25838-69-1Relevant articles and documents
Ustynyuk, N. A.,Vinogradova, V. N.,Petrovskii, P. V.
, (1982)
Homogeneous CO hydrogenation: Ligand effects on the lewis acid-assisted reductive coupling of carbon monoxide
Miller, Alexander J. M.,Labinger, Jay A.,Bercaw, John E.
, p. 4499 - 4516 (2011/01/09)
Structure-function studies on the role of pendent Lewis acids in the reductive coupling of CO are reported. Cationic rhenium carbonyl complexes containing zero, one, or two phosphinoborane ligands (Ph2P(CH 2)nB(C8H14), n = 1-3) react with the nucleophilic hydride [HPt(dmpe)2]+ to reduce [M-CO] + to M-CHO; this step is relatively insensitive to the Lewis acid, as both pendent (internal) and external boranes of appropriate acid strength can be used. In contrast, whether a second hydride transfer and C-C bond forming steps occur depends strongly on the number of carbon atoms between P and B in the phosphinoborane ligands, as well as the number of pendent acids in the complex: shorter linker chain lengths favor such reductive coupling, whereas longer chains and external boranes are ineffective. A number of different species containing partially reduced CO groups, whose exact structures vary considerably with the nature and number of phosphinoborane ligands, have been crystallographically characterized. The reaction of [(Ph2P(CH 2)2B(C8H14))2Re(CO) 4]+ with [HPt(dmpe)2]+ takes place via a hydride shuttle mechanism, in which hydride is transferred from Pt to a pendent borane and thence to CO, rather than by direct hydride attack at CO. Addition of a second hydride in C6D5Cl at -40 °C affords an unusual anionic bis(carbene) complex, which converts to a C-C bonded product on warming. These results support a working model for Lewis acid-assisted reductive coupling of CO, in which B (pendent or external) shuttles hydride from Pt to coordinated CO, followed by formation of an intramolecular B-O bond, which facilitates reductive coupling.
Transition-metal hydrides and carbonyl anions as ligands toward a Pt centre in rhenium-platinum triangular clusters: A qualitative order of 'thermodynamic nucleophilicity'
Bergamo, Mirka,Beringhelli, Tiziana,Ciani, Gianfranco,D'Alfonso, Giuseppe,Moret, Massimo,Sironi, Angelo
, p. 291 - 303 (2008/10/08)
Six novel mixed-metal spiked-triangle complexes [Re2Pt(μ-H)2(CO)9{X}] have been obtained. The metallo-ligands X bound to the Pt vertex are either transition-metal hydrides, such as HMn(CO)5, HRe(CO)4(PPh3), HRe(CO)3(PPh3)2, or carbonyl anions, such as [Mn(CO)5]-, [WCp(CO)3]- and [Co(CO)4]-. Two main synthetic routes have been used to prepare these complexes: (i) replacement of the labile ligand 1,5-cyclooctadiene (COD) of [Re2Pt(μ-H)2(CO)8(COD)] with CO and X; (ii) substitution of the labile 'ligand' HRe(CO)5 in [Re2Pt(μ-H)2(CO)9{HRe(CO)5}] by the ligands X. The neutral species [Re2PtMn(μ-H)3(CO)14] has been obtained by protonation of [Re2Pt(μ-H)2(CO)9{Mn(CO)5}] -. Variable temperature 1H NMR investigations showed that it exists in solution as two isomers a and b, likely differing in the location of one hydride, a having the structure [Re2Pt(μ-H)2(CO)9{HMn(CO)5}], and b the structure [Re2Pt(μ-H)3(CO)9{Mn(CO)5}]. The ligand HMn(CO)5 of a shows a high lability, being in fast exchange with free [HMn(CO)5] even at 193 K. At higher temperature interconversion between the two isomers and exchange between the hydrides bound to Pt in b is observed. The treatment of [Re2Pt(μ-H)2(CO)9{WCp(CO)3}] - with strong acids failed to give the protonated derivative. The strong nucleophile [FeCp(CO)2]- reacted with [Re2Pt(μ-H)2(CO)9{HRe(CO)5}] as a Broensted base rather than as a nucleophile, giving deprotonation instead of substitution of the labile HRe(CO)5 ligand bound to Pt. The complex [Re2Pt(μ-H)2(CO)9{HRe(CO) 4(PPh3)}] has been characterised by X-ray single crystal analysis. It crystallises in the monoclinic space group P21/c (No. 14) with a=9.229(3), b=30.700(8), c=12.915(3) A, β=98.05(2)°, V=3623(2) A3 and Z=4. A series of displacement reactions of the type [Re2Pt(μ-H)2(CO)9{X}]+X′ ? [Re2Pt(μ-H)2(CO)9(X′)] + X allowed the following qualitative order of affinity of the metallo-ligands X for the Pt atom (a scale of 'thermodynamic nucleophilicity') to be established: [Re(CO)5]- > [HRe2(CO)9]-≈[Mn(CO)5] ->[WCp(CO)3]->[Co(CO)4] -> [HRe(CO)4(PPh3)]>[HRe(CO)3(PPh 3)2]>[HRe(CO)5]>[HMn(CO) 5]>[HWCp(CO)3].
