Synthesis, characterization, and catalytic application of novel and immobilized palladium and ruthenium complexes
Sheets, Matthew Ryan
MetadataShow full item record
Transition metal-catalyzed coupling reactions are among the most powerful tools in organic synthesis. Several widely used reactions are discussed, including ring closing metathesis (RCM), allyl ion transfers, and the Heck reaction. These valuable reactions can lead to the construction of C-C and C-heteroatom bonds in the presence of a broad range of functionalities under relatively mild conditions. With regards to ring-closing metathesis, we have shown that a readily assembled ionic liquid-tagged Ru carbene complex is a highly efficient catalyst for the RCM of di-, tri- and tetrasubstituted diene and enyne substrates in minimally ionic solvent systems, with the combined advantage of high reactivity and a high level of recyclability and reusability. Both the catalyst and the ionic liquid can be conveniently recycled and repeatedly reused with only a very slight loss of activity. Given the growing interest in the development of catalyst systems suitable for organic transformations in ionic liquids and the widespread application of olefin metathesis in organic synthesis, this new complex should prove to be of unique utility in both areas. We have shown that a new SeCSe-Pd(II) pincer complex is a highly efficient catalyst for the allylation of aldehydes with allyltributyltin. Notable advantages of this catalyst includes its high stability, straightforward synthesis and superb catalytic activity compared to other transition metal catalysts developed to date for this reaction. The allylation reaction proceeds under mild and neutral reaction conditions in the presence of as little as 5.0 × 10⁻³ mol% of the catalyst. The results from this work further demonstrate the potential utility of organic selenides as alternative ligands in transition metal catalysis. Nucleophilic N-heterocyclic carbenes (NHCs) have emerged as a new class of ligands in transition metal chemistry, as evidenced by an explosive utilization of these ligands as other alternatives to phosphines in transition metal-catalyzed organic reactions such as the Heck reaction. We have found the commercially available triazolium inner salt, (1,4-diphenyl-4 H-1,2,4-triazol-1-ium-3-yl)(phenyl)amide (Nitron), can be used as a convenient source of a new NHC, namely the 3-amino-1H-1,2,4-triazolylidene ligand. Novel Pd complexes based on this ligand were synthesized and found to be highly active catalysts for the Heck reaction.