Trimetallic Complexes Research Articles

Synthesis, solution behaviour and potential anticancer activity of new trinuclear organometallic palladium(II) complex of {S}-1-phenylethyl dithiooxamide: Comparison with the trinuclear heterobimetallic platinum(II) analogue

Addition of H2R2DTO (R = {S}-1-phenylethyl and DTO = dithiooxamide) to the bis(benzonitrile)palladium(II) chloride complex in chloroform afforded the mononuclear Pd(DTO)2·2HCl complex. The complex treated with NaHCO3 for removing of HCl and then reacted with [Pd(ƞ3-allyl)(µ-Cl)]2 for preparation of a new trimetallic organopalladium(II) complex. The molecular structure of the trimetallic complex was determined by X-ray diffraction indicating a planar geometry around each palladium center. Also, variable temperature spectroscopy for this complex was performed in CDCl3 in the range 298–390 K, and simulations of the dynamic spectra were performed using the gNMR program. A comparison between the target-based activity of the Pd(II) complex and its trinuclear heterobimetallic platinum(II) analogue as potential anticancer agents was also conducted. All the biological tests showed that both Pd(II) and Pt(II) complexes can fairly inhibit cathepsin B (Cat-B) and cathepsin L (Cat-L) as well as two out of three activities of 20S proteasome.

Synthesis and kinetics of photochromic carboxy-substituted dithizonatophenylmercury(II)

With the aim of improving water-solubility and providing anchor points for follow-up reactions, the well-known intensely colored green analytical reagent, dithizone (H2Dz), was functionalized by two carboxylic acid substituents. Similarly, sulfacetamide and sulfonyl substituents were also employed, but its dithizone products decomposed in aqueous medium. The crystal structure of the nitroformazan carboxylic acid intermediate is reported. Its bent conformation is maintained by intramolecular hydrogen-bonding. Together with the two added dithizone carboxylate end groups the three spatially removed points are now available for complexation, eg. with phenylmercury(II) moieties. As opposed to the otherwise single-metal PhHgHDz(COOH)2 complex, added heavy mercury atoms in PhHgHDz(COOHgPh)2 inhibit photochromism in the tri-metallic complex. Kinetic studies of the photochromic return reaction of PhHgHDz(COOH)2 show the reaction rate to be linearly dependant on concentration and exponentially dependant on temperature, with rate constant of 0.0084 s−1 at 0 °C, i.e. four times faster than observed for the unsubstituted complex, PhHgHDz.

Syntheses and Structures of Ruthenium Complexes Containing a Ru-H-Tl Three-Center-Two-Electron Bond.

Treatment of CpRuH(PP) (PP=dppm, dppe) with TlPF6 produced [CpRu(H)(Tl)(PP)]PF6 . X-ray diffraction and computational studies suggest that the complexes contain a Ru-H-Tl 3c-2e bond and can be viewed as the first σ-complexes of period 6 main-group hydrides [CpRu{η2 -(H-Tl)}(PP)]PF6 or [Tl{η2 -H-RuCp(PP)}]PF6 . The complexes can be stored as a solid at room temperature for days without appreciable decomposition, but are unstable in solution and evolved to the trimetallic complexes [{CpRu(PP)}2 (μ-Tl)]PF6 .

Electronic Energy Transduction from {Ru(py)4} Chromophores to Cr(III) Luminophores.

Despite the large body of work on {Ru(bpy)2} sensitizer fragments, the same attention has not been devoted to their {Ru(py)4} analogues. In this context, we explored the donor-acceptor trans-[Ru(L)4{(μ-NC)Cr(CN)5}2]4-, where L = pyridine, 4-methoxypyridine, 4-dimethylaminopyridine. We report on the synthesis and the crystal structure as well as the electrochemical, spectroscopical, and photophysical properties of these trimetallic complexes, including transient absorption measurements. We observed emission from chromium-centered d-d states upon illuminating into either MLCT or MM'CT absorptions of {Ru(L)4} or {Ru-Cr}, respectively. The underlying energy transfer is as fast as 600 fs with quantum efficiencies ranging from 10% to 100%. These results document that {Ru(py)4} sensitizer fragments are as efficient as {Ru(bpy)2} in short-range energy transfer scenarios.

