Unusual Phosphoryl Donor Properties of OP(MeNCH₂CH₂)₃N

The title compound (4) in which transannular bridgehead−bridgehead bonding is absent, reacts with phosphoryl and silyl chlorides to give the isolable salts [ZOP(MeNCH₂CH₂)₃N]Cl where Z = Ph₂P(O), 6(Cl); PhP(O)Cl, 7(Cl); ¹/₂PhP(O), 8(Cl); MeSiCl₂, 14(Cl); and SiCl₃, 15(Cl). Spectroscopic evidence for [ROP(MeNCH₂CH₂)₃N]⁺ cations, where R = H, 16; Me, 17; Et, 18, and the isolation of the regioisomeric cations [OP(MeNCH₂CH₂)₃NR]⁺ (R = Me, 19; Et, 20; n-Pr, 21; n-Bu, 22) as their iodide salts is also reported. In the presence of Cl₃PO, PCl₅, or SOCl₂, 4 gives the [ClP(MeNCH₂CH₂)₃N]⁺ cation (26) which is also formed when P(MeNCH₂CH₂)₃N is oxidized with C₂Cl₆. The more sterically hindered analogue of 4, namely OP(i-PrNCH₂CH₂)₃N (28) (whose synthesis is reported herein), reacts with MeI and EtI to afford the isolable salts [OP(i-PrNCH₂CH₂)₃NR]I [R = Me, 29(I); Et, 30(I)]. Cations 29 and 30 display ¹H and ¹³C NMR spectra at room temperature that are consistent with a quaternization-induced rigidity of the cage that renders the (CH₃)₂CH methyl groups inequivalent on the NMR time scale. Acyclic OP(NMe₂)₃ reacts with [R₃O]BF₄ (R = Me, Et) giving the corresponding isolated salts [MeOP(NMe₂)₃]BF₄ and [EtOP(NMe₂)₃]BF₄. Reaction of HCl with OP(NMe₂)₃ afforded sublimable (Me₂N)₃PO·HCl which represents the first protonated phosphoryl species structured by X-ray crystallography. The transannular bond lengths in 6(Cl) and 26(PCl₆) [1.948(5) Å and 1.934(8) Å, respectively] are within experimental error of the corresponding link in the [HP(MeNCH₂CH₂)₃N]⁺ cation [1.967(8) Å].