Gas phase chemistry of the 2-tert-butyl-3-phenylphosphirenylium cation: novel onium ions by nucleophilic attack at phosphorus and de novo P-spiro bicyclic phosphonium ions via [4 + 2+] cycloaddition with dienes

Abstract

The 2-tert-butyl-3-phenylphosphirenylium ion 13 is formed in abundance in the gas phase from 1-chloro-1H-phosphirene 6 upon 70 eV electron ionization. Collision-induced dissociation (CID) and ion-molecule reactions followed by CID of the product ions were performed via pentaquadrupole mass spectrometry to probe the structure and reactivity of 13 towards representative nucleophiles and dienes. Under CID conditions, 13 produces a variety of fragment ions mainly via dissociation processes that are preceded by isomerizations. In ion-molecule reactions, 13 reacts readily with ethers, sulfides, pyridine and aniline to form hitherto unknown oxonium, sulfonium and azonium ions via nucleophilic attack at phosphorus. With butadiene, isoprene, 1-acetoxybutadiene, and with Danishefsky's diene (1-methoxy-3-silyloxybuta-1,3-diene), 13 undergoes [4 + 2+] cycloaddition at phosphorus to generate novel P-spiro bicyclic phosphonium ions. With butadiene and isoprene, a second [4 + 2] cycloaddition occurs which generates P-spiro tricyclic phosphonium ions. Whereas 13 also reacts readily with 1-acetoxybutadiene via[4 + 2+] cycloaddition, most of the nascent P-spiro cycloadducts are unstable and dissociate by the loss of either a neutral ketene or acetic acid molecule. B3LYP/6-31G(d,p) calculations were performed to gain insight into the structures of the product ions. The present study constitutes the first successful attempt to unravel the chemistry of 13, a unique 2 pi-Hückel phosphirenylium ion for which no direct solution chemical reactivity data are as yet available. The present findings also create a parallel with the solution reactivity of 1-halo-1H-phosphirenes and 1-triflato-1H-phosphirenes as precursors to phosphirenylium ions.

Phosphines and Related Tervalent Phosphorus Systems

“…Mass spectrometric techniques have been used to probe the reactions of (272) with nucleophiles and dienes. 779 Phosphenium cations, R 2 P: 1 , are believed to be formed as intermediates in the exchange reactions of the phosphirenium salt (273) with alkynes, to give new phosphirenium salts, e.g., (274). 780 The 2-(phosphirenyl)ethylphosphinidene (275) (generated by thermolysis of a related 2-(phosphirenyl)ethylphosphole in the presence of dimethyl acetylenedicarboxylate) undergoes a selfcondensation to give the 2,4-diphosphabicyclobutane (276).…”

14 Organic gas-phase ion chemistry

“…Eberlin and co-workers studied several cycloaddition reactions of N-acyliminium, 153 acylium, 154 and phosphirenylium ions. 155 The reactions of (CH 3 ) 3 NCLO 1 , PhCLO 1 , (CH 3 ) 2 NCLS 1 , CH 3 CLO 1 , CH 3 CH 2 CLO 1 , CH 2 CHCLO 1 , and several 2-azabutadienyl cations with 1-oxy-substituted 1,3-dienes and ethyl vinyl ether were carried out. Structurally diagnostic chemistry was observed for N-H, N-alkyl, and N-aryl 2-azabutadienyl cations.…”

Exploring the intrinsic polar [4 + 2+] cycloaddition reactivity of gaseous carbosulfonium and carboxonium ions

“…These studies have revealed new reactions and shed light to intrinsic reactivity and reaction mechanisms, and important analytical and synthetic uses for these ion/molecule reactions have been found. The intrinsic (free of solvent and counter ion effects) concerted or stepwise polar cycloaddition reactivity of many classes of gaseous ions have been investigated such as for ionized alkenes, fullerenes, ylides, nitrilium and immonium ions, hetarynium ions, cyclic N‐acyl and N, N‐diacyliminium ions, the nitronium ion, protonated and methylated azabutadienes, phosphenium ions, phosphirenylium ion, ionized α‐oxoketene and the phenyl sulfinyl cation . Perhaps, the most systematically studied class of gas‐phase polar cycloadditions has been the [4 + 2 + ] cycloadditions involving acylium ions (R‐C + = O) and dienes or heterodynes .…”