Ammonium formate hydride donor

Sodium or ammonium formates are also suitable as hydride donors for the hydrogenation of a, 0-unsaturated and aromatic aldehydes with water-soluble Ru complexes [88, 93], With [RuCl2(TPPMS)2], both the catalyst and the formate are in the aqueous phase the phase-transfer problem associated with catalysts not soluble in water and aqueous formate solutions does not arise [93, 94]. These systems olfer interesting theoretical aspects [87, 95, 186]. 

Arylation reactions of aromatic ketimines were developed, and in many cases the products of the reaction were isolated after subsequent hydrolysis. Therefore, these arylations constitute an indirect method for the preparation of arylated aromatic ketones, the direct functionalizations of which are often more difficult. Thus, direct arylation of imine 42 with sodium tetraphenylborate catalyzed by [RhCl(cod)]2 afforded a mixture of mono- and diarylated benzophenone imines (44 and 45) (Scheme 9.16) [53]. The formation of the corresponding amine 46 clearly indicated that 42 also acted as a hydride acceptor in this transformation. Most likely, the reaction occurs via initial coordination by the benzophenone imine to a phenylrho-dium intermediate followed by orfho-rhodation to afford the five-membered rhoda-cyde intermediate 47 (Scheme 9.16). Subsequent reductive elimination generates the monophenylated product 44 and a rhodium hydride, which then reduces imine 42 in the presence of ammonium chloride as proton donor to regenerate the catalytically active speties. 

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