Light-harvesting metallosupramolecular squares composed of perylene bisimide walls and fluorescent antenna dyes

The fluorescent dye 4-dimethylamino-1,8-naphthalimide was incorporated at the bay area of N,N'-bispyridyl perylene bisimide to afford a fourfold-functionalized perylene bisimide ligand. Through self-assembly directed by metal-ion coordination, a multichromophore supramolecular entity composed of sixteen dimethylaminonaphthalimide antennas and a perylene bisimide-walled square core was subsequently constructed from this linear ditopic ligand and 90 degrees metal corner [Pd(dppp)](OTf)2 (dppp=1,3-bis(diphenylphosphino)propane; OTf=trifluoromethanesulfonate) in good yield. The isolated metallosupramolecular square was characterized by elemental analysis and 1H, 13C, and 31P{1H} NMR and UV/Vis spectroscopy. Furthermore, by means of 1H NMR diffusion-ordered spectroscopy (DOSY) the dimension of this assembly was evaluated by employing a previously reported perylene bisimide ligand and its square assembly as references. The results obtained confirm the square framework of the current assembly. The optical properties of this multichromophore dye assembly were investigated by UV/Vis and steady-state and time-resolved fluorescence spectroscopy. It was revealed that light captured by dimethylaminonaphthalimide antennas could be efficiently transported to the perylene bisimide core by a fluorescence resonance mechanism (energy-transfer efficiency E=95%), and this resulted in almost exclusive detection of intense perylene bisimide emission, irrespective of the excitation wavelength applied. The present square scaffold containing aminonaphthalimide antenna dyes exhibits more than seven times higher fluorescence quantum yield (Phifl=0.37) than a previously reported pyrene-bearing perylene bisimide-walled square (Phifl=0.05). Thus, this multichromophore square assembly with aminonaphthalimide antenna dyes is an artificial model for the cyclic light-harvesting complexes in purple bacteria.     

Fluorescent and electroactive cyclic assemblies from perylene tetracarboxylic acid bisimide ligands and metal phosphane triflates

Tetraaryloxy-substituted perylene tetracarboxylic acid bisimides with one or two 4-pyridyl receptor substituents at the imide functionality were synthesized and employed in transition metal directed self-assembly with Pd(II) and Pt(II) phosphane triflates. Upon mixing of the components, quantitative formation of functional molecular square-type complexes containing four dye molecules and model complexes of a 2:1 (perylene bisimide ligand:transition metal ion) stoichiometry was observed. The isolated metallosupramolecular squares were characterized by 1H and 31P [1H] NMR spectroscopy as well as conventional electrospray ionization (ESI) and ESI-FTICR mass spectrometry, which gave evidence for the structure and the high stability of these giant cyclic dye assemblies (molecular weight (3a) 8172, Pt-Pt corner diagonal ca. 3.4 nm). Studies of the optical absorption and fluorescence properties and the electrochemistry and spectroelectrochemistry of both the perylene bisimide ligands and the perylene bisimide metal complexes show that Pt(II) coordination does not interfere with the optical and electrochemical properties of the perylene bisimide ligands; this gives squares with high fluorescence quantum yields (phiF (3a)=0.88) and three fully reversible redox couples. The latter could be unambiguously related to quantitative formation of perylene bisimide radical cations (E1/2 = +0.93 V vs. Fc/Fc+), radical anions (E1/2= - 1.01 V vs. Fc/Fc+), and dianions (E1/2 = -1.14 V vs. Fc/Fc+); these redox reactions change the charge state of the cyclic assembly from +12 to zero. In contrast, Pd(II) coordination influenced the electrochemical properties of the assembly because of an irreversible palladium reduction at E1/2= -1.15 V versus Fc/Fc+. Finally, dynamic ligand exchange processes between different metallosupramolecular assemblies were investigated by multinuclear NMR and electrospray mass spectrometry. These studies confirmed the reversible nature of the pyridine-Pt(II)/Pd(II) coordination process.     

