Stilbazoles metal complexes

Fig. 13. Molecular hyperpolarizabilities of 4 -(2-methylbutyloxy)-4"-stilbazole and some of its metal complexes.

This probably cannot be accounted for on the basis of steric effects, but may have its origin in greater solubility in the case of the stilbazole as opposed to vpy or BPE-containing polymeric metal complex chains, which results in much lower surface coverages. 

Pyridines are known to form a variety of stable metal complexes and so elaborated pyridines are neutral targets for ligands in metallomesogens. Various substituted pyridines have been used in this context and the greatest amount of work has been carried out with the tran5-4-alkoxy-4 -stilbazoles (Figure 78, n-OPhVPy)7 The materials chemistry of these stilbazoles has been reviewed recently. ... 

The EFISHG technique has also been applied to some pyridyl carbonyls of Rh1 or Ir1 by Bruce et al72,13 These complexes (e.g., (9) and (10)) contain stilbazole ligands bearing resolved 2-methylbutyloxy substituents, incorporated with the aim of encouraging noncentrosymmetric crystal packing structures. The observed 1.5- to 3-fold enhancements of (3 of the free stilbazole on complexation are attributable to the er-electron-withdrawing abilities of the metal centers.72,73... 

Metal perturbation of IL photochemistry appears to be less important in [Ru(bipy)2(h- n.s-4-stilbazole)2]2+ and [Ru(bipy)2(cw-4-stilbazole)2]2+. Both complexes undergo wavelength-dependent isomerization of the coordinated stilbazole ligands as the only important photoreaction."4 This wavelength dependence has beep attributed to the presence of two different types of reactive excited states, aRu-t stilbazole CT state which favors formation of the trans isomer and a higher energy IL state localized on stilbazole which decays with nearly equal probability to the two isomers. The latter pathway is qualitatively similar to the isomerization process that obtains upon direct photolysis of the free ligand. Thus coordination to Ru has not altered the characteristic photoreaction mode of the stilbazole molecule. 

Stilbene and azobenzene cause photoisomerization between trans and cis forms, and their structures are simple enough to provide many derivatives thus various combinations with transition metals have been reported. Ru11 complexes with both trans and cis forms of 4-stilbazole (stpy), Ru(bpy)2(fra s-slpy) (43a) and Ru(bpy)2(cz s-stpy) (43b) have been synthesized by Whitten et al., and the trans/cis ratio (Dc/t) of each in the photo-... 

B. Langmuir-Blodgett Films of Metal Stilbazole Complexes Liquid Crystals... 

C. Mesomorphic Stilbazole Complexes of Groups 10 and 11 Metals Hydrogen-Bonded Stilbazole Mesogens... 

Fig. 14. Diagram to show (A) the first excited state of a conjugated donor/acceptor aromatic, (B) inductive charge redistribution caused by isolated donor and acceptor atoms, and (C) a hypothetical charge delocahzation in a group 8 metal stilbazole complex.

The stilbazole complexes of these metals, Pd(II), Pt(II), Ag(I), and Au(I), are considered together because a good deal can be learned by looking at them in this way, particularly as we begin to look at more highly substituted stilbazoles. The liquid-crystal aspects of the silver... 

Photocontrol of chemical and physical functions could be used in this system (Fig. 6.21). Stilbazole, a compound related to natural photoresponsive molecules, was used as the photoresponsive switch [136]. Because stilbazole undergoes isomerization from fhe trans form to fhe cis form on UV irradiation, and fhe reverse in visible hght, via complexation of the pyridine group to fhe metal center of metalloporphyrins, fhe (TPP)Al-OMe-stilbazole system on irradiation wifh UV light serves as an on-switch to speed up the reaction whereas in visible hght fhe system worked as an off-switch to reduce the rate of the once accelerated reaction. 

The ambivalent donor or acceptor role of low-valent metal carbonyl species, such as M(CO)5 [M = chromium, molybdenum, tungsten], in monometallic p-substituted pyridine (or stilbazole) complexes was investigated in detail by Kanis et al. in the early 1990s, and later by Roberto et al. (Figure 1.22). " As already seen before, when the substituent is an... 

Systems Based on Poly(alkoxy)stilbazole Ogands 7.9.10.3.1 Complexes of group 10 metals... 

Ag(I) ions have been used to direct [2-1-2] photodimerizations in solids. Argentophilic forces (i.e., Ag- Ag interactions) were exploited by MacGilhvray and coworkers to assemble and stack a stilbazole (4-stilbz) for reaction Reaction of Ag(I) trifluoroacetate with 4-stilbz produced a disilver complex that organized two pairs of 4-stilbz. The Ag- Ag interaction displayed a metal-metal separation of 3.41 A while the C=C bonds were crisscrossed and separated by 3.82 A (Scheme 6a). The corresponding head-to-head cyclobutane was generated quantitatively in a SCSC reaction. The formation of the photoproduct was ascribed to pedal-like rotation of the C=C bonds in the solid. A similar complex was subsequently used to achieve the first photodimerization of terminal olefins in a solid. Reaction of Ag(l) chlorate with 4-vinylpyridine (4-vp) afforded a disilver complex (Scheme 6b) that generated c/x-l,2-bis(4-pyridyl)cyclobutane stereospecifically and in quantitative yield. 

---