Steric Effects in the Self‐Assembly of Palladium Complexes with Chelating Diamine Ligands

Abstract

The influence of the steric properties of chelating diamines on the self‐assembly of [Pd(N∩N)](NO3)2 complexes with 4,4′‐bpy as bridging ligand has been studied by 1H NMR spectroscopy and X‐ray diffraction (N∩N = N,N,N′,N′‐tetramethylethylenediamine, N,N,N′,N′‐tetraethylethylenediamine, 1,3‐diaminopropane, N,N′‐dimethylpiperazine, homopiperazine and ethylenediamine). Based on crystallographic data, the steric bulk of the chelating amines in the [Pd(N∩N)]2+ cations has been characterised in two different ways. A temperature‐ and concentration‐sensitive trimer/tetramer equilibrium was observed by NMR spectroscopy with every diamine, in which the trimeric species dominated when the chelating amine was the bulky tetraethylethylenediamine. Although the formation of tetramers was preferred with diamines of decreasing steric demands, trimeric aggregates could be observed even with the least congested homopiperazine and ethylenediamine complexes. The distribution of the tectons between the two constituents follows the trend predicted by the steric features of the coordinated diamine ligands. Diffusion NMR spectroscopy has proved to be an efficient tool in the identification of self‐assembled species. The trimer/tetramer equilibrium established with tetramethylethylenediamine as chelating ligand has been observed in solution by using wide‐angle X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Platinum and Palladium Polyamine Complexes as Anticancer Agents: The Structural Factor

“…In fact, as a so metal ion Pd(II) yields stable coordination compounds with nitrogen-containing ligands (preferred over oxygen), namely, with polydentate aliphatic amines [93,95,97,[252][253][254][255][256] (Table 2). Particular care should be taken in choosing these chelating ligands, since their chemical characteristics have been shown to in�uence the stability and the selfassembly properties of the corresponding Pd(II) complexes (e.g., formation of oligomeric species) [97,257]. Actually, it has been observed that the square-planar geometry typical of Pd(II) coordination compounds is slightly distorted according to the nature of the ligands.…”

Antisymbiotic Self‐Assembly and Dynamic Behavior of Metallamacrocycles with Allylic Corners

“…[12][13][14][15][16][17][18] Among them, homometallic molecular squares, formed by the reaction of cis-protected square planar complexes with linear symmetric ditopic ligands, have been the most widely studied. [19][20][21][22][23][24][25] The assembly of metallamacrocycles containing different metal corners and/or nonsymmetric ligands using this method presents additional difficulties due to the possible generation of a mixture of isomers that are difficult to separate. To overcome this, they are generally obtained through modular self-assembly methodology.…”

Sterically‐Directed Consecutive and Size‐Selective Self‐Assembly of Palladium Diphosphane Complexes with an Ar‐BIAN Ligand: Unexpected Formation of Pentameric and Hexameric Aggregates

“…Deviations from the sterically predicted behavior were also reported in studies with [M(P^P)] 2+ complexes (M=Pd, Pt; P^P=dppp, dppf, and depe; dppf=bis(diphenylphosphanyl)ferrocene; depe=bis(diethylphosphanyl)ethane) 13. On the contrary, we have shown with a series of sterically characterized [Pd(N^N)] 2+ complexes that the distribution of the tectons between the [Pd(N^N)(4,4′‐bpy)] n 2 n + trimeric and tetrameric products ( n =3, 4) follows a trend concluded from crystallographic data (N^N=chelating diamine) 14…”

“…2n + trimeric and tetrameric products (n = 3, 4) follows a trend concluded from crystallographic data (N^N = chelating diamine). [14] Interested in how these steric effects are manifested, we planned and synthesized new bis(arylimino)acenaphthenes (Ar-BIANs). These compounds have been known for more than four decades, mostly involving their application in homogeneous catalysis, [15] structural and physicochemical studies, [16] and preparation and structural characterization of complexes with main-group elements.…”