Synthesis, characterization and reactivity of ReOMe 2(bipy)X complexes

Abstract

The complexes cis- and trans-ReOMe 2(bipy)Cl, where cis or trans refers to the Me–Re–Me regiochemistry, were observed to react as follows: (1) with the alkylating agents RMgCl (R=CH 2SiMe 3 and CH 2Ph) and RLi (R=Me) to give ReOMe 2(bipy)R, and (2) with the alkoxides NaOR′ (R′=Me and Et) to give trans-ReOMe 2(bipy)(OR′). The complex ReOMe 2(bipy)CH 2SiMe 3 was observed by 1H NMR spectroscopy to undergo trans to cis isomerization, which proceeded via reversible first-order kinetics, with Δ H°=1.60(4) kcal mol −1 and Δ S°=3.7(1) eu. At room temperature, Δ G°=0.5(1) kcal mol −1 and K eq=0.42(2), indicating a weak thermodynamic preference for the trans isomer. The activation parameters for the trans to cis isomerization were Δ H ‡ 1=26(2) kcal mol− 1 and Δ S ‡ 1=10(7) eu, and those for the reverse cis to trans isomerization were Δ H ‡ −1=27(2) kcal mol −1 and Δ S ‡ −1=14(7) eu. Treatment of a mixture of cis- and trans-ReOMe 2(bipy)CH 2SiMe 3 with anhydrous HCl gave ReOMe(bipy)(CH 2SiMe 3)Cl; similar treatment of ReOMe 3(bipy) and ReOMe 2(bipy)CH 2Ph gave cis-ReOMe 2(bipy)Cl. Exposure of ReOMe(bipy)(CH 2SiMe 3)Cl to AgPF 6 in acetonitrile-d 3 gave the cationic nitrile adduct [ReOMe(bipy)(CH 2SiMe 3)(CD 3CN)][PF 6].