COMBINING THE CHEMISTRY OF PHOSPHOLES AND PHOSPHININES

Lithium 3,4-dimethylphospholide reacts (generally in the presence of Pd(0) and Ni(0) catalysts) with 2-bromo and 2,6-dibromophosphinines to give the corresponding 2-(3,4-dimethylphospholyl)- and 2,6-bis(3,4-dimethylphospholyl)phosphinines (2, 4, 7, 8). When heating these phospholylphosphinines at ca 160 degrees C, the phosphinine ring migrates around the phosphole ring to give transient 5-(2-phosphininyl)-2H-phospholes which can be trapped as [4+2] cycloadducts by diphenylacetylene. The resulting phosphinine substituted 1-phosphanorbornadienes (14-17) can act as chelating ligands towards transition metals (Cr(0), Mo(0), W(0)). Prolonged heating at 180 degrees C of 2-(3,4-dimethylphospholyl)4,5-dimethylphosphinine (4) affords the corresponding phosphinine-phospholyl-phospholyl-phosphinine chain as its P-P bonded dimer (22). The corresponding 2,2'-biphospholide dianion (23) can be prepared from 22 by cleavage of the two P-P bonds by Na-naphthalene in THF. Reaction of 23 with methyl iodide yields a phosphinine-phosphole-phosphole-phosphinine unit (24).