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

Article abstract of DOI:10.1021/om960315g

The complexes Ti(NRAr_F)2(NMe₂)₂ (4, R = C(CD₃)₂CH3, Ar_F = 2,5-C₆H₃FMe), Ti(NRAr_F)₂-(NMe₂)(I) (5), Ti(NRAr_F)₂(NMe₂)(CH₂SiMe ₃) (6), and Ti(NRAr_F)₂(I)(CH₂SiMe₃) (7) have been synthesized in 77, 71, 70, and 84percent 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-C₆H₃Me₂, Ar′ = 2,6-C₆H₃ⁱPr₂) was prepared in 65percent yield via the complexes Ti-(NRAr)(NMe₂)₃ (9) and Ti(NRAr)(NMe₂)₂(OAr′) (10), which were generated in situ, spectroscopically characterized, and not isolated. The complexes Ti(NR′Ar)(NMe₂)₃ (12, R′ = C(CD₃)₂Ph, Ti(NR′Ar)(NMe₂)₂(OAr″) (13, Ar″ = 2,6-C₆H₃^tBu₂), and Ti(NR′Ar)(NMe₂)(OAr″)-(I) (14) were prepared in 83, 83, and 95percent isolated yield, respectively, via a salt-elimination, protonolysis, and dimethylamide deprotection sequence. Treatment of 14 with (i) neopentyllithium, (ii) thermolysis at 65°C, and (iii) excess methyl iodide at 70°C led to the isolation in 62percent yield of the cyclometallated compound Ti(NR′Ar)(O-2,6-C₆H₃[^tBu][CMe ₂CH₂](I) (17) via an intermediate neopentyl complex (15) which was not isolated. The titanium(III) "ate" complex (ArR′N)₂Ti(μ-Cl)2Li(TMEDA)_n (18, TMEDA = Me₂NCH₂CH₂NMe₂, n = ca. 3) was isolated in 80percent yield as green crystals upon treatment of TiCl₃(THF)₃ (THF = tetrahydrofuran) with 2 equiv of Li(NR′Ar)(OEt₂) in a THF/TMEDA mixture. Chloroform treatment of the ate complex 18 led to the titanium(IV) dichloride Ti(NR′Ar)₂Cl₂ (19). The titanium(III) ate complex (ArRN)₂Ti(μ-Cl)₂Li(TMEDA) (20) was isolated in 57percent yield in a manner analogous to the preparation of 18. Alkylation of 20 with LiCH(SiMe₃)₂ led to the mixed amido-alkyl titanium(III) complex Ti(NRAr)₂(CH[SiMe₃]₂) (21) in 72percent isolated yield. A single-crystal X-ray diffraction study carried out for 21 revealed an η³ bonding mode for one of the NRAr ligands and a typical η¹ bonding mode for the other. The diamagnetic dimeric complex (μ-NCPhCPhN)[Ti(NRAr)₂(CH[SiMe₃]₂)]2 (23) was obtained in 82percent yield via the blue benzonitrile adduct Ti(NRAr)₂(CH[SiMe₃]₂)(NCPh) (22), which was not isolated. A robust green pivalonitrile adduct Ti(NRAr)₂(CH[SiMe₃]₂)(NCCMe₃) (24) was observed upon treatment of 21 with pivalonitrile. Addition of azidotrimethylsilane to 24 delivered the titanium(IV) azido complex Ti(NRAr)₂(CH[SiMe₃]₂)(N₃) (25) in 37percent isolated yield. Treatment of 21 with 0.5 equiv of I₂ in benzene provided Ti(NRAr)₂(CH[SiMe₃]₂)(I) (26) in 68percent yield.