Quantification of the electrophilicities of diazonium ions

Article abstract of DOI:10.1002/jlac.199719970111

The kinetics of the reactions of arenediazonium ions with arenes, alkenes, allylsilanes, allylstannanes, and silyl ketene acetals have been studied in acetonitrile solution. The reactions follow second-order kinetics, and in several cases rate-determining attack of the diazonium ion has been proven by kinetic isotope effect studies (1a + 2b), by the independence of the allylsilane reactivities of the rate of desilylation (1a + 10a, d) and by the independence of the rate constants of the diazonium counterion. A decrease of the rate constant with increasing solvent donor ability (correlation with Gutmann's donor number) was found. The reactions of diazonium ions with π-nucleophiles roughly follow the correlation lgk (20°C) = s (E + N), previously derived for the reactions of carbocations with nucleophiles. With the E parameters derived for diazonium ions, rate constants for azo couplings with aromatic and nonaromatic π-nucleophiles can be predicted with an accuracy of ≈10². On the basis of E, the electrophilic reactivities of diazonium ions can be compared with those of carbocations (Figure 9), and the combination with the nucleophilicity parameters N (Figure 10) gives a first clue on possible azo coupling reactions. Literature reports are discussed within this scheme. VCH Verlagsgesellschaft mbH, 1997.