Metals carbonyl hydrides

Already in the early experiments involving treatment of iron tetracarbonyl with ethylenediamine hydrate, we observed that upon acidification of the solutions an extraordinarily intense repugnant smell was released (3). I can still clearly remember the day when I, together with my co-workers Leutert and Vetter, at the Heidelberg Institute, was able to freeze out a volatile water-clear liquid from the decomposition of the ethylenediamine- 

We recognized that the isoelectronic hydrides H2Fe(CO)4 and HCo(CO)4 behaved as pseudo-nickel tetracarbonyls (hydride displacement principle). Moreover, manganese pentacarbonyl hydride (VII, 11), on which we later worked in Munich, was similar in many physical properties to iron pentacarbonyl, leading us to postulate a Drawing-in of the hydrogen 

After our discovery of the metal carbonyl hydrides, other authors (32) pointed out their acidic character in aqueous solution. Potentiometric titrations by Reppe and later by us, showed that in water HCo(CO)4 possesses an acidity (pWa l) comparable to that of nitric acid. The first ionization stage for H2Fe(CO)4 corresponds approximately to that of acetic acid (33), whereas the pentacarbonyl hydrides HM(CO)5 (M = Mn or Re) (VII, 11, 26) are hardly acidic at all. The redox potentials of the cobalt and iron carbonyl hydrides were also measured (33). 

We later prepared the more stable phosphine-substituted mononuclear carbonyl hydrides such as FICo(CO)4 nLn and FHVfn(CO)5 L n= 1 and 2  

L = P(C6H5)3, P(OC6H5)3 etc.] (38, 39). Interestingly, although HV(CO)6 is not known, we were able to isolate the hydride HV(CO)5P(C6H5)3 (40). In contrast to the unsubstituted carbonyl hydrides, we found that the acidity of the aqueous solutions of these compounds was considerably weakened. Recently phosphine-substituted ruthenium carbonyl hydrides, e.g., H2Ru(CO)2(PR3)2 have been reported (31). 

The relationship between metal carbonyl hydrides and dihydrogen complexes of metal carbonyl derivatives has been further explored.The interactions of d ML5 fragments with H2 have been studied by EHMO methods,and the structures and some reactions of n -H2 complexes of Cr, Mo, W, Fe and Co carbonyl derivatives examined.Intramolecular ligand rearrangements in [M(C0)5H] anions (M = Cr or Mo) have been investigated using variable temperature n.m.r. A twist mechanism that provides a pathway for intramolecular axial-equatorial CO exchange is favoured.The catalytic role of these 

Comparison of second-order rate constants for halide displacement from n-BuBr by H derived from anionic metal carbonyl hydrides established the order of reactivity [WH(C0)s] [CrH(C0)s] [RuH(C0)i,] [FeH(C0)(,l. Low temperature n.m.r. studies of 

The synthesis of several new heteronuclear hydrido carbonyl clusters have also been described. Reaction of PPH[FeH(CO)9] with M(C0)5THF (M = Or, Mo or W) yields [FeM(y-H)(CO)9] in which the H atom is presumed to bridge the Fe-M bond. Other Fe containing anionic heterometallic clusters reported in 1984 include [Fe0s3H(C0)i3] and [FeaNKy 3-H) (y-CO) (CO) e Both 

Three independent reports have been published citing evidence for the formation of Cr(C0)5(H2) from Cr(C0)G and H2 under differing reaction conditions. 

Both eis-Cr(C0)i,(H2)2 and Cr(C0)i,(H2) were also tentatively identified in a photolysis study.A neutron diffraction study on PhitP[W2H(CO)io] has revealed W-H and W-W distances of 1.897(5) and 3.340(5) A respectively, and a W-H-W angle of 123.4°. Both the molybdenum anion [Mo2H(CO)io] and the mononuclear anions [MH(C0)s] (M = Cr, Mo or W) have been used for the selective reduction of organic carbonyl compounds.The mixed hetecobimetallic 

A low yield of 0sitH3(C0)n(N0) also results from this reaction. A new Rhi2 metallic array of idealised D2d symmetry was found in [Rhi2H2(U3 C0)(M-C0)9-(00)13], which results from the treatment of [Rhu,(00)25] with CF3C00H, and [Ni30Pt6(CO)it8H6-n] (n = 5 or 4) ions have been prepared and characterised for use as molecular models for cherry crystallites.  

Demartin, M. Manassero, M. Sansoni, L. Garlaschelli, S. Martinengo, and F. Canziani, J. Chem. Soc., Chem. Common., 1980, 903. 

---

A few metal carbonyl hydrides can be prepared by direct reaction of the metal with CO and H2, with the following being a typical reaction ... 

