Amino group combined P/Ge and P/Sn Lewis pairs: synthesis and dipolar addition reactions to alkyne and aldehyde molecules

Abstract

Amino group combined P/Ge-based frustrated Lewis pairs (FLPs) Ph₂PN(R)GeCl₃ (R = 2,6-iPr₂C₆H₃ (1), 2,4,6-Me₃C₆H₂ (2), and C₆H₁₁ (3)) and Ph₂PN(2,6-iPr₂C₆H₃)GeMe₃ (4) as well as P/Sn-based FLP Ph₂PN(2,6-iPr₂C₆H₃)SnMe₃ (5) were prepared and utilized for reactions with alkyne and aldehyde molecules. Compounds 1–3 each reacted with MeO₂CCCCO₂Me to give zwitterionic cyclic vinyls [Ph₂PN(R)GeCl₃](MeO₂CCCCO₂Me) (6–8) and compound 1 reacted with HCCCO₂Me to give the similar compound [Ph₂PN(2,4,6-Me₃C₆H₂)GeCl₃](HCCCO₂Me) (9). Compound 4 reacted with RCCCO₂Me to afford acyclic vinyls 2,6-iPr₂C₆H₃NP(Ph₂)C(R)C(CO₂Me)GeMe₃ (R = CO₂Me (10), H (11)) and 5 reacted with MeO₂CCCCO₂Me to give 2,6-iPr₂C₆H₃NP(Ph₂)C(CO₂Me)C(CO₂Me)SnMe₃ (12). The reactions of 1 with CH₃CH₂CHO and 1,4-(CHO)₂C₆H₄ were also investigated and yielded novel zwitterionic OCPNGe five-heteroatom cycles [Ph₂PN(2,6-iPr₂C₆H₃)GeCl₃][CH(CH₂CH₃)O] (13) and [Ph₂PN(2,6-iPr₂C₆H₃)GeCl₃][p-(OCH)C₆H₄CHO][Cl₃GeN(2,6-iPr₂C₆H₃)PPh₂] (14). Compounds 1–14 were characterized by NMR (¹H, ¹³C, and ³¹P) and CHN elemental analysis, of which 1, 7, and 10–14 were further studied by X-ray crystallography. The reactions of 4 (or 5) with RCCCO₂Me to produce 10–12 present a novel way of obtaining the germyl (or stannyl) and iminophosphoranyl co-substituted vinyls.