Reactions of a Cationic Geminal Zr+/P Pair with Small Molecules

Abstract

The metallocene cation complex [Cp*2ZrCH3](+)[B(C6F5)4](-) inserts the phosphino-substituted alkyne Ph-C≡C-PPh2 into the [Zr]-CH3 bond to form the internally phosphane-stabilized cation [Cp*2Zr-C(═CMePh)PPh2](+) (10). Complex 10 adds alkyl isocyanides as well as pivalonitrile at a lateral site at the bent metallocene wedge with retention of the Zr-P bond. Complex 10 acts as a reactive frustrated Lewis pair toward heterocumulenes, undergoing Zr(+)/P addition reactions to the carbonyl groups of an alkyl isocyanate and of carbon dioxide to form the respective five-membered metallaheterocyclic adducts 13 and 14. With mesityl azide complex 10 undergoes a Zr(+)/P FLP N,N-addition reaction at the terminal azide nitrogen atom to form the four-membered FLP cycloadduct 15. The Zr(+)/P FLP is a reactive hydrogen activator. In a stoichiometric reaction it generates a hydridozirconocene cation that subsequently serves as a hydrogenation catalyst for various olefinic or acetylenic substrates. The Zr(+)/P pair 10 undergoes selective 1,4-addition reactions to conjugated enones and to a conjugated ynone to give the corresponding seven-membered metallacyclic Zr(+)/P FLP addition products. Many compounds of this study were characterized by X-ray diffraction.