The chelate-to-bridging shift of phosphane dipalladacycles: convenient synthesis of double A-frame tetranuclear complexes

Abstract

Palladacycles of the type [Pd(PhPCHPPh-P,P)(C,N:C,N)] (C,N:C,N = bis(N-2,3,4-trimethoxybenzylidene)-4,4'-sulfonyldianiline or -4,4'-oxydianiline) can undergo a spontaneous slow chelate-to-bridging diphosphane coordination shift in solution. Following this strategy a tailor-made synthetic procedure was devised that culminates in isolation of double A-frame tetranuclear palladium complexes.

Chemistry of Tetradentate [C,N : C,N] Iminophosphorane Palladacycles: Preparation, Reactivity and Theoretical Calculations

“…The tests carried out in order to prepare tetranuclear A‐frame species 7 a – f similar to those reported earlier by us, [10] from the dinuclear complexes 3 a – f ( e. g . 3 f → 7f , see Scheme 3), where unsuccessful.…”

“…In a previous work we described formation of double Aframe complexes which could be accomplished by choosing an appropriate flexible bidentate Schiff base ligand, bis(N-2,3,4trimethoxybenzylidene)-4,4'-sulfonyldianiline, or -4,4'oxydianiline, [10] as opposed to the phenylenediimine-C,N : C,N analogues, where this was not possible, due to the restricted flexibility of the ligand imposed by the rigidness of the central phenylene ring itself, hindering opening of the metallacycle ring needed to provide the extra vacant coordination site on the metal for coordination of the second phosphine ligand. [11] These species are closely related to the field of supramolecular coordination complexes (SCCs), [13] and we found Scheme 2.…”

“…The resulting structure shows imaginary frequencies, but they are coincident with the rotation of the methyl groups attached to the phenyl rings and are not considered to significantly affect the energy values used to calculate the energy of the formation reaction of this compound. To further investigate the thermochemistry involved in the transformation of the chelated species into the less common double A-frame structures, as we observed in previous work, [10] the energy of the reaction was calculated with the data obtained for the chelate structures, the resulting A-frame structure and the chloride ion optimized using a B3LYP/6-31G(d) level of theory ( Figure 2).…”

“…The crystal structure of a previous work [10] was used as a base optimized using a B3LYP/3‐21G level of theory. The frequency study was carried out with the same basis as for the chelated f type compounds ( vide supra ), using an ONIOM model studying the close environment of the cyclometalated moiety at a B3LYP/L2DZ2‐ECP/6‐31G(d) level and the rest of the molecule at 3‐21G.…”

Synthesis of a dinuclear palladacycle with a doubly metallated ligand and its reactivity towards diphosphines

“…In this line of research there have been studies of doubly cyclometallated compounds [10,11]. These compounds can react with polydentate ligands such as phosphinesobtaining interesting polymetallic structures, formed by cyclometallated units joined by bidentate ligands [12]. This work belongs to this line of research, investigating the reactivity of a doubly metallated palladacycle with diphosphines, which can then lead to the synthesis of new complex structures.…”