The synthesis, structure, reactivity and electrochemical properties of ruthenium complexes featuring cyanoacetylide ligands

The complex [Ru(CCCN)(dppe)Cp*] (1) is readily obtained (ca. 70%) from the sequential reaction of [Ru(CCH₂)(dppe)Cp*]PF₆ with ⁿBuLi and phenyl cyanate. The complex behaves as a typical transition metal acetylide upon reaction with tetracyanoethene, affording a metallated pentacyanobutadiene. Complex 1 is a useful metalloligand, and its reactions with [W(thf)(CO)₅], [RuCl(PPh₃)₂Cp], [RuCl(dppe)Cp*] or cis-[RuCl₂(dppe)₂] all afforded products featuring the M-CCCN-M′ motif, for which ground state structures indicate a degree of polarisation. Electrochemical and spectroelectrochemical studies reveal moderate interactions between the metal centres in the 35-electron dications [{Cp*(dppe)Ru}(μ-CCCN){RuL₂Cp′}]²⁺ (RuL₂Cp′ = Ru(PPh₃)₂Cp, Ru(dppe)Cp*).     

Synthesis, spectroscopy, electrochemistry, and photochemistry of cyano-bridged mixed-valence coordination compounds containing two different types of intervalent charge-transfer bands

The tetranuclear and pentanuclear mixed-valence coordination compounds Na[(NC)₅Fe^II-μ(CN)-Pt^IV(NH₃)₄-μ(NC)-Fe^II(CN)₄-μ(CN)-Ru^III(NH₃)₅], or FePtFeRu, and [Ru^III(NH₃)₅-μ(NC)-Fe^II(CN)₄-μ(CN)-Pt^IV(NH₃)₄-μ(NC)-Fe^II(CN)₄-μ(CN)-Ru^III(NH₃)₅](OSO₂CF₃)₂, or RuFePtFeRu, were synthesized and characterized by IR and UV-Vis spectroscopy, electron microprobe analysis (EPMA), inductively coupled plasma (ICP), and cyclic voltammetry (CV). Both molecules exhibit Fe^II → Pt^IV intervalent charge transfer (IVCT) absorptions in the 400-450 nm range and Fe^II → Ru^III transition(s) between 750 and 950 nm. The energies, intensities, and half-widths of these transitions correspond well with those of model compounds. The cyclic voltammogram of FePtFeRu between 0.00 and 0.90 V versus SCE exhibits two quasi-reversible Fe waves at 0.56 and 0.74 V versus SCE, while that for RuFePtFeRu has only one Fe redox event at 0.72 V versus SCE. When the potential of the working electrode is scanned negative of −0.38 V versus SCE, however, both complexes undergo an ECE (electrochemical-chemical-electrochemical) mechanism whereby the electrochemical reduction of Ru(III) is followed by a double electron transfer to reduce Pt(IV) to Pt(II). Upon reduction to Pt(II), the cyanide bridges break and the complexes dissociate into smaller fragments. Irradiation of the Fe^II → Pt^IV IVCT transition in both compounds leads to a photolysis solution that contains dissociated Fe(II)-Ru(III) as one of its products. Irradiation of the Fe^II → Ru^III IVCT transition yields a similar UV-Vis spectrum, suggesting that the same intermediate is common to both photolysis mechanisms. The implications of this research within the larger context of multiple electron transfer are also discussed.     

A new precursor for organo-osmium complexes

The use of potassium osmate, K₂[OsO₂(OH)₄], as a precursor for some cyclopentadienyl-osmium complexes is described. The X-ray structures of OsBr(PPh₃)₂Cp, OsCl(dppe)Cp and OsX(dppe)Cp^∗ (X = Cl, Br) are reported.     

Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(NN)2(CN)7] (NN = 2,2′-bipyridine or 1,10-phenanthroline)

Crystallisation of simple cyanoruthenate complex anions [Ru(NN)(CN)₄]²⁻ (NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru(NN)(CN)₄]²⁻ salts, in the formation of small amounts of salts of the dinuclear species [Ru₂(NN)₂(CN)₇]³⁻. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru(NN)(CN)₄]²⁻ following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H₂O)_5.5][Ru₂(bipy)₂(CN)₇] · 11H₂O and [Pr(H₂O)₆][Ru₂(phen)₂(CN)₇] · 9H₂O show that the cyanoruthenate anions form Ru-CN-Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru₂Ln₂(μ-CN)₄ squares and Ru₄Ln₂(μ-CN)₆ hexagons, which alternate to form a one-dimensional chain. In [CH₆N₃]₃[Ru₂(bipy)₂(CN)₇] · 2H₂O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru₂(NN)₂(CN)₇]³⁻ anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru-CN-Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′-^tBu₂-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH₆N₃]₂[Ru(^tBu₂bipy)(CN)₄] · 2H₂O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru₂(phen)₂(CN)₇]³⁻ could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN)₄]²⁻ if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru₂(bipy)₂(CN)₇]³⁻ (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN)₄]²⁻, with a ³MLCT emission at 581 nm.     

Diiron and diruthenium aminocarbyne complexes containing pseudohalides: stereochemistry and reactivity

Acetonitrile is easily displaced from [Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] (R = 2,6-Me₂C₆H₃ (Xyl) (1a); Me (1b)) upon stirring in THF at room temperature in the presence of [NBu₄][SCN]. The resulting complexes trans-[Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCS)(Cp)₂] (R = Xyl (trans-2a); Me (trans-2b)) are completely isomerised to cis-[Fe₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCS)(Cp)₂] (R = Xyl (cis-2a); Me (cis-2b)) when heated at reflux temperature. Similarly, the complexes cis-[M₂{μ-CN(Me)(R)}(μ-CO)(CO)(NCO)(Cp)₂] (M = Fe, R = Me (4a); M = Ru, R = Xyl (4b); M = Ru, R = Me (4c)) and cis-[M₂{μ-CN(Me)(R)}(μ-CO)(CO)(N₃)(Cp)₂] (M = Fe, R = Xyl (5a); M = Fe, R = Me (5b); M = Ru, R = Xyl (5c)) can be obtained by heating at reflux temperature a THF solution of [M₂{μ-CN(Me)(R)}(μ-CO)(CO)(MeCN)(Cp)₂][SO₃CF₃] (M = Fe, R = Xyl (1a); M = Fe, Me (1b); M = Ru, R = Xyl (1c); M = Ru, R = Me (1d)) in the presence of NaNCO and NaN₃, respectively. The reactions of 5 with MeO₂CCCCO₂Me, HCCCO₂Me and (NC)(H)CC(H)(CN) afford the triazolato complexes [M₂{μ-CN(Me)(R)}(μ-CO)(CO){N₃C₂(CO₂Me)₂}(Cp)₂] (M = Fe, R = Xyl (6a); M = Fe, R = Me (6b); M = Ru, R = Xyl (6c)), [M₂{μ-CN(Me)(R)}(μ- CO)(CO){N₃C₂(H)(CO₂Me)}(Cp)₂] (M = Fe, R = Me (7a); M = Ru, R = Xyl (7b)) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃C₂(H)(CN)}(Cp)₂] (8), respectively. The asymmetrically substituted triazolato complexes 7-8 are obtained as mixtures of N(1) and N(2) bonded isomers, whereas 6 exists only in the N(2) form. Methylation of 6-8 results in the formation of the triazole complexes [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃(Me)C₂(CO₂Me)₂}(Cp)₂][CF₃SO₃] (9), [M₂{μ-CN(Me)(R)}(μ-CO)(CO){N₃(Me)C₂(H)(CO₂Me)}(Cp)₂][CF₃SO₃] (M = Fe, R = Me (10a); M = Ru, R = Xyl (10b)) and [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){N₃(Me)C₂(H)(CN)}(Cp)₂][CF₃SO₃], 11. The crystal structures of trans-2b, 4b · CH₂Cl₂, 5a, 6b · 0.5CH₂Cl₂ and 8 · CH₂Cl₂ have been determined.     

