Cycloocta-1,5-diene complexes rhodium

The mass spectra of the cycloocta-1,5-diene complexes C5H5MC8H12 (M = Rh, Ir) both show the molecular ion as the base peak. The rhodium complex exhibits several metastable peaks and a detailed fragmentation scheme has been proposed. The molecular ion fragments by several... 

The complex has enjoyed relatively little use in organic synthesis. For iridium-catalyzed homogeneous hydrogenation of alkenes, Crabtree s iridium complex ((1,5-Cycloocta-diene)(tricyclohexylphosphine)(pyridine)iridium(I) Hexafluoro-phosphate) is generally preferred, although this readily prepared Ir complex is active. It is more reactive than its rhodium counterpart in the catalytic isomerization of butenyl- to allylsilanes. ... 

An example of a rhodium(I) complex with a tridentate phosphine is shown in Figure 2.16 it is formed by the usual route, reaction of the phosphine with [RhCl(cycloocta-1,5-diene)]2. 

The mechanistic basis of iridium-complex-catalyzed enantioselective hydrogenation is less secure than in the rhodium case. It is well known that square-planar iridium complexes exhibit a stronger affinity for dihydrogen than their rhodium counterparts. In earlier studies, Crabtree et al. investigated the addition of H2 to their complex and observed two stereoisomeric intermediate dihydrides in the hydrogenation of the coordinated cycloocta-1,5-diene. The observations were in contrast to the course of H2 addition to Ms-phosphine iridium complexes [69]. 

Aryltrimethylstaimanes arylate aldehydes in the presence of a cationic rhodium complex, [Rh(cycloocta-l,5-diene)(MeCN)2]+, yielding secondary alcohols.114... 

Asymmetric isomerization of allylamines.1 The enantiomeric rhodium(I) complexes with the ligands cycloocta-1,5-diene (cod) and ( + )- or ( - )-binap, Rh ( + )-... 

Interestingly, the propensity of the boron atom to engage in secondary interactions was also examined by Jacobsen. The interaction of the rhodium complex 60 with a model substrate, namely 5-hexen-l-amine, was monitored by 1H NMR spectroscopy.62 The stronger upheld shifts of the alkene resonances compared to those observed upon coordination of the same substrate to the related boron-free salt [Rh(cod)(DIOP)][ClC>4] (cod = cycloocta-1,5-diene) were attributed to a cooperative behavior of the boron and metal centers of 60 that concomitantly interact with the nitrogen atom and alkene moiety, respectively (Figure 20). 

The rhodium A-heterocyclic carbine complex [Rh(IMes)(COD)] [IMes = A,A -bis(2,4,6-trimethylphenyl)imidazol-2-ylidine COD = cycloocta-1,5-diene] catalyses the 4 + 2 + 2-carbocyclization of 1,6-enynes (191) to carbocycles [(192) and (193)] (Scheme 54).226 Computational and experimental evidence of a new reaction pathway for the diastereospecific intermolecular rhodium-catalysed 4 + 2 + 2-carbocyclization (g) reactions of 1,6-enynes with r-components has been reported.227... 

In order to eliminate the possibility for in situ carbene formation Raubenheimer et al. synthesized l-alkyl-2,3-dimethylimidazolium triflate ionic liquids and applied these as solvents in the rhodium catalyzed hydroformylation of l-hejEne and 1-dodecene [178]. Both, the classical Wilkinson type complex [RhCl(TPP)3] and the chiral, stereochemically pure complex (—)-(j7 -cycloocta-l,5-diene)-(2-menthyl-4,7-dimethylindenyl)rhodium(i) were applied. The Wilkinson catalyst showed low selectivity towards n-aldehydes whereas the chiral catalyst formed branched aldehydes predominantly. Hydrogenation was significant with up to 44% alkanes being formed and also a significant activity for olefin isomerization was observed. Additionally, hydroformylation was found to be slower in the ionic liquid than in toluene. Some of the findings were attributed by the authors to the lower gas solubility in the ionic liquid and the slower diffusion of the reactive gases H2 and CO into the ionic medium. 

The strong tendency of cycloocta-1,5-diene to form chelate complexes is emphasized by the observation that rhodium(III) chloride reacts with... 

The most effective catalysts for enantioselective amino acid synthesis are coordination complexes of rhodium(l) with cycloocta-1,5-diene (COD) and a chiral diphosphine such as (i ,i )-l,2-bis(o-anisylphenylphosphino)ethane, the so-called DiPAMP ligand. The complex owes its chirality to the presence of the trisubstituted phosphorus atoms (Section 5.12). 

In metal complexes the ligands may occupy different positions around the central atom. Since the ligands in question are usually either next to one another (cis) or opposite each other (trans), this type of isomerism is often referred to as cis-trans isomerism. Cis-trans isomerism is very common for square planar and octahedral complexes. Consider the square planar complexes shown in structures [5-1H5-4]. Cis-trans isomerism arises from the relative position of the ethylene ligands. Therefore, [5-1] and [5-3] are cis forms and [5-2] and [5-4] are trans forms, respectively. Norbornadiene-palladium dichloride [5-5] and rhodium (Ti-cycloocta-1,5-diene) chloride [5-6] can exist only in the cis structure because of the chelate nature of the diene. 

Via intermediates Cycloocta-1,5-diene from -1,3,5-triene ring via rhodium complexes... 

The synthesis of phenethyltetraphenylcyclopentadiene allowed the preparation of the chiral complex Rh C5Ph4CH(Me)Ph (cod). Chiral-annulated cyclopentadienyl ligands afforded the preparation of complexes such as ( -cycloocta-l,5-diene)[ j -l,2,3-triphenyl-4-methyl-7-isopropyl-lH-indenyl]rhodium, as a mixture of the exo- 424 and endo-AT ) isomers, together with a chiral indenyl complex 426, which did not show any optical activity. ... 

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