Self-assembly organometallic squares with terpyridyl metal complexes as bridging ligands

A series of novel heterometallic square complexes with the general molecular formulas [fac-Br(CO)(3)Re[mu-(pyterpy)(2)M]](4)(PF(6))(8) and [(dppf)Pd[mu-(pyterpy)(2)Ru]](4)(PF(6))(8)(OTf(8) (4), where M = Fe (1), Ru (2), or Os (3), pyterpy is 4'-(4' "-pyridyl)-2,2':6',2' '-terpyridine, dppf = 1,1'-bis(diphenylphosphino)ferrocene and OTf is trifluoromethanesulfonate, were prepared by self-assembly between BrRe(CO)(5) or (dppf)Pd(H(2)O)(2)(OTf)(2) and (pyterpy)(2)M(PF(6))(2). The obtained NMR spectra, IR spectra, electrospray ionization mass spectra, and elemental analyses are all consistent with the proposed square structures incorporating terpyridyl metal complexes as bridging ligands. Multiple redox processes were observed in all square complexes. All four complexes display strong visible absorptions in the region 400-600 nm, which are assigned as metal (Fe, Ru, or Os)-to-ligand (pyterpy) charge transfer (MLCT) bands. Square 3 exhibits an additional weak band at 676 nm, which is assigned to an Os-based (3)MLCT band. For each complex, the bands centered between 279 and 377 nm are assigned as pyterpy-based pi-pi bands and the Re-based MLCT band. Square 3 is luminescent in room-temperature solution, while squares 1, 2, and 4 do not have any detectable luminescence under identical experimental conditions.     

Metallosupramolecular squares: from structure to function

Metallosupramolecular squares have been successfully evolved over the past years as versatile substitutes of the conventional organic macrocycles owing to the development of reliable synthetic protocols and abundant structural variability (metals and ligands). In this review we have presented the fundamental aspects of metallosupramolecular squares such as the strategies for their construction (self-assembly vs. kinetically controlled macrocyclization) and characterization. The major emphasis of this tutorial review lies on the function of metallosupramolecular squares. Thus, the introduction of functionality into these systems has been discussed in detail by highlighting the recent progress toward application in various fields, including molecular recognition, enantioselective sensing, photoluminescence, redox activity and electrochemical sensing, and homogeneous catalysis.     

Synthesis, structural characterization and anion binding studies of palladium macrocycles with hydrogen-bonding ligands

The reactions between [Pd(P-P)(OTf)2] (where P-P=dppp or dppf) and two different bipyridyl ligands (=1,3-bis(4-pyridylmethyl)urea and=1,3- bis(pyridinylmethyl)benzenedicarboxamide) containing hydrogen-bonding units have been studied. The X-ray crystal structures of three of these assemblies have been solved showing them to be the [2+2] metallo-macrocycles [Pd(P-P)(n)]2(OTf)4 [P-P=dppp, n=1, (); P-P=dppp, n=2, (); P-P=dppf, n=1, ()]. To confirm whether the dimeric assembly of one of these species () is retained in solution, several investigations have been carried out. 1H NMR studies in DMSO and high resolution ESI mass spectrometry have shown that is in equilibrium with a larger [3+3] metallo-macrocycle. The equilibrium between these two species can be modified by changing the temperature, concentration or solvent. Also, addition of certain anions (e.g. [H2PO4]-) to the mixture shifts the equilibrium favoring the formation of the [2+2] metallo-macrocycle over the [3+3] (initially present in a larger proportion).     