Electrochemical oxidation of methanol using alcohol-soluble Ru/Pt and Ru/Pd catalysts

The heterobimetallic Ru/Pt and Ru/Pd complexes [η⁵-C₅H₄CH₂CH₂N(CH₃)₂ · HI]Ru(PPh₃)(μ-I)(μ-dppm)PtCl₂ (7), [η⁵-C₅H₄CH₂CH₂N(CH₃)₂ · HI]Ru(PPh₃)(μ-I)(μ-dppm)PtI₂ (8), [η⁵-C₅H₄CH₂CH₂N(CH₃)₂ · HI]Ru(PPh₃)(μ-I)(μ-dppm)PdCl₂ (9), and [η⁵-C₅H₄CH₂CH₂N(CH₃)₂ · HI]Ru(PPh₃)(μ-I)(μ-dppm)PdI₂ (10) were prepared by the reaction of [η⁵-C₅H₄CH₂CH₂N(CH₃)₂ · HI]Ru(PPh₃)I(κ¹-dppm) (6) with Pt(COD)Cl₂, Pt(COD)I₂, and Pd(COD)Cl₂, respectively. Electronic interaction between the two metals is significant for the iodide-bridged compounds 7-10, as evidenced by the shifts of their redox potentials in comparison to the mononuclear complexes. The electrochemical oxidation of methanol was carried out with heterobimetallic complexes 7-10 and leads to the formation of dimethoxymethane (DMM) and methyl formate (MF) as the major oxidation products. The chloride complexes 7 and 9 are the most active catalysts, as evidenced by their TON and current efficiencies. Addition of water at the beginning of the electrolysis results in increased formation of the more oxidized product MF along with higher current efficiencies and TON.     

Further studies on the dialkylation chemistry of [Pt2(μ-S)2(PPh3)4] with activated alkyl halides RC(O)CH2X (X = Cl, Br)

Further studies have been carried out into the reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of activated alkylating agents of the type RC(O)CH₂X (R = organic moiety, e.g. phenyl, pyrenyl; X = Cl, Br). Alkylation of both sulfide centers is observed for PhC(O)CH₂Br, 3-(bromoacetyl)coumarin [CouC(O)CH₂Br], and 1-(bromoacetyl)pyrene [PyrC(O)CH₂Br], giving dications [Pt₂{μ-SCH₂C(O)R}₂(PPh₃)₄]²⁺, isolated as their PF₆⁻ salts. The X-ray structure of [Pt₂{μ-SCH₂C(O)Ph}₂(PPh₃)₄](PF₆)₂ shows the presence of short Pt?O contacts. In contrast, the corresponding chloro compounds [typified by PhC(O)CH₂Cl] and imino analogues [e.g. PhC(NOH)CH₂Br] do not dialkylate [Pt₂(μ-S)₂(PPh₃)₄]. The ability of PhC(O)CH₂Br to dialkylate [Pt₂(μ-S)₂(PPh₃)₄] allows the synthesis of new mixed-alkyl dithiolate derivatives of the type [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₄]²⁺ (R = Et or n-Bu), through alkylation of in situ-generated monoalkylated compounds [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (from [Pt₂(μ-S)₂(PPh₃)₄] and excess RBr). In these heterodialkylated systems ligand replacement of PPh₃ occurs by the bromide ions in the reaction mixture forming monocations [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺. This ligand substitution can be easily suppressed by addition of PPh₃ to the reaction mixture. The complex [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ was crystallographically characterized. X-ray crystal structures of the bromide-containing complexes [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺ (R = Et, Bu) are also reported. In both structures the coordinated bromide is trans to the SCH₂C(O)Ph ligand, which adopts an axial position, while the ethyl and butyl substituents adopt equatorial positions, in contrast to the structures of the dialkylated complexes [Pt₂{μ-SCH₂C(O)Ph}₂(PPh₃)₄]²⁺ and [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ (and many other known analogues) where both alkyl groups adopt axial positions.     

