Synthesis of transition metal alkyls and σbonded metal compounds by the cocondensation of metal vapor and free radicals: A general synthetic technique

The study of σbonded metal compounds has received much attention in the past several years. A problem which has hindered this study has been the unsuccessful preparation of some metal alkyls. Reaction conditions are often such that a slightly stable metal alkyl compound is decomposed by the reaction conditions or the reactants themselves. An idea which shows promise for such syntheses is the cocondensation of metal vapor with radical species on cryogenic surfaces: Using this technique, novel electron deficient metal akyls of marginal thermal stability such as Cd(CF3)2, Pd(CF3)2, Ni(CF3)2, Co(SiF3)2, Pd(SiF3)2, and Ni(SiF3)2 have been prepared. Complexation of these unstable compounds with phosphine or with arenes gives stable, albeit reactive species such as Ni(CF3)2(PMe3)2, Pd(CF3)2(PMe3)2, (n6-toluene)Ni(SiF3)2, and (n6-mesitylene)Co(SiF3)2. The radicals, such as ·CF3 and ·SiF3 are produced in a low temperature glow discharge of a symmetrical gas having a weak central bond (i.e., C2F6 and Si2F6). We have found that many radicals can be cleanly generated in this manner such as ·CH3, ·NF2, ·PF2, ·SH3, ·SCF3, ·OCF3, and ·C(CF3)3. Characterization of the products and future applications of this technique will be discussed.