Titanium complexes stabilized by N-(tert-hydrocarbyl)anilide ligation: A synthetic investigation

The complexes Ti(NRAr(F))(2)(NMe(2))(2) (4, R=C(CD3)(2)CH3, Ar-F=2,5-C(6)H(3)FMe), Ti(NRAr(F))(2)(NMe(2))(I) (5), Ti(NRAr(F))(2)(NMe(2))(CH(2)SiMe(3)) (6), and Ti(NRAr(F))(2)(I)(CH(2)SiMe(3)) (7) have been synthesized in 77, 71, 70, and 84% yield, respectively, in a four step sequence of alternating salt elimination and dimethylamide deprotection steps. The complex Ti(NRAr)(I)(2)(OAr')(11, Ar=3,5-C(6)H(3)Me(2), Ar'=2,6-(C6H3Pr2)-Pr-i) was prepared in 65% yield via the complexes Ti(NRAr)(NMe(2))(3) (9) and Ti(NRAr)(NMe(2))(2)(OAr') (10), which were generated in situ, spectroscopically characterized, and not isolated. The complexes Ti(NR'Ar)(NMe(2))(3) (12, R'=C(CD3)(2)Ph, Ti(NR'Ar)(NMe(2))(2)(OAr '')(13, Ar ''=2,6-C(6)H(3)(t)Bu(2)), and Ti(NR'Ar)(NMe(2))(OAr '')(I) (14) were prepared in 83, 83, and 95% isolated yield, respectively, via a salt-elimination, protonolysis, and dimethylamide deprotection sequence. Treatment of 14 with (i) neopentyllithium, (ii) thermolysis at 65 degrees C, and (iii) excess methyl iodide at 70 degrees C led to the isolation in 62% yield of the cyclometallated compound Ti(NR'Ar)(O-2,6-C6H3[(t)Bu][CMe(2)CH(2)])(I) (17) via an intermediate neopentyl complex (15) which was not isolated. The titanium(III) ''ate'' complex (ArR'N)(2)Ti(mu-Cl)(2)Li(TMEDA)(n) (18, TMEDA=Me(2)NCH(2)CH(2)NMe(2), n=ca. 3) was isolated in 80% yield as green crystals upon treatment of TiCl3(THF)(3)(THF=tetrahydrofuran) with 2 equiv of Li(NR'Ar)(OEt(2)) in a THF/TMEDA mixture. Chloroform treatment of the ate complex 18 led to the titanium(IV) dichloride Ti(NR'Ar)(2)Cl-2 (19). The titanium(III) ate complex (ArRN)(2)Ti(mu-Cl)(2)Li(TMEDA) (20) was isolated in 57% yield in a manner analogous to the preparation of 18. Alkylation of 20 with LiCH(SiMe(3))(2) led to the mixed amido-alkyl titanium(III) complex Ti(NRAr)(2)(CH[SiMe(3)](2)) (21) in 72% isolated yield. A single-crystal X-ray diffraction study carried out for 21 revealed an eta(3) bonding mode for one of the NRAr ligands and a typical eta(1) bonding mode for the other. The diamagnetic dimeric complex (mu-NCPhCPhN)[Ti(NRAr)(2)(CH[SiMe(3)](2))](2) (23) was obtained in 82% yield via the blue benzonitrile adduct Ti(NRAr)(2)(CH[SiMe(3)](2))(NCPh) (22), which was not isolated. A robust green pivalonitrile adduct Ti(NRAr)(2)(CH[SiMe(3)](2))(NCCMe(3)) (24) was observed upon treatment of 21 with pivalonitrile. Addition of azidotrimethylsilane to 24 delivered the titanium(IV) azido complex Ti(NRAr)(2)(CH[SiMe(3)](2))(N-3) (25) in 37% isolated yield. Treatment of 21 with 0.5 equiv of I-2 in benzene provided Ti(NRAr)(2)(CH[SiMe(3)](2))(I) (26) in 68% yield.