Synthesis and Structure of Group 4 Iminophosphonamide Complexes VollmerhausRainer TomaszewskiRobert ShaoPengcheng TaylorNicholas J. WiacekKevin J. LewisStewart P. Al-HumydiAbdulaziz CollinsScott 2005 The syntheses of a variety of iminophosphonamide (PN<sub>2</sub>) ligands (<b>2a</b>−<b>f</b>), the corresponding hydrochloride salts (<b>1a</b>−<b>c</b>), and a number of bis(PN<sub>2</sub>) dichloride complexes of group 4 (<b>3a</b>−<b>e</b>) and their corresponding dialkyls (<b>5a</b>−<b>e</b>) are described. A novel monosubstituted PN<sub>2</sub> “ate” complex <b>4</b> was prepared from ligand <b>2f</b> and Zr(NMe<sub>2</sub>)<sub>4</sub> on treatment with excess Me<sub>2</sub>NH·HCl. Piano-stool PN<sub>2</sub> zirconium dichloride complexes <b>6a</b>−<b>h</b> were accessible on treatment of CpZr(NMe<sub>2</sub>)<sub>3</sub> (Cp = C<sub>5</sub>H<sub>5</sub>, Cp*) with PN<sub>2</sub> ligands <b>2a</b>−<b>e</b>, followed by metathesis with excess Me<sub>3</sub>SiCl or Me<sub>2</sub>NH·HCl (<b>6a</b>−<b>g</b>) or at low <i>T</i> with ethereal HCl (<b>6h</b>). Dialkyl derivatives <b>8a</b>−<b>h</b> could be prepared from <b>6a</b>−<b>h</b> or directly from ligands <b>2</b> and CpMMe<sub>3</sub> (Cp = C<sub>5</sub>H<sub>5</sub>, Cp*; M = Ti or Zr). The intermediate Cp(PN<sub>2</sub>)Zr(NMe<sub>2</sub>)<sub>2</sub>, precursor to <b>6h</b>, rearranged to the novel terminal difluoride complexes <b>7a</b>,<b>b </b>at room temperature. A variety of complexes <b>3</b> and <b>6</b> or their corresponding alkyl derivatives have been characterized by X-ray crystallography. In addition, the novel “ate” complex <b>4</b> and difluoride complexes <b>7a</b>,<b>b</b> have been structurally characterized in this manner. The structures of <b>7a</b>,<b>b</b> in the solid state reveal strong, intramolecular coordination of the NMe<sub>2</sub> 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 NMe<sub>2</sub> groups coupled with the formation of coordination stereoisomers.