The reaction of [Cp*Rh(H2O)3](OTf)2 (1) with nicotine adenine dinucleotide (NAD+, 2), an important co-factor in enzymatic reactions, was studied utilizing 1H-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 data as the well-known Cp*Rh cyclic trimer structure, [Cp*Rh(μ-η1(N1):η 2(N6,N7)-9-(5′-ribose pyrophosphate-5″-ribose-1″-nicotinamide)adeninato] 3(OTf)3, 3, which forms via a self-assembly mechanism as the pH is increased from 3 to 6 (1H-NMR). We also compared 3 with the putative one reported that formed via reaction with [(Cp*Rh)2(μ-Cl2)Cl2] and was tentatively assigned the formula, [Cp*Rh(NAD)Cl](Cl). In fact, both Cp*Rh synthons 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 1H-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 around -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 source, to provide the corresponding biologically active 1,4-dihydro derivative.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry
- Materials Chemistry