TBu 2SiCr(CO) 5 · Na(CF 3SO 3) · 2 THF: a salt-adduct of a chromium-silicon double bond

Abstract

The salt-adduct ( tBu) 2SiCr(CO) 5 · Na(CF 3SO 3) · 2 THF [ 1 · Na(CF 3SO 3)] of a chromium-silicon double bond has been investigated in the solid state and in solution. The triflate Na(CF 3SO 3) does not coordinate rigidly to 1 but exchanges rapidly in non-polar solvents ( 29Si-NMR 150.7 ppm). The X-ray crystal structure of 1 · Na(CF 3SO 3) shows a Cr-Si bond distance of 2.475(1) Å and an Si-O6 bond distance of 1.857(3) Å. The sum of bond angles at Si is 349.5°. In the crystal the molecules of 1 · Na(CF 3SO 3) are linked by heptacoordinate sodium ions to form a helix along the 2 1 direction of the unit cell ( P2 1/c). Upon treatment with pyridine or CO, 1 · Na(CF 3SO 3) eliminates di(tert-butyl)silylene which trimerizes to give cyclic [( tBu) 2Si] 3. 1 · Na(CF 3SO 3) can be transformed with HPMA (hexamethylphosphorotriamide) into ( tBu) 2(HMPA)SiCr(CO) 5, 3. A single crystal X-ray structure determination of 3 shows a Cr-Si bond distance of 2.527(3) Å and an Si-O6 bond distance of 1.777(6) Å. Complex 3 can be described as a σ-donor complex ( tBu) 2(HMPA)Si → Cr(CO) 5.