Ligand properties of aromatic azines: C-H activation, metal induced disproportionation and catalytic C-C coupling reactions

The reaction of aromatic azines with Fe₂(CO)₉ yields dinuclear iron carbonyl cluster compounds as the main products. The formation of these compounds may be rationalized by a C-H activation reaction at the aromatic substituent in ortho position with respect to the exocyclic C-N double bond followed by an intramolecular shift of the corresponding hydrogen atom toward the former imine carbon atom. The second imine function of the ligand does not react. Additional products arise from the metal induced disproportionation of the azine into a primary imine and a nitrile. So also one of the imine C-H bonds may be activated during the reaction. Depending on the aromatic substituent of the azine ligands iron carbonyl complexes of the disproportionation products are isolated and characterized by X-ray crystallography. C-C coupling reactions catalyzed by Ru₃(CO)₁₂ result in the formation of ortho-substituted azines. In addition, ortho-substituted nitriles are identified as side-products showing that the metal induced disproportionation reaction also takes place under catalytic conditions.     

The variation of coordination modes of aromatic imines in iron carbonyl complexes: Is there a correlation between bond lengths in organometallic model compounds and the reactivity of the ligands in catalytic C-C bond formation reactions?

The reaction of aromatic imines with Fe₂(CO)₉ proceeds via a two-step reaction sequence. A C-H activation reaction in ortho-position with respect to the exocyclic imine function is followed by an intramolecular hydrogen transfer reaction towards the former imine carbon atom. The resulting dinuclear iron carbonyl complexes show an aza-ferra-cyclopentadiene ligand which is apically coordinated by the second iron tricarbonyl moiety. Comparing the bond lengths of 43 different compounds, which were synthesized and structurally characterized in our group shows that the iron iron bond length correlates with one of the iron carbon bond lengths. The longer the iron carbon bond between the apically coordinated iron atom and the carbon atom next to the former imine carbon atom is, the shorter is the iron iron bond. The same ligands may be used as the substrates in ruthenium catalyzed C-C bond formation reactions. Whereas most of the imines react via the formal insertion of CO and/or ethylene into the C-H bond in ortho-position to the imine function, the ligands that show the longest iron carbon bond lengths in the model compounds under the same reaction conditions produce different types of isoindolones.     

Regioselective CC bond formation between ethylene and α-naphthylcarbaldimines catalyzed by Ru3(Co)12: NMR spectroscopic investigations on the proceeding of the reaction

The reaction of ethylene with imines derived from α-naphthylcarbaldehyde catalyzed by Ru₃(CO)₁₂ leads to the selective and quantitative formation of products in which one molecule of ethylene has been inserted into the CH bond in ortho position with respect to the exocyclic imine substituent. The stoichiometric reaction of the same ligands with Ru₃(CO)₁₂ leads to dinuclear ruthenium carbonyl complexes showing the same regioselectivity of CH activation but the hydrogen atom is shifted in an intramolecular hydrogen transfer reaction towards the former imine carbon atom. If the catalytic alkylation of α-naphthylcarbaldimines is monitored by NMR the occurrence of the dinuclear product of the stoichiometric reaction is observed before the reaction again quantitatively yields the imines bearing an ethyl group in 2-position of the naphthalene core. This proofs that there must be an equilibrium between the dinuclear ruthenium carbonyl complex which is also observed if α-naphthylcarbaldimines are treated with an equimolar amount of Ru₃(CO)₁₂ and another ruthenium compound where the ethylene might be inserted catalytically into a ruthenium carbon bond.     

