Titanium Complexes Stabilized byN-(tert-Hydrocarbyl)anilide Ligation:  A Synthetic Investigation

Abstract

The complexes Ti(NRAr F ) 2 (NMe 2 ) 2 (4, R ) C(CD 3 ) 2 CH 3 , 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-C 6 H 3 i Pr 2 ) 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(CD 3 ) 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 °C, and (iii) excess methyl iodide at 70 °C led to the isolation in 62% yield of the cyclometallated compound Ti(NR′Ar 17) via an intermediate neopentyl complex (15) which was not isolated. The titanium(III) "ate" complex (ArR′N) 2 Ti(µ-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 TiCl 3 (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(µ-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 η 3 bonding mode for one of the NRAr ligands and a typical η 1 bonding mode for the other. The diamagnetic dimeric complex (µ-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.

Reactions of rac‐(ebthi)M(η2‐Me3SiC2SiMe3) (M=Ti, Zr) with Aryl Nitriles

“…The bonding situation in the four‐membered bridge is determined by the number of electrons transferred during the reaction. A two‐electron reductive coupling gives a diimine ligand (NC(R)C(R)N);3a–d, 12a a four‐electron reductive coupling gives an enediimido ligand (NC(R)C(R)N) 12b. For complex 3 , the decision of whether two or four electrons were involved was made by the comparison of the CN and CC distances of the four‐membered bridge and of the positions of typical signals in the IR and 13 C NMR spectra to those of similar complexes.…”

Low‐Coordinated Titanium(III) Alkyl—Molecular and Surface—Complexes: Detailed Structure from Advanced EPR Spectroscopy

“…Single‐crystal X‐ray diffraction on 2 reveals a tri‐coordinated titanium(III) coordinated to two aryloxides and one alkyl ligand, in an overall distorted trigonal geometry (Figure a). The Ti‐Cα bond length (2.098(3) Å) is unusually short compared to [η 1 ‐( t Bu)‐(Ar)N][η 3 ‐( t Bu)(Ar)N]Ti[CH(TMS) 2 ] (Ti‐Cα= 2.137(7) Å), to [PhC(NSiMe 3 ) 2 ] 2 TiMe (Ti‐Cα=2.120(5) Å) or LTiMe 2 (Ti‐Cα=2.123(3) Å and 2.131(3), LH=(2E,4E)‐N2,N4‐bis(2,6‐diisopropylphenyl)pentane‐2,4‐diimine). Noteworthy, the hydrogen atom on the Cα is found in the difference Fourier map and freely refined (i.e.…”

Chlorido(η5-cyclopentadienyl)bis(dimethylamido)titanium, [TiCl(η5-C5H5)(NMe2)2]

“…The complex contains two dimethylamide groups suitable for reaction with protic reagents, and a single chloride ligand that can react with alkylating reagents or other anionic nucleophiles through a salt-elimination metathesis reaction. The divergent and orthogonal reactivity of halides and dimethylamides has been used to prepare chiral titanium complexes (Johnson et al, 1996).…”