Al/P-Based Frustrated Lewis Pairs: Limitations of Their Synthesis by Hydroalumination and Formation of Dialkylaluminum Hydride Adducts

Aluminum–phosphorus-based frustrated Lewis pairs (Al/P FLPs) are valuable reagents for the dipolar activation or coordination of small molecules or ionic compounds. They are accessible by hydroalumination of alkynylphosphines. However, as reported in this article, the application of this simple method for the synthesis of a broad variety of different compounds is limited to sterically shielded systems. Hydroalumination of Mes2PCCPh with small dialkyl- or diarylaluminum hydrides HAlR2 (R = Me, iBu, Ph) afforded unique adducts in which an HAlR2 molecule was coordinated by the Al/P FLP Mes2PC­(CHPh)­AlR2 via an Al–P and an Al–H–Al 3c bond. A new Al/P FLP was obtained with equimolar quantities of dineopentylaluminum hydride. The less shielded alkynylphosphine Ph2PCCPh yielded a hydride adduct with HAlNp2 and an alkyne adduct with HAltBu2. The latter compound resulted from triple-bond activation and had a five-membered AlPC3 heterocycle in which a CC bond was bonded to the P and Al atoms of an Al/P FLP. Both compounds were isolated in high yields by application of the appropriate stoichiometric ratios of the starting materials.铝磷基受阻路易斯酸碱对（Aluminum–phosphorus-based frustrated Lewis pairs，Al/P FLPs）是用于小分子或离子化合物偶极活化与配位的高价值试剂。该类化合物可通过炔基膦的氢铝化反应制备。然而正如本文所报道的，该简易合成方法的应用范围仅局限于受空间位阻屏蔽的体系，无法用于合成多样的不同化合物。将Mes₂PC≡CPh与小位阻二烷基或二芳基氢化铝HAlR₂（R=Me、iBu、Ph）进行氢铝化反应，可得到独特的加合物：该加合物中，HAlR₂分子被Al/P FLPs Mes₂PC(=CHPh)AlR₂通过Al-P键与Al-H-Al三中心键实现配位。使用等物质的量的二新戊基氢化铝，可得到一种新型Al/P FLP。位阻更小的炔基膦Ph₂PC≡CPh分别与HAlNp₂、HAltBu₂反应，可生成氢化铝加合物与炔烃加合物。后者由三键活化反应生成，其结构包含一个五元AlPC₃杂环，其中C=C双键与Al/P FLP中的P原子和Al原子相连。通过调控反应物的合适化学计量比，可高收率分离得到这两种化合物。