“COVALENT SELF-ASSEMBLY” OF ACYCLIC DIAMINOCARBENE LIGANDS AT METAL CENTERS

Abstract

Chelating bis(acyclic diaminocarbene) ligands can be prepared by addition of diamines or hydrazines to coordinated isocyanide ligands in a process that resembles self-assembly. This procedure is potentially generalizable to a range of structurally and electronically diverse bis(carbene) ligands with catalytic utility. A series of 12 palladium complexes of 5-membered chelate bis(carbene) ligands have been prepared by a simple aqueous protocol and screened to identify moderately active, air tolerant Suzuki-Miyaura cross-coupling catalysts. Aryl isocyanide synthons provided more structurally elaborate acyclic diaminocarbenes, including chiral examples that supported enantioselective electrophilic catalysis at palladium. These carbene ligands have distinct stereoelectronic properties that complement those of the widely used N-heterocyclic carbenes.

ACKNOWLEDGMENTS

I thank my student advisees at Oklahoma State University who contributed to this research: Adriana I. Moncada (M.S. 2005), Sudhakar Manne (M.S. 2005), Yuri Kogiso (B.S. 2005), and Yoshitha A. Wanniarachchi (Ph.D. candidate). Prof. Joseph M. Tanski (Vassar College) collaborated on some of the X-ray crystallographic studies, and Prof. Thomas R. Cundari (University of North Texas) provided valuable computational assistance. We gratefully acknowledge the financial support of Oklahoma State University, the American Chemical Society Petroleum Research Fund (Grant No. 40196-G1), and the National Science Foundation (CAREER Award CHE-0645438).

Notes

^a Yields determined by ¹ H NMR.

^a Yields determined by ¹H NMR; isolated yields in parentheses.

^a [BAr ^F ₄]⁻ = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate.

^b Yields determined by ¹⁹F NMR; isolated yields in parentheses.

^c A significant amount of the amide elimination product was also detected, typically 10–20%.

^d DIMes^Me = 1,1′-dimesityl-3,3′-methylenediimidazol-2,2′-diylidene; see compound 21.

Additional information

Notes on contributors

LeGrande M. Slaughter

LeGrande M. Slaughter is an assistant professor in the Department of Chemistry at Oklahoma State University, where he began his independent career in August 2002. His research interests include ligand design, structure-activity relationships in homogeneous catalysis, and organometallic reaction mechanisms.