Related Experiment Video
Updated: May 22, 2026
Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)
Published on: November 22, 2016
Unexpected acidity enhancement triggered by AlH3 association to phosphines
Ana Martín-Sómer1, Al Mokhtar Lamsabhi, Otilia Mó
1Departamento de Química, Facultad de Ciencias, Módulo 13, Universidad Autónoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, 28049-Madrid, Spain.
Phosphine-aluminum hydride complexes exhibit significantly enhanced acidity compared to isolated phosphines. This acidity increase is attributed to the stabilization of deprotonated species upon aluminum hydride association.
Area of Science:
- Computational Chemistry
- Inorganic Chemistry
Background:
- Phosphines are Lewis bases.
- Aluminum hydride (AlH3) is a Lewis acid.
- Understanding adduct stability and reactivity is crucial.
Purpose of the Study:
- Investigate complexes formed between phosphines (R-PH2) and aluminum hydride (AlH3).
- Quantify the acidity enhancement in these complexes.
- Compare the acidity of phosphine-alane complexes with phosphine-borane analogues.
Main Methods:
- High-level G4 ab initio calculations were employed.
- Studied phosphines with various substituents (R = H, CH3, c-C3H5, C6H5).
- Analyzed the stabilization of deprotonated species.
Main Results:
- Phosphine-AlH3 complexes are significantly more acidic than isolated phosphines, with enhancements up to 174 kJ mol(-1).
- Acidity enhancement is substituent-dependent, reduced by phenyl group conjugation.
- Phosphine-AlH3 complexes are unexpectedly more acidic than phosphine-BH3 analogues.
Conclusions:
- Aluminum hydride association dramatically enhances phosphine acidity.
- Enhanced stability of anionic deprotonated species drives acidity.
- Aluminum trihydride offers superior stabilization compared to borane in these complexes.
Related Concept Videos
02:38Electrophilic Addition to Alkynes: Halogenation
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:24Introduction to Electrophilic Addition Reactions of Alkenes
Addition and elimination reactions can be...
01:15α-Bromination of Carboxylic Acids: Hell–Volhard–Zelinski Reaction
01:14Aldehydes and Ketones to Alkenes: Wittig Reaction Mechanism
The reaction begins with the nucleophilic addition between a phosphorus ylide and the carbonyl compound. Due to its carbanionic character, phosphorus ylide acts as a strong nucleophile and attacks the electrophilic carbonyl group. This generates a charge-separated dipolar intermediate called betaine. The negatively charged oxygen atom and...
01:19Acid Halides to Alcohols: LiAlH4 Reduction
The mechanism proceeds in three steps. First, the nucleophilic hydride ion attacks the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs as a leaving group, generating an aldehyde. A second nucleophilic attack by the hydride yields an alkoxide ion, which, upon protonation, gives a primary alcohol as...
01:12Acid Halides to Esters: Alcoholysis