Electronic structures and reactivity aspects of ruthenium-nitrosyls

Nitrosyl complexes with {Ru-NO}⁶ (4(ClO₄)₃) and {Ru-NO}⁷ (4(ClO₄)₂) configurations have been isolated in the selective molecular framework of [Ru(tpm)(pap)(NO)]ⁿ⁺ (tpm = tris(1-pyrazolyl)methane and pap = 2-phenylazopyridine). The DFT optimized structures of [Ru^II(tpm)(pap)(NO⁺)]³⁺ (4³⁺) and [Ru^II(tpm)(pap)(NO)]²⁺ (4²⁺) predict that the Ru-N-O groups in the complexes are in almost linear and bent geometries, respectively. In agreement with largely NO centered reduction a sizeable shift in ν(NO) frequency of 324 cm⁻¹ has been observed on moving from {Ru^II-NO⁺} state in 4³⁺ to {Ru^II-NO) state in 4²⁺. The DFT proposed NO centered spin in {Ru^II-NO) (4²⁺) (Mulliken spin-densities: 0.860 (NO) and 0.087 (Ru)) has been evidenced by its free radical EPR spectrum with g = 1.989. The strongly electrophilic {Ru^II-NO⁺} state in 4³⁺ (ν(NO): 1962 cm⁻¹) can be transformed to the corresponding complex (3⁺) in the presence of nucleophile, OH⁻ with k = 2.03 × 10⁻¹ M⁻¹ s⁻¹ at 298 K in CH₃CN. On irradiation with light the acetonitrile solution of [Ru^II(tpm)(pap)(NO⁺)]³⁺ (4³⁺) undergoes facile photorelease of NO (k_NO, s⁻¹ = 0.1 × 10⁻¹ and t_1/2, s = 69.3) with the concomitant formation of the solvate [Ru^II(tpm)(pap)(CH₃CN)]²⁺ (2²⁺). The photoreleased NO can be trapped as an Mb-NO adduct.     

Stepwise syntheses, structure and spectroscopic studies of ruthenium complexes of 2,6-bis(benzimidazol-2-yl)pyridine with o-iminoquinone ancillary ligand

The ruthenium complexes [Ru^II(bbp)(L)(Cl)] (1), [Ru^II(bbp)(L)(H₂O)] (2) and [Ru^II(bbp)(L)(DMSO)] (3) {bbp = 2,6-bis(benzimidazol-2-yl)pyridine, L = o-iminoquinone} have been synthesized in a stepwise manner starting from [Ru^III(bbp)Cl₃]. The single crystal X-ray structures, except for the complex 2, have been determined. All the complexes were characterized by UV-Vis, FT-IR, ¹H NMR, Mass spectroscopic techniques and cyclic voltammetry. The Ru^III/Ru^II couple for complexes 1, 2, and 3 appears at 0.63, 0.49, 0.55 V, respectively versus SCE. It is observed that complex 2, on refluxing in acetonitrile, results into [Ru^II(bbp)(L)(CH₃CN)], 4 which has been prepared earlier in a different method. The structural, spectral and electrochemical properties of complexes 1, 2 and 3 were compared to those of earlier reported complex 4, [Ru^II(bbp)(L)(CH₃CN)].     

Activity of homobimetallic ruthenium alkylidene complexes on intermolecular [2+2+2] cyclotrimerisation reactions of terminal alkynes

The activity of homobimetallic ruthenium alkylidene complexes, [(p-cymene)Ru(Cl)(μ-Cl)₂Ru(Cl)(CHPh)(PCy₃)] [Ru-I] and [(p-cymene)Ru(Cl)(μ-Cl)₂Ru(Cl)(CHPh)(IPr)] [Ru-II], on intermolecular [2+2+2] cyclotrimerisation reactions of monoynes has been investigated for the first time. It was found that these complexes can catalyse the chemo and regioselective cyclotrimerisation reactions of alkynes at both 25 and 50 °C in polar, aprotic solvents. The catalytic activity of [Ru-I] and [Ru-II] was compared to other well-known ruthenium catalysts such as Grubbs first generation catalyst [RuCl₂(CHPh)(PCy₃)₂] [Ru-III], [RuCl(μ-Cl)(p-cymene)]₂ [Ru-IV] and [RuCl₂(p-cymene)PCy₃] [Ru-V] complexes. To examine the effect of the steric hinderance of substrates on the regioselectivity of the reaction, a series of sterically hindered silicon containing alkynes (1a, 1b, 1c) were used. It was shown that the isomeric product distribution of the reaction shifts from 1,2,4-trisubstituted arenes to 1,3,5-trisubstituted arenes as the steric hinderance on the substrates increases. These homobimetallic ruthenium alkylidene complexes also catalysed regio- and chemo-selective cross-cyclotrimerisation reactions between silicon-containing alkynes (1a, 1b, 1c) and aliphatic alkynes (1d-g).     

