Trimetallic Complexes Research Articles

Preparation, Properties, and Reactivity of (Aminoferrocenyl)(ferrocenyl)carbene(pentacarbonyl)chromium(0) as Bulky Isolobal Trimetallo‐amide

AbstractNucleophilic substitution of the ethoxy substituent in the Fischer carbene complex (ethoxy)(ferrocenyl)carbene(pentacarbonyl)chromium(0) (1) by ferrocenyl amide [Fc‐NH]– [2‐H]– gives the hetero trimetallic complex (aminoferrocenyl)(ferrocenyl)carbene (pentacarbonyl)chromium(0) (3). As the Cr(CO)5 fragment is isolobal to oxygen or sulfur 3 can be viewed as an isolobal metallo analogue to diferrocenylamide (Fc)(FcNH)C=O (4) and diferrocenylthioamide (Fc)(FcNH)C=S (5). The impact of the formal replacement of O/S by Cr(CO)5 in 3 is studied with respect to steric and electronic consequences as well as reactivity by spectroscopic, diffraction, electrochemical and theoretical methods.

Luminescent Mechanochromism in a Gold(I)–Copper(I) N-Heterocyclic Carbene Complex

The silver(I) species [Ag(benzim(CH2py)2)2]PF6 (1) was prepared by refluxing the ligand precursor [H(benzim(CH2py)2)2]PF6 with Ag2O and aqueous sodium hydroxide in dichloromethane. Simple transmetalation of 1 with tetrahydrothiophenegold(I) chloride forms the gold(I) analogue [Au(benzim(CH2py)2)2]PF6 (2). The addition of 2 equiv of [Cu(NCCH3)4]PF6 to 2 in acetonitrile produces a blue-luminescent, trimetallic complex, [AuCu2(benzim(CH2py)2)2(NCCH3)4](PF6)3·2CH3CN (3·2CH3CN). When blue-luminescent 3·2CH3CN is exposed to air, the complex loses four acetonitrile molecules, and the emission of the desolvated complex (4) appears aquamarine. Crystallization of 4 from different solvents produces the complexes [AuCu2(benzim(CH2py)2)2](PF6)3 (5) and [AuCu2(benzim(CH2py)2)2(NCCH2CH3)2](PF6)3 (6). Upon grinding, both 3·2CH3CN and 4 exhibit mechanochromic transformations to a yellow-luminescent powder (ground-4). The reversible mechanochromic transformation of 3·2CH3CN to ground-4 is a crystalline-to-amorphous conversion accompanied by partial desolvation. The luminescent mechanochromism of 4 to ground-4 is an "amorphous-to-amorphous" process and does not require solvent loss. In addition to their mechanochromic properties, both 3·2CH3CN and 4 exhibit luminescent thermochromism through desolvation to form a weak luminescent powder (7).

Synthesis, spectral, DFT, and semi-empirical study of trimetallic complexes with pyrazole-3,5-dicarboxylic acid containing Sn(IV) and Hg(II)

Trimetallic compounds have been synthesized by treating pyrazole-3,5-dicarboxylic acid with CS2, di-, and triorganotin(IV) chlorides and HgCl2 under reflux. The complexes have been characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy. Dipole moments and charges were calculated by the semi-empirical method. Two complexes were studied by DFT (BLYP/3-21G, B3LYP-3-21G) and semiempirical methods (PM3, PM6, MNDO, AM1, ab initio). IR data indicated that Sn was attached to oxygen of the carboxylic groups in a bidentate manner and adopted trigonal bipyramidal geometry. Hg was bonded to both S atoms of a ligand and exhibited square planner geometry in solid state. NMR data confirmed the four coordinated geometry of compounds in solutions.

