Dititanium Complexes of Preorganized Binucleating Bis(amidinates)

Four different dianionic bis(amidinate) ligands (iPrLDBF2-, tBu,EtLDBF2-, iPrLXan2-, tBu,EtLXan2-) 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
iPrLDBFTi2(NMe2)6 (1), tBu,EtLDBFTi2(NMe2)6 (2), iPrLXanTi2(NMe2)6 (3), and tBu,EtLXanTi2(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 C2 and Cs 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 iPrLXanTi2(NMe2)2Cl4 (5) in low-moderate yield. Alternatively,
5 is also prepared by reaction of iPrLXanH2 with 2 equiv of Ti(NMe2)2Cl2 in good yield. Compound 3 reacts with CO2
to form the red carbamate derivative iPrLXanTi2(NMe2)4(O2CNMe2)2 (6) in moderate yield. Infrared data for 6 indicates
bidentate coordination of the carbamate ligands. Metathesis reaction of iPrLXanLi2 with 2 equiv of CpTiCl3 affords
iPrLXanTi2Cp2Cl4 (7) in moderate yield. Reduction of 7 with 1% Na amalgam in toluene solution affords the paramagnetic
dititanium(III) complex iPrLXanTi2Cp2Cl2 (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 σ-alkyl derivatives iPrLDBFTi2Cp2Me4 (9), tBu,EtLDBFTi2Cp2Me4 (10), and iPrLXanTi2Cp2Me4 (11) in good yields. Structural data are presented for
compounds 4, 5, 8, and 9.