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Solvent-Dependent Structure of Iridium Dihydride Complexes: Different Geometries at Low and High Dielectricity of the
Alexey V Polukeev1, Rocío Marcos2, Mårten S G Ahlquist2
1Centre for Analysis and Synthesis, Department of Chemistry, Lund University, PO Box 124, 22100, Lund, Sweden.
Abstract:
The hydride iridium pincer complex [(PCyP)IrH2] (PCyP=cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane, 1) reveals remarkably solvent-dependent hydride chemical shifts, isotope chemical shifts, JHD and T1(min), with rHH increasing upon moving to more polar medium. The only known example of such behaviour (complex [(POCOP)IrH2], POCOP=2,6-(tBu2PO)2C6H3) was explained by the coordination of a polar solvent molecule to the iridium (J. Am. Chem. Soc. 2006, 128, 17114). Based on the existence of an agostic bond between α-C-H and iridium in 1 in all solvents, we argue that the coordination of solvent can be rejected. DFT calculations revealed that the structures of 1 and [(POCOP)IrH2] depend on the dielectric permittivity of the medium and these compounds adopt trigonal-bipyramidal geometries in non-polar media and square-pyramidal geometries in polar media.
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