Metal-arene complex

Few compounds are known in this state, confined to Ce even so, the oxidizing power of Ce, together with the tendency for species like LiR or NaR to be reducing, makes these rare. Alkoxides [Cp3Ce(OR)] (R = Pd, BuO and [Cp2Ce(OBu )2] have been synthesized. One such route is  

The compounds of Nd, Gd-Er, Lu, and Y are stable to around 100 °C the La, Pr, and Sm compounds decompose at 0, 40 and —30 °C, respectively. The compounds of Ce, Eu, Tm, and Yb could not be isolated. This cannot be explained simply by steric effects or redox behaviour of the metals (i) compounds can be isolated with quite large early metals (Nd, Gd) but not with small ones like Yb (ii) the compounds formally involve metals in the (0) state, so metals like Eu and Yb would have been expected to be successful in supporting low oxidation states. Steric factors may have their place, as the compounds of the earlier lanthanides (La-Pr) are less stable than might be expected, possibly because the ligands may not be bulky enough to stabilize the lanthanide atom against decomposition pathways. 

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General Structural Features. The general structure of halfsandwich ruthenium(II)-arene complexes is shown in Fig. 12. The structural, stereochemical and electronic features of metal-arene complexes have been discussed (63). A typical piano-stool geometry consists of an rj6-arene occupying three coordination sites of the pseudo-octahedral complex, leaving the three legs X, Y, and Z available for coordination. The sites X and Y can be taken up by two monodentate ligands, but are more commonly... 

James et al. reported a case of product inhibition in the Rh-catalyzed enantioselective hydrogenation of N-phenyl benzaldehyde imine [37]. These authors were able to isolate the deactivated catalyst, and to obtain its X-ray structure, which showed, surprisingly, that it was a rhodium complex with the product bound through a rf-n-axene interaction (Scheme 44.5). More cases of inhibition via formation of metal arene complexes will be detailed in Section 44.5. 

The synthesis of 77 -complexes was accomplished by reacting zwitterionic phosphonio-benzophospholides such as 25 and 26 with metal-arene complexes [M(arene)(CO)3] (M=Cr, Mo, Mn ) in a non-coordinating solvent (Scheme 17). The reactions proceeded with high regioselectivity and gave no evidence for the formation of a-complexes involving phosphorus lone-pairs [32,42,43],... 

By coordinating to arenes, transition metals can facilitate ring lithiation by decreasing the electron density in the ring and acidifying the ring protons. We shall consider briefly the two most important metal-arene complexes in this regard—arenechromium tricarbonyls and ferrocenes. 

Trifluorophosphine is a very convenient ligand in metal atom chemistry to use along with other ligands, e.g., in the stabilization of metal arene complexes (Section III,B). Reaction of a mixture of PF3 and PH3 with nickel vapor yields Ni(PF3)3PH3 and Ni(PF3)2(PH3)2 but no Ni(PH3)4. Attempts to make Ni(PH3)4 lead to hydrogen evolution from the ligand during or after condensation with the nickel vapor (128). 

The synthetic potential of transition metal atoms in organometallic chemistry was first demonstrated by the formation of dibenzenechrom-ium (127). Apart from chromium, Ti, V, Nb, Mo, W, Mn, and Fe atoms each form well-defined complexes with arenes on condensation at low temperatures. Interaction has also been observed between arenes and the vapors of Co, Ni, and some lanthanides. Most important, the synthesis of metal-arene complexes from metal vapors has been successful with a wide range of substituted benzenes, providing routes to many compounds inaccessible by conventional reductive preparations of metal-arene compounds. 

Some examples of polynuclear polymeric metal arene complexes, obtained by cryosynthetic reactions from tin, titanium, vanadium, chromium, and molybdenum, are represented [202,542,543]. However, the preparative possibilities of such syntheses are not yet clear [201,202]. 

The use of transition-metal arene complexes to facilitate nucleophilic aromatic substitution features in a route to derivatives of thiosalicylic acid and hence to thioxanthone. The cyclopentadienyl iron complex of 2-chlorobenzoic acid is converted into the benzamide prior to displacement of the chloride by thiophenoxide. Photolytic decom-plexation followed by directed remote metallation of the diaryl sulfide yielded the heterocycle (Scheme 207) <2000SL975>. 

Peacock AFA, Sadler PJ (2008) Medicinal organometallic chemistry designing metal arene complexes as anticancer agents. Chem Asian J 3 1890-1899... 

Presumably, a PET is involved also in the cationic photopolymerization of epoxides with metal arene complexes [181, 182]. 

The Fischer-Hafner synthesis of sandwich compounds (33) does not permit functional groups to be incorporated into the arenes because of side reactions with the Lewis acid catalyst (Friedel-Crafts reducing conditions). This is not the case when metal atoms are used directly. Many metal-arene complexes have been identified that contain F, Cl, CH30, R2N and C02R substituents. It is reasonable to assume that polymer-bound phenyl substituents containing these functional groups will yield similar sandwich complexes. 

An interesting aspect is the application of these arene functionalised imidazolium salts as organometallic ionic liquids [139,142,143] whereby the imidazolium salt functions as the ionic liquid itself [139,143] or as the ionic liquid compatible part of the compound using the transition metal arene complex as a catalyst in biphasic applications [142],... 

Braga, D. and Grepioni, F. (1991). Effect of molecular shape on crystal building and dynamic behavior in the solid state from crystalline arenes to crystalline metal arene complexes. Organometallics, 10, 2563-9. [85]... 

The suggestion by Fischer et al. (210) that (l,3,r)-cyclooctatriene)tri-carbonylchromium is a ferrocene-type metal-arene complex (27), has been confirmed by X-ray diffraction (10). The molecular structure... 

The reactions involving the metals are usually carried out in liquid ammonia or an ether such as THF as solvent (equations 19-611 and 19-712), and can be accelerated by sonication. They involve electron transfer processes, and can also be accomplished with a metal-arene complex M Arll-, or with the metal and a trace of an arene as catalyst. The composition of the product can be determined by adding an excess of bromobenzene and analysing for PhBr and R3SnPh by GLC.12... 

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