Zwitterionic 2-Phosphaethene-thiolates [(LC)P=CS(LC/P)]+ as PCS Building Blocks (LC=NHC, LP=PR3)

Abstract

The zwitterionic compounds [(L_C)P=CS(L_C/P)]⁺ (3⁺, L_C=NHC, L_P=PR₃), featuring cationic substituents at the phosphorus and carbon atoms, are synthesized as their triflate salts at a multi-gram scale from the reaction of Lewis base adducts of CS₂, namely L_C/P−CS₂ (4), with a combination of [(L_CP)₄][OTf]₄ (1[OTf]₄) and Ph₃P. The feasibility of using 3⁺ as PCS building blocks is showcased in their reactions with representative electrophiles (MeOTf) and nucleophiles (MesMgBr, Ph₃PCH₂), leading to selective functionalization of the PCS core at the S- and P-terminus, respectively. Additionally, it is reported that 3⁺ can function as ambident nucleophiles with AgOTf (2 equivalents), affording unprecedented linear coordination polymer [Ag₂(OTf)₃-μ₂:κP,κS−((L_C)P=CS(PCy₃))]⁺ (6 b), where the PCS moiety acts as a bridging ligand in transition metal complexes for the first time. Reduction of 3⁺ facilitates the cleavage of the P- and C-bound substituents leading to the formation of the [PCS]⁻ anion. Moreover, cycloaddition reactions of 3⁺ with 1[OTf]₄ are shown to selectively yield five- and eight-membered polyphosphorus heterocycles. Preliminary results suggest the possibility of activating the C−S bond in [(L_C)P=CS(L_C)]⁺, resulting in the formation of [(L_C)P=C(L_C)−P(L_C)][OTf]₂, 12[OTf]₂, which may serve as a synthon for the PCP unit in future studies.