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The structure of [PPh(3)(benzyl)][B(10)H(11)] was determined at -123 degrees C and 24 degrees C by single-crystal X-ray analyses. The B(10) core of [B(10)H(11)](-) is similar in shape to that of [B(10)H(10)](2)(-). The 11th H atom asymmetrically caps a polar face of the cluster and shows no tendency for disorder in the solid state. Variable temperature multinuclear NMR studies shed light on the dynamic nature of [B(10)H(11)](-) in solution. In addition to the fluxionality of the cluster H atoms, the boron cage is fluxional at moderate temperatures, in contrast to [B(10)H(10)](2)(-). Multiple exchange processes are believed to take place as a function of temperature. Results of ab initio calculations are presented. Crystal data: [PPh(3)(benzyl)][B(10)H(11)] at -123 degrees C, P2(1)/c, a = 9.988(2) A, b = 18.860(2) A, c = 15.072(2) A, beta = 107.916(8) degrees, V = 2701.5(7) A(3), Z = 4; [PPh(3)(benzyl)][B(10)H(11)] at 24 degrees C, P2(1)/c, a = 10.067(5) A, b = 19.009(9) A, c = 15.247(7) A, beta = 107.952(9) degrees, V = 2775(2) A(3), Z = 4.

The formation of phosphanylboranes, R2P -BX2, from hydrogen or hydrogen halide elimination reactions between appropriate phosphane and borane reagents was examined intently for a number of These studies led to the isolation and partial characterization of several molecular ring compounds (RzPBX2), (n = 2, 3) as well as oligomeric species. Some of this chemistry has recently been revisited and extended in order to obtain monomeric boraphosphene species that contain a -P = B -double bond and to define new classes of boron-phosphorus ring and cage compounds["-5o1. These results make it clear that there is considerable potential for the development of additional chemistry from phosphanylborane reagents. In that regard, we report here the use of several phosphanylboranes as reagents for the formation of more complex compounds as well as some aspects of their derivative chemistry. ReactionsIn the past, the majority of phosphanylborane chemistry has been developed with phosphide fragments that contain strongly bonded alkyl or aryl substituents. Relatively few compounds have been reported that possess potentially labile substituents, such as organosilyl groups or hydrogen. We have previously noted that the silylphosphanylboranes 1 a -c, when combined with a second equivalent of LiP(SiMe3)2 in hexane or benzene, produce in good yield the corresponding diphosphadiboretane~ [~~], [R2NBP-(SiMe3)12 (6a-c), and an equivalent of P(SiMe3)3, as illustrated in eq. (5). It was assumed that (diorgany1amino)bis-[(trimethylsilyl)phosphanyl]boranes, R2NB[P(SiMe3)2]2 (5a-c), were formed as intermediates in each case, but none were isolated due to the facile elimination of P(SiMe3)3. In the present study, one bis(phosphanyl)borane, 5b, was prepared and isolated as outlined in eq. (5). However, the corresponding analogs 5a, 5c, and 5d were not detected in NMR spectra recorded from 1 : 1 reaction mixtures prepared from 1 a, 1 c, and 1 d with LiP(SiMe&. It is therefore assumed

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