Dinuclear Bis Research Articles

Dinuclear Ruthenium Complexes Bearing Dicarboxylate and Phosphine Ligands. Acceptorless Catalytic Dehydrogenation of 1-Phenylethanol

Reaction of RuH2CO(PPh3)3 with tetrafluorosuccinic acid at 100 °C gave rise to the formation of the dinuclear bis(tetrafluorosuccinate)-bridged Ru(II) complex 2, containing two water ligands. Exchange of the PPh3 in complex 2 with various diphosphine ligands afforded a series of analogous complexes 3. Reaction of the latter with 1-phenylethanol at 130 °C or with 2-propanol/Et3N at room temperature furnished the dinuclear dihydrido-bridged Ru(II) complexes 4. Complexes 2 and 4 were characterized by X-ray diffraction analysis. Both bis(tetrafluorosuccinate)-bridged complexes 3 and dihydrido-bridged complexes 4 catalyze the acceptorless dehydrogenation of 1-phenylethanol to acetophenone and dihydrogen with good yields and excellent selectivity under relatively mild conditions in the absence of acid or base. A tentative catalytic cycle for the dehydrogenation of secondary alcohols by Ru(II) complexes of type 3 is presented.

Metal–metal interactions in dinuclear ruthenium complexes containing bridging 4,5-di(2-pyridyl)imidazolates and related ligands

The dinuclear bis(2,2'-bipyridine)ruthenium complex of 4,5-di(2-pyridyl)imidazolate has been prepared and separated into its (meso and rac) diastereoisomers. The 2-phenyl substituted analogue forms the meso isomer selectively. All three complexes have been characterised by 1H NMR and X-ray crystallography. Electrochemical measurements and spectroelectrochemistry of the mixed-valence states reveal strong metal-metal interactions and IVCT bands that are highly dependent on the electrolyte.

X-ray Diffraction and EXAFS Studies of Hydroxo−Cu(II) Complexes Based on a Calix[6]arene-N3 Ligand: Evidence for a Mononuclear−Dinuclear Equilibrium Controlled by Supramolecular Features

The formation of hydroxo complexes based on a calix[6]trisimidazole ligand is described. Deprotonation of the mononuclear Cu(II)-aqua complex gives rise to a dinuclear bis(mu-hydroxo) complex that has been characterized by X-ray diffraction analysis. Spectroscopic studies (EPR and UV-vis), conducted in dichloromethane solutions in the presence of various coordinating cosolvents (DMF, EtOH, or RCN) or with acetamide, revealed the coexistence of a mononuclear hydroxo species. The latter could be trapped by acetic acid to provide an acetato-Cu(II) complex that presents close spectroscopic features. An EXAFS study first conducted on the hydroxo-Cu(II) complex led to an excellent fit for the dinuclear core. It then allowed for the characterization of the mononuclear acetato complex with an acetamide guest included in the calixarene cavity. Hence, this study illustrates the flexibility of calixarene-based ligands and the role of the second coordination sphere in the stabilization of acidic or basic Cu(II) complexes.

Separation of actinides and lanthanides: Synthesis and molecular structure of a new di-μ-phenoxo-bridged dinuclear bis(dioxouranium(VI)) complex

The new phenoxo-bridged uranyl [(UO 2) 2L 2(thf) 2] [H 2L = N(2-oxyphenyl)-3-methoxy salicylaldiminato (C 14H 11NO 3)] compound has been synthesized and characterized. The 3D structure of the free ligand is also reported. The complex crystallizes in the monoclinic space group P2 1/ c with lattice parameters a = 19.5915(15) Å, b = 10.4096(9) Å, c = 17.5216(14) Å and β = 99.9960(7)° with z = 4. The compound consists of a dinuclear unit composed of two dioxouranium(VI) ions, bridged by two phenoxide oxygens. The coordination around each uranium atom can be regarded as approximately pentagonal bipyramidal. The two uranyl groups are separated by 3.9192(5) Å. The title complex is one of the few examples for bis-uranyl groups bridged by phenoxo ligands. These types of ligands are candidates for the sequestration of the uranium from nuclear waste and provide a good selectivity over competing lanthanide cations in solution. The ligand has been found to selectively bind to a representative actinide ( UO 2 2 + ) rather than to lanthanum (Ln 3+), which is probably related to the larger ionic radii of Ln(III). So, the ligand is not suitable to clutch two lanthanide metals via the phenolate bridge (Ln–O (phenol)–Ln). The spherical shape and the larger size of the Ln(III) ions apparently do not allow a fit within the byte angle of phenolate bridge.

