Transition metal chalcogeno complexes

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Chapter One: Introduction


Transition metal chalcogeno complexes have attracted considerable attention due to their structural diversity [1-6], chemical reactivity, relevance to catalysis [7-12], and biological applications as models for metalloenzymes [13-16].(6.D)

Organoiron and sulfides and selenides [CpFe(CO)2]2(µ-Ex) (E= S, Se ; x= 1-5) are a special part transition metal chalcogeno complexes. The preparation of this complexes and there reaction will explain below.

Organoiron chalcogenonied complexes

Iron sulfide bridged dimers

The coordination chemistry of sulfur and polysulfides is of particular interest because of the diverse bonding modes of coordination and its ligation in metal complexes is of interest in several contexts. In biochemistry, inorganic sulfide and possibly polysulfide appear as critical ligands in metalloenzymes such as ferredoxin, nitrogenase, and the xanthine oxidases, primarily in association with iron or molybdenum1. In the context of industrial technology, inorganic sulfur is among the more common and troublesome catalyst poisons;2 and as greater effort is directed toward the utilization of oil tars and sludges, catalytic desulfurization and removal of metal ions possibly complexed with sulfide or polysulfide will become an increasingly significant problem.3 Additionally, in the broad area of metal-cluster chemistry sulfur ligands have proven very versatile in the construction of transition-metal cluster complexes, including heteronuclear clusters of potential catalytic utility.4-6

Iron sulfide bridged dimers CpFe(CO)2]2(µ-Sx) (x= 1-5) was prepared by insertion of elemental sulfur into the iron-iron bond of the dimer [CpFe(CO)2]2 as shown in equation 1.1, this reaction is an example of redox reaction.(16.A)

The organoiron tri- and tetra-sulfides, (µ-S3)[CpFe(CO)2]2 and (µ-S4)[CpFe(CO)2]2 have been structurally characterized and their structures are shown in Figure 1.1 (anas).

In another hand, organoiron sulfide can be prepared by substitution reactions involving organoiron or sulfur nucleophiles, symbol for the reaction of Na[CpFe(CO)2] with SCl2, S2Cl2 and SOCl2, and the reaction of CpFe(CO)2Br with Li2S, Li2S2, Li2S4 and H2S in the present of base.(16.A)

These complexes are fairly stable as solids, but in solution they are sensitive to oxygen and light (19.A). Analogous class of substituted cyclopentadienyl organoiron sulfides (µ-S3)[CpFe(CO)2]2 (Cp'= tBuC5H4, 1,3-tBuC5H3) has been prepared in a similar way [23].(anas)

Iron selenides bridged dimers

organoiron selenides [(C5H5)Fe(CO)2]2(µ-Se), [(tBuC5H4)Fe(CO)2]2(µ-Se) and [(I,3-tBuC5H3)Fe(CO)2]2(µ-Se) respectively, were formed from the reactions of the iron dimers [(C5H5)Fe(CO)2]2(µ-Se), [(tBuC5H4)Fe(CO)2]2(µ-Se), [(1,3-tBuC5H3)Fe(CO)2]2(µ-Se) with elemental selenium. The reaction of the organoiron dimers with elemental selenium can be represented in Scheme 1.1(14.A).

These complexes are fairly stable as solid, but decompose in solution in the presence of light with deposition of elemental selenium. The presence of tert-butyl groups on the cyclopentadienyl ring of the iron dimers leads to a remarkable variation in reactivity and structure relative to the unsubstituted analogs, it is observed that the formation of the selenides enhanced by increase substitution on the ring, due to increase the thermal stability of the dimmers. And the steric effects of the tert-butyl substituents seem to affect strongly the type of the selenide formed in these reactions. (14.A)

In addition to, The organoiron selenide [(C5H5)Fe(CO)2](µ-Se) has been prepared by the reaction of Na+[(C5H5)Fe(CO)2]- with Se2C12.(20.A)

