Mononuclear titanium complexes that contain aminopyridinato ligands

2-(Methylamino)pyridine (Me-APy-H), 2-anilinopyridine (Ph-APy-H), and 4-methyl-2-((trimethylsilyl)amino)pyridine (TMS-Apy-H) were used to synthesize mononuclear monochloro complexes that contain two or three such aminopyridines as strained amido ligands. The reaction of 2 or 3 equiv of in situ generated lithium aminopyridinate with TiCl4(THF)(2) or TiCl4 afforded just in the case of Me-APy-H a red crystalline product (Me-APy)(3)TiCl (1a) but in unacceptably low yield, An alternative way to synthesize 1a and (Ph-APy)(3)TiCl (1b) is amine elimination, starting from mixed chlorodimethylamido complexes like (Me(2)N)(3)TiCl or (Me(2)N)(2)TiCl2. The reaction of (Me(2)N)(3)TiCl with 2 equiv of Me-APy-H, Ph-APy-H or TMS-APy-H afforded (Me-APy)(2)Ti(NMe(2))Cl (2a), (Ph-APy)(2)Ti(NMe(2))Cl (2b), or (TMS-APy)(2)Ti(NMe(2))Cl (2c). These compounds represent novel unusual highly nitrogen-coordinated titanium complexes. X-ray diffraction studies of 1a established its monomeric structure as having a disturbed pentagonal bipyramidal coordination geometry, X-ray crystal structure investigations of 2a-c proved these compounds to be monomeric with a slightly distorted octahedral coordination geometry. The eta(2) binding mode of the strained aminopyridinato ligands is discussed in comparison to the related amidinato ligand system by averaging bond distances and angles of the determined structures. The N-Py-C-N-amido angle of 108(1)degrees instead of the desired 120 degrees indicates the highly strained tweezers-like bonding mode. The Ti-N-Py distances vary within the known range. The Ti-N-amido distances are more than 0.1 Angstrom longer than the expected values and indicate weak amido bonds. Variable-temperature NMR investigations of complex 2c are indicative of exchange processes which proceed most likely via tetrahedral transition states. Crystallographic data (distances, Angstrom; angles, deg): 1a, C18H21ClN6Ti, a = 9.313(1), b = 10.277(1), c = 11.302(1), alpha = 98.15(1), beta = 108.28(1), gamma = 102.98(1), triclinic, <P(1)over bar>, Z = 2; 2a, C14H20ClN5Ti, a = 8.725(1), b = 9.258(1), c = 10.778(1), alpha = 83.288(7), beta = 79.977(9), gamma = 78.766(8), triclinic, <P(1)over bar>, Z = 2; 2b, C24H24ClN5Ti, a = 17.652(3), b = 7.959(1), c = 18.017(3), beta = 111.37(1), monoclinic, P2(1)/a, Z = 4; 2c, C20H36ClN5Si2Ti, a = 10.786(1), b = 14.053(1), c = 18.144(1), beta = 97.06(1), monoclinic, P2(1)/c, Z = 4.