The reaction of ortho-halogenated aromatic aldazine ligands with Fe2(CO)9: symmetrical cleavage of the azine and carbon-halogen activation

Azine ligands derived from hydrazine and benzaldehyde derivatives bearing halogen substituents in ortho-position with respect to the carbonyl function upon treatment with Fe₂(CO)₉ show two typical reaction principles. One is the symmetrical cleavage of the N-N bond of the azine to yield either di- or trinuclear iron carbonyl compounds [Fe₂(CO)₆(μ₂-NCHR)₂] and [Fe₃(CO)₉(μ₂-NCHR)(μ₂-η²-NCHR)] each showing two arylidenimido moieties. In addition, a trinuclear iron carbonyl cluster compound exhibiting a tetrahedral Fe₃N cluster core is isolated. The cluster shows only one half of the former azine ligand. It is a ionic compound of the general formula [Fe₃(CO)₉(μ₃-η²-NCHR)]Na × H₂O. This trinuclear cluster compound is quantitatively converted into [Fe₃(CO)₉(μ₂-H)(μ₃-η²-NCHR)] upon treatment with phosphorous acid. Most interestingly, we were also able to isolate two types of compounds in which an activation of one of the carbon halogen bonds in ortho-position with respect to the imine functions of the azine has occured in terms of an ortho-metallation reaction. In the N-N bond of the azine is still preserved, whereas in [Fe₃(CO)₉(μ₃-η³-NCHR)] again only one half of the former azine ligand is coordinated in an arylidenimido fashion. In both types of compounds one additional iron carbon bond is present due to the activation of an aromatic carbon halogen bond. The reaction of iron carbonyls with 2,6-difluorobenzonitrile produces [Fe₃(CO)₉(μ₃-η²-NCR)] as the sole product. All new iron carbonyl compounds are characterized by means of X-ray crystallography.     

A new stoichiometric hydroformylation of olefins mediated by HCo3(CO)9

3,3-Dimethylbutene is converted into 4,4-dimethylpentanal at ?15°C in the presence of HCo₃(CO)₉ and HCo(CO)₄ under argon. Under the same conditions there is no reaction in the presence of HCo(CO)₄ alone. Labeling experiments show that in the formed aldehyde the hydrogen atom of the formyl group has come from the mononuclear complex, and the hydrogen atom of the alkyl moiety from the trinuclear cluster.     

Novel diazadienes based on 1,3,4-oxadiazines: Ligands in iron carbonyl complexes and substrates in catalytic [2+2+1] cycloaddition reactions

N,N′-(4-methyl-4H-1,3,4-oxadiazine-5,6-diylidene)-bis-aniline derivatives react with Fe₂(CO)₉ to give dinuclear iron carbonyl complexes. One of the iron atoms is bonded symmetrically to both exocyclic imine nitrogen atoms. The second iron atom shows a side-on coordination towards the CN bond next to the oxadiazine oxygen atom. In addition, the iron atoms are connected via a metal metal bond. The same oxadiazine derivatives produce chiral spiro-lactams in a ruthenium catalyzed formal [2+2+1] cycloaddition reaction with carbon monoxide and ethylene.     

The reaction of Ru3(CO)12 and Os3(CO)12 with PH2Ph; the x-ray crystal structures of HRu3(CO)10(PHPh) and H2Ru3(CO)9(PPh)

Twelve new trinuclear complexes containing terminal PH₂Ph, edge-bridging PHPh and/or capping PPh ligands have been isolated from the reaction of M₃(CO)₁₂ (M = Ru or Os) with PH₂Ph in refluxing solvents. HRu₃(CO)₁₀(PHPh) (IIIa) crystallises in the monoclinic space group P2₁/c with a = 8.761(3), b = 11.402(4), c = 22.041(7) Å,β = 98.89(2)°, and Z = 4. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by blocked-cascade least squares to R = 0.027 for 3676 unique observed intensities. The X-ray analysis shows that one edge of the Ru₃ triangle is bridged by a hydride and the PHPh ligand, and that the phosphorus-bound hydrogen atom lies over the metal triangle and the phenyl group away from it. This provides an explanation for the ready formation of the capped species H₂Ru₃(CO)₉(PPh) (Va) on pyrolysis of the edge-bridged complex as opposed to the previously reported conversion of HOs₃(CO)₁₀(NHPh) to an orthometallated derivative under similar conditions. An X-ray analysis of H₂Ru₃(CO)₉-(PPh) (Va) confirms the capped geometry. the complex crystallises in the monoclinic space group P2₁/n with a = 9.323(4), b = 15.110(6), c = 45.267(15) Å,β = 91.84(3)°, and Z = 12. the structure was solved and refined using the same techniques as described previously. The final residual R is 0.061 for 4839 reflections. Some reactions of Va show that the phosphorous cap is difficult to displace and stabilises the molecule with respect to decomposition to non-cluster species.     