Systematic studies of the thermodynamic and kinetic acidity of metal hydrides in acetonitrile were carried out by Norton et al. [10, 11]. A review of the acidity of metal hydrides presents extensive tabulations of pKa data [12] only a few of the trends will be mentioned here. Metal hydrides span a wide range of pKa values considering only metal carbonyl hydrides shown in Table 7.1, the range exceeds 20 pfCa units. As expected, a substantial decrease in acidity is... 

Table 7.1 pKa values of neutral metal carbonyl hydrides in CH3CN. 

Darensbourg et al. have conducted extensive studies of the nucleophilic reactivity of a series of anionic metal carbonyl hydrides [24], which have been used for the reduction of alkyl halides [25], acyl chlorides [26], and ketones [27]. The... 

Several anionic metal carbonyl hydrides stoichiometrically convert acyl chlorides to aldehydes. The anionic vanadium complex [Cp(CO)3VH] reacts quickly with acyl chlorides, converting them to aldehydes [44]. Although no further reduction of the aldehyde to alcohol was observed, the aldehydes reacted further under the reaction conditions in some cases, so a general procedure for isolation of the aldehydes was not developed. 

Hydrogen forms an extensive series of compounds with the metal carbonyls, and the nature of the H bonding within these complexes has been a point of debate for a considerable period. Both the chemistry and structure of metal carbonyl hydride compounds have been exten-... 

The interaction of water with the metal carbonyls of osmium and ruthenium has proved to be a very facile route to the metal carbonyl hydrides (86). The corresponding oxygen derivative, H20s3(C0)90, has not been identified in these reactions. There is a wide range of products, summarized in the following chemical equations ... 

Metal-Hydrogen Bond Enthalpy Contributions. Metal Carbonyl Hydrides... 

The simple metal carbonyl hydride species HRh(CO)4 has been sought by many researchers including Hieber [97], Chini [98], Vidal [99] and Whyman [100]. Vidal was able to obtain evidence for new MIR bands when Rh4(CO)i2 was subjected to ca. 1400 bar CO/H2 pressure, and Whyman was able to corroborate this finding at ca. 400 bar CO/H2 pressure. 

Methyl acetate probably originates from the reaction of methanol with the intermediate cobalt-acyl complex. The reaction leading to the formation of acetaldehyde is not well understood. In Equation 8, is shown as the reducing agent however, metal carbonyl hydrides are known to react with metal acyl complexes (20-22). For example, Marko et al. has recently reported on the reaction of ri-butyryl- and isobutyrylcobalt tetracarbonyl complexes with HCo(CO) and ( ). They found that at 25 °C rate constants for the reactions with HCo(CO) are about 30 times larger than those with however, they observed that under hydroformylation conditions, reaction with H is the predominant pathway because of the greater concentration of H and the stronger temperature dependence of its rate constant. The same considerations apply in the case of reductive carbonylation. Additionally, we have found that CH C(0)Co(C0) L (L r PBu, ... 

Sterically hindered alkenes can be hydrogenated at —50°C using triflic acid and a hydride donor.483 In addition to Et3SiH, transition-metal carbonyl hydrides such as HM(CO)3Cp (M = W, Mo, Os) and HMn(CO)5 (M = Mn, Re) are suitable hydride donors. Alkenes that form tertiary carbocation on protonation are hydrogenated in high yields (90-100%), whereas yields for styrenes are lower (50-60%). Alkynes are converted to the corresponding saturated hydrocarbon by using HW(CO)3Cp in combination with triflic acid.484... 

In this chapter we have examined examples of polynuclear metal carbonyl complexes as well as simple metal carbonyl hydrides. Consider now the polynuclear carbonyl hydride complex, H,Os,(CO)i2- Rationalize the formulation of this species. From your application of the 18-electron rule, what can you say about the structure of this molecule1 How is it similar to or different from the complex Os COln shown in Figure 5.9 (See Churchill M. R. Wasserman, H. J. Iticrg, Chen. 1980, 19, 2391-2395.)... 

Jonas, V., Thiel, W., 1996, Theoretical Study of the Vibrational Spectra of the Transition-Metal Carbonyl Hydrides... 

Of the monomeric metal carbonyl hydrides [HMn(CO)s,H2Fe(CO)4,HCo(CO)4], only HMn(CO)s has been analyzed crystallographically 10 4S). The lack of results for H2Fe(CO)4 and HCo(CO)4 is probably related to the fact that the compounds are thermally unstable. The neutron diffraction analysis of HMn(CO)s by La Placa and co-workers45) produced a Mn—H distance of 1.60(2) A. This result, together with the earlier measurement of the Re—H distance of 1.68(1)A in K2ReH9, provided conclusive proof that M—H distances in metal hydride complexes are normal (i.e., are consistent with the known covalent radii of the elements), and not anomalously short as suggested by some researchers (this controversy is reviewed in Refs. 1—3). 

---