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Carbonylvanadium Halfsandwich Complexes: Preparation, Structure, and 51V-NMR Spectra of Derivatives of η5-C5H5V(CO)4
Hoch, Martin,Rehder, Dieter
, p. 1541 - 1552 (2007/10/02)
The reactions between V(CO)6 and alkylcyclopentadienes Cp'H yield a large number of halfsandwich complexes of the composition Cp'V(CO)4 I ( open Cp derivatives) and III (anellated Cp derivatives).The compounds are formed as by-products.The reactivity of the cyclopentadienes leading to the type III complexes drastically increases as the reactions are performed with Cp'Br (Cp = indenyl, fluorenyl).With acenaphthylene, azulene, and guaiazulene double-halfsandwich complexes 2 are obtained, which are present in solution in several meso forms.In the acenaphthylene complex one CO per Cp'V(CO)4 moiety can be replaced photochemically by PPh3.Doubly alkylated derivatives of type I form 1,2- and 1,3-isomers.The two diastereomeric pairs of enantiomes are observed in cases where there are two elements of chirality *N*, C5H5V(CO)2NN*>.Three centres of chirality *> yield four diastereomers.The differentiation of the isomers is performed on the basis of the 51V-NMR spectra. ?(51V) values span the range between -1534 and -1118 ppm , relative to VOCl3. η7-C7H7V(CO)3 (-1485 ppm) falls within this range, while shielding is clearly higher in 6-toluene-V(CO)4>(+) (-1660 ppm) than in the η5-Cp complexes.MeC(O)C5H4V(CO)4 (16), which can be obtained by Friedel-Crafts acylation, is reduced to the alcohol and converted into the oxime and phenylhydrazone.Force constants and band positions of the Cp'(CO)3(13CO) isotopomers of the type III complexes have been calculated.The crystal and molecular structures of C5H5V(CO)4 (refined determination) and 16 have been obtained from single crystal X-ray analyses.
