1060751-97-4Relevant academic research and scientific papers
Hydride abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz = C5(CH2Ph)5): New cationic complexes stabilized by η5:η2-C5H 4:C6H5 bonding of the pentabenzylcyclopentadienyl ligand
Antunes, M. Augusta,Alves, Luis G.,Namorado, Sonia,Ascenso, Jose R.,Veiros, Luis F.,Martins, Ana M.
, p. 4387 - 4396 (2012/07/14)
Hydride abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz = C5(CH2Ph)5) using trityl cations led to [M{η5:η2-C5Bz 4CH2Ph}(CO)3]BArF (BArF = B(3,5-C6H3(CF3)2)4; M = Mo (3), W (4)) or [MCpBz(CO)3(FBF3)] (M = Mo (5), W (6)) depending on the trityl counterions. The stabilization of the acidic metal centers in 3 and 4 is made through the coordination of a C=C bond of one phenyl ring, generating ansa-bridged cyclopentadienyl-phenyl carbonyl complexes. 5 and 6 are zwitterionic compounds stabilized by the coordination of the BF4 anion. An exchange process between coordinated and noncoordinated phenyl rings occurs in dichloromethane solutions of 3. VT NMR experiments gave the exchange rate at various temperatures and ΔG? 298 = 10.1 ± 0.2 kcal mol-1. In 4 the phenyl bonding is static at room temperature, on the NMR time scale. Reactions of 3 and 4 with CO and H2O led to [MCpBz(CO)4]BAr F (M = Mo (7), W (8)) and [MCpBz(CO)3(OH 2)]BArF (M = Mo (11), W (12)). In CH2Cl 2 solutions 3 and 4 convert slowly to 7 and 8, respectively. DFT calculations attest to the stability of 3 to H2O bonding and also show that the replacement of phenyl coordination by CO is a favorable process (ΔH = -13.8 kcal mol-1).
Ionic hydrogenation of ketones with molybdenum pentabenzylcyclopentadienyl hydride catalysts
Namorado, Sonia,Antunes, Maria Augusta,Veiros, Luis F.,Ascenso, Jese R.,Duarte, M. Teresa,Martins, Ana M.
, p. 4589 - 4599 (2009/02/07)
A study of the reactivity of [MoCpBz(CO)3H] (Cp Bz = pentabenzylcyclopentadienyl) as a catalyst precursor for the ionic hydrogenation of 3-pentanone is presented. The complexes [MCp Bz(CO)3OTf] (M = Mo (3), W (4)), [MoCpBz(CO) 3(O=CEt2)]BF4 (9), and [MoCp Bz(CO)3(O=CMe2)]BF4 (12) are described. 9+ and [MoCpBz(CO)3(OHCHEt 2)]+ (8+) were identified by NMR under catalytic conditions. The reaction of [WCpBz(CO)3H] with triflic acid led to [WCpBz(CO)3(H)2] + (7+), which was identified by NMR as a dihydride complex. The influence of steric and electronic effects on the catalyst activity is discussed on the basis of experimental results and a mechanism proposal resulting from DFT calculations. The proposed mechanism includes facile protonation of the acetone O atom promoted by a dihydride Mo(IV) complex, followed by slower hydride transfer from the metal center to the carbonyl C atom. The results indicate strong coordination of both the product (isopropyl alcohol) and the reactant (acetone), leading to some blocking of the catalyst active site. Regeneration of the catalyst active species is the rate-limiting step of the catalytic cycle. The steric bulk of the CpBz ligand increases the catalyst activity.
