Synthetic routes to novel N-phosphorylated 1,2,4-triazolium salts have been developed. Treatment of the specified salts with strong base produces new stable Nphosphorylated 1,2,4-triazol-5-ylidenes, which add Se in two stages (first at the carbene carbon and then at phosphorus) and rearrange to C-phosphorylated triazoles with heating. The capacity of such N-phosphorylated triazol-5-ylidenes to act as bidentate ligands toward transition-metal centers has also been demonstrated; in particular, the formation of two dinuclear silver carbene complexes is described herein. The structures of one representative carbene and of one carbene complex were determined by an X-ray study.
Dinuclear silver(I) complexes with bridging Nphosphorylated
azolylidene ligands have been synthesized.
Subsequent transfer of the ligands to other group 11 metal
centers (Cu, Au) has been accomplished, highlighting the
usefulness of the silver complexes as an easy to handle, air- and
moisture-stable source of these ligands. Preliminary results
indicate that dinuclear copper(I) complexes with Nphosphorylated
imidazolylidene ligands display notable
catalytic efficiency in nitrene transfer reactions
The deprotonation of N‐di‐tert‐butylphosphanyl‐N‐aryl‐N′‐diisopropylformamidinium salts led to a new type of stable acyclic N‐phosphanyl‐diaminocarbene (PADC). Carbenes 8a–8d were separated as single compounds. The molecular structure of 8c was determined by X‐ray diffraction analysis. The PADC 8 possess an optimal substitution pattern at the nitrogen atoms, and the N–Ccarbene–N bond angle is 120.7°. Structural changes near the carbenic carbon atom, such as substitution of phenyl with mesityl, phosphanyl with selenophosphoryl, or the diisopropylamino group with 2,2,6,6‐tetramethylpiperidino, rendered them unstable. The PADCs underwent N,C‐phosphorus shifts to afford new C‐phosphanylformamidines.
Complexes of palladium(II) with newly disclosed, N-phosphanyl acyclic diaminocarbene ligands are synthesized for the first time and structurally characterized. The ligands coordinate palladium(II) in a chelating fashion, yielding remarkably stable complexes which can be stored without special precautions in the solid state. Related palladium(II) complexes with an isomerized chelating ligand, formed upon 1,2-migration of the phosphanyl group from the nitrogen to the adjacent carbon atom, have also been isolated in some instances and structurally characterized. The complexes efficiently act as precatalysts for Suzuki coupling reactions of aryl chlorides, where their productivity compares favourably with that of related palladium complexes with acyclic diaminocarbene ligands. In addition, the complexes show a distinct tendency to form as the byproduct the reductive homocoupling product of aryl chloride. This observation, together with ad hoc performed control tests, suggests that Pd colloids are involved in the formation of catalytically competent species.
The first annelated bis-and mono-3H-1,3azaphosphole ferrocene sandwich compounds have been synthesized from aminoferrocenes, and their X-ray structures are compared to those of their selenide-protected PSe analogues, showing net discrepancies both in metallocene backbone conformation and in fused-ring planarity.
Using
DFT and ab initio calculations, we demonstrate that noncyclic
formamidines can undergo thermal rearrangement into their isomeric
aminocarbenes under rather mild conditions. We synthesized the silylformamidine,
for which the lowest activation energy in this process was predicted.
Experimental studies proved it to serve as a very reactive nucleophilic
carbene. The reactions with acetylenes, benzenes, and trifluoromethane
proceeded via insertion into sp, sp2, and sp3 CH bonds. The carbene also reacted with the functional groups, such
as CHO, COR, and CN at double or triple bonds, displaying high mobility
of the trimethylsilyl group. The obtained silylformamidine can be
considered as a latent nucleophilic carbene. It can be prepared in
bulk quantities, stored, and used when the need arises. Calculation
results predict similar behavior for some other silylated formamidines
and related compounds.
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