Reactivity Studies of the Zirconium Alkylidene Complexes [η5-C5H3-1,3-(SiMe2CH2PPri2)2]ZrCHR(Cl) (R = Ph, SiMe3)

Reactivity studies of the zirconium alkylidene complexes [P 2 Cp]Zr CHR(Cl) ( 1a, R = Ph; 1b, R = SiMe 3; [P 2 Cp] = η 5 -C 5 H 3 -1,3-(SiMe 2 CH 2 PPr i 2 ) 2 ) are described. The reaction of 1 with ethylene follows second-order kinetics to give the ethylene complex [P 2 Cp]Zr(η 2 -C 2 H 4 )Cl ( 2 ), the structure of which was determined by X-ray crystallography. Addition of acetone to 1 generates the alkene RCH CMe 2, although the anticipated Zr oxo species could not be isolated from this reaction. An insertion of CO into the Zr C bond of 1 yields the ketene complex [P 2 Cp]Zr(η 2 - C, O -OC CHR)Cl ( 3 ), while the reaction with tert -butyl isocyanide gives the analogous ketenimine complex [P 2 Cp]Zr(η 2 - C, N -Bu t NC CHR)Cl ( 4 ). The structure of ketene 3a (R = Ph), determined by X-ray diffraction, exhibits the E geometry, with the position of the ketene unit with respect to the ancillary [P 2 Cp] ligand being opposite to that in the configuration of the precursor alkylidene 1a . The ketene complex 3 reacts with ethylene to give [P 2 Cp]Zr(η 2 - C, O -CH 2 CH 2 C(O) CHR)Cl ( 5 ). The molecular structure of 5b (R = SiMe 3 ) was obtained by X-ray diffraction and reveals a five-membered zirconaoxacycle arising from the insertion of ethylene into the Zr−C bond of the ketene, which is subsequently coordinated to the metal as an enolate ligand. 5 undergoes a final insertion reaction with CO to give the asymmetric η 2 -acyl−ylide complex 6 . For each reaction detailed above, dissociation of a labile pendant phosphine donor provides an open site for reactivity.