Professor Bergman’s group has generated reactive organometallic intermediates capable of undergoing intermolecular oxidative addition with the normally inert C-H bonds in alkanes and other organic molecules. This process holds potential for converting alkanes into functionalized organic molecules such as alkenes and alcohols. Another area of investigation has involved the study of organometallic complexes having metal-oxygen, -nitrogen and -sulfur bonds to obtain information about the mechanisms of metal-mediated oxidation, amination and desulfurization processes. Some of the group’s research in organometallic chemistry moved during the past few years into the development and mechanistic understanding of catalytic reactions, especially in applications to problems in organic synthesis, and the intersection of organometallic chemistry with molecular recognition. Several of the compounds prepared in these projects have been utilized in highly enantioselective asymmetric induction reactions, and others act as homogeneous catalysts for new carbon-hydrogen and carbon-heteroatom bond-forming processes such as hydroamination of alkynes and allenes. The advent of readily available computational methodology, especially for carrying out density functional (DFT) calculations, has been increasingly incorporated into many of the above research activities, and has provided a powerful addition to the arsenal of tools available for understanding the detailed course of organic and organometallic reactions. Much of this work has been facilitated by collaborations with other faculty members in the department of chemistry and elsewhere.
Currently ongoing is a collaboration with the K. N. Raymond and F. D. Toste groups aimed at exploring the possibility of carrying out organometallic reactions in the cavities of water-soluble cluster complexes (so-called “nanovessels”) that had been developed earlier in the Raymond group. The first achievement of this collaboration was the demonstration that cationic iridium complexes synthesized in our laboratory, related to those described in the previous section of this report, are successfully encapsulated into the cavities of the Raymond nanovessels. We then demonstrated that these encapsulated complexes are capable of carrying out C-H activation reactions on water-soluble organic molecules. There is now strong evidence that these reactions take place inside the nanovessel cavities, and that this is responsible for dramatic (and as yet not well understood) selectivity differences between the reactions carried out inside and outside of the nanovessels. In a parallel project, a series of organic rearrangements and hydrolyses have been identified that experience acceleration in rate when they take place inside the nanovessel cavities. Small quantities of nanovessel can be used to catalyze the rearrangement of much larger quantities of organic substrate. Several of these reactions have been shown to follow Michaelis-Menten kinetics, emphasizing their relevance to operation of biological catalysts such as enzymes.
A second ongoing collaboration, in this case with the J. Arnold group, is directed toward the synthesis of complexes with early metal-nitrogen and –oxygen single and double bonds, and in the understanding and applications of their reactions in organic and inorganic chemistry. Many reactions of these materials with unsaturated organic compounds have been uncovered, including cycloaddition reactions between the M=N bonds in imido (or nitrene) complexes and unsaturated organic compounds, such as alkynes, alkenes, allenes, nitriles and imines. Catalytic processes useful in alkene hydroamination, imine metathesis and heterocumulene metathesis have grown out of this work.