The Low Basicity of Phosphabenzenes: First Examples of Protonation, Alkylation, and Silylation Reactions

Abstract

Strong yet gentle: Where triflate reagents fail, carborane‐based sources of H+, CH3+, and [R3Si]+ electrophiles add to phosphabenzenes preferentially at the P atom rather than C (see picture).

Recent Developments in the Chemistry of Pyridyl-functionalized, Low-coordinate Phosphorus Heterocycles

“…27 Thus, the reaction of 5 with triflic acid will lead exclusively to protonation of the nitrogen atom of the pyridine moiety, even with an excess of CF 3 SO 3 H. This was confirmed crystallographically for the salt 5¢HOSO 2 CF 3 (7) (Figure 7). 28 The result of the X-ray crystallographic study shows the structural difference between the phosphinine and the pyridine heterocycle.…”

Reactivity of Aromatic Phosphorus Heterocycles – Differences Between Nonfunctionalized and Pyridyl‐Substituted 2,4,6‐Triarylphosphinines

“…As expected and as observed previously, the addition of a slight excess of CF 3 SO 3 H to 1 in CD 2 Cl 2 does not lead to any change in the 31 P{ 1 H} NMR spectrum, because the pK b value of the phosphinine is too high for the formation of the corresponding phosphininium salt 3 (Scheme 2). [20,21] Scheme 2. Reactions of 2,4,6-triarylphosphinines with CF 3 SO 3 H.…”

Differences in the η1-ligating properties of 2,4,6-tritertiarybutyl-phosphabenzene, and 2,4,6-tritertiarybutyl-1,3,5-triphosphabenzene,

“…Recently, we showed for the first time that both 1 and 2 could be protonated, alkylated and silylated at phosphorus using appropriate electrophilic reagents having halogenated carborane anions [15], despite the extremely weakly basic and poor nucleophilic nature of both ring systems [10,[15][16][17]. We now report on the unexpected and strikingly different r-ligating ability of the two rings 1 and 2 toward platinum metals.…”

“…We now report on the unexpected and strikingly different r-ligating ability of the two rings 1 and 2 toward platinum metals. Although the coordination chemistry of several monophosphinine ring systems has been widely studied [10,12], only a few r-complexes of 2 have been structurally characterised [15,18]. We now describe the syntheses and single-crystal X-ray structural characterisation of the 2,4,6-tritertiarybutylphosphabenzene complexes trans-[PtCl 2 (PEt 3 )(g 1 -PC 5 ].…”