6-Halogenopyridin-2-olato complexes with the diruthenium(2+) core: Equilibria between head-to-head and head-to-tail structures

The dinuclear bis(6-X-pyridin-2-olato) ruthenium complexes [Ru₂(μ-XpyO)₂(CO)₄(PPh₃)₂] (X = Cl (4B) and Br (5B)), [Ru₂(μ-XpyO)₂(CO)₄(CH₃CN)₂] (X = Cl (6B), Br (7B) and F (8B)) and [Ru₂(μ-ClpyO)₂(CO)₄(PhCN)₂] (9B) were prepared from the corresponding tetranuclear coordination dimers [Ru₂(μ-XpyO)₂(CO)₄]₂ (1: X = Cl; 2: X = Br) and [Ru₂(μ-FpyO)₂(CO)₆]₂ (3) by treatment with an excess of triphenylphosphane, acetonitrile and benzonitrile, respectively. In the solid state, complexes 4B-9B all have a head-to-tail arrangement of the two pyridonate ligands, as evidenced by X-ray crystal structure analyses of 4B, 6B and 9B, in contrast to the head-to-head arrangement in the precursors 1-3. A temperature- and solvent-dependent equilibrium between the yellow head-to-tail complexes and the red head-to-head complexes 4A-7A and 9A, bearing an axial ligand only at the O,O-substituted ruthenium atom, exists in solution and was studied by NMR spectroscopy. Full ¹H and ¹³C NMR assignments were made in each case. Treatment of 1 and 2 with the N-heterocyclic carbene (NHC) 1-butyl-3-methylimidazolin-2-ylidene provided the complexes [Ru₂(μ-XpyO)₂(CO)₄(NHC)], X = Cl (11A) or Br (12A). An XRD analysis revealed the head-to-head arrangement of the pyridonate ligands and axial coordination of the carbene ligand at the O,O-substituted ruthenium atom. The conversion of 11A and 12A into the corresponding head-to-tail complexes was not possible.     

Synthesis and reactivity of osmium (VI) nitrido complexes containing pyridine-carboxylato ligands

A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands Os^VI(N)(L)₂X (L = pyridine-2carboxylate (1), 2-quinaldinate (2) and X = Cl (a), Br (1b and 2c) or CH₃O (2b)) and [Os^VI(N)(L)X₃]⁻ (L = pyridine-2,6-dicarboxylate (3) and X = Cl (a) or Br (b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of Os^VI(N)(L)₂X (1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes Os^VI(NPPh₃)(L)₂X (4 and 5). The kinetics of nitrogen atom transfer from the complexes Os^VI(N)(L)₂Br (2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH₃CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/dt = k₂[Os(VI)][PPh₃]. Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) reacts also with [PPN](N₃) to give an osmium(III) dichloro complex, trans-[PPN][Os^III(L)₂Cl₂] (6). Reaction of Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) with lithium sulfide produces an osmium(II) thionitrosyl complex Os^II(NS)(L)₂Cl (7). These complexes have been structurally characterised by X-ray crystallography.     

{Ru-NO} and {Ru-NO} configurations in [Ru(trpy)(tmp)(NO)] (trpy = 2,2:6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline): An experimental and theoretical investigation

