Complexes bifunctional

Fig. 12. (a) General structure of the half-sandwich, piano-stool ruthenium—arene complexes (b) X and Y are commonly occupied by a bidentate ligand L giving a monofunctional complex (c) tethering of a monodentate ligand to the arene results in a bifunctional complex. 

The tethered bifunctional complexes [Rulr rr -CsHsCH (CH2)nNH2)Cl2] (n — 1,2) (13a,b) readily bound to CT DNA but failed to produce stop sites on the pSP73KB plasmid DNA for RNA synthesis and very low amounts of cross-linking were observed, indicating the formation mainly of monofunctional adducts on DNA. This, together with a small observed unwinding angle, may explain why these complexes exhibit low cytotoxicities (64). 

Several other bifunctional complexes containing different metals such as Ru, Rh, and Ir have been proposed to operate through the outer-sphere route (44—49). In some cases, this mechanism allowed to explain the observed enantioselectivity without substrate coordination (48,49-52). 

An amino alcohol-based iridium bifunctional complex 1058 is an efficient catalyst for the formation of dihydrocou-marin from the 1,5-diol 1059 (Equation 412) <20020L2361>. 

Recently, bifunctional complexes such as [(r 5-C5Me5)Ir(dppz)(jr-peptide-KS KN) Pt(H20)2(NH3) )]4+ (30) have been designed, which show both intercalative (Ir-dppz) and covalent (Pt) DNA-binding properties [70], The cytotoxicity and cellular uptake of some of these interesting complexes have also been studied [71]. 

New hgands that show improved biological kinetic stability are needed to form stable Cu(ll) bifunctional complexes. For this purpose, a series of ligands that sequester radiocopper have been developed. l-N-(4-aminobenzyl)-3,6,10,13,16,19-hexaazabicyclo(6.6.6)eicosane-l,8-diamine (SarAr, Fig-... 

Kimura et al. have prepared bifunctional complexes [Ru(bpy)2(bpy-cyclam-Ni)] " and [Ru(phen)2(phen-cyclam-Ni)], in which the reac-... 

The enzymes are functionally similar to their mammalian counterparts. The dihydro-orotate oxidase, unlike that of the kinetoplastids, is associated with the parasite mitochondrion (99). However, the last two enzymes, the cytoplasmic orotate PRTase and OMP decarboxylase, are separate enzymes instead of being arranged in a bifunctional complex as is found in mammalian cells (99,100). Metabolic studies indicate that CTP synthetase must be present. 

Ligand-metal bifunctional catalysis provides an efficient method for the hydrogenation of various unsaturated organic compounds. Shvo-type [83-85] Ru-H/OH and Noyori-type [3-7] Ru-H/NH catalysts have demonstrated bifimctionality with excellent chemo- and enantioselectivities in transfer hydrogenations and hydrogenations of alkenes, aldehydes, ketones, and imines. Based on the isoelectronic analogy of H-Ru-CO and H-Re-NO units, it was anticipated that rhenium nitrosyl-based bifunctional complexes could exhibit catalytic activities comparable to the ruthenium carbonyl ones (Scheme 29) [86]. 

The bifunctional complexes 29 and 30 demonstrated low activities in transfer hydrogenations of acetophenone and cyclohexanone (Scheme 32). For instance, the reaction of acetophenone in 2-propanol catalyzed by 0.45 mol% of complex 29 afforded within 1 h a 50% conversion corresponding to a TON value of 109. A maximum conversion of 66% was eventually achieved reaching the equilibrium state between acetophenone and 1-phenylethanol. The transfer hydrogenation of cyclohexanone catalyzed by 0.33 mol% of complex 30 afforded within 65 min a conversion of 54% corresponding to a TON of 162. The low TON values were attributed to the decomposition of the catalyst due to the instability of 30 in 2-propanol. 

Taking into account both the coordinative unsaturation of 35 and 36, and the Lewis basicity of the nitrosyl oxygen atoms, the 16e cationic firagment [Re (N0)2(PR3)2] can be considered as a bifunctional complex possessing the free acidic site provided by the metal and the basic site provided by the Onq atom. This was anticipated to provoke bipolar or bifunctional reactivity in small molecule activation. Indeed, 35 and 36 demonstrated facile reactions activating H-X (X = H, Si) bonds [32]. 

Gambarotta, S., F. Arena, C. Floriani, and P. Zanazzi (1982). Carbon dioxide fixation. Bifunctional complexes containing acidic and basic sites working as reversible carriers. /. Am. Chem. Soc. 104(19), 5082-5092. 

At the molecular level, two consecutive steps of the pathway dehydroquinate hydrolyase (DHQase)and shikimate NADP oxidoreductase (SHORase) are associated as a bifunctional complex (Ref. 3). Moreover, it has been shown that ... 

Recently, the mechanism of enantioselective Michael addition of malonic esters and keto esters to cyclic conjugated enones catalyzed by Ru bifunctional complexes 1 was studied in detail. ... 

Fig. 8 General structure for BINOL-Al-type bifunctional complexes...

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