Cp2ti(κ2 -tbuncntbu): A complex with an unusual κ2 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

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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- 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.

Original languageEnglish (US)
Pages (from-to)8006-8018
Number of pages13
JournalJournal of the American Chemical Society
Volume142
Issue number17
DOIs
StatePublished - Apr 29 2020

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