A 1,8-naphthalenediol-based unsymmetrical dinucleating ligand

A facile synthesis of 2-formyl-1,8-naphthalenediol is reported. Its potential as a general precursor for the preparation of unsymmetrical multidentate chelating ligand systems based on 1,8-naphthalenediol is demonstrated by the synthesis of the dinucleating ligand L(4-)(H(4)L=N,N'-bis(2-(1,8-naphthalenediol)methylidene)propylenediamine). Reaction of H(4) L with copper acetate results in the formation of the unsymmetrical dinuclear Cu(II) complex [LCu(2)](3), which has been structurally characterized by single-crystal X-ray diffraction. One Cu(II) ion is coordinated by a N(2)O(2) compartment of L(4-) and the other Cu(II) ion is coordinated by an O(4) compartment of L(4-) while they are bridged by two aryloxide functions of L(4-). A dimerization of two molecules of 3 to a tetranuclear entity 3(2) occurs through formation of weak apical Cu--O interactions. Analysis of the temperature dependent magnetic susceptibility measurements (2--290 K) established a strong intradimer exchange coupling J(12)=-371 cm(-1). This strong superexchange interaction fits nicely in a magneto-structural correlation which has been established for dinuclear bis(phenoxide)-bridged Cu(II) complexes demonstrating the electronic equivalence of the aryloxides of a phenol and 1,8-naphthalenediol.

Schiff Base Formation upon Complexation of Tris(acetylacetonato)iron with N[(CH2CH2NH2)(CH2CH2OH)(CH2CH2CH2OH)

AbstractThe reaction of the unsymmetrical aliphatic tripodal ligand N[(CH2CH2NH2)(CH2CH2OH)(CH2CH2CH2OH)] (H4‐3) with tris(acetylacetonato)iron(III) gives the dinuclear bis(μ‐alkoxo) bridged complex [Fe{N(CH2CH2N=C(CH3)CHC(CH3)O)‐ (CH2CH2CH2O)(CH2CH2O)}]2 [Fe(η5, μ‐4)]2 (5). The new ligand 43‐ is obtained by reaction of the primary amine function of H4‐3 with one of the acetylacetonato ligands under imine formation. The iron atoms in complex 5 are coordinated in an octahedral fashion within an N2O4 environment. Complex 5 contains three different alkoxo donor groups.

Diastereoisomeric dinuclear ruthenium complexes of 2,5-di(2-pyridyl)thiazolo[5,4-d]thiazole

The first metal complexes of 2,5-di(2-pyridyl)thiazolo[5,4-d]thiazole (5) are described. X-Ray crystal structures are reported for the free ligand 5, a dinuclear copper complex 6 and the two diastereoisomers, 7meso and 7rac, of the dinuclear bis(2,2'-bipyridine)ruthenium complex. The two diastereoisomers of 7 and the 4,4'-dimethyl-2,2'-bipyridine analogue 8 are readily separated by cation exchange chromatography. 1H NMR and visible absorption spectra and electrochemical data for the four dinuclear ruthenium complexes reveal that these have relatively small HOMO-LUMO energy gaps and exhibit relatively weak metal-metal interactions.

Oxygen binding to sulfur in nitrosylated iron--thiolate complexes: relevance to the Fe-containing nitrile hydratases.

