142560-39-2Relevant academic research and scientific papers
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.
Synthesis, substitution, and isomerization reactions of trans-Re(CO)4LX (L = group 15 donor ligands; X = Br, I)
Ingham, Wayne L.,Coville, Nell J.
, p. 2551 - 2558 (2008/10/08)
The cleavage of Re2(CO)8L2 with X2 (X = I, L = PPh3, P(OMe)Ph2, P(OMe)3, P(OMe)2Ph, PMePh2, PMe2Ph, P(OPh)3, P(O-o-tol)3, P(OiPr)3, P(CH2C6H5)3; X = Br, L = PPh3, P(OMe)3, P(OMe)2Ph, PMe2Ph, P(OPh)3, P(CH2C6H5)3) in CH2Cl2 gives trans-Re(CO)4LX in yields between 20% and 50% as well as cis-Re(CO)4LX (>50%). Reactions of Re2(CO)9L with Br2, by contrast, gave only cis-Re(CO)4LBr and Re(CO)5Br, while reactions of Re2(CO)9PBz3 (Bz = CH2C6H5) with I2 gave Re(CO)5I as well as a mixture of cis- and trans-Re(CO)4PBz3I (ratio 72:28). The PBz3-containing product ratio could be modified by addition of I-(35:65 isomer ratio) and Br- (15:85, cis-trans ratio; product contained mixture of Re(CO)4PBz3I and Re(CO)4PBz3Br). The data for the cleavage reactions of Re2(CO)10-nLn (n = 1, 2) can be explained by an electrophilic attack of halogen, followed by two competing pathways (concerted, associative) involving attack of the nucleophile. It is predicted that in the total product spectrum (Re(CO)5X, Re(CO)4LX) that a maximum of 50% trans-Re(CO)4LX can be obtained by the halogen cleavage route. An IR kinetic investigation of the trans- to cis-Re(CO)4LX isomerization reaction is consistent with an intramolecular rearrangement process that is influenced by the halide (I 3 3 ～ P(OPh)3 ～ PMe2Ph 2 ～ PPh3 iPr)3 3). Reaction of trans-Re(CO)4PBz3I with L (L = P(OPh)3, t-BuNC) at 100°C in C6D6 revealed that isomerization (60%) was more rapid than substitution (3NO/CH3CN or PdO/t-BuNC gave product ratios of cis-and trans-Re(CO)3(PBz3)LI (L = CH3CN, t-BuNC) that were consistent with substitution preceding isomerization. The Re-CO bonds in trans-Re(CO)4PBz3I are less prone to cleavage than equivalent cis Re-CO bonds in cis-Re(CO)4PBz3I.
