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Sterically‐Directed Consecutive and Size‐Selective Self‐Assembly of Palladium Diphosphane Complexes with an Ar‐BIAN Ligand: Unexpected Formation of Pentameric and Hexameric Aggregates
Author(s) -
HollóSitkei Eszter,
Szalontai Gábor,
Lois Isabella,
Gömöry Ágnes,
Pollreisz Ferenc,
Párkányi László,
Jude Hershel,
Besenyei Gábor
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200901126
Subject(s) - steric effects , chemistry , palladium , ligand (biochemistry) , medicinal chemistry , stereochemistry , trifluoromethanesulfonate , ferrocene , chelation , nuclear magnetic resonance spectroscopy , crystallography , organic chemistry , catalysis , electrochemistry , biochemistry , receptor , electrode
The coordination properties of N , N ′‐bis[4‐(4‐pyridyl)phenyl]acenaphthenequinonediimine (L 1 ) and N , N ′‐bis[4‐(2‐pyridyl)phenyl]acenaphthenequinonediimine (L 2 ) were investigated in self‐assembly with palladium diphosphane complexes [Pd(P^P)(H 2 O) 2 ](OTf) 2 (OTf=triflate) by using various analytical techniques, including multinuclear ( 1 H, 15 N, and 31 P) NMR spectroscopy and mass spectrometry (P^P=dppp, dppf, dppe; dppp=bis(diphenylphosphanyl)propane, dppf= bis(diphenylphosphanyl)ferrocene, and dppe=bis(diphenylphosphanyl)ethane). Beside the expected trimeric and tetrameric species, the interaction of an equimolar mixture of [Pd(dppp)] 2+ ions and L 1 also generates pentameric aggregates. Due to the E / Z isomerism of L 1 , a dimeric product was also observed. In all of these species, which correspond to the general formula [Pd(dppp)L 1 ] n (OTf) 2 n ( n =2–5), the L 1 ligand is coordinated to the Pd center only through the terminal pyridyl groups. Introduction of a second equivalent of the [Pd(dppp)] 2+ tecton results in coordination to the internal, sterically more encumbered chelating site and induces enhancement of the higher nuclearity components. The presence of higher‐order aggregates ( n =5, 6), which were unexpected for the interaction of cis ‐protected palladium corners with linear ditopic bridging ligands, has been demonstrated both by mass‐spectrometric and DOSY NMR spectroscopic analysis. The sequential coordination of the [Pd(dppp)] 2+ ion is attributed to the dissimilar steric properties of the two coordination sites. In the self‐assembled species formed in a 1:1:1 mixture of [Pd(dppp)] 2+ /[Pd(dppe)] 2+ /L 1 , the sterically more demanding [Pd(dppp)] 2+ tectons are attached selectively to the pyridyl groups, whereas the more hindered imino nitrogen atoms coordinate the less bulky dppe complexes, thus resulting in a sterically directed, size‐selective sorting of the metal tectons. The propensity of the new ligands to incorporate hydrogen‐bonded solvent molecules at the chelating site was confirmed by X‐ray diffraction studies.

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