Discrete Polymetallic Arrangements of AgI and CuI Ions Based on Multiple Bridging Phosphane Ligands and π–π Interactions

AbstractA simple and straightforward approach to new polymetallic AgI and CuI supramolecules is presented. The reaction of N,P,N,P,N ligand 2 with AgI ions affords a trimetallic complex bearing a triangular Ag3 core; metallophilic interactions are stabilized by ligands that display a multiple bridging coordination mode as 10‐electron donors. Heteroleptic polymetallic AgI and CuI complexes based on ligand 2 and the 1,12‐diazaperylene (dape) ligand are obtained by an alternative molecular organization of the polymetallic arrays compared to that in homoleptic complexes of ligand 2.

Di- and tri-nuclear-palladium complexes bearing piperidoimidazolin-2-ylidenes: synthesis, characterization, and catalytic applications

A series of di- and tri-nuclear Pd(II) complexes with piperidoimidazolin-2-ylidenes anchored to benzene ring via methylene spacers were synthesized. The obtained complexes were fully characterized by IR, 1H NMR, 13C NMR spectroscopy and elemental analysis. Molecular structures of two of the products have been determined by means of X-ray crystallography. Their catalytic performances in Suzuki-Miyaura and Mizoroki-Heck cross-coupling reactions were thoroughly investigated. The catalytic reactivity of new di- and tri-metallic complexes was compared with the monometallic systems. It is observed that the activities of the tri-nuclear Pd(NHC) complexes were higher than the corresponding mono- and di-nuclear complexes under the same conditions.

Multimetallic complexes based on a diphosphine-dithiocarbamate "Janus" ligand.

The HCl salt of the aminodiphosphine ligand HN(CH2CH2PPh2)2 reacts with [M(CO)4(pip)2] (M = Mo, W; pip = piperidine) to yield [M{κ(2)-HN(CH2CH2PPh2)2}(CO)4]. The molybdenum analogue readily loses a carbonyl ligand to form [Mo{κ(3)-HN(CH2CH2PPh2)2}(CO)3], which was structurally characterized. The same ligand backbone is used to form the new bifunctional ligand, KS2CN(CH2CH2PPh2)2, which reacts with nickel and cobalt precursors to yield [Ni{S2CN(CH2CH2PPh2)2}2] and [Co{S2CN(CH2CH2PPh2)2}3]. Addition of [AuCl(tht)] (tht = tetrahydrothiophene) to [Ni{S2CN(CH2CH2PPh2)2}2] leads to formation of the pentametallic complex, [Ni{S2CN(CH2CH2PPh2AuCl)2}2]. In contrast, addition of [PdCl2(py)2] (py = pyridine) to [Ni{S2CN(CH2CH2PPh2)2}2] does not lead to a trimetallic complex but instead yields the transmetalated cyclic compound [Pd{S2CN(CH2CH2PPh2)2}]2, which was structurally characterized. The same product is obtained directly from [PdCl2(py)2] and KS2CN(CH2CH2PPh2)2. In contrast, the same reaction with [PtCl2(NCPh)2] yields the oligomer, [Pt{S2CN(CH2CH2PPh2)2}]n. Reaction of KS2CN(CH2CH2PPh2)2 with cis-[RuCl2(dppm)2] provides [Ru{S2CN(CH2CH2PPh2)2}(dppm)2](+), which reacts with [AuCl(tht)] to yield [Ru{S2CN(CH2CH2PPh2AuCl)2}(dppm)2](+). Addition of [M(CO)4(pip)2] (M = Mo, W) to the same precursor leads to formation of the bimetallic compounds [(dppm)2Ru{S2CN(CH2CH2PPh2)2}M(CO)4](+), while treatment with [ReCl(CO)5] yields [(dppm)2Ru{S2CN(CH2CH2PPh2)2}ReCl(CO)3](+). Reaction of KS2CN(CH2CH2PPh2)2 with [Os(CH═CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole) provides [Os(CH═CHC6H4Me-4){S2CN(CH2CH2PPh2)2}(CO)(PPh3)2], but reaction with the analogous ruthenium precursor fails to yield a clean product.

English

English

Synthesis and structure of trinuclear W3S4 clusters bearing aminophosphine ligands and their reactivity toward halides and pseudohalides.

