Dititanium complexes of preorganized binucleating bis(amidinates)

Four different dianionic bis(amidinate) ligands (L-iPr(DBF)2-, L-tBu,Et(DBF)2-, L-iPr(Xan)2-, L-tBu,Et(Xan)2-) featuring rigid dibenzofuran (DBF) and 9,9-dimethylxanthene (Xan) backbones have been used to prepare several new dititanium complexes. Reaction of the free-base bis(amidines) (LH2) with 2 equiv of Ti(NMe2)(4) forms the hexaamido derivatives (LDBFTi2)-L-iPr(NMe2)(6) (1), (LDBFTi2)-L-tBu,Et(NMe2)(6) (2), (LXanTi2)-L-iPr(NMe2)(6) (3), and (LXanTi2)-L-tBu,Et(NMe2)(6) (4) in good yields. Compound 4, which features an unsymmetrically substituted bis(amidinate) ligand, was isolated as an 8:1 mixture of rotational diastereomers with C-2 and C-s symmetry, respectively. The two diastereomers interconvert upon heating, and at equilibrium the C2 isomer is preferred thermodynamically by 0.2 kcal/mol. Compound 3 reacts with excess Me3SiCl in toluene to form the mixed amido-chloride derivative (LXanTi2)-L-iPr(NMe2)(2)Cl-4 (5) in low-moderate yield. Alternatively, 5 is also prepared by reaction of (LXanH2)-L-iPr with 2 equiv of Ti(NMe2)(2)Cl-2 in good yield. Compound 3 reacts with CO2 to form the red carbamate derivative (LXanTi2)-L-iPr(NMe2)(4)(O2CNMe2)(2) (6) in moderate yield. Infrared data for 6 indicates bidentate coordination of the carbamate ligands. Metathesis reaction of (LXanLi2)-L-iPr with 2 equiv of CpTiCl3 affords (LXanTi2Cp2Cl4)-L-iPr (7) in moderate yield. Reduction of 7 with 1 % Na amalgam in toluene solution affords the paramagnetic dititanium(III) complex (LXanTi2Cp2Cl2)-L-iPr (8) in good yield. Structural studies reveal that 8 features two bridging chloride ligands. Reaction of the free-base bis(amidines) with 2 equiv of CpTiMe3 forms the red sigma-alkyl derivatives L-iPr(DBF)- Ti2CP2Me4 (9), (LDBFTi2CP2Me4)-L-tBu,Et (10), and (LXanTi2CP2Me4)-L-iPr (11) in good yields. Structural data are presented for compounds 4, 5, 8, and 9.