Azobenzene metal complexes

Azobenzene, 2-hydroxy-5-methyl-2 -carboxymethyleneoxy-metal complexes... 

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

Metal complex dyestuffs derived from tetradentate azo compounds (147) have very limited commercial significance but merit brief discussion on chemical grounds. The first dyestuffs of this type to be used commercially contained the o-hydroxy-o -carboxymethyleneoxydiarylazo system, e.g. (148). These were dyed on cotton and aftertreated with a copper salt to produce the copper complex dyestuff which was reported71 to be a triannelated species (149). Formation of complexes of this type has been confirmed105 in the case of 2-hydroxy-5-methyl-2 -carboxymethyleneoxy-azobenzene, which yields the complex (150) on treatment with copper acetate under mild conditions. Under more severe conditions, however, the complex (151) is produced. Loss of the carboxymethyl group from dyes of this type has also been shown105 to occur under dyebath conditions. This may be compared with the demethylation of o-methoxy-o -hydroxydiarylazo compounds (Section 58,2.3. l(iii)(a)) under similar conditions. 

The relative instability of free diazenes (215) often precludes the direct reaction of these species with transition metal complexes. However azobenzene reacts with Ni° (264) species to yield materials such as [Ni(tBuNC)2(PhN2Ph)] (140, 265). Similarly, ditolyldiazene reacts with [Ni(cyclooctadiene)2] in the presence of tritolylphosphine to give [Ni(N2Ar2)(PAr3)2] (Ar = p-CH3C6H4) (200). 

Azoferrocene, 77, is a jr-conjugated ferrocene dimer and one of the simplest analogues of azobenzene, having two redox-active metal complex units. 

Back in 1899, Werner and Stiasny (49) had studied the action of nitric acid on azobenzene and produced a series of nitro-azobenzenes and nitro-azoxybenzenes, but Werner carried the work no further. Werner then became interested in the analogy between the lakes of mordant dyes and the metallic derivatives of /3-diketones and proposed the view that mordant dyes were internal metallic complexes. This resulted in three papers published in the 1908-09 period. The first (43) reporting the complex metal salts formed from oximes, diketones, and several metals, came to the conclusion that the formation of mordant dyes depends on the formation of complex metal salts. He found that dyes capable of combining with mordants possessed both a salt-forming complex and a group capable of forming a coordinate link with a metal ion. 

Support for the existence of N —Np isomerism in 2 1 metal complexes of o,o -dihydroxydiaryl-azobenzenes has been provided by the application of proton magnetic resonance to the investigation of diamagnetic 2 1 cobalt(III) complexes. A systematic study was carried out of the chemical shifts of the methyl group proton signals in two series of related azomethines on conversion to their 2 1 cobalt(III) complexes. Cobalt complex formation by the first series (98—100) can be regarded as akin to coordination (101-103) in the analogous azo series whilst cobalt complex formation by the second series (104—106) corresponds to Np coordination (107-109) in... 

Azobenzene, 2-hydroxy-5-methyl-2 -carboxymethyleneoxy-metal complexes dyes, 75 Azo compounds o-amino-o -hydroxydiaryl transition metal complexes, 57 o,o -diaminodiaryl cobalt complexes, 58,60 o, o -dihydroxy diaryl copper complexes, 55,57 p/Ca,47... 

Dinuclear ort/zo-metallated complexes consist of two ligands joined through a central bridge (Fig. 1). They have been widely studied, and several types of mesogenic, metal complexes derived from azobenzene, benzylideneaniline, benzalazine (imine) and phenylpyrimidine derivatives, with a wide variety of intermetallic bridges, such halogens, thiocyanates, carboxylates, have been reported [8, 9]. 

In this paper we describe two newly developed conductive LB films an LB film with metallic conductivity using transition metal complexes [23], and a photochemical switching LB film using a TCNQ radical salt, containing an azobenzene unit in the hydrophobic part of the amphiphilic molecule [13]. 

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