3H-Benzophosphepine Complexes: Versatile Phosphinidene Precursors
2005-12-07T00:00:00Z (GMT)
by
The synthesis of a variety of benzophosphepine complexes [R = Ph, t-Bu, Me; MLn = W(CO)5,
Mo(CO)5, Cr(CO)5, Mn(CO)2Cp] by two successive hydrophosphinations of 1,2-diethynylbenzene is
discussed in detail. The first hydrophosphination step proceeds at ambient temperature without additional
promoters, and subsequent addition of base allows full conversion to benzophosphepines. Novel benzeno-1,4-diphosphinanes were isolated as side products. The benzophosphepine complexes themselves serve
as convenient phosphinidene precursors at elevated, substituent-dependent temperatures (>55 °C). Kinetic
and computational analyses support the proposal that the phosphepine−phosphanorcaradiene isomerization
is the rate-determining step. In the absence of substrate, addition of the transient phosphinidene to another
benzophosphepine molecule is observed, and addition to 1,2-diethynylbenzene furnishes a delicate bidentate
diphosphirene complex.