Iron-nitrosyl complex containing S-bonded monosulfinate [PPN][(NO)Fe(S,SO2-C6H4)(S,S-C6H4)] (3) has been isolated from sulfur oxygenation of complex [PPN][(NO)Fe(S,S-C6H4)2] (2) which is obtained from addition of NO molecule to [PPN][(C4H8O)Fe(S,S-C6H4)2] (1) in organic solvents. This result reveals that binding of NO to the iron center promotes sulfur oxygenation of iron dithiolates by dioxygen and stabilizes the S-bonded sulfinate iron species. Analysis of the bond angles for complexes 2 and 3 reveals that iron is best described as existing in a distorted trigonal bipyramidal coordination environment surrounded by one NO, three thiolates, and one sulfinate in complex 3, whereas the distorted square pyramidal geometry is adopted in complex 2. Complex 3 further reacts in organic solvents with molecular oxygen in the presence of [PPN][NO2] to produce the dinuclear bis(sulfinate) complex [PPN]2[(NO)Fe(SO2,SO2-C6H4)(S,S-C6H4)]2 (4). Complex 3 showed reaction with PPh3 in THF/CH2Cl2 to yield complex 2 and Ph3PO. Upon photolysis of CH2Cl2 solution of complex 3 under N2 purge at ambient temperature, the UV-vis and IR spectra consistent with the formation of complex 2 demonstrate that complex 2 and 3 are photochemically interconvertible. Obviously, complex 3 is thermally quite stable but is photochemically active toward [O] release. Also described are the X-ray crystal structures of 3 and 4.

Syntheses of Dimetallamacrocycles by Intramolecular Oxidative Couplings of Dinuclear Bis(1,3‐butadiynyl) Complexes: A New Approach to Steric Shielding in (sp‐Carbon chain)dirhenium Complexes [(η5‐C5Me5)Re(NO)(PR3)(C≡CC≡CC≡CC≡C)(R3P)(ON)Re(η5‐C5Me5)

AbstractReactions of the chiral racemic carbonyl complex [(η5‐C5Me5)Re(NO)(NCCH3)(CO)]+·BF4− and diphosphanes Ph2P(CH2)nPPh2 [2.4:1.0 mol ratio; n = 10 (a), 14 (b)] give the (bridging phosphane)dirhenium complexes [(η5‐C5Me5)Re(NO)(CO){μ‐[PPh2(CH2)nPh2P]‐P,P}(OC)(ON)Re(η5C5Me5)]2+·2BF4− (73−80%), which are reduced (LiAlH4) to the dimethyl complexes [(η5‐C5Me5)Re(NO)(CH3){μ‐[PPh2(CH2)nPh2P]‐P,P}(ON)(H3C)Re(η5‐C5Me5)] (92−96%). Reactions with HBF4·OEt2/C6H5Cl, HC≡CC≡CSiMe3, and tBuOK give, via π‐HC≡C adducts (89−94%), the bis(trimethylsilylbutadiynyl) complexes [(η5‐C5Me5)Re(NO)(C≡CC≡ CSiMe3){μ‐[PPh2(CH2)nPh2P]‐P,P}(Me3SiC≡CC≡C)(ON)Re(η5‐C5Me5)] (9a,b; 95−66%). Desilylation (wet nBu4NF) yields labile bis(butadiynyl) complexes, which are coupled [Cu(OAc)2/pyridine] to the μ‐octatetraynediyl complexes [(η5‐C5Me5)Re(NO){μ‐[PPh2(CH2)nPh2P]‐P,P}{μ‐(C1≡CC≡CC≡CC≡C8)‐C1,C8}(ON)Re(η5‐C5Me5)] (3a,b; 10−23% from 9a,b). These represent some of the few cases of intramolecular oxidative homocouplings of terminal alkynes in metal coordination spheres. The electrochemical properties of 3a,b, which undergo two one‐electron oxidations, are compared to nonmacrocyclic analogs that lack the diphosphane bridge. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Cover Picture: Syntheses of Dimetallamacrocycles by Intramolecular Oxidative Couplings of Dinuclear Bis(1,3‐butadiynyl) Complexes: A New Approach to Steric Shielding in (sp‐Carbon chain)dirhenium Complexes [(η5‐C5Me5)Re(NO)(PR3)(C≡CC≡CC≡CC≡C)(R3P)(ON)Re(η5‐C5Me5)] (Eur. J. Inorg. Chem. 12/2003)

