Synthesis and Structure of Group 4 Iminophosphonamide Complexes

The syntheses of a variety of iminophosphonamide (PN2) ligands (2af), the corresponding hydrochloride salts (1ac), and a number of bis(PN2) dichloride complexes of group 4 (3ae) and their corresponding dialkyls (5ae) 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 6ah were accessible on treatment of CpZr(NMe2)3 (Cp = C5H5, Cp*) with PN2 ligands 2ae, followed by metathesis with excess Me3SiCl or Me2NH·HCl (6ag) or at low T with ethereal HCl (6h). Dialkyl derivatives 8ah could be prepared from 6ah 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.