Hydridocarbonyl complexes

Although, between 20 and 60°C, [Re(CO)g]+ behaves similarly to the manganese compound, giving the hydridocarbonyl complex HRe(CO)5, at -78°C, we were able to isolate and characterize, the extremely unstable Re(CO)5CONH2 (112) ... 

Interestingly, treatment of the mononuclear 1//-diphosphirene complex 106 with 2 equiv of trifluoromethanesul-fonic acid at -78 °C led to the diphosphirenylium binuclear complex 162. This species was not formed by the protolysis of 161. Instead, protonation of an iron center occurred leading to the hydridocarbonyl complex 163. Compound 162 was quantitatively converted into the neutral binuclear complex 161 by exposure to diisopropylamine. The tricoordinate phosphorus atom in 161 imparts ligand properties to the cage. This was substantiated by the synthesis of red trinuclear complex 164 when 161 was combined with an excess of [Fe2(CO)9] in THF at room temperature (70% yield) (Scheme 52) <1999CC1535>. 

Catalytic hydrogenations over CojfCOjg (using Hj and CO) or with stoichiometric quantities of preformed hydridocarbonyl complex CoH(CO)4 are useful for the partial selective reductions of polycyclic aromatic compounds. Isolated benzene rings are not affected. Naphthalene is reduced to tetralin, at 200°C under a pressure of 20 X 10 kPa and anthracene to 9,10-dihydroanthracene (99%). The substituted phenanthrene nucleus is stable under these conditions as illustrated by hydrogenation of perylene 1 and pyrene 2. ... 

The KOH-alcohol reduction is a general one for the preparation of hydrido or hydridocarbonyl complexes, but detailed mechanistic studies are lacking. 

There is an interesting report of carbonyl substitution in the reaction between phosphorus pentafluoride and MeSiH2Co(CO)4 (114, 7). There is evidence that PF5 is reduced by the silicon-hydrogen bonds yielding HCo(CO)4, fluorosilane, and trifluorophosphine the latter subsequently displaces carbon monoxide from the hydridocarbonyl complex. 

Similarly, reaction with vinyl ethers generates less active Fischer carbene species. Grubbs and coworkers have prepared and characterized a series of these complexes, via metathesis of the corresponding alkene with G1 or G2 (e.g. Scheme 2.34). While these species can still perform metathesis, they are poorly active, and require high temperatures at which there are competing decomposition reactions to yield hydridocarbonyl complexes. 

This reaction (Eq. 4.11) produces the unusual formyl ligand, which is important in CO reduction to MeOH (Section 12.3). It is stable in this case because the 18e complex provides no empty site for rearrangement to a hydridocarbonyl complex. 

In transition metal hydridocarbonyl complexes, Fermi resonance interaction occurs between the carbonyl and metal-hydride stretching vibration. Hence, a significant shift of the CO stretching frequency may be observed on deuteration of a complex, e.g. 30cm , and anomalous vm-h/i m-d ratios are observed instead of being [Pg.414]

A somewhat related problem is the nature of the bridged carbonyl group between two metal centers. Obvious correlations with organic ketonic behavior in general provide difficulties. In general nucleophilic attack by OR- (R = H or Me) does appear to occur at the carbon center. For R = Me, stable M- C02R complexes may often be isolated, but for R = H, transfer of hydrogen to the metal with elimination of C02 occurs readily, to yield the hydridocarbonyl. 

Some notable examples of these rules are tris (triphenylphosphine) -halogenorhodium(I) studied by Osborn et al. (2) and hydridocarbonyl-tris(triphenylphosphine)rhodium(I) reported by O Connor et al. (3). A common feature of these two complexes is that the coordinative unsaturation is caused by dissociation of phosphines and that M-H bonds... 