Mixed-valency with cyanides as terminal ligands: Diruthenium(III,II) complexes with the 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine bridge and variable co-ligands (CN vs. bpy or NH3)

New diruthenium complexes (PPN)₄[(NC)₄Ru(μ-bptz)Ru(CN)₄], (PPN)₄1, and [(bpy)₂Ru(μ-bptz)Ru(CN)₄], 2, (PPN⁺ = bis(triphenylphospine)iminium; bptz = 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine; bpy = 2,2′-bipyridine), were synthesised and characterised by spectroscopic and electrochemical techniques. The comproportionation constant K_c = 10^7.0 of the mixed-valent species [(NC)₄Ru(μ-bptz)Ru(CN)₄]³⁻ as obtained by oxidation of 1⁴⁻ in CH₃CN is much lower than the K_c = 10^15.0 previously detected for [(H₃N)₄Ru(bptz)Ru(NH₃)₄]⁵⁺, reflecting the competition between CN⁻ and bptz for the π-electron density of the metals. Comparison with several other bptz-bridged diruthenium(II,III) complexes reveals an approximate correlation between K_c and the diminishing effective π acceptor capacity of the ancillary terminal ligands. In addition to the intense MLCT absorption at λ_max = 624 nm, the main IVCT (intervalence charge transfer) band of 1³⁻ was detected by spectroelectrochemistry at λ_max = 1695 nm (in CH₃CN; ε = 3200 M⁻¹ cm⁻¹). The experimental band width at half-height, Δν_1/2 = 2700 cm⁻¹, is slightly smaller than the theoretical value Δν_1/2 = 3660 cm⁻¹, calculated from the Hush approximation for Class II mixed-valent species. In agreement with comparatively moderate metal-metal coupling, the mixed-valent intermediate 1³⁻ was found to be EPR silent even at 4 K. The unsymmetrical mixed-valent complex [(bpy)₂Ru^II(μ-bptz)Ru^III(CN)₄]⁺, obtained in situ by bromine oxidation of 2 in CH₃CN/H₂O, displays a broad NIR absorption originating from an IVCT transition at λ_max = 1075 nm (ε ≈ 1000 M⁻¹ cm⁻¹, Δν_1/2 ≈ 4000 cm⁻¹). In addition, the lifetime of the excited-state of the mononuclear precursor complex [Ru(bptz)(CN)₄]²⁻ was measured in H₂O by laser flash photolysis; the obtained value of τ = 19.6 ns reveals that bptz induces a metal-to-ligand electronic delocalisation effect intermediate between that induced by bpy and bpz (bpz = 2,2′-bipyrazine) in analogous tetracyanoruthenium complexes.     

Exploring the properties of mixed valence cyanide bridged dinuclear complexes: Solvent stabilization of electronic isomers

We report here the synthesis and properties of a family of mixed-valence cyanide-bridged dinuclear complex ions trans-[(L′L₄Ru^II(μ-NC)Fe^III(CN)₅]⁻ (with L = pyridine or 4-dimethylaminopyridine (dmap) and L′ = pyridine, 4-methoxypyridine (meopy) or 4-dimethylaminopyridine)) whose properties could be adjusted smoothly by changing the acceptor properties of the solvent and the σ donor properties of the L′ pyridine ligand. In solution these complexes exhibit an intense solvent-dependent MM′CT (Ru^II → Fe^III) absorption in the near infrared region. Analysis of this band in different complexes and solvents suggests an enhanced interaction as the energies of the metal centers come closer. From this trend the anion trans-[(dmap)₅Ru(μ-NC)Fe(CN)₅]⁻ (dmap = 4-dimethylaminopyridine) in water is expected to belong to the class II-III, but its spectral properties indicates a ground state with Ru(III)-Fe(II) character. The stabilization of this electronic isomer is probably related to the better donor properties of the hexacyanoferrate(II) moiety and its stronger interaction with water.     

Dinuclear ruthenium(II) catecholato and 2,3-naphthalenediolato complexes featuring κ-diaryloxo/η-arene coordination mode

A new dinuclear ruthenium(II) catecholato complex [Cp*Ru(κ²:η⁶-μ₂-1,2-O₂C₆H₄)RuCp*] (3; Cp* = η⁵-C₅Me₅) has been prepared by the reaction of [Cp*RuCl]₄ with 2 equiv. of disodium catecholate in THF. Complex 3 has a dinuclear structure, in which one of the Cp*Ru fragments is κ²-bonded to the two oxygen atoms and the other is η⁶-bonded to the aromatic ring. Similar treatment of [Cp*RuCl]₄ with disodium 2,3-naphthalenediolate affords an analogous κ²:η⁶-bonded dinuclear complex [Cp*Ru(κ²:η⁶-μ₂-2,3-O₂C₁₀H₆)RuCp*] (4) with selective π-complexation at the oxygen-substituted naphthalene ring. The molecular structure of 4 has been determined by X-ray crystallography. The oxygen-bound ruthenium atoms in complexes 3 and 4 are coordinatively unsaturated and readily uptake 1 equiv. of carbon monoxide to give the corresponding carbonyl adducts [Cp*Ru(CO)(κ²:η⁶-μ₂-1,2-O₂C₆H₄)RuCp*] (5) and [Cp*Ru(CO)(κ²:η⁶-μ₂-2,3-O₂C₁₀H₆)RuCp*] (6), respectively.     