Reaction of iron chalcogenide dimers

The chalcogenide bridges in the iron dimers complexes are electron rich and are susceptible to attack by electrophiles (7.A), due to the presence of lone pairs of electrons on the sulfur or selenium atom (13.A). The reaction of these chalcogenides with electrophiles produce three classes of iron complexes, these products will discuss in the next pages. (5.A)

Chalcogenosulfonate iron complexes

The reaction with sulfonyl chlorides with iron cyclopentadienyl dimers will gave the expected chalcogenosulfonate complexes CpFe(CO)2ESO2R (E = S, Se). (5.A)

Thiosulfonato iron complexes (1.A)

Thiosulfonato complexes are important complexes in petrochemistry, due to present an oxopolysulfur ligand. This ligand play a major role in the catalyst use to convert the product of hydrodesulfurization (HDS) (sulfur removal from petroleum) H2S to elemental sulfur.

It was found that the treatment of the iron polysulfanes (µ-Sx)[CpFe(CO)2]2 (x= 3, 4) with sulfonyl chlorides RSO2Cl (R= CF3, CCl3, C6F5) gave the corresponding iron thiosulfonato complexes CpFe(CO)2SS(O)2R in good yields, and CpFe(CO)2Cl as a by-product as shown in equation 1.2.

The mechanism of this reaction is probably similar to that proposed for the preparation of CpFe(CO)2SCOR (see section 1.3.3).

These thiosulfonato complexes are air stable as solids and air sensitive in solution. They are soluble in common organic solvents but insoluble in hexanes. Sulfonyl chlorides with no electron-withdrawing groups (R= CH3, C6H5, C6H4CH3) or even with moderate electron withdrawing groups (2,5-(NO2)2C6H3, 4-NO2C6H4) did not react with the iron sulfide dimers.

This complexes were characterized by IR, NMR spectroscopy and elemental analysis and The molecular structure of CpFe(CO)2SSO2CCl3 was determined and shown in figure1.1.

selenosulfonato iron complexes (10.A)

Organometallic selenium complexes have many industrial importance, such as solid state precursors [6-9], and solar energy technology.

In a similar fashion selenosulfonato complexes prepared by the reaction of iron selenide with Sulfonyl chlorides, so the reaction of iron selenide (µ-Se)[CpFe(CO)2]2 with sulfonyl chlorides RSO2Cl (R=C6H5, 4-C6H4Cl, 4-C6H4Br, 4-C6H4tBu, 4-C6H4Me, CH3) gave the novel iron selenosulfonato complexes CpFe(CO)2SeSO2R in good yields, (equation 1.3).

Selenosulfonato complexes show higher reactivity toward sulfonyl chlorides than analogues thiosulfonato complexes this may attributed to the presence of the electronrich selenium atom.

The selenosulfonato complexes were characterized and the molecular structure of CpFe(CO)2SeSO2C6H5 was determined by X-ray diffraction analysis as shown in Figure 1.4.

Chalcogenocarbonate iron complexes

Recently, it has been found that iron sulfide dimers reacted with chloroformates and its thio-derivatives to give three classes of chalcogenocarbonate complexes.

Mono-chalcogenocarbonate iron complexes

A series of cyclopentadienyldicarbonyliron monothiocarbonate complexes, CpFe(CO)2SCO2R, were prepared by the reaction of (µ-Sx)[CpFe(CO)2]2 with the corresponding chloroformates ROCOCl [R= Et, iso-Bu, Ph, 4-C6H4NO2, Me] as shown in equation. 1.4. The chloro-derivative CpFe(CO)2Cl, was also obtained as a side product of this equation.

The thiocarbonate complexes are air stable as solids and are air sensitive in solutions. They are soluble in most common polar organic solvents but insoluble in hydrocarbons. The structures of these complexes were established by elemental analysis, IR and 1H NMR spectroscopy. And the molecular structure of CpFe(CO)2SCO2Et shown in Figure 1.5 (9.A).

