The (imido)­niobium­(V)–alkylidene complexes Nb­(CHSiMe3)­(NR)­[OC­(CF3)3]­(PMe3)2 (R = 2,6-Me2C6H3, 2,6- i Pr2C6H3, 1-adamantyl), which could be isolated from the dialkyl analogues by α-hydrogen elimination in the presence of PMe3, exhibited remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene, and the polymerizations proceeded in a living manner. Metathesis polymerizations of (unstrained) disubstituted acetylenes also took place, affording polymers with uniform (narrow) molecular weight distributions.

Reactions of Nb(NAr)(N=C t Bu 2 ) 3 ( 3a , Ar = 2,6-Me 2 C 6 H 3 ) with 1.0, 2.0, or 3.0 equiv of Ar′OH (Ar′ = 2,6- i Pr 2 C 6 H 3 ) afforded Nb(NAr)(N=C t Bu 2 ) 2 (OAr′), Nb(NAr)(N=C t Bu 2 )(OAr′) 2 , or Nb(NAr)(OAr′) 3 , respectively (at 25 °C), whereas the reaction with 2.0 equiv of 2,6- t Bu 2 C 6 H 3 OH afforded Nb(NAr)(N=C t Bu 2 ) 2 ( O -2,6- t Bu 2 C 6 H 3 ) upon heating (70 °C) without the formation of bis(phenoxide) and the reaction of 3a with 2.0 equiv of 2,4,6-Me 3 C 6 H 2 OH afforded Nb(NAr)(N=C t Bu 2 )( O -2,4,6-Me 3 C 6 H 2 ) 2 (HN=C t Bu 2 ). Similar reactions of 3a with 1.0 equiv of (CF 3 ) 3 COH or 2.0 equiv of (CF 3 ) 2 CHOH afforded Nb(NAr)(N=C t Bu 2 ) 2 [OC(CF 3 ) 3 ](HN=C t Bu 2 ) or Nb(NAr)(N=C t Bu 2 )[OCH(CF 3 ) 2 ] 2 (HN=C t Bu 2 ), respectively. On the basis of their structural analyses and the reaction chemistry, it was suggested that these reactions proceeded via coordination of phenol (alcohol) to Nb and the subsequent proton (hydrogen) transfer to the ketimide (N=C t Bu 2 ) ligand. The reaction of Nb(NAr)(N=C t Bu 2 ) 2 (OAr′) with 1.0 equiv of 2,4,6-Me 3 C 6 H 2 OH gave the disproportionation products Nb(NAr)(N=C t Bu 2 )(OAr′) 2 and Nb(NAr)(N=C t Bu 2 )( O -2,4,6-Me 3 ...

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The tripodal ‘click’ ligand tris(4‐trimethylsilyl‐1,2,3‐triazolylmethyl)amine (TTTA) is effective at promoting copper‐catalysed single‐electron transfer living radical polymerization of methyl methacrylate in bulk. The corresponding copper species allow well‐controlled polymerizations under aerobic conditions.