Preparation and characterization of the rhenium silyl esters (η5-C5Me5)(CO)(NO)ReC(O)OSiR3 (SiR3 = SiMe2Ph, SiEt3)

Article abstract of DOI:10.1016/S0022-328X(96)06898-2

Three synthetic approaches to the rhenium silyl esters Cp * (CO)(NO)ReC(O)OSiEt₃ (3) and Cp * (CO)(NO)ReC(O)OSiMe₂Ph (4) were evaluated. (a) Treatment of a CH₂Cl₂ solution of Cp * (CO)₂(NO)Re⁺BF^-₄ with a silanolate NaOSiEt₃ (5) or NaOSiMe₂Ph (6) provided 90% isolated yields of 3 and 4. These stable orange-yellow solids are extremely moisture sensitive: traces of water hydrolyze them to Cp * (CO)(NO)ReCO₂H and the parent silanol. IR and NMR spectral data of 3 and 4 are consistent with nonchelating μ(η¹-C:η¹-O) metalloester structures. Less efficient preparative routes to 3 and 4 include treatment of (b) Cp * (CO)(NO)ReCO₂H with the requisite chloroalkylsilane and NⁱPr₂Et, and (c) Cp * (CO)(NO)ReCO^-₂Na⁺ (7Na⁺) with the chloroalkylsilane. The new rhenium CO₂ adducts Cp * (CO)(NO)ReCO^-₂M⁺ (7Li⁺, 7Na⁺) were generated by deprotonation of Cp * (CO)(NO)ReCO₂H with excess LiH or NaH THF suspensions at 0°C. Both 7Li⁺ and 7Na⁺ were characterized by their solution IR spectra and by the formation of their derivatives with silyl and tin chlorides.