Also it was found that the monothiocarbonate ligands are not good bidentate ligands. All attempts to prepare the bidentate complexes CpFe(CO)SCO2R, in which the thiocarbonate ligands is bonded to the iron through both S and O atoms, were unsuccessful.

The analoguse selnocarbonates CpFe(CO)2SeCO2R [R= Me, Et, iso-Bu, Ph, 2-C6H4Cl, 4 C6H4ClMe, 4-C6H4NO2] were obtained in good yields when slight excess chloroformates was reacted with (µ-Se)[CpFe(CO)2]2 (equation 1.5) (7.D).

A perspective view of CpFe(CO)2SeCO2Et is displayed in Figure 1.6

Chalcogenothiocarbonate iron complexes

Dithiocarbonate metal complex and its dithioacid ligands have obtained continuous attraction due to their interesting structural and chemical properties as well as their wide range of application in biological systems. The dithioacide ligands X-CS2- (X = OR, SR, NR2), have a rich coordination and organometallic chemistry.

In a similer way the reaction of (µ-Sx)[CpFe(CO)2]2 with various aryl chlorothionoformates proceeds smoothly to give the corresponding dithiocarbonate complexes CpFe(CO)2SC(S)OAr (Ar = Ph, 4-C6H4Cl, 4-C6H4F, C6F5, 4-C6H4CH3 ) as shown in equation 1.6 (6.A).

The structure of CpFe(CO)2SC(S)O-4-C6H4Cl was determined by single-crystal X-ray analysis and is shown in Figure 1.7.

The chelate form of these complexes CpFe(CO)(?2S,S-S2COAr) obtained in high yield by irradiated with UV-light for short time, (equation 1.7)

In the other hand the reaction of the iron selenide with chlorothionoformates (ROC(S)Cl) give stable selenothiocarbonates complexes of general formula CpFe(CO)2SeC(S)OR, where R = Ph, 4-C6H4Cl, 4-C6H4F, C6F5, 4-C6H4CH3). Also found that these complexes can be converted to the chelated complexes CpFe(CO)(?2Se,S-SeC(S)OR) upon photolysis, (Scheme) 1.2(8.A)

The structure of CpFe(CO)2SeC(S)O-4-C6H4Cl was determined crystallographically and is shown in Figure 1.8

Chalcogenodithiocarbonate iron complexes

The iron trithiocarbonato complex CpFe(CO)2(?S-SCS2Ph) and its selenodithiocarbonato analogue CpFe(CO)2(?Se-SeCS2Ph) were generated in good yields by the reactions of (µ-Ex)[CpFe(CO)2]2 (E = S; x = 2, 3. E = Se; x = 1) with chlorodithionoformates PhSC(S)Cl as shown in equation 1.8 (3.A).

The orange complex CpFe(CO)2(?S-SCS2Ph) and the brown complex CpFe(CO)2(?Se-SeCS2Ph) are air stable as solids and in solution. They are soluble in common polar organic solvents but insoluble in hydrocarbons. The identities of CpFe(CO)2(?S-SCS2Ph), and CpFe(CO)2(?Se- SeCS2Ph) have been confirmed by crystal structure determination and shown in Figure 1.9 and 1.10 respectively.

Photolyzing a solutions of complexes CpFe(CO)(?E,S-ECS2Ph) (E= S, Se) in the absence of added ligand produces the chelate complexes CpFe(CO)(?2E,S-ECS2Ph) (E= S, Se) as shown in equation 1.9. The trithiocarbonate ligand of CpFe(CO)2(?2S-SCS2Ph) is bonded to the iron metal through the two sulfur atoms. In a similar fashion, the dithioselenocarbonate ligand of CpFe(CO)2(?2Se-SeCS2Ph) is bonded to the metal through the selenium and sulfur atoms.

