Carbonylnickelates. 3. Synthesis and chemical characterization of the [Ni12(CO)21H4-n]n- (n=2, 3, 4) clusters.

The hydrolysis of the [Ni6(CO)12]2- dianion under buffered conditions results in the synthesis of the interstitial hydride derivatives [Ni12(CO)21H2]2- and [Ni12(CO)21H]3-. The two compounds are related by an easily reversible protonation-deprotonation equilibrium. In contrast, deprotonation of [Ni12(CO)21H]3- to the corresponding [Ni12(CO)21]4- tetraanion is possible only under severe conditions. The tetraanion has been obtained as a byproduct of the synthesis of [Ni6(CO)12]2- by reduction of Ni(CO)4 in KOH-saturated methanolic solution. The [Ni12(CO)21H4-n]n- (n = 2, 3, 4) derivatives have been isolated in pure crystalline form with a variety of tetrasubstituted ammonium or phosphonium cations. All these dodecanuclear nickel carbonyl clusters are rapidly degraded by carbon monoxide (25\ub0C, 1 atm) and possess limited thermal stability. Degradation of [Ni12(CO)21H2]2- by carbon monoxide in THF solution affords the binuclear hydride derivative [Ni2(CO)6H]- and Ni(CO)4. Degradation of [Ni12(CO)21H]3-, in addition to the former products, gives rise to [Ni5(CO)12]2-, which becomes the only product, together with Ni(CO)4, when starting from [Ni12(CO)21]4-

Synthesis of bimetallic Fe-Ni carbonyl clusters: crystal structure of [N(CH3)3CH2Ph][Fe3Ni(CO)8(\uf06d-CO)4(\uf06d-3-H)].

Redox condensation of [Fe3(CO)11]2- with Ni(CO)4 in tetrahydrofuran affords the tetranuclear dianion [Fe3Ni(CO)12]2-. Subsequent protonation with acids results in formation of the corresponding [Fe3Ni(CO)12H]- anion. This monoanionic species has also been obtained by reaction of [Fe3(CO)11]2- with NiCl2\ub7xEtOH. Both Fe3Ni systems have been isolated in the solid state in high yield with a variety of tetrasubstituted ammonium and phosphonium salts. An X-ray diffraction study of the trimethylbenzylammonium salt of [Fe3Ni(CO)12H]- reveals a structure with a tetrahedron of metal atoms surrounded by eight terminal and four edge-bridging carbonyl groups. The hydride ligand has been located over the center of an Fe2Ni face at a distance of 0.60 (3) \uc5 from the trimetal plane. The corresponding [Fe3Ni(CO)12]2- dianion is suggested to posses an analogous structure on the basis of its IR spectrum. Crystallographic data for [C10H16N]+[C12HFe 3NiO12]-: fw 713.64, triclinic, space group P1, Z = 2, a = 7.416 (1) \uc5, b = 13.849 (2) \uc5, c = 14.108 (2) \uc5, \u3b1 = 103.13 (2)\ub0, \u3b2 = 103.15 (2)\ub0, \u3b3 = 99.23 (2)\ub0, R(F2) = 0.030 for 3860 reflections measured at room temperature

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

The hydroformylation of cyclohexene, 1-pentene and styrene under mild conditions (25-50 \ub0C, 1 atm equimolar mixture of CO and H2) has been investigated using as catalyst precursor either the Co4-nRhn(CO)12 + x L (n = 0, 2, 4; x = 0 - 9) system or preformed Rh4CO)12-xLx (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/Co4-nRhn(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 Rh4(CO)12 as well as Rh6(CO)16, and trisubstituted phosphites as ligands, infrared spectroscopy and 31P NMR invariably show the presence of Rh4(CO)9L3 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 PPh3, evidence of fragmentation to Rh2(CO)6(PPh3)2 or to Rh2(CO)4(PPh3)4 species has been obtained at the higher PPh3/Rh4(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

Bimetallic Iron-Rhodium anionic carbonyl clusters [Fe2Rh(CO)x]- (x= 10 or 11), [FeRh4(CO)15]2-, [Fe2Rh4(CO)16]2- and [FeRh5(CO)16]-.

The syntheses and interconversions of mixed iron-rhodium carbonyl clusters are described; a combination of X-ray analysis and multinuclear n.m.r. measurements allowed the structural characterisation of [FeRh 4(CO)15]2-, [FeRh5(CO) 16]-, and [Fe2Rh4(CO) 16]2-, which can all be obtained from the unstable cluster, [Fe2Rh(CO)x]- (x = 10 or 11)