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

María Gómez-Pantoja,Cristina Santamaría,Juan I González-Pérez,Avelino Martín,Manuel Temprado,Miguel Mena

doi:10.1021/acs.organomet.1c00300

Abstract

A detailed study of the reaction of the dinuclear [{Ti(η5-C5Me5)R2}2(μ-O)] (R = Me 1, CH2Ph 2) compounds with a series of organic isonitriles (R′NC, R′ = tBu, iPr, CH2SiMe3, Xyl) (Xyl = 2,6-Me2C6H3) and nitriles (R′CN, R′ = tBu, iPr, SiMe3) has been carried out. Single-crystal X-ray structural studies revealed a variety of reactivity and structural moieties. Theoretical calculations (density functional theory, DFT) were used to understand the mechanism of some uncommon reactions observed experimentally. Reactions of 1 and 2 with isocyanides tBuNC, iPrNC, and Me3SiCH2NC led to the formation of dimetallic η2-iminoacyl species [{Ti(η5-C5Me5)(R′NCR)R}2(μ-O)] (R = Me, R′ = tBu 3, iPr 4, CH2SiMe3 5; R = CH2Ph, R′ = CH2SiMe3 6). Complex 4 underwent net rearrangements at room temperature to give the imido-vinylamido derivative [Ti2(η5-C5Me5)2(μ-O)(μ-NiPr) {N(iPr)CMe═CMe2}Me] (7), whereas the reaction of complex 2 with XylNC rendered the N─C bond cleavage product [{Ti(η5-C5Me5)(CH═CHPh)}(μ-O)(μ-κ2-N,C─N(MeC6H3)CH2){Ti(η5-C5Me5)}] (8). The reactions of 1 with nitriles tBuCN and iPrCN gave the ketimido products [{Ti(η5-C5Me5)Me(CN(Me)R′)}2(μ-O)] (R′ = tBu 9, iPr 10), whereas the analogous processes with 2 gave the alkenyl-imido complexes [{Ti(η5-C5Me5)(CH2Ph)2}(μ-O){Ti(η5-C5Me5)(═NC(R′)═C(H)Ph)(NCR′)}] (R′ = tBu 11, iPr 12) with the concomitant coordination of a nitrile molecule. Complex 1 reacts with Me3SiCN to afford the nitrile–isonitrile isomerization product [{Ti(η5-C5Me5)Me2}(μ-O){Ti(η5-C5Me5)(κ2-C,N-Me2CNSiMe3)(CNSiMe3)] (13).

Highlights

Migratory insertion processes leading to the formation of iminoacyl (RC NR) or ketimido ( N CR2) functionalities have received widespread attention
The double migratory insertions of two methyl groups to a coordinated isocyanide to give an azametallacyclopropane species are known for a few examples with early transition metals.60−65
Based on the irreversibility of the insertion processes at 25 °C and the minor differences computed for the activation Gibbs energy for the formation of the two more kinetically favorable species syn-4a and syn-4b (ΔΔG⧧(25 °C) = 0.5 kcal mol−1, see Figure S4), the concomitant formation of isomer 4b together with 4a, the latter with a molecular disposition equivalent to the solid-state structure of 4, should be expected