title: Comparative measure of the electronic influence of highly substituted aryl isocyanides.
abstract: To assess the relative electronic influence of highly substituted aryl isocyanides on transition metal centers, a series of C4v-symmetric Cr(CNR)(CO)5 complexes featuring various alkyl, aryl, and m-terphenyl substituents have been prepared. A correlation between carbonyl-ligand (13)C{(1)H} NMR chemical shift (δCO) and calculated Cotton-Kraihanzel (C-K) force constant (kCO) is presented for these complexes to determine the relative changes in isocyanide σ-donor/π-acid ratio as a function of substituent identity and pattern. For nonfluorinated aryl isocyanides possessing alkyl or aryl substitution, minimal variation in effective σ-donor/π-acid ratio is observed over the series. In addition, aryl isocyanides featuring strongly electron-releasing substituents display an electronic influence that nearly matches that of nonfluorinated alkyl isocyanides. Lower σ-donor/π-acid ratios are displayed by polyfluorinated aryl isocyanide ligands. However, the degree of this attenuation relative to nonfluorinated aryl isocyanides is not substantial and significantly higher σ-donor/π-acid ratios than CO are observed in all cases. Substituent patterns for polyfluorinated aryl isocyanides are identified that give rise to low relative σ-donor/π-acid ratios but offer synthetic convenience for coordination chemistry applications. In order to expand the range of available substitution patterns for comparison, the syntheses of the new m-terphenyl isocyanides CNAr(Tripp2), CNp-MeAr(Mes2), CNp-MeAr(DArF2), and CNp-FAr(DArF2) are also reported (Ar(Tripp2) = 2,6-(2,4,6-(i-Pr)3C6H2)2C6H3); p-MeAr(Mes2) = 2,6-(2,4,6-Me3C6H2)2-4-Me-C6H2); p-MeAr(DArF2) = 2,6-(3,5-(CF3)2C6H3)2-4-Me-C6H2); p-FAr(DArF2) = 2,6-(3,5-(CF3)2C6H3)2-4-F-C6H2).
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, Mail Code 0358, La Jolla, California, 92093-0358, United States.
authors.forename: Alex E
authors.initials: AE
authors.lastname: Carpenter
authors.forename: Charles C
authors.initials: CC
authors.lastname: Mokhtarzadeh
authors.forename: Donald S
authors.initials: DS
authors.lastname: Ripatti
authors.forename: Irena
authors.initials: I
authors.lastname: Havrylyuk
authors.forename: Ryo
authors.initials: R
authors.lastname: Kamezawa
authors.forename: Curtis E
authors.initials: CE
authors.lastname: Moore
authors.forename: Arnold L
authors.initials: AL
authors.lastname: Rheingold
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Figueroa