Synthesis and structures of 1-phosphaindene derivatives with five- and four-coordinate phosphorus atom

The reactions of 1,1,1,2,3-pentachloro-1-phosphaindene (1) with phenylacetylene and catechol were found to lead to the regioselective formation of the addition product, 1,1,2,3-tetrachloro-1-(2-chloro-2-phenylvinyl)-1-phosphaindene (6), and spirophosphorane, 1,2-bis{(2′,3′-dichloro-2H-2λ⁵-spiro[benzo[d][1,3,2]dioxaphosphole-2,1′-phosphaindene]-2-yl)oxy}benzene (13). The hydrolysis of compound 6 proceeds through the intermediate formation of (Z)-2,3-dichloro-1-(2-chloro-2-phenylvinyl)phosphaindene 1-oxide (9) and affords the P—C bond cleavage product, [(Z)-2-chloro-2-phenylvinyl]-{(2-[(Z)-1,2-dichlorovinyl]phenyl}phosphinic acid (10). The structures of compounds 1, 6, and 13 were determined by X-ray diffraction. Compound 6 is the first example of monocyclic phosphoranes containing the phosphorus atom in a nearly ideal trigonal-bipyramidal configuration with an antiapicophilic (diequatorial) arrangement of the five-membered ring at the base. Quantum chemical calculations showed that this structure is favorable due to conjugation effects. Compound 13 has a planar chirality in the crystal (space group P2₁).