The homogeneous ruthenium catalyzed carbonylation of piperidine was studied, starting with Ru-3(CO)(12) in n-hexane solvent, at 333 K under 0.1-1.0 MPa CO and 10 ml piperidine. The analytic method was in situ high-pressure infrared spectroscopy. It was observed that the precursor Ru-3(CO)(12) (2011. 2028 and 2059 cm(-1)) disappeared from solutions after a few hours of reaction time at 333 K and 1.0 MPa CO. The major observable organometallic species, which accounted for the majority of the ruthenium mass balance in the active system was Ru(CO)(5) (1966, 2002 and 2037 cm(-1)). Numerous new bands also appeared in the mid-infrared during the active catalysis. The turnover frequency based on the nominal loading of ruthenium in the system was circa 0.06 h(-1). The reaction is very dean but slow. A tentative catalytic cycle is suggested for this system. Particularly interesting, is the path dependence of this system. If the system is started at 0.1 MPa CO, it rapidly degrades. However, if the system is started at 1.0 MPa CO, until cluster fragmentation is complete and then the system pressure is reduced, a very active system is obtained. Finally, Ru-2(CO)(6)Cl-4 was also used successfully as a precursor for piperidine carbonylation.