Generation of Oxozirconocene Complexes from the Reaction of Cp₂(THF)ZrN-t-Bu with Organic and Metal Carbonyl Functionalities:  Apparently Divergent Behavior of Transient [Cp₂ZrO]

The reactivity of Cp 2 (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: (Cp 2 Zr O) n ( 3 ), (Cp 2 Zr) 2 (μ-O)(μ-N- t -Bu) ( 9 ), and (Cp 2 Zr) 2 O 3 CCPh 2 ( 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 Ph 2 C 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 Ph 2 C 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 Cp 2 Zr(NH- t -Bu)(OCR 3 CR 2 R 1 ) (R 1 = H, R 2 and R 3 = (CH 2 ) 3 CH(CCH 3 ) 3 ( 5e ); R 1 = R 2 = H, R 3 = C(CH 3 ) 3 ( 5f ); R 1 = R 2 = CH 3, R 3 = CH(CH 3 ) 2 ( 5g )). Possible mechanisms for these transformations, as well as the factors that might control the dependence of the fate of “Cp 2 Zr O” on its method of generation, are discussed.