Half-sandwich complexe

In the context of pyridin synthesis from alkynes and nitriles homogeneously catalyzed by (cyclopentadienyl)cobalt complexes (Eq. 13), it was found that electron-withdrawing groups on the cyclopentadienyl ring significantly increase the activity [63]. During the screening of various cobalt half-sandwich complexes... 

The remarkable 19-electron molybdenum half-sandwich complex Mo(r 5-C5HPh4)(CO)2L2 (L2 = 2,3-bis(diphenylphosphino)maleic anhydride) (44) was prepared from [Mo(r)5-C5HPh4)(CO)3]2 and L2 and its structure in the solid state determined [65]. The average distance from molybdenum to the ring ligand is... 

Electron rich half-sandwich complexes — metal bases par excellence. H. Werner, Angew. Chem., Int. Ed. Engl., 1983, 22, 927-949 (170). 

Dihydro-lH-l,2-azaboroles derive from cyclopentadiene by the isoelectronic replacement of a C=C group by a BN moiety ". The neutral rings react in xs boiling Fe(CO)j without any other solvent to form red-brown iron-dihydro-1,2-azaborolyldi-carbonyl dimers as their cis and transisomers in 56% yield, or with CojfCOg in petroleum ether at 60-80°C to the half-sandwich complex (dihydro-1,2-azaborolyl)Co(CO)2 (40%). The CO group can easily be substituted by olefins ... 

Some half-sandwich complexes with dihydro-l,2-azaborolyl ring ligands have been described, too ... 

However an unexpected new cyclic ruthenium phosphorus ylide half-sandwich complex 42 has been obtained by reaction of 41 with dichloromethane as solvent [79]. The cyclisation involves a C-Cl activation and corresponds to the incorporation of the methylene moiety in the P-C bond and to the ortho-metal-lation of one phenyl of the phosphine. An other novel unusual phosphonium ylide ruthenium complex 43 has also recently been described [80]. 

Ferrocene and Half Sandwich Complexes as Catalysts with Iron Participation... 

Abstract The unique and readily tunable electronic and spatial characteristics of ferrocenes have been widely exploited in the field of asymmetric catalysis. The ferrocene moiety is not just an innocent steric element to create a three-dimensional chiral catalyst enviromnent. Instead, the Fe center can influence the catalytic process by electronic interaction with the catalytic site, if the latter is directly coimected to the sandwich core. Of increasing importance are also half sandwich complexes in which Fe is acting as a mild Lewis acid. Like ferrocene, half sandwich complexes are often relatively robust and readily accessible. This chapter highlights recent applications of ferrocene and half sandwich complexes in which the Fe center is essential for catalytic applications. 

Catalysis by Iron in Half Sandwich Complexes 2.1 Fe(O)- and Fe(I)-Catalysts... 

The studies described in Sects. 2.1 and 2.2 showcase the high synthetic potential of Fe half sandwich complexes in the field of catalysis and should pave the way for additional exciting developments in the near future. 

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