Secondo Martinengo

New mixed tetranuclear metal carbonyls of group VIIIB

Abstract The new mixed tetranuclear carbonyls Co 3 Rh(CO) 12 , Co 2 Rh 2 (CO) 12 , Co 2 Ir 2 (CO) 12 , Rh 3 Ir(CO) 12 and Rh 2 Ir 2 (CO) 12 are easily synthesised by reacting tetracarbonylmetallate anions with halocarbonyls or with metallic cations in aqueous solution. Infrared spectra of all these compounds reveal the presence of both terminal and bridging carbonyl groups, in most cases consistent with a Co 4 (CO) 12 -Rh 4 (CO) 12 like structure. Thermal stability decreases as the rhodium content increases, as shown by the facile redistribution to tetranuclear species containing less rhodium and to hexanuclear species, such as Co 2 Rh 4 (CO) 16 . Mass spectra are generally complicated, except in the case of Co 2 Ir 2 (CO) 12 , and parallel the thermal stability. All compounds containing cobalt react readily with Lewis bases. Preliminary X-ray data for Co 2 Rh 2 (CO) 12 , Co 2 Ir 2 (CO) 12 and Co 2 Rh 4 (CO) 16 are also reported.

Improved synthesis of dodecacarbonyltetrarhodium at atmospheric pressure

A convenient two step synthesis of Rh4(CO)12 at room temperature and atmospheric pressure is reported. This involves reduction of the hexachlororhodate(III) anion to dicarbonyldichlororhodate(I) anion with copper metal, followed by further reduction with carbon monoxide and water in presence of sodium citrate buffer. Yields of 86–99% are obtained.

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.

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.

Synthesis and properties of tetradecacarbonylhexacobaltate tetraanion derivatives

Abstract The anion [Co6(CO)14]4− has been obtained by reducing Co4(CO)12 with an alkali metal (Li, Na, K) in tetrahydrofuran, or with cobaltocene as a homogeneous reducing agent. In both cases the initial product was the anion [Co6(CO)15]2−, which was subsequently reduced to [Co6(CO)14]4−. In toluene, cobaltocene reacted with Co2(CO)8 to give cobalticinium tetracarbonylcobaltate, while with Co4(CO)12 the brown salt {[(π-Cp)2Co][Co4(CO)11−12]}n was precipitated as the first reaction product. This anion is believed to be the first intermediate in the reduction of Co4(CO)12. The salts M4[Co6(CO)14][MK, NEt4 and (π-Cp)2Co] have been characterized by analysis. The solutions containing the anion [Co6(CO)14]4− reacted with carbon monoxide giving tetracarbonylcobaltate(1−) derivatives. The salt Na4[Co6(CO)14] has been obtained in two different isomeric forms; the considerable differences observed in the IR spectra of several salts [Li, Na, K, NEt4 and (π-Cp)2Co] are in accord with the postulated existence of several isomeric forms of the anion [Co6(CO)14]4−.

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.

Heterometallic adducts of [Rh6(CO)15C]2–, including the novel double- and triple-decker sandwich compounds [Agn{Rh6(CO)15C}2](4–n)–(n= 1 and 3) and [Agn{Rh6(CO)15C}3](6–n)–(n= 2 and 4) and the X-ray structural characterisation of [PPh4]3[Ag{Rh6(CO)15C}2]

Multinuclear n.m.r. measurements have been used to establish the formation of the following new adducts of [Rh6(CO)15C]2– by capping the trigonal face of the Rh6 trigonal prism: [{M(PEt3)}{Rh6(CO)15C}]–(M = Ag or Au), [Agn{Rh6(CO)15C}2](4–n)–(n= 1 or 3), [Agn{Rh6(CO)15C}3](6–n)–(n= 2 or 4), [Agn{Rh6(CO)15C}n]n–(n > 3), and [Ag2{Rh6(CO)15C}]. There is no evidence for dissociation of any of these species on the n.m.r. time-scale, whereas n.m.r. spectra suggest that dissociation of [Cu(NCMe)]+ occurs in [{Cu(NCMe)}n{Rh6(CO)15C}](2–n)–(n= 1 or possibly 2) both at room and low temperature. X-ray crystallographic analysis of [Ag{Rh6(CO)15C}2]3– shows that a silver atom is sandwiched between trigonal faces of two staggered Rh6 trigonal-prismatic units and the nature of the silver–rhodium interaction is discussed.

An NMR study of carbide clusters

Abstract 13C and13C-103Rh} data on [Rh6(CO)15C]2− and [Rh6(CO)13C]2− are reported and compared. [Rh6(CO)13C]2− undergoes a unique facile intramolecular CO migration around the equator of the Rh6 octahedron; at 25°C, [Rh6(CO)15C]2− undergoes preferential intermolecular CO exchange at sites which have the longest RhCO bonds and direct exchange of terminal carbonyls is easier than edge-bridging carbonyls with approximately similar RhCO bond lengths.

New carbide clusters in the cobalt sub-group. Part 7. Preparation and structural characterization of carbido-hexa-µ-carbonyl-heptacarbonyl-polyhedro-hexarhodate(2–) as its bis(tetraphenylphosphonium) salt

The anion [Rh6C(CO)13]2– has been prepared by refluxing a solution of K2[Rh6C(CO)15]·6CH3O(CH2)4OCH3 in PriOH at 100 °C for 2 h under nitrogen and pumping off the evolved CO. The new anion has been characterized by a crystallographic study on the salt [PPh4]2[Rh6C(CO)13], which crystallizes in the monoclinic space group P21/c with cell constants a= 24.232(8), b= 12.587(5), c= 19.754(7)A, and β= 92.0(5)°. The structure has been solved by direct methods and refined by least-squares calculations to R= 0.055 for 4 350 significant diffraction intensities. The anion contains a distorted octahedron of rhodium atoms with the carbide ion in the centre [Rh–Rh 2.733–3.188(2), Rh–C(carbide) 1.99–2.15(1)A]. Six of the carbonyl groups are edge bridging, spanning consecutive edges of the three octahedron equators, and seven are terminal. The idealized molecular symmetry is Cs-m. A strong dependence of the metal–metal distances on the ligand geometry has been noticed, and the driving force of the octahedron deformation is very likely the steric requirement of the interstitial carbon.

New carbide clusters in the cobalt sub-group. Part 5. Crystallographic characterization of deca-µ-carbonyl-carbido-octacarbonyl-polyhedro-octacobaltate(2–) in its bis(benzyltrimethylammonium) salt

The title complex crystallizes in the triclinic space group P with unit-cell dimensions a= 19.02(2), b= 10.37(1),c= 12.81(1)A, α= 116.43(8), β= 88.90(8), γ= 95.53(8)°, and Z= 2. The structure has been determined by conventional methods from X-ray single-crystal counter data and refined by least-squares calculations to R 0.064 for 3 539 significant diffraction intensities. The [Co8C(CO)18]2– anion contains a deformed tetragonal antiprism of metal atoms (D2 idealized symmetry) with an average Co–Co distance of 2.52 A. The carbide atom occupies the centre of the cluster; two kinds of Co–C(carbide) distances are present (means 1.99 and 2.15 A). There are eight terminal carbonyl ligands, one per metal atom, and the other ten carbonyls range from partially bent to symmetrically edge-bridging.