The aminophosphine ligand (2-aminoethyl)diphenylphosphine (edpp) has been coordinated to the W3(μ-S)(μ-S)3 cluster unit to afford trimetallic complex [W3S4Br3(edpp)3](+) (1(+)) in a one-step synthesis process with high yields. Related [W3S4X3(edpp)3](+) clusters (X = F(-), Cl(-), NCS(-); 2(+)-4(+)) have been isolated by treating 1(+) with the corresponding halide or pseudohalide salt. The structure of complexes 1(+) to 4(+) contains an incomplete W3S4 cubane-type cluster unit, and only one of the possible isomers is formed: the one with the phosphorus atoms trans to the capping sulfur and the amino groups trans to the bridging sulphurs. The remaining coordination position on each metal is occupied by X. Detailed studies using stopped-flow, (31)P{(1)H} NMR, and ESI-MS have been carried out in order to understand the solution behavior and the kinetics of interconversion among species 1(+), 2(+), 3(+), and 4(+) in solution. Density functional theory (DFT) calculations have been also carried out on the reactions of cluster 1(+) with the different anions. The whole set of experimental and theoretical data indicate that the actual mechanism of substitutions in these clusters is strongly dependent on the nature of the leaving and entering anions. The interaction between an entering F(-) and the amino group coordinated to the adjacent metal have also been found to be especially relevant to the kinetics of these reactions.

Slow hydrolysis of an organozirconium complex: The first polyoxometallic heptanuclear zirconium oxide

Herein we report controlled hydrolysis of an organozirconium trimetallic complex, [Cp*2(Me)Zr(μ-O)Zr(NMe2)2(μ-O)Zr(Me)Cp*2] (Cp* = η5-C5Me5) by slow hydrolysis pathway inside the glovebox resulting in unexpected formation of the first heptanuclear zirconium complex. The basic core of this zirconium complex is reminiscent of a butterfly like structure.

Evaluation of trimetallic Ru(II)- and Os(II)-Arene complexes as potential anticancer agents

Schiff-base ligands, tris-2-(salicylaldimine ethyl)amine and tris-2-(2-pyridylimine ethyl)amine (1 and 2) were prepared and complexed to Ru(II) and Os(II) entities to form new trimetallic complexes (3–10). The complexes are air- and moisture-stable and have been characterized fully using elemental analysis, FT-IR and NMR spectroscopy as well as HR-ESI-TOF-MS spectrometry. Related mononuclear analogues (11–14) were also prepared via the Schiff-base condensation reaction of propyl amine and the appropriate aldehyde to form propysalicylaldimine and propyl-2-pyridylimine ligands. Upon complexation with the respective metal dimers, ([OsCl2(p-cym)]2 and [OsBr2(p-cym)]2) complexes (11–14) formed and were characterized by elemental analysis, NMR, FT-IR spectroscopy and mass spectrometry. The cytotoxicity of the trimetallic complexes (3–10) and their mononuclear analogues were established against human osteosarcoma (MG63), human ovarian (A2780cisR; cisplatin-resistant) cancer cells and model human non-cancerous cells (KMST6, fibroblast). All the complexes exhibited moderate to high anti-cancer activities and the most potent complexes were further evaluated for their ability to inhibit DNA topoisomerase I (Topo I) – an enzyme key to cellular genetic processes, such as DNA replication and transcription.

Macrocyclic Salen–Bis-NHC Hybrid Ligands and Their Application to the Synthesis of Enantiopure Bi- and Trimetallic Complexes

Salen and NHC ligands are among the most important ligands for homogeneous catalysis. We have recently reported bimetallic complexes, in which both motifs have been merged for the first time. However, the intermetallic distances, which play a crucial role for cooperative bimetallic catalysis, were probably not appropriate in these first-generation hybrid catalysts. To generate heterobimetallic salen/NHC hybrid complexes with intermetallic distances suitable for cooperative catalysis, chiral macrocyclic hybrid ligands featuring a salen and two linked NHC donor moieties have been prepared in the present study. For the ligand formation, chiral enantiopure diamines as well as chiral enantiopure bisimidazoles were employed, and a matched/mismatched situation was found depending on the configuration of both chirality sources. Regioselective complexation of Zn(II), Ni(II), and Pd(II) by the salen N2O2 coordination sphere was efficiently accomplished. Subsequent coordination of the NHC units was achieved for Ag(I...

