An in situ spectroscopic study of the ruthenium catalyzed carbonylation ofpiperidine starting with triruthenium dodecacarbonyl - The importance of path dependence in homogeneous catalysis

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 MP a CO and 10 ml piperidine. The analytic method was in situ high-pressure in frared 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 reac tion time at 333 K and 1.0 MPa CO. The major observable organometallic spec ies, 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 band s also appeared in the mid-infrared during the active catalysis. The turnov er frequency based on the nominal loading of ruthenium in the system was ci rca 0.06 h(-1). The reaction is very dean but slow. A tentative catalytic c ycle is suggested for this system. Particularly interesting, is the path de pendence 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 f ragmentation is complete and then the system pressure is reduced, a very ac tive system is obtained. Finally, Ru-2(CO)(6)Cl-4 was also used successfull y as a precursor for piperidine carbonylation. (C) 2001 Elsevier Science B. V. All rights reserved.