COMPARATIVE REACTIVITY OF DIALKYL(TRICHLO ROSILYL)PHOSPHANES AND TRIMETHYLSILYLPHOSPHANES WITH DICHLORODIMETHYLSTANNANE - EXCHANGE-REACTIONS AND STRUCTURES OF CYCLIC CHLOROSTANNYLPHOSPHANE DICHLORODIMETHYLSTANNANE ADDUCTS

Di-isopropyl(trichlorosilyl)phosphane (2a) is less reactive towards Me (3)SnCl, (t)Bu(2)PSnMe(2)Cl (5b) and Me(2)SnCl(2) than di-isopropyl(tr imethylsilyI)phosphane (3a). Compound 3a reacts with each of the organ otin chlorides to provide (i)Pr(2)PSnMe(3) (1a), ((Pr2P)-Pr-i)(2)SnMe( 2) (6a) or mixtures of ((t)Bu(2)P)(n)((Pr2P)-Pr-i)(2-n)SnMe(2) (n = 0, 1, 2: 6a, c, b), but 2a reacts with Me(2)SnCl(2), providing only (Pr2 P)-Pr-i(mu-SnMe(2)Cl)(2)Cl (4a), which has the composition of a 1:1 ad duct of (i)Pr(2)PSnMe(2)Cl (5a) with Me(2)SnCl(2). Compound 4a is not further attacked by excess of 2a. Similarly, di-t-butyl(trichlorosilyl )phosphane (2b) reacts only with two equivalents of Me(2)SnCl(2) provi ding (t)Bu(2)P(mu-SnMe(2)Cl)(2)Cl (4b). X-Ray structure determinations of the unusual compounds R(2)P[(mu-SnMe(2)Cl)(2)Cl] (4) (4a: R = Pr-i ; 4b: R = (t)Bu) reveal that the cyclic 'adducts' 4 are the first comp ounds described containing two tin atoms of coordination number five b ridged by a four-coordinated (slightly distorted) tetrahedral phosphor us atom. The cyclic structures of 4 involving stannylphosphanes 5a,b a s donors and accepters towards Me(2)SnCl(2) are consistent with previo us predictions from Sn-119m Mossbauer, NMR and IR/Raman data of 4b. Th e solid-state structures of 4a and 4b allow an insight into the role o f pentacoordinated tin in the course of silyl/stannyl-phosphane exchan ge reactions and the long-known rapid self-exchange reactions of trime thylstannylphosphanes with trimethylstannyl halides.