Ugo Sartorelli

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.

Fluxional behaviour of Rh4(CO)8{P(OPh)3}4: A 13C-{31P, 1H} NMR study

Abstract Variable temperature 13 C-{ 31 P, 1 H} NMR studies on Rh 4 (CO) 8 {P(OPh) 3 } 4 show that the solid state structure is maintained in solution at low temperature; at higher temperatures carbonyl migration occurs around the metal polyhedron with the lowest energy migration occurring via a Cotton type mechanism which also involves a rocking motion about the unique rhodium in the basal plane. At +82°C, the fast exchange limiting 13 C-{ 31 P, 1 H} and 31 P spectra exhibit a quintet and doublet of quartets, respectively.

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.

New tetrahedral clusters of iridium. Crystal and molecular structure of μ3-phenylphosphidotri-μ-carbonyltricarbonyltetrakis(triphenylphosphine)-tetrahedro-tetrairidium

Abstract The reaction of Ir4(CO)12 with PPh3 in toluene, under forcing conditions, yields a mixture of products, one of which has been identified by X-ray diffraction as Ir4(μ3-PPh)(μ2-CO)3(CO)3(PPh3)4. It is the first iridium cluster to contain four triphenylphosphine groups and a phenylphosphido ligand. The metal tetrahedron displays a trigonal pyramidal distortion with average apical and basal edges of 2.747 and 2.894 », respectively. The latter value is ca. 0.18 » longer than the usual metal-metal bond length in iridium tetrahedra.

Multinuclear magnetic resonance studies on [Rh4(CO)12–xLx][L = P(OPh)3, x= 1–4]

Direct 103Rh n.m.r. studies on [Rh4(CO)12–xLx][L = P(OPh)3, x= 1–4] at low temperatures support the solution structures previously proposed and, although the apical rhodium resonance always occurs at lowest frequency, there is little variation in δ(103Rh) with increasing ligand substitution. Measurements of 13C-{103Rh} allow unambiguous assignment of the 13C n.m.r. spectra when x= 1 and 3 and δ(13COax) is always at lowest frequency with 1J(103Rh–13COax)≃1J(103Rh–13COap) < 1J(103Rh–13COrad); this suggests a new assignment for the 13C n.m.r. spectrum of [Rh4(CO)12].

Neutral substituted carbonyl clusters of iridium. Synthesis and X-ray characterization of tri-μ3-carbonyl-μ-carbonylheptacarbonylpentakis(trimethylphosphite)-octahedro-hexairidium

Abstract The reaction of Ir 6 (CO) 16 with P(OMe) 3 in toluene yields Ir 6 (CO) 11 [P(OMe) 3 ] 5 which has been shown by X-ray diffraction to contain an octahedral cluster of iridium atoms bearing five terminal trimethylphosphite ligands, three face-bridging, one edge-bridging and seven terminal carbonyl groups.

Neutral substituted carbonyl clusters of iridium. Synthesis and X-ray structure of μ3-carbonyltri-μ-carbonyloctacarbonyltetrakis(triphenylphosphite)-octahedro-hexairidium

The reaction of Ir 6 (CO) 16 with P(OPh) 3 in toluene yields Ir 6 (CO) 12 [P(OPh) 3 ] 4 which has been shown by X-ray diffraction to contain an octahedral cluster bearing four terminal P(OPh) 3 ligands, one face-bridging, three edge-bridging and eight terminal carbonyl groups. The carbonyl arrangement is different from that found in the analogous rhodium complex.

Synthesis and structural characterization of tetra-μ3-carbonylhexacarbonyltris[bis(diphenylphosphino)methane]-hexarhodium

Abstract The title compound Rh6(CO)10(DPM)3 (DPM  bis(diphenylphosphino)-methane), obtained by heating Rh6(CO)16 and DPM in toluene, contains an octahedral rhodium cluster, with a mean RhRh bond length of 2.783 A, which bears four triple bridging and six terminal carbonyl ligands, and three DPM molecules chelating pairs of adjacent metal atoms (mean RhP 2.307 A). Thus each Rh atom is connected to one phosphorous atom and to one terminal and two triple-bridging carbonyl ligands.