Constructing homo- and hetero-metallic molecular topologies using pyridylcarboxylates as spacers: preparation of a half-ring complex with active coordination sites

Addition of isonicotinic acid NC(5)H(4)CO(2)H (or isonicH) to [Pt(dppf)(MeCN)(2)](2+)2OTf(-)(dppf = 1,1'-bis(diphenylphosphino)ferrocene, OTf = triflate) affords a mixture of the homometallic molecular square [Pt(4)(dppf)(4)(mu-O(2)CC(5)H(4)N)(4)](4+)4OTf(-), 1 and its precursor intermediate [Pt(dppf)(eta(1)-NC(5)H(4)CO(2)H)(2)](2+)2OTf(-), 2. The latter captures [Pd(dppf)(MeCN)(2)](2+)2OTf(-) to give a heterometallic square, [Pt(2)Pd(2)(dppf)(4)(mu-O(2)CC(5)H(4)N)(4)](4+)4OTf(-), 3. Slight skeletal modification of the ligand leads to different assemblies. This is illustrated by the addition of NC(5)H(4)CH(2)CO(2)H.HCl to [Pt(dppf)(MeCN)(2)](2+)2OTf(-) to give [PtCl(dppf)(NC(5)H(4)CH(2)CO(2)H)](+)OTf(-), 4, which reacts with another equivalent of AgOTf to yield the dibridged complex [Pt(2)(dppf)(2)(mu-NC(5)H(4)CH(2)CO(2))(2)](2+)2OTf(-), 5. All complexes, with the exception of , have been structurally characterized by single-crystal X-ray crystallography. Complexes 2 and 4 are potential precursors to further molecular topologies.     

Self-assembly of transition-metal-based macrocycles linked by photoisomerizable ligands: examples of photoinduced conversion of tetranuclear-dinuclear squares

A series of hetero- and homometallic square complexes bridged by a photoactive 4,4'-azopyridine (AZP) or 1,2-bis(4-pyridyl)ethylene (BPE) ligand, cyclobis[[cis-(dppf)M](mu-L)(2)(fac-Re(CO)(3)Br)](OTf)(4) (M = Pd, L = trans-AZP (5); M = Pt, L = trans-AZP (7); M = Pd, L = trans-BPE (8); M = Pt, L = trans-BPE (10)), cyclo[[cis-(dppf)M](mu-L)(2)(fac-Re(CO)(3)Br)](OTf)(2) (M = Pd, L = cis-AZP (6); M = Pd, L = cis-BPE (9)), [cis-(dppf)Pd(mu-trans-AZP)](4)(OTf)(8) (11), and [cis-(dppf)Pd(mu-cis-AZP)](2)(OTf)(4) (12), where dppf is 1,1'-bis(diphenylphosphino)ferrocene and OTf is trifluoromethanesulfonate anion, were prepared by thermodynamically driven self-assembly processes. The photophysical and photochemical properties of these complexes have been investigated, and all of them show a lack of luminescence in room temperature solution. Upon irradiation at 313 or 366 nm, Pd(II)-Re(I)-containing tetranuclear squares 5, 8, and 11 undergo photoisomerization and convert to their corresponding dinuclear complexes 6, 9, and 12, whereas Pt(II)-Re(I)-based squares 7 and 10 show only slow square disassembling processes. The tetranuclear squares can be fully recovered by heating the photoisomerized solution for several hours.     

Sterically‐Directed Consecutive and Size‐Selective Self‐Assembly of Palladium Diphosphane Complexes with an Ar‐BIAN Ligand: Unexpected Formation of Pentameric and Hexameric Aggregates

