Divalent Titanium via Reductive N−C Coupling of a TiIV Nitrido with π‐Acids

Abstract The nitrido‐ate complex (PN) 2 Ti (N) μ 2 ‐K (OEt 2) 2 (1) (PN − = (N‐ (2‐P i Pr 2 ‐4‐methylphenyl) ‐2, 4, 6‐Me 3 C 6 H 2) reductively couples CO and isocyanides in the presence of DME or cryptand (Kryptofix222), to form rare, five‐coordinate Ti II complexes having a linear cumulene motif, K (L) (PN) 2 Ti (NCE) (E=O, L=Kryptofix222, (2) ; E=NAd, L=3 DME, (3) ; E=N t Bu, L=3 DME, (4) ; E=NAd, L=Kryptofix222, (5) ). Oxidation of 2 – 5 with FcOTf afforded an isostructural Ti III center containing a neutral cumulene, (PN) 2 Ti (NCE) (E=O, (6) ; E=NAd (7), N t Bu (8) ) and characterization by CW X‐band EPR spectroscopy, revealed unpaired electron to be metal centric. Moreover, 1e − reduction of 6 and 7 in the presence of Kryptofix222cleanly reformed corresponding discrete Ti II complexes 2 and 5, which were further characterized by solution magnetization measurements and high‐frequency and ‐field EPR (HFEPR) spectroscopy. Furthermore, oxidation of 7 with Fc*B (C 6 F 5) 4 resulted in a ligand disproportionated Ti IV complex having transoid carbodiimides, (PN) 2 Ti (NCNAd) 2 (9). Comparison of spectroscopic, structural, and computational data for the divalent, trivalent, and tetravalent systems, including their 15 N enriched isotopomers demonstrate these cumulenes to decrease in order of backbonding as Ti II →Ti III →Ti IV and increasing order of π‐donation as Ti II →Ti III →Ti IV, thus displaying more covalency in Ti III species. Lastly, we show a synthetic cycle whereby complex 1 can deliver an N‐atom to CO and CNAd.