Recent Developments in the Field of Pentaaryl Antimony Compounds

10 Recent Developments in the Field of Pentaaryl Antimony Compounds 

For the pentaarylphosphorane and pentaarylarsorane type the combination of each two phenyl groups to form a 2,2 -biphenylylene ligand had led to spirocyclic species which generally were of much higher stability then the simple pentaphenyl derivatives. In the antimony series, however, such a distinct stabilizing effect was no longer observable. 

Although bis-2,2 -biphenylylenephenylstiborane (5-phenyl-5,5 -spirobi[5Zf-diben-zostibole]) (150) was first prepared by the tosylimine method134), it was later shown that the more traditional procedure starting from appropriate stibine dihalides 2S) was more convenient for the synthesis of such compound types13S). 

the mixed spirocyclic stiborane 151 as well as the monocyclic derivative 153 were obtainable by both possible ways as shown in the reaction scheme. 

Attempts to synthesize by analogous procedures bis-2,2 -biphenylylenemethylstibo-rane (157) from 2,2 -biphenylylenemethylstibine dibromide 154 and 2,2 -dilithio-biphenyl failed, because of the obvious instability of the initially formed stibonium structure 155 which readily loses methyl bromide. The carbanionic stibine 156 so 

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