The unexpected reactions of boron trihalides with 7-phosphanorbornadiene complexes

Abstract

The reactions of BX3 (X = Cl, Br) with 7-R-7-phosphanorbornadiene–M(CO)5 (M = Mo, W) complexes (1) yields products 2 and 4 in which the RP–M(CO)5 unit is inserted into one of the carboxyl units of the phthalic derivative as a result of the collapse of the bridge. When X = Br, 4 cyclizes to give new six-membered heterocycles 5 with quasiplanar structures. When treated by an excess of BBr3, heterocycles 5 undergo ring contraction to afford five-membered oxocyclic products 6.