Phosphazenylphosphine: Die elektronenreichsten ungeladenen Brønsted‐ und Lewis‐Phosphor‐Basen

Abstract

Wire ntdeckten,d ass Phosphazenylphosphine (PAPs) stärkere P-Superbasen darstellen als ihre korrespondierenden Schwesinger-Phosphazen-N-Superbasen. Ein einfacher synthetischer Zugang zu diesen PR 3 -Derivaten sowie ihre Homologisierung,X RD-Strukturen, Protonenaffinitäten (PA) und Gasphasenbasizitäten (GB), berechnete wie auch experimentelle pK BH þ -Werte werden beschrieben. Im Gegensatz zu ihren N-basischen Verwandten entpuppen PAPs sich darüber hinaus als privilegierte Liganden in der Übergangsmetallchemie.T atsächlich stellen sie die stärksten bislang bekannten P-Donorliganden dar und überragen sowohle tablierte als auchkürzlicheingeführte Liganden, wie PtBu 3 oder Imidazolin-2-ylidenaminophosphine (IAPs), hinsichtlich niedrigerer elektronischer Tolman-Parameter (TEP) und grçßerer Kegelwinkel.

Palladium Complexes Based on Ylide‐Functionalized Phosphines (YPhos): Broadly Applicable High‐Performance Precatalysts for the Amination of Aryl Halides at Room Temperature

“…Comparison of the three different ligandss hows that all render highly active Pd species. Sincea ll YPhos ligands are strong donors, [24] the electronic differenceb etween the cyclohexyl and tBu groups seemst ob eo nly of minor importance. However,m arked differences in the performance can be seen in cases in which the different steric bulk of the ligandsb ecomes important or side reactions (b-hydride elimination, diarylation) play ar ole.…”

Pyridinylidenaminophosphines: Facile Access to Highly Electron‐Rich Phosphines

“…[15][16][17][18][19][20] More recently, the family of highly electron-rich phosphines with p-donor substituents has been extended by the groups of Gessner and Sundermayer using phosphoniumylidyl (R 3 P= CRÀ) and phosphazenyl (R 3 P=NÀ) groups, respectively. [21,22] Although strongly donating phosphines have great potential as ligands in coordination chemistry and catalysis, [12,23] their broad application as ligands, but more importantly in stoichiometric reactions, is often hampered by their rather difficult synthesis. In this respect, readily available, cheap phosphines like PPh 3 or P(nBu) 3 are typically used in phosphine-mediated transformations such as Wittig, [24] Mitzunobu, [25] Appel, [26] or Staudinger [27] reactions.Given these considerations, we envisaged that pyridinylidenaminophosphines (PyAPs) might be a potentially very useful family of electron-rich phosphines owing to the following beneficial factors: 1) Aminopyridines are commercially available, cheap compounds which should enable a very short synthetic route to aminopyridin-substituted phosphines; 2) the pyridinylidenamino groups can be regarded as remote carbene analogues of imidazoline-2-ylidenamino groups and should therefore similarly enhance the electron density at the phosphorus atom; 3) The selection of the R group at the pyridine N atom and the position relative to the exocyclic N should provide an easy means for stereoelectronic finetuning of the resulting phosphines (Figure 1 a).With respect to the straightforward access, it is surprising that very little is known about the synthesis of PyAPs and their properties are unexplored: Nifantyev and co-workers prepared two PyAPs from the reaction of 1-ethylpyridin-2-imine with dialkylchlorophosphines when they studied the prototropic equilibrium of phosphorylated aminopyridines (Figure 1 c).…”

“…[15][16][17][18][19][20] More recently, the family of highly electron-rich phosphines with p-donor substituents has been extended by the groups of Gessner and Sundermayer using phosphoniumylidyl (R 3 P= CRÀ) and phosphazenyl (R 3 P=NÀ) groups, respectively. [21,22] Although strongly donating phosphines have great potential as ligands in coordination chemistry and catalysis, [12,23] their broad application as ligands, but more importantly in stoichiometric reactions, is often hampered by their rather difficult synthesis. In this respect, readily available, cheap phosphines like PPh 3 or P(nBu) 3 are typically used in phosphine-mediated transformations such as Wittig, [24] Mitzunobu, [25] Appel, [26] or Staudinger [27] reactions.…”

Phosphorus‐Containing Superbases: Recent Progress in the Chemistry of Electron‐Abundant Phosphines and Phosphazenes

“…[11,102] Sundermeyer et al developed the strongest phosphine Brønsted bases known so far via attachment of Schwesinger's phosphazenyl groups at the tricoordinate P-atom. [103][104][105] The monophosphazenylphosphines 30 a-d are produced by treatment of PCl 3 with the respective phosphanimine (R 2 N) 3 P=NSiMe 3 followed by aminolyses (Scheme 12). The applied phosphanimine derivatives are synthesized via a Staudinger reaction with trimethylsilyl azide.…”

“…[9,[86][87][88]94,95] Phosphazenylphosphines 31a and 31b as well as the biphosphazenyl derivative (dma)P 6 P (32) are only accessible in their protonated form starting from (Me 2 N) 2 PCl or (Et 2 N) 2 PCl, respectively, and reaction with mono-or diphosphazenes in THF solution (Scheme 13). [103][104][105] Advantageously, the employed dialkylaminochlorophosphines contain a built-in auxiliary base; this avoids the formation of inseparable mixtures of phosphonium and ammonium salts as the products. The subsequent anion exchange reaction with NaBF 4 delivers the desired tetrafluoroborate salts in excellent yields (> 83 %, Scheme 13).…”