The coordination properties of N,N′‐bis[4‐(4‐pyridyl)phenyl]acenaphthenequinonediimine (L¹) and N,N′‐bis[4‐(2‐pyridyl)phenyl]acenaphthenequinonediimine (L²) were investigated in self‐assembly with palladium diphosphane complexes [Pd(P^P)(H₂O)₂](OTf)₂ (OTf=triflate) by using various analytical techniques, including multinuclear (¹H, ¹⁵N, and ³¹P) NMR spectroscopy and mass spectrometry (P^P=dppp, dppf, dppe; dppp=bis(diphenylphosphanyl)propane, dppf= bis(diphenylphosphanyl)ferrocene, and dppe=bis(diphenylphosphanyl)ethane). Beside the expected trimeric and tetrameric species, the interaction of an equimolar mixture of [Pd(dppp)]²⁺ ions and L¹ also generates pentameric aggregates. Due to the E/Z isomerism of L¹, a dimeric product was also observed. In all of these species, which correspond to the general formula [Pd(dppp)L¹]_n(OTf)_2n (n=2–5), the L¹ ligand is coordinated to the Pd center only through the terminal pyridyl groups. Introduction of a second equivalent of the [Pd(dppp)]²⁺ tecton results in coordination to the internal, sterically more encumbered chelating site and induces enhancement of the higher nuclearity components. The presence of higher‐order aggregates (n=5, 6), which were unexpected for the interaction of cis‐protected palladium corners with linear ditopic bridging ligands, has been demonstrated both by mass‐spectrometric and DOSY NMR spectroscopic analysis. The sequential coordination of the [Pd(dppp)]²⁺ ion is attributed to the dissimilar steric properties of the two coordination sites. In the self‐assembled species formed in a 1:1:1 mixture of [Pd(dppp)]²⁺/[Pd(dppe)]²⁺/L¹, the sterically more demanding [Pd(dppp)]²⁺ tectons are attached selectively to the pyridyl groups, whereas the more hindered imino nitrogen atoms coordinate the less bulky dppe complexes, thus resulting in a sterically directed, size‐selective sorting of the metal tectons. The propensity of the new ligands to incorporate hydrogen‐bonded solvent molecules at the chelating site was confirmed by X‐ray diffraction studies.     

Metallo-supramolecular self-assembly: the case of triangle-square equilibria

For the efficient self-assembly of metallo-supramolecular complexes, not only reversibility is required but also two other properties have to be controlled as well: (i) The right binding sites need to be programmed into the building blocks at the appropriate positions. (ii) The building blocks must be rigid enough to support the geometrical arrangement and to avoid the unfavorable entropy effects connected with the conformational fixation of flexible molecules. A series of different bis-pyridyl ligands is reported which self-assemble with (dppp)M(OTf) 2 complexes (dppp = 1,3-bis-(diphenylphosphino)propane; M = Pd (II), Pt (II)) to yield squares and/or triangles as the products. Enthalpic contributions (higher strain in the triangle) and entropic contributions (higher number of triangles from the same building blocks) determine the equilibrium. The effects of concentration, temperature, and solvent properties on the equilibrium have been studied. To characterize the complexes under study, a combination of (1)H, (31)P, and diffusion-ordered NMR spectroscopy, electrospray-ionization Fourier-transform ion-cyclotron-resonance mass spectrometry, and X-ray crystallography is needed. Variable-temperature NMR spectroscopy provides evidence for fast ligand-exchange processes occurring for the Pd complexes, while the Pt complexes exchange ligands much more slowly.     

Pd(I) phosphine carbonyl and hydride complexes implicated in the palladium-catalyzed oxo process

Reduction of compound "Pd(bcope)(OTf)2" [bcope = (c-C8H14-1,5)PCH2CH2P(c-C8H14-1,5); OTf = O3SCF3] with H2/CO yields a mixture of Pd(I) compounds [Pd2(bcope)2(CO)2](OTf)2 (1) and [Pd2(bcope)2(mu-CO)(mu-H)](OTf) (2), whereas reduction with H2 or Ph3SiH in the absence of CO leads to [Pd3(bcope)3(mu3-H)2](OTf)2 (3). Exposure of 3 to CO leads to 1 and 2. The structures of 1 and 3 have been determined by X-ray diffraction. Complex [Pd2(bcope)2(CO)2](2+) displays a metal-metal bonded structure with a square planar environment for the Pd atoms and terminally bonded CO ligands and is fluxional in solution. DFT calculations aid the interpretation of this fluxional behavior as resulting from an intramolecular exchange of the two inequivalent P atom positions via a symmetric bis-CO-bridged intermediate. A cyclic voltammetric investigation reveals a very complex redox behavior for the "Pd(bcope)(OTf)2"/CO system and suggests possible pathways leading to the formation of the various observed products, as well as their relationship with the active species of the PdL2(2+)/CO/H2-catalyzed oxo processes (L2 = diphosphine ligands).     