The ruthenium-nitrosyl complexes [Ru^II(trpy)(tmp)(NO⁺)](ClO₄)₃ ([4](ClO₄)₃) and [Ru^II(trpy)(tmp)(NO)](ClO₄)₂ ([5](ClO₄)₂) with {Ru-NO}⁶ and {Ru-NO}⁷ configurations, respectively (trpy = 2,2′:6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been isotaled. The nitrosyl complexes [4]³⁺ and [5]²⁺ have been generated by following a stepwise synthetic procedure: [Ru^II(trpy)(tmp)(X)]ⁿ, X/n = Cl/+ (1⁺) → CH₃CN/2+ (2²⁺) → NO₂/+ (3⁺) → NO⁺/3+ (4³⁺) → NO/2+ (5²⁺). The single-crystal X-ray structures of two precursor complexes [1]ClO₄ and [3]ClO₄ have been determined. The DFT optimized structures of 4³⁺ and 5²⁺ suggest that the Ru-N-O geometries in the complexes are linear (177.9°) and bent (141.4°), respectively. The nitrosyl complexes with linear (4³⁺) and bent (5²⁺) geometries exhibit ν(NO) frequencies at 1935 cm⁻¹ (DFT: 1993 cm⁻¹) and 1635 cm⁻¹ (DFT: 1684 cm⁻¹), respectively. Complex 4³⁺ undergoes two successive reductions at 0.25 V (reversible) and −0.48 V (irreversible) versus SCE involving the redox active NO function, Ru^II-NO⁺ ? Ru^II-NO and Ru^II-NO → Ru^II-NO⁻, respectively, besides the reductions of trpy and tmp at more negative potentials. The DFT calculations on the optimized 4³⁺ suggest that LUMO and LUMO+1 are dominated by NO⁺ based orbitals of around 65% contribution along with partial metal contribution of ∼25% due to (dπ)Ru^II → π∗(NO⁺) back-bonding. The lowest energy transitions in 4³⁺ and 5²⁺ at 360 nm and 467 nm in CH₃CN (TD-DFT: 364 and 459 nm) have been attributed to mixed MLLCT transitions of tmp(π) → NO⁺(π∗), Ru(dπ)/tmp(π) → NO⁺(π^∗) and Ru(dπ)/NO(π) → trpy(π^∗), respectively. The paramagnetic reduced species 5²⁺ exhibits an anisotropic EPR spectrum with g₁ = 2.018, g₂ = 1.994, g₃ = 1.880 (〈g〉 = 1.965 and Δg = 0.138) in CH₃CN, along with ¹⁴N (I = 1) hyperfine coupling constant, A2 = 35 G at 110 K due to partial metal contribution in the singly occupied molecular orbital (DFT:SOMO:Ru (34%) and NO (53%)). Consequently, Mulliken spin distributions in 5²⁺ are calculated as 0.115 for Ru and 0.855 for NO (N, 0.527; O, 0.328). The reaction of moderately electrophilic nitrosyl center in 4³⁺ with the nucleophile, OH⁻ yields the nitro precursor, 3⁺ with the second-order rate constant value of 1.7 × 10⁻¹ M⁻¹ s⁻¹ at 298 K in CH₃CN-H₂O (10:1). On exposure to light (Xenon 350 W lamp) both the nitrosyl species, 4³⁺ ({Ru^II-NO⁺}) and 5²⁺ ({Ru^II-NO}) undergo photolytic Ru-NO bond cleavage process but with a widely varying k_NO, s⁻¹ (t_1/2, s) of 1.56 × 10⁻¹(4.4) and 0.011 × 10⁻¹(630), respectively.     

Effects of flexible bridging ligands on DNA-binding of dinuclear ruthenium(II)-2,2′-bipyridine complexes

For reactions of [{RuCl(bpy)₂}₂(μ-BL)]²⁺ (bpy = 2,2′-bipyridine, BL = H₂N(CH₂)_nNH₂ (n = 4-8, 12), [Ru₂-BL]²⁺) with mononucleotides, the MLCT absorption bands of [Ru₂-BL]²⁺ blue-shifted with hyperchromism for GMP and hypochromism for TMP with time. Reactions of [Ru₂-BL]²⁺ with GMP or TMP proceed via initial Cl⁻ ions replacement by coordination to N7 of GMP and N3 of TMP, respectively. In competition binding experiments for [Ru₂-BL]²⁺ with GMP versus TMP, only GMP selectively coordinated to ruthenium(II). For reactions with calf thymus (CT) DNA, [Ru₂-BL]²⁺ complexes selectively bind to guanine residues of DNA. The higher degrees of binding of [Ru₂-BL]²⁺ to CT-DNA were observed with increasing n values for H₂N(CH₂)_nNH₂, which may be explained by the length of the bridging ligands. Studies on the inhibition of the restriction enzyme Acc I revealed that [Ru₂-BL]²⁺ complexes appear to be covalently favorable for the type of difunctional binding. In addition, it is very interesting to observe that circular dichroism spectroscopy of the supernatants obtained following the reactions of CT-DNA with racemic [Ru₂-BL]²⁺ show enrichments of the solutions in the ΔΔ isomers, demonstrating preferences of the ΛΛ isomers for covalent binding to CT-DNA.     

