(T)BU(2), SI=CR(CO)5.NA(CF3SO3).2THF - A SALT-ADDUCT OF A CHROMIUM SILICON SILICON DOUBLE-BOND

The salt-adduct ((t)Bu)2Si=Cr(CO)5 . Na(CF3SO3) . 2 THF [1 . Na(CF3SO3 )] of a chromium-silicon double bond has been investigated in the soli d state and in solution. The triflate Na(CF3SO3) does not coordinate r igidly to 1 but exchanges rapidly in non-polar solvents (Si-29-NMR 150 .7 ppm). The X-ray crystal structure of 1 . Na(CF3SO3) shows a Cr-Si b ond distance of 2.475(1) angstrom and an Si-O6 bond distance of 1.857( 3) angstrom. The sum of bond angles at Si is 349.5-degrees. In the cry stal the molecules of 1 . Na(CF3SO3) are linked by heptacoordinate sod ium ions to form a helix along the 21 direction of the unit cell (P2(1 )/c). Upon treatment with pyridine or CO, 1 . Na(CF3SO3) eliminates di (tert-butyl)silylene which trimerizes to give cyclic [((t)Bu)2Si]3. 1 . Na(CF3SO3) can be transformed with HPMA (hexamethylphosphorotriamide ) into ((t)Bu)2(HMPA)Si=Cr(CO)5, 3. A single crystal X-ray structure d etermination of 3 shows a Cr-Si bond distance of 2.527(3) angstrom and an Si-O6 bond distance of 1.777(6) angstrom. Complex 3 can be describ ed as a sigma-donor complex ((t)Bu)2(HMPA)Si --> Cr(CO)5.