Metal hexacarbonyls

Mikulski CM, Harris N, Iaconianni FJ, et al. 1980. Group-VI metal hexacarbonyl reactions with diisopropyl methylphosphonate. Inorganic Nuclear Chemistry 16(2) 79-89. 

The catalyst system is not poisoned by thiophene, for Cr(C0)sSR2 species readily revert to Cr(C0)3 in the presence of CO. Similarly, the group 6b metal hexacarbonyls have also been shown to be active in the presence of NaSH (2l). However, this catalyst system... 

Major differences were noted between the systems derived from Fe(CO)c and M(CO) (M = Cr, Mo, and W) with respect to the effect of the base concentration on the reaction rate. Thus in the case of the catalyst system derived from Fe(CO)5 tripling the amount of KOH while keeping constant the amounts of the other reactants had no significant effect on the rate of H2 production (11). However, in the case of the catalyst system derived from W(CO)g the rate of production increased as the amount of base was increased regardless of whether the base was KOH, sodium formate, or triethylamine (12). This increase may be interpreted as a first order dependence on base concentration provided some solution non-ideality is assumed at high base concentrations. Similar observations were made for the base dependence of H2 production in catalyst systems derived from the other metal hexacarbonyls Cr(CO) and Mo(CO) (12). Thus the water gas shift catalyst system derived from Fe(CO)5 has an apparent zero order base dependence whereas the water gas shift catalyst systems derived from M(CO)g (M - Cr, Mo, and W) have an approximate first order base dependence. Any serious mechanistic proposals must accommodate these observations. 

A further useful reaction sequence, reported by Aumann [219], is based on the Diels-Alder reaction of 2-pyranylidene complexes with enamines (Figure 2.36). Retro-Diels-AIder reaction of the initially formed 3-oxabicycIo[2.2.2]octan-2-ylidene complex leads to elimination of metal hexacarbonyl and formation of a substituted cyclohexadiene. Although this sequence can also be performed with the corresponding carbonyl compounds (2//-2-pyranones), these normally... 

The ligand behavior of the arsenic-based compound 9 (Figurel3) structurally related to P4S3, is of interest in this context. It was shown that 9 reacts with group VI metal hexacarbonyls under UV irradiation to give the adducts nCH3C(CH2As)3]j M(CO)5 n (N = 1,... 

The number of such independent terms in a metal hexacarbonyl is 13 (10 if we discard quartic terms containing the distortion of some CO group raised to an odd power), in addition to the three harmonic force and interaction constants. Thus the number of physical quantities exceeds the number of parameters that may, with the available data, be fitted to Eq. (18). There is the further possibihty that the observed frequencies are distorted by interaction with solvent in a way that is not adequately compensated for by Eq. (18). The classical amplitude of a triply excited oscillator is greater than that for one that is only singly excited, and so jostling of solvent and solute molecules, and variability and asymmetry in the solvent sheath, may become important. This may explain the observation that binary and more especially ternary i.r. bands are considerably broader than are fundamentals in the same solvents. 

Both mononuclear [M(CO)5(C2H2N4)] and binuclear complexes [ M(CO)5 2(C2H2N4)] are formed when unsubstituted tetrazine (C2H2N4) is added to a photoirradiated solution of the metal hexacarbonyl [M(CO)6] (M = Cr, Mo, W) in ethanol. For the mononuclear complexes two signals were obtained in the H NMR spectra while in the binuclear complexes only one signal was found (76ZN(B)1489). 

Replacement of one of the CO groups of a metal hexacarbonyl by another ligand reduces the symmetry from Oh to C4v. 

The Electronic Structures of Octahedral Metal Complexes. I. Metal Hexacarbonyls and... 

Electronic Spectra of d6 Metal Hexacarbonyls and Hexacyanides. A. Metal Hexacarbonyls-—The electronic spectrum of Cr(CO)6 in the vapor phase shows two intense absorption bands at 35,780 and 44,480... 

Magnitude op the d-d Splitting Parameter A for Different Metal Hexacarbonyls and Hexacyanides... 

Corporation and the Climax Molybdenum Co. for We thank Dr. C. S. Naiman for allowing us to see his providing samples of the metal hexacarbonyls, and to theoretical work on FefCNje3- prior to publication. 

Acetyl migration occurs in the reaction of Tl(MeCOCHCOMe) with Pms Pd(PhCN)2Cl2, which yields an A-acetyl-jS-ketoimine chelate (17).471 Mossbauer data indicate that Sn(MeCOCHCOMe)2 has a trigonal pyramidal geometry with one oxygen atom from each acetylacetonate ligand in an axial position.472 The equatorial lone electron pair is both stereochemically and chemically active. Complexes in which the metal acts as the donor rather than the acceptor are formed by photolysis of Sn(MeCOCHCOMe)2 and Group VI metal hexacarbonyls in THF. The products, Sn(MeCOCHCOMe)2M(CO)5 (M = Cr, Mo, W), evidently contain tin-metal bonds. The low... 

Metal Hexacarbonyls. Strohmeier and Gerlach (68) noted that the ultraviolet irradiation of chromium, molybdenum, or tungsten hexacarbonyls caused photodissociation into M(CO)B and CO. In donor solvents, the M(CO)6 was stabilized forming a yellow product whereas in cyclohexane the colorless M(CO)a was reformed (69). 

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). 

Table 10. Products obtained from ethylene over group VI metal hexacarbonyls...

A nonpressure synthesis may be used the treatment of metal ethoxy-carbonyl pentacarbonyl with dry hydrogen chloride releases the metal hexacarbonyl cation. 

---