Synthesis, structure and reactivity of complexes containing [M(S2)2] fragments (M=Ru, Os; (S2)=1,2-benzenedithiolate (2−))

Subsequent addition of 1,2-benzenedithiol (S₂-H₂) and nBuLi to a solution of [Ru(NO)Cl₃ · xMeOH] in THF afforded exclusively the monomeric species NBu₄[Ru^II(NO)(S₂)₂] (1). Formation of dimeric (NBu₄)₂[Ru^II(NO)(S₂)₂]₂ (2) has been confirmed when the deprotonated ligand S₂-Li₂ was added to [Ru(NO)Cl₃ · xMeOH] and allowed to stir for 30 h. The monomer 1 undergoes aerial oxidation to give (NBu₄)₂[Ru^IV(S₂)₃] (3). The reaction between RuCl₃ · xH₂O and S₂-H₂ in the presence of NaOMe, afforded the dinulear Ru^III species (NMe₄)₂[Ru^III(S₂)₂]₂ (4). A modified method for the preparation of 1 is being employed to synthesize the osmium analogue NBu₄[Os(NO)(S₂)₂] (5) effectively. The solid state structures of 1, 2 and 3 were determined by X-ray crystal structure analysis. A comparison of relevant bond distance data suggests that 1,2-benzenedithiolate acts as an “innocent” ligand.     

fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Synthesis and reactivity with amines of new diiron alkynyl methoxy carbene complexes

The new diiron alkynyl methoxy carbene complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)CCR′}(Cp)₂]⁺ (R = 2,6-Me₂C₆H₃ (Xyl), R′ = Tol, 3a; R = Xyl, R′ = Ph, 3b; R = Xyl, R′=Buⁿ, 3c; R = Xyl, R′=SiMe₃, 3d; R = Me, R′ = Tol, 3e; R = Me, R′ = Ph, 3f) are obtained in two steps by addition of R′CCLi (R′ = Tol, Ph, Buⁿ, SiMe₃) to the carbonyl aminocarbyne complexes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)₂(Cp)₂]⁺ (R = Xyl, 1a; Me, 1b), followed by methylation of the resulting alkynyl acyl compounds [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO){C(O)CCR′}(Cp)₂] (R = Xyl, R′ = Tol, 2a; R = Xyl, R′ = Ph, 2b; R = Xyl, R′ = Buⁿ, 2c; R = Xyl, R′ = SiMe₃, 2d; R = Me, R′ = Tol, 2e; R = Me, R′ = Ph, 2f). Complexes 3 react with secondary amines (i.e., Me₂NH, C₅H₁₀NH) to give the 4-amino-1-metalla-1,3-dienes [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)CHC(R′)(NMe₂)}(Cp)₂]⁺ (R = Xyl, R′ = Tol, 4a; R = Xyl, R′ = Ph, 4b; R = Me, R′ = Ph, 4c) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CHC(Tol)(NC₅H₁₀)}(Cp)₂]⁺, 5. The addition occurs stereo-selectively affording only the E-configured products. Analogously, addition of primary amines R′NH₂ (R′ = Ph, Et, Prⁱ) affords the 4-(NH-amino)-1-metalla-1,3-diene complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CHC(R)(NHR′)}(Cp)₂]⁺ (R = Ph, 6a; Et, 6b; Prⁱ, 6c). In the case of 6a, only the E isomer is formed, whereas a mixture of the E and Z isomers is present in the case of 6b,c, with prevalence of the latter. Moreover, the two isomeric forms exist under dynamic equilibrium conditions, as shown by VT NMR studies. Complexes 6 are deprotonated by strong bases (e.g., NaH) resulting in the formation of the neutral vinyl imine complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(OMe)CHC(NR)(Tol)}(Cp)₂] (R = Ph, 7a; Et, 7b; Prⁱ, 7c); the reaction can be reverted by addition of strong acids. X-ray crystal structures have been determined for 3a[CF₃SO₃] · Et₂O, 4c[CF₃SO₃], 6a[BF₄] · CH₂Cl₂, 6c[CF₃SO₃] · 0.5Et₂O and 7a · CH₂Cl₂.     

