Dihydrogen carbon monoxide complex

Ogata H, Mizogushi Y, Mizuno N, et al. Structural studies of the carbon monoxide complex of [NiFe]hydrogenase from Desulfovibrio vulgaris Miyazaki F suggestion for the initial activation site for dihydrogen. J Am Chem Soc. 2002 124(39) 11628-35. 

The reaction of OsHCl(CO)(P Pr3)2 with HC1 gives the dichloro derivative OsCl2( n2-H2)(CO)(PIPr3)2.35 In solution, this complex is stable under argon for a matter of days. However, the dihydrogen unit is highly activated toward heterolytic cleavage, as demonstrated by deprotonation with NaH and by reactions with carbon monoxide and /ert-butyl isocyanide, which afford OsHCl(CO)L(P Pr3)2 (L = CO, r-BuNC) and HC1. 

In the case of the tantalum complexes 100, reversible hydrogen migration may occur at room temperature in the presence of carbon monoxide, or at 70°C with dihydrogen or dimethylphosphino ethane to afford complexes 106, 107, and 108, respectively.92,95 In contrast, the phosphametallacycle remains intact when 100 is treated with halogenated reagents such as CH3X (X = Cl, Br, I).92,95... 

We have already reviewed the activation of alkenes, alkynes, and carbon monoxide towards nucleophilic attack. The heterolytic splitting of dihydrogen is also an example of this activation it will be discussed in Section 2.10. The reaction of nucleophiles with silanes co-ordinated to an electrophilic metal can be regarded as an example of activation towards nucleophilic attack (Figure 2.28). Complexes of Ir(III) and Pd(II) give t.o.f. for this reaction as high as 300,000 mol.mol. fh"1. 

In addition to catalyzing hydroformylation, the platinum SPO complexes are excellent hydrogenation catalysts for aldehydes (as already demonstrated by the side products of hydroformylation), in particular, in the absence of carbon monoxide. Further, in ibis process, the facile heterolytic splitting of dihydrogen may play a role. The hydrogenation of aldehydes requires the presence of carboxylic acids, and perhaps the release of alkoxides from platinum requires a more reactive proton donor than that available on the nearby SPO. For example, 4 hydrogenates 2-methylpropanal at 95 °C and 40 bar of H2 to give the alcohol, with a TOF of 9000 mol moN h (71). 

The reaction is first order in rhodium catalyst concentration, first order in dihydrogen pressure and has an order of minus one in carbon monoxide pressure. In our Scheme 6.1 this would be in accord with a rate-determining step at the end of the reaction sequence, e.g. reaction 6. Since the reaction order in substrate is zero, the rhodium catalyst under the reaction conditions predominates as the alkyl or acyl species any appreciable amount of rhodium hydride occurring under fast pre-equilibria conditions would give rise to a positive dependence of the rate of product formation on the aUcene concentration. The minus one order in CO suggests that the acyl species rather than the alkyl species is dominant under the reaction conditions. The negative order in CO is explained [29,30] by equilibrium 7. The saturated complex loses CO, and subsequently the unsaturated 16-electron species reacts with H2 to give aldehyde and rhodium hydride (reaction 6). 

M(C0)5X , and H2 in the presence of a general base to provide anionic metal hydrides. This process was shown to be first-order in both metal complex and dihydrogen and was not inhibited by addition of carbon monoxide. Consistent with the rds in catalysis being formation of the metal hydride intermediate, the metal catalyzed reaction of RX/CO2/H2 to provide HCOOR is not inhibited by CO. The well-established formation of metalloformate, M(C0)s02CH", from M(C0)5H and CO2 is followed by a less facile process involving the reaction of the metalloformate with RX. This latter reaction is first-order in both metal complex and alkyl halide and is inhibited by carbon monoxide. 

In solution at room temperature, the alkenyl compounds 127 evolve into mixtures of five products. However, under carbon monoxide atmosphere, they lead to the cyclic heterocarbene derivatives 129, probably, via the intermediates 128. Treatment of tetrahydrofuran solutions of 129 with LiCH3 at room temperature produces the deprotonation of the central CHPh carbon atom of the hetero-metalacycle and the formation of 130. In benzene as solvent, complexes 130 react with molecular hydrogen to yield the corresponding azabutadienes 132 and the well known dihydride-dihydrogen complex OsH2(il2-H2)(CO)(P Pr3)2 (131) [49]. 

J. R. Fisher, A. J. Mills, S. Sumner, M. P. Brown, M. A. Thomson, R. J. Ihiddephatt, A. A. Frew, L. Manojovic-Muir, K. W. Muir, Reversible displacement of dihydrogen by carbon monoxide in binuclear platinum complexes. Characterization of binuclear carbonyl complexes of platinum(I), Organometalhcs 1 (1982) 1421-1429. 

The 7 -allyl rhodium complex, Rh( -C3H5)3, can be incorporated into an acidic zeolite with the formation and loss of propene, and several species formed in subsequent reactions with dihydrogen, hydrogen chloride, carbon monoxide, and phosphines, have been investigated [270, 287]. The same intrazeolite triallyl complex has been studied as an alkene hydrogenation catalyst [288],... 

The hydroformylation or oxo reaction, or oxo synthesis discovered by Otto Roelen and patented in 1938 (1) is the addition of carbon monoxide and dihydrogen to an olefin double bond in the presence of a transition metal complex as the catalyst. The discovery of the reaction regarding the cobalt catalyzed Fischer-Tropsch reactions. Roelen s observation that ethylene, H2, and CO were converted into propanal, and at higher pressures, diethyl ketone, marked the beginning of hydroformylation catalysis (2). The term of hydroformylation relates to the formal addition of hydrogen and a formyl group to the olefin substrate. 

Preparative work and spectroscopic investigations have shown that under carbon monoxide and dihydrogen pressure at elevated pressure precursors of the hydroformylation catalysts form an equilibrium mixture of carbonyl complexes. 

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