O-HYDROXYARYLPHOSPHINES AND DIPHOSPHINES - METALATION-REARRANGEMENT VERSUS P-O REDUCTION OF O-HALOGENOARYLOXYPHOSPHINES BY SODIUM

o-Bromo- and o-chloroaryloxyphosphines 1 may react with sodium in two competing ways: (i) metal halogen exchange followed by rapid intramole cular 1,3-rearrangement to give sodium o-hydroxylato-arylphosphines 2, later converted to their OSiMe(3) derivatives 3, and (ii) reductive c leavage of the P-O bond to give diphosphines 4 or phosphides. The o-me tallation is preferred with the more reactive bromides and bulky phosp hino substituents or screened P-O bonds by substituents at 6-position. The reduction is favoured in the case of the less reactive aryl chlor ides, small alkyl and flat phenyl substituents at phosphorus. Mixtures of meso- and rac-diphosphines are formed from asymmetric derivatives ArOPRR'. The meso-isomer of 1,2-di(tert-butyl)-1,2-diphenyldiphosphine is preferred.