A 2‐Phosphonio‐Substituted 1‐Phospha‐1‐alkene: Resonance between P^III Alkene and P^V Ylide

Abstract

How realistic is a resonance of the type A ↔ B ↔ C? This question could be answered from the NMR spectroscopic data of 1, the first representative of the 2‐phosphonio‐substituted 1‐phospha‐1‐alkenes. A considerable amount of the resonance structures B and C was found in the actual structure of 1 (R = 2,4,6‐tBu3C6H2).

Nickel Complexes Containing New Carbon−Phosphorus Unsaturated Ligands: First Examples of Phosphavinylidene−Phosphorane [R3PCPR‘] and Phosphavinyl Phosphonium [C(H)(PR3)P(R‘)]+Ligands

“…Interestingly, the coordination chemistry of ylides, which is mainly limited to η 1 -C-coordination, is dramatically different than that of phosphaalkenes. There are also examples of σ 4 -phosphorus analogues of diphosphaallenes, i.e., (R 3 PCPR 3 ) and diphosphaallyls ([(R 3 P)HCPR 3 ] + ), as well as mixed σ 2 ,σ 4 -diphosphaallyls [(R 3 P)HCPR‘] + . − However, there are no examples of mixed σ 2 ,σ 4 -diphosphaallenes (R 3 PCPR‘). Of these σ 4 -diphosphaallene and diphosphaallyl compounds, only the σ 4 ,σ 4 -diphosphaallenes (R 3 PCPR 3 ) have been investigated as ligands, exhibiting a preferential η 1 -C-coordination as in the R‘ 2 CPR 3 compounds due to the strongly carbanionic character of the ylidic carbon …”

A Stable P‐Heterocyclic Carbene

“…We therefore designed an original synthetic approach: a formal [3+2] cycloaddition of the transient diphosphaallylic cation 2 with a dipolarophile (Scheme 2). Addition of silver trifluoromethanesulfonate or gallium trichloride to a dichloromethane solution of the readily available phosphaalkene 1, [29,30] at À78 8C, in the presence of a large excess of acetonitrile (30-45 equiv) afforded the desired salts 3 a and 3 b, respectively. They were isolated after recrystallization as white crystals (see Experimental Section).…”

Protonation of P-Stereogenic Phosphiranes: Phospholane Formation via Ring Opening and C–H Activation

“… 22 This reactive intermediate could undergo intermolecular O–H activation of water to yield byproduct 7 , 18 in competition with intramolecular C–H activation of an ortho t -Bu group to give cations 3 – 4 . Such cyclophosphination is a common process in Mes*P chemistry, as with the phosphenium ion [Mes*PSMes*] + , 23 and in protonation of the phosphaalkene Mes*P=CH 2 , which yielded a phospholanium cation similar to 3 – 4 , via the proposed phosphenium intermediate [Mes*PCH 3 ][OTf]. 24 …”