Osborne complex

The first successful hydrogenation reactions in ionic liquids were studied by the groups of de Souza [45] and Chauvin [46] in 1995. De Souza et al. investigated the Rh-catalyzed hydrogenation of cyclohexene in l-n-butyl-3-methylimidazolium ([BMIM]) tetrafluoroborate. Chauvin et al. dissolved the cationic Osborn complex [Rh(nbd)(PPh3)2][PFg] (nbd = norbornadiene) in ionic liquids with weakly coordinating anions (e.g., [PFg] , [BFJ , and [SbF ] ) and used the obtained ionic catalyst solutions for the biphasic hydrogenation of 1-pentene as seen in Scheme 5.2-7. 

Scheme 5.2-7 Biphasic hydrogenation of 1-pentene with the cationic Osborn complex ...

Scheme 5.2-7 Biphasic hydrogenation of 1 -pentene with the cationic Osborn complex [Rh(nbd)(PPh3)2][PF6] (nbd = norbornadiene) in ionic liquids with weakly coordinating anions.

Osborn s discovery (14) that aluminum halides bimTto oxo ligands in tungsten oxo neopentyl complexes, and that these complexes decompose to give systems which will efficiently metathesize olefins, raised more questions concerning the role of the Lewis acid. A subsequent communication (20) answered some of the questions the aluminum halide removes We oxo ligand and replaces it with two halides to yield neopentylidene complexes (equation 8). 

The cationic complexes Rh(diene)L >+ (L is a tertiary phosphine, phosphite, or arsine) were reported by several groups in 1969- 1970 (7, p. 270), but Osborn et al. 129-132) first reported on their potential for hydrogenation of olefins, acetylenes, and ketones. Full details on these systems have now appeared 133-135), and the important equilibria governing the active catalysts are given in Eqs. (23)-(25). An important difference from... 

Compared with the Osborn-type cationic rhodium complexes (Section III,A,3), the iridium analogs are much less active for asymmetric hydrogenation of ketones (280). 

Osborn and Green s elegant results are instructive, but their relevance to metathesis must be qualified. Until actual catalytic activity with the respective complexes is demonstrated, it remains uncertain whether this chemistry indeed relates to olefin metathesis. With this qualification in mind, their work in concert is pioneering as it provides the initial experimental backing for a basic reaction wherein an olefin and a metal exclusively may produce the initiating carbene-metal complex by a simple sequence of 7r-complexation followed by a hydride shift, thus forming a 77-allyl-metal hydride entity which then rearranges into a metallocyclobutane via a nucleophilic attack of the hydride on the central atom of the 7r-allyl species ... 

The cycline-dependent kinases (complex cyclines A/E and CDK2) are able to phosphorylate the ER in serine, particularly in the S104 and S106 belonging to TAF1, and with consequences similar to those of the pathway of the MAP kinases (Osborne et al. 2001 Powles 2002). 

CHCMe3)(Solvent)][BAr[3,5-(CF3)2C6H3]4. Cationic alkylidene complexes in general are rare, although they are likely to be the most active species in the systems pioneered by Osborn and coworkers [99,100]. 

The synthesis of cationic rhodium complexes constitutes another important contribution of the late 1960s. The preparation of cationic complexes of formula [Rh(diene)(PR3)2]+ was reported by several laboratories in the period 1968-1970 [17, 18]. Osborn and coworkers made the important discovery that these complexes, when treated with molecular hydrogen, yield [RhH2(PR3)2(S)2]+ (S = sol-vent). These rhodium(III) complexes function as homogeneous hydrogenation catalysts under mild conditions for the reduction of alkenes, dienes, alkynes, and ketones [17, 19]. Related complexes with chiral diphosphines have been very important in modern enantioselective catalytic hydrogenations (see Section 1.1.6). 

Osborn R.N., Jackson D.H., 1988. Leaders, Riverboat Gamblers, or Purposeful Unintended Consequences in the management of complex dangerous technologies, Academy of Management Journal Vol. 31 (4), pp. 924-947. 

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... 

Iridium is now a well-accepted choice for homogeneous catalysis, thanks to the historical developments discussed. Shrock and Osborn s work on [(cod)RhL2] complexes that showed how lowering the L M ratio from 3 to 2 gave excellent... 

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