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) Tre atment 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 sil anol. IR and NMR spectral data of 3 and 4 are consistent with nonchela ting mu(eta(1)-C:eta(1)-O) metalloester structures. Less efficient pre parative 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 CO 2 adducts Cp(CO)(NO)ReCO2-M+ (7Li(+), 7Na(+)) were generated by depro tonation of Cp(CO)(NO)ReCO2H with excess LIH or NaH THF suspensions a t 0 degrees C. Both 7Li(+) and 7Na(+) were characterized by their solu tion IR spectra and by the formation of their derivatives with silyl a nd tin chlorides.