Synthesis, crystal structures, and quantum chemical calculations of trialkyl-substituted 1λ3,3λ3,5λ3-triphospha dewarbenzenes

Abstract

This work has involved the reaction of kinetically stable 2-tert-buty-lλ3-phospha-alkyne, tBu–C[tbnd]P, with dichloro(dialkylamino)arsines, in which the isolated products were characterized by spectroscopic methods; additionally, the results of X-ray structure analyses were confirmed by quantum chemical calculations using Gaussian 98 molecular modeling software. The arsenic component of the starting material is completely lost, probably as a precipitate of insoluble “arsenic(I) chloride,” and unusual oligocycle 2,4,6-tri-tert-butyl-3-chloro-1-dialkylamino-1λ5σ4,3λ3σ3,5λ3σ2-triphosphabicyclo[2.2.0]hexa-1,5-diene (1) – an ylide with an unusually long P–Cl bond (245.5 p.m.) – could be isolated. From these reactions, compounds 1a to 1d differing by their substituents at nitrogen were isolated as deep red, cuboid-shaped single crystals. X-ray structure analyses reveal molecules which are characterized by an ylidic and a regular P–C double bond of almost equal length [P1⊕–C2⊖av.172.2 p.m., P5–C6av.169.6 p.m.]. In addition to these two characteristic features the average bond length P3–C2 is found to be considerably shortened to a value of 172.7 p.m., whereas the adjacent phosphorus–chlorine bond P3–Cl1 is strongly elongated to 245.5 p.m.