“Through-space” P spin-spin couplings in ferrocenyl tetraphosphine coordination complexes: Improvement in the determination of the distance dependence of JPP constants

From the analysis of several nickel and palladium halide complexes of a constrained ferrocenyl tetraphosphine, the existence in solution phase of unique ³¹P-³¹P “through-space” nuclear spin-spin coupling constants (J_PP) had been previously evidenced. Due to the blocked conformation of the species in solution, and based on the NMR spectra obtained for the complexes and their corresponding solid state X-ray structures, these J_PP constants had been shown to clearly depend on the mutual spatial position of the corresponding phosphorus atoms. Herein, the quantitative correlation disclosed at that time (P?P distance dependence of coupling constants) is remarkably confirmed, and mathematically refined owing to the study of a new palladium dibromide tetraphosphine complex, for which the synthesis and the solution NMR and solid state X-ray characterizations are reported.