OBSERVATION OF P-31-P-31 INDIRECT SPIN-SPIN COUPLING IN COPPER-BIS(PHOSPHINE) COMPLEXES BY 2-DIMENSIONAL SOLID-STATE NMR

The first observations of P-31-P-31 indirect spin-spin (J) coupling in copper(I) phosphine complexes are reported for solid Cu(PPh(3))(2)X ( X = NO3-, BH4-). Values of (2)J(P-31,P-31), 157 +/- 5 and 140 +/- 5 Hz for Cu(PPh(3))(2)NO3 and Cu(PPh(3))(2)BH4, respectively, have been ob tained from two-dimensional (2D) J-resolved P-31 NMR spectra obtained under slow magic-angle spinning (MAS) conditions. In both complexes, t he two phosphine ligands are crystallographically equivalent; thus, th e two P-31 nuclei have identical isotropic chemical shifts. Under rapi d sample spinning conditions, the P-31 MAS NMR spectra exhibit relativ ely sharp overlapping asymmetric quartets arising from (1)J(Cu-63/65,P -31) and residual Cu-63/65-P-31 dipolar interactions. No evidence of ( 2)J(P-31,P-31) is apparent from the spectra obtained with rapid MAS; h owever, under slow MAS conditions there is evidence of homonuclear J-r ecoupling. Peak broadening due to heteronuclear dipolar interactions p recludes measurement of (2)J(P-3l,P-31) from standard 1D P-31 MAS NMR spectra. It is shown that this source of broadening can be effectively eliminated by employing the 2D J-resolved experiment. For the two cop per(I) phosphine complexes investigated in this study, the peak widths in the f(1) dimension of the 2D J-resolved P-31 MAS NMR spectra are a bout three times narrower than those found in the corresponding ID P-3 1 MAS NMR spectra.