Hydride complexes Preparation

When irradiation of enamide 18 was carried out in the presence of a chiral metal hydride complex prepared from lithium aluminum hydride (LAH) and a chiral amino alcohol such as quinine, quinidine, A-methylephedrine,... 

Table 1. Trifluorophosphine-Hydride Complexes Prepared from Transition-Metal Salts...

Gruber, S. Neuburger, M. Pfaltz, A. Characterization and reactivity studies of dinuclear iridium hydride complexes prepared from iridium catalysts with N, P and C, N ligands under hydrogenation conditions. Organometallics 2013,32,4702-4711. 

Ruthenium hydride complexes, e.g., the dimer 34, have been used by Hofmann et al. for the preparation of ruthenium carbene complexes [19]. Reaction of 34 with two equivalents of propargyl chloride 35 gives carbene complex 36 with a chelating diphosphane ligand (Eq. 3). Complex 36 is a remarkable example because its phosphine ligands are, in contrast to the other ruthenium carbene complexes described so far, arranged in a fixed cis stereochemistry. Although 36 was found to be less active than conventional metathesis catalysts, it catalyzes the ROMP of norbornene or cyclopentene. 

Scheme 10 Ruthenium carbene complexes from ruthenium hydride species prepared in situ [18]...

A ruthenium porphyrin hydride complex was lirst prepared by protonation of the dianion, [Ru(TTP) in THF using benzoic acid or water as the proton source. The diamagnetic complex, formulated as the anionic Ru(If) hydride Ru(TTP)(H )(THF)l , showed by H NMR spectroscopy that the two faces of the porphyrin were not equivalent, and the hydride resonance appeared dramatically shifted upheld to —57.04 ppm. The hydride ligand in the osmium analogue resonates at —66.06 ppm. Reaction of [Ru(TTP)(H)(THF)j with excess benzoic-acid led to loss of the hydride ligand and formation of Ru(TTP)(THF)2. 

The reaction of CpFe(CO)2Me with R3SiH gives the bis(silyl)hydride complex 21. Photoreaction of 21 in DMF afforded the corresponding disiloxane (Scheme 52). We believe that the oxygen in the disiloxane is derived from DMF, because NMes is concomitantly formed in this reaction. It is considered that the silyl species a, which is prepared via reductive elimination of RsSiH from 21 in situ, is the active species within the catalytic cycle. Therefore, the generation of a bis(silyl)hydride species is the dormant step. We are currently studying the details of the reaction mechanism. 

The zinc hydride complex [TpBut]ZnH, the first metal hydride derivative of the type [Tp1 ]MH to be prepared, is readily synthesized by metathesis of ZnH2 with Tl[TpBut] [Eq. (28)] 80,138). 

Z,Z)-l,4-Dialkoxy-l,3-dienes can be readily prepared from propargyl ethers and molybdenum carbene complexes (equation 185)307. High stereoselectivity in this reaction may be due to the formation of stable vinyl hydride complex with the enol ether. 

Systems which fulfil these conditions are tris(2,2 -bipyridyl)rhodium complexes [63] and, more effectively, substituted or unsubstituted (2,2 -bipyridyl) (pentamethylcyclopentadienyl)-rhodium complexes [64], Electrochemical reduction of these complexes at potentials between — 680 mV and — 840 mV vs SCE leads to the formation of rhodium hydride complexes. Strong catalytic effects observed in cyclic voltammetry and preparative electrolyses are... 

However, considerable amounts of 2,3-dihydrofuran 50 and tetrahydro-furan-2-carbaldehyde 53 were present because of an isomerization process. The isomerization takes place simultaneously with the hydroformylation reaction. When the 2,5-dihydrofuran 46 reacts with the rhodium hydride complex, the 3-alkyl intermediate 48 is formed. This can evolve to the 2,3-dihydrofuran 50 via /3-hydride elimination reaction. This new substrate can also give both 2- and 3-alkyl intermediates 52 and 48, respectively. Although the formation of the 3-alkyl intermediate 48 is thermodynamically favored, the acylation occurs faster in the 2-alkyl intermediates 52. Regio-selectivity is therefore dominated by the rate of formation of the acyl complexes. The modification of the phosphorus ligand and the conditions of the reaction make it possible to control the regioselectivity and prepare the 2- or 3-substituted aldehyde as the major product [78]. As far as we know, only two... 

A chiral hydride complex, tentatively assumed to be 86, prepared by partially reacting LAH with (- )-N-methylephedrine (1 equivalent) and /V-ethylaniline (2 equivalents) was found to reduce 2-acetyl-5,8-dimethoxy-3,4-dihydronaphtha-lene (87) quantitatively to the (- )-carbinol (88) with 92% e.e. (94,95). Carbinol 88, which was obtained optically pure by recrystallization, could be converted to (/ )-(-)-2-acetyl-5,8-dimethoxy-l,2,3,4-tetrahydro-2-naphthol (89). The lat-... 

When carbon monoxide is bubbled through a methanol solution of (dppp)Pd(triflate)2 a carbomethoxy-palladium species is formed, which can undergo insertion of alkenes and hence this is a feasible alternative initiation route to chain-growth polymerisation (Figure 12.4) [13], To ensure a clean formation of the carbomethoxy species, however, exclusion of water is a prerequisite. If during the preparation water was present the formation of a palladium hydride complex (dppp)PdFT was observed (reaction (1), Figure 12.2). 

Some of the evidence for such structures comes from the change in product distribution of the butenes as a function of cyanide concentration when butadiene is hydrogenated with pentaeyanocobaltate(II) catalyst or when the a butenyl complex is reduced with the hydride complex [HCo(CN)5] . Thus 1-butene is the major product in the presence of excess CN, and major product in the absence of excess cyanide. The 1-butene presumably arises from the cleavage of a tr complex, and the 2-butene via an intermediate w-allyl complex. The Tr-allyl complexes of cobalt tricarbonyl are well-characterized and can be prepared either from butadiene and HCo(CO)4 or from methallyl halide and NaCo(CO)4 [49). 

Ikariya and Noyori et al. also reported the synthesis of new chiral Cp Rh and Cp Ir complexes (13 and 14) bearing chiral diamine ligands [(R,R)-TsCYDN and (R,R)-TsDPEN] (Scheme 5.10) these are isoelectronic with the chiral Ru complex mentioned above, and may be used as effective catalysts in the asymmetric transfer hydrogenation of aromatic ketones [42], The Cp Ir hydride complex [Cp IrH(R,R)-Tscydn] (14c) and 5-coordinated amide complex (14d), both of which would have an important role as catalytic intermediates, were also successfully prepared. 

Hydrido-carbonyl and -phosphine complexes. A series of hydride complexes [IrHCl(PPh3)2(RCOO)] (R = Me, Et, Pr, H, Ph, CF3, MeCHCl, or P-NO2-CgH4) (44) have been prepared via the protonation of [Ir(N2)Cl(PPh3)2] w ith... 

Insertion of mono- or bis(aryldiazonium) cations into the Re—bonds of the hydride complexes [ReH(CO)5 (PR3)J (PR3 = P(OEt)3, PPh(OEt)2, PPh2(OEt) =1 ) results in the formation of cationic aryldiazene complexes of the compositions [Re(HNNAr)(CO)5 (PR3) ]" or [ Re(CO)5 (PR3) 2(/r-HNNArNNH)] +. " Bifunctional diazene/diazonium derivatives which can be prepared in this way are excellent building blocks for heterobinuclear and heterotrinuclear compounds with bis(aryldiazene) bridging ligands as has been demonstrated for Re-Ru, Re-Os,... 

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