Easy access to bio-inspired osmium(II) complexes through electrophilic intramolecular C(sp2)-H bond cyclometalation

Mild electrophilic C(sp(2))-H cyclometalation of 2-phenylpyridine and N,N-dimethylbenzylamine by the chloro-bridged osmium(II) dimer [OSCl(mu-Cl)(eta(6)-C6H6)](2) in acetonitrile affords cyclometalated pseudotetrahedral Os-II complexes [Os(C similar to N)(eta(6)-C6H6)(NCMe)]PF6 (C similar to N = o-C(6)H(4)py-kappa C,N (2) and o-C6H4CH2NMe2-kappa CN (5), respectively) in good to excellent yields. The cyclometalation reactions are super sensitive to the nature of an external base. Sodium hydroxide is essential for cyclometalation of 2-phenylpyridine, but NaOH retards metalation of N,N-dimethylbenzylamine, the tertiary amine being self-sufficient as a base. Further reactions of compounds 2 and 5 with 1,10-phenanthroline or 2,2'-bipyridine (N similar to N) lead to the substitution of the eta(6)-bound benzene to produce octahedral species [Os(C similar to N)(N similar to N)(NCMe)(2)]PF6 or [Os(C similar to N)(N similar to N)(2)]PF6 in MeCN or MeOH as solvent, respectively. The cis configuration of the MeCN ligands in [Os(C similar to N)(phen)(NCMe)(2)]PF6 has been confirmed by an X-ray crystallographic study. Electrochemical investigation of the octahedral osma(II)cycles by cyclic voltammetry showed a pseudoreversible M-III/II redox feature at (-50)-(+109) and 190-300 mV versus Ag/AgCl in water and MeCN, respectively.. As a possible application of the compounds, a rapid electron exchange between the reduced active site of glucose oxidase enzyme from Aspergillus niger and the electrochemically generated Os-III species has been demonstrated. The corresponding second-order rate constants cover the range (0.7-4.8) x 10(6) M-1 s(-1) at 25 degrees C and pH 7.