Cyclobutadienyl complexes

This section surveys methods with emphasis on substituted cyclobutadienyl complexes. 

An improved synthesis uses Ni(0) generated by treating NiCl2 with Li napthalide anion . The Ni(0) produced by this method is kept in solution by complexation or C—H oxidative addition with the naphthalide and is more reactive toward dihalotetra-methylcyclobutene than Ni(CO)4. Thus [ij -C4(CH3)4)]NiX2 2 (X = Cl, Br) are obtained quantitatively at RT by reacting these Ni(0) solutions with dihalotetramethylcyclobutene. This method can be extended to the synthesis of other j/ -cyclobutadienyl complexes. 

Probably the first well-characterized reaction of acetylenes is the reaction of diphenylacetylene with palladium(II) chloride to give a crystalline compound (i31). It was later shown to be a 7r-allyl complex which could be converted to a tetraphenyl cyclobutadienyl complex by acid ... 

Studies of Pt alloyed with group-lB elements l indicate that hydrogenolysis may also occur via metallocyclopentadicnyl or cyclobutadienyl complexes (Figs.3.37) centered at a single atom. Complexes of type 6, see Figs.(3.37), have indeed been found as intermediates in the formation of benzene l from acetvlene and have also been proposed as intermediates for hydrogenolysis on Ir Three-carbon-... 

Metae-Acetylene tt Complexes, and Metal-Cyclobutadienyl and -Cyclopentadienyl ir Complexes... 

The photochemistry of the isoelectronic series (tj6-benzene)Cr(CO)3, (17s -cyclo-pentadienyl)MN(CO)3, and (i74-cyclobutadienyl)Fe(CO)3 all involve CO photosubstitution as their principal primary photoprocess.2 ) None of these are thought to undergo substitution of the 6-electron donor w-system with high quantum efficiency as previously suspected. The similarity in reactivity shows the value of isoelectronic relationships in these complexes, but no detailed treatment of the electronic structure of d6 (arene)M(CO)3 complexes has appeared. 

Fritch, J. R., Vollhardt, K. P. C. Cyclobutadiene-metal complexes as potential intermediates of alkyne metathesis flash thermolysis of substituted 4-cyclobutadienyl- 5-cyclopentadienylcobalt complexes. Angew. Chem. 1979,91,439-440. 

Continuing their investigations of conjugated polymers incorporating (ip-cyclopentadi-enyl)(T]4-cyclobutadienyl)cobalt complexes, Endo has discovered a new route to polythiophenes that involves reaction of organocobalt polymers with S8 (Scheme 4.15).50 When polymer 49... 

Four possible general structural types are illustrated in Fig. 3. Structure types A and B are represented by the mono- and bis(tricarbonyl-chromium) complexes (ML = Cr(CO)3) and double decker and triple decker sandwich complexes (e.g. MLx = FeCp RufCgHg) CoCp ). The benzene rings of the cyclophane ligands can be replaced by cyclopentadienyl- or cyclobutadienyl-ligands. 

The simple structures of THF-solvated 2,6-di(l-naphthyl)phenyllithium and 2,6-di(phenyl)phenyhithium have been reported to be respectively mono- and dinuclear. The solid-state structure of (DME Li)2C4(SiMc3)4 has recently been found to incorporate DME-chelated metal centres above and below a four-membered, flat cyclobutadienyl ring (within which mean O-C = 1.495 A). A similar structure has also been revealed for (DME Li)2C4Ph2(SiMe2CH2)2. The two electron reduction of 2,3-bis(dimethylsilyl)-l,l,4,4-tetramethyl-l,4-disila-1,4-dihydronaphthalene using elemental lithium affords a complex in which the two metal centres bridge an isolated C = C bond. In the same way, alkali metal ions reside above and below each of two C=C interactions in the tetrametal salt which results from the treatment of 2,3,6,7-tetrakis(trimethylsilyl)-l,l,4,4,5,5,8,8-octamethyl-1,4,5,8-tetrasila- 1,4,5,8-tetrahydroanthracene with Li(0). ... 

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