* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Nugget
Survey
Document related concepts
Transcript
High Oxidation State, Late Transition Metals Featuring Metal-Ligand Multiple Bonds: Strategies for Sequential C-H Bond Activation and Functionalization Theodore A Betley, Chemistry & Chemical Biology, Harvard University In the field of homogenous catalysis, few reports have appeared offering general, chemically mild methods for the introduction of nitrogen- or oxygen-containing functional groups into simple hydrocarbon substrates. The combination of small-molecule activation with C—H bond functionalization represents a significant advance in converting inexpensive chemical feed stocks (e.g. hydrocarbons) to valuable functional molecules with minimal or complete absence of waste generation. We are developing multi-electron redox transformations by mid-to-late, first row transition metal complexes targeting methods for the functionalization of C–H bonds. We have synthesized a new class of electrophilic complexes featuring transiently-formed, or metastable metal-ligand multiple bonds capable of mediating C–H functionalization. The coordination chemistry was investigated for the redox-active dipyrromethane and tris(pyrrolyl)ethane supported transition metal complexes to establish the electronic structure for the pyrrole-based ligand donors. Dipyrromethene (or semiporphyrin) supported ferrous complexes were found to effect a range of intra- and intermolecular C–H bond functionalization reactions - allowing for the construction of new C–N, C–C and C–O bonds from unactivated C–H bonds, culminating in catalytic amination reactions. While electron-releasing ligands (phosphines, carbenes, and β-diketiminates) have been elegantly employed to stabilize metal-ligand multiple bond formation on mid-late transition metal platforms, we posit that the weak-field ligand environment is critical to the overall efficacy of the dipyrromethene-supported catalyst system.