![]() After the exploration of the coordination chemistry of the bulky (but also electronically diverse) m-terphenyl isocyanides, 57–69 it became evident that isocyanides are more than bulky surrogates of carbonyl ligands. This, finally, resulted in a (not fully justified) generalization of their chemical behaviour for all isocyanides. A nice overview of this point is given in ref. Approximately 40 percent of all studies with isocyanides are done with these two representatives. tert-butyl or cyclohexyl isocyanide in many papers about the related chemistry. Systematic studies about this point are rare, which is attributed to the preferred use of commercially available and stable ligands such as e.g. In particular, electronic effects due to electron withdrawing or electron donating substituents on (phenyl) isocyanides have been underestimated in the coordination chemistry of these compounds. 46,53–55 These findings are not necessarily trivial since the ligand exchange behaviour of isocyanides has been found to be strongly dependent on steric and electronic factors. ![]() The formation of 1 : 1 complexes with common isocyanides has also been observed for reactions of, 20 and for reactions of robust isocyanides with the corresponding phenyl- or tolyl- or xylylimido complexes. Scheme 1 Reaction of with various isocyanides. Even so, only a small amount of pure products could be obtained from some of the sensitive isocyanides. For this reason, relatively short reaction times and only a slight excess of the ligands have been used in optimized procedures. The gradual (not metal-driven) decomposition of the isocyanides, however, caused significant problems during the isolation of pure products in these cases. In both cases, exclusively 1 : 1 ligand exchange products could be isolated. The reactions have first been performed with an excess of ligands and for the more stable ligands (CN tBu and CNPh i-prop2) also prolonged reactions at higher temperatures have been tested. These ligands as well as other common isocyanides such as CN tBu or CNPh i-prop2 react with ( 1) with the formation of mono-substituted complexes of the composition ( Scheme 1). This allows for milder reaction conditions and lower temperatures, which is particularly beneficial for sensitive isocyanides such as CNPh, CNMes or CNPh pNO2 of the present study. Results and discussion The attachment of a fluorine atom to the phenylimido ligand of increases the room temperature-solubility by a factor of 5 in both dichloromethane and acetonitrile. 1 Isocyanides used throughout this paper. In the present report, we present a series of (fluorinated) phenylimidorhenium( V) complexes with a variety of different alkyl and aryl isocyanides ( Fig. A modulation of the solubility of the phenylimido starting material without significant interference with the chemical behaviour of other ligands has recently been demonstrated with the use of p-fluoro-substituted phenylimido ligands in complexes, M = Tc or Re ( 1). esterification, formation of Schiff bases, etc.), which frequently causes undesired side-reactions and/or lower yields. 46–50 Such residues, however, sometimes undergo undesired reactions with co-ligands and/or solvents ( e.g. 37,40,44,45 Alternatively, substitutions on the arylimido ligand with the carboxylic, hydroxylic or amine group provide an enhanced solubility. The corresponding bromido complex is slightly more soluble and is, thus, occasionally used as a better suitable starting material. Thus, predominately reactions with strong chelators or with robust ligands, 22–45 which resist harsh reaction conditions, give pure products in good yields. Unfortunately, the rhenium compound is significantly less soluble than its technetium analog. 21 A similar use of the phenylimido compound as the starting material may give access to a wide variety of phenylimido complexes. ![]() The phenylimido complex is isoelectronic to the oxidorhenium( V) compound, which is frequently used as a common precursor for ligand exchange procedures. 19,20 A number of interesting reactivity features have been observed during this study, which makes it interesting to have a look at the related chemistry of rhenium. Reactions of ( 3+ unit could be isolated.
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