Bulky Amidinate Complexes of Tin(IV). Synthesis and Structure of Sn(RNC(R‘)NR)₂Cl₂ (R = Cyclohexyl, R‘ = H, Me; R = SiMe₃, R‘ = tBu)

Reaction of 2 equiv of lithium dicyclohexylformamidinate with SnCl 4 afforded the new species Sn(CyNC(H)NCy) 2 Cl 2 (Cy = cyclohexyl) ( 1 ). Addition of MeLi and t BuLi to CyN C NCy and Me 3 SiN C CSiMe 3, respectively, provided an entry to the high-yield syntheses of Sn(CyNC(Me)NCy) 2 Cl 2 ( 2 ) and Sn(Me 3 SiNC(CMe 3 )NSiMe 3 ) 2 Cl 2 ( 3 ). Spectroscopic and elemental analysis confirmed the formulas of these new species. Compounds 1 and 3 were further characterized by X-ray crystallography and shown to possess distorted octahedral coordination geometries of the metal center with the cis-dichloride groups. The structural determination of 3 represents the first structural confirmation of the new bulky amidinate ligand (Me 3 SiNC(CMe 3 )NSiMe 3 ) - . Comparison of the solution structures of 1 − 3 was provided by NMR spectroscopy, which showed that while 1 was fluxional at room temperature, 2 and 3 exhibited restricted fluxionality. Differences in the solid state structures of 1 and 3 were attributed to the steric interactions within the ligands. Crystal data for 1: orthorhombic, Pnca, a = 17.553(5) Å, b = 20.275(9) Å, c = 9.757(6) Å; empirical formula SnCl 2 N 4 C 26 H 46 (toluene), R F 0.044, R w 0.051. Crystal data for 3: monoclinic P 21/ n, a = 13.515(8) Å, b = 16.179(8) Å, c = 15.974(4) Å, β = 97.69(6)°, empirical formula SnCl 2 Si 4 N 4 C 22 H 54, R F 0.032, R w 0.045.