Single and double nucleophilic attack on cluster-bonded allenylidenes: Synthesis of phosphorus heterocycles

Further studies of the attack of bidentate tertiary phosphines, such as dppm and dppe, and the related diarsine dpam, on Ru₃(μ-H){μ₃-C₂CHR(OH)}(CO)₉ (R = H, Me) are described, together with the X-ray determined structures of [Ru₃(μ₃-C₂CH₂PPh₂CH₂CH₂PPh₂)(CO)₉]BF₄ (6) and Ru₃(μ-H){μ₃-C₂CHMePPh₂CHPPh₂}(CO)₉ (7) (containing diphospha heterocycles), Ru₃(μ-H){μ₃-CH₂(OH)C₂PPh₂CH₂PPh₂}(CO)₈ (8) (containing a phosphonium-alkynyl ligand also coordinated to a cluster Ru atom) and Ru₃(μ-H)(μ₃-CCCHAsPh₂CH₂AsPh₂)(CO)₉ (9) (containing an arsino-allenylidene ligand). These complexes are formed by nucleophilic attack of the Group 15 ligand on an alkynyl or allenylidene ligand on the cluster.     

Synthesis of the manganese-monocarbollide dianion [1-NHBu-2,2,2-(CO)3-closo-2,1-MnCB10H10]: Reactions with transition metal cations

Reaction of [Mn(NCMe)₃(CO)₃][PF₆] with Li₃[7-NHBu^t-nido-7-CB₁₀H₁₀] in THF (THF = tetrahydrofuran) affords the twelve-vertex manganacarborane dianion [1-NHBu^t-2,2,2-(CO)₃-closo-2,1-MnCB₁₀H₁₀]²⁻, isolated as the bis-[N(PPh₃)₂]⁺ salt (5a). This species reacts with {Pt(dppe)}²⁺ (dppe = Ph₂PCH₂CH₂PPh₂) to afford the bimetallic complex [1-NH₂Bu^t-2,3-{Pt(dppe)}-2,2,2-(CO)₃-closo-2,1-MnCB₁₀H₉] (7) which has an Mn-Pt bond. In contrast, with {Cu(PPh₃)}⁺ the anion of 5a yields a CuMnCu trimetallic compound [1-{NH(Bu^t)Cu(PPh₃)}-2,3,7-{Cu(PPh₃)}-3,7-(μ-H)₂-2,2,2-(CO)₃-closo-2,1-MnCB₁₀H₈] (8) in which one of the Cu centers is bonded to Mn, whilst the other is attached to the pendant NHBu^t group. Upon treatment with Ag⁺, compound 5a is oxidized giving the very unusual Mn(III)-carbonyl complex [1,2-μ-NHBu^t-2,2,2-(CO)₃-closo-2,1-MnCB₁₀H₁₀] (9a) in which the carborane ligand formally acts as an eight-electron donor to manganese. The novel structural features of compounds 7, 8, and 9a have been confirmed by X-ray diffraction studies.     

Syntheses, characterization, and DFT investigation of new mononuclear acetonitrile- and chloro-ruthenium(II) terpyridine complexes