Light harvesting and directional energy transfer in long-lived homo- and heterotrimetallic complexes of Fe(II), Ru(II), and Os(II).

A new family of trimetallic complexes of the form [(bpy)2 M(phen-Hbzim-tpy)M'(tpy-Hbzim-phen)M(bpy)2](6+) (M=Ru(II), Os; M'=Fe(II), Ru(II), Os; bpy=2,2'-bipyridine) derived from heteroditopic phenanthroline-terpyridine bridge 2-{4-[2,6-di(pyridin-2-yl) pyridine-4-yl]phenyl}-1H-imidazole[4,5-f][1,10]phenanthroline (phen-Hbzim-tpy) were prepared and fully characterized. Zn(2+) was used to prepare mixed-metal trimetallic complexes in situ by coordinating with the free tpy site of the monometallic precursors. The complexes show intense absorptions throughout the UV/Vis region and also exhibit luminescence at room temperature. The redox behavior of the compounds is characterized by several metal-centered reversible oxidation and ligand-centered reduction processes. Steady-state and time-resolved luminescence data show that the potentially luminescent Ru(II)- and Os(II)-based triplet metal-to-ligand charge-transfer ((3)MLCT) excited states in the triads are quantitatively quenched, most likely by intercomponent energy transfer to the lower lying (3)MLCT (for Ru and Os) or triplet metal-centered ((3)MC) excited states of the Fe(II) subunit (nonluminescent). Interestingly, iron did not adversely affect the photophysics of the respective systems. This suggests that the multicomponent molecular-wire-like complexes investigated here can behave as efficient light-harvesting antennas, because all the light absorbed by the various subunits is efficiently channeled to the subunit(s) in which the lowest-energy excited states are located.

New class of scorpionate: tris(tetrazolyl)-iron complex and its different coordination modes for alkali metal ions.

We report formation of a new metallascorpionate ligand, [FeL3](3-) (IPtz), containing a Fe core and three 5-(2-hydroxyphenyl)-1H-tetrazole (LH2) ligands. It features two different binding sites, oxygen and nitrogen triangles, which consist of three oxygen or nitrogen donors from tetrazole. The binding affinities of the complex for three alkali metal ions were studied using UV spectrophotometry titrations. All three alkali metal ions show high affinities and binding constants (>3 × 10(6) M(-1)), based on the 1:1 binding isotherms to IPtz. The coordination modes of the alkali metals and IPtz in the solid were studied using X-ray crystallography; two different electron-donor sites show different coordination numbers for Li(+), Na(+), and K(+) ions. The oxygen triangles have the κ(2) coordination mode with Li(+) and κ(3) coordination mode with Na(+) and K(+) ions, whereas the nitrogen triangles show κ(3) coordination with K(+) only. The different binding affinities of IPtz in the solid were manipulated using multiple metal precursors. A Fe-K-Zn trimetallic complex was constructed by assembly of an IPtz ligand, K, and Zn precursors and characterized using X-ray crystallography. Oxygen donors are coordinated with the K ion via the κ(3) coordination mode, and nitrogen donors are coordinated with Zn metal by κ(3) coordination. The solid-state structure was confirmed to be a honeycomb coordination polymer with a one-dimensional infinite metallic array, i.e., -(K-K-Fe-Zn-Fe-K)n-.

