MECHANISMS OF DECOMPOSITION OF GROUP-VI DIALKYLS AND ALKYLHYDRIDES INTHE GAS-PHASE FROM STUDIES OF DESIGNED PRECURSORS

R(2)X (X = Te, Se or S), RXMe (X = Te or Se) and RXH (X = Se or S) (R = hex-5-enyl) have been prepared and decomposed in vacuo at 500-800 de grees C. From analyses of the C-6 products obtained it is shown that t he major decomposition pathway for R(2)X is cleavage of an X-R bond to give R., which cyclizes, and R'X. (R' = hexenyl or methyl). RX. eithe r loses a second R.(X = Te) or cyclizes to a heterocyclic radical whic h further decomposes to give conjugated hexadienes. Minor pathways giv ing hex-1-ene and hexa-1,5-diene operate for R(2)X and these involve R XH as an intermediate formed either by beta-H abstraction in the paren t alkyl or by ''H.'' addition to RX.. For RXMe, the major pathway invo lves homolytic cleavage of the X-R bond, although competitive (31%) cl eavage of the X-Me bond occurs for X = Se. For RXH, the major decompos ition pathway is loss of H. with the SH bond being less easily broken than the Se-H, but reductive elimination of RH (23-25% for X = Se, 11% for X = S), X-R bond cleavage (4% for X = Se and 16% for X = S) and p ossibly beta-hydrogen abstraction (4% for X = Se, 6% for X = S) are al l competing reactions.