Carbonyl complexes of chromium

Fig. 15.2 Structures of the simple carbonyl complexes of chromium, iron, and nickd.

Fig. IO. Carbonyl complexes of chromium and tungsten with large y.

Complexation of 100 with carbonyl complexes of chromium, molybdenum, and tungsten yielded liquid crystalline complexes lOla-c [114] (Scheme 50). All derivatives 101 melted at similar temperatures into the columnar rectangular mesophase (deduced from WAXS and SAXS measurements). However, the clearing points were strongly dependent on the metal center and increased with increasing atom number. Upon complexation, the aza crown macrocycle loses its flexibility, with the metal carbonyl fragment located above the crown leading to a cone-shaped... 

In contrast to the chalcogen-bridged complexes, no similar oxygen-bridged compounds of iron, cobalt, or nickel exist. However, we obtained such oxo or i-ol-carbonyl complexes of chromium and its homologs, as well as of rhenium. The compounds are the products of the reactions of the respective metal carbonyls with bases (VII). 

The photochemistry of transition carbonyl complexes of chromium or iron with phosphirane or l//-phosphirene ligands is studied with time-dependent DFT theory to explore the propensity of the excited metal-phosphine-carbonyl complexes to expel their ligands <2003JA3558>. The complexes of these phosphorus heterocycles show similar behavior as carbonyl complexes with the PH3 ligand and they differ mainly in their enhanced a-donating ability. The calculations point that the excited complexes prefer the expulsion of the phosphorus substituents, which can be an alternative method to demetalate transition metal complexes of organophosphorus compounds. 

The neutral complexes of chromium, molybdenum, tungsten, and vanadium are six-coordinate and the CO molecules are arranged about the metal in an octahedral configuration as shown in stmcture (3). Vanadium carbonyl possesses an unpaired electron and would be expected to form a metal—metal bond. Steric hindrance may prevent dimerization. The other hexacarbonyls are diamagnetic. 

Sulfoxide adducts of chromium, molybdenum, and tungsten carbonyls have been studied as catalysts for the polymerization of monomers such as vinyl chloride (248). Simple adducts of the type [M(CO)5(Me2SO)] may be prepared by carbonyl displacement from the corresponding hexacarbonyl. Photochemical reactions are frequently necessary to cause carbonyl displacement in this manner, many carbonyl complexes of higher sulfoxides have been prepared (255, 256). Infrared (257) and mass spectral studies (154) of these complexes have appeared, and infrared data suggest that S-bonding may occur in Cr(0) sulfoxide complexes, although definitive studies have not been reported. 

Only more recent investigations of organic isocyanide complexes of chromium are in this section, because general synthetic methods for metal isocyanide complexes, including mixed carbonyl isocyanides, and the nature of the metal-isocyanide bond are discussed in Sections... 

Subsequent to the initial work outlined above, high field H and 13C NMR studies of 11 and model compounds supported the original suggestion for its structure80-83. In terms of model compounds one of the key approaches taken was to use the metal carbonyl complexes of the homotropenylium ion system. Thus the molybdenum, 12, chromium, 13, and... 

In 1980 we published a survey (1) of our major results in this area as of late 1979. These results include extensive work on binuclear CF N PF complexes of cobalt (2,3,4,5) and nickel (6). This paper summarizes our more recent results in this area with particular emphasis on binuclear complexes of chromium, molybdenum, and tungsten as well as some new results on iron carbonyl derivatives. 

Aza analogs of cyclopentadienylmanganese tricarbonyl have also been prepared.158 160,162 Application of this sequence to pyrazole, imidazole, and 1,2,4-triazole, however, led not to aza analogs but to coordination polymers.168 A mixed manganese and chromium carbonyl complex of 2-benzylpyrrole has been prepared.163a... 

This section highlights some of the significant features of chromium(O) carbonyls and of the chemistry of this oxidation state. Further information can be found in the articles Carbonyl Complexes of the Transition Metals and Organic Synthesis using Transition Metal Carbonyl Complexes, and in the review literature. ... 

Among the types of complexes found here are formyl, acyl, alkyl, and aryl carbonyls, carbonyl cyanides," " carbonyl isocyanides and acetylides," and thiocarbonyl and seleno-carbonyl complexes." Of the greatest significance, however, are the chromium carbenes, for example, (CO)sCr=C(OR)R". This chemistry has been thoroughly reviewed " nevertheless, these compounds will be briefly discussed here. 

The oxidation of substituted dicarbonyl complexes of chromium(I) featuring the bidentate ligands dppm and dppe has been examined. Chromium(O) starting materials, Cr(CO)2(dppm)2 and Cr(CO)2(dppe)2, both with cis carbonyl configurations, were oxidized to trans cations [Cr(CO)2(dppm)2]+ and [Cr(CO)2(dppe)2]" chemical and electrochemical methods were employed. Chemical oxidation of the dppm compound proved more facile than that of the dppe analogue this had been predicted on the basis of electrochemical studies. The dicarbonyl hydride, [Cr (CO)2(dppm)2H]+, was isolated from the oxidation reaction of [Cr(CO)2(dppm)2] with O2/HCIO4, while the same reaction conditions oxidized the neutral dppe complex to the cation. 

Carbonyl Complexes of the Transition Metals Chromium Inorganic Coordination Chemistry Dinuclear... 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

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