Preparation and characterization of the rhenium silyl esters (eta(5)-C5Me5)(CO)(NO)ReC(O)OSiR3 (SiR3=SiMe2Ph, SiEt3)

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+BF4- with a silanolate NaOSiEt3 (5) or NaOSiMe2Ph (6) provided 90% isolated yields of 3 and 4. These stable orange-yellow solids an 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 mu(eta(1)-C:eta(1)-O) metalloester structures. Less efficient preparative routes to 3 and 4 include treatment of (b) Cp*(CO)(NO)ReCO2H with the requisite chloroalkylsilane and (NPr2Et)-Pr-i, and (c) Cp*(CO)(NO)ReCO2-Na+ (7Na(+)) with the chloroalkylsilane. The new rhenium CO2 adducts Cp*(CO)(NO)ReCO2-M+ (7Li(+), 7Na(+)) were generated by deprotonation of Cp*(CO)(NO)ReCO2H with excess LIH or NaH THF suspensions at 0 degrees C. Both 7Li(+) and 7Na(+) were characterized by their solution IR spectra and by the formation of their derivatives with silyl and tin chlorides.