Hetero- and homo-nuclear bimetallic ruthenol complexes by dehydrogenative metallacyclization of Ru(CO)3(bi-1,7-cyclooctadienyl), preparation and x-ray structure of Fe(CO)3(C16H22), RuFe(CO)6(C16H22) and Ru2(CO)6(C16H20)

The reaction of M₃(CO)₁₂ (M = Ru, Fe) with excess bi-2,7-cyclooctadienyl (C₁₆H₂₂) 1 gave a mononuclear complex M(CO)₃(1,2,1′-2′-η⁴-C₁₆H₂₂), 2a (M = Ru) or 3a (M = Fe), in good yield. Treatment of 2a with Fe₃(CO)₁₂ or reaction of 3a with Ru₃(CO)₁₂ gave the heterobimetallic complex RuFe(CO)₆(C₁₀H₂₂) consisting of a ruthenacyclopentadiene unit coordinated to an Fe(CO)₃ fragment, as confirmed by ¹H NMR and X-ray studies. The corresponding homobimetallic complex Ru₂(CO)₆(C₁₆H₂₂) was obtained from the 1:1 reaction of 2a with Ru₃(CO)₁₂, while the direct reaction of 1 with Ru₃(CO)₁₂ gave Ru₂(CO)₆(C₁₆H₂₀) preferentially with a loss of two hydrogen atoms. The pathway for formation of these bimetallic complexes was interpreted as a dehydrogenative metallacyclization followed by hydrogen transfer.     

Photochemische synthese von H2Fe3-komplexen und ihre aktivität bei der photokatalytischen hydrierung von olefinen und dienen

The photochemical reaction of the trinuclear complex Fe₃(CO)₁₀NSi(CH₃)₃ under hydrogen leads to substitution of the bridging carbonyl group by two hydrogens. The resulting complex H₂Fe₃(CO)₉NSi(CH₃)₃ acts as a catalyst in the photochemical hydrogenation of olefins and dienes.     

Reactions of isonitriles with [Fe3(CO)12] and [Ru3(CO)12] monitored by electrospray mass spectrometry: structural characterisation of [Fe3(CO)10(CNPh)2] and [Ru4(CO)11(μ3-η-CNPh)2(CNPh)]

The reactions of [Fe₃(CO)₁₂] or [Ru₃(CO)₁₂] with RNC (R=Ph, C₆H₄OMe-p or CH₂SO₂C₆H₄Me-p) have been investigated using electrospray mass spectrometry. Species arising from substitution of up to six ligands were detected for [Fe₃(CO)₁₂], but the higher-substituted compounds were too unstable to be isolated. The crystal structure of [Fe₃(CO)₁₀(CNPh)₂] was determined at 150 and 298 K to show that both isonitrile ligands were trans to each other on the same Fe atom. For [Ru₃(CO)₁₂] substitution of up to three COs was found, together with the formation of higher-nuclearity clusters. [Ru₄(CO)₁₁(CNPh)₃] was structurally characterised and has a spiked-triangular Ru₄ core with two of the CNPh ligands coordinated in an unusual μ₃-η² mode.     

