Alessandro Ceriotti

Hexagonal close packing of metal atoms in the new polynuclear anions [Rh13(CO)24H5–n]n–(n= 2 or 3); X-ray structure of [(Ph3P)2N]2[Rh13(CO)24H3]

The [Rh13(CO)24H5–n]n–(n= 2 or 3) anions have been isolated from the reaction of the [Rh12(CO)30]2– dianion with hydrogen; they are structurally related to a close hexagonal packing of rhodium atoms having mean distances of 2.81 A.

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.

[Pt19(CO)21(NO)]3− and [Pt38(CO)44]2−: Nitrosyl Bending through Intramolecular Electron Transfer as an Intermediate Step in the Nucleation Process from Polydecker to ccp Platinum Carbonyl Clusters

The intermediacy of CO/NO substitution in the condensation of [Pt19(CO)22]4− into [Pt38(CO)44]2− (structure shown) has been demonstrated. Two high-nuclearity carbonyl metal clusters, including one with an unprecedented nitrosyl ligand, have been synthesized and structurally characterized.

Iron, cobalt and nickel carbide-carbonyl clusters by CO scission

A new approach to the synthesis in good yields of known cobalt and iron carbidecarbonyl clusters by CO cleavage in mild conditions is reported. Cleavage of CO results from attaching an acetyl or benzoyl carbocation to the oxygen atom, and by transfer of electrons from an external source. This synthetic approach to carbide molecular clusters may be of some significance with respect to the formation of carbide atoms on to metal crystallites. Attempts to synthesize nickel carbide clusters with the same approach have only been partly successful. The new [Ni9C(CO)17]2~ and [Ni8C(CO)13]2~ have been obtained more conveniently from the reaction of [Ni6(CO)12]2- with CC14. The related reaction of [Ni6(CO)12]2- with Co3(CO)9CCl results in the formation of the mixed-metal carbide cluster [Co3Ni9C(CO)20]3_. This compound is degraded under a carbon monoxide and hydrogen mixture (25 °C, 1 atm) to Ni(CO)4, [Co(CO)4]~ and ethane. Intermediate formation of [Co3Ni7(C-C) (CO)15]3-, in which the two carbide atoms show an interatomic separation of 1.43 A, or of a related species, would provide a possible pathway for C-C bond formation.

Nickel carbonyl clusters containing interstitial carbon-congener atoms: synthesis and structural characterisation of the [Ni12(µ12-E)(CO)22]2–(E = Ge, Sn) and [Ni10(µ10-Ge)(CO)20]2– dianions

The first example of carbonyl clusters containing fully interstitial germanium and tin atoms have been isolated from the reaction of their chlorides with [Ni6(CO)12]2–; the structures of the icosahedral [Ni12Ge(CO)22]2– and [Ni12Sn(CO)22]2– and the pentagonal antiprismatic [Ni10Ge(CO)20]2– have been established from X-ray diffraction studies.

The crystal and molecular structure of trans-chlorocarbonylbis(triphenylphosphine)rhodium(I) in its monoclinic form

Abstract The structure of the title compound, RhCl(CO)(PPh 3 ) 2 , has been investigated in its monoclinic modification. It belongs to space group P 2 1 / n (No. 14), with cell constants a 12.182(3), b 24.285(5), c 11.894(3) A, β 113.10(2)°, Z = 4. The structure was solved by conventional Patterson and Fourier methods, on the basis of 4295 significant counter data, by least-squares methods to a final conventional R values of 0.051. The complex exhibits a square planar coordination, with the two bulky phosphine ligands in mutually trans positions. The mean value of the RhP bond lengths is 2.326 A. The RhCl, RhC and CO bond lengths are 2.371(2), 1.810(7), and 1.144(8) A, respectively. The structure is compared with those of similar species and the small differences observed between the monoclinic and triclinic modifications of this compound are discussed.

Synthesis and characterisation of [Rh7(CO)16X]2− anions (X = Br, I)

The reaction of Rh6(CO)16 with an excess of tetraalkylammonium halides in tetrahydrofuran gives the heptanuclear [Rh7(CO)16X]2− anions (X = Br, I), which have been isolated and characterised. The same anions were obtained by condensation of the Rh2(CO)4X2 carbonyl halides with the hexanuclear [Rh6(CO)15]2− anion, or by reaction of the [Rh7(CO)16]3− anion with iodine.

Synthesis and X-ray structure of [Ni16(CO)23C4]4–: a tetracarbide anionic cluster containing two interstitial C2 fragments

Reaction of [Ni10(CO)16C2]2– with four equivalents of PPh3 in tetrahydrofuran quantitatively afforded the novel brown [Ni16(CO)23C4]4– tetra-anion, whose metal frame has been shown by X-ray diffraction studies to consist of a unique hexadecanuclear truncated ν2-octahedron caging two interstitial C2 moieties with a very short interatomic C-C separation of 1.38 A.

Synthesis, NMR, and structural characterization of the [Ni9Pt3(CO)21H4-n]n− (n = 4, 3, 2) anionic clusters

Abstract The preparations of bimetallic carbonyl clusters having the general formula [Ni 9 Pt 3 (CO) 21 H - n ] n − ( n = 4, 3, 2) are described. X-ray studies on [NEt 4 ] 3 [Ni 9 Pt 3 (CO) 21 H] show that it is isostructural with [Ni 12 (CO) 21 H] 3− , with the platinum atoms occupying the inner triangle of the central Ni 3 Pt 3 planar triangulated array. The interstitial coordination of the hydride atoms in these compounds is inferred from 1 H and 195 Pt NMR and X-ray data.

SYNTHESIS AND CHEMICAL BEHAVIOR OF THE [CO3NI7(CO)16C2]2- AND [CO3NI7(CO)15C2]3- DICARBIDE CLUSTERS - X-RAY CRYSTAL-STRUCTURE OF [PPH4]2[CO3NI7(CO)16C2]

The synthesis and properties of the new dicarbidocarbonyl bimetallic clusters [Co3Ni7(CO)16C2]2− (I), [Co3Ni7(CO)16C2]3− (II), and [Co3Ni7(CO)15C2]3− (III), are described. Compound I, which is paramagnetic, has been synthesized in high yields by redox-condensation of Co3(CO)9CCl with [Ni9(CO)17C]2−, whereas the diamagnetic trianions II and III have been respectively obtained by reduction of I, with sodium metal in THF and sodium hydroxide in methanol. The anion I has been isolated in a crystalline state in association with several tetrasubstituted ammonium or phosphonium cations, which are characterized by elemental analysis and by a single-crystal X-ray diffraction study, of the tetraphenylphosphonium salt. The anion I has a metal frame based on a 3,4,3-C2h stack of metal atoms, which may be regarded as derived by condensation of two either octahedral or trigonal-prismatic moieties. The resulting deca-vertices metal polyhedron encapsulates a C2 fragment showing a short CC interatomic separation of 1.48 A. The three cobalt atoms cannot be distinguished from the remaining seven nickel atoms and are probably randomly distributed over the ten vertices. The M-M distances are scattered over the range 2.34–2.80 A, and each carbide carbon is encapsulated in a seven-vertices cage which may be described as a distorted capped trigonal prism. The carbonyl stereochemistry comprises six carbonyl groups terminally bonded to the atoms of the top and bottom triangular layers, and ten edge-bridging CO which span the ten inter-layer edges. The structure of this decanuclear dicarbide cluster is compared with those reported for related species and a rationalization is offered for the variations of the metal geometry and the CC interatomic separation.