AbstractThe cover picture shows the first example of an isolated organometallic compound containing two terminal alkynes undergoing an intramolecular oxidative coupling. Twenty‐two‐ and twenty‐six‐membered rings or “metallamacrocycles” are obtained in 18−41 % yields. The intramolecular oxidative coupling of organic compounds containing two terminal alkynes has played a critical role in the development of macrocycle chemistry, particularly with annulenes and dehydroannulenes, and macrocyclizations are playing an increasingly important role in organometallic chemistry, particularly as attention turns to architecturally novel types of target molecules that may have applications in materials chemistry or nanotechnology. Details are discussed in the article by J. A. Gladysz et al. on p. 2211 ff.

Syntheses, Structural Characterizations, and Metathesis Studies of New Dimeric Group 14 Metal Complexes Derived from Silacycloalkyl Diamide

The syntheses and solid-state structures of a series of group 14 metal complexes stabilized by cyclic silyldiamide ligands (cyclo)Si(tBuNH)2 (1) derived from a silacycloalkyl unit [(cyclo)Si = −(CH2)nSi−; n = 3 (a), 4 (b), and 5 (c)] are reported. Thus, a variety of dimeric spiro-siladiazametallacyclobutane complexes, [(cyclo)Si(tBuN)2M]2 (M = Sn (2); Pb (3)), have been prepared by the reaction of the dilithium salt of 1 with MCl2. The structures of 2a, 2d, and 3a were determined by X-ray crystallography, which showed that all are composed of cycloadducts of two monomeric units. The reactions of 2 with AlCl3 in toluene at room temperature afforded the unusual dinuclear aluminum complexes [(cyclo)Si(tBuN)2(AlCl2)2] (4). The complexes 4 were converted to the dimethyl complexes of the type [(cyclo)Si(tBuN)2(AlMe2)2] (5) with MeMgBr. Complexes 4b and 5c were characterized by X-ray crystallography. As a result of the formation of the siladiazaalumacyclobutane ring, the aluminum atoms in 4 and 5 adopt distorted tetrahedral configurations with the two chloride or methyl ligands. In addition, the reactions of 2 with ZrCl4·(THF)2 produce unsymmetrical dinuclear bis(diamido)zirconium(IV) complexes [{(cyclo)Si(tBuN)}2Zr2(Cl)(μ-Cl)3(THF)] (6).

Chiral platinum and palladium complexes containing functionalized C2-symmetric bisaminoaryl ‘Pincer’ ligands

The synthesis of enantiopure (oxo-functionalized) C 2-symmetric NCN pincer ligands is described. A key step is the symmetric functionalization of the benzylic positions, which was achieved by enantioselective ketone reduction and subsequent stereoselective substitution protocols. The introduction of α-alkyl substituents has a pronounced effect on the cavity for metal binding. For example, lithiation of the α-ethyl-functionalized pincer ligand afforded mixed (alkyl)(aryl)lithium aggregates rather than dinuclear bis(aryl) lithium [Li(NCN)] 2 species as usually observed for NCN–lithium complexes. Similar effects were established for the ( trans)-metalation reaction, which proceeded significantly slower when the steric demand of the α-substituent is increased. The potential of the corresponding enantiopure palladium and ruthenium complexes as enantioselective catalyst has been probed in the asymmetric aldol condensation and hydrogen transfer reactions. The low enantiomeric excess of the products of both reactions indicated that face-discrimination of substrates is not induced by these catalysts and that the chiral information must be located in closer proximity to the metal center.

