Dinitrogen Cleavage and Multicoupling with Isocyanides in a Dititanium Dihydride Framework.

Dinitrogen (N2 ) activation and functionalization through N-N bond cleavage and N-C bond formation are of great interest and importance but remain highly challenging. We report here for the first time N2 cleavage and selective multicoupling with isocyanides in a dititanium dihydride framework. The reaction of a dinitrogen dititanium dihydride complex [{(acri PNP)Ti}2 (μ-η1 :η2 -N2 )(μ-H)2 ] ( 1 ) with an excess (four or more equivalents) of p -methoxyphenyl isocyanide at room temperature gave a novel amidoamidinatoguanidinate complex [(acri PNP)Ti{NC(═NR)NC(═NR)CH2 NR}Ti(acri PNP)(CNR)] ( 2 , acri PNP = 4,5-bis(diisopropylphosphino)-2,7,9,9-tetramethyl-9 H -acridin-10-ide; R = p -MeOC6 H4 ) through N2 splitting and coupling with three isocyanide molecules. When 1 equiv of p -methoxyphenyl isocyanide was used to react with 1 at -30 °C, the hydrogenation of the isocyanide unit by the two hydride ligands in 1 took place, affording an amidomethylene-bridged dititanium dinitrogen complex [{(acri PNP)Ti}2 (μ-η1 :η2 -N2 ){μ-η1 :η2 -CH2 N( p -MeOC6 H4 )}] ( 3 ), which upon reaction with another equivalent of p -methoxyphenyl isocyanide at room temperature gave an amidomethylene/nitrido/carbodiimido complex [(acri PNP)Ti(N═C═NR)(μ-N)(μ-η1 :η2 -CH2 NR)Ti(acri PNP)] ( 4 ) through N2 cleavage and N═C bond formation. Further reaction of 4 with 1 equiv of p -methoxyphenyl isocyanide led to an unprecedented four-component (carbodiimido, nitrido, isocyanide, and amidomethylene) coupling, yielding an amidoamidinatoguanidinate complex [{(acri PNP)Ti}2 {NC(═NR)NC(═NR)CH2 NR}] ( 5 ), which on reaction with another equivalent of p -methoxyphenyl isocyanide afforded the isocyanide-coordinated analogue 2 . The reaction of 1 with 2-naphthyl isocyanide also took place in a similar multicoupling fashion. Moreover, the cross-coupling reactions of the p -methoxyphenyl isocyanide-derived amidomethylene/nitrido/carbodiimido complex 4 with 2-naphthyl isocyanide, cyclohexyl isocyanide, and tert -butyl isocyanide were also achieved, which afforded the corresponding amidoamidinatoguanidinate products consisting of two different isocyanides. Density functional theory (DFT) calculations further elucidated the mechanistic details.