A series of mononuclear acetonitrile complexes of the type [Ru(CH₃CN)(L)(terpy)]²⁺ {L = phen (1), dpbpy (3), and bpm (5)}, and their reference complexes [RuCl(L)(terpy)]⁺ {L = phen (2), dpbpy (4), and dpphen (6)} were prepared and characterized by electrospray ionization mass spectrometry, UV-vis spectroscopy, and cyclic voltammograms (CV). Abbreviations of the ligands (Ls) are phen = 1,10-phenanthroline, dpbpy = 4,4′-diphenyl-2,2′-bipyridine, bpm = 2,2′-bipyrimidine, dpphen = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, and terpy = 2,2′:6′,2″-terpyridine. The X-ray structures of the two complexes 2 and 3 were newly obtained. The metal-to-ligand charge transfer (MLCT) bands in the visible region for 1, 3, and 5 in acetonitrile were blue shifted relative to those of the reference complexes [RuCl(L)(terpy)]⁺. CV for all the [Ru(CH₃CN)(L)(terpy)]²⁺ complexes showed the first oxidation wave at around 0.95 V, being more positive than those of [RuCl(L)(terpy)]⁺. The time-dependent-density-functional-theory approach (TDDFT) was used to interpret the absorption spectra of 1 and 2. Good agreement between computed and experimental absorption spectra was obtained. The DFT approach also revealed the orbital interactions between Ru(phen)(terpy) and CH₃CN or Cl⁻. It is demonstrated that the HOMO-LUMO energy gap of the acetonitrile ligand is larger than that of the Cl⁻ one.     

The synthesis and characterization of mixed ligand Ru(II) complexes with dipyrido(2,3-a:3′,2′-j)phenazine (dpop′) and 2,3,5,6-tetra(2-pyridyl)-pyrazine (tppz)

The synthesis of the mixed ligand mono metallic [Ru(dpop′)(tppz)]²⁺ and bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]⁴⁺ (dpop′ = dipyrido(2,3-a:3′,2′-j)phenazine; tppz = 2,3,5,6 tetra-(2-pyridyl)pyrazine) complexes is described. The [Ru(dpop′)(tppz)]²⁺ complex display an intense absorption at 518 nm which is assigned to a Ru(dπ) → dpop′ (π∗) MLCT transition, and at 447 nm which is assigned to a Ru(dπ) → tppz(π∗) MLCT transition. It undergoes emission at RT in CH₃CN with λ_em = 722 nm. The bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]⁴⁺ complex shows a low energy absorption shoulder near 635 nm assigned to a Ru(dπ) → tppz(π∗) MLCT transition and an intense peak at 542 nm due to Ru(dπ) → dpop′ (π∗) MLCT transition. The bimetallic complex also emits at RT in CH₃CN with λ_em = 785 nm. Cyclic voltammetry shows reversible Ru^+2/+3 oxidations at 1.68 V for the monometallic complex and Ru^+2/+3 oxidation couples at +1.94 and +1.70 V for the bimetallic complex.     

Construction of carbon chains on ruthenium and osmium carbonyl clusters

We have used the elimination of AuX(PR₃) (X = halide, R = Ph, tol) that occurs in reactions of alkynylgold(I)-phosphine complexes with M₃(μ-H)₃ (μ₃-CBr) (CO)₉ (M = Ru, Os) to prepare the complexes M₃(μ-H)₃(μ₃-CCCR)(CO)₉ [M = Ru, R = Ph 2, CCSiMe₃3, Fc 4, CCFc 6-Ru, CC[Ru(PPh₃)₂Cp] 8; M = Os, R = CCFc 6-Os, CCCCFc 7], Fc′{(μ₃-CCC)Ru₃(μ-H)₃(CO)₉}₂5, and bis-cluster-capped carbon chain complexes {M₃(μ-H)₃(CO)₉}₂{μ₃:μ₃-C(CC)_nC} (M = Ru, n = 2 9, 3 10-Ru; M = Os, n = 3 10-Os) and {(L)(OC)₈(μ-H)₃M₃}C(CC)_nC{Co₃(μ-dppm)(CO)₇} (n = 1, M = Ru, L = CO 11, PPh₃12-Ru/P; n = 2, L = CO 12-Ru, PPh₃13; M = Os, L = CO 12-Os) in good to excellent yields. X-ray structural determinations of 2-5, 6-Ru, 6-Os, 7, 9, 11, 12-Ru, 12-Os and 12-Ru/P are reported.     

