Vincenzo G. Albano

New nickel–carbon dioxide complex: synthesis, properties, and crystallographic characterization of (carbon dioxide)-bis(tricyclohexylphosphine)nickel

[Ni(CO2)(PCy3)2],0·75(C7H8), where Cy = cyclohexyl, can be made either by treating [Ni(PCy3)3] or [{Ni(PCy3)2}2N2] with CO2 in toluene, or by direct reduction of [NiBr2(PCy3)2] with sodium sand under CO2; the complex is planar, the CO2 ligand possesses bent geometry and is co-ordinated through the carbon atom and one of the oxygen atoms.

High Nuclearity Metal Carbonyl Clusters

Publisher Summary The chapter focuses on the compounds containing five or more metal atoms. The slow rate of publication in this area is mainly due to the number of steps required by this research, i.e., synthesis, crystallization, structural identification, and chemical characterization. More than fifty different examples of high nuclearity carbonyl clusters (HNCC) arc presently known, all of which contain Group VIII transition metals. In post-transition metals the increased separation between the (n - 1) d and ns-np orbital is probably responsible for the low stability of their bonds with the highly π-acidic carbon monoxide ligand; a number of high nuclearity clusters with less π -acidic ligands, such as tertiary phosphines or organic donor groups, is known. Approximate calculations on some of the more crowded clusters, such as [Fe 4 (CO) 13 ] 2- , Fe 5 (CO) 15 C, and Ru 6 (CO) 18 H 2 , show that, at the level of the carbon atoms, about 96% of the available surface is occupied. This figure seems very high particularly if the distribution of the carbonyl groups is not considered as homogeneous. The high Nuclearity clusters of the transition metals that precede Group VIII are, therefore, expected to be destabilized by steric crowding, although some carbides and mixed nitrosyl-carbonyl derivatives should be sterically possible.

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.

Five-coordinate alkene complexes of palladium(II) and platinum(II)

Abstract The review is focused on five-coordinate Pd(II)- and Pt(II)-alkene complexes with a trigonal bipyramidal arrangement of the ligands. Synthetic methods are extensively described and the characterization procedures of 243 compounds are listed. Stereochemical and reactivity aspects are reported. A chart with the X-ray structural parameters of 19 complexes and a list of 76 references are included.

Crystal and molecular structure of (dithiformato)bis(triphenylphosphine)dicarbonylrhenium, Re(HCS2)(CO)2[P(C6H5)3]2

Abstract The addition of CS2 to hydridotris(trisphenylphosphine)dicarbonylrhenium results in the formation of (dithioformato)bis(triphenylphosphine)dicarbonylrhenium. This complex crystallizes in the triclinic space group P I ; the reduced cell has dimensions: a 10.481(15) A, b = 12.471(15)A, c = 14.878(15) A, a = 81.799(7)°, β = 74.03(7)°, > = 107.37(7)°, V = 1735 A3. The observed density is 1.63(2) g/cm3 while the computed density for Z = 2 is 1.615 g/cm3. Intensities of 2682 independent reflections, having σ(I)/I⪡0.25, were measured by counter methods using a molybdenum source and a silicon monochromator. The structure was refined by full matrix least squares to a final R factor of 0.039. The crystal consists of a packing all discrete monomeric molecules; the distorted octahedral coordination around the metal atom has approximately a C2v symmetry. The dithioformate anion chelates on rhenium atom with bonding parameters ReS 2.500(3) A and 2.532(5) A, CS 1.64(2) A and 1.68(2) A and SCS 116.7(1)°. The mean length of the two ReP bonds is 2.42 A and that of the two ReC bonds is 1.91 A. The ReCO interactions appear to be disordered and so does the chelate anion. On the basis present determination probable structures are suggested for other addition products formed from CS2 and RhIII and IrI complexes.

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.

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.

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−.

Synthesis and properties of pentadecacarbonyl- hexacobaltate dianion derivatives

Abstract The anion [Co 6 (CO) 15 ] 2- has been obtained in 80-90% yield by treating Co 2 (CO) 8 with ethanol in vacuum at 60°. Acetone and methanol give less satisfactory results; isopropanol, dioxane and tetrahydrofuran give Co 4 (CO) 12 . Preformed tetracarbonylcobaltates of the type [Co(ROH) 6 ][Co(CO) 4 ] 2 (R = Me, Et) react with isopropanol in vacuum at 60° to give a mixture of [Co 6 (CO) 15 ] 2- derivatives and Co 4 (CO) 12 in a one to two ratio. A reaction scheme which explains such a ratio, and involving the intermediate formation of Co 6 (CO) 16 is proposed. The salts [Cat] 2 [Co 6 (CO) 15 ] (Cat = K, Cs, NMe 4 , NEt 4 , NBu 4 ) have been characterized by analysis and IR spectroscopy. The anion [Co 6 (CO) 15 ] 2- is diamagnetic. Solutions of [Co 6 (CO) 15 ] 2- derivatives react easily with carbon monoxide giving tetracarbonylcobaltate monoanion derivatives.

On the stabilization of five-coordinate trigonal-bipyramidal palladium(II) species. Crystal structure of (2,9-dimethyl-1,10-phenanthroline)methylchloropalladium(II)

Abstract The role of the steric requirements of the NN′ chelate ligand in the stabilization of trigonal-bipyramidal [Pd(NN′)(olefin)RX] complexes is discussed. The crystal structure of the precursor (2,9-dimethyl-1,10,phenanthroline)methylchloropalladium(II) (1a) has been determined. The molecule adopts a significantly distorted square-planar coordination geometry in order to accomodate the crowding in the coordination plane. The most significant distortions involves the coordinated methyl group and the dimethylphenanthroline molecule, whose mean plane lies out of the coordination plane by 39.3°. There is ready CO insertion into the PdMe bond of 1a to give an acyl derivative. The formation of a five-coordinate acyl derivative by subsequent uptake of an olefin also illustrates the importance of the steric effects of NN′ ligands.