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43703-AC1
C-C-C N-Heterocyclic Carbene Pincer Complexes: A General Method of Preparation Critical for Applications in Catalysis
A general solution to the preparation of pincer complexes that require the formation of two N-heterocyclic carbenes (NHC's) and the activation of an aryl C-H bond has been developed.� Continued work on this methodology has been carried out during the project period with new coworkers learning the method and developing large scale syntheses.� The reaction of a phenylene-bridged bis(imidazolium) salt with Zr(NMe2)4 generated the requisite CCC-NHC Zr pincer complex 2 (Scheme 1), which has been characterized by X-ray crystallography (Figure 1).�
Scheme 1.� Synthesis of CCC-NHC Zr pincer complex of 2.� Complex 3 was identified in the X-ray crystal structure and occupies 9% of the crystal sites.
Figure 1.� ORTEP diagram (50% probability ellipsoids, hydrogens omitted for clarity) of complex 2 and 3.� A solid solution was observed in the crystal with 91% of the crystal showing two amido groups and one iodide group and 9% of the crystal showing one amido group and two iodides.
Importantly, it has been found that CCC-NHC Zr pincer complexes can be generated in situ and transmetallated with an appropriate Rh source to generate CCC-NHC Rh pincer structures (4, 5, Scheme 2), which have also been characterized by X-ray crystallography (Figure 2).
Scheme 2.� Transmetallation from Zr to Rh in the preparation of late transition metal CCC-NHC Rh pincer complexes 4 and 5.
Figure 2. a) ORTEP plot (50% probability, hydrogens omitted for clarity) of the asymmetric unit of CCC-NHC Rh pincer complex 5.� b) ORTEP plot (50% probability, hydrogens and carbons of the butyl groups omitted for clarity) of the edge-on view of the iodo-bridged Rh dimer structure that completes the octahedron of each molecule.� Rh � Rh = 4.01 �.
����������� These two methodologies, metallation of CCC-NHC precursors with transition metal amido complexes combined with transmetallation, hold great promise for opening general synthetic pathways to a wide variety of transition metal CCC-NHC pincer complexes.
