Metal−Organic Cooperative Catalysis in C−H and C−C Bond Activation and Its Concurrent Recovery

Young Jun Park was born in 1971. He received his B.S., M.S., and Ph.D. degrees in chemistry from Yonsei University in 1995, 1997, and 2003, respectively. He worked as a postdoctoral associate in the Department of Chemistry and the Center for Bioactive Molecular Hybrid at Yonsei University under the guidance of Professor Chul-Ho Jun.

Jung-Woo Park was born in 1984. He received his B.S. at Yonsei University in Seoul, Korea, in 2005. He joined Professor Jun’s group in 2005 working as a research scientist and is now a Ph.D. student at Yonsei University. His current research interests are the study of novel transition metal catalysis and syntheses of organic–inorganic hybrids.

Chul-Ho Jun was born in 1953. He graduated from Department of Chemistry of Yonsei University in 1976. He received his Ph.D. degree from Brown University in 1986 on C−C bond activation by organometallic compounds. From 1991 to 1992, he held a postdoctoral fellowship at Yale University. Starting in 1976, he worked as a research scientist at the Agency for Defense Development in Korea. In 1993, he moved to Yonsei University as an Associate Professor, and then, in 1995, he was promoted to full Professor. He was one of the directors of the National Research Laboratory of Korea (2000−2005). He spent his sabbatical stay at Department of Chemistry of Harvard University in 2003. His research interests are design and synthetic approach of the transition metal catalyzed C−H and C−C bond activation and application to the recyclable catalysis and syntheses of organic–inorganic hybrid.

The development of an efficient catalytic activation (cleavage) system for C−H and C−C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C−H and C−C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate.

In this Account, we describe our entire efforts to activate C−H or C−C bonds adjacent to carbonyl groups by employing a new concept of metal−organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C−C triple bond cleavage, hydrative dimerization of alkynes, and skeletal rearrangements of cyclic ketones was realized through MOCC. In particular, in the quest for an optimized MOCC system composed of a Wilkinson’s catalyst (Ph₃P)₃RhCl and an organic catalyst (2-amino-3-picoline), surprising efficiency enhancements could be achieved when benzoic acid and aniline were introduced as promoters for the aldimine formation process. Furthermore, a notable accomplishment of C–C bond activation has been made using 2-amino-3-picoline as a temporary chelating auxiliary in the reactions of unstrained ketones with various terminal olefins and Wilkinson’s catalyst. In the case of seven-membered cyclic ketones, an interesting ring contraction to five- or six-membered ones takes place through skeletal rearrangements initiated by the C−C bond activation of MOCC.

On the other hand, the fundamental advances of these catalytic systems into recyclable processes could be achieved by immobilizing both metal and organic components using a hydrogen-bonded self-assembled system as a catalyst support. This catalyst-recovery system provides a homogeneous phase at high temperature during the reaction and a heterogeneous phase at room temperature after the reaction. The product could be separated conveniently from the self-assembly support system by decanting the upper layer. The immobilized catalysts of both 2-aminopyridine and rhodium metal species sustained high catalytic activity for up to the eight catalytic reactions.

In conclusion, the successful incorporation of an organocatalytic cycle into a transition metal catalyzed reaction led us to find MOCC for C−H and C−C bond activation. In addition, the hydrogen-bonded self-assembled support has been developed for an efficient and effective recovery system of homogeneous catalysts and could be successful in immobilizing both metal and organic catalysts.