John Bleeke

John Bleeke

​Professor of Chemistry
Director of Undergraduate Studies in Chemistry
PhD, Cornell University
MS, Cornell University
BA, Carthage College
research interests:
  • Mechanistic Studies of Transition Metal Mediated Reactions
  • Metallabenzenes and Other Aromatic Metallacycles
  • Synthesis and Reactivity of Transition Metal Organometallic Compounds
  • The Organic Chemistry of Metal Bound Polyenyl Ligands

contact info:

mailing address:

  • Washington University
    CB 1134
    One Brookings Dr.
    St. Louis, MO 63130-4899

Since joining the chemistry faculty in 1981, Profesor Bleeke has established a nationally and internationally recognized research program in the area of transition metal organometallic chemistry. He is particularly well known for his research with metallabenzenes and other aromatic metallacycles.

Ever since Kekulé's intuitive idea on the structure of benzene, "aromaticity" has been one of the most fascinating and provocative research topics in chemistry. While benzene is the archetypical aromatic compound, it is now well known that heterocyclic analogues of benzene also exhibit aromatic properties. These heterocyclic benzenoid compounds, in which a CH group is formally replaced by an isoelectronic heteroatom, include pyridine, phosphabenzene, pyrylium, and thiopyrylium. In contrast, virtually nothing is known about metallacyclic benzenoid compounds, i.e., benzene analogues in which a CH group has been formally replaced by a transition metal and its associated ligands. Such "metallabenzenes" represent a fundamentally new class of aromatic compounds in which metal d orbitals participate fully with carbon p orbitals in the formation of ring-bonds.

We have succeeded in synthesizing metallabenzenes using an approach that employs pentadienide reagents as the source of the ring carbon atoms. As shown in the scheme below, treatment of (Cl)Ir(PEt3)3 with potassium 2,4-dimethylpentadienide produces the 1-metallacyclohexa-2,4-diene complex 1, via iridium-mediated activation of a C-H bond on the terminus of the 1-pentadienyl ligand in intermediate A. Compound 1 is then "dehydrogenated" in two steps: a) removal of the hydride ligand with methyltriflate and b) deprotonation of the alpha-ring carbon with base. The red crystalline product, "iridabenzene" 2, is obtained in high yield.

The solid state structure of 2 has been determined by single crystal X-ray diffraction. As expected, the six-membered ring is nearly planar and bonding within the ring is delocalized. The C-C bond lengths are similar to those found in benzene itself and the Ir-C distances are intermediate between normal single and double bonds. In the 1H NMR, the ring protons appear at low-field chemical shift values, as expected for an aromatic molecule capable of sustaining an induced ring current.

As shown in the scheme at right, iridabenzene 2 exhibits a rich and varied reaction chemistry. While some of these reactions mimic those of conventional organic arenes, others differ sharply due to the powerful influence of the transition metal center. From these studies, the guidelines for what constitutes "aromatic behavior" in metallacycles are beginning to emerge.

Selected Publications

J.R. Bleeke, B.L. Lutes, M. Lipschutz, D. Sakellariou-Thompson, J.S. Lee, and N.P. Rath, “Synthesis, Structure, Spectroscopy, and Reactivity of Oxapentadienyl-Cobalt-Phosphine Complexes”, Organometallics, 29, 5057-5067 (2010).

J.R. Bleeke, B.L. Lutes, and N.P. Rath, , “Synthesis, Structure, Spectroscopy, and Reactivity of Thiapentadienyl-Cobalt-Phosphine Complexes”, Organometallics, 28, 4577-4583 (2009).

J.R. Bleeke, P. Putprasert, T. Thananatthanachon, and N.P. Rath, "Synthesis and Characterization of Fused-Ring Iridapyrroles", Organometallics, 27, 5744-5747 (2008).

J.R. Bleeke, T. Thananatthanachon, and N.P. Rath, "Silapentadienyl-Iridium-Phosphine Chemistry", Organometallics, 27, 2436-2446 (2008).

J.R. Bleeke, "Aromatic Iridacycles", Acc. Chem. Res., 40, 1035-1047 (2007).

J.R. Bleeke, T. Thananatthanachon, and N.P. Rath, "Synthesis, Structure, and Spectroscopy of Silaallyl- and Silapentadienyl-Iridium-Phosphine Complexes", Organometallics, 26, 3904-3907 (2007).

J.R. Bleeke, M. Shokeen, E.S. Wise, and N.P. Rath, "Thiapentadienyl-Rhodium-Phosphine Chemistry", Organometallics, 25, 2486-2500 (2006).

J.R. Bleeke, "Synthesis and Reactivity of Heteropentadienyl-Transition-Metal Complexes", Organometallics, 24, 5190-5207 (2005).

J.R. Bleeke, E.S. Wise, M. Shokeen, and N.P. Rath, "Synthesis, Structure, and Spectroscopy of (Thiapentadienyl)rhodium Phosphine Complexes", Organometallics, 24, 805-808 (2005).

Awards

25 Year Service Award from Washington University, 2006.
Special Recognition for Excellence in Mentoring, Graduate Student Senate, Washington University,2004-2005.
Faculty Mentor for Pew Teacher-Scholar (Postdoctoral Program), 1989-1990.
National Science Foundation Predoctoral Fellow, 1976 1979.
Cornell Debye Fellow, 1976.
National Merit Scholar, 1972.