Synthesis of cis- and trans-ReOMe2(bipy)Cl and related cationic oxorhenium(V) complexes

Abstract

The purpose of this study was to prepare high oxidation-state rhenium oxomethyl complexes, including cationic compounds, and test selected examples for olefin polymerization activity. Reaction of ReOMe2(PMe3)2Cl with pyridine N-oxide and 2,2′-bipyridine (bipy) gave cis-ReOMe2(bipy)Cl. Conversely, treatment of ReO(bipy)Cl3 with AlMe3 gave trans-ReOMe2(bipy)Cl. The compound cis-ReOMe2(bipy)Cl isomerized quantitatively to trans-ReOMe2(bipy)Cl upon heating in benzene (ΔH ‡ = 29(3) kcal mol–1, ΔS ‡ = 6(9) e.u.; at 79 °C, kobs = 1.34(9) × 10–2 min–1 and t1/2 = 52 min). Reaction of cis-ReOMe2(bipy)Cl with AgX (X– = PF6–, BF4–, or BPh4–) in acetonitrile gave the cationic acetonitrile adducts [ReOMe2(bipy)(CH3CN)]X. Treatment of the PF6– salt with PR3 (PR3 = PMe3, P(OMe)3, PMe2Ph, P(n-Bu)3, and PMePh2) yielded the cationic PR3 adducts cis-[ReOMe2(bipy)(PR3)][PF6]. The BF4– salt of the PMe3 adduct, cis-[ReOMe2(bipy)(PMe3)][BF4], was prepared by the reaction of ReOMe2(PMe3)2Cl with [Ag(CH3CN)2][BF4] in acetonitrile followed by treatment with bipy in CH2Cl2. Single crystal X-ray crystallographic analyses of cis-ReOMe2(bipy)Cl, trans-ReOMe2(bipy)Cl, and cis-[ReOMe2(bipy)(PMe3)][BF4] revealed that they have distorted octahedral structures. Analogs of cis-ReOMe2(bipy)Cl, trans-ReOMe2(bipy)Cl, and cis-[ReOMe2(bipy)(PMe3)][BF4] were also prepared in which the bipy ligand was replaced with 1,10-phenanthroline (phen). An additional analog of cis-[ReOMe2(bipy)(PMe3)][BF4] was prepared in which the bipy ligand was replaced by 4,4′-dimethyl-2,2′-bipyridine. In preliminary experiments, ethylene was polymerized using both cis-ReOMe2(bipy)Cl and trans-ReOMe2(bipy)Cl as catalyst precursors.