Copper complexes cubanes

The colorless tetramer Ccu(py)l] is fairly stable only in non- or weakly coordination solvents such as benzene, CH Cl, or acetone. At room temperature in solution this copper complex shows an intense red photoluminescence ( 0.04 a f nax = nm (54). The emitting state is a metal-centered 3d 4s excited state which is strongly modified by Cu(I)-Cu(I) interaction in the tetramer. This consists of a (Cul) cubane core. 

The preparation of 57b-d was then carried out in the greener dimethyl carbonate solvent at 70 °C. Indeed, in this solvent, the phosphine was trapped by CuCl as the copper-phosphine cubane [CuCKPPhj)], which precipitated and made the work-up easier and more efficient, as it required only 2.5 equiv. of CuCl. This protocol, followed by phosphine exchange, led to complexes 57b-d in 24%, 36%, and 50% yields, respectively [71]. 

Amino acid is one of the most important biological ligands. Researches on the coordination of metal-amino acid complexes will help us better understand the complicated behavior of the active site in a metal enzyme. Up to now many Ln-amino acid complexes [50] and 1 1 or 1 2 transition metal-amino acid complexes [51] with the structural motifs of mononuclear entity or chain have been synthesized. Recently, a series of polynuclear lanthanide clusters with amino acid as a ligand were reported (most of them display a Ln404-cubane structural motif) [52]. It is also well known that amino acids are useful ligands for the construction of polynuclear copper clusters [53-56], Several studies on polynuclear transition metal clusters with amino acids as ligands, such as [C03] [57,58], [Co2Pt2] [59], [Zn6] [60], and [Fe ] [61] were also reported. 

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... 

Table 35 Crystallographic Data for Some Tetranuclear Cubane Copper(II) Complexes... 

Reactions of limited proportions of amine and phosphine Lewis bases with non-molecular copper and silver halides generate crystalline cubanes. Crystallographic determinations of molecular structure have been reported for at least 31 complexes with cf or d10 metal configurations, spanning the following types or homologous series of compounds. Compilations of data occur in references 157, 158 and 167. 

In these compounds, an alternative structure to the cubane cluster is found, for example in [Ph3PAgI]4.106 This is the chair or step type of arrangement, illustrated in Figure 2, in which two of the four halogen atoms retain a coordination number of three. This arrangement has also been found in some copper(I) halide complexes with bis(diphenylphosphino)methane.1O7 10S The pyramidal coordination of the halogen atom is similar to that in the cubane structure, although often more distorted. 

To relieve the strain of sterically demanding ligands, a metal often remains coordinatively unsaturated. Copper(I) halides and phosphines form cubane-like metal cluster compounds, Lm(CuX) ,12 With the bulky trimesitylphosphine, a monomeric two-coordinate [CuBr(Pmes)3] is formed, Br—Cu—P = 173.7°.252 The d(Cu—P) of 2.193 A is comparable to that in normal tet-rameric complexes, but d(Cu—Br) at 2.225 A is shorter, no doubt due to the reduced coordination number. Heating crowded complexes can also result in a reduction in coordination number (see equation 65). 

A similar mixed ox a- thia macrocycle incorporating a rigid horseshoeshaped aromatic moiety, l,ll,21-trioxa-8,14-dithia[2,9,2]paracyclophane, L40, has been synthesized and reacted with copper iodide in MeCN solution (Scheme 19).160 Its polymeric copper iodide complex [Cu4I4(L40)2] 40 crystallizes, in a 2 1 metal to ligand ratio, as an ID infinite array of cubane-like units consisting of four copper atoms, four i3-iodine atoms, and four sulfur atoms, stemming from four different macrocycles. The Cu—Cu distances are about 2.731 A. Unfortunately, the photophysics of this compound have not been studied. 

It has been known that the reaction of copper(I) iodide with Lewis bases, such as aniline derivatives, produced complexes with single cubane-like CU4I4 cluster, in which the aniline derivatives act as the terminal ligands coordinating to the copper(I) centers [7-10]. Thus, it is reasonable to expect macrocyclic or extended complexes constructed by CU4I4 cluster units through replacing aniline derivatives with ditopic... 

Electron transport between cubane [Fe4S4] clusters, cytochrome c, or Cu + centers in blue copper proteins " and the periphery of the proteins has been examined by complexing ruthenium species to surface histidines. In the case of the iron sulfur cubane in Chromatium vinosum, four surface histidines served as points of ruthenium attachment. The rates of electron transport from the Fe4S4 core to ruthenium varied over two orders of magnitude and were used to diagnose the preferred channel for electron transport. Cysteine and lysine residues have also been used as binding sites in studies of cytochrome c and cytochrome P450 cam proteins. 

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