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{κ2 -C,C-(Me3 SiC3 SiMe3 )}] (2-M) (BDI=[ArNC(CH3 )]2 CH- , Ar=2,6-i Pr2 C6 H3 ; 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 (Me3 SiC3 SiMe3 )]. 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 (N2 O) 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 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.

Ligating properties of anionic Fischer-type carbene complexes, [(CO)(5)M[double bond, length as m-dash]C(X)Y](-)

With the simplest of anionic Fischer-type carbene complexes acting as ligands, Cp(2)Zr(Cl){OCMe}M(CO)(5) compounds (M = Cr or W) promote alpha-olefin oligomerization and polymerization in the presence of MAO. Attaching an N-heterocyclic ring to the carbene carbon atom in similar precursors, allows a variety of hard metal ions and fragments to be captured by external bidentate coordination. The outcome of the attachment of a phosphorus or sulfur functionality to an alpha-carbon of an O-anionic carbene is formation of a bidentate ligand and then internal four-membered carbene-heteroatom chelate formation. alpha-Deprotonated carbene complexes are also precursors for remote, one-N, six-membered carbene complexes of various metals whereas alpha-C-, alpha-N- or alpha-O-deprotonated as well as beta-deprotonated Fischer-type carbene complexes display unique synthon properties towards Ph(3)PAu(+) and partake in unusual ensuing coordination of liberated group 6 metal carbonyl moieties to form dinuclear products.