New Reactivity Patterns in 3H‐Phosphaallene Chemistry [Aryl‐P=C=C(H)‐tBu]: Hydroboration of the C=C Bond, Deprotonation and Trimerisation

Abstract

3H-Phosphaallenes,R ÀP=C=C(H)CÀR' (3), are accessiblei namultigram scale on an ew and facile route and show af ascinating chemical reactivity.B H 3 (SMe 2)a nd 3a (R = Mes*, R' = tBu) afforded by hydroboration of the C=C bonds of two phosphaallene molecules an unprecedented borane (7)w ith the Ba tom bound to two P=Cd ouble bonds.T his compound represents an ew FLP based on aB and two Pa toms. The increased Lewisa cidity of the Ba tom led to ad ifferent reaction course upon treatment of 3a with H 2 B-C 6 F 5 (SMe 2). Hydroboration of aC =Cb ond of af irst phosphaallene is followed in at ypicalF LP reaction by the coordination of as econd phosphaallene molecule via BÀCa nd PÀ Bb ond formation to yield aB P 2 C 2 heterocycle (8). Its BÀP bond is short and the B-bound Pa tomh as ap lanar surrounding. Treatment of 3a with tBuLi resultedi nd eprotonation of the b-C atom of the phosphaallene (9). The Li atom is bound to the Pa tom as demonstrated by crystal structure determination, quantum chemical calculations and reactions with HCl, Cl-SiMe 3 or Cl-PtBu 2 .T he thermally unstable phosphaallene PhÀP=C=C(H)-tBu gave au nique trimerics econdary product by PÀP, PÀCa nd CÀCb ond formation.I tc ontains aP 2 C 4 heterocycle and was isolated as aW (CO) 4 complex with two Pa toms coordinated to W(15).

B-substituted group 1 phosphides: synthesis and reactivity

“…The nucleophilicity of phosphides, and thus their reactivity, may be influenced by the electronic properties of the phosphorus atom. Since the combination of phosphorus as a Lewis base (LB) and the boron atom as a Lewis acid (LA) is a well explored field of frustrated Lewis pairs (FLPs) for the activation of small molecules, 1,15 we decided to study the effect of the boron atom on the reactivity of group 1 phosphides. Since the boron atom as a LA should interact with the lone electron pair of the phosphorus atom of the phosphides via the B ← P interaction, the built-in boron in the structure of group 1 phosphides should influence their nucleophilicity.…”