New, ready degradation reactions of bisphosphines

Abstract

2-Bis(diphenylphosphino)methyl-6-methylpyridine (1a) and 2-bis(diphenylphosphino)methylpyridine (1b) undergo ready degradation to monophosphine derivatives on aerial oxidation, quaternisation, reaction with bromine, or warming with acetic acid. Similar reactions take place with the corresponding palladium(II) complexes. Oxidation with manganese dioxide and reaction with sulphur lead to bisphosphine oxides and sulphides, respectively. Bis(diphenylphosphino)methane (13b), 1,1-bis(diphenylphosphino)ethane (13a), and αα-bis(diphenylphosphino)toluene (13c) generally do not undergo a similar loss of phosphorus, although treatment of (13c) with methy iodide under more vigorous conditions gave benzylmethyldiphenylphosphonium iodide.

A mechanism involving an increase in co-ordination at one phosphorus atom, followed by nucleophilic attack at the other is suggested, and the importance of the stability of the leaving carbanion is discussed.