Gold -porphyrin complex

With a tridentate ligand Au(terpy)Cl3.H20 has, in fact, AuCl(terpy)2"1" with weakly coordinated chloride and water while Au(terpy)Br(CN)2 has square pyramidal gold(III) the terpyridyl ligand is bidentate, occupying the axial and one basal position [124]. Macrocyclic complexes include the porphyrin complex Au(TPP)Cl (section 4.12.5) cyclam-type macrocyclic ligands have a very high affinity for gold(III) [125],... 

Gold] III) porphyrins have been used as acceptors in porphyrin diads and triads due to their ability to be easily reduced, either chemically or photochemically. A new method for incorporating gold(III) into porphyrins (Figure 1.67a) has been described and consists of the disproportionation of [Au(tht)2]BF4 in its reaction with the porphyrin in mild conditions [321]. The metallation of [16]-hexaphyrin with NaAuCl4 yielded the aromatic gold(III) complexes (Figure 1.67b) and the two-electron reduction of the aromatic complexes provided the antiaromatic species [322]. 

A ring localized hydrogenation can be a consequence of the disproportionation of photochemically formed 7t-anion radicals. Such a process was found [243] to proceed in aqueous solutions containing two gold(III) porphyrins Au(Por)Cl, where Por = TMPyP or TPyP, and electron donors (EDTA or TEA), jt-radicals abstract protons from HaO+ ions (pH < 4) and give the parent porphyrin complexes Au(Por)Cl and reduced phlorins Au(H2Por)Cl. 

Upon excitation of the metal complex centre, triplet energy transfer to the donor appended porphyrin rapidly quenches the excited state of the central ruthenium bis-terpyridyl unit, whereas excitation of the gold porphyrin, leads in less than 1 ps to the triplet-excited state [23], which is unreactive to-... 

The first experiments in this direction were carried out on the triads 244+ and 254+ (Fig. 8), by exciting preferentially the metal centre around 340-355 nm. Excitation at this wavelength region produces to a predominant extent the excited state localized on the iridium complex unit, the ligand centered triplets PH2 - 3Ir - PAu or PZn - 3Ir - PAu [48]. Energy transfer to the porphyrin triplets dominates the deactivation of PH2 - 3Ir - PAu in 244+, with rate constants of 2.9 x 1010 s 1 for the transfer to the gold porphyrin localized excited state and ca. 1011 s 1 to the free base porphyrin localized excited state, respectively (Scheme 9). 

Kinetic studies have demonstrated that photo-induced electron transfer between the zinc and the gold porphyrin occurs at a rate of (1.7 ps)-1 in Cu(I)-complexed [2]-rotaxane 102, which is much higher than in the case of the free rotaxane 107 (36 ps)-1.73 The higher photoinduced electron transfer rate in the Cu(I) complex 102 than in the demetallated system 107 was explained also in terms of a superexchange mechanism. 

Figure 10. A self-assembled monolayer comprised of terminal porphyrins, intermediate ferrocences, and surface thiols attached on gold surface. The sold line is the photoaction spectrum, the dashed line is the absorption spectrum. Panels a) and b) show the proposed mechanisms, and c) provides the structure of the thiol ferrocene-porphyrin complex.

In compound 2", the porphyrin incorporates a trivalent gold which was selected for two reasons (i) it forms very stable porphyrin complexes and will thus not be lost during the synthesis of the second porphyrin nucleus [13] and (ii) because of its strong electropositive character, it confers to the aromatic porphyrin ring to which it is complexed a remarkable electron-accepting abihty with a resulting very accessible reduction potential [41-44[. The reactions leading to the transition metal-complexed [2]- and [3[rotax-anes 8 and respectively, are indicated in Fig. 5 [45[. 

The precursor C to the rotaxane E, called prerotaxane, is obtained in one step from a gold porphyrin macrocycle A and a difunctionalized thread B, thanks to the gathering properties of the transition metal (black dot). Construction of the porphyrin blocking groups is the kineticaUy templated key step leading to the metal-complexed rotaxane structure D. The desired rotaxane E is obtained after removd of the metal template from D. 

---