Copper structural constraints

The existence of the neutral rhenium carbonyl [Re(C0)4] was first claimed in 1965 206 but, although it is easily sublimed, it has not yet been characterized by mass spectrometry and the value of n is still not known. This colourless substance [v (CO) 2055 and 1995 cm-1 in CHC13] has been obtained as a by-product in the synthesis of Re2(CO)i0 starting from Re2S7, copper powder, and carbon monoxide at 85 atm, 200 °C206>. There has also been a report of the compound Re4(CO)10(PPh2Me)6, which can be considered to be a substitution product of the hypothetical species, Re4(CO)i6 it has been obtained by a photochemical reaction between Re2(CO)j0 and PPh2Me194. In both cases, and particularly in the phosphine derivative, a tetrahedral structure seems improbable because of steric constraints. 

The influence of geometric constraints imposed by coordinated Kgands in combination with the differences in donor atom preferences among the various oxidation states makes it possible to exert a considerable amount of control over copper redox potentials. In fact, the influence of Kgand structure upon the electrochemical properties of copper is one of the most common themes in copper studies. 

Copper ions have been reduced in colloidal assemblies differing in their structures (55,56). In all cases, copper metal particles are obtained. Figure 9.3.1 shows the freeze-fracture electron microscopy (FFEM) for the various parts of the phase diagram. Their structures have been determined by SAXS, conductivity, FFEM, and by predictions of microstructures that require only notions of local curvature and local and global packing constraints. 

Figure 4 Aliphatically tethered Cu -peroxo complexes (a) and (b). Figure 4(c) depicts the distortion, or butterflying, of the Cu202 core facilitated by the ligand constraints the aliphatic tether imposes on the copper complex. Figure 4(d) depicts the structure of oxyHc from Limulus polyphemus, which shows some degree of butterflying of the Cu202 core...

The transition metal-mediated nitrenoid transfer to olefins represents a very concise route to the aziridine structure very often, however, an excess of the olefinic substrate is required for preparatively useful yields. In this arena, Andersson and co-workers have studied the copper-catalyzed aziridination of olefins using [A -(arenesulfonyl)imino]phenyliodinanes 446 as nitrene precursors, and have reported on conditions which give good to excellent yields of aziridines 447 without the constraint of having to use an excess of alkene (Scheme 116). 

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