New Chiral Amide Ligands Derived from (±)-trans-1,2-Diaminocyclohexane. Applications in Titanium(IV) Chemistry

Titanium(IV) hydrocarbyl compounds containing chiral bis(amide) ligands derived from (±)- trans -1,2-(NHSiR 3 ) 2 -cyclohexanes ( 6a − c: SiR 3 = SiMe 3 ( a ), SiMe 2 Ph ( b ), SiMePh 2 ( c ) are described. The reaction of (±)- trans -1,2-diaminocyclohexane with SiR 3 Cl and NEt 3 affords diamines 6a − c in 60−80% yield. Double deprotonation of 6a − c with 2 equiv of n -BuLi yields the dilithio salts Li 2 [(±)- trans -1,2-(NSiR 3 ) 2 -cyclohexane] (7a − c) in 70−97% yield. The reaction of 7a, b with TiCl 4 (THF) 2 in toluene yields mixtures of {(±)- trans -1,2-(NSiR 3 ) 2 -cyclohexane}TiCl 2 ( 8a, b ) and bis(ligand) complexes { trans -1,2-(NSiR 3 ) 2 -cyclohexane} 2 Ti ( 9a, b; mixture of diastereomers). The reaction of 7c with TiCl 4 yields {(±)- trans -1,2-(NSiMePh 2 ) 2 -cyclohexane}TiCl 2 ( 8c; 15% isolated yield). The reaction of 6a, b and Ti(CH 2 Ph) 4 yields {(±)- trans -1,2-(NSiR 3 ) 2 -cyclohexane}Ti(CH 2 Ph) 2 ( 10a, b ) cleanly, but these species are difficult to isolate due to their high solubility. Iodinolysis of 10a, b with I 2 yields {(±)- trans -1,2-(NSiR 3 ) 2 -cyclohexane}TiI 2 ( 11a, b ) in 60−80% isolated yield. 11a, b can be prepared in 60−80% isolated yield (vs Ti(CH 2 Ph) 4 ) in a “one-pot” reaction by treatment of Ti(CH 2 Ph) 4 with 6a, b followed by iodinolysis. The dimethyl and diphenyl derivatives {(±)- trans -1,2-(NSiR 3 ) 2 -cyclohexane}TiMe 2 ( 12a, b ) and {(±)- trans -1,2-(NSiR 3 ) 2 -cyclohexane}TiPh 2 ( 13a, b ) are prepared by the reaction of 11a, b and RMgX reagents. X-ray crystallographic analyses establish that 10a and 11a have distorted tetrahedral structures with small N−Ti−N angles (ca. 92°) and large X−Ti−X angles (ca. 116°).