N-Substituted Guanidinate Anions as Ancillary Ligands in Group 4 Chemistry. Syntheses and Characterization of M{RNC[N(SiMe₃)₂]NR}₂Cl₂, [M{CyNC[N(SiMe₃)₂]NCy}Cl₃]⁻ (M = Zr, Hf; R = iPr, Cy), and Zr{CyNC[N(SiMe₃)₂]NCy}(CH₂Ph)₃

Addition of N(SiMe 3 ) 2 anion equivalents to carbodiimides, RN C NR (R = cyclohexyl, isopropyl), generated tetrasubstituted guanidinates which provided entry to a series of bis- and mono(guanidinate) complexes of Zr and Hf exhibiting the general formulas {RNC[N(SiMe 3 ) 2 ]NR} 2 MCl 2 (R = isopropyl, M = Zr ( 1 ), Hf ( 2 ); R = cyclohexyl, M = Zr ( 3 ), Hf ( 4 ) and {CyNC[N(SiMe 3 ) 2 ]NCy}MCl 4 ] - (M = Zr ( 5 ), Hf ( 6 )) depending on the metal:ligand ratio used in the reaction. In addition to spectroscopic characterization, definitive evidence for the molecular structures of these products is provided through single-crystal X-ray analyses for 1, 3, 4, 5, and 6, which are presented. These results further define the ligand-bonding parameters and provide clear evidence that the planar N(SiMe 3 ) 2 functional groups and the MNCN planes have a nearly perpendicular orientation and therefore do not experience significant π overlap. Complex 5 provides an access to the organometallic derivative {CyNC[N(SiMe 3 ) 2 ]NCy}Zr(CH 2 Ph) 3 ( 7 ) by reaction with 3 equiv of PhCH 2 MgCl. Single-crystal X-ray analysis confirmed the connectivity of this species and indicated an η 2 -benzyl group. These results provide the first reported example of an organozirconium complex supported by a guanidinate ligand.