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            Not, available (Ed.)Abstract Described here is a direct entry to two examples of 3d transition metal catalysts that are active for the cyclic polymerization of phenylacetylene, namely, [(BDI)M{κ2‐C,C‐(Me3SiC3SiMe3)}] (2‐M) (BDI=[ArNC(CH3)]2CH−, Ar=2,6‐iPr2C6H3;M=Ti, V). Catalysts are prepared in one step by the treatment of [(BDI)MCl2] (1‐M,M=Ti,V) with 1,3‐dilithioallene [Li2(Me3SiC3SiMe3)]. Complexes2‐Mhave been spectroscopically and structurally characterized and the polymers that are catalytically formed from phenylacetylene were verified to have a cyclic topology based on a combination of size‐exclusion chromatography (SEC) and intrinsic viscosity studies. Two‐electron oxidation of2‐Vwith nitrous oxide (N2O) cleanly yields a [VV] alkylidene‐alkynyl oxo complex [(BDI)V(=O){κ1‐C‐(=C(SiMe3)CC(SiMe3))}] (3), which lends support for how this scaffold in2‐Mmight be operating in the polymerization of the terminal alkyne. This work demonstrates how alkylidynes can be circumvented using 1,3‐dianionic allene as a segue into M−C multiple bonds.more » « less
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