Dinitrogen Functionalization with Allene, Isocyanide, and Carbon Monoxide in a Dititanium Framework

Dinitrogen (N₂) functionalization with carbon building blocks to construct complex carbon-nitrogen architectures under mild conditions represents a long-standing challenge of fundamental interest and practical importance. Here, we report an unprecedented functionalization of dinitrogen via multicoupling with allene, isocyanide, and carbon monoxide (CO) enabled by a dititanium platform. Reaction of the dinitrogen/oxymethylene complex [{(^acriPNP)Ti}₂(μ-η¹:η²-N₂)(μ-η¹:η²-OCH₂)] (1), formed from [{(^acriPNP)Ti}₂(H)(μ-H)₃], N₂ and CO, with phenylallene (PhCH=C=CH₂) at room temperature, selectively affords a phenylpropenylhydrazido/formyl complex [(^acriPNPTi)₂{μ-η¹:η²-NNC(CH₃)=CHPh}(μ-η¹:η²-CHO)] (2). This transformation proceeds through the formation of N-C bonds between the N₂ unit and the central carbon of the allene, followed by hydrogen migration from the oxymethylene ligand to the terminal carbon of the allene. Treatment of 2 with two equivalents of benzyl isocyanide furnishes a novel multicomponent coupling product [(^acriPNP)(O)Ti{μ-κ²:κ⁵-CPh=CMeNNC(=NCH₂Ph)CH=C(^acriPNP)}TiNHCH₂Ph] (4), accompanied by formyl deoxygenation and debenzylamination (C≡N bond cleavage) of one isocyanide molecule as well as C-P bond formation with a PNP ligand. A related multicomponent coupling product [(^acriPNP)(O)Ti{μ-κ²:κ⁵-CHPhC(Me)=NN=C(NCH₂Ph)CH=C(^acriPNP)}{Ti=O}] (7) is obtained by sequential reaction of 2 with benzyl isocyanide (1.0 equiv) and CO (1 atm). The mechanistic details of these transformations are elucidated by isotope-labeling experiments, isolation of key intermediate, and density functional theory (DFT) calculations. This work demonstrates the capacity of a dititanium framework to orchestrate integrated bond-forming and bond-cleaving events for multicomponent dinitrogen functionalization, providing a new strategy for assembling complex N-N-containing architectures directly from N₂.