Bis[μ-N,N′-(pyridine-2,6-diyl)bis(trimethylsilylamido)-1κ2N1,N2;2:3κ2N6:N6]bis(tetrahydrofuran)-2:3κ2O-1-nickel(II)-2,3-lithium(I)

The title complex, [Li2Ni(C11H21N3Si2)2(C4H8O)2], is a trimetallic complex of two LiIcations and a NiIIcation bridged by twoN,N′-(pyridine-2,6-diyl)bis(trimethylsilylamide) ligands that crystallizes in theFdd2 space group. The molecule hasC2rotational symmetry, with the NiIIcation located on the twofold axis. The coordination sphere of the NiIIcation is composed of two amido N and two pyridyl N-atom donors in a distorted square-planar geometry. The LiIcations are coordinated by two amido N-atom donors and a tetrahydrofuran molecule with a long interaction with a pyridyl N-atom donor. The coordinating tetrahydrofuran ligand and a trimethylsilyl group are disordered. Intra- or intermolecular hydrogen bonding, as well as π–π stacking, are not observed between the molecules, likely indicating that weak electrostatic interactions are the dominant feature leading to the crystal structure.

(Di‐tert‐butylphosphanylethyl)cyclopentadienylnickel Chelates with Alkyl, Alkenyl, Aryl, and Alkynyl Ligands: Hints to Cumulenylidene Resonance Forms

Cyclopentadienylalkylphosphane chelate complexes have been investigated in depth for many transition matals, but to a much lesser extent for nickel. On the basis of earlier investigations of cyclopentadienylalkylphosphane nickel chelates, a number of new alkyl, aryl, alkenyl, and alkynyl complexes, including some bearing functional groups, were prepared and fully characterized. These include for the first time di‐ and trimetallic complexes as well as compounds with a ferrocene unit as part of the extended π system. A number of quaternized 2‐pyridylethynyl complexes are presented, for which cyclovoltammograms, NMR spectroscopic data, and DFT calculations provide hints to a significant contribution of cumulenylidene resonance forms.

Trackable Metallodrugs Combining Luminescent Re(I) and Bioactive Au(I) Fragments.

Hetero-bimetallic and -trimetallic complexes were synthesized by the combination of different metallic fragments, a luminescent Re(I) species, and a bioactive Au(I) derivative. A ditopic P,N-donor ligand (L) was used as linker between both metals, affording six new bipyridine (bipy) Re(I)/Au(I) hetero-metallic complexes of the type fac-[Re(bipy)(CO)3(LAuCl)]+ (4-6) and [(fac-[Re(bipy)(CO)3(L)])2Au]3+ (7-9) after a thorough synthetic procedure. Their emission is associated with a triplet metal-to-ligand charge transfer (Re(dπ) → bipy(π*)) transition and red-shifted in polar solvents with lifetimes in the range of nanoseconds and quantum yield values up to 12.5%. Cytotoxicity values in A549 cells of hetero-trimetallic species are almost twice that for the hetero-bimetallic (ca. 37 vs 69 μM, respectively), being the L-Au fragment the source of the antiproliferative activity. Species 7 and 8 showed similar behavior by fluorescence microscopy, with a nonuniform cytoplasmatic distribution, a clear accumulation in single spots at the edge of the inner cell membrane as well as in areas within the nucleus. Preliminary studies suggest the DNA as one of the targets and passive diffusion as the entrance pathway.

The Stepwise Reaction of Rhodium and Iridium Complexes of Formula [MCl2 (κ4 C,N,N',P-L)] with Silver Cations: A Case of trans-Influence and Chiral Self-Recognition.

Acetonitrile suspensions of the dichlorido complexes [MCl2 (κ4 C,N,N',P-L)] [M=Rh (1), Ir (2)] react with AgSbF6 in a 1:2 molar ratio affording the bis-acetonitrile complexes [M(κ4 C,N,N',P-L)(NCMe)2 ][SbF6 ]2 (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido-bridged compounds [{MCl(κ4 C,N,N',P-L)}2 (μ-Cl)][SbF6 ] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato-complexes [MCl(κ4 C,N,N',P-L)(Solv)][SbF6 ] (Solv=H2 O, MeCN, 7-10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ4 C,N,N',P-L)(NCMe)(μ-Cl)}2 Ag][SbF6 ]3 in which a silver cation joints two cationic monosubstituted acetonitrile-complexes [MCl(κ4 C,N,N',P-L)(NCMe)]+ through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh2 group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self-recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X-ray diffraction methods.

