C−H and C−CN Bond Activation of Acetonitrile and Succinonitrile by [Tp′Rh(PR₃)]

Abstract

The [Tp′Rh(PR 3 )] fragments, where Tp′ = tris(3,5-dimethylpyrazolyl)borate, R 3 = Me 3 ( a ) or PhMe 2 ( b ), were shown to be applicable for the activation of the C−H and C−CN bonds of acetonitrile. The photoirradiation of Tp′Rh(PR 3 )H 2 ( 1a, b ) in acetonitrile at room temperature afforded the complexes Tp′Rh(PR 3 )(CH 2 CN)H ( 3a, b ), by the selective oxidative addition of the primary C−H bond of acetonitrile to the [Tp′Rh(PR 3 )] fragment generated by the dehydrogenation of 1 . The thermal reactions of Tp′Rh(PMe 3 )(Ph)H ( 2a ) or Tp′Rh(κ 2 -C 6 H 4 -2-PMe 2 )H ( 2b ) in acetonitrile at 80 °C also resulted in the formation of 3a and 3b, respectively, by the oxidative addition of the C−H bond to the [Tp′Rh(PR 3 )] fragment, generated by the reductive elimination of benzene (from 2a ) or intramolecular reductive elimination of the PPhMe 2 ligand (from 2b ). Heating the isolated C−H bond activated complexes 3a, b in acetonitrile at higher temperature (100 °C) for longer times (≈5 days) resulted in the formation of the corresponding C−CN bond activated complexes, Tp′Rh(PR 3 )(CH 3 )(CN) ( 4a, b ), respectively. The molecular structures of the C−H activated product 3a, b (kinetic product) and C−CN activated product 4a, b (thermodynamic product) were fully characterized by NMR spectroscopy, elemental analysis, and X-ray crystallographic analysis. Furthermore, the secondary C−H bond activated product of succinonitrile, Tp′Rh(PMe 3 )[CH(CN)CH 2 CN]H ( 5 ), was isolated by the thermal reaction of 2a with succinonitrile (20 equiv) at 100 °C, and the molecular structure was characterized by NMR spectroscopy and X-ray crystallographic analysis. The cleavage of CH 3 CN was also investigated using DFT models to compare thermodynamics and identify transition-state geometries.