By how much is protonated benzene stabilized by coordination of iron tricarbonyl?
Rate and equilibrium measurements for the hydrolysis of the Fe(CO)3-coordinated cyclohexadienyl cation lead to pKR = 4.7 compared with pKR = -2.1 for the uncoordinated ion. The hydrolysis yields exo-coordinated cyclohexadienol 10(7)-fold more rapidly than its endo-isomer, despite the isomers being of similar stability. DFT calculations of the energy of isodesmic transfer of Fe(CO)3 from cyclohexadiene to benzene lead to an estimate of pKa 8 for loss of a proton from the coordinated cyclohexadienyl cation to form Fe(CO)3-coordinated benzene. This implies that the coordinated cation is 33 log units (46 kcal) less acidic than the uncoordinated ion.
Galvin
Martin
M
School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland.
Guthrie
J Peter
JP
McDonnell
Claire M
CM
O'Ferrall
Rory A More
RA
Pelet
Sandrie
S
D001554:Benzene / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D002248:Carbon Monoxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D058085:Iron Compounds / Q000737:chemistry*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D011522:Protons; D013057:Spectrum Analysis
D001555:Benzene Derivatives; D058085:Iron Compounds; D011522:Protons; D002248:Carbon Monoxide; D001554:Benzene