Coordination Chemistry of a Model for the GP Cofactor in the Hmd Hydrogenase: Hydrogen-Bonding and Hydrogen-Transfer Catalysis

Abstract

Cp(*)M(2+) complexes (M = Rh, Ir; Cp(*) = C(5)Me(5)) are described for 6-(carboxymethyl)-4-methyl-2-hydroxypyridine (cmhpH(2)), an analogue of the guanylylpyridone cofactor in the hydrogenase Hmd. Three findings indicate that Cp(*)M(Hcmhp)(+) stabilizes the binding of hydrogen-bond acceptors to the sixth coordination site: (i) water binds in preference to Cl-, (ii) the adduct Cp(*)Rh(cmhp)(2-hydroxypyridine) exhibits a very short intramolecular hydrogen bond (r(o-o) = 2.38 A; (1)H NMR delta(H) 17.2), and (iii) Cp(*)Ir(cmhpH)Cl efficiently catalyzes the dehydrogenation of PhCH(OH)Me to PhC(O)Me.