Reduction of Bis(phosphonio)isophosphindolides to Phosphane-Functionalized Benzo[c]phospholides

Abstract

Bis(phosphonio)benzo[c]phospholides (isophosphindolides) 1a,b have been found to react with magnesium or alkali metal naphthalenides MC10H8 (M = Li, Na, K) with reduction of one or both of the phosphonio groups. The main products are the mono- or bis(phosphanyl)-substituted heterocycles 2, 3, 6, 7, which have been characterized by in situ NMR studies and in some cases isolated. Subsequent reaction of 2 with excess [Ni(CO)4] gave the complex 4, which has been characterized by X-ray diffractometry. Reactions of 1a with alkali metals followed a more complicated course and gave a mixture of 2, 3, and the substitution product 8, which was further reduced to the phosphanido-substituted benzo[c]phospholide 9. The latter could be formed selectively by first converting 1a into 8 by treatment with PhNa and then treating this with lithium. NMR data of the phosphane-substituted benzo[c]phospholides and the structural features of 4 are discussed.