Hydrogen bonding patterns in pyrazole Pt(II- and IV) chloride complexes

The solid-state packing arrays of the platinum(II) trans- and cis-[PtCl₂(PzH)₂] (1 and 2) and platinum(IV) trans- and cis-[PtCl₄(PzH)₂] (3 and 4) complexes have been examined and the occurrence of N-H ? Cl hydrogen-bonding associations in those structures has been discussed. Although different packing motifs are observed, in all cases molecules are interacting mostly via NH ? Cl and CH ? Cl associations. The square planar 1 and 2 form stacked arrays of PtCl₂(PzH)₂, which are supported by NH ? Cl and CH ? Cl hydrogen bonding. The isomeric structure of the complexes and orientation of the PzH rings determine NH ? Cl bonding mode (intermolecular or intramolecular) and also the extent of the platinum-platinum interaction. The synthetic procedures for the preparation of 1-4 along with elemental and X-ray analyses, TG/DTA, FAB⁺-MS, IR, and ¹H and ¹³C{¹H} NMR data are also given in this article.     

Hexa-coordinated aluminum and gallium cations derived from indazole

trans-Dichloro-tetrakis-(indazole)aluminum(III) tetrachloroaluminate(III) 1 and trans-dichloro-tetrakis-(indazole)gallium(III) tetrachlorogallate(III) 3 were obtained by the asymmetric cleavage of the chloride-bridged dimers [AlCl₃]₂ and [GaCl₃]₂ with two moles of indazole and characterized by NMR, X-ray diffraction, EA and IR. The synthesis of 3[1] was improved (yield 86%) using methylene chloride at room temperature. The addition of THF to a solution of 1/CH₂Cl₂ afforded in good yield complex 2 {[AlCl₂(IndH)₄]⁺[AlCl₄]⁻·4THF}. The crystal structures of these complexes are monoclinic in the space groups P2(1)/n (1), C2/c (2) and P2(1)/n (3). The unit cells of 1-3 contain ion pairs [ECl₂(IndH)₄]⁺ [ECl₄]⁻ (E = Al and Ga) with multiple hydrogen interactions (Cl?H 2.434-2.925 Å, O?H 1.984-2.665 Å, C?H 2.769-2.888 Å). The [ECl₂(IndH)₄]⁺ cations show hexa-coordinated octahedral aluminum and gallium atoms with two chlorine atoms in anti positions and four coplanar nitrogen atoms from the indazole ligands. The [ECl₄]⁻ anions have a tetrahedral coordination geometry around the central atom. In the lattice, the presence of THF molecules simplifies the weak interactions network in 2, so one anion interacts with two [MCl₂(Ind-H)₄]⁺ cations and two THF molecules through Cl?H intermolecular interactions (2.855-2.922 Å) and one [MCl₂(Ind-H)₄]⁺ cation interacts with two cations through ClL₄MCl?H interactions (2.922 Å). Whereas in 1 and 3, six anions interact through Cl?H intermolecular interactions (2.795-2.925 Å) with one [MCl₂(Ind-H)₄]⁺ cation and this latter interacts with other three [MCl₂(Ind-H)₄]⁺ cations through C?H interactions (2.769-2.888 Å). Additionally, every chlorine atom in the [MCl₂(Ind-H)₄]⁺ cationic moieties is bounded by NCH?ClM or NH?ClM intramolecular-tetrafurcated hydrogen bonds (2.434-2.907 Å).     

