Coordination in organic solvents

Anions which may be termed as innocent from the point of coordination readily coordinate in organic solvents like methanol and acetonitrile [28-30], Using 139La NMR,... 

Yang and Jenekhe [186,187] reported a successful solubilization of aromatic polyimines in organic solvents via their soluble coordination complexes, which facilitated their solution characterization by NMR and processing films and coatings by spin coating and other techniques. This has created opportunities for various studies of the aromatic polyimines. 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

The value of the tris(pyrazolyl)hydroborato complexes [TpRR ]ZnOH is that they are rare examples of monomeric four-coordinate zinc complexes with a terminal hydroxide funtionality. Indeed, [TpBut]ZnOH is the first structurally characterized monomeric terminal hydroxide complex of zinc (149). As such, the monomeric zinc hydroxide complexes [TpRR ]ZnOH may be expected to play valuable roles as both structural and functional models for the active site of carbonic anhydrase. Although a limitation of the [TpRR ]ZnOH system resides with their poor solubility in water, studies on these complexes in organic solvents... 

Normally, the addition of C-nucleophiles to chiral a-alkoxyaldehydes in organic solvents is opposite to Cram s rule (Scheme 8.15). The anti-Cram selectivity has been rationalized on the basis of chelation control.142 The same anti preference was observed in the reactions of a-alkoxyaldehydes with allyl bromide/indium in water.143 However, for the allylation of a-hydroxyaldehydes with allyl bromide/indium, the syn isomer is the major product. The syn selectivity can be as high as 10 1 syn anti) in the reaction of arabinose. It is argued that in this case, the allylindium intermediate coordinates with both the hydroxy and the carbonyl function leading to the syn adduct. 

A few sulfonated bidentate ligands have been used for which the coordination behavior has been well established for their nonsulfonated analogs the sulfonated ligands showed a behavior that was very much the same as that of their parent ligands in organic solvents. NAPHOS as in rhodium complex (127) behaves the same as BISBI (58), as does its sulfonated analog BINAS (128), which was developed and extensively studied by Herrmann and co-workers.410"413 The catalytically active rhodium complexes [HRh(CO)2(P-P)] of NAPHOS and BINAS have been characterized by IR and NMR spectroscopy.414... 

Diethynyl-pyridine was reacted with 2 equiv. of (Me2S)AuCl to give a gold alkynyl as an insoluble coordination polymer of unknown structure. This product could be dissolved in organic solvents with cBuNG to afford the bis(isocyanide) complex with an angular structure (Scheme 50).214... 

In asymmetric hydrogenation of olefins, the overwhelming majority of the papers and patents deal with hydrogenation of enamides or other appropriately substituted prochiral olefins. The reason is very simple hydrogenation of olefins with no coordination ability other than provided by the C=C double bond, usually gives racemic products. This is a common observation both in non-aqueous and aqueous systems. The most frequently used substrates are shown in Scheme 3.6. These are the same compounds which are used for similar studies in organic solvents salts and esters of Z-a-acetamido-cinnamic, a-acetamidoacrylic and itaconic (methylenesuccinic) acids, and related prochiral substrates. The free acids and the methyl esters usually show appreciable solubility in water only at higher temperatures, while in most cases the alkali metal salts are well soluble. 

Quite recently it was shown that phosphonic esters, trimethylsilyl [124, 143] and alkyl esters [124,143, 145] could also be used to modify the surface of titanium or aluminum oxide in organic solvents at moderate temperatures. Unlike Si-O-C bonds, P-O-C bonds are not easily hydrolyzed, and their cleavage on an oxide surface was unexpected. Most probably, coordination of the phosphoryl oxygen to the surface assists the condensation by increasing the electrophilicity of the P atom, thus facilitating the condensation of P-0-R groups with surface hydroxyls (Scheme 7) [124]. The chemisorption of... 

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