Journal of the American Chemical Society, Vol.142, No.17, 8006-8018, 2020
Cp2Ti(kappa(2)-(BuNCNBu)-Bu-t-Bu-t): A Complex with an Unusual kappa(2) Coordination Mode of a Heterocumulene Featuring a Free Carbene
Although there are myriad binding modes of heterocumulenes to metal centers, the monometallic kappa(2)-ECE (E = O, S, NR) coordination mode has not been reported. Herein, the synthesis, isolation, and physical characterization of Cp2Ti- (kappa(2)-tBuNCI\I`Bu) (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 C-13 NMR spectroscopic analysis indicate that 3 is best described as a free carbene with partial Ti-C-beta bonding that results from Ti-N pi-bonding mixing with N-C-N sigma-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, (Cp2Ti)(2)(mu-eta(1),eta(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.