We describe a direct entry to two first row transition metal catalysts active for the cyclic polymerization of phenylacetylene, namely, (BDI)M(κ²-Me₃SiC₃SiMe₃) (2-M) (BDI = [ArNC(CH₃)]₂CH⁻, Ar = 2,6-ⁱPr₂C₆H₃; M = Ti , V). These systems are prepared in one step by the treatment of (BDI)MCl₂ with 1,3-dilithioallene [Li₂(Me₃SiC₃SiMe₃)] followed by purification. 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 and intrinsic viscosity studies. Two-electron oxidation of 2-V with pyridine N-oxide yields a [V^V] alkylidene oxo complex (BDI)V(=O)(k¹-(=CSiMe₃C≡CSiMe₃)) (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 metal alkylidynes can be circumvented using 1,3-dianionic allene as a segue into M-C multiple bonds.

Previous work in the synthesis of metallacycles and their connection to the formation of cyclic polyphenylacetylene (c-PPA)

John Russell

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