Triazole complexes iridium

The catalyst is also effective for the reduction of styrenes, ketones, and aldehydes. Cyclohexenone 16 was reduced to cyclohexanone 11 by transfer hydrogenation, and using a higher catalyst loading, styrene 17 was reduced to ethylbenzene 18. The elaboration of [Ir(cod)Cl]2 into the triazole-derived iridium carbene complex 19 provided a catalyst, which was used to reduce aUcene 20 by transfer hydrogenation [25]. 

Relatively little has been reported on the electronic spectra of triazole and triazolate complexes. Copper(II) benzotriazolate adducts and benzotriazolate complexes show ligand-field maxima in the range 12.5-15.9 kK, in agreement with the proposed octahedral coordination geometry (172). Electronic spectra have also been reported for rhodium(I) and iridium(I) benzotriazolate complexes (33). 

Just as with nondoped red fluorescent dyes, nondoped phosphorescent iridium complexes consisting of two chelating phenyl-substituted quinazoline and one (2-pyridyl) pyrazolate or triazolate have recently been reported by Chen et al. (278-280) (Scheme 3.88) [308]. All of these complexes exhibited bright red phosphorescence with relatively short excited state lifetimes of 0.4-1.05 ps. PHOLEDs fabricated using the compounds A and B with relatively... 

Following on the triazole mohf a series of new iridium(I) l,2,4-triazole-3-ylidene NHC complexes [lr(cod)(NHC)L]BF4 (56a-c, L=PPh3, pyridine Scheme 4.23) were synthesized and tested and good results found for TH on C=0, C=N and C=C double bonds in 2-propanol with K2CO3 [52]. 

Mesoionic bis-NHCs have also given a number of bridging complexes of rhodium and iridium, such as those depicted in Figure 10.9 [89]. Worth mentioning is the example reported by Bertrand and coworkers m which the 1,2-dihapto ligand is an anionic l,2,3-triazole-4,5-dilylidene that is boimd to two different rhodium fragments (31 and 32) [90]. 

Iridium dimer complexes catalyse the 3 + 2-cycloaddition reactions of organic azides with bromoalkynes to furnish 1,5-disubstituted 4-bromo-1,2,3-triazoles in excellent yields under mild conditions. Ruthenium(II)-azido complexes undergo 3 + 2-cycloaddition reactions with strained cyclooctynes under ambient temperatures. No reaction was observed with non-activated terminal or internal alkynes under the same conditions. Dithioic acid copper catalysts (60) catalyse the 3 + 2-cycloaddition reaction of azides with alkynes to form 1,4-disubstituted-1,2,3-triazoles in various solvents and under various temperatures. Thermal Huisgen 3 + 2-cycloaddition reactions of azides and bis(trimethylsilyl)acetylene formed 4,5-bis(trimethylsilyl)-l/f-l,2,3-triazoles in low to high yields (15-95%). The Cu(I)-catalysed 3 + 2-cycloaddition... 

Pentamethylcyclopentadienylrhodium (or iridium) azido complexes 38 react with ditrifluoromethylacetylene to give the corresponding 1,2,3-triazole rhodium complex 39. Subsequent treatment with NH4CI opened the route to free NH-triazole 40 [44],... 

The water-soluble NHC iridium(i) complex [lr(trz)(CO)2l]OTf 553 (trz= l,2,4-triazol-2-ium-5-ylidene) and a pyridylimidazolylidene species exhibiting a metallacycle structure 554 were also described.The molecular structures of 554 and its precursor containing an agostic Ir- H- C interaction have been reported and the former is presented in Figure 47. 

Messerle and coworkers reported that a cationic iridium(lll) complex with a methyl-bridged bipyrazoyl or pyrazoyl-l,2,3-triazole (N-N) ligand [lr(N-N)Cp Cl] B Ar 4 (B Ar ".j = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) had catalytic activity for the synthesis of tricyclic indoles [161]. The process... 

Scheme 10 Synthesis of the cyclometallated iridium(III) complexes (72a-d, 73a-g, and 74a-b) from phenyl-l,2,3-triazole ligands 71a-d (i) IrCl3 3H20, 2-ethoxyethanol or 2-methoxyethanol/ H2O (3 1), reflux, 14-24 h (ii) for 73a and 73d (a) L-L, CH2Cl2/MeOH, reflux, 14 h (b) NHtPFg for 73b and 73c L-L, EtOH, Na2C03, reflux, 14 h for 73e and 73f (a) L-L, CHClj/MeOH, reflux, 3 h (Hi) (a) 2-ethoxyethanol, dmbpy, 120°C (b) NlLtPFg (iv) dg-DMSO or da-MeCN, RT...

Cationic complex 72, related to Crabtree s catalyst, was one of the first NHC complexes used for TH of ketones, alkenes and nitro compounds in refluxing isopropanol (Figure 13.8). Related neutral complexes 73 were also very active in the reduction of acetophenone in KOH/i-PrOH. Oro and co-workers prepared the cationic Rh and Ir complexes 74 and 75 with O-donor-func-tionalized NHC ligands (Figure 13.8). The iridium complexes were found to be efficient pre-catalysts for the TH of cyclohexanone in KOH/i-PrOH with TOFs < 4600 h. Cationic triazol-5-ylidene complexes 76 were highly active for the TH of C=0 and C=C functions as well as for reductive amination of aldehydes. ... 

---