Effect of Ring Size on the Complexation and Decomposition of Benzenediazonium Ion in the Presence of Crown Ethers in 1,2-Dichloroethane and the Gas Phase

Abstract

The host-guest complexation and the kinetics of the thermal dediazoniation of benzenediazonium tetrafluoroborate in the presence of unsubstituted and (di)benzene-and dicyclohexane-substituted crown ethers containing 4-10 oxygen atoms were studied by UV spectrophotometry in 1,2-dichloroethane at 40°C. The complexation equilibrium constants K and the stabilizing ability of the complexation (k 2 /k 1 ) were calculated by a kinetic method. Complexation in the gas phase was observed and characterized by fast atom bombardment mass spectrometry (FAB-MS). All complexing agents except 12-crown-4 formed 1:1 complexes [crown ether-PhN 2 ] + under FAB conditions. The complexation caused a hypsochromic shift ⌬ max in the UV spectrum of the benzenediazonium salt, which was largest for hosts containing six oxygen atoms. The thermodynamic and kinetic stability were much greater for insertion-type complexes containing six or more oxygen atoms in the host molecule than for the charge-transfer complexes formed with 15-crown-5. In contrast, 12-crown-4 destabilized benzenediazonium ion owing to the increase in homolytic dediazoniation. 21-Crown-7 was the strongest complexing and stabilizing agent for benzenediazonium ion; with a larger hole size in the host the effects weakened. The effects of benzene and cyclohexane substituents in crown ethers on the thermodynamic and kinetic stability were small compared with the effects of the number of oxygen atoms.

Stability of 1-naphthalenediazonium ion in solution. Complexation and decomposition of 1-naphthalene- diazonium tetrafluoroborate in the presence of crown ethers and acyclic polyethers in 1,2-dichloroethane and the gas phase under fast atom bombardment conditions

“…14,21 The peak of this complex has also been detected in the FAB mass spectrum. 14 The strength of complexation is much more difficult to predict for flexible organic molecules than for rigid metal cations.…”

“…14,21 The peak of this complex has also been detected in the FAB mass spectrum. 14 The strength of complexation is much more difficult to predict for flexible organic molecules than for rigid metal cations. We have used spectroscopic and kinetic methods to investigate, in solution, the effects of ring size and substituent of the crown ether, the length of the chain in acyclic polyethylene glycol, the character and position (ortho-effect) of the substituent of the benzenediazonium ion, the temperature, the solvent and the pressure on the host-guest complexation between crown ethers and arenediazonium ions.…”

“…13 The host-guest complexation in solution has usually been studied by spectroscopic, thermodynamic and kinetic methods. [10][11][12][13][14][15] Modern mass spectrometry with fast atom bombardment (FAB-MS), which is easily implemented with various mass spectrometric systems, and more recently electrospray ionization (ESI-MS), has emerged as a viable method for studying the host-guest complexation of large macro(poly)cycles with metal and organic ions in the gas phase. 16 Gokel and Cram reported in 1973 17 that crown ethers of suitable dimensions solubilize arenediazonium ions through complexation in non-polar solvents in which they otherwise are insoluble.…”

“…3,[10][11][12][14][15][16][17][18][19][20][21][22] Publications describing both the thermodynamic and the kinetic stability of these complexes are relatively few, however. 14,15,19,21,22 Polyether-arenediazonium ion systems (polyether = crown ether or acyclic polyether [22][23][24] ) are the only host-guest systems for which the thermodynamic stabilities have been calculated from their kinetic data. As far as we know, the host-guest complexation of polyethers with naphthalenediazonium ions has not been studied by any other groups (T. Kuokkanen and J. Palokangas, 2-naphtalenediazonium ion under study).…”

“…13,18,[20][21][22][23]25 Complexation in the gas phase under FAB conditions has been detected and characterized by mass spectrometry (FAB-MS). 14,24 Continuing our studies on the interactions of cyclic and acyclic polyethers with stable organic cations, we have now investigated, by spectroscopic and kinetic methods, the complexation of the 1-naphthalenediazonium ion with some crown ethers and PEGs. In addition, effects of solvent, temperature and pH on the thermal stability of the uncomplexed ion have been explained.…”