Synthesis,spectroscopic characterization and crystal and molecular structure of HRu3(OCN(CH3)2)(CO)10

Dimethylamine reacts with Ru₃(CO)₁₂ to produce the η²-hydrido-η-formamido cluster complex HRu(OCN(CH₃)₂)(CO)₁₀ (I). This formulation is consistent with spectroscopic features such as the absence of v(NH) in the infrared, the presence in the Raman of v(RuHRu) at 1400 cm^?1 (v(RuDRu) at 990 cm^?1) and indication in the ¹H NMR of diastereotopic methyl groups bonded to the nitrogen atom. Since these data could not lead to an unequivocal structure assignment a single crystal X-ray study at 115 K was undertaken. The complex crystallizes in the triclinic space group, P$\text{1}$ with cell dimensions; a 7.299(33) », b 9.5037(40) », c 13.7454(57) », α 91.876(34)°, β 96.387(34)°, γ 95.341(34)° and Z = 2. The structure was solved by a combination of Patterson and Fourier techniques and refined by full matrix least squares to a final R = 0.054 and R_ω = 0.074 for 3074 unique reflections. The three ruthenium atoms define a triangle of unequal sides with both the hydride and formamido groups bridging the longest edge; the formamido group is coordinated through the carbon and oxygen atoms. The edge of the ruthenium triangle bridged both by the hydrogen atom and the formamido group is 2.8755(15) »; the other two edges of the ruthenium triangle are observed to be 2.8319(15) and 2.8577(14) », respectively. In the formamido group the distance CO 1.287(9) » and CN 1.340(10) » reflect partial double bond charater in each bond consistent with observation of two chemically distinct methyl groups on the dinitrogen atom. The hydrogen atom bridging one edge of the ruthenium triangle is asymmetrically positioned at 1.73(9) » from the ruthenium atom bonded to the oxygen atom and 1.91(9) » from the ruthenium atom bonded to the carbon atom of the carboxamido group.     

Conformational Analysis,RIS Models and Single‐Chain Properties of Structurally Modified Polycarbonates, 1. Effect of Cyclohexyl and Phenyl Ring Substitutions

Conformational properties of segments and chains of structurally different polycarbonates are investigated in detail. Conformational analysis and rotational isomeric state (RIS) models for some of the polycarbonates and single‐chain properties of all the polycarbonates are reported here for the first time. Substitution of the methyl group on the bisphenol phenyl rings results in increased energy barriers to rotations as well as changes in positions of local minima, compared to the case without substitutions. Conformational structure about the isopropylidene linkage C_α atom is not altered by ortho methyl substitutions on the rings. Substitution by a cyclohexyl ring rigidly attached to the C_α atom restricts conformational mobility within the bisphenol unit. Rotational flexibility of the phenyl–oxygen bond is hindered by additional substitutions on the cyclohexyl ring. The carbonate group prefers the trans–trans conformation in all the polycarbonates. The energy difference between the cis–trans and trans–trans states of the carbonate group is lowered by the ortho methyl substituent on the phenyl rings. There is a reduction in 〈R²〉, 〈S²〉, and C_n accompanying the substitutions. The introduction of other substituents on a cyclohexyl polycarbonate results in an increase in all chain dimensions including the persistence length. Also, the cyclohexyl or trimethylcyclohexyl substituents do not significantly alter the overall average shape of the chains. Substitutions both on the phenyl rings and at the isopropylidene linkage lead to a compaction of the polymer chain, but the effect is more pronounced when due to substituents on phenyl rings.     

Synthesis of heterometallic cluster compounds from Fe3(μ3-Te)2(CO)9 and comparisons with analogous sulfide clusters

