Carboxylate Exchange Reactions Research Articles

Photosensitizing Metal-Organic Layers for Efficient Sunlight-Driven Carbon Dioxide Reduction.

Metal-organic layers (MOLs), a free-standing monolayer version of two-dimensional metal-organic frameworks (MOFs), have emerged as a new class of 2D materials for many potential applications. Here we report the design of a new photosensitizing MOL, Hf12-Ru, based on Hf12 secondary building units (SBUs) and [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) derived dicarboxylate ligands. After modifying the SBU surface of Hf12-Ru with M(bpy)(CO)3X (M = Re and X = Cl or M = Mn and X = Br) derived capping molecules through carboxylate exchange reactions, the resultant Hf12-Ru-Re and Hf12-Ru-Mn MOLs possess both [Ru(bpy)3]2+ photosensitizers and M(bpy)(CO)3X catalysts for efficient photocatalytic CO2 reduction. The proximity of the MOL skeleton to the capping ligands (1-2 nm) facilitates electron transfer from the reduced photosensitizer [Ru(bpy)3]+ to MI(bpy)(CO)3X (M = Re, Mn) catalytic centers, resulting in CO2 reduction turnover numbers of 8613 under artificial visible light and of 670 under sunlight. MOLs thus represent a novel platform to assemble multifunctional materials for studying artificial photosynthesis.

Equatorial π-stacking interactions in diruthenium (II,III) tetracarboxylate complexes containing extended π-systems

The synthesis of three new valent-averaged tetracarboxylatodiruthenium (II,III) complexes, [Ru2(1-naphthylacetate)4(H2O)2](PF6)⋅4THF, 1⋅4THF, [Ru2(2-naphthoate)4(THF)2](PF6)⋅3THF, 2⋅3THF, and [Ru2(coumarin-3-carboxylate)4(MeOH)2](PF6)⋅MeOH⋅H2O, 3⋅MeOH⋅H2O, was accomplished using a well documented carboxylate exchange reaction. All three complexes were thoroughly characterized using infrared and UV–Vis spectroscopies, elemental analysis and X-ray diffraction. Due to the extended π-systems present, two of the complexes, 2⋅3THF and 3⋅MeOH⋅H2O, display extensive π-stacking in two dimensions, with similar interactions notably absent in 1⋅4THF due to the perpendicular orientation of the naphthyl rings. Modest H-bonding is seen in complexes 1⋅4THF and 3⋅MeOH⋅H2O. As these types of complexes are noted secondary building units (SBU’s) in the construction of metal–organic frameworks (MOF’s), the significance of these interactions in stabilizing even larger, supramolecular structures, are noted.

Structural, spectroscopic and theoretical studies of diosmium(iii,iii) tetracarboxylates

The preparation of Os2(TiPB)4Cl2 (1; TiPB = 2,4,6-triisopropylbenzoate) and Os2(TiPB)2(OAc)2Cl2 (2) by carboxylate exchange reactions with Os2(OAc)4Cl2 is reported. The structure of 1 has been determined by single-crystal X-ray studies, and shows a paddlewheel arrangement of the ligands about the triply bonded diosmium core. Both compounds have magnetic moments at room temperature that are consistent with the presence of two unpaired electrons, and their cyclic voltammograms show a single redox process corresponding to the Os2(5+/6+) redox couple. The electronic absorption spectra of 1 and 2 display an absorption at ~395 nm, corresponding to the π(Cl) →π*(Os2) LMCT transition, as well as numerous weaker absorptions at lower energy. Density functional theory (DFT) calculations on Os2(OAc)4Cl2 at different levels of theory (B3LYP and PBE0) have been used to probe the electronic structure of diosmium tetracarboxylates. The calculations show that these compounds have a σ(2)π(4)δ(2)δ*(1)π*(1) electronic configuration, and time-dependent DFT was used to help rationalize their optical properties.

New diruthenium complexes formed via modification with 1,1′-ferrocene dicarboxylic acid

Carboxylate exchange reactions between Ru 2(DArF) 3(OAc)Cl ( 1) and 1,1′-ferrocene dicarboxylic acid resulted in the new compounds [Ru 2(DArF) 3Cl] 2(μ-1,1′-(O 2CFcCO 2) ( 3), where DArF is either N, N′-di(3,5-dichlorophenyl)formamidinate (D(3,5-Cl 2Ph)F, a), or N, N′-di(3-methoxyphenyl)formamidinate (DmAniF, b). The exchange reactions between Ru 2(DArF) 2(OAc) 2Cl ( 2) and 1,1′-ferrocene dicarboxylic acid yielded the new compounds Ru 2(DArF) 2(O 2CFcCO 2)Cl ( 4a and 4b). The dimeric nature of compounds 3 was confirmed by both the MS data and an X-ray structural study of 3b. The monomeric nature of compounds 4a and 4b was confirmed by the MALDI-TOF MS data. Both compounds 3 and 4 were also characterized with cyclic (CV) and differential pulse voltammetry (DPV) and room temperature magnetic susceptibility measurements.

