Alkane‐ and areneoxodiazonium ions: experimental results leading to an ab initio theoretical investigation

Abstract

Alkaneoxodiazonium ions (R-N=N=O) and (R-O-N 2 ) , which are closely analogous to alkanediazonium ions (R-N 2 ) , were detected as reactive intermediates in acid-catalysed reactions of nitrosohydroxylamines and deamination-type reactions. The isomers were compared by high-level MO investigations of the reactions of nitrous oxide with cationic electrophiles H , CH 3 , Me 3 C and PhCH 2 . Strongly bonded species are formed in reactions with the powerfully electrophilic H and CH 3 , and the resulting ions differ considerably in stabilities; less stable species are formed with Me 3 C and PhCH 2 and the complexes so formed have similar stabilities. Two isomers of Ph(N 2 O) , analogous to phenyldiazonium ion, PhN 2 , are calculated to be stable ions with the end-N-bonded isomer being preferred over the O-bonded ion at the MP4(SDQ)/6-311G(d,p)//MP2(fc)/6-31G(d,p) and G3 levels of theory. Both are non-planar with the phenyl ring at 90°to the non-linear N 2 O residue. Syntheses of salts of Ar(N 2 O) are now planned. Scheme 1. Electronic con®gurations of arene-and alkanediazonium ions Scheme 2. Pro®les for heterolysis of alkane-and arenediazonium ions JOURNAL OF PHYSICAL ORGANIC CHEMISTRY

R(Ar)O–N2+ vs. R(Ar)–N2O+: Are Alkoxy‐(Aryloxy‐)diazonium Ions or Alkyl‐(Aryl‐)N‐nitroso‐onium Ions Formed in the Gas‐Phase Reactions of N2O with H+, Me+, Ph+, PhCH2+, Tr+ and PhCO+?

“…There is a considerable energy barrier connecting the two isomers via a TS placed 35.6 kcal mol –1 above MeO–N 2 + (Table S1 and Figure S2). The optimized geometries of the O ‐methylated and N ‐methylated cations computed by MP2/6‐31+G(d,p) (Figure S1) differ somewhat (in particular for bond‐angles) to those reported at the QCISD/6‐311G(d,p) level (with MeN 2 O + being preferred by 3.6 kcal mol –1 at this level) 10…”

“…At the MP2/6‐31+G(d,p) level, Me–N 2 O + and MeO–N 2 + are both minima ( C s geometry) (Figure S1), with MeN 2 O + computed to be 8.9 kcal mol –1 more stable (Table S1). A difference of 9.4 kcal mol –1 was previously computed at the MP2/6‐31G(d,p) level 10. There is a considerable energy barrier connecting the two isomers via a TS placed 35.6 kcal mol –1 above MeO–N 2 + (Table S1 and Figure S2).…”

“…inf.). A difference of 1.8 kcal mol –1 was previously computed at the MP2/6‐31G(d,p) level 10. An opposite stability order favoring HO–N 2 + was reported at other levels, including MP4(SDQ) and QCISD(T).…”

“…Structures A and C correspond to the previously reported ones by MP2(fc)/6‐31G(d,p). The resulting structures represent, however, weakly bonded ion/molecule complexes, with dissociation energies of 18.7 kJ mol –1 (for A ) and 14.5 kJ mol –1 (for C ) by MP2/6‐31G(d,p) 10…”

“…Ab initio calculations at various levels have indicated that both H–N 2 O + or HO–N 2 + are viable, but their relative stabilities greatly depend on the level of electron‐correlation 9. More recently, Eckert‐Maksic and co‐workers10 reported a high‐level MO study on RO–N 2 + /R–N 2 O + pairs at various levels, with R = H + , Me + , t Bu + and Ph + . They concluded that H + , Me + and Ph + bind strongly to N 2 O to either nitrogen or oxygen, and with the relative energies of the resulting cations being dependent on the calculation level, but t Bu + and PhCH 2 + were found to from weakly bound adducts with N 2 O.…”