Metal-carbonyl-hydride complex

The treatment of many of the metal carbonyls with bases affords complex polynuclear carbonylates (see (140) for a recent review). As is the case for the mononuclear carbonylate anions, hydrolysis of the anions, often with dilute acids, affords diamagnetic metal carbonyl hydride complexes (see Table VI). The majority of these complexes which are described below have not been studied by infrared and proton magnetic resonance spectroscopy their formulations are based primarily on analysis and mode of decomposition, and thus remain tentative. 

Brown has shown that metal-carbonyl-hydride complexes such as [Re(H)(CO)s] can nndergo CO substitntion by a phosphine (PBus) according to the H-atom-transfer-chain mechanism A classic type of initiation to introduce the radical species into the chain is to photolyze the metal-carbonyl dimer, which generates the reactive 17-electron metal-carbonyl monomer ... 

General Methods. Methanol used in kinetic runs was distilled from sodium methoxide or calcium hydride in a nitrogen atmosphere before use. Freshly distilled cyclohexanol was added to the methanol in the ratio 6.0 ml cyclohexanol/200 ml MeOH and was used as an internal standard for gas chromatographic (GC) analysis. Benzaldehyde was distilled under vacuum and stored under nitrogen at 5°. Other aldehydes (purchased from Aldrich) were also distilled before use. The corresponding alcohols (purchased from Aldrich) were distilled and used to prepare GC standards. All metal carbonyl cluster complexes were purchased from Strem Chemical Company and used as received. Tetrahydrofuran (THF) was distilled from sodium benzophenone under nitrogen before use. 

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. 

Molybdenum and tungsten carbonyl hydride complexes were shown (Eqs. (16), (17), (22), (23), (24) see Schemes 7.5 and 7.7) to function as hydride donors in the presence of acids. Tungsten dihydrides are capable of carrying out stoichiometric ionic hydrogenation of aldehydes and ketones (Eq. (28)). These stoichiometric reactions provided evidence that the proton and hydride transfer steps necessary for a catalytic cycle were viable, but closing of the cycle requires that the metal hydride bonds be regenerated from reaction with H2. 

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-... 

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, ... 

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.)... 

Although in m iny respects carbonyl hydride complexes mav he regarded as acids, they also show sonic similarities lo the basic hvdndcs of the main gioup metals te.g.. 

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). 

The chemistry of the metal carbonyl hydrides and metal carbonylates remained the principal research topic for Hieber until the 1960s. He mentioned in his account [25], that it was a particular pleasure for him that in his laboratory the first hydrido carbonyl complexes of the manganese group, HMn(CO)5 and HRe(CO)5, were prepared by careful addition of concentrated phosphoric acid to solid samples of the sodium salts of the [M(CO)5] anions, giving the highly volatile hydrido derivatives in nearly quantitative yield [45, 46]. In contrast to HCo(CO)4 and its rhodium and iridium analogues, the pentacarbonyl hydrido compounds of manganese and rhenium are thermally remarkably stable, and in... 

Apart from the work on binary metal carbonyls and metal carbonyl hydrides, Flieber and his school also greatly extended the field of carbonyl(ni-trosyl) metal complexes. The first compound of the general composition M(CO)x(NO)- was obtained by Robert L. Mond and Albert Wallis as early as in 1922 [67]. While studying the reactivity of Co2(CO)8 toward various substrates, they observed that slowly at room temperature, but almost instantaneously at 40°C, nitric oxide gas reacts with cobalt tetracarbonyl to form a cherry-red liquid, with the evolution of carbon monoxide . This liquid was... 

Liquid and supercritical noble gases are ideal media for studying H2 species since H2 is completely miscible under these conditions. The group VI metal carbonyl hydrides, M(CO)5(H2), and cis-Cr(CO)4(H2)2 were formed photochemically in liquid Xe/If2 mixtures. H2 and N2 complexes of a number of half-sandwich compounds were formed in supercritical Xe. These included (C Rn)M(CO)2Y, where R = H, Me, M = Mn, Re (n = 5), Cr (n = 6), and (C4H4)Fe(CO)2Y, where Y = H2 or N2. In all cases except Re, nonclassical H2 complexes were formed. ... 

A plethora of metal complexes have been stated to catalyze the hydroformylation reaction. Oxo catalysts typically consist of a transition metal atom (M) which enables the formation of a metal carbonyl hydride species. Optionally, these complexes may be modified by ligands (L). A general composition is represented by Structure 1. 

Although in many respects carbonyl hydride complexes max be regarded as acids, they also shoxv some similarities to the basic hydrides of Ihe main group metals le.g.. 

Protolysis also is a useful way of preparing Z —CO— adducts with the early transition metal centers. Typically, the early transition metal alkyls have carbanionic character and readily react with the acidic metal carbonyl hydrides. In the reaction of Cp2ZrMe2 with CpMo(CO)3H, methane is evolved and Cp2ZrMe2(OC)Mo(CO)2Cp forms (60,61). A low-frequency Z —CO— stretching frequency is observed at 1545 cm - and the formulation is confirmed by an X-ray structure determination. When this complex is placed under a CO atmosphere, a migratory insertion reaction occurs (Scheme 1) to produce a species having both f/2-acetyl and Z —CO— ligands. 

The chemistry of transition metal hydride (TMH) complexes started back in 1931 with the discovery of H2Fe(CO) by Hieber and coworkers [1]. This compound indeed contains two single iron-hydrogen bonds. In subsequent years, related metal carbonyl hydrides appeared, such as HCo(CO) [2,3]. During the same period of time, the industrially important hydrofomylation process was discovered [4,5]. Back then, it was not clear that these two findings were directly related to each other. As we know nowadays, HCo(CO)4 plays an important role in the hydrofomylation process [6], and constitutes probably the first application of TMHs in catalytic processes. 

Organometallic compounds with a 17-electron configuration are often labile toward associative ligand exchange. Radical chain mechanisms are well established for phosphine substitution on metal carbonyl hydrides (Scheme 23), the 17-electron chain carrier being in most cases non hydridic. This mechanism, however, was also shown to operate for OsH2(CO)4 via the 17-electron hydride complex OsH(CO)4 [137]. Thus, phosphine addition to the radical prevails over the dimerization, which indeed occurs in the absence of phosphine [33] (section 6.5.7), and over other possible decomposition pathways. The second step of the chain propagation process in Scheme 23, for this osmium system, is another example of atom transfer to a hydride radical (section 6.5.6). 

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