Ethylene polymerizations were conducted using β-diketimine complexes of Zr [LZrX 3 (1) and L 2 ZrX 2 (2) with L ) MeC(NAr)CHC(NAr)Me and X ) Cl, R (R ) Me, Bn)] as well as Cp(L)ZrX 2 (3) in the presence of MAO. Complexes 1 possess low polymerization activities (ca. 10 5 g PE/(mol Zr h)) and provide PEs with a trimodal, molecular weight distribution. Both 2 and 3 behave as single-site catalysts under these conditions, with the activity of the latter being considerably higher than the former (ca. 10 6 -10 7 vs 10 5 g PE/(mol Zr h)). Induction periods of 10-20 min at 70 °C were observed in polymerizations involving 3 (Ar ) Ph, X ) Cl, Me) when activated by MAO. The use of [Ph 3 C][B(C 6 F 5 ) 4 ] and 3b (Ar ) Ph, X ) Me) in the presence of small amounts of MAO (ca. 100:1 Al:Zr) led to rapid monomer uptake and an increase in catalytic activity by about a factor of 4. Lower activities were observed in the presence of Me 3 Al or i Bu 3 Al. Little or no polymerization activity was observed when excess 3b was used as a scrubbing agent (in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ]), and rapid loss of activity was observed when excess 3b was added to a catalyst system already producing PE. Complex 3b reacts withwhich was characterized by X-ray crystallography. Complex 4 forms dinuclear complexes with 3b or Me 3 Al in solution at room temperature. These complexes, [Cp(L)Zr(µ-Me) 2 AlMe 2 ][B(C 6 F 5 ) 4 ] (6) or [(Cp(L)ZrMe) 2 -(µ-Me)][B(C 6 F 5 ) 4 ] (7), are fluxional in solution; at lower temperature, the solution NMR spectra are consistent with the structures shown. Complex 3b is a potent inhibitor of ethylene polymerization by 4, forming 7, which is resistant to dissociation. The presence of AlMe 3 (or MAO) appears to reversibly displace 3b from 7, allowing the reaction of 3b with [Ph 3 C]-[B(C 6 F 5 ) 4 ] to proceed to completion.

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The syntheses of a variety of iminophosphonamide (PN2) ligands (2a−f), the corresponding hydrochloride salts (1a−c), and a number of bis(PN2) dichloride complexes of group 4 (3a−e) and their corresponding dialkyls (5a−e) are described. A novel monosubstituted PN2 “ate” complex 4 was prepared from ligand 2f and Zr(NMe2)4 on treatment with excess Me2NH·HCl. Piano-stool PN2 zirconium dichloride complexes 6a−h were accessible on treatment of CpZr(NMe2)3 (Cp = C5H5, Cp*) with PN2 ligands 2a−e, followed by metathesis with excess Me3SiCl or Me2NH·HCl (6a−g) or at low T with ethereal HCl (6h). Dialkyl derivatives 8a−h could be prepared from 6a−h or directly from ligands 2 and CpMMe3 (Cp = C5H5, Cp*; M = Ti or Zr). The intermediate Cp(PN2)Zr(NMe2)2, precursor to 6h, rearranged to the novel terminal difluoride complexes 7a,b at room temperature. A variety of complexes 3 and 6 or their corresponding alkyl derivatives have been characterized by X-ray crystallography. In addition, the novel “ate” complex 4 and difluoride complexes 7a,b have been structurally characterized in this manner. The structures of 7a,b in the solid state reveal strong, intramolecular coordination of the NMe2 group to the metal center, resulting in eight-coordinate complexes. One of these complexes is fluxional in solution, suggesting rapid exchange of bound versus free NMe2 groups coupled with the formation of coordination stereoisomers.