Chromium carbonyls, nitrosyls

The chemistry of the dicarbonyl(7 -cyclopentadienyl)nitrosyl and the chloro-(i7 -cyclopentadienyl)dinitrosyl complexes of chromium, molybdenum, and tungsten [i.e., fT -CsHs)M(CO)j(NO)] and [(i7 -CsHs)M(NO)2Cl] has not been studied extensively, partly because of the various difficulties associated with their preparation. The procedures described below are of general applicability to all three metals and lead to the desired compounds in high yields. The carbonyl nitrosyl complexes are the synthetic precursors of the chloro nitrosyl complexes and so their preparation is described first. 

The spirit is to show some of the results, but also to guide users of the approach by pointing to the problems and limitations of the method. The review covers some of the newer applications in the spectroscopy of organic molecules acetone, methylenecyclopropene, biphenyl, bithiophene, the protein chromophores indole and imidazole, and a series of radical cations of conjugated polyenes and polyaromatic hydrocarbons. The applications in transition metal chemistry include carbonyl, nitrosyl, and cyanide complexes, some dihalogens, and the chromium dimer. 

This effect is unusual and, for instance, in the carbonyl and nitrosyl derivatives of chromium, molybdenum, and tungsten there is no shift of the CO or NO stretching bands in the isostructural derivatives with an increasing atomic number. 

CoNO(CO)3 Cobalt nitrosyl tri-carbonyl, 2 238, 239 Cr(CN)6K3 Potassium hexacyano-ohromate(III), 2 203 Cr(C2H302)2 Chromium(II) acetate, 1 122... 

The nitrosyl carbonyls CpM(NO)(CO)2 [M=Cr (21, 7S), Mo (57), W (19)) can be made by the action of nitric oxide on [CpCr(CO)3]2, [CpMo(CO)3] , or [CpW(CO)3] , respectively. The chromium complex undergoes a Friedel-Crafts acetylation to give (CsH4COCH3)Cr(NO)(CO)2 (21). A series of molybdenum complexes CpMo(NO)l2L [L = PPh3, P(OPh)3, py, and bipy] has been made from L and [CpMo(NO)l2]2 (57). The cationic manganese species [CpMn(NO)(CO)2], obtained by the action of nitrite and acid on CpMn(CO)3, can be precipitated as the yellow hexafluorophosphate salt (51). With sodium borohydride this affords [CpMn(NO)(CO)]2 which probably contains bridging NO groups (see below) (58). The complex [CpMn(NO)S2] is probably similar in structure... 

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