89397-42-2Relevant academic research and scientific papers
Metallacarboranes in Catalysis. 3. Synthesis and Reactivity of exo-nido-Phosphinerhodacarboranes
Long, Judith A.,Marder, Todd B.,Behnken, Paul E.,Hawthorne, M. Frederick
, p. 2979 - 2989 (2007/10/02)
The carbon-substituted closo-bis(triphenylphosphine)hydridorhodacarborane , the carbon-substituted exo-nido-bis(triphenylphosphine)rhodacarborane complexes , and the salt (1+)(1-) were prepared by the reaction of the carborane anions (1-) (Ia-e) with in benzene.Complexes IIa,c exhibited a closo-exo-nido equilibrium in solution.The exo-nido complexes can be regarded as being composed of an (1+) cation bound to a (1-) anion cage via two exo polyhedral three-center, two-electron interactions (Rh-H-B bridges) with terminal hydrogen atoms.The (1+) moiety can apparently rotate with respect to and, in some cases, migrate about the polyhedral surface of the cage.Complex IIA reacted with 2 equiv of PCy3 ( Cy = cyclohexyl) to generate the mixed phosphine exo-nido complex (IIIa).Reaction of the exo-nido-bis(triphenylphosphine)rhodacarboranes with good ? donors or CO displaced the rhodium from the carborane cage to give cationic species of the form (1+), (1+), (1+) (L = PPh3, S = solvent); (1+) (L = PEt3); (1+) (L-L = dppe); and (1+) (L-L-L = Ph2PCH2CH2P(Ph)CH2CH2PPh2 = triphos, L' = PPh3).The (1+) complexes (Va-e) reacted further to generate closo species of the general formula .The 3,1,2-isomer was obtained when R = R' = Me (VIIc), R, R' = μ-(CH2)3- (VIId), and R, R' = μ-(1',2'-CH2C6H4CH2-) (VIIa); but in the cases of R = Ph, R' = Me and R = 1'-(closo-1',2'-C2B10H11), R' = H, a polytopal rearrangement occurred, resulting in the formation of , R = Me, R' = Ph (VIb) and R = H, R' = 1'-(closo-1',2'-C2B10H11) (VIe).The complexes IIa-d and IIIa underwent oxidative addition of H2 to give dihydrido Rh(III) products in which the (1+) or (1+) fragment remains bonded to the carborane cage through two three-center, two-electron Rh-H-B interactions.Molecular structures of two representative exo-nido-rhodacarboranes (IIb and IIIa) along with that of closo-rhodacarborane (IIa) have been determined and are formally presented in the following paper of this series.
Metallacarboranes in Catalysis. 5. Interconversion of closo-Bis(phosphine)hydridorhodacarboranes by Rhodium Transfer between η5-nido-Carborane Anions
Long, Judith A.,Marder, Todd B.,Hawthorne, M. Frederick
, p. 3004 - 3010 (2007/10/02)
Both the hydride and dicarbollide ligands of a series of closo, formally six-coordinate Rh(III), bis(triphenylphosphine)hydrido η5-(nido-C2B9H9RR') complexes were easily replaced by a series of (1-) ligands using thermal reactions.The following trend for ease of displacement of the nido-carborane anion in cage-carbon-substituted complexes has been found: 7,8-disubstituted > 7,8-monosubstituted > 7,8-unsubstituted > 7,9-unsubstituted ca. 2,9-unsubstituted.Kinetic studies of the reaction of (R = Me, R' = H) (IVd) with (1-) (Ia) and (1-) (III) in THF at 29 deg C showed no anion concentration dependence and a common first-order rate constant for the two reactions although in the case of (1-) (II), anion dependence was observed.Similar kinetic studies of the reaction of (IVf) with anions Ia, II, and III in THF at -63 deg C proved these exchanges with exo-nido substrates to be much faster than the reactions involving closo substrates.In the cases of Ia and II, the less stable kinetic product of the reaction, the exo-nido tautomer, was initially observed along with its conversion to the more stable closo tautomer.Analysis of the anion concentration dependence of the rates of these reactions suggested the existence of a spectroscopically invisible intermediate, presumably an isomer of the exo-nido starting complex.Formation of an analogous intermediate appears to be the rate-determining step in reaction of closo-IVd with anions Ia and III.In addition, the dissociation of either PPh3 or nido-carborane anion does not appear to be involved in any of these cage exchange reactions.Anion III was found to be a more effective nucleophile than Ia which, in turn, was more nucleophilic than II.
