Reactivity studies of the zirconium alkylidene complexes [η⁵-C₅H₃- 1,3-(SiMe₂CH₂PPr(i)₂)₂]Zr=CHR(Cl) (R = Ph, SiMe₃)

Reactivity studies of the zirconium alkylidene complexes [P₂Cp]Zr=CHR(Cl) (1a, R = Ph; 1b, R = SiMe₃; [P₂Cp] = η⁵-C₅H₃-1,3- (SiMe₂CH₂PPr(i)₂)₂) are described. The reaction of 1 with ethylene follows second-order kinetics to give the ethylene complex [P₂Cp]Zr(η²- C₂H₄)Cl (2), the structure of which was determined by X-ray crystallography. Addition of acetone to 1 generates the alkene RCH=CMe₂, 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 [P₂Cp]Zr(η²-C,O-OC=CHR)Cl (3), while the reaction with tert-butyl isocyanide gives the analogous ketenimine complex [P₂Cp]Zr(η²-C,N- Bu¹NC=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 [P₂Cp] ligand being opposite to that in the configuration of the precursor alkylidene 1a. The ketene complex 3 reacts with ethylene to give [P₂Cp]Zr(η²-C,O-CH₂CH₂C(O)=CHR)Cl (5). The molecular structure of 5b(R = SiMe₃) 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 η²-acyl-ylide complex 6. For each reaction detailed above, dissociation of a labile pendant phosphine donor provides an open site for reactivity.