Iron complexes acetylene

Iron complex/irradiation 6n + 2 r]-CycIoaddition with iron complexes Acetylene derivs. as trienophiles... 

Cp(PMe3)2RuC=CH and the corresponding vinyl compound react with 1 to give the expected hydrozirconated complexes [225, 226]. Hydrozirconation reactions were also observed with the vinyl and acetylenic ferrocenyl complexes [227]. In marked contrast, the iron complex Cp (dppe)Fe-C=CH reacts anomalously with Schwartz s reagent to form acetylide Cj-bridged heterodinuclear complexes (Scheme 8-31) [228]. 

In contrast to the reaction of an i72-CS2-rhodium complex with dimethyl acetylenedicarboxylate which gives rise to a metallocycle,186 the iron complexes 103 are converted by activated acetylenes into air-sensitive carbene complexes 104. Decomposition of the latter in air provides an unusual synthetic route to substituted tetrathiofulvene derivatives (Scheme 121).187... 

Atomic absorption spectrometry coupled with solvent extraction of iron complexes has been used to determine down to 0.5 pg/1 iron in seawater [354, 355]. Hiire [354] extracted iron as its 8-hydroxyquinoline complex. The sample is buffered to pH 3-6 and extracted with a 0.1 % methyl isobutyl ketone solution of 8-hydroxyquinoline. The extraction is aspirated into an air-acetylene flame and evaluated at 248.3 nm. 

As may be anticipated from the chemistry of the related iron complex, which has been extensively reviewed (108), the interaction of alkynes with both Ru3(CO)i2 and Os3(CO)j2 leads to a range of complexes involving addition of one or more acetylenic units to the cluster. 

While computations involving [96]+ did not converge, the calculated structure of the dication is in good agreement with the experimentally observed cumulenic form. In terms of the simple Hfickel model, double oxidation of 96 is consistent with the depopulation of the higher lying 4ji level. In the case of the iron complex 107, the first two oxidation processes resulted in an increase in the acetylenic character of the carbon chain and... 

The reaction between acetylenes and ruthenium carbonyls produces a series of n complexes with cyclic ligands which, as in the iron system, have either the metal or a CO group incorporated into the ring. Accordingly, 3-hexyne 536) and hexafluoro-2-butyne 90) react with Ru3(CO)i2 to give the (substituted cyclopentadienone)tricarbonylruthenium complexes with structures presumably comparable to those of the iron complexes (93-95). Although diphenylacetylene will not react directly with Ru3(CO)i2 to produce this type of complex 536), it can be prepared 90) by treating Ru3(CO)i2 with tetracyclone in benzene under reflux. 

This is a general reaction for alkynes (acetylene, phenylacetylene, diphenylacetylene, cyclodecyne, etc.) that occurs at RT, producing 75% yields of products. The two cobalt atoms and two carbons form a tetrahedron. Analogous iron complexes are prepared in low yield by reaction of diphenylacetylene with Fe3(CO)i2 . Similar molybdenum complexes are prepared by addition of alkynes to molybdenum multiple bonds ... 

Generally the reaction of unsaturated aldehydes (aromatic, olefmic and acetylenic) with chiral boronates has provided homoallylic alcohols in low to moderate enantioselectivity [124]. However, the enantioselectivity of the allyl- and 2-bu-tenylborations of benzaldehyde and unsaturated aldehydes is significantly improved when a metal carbonyl complex is utilized as the substrate [131]. For example, the reaction of iron carbonyl-complexed diene 225, chromium carbonyl-complexed benzaldehyde 226 and dicobalt hexacarbonyl-complexed acetylene 227 all give significantly increa.sed allyl and 2-butenylboration selectivities compared to the parent aldehydes (Fig. 10-6). In the case of chiral substrates 225 and 226, these species can be obtained in enantioenriched form by kinetic resolution by use of the asymmetric allylboration reaction. 

The best known example is the cyclization of butadiene and acetylene 121 14°). Butadiene forms cyclooctadiene and cyclododecatriene by the catalytic action of nickel, iron, and other metal complexes. By an experiment using an iron complex with deuterated butadiene, it was proved that no hydrogen shift takes place in the cyclization reaction 70>. 

In spite of the differences in the electronic configuration of iron, cobalt, and nickel, the manner in which their respective carbonyls function as catalysts is essentially the same, differing only in detail. Under the proper conditions, for example, any of these metal carbonyls catalyze the reaction of acetylene, carbon monoxide, and alcohols to form acrylates. An iron complex, XI, in which most of the terminal carbonyls have been replaced by cyclopentadienyl groups, has been found to function, hke dicobalt octa-carbonyl, as a homogeneous hydrogenation catalyst 16) ... 

C ]H,o, Fluorene, iridium complex 29 232 C]3H jNO, Formanide,lV-ll-(l-naphthal-enyl)ethyl]-, rhenium complex 29 217 CijHijP, Phosphine, methyldiphenyl-, iron complex 26 61, 28 171 molybdenum complex, 27 9 nickel complex, 28 101 tungsten complexes. 27 10, 28 328,28 331 CijHio, Acetylene, diphenyl-, molybdenum complex, 26 102-105, 28 11, 13 C14H12, Benzene, 1,2-ethenediylbis-, platinum complex, 26 140 C14H14, Benzene. l,l -(l,2-ethanediyl)-bis-, 26 192... 

Iron complexes containing bidentate alkyl and aryl phosphorus ligands cleave a variety of C-H bonds under mild conditions, Hydrido acetylide complexes were prepared by oxidative addition of primary acetylenes in the Fe(DPPE)2 and the Fe(DMPE)2 systems [DPPE = bis(diphenylphos-phino)ethane, DMPE = bis(dimethylphosphino)ethane]. The Fe(DMPE)2 system also cleaves C-H bonds of activated methyl groups, aromatic compounds, and certain other sp hybridized molecules. The C-H cleavage reactions are reversible, resulting in equilibrium mixtures of isomeric products in many cases. Studies of substituted benzenes show that while product stability is favored by electron withdrawing substituents, steric effects play a predominant role in the determination of product distribution. 

Liberation of excess cyclobutadiene from its iron complex in the presence of acetylenes leads to a double addition, affording the previously unknown tetracyclic system (831 R = Ph or OMe). Trapping with phenyl vinyl ketone affords (832X nhich has been converted by reduction, alkylation, and photolysis into the new tri-cyclo[3,1,1,0 ]heptanols (833). ... 

Cycloaddition.— Reactions of electrophilic olefins and acetylenes with tricarbonyl-iron complexes of cycloheptatriene and cyclo-octatetraene lead to 1,3-exo-products. Troponetricarbonyliron and tcne, however, have now been found to give complex (20) which results from previously unobserved 1,5-exo-cycloaddition. A dipolar intermediate (21) resulting from initial attack by the electrophile on the hydrocarbon... 

The reaction of / -(cw-azo)-hexacarbonyldi-iron complexes (26) with diphenyl-acetylene results in [4+4] cycloaddition probably in a stepwise manner to give (27) and (28) followed by [4 + 2] addition to give ultimately (29). Preliminary kinetic... 

The treatment of metal carbonyls (especially those of iron) with acetylenes affords, together with other products, cyclopentadienone and quinone complexes, in which one or two carbonyl groups respectively have been incorporated with two acetylene molecules into a cyclic organic ir-bonding system. These complexes can also be obtained by direct reaction between iron carbonyls and cyclopentadienone or quinone ligands. Other products in these reactions include complexes of substituted ( clobutadienes, and ir-cyclopentadienyl derivatives. Some examples are shown in Figure 49. 

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