Heteronuclear synthesis

Synthesis of Heteronuclear and Polynuclear Metal Carbonyls. Heteronuclear metal carbonyls are usually synthesized either by metathesis (27) or addition (28,40). 

Carriedo, G.A., Riera, V., Sanchez, G. and Solans, X. (1988) Synthesis of new heteronuclear complexes with bridging... 

Heterojunction with intrinsic thin layer (HIT) photovoltaic cell, 23 46-47 Heteroleptic uranium complexes, 25 441 Heterologous promoters, 22 453 Heteronano interface (HNI), 23 838 Heteronium bromide, 4 359t Heteronuclear metal carbonyls, synthesis of, 26 69-71... 

Probably, one of the most valuable advances in this field has dealt with the first chemoenzymatic synthesis of the stable isotope-enriched heparin from a uniformly double labelled 13C, 15N /V-acetylheparosan from E. coli K5. Heteronuclear, multidimensional nuclear magnetic resonance spectroscopy was employed to analyze the chemical composition and solution conformation of N-acety 1 hcparosan, the precursors, and heparin. Isotopic enrichment was found to provide well-resolved 13C spectra with the high sensitivity required for conformational studies of these biomolecules. Stable isotope-labelled heparin was indistinguishable from heparin derived from animal tissues and might be employed as a novel tool for studying the interaction of heparin with different receptors.30... 

Whereas a large number of metal-sulfur clusters are present in nature, carbonyl clusters are exclusively products of chemical synthesis. They have been widely used in industrial catalytic processes17 and some of these processes are triggered by the redox aptitude of these species.lc g As for the metal-sulfur clusters, we will briefly discuss their structures and their propensity to donate/accept electrons in order of increasing nuclearity. We will consider only homonuclear and homoleptic metal-carbonyl derivatives. However, it is noted that heteronuclear derivatives are gaining considerable interest due to the synergistic effect of metal-metal bonds possessing a polar character.lc,ld... 

In the spontaneous self assembly approach to synthesis, the inherent kinetic lability of the Fe/Mo/S system allows for the fcnmation of various thermodynamically stable, heteronuclear products that, as of now, do not include one with the desir le Fe/Mo/S atom ratio of 6-7 1 6-8. 

In addition, surface-mediated synthesis results a powerful tool in the preparation of surface carbonyl species (homo- or heteronuclear) that are further precursors of supported, tailored metallic catalysts. 

In order to gain more control over this reaction, chromium salphen dimers were synthesized. The synthetic route was developed in such a manner that the bridging length between the two salphen units can easily be varied and that the synthesis of heteronuclear metal complexes is possible. Since the ligand substitution pattern is highly important for the activity of the catalyst as well as the characteristics of produced polymer, an analogous monomeric Cr(lll) complex was synthesized for comparison [102] (Fig. 35). 

Digermanium hexachloride, synthesis in electric discharge, 6 173, 272 Diglycolic acid, complex formation by, 3 276 Digold heteronuclear cluster compounds. X-ray crystallography, 39 358-362... 

Tertiary phosphite complexes of platinum(O) can be prepared by the hydrazine reduction of PtCl2 P(OR)3 2 (equation 384), or by replacement of triphenylphosphine in Pt(PPh3)3 (equation 385).1233 Alternatively the complexes can be prepared from Pt(j73-C3H5)(r/5-Cp) and the phosphite.1268 Heteronuclear INDOR measurements show that 2/(PP) has a value of +81 Hz in Pt P(OMe)3 4. A detailed synthesis of Pt P(OEt)3 4 has been published from K2PtCl4 and triethyl phosphite with KOH (equation 386).1267 The product is obtained as colorless crystals which can be handled in air. 

The addition of transition metal fragments ML (L = two-electron donor ligand) across formally unsaturated metal-metal or metal-carbon bonds is a well-developed synthetic route to heteronuclear clusters (1,2,11,12,27) and has received theoretical justification from Hoffmann s isolobal principle (46). The addition of a PtL2 fragment across an M=M double bond may be considered as analogous to the reaction of a carbene with an olefin, resulting in a cyclopropane. The use of isolobal analogies in the directed synthesis of heteronuclear clusters has been reviewed (11,12,27). 

Fig. 7. H-15N heteronuclear single-quantum coherence (HSQC) spectrum of yeast ubiquitin synthesized by wheat germ cell-free protein synthesis system, not purified (0.1 vaM, 128 [tl] 512 [t2] complex points, 512 scans), obtained at the H resonance frequency of 500 MHz. Spectral widths are 1600 and 6250 Hz in FI and F2, respectively.

The most common strategy in the synthesis of heteronuclear complexes is the use of bidentate donor ligands bearing different donor centers. In that way both donor atoms can be coordinated selectively to two different metal centers in a consecutive way. If the space between the donor atoms of the ligands is short, interactions between both metals usually appear, normally intramolecular. Sometimes, albeit not very often, the bidentate units bind to one another, leading to extended structures through metallophilic interactions. As we have commented, in the case of gold-silver derivatives the number of luminescent studies of these derivatives is very scarce. 

Fig. 1. Examples of the synthesis of heteronuclear gold cluster complexes by the reaction of Au(PPh3)Cl with transition metal anions.

Heteronuclear gold cluster compounds have, therefore, been proposed as potential precursors for the synthesis of selective catalysts and also as models of the modifications to the substrate that arise at a molecular level. Braunstein has reviewed in more detail the catalytic applications of gold-containing polymetallic systems (212). 

As for the multiply bonded systems of heavier group 14 elements, all the homonuclear double bonds were successfully isolated and characterized by the end of the last century. However, the chemistry of heteronuclear double bonds and those of conjugated systems are still in growth. The synthesis and isolation of unprecedented cumulative systems such as 217 and aromatic systems containing Ge, Sn and Pb atoms, e.g. 219-222 (Scheme 68), will also be within the range of this future chemistry. Likewise, the synthesis and isolation of the triply bonded systems 223 (Scheme 68) should be one of the most challenging projects in this field. 

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