Multinuclear NMR spectroscopic studies of aryltrimethylsilanes and aryldimethylphosphaneboranes

Article abstract of DOI:10.1016/0022-328X(89)87163-3

Proton, boron-11, carbon-13, silicon-29, and phosphorus-31 NMR chemical shifts and coupling constants are reported for nine ortho- and 2,6-disubstituted aryltrimethylsilanes and five similarly substituted aryldimethylphosphaneboranes.Resonances in the natural-abundance carbon-13 NMR spectra for both sets of derivatives are assigned on the basis of additivity relationships, proton-coupled spectra, and relative magnitudes of 31P-¹³C)> coupling constants.Carbon-13 chemical shifts and <¹J(¹³C-¹H)> coupling constants indicate that the P(BH3)(CH3)2 group is electron-withdrawing.The 13C chemical shifts of aryl C(5) carbons can be attributed to steric inhibition of resonance of about the same magnitude as that produced by ortho-Si(CH3)3.Chemical shift and coupling constant data from previous work are expanded in terms of Taft's dual substituent constants ?₁ and ?_R⁰.Least squares solutions of these equations for aryldimethylphosphaneborane derivatives provide values of 0.41 for ?₁ and 0.04 for ?_R⁰ for the P(BH3)(CH3)2 group.These constants produce reasonable agreement wit observed 13C chemical shifts and coupling constants in the ortho derivatives.