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Reactivity of a Dititanium Bis(pentalene) Complex toward Heteroallenes and Main-Group Element–Element Bonds

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posted on 20.12.2016, 17:06 authored by Alexander F. R. Kilpatrick, Jennifer C. Green, F. Geoffrey N. Cloke
The reactivity of the TiTi double bond in (μ,η55-Pn)2Ti2 (1; Pn = 1,4-{SiiPr3}2C8H4) toward isocyanide and heteroallene substrates, and molecules featuring homonuclear bonds between main-group elements (E–E) has been explored. Reaction of 1 with methyl isocyanide or 1,3-N,N′-di-p-tolylcarbodiimide resulted in the formation of the 1:1 adducts (μ,η55-Pn)2Ti2(μ,η2-CNMe) (2) and (μ,η55-Pn)2Ti2(μ-C­{N­(4-C6H4CH3)}2) (3), respectively, which are thermally stable up to 100 °C in contrast to the analogous adducts formed with CO and CO2. Reaction of 1 with phenyl isocyanate afforded a paramagnetic complex, [(η8-Pn)­Ti]2(μ,κ22-O2CNPh) (4), in which the “double-sandwich” architecture of 1 has been broken and an unusual phenyl-carbonimidate ligand bridges two formally Ti­(III) centers. Reaction of 1 with diphenyl dichalcogenides, Ph2E2 (E = S, Se, Te), led to the series of Ti–Ti single-bonded complexes (μ,η55-Pn)2[Ti­(EPh)]2 (E = S (5), Se (6), Te (7)), which can be considered the result of a 2e redox reaction or a 1,2-addition across the TiTi bond. Treatment of 1 with azobenzene or phenyl azide afforded [(η8-Pn)­Ti]2(μ-NPh)2 (8), a bridging imido complex in which the pentalene ligands bind in an η8 fashion to each formally Ti­(IV) center, as the result of a 4e redox reaction driven by the oxidative cleavage of the TiTi double bond. The new complexes 28 were extensively characterized by various techniques including multinuclear NMR spectroscopy and single-crystal X-ray diffraction, and the experimental work was complemented by density functional theory (DFT) studies.