| Summary: | Nine new bidentate chelating heterocyclic ligands, namely 4,4'-bis-t-butyl-2,2'bipyrimidine (41), 2,2'-bi-(5S,8R)-5,6,7 ,8-tetrahydro-8,9,9-trimethy 1-5,8-methanoquinazoline (42), 2,4-bis-(1-pyrazolyl)pyrimidine (53), 1-methyl-2-(2 pyridinyl)perimidine (94), 2-(2- pyrimidinyl)perimidine (95), 2,6-bis-[6-(2-pyridinyl)-4-pyrimidinyl]pyridine (110), 2,6-bis-(1-pyrazolyl)-1,5-naphthyridine (132), 2,2'-bis-(1-pyrazolyl)-4,4'-bipyridine (144) and 2,2'-bis-(3,5- dimethyl-l-pyrazolyl)-4,4'-bipyridine (145), have been prepared and characterised by NMR spectroscopy and mass spectrometry and, in some cases, by elemental analyses. X-Ray crystal structures have been determined for the two 4,4'-bipyridine derivatives, 144 and 145. A new synthesis for the known ligand 4,4'-dimethyl-2,2'-bipyrimidine (40) is also reported.
The coordination chemistry of the above ligands, the known bridging ligand 2,2':4',4":2",2'''-quaterpyridine (25) and two known compounds, 2-(2 pyridinyl)perimidine (93) and 4,6-bis-(2-pyridinyl)pyrimidine (109), has been investigated. Complexes with the metals copper(I), palladium(II) and molybdenum(0) are described for some of the ligands, including an X-ray crystal structure for the palladium(II) complex of 94. The majority of the complexes described are of ruthenium(II). These include monoruthenium complexes {RuBL(L)₂²⁺ with
BL=bidentate chelating ligand and L=4,4'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb)}, biruthenium complexes {(L)₂Ru(μ-BL)Ru(L')₂⁴⁺ with μ-BL=doubly bidentate bridging ligand and L=bpy or dmb and L'=bpy or dmb} and tetraruthenium complexes {Ru[(μ-BL)Ru(bpy)₂]₃⁸⁺}. ¹ H NMR spectroscopy, electronic absorption spectroscopy and cyclic voltammetry have been used to study the nature of the metal-ligand and metal-metal interactions in these complexes. With the seven different bridging ligands (40,109, 110, 25,144, 145 and 132), the metal-metal distance in the biruthellium complexes has been varied systematically, in the order shown, resulting in a general trend of increasing metal-metal distance and decreasing metal-metal interaction.
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