Carbon−Carbon Coupling in Dinuclear Cycloaurated Complexes Containing Bridging 2-(Diphenylphosphino)phenyl or 2-(Diethylphosphino)phenyl. Role of the Axial Ligand and the Fine Balance between Gold(II)−Gold(II) and Gold(I)−Gold(III)

Reactions of the homovalent bis(benzoato)digold(II) complexes [AuII2(O2CPh)2(μ-2-C6H4PR2)2] (R = Ph (1a), Et (1b)) with the anions CH3-, C6F5-, and SCN- have been investigated. Dimethylmagnesium gives the stable heterovalent complexes [AuI(μ-2-C6H4PR2)2AuIII(CH3)2] (R = Ph (2a), Et (2b)), whereas (pentafluorophenyl)lithium gives the homovalent complexes [AuII2(C6F5)2(μ-2-C6H4PR2)2] (R = Ph (3a), Et (3b)). On prolonged heating in toluene, the latter rearrange to give predominantly dinuclear bis(pentafluorophenyl)digold(I) complexes of the corresponding (2,2‘-biphenylyl)bis(tertiary phosphines) [AuI2(C6F5)2(μ-2,2‘-R2PC6H4C6H4PR2)] (R = Ph (4a), Et (4b)), resulting from coupling of the C6H4PR2 units. Minor products of these rearrangements are the zwitterionic heterovalent complexes [(C6F5)2AuIII(μ-2-C6H4PR2)2AuI] (R = Ph (5a), Et (5b)). The structure of 5a differs from that of 2a by rotation of one of the bridging 2-C6H4PPh2 groups through 180°. Precursors to 4a/5a and 4b/5b have been detected by 31P NMR spe...

Double-helical dinuclear bis(dipyrromethene) complexes formed by self-assembly

Bis(dipyrromethene) ligands linked by an alkyl spacer between beta and beta' positions are shown to give helical dimers or monomers, dependent upon the length of the alkyl linker, upon complexation. Ligands consisting of methylene, ethylene, and propylene linkers -(CH(2))(n)()- (n = 1, 2, and 3) give helical dimers, while longer linking chains (n = 4, 5, or 6) give monomers or mixtures of dimers and monomers. X-ray crystal structures of the dimeric zinc complexes (n = 1, 2, and 3) reveal that the angles between dipyrromethene planes and the extent of helicity in the complexes differ as the length of the linker varies. The extent of helicity was assessed and found to be dependent upon the length and, specifically, the conformational preferences of the alkyl spacer unit. The presence of an ethylene linker gave complexes of greatest helicity. The use of a methylene spacer gave less helical structures upon complexation, while propylene spacers gave only slightly helical complexes. Our studies identify the crucial importance that the conformational preferences of the beta-beta' alkyl spacer group plays in the coordination algorithm of self-assembly to form dipyrromethene based complexes.

Synthesis and characterization of a new dinuclear bis(μ-oxo)manganese(III)/manganese(IV) complex

[(pmap)Mn-(μ-O) 2-Mn(pmap)](ClO 4) 3, a dinuclear bis(μ-oxo)manganese (III, IV) complex, was synthesized by the reaction of Mn(ClO 4) 2 with bis[2-(2-pyridyl)ethyl]-2-pyridylmethylamine (=pmap) and hydrogen peroxide. The complex was characterized structurally and EPR-measurements showed the characteristic 16 line signal for a bis-(μ-oxo)Mn(III)/Mn(IV) dimer. The corresponding complex with tris[2-(2-pyridyl)ethyl]amine (=tepa) could not be synthesized; it is most likely that in this complex, the MnMn separation would be too long for a bis(μ-oxo) bridge.

