Jerrick J. J. Juliette

Titanocene imido complexes: Generation as reactive intermediates, isolation, and structural characterization

Abstract Nitriles react with 2,3-dimethyl-1,1-bis(cyclopentadienyl)titanacyclobut-2-ene to afford either azatitanacyclohexadienes or diazatitanacyclooctatrienes. The latter appear to be formed via the intermediacy of butadienylimido complexes, which can be intercepted by the addition of trimethylphosphine. Bis(cyclopentadienyl)titanium bis(trimethylphosphine) undergoes ligand substitution reactions with nitriles. Loss of trimethylphosphine from the 2,4,6-trimethylbenzonitrile complex appears to lead to reductive coupling of the nitrile, affording a dimeric imido complex.

Regioselectivity of metallacycle formation via intramolecular CH activation

Abstract Carbometalation of alkynes by dimethyltitanocene affords vinyl complexes which serve as intermediates for the formation of titanacyclic products through subsequent hydrogen abstraction/methane elimination. Although multiple sites for hydrogen abstraction are present in the intermediate vinyl complexes, the hydrogen abstraction step is in most cases highly regioselective, leading to the formation of either titanacyclobutenes (via γ-H abstraction) or titanacyclopropanes (via β-H abstraction). Rotational isomerization, restricted in the case of larger vinyl group substituents, provides a simple and consistent explanation for the observed regioselectivities, and this effect is sufficiently pronounced to lead to preferential γ-aliphatic CH activation even in the presence of γ-aromatic hydrogens. The titanacyclopropanes may be alternatively formulated as allene complexes of titanocene. An independently prepared trimethylphosphine-ligated analog of 3-methyl-1,2-butadiene, representing the first titanocene allene complex to be reported, undergoes reductive coupling reactions with excess 3-methyl-1,2-butadiene and with alkynes.

Nitrosoarene and nitrosoalkane insertion reactions of titanacyclobutenes

Abstract Titanacyclobutenes react with 2-methyl-2-nitrosopropane and nitrosoarenes to afford products of insertion into the TiCH 2 bond of the metallacycle. Structural confirmation was obtained through single crystal X-ray diffraction analysis of the insertion product of the diphenyltitanacyclobutene and 2-methyl-2-nitrosopropane: C 29 H 31 NOTi, monoclinic, P 2 1 / n , a =7.984(2), b =20.383(8), c =15.005(4) A, β=100.55(2)°, V =2400(2) A 3 , Z =4. The insertion products display dynamic NMR behavior consistent with pyramidal inversion at nitrogen, with activation barriers of c . 14 kcal mol −1 . Hydrolysis of the insertion products affords the corresponding hydroxylamines, while treatment of them or of the titanacyclobutenes with excess nitrosoarene results in metallacycle degradation and formation of azoxyarene.