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3H-Benzophosphepine Complexes:  Versatile Phosphinidene Precursors

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posted on 07.12.2005, 00:00 authored by Mark L. G. Borst, Rosa E. Bulo, Danièle J. Gibney, Yonathan Alem, Frans J. J. de Kanter, Andreas W. Ehlers, Marius Schakel, Martin Lutz, Anthony L. Spek, Koop Lammertsma
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.