65337-89-5Relevant academic research and scientific papers
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.
Metallacarboranes in Catalysis. 2. Synthesis and Reactivity of Closo Icosahedral Bis(phosphine)hydridorhodacarboranes and the Crystal and Molecular Structures of Two Unusual closo-Phosphinerhodacarborane Complexes
Baker, R. Thomas,Delaney, Mark S.,King, Roswell E.,Knobler, Carolyn B.,Long, Judith A.,et al.
, p. 2965 - 2978 (2007/10/02)
A series of closo icosahedral rhodacarboranes bearing substituents at carbon has been synthesized by the reaction of with the correspondingly C-substituted nido-carborane anions: from (1-) where R = R' = H; R = R' = D; R = H and R' = Ph, Me, and n-Bu; from (1-) where R = H, Ph, and Me; and from (1-).These closo icosahedral rhodacarboranes are catalytically active in alkene isomerization and hydrogenation reactions, among others.The B-D-B-bridge deuterated (1-) gave when reacted with , establishing the regiospecific transfer of BHB hydrogen to Rh-H in the synthesis reaction.The complex is apparently transformed to by a polytopal rearrangement under mild conditions.The optically active catalyst was employed to hydrogenate ethyl α-phenylacrylate to give ethyl α-phenylpropionate in 3percent enantiomeric excess.In the absence of hydrogen this chiral catalyst reacted with certain esters of the acrylic type to yield alkyl chelates in which the alkene function of the ester had undergone migratory insertion into the Rh-H and the ester carbonyl oxygen became bound to Rh.One of these chelates, derived from the d-catalyst and n-butyl acrylate, was characterized crystallographically.The compound crystallizes in the space group P212121 with unit cell parameters a = 24.578 (5) Angstroem, b = 12.543 (2) Angstroem, and c = 10.377 (2) Angstroem, four molecules per unit cell.The structure was solved by conventional heavy-atom methods and refined to a final value of R = 0.069, Rw = 0.080 (3159 reflections).The absolute configuration of the d-catalyst and the (1-), from which it was derived, was thus established.Reaction of the unsubstituted compounds and (L = PPh3) with more basic phosphines gave the corresponding L2 compounds with L = PEt3, PMe2Ph, and for the 3,1,2-isomer, L2 = Ph2PCH2CH2PPh2.Reaction of the unsubstituted 3,1,2-isomer (L = PPh3) with HCl in CHCl3 gave .The analogous chloro compound in which L = PMe2Ph was prepared by the reaction of the Rh-H species with CH2Cl2.Reaction of with HCl/CHCl3 produced the coordinatively unsaturated 16-electron species .This complex reacted with CO and ligands to produce coordinatively saturated adducts.A crystallographic study of the 16-electron 2,1,7-chloride was carried out.This compound crystallizes in the monoclinic system P21/n, a = 13.840 (5) Angstroem, b = 17.000 (7) Angstroem, c = 13.771 (6) Angstoem, and β = 118.98 (2) deg, four molecules of complex and...
