Wilkinson-Osborn catalyst

The earliest homogeneous hydrogenation catalyst was Wilkinson catalyst [RhCl(PPh3)3] 1 which was active at 1 atm of H2 pressure at room temperature for monosubstituted and cis-disubstituted alkenes such as cyclohexene. The second-, [Rh(COD)(PPh3)2]PFg 2, and third-, [Ir(COD)(PCy3)(pyr)]PF6 3, generation catalysts were developed by Osborn-Schrock and Crabtree, respectively. 

A key feature of the mechanism of Wilkinson s catalyst is that catalysis begins with reaction of the solvated catalyst, RhCl(PPh3)2S (S=solvent), and H2 to form a solvated dihydride Rh(H)2Cl(PPh3)2S [1], In a subsequent step the alkene binds to the catalyst and then is transformed into product via migratory insertion and reductive elimination steps. Schrock and Osborn investigated solvated cationic complexes [M(PR3)2S2]+ (M=Rh, Ir and S= solvent) that are closely related to Wilkinson s catalyst. Similarly to Wilkinson s catalyst, the mechanistic sequence proposed by Schrock and Osborn features initial reaction of the catalyst with H2 followed by reaction of the dihydride with alkene for the case of monophosphine-ligated rhodium and iridium catalysts [12-17]. Such mechanisms commonly are characterized... 

The discovery of Wilkinson s catalyst led to the development of a new class of complexes capable of promoting hydrogenation these have the general formula I. M+ (M = Rh or Ir). The Rh series was first reported by Schrock and Osborn 81 equation 9.30 demonstrates how such a complex may be prepared. The cationic Rh(I) complex (60), interacts with a solvent such as THF or acetone to give a 12-electron, unsaturated diphosphine intermediate (61), which is considered the active catalyst. The catalytic cycle begins this time with alkene binding, followed by the oxidative addition of H2. 

Asymmetric hydrogenation is the archetype of homogeneous catalysis [26]. Wilkinson and Osborn reported that [RhCl(PPh3)3] catalyzes the homogeneous hydrogenation of olefins [27]. This hydrogenation catalyst was rapidly adapted to an enantioselective... 

In contrast to the relatively high solvent dependence, the Osborn system shows a relatively small dependence on L. Wilkinson s catalyst requires PPh3 or ligand of very similar cone angle, because the steric... 

Hydrogenation by homogeneous catalysis has been widely studied over the years both with respect to mechanism and application. Ruthenium, iridium, and rhodium are the most frequently used metals. The best known is the rhodium catalyst RhClfPPh ), that was first discovered by Wilkinson and bears his name (see Jardine et al., 1967 Osborn et al., 1966 James, 1973). 

Young JF, Osborn JA, Jardine FH, Wilkinson G (1965) Hydride intermediates in homogeneous hydrogenation reactions of olefins and acetylenes using rhodium catalysts. Chem Conunun 131 132... 

In 1965, Wilkinson (together with his former Ph.D. student John Osborn), and Coffey independently discovered the first homogeneous olefin hydrogenation catalyst, Wilkinson s catalyst, [RhCl(PPh3)3]. In 1970, Henri Kagan reported in a patent... 

The results of mechanistic studies are much less secure than in the case of the hydrogenation reaction. A mechanism similar to that of the classic oxidative addition onto a metal center has been proposed with olefin insertion into the M-H bond or more hypothetically into the M-SiR 3 bond. The Wilkinson-Osborn catalyst, among others, follows this mechanism. 

The development of homogeneous olefin hydrogenation catalysts based on soluble rhodium and iridium complexes, in particular Wilkinson s catalyst (33) [27], Crabtree s catalyst (34) [41], and the Schrock-Osborn catalyst (35)... 

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