Metallacyclobuta-(2,3)-diene: A Bidentate Ligand for Stream-line Synthesis of First Row Transition Metal Catalysts for Cyclic Polymerization of Phenylacetylene.

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{κ 2 -C,C-(Me 3 SiC 3 SiMe 3 )}] (2-M) (BDI=[ArNC(CH 3 )] 2 CH - , Ar=2,6- i Pr 2 C 6 H 3 ; M=Ti, V). Catalysts are prepared in one step by the treatment of [(BDI)MCl 2 ] (1-M, M=Ti, V) with 1,3-dilithioallene [Li 2 (Me 3 SiC 3 SiMe 3 )]. Complexes 2-M have 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 of 2-V with nitrous oxide (N 2 O) cleanly yields a [V V ] alkylidene-alkynyl oxo complex [(BDI)V(=O){κ 1 -C-(=C(SiMe 3 )CC(SiMe 3 ))}] (3), which lends support for how this scaffold in 2-M might 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.