Formation of ammonia in the reactions of a tungsten dinitrogen with ruthenium dihydrogen complexes under mild reaction conditions

Treatment of cis-[W(N2)2(PMe2Ph)4] (5) with an equilibrium mixture of trans-[RuCl(eta 2-H2)(dppp)2]X (3) with pKa = 4.4 and [RuCl(dppp)2]X (4) [X = PF6, BF4, or OTf; dppp = 1,3-bis(diphenylphosphino)propane] containing 10 equiv of the Ru atom based on tungsten in benzene-dichloroethane at 55 degrees C for 24 h under 1 atm of H2 gave NH3 in 45-55% total yields based on tungsten, together with the formation of trans-[RuHCl(dppp)2] (6). Free NH3 in 9-16% yields was observed in the reaction mixture, and further NH3 in 36-45% yields was released after base distillation. Detailed studies on the reaction of 5 with numerous Ru(eta 2-H2) complexes showed that the yield of NH3 produced critically depended upon the pKa value of the employed Ru(eta 2-H2) complexes. When 5 was treated with 10 equiv of trans-[RuCl(eta 2-H2)(dppe)2]X (8) with pKa = 6.0 [X = PF6, BF4, or OTf; dppe = 1,2-bis(diphenylphosphino)ethane] under 1 atm of H2, NH3 was formed in higher yields (up to 79% total yield) compared with the reaction with an equilibrium mixture of 3 and 4. If the pKa value of a Ru(eta 2-H2) complex was increased up to about 10, the yield of NH3 was remarkably decreased. In these reactions, heterolytic cleavage of H2 seems to occur at the Ru center via nucleophilic attack of the coordinated N2 on the coordinated H2 where a proton (H+) is used for the protonation of the coordinated N2 and a hydride (H-) remains at the Ru atom. Treatment of 5, trans-[W(N2)2(PMePh2)4] (14), or trans-[M(N2)2(dppe)2] [M = Mo (1), W (2)] with Ru(eta 2-H2) complexes at room temperature led to isolation of intermediate hydrazido(2-) complexes such as trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf (19), trans-[W(OTf)(NNH2)(PMePh2)4]OTf (20), and trans-[WX(NNH2)(dppe)2]+ [X = OTf (15), F (16)]. The molecular structure of 19 was determined by X-ray analysis. Further ruthenium-assisted protonation of hydrazido(2-) intermediates such as 19 with H2 at 55 degrees C was considered to result in the formation of NH3, concurrent with the generation of W(VI) species. All of the electrons required for the reduction of N2 are provided by the zerovalent tungsten.     

Self-assembly in palladium(II) and platinum(II) chemistry: the biomimetic approach

The self-assembly of complex cationic structures by combination of cis-blocked square planar palladium(II) or platinum(II) units with bis(pyridyl) ligands having bridging amide units has been investigated. The reactions have yielded dimers, molecular triangles, and polymers depending primarily on the geometry of the bis(pyridyl) ligand. In many cases, the molecular units are further organized in the solid state through hydrogen bonding between amide units or between amide units and anions. The molecular triangle [Pt(3)(bu(2)bipy)(3)(mu-1)(3)](6+), M = Pd or Pt, bu(2)bipy = 4,4'-di-tert-butyl-2,2'-bipyridine, and 1 = N-(4-pyridinyl)isonicotinamide, stacks to give dimers by intertriangle NH.OC hydrogen bonding. The binuclear ring complexes [[Pd(LL)(mu-2)](2)](CF(3)SO(3))(4), LL = dppm = Ph(2)PCH(2)PPh(2) or dppp = Ph(2)P(CH(2))(3)PPh(2) and 2 = NC(5)H(4)-3-CH(2)NHCOCONHCH(2)-3-C(5)H(4)N, form transannular hydrogen bonds between the bridging ligands. The complexes [[Pd(LL)(mu-3)](2)](CF(3)SO(3))(4), LL = dppm or dppp, L = PPh(3), and 3 = N,N'-bis(pyridin-3-yl)-pyridine-2,6-dicarboxamide, and [[Pd(LL)(mu-4)](2)](CF(3)SO(3))(4), LL = dppm, dppp, or bu(2)bipy, L = PPh(3), and 4 = N,N'-bis(pyridin-4-yl)-pyridine-2,6-dicarboxamide, are suggested to exist as U-shaped or square dimers, respectively. The ligands N,N'-bis(pyridin-3-yl)isophthalamide, 5, or N,N'-bis(pyridin-4-yl)isophthalamide, 6, give the complexes [[Pd(LL)(mu-5)](2)](CF(3)SO(3))(4) or [[Pd(LL)(mu-6)](2)](CF(3)SO(3))(4), but when LL = dppm or dppp, the zigzag polymers [[Pd(LL)(mu-6)](x)](CF(3)SO(3))(2)(x) are formed. When LL = dppp, a structure determination shows formation of a laminated sheet structure by hydrogen bonding between amide NH groups and triflate anions of the type NH-OSO-HN.     

