Bioorganometallic chemistry Part 12. Reaction of [Cp*Rh(H2O)(3)](OTf)(2) with nicotinamide adenine dinucleotide in water: synthesis, structure, and apH-dependent H-1-NMR and voltammetric study of the cyclic trimer product, [Cp*Rh(mu-eta(1)(N1):eta(2)(N6,N7)-9-(5 '-ribose pyrophosphate-5 ''-ribose-1 ''-nicotinamide)adeninato](3)(OTf)(3)

The reaction of [Cp*Rh(H2O)(3)](OTf)(2) (1) with nicotine adenine dinucleot ide (NAD(+), 2), an important co-factor in enzymatic reactions, was studied utilizing H-1-NMR spectroscopy, electrospray ionization mass spectroscopy (ESI/MS), cyclic voltammetry (CV), and isolation techniques, as a function of pH. The product was formulated from the above-mentioned spectroscopic da ta as the well-known Cp*Rh cyclic trimer structure, [Cp*Rh(mu-eta(1)(N1):et a(2)(N6,N7)-9-(5'-ribose pyrophosphate-5 "-ribose-1 "-nicotinamide)adeninat o](3)(OTf)(3), 3, which forms via a self-assembly mechanism as the pH is in creased from 3 to 6 (H-1-NMR). We also compared 3 with the putative one rep orted that formed via reaction with [(Cp*Rh)(2)(mu-Cl-2)Cl-2] and was tenta tively assigned the formula, [Cp*Rh(NAD)Cl](Cl). In fact, both Cp*Rh syntho ns provide the same cyclic trimer product at pH 6, while a presumed mixture of [Cp*Rh(NAD)] and Cp*Rh aqua intermediates (at least eight Cp*Rh H-1-NMR signals are evident) were formed at pH 3.0. A full analysis of the CV data reveals that some Cp*Rh aqua complexes are electroactive at potentials aro und -1.2 V versus Ag \ AgCl, but probably not the cyclic trimer, complex 3. Unfortunately, we were not able to utilize complex 3 in an intramolecular, regioselective reduction reaction, with sodium formate as the hydride sour ce, to provide the corresponding biologically active 1,4-dihydro derivative . Published by Elsevier Science S.A.