Transition‐Metal Complexes with Ferrocene‐Bridged Bis(imidazolin‐2‐imine) and Bis(diaminocyclopropenimine) Ligands

The reaction of the ferrocene-bridged bis(imidazolin-2-imine) ligand N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,1′-ferrocenediamine [fc(NIm)2] with MCl2 salts furnished the complexes [{fc(NIm)2}MCl2] (M = Mn, Fe, Co, Ni, Cu, Zn), which were structurally and spectroscopically characterized. The iron complex was oxidized by reaction with ferrocenium hexafluoroantimonate, and both compounds, [{fc(NIm)2}FeCl2] and [{fc(NIm)2}FeCl2]SbF6, were further studied by means of Mossbauer spectroscopy, SQUID magnetometry, and single-crystal X-ray diffraction, revealing that oxidation occurred at the tetrahedral FeN2Cl2 moiety. The CuX (X = Cl, Br, I) complexes of fc(NIm)2 were synthesized, affording dimeric (X = Cl, Br) or polymeric (X = I) structures. In addition, the ligand bis(N,N,N′,N′-tetraisopropyl-2,3-diaminocyclopropen-1-ylidene)-1,1′-ferrocenediamine [fc(NCyp)2], was prepared and the trimetallic complex [{fc(NCyp)2}Pd2Cl4] was synthesized and structurally characterized. The attempted synthesis of the corresponding nickel complex furnished single crystals of the composition [{fc(NHCyp)2}Cl(NiCl3)]; X-ray diffraction analysis afforded the first crystal structure of the [Ni2Cl6]2– anion.

Heteroleptic monometallic and trimetallic ruthenium(II) complexes incorporating a π-extended dipyrrin ligand: Light-activated reactions with the A549 lung cancer cell line

A heteroleptic monometallic ruthenium(II) and a heteroleptic trimetallic ruthenium(II) complex have been synthesized and characterized. Both complexes have an overall 3+ charge, with the charge density greater for the monometallic complex. The electronic spectra of the monometallic ruthenium(II) complex exhibits intense π-π* transitions associated with the bipyridyl groups along with overlapping metal to ligand charge transfer (MLCT) and ligand centered π-π* transitions ranging from 520nm to approximately 600nm. The trimetallic ruthenium(II) complex, on the other hand, displays more well defined transitions with the expected π-π* transition of the bipyridyl groups at 294nm and Ru(dπ) to bpy(π*) MLCT transitions at 355nm and 502nm. In addition to these absorption bands an intense transition, 578nm, resulting from overlapping dipyrrin (π-π*) and Ru(dπ) to dipyrrin(π*) transitions is observed. Electrochemical and spectroelectrochemical experiments were used to help in assigning these transitions. Irradiation of the complexes in the presence of plasmid DNA within the photodynamic therapy window (600nm to 850nm) reveal, using electrophoresis, that both complexes are capable of causing photo-damage to the DNA backbone. The trimetallic ruthenium(II) complex; however, also shows the ability to generate photoinduced DNA damage in the absence of oxygen, suggesting a photo-oxidative process. Studies of the complexes toward lung cancer cells (A549 cell line) in the absence of light indicate little cytotoxicity up to 50μM. Upon irradiation of the cells with a low power 420nm light source the trimetallic complex showed considerably greater photo-cytotoxicity compared to the monometallic analog. A dose-dependent response curve gives an IC50 of 92μM for complex B.

Coordination chemistry of phosphinocarbynes: phosphorus vs. carbyne site selectivity.

The phosphinocarbyne complex [W([triple bond, length as m-dash]CPPh2)(CO)2(Tp*)] (1: Tp* = hydrotris(dimethylpyrazolyl)borate) coordinates transition metal fragments via the phosphine to form bimetallic species [W{[triple bond, length as m-dash]CPPh2RhCl2(Cp*)}(CO)2(Tp*)] (2) and [W([triple bond, length as m-dash]CPPh2AuCl)(CO)2(Tp*)] (3). Appropriately tailored sterics allow for complexation of a second equivalent of AuCl to afford the trimetallic complex [W{η2-C(AuCl)PPh2AuCl}(CO)2(Tp*)] (4), containing an Au-W-C dimetallacyclopropene connectivity. Similarly, AuCl binds to the carbyne linkage in [W{[triple bond, length as m-dash]CP([double bond, length as m-dash]S)Ph2}(CO)2(Tp*)], yielding [W{η2-C(AuCl)P([double bond, length as m-dash]S)Ph2}(CO)2(Tp*)] (5). In the case of auration of the ditungsten species [W2(μ-C2PPh)(CO)4(Tp*)2] (6), variation in the stoichiometry leads to trimetallic [W2(μ-C2PPhAuCl)(CO)4(Tp*)2] (7) and pentametallic [W2{μ-(η2-CAuCl)2PPhAuCl}(CO)4(Tp*)2] (8) complexes, via a proposed tetrametallic intermediate [W2{μ-(η2-CAuCl)2PPh}(CO)4(Tp*)2], the site selectivity being dictated by aurophilic interactions.

