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

The osma(II)cycles [Os(phpy)(LL)2]PF6 (LL = 1,10-phen (3a) and
4,4‘-Me2-2,2‘-bpy (3b)) are made from [(η6-C6H6)Os(μ-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 [(η6-C6H6)Os(phpy)Cl] or [(η6-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 × 107 M-1 s-1 for 3a at 25
°C, pH 7.