Generation of Oxozirconocene Complexes from the Reaction of Cp₂(THF)ZrN-<i>t</i>-Bu with Organic and Metal Carbonyl Functionalities: Apparently Divergent Behavior of Transient [Cp₂ZrO]

The reactivity of Cp2(THF)ZrN-t-Bu (1a) toward a series of organic and metal carbonyl complexes has been examined. The ZrN linkage of 1a undergoes imido/oxo exchange reactions with the carbonyl compounds and generates three different types of oxozirconocene products: (Cp2ZrO)n (3), (Cp2Zr)2(μ-O)(μ-N-t-Bu) (9), and (Cp2Zr)2O3CCPh2 (12) were obtained from the reactions of 1a with RR‘CO (R = R‘ = Me (2b); R = Ph, R‘ = H (2c); R = i-Pr, R‘ = H (2d)), CpCo(CO)2 (7), and Ph2CCO (10), respectively. The coproducts in these reactions were imines RR‘CN-t-Bu (4b−d), isonitrile complexes CpCo(CO)(CN-t-Bu) (8a), and ketenimines Ph2CCN-t-Bu (11a), respectively. With more highly hindered carbonyls containing α-hydrogen atoms, the reaction followed a different pathway leading to the formation of the enolate complexes Cp2Zr(NH-t-Bu)(OCR3CR2R1) (R1 = H, R2 and R3 = (CH2)3CH(CCH3)3 (5e); R1 = R2 = H, R3 = C(CH3)3 (5f); R1 = R2 = CH3, R3 = CH(CH3)2 (5g)). Possible mechanisms for these transformations, as well as the factors that might control the dependence of the fate of “Cp2ZrO” on its method of generation, are discussed.