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

The effects of solvent, temperature and pH on the rate of decomposition of uncomplexed 1-naphthalenediazonium tetrafluoroborate were studied by UV spe ctrometry. The complexation of the 1-naphthalenediazonium ion with crown et hers containing 4-10 oxygen atoms and some acyclic polyethers was detected and characterized in the gas phase by fast atom bombardment mass spectromet ry (FAB-MS). In addition, the host-guest complexation and the kinetics of t he thermal dediazoniation of 1-naphthalenediazonium ion in the presence of four crown ethers and two acyclic polyethers were studied in 1,2-dichloroet hane (DCE) solution at 40 degrees C by UV spectrometry. All hosts, except 1 2-crown-4, formed 1:1 complexes under FAB conditions. The values of the the rmodynamic stability K and the stabilizing ability of the complexation (k(2 )/k(1)) in DCE were calculated from the kinetic data. The thermodynamic and kinetic stabilities were observed to be greater for the inclusion complex of the 1-naphthalenediazonium ion formed with crown ethers containing at le ast six oxygen atoms than for the non-spesific adduct formation formed with 15-crown-5. This was also true for tetraglyme, whose chain is too short to be capable of being fully wrapped around the diazonium group as in the com plex of PEG 1000. Crown ethers with seven oxygen atoms are the strongest co mplexing agents for all the aromatic diazonium ions studied, for the 1-naph thalenediazonium ion investigated here and for arenediazonium ions examined earlier. The values of the activation enthalpy Delta H-not equal for the t hermal dediazoniation of the uncomplexed salt in both the acidic aqueous so lution and DCE were observed to be high, and the corresponding values of ac tivation entropy Delta S-not equal were clearly positive. The results are c onsistent with a heterolytic S(N)1-like mechanism involving the decompositi on of the uncomplexed and complexed 1-naphthalenediazonium ion into a highl y reactive naphthyl cation, followed by fast product-determining reactions with nucleophiles to give the products. Copyright (C) 2000 John Wiley & Son s, Ltd.