ABSTRACT Mechanistic studies on reductive elimination from triorgano(tertiaryphosphine)gold(III) and diorgano(l,2-bis(dialkylphosphino)ethane)nickel(II) complexes are described. Three types of reductive elimination routes, namely dissociative, nondissociative and associative pathways, are demonstrated from kinetics of the thermolyses of organogold(III) and -nickel(II) complexes. Dissociation of tertiary phosphine from organogold(III) complexes leading to reductive elimination is enhanced, when the organic leaving group is electron donating as well as when the phosphine ligand is bulky and less electron donating. Rate of phosphine dissociation decreases when the aryl and alkenyl groups cis to P are sterically bulky. The more compatct tertiary phosphine ligand can induce reductive elimination effectively from the square planar cis-diorganonickel(II) complex, in contrast to the dissociative reductive elimination of trans-diorganonickel(II) complexes. An associative mechanism involving a five coordinate intermediate has been proposed. Leaving group selectivity in the reductive elimination is estimated. The more electron donating organic ligand eliminates preferentially in both cases. It is noteworthy that sp2-character in the leaving organic groups such as aryl and alkenyl facilitate reductive elimination.
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