Mono- and Bi-nuclear Complexes of the Doubly Bidentate, Bridging Ligand 4,6-Di(2-pyridyl)pyrimidine.

Abstract

Thirteen mononuclear, homobinuclear and heterobinuclear transition metal complexes of 4,6-di(2- pyridyl)pyrimidine have been prepared. Assignments of the 1H n.m.r. spectra of the molybdenum(0) and ruthenium(II) complexes were achieved by a combination of one- and two-dimensional n.m.r. techniques, especially 1D-TOCSY. For the ruthenium complexes, electronic absorption spectroscopy and cyclic voltammetry were used to probe the nature of the metal{ligand and, for the binuclear complexes, metal-metal interactions. The complexes have low HOMO−LUMO energy gaps. Meta-metal interactions are shown to be of similar magnitude to those in complexes of the better-studied ligands 2,2′-bipyrimidine and 2,3-di(2-pyridyl)pyrazine.

4,5-Di(2-pyridyl)-1,2,3-triazolate: the elusive member of a family of bridging ligands that facilitate strong metal–metal interactions

“…1. 2, 4 Some years ago 5 we reported the corresponding values for the related ligands (3) and ( 4), which exhibited extraordinary amplifications of the metal-metal interactions. Our initial work suggested that the magnitude of these interactions was dependent on the particular stereoisomer (meso or rac) 6 of the dinuclear complex, but this was later shown to be due to specific associative interactions with the counteranions.…”

Stereoselective formation of a meso-diruthenium(ii,ii) complex and tuning the properties of its monoruthenium analogues

“…They also clearly indicate strong σ-donation from the saturated ligand backbone to the metal-based orbitals, thus increasing the energy of the HOMO. This trend is in accordance with the conclusions of Bolink et al 28 At positive potentials, complexes 1-meso-4 show quasi-reversible Ru(II) to Ru(III) oxidations at 0.70-0.90 V vs. SCE which is 350-550 mV less positive compared to Ru(III/II) couple in [Ru(bpy) 3 ] 2+ and [Ru(bpy) 2 (L2)][(PF 6 ) 2 ], 29,30 thus confirming that L1 is a stronger donor than bpy and L2. The butoxyether-substituted pyrimidyl moiety in complex 3 acts as the strongest σ-donor as suggested by the low oxidation potential of 3 as compared to 2 and 4.…”

Metal–metal interactions in dinuclear ruthenium complexes containing bridging 4,5-di(2-pyridyl)imidazolates and related ligands

“…7 Electrochemical studies of dinuclear ruthenium complexes of these ligands revealed remarkably strong metal-metal interactions, greater than those found in the corresponding complexes of (1), despite the greater inter-metal separation, and greater than those previously reported in complexes of 2,3-di(2-pyridyl)pyrazine (5) 8 and 4,6-di(2-pyridyl)pyrimidine (6) 9 despite the obvious similarities in geometry. Furthermore, we observed an intriguing difference between the magnitude of the metal-metal interactions for the two diastereoisomeric (meso and rac) forms of the dinuclear complexes containing the Ru(bpy) 2 terminal moieties (bpy = 2,2'-bipyridine).…”

“…For complexes (9) and (10) we see two 2e -reversible reduction processes that correspond to reduction of two different bpy rings. With dinuclear ruthenium complexes containing π-deficient diazine briding ligands, such as (1), (5) and (6), the first reduction usually involves electron transfer into the bridging ligand.…”