A mixed valence manganese triangle in a trigonal lattice: structure and magnetism

The synthesis, structural and magnetic characterisation of trinuclear manganese cluster, [Mn(3)O(O(2)C-anth)(6)(HOCH(3))(3)] 1 (where O(2)C-anth = 9-anthracenecarboxylate), with crystallographic three-fold (C(3)) symmetry, are described. The cluster was prepared by a carboxylate exchange reaction between HO(2)C-anth and [Mn(12)O(12)(O(2)CMe)(16)(H(2)O)(4)] with concomitant fragmentation of the dodecanuclear Mn core of the starting material to form a trinuclear Mn(3)(μ(3)-O) cluster capped by six carboxylate ligands. Bond valence sum calculations and SQUID magnetometric measurements establish the oxidation states of the metal ions as Mn(II)·2 Mn(III) which are antiferromagnetically coupled.

Diruthenium Compounds Bearing Equatorial Fc-containing Ligands: Synthesis and Electronic Structure

Previously, the synthesis of compounds Ru(2)(D(3,5-Cl(2)Ph)F)(4-n)(O(2)CFc)(n)Cl (n = 1, 3a; 2, 4a), where D(3,5-Cl(2)Ph)F is N,N'-di(3,5-dichlorophenyl)formamidinate, from the carboxylate exchange reactions between Ru(2)(D(3,5-Cl(2)Ph)F)(4-n)(OAc)(n)Cl and ferrocene carboxylic acid was communicated. Reported herein is the preparation of analogous compounds Ru(2)(DmAniF)(4-n)(O(2)CFc)(n)Cl (n = 1, 3b; 2, 4b), where DmAniF is N,N'-di(3-methoxyphenyl)formamidinate, from Ru(2)(DmAniF)(4-n)(OAc)(n)Cl. Compounds 3 and 4 were characterized with various techniques including X-ray structural determinations of 3a and 4a. Voltammetric behaviors of compounds 3 and 4 were investigated, and stepwise one-electron ferrocene oxidations were observed for both compounds 4a and 4b. Spectral analysis of the monocations [4](+) indicated that they are the Robin-Day class II mixed valent [Fc···Fc](+) species. Measurement and fitting of magnetic data (χT) of 4a between 2 and 300 K revealed a typical zero-field splitting of a S = 3/2 center with D = 77 cm(-1), while those of [4a]BF(4) are consistent with the presence of S = 3/2 (Ru(2)) and S = 1/2 (Fc(+)) centers that are weakly coupled (zJ = -0.76 cm(-1)).

Dependence of the Chemical Properties of Macrocyclic [NiII2L(μ-O2CR)]+ Complexes on the Basicity of the Carboxylato Coligands (L2− = macrocyclic N6S2 ligand)

The dependence of the properties of mixed ligand [Ni(II)(2)L(μ-O(2)CR)](+) complexes (where L(2-) represents a 24-membered macrocyclic hexaamine-dithiophenolato ligand) on the basicity of the carboxylato coligands has been examined. For this purpose 19 different [Ni(II)(2)L(μ-O(2)CR)](+) complexes (2-20) incorporating carboxylates with pK(b) values in the range 9 to 14 have been prepared by the reaction of [Ni(II)(2)L(μ-Cl)](+) (1) and the respective sodium or triethylammonium carboxylates. The resulting carboxylato complexes, isolated as ClO(4)(-) or BPh(4)(-) salts, have been fully characterized by elemental analyses, IR, UV/vis spectroscopy, and X-ray crystallography. The possibility of accessing the [Ni(II)(2)L(μ-O(2)CR)](+) complexes by carboxylate exchange reactions has also been examined. The main findings are as follows: (i) Substitution reactions between 1 and NaO(2)CR are not affected by the basicity or the steric hindrance of the carboxylate. (ii) Complexes 2-20 form an isostructural series of bisoctahedral [Ni(II)(2)L(μ-O(2)CR)](+) compounds with a N(3)Ni(μ-SR)(2)(μ-O(2)CR)NiN(3) core. (iii) They are readily identified by their ν(as)(CO) and ν(s)(CO) stretching vibration bands in the ranges 1684-1576 cm(-1) and 1428-1348 cm(-1), respectively. (iv) The spin-allowed (3)A(2g) → (3)T(2g) (ν(1)) transition of the NiOS(2)N(3) chromophore is steadily red-shifted by about 7.5 nm per pK(b) unit with increasing pK(b) of the carboxylate ion. (v) The less basic the carboxylate ion, the more stable the complex. The stability difference across the series, estimated from the difference of the individual ligand field stabilization energies (LFSE), amounts to about 4.2 kJ/mol [Δ(LFSE)(2,18)]. (vi) The "second-sphere stabilization" of the nickel complexes is not reflected in the electronic absorption spectra, as these forces are aligned perpendicularly to the Ni-O bonds. (vii) Coordination of a basic carboxylate donor to the [Ni(II)(2)L](2+) fragment weakens its Ni-N and Ni-S bonds. This bond weakening is reflected in small but significant bond length changes. (viii) The [Ni(II)(2)L(μ-O(2)CR)](+) complexes are relatively inert to carboxylate exchange reactions, except for the formato complex [Ni(II)(2)L(μ-O(2)CH)](+) (8), which reacts with both more and less basic carboxylato ligands.

