Synthesis and Structure of Group 4 Iminophosphonamide Complexes

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.