Stoichiometry controlled self-assembly of tri- and octa-nuclear palladium–yttrium complexes

Abstract

Palladium complexes with template-centred, bidentate bis-phosphine donors were prepared in a one-step process via base-assisted condensation of a ditopic catechol phosphine 1 (LH 2 ) with simple yttrium and palladium salts. It was found that the assembly of either one or two Pd-bisphosphine units on one template was possible in a controlled way by adjusting the stoichiometric ratio of the reactants. Thus, reaction of YCl 3 , (cod)PdCl 2 , and 1 in a 1 : 4 : 2 molar ratio produced a complex of composition [Y(H 2 L 2 Pd)(L 2 Pd)(dmf)]Cl whereas reaction of the same reactants in 1 : 2 : 1 molar ratio gave a polynuclear assembly [O(YL 2 Pd) 4 (dmf) 4 H]Cl 3 . Both products were characterised by single-crystal X-ray diffraction studies and spectroscopic data (NMR, ESI-MS) which indicated that the assemblies found in the crystalline state persist also in solution.Scheme 1

Heterobimetallic catechol-phosphine complexes with palladium and a group-13 element: structural flexibility and dynamics

“…Complexes [GaCl(L)(catphos) 2 Pd] built around a larger Ga(III) centre that is either pentacoordinate (L = -) or accommodates a secondary ligand (L = DMF) seem to provide a perfect match, which is reflected in both high formation tendency and increased stability in solution. The still larger In(III) cation supports formation of a complex [InCl-(catphos) 2 Pd], which dimerises in the solid state under formation of intermolecular In-O bonds but rearranges in solution to give rise to a trinuclear assembly of composition [In{(catphos) 2 Pd} 2 ]H. The superior stability of this species is underlined by its formation as main product in the reaction of equimolar amounts of In(acac) 3 and [Pd(catphosH) 2 ], and confirms the hypothesis 5,6 that the tendency of large metal cations to adopt higher coordination numbers provides a strong driving force for formation of the M{(catphos) 2 Pd} 2 binding motif. NMR studies allowed to follow the dynamic averaging of the four different catechol phosphine environments in the trinuclear framework, and to propose a mechanism for this process which involves a sequence of discernible proton transfer and ligand rearrangement steps, and may serve as a model for the explanation of analogous dynamics in related complexes.…”

“…However, the mechanistic explanation remains valid even if the metal centre extends its coordination by binding of one or both of the "free" catecholate oxygen donors, and may thus serve as a general model which can also explain the rapid dynamic averaging of ligand environments in other protonated catechol phosphine complexes. 6 The finding that even extended storage of solutions of 8 does not result in perceptible disintegration attests this complex a higher stability compared to binuclear 7 (which is also fully in accord with the observed formation of 8 during degradation of 7). This trend is in contrast to the case of the gallium complexes 3a,b, which give no evidence for the formation of an analogous trinuclear assembly, and highlights once more the importance of template size as a critical factor for the stabilisation of multimetallic aggregates with bridging catechol phosphines.…”

“…The terminal oxygen atoms of catecholate ligands in A and B still exhibit some basicity which allows them to act as hydrogen bond acceptors 4 or undergo protonation. 6 Interestingly, it was found that the bite angle of the multidentate array varies with the size and preferred coordination geometry of the template, and the choice of suitable templates from different groups of the periodic table allowed thus to construct e.g. trans-chelating bisphosphine moieties with bite angles close to 180°7 and cis-chelating bisphosphine units with bite angles between 102°to 97°5 from the same catechol phosphine building block.…”

“…The P 2 O 2 donor set around the Pd atom in type A complexes shows hemilabile behaviour, and some complexes were found to exhibit catalytic activity in CC cross-coupling reactions. 5 The synthesis of the oligonuclear complexes A, B can be either accomplished in a single step by spontaneous condensation of ligand 2 with two simple metal salts, 5,6 or stepwise by introducing the metal atoms one after the other (Scheme 2). 4,7 In the sequential reactions, the first metal atom interacts with one coordination site of two catechol phosphines to produce complexes of types C or D, respectively, which then act as bi-or multidentate donors towards a second metal atom.…”

Ruthenium Catechol Phosphane Complexes as Metalloligands for the Controlled Assembly of Heterobimetallics

“…A specific illustration of this concept is given by catechol phosphanes such as 1 or 2 (Scheme ), which were used as platforms to construct dinuclear or extended supramolecular architectures,, , respectively, or enabled the generation of metalloligands such as 3 enabling the construction of defined heterometallic complexes such as 4 or 5 …”