A Study of Through-Space and Through-Bond <i>J</i>_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, <i>i</i>Pr₂P-Ace-PPh₂ (<b>L</b>, Ace = acenaphthene-5,6-diyl), was prepared and fully characterized by various techniques, including multinuclear NMR and single-crystal X-ray diffraction. The heteroleptic nature of the <i>peri</i>-substituted ligand <b>L</b> allows for the direct observation of the <i>J</i>_PP couplings in the ³¹P­{¹H} NMR spectra. Magnitudes of <i>J</i>_PP are correlated with the identity and geometry of the metal and the distortions of the ligand <b>L</b>. The forced overlap of the phosphine lone pairs due to the constraints imposed by the rigid acenaphthene skeleton in <b>L</b> results in a large ⁴<i>J</i>_PP of 180 Hz. Sequestration of the lone pairs, either via oxidation of the phosphine or via metal chelation, results in distinct changes in the magnitude of <i>J</i>_PP. For tetrahedral <i>d</i>¹⁰ complexes (<b>[LMCl</b>_<b>2</b><b>]</b>, M = Zn, Cd, Hg), the <i>J</i>_PP is comparable to or larger than (193–309 Hz) that in free ligand <b>L</b>, although the P···P separation in these complexes is increased by ca. 0.4 Å (compare to free ligand <b>L</b>). The magnitude of <i>J</i>_PP diminishes to 26–117 Hz in square planar <i>d</i>⁸ complexes (<b>[LMX</b>_<b>2</b><b>]</b>, M = Ni, Pd, Pt; X = Cl, Br) and the octahedral Mo⁰ complex (<b>[LMo­(CO)</b>_<b>4</b><b>]</b>, 33 Hz). Coupling deformation density calculations indicate the through-space interaction dominates in free <b>L</b>, while in metal complexes the main coupling pathway is via the metal atom