Photolysis with iron carbonyls

The iron-alkyne interaction is important because there are practical applications in organic synthesis, such as the iron carbonyl-mediated coupling of alkynes and CO. As a result, the reactions of alkynes with iron carbonyls have thus been the subject of many studies since the first report in 1953. Surprisingly, up until 1997, however, there was only one well-documented example of an Fe(CO)4(r7 -alkyne) species 3 (see Scheme 7). This is in part because complexes of this type are highly sensitive to the preparative conditions. Takats and co-workers have prepared a series of complexes of this type 3a-3e from Fe(CO)s (see Scheme 7) under carefully controlled photolysis conditions. The complexes Fe(CO)4(77 -alkyne) are shown to react with an excess of alkyne and CO, thus confirming early proposals that they are key intermediates in the coupling of alkynes with CO. ... 

The di(/x-disulfido)diiron complex 243 (L = Gp ) is converted into the di(/U3-sulfido)triiron complex 244 by thermal reaction with iron carbonyls. Selective mono-GO substitution of 244 by PPh3 is accelerated by photolysis or by treatment with reductant (benzophenone ketyl) or oxidant (ferrocenium cation). ... 

Photolysis is a convenient route - to iron carbonyl derivatives using FefCO), and this route may be better than oxidative addition to Fej(CO),2. One illustration is the 1 1 reaction of FefCO), with (Me2GeH)20 under mercury lamp irradiation for 1 h. in pentane to produce ... 

Tlie matrix samples with varying molar ratios (Fe(C0) /N2 = 1/800 V 1/100) were deposited at the same time interval between pulses. The molar ratio was found to affect the photolysis product distribution at lower iron carbonyl concentrations, unstable products were less likely to recombine ivith the dissociated CO and could survive as trapped in matrices. Hence Fe(CO)j and Fe(C0)2 were observed. 

If the photolysis of Fe(CO)s is carried out in acetic acid as solvent with no added ligand, the dimeric iron carbonyl complex Fe2(CO)9 is formed ... 

The reactions of iron carbonyls with alkynes however can often lead to a range of products that are difficult to separate. Manning and co-workers have found that photolysis of Fe(GO)3 P(OPh)3l2 with alkynes gives products Fe(GO)2 P(OPh)3 2( 7 -alkyne) 5 via the orthometallated iron-hydride intermediate HFe(GO)2 P(OPh)3 - (PhO)2POG6H4 4. Maleoyl complexes 6 are also formed with internal alkynes. However, the ferrole derivative 7 is obtained by reaction with the terminal alkyne HG=GPh (see Scheme 8). Grystal structures of the complexes 5a and 6c have been determined and confirm their formulations. The alkyne carbon-carbon distance in 5a is 1.274(4) A which lies toward the shorter end of the range of reported carbon-carbon distances of coordinated diphenylacetylene (1.24-1.35 A). 

Knox and co-workers synthesized a triruthenium cluster by the reaction of the coordinatively unsaturatcd diruthenium alkyne complex (CpRu)2(/r-CO)(/r-RCCR) 39 with a monometallic carbonyl complex M(CO)4(L) (M = Fe, Ru). Two isomers, 40 and 41, were formed in the reaction of 39 with Ru(CO)4(CH2 = CH2) (Equation (13)). The ratio between 40 and 41 was shown to be dependent on the nature of the substituents of the alkyne. In the case of diphenylacetylene complex, coalescence of the H signals of these isomers, 40a and 41a, was observed. This shows that isomerization between the two isomers took place at considerable rate. In contrast, the reaction of 39 with Fe(CO)4(thf) exclusively afforded a 3- ( )-alkyne complex, in which the alkyne moiety was 7r-coordinated to an iron center. Knox and co-workers also reported the syntheses of triruthenium /i3-alkylidyne complexes by the photolysis of a bimetallic /r-alkylidene complex and a bimetallic diruthenacy-clopentenone complex. In these reactions, formation of the triruthenium frameworks was rationalized by the coupling reaction of the monometallic coordinatively unsaturated species generated by the photolysis with the starting bimetallic complexes. 

In similar investigative studies for bimetalhc single-source precursors, an iron indane derivative was synthesized by the reaction Na[(Cp)(CO)2Fe]0.5THF with BrIn[(CH2)3NMe2]2 in THF (Scheme 18)). The analogous Ni, Co, and Mn intermetallic complexes were also successfully prepared with either cyclopentadiene or carbonyl ligands. Photolysis of the indium-iron derivative [ Cp(CO)2Fe 2ln(CH2)3NMe2)2]... 

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