Convenient routes to mono- and dinuclear (C 5Me 5)iron(II) complexes bearing acyl, alkynyl, aryl and thienyl ligands

Treatment of the cations [Fe(C 5Me 5)(CO) 2(L)][PF 6] ( 1a, L=CO; 1c, L=PPh 3) with LiCCSiMe 3 gives the corresponding acyl derivatives [Fe(C 5Me 5)(CO) 2{C(O)CCSiMe 3}] ( 2) and [Fe(C 5Me 5)(CO)(PPh 3){C(O)CCSiMe 3}] ( 4), respectively. The nucleophile adds at the carbonyl ligand, but in the case of 1a, competitive attack occurs at the metal centre leading to the formation of the alkynyl complex [Fe(C 5Me 5)(CO) 2{CCSiMe 3}] ( 3). The latter species is formed as the only product from the acetonitrile complex [Fe(C 5Me 5)(CO) 2(CH 3CN)][PF 6] ( 1b), under the same conditions. Similarly, the dinuclear bis(acyl) complex [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-C(O)-] 2(2,2′-C 4H 2S) ( 6) is obtained from 1a by using 0.5 equivalents of the dilithium salt 2,2′-Li 2C 4H 2S/TMEDA. Complete decarbonylation by UV irradiation of 3 or 6 in the presence of dppe affords the corresponding disubstituted complexes [Fe(C 5Me 5)(dppe){CCSiMe 3}] ( 5) and [Fe(C 5Me 5)(dppe)] 2{μ-η 1,η 1′-2,2′-C 4H 2S} ( 7), respectively. Complexes [Fe(C 5Me 5)(CO) 2{CH(OMe)C 6H 4- p-Br}] ( 9) and [Fe(C 5Me 5)(CO) 2{CH(OMe)-2-C 4H 3S}] ( 10) are synthesised from the methoxycarbene complex [Fe(C 5Me 5)(CO) 2(CHOMe)][PF 6] ( 8); the nucleophilic addition of the organolithium reagents occurs at the carbene ligand. Dinuclear complexes such as the thiophene derivative [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-CHOMe-] 2(2,2′-C 4H 2S) ( 11) and the biphenylene complex [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-CHOMe-] 2( p-C 6H 4-C 6H 4) ( 12) are obtained by using the appropriate dilithiated nucleophiles. Protonolysis of 12 gives the bis(carbene) complex [Fe(C 5Me 5)(CO) 2{μ-η 1,η 1′-CH-] 2( p-C 6H 4-C 6H 4) ( 13), which is stable at −50°C.

Synthesis and crystal structure of mono-chelating (chiral) ether side chain cyclopentadienyl lanthanide complexes with a symmetric tetradentate ligand

LnCl 3 reacted with three equivalents of methoxyethylcyclopentadienyl potassium in tetrahydrofuran (THF), followed by treatment with trans-(±)-2,2′-[1,2-cyclohexanediylbis(iminomethyl)] diphenol gave a binuclear mono(methoxyethylcyclopentadienyl)samarium complex [(η 5:η 1-Cp′Sm] [(μ:η-OC 20H 20N 2O)] 2[η 5-Cp′Sm] ( 1), and bis(methoxycyclopentadienyl) ytterbium, [Cp 2′Yb] 2(OC 20H 20N 2O) ( 2) (Cp′=MeOCH 2CH 2C 5H 4). The X-ray determination of complex 1 shows that the molecule is a dimer, in which two (MeOCH 2CH 2C 5H 4)Sm(μ:η 1-OC 20H 20N 2O) units are connected to two bridging oxygen atoms of Schiff base ligands. The average Sm–C distance is 2.769(7) Å, while that of Sm–O (bridging Schiff base oxygens) is 2.401(4) Å. Further studies on the reaction of Cp 2′DyCl (Cp′H=MeOCH 2CH 2CpH) with the disodium salt of trans-(±)-2,2′-[1,2-cyclohexanediylbis(iminomethyl)]diphenol resulted in an analogue of complex 1: [(MeOCH 2CH 2C 5H 4)Dy(OC 20H 20N 2O)] 2 ( 3). However, Cp 2″DyCl reacted with disodium salt of trans-(±)-2,2′-[l,2-cyclohexanediylbis(iminomethyl)]diphenol to give rise to the isolation of dinuclear bis(tetrahydrofurfurylcyclopentadienyl) dysprosium complex with one molecular ligand, (Cp 2″Dy) 2(OC 20H 20N 2O) ( 4) (Cp″H=C 4H 7OCH 2C 5H 5).

