Low-potential cyclometalated osmium(II) mediators of glucose oxidase.

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