of two distinct and subsequent hydroformylation steps. The difference in the hydroformylation rates of the norbornenyl and cyclopentenyl moieties is so marked that dicyclopentadiene is almost completely converted to monoformyltricyclodecenes prior to the subsequent hydroformylation of the cyclopentenyl ring to any significant extent. The second hydroformylation step is also completely inhibited by adopting milder conditions (1 atm, 70–90 °C); at atmospheric pressure an isomeric mixture of 8-formyltricyclodec-*-enes (* =3,4) or di(tricyclodecenyl)ketones can be selectively obtained, mainly depending on the L/M ratio adopted. The monoformyltricyclodecenes, diformyltricyclodecanes and the di(tricyclodecenyl)ketones have been isolated in a pure state either by vacuum distillation or by liquid chromatography, and have been spectroscopically characterized by IR, 1H and 13C NMR, and mass spectroscopy. Bimetallic CoRh species, such as CoRh(CO)6(PPh3), probably play a key role in generating an active catalytic system in the experiments under pressure, as suggested by a synergetic effect between the two metals and almost quantitative recovery of either CoRh(CO)6(PPh3) or CoRh(CO)5(PPh3)2, depending on the adopted L/M ratio. In contrast, the system at ambient pressure is not only complicated by clusterization equilibria of the above species, but also by degradation reactions of PPh3 and carbonyl-substitution reactions with dicyclopentadiene which ultimately afford MCp(CO)2(M = Co, Rh; Cp = η5-C5H5) species. Irreversible formation of these latter species is probably at the origin of the deactivation process of the catalytic system. A possible mechanism which accounts for the change in selectivity from aldehydes to ketones depending on the L/M+Mt molar ratio, as well as the synergetic effect of cobalt and rhodium in the formation of the latter, is also suggested.

Chemistry of iridium carbonyl cluster. Preparation of Ir4(CO)12

Abstract Ir 4 (CO) 12 has been prepared by a two-step reductive carbonylation of IrCl 3 · 3H 2 O in ethanol or of K 2 IrCl 6 in 2-methoxyethanol at atmospheric pressure. The iridium trichloride is first transformed into [Ir(CO) 2 Cl 2 ] − , which is subsequently reduced to Ir 4 (CO) 12 . A simple method for purification of the metal carbonyl is also described.

The redox behaviour of the cluster anion [Fe4N(CO)12]−. Electron transfer chain catalytic substitution reactions. Crystal structure of [Fe4N(CO)11PPh3)]−

Abstract The electrochemical investigation of the redox properties of the monoanion [Fe4N(CO)12]− points out its ability to undergo sequentially two one-electron reductions. The first step leads to the quite stable dianion [Fe4N(CO)12]:2−; the EPR results indicate that in frozen solution an equilibrium exists between two different molecular geometries of such a dianion. The second electron addition produces the relatively short-lived trianion [Fe4N(CO)12]3−. In the presence of monodentate phosphines, the redox change [Fe4N(CO)12]−/2− triggers the electrocatalytic substitution of one CO group to afford the substituted monoanions [Fe4N(CO)11(PR3)]−. As a matter of fact, sub-stoichiometric amounts of Ph2CO − produce [Fe4N(CO)11(PPh3)]−, the crystal structure of which has been solved. Crystal data for [N(PPh3)2][Fe4N(CO)11(PPh3)]: triclinic, space group P 1 (No. 2), a=11.009(6), b=17.285(4), c=17.380(2) A, α=103.11(3), β=91.18(2), γ=105.26(3)°, Z=2, Dc=1.444 g cm−3, Mo Kα radiation (λ=0.71073 A), μ(Mo Kα)=10.5 cm−1, R=0.048 (Rw=0.054) for 5010 independent reflections having I > 3σ(I). Preliminary evidence is given that in the presence of bidentate phosphines one CO ligand substitution occurs at room temperature, whereas two CO groups are replaced at higher temperatures.

Synthesis and x-ray characterization of Rh4(CO)8 [P(OPh)3]4 and Rh6(CO)12[P(OPh)3]4

The structures of the compounds Rh 4 (CO) 8 [P(OPh) 3 ] 4 and Rh 6 (CO) 12 - [P(OPh) 3 ] 4 have been determined and shown to be derived from those of the parent species Rh 4 (CO) 12 and Rh 6 (CO) 16 by replacement of terminal carbonyl groups.

Molybdenum and tungsten hydroxocarbonylhydrides and hydroxocarbonylnitrosyls

Abstract The results of an investigation on a series of molybdenum and tungsten hydroxocarbonyl complexes related to the «acidic species» formulated by Hieber as H3M2(CO)6(OH)3 (M=Mo, W) are reported. By allowing these compounds to react with tertiary phosphine oxides, complexes are obtained which have been characterized as tertiary phosphine oxide adducts of tetrakis (μ3-hydroxotricarbonylhydrido metal); {[HO)M(CO)3H]4 . 4 OPR3}. The nitrosyl derivatives are also described and contain a similar tetrameric unit with four NO groups in place of the four hydrogen atoms and four CO groups: {[(HO)M(CO)2(NO)]4.4-OPR3}. NMR and IR investigation led us to propose, for Hiebers «acidic species» and for the derived nitrosyl species, the formulae: {[(HO)M(CO)3H]4.4-H2O} and {[(HO)M(CO)2(NO)]4 . 4H2O} respectively.