Cp<sub>2</sub>Ti(κ<sup>2</sup><i>-</i><sup><i>t</i></sup>BuNCN<sup><i>t</i></sup>Bu): A Complex with an Unusual κ<sup>2</sup> Coordination Mode of a Heterocumulene Featuring a Free Carbene
Evan P. Beaumier, Christopher P. Gordon, Robin P. Harkins, Meghan E. McGreal, Xuelan Wen, Christophe Copéret, Jason D. Goodpaster, Ian A. Tonks
Abstract
Although there are myriad binding modes of heterocumulenes to metal centers, the monometallic κ2-ECE (E = O, S, NR) coordination mode has not been reported. Herein, the synthesis, isolation, and physical characterization of Cp2Ti(κ2-tBuNCNtBu) (3) (Cp = cyclopentadienyl, tBu = tert-butyl), a strained 4-membered metallacycle bearing a free carbene, is described. Computational (DFT, CASSCF, QT-AIM, ELF) and solid-state CP-MAS 13C NMR spectroscopic analysis indicate that 3 is best described as a free carbene with partial Ti–Cβ 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 S8 yields a Ti-thioureate (5). Additionally, a related bridged dititanamidocarbene, (Cp2Ti)2(μ-η1,η1-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.