Synthesis and redox properties of crowded triarylphosphines possessing ferrocenyl groups

Crowded triarylphosphines possessing ferrocenyl groups [(4-ferrocenyl-2,6-diisopropylphenyl)(n)(2,4,6-triisopropylphenyl)(3-n)P (5a, n = 1; 5b, n = 2; 5c, n = 3)] were synthesized by the reaction of the corresponding arylcopper(I) reagents with the diarylchlorophosphines. Structures of the triarylphosphines were studied by 1H, 13C, and 31P NMR spectroscopies, and the characteristic patterns of the proton signals of the 2,6-isopropyl groups and upfielded 31P chemical shifts suggest structural similarities of the triarylphosphine moiety to the previously reported tris(2,4,6-triisopropylphenyl)phosphine (2). X-ray crystallography of 5c also revealed that the structure around the phosphorus is similar to that of 1, where the average bond angle and length around the phosphorus atom are 110.8 degrees and 1.854 A, respectively. According to the electrochemical measurements, phosphines 5a, 5b, and 5c are reversibly oxidized in two, three, and four steps, respectively, which suggests significant electronic interaction among the triarylphosphine and the ferrocene redox centers as well as weak interaction among the ferrocene redox centers. The EPR spectra obtained at cryogenic temperature after oxidation of phosphines 5a, 5b, and 5c are superpositions of those for the cation radicals of the crowded triarylphosphine and ferricinium. The solution spectra obtained at 293 K, which consist of two lines typical of the cation radical of the crowded triarylphosphines, become weaker as the number of the ferrocenyl groups increases and the cation radical of 5c does not show EPR signals. These findings suggest not only instability of the tetra(cation radical) of 5c but also the course of oxidation where the ferrocenyl groups in the periphery of the molecules are oxidized at first.     

Ferrocene-containing [2]- and [3]rotaxanes. Preparation via an end-capping cross-metathesis reaction and electrochemical properties

Cross-metathesis reactions of terminal olefins with acrylic esters catalyzed by a Ru-carbene complex ((H2IMes)(PCy3)Cl2Ru = CHPh, H2IMes = N,N-bis(mesityl)-4,5-dihydroimidazol-2-ylidene) were applied to the end-capping of [2]pseudorotaxanes composed of dibenzo[24]crown-8 (DB24C8) and ferrocenylmethylammonium derivatives as the macrocyclic and axle components. A [3]rotaxane consisting of two DB24C8s and an axle molecule having ferrocenyl groups at both ends was obtained from the cross-metathesis reaction of two [2]pseudorotaxanes with Fe(C5H4CH2OCOCH = CH2)2. Cyclic voltammograms of the ferrocene-containing rotaxanes show reversible redox reactions whose potentials vary depending on the presence or absence of cationic dialkylammonium groups in the vicinity of the ferrocene units.     