A hydridocarbonyl compound, trans-[RhH(CO)L2] (Complex 7, L = P(iso-Pr)3), prepared from RhHL3 and methanol, reacts with water in pyridine producing H2 (> 70%) and Complex 6a which could be confirmed by its crystalline BPh4 salt. The formation of Complex 6a from Complex 7 probably involves the intermediate Complex 5a (see Scheme I). 

Adding CO to Complex 3 gives the white, hydridocarbonyl HIrCl2 (CO)(PCy3)2. The equivalent phosphines (P-31 NMR), single KIr-Cl),... 

With respect to the derivatives of metal carbonyls, the substituted metal carbonyls of the VIB Group (e.g., Mo(CO)apya), the halogenocar-bonyls of iron, ruthenium, iridium, and platinum, the hydridocarbonyls H2Fe(CO)4 and HCo(CO)4 discovered in 1931 and 1934, and the nitrosyl carbonyls FelCOj NOjg and Co(CO)3NO were the most important (/). The known anionic CO complexes were limited to [HFe(CO)J and [Co(CO)J-. For studies of substitution reactions of metal carbonyls at this time, work was almost totally limited to reactions involving the classical N ligands such as NH3, en, py, bipy, and phen. 

The structures of the isoelectronic hydridocarbonyls H2Fe(CO)4 and HCo(CO)4 were the central theme of numerous studies over a period of many years after their discovery by Hieber. Because of their very similar physical characteristics, these complexes were considered to be pseudo nickel tetracarbonyls (H2Fe = HCo = Ni) in which, even then, the... 

If this reaction of KNH2 and CO in liquid NH3 is extended to coordi-natively bonded CO in cationic carbonyl complexes, instead of the formation of formamide, carbonylcarbamoyl compounds of the type M(CO) —CONH2 result, and instead of H2 and K.OCN (or CO(NHK)2), hydridocarbonyls and NH4OCN [or CO(NH2)2] are formed. 

The homogeneous complex RhCl(dpm)3 acts also as hydroformylation catalyst [159], Upon illumination of the catalytic photosystem Ru(bpy) +/ascorbic acid/RhCl(dpm)3- in the presence of ethylene and carbon monoxide, propionaldehyde is obtained as photoproduct. Similarly, propene yields the hydroformylation product butyraldeyde. The facts that no hydrogenation products are produced in this assembly, and that hydridocarbonyl-tris-(diphenylphos-phinobenzene-3-sulphonate) rhodium(I), RhHfCOXdpm) -, substitutes RhCl(dpm)3- as catalyst in the photosystem to yield the hydroformylation products at similar efficiency, suggest that the homogeneous catalyst RhClfdpmJj -is transformed into a new catalytic species under CO. A possible route for the interconversion of RhCl(dpm)3 into the hydroformylation catalyst is provided in Scheme 4. 

Hydridocarbonyls and carbonyl complexes containing C, N, O or S donor ligands are covered in later sections of this review. 

Isomerization of terminal olefins by HCo(CO)4, or more likely by the coordinatively unsaturated HCo(CO)3 in equilibrium with it, proceeds rapidly at room temperature. The isomerization is catalytic but the HCo(CO)3 4 is consumed irreversibly by simultaneous hydroformylation, which removes 2 mol of the hydridocarbonyl for each mole of reacted olefin. The competition between these two reactions (as well as the bimolecular decomposition of the hydrocarbonyl to and Co2(CO)g) depends on the conditions of the experiment. The results obtained with 4-methyl-1-pentene under one atmosphere of N2 are shown in Fig. 1 and the catalytic cycle, which rationalizes the stepwise isomerization, is shown in Fig. 2. In Fig. 2 HM represents either HCo(CO)4 or HCo(CO)3. In experiments on the isomerization of PhCD2CH=CH2 with HCo(CO)4 in the presence of unlabeled p-allyltoluene both PhCI>=CHCH3 and labeled 4-propenyltoluene were found in the products indicating hydrogen transfer between olefins via complexed HM. The... 

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