EFFECTS OF MULTIPLE SUBSTITUENTS ON THE PHYSICAL-PROPERTIES OF PENTACARBONYLARYLISOCYANIDECHROMIUM COMPOUNDS

Eight arylisocyanides containing one or more electron-withdrawing subs tituents were synthesized. The sigma-donating and pi-accepting abiliti es of these isocyanides were evaluated by examining the spectroscopic and electrochemical properties of the pentacarbonyl(isocyanide)chromiu m derivatives. Linear relationships between the Hammett parameters of the para-substituted isocyanides, C-13 NMR chemical shifts, and nu(CN) with the E1/2 were found. Ortho substitutions of the isocyanide stabi lized the HOMO of the Cr(CO)5L more than para substitutions. Furthermo re, each successively added substituent caused a similar shift in the observed oxidation potential relative to its position on the isocyanid e.