Synthesis, structure and electrochemistry of mononuclear and dinuclear ruthenium–thiophenecarboxylate complexes

Three 3-thiophenecarboxylate-containing and one 2,2′-bithiophene-5-carboxylate-containing diruthenium complexes, [Ru 2(μ-O 2CR) 4(MeOH) 2]PF 6 (R = –C 4H 3S 1, –CH 2C 4H 3S 2, –CH CHC 4H 3S 3 and –C 8H 5S 2 4), were prepared using a facile carboxylate exchange reaction and characterized using elemental analysis, IR and UV–Vis spectroscopy. “Disassembly” of complexes 1– 4 using 1,2-bis(diphenylphosphino)-ethane (dppe) yielded the mononuclear ruthenium(II) complexes, [Ru(η 2-O 2CR)(dppe) 2]PF 6 (R = –C 4H 3S 5, –CH 2C 4H 3S 6, –CH CHC 4H 3S 7 and –C 8H 5S 2 8), which were characterized as above as well as by 1H and 31P NMR and single crystal X-ray analysis. All of the complexes were studied using cyclic voltammetry to assess the ability of the thiophene moieties to undergo oxidative polymerization with complex 4 showing the greatest promise.

Unligated Diruthenium(II,II) Tetra(trifluoroacetate): The First X-ray Structural Study, Thermal Compressibility, Lewis Acidity, and Magnetism

The title compound, [Ru(2)(O(2)CCF(3))(4)] (1), has been obtained without any exogenous ligands and crystallized by deposition from the gas phase at 170 degrees C. Its crystal structure has been determined for the first time to confirm an infinite chain motif built on axial Ru...O interactions of the diruthenium(II,II) units. The X-ray diffraction studies at variable temperatures showed no phase transitions in the range of 295-100 K but revealed a significant decrease in the volume per atom from 14.2 to 13.3 A(3). This noticeable thermal compressibility effect is discussed in connection with the solid-state packing of the [Ru(2)(O(2)CCF(3))(4)](infinity) chains. The highly electrophilic character of the diruthenium(II,II) units has been shown by the gas-phase deposition reaction of [Ru(2)(O(2)CCF(3))(4)] with an aromatic donor substrate, namely [2.2]paracyclophane (C(16)H(16)). As a result of the above reaction, a new arene adduct [Ru(2)(O(2)CCF(3))(4).C(16)H(16)] (2) has been isolated in crystalline form. It has an extended one-dimensional (1D) chain structure comprised of alternating building units and based on the rare bridging mode of [2.2]paracyclophane, [Ru(2)(O(2)CCF(3))(4).(mu(2)-eta(2):eta(2)-C(16)H(16))](infinity). The magnetic susceptibility of 1 and 2 has been measured and compared in the range of 1.8-300 K. In addition, in the course of synthesis of 1 by the carboxylate exchange reactions, a new mixed-carboxylate diruthenium(II,II) core complex [Ru(2)(O(2)CCF(3))(3)(O(2)CC(2)H(5))] (3), bearing no exogenous ligands, has also been isolated and structurally characterized. It exhibits an interesting polymeric structure in which the ruthenium(II) centers selectively form axial interdimer contacts with the O-atoms of the propionate groups only.