Stereosensitive formation and interconversion of sulfur-bridged cobalt(III)-mercury(II) polynuclear complexes with d- and/or l-penicillaminates

The reaction of trans(N)-[Co(d-pen)₂]⁻ (pen = penicillaminate) with HgCl₂ or HgBr₂ in the molar ratios of 1:1 gave the sulfur-bridged heterodinuclear complex, [HgX(OH₂){Co(d-pen)₂}] (X = Cl (1a) or Br (1b)). A similar reaction in the ratio of 2:1 produced the trinuclear complex, [Hg{Co(d-pen)₂}₂] (1c). The enantiomers of 1a and 1c, [HgCl(OH₂){Co(l-pen)₂}] (1a′) and [Hg{Co(l-pen)₂}₂] (1c′), were also obtained by using trans(N)-[Co(l-pen)₂]⁻ instead of trans(N)-[Co(d-pen)₂]⁻. Further, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]⁻ with HgCl₂ in the molar ratio of 1:1 resulted in the formation of [HgCl(OH₂){Co(d-pen)(l-pen)}] (2a). During the formations of the above six complexes, 1a, 1b, 1c, 1a′, 1c′, and 2a, the octahedral Co(III) units retain their configurations. On the other hand, the reaction of cis · cis · cis-[Co(d-pen)(l-pen)]⁻ with HgCl₂ in the molar ratio of 2:1 gave not [Hg{Co(d-pen)(l-pen}₂] but [Hg{Co(d-pen)₂}{Co(l-pen)₂}] (2c), accompanied by the ligand-exchange on the terminal Co(III) units. The X-ray crystal structural analyses show that the central Hg(II) atom in 1c takes a considerably distorted tetrahedral geometry, whereas that in 2c is of an ideal tetrahedron. The interconversion between the complexes is also examined. The electronic absorption, CD, and NMR spectral behavior of the complexes is discussed in relation to the crystal structures of 1c and 2c.     

Functional phosphines. Part XIV. Cationic (P,N)2-coordinated hydrides of iridium(III): catalysts for CO hydrogenation or transfer hydrogenation?

Treatment of trans-[IrCl(CO)(PPh₃)₂] with Ph₂PCH₂CH₂NH₂ in refluxing para-xylene gave (OC-6-43)-[Ir(H)(Cl)(Ph₂PCH₂CH₂NH₂)₂]Cl (1) which interacted with K[BH(s-Bu₃)] to produce a mixture of (OC-6-22)-[IrH₂(Ph₂PCH₂CH₂NH₂)₂]Cl (2a) and (OC-6-32)-[Ir(H)(Cl)(Ph₂PCH₂CH₂NH₂)₂]Cl (2b). The trans-dihydride 2a was isolated in pure form from the reaction between 1 and KOH/i-PrOH. Different from its isoelectronic (P,N)₂-coordinated Ru^II analogues, the cationic chloro hydrido complex 1 does not act as a catalyst for the direct hydrogenation of acetophenone by molecular H₂, if activated by strong alkoxide base, but rather catalyzes the transfer hydrogenation of the CO bond with methanol or isopropanol as proton/hydride sources. Dihydrido complex 2a is ascribed the role of the actual catalyst as it supports the transfer hydrogenation reaction even in the absence of base. The crystal structure of the addition compound 1 · 2EtOH has been determined.     

Unexpected structural and electronic effects of internal rotation in diruthenium paddlewheel complexes containing bulky carboxylate ligands

A series of complexes containing the bulky carboxylate ligand 2,4,6-triisopropylbenzoate (TiPB) of type trans-[Ru₂(TiPB)₂(O₂CCH₃)₂X] [X = Cl (1), PF₆ (2)] and [Ru₂(TiPB)₄X] [X = Cl (3), PF₆ (4)] have been synthesised. The corresponding complexes trans-[Ru₂(TiPB)₂(O₂CCH₃)₂] (5) and [Ru₂(TiPB)₄] (6) were also isolated. Magnetic susceptibility measurements indicate that the diruthenium cores have the expected three (1-4) or two (5 and 6) unpaired electrons consistent with σ²π⁴δ²(δ^∗π^∗)³ and σ²π⁴δ²δ^∗2π^∗2 electronic configurations. Compounds 1-4 and 6 were structurally characterised by X-ray crystallography, and show the expected paddlewheel arrangement of carboxylate ligands around the diruthenium core. The diruthenium cores of complexes 3, 4 and 6 are all distorted to minimise steric interactions between the bulky carboxylate ligands. The Ru-Ru bond length in the complex 6 [2.2425(6) Å] is the shortest observed for a diruthenium tetracarboxylate and, surprisingly, is 0.014 Å shorter than in the analogous complex 4, despite an increase in the formal Ru-Ru bond order from 2.0 (6) to 2.5 (4). This is rationalised in terms of the extent of internal rotation, or distortion, about the diruthenium core. This was supported by density functional theory calculations on the model complexes [Ru₂(O₂CH)₄] and [Ru₂(O₂CH)₄]⁺, that demonstrate the relationship between Ru-Ru bond length and internal rotation. Electrochemical and electronic absorption data were recorded for all complexes in solution. Comparison of the data for the ‘bis-bis’ (1, 2 and 5) and tetra-substituted (3, 4 and 6) complexes indicates that the shortening of the Ru-Ru bond length results in a small increase in energy of the near-degenerate δ^∗ and π^∗ orbitals.     

