Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides

Abstract

The reactivity of the "tuck-over" species [Ti2( 5 -C5Me5)(CH2Ph)3(- 5 -C5Me4CH2-C)(-O)] ( 1) and [Ti2((2) towards isocyanides has been examined both synthetically and theoretically. Treatment of 1 with the isocyanides RNC, R = Me3SiCH2, 2,6-Me2C6H3, tBu, iPr, leds to a series of  2 -iminoacyl species (3-6) where the molecule of isocyanide inserts into one of the terminal metal-alkyl bonds. The analogous reaction of the "tuck-over" metallacycle species 2 with 2,6-Me2C6H3NC and tBuNC results in the initial insertion of one isocyanide into the terminal Ti-alkyl bond to form the iminoacyl complexes 7 and 8, followed by a second insertion into the metallacycle moiety to generate 9, in the case of tert-butylisocyanide. DFT calculations support the selective reactivity observed experimentally with a kinetic and thermodynamic preference for RNC insertion on the terminal alkyl groups bound to both metallic centers over the alternative insertion on the "tuck-over" ligand.

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

“…The Ti–C α (av. 2.16(2) Å) bond lengths are in the expected range for a Ti­(IV)-C­(sp 3 ) bond, and the distances C β -C γ (av. 1.32(8) Å) are assignable to carbon–carbon double bonds.…”

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.…”

“…Curiously, the formation of a η 2 -iminoacyl complex, analogous to compounds 3−6, was not detected. It is noteworthy that, despite having all of the necessary reagents and similar experimental conditions to those used to obtain the "tuck over" complex [Ti 2 (η 5 -C 5 Me 5 )(μ-η 5 -C 5 Me 4 CH 2 −κC) (CH 2 Ph) 3 (μ-O)] 28 and its η 2 -iminoacyl derivative, 44 none of them were detected (Scheme 4).…”

Titanium-Mediated C–C Coupling of Imidoylstannanes for the Synthesis of Tetraaryl Diimines. Isolation of Titanium Iminoacyl and Ene-diamido Intermediates

“…Complex 3 is monomeric with an η 2 -coordinated iminoacyl ligand and five-coordinated titanium center. The Ti(1)–C(14) and Ti(1)–N(3) bond lengths of 2.024(3) and 2.000(3) Å, respectively, are only slightly shorter than those reported for titanium η 2 -iminoacyl complexes supported by cyclopentadienyl ligands . Complex 4 is the first example of an ene-diamido titanium complex with a tetraaryl-substituted framework.…”

“…However, it could be detected by 1 H NMR (Figure S1 in Supporting Information). Bis-iminoacyl titanium complexes have been previously prepared by the insertion of isocyanides into titanium–alkyl bonds, and the structural analysis of the iminoacyl complexes indicated that the complexes are highly symmetrical with the η 2 -R′CNR units lying parallel to each other in a head-to-tail fashion . We reasoned that the intermediate A could undergo a facile intramolecular C–C coupling reaction in refluxing toluene to give the titanium complex 4 .…”