Is Allylphosphine a Carbon or a Phosphorus Base in the Gas Phase?

Abstract

The gas-phase basicity of allylphosphine (2-propenylphosphine) was measured by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry techniques. A complete survey of the allylphosphine-H + potential energy surface, carried out through the use of high-level G2(MP2) and B3LYP/6-311+G(3df,2p) calculations, allows us to conclude that, under low-pressure, low-energy ICR conditions, the interaction between the protonated reference base, B ref H + , and allylphosphine leads to a complex in which B ref H + attaches to the phosphorus atom of allylphosphine, where the electrostatic potential is strongly attractive. Hence, in the first step only the phosphorus protonated species should be formed. Its isomerization to yield the C β -protonated form, which is the global minimum of the potential energy surface, implies a very high activation barrier that cannot be overtaken under normal experimental ICR conditions. Therefore, the main conclusion of our study is that allylphosphine behaves as a phosphorus base in the gas phase, even though the C β -protonated structure is the most stable protonated species. We have also shown that both C β -and C γ -protonation triggers a cyclization of the system. An analysis of the bonding of the different protonated species as compared with that of the neutral system is presented.

Phosphines and Related Tervalent Phosphorus Systems

“…A kinetic study has compared the effectiveness of tertiary phosphines and phosphite esters in the catalysis of the cleavage of the silicon-silicon bond of methylchlorodisilanes, providing evidence for the involvement of a stabilised silylene intermediate. 585 The anion of the g-phosphino-b-diketimine (197) has been shown to react with arsenic trichloride to give the phosphinoarsino-b-diketimine (198) 587 a discussion as to whether allylphosphine is a carbon or a phosphorus base in the gas phase, 588 the relative merits of QSAR and QALE correlations in assessing donor properties of tervalent P systems 589 and a new assessment of the stereoelectronic profile of phosphine and phosphite ligands. 590 Trimethylphosphine has been used to probe the acid sites in a dealuminated nanosized zeolite using 31 P CP/MAS NMR and other NMR techniques.…”