Palladium complexes of multidentate pyrazolylmethyl pyridine ligands: Synthesis, structures and phenylacetylene polymerization

The compounds, 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (MeNNN) (L1) and 2,6-bis(3,5-ditertbutylpyrazol-1-ylmethyl)pyridine (tBuNNN) (L2), react with either [Pd(NCMe)(2)Cl-2] or [Pd(COD)ClMe] to form the mononuclear palladium complexes [Pd(MeNNN)Cl-2] (1), [Pd(MeNNN)ClMe] (2), [Pd((tBu)(N) over cap(N) over capN)Cl-2](3) and [Pd((tBu)(N) over cap(N) over capN)ClMe] (4). Reactions of 1, 2 and 4 with the halide abstractor, NaBAr4 (Ar = 3,5-(CF3)(2)C6H3), led to the formation of stable tridentate cationic species [Pd((Me)(N) over cap(N) over capN)Cl](+)(5), [Pd((Me)(N) over cap(N) over capN)Me](+) (6) and [Pd((tBu)(N) over cap(N) over capN)Cl](+) (7) respectively. The analogous carbonyl linker cationic species [Pd{(3,5-Me(2)pz-CO)(2)py}Cl](+) (9) and [Pd{(3,5-(t)Bu(2)pz-CO)(2-py)}Cl](+) (10), prepared by halide abstraction of the neutral complexes [Pd{(3,5-Me(2)pz-CO)(2)py}Cl-2] and [Pd{(3,5-(t)Bu(2)pz-CO)(2)-py}Cl-2] by NaBAr4, were however less stable with t(1/2) of 14 and 2 days respectively. Attempts to crystallize 1 and 3 from the mother liquor resulted in the isolation of the salts [Pd((Me)(N) over cap(N) over capN)Cl](2)[Pd2Cl6] (11) and [Pd((tBu)(N) over cap(N) over capN)Cl](2)[Pd2Cl6] (12). Although when complexes 1-4 were reacted with modified methylaluminoxane (MMAO) or NaBAr4, no active catalysts for ethylene oligomerization or polymerization were formed, activation with silver triflate (AgOTf) produced active catalysts that oligomerized and polymerized phenylacetylene to a mixture of cis-transoidal and trans-cisoidal polyphenylacetylene. (c) 2006 Elsevier Ltd. All rights reserved.