Phosphaaluminirenes: Synthons for Main Group Heterocycles

• Published in: Journal of the American Chemical Society Vol. 141; no. 42; pp. 16971 - 16982
• Main Authors: Liu, Liu Leo, Zhou, Jiliang, Cao, Levy L, Stephan, Douglas W
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 23.10.2019; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; COORDINATION CHEMISTRY; ALUMINUM; SILYLENE; AROMATICITY; CHEMICAL-SHIFTS; CARBON-MONOXIDE; ALUMINACYCLOPROPENE; BUILDING-BLOCKS; RAY CRYSTAL-STRUCTURE; PHOSPHORUS-COMPOUNDS
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b09330

The phosphaaluminirenes HC­[(CMe)­(NDipp)]2Al­[C­(R)P] (Dipp = 2,6-i-Pr2C6H3, R = tBu or adamantyl) 2 and 3, featuring an unsaturated three-membered AlCP ring, have been synthesized as crystalline solids via a [1 + 2] cycloaddition reaction of the aluminum­(I) complex HC­[(CMe)­(NDipp)]2Al (1) with phosphaalkynes. Computational investigations infer three-centered 2π-electron aromaticity of the AlCP rings. Compound 3 is readily protonated by tBuOH to induce a ring-opening σ-bond metathesis, giving an alumina-substituted P-hydrogeno phosphaalkene 4. Remarkably, the high strain of the AlCP ring of 3 allows for facile ring enlargement in reactions with CyNC, bis­(diisopropylamino) cyclopropenylidene (BAC), elemental Se, Ph2CO, PhCHCHCOPh, and PhCN at room temperature. These furnish a series of unprecedented main group heterocycles 5–10 with the CP unsaturated bonds remaining intact. The mechanisms are considered in light of thorough density functional theory (DFT) calculations.