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

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 [Fc][OTf] 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.