More user-friendly phosphines? Molecular structure of methylphosphine and its adduct with borane, studied by gas-phase electron diffraction and quantum chemical calculations
The molecular structures of methylphosphine (CH3PH2) and methylphosphine-borane (CH3PH2?BH3) have been determined from gas-phase electron diffraction data and rotational constants, employing the SARACEN method. The experimental geometric parameters generally showed a good agreement with those obtained using ab initio calculations and previous microwave spectroscopy studies. In order to assess the accuracy of the calculated structures a range of ab initio methods were used, including the CCSD(T) method, with correlation-consistent basis sets. The structural environment around the phosphorus atom was found to change significantly upon complexation with borane, with the P-C bond length shortening and the bond angles widening. The Royal Society of Chemistry 2008.
Noble-Eddy, Robert,Masters, Sarah L.,Rankin, David W. H.,Wann, Derek A.,Khater, Brahim,Guillemin, Jean-Claude
Synthesis, photoelectron spectroscopy and quantum chemical study of kinetically unstabilized phosphines complexed by borane
Ethynyl- and allenylphosphine-boranes have been prepared by addition at low temperature of borane on the free phosphine. Purification was performed by selective trapping in vacuo and the complexes were characterized by NMR and infrared spectroscopy and ma
The Ever-surprising chemistry of boron: Enhanced acidity of phosphine·boranes
The gas-phase acidity of a series of phosphines and their corresponding phosphine·borane derivatives was measured by FT-ICR techniques. BH 3 attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol-1). This acidity-enhancing effect of BH3 is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High- level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH3 association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH3 group is present. Our study also shows that deprotonation of ClCH2PH2 and ClCH 2PH2·BH3 is followed by chloride departure. For the latter compound deprotonation at the BH3 group is found to be more favorable than PH2 deprotonation, and the subsequent loss of Cl- is kinetically favored with respect to loss of Cl - in a typical SN2 process. Hence, ClCH2PH 2·BH3 is the only phosphine·borane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.
Hurtado, Marcela,Yanez, Manuel,Herrero, Rebeca,Guerrero, Andres,Juan Z. Davalos,Jose-Luis, M. Abboud,Khater, Brahim,Guillemin, Jean-Claude
supporting information; experimental part
p. 4622 - 4629
(2009/12/29)
P-H bond activation of primary phosphine-boranes: Access to α-hydroxy and α,α′-dihydroxyphosphine-borane adducts by uncatalyzed hydrophosphination of carbonyl derivatives
Primary P-phenyl and P-methyl phosphine-boranes 1 and 2 are prepared by complexation of the free phosphines with BH3 · SMe2. They are stable and can be purified by distillation. Under basic conditions, they lead selectively to secondary alkylphosphine-boranes and under neutral conditions to the corresponding mono- and bis-hydroxyphosphine-boranes 5 and 6. All these new compounds are purified by chromatography on silica gel. A competitive hydroboration induced by the decomplexation of BH3 is observed as a minor process. Conditions for the decomplexation of phosphine-borane adducts are presented.