Fe₃Te₂(CO)₉ is shown to be a useful precursor to a variety of heterometallic carbonyl clusters in reactions which appear to proceed via the intermediacy of Fe₂(Te₂)(CO)₆. Fe₃Te₂(CO)₉ decomposed in polar solvents to give Fe₂(Te₂)(CO)₆ which could be dimerized to Fe₄Te₄(CO)₁₂. Fe₃Te₂(CO)₉ reacted with C₅H₅Co(CO)₂ and Pt(C₂H₄)(PPh₃)₂ to give good yields of (C₅H₅CO)Fe₂Te₂(CO)₇ and Fe₂PtTe₂(CO)₆(PPh₃)₂, respectively. (C₅H₅Co)Fe₂Te₂(CO)₇ underwent reversible decarbonylation to give a mixture of two isomers of (C₅H₅Co)Fe₂Te₂(CO)₆ as established by ¹²⁵Te NMR spectroscopy. Upon reaction with Co₂(CO)₈, Fe₃Te₂(CO)₉ gave Co₂FeTe(CO)₉ or Co₄Te₂(CO)₁₁ depending on the reaction conditions. Co₄Te₂(CO)₁₁, like Fe₃Te₂(CO)₁₀ and (C₅H₅Co)Fe₂Te₂(CO)₇, can be reversibly decarbonylated. The assembly of Co₂FeTe(CO)₉ may be mechanistically related to the conversion of Fe₂(S₂)(CO)₆ to FeCo₂S(CO)₉ which was found to proceed via Co₂Fe₂S₂(CO)₁₁. Alternatively, Co₂Fe₂S₂(CO)₁₁ reacted photochemically with [C₅H₅Mo(CO)₃]₂ to give the known, chiral cluster (C₅H₅Mo)CoFeS(CO)₈. While Fe₂(Te₂)(CO)₆ thermally dimerized to Fe₄Te₄(CO)₁₂, Fe₂(S₂)(CO)₆ gave the analogous dimer only upon photolysis. In contrast to the stability of (C₅H₅CO)Fe₂Te₂(CO)₇, the reaction of C₅H₅Co(CO)₂ with Fe₂(S₂)(CO)₆ gave only (C₅H₅CO)Fe₂S₂(CO)₆ which is proposed to be structurally related to Fe₃S₂(CO)₉ and not (C₅H₅Co)₃S₂ or Fe₂PtS₂(CO)₆(PPh₃)₂.     

Öffnung einer FeFe-Bindung in [Fe3(CO)9(μ3-SR)]− durch elektrophile reagenzien aus der fünften und sechsten hauptgruppe

The anions of the cluster salt [Fe₃(CO)₉(μ₃-SR)][t-C₄H₉NH₃] (R = t-C₄H₉ (I); R = C₆H₁₁ (II)) react with monohalides XCl (X = PR′₂, AsR′₂, SbR′₂, SR′, SeR′; R′ = Alkyl, Aryl) to give the neutral complexes Fe₃(CO)₉(μ₃-SR)(μ₂-X) (III–XII).X-ray analyses show that in these products one of the FeFe bonds is opened and bridged by the μ₂-ligand X. In some cases, the synthesis of the trinuclear clusters is accompanied by formation of the dinuclear species Fe₂(CO)₆(μ₂-SR)(μ₂-X) (X = PPh₂, (XIII); X = SPh, (XIV) as by-products. In a formal sense this corresponds to loss of an Fe(CO)₃ group from the trinuclear complexes. The geometry of Fe₂(CO)₆(μ₂-SC₆H₁₁)(μ₂-PPh₂) (XIII) has been elucidated by X-ray analysis.     

Gezielte synthesen von zweifach μ3-verbrückten dreikernigen eisenclustern Fe3(CO)9(μ3-S)(μ3-X) (X = PR,AsR, SO) aus [Fe3(CO)9(μ3-S-t-C4H9)]−

The cluster anion [Fe₃(CO)₉(μ₃-S-t-C₄H₉)]^?, which is easily obtained by deprotonation from the cluster compound Fe₃(CO)₉(μ₂-H)(μ₃-S-t-C₄H₉), reacts with XCl₂ by elimination of t-C₄H₉Cl and Cl^? to give the clusters Fe₃(CO)₉(μ₃-S)(μ₃-X) (X = PR: I, X = AsR: II, X = SO: III), in which one edge of the iron triangle is opened. The μ₃-PR-bridged clusters I can also be obtained by reactions of SCl₂ with the anions [Fe₃(CO)₉(μ₃-PR)]^2?, prepared from Fe₃(CO)₉(μ₂-H)₂(μ₃-PR) by deprotonation. The geometry of I and II is exemplified by X-ray structure analyses. Experimental evidence for a reaction pathway, proposed for the high yield syntheses of I, is discussed.     

