Correlation of the hydrogénation catalytic activity of dinuclear complexes of rhodium(I) with the formation of carbonyl-bridged complexes

Abstract

Methanolic solutions of the dinuclear cationic complexes of rhodium(I), [Rh2(μ-X)(CO)2(Ph2ECH2EPh2)2]+ (X = Cl, Br; E = P, As) and iridium(I), [Ir2Cl(CO)3(Ph2PCH2PPh2)2], are each active catalysts for the hydrogenation of alkynes to alkenes, and alkenes to alkanes. Neutral complexes with pseudohalide ligands have also been investigated but only the cyano-complex [Rh2(CN)2(CO)2(Ph2PCH2PPh2)2], and the arsine analog, are of significant catalytic activity. Only those complexes which reversibly form bridged complexes with ligands such as CO are also catalytically active.Similar complexes with dithioether ligands are not efficient catalysts under the conditions tested.

Kinetics and mechanism of the phase-transfer-catalyzed carbonylation of benzyl bromide by cobalt tetracarbonyl anion

“…According to this scheme, the main pathway for production of 9 and 10 would be a simple SN2 reaction for step 1 followed by transient production of the unstable hydroxycarbonyl anion 13 (Scheme IV).…”

“…A catalytic cycle is proposed for this liquid-liquid system, in which it is shown that the catalyst (Bu4N+Co(CO)4") stays in the organic phase, and the product (the phenylacetate anion) is expelled into the aqueous phase. It is also shown that the rate-limiting reaction is not the nucleophilic displacement (1) (reaction of benzyl bromide with the cobalt carbonyl anion) but the cleavage of the acylcobalt carbonyl 4 by the ion pair Bu4N+OH" at the liquid-liquid interface. The presence of byproducts such as toluene and diphenylethane is accounted for in terms of the decomposition of a transient hydroxycarbonyl species 13 through loss of carbon dioxide.…”

“…1974 direction. Expected effects are as follows: (1) good separation between the catalyst and the product;…”