Biquinoline complexes

The electrochemical properties of another series of Cu(I) complexes, based on substituted bipyridine and quinoline derivatives, have been also investigated68 (Fig. 17.31). To stabilize the Cu(I) oxidation state of Cu(I) polypyridine complexes, electron-withdrawing substitutents like esters have been considered. The same effect was also obtained with pyridyl-quinoline and biquinoline complexes, thanks to the increased 7i-accepting properties of the quinoline condensed aromatic ring. 

Pseudotetrahedral complexes such as 17 (Scheme 1.17) were observed to possess a particularly rich substitution chemistry [37]. Complex 17 reacted cleanly with o-phenylenediammonium to give the covalent substitution product 18 shown in Scheme 1.17. This imine substitution was driven by the same pk, effect employed in the l-to-2 transformation of Scheme 1.2. In addition, 17 reacted cleanly with copper bis(biquinoline) complex 10 to give the coordinative substitution product 20. This ligand exchange appears to have been sterically driven the substitution of one of the encumbering di(imine) ligands for a less bulky biquinoline provided the driving force for this reaction [45],... 

In contrast with 17, complex 21 (Scheme 1.18) did not undergo ligand substitution with the copper(I) bis(biquinoline) complex, possibly as a result of the different steric properties of the two complexes. The imine exchange reaction with phenylenediammonium worked well, creating the possibility of a new kind of domino or cascade reaction (Scheme 1.18). The intermediate product 18 (from... 

Amine complexes stabilized with phosphine ligands of the type [AuL(PR3)]+ have been obtained for L = bipy,2310 phen,2310,231 quinoline,23 1 acridine,2311 benzo[h]quinoline,2311 naphthyr-idine (388)2311 2,2 -biquinoline,2311 di-2-pyridyl-ketone,2311 di-2-pyridylamine,2311 2-(2-pyridyl)-benzimidazole, 2311 ferrocenylpyridine, 2-nitroaniline,2312 4-methoxyaniline,2312 NHPh2, 2 NHEt2,2312 NMe3,2312 quinuclidine,2313 NEt3,2314 2-aminothiazoline,2315 histidine,2316... 

Biaryl synthesis from aryl halides is a more interesting reaction due to the value of these molecules and their difficult access by chemical methods. The first electrosyntheses were simultaneously done in 1979-80 by three groups [21-23] who used NiCljPPha (1-20%) as catalyst precursor in the presence of excess PPhs. Later, several groups investigated the use of bidentate phosphines like dppe associated with nickel in the synthesis of various biaryls, and notably 2,2 -bipyridine and of 2,2 -biquinoline from respectively 2-chloropyridine and 2-chloroquinoline [24], More recently new nickel complexes with l,2-bis(di-2-alkyl-phosphino)benzene have been studied from both fundamental and synthetic points of view [25]. They have been applied to the coupling of aryl halides. 

Oppenauer-type oxidation of secondary alcohols can be a convenient procedure for obtaining the corresponding carbonyl compounds. It was found recently [19], that Ir(I)- and Rh(I)-complexes of 2,2 -biquinoline-4,4 -dicarboxylic acid dipotassium salt (BQC) efficiently catalyze the oxidation of secondary alcohols with acetone in water/acetone 2/1 mixtures (Scheme 8.5). The reaction proceeds in the presence of Na2C03 and affords medium to excellent yields of the isolated ketones. The process is much faster in largely aqueous solutions, such as above, than in wet organic solvents in acetone, containing only 0.5 % water, low yields were observed (15 % vs. 76 % in case of cyclohexanol). 

The formation of five-coordinate gold(III) has been demonstrated clearly in the complexes of 2,9-dimethyl-l,10-phenanthroline and 2,2 -biquinoline, which have the distorted square pyramidal structures (91) and (92). However, the structures of the ligands prevent square planar coordination, so that these examples are atypical.613-615 However, a related organometallic derivative, [AuCl(C4Ph4)(phen)], is known and has a similar distorted square pyramidal structure.616... 

The MLCT bands of these complexes are broad and red-shifted by 140 nm, compared to the complex 1. The lowest-energy MLCT transitions within this series were shifted from 486 to 608 nm, and the HOMO level varied over an extent of 0.45 V vs SCE. The energy of the MLCT transition in these complexes decreases with the decrease in the it-acceptor strength of the ancillary ligand, i.e., CN , NCS , H20, or Cl . The red shift of the absorption maxima in complexes containing 4,4/-dicarboxy-2,2-biquinoline (dcbiq) (7) as... 

