Synthesis, structure, and reactivity of zirconium alkyl complexes bearing ancillary pyridine diamide ligands

Zirconium alkyl complexes bearing a linked pyridine diamide ligand [2,6-(RNCH2)(2)NC5H3](2-) (R = 2,2,6-diisopropylphenyl, a, (BDPP); R = 2,6-diethylphenyl, b, (BDEP); R = 2,6-dimethylphenyl, c, (BDMP)) have been synthesized. The bis(benzyl) derivatives (2a-c) undergo an eta(1)-, eta(2)-benzyl flip, which is likely a result of the electrophilic nature of the zirconium metal center. The bis(trimethylsilylmethyl) derivative (BDPP)Zr(CH2SiMe3)(2) (3a) is also fluxional; however, this behavior is attributable to the steric crowding in this complex. In contrast, the analogous compounds bearing the less bulky BDEP and BDMP ligands do not show fluxional behavior. The butadiene complexes (BDPP)Zr(C4H6) (5a) (determined by X-ray crystallography), (BDEP)Zr(C4H6) (5b), and (BDMP)Zr(C4H6) (5c) adopt an s-cis bent metallacyclo-3-pentene structure with significant rr-donation from the double bond. Consistent with the rigid nature of these complexes, no insertion chemistry is observed below 90 degrees C. Alkenes and alkynes react (>90 degrees C) via insertion into the Zr-C cr-bond to give sigma,pi-allyl produces.