ONE-POT SYNTHESIS OF CPRE(CO)(2)H-2 AND TRANS-CPRE(CO)(2)(SNPH(3))(2)FROM CIS-CPRE(CO)(2)BR-2 AND TRANS-CPRE(CO)(2)BR-2 AND PB3SNH - INVOLVEMENT OF A RADICAL-CHAIN SEQUENCE IN THE FORMATION OF CPRE(CO)(2)H-2

Treatment of cis- or trans-CpRe(CO)(2)Br-2 (1) with Ph(3)SnH yields th e corresponding dihydride CpRe(CO)(2)H-2 (2) and Ph(3)SnBr. Conducting the same reaction in the presence of pyridine or Et N-3 gives trans-C pRe(CO)(2)(SnPh(3))(2) (3). The molecular structure of 3 has been dete rmined by X-ray crystallography. 3 crystallizes in the monoclinic spac e group P2(1)/c with a = 25.099(2), b = 9.4205(8), c = 16.388(2) Angst rom, beta = 103.632(8)degrees, V = 3765.7(6) Angstrom(3), and D-calc = 1.777 g cm(-3) for Z = 4. The refined structure gave R and R(w) value s of 0.0317 and 0.0444, respectively, for 3753 observed reflections. A plausible mechanism for the formation of the dihydride CpRe(CO)(2)H-2 that involves the chain-propagating radicals CpRe(CO)(2)Br-. and CpRe (CO)(2)H-. is presented.