Ferrocenyl phosphine mobility, positional isomerism and NMR fluxionality in triangular palladium sulfide aggregates. Crystal and molecular structures of [Pd3Cl2(η2-dppf)(µ-dppf)(µ3-S)2] and [Pd3Cl(η2-dppf)2(PPh3)(µ3-S)2]X [X = Cl or NO3, dppf = Fe(η5-C5H4PPh2)2]

Abstract

Three {Pd₃S₂} aggregates, [Pd₃Cl₂(η²-dppf)(µ-dppf)(µ₃-S)₂] and [Pd₃Cl(η²-dppf)₂(PPh₃)(µ₃-S)₂]X [X = Cl or NO₃, dppf = 1,1′-bis(diphenylphosphino)ferrocene] have been synthesized from metal addition to a {Pd₂S₂} molecular core in [Pd₂(dppf)₂(µ-S)₂]. X-Ray single-crystal crystallographic analysis revealed a common sulfide-bicapped triangle with insignificant Pd· · ·Pd interactions. The former is neutral with a bridging and a chelating dppf ligand as well as two terminal chlorides. The dynamic behaviour has been studied by variable temperature ³¹P and 2-D COSY NMR. A phosphine–chloride interchange and phosphine–phosphine exchanges enable the two dppf ligands to migrate around the Pd₃ plane. The solid-state structure corresponds to the static structure in solution at 198 K. The mixed phosphine complex 5a (X = Cl) is ionic with two Pd–dppf chelating rings and a {Pd(PPh₃)Cl} moiety. With a PPh₃ group taking up one site, it is stereochemically rigid. The other two complexes were studied by electrospray mass spectrometry (ESMS) in solution. The {Pd₃S₂} core in the mixed phosphine (X = NO₃) is relatively stable to fragmentation under ESMS conditions.