Synthesis of phosphine-borane complexes of P-heterocycles

Abstract Dihydro-1H-phosphole-boranes 5 and 10 were prepared from phosphine oxides 1 and 9 respectively. Reaction of borane 5 with dichlorocarbene gave dihydrophosphole-dichloromethylborane 6 and tetrahydro derivative 7a as the main products, and dichlorocyclopropane 8 as the minor component. Dichlorocarbene addition reaction of boranes 10 did not afford the corresponding phosphabicyclohexanes, but the dichloromethylborane complexes of the dihydro- and tetrahydrophospholes ( 11 and 7 respectively). Phosphabicyclohexaneborane 13 was synthesized from P-oxide 12 by change in the functionality. The dihydrophosphinine-boranes ( 16 ) were prepared by cyclopropane ring opening of phosphabicyclohexane 13 , or by change in the functionality of P-oxide 15 . Reaction of dihydrophosphinine-boranes 17 with dichlorocarbene gave traces of dihydrophosphinine-dichloromethylborane 18 instead of the phosphepine. The phosphepine-borane ( 20 ) was synthesised from oxide 19 . The preparation of unsaturated phosphine-boranes was complicated by reduction side-reactions. The products were characterized by 31 P, 11 B, 1 H and 13 C NMR, as well as MS data.