Cp₂Ti(κ²-tBuNCNtBu): A Complex with an Unusual κ² Coordination Mode of a Heterocumulene Featuring a Free Carbene

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Although there are myriad binding modes of heterocumulenes to metal centers, the monometallic κ 2 -ECE (E = O, S, NR) coordination mode has not been reported. Herein, the synthesis, isolation, and physical characterization of Cp 2 Ti(κ 2 - t BuNCN t Bu) ( 3 ) (Cp = cyclopentadienyl, t Bu = tert -butyl), a strained 4-membered metallacycle bearing a free carbene, is described. Computational (DFT, CASSCF, QT-AIM, ELF) and solid-state CP-MAS 13 C NMR spectroscopic analysis indicate that 3 is best described as a free carbene with partial Ti–C β bonding that results from Ti–N π-bonding mixing with N–C–N σ-bonding of the bent N–C–N framework. Reactivity studies of 3 corroborate its carbene-like nature: protonation with [LutH]I results in the formation of a Ti-formamidinate ( 4 ), while oxidation with S 8 yields a Ti-thioureate ( 5 ). Additionally, a related bridged dititanamidocarbene, (Cp 2 Ti) 2 (μ-η 1,η 1 -CyNCNCy) ( 10 ) (Cy = cyclohexyl) is reported. Taken together, this work suggests that the 2-electron reduction of heterocumulene moieties can allow access to unusual free carbene coordination geometries given the proper stabilizing coordination environment from the reducing transition metal fragment.