Carbene complexes phosphorus-stabilized

An aminophosphinidene complex Cp Os(CO)2 PCl(N-Tr2) was prepared by reaction of [Cp Os(CO)2] with Tr2NPCl2. As with Fischer carbenes (see Fischer-type Carbene Complexes), the nitrogen group stabilizes the electron-deficient phosphorus atom of the phosphinidene ligand. Based on a crystal structure of the ruthenium analog, there is likely... 

The phosphorus and sulfur ylides are more stable than the nitrogen and oxygen analogs (66). The former species are comprised of carbenes complexed to soft donors, whereas in the latter the carbenes are not stabilized by the adjoining hard bases. The high stability of CH2I compared to that of CHjF is at variance with the classical theory of inductive effect, but it is exactly as predicted on the basis of HSAB principle if regarded as [X complexes. 

Reuclin R, Griinstein D, Le Goff X-F, Le Floch P, Mezailles N (2010) Phosphorus stabilized carbene complexes bisphosphonate dianion synthesis, reactivity and DFT studies of 0 C 0 zirconium(IV) complexes. Dalton Trans 492-499. doi 10.1039/b915468j... 

As well as phosphorus ligands, heterocyclic carbenes ligands 10 have proven to be interesting donor ligands for stabilization of transition metal complexes (especially palladium) in ionic liquids. The imidazolium cation is usually presumed to be a simple inert component of the solvent system. However, the proton on the carbon atom at position 2 in the imidazolium is acidic and this carbon atom can be depro-tonated by, for example, basic ligands of the metal complex, to form carbenes (Scheme 5.3-2). 

The most recent development concerns the heterocyclic (amino)(ylide)carbenes AYC. Such compounds have been known for some years [203] but so far had little impact compared to their diamino stabilized relatives. Both phosphorus ylide (86) and sulfur ylide (87) stabilized AYC ligands have been generated in situ and were stabilized at suitable metal centers (Fig. 27) [204, 205]. The palladium complex 88 with an anionic (amino) [bis(ylide)]carbene is also known [206]. 

The lower stability of (phosphino)(silyl)carbene-group 13 (IIIA) element Lewis acid adducts compared to that of the corresponding imidazol-2-ylidene adducts is easily rationalized by considering the inferior ability of phosphorus to stabilize a positive charge in the ot-position. In other words, once complexed, the carbene... 

As well as phosphorus ligands, heterocyclic carbene ligands 10 have proven to be interesting donor ligands for stabilization of transition metal complexes (especially palladium) in ionic liquids. The imidazolium cation is usually presumed to... 

CO)sCr=C(OR)R complexes allenes. Photolysis of a mixture of the chromium carbene 1 and the stabilized phosphorus ylide 2 under CO gives the allene 3 in 60% > ield. Hydrolysis of 3 with HaO in ether provides the /3-substituted (Z)-enone 4. The allene 3 rearranges to a (Z)-l,3-diene (5). Pyridiniump-toluenesulfonamide is an effective catalyst for this rearrangement. 

Two independent papers were published discussing the preparation and structure of carbene-stabilized complexes of phosphorus(V) fluorides. In the first paper, cyclic and acyclic 2,2-(difluoroallylamines) (54a,b) were for the first time used as a carbene precursors in oxidative addition to substituted and unsubstituted phosphorus halides (fluorides or chlorides) to form adducts (55a-d). These octahedral and hydrolytically stable complexes were obtained in quantitative yields and were fully characterized in the solid state by single-crystal X-Ray diffraction (Scheme 17). 

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