CONVERSION OF RHENIUM ALKYLIDYNE COMPLEXES THAT CONTAIN UNSUPPORTED METAL-METAL DOUBLE-BONDS INTO RELATIVES THAT CONTAIN MU-ALKYLIDYNE LIGANDS

Photolysis of compounds of the type [Re(CCMe(2)R)(OR')(2)](2) (R = Me or Ph; OR' = O(t)Bu, OCMe(2)(CF3), or OCMe(CF3)(2)) in benzene with a medium pressure mercury lamp yields compounds of the type [Re(OR')(2)] (2)(mu-CCMe(2)R)(2) in an intramolecular and irreversible manner. [Re( CCMe(2)R)(OR')(2)](2) and [Re(OR')(2)](2)(mu-CCMe(2)R)(2) (OR' = O(t)B u or OCMe(2)(CF3)(2)) both react with excess carbon monoxide in severa l solvents to afford the dimers [Re(OR')(2)(CO)](2)(mu-CCMe(2)R)(2) qu antitatively. An X-ray study of [Re(O(t)Bu)(2)(CO)](2)(mu-C(t)Bu)(2) s hows it to consist of two distorted trigonal bipyramids connected by t wo symmetrically bridging neopentylidyne ligands. The unbridged dimers of general formula [Re(CCMe(2)R)(OR')(2)](2) do not react readily wit h simple substrates such as phosphines, olefins, or acetylenes, althou gh [Re(CCMe(2)R)(O(t)Bu)(2)](2) can be oxidized by iodine to yield Re( CCMe(2)R)(O(t)Bu)(2)I-2 in good yield. In contrast, {Re[OCMe(CF3)(2)]( 2)}(2)(mu-C(t)Bu)(2) reacts with one equivalent of phenylacetylene to give a species in which one of the two bridging alkylidyne ligands is retained.