Novel Trisphosphine Ligand Containing 1,3,5-Triazine Core, [2,4,6-C3N3{C6H4PPh2-p}3]: Synthesis and Transition Metal Chemistry

The trisphosphine ligand with triazine core, 2,4,6-tris{4-(diphenylphosphino)phenyl}-1,3,5-triazine (2), was synthesized in moderate yield by reacting 2,4,6-tris(4-bromophenyl)-1,3,5-triazine with 3 equiv of KPPh2. The tris(phosphine) 2 undergoes facile oxidation to give trischalcogenides 2,4,6-C3N3{C6H4P(E)Ph2-p}3 (E = O, 3; S, 4; Se, 5) on treatment with aqueous H2O2, elemental sulfur, or selenium. The reaction between 2 and [AuCl(SMe2)] yielded a trinuclear complex, [(AuCl)3{2,4,6-C3N3(C6H4PPh2-p)3}] (6), which on further treatment with pyridyl ligands such as 2,2'-bipyridine (2,2'-bpy) and 1,10-phenanthroline (1,10-phen) produced the mixed-ligand complexes [{Au(2,2'-bpy)}3{2,4,6-C3N3(C6H4PPh2-p)3}](OTf)3 (7) and [{Au(1,10-phen)}3{2,4,6-C3N3(C6H4PPh2-p)3}](OTf)3 (8), where OTf indicates trifluoromethansulfonate. Several trimetallic complexes such as [{Ru(η(6)-cymene)Cl2}3{2,4,6-C3N3(C6H4PPh2-p)3}] (9), [{Pd(η(3)-C3H5)Cl}3{2,4,6-C3N3(C6H4PPh2-p)3}] (10), [{Rh(COD)Cl}3{2,4,6-C3N3(C6H4PPh2-p)3}] (11) and [{Ir(COD)Cl}3{2,4,6-C3N3(C6H4PPh2-p)3}] (12) have also been synthesized and characterized. The reactions of 2 with [M(COD)Cl2] and CuI afforded metallo-cyclophane type complexes, [(MCl2)3L2] (M = Pd; 13, Pt; 14) (L = 2,4,6-tris{4-(diphenylphosphino)phenyl}-1,3,5-triazine) and [(CuI)3L2] (15), in good yield.

Activities comparison of Schiff base zinc and tri-zinc complexes for alternating copolymerization of CO2 and epoxides

A series of salicylaldiminato-zinc and -tri-zinc complexes containing various Schiff base ligands were prepared using quick methods and then well identified by full characterization. All zinc complexes were examined as catalysts for the copolymerization of CO2 and cyclohexene oxide. Many factors such as electron-donating or -withdrawing substituents on the benzene rings of the ligands, as well as chloride anions or acetate groups bound to the zinc centers, are found to greatly influence on the insertion of CO2 and ring-opening of epoxides. Tri-metallic complexes 2a and 2b exhibited excellent catalytic activities, and thus the copolymerization conditions such as temperature, pressure and reaction time were optimized. The molecular weights of the resulting copolymers determined by gel permeation chromatography display a bimodal distribution with relatively wide polydispersities. The results of the investigation indicate that the catalytic activities of zinc complexes are highly dependent on the electronic density and steric environment around the Zn metal centers.

Class III Delocalization in a Cyanide‐Bridged Trimetallic Mixed‐Valence Complex

The NIR and IR spectroscopic properties of the cyanide-bridged complex, trans-[Ru(dmap)4 {(μ-CN)Ru(py)4 Cl}2 ](3+) (py=pyridine, dmap=4-dimethylaminopyridine) provide strong evidence that this trimetallic ion behaves as a Class III mixed-valence species, the first example reported of a cyanide-bridged system. This has been accomplished by tuning the energy of the fragments in the trimetallic complex to compensate for the intrinsic asymmetry of the cyanide bridge. Moreover, (TD)DFT calculations accurately predict the spectra of the trans-[Ru(dmap)4 {(μ-CN)Ru(py)4 Cl}2 ](3+) ion and confirms its delocalized nature.