Chiral Organometallic Triangles with Rh−Rh Bonds. 2. Compounds Prepared from Enantiopure cis-Rh2(C6H4PPh2)2(OAc)2(HOAc)2 and Their Catalytic Potentials

Enantiomers of the orthometalated dirhodium compound cis-Rh2(C6H4PPh2)2(OAc)2(HOAc)2 (R-1 and S-1) were prepared from carboxylate exchange reactions of the resolved diasteroisomers of cis-Rh2(C6H4PPh2)2(protos)2(H2O)2 (protos = N-4-methylphenylsulfonyl-l-proline anion) and acetic acid. These compounds react with excess Me3OBF4 in CH3CN, producing the enantiomers of [cis-Rh2(C6H4PPh2)2(CH3CN)6](BF4)2 (R-2 and S-2) which have six labile and replaceable CH3CN ligands in equatorial and axial positions. Reactions of R-2 and S-2 with tetraethylammonium salts of the linear dicarboxylic acids, terephthalic acid (HO2CC6H4CO2H), oxalic acid (HO2CCO2H), and 4,4'-diphenyl-dicarboxylic acid (HO2CC6H4C6H4CO2H) afford the enantiopure triangular supramolecules [cis-Rh2(C6H4PPh2)2(O2CC6H4CO2)(py)2]3, RRR-3 and SSS-3, Rh6(cis-C6H4PPh2)6(O2CCO2)3(py)5(CH2Cl2), RRR-4 and SSS-4, and Rh6(cis-C6H4PPh2)6(O2CC6H4C6H4CO2)3(py)4(CH2Cl2)2, RRR-5 and SSS-5, respectively. The absolute structures of each of the enantiomers of 1, 3, 4, and 5 were determined by X-ray diffraction analyses. The enantiomers of 3, 4, and 5 were found to be enantiomorphically isostructural, whereas R-1 and S-1 crystallized in different space groups. In 4 and 5, CH2Cl2 molecules coordinate to rhodium atoms in the axial positions. The 1H and 31P[1H] NMR spectra of all compounds are reported. The triangular compounds are redox-active, and their electrochemistry is also discussed. An assay of the catalytic activity/selectivity performance of the triangles for typical metal carbene transformation, using the model intermolecular cyclopropanation of styrene with ethyl diazoacetate in both homogeneous and heterogeneous phases, show that these chiral triangles are very active and have remarkable selectivity when compared with simple Rh2 paddle-wheel catalysts with chiral amidate ligands.

Tripodal benzimidazolate complexes of tricarbonylmolybdenum(0) and of iron(III)

The reactions of the tripodal ligands N,N-bis(benzimidazol-2-ylmethyl)amine (L1), N,N-bis(benzimidazol-2-ylmethyl)methylamine (L2), and N,N-bis(1 -methylbenzimidazol-2-ylmethyl)-methylamine (L3) with molybdenum hexacarbonyl and tris(acetonitrile)tricarbonylmolybdenum to give (benzimidazolato)tricarbonylmolybdenum complexes, and of L1 and L3 with iron(III) salts to give di-iron(III) complexes containing the [Fe2(µ-O)(µ-RCO2)2]2+ core are described. The application of the molybdenum complexes as i.r. spectroscopic probes for the ligand bands in the dinuclear species is reported, together with the mass spectra and electronic spectra of the di-iron(III) species. The di-iron(III) complexes show an ability to undergo carboxylate exchange reactions.

Synthesis, spectroscopic, electrochemical, and magnetic properties of dimolybdenum(II,II), diruthenium-(II,III) and -(II,II) complexes containing bridging aspirinate (2-acetoxybenzoate) ligands

Carboxylate exchange reactions were used to prepare the dimolybdenum(II,II) tetra-aspirinate complex, [MO2(µ-asp)4](1), and the soluble aspirinate/trifluoroacetate, [Mo2(µ-asp)-(µ-O2CCF3)3]·2H2O (2)(asp = aspirinate = 2-acetoxybenzoate). Similar metathesis reactions were used for the synthesis of the diruthenium(II,III) complexes, [Ru2(µ-asp)4Cl](3), [Ru2(µ-asp)2(µ-O2CC6H5)2Cl]·H2O (4), and [Ru2(µ-asp)4(O2CCF3)]·2H2O (5). A methanolic solution of (3) reacts with an aqueous solution of AgNO3at 20 °C to give the Ru25+ nitrate/aspirinate, [Ru2(asp)4(NO3)]·H2O (6). When this reaction is repeated at 70 °C the Ru24+ nitroso/aspirinate, [Ru2(asp)4(NO)]·4H2O (7), is isolated. Complex (7) also formed when a methanolic solution of (6) was either refluxed (70 °C) for 3 h, or allowed to stand (20 °C) for a period of 3–4 weeks. The conversion of (3) and (6) into (7) represents a reduction of both the bimetallic core (Ru25+ to Ru24+) and the nitrate group (NO3–; to NO). Infrared absorption spectra, conductivity, cyclic voltammetry, and magnetic susceptibility data are given.