Ligand redox non-innocent behaviour in ruthenium complexes of ethynyl tolans

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(CCC₆H₄CCSiMe₃)(L₂)Cp′] and [Ru(CCC₆H₄CCC₆H₄R-4)(L₂)Cp′] (R = OMe, Me, CO₂Me, NO₂; L₂ = (PPh₃)₂, Cp′ = Cp; L₂ = dppe; Cp′ = Cp^∗) have been synthesised. One-electron oxidations of these complexes gave the corresponding radical cations, which were significantly more chemically stable in the case of the Ru(dppe)Cp^∗ derivatives. The representative complex [Ru(CCC₆H₄CCC₆H₄OMe-4)(dppe)Cp^∗] was further examined by spectroelectrochemical (IR and UV-Vis-NIR) methods. The results of the spectroelectrochemical studies, supported by DFT calculations, indicate that the hole is largely supported by the ‘RuCCC₆H₄’ moiety in a manner similar to that described previously for simple aryl ethynyl complexes, rather than being more extensively delocalized along the entire conjugated ligand.     

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.     

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.     

Heterobimetallic platinum(II)-palladium(II) complexes bridged by fluorobenzenethiolates. Structure and equilibria

Synthesis of the heterobimetallic platinum(II)-palladium(II) complexes with poly fluorinated benzenethiolates as intermetallic bridges, [(dppe)Pd(μ-SR_F)₂Pt(dppe)](SO₃CF₃)₂ with SR_F = p-SC₆F₄(CF₃) (1), SC₆F₅ (2), p-SC₆HF₄ (3) and o-SC₆H₄(CF₃) (4), have been accomplished either by a redistribution reaction in mixtures of the homonuclear bimetallic species, [(dppe)Pd(μ-SR_F)₂Pd(dppe)]²⁺/[(dppe)Pt(μ-SR_F)₂Pt(dppe)]²⁺ or by assembling the monometallic building blocks [(dppe)M(μ-SR_F)₂]/[(dppe)M′(solvent)₂]²⁺, M, M′ = Pd or Pt. Both experimental systems reach an equilibrium state which is independent of the temperature within the probed range, −90 °C to +50 °C. A single crystal of the heterobimetallic compound [(dppe)Pd(μ-SC₆F₅)₂Pt(dppe)](SO₃CF₃)₂(acetone)₂ (2) was isolated and analyzed by X-ray diffraction. Comparison with the corresponding structures exhibited by the homobimetallic analogous, [Pd₂(μ-SC₆F₅)₂(dppe)₂](SO₃CF₃)₂(acetone)₂ (5) and [Pt₂(μ-SC₆F₅)₂(dppe)₂](SO₃CF₃)₂(acetone)₂ (6) shows that all three structures are isostructural in space group . All three compounds exhibit a centrosymmetric planar [M₂(μ-S)₂] ring in which the sulfur substituents are arranged in an anti configuration.     

Reaction of iron and ruthenium halogenide complexes with GaCp and AlCp: Insertion, Cp transfer reactions and orthometallation

The reactions of the Fe(II) and Ru(II) halogenide complexes [Fe(PPh₃)₂Br₂], [Fe(NCCH₃)₂Br₂], [Ru(PPh₃)₃Cl₂], and [Ru(dmso)₄Cl₂] with GaCp^∗ and AlCp^∗, respectively, are investigated. The reactions of [FeBr₂L₂] with ECp^∗ exclusively proceed via Cp^∗ transfer, leading to [FeCp^∗(GaCp^∗)(GaBr₂)(PPh₃)] (1) (L = PPh₃, E = Ga), [FeCp^∗(GaCp^∗)₂ (GaBr₂)] (2) (L = NCCH₃, E = Ga) and [FeCp^∗(μ³-H)(κ²-(C₆H₄)PPh₂)(AlCp^∗)(AlBr₂)] (3) (L = PPh₃, E = Al), the latter of which is formed via orthometallation of one PPh₃ ligand. The reaction of [Ru(dmso)₄Cl₂] leads to the homoleptic complex [Ru(GaCp^∗)₆Cl₂] (4) in high yields, while [Ru(PPh₃)₃Cl₂] gives 4 in rather low yields. The reason for this difference in reactivity is investigated and it is shown that Cp^∗ transfer and orthometallation are the limiting side reactions of the reaction of [Ru(PPh₃)₃Cl₂] with GaCp^∗. All compounds were characterized by NMR spectroscopy, and single crystal X-ray diffraction studies were performed for 1, 3, and 4.