Tris- , complexes copper

Another illustration of the structural changes that may result as a consequence of alkyl substitution at the 3-position of the pyrazolyl group is provided by the structures of the dimeric copper(I) complexes [Tp]Cu 2 (36), [TpMe2]Cu 2 (36), [TpPh2]Cu 2 (37), and [TpBut]Cu 2 (37), which differ in the manner in which the tris(pyrazo-lyDhydroborato ligand bridges the two copper centers (Fig. 16). 

Partial hydrolysis of a potentially heptadentate Schiff-base tripodal ligand derived from tris-(2-aminoethyl)amine and 2-hydroxyacetophenone, induced by copper(II) salts, was reported and the final copper(II) complex (377) was characterized.333 Using salicylaldehyde as a co-ligand, with a copper(II) complex (378), catalytic epoxidation was demonstrated 334... 

The first copper(I) complex of tris(hydroxymethyl)phosphine ((760) tetrahedral) has been reported by Samuelson and co-workers. This group addressed the question of anion-controlled nuclearity and metal-metal distances in copper(I)-bis(diphenylphosphino)methane complexes, and in this endeavor they reported the structures of complexes (761) (Cu-Cu separation 3.005-3.128 A), (762) (Cu-Cu separation 3.165 A) and (763) (tetrahedral Cu-Cu 3.293 A). 6 They synthesized and provided structural evidence of oxy anion- encapsulated copper(I) complexes of this ligand. The complexes (764) (distorted tetrahedral Cu-Cu 3.143 A), (765) (distorted tetrahedral Cu-Cu 3.424A), (766) (distorted trigonal Cu-Cu 3.170A), and (767) (Cu-Cu 3.032-3.077A) were reported. They studied solid-state emission spectra of these complexes.567 During this pursuit they... 

A plethora of polynuclear copper(I) complexes with bi-, tri-, and tetracon-necting dithiophosphato ligands have been discovered. These include cyclic dimers, [CuS2P(OEt)2 PPh3]2,43 tetrahedral Cu4[S2P(OPr )2]4,44 prismatic Cu6 S2P(OR)2 6, cubane Cu8(p8-E )[S2P(OEt)2]6 (E = S, Se),45 (also known for silver)46 and [Cu8 S2P(OPr )6(p8-X)][PF6] (X = Cl, Br).47 A supramolecular chain-like array of cubane units interconnected through iodine bridges was found in Cu8(S)[S2P(OEt)2]6(p-I) x.48... 

One example was reported by Tolman and coworkers (78) who found that the copper(I) complex C Tp112 (TpR2=tris(3-(R2)-5-methylpyrazol-l-yl)hydroborate) promotes NO disproportionation via a weakly bound CuITpR2(NO) intermediate (formally a MNO 11 species). The products are N20 and a copper(II) nitrito complex (Eq. (36)). The rate law established the reaction to be first-order in copper complex concentration and second-order in [NO], and this was interpreted in terms of establishment of a pre-equilibrium between NO and the Cu(I) precursor and the Cux(NO) adduct, followed by rate-limiting electrophilic attack of a second NO molecule (mechanism B of Scheme 5) (78b). 

In a related observation, reported by Tanaka et al. (81), the copper(II) complex Cu(tpa)2+ (tpa = tris[(2-pyridyl)methyl] amine) was shown to serve as a catalyst for the electrochemical reduction of nitrite to N20 and traces of NO in aqueous solution. NO and/or a copper nitrosyl complex would appear to be the likely intermediates in this process (81a). 

Wang and Stack (211) reported seven four-coordinate bis(phenolato)copper(H) complexes that were chemically one-electron oxidized with tris(4-bromo-phenyl)aminium hexachloroantiomonate to the corresponding EPR silent (phe-noxyl)copper(II) species. These compounds are schematically shown in Fig. 28. In a subsequent paper (212), these authors showed by Cu K-edge XAS that oxidation of the neutral species to the monocation is ligand centered with formation of (phe-noxyl)copper(II) species, in excellent agreement with similar experiments on GO. 

Recently, a somewhat different synthetic approach has been reported. Halcrow et al. (215) synthesized a series of five-coordinate copper(II) complexes comprising a tridentate tris(pyrazolyl)borate ligand and a bidentate phenol derivative. Neutral complexes [Cun(TpPh)(bidentate phenolate)] were synthesized and structurally characterized [Tpph] = hydrido-tris(3-phenylpyrazol-l-yl)borate. The species [Cun(TpPh)(2-hydroxy-5-methyl-3-methylsulfanylbenzaldehydato)] can electro-chemically be converted to the (phenoxyl)copper(II) monocation, which has been characterized in solution by UV-vis spectroscopy. It displays two intense absorption maxima at 907 nm (e = 1.2 x 103 M 1 cm-1), and 1037 (1.1 x 103 M l cm-1), resembling in this respect the radical cofactor in GO (Fig. 7). 

The above considered reactions model the reductive half cycle of GO where a primary alcohol is oxidized to an aldehyde with concomitant reduction of a (phe-noxyl)copper(II) complex to the reduced (phenol)copper(I) species. In the first two cases, reoxidation of the reduced catalyst was achieved by an external oxidant such as tris(4-bromophenyl)aminium or an electrode but not dioxygen. 

Lehn and coworkers52 reported the synthesis, crystal structure and dinuclear copper(I) complexes of tris-carotenoid macrobicyclic ligands. The macrobicycles 89 and 90 were obtained in good yields in a one-step macrobicyclisation condensation between the tripode N(CH2CH2NH2)3 and the polyolefinic dialdehydes 93 and 94. 

It is worthwhile to analyze why co-existing soft ligands assist low oxidation numbers. If we want to make a copper(I) compound, it is very difficult to try the aqua ion, the fluoride or the anhydrous sulphate because they disproportionate to the metallic element and a higher oxidation state, here Cu(II). However, as seen in Eq. (7) it is easier to make the ammonia complex Cu(NH3)2 under anaerobic conditions, and even easier to make copper(I) complexes of pyridine and of conjugated bidentate ligands such as 2,2 -dipyridyl and 1.10-phenanthroline. The experimental problems are reversed in the case of iodides and cyanides, where it is easy to precipitate Cul or CuCN or to prepare solutions in an excess of the ligand containing Cul J,... 

Macrobicyclic cascade cryptands have also been prepared such as the series of bis(tren) derived (tren = tris(2-aminoethyl) amine, see Section 4.4.3) compounds 5.9. The di-nickel(II) and di-copper(II) complexes of the cages with various spacers all bind a metal cation into each tren unit. These metal... 

---