Determination of the relative signs of 2J(31P–31P) in complexes of tungsten(0) and molybdenum(0) using two-dimensional [31P–31P]-COSY-45 nuclear magnetic resonance chemical shift correlation

Abstract

Two-dimensional [³¹P–³¹P]-COSY-45 n.m.r. spectroscopy has been used to determine the magnitudes and relative signs of J(³¹P–³¹P) in three- and four-spin systems. The complexes studied are of molybdenum(0) and tungsten(0) with CO and Ph₂PC(CH₂)PPh₂(vdpp), Ph₂PCH₂PPh₂(dppm), Ph₂PCH(CH₂CH₃)PPh₂(1,1-dppp), PEt₃, or PPhEt₂ as ligands. It is found that ²J(³¹P–³¹P)(cis) when the P atoms are coupled via both P–M–P and P–C–P linkages and ²J(³¹P–³¹P)(trans) are of the same sign, presumably positive, and both are of opposite sign to J(³¹P–³¹P)(cis) when the P atoms are linked via the P–M–P pathway only. This suggests a dominant positive contribution to cisoid ³¹P–³¹P coupling via the P–C–P pathway.