Transition metal hexacarbonyls

A. W. Ehlers and G. Frenking,/. Chem. Soc., Chem. Commun., 1709 (1993). Theoretical Studies of the M—CO Bond Lengths and First Dissociation Energies of the Transition Metal Hexacarbonyls CrfCO), MofCO) and W(CO)j. 

D. A, Kariuki and S. F. A. Kettle, Inorg. Chem., 1978, 17, 141. Raman spectra of mixed crystals of transition-metal hexacarbonyls. 

Table 7. Linewidths, Electric Nuclear Quadrupole Moments and Shift Differences [M04] - [M(CO)6] for Transition Metal Hexacarbonyls...

Transition metal hexacarbonyls such as W(CO)e, Mo(CO)e, and Cr(CO)6 are important precursors in orga-nometallic chemistry [38-41]. Because of their high... 

It is, however, for the transition metals themselves that DFT has proven to be a tremendous improvement over HF and post-HF methods, particularly for cases where tlie metal atom is coordinatively unsaturated. The narrow separation between filled and empty d-block orbitals typically leads to enormous non-dynamical correlation problems with an HF treatment, and DFT is much less prone to analogous problems. Even in cases of a saturated coordination sphere, DFT methods typically significantly ouqierform HF or MP2. Jonas and Thiel (1995) used the BP86 functional to compute geometries for the neutral hexacarbonyl complexes of Cr, Mo, and W, the pentacarbonyl complexes of Fe, Ru, and Os, and the tetracarbonyl... 

While the first transition metal carbene complex was reported in 1964134, the first cyclopropylcarbene complex salt [(CO)5Cr=C(chromium hexacarbonyl, followed by tetramethylammonium bromide135. Subsequent reaction with trimethyloxonium fluoro-borate gave methoxycarbene complex (CO)5Cr=C(OMe)(c-Pr) (equation 62)136. 

It is worthwhile to note that in the reaction of the group 6B metal hexacarbonyls with the azide anion to provide isocyanatometallates, a concerted mechanism is proposed based on kinetic parameters which involves a three-centered transition state (7), and that the activation enthalpy is some 22.6 kJ lower for tungsten than for chromium (52). This reactivity sequence correlates with an increase in M-CO bond distances going from chromium to tungsten hexacarbonyl (53-55). 

The study of species in which ethylene is coordinated to transition metal centres holds great interest in areas of catalytic and polymerization chemistry (7). The bonding of the ethylene ligand to the metal centre in such species has been compared to that of the dihydrogen complexes described above (14,15,22). Photolysis of chromium hexacarbonyl, Cr(CO)6, in conventional solvents in the presence of dissolved ethylene gas is known to lead initially to a highly labile species in which one CO ligand is replaced by ethylene. Further photolysis leads to a more stable compound which contains two ethylene ligands trans to each other across the metal centre (25), equation 3. The conventional synthesis is experimentally difficult the two photochemical... 

In numerous experiments we have found that liquid NH3 can replace CO or other ligands in metal carbonyls or their derivatives and also that NH3 can become an additional ligand bonded to a transition metal. Thus, the hexacarbonyls of Group VIB can form pentacarbonylammine or tri-carbonylammine derivatives, depending upon the temperature conditions (92) ... 

The cyanocarbonylchromates(O) [Cr(CO)5CN]- and cis-[CifCOMCN) ] -, which are formed by the oxidation of [Cr l,(CO)s]2-with aqueous solutions of KCN or with (CN)2 or ICN have been discussed earlier (55, 56). Further studies have shown that the reaction of metal carbonyls or their derivatives with solutions of KCN in liquid NH3 is a most advantageous method for the synthesis of new cyanocarbonyl metalates of transition metals, since, in liquid NH3, alkali cyanides are not subject to solvolysis, and also since the broad temperature range of -78 to +120°C may be employed. Thus, we have been able to obtain quantitative yields of the tricyano-tricarbonyl metalates (0)/ac-[M(CO)3(CN)3]3 (M = Cr, Mo, W) by direct reaction of the hexacarbonyls (21) ... 

Dichlorodinitrosylmolybdenum and tungsten have been prepared by the reaction of the appropriate hexacarbonyl with nitrosyl chloride in dichloromethane.1 The corresponding dibromo derivatives have been prepared by a similar reaction with nitrosyl bromide.2 These are the only synthetic routes to these compounds they are rapid (3 hours) and convenient. The corresponding chromium compounds are unknown. This method is a general route to transition-metal nitrosyl halide... 

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