A THERMALLY STABLE CARBONYL COMPLEX OF ZIRCONIUM .4. STRUCTURE AND REACTIVITY RAMIFICATIONS OF STRONG DELTA[-PI-ASTERISK ELECTRON DONATION

The first isolable d0 CO complex of Zr(IV), [Cp2Zr(eta3-C3H5)CO]+BPh4 - (25, has been prepared by treatment of [Cp2Zr(eta3-C3H5)]+BPh4- (1) with CO. The remarkable stability of this complex is attributed to st rong sigma-->pi donation from the neighboring allyl ligand, completel y inhibiting fluxionality in the allyl fragment. The structure of comp lex 2 is compared to that of [(CpZr(eta3-C3H5)(NC3H3NCH3)]+BPh4- (3), in which the allyl ligand is fluxional and eta3-bound to the metal ce nter, and [CP2Zr(eta1-CH2CH=CH2)(PMe3)]+BPh4- (4), which has a termin ally coordinated allyl group. The reactivity of these complexes toward ligand substitution is also explored.