Synthesis and characterization of supramolecular complexes of a tetranuclear metallocycle with platinum(II) bis-ethynylphenylethynylpyridine organometallic complexes

A novel Pt(II) organometallic complex with 4-(4-ethynyl-phenylethynyl)-pyridine (DEBPy-H), namely [Pt(dppp)(DEBPy)₂] (dppp = 1,3-bis-(diphenylphosphino)-propane), has been prepared by two synthetic routes. The DEBPy-H ligand was prepared by a shorter synthetic pathway and in higher yield than the method of previous reports. New Pt(II) organometallic complexes with DEBPy-H and four bidentate ligands [Pt(L–L)(DEBPy)₂] (L–L = 1,2-bis-(diphenylphosphino)-benzene, bis-(dicyclohexyl)-ethane, 4,4′-dimethyl-2,2′-bipyridine, or 5,5′-dimethyl-2,2′-bipyridine) have also been prepared. These five Pt(II) complexes have two pyridyl units as an available coordination site that can operate as a metalloligand in nanoscale tectonics. A supramolecular complex of a tetranuclear metallocycle, [Pt(dppp)(DEBPy)₂]₂[Pt(dppp)]₂(OTf)₄, was synthesized from [Pt(dppp)(DEBPy)₂] and [Pt(dppp)(OTf)₂] as a corner connection through coordination-driven self-assembly. This supramolecular Pt(II) complex exists as a tetranuclear structure of the square type according to the interpretation of the ESI-mass and NMR spectra in solution. Five Pt(II) organometallics demonstrated the formation of similar tetranuclear metallocycles with [Pt(dppp)(OTf)₂], as indicated by their ESI-mass and UV–vis spectra in solution.     

Hexanuclear Gold(I) Phosphide Complexes as Platforms for Multiple Redox‐Active Ferrocenyl Units

The synthesis, X‐ray crystal structures, electrochemical, and spectroscopic studies of a series of hexanuclear gold(I) μ₃‐ferrocenylmethylphosphido complexes stabilized by bridging phosphine ligands, [Au₆(P?P)_n(Fc‐CH₂‐P)₂][PF₆]₂ (n=3, P?P=dppm (bis(diphenylphosphino)methane) ( 1 ), dppe (1,2‐bis(diphenylphosphino)ethane) ( 2 ), dppp (1,3‐bis(diphenylphosphino)propane) ( 3 ), Ph₂PN(C₃H₇)‐PPh₂ ( 4 ), Ph₂PN(Ph‐CH₃‐p)PPh₂ ( 5 ), dppf (1,1′‐bis(diphenylphosphino)ferrocene) ( 6 ); n=2, P?P=dpepp (bis(2‐diphenylphosphinoethyl)phenylphosphine) ( 7 )), as platforms for multiple redox‐active ferrocenyl units, are reported. The investigation of the structural changes of the clusters has been probed by introducing different bridging phosphine ligands. This class of gold(I) μ₃‐ferrocenylmethylphosphido complexes has been found to exhibit one reversible oxidation couple, suggestive of the absence of electronic communication between the ferrocene units through the Au₆P₂ cluster core, providing an understanding of the electronic properties of the hexanuclear Au^I cluster linkage. The present complexes also serve as an ideal system for the design of multi‐electron reservoir and molecular battery systems.     

Ferrocene-decorated (phthalocyaninato)(porphyrinato) double- and triple-decker rare earth complexes: synthesis, structure, and electrochemical properties