The molecular structure of CpFe(CO)2(?2Se-SeCS2Ph) represented in Figure 1.11

In addition to, the trithiocarbonato complexes CpFe(CO)2(?S-SCS2R) have been made by substitution of the iodide ligand of CpFe(CO)2I by the trithiocarbonate anions RSCS-2 (R= Me, Et, Ph) [15]. The chelated forms, CpFe(CO)( ?2S,S-S2CSR) were obtained by photolysis of the dicarbonyl analogs [15].

Chalcogenocarboxylate iron complexes

The reaction of chalcogenides complxes (µ-Ex)[CpFe(CO)2]2 (E= S, Se ; x= 1-5) with acid chlorides is reported to give the chalcogenocarboxylate complexes of the general formula CpFe(CO)2ECOR (E = S, Se) [4-6]. (5.A)

Thiocarboxylate iron complexe

The reactions of organoiron sulfides, (µ-Sx)[FeCp(CO)2]2 (x= 3, 4) with acid chlorides, RCOCl, produce the new organoiron thiocarboxylates, FeCp(CO)2SCOR, where R = 2-CH3C6H4, 2-CH3COOC6H4, 3,5-(O2N)2C6H3, 2-O2NC6H4 and 2-FC6H4 in moderate yields, in addition to FeCp(CO)2Cl in low yield, (equation 1.10) (12.A).

It was observed that the iron thiocarboxylate compounds containing R groups with electron-withdrawing substituents like NO2 or F show the greatest thermal stability, this enhanced thermal stability can be attributed to relatively stronger iron-sulfur bonds in the nitro and fluoro compounds.

It is believed that the reaction of organoiron sulfides with acid chloride follow the proposed mechanism shown below.

The molecular structure of FeCp(CO)2SCO(2-O2NC6H4) is shown in Figure 1.12. It can be seen that the thiocarboxylate ligand is S-bonded to the Fe atom in the FeCp(CO)2 unit, with a cis configuration of Fe-S bond relative to C=O bond. The structure also shows a tram configuration of Fe-Cp bond relative to C-S bond. The NO2 group lies in a plane approximately perpendicular to the plane of the benzene ring and in the same direction as the thiocarboxylate C=O group.

However, organoiron sulfanes, (µ-Sx)[FeCp(CO)2]2 (X = 3,4) react with LiBEt3H at -97°C gives the anionic species [Cp(CO)2FeSx]- (x = 1, 2 or 3), and the latter complexes [Cp(CO)2FeSx]- reacts with acid chlorides RCOCl to give monothiocarboxylate complexes FeCp(CO)2SCOR (R= CH3, C6H5, 3-MeOC6H4, C(CH3)3, 4-O2NC6H4, 1-C10H7).(19.A)

In the anther hand, substituted cyclopentadienyl iron sulfides complexes [(tBuC5H4)Fe(CO)2]2(µ-Sx) and [(I,3-tBuC5H3)Fe(CO)2]2(µ-Sx) reacted smoothly with acid chlorides (RCOCl) (R= alkyl, aryl) to give the corresponding substituted cyclopentadienyl thiocarboxylate iron complexes tBuC5H4Fe(CO)2SCOR and I,3-tBuC5H3Fe(CO)2SCOR, (equation 1.11) [23] (anas).

Selenocarboxylate iron complexe

The organoselenide and its substituted cyclopentadienyl organo selenide [(C5H5)Fe(CO)2]2(µ-Se), [(tBuC5H4)Fe(CO)2]2(µ-Se) and [(I,3-tBuC5H3)Fe(CO)2]2(µ-Se) react with acid chloride to give the Se-bonded selenocarboxylate derivatives, (equation 1.12) The organoironselenides in this reaction bear a close resemblance to their sulfide analogs.

It is believed that the reaction of organoiron selenides with acid chloride follow the proposed mechanism shown below.

This mechanism represents the only possible route that explains the formation of monoselenocarboxylate derivatives from both mono- and diselenides.

