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Redox‐Active p ‐Quinone‐Based Bis(pyrazol‐1‐yl)methane Ligands: Synthesis and Coordination Behaviour
Author(s) -
Scheuermann Sebastian,
Kretz Tonia,
Vitze Hannes,
Bats Jan W.,
Bolte Michael,
Lerner HansWolfram,
Wagner Matthias
Publication year - 2008
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.200701615
Subject(s) - chemistry , ligand (biochemistry) , stereochemistry , redox , substituent , medicinal chemistry , quinone , benzoquinone , octahedron , hydroquinone , deprotonation , crystal structure , crystallography , ion , inorganic chemistry , biochemistry , receptor , organic chemistry
The synthesis, structural characterisation and coordination behaviour of mono‐ and ditopic p ‐hydroquinone‐based bis(pyrazol‐1‐yl)methane ligands is described (i.e., 2‐(pz 2 CH)C 6 H 3 (OH) 2 ( 2 a ), 2‐(pz 2 CH)‐6‐( t Bu)C 6 H 2 (OH) 2 ( 2 b ), 2‐(pz 2 CH)‐6‐( t Bu)C 6 H 2 (OSi i Pr 3 )(OH) ( 2 c ), 2,5‐(pz 2 CH) 2 C 6 H 2 (OH) 2 ( 4 )). Ligands 2 a , 2 b and 4 can be oxidised to their p ‐benzoquinone state on a preparative scale ( 2 a ox , 2 b ox , 4 ox ). An octahedral Ni II complex [ trans ‐Ni( 2 c ) 2 ] and square‐planar Pd II complexes [Pd 2 b Cl 2 ] and [Pd 2 b ox Cl 2 ] have been prepared. In the two Pd II species, the ligands are coordinated only through their pyrazolyl rings. The fact that [Pd 2 b Cl 2 ] and [Pd 2 b ox Cl 2 ] are isolable compounds proves that redox transitions involving the p ‐quinone substituent are fully reversible. In [Pd 2 b ox Cl 2 ], the methine proton is highly acidic and can be abstracted with bases as weak as NEt 3 . The resulting anion dimerises to give a dinuclear macrocyclic Pd II complex, which has been structurally characterised. The methylated ligand 2‐(pz 2 CMe)C 6 H 3 O 2 ( 11 ox ) and its Pd II complex [Pd 11 ox Cl 2 ] are base‐stable. A new class of redox‐active ligands is now available with the potential for applications both in catalysis and in materials science.