C‐Silyl‐N,N‐dialkyl‐N′‐arylformamidines: Synthesis and Reactions with Phosphorus(III) Chlorides

Abstract

A method for the synthesis of new C‐silyl‐N,N‐dialkyl‐N′‐arylformamidines was developed. These derivatives were formed by the deprotonation of N‐(trimethylsilyl)formamidinium salts to give the corresponding N‐trimethylsilyl carbenes followed by a 1,2‐migration of the silyl group. The reactions of C‐silylformamidines with phosphorus(III) chlorides were then studied. The reactions between chlorodiphenylphosphane and the C‐silylformamidines readily afforded C‐phosphanylformamidines in high yields. The reactions of dichlorophosphanes and C‐silylformamidines yielded previously unknown phosphanes that feature two formamidine substituents. In the reaction with phosphorus trichloride, the sterically least encumbered formamidine gave a stable two‐coordinate compound through the formation of an intermediate tris(phosphane). The reactions of the sterically more encumbered formamidines led to the substitution of only two chlorine atoms to give a chlorophosphane or benzazaphosphole. The structures of key compounds were proven by X‐ray crystal structure analyses.

Dichlorophosphoranides Stabilized by Formamidinium Substituents

“…In our previous work, we have shown that silylformamidine 4a reacts with phosphorus trichloride in a 2 : 1 ratio producing chlorophosphine 10 [7].…”

“…Recently, we have developed a method for the synthesis of C-trimethylsilyl-N,N-dialkyl-N′arylformamidines and studied their reactions with phosphorus trichloride and chlorophosphines. A set of chlorophosphines featuring two formamidine substituents were isolated as stable compounds [7]. We assumed that dichlorophosphines featuring the formamidine substituents can be prepared by this method as well.…”

Polydentate Phosphane Ligands Featuring N,N,N’‐Trialkylformamidines

“…Thus, the reaction of silylformamidine 3 c with phosphorus trichloride in a 2 : 1 ratio exhibited a signal at δ p =45 ppm in 31 P NMR, that we assigned to chlorophosphane 16 . Recently, an analogous chlorophosphane was separated and characterized with δ p =31 ppm [10,14] . The signal attributed to chlorophosphane 16 disappeared in 4 days at room temperature and the signal of the final diazaphospholium salt 13 c (δ p =155 ppm) emerged (Scheme 6).…”

“…An attempt to introduce three formamidine substituents at the phosphorus atom failed. Instead, a stable two‐coordinate compound was isolated [10] Recently phosphanes featuring N,N,N’‐trialkylformamidine substituents were used for preparation of Ru and Rh catalysts, unfortunately their preparation was not described [11] . Ligands of this type have been used to prepare complexes with a set of transition metals [12] .…”