Synthesis, characterization and reactivity of ReOMe2(bipy)X complexes

The complexes cis- and trans-ReOMe2(bipy)Cl, where cis or trans refers to t he Me-Re-Me regiochemistry, were observed to react as follows: (1) with the alkylating agents RMgCl (R = CH2SiMe3 and CH2Ph) and RLi (R = Me) to give ReOMe2(bipy)R, and (2) with the alkoxides NaOR ' (R '= Me and Et) to give t rans -ReOMe2(bipy)(OR '). The complex ReoMe(2)(bipy)CH2SiMe3 was observed b y H-1 NMR spectroscopy to undergo trans to cis isomerization, which proceed ed via reversible first-order kinetics, with DeltaH degrees = 1.60(4) kcal mol (-1) and DeltaS degrees = 3.7(1) eu. At room temperature, DeltaG degree s = 0.5(1) kcal mol (-1) and K-eq = 0.42(2), indicating a weak thermodynami c preference for the trans isomer. The activation parameters for the trans to cis isomerization were DeltaH(double dagger) = 26(2) kcal mol (-1) and D eltaS(double dagger) (1) = 10(7) eu, and those for the reverse cis to trans isomerization were DeltaH(double dagger) (-1) = 27(2) kcal mol(-1) and Del taS(double dagger) (-1) = 14(7) eu. Treatment of a mixture of cis- and tran s -ReOMe2(bipy)CH2SiMe3 with anhydrous HCl gave ReOMe(bipy)(CH2SiMe3)Cl; si milar treatment of ReOMe3(bipy) and ReOMe2(bipy)CH2Ph gave cis-ReOMe2(bipy) Cl. Exposure of ReOMe(bipy)(CH2SiMe3)Cl to AgPF6 in acetonitrile-d(3) gave the cationic nitrile adduct [ReOMe(bipy)(CH2SiMe3)(CD3CN)][PF6]. (C) 2001 E lsevier Science Ltd. All rights reserved.