Space‐Separated 1,10‐Phenanthroline, 4,5‐Diazafluorene, or 3,6‐Di(2‐pyridyl)pyridazine Units as Ligands in Diruthenium Complexes: Preliminary Studies of Metal–Metal Interactions

Abstract

There has been much activity in the field of intramolecular energy transfer and electron transfer in large molecular assemblies, and the next advances will clearly require sophisticated molecular design. Where metal complexes are involved as the light-harvesting chromophore['] the design and construction of ligands becomes an important component. Studies on intramolecular electron transfer have been reported in which metal complexes have been tethered to redox-active chromophores, but almost all of these systems contain flexible linkages.[21 Elegant syntheses have been reported recently for fully conjugated diad systems incorporating the 1 ,lo-phenanthroline moiety as the bidentate ligandJ3] and we have described the first molecular rack (molrac) in which two units of the same ligand are spatially separated.[41 We report here on the preparation of a new set of rigid bis(bidentate ligand) structures in which the individual bidentate ligands (1 ,lO-phenanthroline, 4,Sdiazafluorene, or 3,6-di(2-pyridyl)pyridazine) are fused to an alicyclic framework.The versatile spacers in molracs permit the development of bridging ligands in which the ligating groups are placed at a set distance and relative orientation in space. These compounds should allow assessment of the factors controlling intramolecular energy-and electron-transfer processes in polymetallic species, as well as lead to new reagents for the study of self-assembly processes.f51 Rigid alicyclic frameworks have been used in molrac systems since they have proven their worth in diad and triad systems devoid of metal centersf6' and are available in an increasing range of shapes and sizes.[4. '-lo] The typical olefinic spacers in the molracs have norbornene or cyclobutene diester end groups (or mixtures thereof), and these offer different dienophilic character. When the cycloaddition reagents 3, 2, and 1 (Scheme 1) are used to deliver the specific [' I Prof.

Photolysis of Fused Cyclobutatriazolines: An Adventitious Route to 3,6-Di(2-pyridyl)pyridazonorbornadiene

“…Breakdown of these intermediates has different outcomes in the two processes, which depend on which cyclopropyl σ-bond is broken: route a leads to the rearranged product (21), while route b returns the starting material of the di-π-methane reaction. However, in the fragmentation process, the two pathways yield different products: route a gives the rearrangement product (21), whereas route b gives the unrearranged isomer (2).…”

“…6 Also, the diazafluorene reagent (7) is available in two steps by the 1,3-dipolar addition of diazodiazafluorene (6) to norbornadiene (1), followed by photochemical ejection of dinitrogen (Scheme 1). 7 In this paper, we report the synthesis of the 3,6-dipyridyl-norbornadienepyridazine (2) in an unexpected fashion after more direct routes from norbornadiene (1) had been unsuccessful.…”

“…1,2 One strategy has been to proceed via norbornene reagents incorporating N,N-bidentate ligands, e.g. (2), since there has been much improvement in the methods for coupling norbornenes to form scaffold structures developed in our laboratory over the last few years.…”

“…1,2 One strategy has been to proceed via norbornene reagents incorporating N,N-bidentate ligands, e.g. (2), since there has been much improvement in the methods for coupling norbornenes to form scaffold structures developed in our laboratory over the last few years. [3][4][5] We have already shown that the norbornene reagent (5) containing the o-phenanthroline ligand can be prepared by the Diels-Alder addition of the cyclopentadienone (4) to norbornadiene (1).…”

Synthesis, electrochemistry and photophysics of rigid norbornylogous-bridged complexes of ruthenium and osmium

“…1,2 The synthesis of suitably rigid saturated hydrocarbon bridges possessing a range of well defined lengths has proved to be a significant challenge. Several conformationally rigid ligands incorporating 1,10-phenanthroline, 34, 35 4,5-diazafluorene, 29,36, 37 and annulated pyridazine 32,33, 36 units have been reported capable of co-ordinating luminescent transition metal polypyridine centres. Whilst some of the corresponding metallated species have been structurally characterised, only limited photophysical data have been reported.…”