Mixed-ligand diimine dithiolate complexes of Zn(II) were among the first compounds classified as having a LLCT excited state (131). The complexes Zn(phen)(tdt) (41), Zn(bpy)(tdt) (42), and Zn(biq)(tdt) (43), where biq = 2,2 -biquinoline, were reported to have absorption bands at wavelengths of 475 nm (80 M-1 cm-1), 465 nm (65 A/-1 cm-1), and 590 nm (40 M-1 cm-1), respectively. The LLCT transition is attributed to a HOMO that is localized on the dithiolene and a LUMO that is localized on the diimine, with a clear relationship to the MMLL CT transition described for the square-planar M(di-imine)(dithiolate) complexes (M = Ni, Pd, Pt) described in Section II.C. However, the relative orientations of the two planar ligands in the <78 square planar and the dw pseudotetrahedral complexes are quite different, and have a profound influence on the absorption and emission properties. 

The photoluminescent behavior of a complex of the type Zn(diimine)(dtsq), where diimine = 2,2 -biquinoline, phen (44), or 4,7-diphenyl-2,9-dimethyl-phen (batho) and dtsq = dithiosquarate, have been reported by Gronlund et al (135). The phen and batho complexes display broad, featureless luminescence spectra in the solid state at room temperature. Upon cooling to 77 K, the emission spectrum of Zn(batho)(dtsq) resolves into three sharp peaks overlapping the broad emission feature these sharp peaks are assigned to a diimine localized ji-ji emission. The Zn(diimine)(dithiolate) solids degrade upon UV laser excitation, which has inhibited accurate lifetime measurements. 

Balzani et al. (70) employed a strategy focusing on complexes as metals and as ligands (71,72), for developing a number of interesting supramolecular systems. Ditopic polypyridyl ligands, for example, 2,3- and 2,5-dipyridylpyrazine (2,3-dpp and 2,5-dpp), 2,2 -biquinoline (biq), tetrapyrido[3,2-fl 2, 3 -c 3",2"-/z 2", 3 "-/]-phenazine (73,74) (tppz), and 2,3,5,6-tetrakis(2-pyridyl)pyrazine (75-77) (tpypz), in combination with monotopic ligands (e.g., bpy and phen) were utilized in the preparation of a number of homo- and heteropolynuclear complexes of well-defined structures (Fig. 2). 

In recent years, many chiral catalysts for the enantioselective synthesis of optical active 1,5-dicarbonyl compounds have been developed, such as chiral crown ethers with potassium salt bases and chiral palladium complexes, including bimetallic systems. Nakajima and coworkers reported on enantioselective Michael reactions of S-keto esters to a,/3-unsaturated carbonyl compounds in the presence of a chiral biquinoline N,N dioxide-scandium complex, which catalyzed the additions in high yields and with enan-tioselectivities up to 84% ee . Kobayashi and coworkers found that the combination of Sc(OTf)3 with the chiral bipyridine ligand 149 (equation 41) was also effective as a chiral catalyst for asymmetric Michael additions of 1,3-dicarbonyl compounds 147 to a,/3-unsaturated ketones 148. The corresponding Michael adducts 150 were obtained in good to high yields with excellent enantiomeric excesses in most cases (Table 10). 

Annealing two benzene rings to the bpy framework leads either to biquinoline or isomeric Ao-biquinoline. Their respective complexes differ significantly in their redox behavior [74, 153, 227, 228] The first reduction of [Ru(biq)3] + is by 0.77 V more positive than that of [Ru(i-biq)3] +, in accordance with the trend in the reduction potentials of the free ligands. The difference between the oxidation and reduction potential for [Ru(biq)3] + is unusually small, 2.20 V, relative to [Ru(i-biq)3] +, 2.63 V, and most other Ru-polypyridines. 

The H NMR, IR, mass, and UV/vis spectra have been reported. This procedure may be used to prepare analogous complexes containing related bidentate ligands (e.g., 1,10-phenanthroline, 2,2 -biquinoline, 2,2 -iminodipyridine, 1,2-ethanediamine). ... 

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