The homogeneous production of methyl formate from methanol, syngas, CO and H-2 co-catalyzed by Mo(CO)(6) in the presence of an alkali methoxide (KOCH3) is reported. A slight increase in the amount of methyl formate produced by the mixture of Mo(CO)(6)/KOCH3 over the alkali methoxide (KOCH3) alone, is probably due to the electrophilic nature of Mo-coordinated carbon monoxide compared to free carbon monoxide. The mechanism proposed for the production of methyl formate proceeds via a methoxycarbony! intermediate ([Mo(CO)(5)(COOCH3)](-)), which is then protonated by methanol to eliminate methyl formate. The methoxycarbonyl adduct was shown to play an important role in the formation of methyl formate from the Mo(CO)(6)/KOCH3 system. The role of this intermediate in the catalytic synthesis of methyl formate from Mo(CO)(6)/KOCH3/CO/MeOH, Mo(CO)(6)/KOCH3/syngas/MeOH, Mo(CO)(6)/KOCH3/H-2/MeOH and Mo(CO)(6)/KOCH3/N-2/MeOH is discussed. HP-IR experiments under H-2 and N-2 atmospheres clearly showed the formation of mu-HMO2(CO)(10)(-) as the methoxycarbonyl intermediate diminishes. The significant role of methanol in the protonation of the methoxycarbonyl adduct is also discussed, as is the effect of polar aprotic solvents such as tetrahydrofuran (THF) and triethylene glycol dimethyl ether (triglyme) in the catalytic synthesis of methyl formate under CO, H-2 and syngas. The amount of methyl formate that is formed is solvent dependent, with methanol showing the highest yield. The stoichiometric effect of Mo(CO)(6) to KOCH3 in the production of methyl formate is also reported. (C) 2011 Elsevier B.V. All rights reserved.