Hydrido complexes reaction

The mechanism of reductive elimination of a hydrido alkyl complex is therefore often approached in an indirect manner. The hydrido-alkyl complex is made not by oxidative addition of the alkane but by some other route. The decomposition of the hydrido-alkyl complex to give alkane is then studied for mechanistic information. Reductive eliminations of an aldehyde from an acyl-hydrido complex, Reaction 2.7, and acetyl iodide from an iodo-acyl complex,... 

Organic groups may also provide hydrogen in forming the hydrido complex. Thus, the disproportionation of a butenylcobalt complex yielding an equimolar mixture of butenes and butadiene 21, 22) appears to involve the intermediate formation of hydrido complex (Reactions 3 and 4). 

While the parent allylcobalt complex (R = R = H) was stable in an aqueous alkaline solution, the butenylcobalt complex (R = CH3, R = H) gradually evolved an approximately equimolar mixture of butenes and butadiene, suggesting a disproportionation involving the intermediate formation of hydrido complex (Reactions 3 and 4) (20, 22). Since apparently the same butenylcobalt complex is formed by adding hydrido complex to butadiene, the reduction of allylic halides is discussed with the intimately related hydrogenation of dienes later in the text. 

Butadiene, Using butadiene as the model substrate, it has been found that the catalytic hydrogenation of dienes occurs in three steps (1) reversible addition of hydrido complex to butadiene to form a butenylcobalt complex (Reaction 3) (2) cleavage of the butenylcobalt complex by hydrido complex to form butenes and pentacyanocobaltate(II) (Reaction 4) and (3) hydrogen absorption by pentacyanocobaltate(II) to reform hydrido complex (Reaction 1) 20, 21), The butenylcobalt complex has the same properties as the complex obtained via reaction of y-methyl-allyl bromide with pentacyanocobaltate(II) (21, 22). 

These reactions give products similar to those described in 8.3.2.1. Transition-mclal hydrido complexes react with a halogen derivative of a group-IB metal to form a hydrogen halide and the required metal-metal bond ... 

Fe(0)(CO)s HgCl2 + HgCl2 Fe(II)(CO)4(HgCl)2 + COCI2 (f) A similar reaction not involving oxidation is that of a hydrido complex with HgCl2... 

Yoshida and Otsuka found that platinum(O) complexes [PtLj] (26) (a L = PEtj b L = P Prj) and rhodium hydrido complexes such as [RhHLj] (L = P Prs 33, PEts), [RhiHidr-NJlPCyslJ (34), tram-[RhH(N2)(PPh Bu2)J, and [RhH(P Bu3)J, all of which carry electron-donating alkylphosphine ligands, can catalyze the water gas shift reaction under fairly mild conditions (100-150°C CO 20 kg/cm ) (Eq. 6.32) [23, 60]. Among these complexes, [RhH(P Pr3)3] (33) was the most active catalyst precursor. Several complexes were isolated from or detected in the reaction mixture... 

When irradiated in the presence of norbornadiene and high-pressure synthesis gas, rhodium chloride is converted to a catalyst which is active for a variety of reactions. /2A/. The salt is probably converted photochemically to the rhodium norbornadiene complex 9. This dimer may undergo a consecutive photoreaction to give the monomeric hydrido complex 10, which is the actual catalyst for polymerisation, hydrogenation, and hydroformylation reactions. 

The interesting complex chemistry of rhodium has been rather neglected this is probably because most of the synthetic methods for obtaining complexes have been tedious. In general, substitutions of chlorine atoms bonded to rhodium by other ligands are slow, and products have usually been mixtures. The situation is now changing, since novel catalytic approaches to rhodium complexes have been developed.1 The catalysis in the present synthesis involves the rapid further reaction of the hydrido complex formed from l,2,6-trichIorotri(pyridine)rho-dium(III) in the presence of hypophosphite ion. 

The monosubstituted adduct offers the ready synthesis of a whole range of monosubstituted adducts (see Scheme 6) it is often possible to isolate in these reactions intermediates that are not readily obtained by alternative methods. Thus, in the reaction with halogen acids to yield the bridged hydrido complexes HOs3(CO)10X, it is possible to identify the intermediate HOs3(CO)uX complex in which the halogen functions as a one-electron donor bonding to only one metal center (158). 

A number of the heavier group 10 metallacarboranes have been synthesized and many structurally characterized. As part of their investigations of the metal complexes of the monocarbaboranes, Stone and co-workers studied the reactions of the hydrido complexes [PtH(PEt3)2(T]S-7-CB10H11)] with [AuCl(PPh3)], [HgCIPh], and [CuCl(PPh3)]4 to... 

Deinsertion is not limited to hydrido complexes since alkyl and halogeno derivatives undergo the same type of reaction ... 

Electrophiles such as halogens may cleave the transition metal-silicon (or germanium) bonds. We have already seen that in the case of the hydrido complexes they induce deinsertion reactions with retention of configuration at silicon (cf. Sect. 3.1). 

First attempts to isolate monocarbene-hydrido complexes by oxidative addition of A -(2-pyridyl)imidazolium cations to Pd° with utilization of the chelate effect of the donor-functionalized carbene ligand failed and only the dicarbene complexes such as 29 were isolated [112]. The iridium hydrido complex 30 was obtained in the oxidative addition of an W-(2-pyridylmethyl)imidazolium cation to iridium(I) (Fig. 11) [113]. This reaction proceeds most likely via the initial coordination of the nitrogen donor which brings the imidazolium C2-H bond in close proximity to the metal center. No reaction was observed with Rh under these conditions. 

Recently, the oxidative addition of C2-S bond to Pd has been described. Methyl levamisolium triflate reacts with [Pd(dba)2] to give the cationic palladium complex 35 bearing a chiral bidentate imidazolidin-2-ylidene ligand [120]. The oxidative addition of the levamisolium cation to triruthenium or triosmium carbonyl compounds proceeds also readily to yield the carbene complexes [121], The oxidative addition of imidazolium salts is not limited to or d transition metals but has also been observed in main group chemistry. The reaction of a 1,3-dimesitylimidazolium salt with an anionic gallium(I) heterocycle proceeds under formation of the gaUium(III) hydrido complex 36 (Fig. 12) [122]. 

The crystal structure of [Ni(l,10-phen)3] [Mn(CO)5]2 has been reported. The anions are trigonal-bipyramidal with only very small distortions. The reactions of [Mn(CO)g] with M3(CO)j2 (M = Fe, Ru, or Os) are extremely complex and very dependent on the conditions employed, and only Me N-[MnOs2(CO) 2] could be isolated in an analytically pure state. Acidification of these complex mixtures leads to a series of hydrido-complexes, some of which have been reported previously. New hydrides isolated include [HMnOs2-(00)32], [HMnOs3(CO)j J, and [H3MnOs3(CO)33].i ... 

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