The reaction of Ir4(CO)12 with bases

The reaction of Ir₄(CO)₁₂ with potassium hydroxide in methanol and/or with sodium in tetrahydrofuran leads to the carbonyliridate anions [HIr₄(CO)₁₁]^?, [Ir₆(CO)₂₂]^2?, [Ir₈(CO)₂₀]^2?, [Ir₆(CO)₁₅]^2? and [Ir(CO)₄]^? obtained as salts with bulky cations. From these, the tetranuclear carbonyl hydride H₂Ir₄(CO)₁₁ and the hexanuclear carbonyl compound Ir₆(CO)₁₆ are also obtained.     

A synthetic route to heteronuclear clusters containing iridium and rhodium: X-ray crystal structures of [IrOs3(μ-H)2(μ-Cl)(CO)12] and [Ir2Rh2(μ-CO)(μ3-CO)2(CO)4(η-C5Me5)2]

The iridium and rhodium complexes [MCl(CO)₂(NH₂C₆H₄Me-4)] (M = Ir or Rh) react with [Os₃(μ-H)₂(CO)₁₀] to give the tetranuclear clusters [MOs₃(μ-H)₂(μ-Cl)(CO)₁₂]; the iridium compound being structurally identified by X-ray diffraction. Similarly, [IrCl(CO)₂(NH₂C₆H₄Me-4)] and [Rh₂(μ-CO)₂(η-C₅Me₅)₂] afford the tetranuclear cluster [Ir₂Rh₂(μ-CO)(μ₃-CO)₂(CO)₄(η-C₅Me₅)₂], also characterised by single-crystal X-ray crystallog     

Kristallstruktur, 1H-NMR- und massenspektrum von tricarbonylferracyclopentadien-tricarbonyleisen,C4H4Fe2(CO)6

The preparation, mass and ¹H NMR spectra and the crystal structure of C₄H₄Fe₂(CO)₆ are described.The compound can be prepared in a simple way by reaction of Fe₃(CO)₁₂ with thiophene (yield 17%). It forms monoclinic crystals (space group P2₁/c) with four formula units in the unit cell. The positions of all atoms (except H atoms) have been determined and refined until an R value of 0.058 was reached. Within the practically planar ferracyclopentadiene ring, multiple bond orders must be assumed for all bonds. One of the six CO groups in the molecule is bent and represents a strongly unsymmetrical bridging carbonyl group (“semibridging carbonyl group”).     

Bis{μ‐(E)‐2‐[(2‐pyridylamino)(2‐pyridylimino)methyl]benzato}bis[acetatozinc(II)] tetrahydrate

In the C₂‐symmetric dinuclear title complex, [Zn₂(C₁₈H₁₃N₄O₂)₂(C₂H₃O₂)₂]·4H₂O, each Zn^II ion is five‐coordinated in a distorted trigonal bipyramidal fashion by one carboxylate O atom from one benzoate ligand, one imine N atom and two pyridyl N atoms from a second benzoate ligand, and one O atom from an acetate anion. The two Zn atoms are bridged by the two benzoate ligands, forming a dinuclear structure with a 14‐membered macrocycle. Adjacent dinuclear units are further connected by extensive hydrogen bonds involving the solvent water molecules, giving a three‐dimensional hydrogen‐bonded framework. The framework can be regarded as an example of the four‐connected node network of the PtS topology.     

The molecular structures of H2Os3(CO)10, H(SC2H5)Os3(CO)10 and (OCH3)2Os3(CO)10

X-ray crystallographic analyses of H₂Os₃(CO)₁₀, H(SC₂H₅)Os₃(CO)₁₀ and (OCH₃)₂Os₃(CO)₁₀ are reported. Although hydrogen atom positions have not been located, the essential isostructural nature of the three commplexes establishes the hydride ligands as bridging two metal atoms, separated by 2.670 Å, with a formal bond order of two; the bridging hydrido- and thiolato-ligands span an osmium---osmium bond of length 2.863 Å and formal bond order one; the two μ-methoxy ligands bridge two metal atoms separated by 3.078 Å which, by simple 18 electron rule counting, has a metal---metal bond order of zero. Some general comments are made on the structures of polynuclear transition metal carbonyls.