Discrete bimetallic Co(II) phosphinate complexes supported by 2,6-dimesitylphenylphosphinate ligand

Reactions of Co(II) sources with 2,6-dimesitylphenylphosphinate were conducted in two phase (toluene/water) solvent systems. The presence of small coordinating anions (X) and neutral ligands (L) was found to be a determining factor for the outcome of these reactions. When both were present, discrete bimetallic complexes of the type [X-Co-μ-(DmpP(H)O2)3-Co-L] were produced (X=Cl−, L=p-fluorobenzylnitrile (1a), p-cyanoaniline (1b), acetonitrile (1c), or pyridine (1d); X=Br−, L=DMF (2); X=thiocyanate, L=H2O (3)). In these complexes both Co(II) centers are in distorted tetrahedral ligand geometries that are formed by the three oxygens of the bridging phosphinate ligands and either X or L ligands. In the absence of a coordinating anion and with p-cyanoaniline as a small neutral ligand bimetallic cation [p-NH2-C6H4-CN-Co-μ-(DmpP(H)O2)3-Co(H2O)3]+ (4) was obtained. Cation 4 contains a tetrahedral and an octahedral Co(II) center; an additional phosphinate serves as a counterion and is attached to the cation via hydrogen bonding to water molecules coordinated to the octahedral cobalt center. Complexes 1a–d, 2, 3, and 4 [DmpP(H)O2] were characterized by elemental analyses, spectroscopic (UV–Vis and IR) and magnetic measurements, and by single crystal X-ray diffraction experiments. When Co(BF4)2 was reacted with two equivalents of DmpP(H)O2− with no other neutral ligands present, slow evaporation of the reaction mixtures produced blue powdery solids. In one of such reactions several large blue crystals were produced and analyzed by single crystal X-ray diffraction. The compound was characterized as trimetallic complex [((H2O)DmpP(H)O2-Co-(μ-DmpP(H)O2)2)2Co] (5). The formation of compound 5 suggests that under selected conditions formation of oligomeric/polymeric compounds with the general formula “Co(DmpP(H)O2)2” may be possible.

Donor-Solvent-Dependent Cluster Formation of (C5Me5)SmI2(THF)x-Type Half-Sandwich Complexes

In this study, we demonstrate the structural variety of the Cp*SmIy system with respect to the amount of donor molecules (THF) present. The reaction of SmI2(THF)2 with 0.5 equiv of bis(pentamethylcyclopentadienyl)lead(II), PbCp*2, in THF gives the highly solvated monomeric complex Cp*SmI2(THF)3, when crystallized from THF. The same reaction performed in n-hexane followed by crystallization from toluene gave the partially solvated trimetallic complex [Cp*3Sm3I(μ2-I)3(μ3-I)2(THF)2]. Recrystallization of the Sm3 cluster from either C6D6 at ambient temperature or toluene at −40 °C produced the tetrametallic complex [Cp*4Sm4I(μ2-I)4(μ3-I)2(μ4-I)(THF)]. Reaction of SmI2, obtained via treatment of SmI2(THF)2 with excess AlEt3 in n-pentane, with 0.5 equiv of PbCp*2 in toluene led to the donor-free mixed-valent pentametallic complex [Cp*5Sm5(μ2-I)4(μ3-I)4(μ5-I)]. All compounds were characterized by single-crystal X-ray structure analysis.