A series of four mixed (phthalocyaninato)(porphyrinato) rare earth double-decker complexes (Pc)M[Por(Fc)(2)] [Pc = phthalocyaninate; Por(Fc)(2) = 5,15-di(ferrocenyl)-porphyrinate; M = Eu (1), Y (2), Ho (3), Lu (4)] and their europium(III) triple-decker counterpart (Pc)Eu(Pc)Eu[Por(Fc)(2)] (5), each with two ferrocenyl units at the meso-positions of their porphyrin ligands, have been designed and prepared. The double- and triple-decker complexes 1-5 were characterized by elemental analysis and various spectroscopic methods. The molecular structures of two double-deckers 1 and 4 were also determined by single-crystal X-ray diffraction analysis. Electrochemical studies of these novel sandwich complexes revealed two consecutive ferrocene-based one-electron oxidation waves, suggesting the effective electronic coupling between the two ferrocenyl units. Nevertheless, the separation between the two consecutive ferrocene-based oxidation waves increases from 1 to 4, along with the decrease of rare earth ionic radius, indicating the effect of rare earth size on tuning the coupling between the two ferrocenyl units. Furthermore, the splitting between the two ferrocene-based one-electron oxidations for triple-decker 5 is even smaller than that for 1, showing that the electronic interaction between the two ferrocene centers can also be tuned through changing the linking sandwich framework from double-decker to triple-decker. For further understanding of the electronic coupling between ferrocenyl groups, DFT calculation is carried out to clarify the electronic delocalization and the molecular orbital distribution in these double-decker complexes.     

Silver(I) and copper(I) complexes with ferrocenyl ligands bearing imidazole or pyridyl substituents

The reactions between five ferrocenyl derivatives containing both a CO and at least an imidazole or pyridine nitrogen atom and AgPF₆, AgOTf, or [Cu(NCCH₃)₄]PF₆ precursors were studied. The ligand {[bis(2-pyridyl)amino]carbonyl}ferrocene (L3), derived from (2-pyridyl)amine, favored tetrahedral coordination of Ag⁺ (with two ligands) and of Cu⁺ (with two acetonitrile ligands left from the precursor). In all the other ligands, both metal centers coordinated linearly to two ligands, preferring the imidazole or pyridinic nitrogen to other nitrogen atoms (amine) or oxygen donors.When the counter anions were triflate, the crystal structure showed a dimerization of the complex, with the ferrocenyl moieties occupying cis positions, by means of a weak Ag?Ag interaction. This was shown experimentally in the crystal structure of complex [Ag(L1)₂]OTf (L1 = ferrocenyl imidazole) and in the presence of peaks corresponding to {Ag₂(L2)₃(OTf)}⁺ and {Ag₂(L2)₄(OTf)}⁺ in the mass spectra of [Ag(L2)₂]OTf (L2 = ferrocenyl benzimidazole). In all complexes containing PF₆, there was no evidence for dimerization. Indeed, in the crystal structure of [Ag(L2)₂]PF₆, the ferrocenyl moieties occupy trans positions and the metal centers are far from each other. DFT calculations showed that the energy of the cis and trans conformers is practically the same and the balance of crystal packing forces leads to dimerization when triflate is present.     

Construction of functionalized metallosupramolecular tetragonal prisms via multicomponent coordination-driven self-assembly

A new approach for the construction of functionalized metallosupramolecular tetragonal prisms via multicomponent, coordination-driven, template-free self-assembly is described. The combination of tetra-(4-pyridylphenyl)ethylene, a 90° Pt(II) acceptor, and ditopic bipyridine or carboxylate ligands functionalized with hydroxyl or amine groups, hydrophobic alkyl chains, or electrochemically active ferrocene, yields a suite of seven self-assembled tetragonal prisms under mild conditions. These three-dimensional metallosupramolecules were characterized by multinuclear NMR ((31)P and (1)H) and mass spectrometry. Their shapes and sizes were established using Merck Molecular Force Field (MMFF) simulations. In addition, their approximate sizes were further supported by pulsed-field-gradient spin-echo (PGSE) NMR experiments.     

Synthesis,structure and physical properties of an iron(II) complex with four ferrocenyl groups

A novel tridentate ligand with two ferrocenyl groups and its iron(II) complex were synthesized and these structures and physical properties are presented. The pentanuclear iron(II) complex is composed of one central ion(II) ion and four ferrocenyl groups, in which the central iron(II) ion was coordinated by two tridentate ligands. Electrochemical measurement for the complex in MeCN showed irreversible redox waves, and the redox process can be understood by EC mechanism.