Exceptionally large “through-space” nuclear spin coupling in a 2,4,6-tri(phosphanyl)–1,3,5-triphosphabenzene

We describe the synthesis of a phosphanyl-functionalized 1,3,5-triphosphabenzene that exhibits remarkably large indirect spin-spin coupling (432 Hz) between phosphorus-31 nuclei. The magnitude of this coupling interaction is indicative of highly effective orbital overlap between two lone-pair type orbitals, each of which possesses significant s-orbital character. This was probed computationally using density functional theory calculations in order to deconvolute individual transmission pathways by dividing these into "through-space" and "through-bond" type interactions. The "through-space" transmission pathway can be chemically disrupted by oxidation of the pendant phosphanyl groups using either elemental sulfur or selenium. By engaging the phosphanyl s-orbitals in bonds to the chalcogen elements, the indirect interaction is perturbed, and the NMR spectra of the resulting compounds exhibit conventional "through-bond" coupling.