Transition‐Metal Complexes with Ferrocene‐Bridged Bis(imidazolin‐2‐imine) and Bis(diaminocyclopropenimine) Ligands

The reaction of the ferrocene‐bridged bis(imidazolin‐2‐imine) ligand N,N′‐bis(1,3‐diisopropyl‐4,5‐dimethylimidazolin‐2‐ylidene)‐1,1′‐ferrocenediamine [fc(NIm)2] with MCl2 salts furnished the complexes [{fc(NIm)2}MCl2] (M = Mn, Fe, Co, Ni, Cu, Zn), which were structurally and spectroscopically characterized. The iron complex was oxidized by reaction with ferrocenium hexafluoroantimonate, and both compounds, [{fc(NIm)2}FeCl2] and [{fc(NIm)2}FeCl2]SbF6, were further studied by means of Mössbauer spectroscopy, SQUID magnetometry, and single‐crystal X‐ray diffraction, revealing that oxidation occurred at the tetrahedral FeN2Cl2 moiety. The CuX (X = Cl, Br, I) complexes of fc(NIm)2 were synthesized, affording dimeric (X = Cl, Br) or polymeric (X = I) structures. In addition, the ligand bis(N,N,N′,N′‐tetraisopropyl‐2,3‐diaminocyclopropen‐1‐ylidene)‐1,1′‐ferrocenediamine [fc(NCyp)2], was prepared and the trimetallic complex [{fc(NCyp)2}Pd2Cl4] was synthesized and structurally characterized. The attempted synthesis of the corresponding nickel complex furnished single crystals of the composition [{fc(NHCyp)2}Cl(NiCl3)]; X‐ray diffraction analysis afforded the first crystal structure of the [Ni2Cl6]2– anion.

Ultrafast kinetics of supramolecules with a Ru(II)- or Os(II)-polypyridyl light absorber, cis-Rh(III)Cl2-polypyridyl electron collector, and 2,3-bis(2-pyridyl)pyrazine bridge

The femtosecond transient absorption spectra (fsTA) and excited state kinetics for a series of six structurally related mixed-metal polypyridyl supramolecules are reported. Each complex consists of one or two light absorbers (LA) with Ru(II) or Os(II) centers attached to a Rh(III)-centered electron collector (EC) by an aromatic bridging ligand (BL). The resulting bimetallic and trimetallic complexes have LA-BL-EC and LA-BL-EC-BL-LA architectures, respectively. Excitation at 470nm light populates metal-to-bridging ligand charge transfer states (MLCT), showing a transient absorption band near 380nm due to π→π∗ transitions of a bridging ligand-localized radical anion and a transient bleach around 525nm resulting from formal oxidation of the LA metal in the excited state. Loss of the ligand localized radical signal during the first 10ps reflects conversion of the excited state population from an MLCT state into metal-to-metal (i.e. M(dπ)-to-Rh(dσ∗)) charge transfer states (MMCT). Each complex shares a similar ultrafast component, indicating that the kinetics governing MLCT→MMCT population transfer do not depend on the nature of the LA. Return to the ground state, however, is strongly LA dependent and controlled by the free-energy difference between the MMCT state and ground state, as well as an associated large reorganization energy.

Efficient Synthesis of One‐ and Two‐Dimensional Multimetallic Gold–Bis(dithiolene) Complexes

Multimetallic complexes having π‐conjugated dithiolate ligands have recently received attention because of their unique solid‐state properties. Reported herein are efficient and versatile routes for the synthesis of structurally well‐defined multimetallic gold–bis(dithiolene) complexes. A dichlorogold(III) complex having a benzene‐1,2‐dithiolate ligand was prepared as a key terminal unit. A one‐dimensional dimetallic gold complex was synthesized in good yield by using benzene‐1,2,4,5‐tetrathiolate as a bridging ligand. Furthermore, by using benzenehexathiolate as a bridging ligand, this strategy was applied to the synthesis of a two‐dimensional trimetallic complex with a starburst structure. The solid‐state structures of the anionic complexes were unambiguously confirmed by X‐ray diffraction analyses.

Insertion Reactions of Neutral Phosphidozirconocene Complexes as a Convenient Entry into Frustrated Lewis Pair Territory.

Neutral phosphidozirconocene complexes [Cp2Zr(PR2)Me] (Cp=cyclopentadienyl; 1a: R=cyclohexyl (Cy); 1b: R=mesityl (Mes); 1c: R=tBu) undergo insertion into the Zr-P bond by non-enolisable carbonyl building blocks (O=CR'R''), such as benzophenone, aldehydes, paraformaldehyde or CO2, to give [Cp2Zr(OCR'R''PR2)Me] (3-7). Depending on the steric bulk around P, complexes 3-7 react with B(C6F5)3 to give O-bridged cationic zirconocene dimers that display typical frustrated Lewis pair (FLP)/ambiphilic ligand behaviour. Thus, the reaction of {[Cp2Zr(μ-OCHPhPCy2)][MeB(C6F5)3]}2 (10a) with chalcone results in 1,4 addition of the Zr(+)/P FLP, whereas the reaction of {[Cp2Zr(μ-OCHFcPCy2)][MeB(C6F5)3]}2 (11a; Fc=(C5H4)CpFe) with [Pd(η(3)C3H5)Cl]2 yields the unique Zr-Fe-Pd trimetallic complex 13a, which has been characterised by XRD analysis.