Di- and Trinuclear Alkyne- and Vinylidenerhodium(I) Complexes Including the X-ray Crystal Structure of a Dendrimer-Like Rh3 Compound

The dimer [RhClL2]2 (1; L = PiPr3) reacts with 1,3,5-C6H3(C≡CH)3 to give in the initial step the tris(alkyne)trirhodium compound 2, which rearranges in toluene at 60 °C to yield the isomeric tris(vinylidene) complex 3. Treatment of either 2 or 3 with pyridine affords the trinuclear tris(alkynyl)trihydridorhodium(III) complex 4. The trisilyl derivative 1,3,5-C6H3(C≡CSiMe3)3 reacts with 1 to form the mononuclear compound 5, in which only one of the C≡C bonds is coordinated to Rh. The diynes 1,3- and 1,2-C6H4(C≡CH)2 behave analogously to 1,3,5-C6H3(C≡CH)3 and upon treatment with 1 yield initially the bis(alkyne)dirhodium complexes 6 and 7 and subsequently the bis(vinylidene)dirhodium isomers 8 and 9. The reactions of 1,2-, 1,3-, and 1,4-C6H4(C≡CSiMe3)2 with 1 take a similar course and give the bis(alkyne) and bis(vinylidene) compounds 10–12 and 13–15, respectively. In the same way, the dinuclear bis(alkyne) and bis(vinylidene) complexes 16 and 17 have been prepared from 1 and the naphthalene derivative 1,5-C10H6(C≡CH)2. The molecular structures of 17 and of the dendrimer-like Rh3 compound 3 have been determined by X-ray crystallography.

Structural Variation in Manganase Complexes: Synthesis and Characterization of Manganese Complexes from Carboxylate-containing Chelating Ligands.

Three manganese(II) complexes, [Mn(II)(2)L(1)(2)(H(2)O)(4)](ClO(4))(2).H(2)O (1, L(1)H = (bis(2-pyridylmethyl)amino)acetic acid), [Mn(II)(2)L(2)(2)(H(2)O)(2)](BPh(4))(2).2EtOH.2H(2)O (2, L(2)H = 3-(bis(2-pyridylmethyl)amino)propionic acid), {[Mn(II)(2)L(2)(2)(H(2)O)(MeCN)](BPh(4))(2).2MeCN}(infinity) (3), and a manganese(IV) complex [Mn(IV)(2)O(2)L(2)(2)](ClO(4))(2).4H(2)O (4) were synthesized and characterized by X-ray crystallography. The compound 1 was a dinuclear Mn(II)(2) complex which crystallized in the monoclinic crystal system, space group P2(1)/n, with Z = 4, a = 12.19(1) Å, b = 14.623(8) Å, c = 21.72(1) Å, beta = 96.29(6) degrees, V = 3849(4) Å(3). The complex cation had an approximate C(2) symmtery. The two manganeses were both seven-coordinate and doubly bridged by one oxygen atom of carboxylate groups in &mgr;(2),eta(1)-mode. The compound 2 was also a dinuclear Mn(II)(2) complex which crystallized in the monoclinic crystal system, space group P2(1)/n, with Z = 2, a = 16.760(2) Å, b = 9.643(2) Å, c = 23.533(2) Å, beta = 92.984(8) degrees, V = 3798.4(7) Å(3). The complex cation of 2 also had two seven-coordinate manganese ions, but unlike 1 the nonbridging carboxylate oxygens weakly coordinate to the manganese ions. The compound 3 crystallized in the orthorhombic crystal system, space group P2(1)2(1)2(1), with Z = 4, a = 27.888(3) Å, b = 29.054(2) Å, c = 9.428(2) Å, V = 7638(2) Å(3). The cationic portion of 3 consisted of infinite chains of Mn(II) (two Mn(II) ions per an asymmetric unit) bridged by carboxylates in bidentate syn/anti mode. The compound 4 was a dinuclear bis(&mgr;-oxo) Mn(IV)(2) complex which crystallized in the trigonal crystal system, space group R&thremacr;, with Z = 8, a = 23.962(4) Å, c = 17.190(3) Å, V = 8547(3) Å(3). All these structures are made up from a common fragment "L(n)()Mn" assembling in various topologies. Variable-temperature magnetic susceptibility measurements revealed that the Mn(II) ions in 1-3 were weakly antiferromagnetically coupled (J = -0.631(6), -0.655(5), and -0.20(1) cm(-)(1) for 1-3), and that the Mn(IV) ions in 4 were strongly antiferromagnetically coupled (J = -97.5(5) cm(-)(1)). The cyclic voltammogram of 4 showed two reduction waves with E(1/2) values of -0.52 and 0.28 V (vs ferrocene). These E(1/2) values are more negative by 0.1 V than those of the closely related complex [Mn(III)Mn(IV)O(2)L(1)(2)](ClO(4)).

