A study of through-space and through-bond J_PP coupling in a rigid nonsymmetrical bis(phosphine) and its metal complexes

A series of representative late d-block metal complexes bearing a rigid bis(phosphine) ligand, iPr₂P-Ace- PPh₂ (L, Ace = acenaphthene-5,6-diyl), was prepared and fully characterised by various techniques, including multinuclear NMR and single crystal X-ray diffraction. The heteroleptic nature of the peri- substituted ligand L allows for the direct observation of the J_PP couplings in the ³¹P{¹H} NMR spectra. Magnitudes of J_PP are correlated with the identity and geometry of the metal, and the distortions of the ligand L. The forced overlap of the phosphine lone pairs due to the constraints imposed by the rigid acenaphthene skeleton in L results in large ⁴J_PP of 180 Hz. Sequestration of the lone pairs, either via oxidation of the phosphine, or metal chelation, results in distinct changes in the magnitude of J_PP. For tetrahedral d¹⁰ complexes ([LMCl2], M = Zn, Cd, Hg), the JPP is comparable or larger (193–309 Hz) to that in free ligand L, although the P···P separation in these complexes is increased by ca. 0.4 Å (compare to free ligand L). The magnitude of J_PP diminishes to 26–117 Hz in square planar d⁸ complexes ([LMX2], M = Ni, Pd, Pt, X = Cl, Br) and octahedral Mo⁰ complex [LMo(CO)4], 33 Hz). Coupling Deformation Density calculations indicate the through-space interaction dominates in free L, whilst in metal complexes the main coupling pathway is via the metal atom.