Structural, spectroscopic and redox studies of a new ruthenium(III) complex with an imidazole-rich tripodal ligand

The present paper describes a new tripodal ligand containing imidazole and pyridine arms and its first cis-[Ru^III(L)(Cl)₂]ClO₄ complex (1). The crystal structure of 1 shows Ru^III in a distorted octahedral geometry, in which two chloride ions, cis-positioned to each other, are coordinated besides the four nitrogen atoms from the tetradentate ligand L. The cyclic voltammogram of 1 exhibits three redox processes at −67, +73 and +200 mV versus SCE, which are attributed to the Ru^III/Ru^II couple in the cis-[Ru^III(L)(Cl)₂]⁺, cis-[Ru^II(L)(H₂O)(Cl)]⁺ and cis-[Ru^II(L)(H₂O)₂]²⁺, respectively. After chemical reduction (Zn(Hg) or Eu^II) only the cis-[Ru^II(L)(H₂O)₂]²⁺ species is observed in the cyclic voltammetry. Complex 1 absorbs at 470 nm (ε=1.4×10³ mol⁻¹ L cm⁻¹), 335 nm (ε=7.9×10³ mol⁻¹ L cm⁻¹), 301 nm (ε=6.7×10³ mol⁻¹ L cm⁻¹) and 264 nm (ε=9.9×10³ mol⁻¹ L cm⁻¹), in water solution (CF₃COOH, 0.01 mol L⁻¹, μ=0.1 mol L⁻¹ with CF₃COONa). Spectroelectrochemical experiments show a decrease of the bands at 335 and 301 nm, which are attributed to LMCT transitions from the chloride to the Ru^III center and the appearance of a broad band at 402 nm ascribed to MLCT transition from the Ru^II center to the pyridine ligand. The lability of the water ligands in the cis-[Ru^II(L)(H₂O)₂]²⁺ species has been investigated using the auxiliary ligand pyrazine. Reactions in the presence of stoichiometric and excess of pyrazine yield the same species, cis-[Ru^II(L)(H₂O)(pz)]²⁺, which exhibits a reversible redox process at 493 mV versus SCE and absorbs at 438 nm (ε=5.1×10³ mol⁻¹ L cm⁻¹) and 394 nm (ε=4.2×10³ mol⁻¹ L cm⁻¹). Experiments performed with a large excess of pyrazine gave a specific rate constant k₁=(2.8±0.5)×10⁻² M⁻¹ s⁻¹, at 25 °C, in CF₃COOH, 0.01 mol L⁻¹, μ=0.1 mol L⁻¹ (with CF₃COONa).     

Synthesis, structure and electronic spectra of new three-coordinated copper(I) complexes with tricyclohexylphosphine and diimine ligands

Three new copper(I) complexes with tricyclohexylphosphine (PCy₃) and different diimine ligands, [Cu(phen)(PCy₃)]BF₄ (1) (phen = 1,10′-phennanthroline), [Cu(bpy)(PCy₃)₂]BF₄ (2) (bpy = 2,2′-bipyridine) and [Cu(MeO-CNN)(PCy₃)]BF₄ (3) (MeO-CNN = 6-(4-methoxyl)phenyl-2,2′-bipyridine), have been synthesized and characterized. X-ray structure reveals that complexes 1 and 3 are three-coordinated with trigonal geometry, while complex 2 adopts distorted tetrahedron geometry. Complexes 1 and 3 exhibit ligand redistribution reactions in chloromethane solution by addition of excess amount of PCy₃, in which three-coordinated 1 changes into four-coordinated [Cu(phen)(PCy₃)₂]⁺, and 3 leads to form [Cu(PCy₃)₂]BF₄ and CNN-OMe. All the three complexes display yellow ³MLCT emissions in solid state at room temperature with λ_max at 558, 564 and 582 nm for 1, 2 and 3, respectively, and red-shift to 605, 628 and 643 nm at 77 K in dichloromethane solution.     

