Exploration of isomeric bis(phosphanyl)-substituted carbenium ions: identification and synthesis of the most stable isomer

Abstract

Isomeric bis(phosphanyl) carbenium ions have been investigated by theoretical [MP2/6-31G(d,p) level of theory] and experimental means. On the potential energy surface (PES) of phosphorus cations of the formula [P 2 CH 5 ] ϩ , five stable isomers are found. Their structures follow the stability order (∆E rel /kcal mol Ϫ1 ): P-protonated diphosphiranium, [(. The stability order is very different for the family of the four related stable [P 2 CH(NH 2 ) 4 ] ϩ ions 1b, 2b, 4b, 5b in which the phosphorus-bound hydrogens (and one carbon-bound hydrogen in the case of 1b) have been replaced by NH 2 groups: 2b (Ϫ39.6) ӷ 1b (0.0) > 5b (2.2) ≥ 4b (3.7). None of these ions has a structure comparable to the classical amidinium ion [HC(NH 2 ) 2 ] ϩ . While all amino carbenium ions have a positively charged carbon atom, all phosphorus analogues carry a negative charge on carbon. In some, even the p(π)-population exceeds unity suggesting that these should be considered as cationic methanides. Experimentally, a derivative of the diphosphiranium ion 1a could be prepared by methylation of 1,2-bis-(2,4,6-tri-tertbutylphenyl)diphosphirane with MeO 3 SCF 3 , and this new compound 8 was characterized by NMR methods. Although the most stable member in this family, it could only be observed under stable ion conditions (T < Ϫ40 ЊC, five-fold excess of MeO 3 SCF 3 ) and decomposes at higher temperatures.

PC Bonds as Building Blocks for Three‐ and Four‐Membered Heterocyclic Cations: Synthesis, Structures and Mechanistic Studies

“…Intriguingly, the asymmetrically substituted diphosphiranium cation E has been calculated to be 47.1 kcal mol À1 lower in energy than the known symmetrically substituted A. [11] It is therefore surprising that, until the present studies, a diphosphiranium cation of type E had eluded isolation. There have been two reports of the spectroscopic detection of species of type E. The first involved methylating the neutral diphosphirane (Mes*P) 2 CH 2 with MeOTf to afford diphosphiranium [Mes*(Me)PCH 2 PMes*]OTf (cf.…”

“…In contrast, the acyclic phosphinomethylenephosphonium form C is just 24.5 kcal mol À1 lower in energy than cyclic A. [11] Thus, through judicious choice of substituents, both cyclic A and Abstract: The activation of the P=C bond of phosphaalkenes with electrophiles is investigated as a means to prepare and characterize unusual organophosphorus compounds. Treatment of RP=CHtBu (1 a: R= tBu; 1 b: R= 1adamantyl) with HOTf (0.5 equiv) affords diphosphiranium salts [RP À CHtBu À PR (CH 2 tBu)]OTf ([2 a]OTf and [2 b]OTf), each containing a threemembered P 2 C ring.…”

“…E), which was detected spectroscopically at low temperatures. [11] The second involved treating the phosphaalkenes Mes*P=CH 2 or MesP=CPh 2 with electrophiles (E = GaCl 3 , H + , or [P-A C H T U N G T R E N N U N G (NEt 2 ) 2 ] + ) to afford diphosphiranium species that were detected spectroscopically in solution, but could not be isolated. [7] Presumably, the diphosphiranium cation is derived from the cyclization of a phosphinophosphenium species G through intramolecular donor/acceptor-adduct formation.…”

Phosphines and Related Tervalent Phosphorus Systems

“…669 Treatment of the diphosphenium salt (223) with lithium diisopropylamide results in a high yield conversion into the diphosphirane (224), alkylation of which gives a diphosphiranium salt. 670 (226) The synthesis of conjugated polymers of the poly(p-phenylenevinylene) type involving diphosphene and phosphaalkene units in the polymer backbone has started to attract interest. Routes to oligomeric systems, e.g., (226), 672 and related polymeric systems, 673,674 including a fluorescent poly(p-phenylenephosphaalkene) system 675 have been developed.…”

Cyclic Bis(phosphanyl)carbenium Ion by Protonation of a 1,3‐Diphosphacyclobutane‐2,4‐diyl

“…The stabilization of the carbenium ion, however, is insufficient to compensate for the inversion barrier of two phosphorus atoms. Ab initio calculations indicate that the parent 7 is nonplanar and without conjugative stabilization 9. Hitherto, two derivatives of 7 have been reported based on NMR evidence; however, this assignment is not completely certain owing to downfield resonances in the 31 P NMR spectra 10…”