Gadolinium Complexes of Bifunctional Diethylenetriaminepentaacetic Acid (DTPA)-bis(amides) as Copper Responsive Smart Magnetic Resonance Imaging Contrast Agents (MRI CAs)

We present the synthesis and characterization of DTPA-bis(histidylamide) (1a), DTPA-bis(aspartamide) (1b), and their gadolinium complexes of the type (2a:L = 1a; 2b:L = 1b). Thermodynamic stabilities and relaxivities of 2a-b compare well with Omniscan, a well-known commercial, extracellular (ECF) MRI CA which adopts the DTPA-bis(amide) framework for the chelate: = 5.5 and 5.1 for 2a and 2b, respectively. Addition of the Cu(II) ion to a solution containing 2b triggers relaxivity enhancement to raise as high as 15.3 , which corresponds to a 300% enhancement. Such an increase levels off at the concentration beyond two equiv. of Cu(II), suggesting the formation of a trimetallic () complex in situ. Such a relaxivity increase is almost negligible with Zn(II) and other endogenous ions such as Na(I), K(I), Mg(II), and Ca(II). In vivo MR images and the signal-to-noise ratio (SNR) obtained with an aqueous mixture of 2b and Cu(II) ion in an 1:2 ratio demonstrate the potentiality of 2 as a copper responsive MRI CA.

Multimetallic Complexes Featuring a Bridging N-heterocyclic Phosphido/Phosphenium Ligand: Synthesis, Structure, and Theoretical Investigation

By incorporating an N-heterocyclic phosphenium/phosphide (NHP) ligand into a chelating pincer ligand framework (PPP(+)/PPP(-)), we have elucidated several different and unprecedented binding modes of NHP ligands in homobimetallic, heterobimetallic, and trimetallic metal complexes. One-electron reduction of the previously reported (PPP)(-)/M(II) complexes (PPP)M-Cl (M = Pd (1), Pt (2)) results in clean formation of the symmetric homobimetallic M(I)/M(I) complexes [(μ-PPP)Pd]2 (5) and [(μ-PPP)Pt]2 (6). The tridentate NHP ligand has also been utilized as a bridging linker in the M/Co heterobimetallic compounds (OC)3Co(u-PPP)M(CO) (M = Pd (7), Pt (8)), synthesized via salt elimination from mixtures of 1 and 2 and Na[Co(CO)4]. Furthermore, an NHP-bridged trimetallic complex (PPP)2Pd3Cl2 (9) can be synthesized in a manner similar to precursor 1 (Pd(PPh3)4 + (PPP)Cl) via careful adjustment of reaction stoichiometry. Examination of the interatomic distances and angles in complexes 5-9, in tandem with density functional theory calculations have been used to evaluate and characterize the bonding interactions in these complexes.

Ferrocenyl‐Functionalized Tetranuclear Gold(I) and Gold(I)–Copper(I) Complexes Based on Tridentate Phosphanes

Tetranuclear AuI–FeII dimetallic and AuI–CuI–FeII trimetallic complexes bearing ferrocenyl (Fc) groups have been assembled by using two triphosphane ligands, namely, (PPh2CH2)2PPh (dpmp) and (PPh2)3CH (tppm). The compositions and structural type of the clusters are dependent on the stereochemistry of the P donor ligands. The complexes [tppmAu3Cu(C2R)3]PF6 [R = Fc (1) and 4-C6H4-Fc (2)] adopt a trigonal pyramidal {Au3Cu} arrangement of the coordinating metal core, whereas for the compounds with the linear triphosphane [Au4(dpmp)2(C2R)2](PF6)2 [R = Fc (3) and 4-C6H4-Fc (4)], a planar rhomboidal {Au4} framework was found. Clusters 1–4 were characterized by NMR spectroscopy and ESI-MS measurements. The solid-state structures of 1, 3, and 4 have been determined by X-ray crystallography. The electrochemical properties of 1–4 were studied and revealed redox processes attributed to the Fc functions. Oxidation of the Fc units in 1, 2, and 4 occurs independently. In 3, an electron transfer process mediated by the {Au4} metal core was observed.

The Gold(I)- and Silver(I)-Catalyzed Nicholas Reaction

The Au(I) and Ag(I) catalytic Nicholas type reaction has been developed for oxygen and carbon nucleophiles. This process occurs with high reaction yields and selectivity, avoiding the main shortcomings of the acid-promoted standard Nicholas reaction. A catalytic reaction pathway involving trimetallic complex intermediates is proposed.