Syntheses, structures, and magnetic properties of 3d-4f heterometallic complexes constructed from pyrazole-bridged CuLn dinuclear units

A series of pyrazole-bridged heterometallic 3d-4f complexes, [CuDy(ipdc)₂(H₂O)₄] · (2H₂O)(H₃O⁺) (1) and [CuLn(pdc)(ipdc)(H₂O)₄] · H₃O⁺ (Ln = Ho (2), Er (3), Yb (4); H₃ipdc = 4-iodo-3,5-pyrazoledicarboxylic acid; H₃pdc = 3,5-pyrazoledicarboxylic acid), {[Cu₃Ln₄(ipdc)₆(H₂O)₁₆] · xH₂O}_n (Ln = Sm (5), x = 8.5; Ln = Eu (6), x = 7; Ln = Gd (7), Tb (8), x = 9), have been synthesized and structurally characterized. Ligand H₃ipdc was in situ obtained by iodination of ligand H₃pdc. Complexes 1-4 are pyrazole-bridged heterometallic dinuclear complexes, and 2-4 are isostructural. Complexes 5-8 are isostructural and comprised of an unusual infinite one-dimensional tape-like chain based on pyrazole-bridged heterometallic dinuclear units. The magnetic properties of compounds 1-4, 7 and 8 have been investigated through the magnetic measurement over the temperature range of 1.8-300 K.     

Photoinduced energy transfer between Re(I) and Ru(II) termini connected through a new exo-ditopic bis-phenanthroline ligand fused to a central macrocycle spacer: Synthesis, structure, and electrochemical and photophysical properties of a heterodinuclear complex

A new ligand L¹ has been prepared in which two 1,10-phenanthroline fragments are separated by an 18-crown-6 macrocyclic spacer. This was used to prepare the heterodinuclear complex [(bipy)₂Ru(μ-L¹)Re(CO)₃Cl][PF₆]₂ [Ru(L¹)Re] in which the {Ru(bipy)₂(phen)}²⁺ and {Re(CO)Cl(phen)} chromophores are separated by a saturated and fairly flexible crown-ether fragment. On the basis of photophysical studies on Ru(L¹)Re and associated mononuclear Ru(II) and Re(I) complexes, Re → Ru photoinduced energy-transfer occurs with a rate constant of 1.9 × 10⁸ s⁻¹ in solution room temperature leading to near-complete quenching of the Re(I)-based luminescence. At 77 K the Re(I)-based luminescence component is completely quenched. Calculations on the efficiency of both Förster and Dexter energy-transfer as a function of Re?Ru distance in this system suggest that a folded conformation of the complex, in which the Re?Ru separation is much shorter than that implied by the extended conformation detected crystallographically, is responsible for the energy-transfer, since neither Förster nor Dexter Re → Ru energy-transfer should be possible with the complex in an extended conformation. Addition of K⁺ or Ba²⁺ salts to solutions of Ru(L¹)Re had no effect on the photophysical properties, probably because the association constants are too low to give significant metal-ion binding in the macrocycle at the low concentrations employed.     

Ruthenium(VI) and osmium(VI) nitrido complexes with halogenated phenoxide and thiophenoxide ligands

Treatment of [Buⁿ₄N][Ru(N)Cl₄] with Na(OR) afforded [Buⁿ₄N][Ru(N)(OR)₄] (R = C₆F₅ (1), C₆F₄H (2), C₆Br₅ (3)), whereas that with [Buⁿ₄N][Os(N)Cl₄] gave [Buⁿ₄N][Os(N)(OR)₃Cl] (R = C₆F₅ (4), C₆F₄H (5), C₆Br₅ (6)). Treatment of [Buⁿ₄N][M(N)Cl₄] with Na(SC₆F₄H) and Na(Sxyl) (xyl = 2,6-dimethylphenyl) afforded [Buⁿ₄N][M(N)(SC₆F₄H)₄] (M = Ru (7), Os (8)) and [Buⁿ₄N][M(N)(Sxyl)₄] (M = Ru (9), Os (10)), respectively. The crystal structures of compounds 1, 6 and 9 have been determined.