Multinuclear and Multifunctional iron complexes

In addition, the reaction of polysulfides or polyselenides complexes with diacid chloride (ClCORCOCl) gave either the mono-iron or di-iron chalcogenocarboxylate complexes , depending on the molar ratio of the reactants. [11](13.A)

A controlled reaction of polysulfides or polyselenides with terephthaloyl chloride (ClCO(C6H4)COCl) give the mono-iron thioterephthalates complexes Cp`Fe(CO)2SCO-4-C6H4COCl (Cp`= C5H5, tBuC5H4; E= S, Se), The presence of a free acid chloride group in these complexes makes them valuable precursors for many reactions. An important reaction of these complexes would be the reaction with organometal sul­fides and selenides. Such a reaction offers a facile method for the synthesis of a large variety of homo ­and hetero bimetallic bithio-, biseleno- and thioseleno- terephthalate complexes [Cp`Fe(CO)2ECO]2(4-C6H4) (Cp`= C5H5, tBuC5H4) (E= S, Se) (Scheme 1.3).(13.A)

In anther hand, the presence of a free acid chloride group in the mono-iron thioterephthalates complexes make them susceptible to attack by electrophiles or the so-called the transformation reaction organic and inorganic. Nucleophiles such as amines, phenols, carboxylic acids and thiols reacted with the latter iron complexes to give the bi-functional products CpFe(CO)2ECO-4-C6H4COX (X = R2N, OAr, RCOO, SR) (E= S, Se) All theses complexes were obtained in a good yields with the exception of phenols, it seems that the reactivity of phenol enhanced with its nucleophilicty of the phenols, (Scheme) 1.5 (5.A) (Anas). Moreover, biological studies on some of theses bifunctional complexes showed that these systems possess promising biological activity, for example, the selenium containing products had antifungal and antibacterial effects. However, both the sulfur and selenium containing compounds showed mutagenic and antifungal activity [15]. (5.A)

In the same way, Treatment of the iron sulfides (µ-Sx)[CpFe(CO)2]2 with (chlorosulfonyl)benzoyl chloride (3-ClCOC6H4SO2Cl) gave the novel organoiron thiocarboxylate complex CpFe(CO)2SCO-3-C6H4SO2Cl as a stable solid which contains a free sulfonyl chloride group. This complex reacts with nucleophiles (YH) to give stable complexes CpFe(CO)2SCO-3-C6H4SO2Y (Y= R2N, ArO, RS) (Scheme 1.6). The biiron complex CpFe(CO)2SCO-3-C6H4SO2SFe(CO)2Cp, which may result from the reaction of the sulfonyl group with the iron sulfides, could not be obtained from this reaction even when excess of the iron sulfide was added. This result is in agreement with our earlier finding that only strongly electrophilic sulfonyl chlorides react with the iron sulfides [6](4.A).

The identities of CpFe(CO)2SCO-3-C6H4SO2N(CH3)CH2Ph have been confirmed by crystal structure determination and shown in Figure 1.13.

Recently, the synthesis of the acid [CpFe(CO)2ECO-4-C6H4CO2H] and the amide [CpFe(CO)2ECO-4-C6H4CONH2] (E = S, Se) derivatives from the reaction of terephthaloyl chloride with NaOH and NaNH2, respectively was reported. [26] The terephthalic acid derivatives, [CpFe(CO)2ECO-4-C6H4CO2H] were reacted with the terephthaloyl chloride analogues in the presence of pyridine to give the new anhydride bridged diiron dichalcogen complexes, (Figure 1.14) [26](anas).

E = (S, S); (S, Se); (Se, Se)

Moreover, the amide [CpFe(CO)2ECO-4-C6H4CONH2] reacted with the terephthaloyl chloride analogues in the presence of few drops of pyridine to give the new stable imide bridged diiron dichalcogen complexes, (Figure 1.15) [26].

E = (S, S); (S, Se); (Se, Se)