Bimetallic phase-transfer reaction

This is an authentic bimetallic phase transfer reaction in which the second metal species intercepts an organocobalt intermediate. 

C in the presence of CO, H2O, base and a phase transfer catalyst (particularly 18-crown-6, 87 turnovers). Aromatic nitro compounds are reduced under mild conditions in a genuine bimetallic phase transfer catalysed reaction (reaction 7) , or by a (PtClj (PPhs )2 ]/SnCli,/Et3N system under more forcing conditions. ... 

Bimetallic phase-transfer-catalysis is a process whereby a reaction that occurs using two different metal complexes, does not proceed in the absence of either metal species, or proceeds only at reduced rate. An apparent system of this class has been reported, in which Co2(CO)g and [RhCl(l,5-hexadiene)]2 mutually increased their reactivity when used as catalysts for the conversion of nitrobenzene to aniline in a biphasic system (benzene, aqueous NaOH, dodecyltrimethylammonium chloride) in a carbon monoxide atmosphere [73]. However, another member of the same research group later showed [74] that the apparent bimetallic promotion was due to the fact that the alkylammonium salt used as a phase-transfer agent actually inhibited the activity of the active rhodium complex (apparently a cluster, which is active in the absence of both the alkylammonium salt and the cobalt compound) by rendering it insoluble. The added Co2(CO)g reacts with the alkylammonium salt to generate... 

The bimetallic catalyst system Ru3(CO)i2/Co2(CO)g catalyzes the reaction of terminal acetylenes with methyl iodide and 1 atm of CO under phase-transfer conditions to give y-oxocarboxylic add (Eq. 11.12) [44]. 

Another approach to the synthesis of p hydroxy-a-amino acids is by aldol reaction of imines derived from amino adds. The benzophenone imine of glycine (7.102) undergoes highly enantioselective aldol addition with a range of aliphatic aldehydes, including (7.71) xmder phase-transfer conditions in the presence of the bromide salt of phase-transfer catalyst (7.103). A similar transformation is catalysed, in low to moderate ee, by the bimetallic catalysts developed by Shibasaki and CO workers. ... 

The reduction steps on active Co sites are strongly affected by activated hydrogen transferred from promoter metal particles (Pt and Ru). Several indications for the existence and importance of hetero-bimetallic centers have been obtained.63 [Cp Co(CO)2] in the presence of PEt3 and Mel catalyzes the carbonylation of methanol with initial rates up to 44 mol L 1 h 1 before decaying to a second catalytic phase with rates of 3 mol L 1 h-1.64 HOAc-AcOMe mixtures were prepared by reaction of MeOH with CO in the presence of Co(II) acetate, iodine, and additional Pt or Pd salts, e.g., [(Ph3P)2PdCl2] at 120-80 °C and 160-250 atm.65... 

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