VARIABLE TEMPERATURE NMR-STUDIES OF CARBONYL-(PHOSPHONIUM-BIS-METHYLIDE)RHODIUM(I) COMPLEXES

A phosphorus-ylide-rhodium complex of empirical formula [RhC6H10PO2] has been investigated by nuclear magnetic resonance. Both the 1H and 31P magnetic resonance measurements indicate two species present simultaneously in a toluene-d8 solution. From these studies, these species have been assigned to monomeric and dimeric structures. The assignments are further confirmed by a 1H nuclear magnetic resonance temperature dependence study. The 1H NMR temperature data fits the Van 't Hoff equation indicating a true equilibrium between the monomeric and dimeric species at different temperatures. A value of -10.5 kcal/mol for the heat of reaction (ΔH0) is calculated from a least squares fitting. The temperature profile indicates the dimer is the more preferred species at lower temperatures. © 1979.