Complexes comprising ‘dangling’ phosphorus arms and tri(hetero)metallic butenynyl moieties

Trans-RuCl2(PP3)2 (1a) (PP3 = tris[2-(diphenylphosphino)ethyl]phosphine) was prepared by reaction of RuCl2(PPh3)3 with 2 eq. PP3. Through coordination of two potentially tetradentate ligands in a bidentate arrangement, four uncoordinated phosphine moieties remain readily available for subsequent reaction. This is demonstrated through their facile oxidation with hydrogen peroxide, providing trans-RuCl2(PP[PO]2)2 (1b) (PP[PO]2 = bis[2-(diphenylphosphine oxide)ethyl][2-(diphenylphosphino)ethyl]phosphine). Whilst chloride abstraction reactions from 1a appear slow (typical for trans dichlorides), cis-RuCl2(PP3) is shown to react rapidly with ethynylferrocene under ‘Dixneuf’ conditions (CH2Cl2, NaPF6, NEt3), providing the tri(hetero)metallic butenynyl complex [(PP3)Ru(η3–FcC3CHFc)]PF6 (2, Fc = ferrocenyl). The pendant groups of 1a-b offer great potential for future coordination studies (for example, to prepare mixed transition metal/lanthanide materials), whereby the facile synthetic route to 2 suggests a path towards examination of complex mixed-valence systems comprising multiple redox-active centres.

Synthesis and reactivity of di- and tri-metallic complexes containing the TpRu(PPh3) fragment

Treatment of the TpRu complex Tp(PPh3)2RuCl (Tp = HB(pz)3, pz = pyrazolyl) (1) with ethynylferrocene in MeOH gave the trimetallic alkenyl ketone complex Tp(PPh3)Ru{C(Fc) = CHC(O)CH2(Fc)} (Fc=(η5-C5H4)Fe(η5-C5H5)) (2). Intriguingly, a similar reaction was performed in the presence of NaOMe afforded the dimetallic acetylide complex Tp(PPh3)2Ru–CC-Fc (3). A number of new cationic vinylidene complexes [Tp(PPh3)2Ru{ = CC(Fc)CH2R}]+ [4a, R = CN; 4b, R = HCCH2; 4c, R = CHC(CH3)2; 4d, R = Ph] have been prepared by electrophilic addition of organic halides to complex 3. The substitution reaction of 4a with pyrazole is followed by an intramolecular nucleophilic addition of the nitrogen atom at the α-carbon atom and removal of HI to afford the metallacyclic complex, Tp(PPh3)Ru(C3H3NN)CC(Fc) CH2CN (5a). All of the complexes are identified by spectroscopic methods as well as elementary analysis. The structure of 2 has been determined by X-ray diffraction analysis. Pathways for the synthesis of these compounds are proposed.

Alkyl Chain Growth on a Transition Metal Center: How Does Iron Compare to Ruthenium and Osmium?

Industrial Fischer-Tropsch processes involve the synthesis of hydrocarbons usually on metal surface catalysts. On the other hand, very few homogeneous catalysts are known to perform a Fischer-Tropsch style of reaction. In recent work, we established the catalytic properties of a diruthenium-platinum carbene complex, [(CpRu)2(μ2-H)(μ2-NHCH3)(μ3-C)PtCH3(P(CH3)3)2](CO)n+ with n = 0, 2 and Cp = η5-C5(CH3)5, and showed it to react efficiently by initial hydrogen atom transfer followed by methyl transfer to form an alkyl chain on the Ru-center. In particular, the catalytic efficiency was shown to increase after the addition of two CO molecules. As such, this system could be viewed as a potential homogeneous Fischer-Tropsch catalyst. Herein, we have engineered the catalytic center of the catalyst and investigated the reactivity of trimetal carbene complexes of the same type using iron, ruthenium and osmium at the central metal scaffold. The work shows that the reactivity should increase from diosmium to diruthenium to diiron; however, a non-linear trend is observed due to multiple factors contributing to the individual barrier heights. We identified all individual components of these reaction steps in detail and established the difference in reactivity of the various complexes.