Nuclear Magnetic Resonance Spectroscopic Study of substituent Effect Transmission in Aryldimethylphosphane-Boranes
Abstract
Proton, carbon-13, phosphorus-31, and boron-11 NMR coupling constants and chemical shifts are reported for seven meta-and para-substituted aryldimethylphosphane-boranes, XC H P(CH ) .BH . These data have been correlated with Hammett σ constants and with the substituent constants σ andσ . Parameters of the regression equations suggest that the P(CH ) BH substituent functions as an electron-withdrawing group and that in simple aromatic systems it is probably a better π acceptor than the isoelectronic Si(CH ) group. Values of C-4 ring carbon chemical shifts in p-XC H Y, where Y = C(CH ) , Si(CH ) , and P(CH ) BH , are consistent with migration of 7r-electron density to the P(CH ) BH group, particularly when X can release electron density by resonance. © 1985, American Chemical Society. All rights reserved. 6 4 3 2 3 I R 3 2 3 3 3 6 4 3 3 3 3 3 2 3 3 2 3 o