Synthesis and Characterization of Mononuclear and Dinuclear Ruthenium Complexes with Tris(2-pyridylmethyl)amine and Tris(5-methyl-2-pyridylmethyl)amine.

Novel Ru(II) and Ru(III) complexes having TPA (tris(2-pyridylmethyl)amine, L1) and 5-Me(3)-TPA (tris(5-methyl-2-pyridylmethyl)amine, L2) were prepared to establish their synthetic routes and to elucidate coordination geometry and interactions between tightly bound tripodal tetradentate ligands and Ru(II)/Ru(III) centers. They include mononuclear Ru(II) complexes [RuCl(DMSO)(L)]ClO(4) (1 (L1), 2 (L2)), dinuclear bis-&mgr;-chloro Ru(II) complexes [RuCl(L)](2)(ClO(4))(2) (3 (L1), 4 (L2)), and mononuclear Ru(III) complexes [RuCl(2)(L)]ClO(4) (5 (L1), 6 (L2)). They were characterized by X-ray crystallography (for 2, 3, and 5), (1)H NMR spectroscopy, and cyclic voltammetry. For compound 2, the crystal structure was determined to possess S-bound DMSO ligand which was trans to pyridine and Cl(-) trans to the tertiary amino group of L2, and this isomer was obtained exclusively. Complex 1 was also isolated as a single isomer. Complex 3 was revealed to be a dinuclear bis-&mgr;-chloro Ru(II) species with the center of symmetry midway between two Cl(-). (1)H NMR spectra of Ru(II) complexes 1-4, the molecular structure of 2, and comparison of the molecular structure of 3 with 5 suggest that the interaction between the Ru(II) center, pyridyl moieties, and the DMSO ligand is strengthened by pi-back-bonding from the Ru(II) center to the ligands in addition to sigma-bonding of the tertiary amino group. Electrochemical measurements on 1-6 in CH(3)CN revealed that the methyl groups on pyridyl rings exert electron-donating effects onto the Ru centers to lower each redox process and such effect strengthens the Ru-S bonding in 2 compared with that in 1, accommodating pi-back-bonding from Ru(II) center to other pi-acceptors such as DMSO in 2 enough to prevent isomerization of DMSO binding mode. The dinuclear complexes 3 and 4 showed relatively large comproportionation constants, which suggest mixed-valent Ru(II)Ru(III) states would be stabilized.