INFRARED, CONDUCTANCE, AND KINETIC EVIDENCE FOR ALKALI-METAL ION INTERACTIONS WITH DERIVATIVES OF MANGANESE CARBONYLATES
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A combination of ir, kinetic, and conductivity data has been used to define the nature and importance of ion-pairing phenomena in alkali metal manganese carbonylates. Infrared analysis indicates the contact ion interactions observed for-NaMn(CO)4L (L = PMe2Ph, PPh3, P(OPh)3, and CO) to be that of Na+ interacting with the oxygen of an equatorial CO group. Conductometric titrations indicate specific interaction of two to four HMPA molecules per Na+ or Li+ and one 15-crown-5-macrocyclic polyether per Na+ or Li+ in the formation of solvent-separated ion pairs and free ions of M+Mn(CO)5-. The importance of these complexed cations is manifest in the activation parameters for reactions of alkyl halides with M+Mn(CO)4L-(L = CO and P(OPh)3) in THF. In the presence of a cation-complexing agent such as HMPA, the rate of addition of RX to form cis-RMn(CO)4L is drastically lowered as a result of a larger negative entropy of activation. Center-to-center distance parameters and dissociation constants for ion pairs as derived from conductance dependence on concentration are discussed in terms of the electronic nature of the anion and the solvation sphere of the cation. A particularly interesting observation on distance parameters as related to asymmetric anions is noted. 1976, American Chemical Society. All rights reserved.