Arylimido‐Bridged Dinuclear Ti(μ‐NAr)₂Ti Scaffold for Alkyne Insertion into the ortho‐C−H Bond of Arylimido Ligands

Abstract

Dinuclear titanium dialkyl complexes bridged by two μ-arylimido ligands, [CpTi(CH SiMe )(μ-NAr)] (Cp=cyclopentadienyl) activated an ortho-aryl C-H bond of an μ-arylimido ligand to form a four-membered titanacycle. The subsequent insertion reaction of 1-(trimethylsilyl)propyne into a metal-carbon bond of the four-membered titanacycle yielded the corresponding six-membered titanacycle. Further ortho-C-H bond activation of the other μ-arylimido ligand and an insertion reaction proceeded to give dinuclear titanium complexes with two six-membered titanacycles. An Eyring plot in the temperature range 130-150 °C revealed activation parameters for the alkenylation reaction, and deuterium-labeling experiments showed that the C-H bond activation step is the rate determining step. Relative Gibbs free energies of the starting complexes, reaction intermediates, and transition states were calculated by using DFT calculations.

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

“…1.32(8) Å) are assignable to carbon–carbon double bonds. The presence of the μ-imido fragment shortens significantly the distance Ti1···Ti2 (2.782(2) Å), in comparison with 1 (2.905(1) Å) or another related compounds. − …”

“…1.89(3) Å are slightly shorter than those found for the titanium μ-imido μ-oxo complex, [{Ti­(η 5 -C 5 Me 5 )­(μ-O)} 3 (CHCHPh)­(μ-NPh)] (1.957­(6)–1.948­(6) Å), but close to those reported for dinuclear titanium μ-imido compounds such as [Ti­(η 5 -C 5 H 5 )­(CH 2 SiMe 3 )­(μ-NAr)] 2 (Ar = 3,5-Me 2 C 6 H 3 ) (av. 1.86–2.07 Å) and [{(Ti­(η 5 -C 5 Me 5 )­Cl)­(μ-N­(4-ClC 6 H 4 ))} 2 ] (1.911(2) Å) . The Ti–C α (av.…”

Selective propargylic C(sp3)–H activation of methyl-substituted alkynes versus [2 + 2] cycloaddition at a titanium imido template

“… 8 Mashima, Tsurugi, and co-workers reported the activation of ortho C(sp 2 )–H aryl bonds at the N -aryl-substituent in imido bridged titanium complexes IV when reacted with 1-(trimethylsilyl)propyne to give the six-membered dinuclear titanium complex V ( Scheme 1 , third from top). 9 Herein, we report on another exception to the perceived well-understood chemistry of early transition metal imido complexes. The reactions of the bis(cyclopentadienyl)-based titanium imido complex 1b with methyl-substituted alkynes lead to the formation of five-membered titanium azadiene complexes 2a,b by initial C–H activation of an internal alkyne ( Scheme 1 , bottom).…”

Cp2Ti(II) Mediated Rearrangement of Cyclopropyl Imines

“…The titanocene framework has provided an excellent platform for the study of titanacycles and their chemistry. , Many 6-membered, C- and N-coordinated unsaturated titanacycles have been studied; generally, 5- or 6-membered titanacycles can be formed through insertion of alkyne or nitrile into smaller 3- or 4-membered titanacycles or through reaction of carbodiimides with a “Cp 2 Ti II ” source. − There have been no reports of the isolation of azatitanacycles similar to IM1 . We envisioned that the synthesis of this azatitanacycle on the titanocene framework would provide a good platform for further studies of its reactivity in the context of the catalytic reaction. − …”