C–H Activation on an Oxo-Bridged Dititanium Complex: From Alkyl to μ-Alkylidene Functionalities

Abstract

Thermal treatment of the dinuclear compound [{Ti(η 5 -C 5 Me 5 )(CH 2 SiMe 3 ) 2 } 2 (μ-O)] (1) provides the formation of the metallacycle derivatives [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-CH 2 SiMe 2 CH 2 )(CH 2 SiMe 3 ) 2 (μ-O)] (2) and [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-CH 2 SiMe 2 CH 2 ) 2 (μ-O)] (3) and the μ-alkylidene complex [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-CH 2 SiMe 2 CH 2 )(μ-CHSiMe 3 )(μ-O)] ( 4) by sequential carbon−hydrogen activation processes. The reaction of 3 with tert-butylisocyanide, in 1:1 and 1:2 ratios, leads to the η 2 -iminoacyl complexes [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-tBuNCCH 2 SiMe 2 CH 2 )(μ-CH 2 SiMe 2 CH 2 )(μ-O)] ( 5) and [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-tBuNCCH 2 SiMe 2 CH 2 ) 2 (μ-O)] ( 6), respectively. The molecular structures of complexes 3, 4, 5, and 6 have been determined by single-crystal X-ray diffraction analyses.

Intermetallic Cooperation in C–H Activation Involving Transient Titanium-Alkylidene Species: A Synthetic and Mechanistic Study

“…As to more remarkable features in 4 , the Ti–O distances (Ti1–O1 1.823(2) and Ti2–O1 1.813(2) Å) are comparable with those of dinuclear complexes [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-CH 2 SiMe 2 CH 2 ) 2 (μ-O)] ( 2b , avg 1.811(2) Å) and [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ-CH 2 SiMe 2 CH 2 )­(μ-CHSiMe 3 )­(μ-O)] ( 2c , 1.830(7) Å), in contrast with those found in Bottomley’s work (1.961(3) and 1.787(3) Å) or [Ti 2 (η 5 -C 5 Me 5 ) 2 (μ- t BuNCCH 2 SiMe 2 CH 2 )­(μ-CH 2 SiMe 2 CH 2 )­(μ-O)] (1.777(3) and 1.875(3) Å), with a different number of electrons at the metal centers in both cases. Additionally, the presence of the more flexible alkylmetallacycle bridging group makes the values of Ti1···Ti2 (3.050(1) Å) and Ti1–O–Ti2 angle (Ti1–O1–Ti2 114.1(1)°) bigger than those shown by Bottomley’s work (2.725(2) Å and 93.1(1)°).…”

“…Additionally, the presence of the more flexible alkylmetallacycle bridging group makes the values of Ti1···Ti2 (3.050(1) Å) and Ti1–O–Ti2 angle (Ti1–O1–Ti2 114.1(1)°) bigger than those shown by Bottomley’s work (2.725(2) Å and 93.1(1)°). In contrast, the Ti-methylene bond lengths (2.12–2.16 Å) compare well with those of other Ti IV –C­(sp 3 ) bond species. , …”

“…In view of the results achieved with tetralkyl complex [{Ti­(η 5 -C 5 Me 5 )­(CH 2 SiMe 3 ) 2 } 2 (μ-O)] ( 2 ), , we decided to synthesize the analogous species comprising the neopentyl ligand (CH 2 CMe 3 ) and analyze its thermal behavior. Upon monitoring the reaction of chloroderivative [{Ti­(η 5 -C 5 Me 5 )­Cl 2 } 2 (μ-O)] ( 1 ) with 4 equiv of LiCH 2 CMe 3 in an NMR tube in benzene- d 6 at room temperature, the presence of neopentane and the formation of a mixture of tetralkyl compound [{Ti­(η 5 -C 5 Me 5 )­(CH 2 CMe 4 ) 2 } 2 (μ-O)] ( 3 ) and tuck-over complex [Ti 2 (η 5 -C 5 Me 5 )­(μ-η 5 -C 5 Me 4 CH 2 -κC)­(CH 2 CMe 3 )­(μ-CH 2 CMe 2 CH 2 )­(μ-O)] ( 4 ), as determined later by X-ray diffraction analysis, was revealed.…”

A Bridging bis-Allyl Titanium Complex: Mechanistic Insights into the Electronic Structure and Reactivity

“…These spectra show the equivalence of the  5 -C5Me5 ligands, with only one signal in the 1 H NMR spectrum ( = 1.67) and two in the 13 C{ 1 H} NMR spectrum 10 ( = 10.9 C5Me5; 116.0 C5Me5), significantly shifted of the usual region for high valent dinuclear pentamethylcyclopentadienyl -oxo titanium complexes. 19,23 The allyl ligand displays a broad doublet centered at  1.05 for the anti/syn protons. A peak found at  1.67 was assigned to the anti/syn proton of the allyl group, but it is overlapped by the resonance for the ring methyl protons.…”

Structural Diversity in the Reactions of Dimetallic Alkyl Titanium Oxides with Isonitriles and Nitriles

“…For example, Ti1−O1 (1.862(2) Å) is clearly longer than Ti2−O1 (1.786(2) Å), according to the higher electronic deficiency on Ti2, and these are comparable values to those observed in other dinuclear oxotitanium asymmetric species. 44,66 The trimethylsilyl-isocyanide is end-on bonded and nearly linear (Ti1−C51−N51 175.0(3)°), with Ti1−C51 of 2.092(3) Å and a short bond distance N51−C51 of 1.160(4) Å typical of the carbon−nitrogen triple bond, comparable to those found in coordinated isocyanide Ti(IV) complexes. 67−70 The azatitana-cyclopropane moiety in 13 shows typical single bond distances Ti1−N41 (1.956(2) Å), Ti1−C41 (2.185(3) Å), and C41−N41 (1.408(4) Å), 29 similar to the values found for the few examples of titanaaziridine derivatives 71−75 and for other early transition metals, especially tantalum.…”