Synthesis, characterization and reactivity of a RhNO complex with a PCN pincer ligand

CECILIA GALLEGO; JUAN PELLEGRINO; CARINA GAVIGLIO; YEHOSHOA BEN-DAVID; DAVID MILSTEIN; FABIO DOCTOROVICH

CABA

Simposio; Exploring the Frontiers of Chemistry: Challenges for the 21st Century; 2019

Studies of characterization and reactivity of nitrosyl complexes are of high importance to attain further understanding of nitric oxide?s role in biology. This ligand is also particularly attractive in coordination chemistry for its rich redox activity, which gives place to three limit bonding descriptions. Nevertheless, electronic delocalization is best described by Enemark-Feltham notation {MNO}n.1Pincer ligands, on the other hand, are also broadly studied due to their relative stability and the possibility they introduce of tuning the metallic center reactivity by changing sterical and electronic parameters. In prior works, the combination of both these types of ligands was studied in a {RhNO}8species with a PCP ligand and activation of carbon-halogen bonds by {RhNO}9 has been reported.2 In this work, we synthesized a {RhNO}8 complex with a PCN pincer ligand: [Rh(PCN)(NO)]+ (PHCN=N-[[3-(ditert-butylphosphanylmethyl)phenyl]methyl]-N-ethylethanamine), which wouldbe expected to favour higher oxidation states and reduce steric hindrance around the metallic center.{RhNO}8was obtained by a four-step synthesis, where only the first step is reported:3PCHN + [Rh(COE)2Cl]2→Rh(PCN)(H)(Cl) (1)→Rh(PCN)(NO)Cl (2)→[Rh(PCN)(NO)]+ (3+)COE=CycloocteneAll of these compounds were characterized by 31P-NMR, 1H-NMR, FTIR and X-ray diffraction. Redox reactivity of complex (3+)and of that of its pentacoordinate derivatives, (2) and [Rh(PCN)(NO)(CH3CN)]+(4+), was found to distinguish itself from analogous PCP complexes due to a relative stabilization of higher oxidation states. Oxidation of these three complexes was studied by FTIR spectroelectrochemistry.Reduction of complex (3+) to yield an air sensitive {RhNO}9 species [Rh(PCN)(NO)]?(3?) was also carried out. Complex (3?) was proved able to activate carbon-halogen bonds in aryl halides, in much a similar way as that of its PCP analogue.REFERENCES1Enemark, J. H.; Feltham, R. D. Coord.Chem. Rev. 1974, 13, 339.2Pellegrino. J.; Gaviglio, C.; Milstein, D.; Doctorovich, F. Organometallics.2013, 32, 6555.3Cohen, R., Rybtchinski, B., Gandelman, M., et. al.J. Am. Chem. Soc., 2003, 125(21), 6532.