Low-Potential Cyclometalated Osmium(II) Mediators of Glucose Oxidase

The osma(II)cycles [Os(phpy)(LL)2]PF6 (LL = 1,10-phen (3a) and 4,4ʹ-Me2-2,2ʹ-bpy (3b)) are made from [((eta)^6-C6H6)Os((mu)-Cl)Cl]2 (1) either via transmetalation using the [Hg(phpy)2] organomercurial in MeOH or via the sp2-C-H bond cleavage of 2-phenylpyridine (phpyH) in MeCN to afford [((eta)^6-C6H6)Os(phpy)Cl] or [((eta)^6-C6H6)Os(phpy)(MeCN)]PF6, respectively. The latter two react cleanly with LL to give 3a and 3b, the MII/III redox potentials of which equal 30 and -100 mV (vs Ag/AgCl), respectively. The electrochemically made OsIII species oxidize rapidly reduced glucose oxidase. The second-order rate constant equals 1.1 × 10^7 M^-1 s^-1 for 3a at 25 °C, pH 7.