Triphenylphosphineoxide nitrosyl complexes of molybdenum

Summary The tetramethylthiourea (TMTU) complexes of cobalt(II) and nickel(II) halides have been studied in the solid state by electronic, i.r. and far i.r. spectroscopy and magnetochemically. The tetrahedral Co(TMTU)₂X₂ (X = Cl, Br, 1) and Ni(TMTU)₂X₂ (X = Cl, Br) complexes have normal magnetic moments, electronic spectra and crystal field parameters; Ni₂ (TMTU)₃I₄ is diamagnetic. The cobalt complexes have normal (CoX) and (CoX) vibrational frequencies. Ni(TMTU)₂Cl₂ and Ni₂(TMTU)₃I₄ have (NiX) frequencies corresponding to long or bridging Ni-X bonds, while Ni(TMTU)₂Br₂ has normal (NiBr) frequencies for terminal Ni-Br bonds. The (MS) frequencies are similar to those of cobalt(II) and nickel(II) complexes of other thioureas.     

Isocyanide complexes of molybdenum nitrosyl

Reaction of π-cyclopentadienylmolybdenum nitrosyl halide with CNR (R = alkyl) gives [(π-C₅H₅)Mo(NO)X₂(CNR)] (X = Br or I), [Mo(NO)(CNR)₅]X (X = I or PF₆) and [Mo(NO)(CNR)₄I]; treatment of [Mo(NO)(CNR)₅]I with R′NH₂ gives [Mo(NO)(CNR)₄ {C(NHR)(NHR′)}]I or [Mo(NO)(CNR)₄(NH₂R′)]I (R′ = alkyl) depending on temperature.     

Cyclometalated ruthenium chloro and nitrosyl complexes

The novel cyclometalated Ru(III) complex, [Ru(eta(2)-phpy)(trpy)Cl][PF(6)].toluene 1, and the [Ru-NO](6) complex, [Ru(eta(2)-phpy)(trpy)NO][PF(6)](2) 2, where trpy is 2,2': 6',2'-terpyridine and phpy is 2-phenylpyridine, have been prepared and characterized by elemental analysis, IR, (1)H NMR, and electronic absorption spectroscopies, cyclic voltammetry, and crystallography. The crystal structure of 1 showed the chloride ion trans to the sigma-bonding phenyl group of phpy and is an unusual example of a stable paramagnetic cyclometalated complex. The crystal structure of 2 shows the nitrosyl ligand trans to the sigma-bonding phenyl group of phpy. The significant distortion of the normally linear Ru-NO bond angle (167.1(4) degrees) can be largely ascribed to the strong sigma-donor properties of the phenyl group.     

Ruthenium nitrosyl complexes in nitric acid solutions

Nine nitrosyl ruthenium complexes have been separated and identified in aqueous solutions of nitric acid. The separation method was low temperature, gradient elution, reverse phase partition chromatography using tri-n-butyl phosphate on a kiesel gel 60 support using ¹⁰⁶Ru labelled complexes in the nitric acid phase. The identification of the complexes was deduced from the relationships between the products of aquation and nitration and paper chromatography using both methyl-iso-propyl ketone and nitric acid-acetone elutions. The proportion of each complex at equilibrium in various concentrations of nitric acid have been measured. The rates of nitration in 10 M nitric acid, and of equation in 0.45 M nitric acid have been determined at 0°C.     

The reactions of nitrosyl complexes with cysteine

The reaction kinetics of a set of ruthenium nitrosyl complexes, {(X)5MNO}n, containing different coligands X (polypyridines, NH3, EDTA, pz, and py) with cysteine (excess conditions), were studied by UV-vis spectrophotometry, using stopped-flow techniques, at an appropriate pH, in the range 3-10, and T = 25 degrees C. The selection of coligands afforded a redox-potential range from -0.3 to +0.5 V (vs Ag/AgCl) for the NO+/NO bound couples. Two intermediates were detected. The first one, I1, appears in the range 410-470 nm for the different complexes and is proposed to be a 1:1 adduct, with the S atom of the cysteinate nucleophile bound to the N atom of nitrosyl. The adduct formation step of I1 is an equilibrium, and the kinetic rate constants for the formation and dissociation of the corresponding adducts were determined by studying the cysteine-concentration dependence of the formation rates. The second intermediate, I2, was detected through the decay of I1, with a maximum absorbance at ca. 380 nm. From similar kinetic results and analyses, we propose that a second cysteinate adds to I1 to form I2. By plotting ln k1(RS-) and ln k2(RS-) for the first and second adduct formation steps, respectively, against the redox potentials of the NO+/NO couples, linear free energy plots are obtained, as previously observed with OH- as a nucleophile. The addition rates for both processes increase with the nitrosyl redox potentials, and this reflects a more positive charge at the electrophilic N atom. In a third step, the I2 adducts decay to form the corresponding Ru-aqua complexes, with the release of N2O and formation of cystine, implying a two-electron process for the overall nitrosyl reduction. This is in contrast with the behavior of nitroprusside ([Fe(CN)5NO]2-; NP), which always yields the one-electron reduction product, [Fe(CN)5NO]3-, either under substoichiometric or in excess-cysteine conditions.     

Iridium nitrosyl complexes of 2-aminophenol derivatives

Summary The synthesis and characterisation of products obtained by the interaction between [Ir(NO)(MeCN)₂(PPh₃)₂]²⁺ and 2-aminophenol derivatives are reported. Tetracoordinate d⁸complexes of the type Ir(NO)(2-ap)(PPh₃) and pentacoordinate d complexes₆of the type [Ir(2-ap)(PPh₃)₃]⁺ where 2-ap=2-aminophenol, 2-amino-4-nitrophenol, 2-amino-5-methylphenol, 2-3-aminonaphthol and 2-amino-4-methylphenol are obtained. The Ir(NO)(PPh₃)₃ complex is always present as a byproduct. Physical properties, i.r. spectra and conductivity data of the complexes are tabulated. Reaction schemes for the formation of the three complexes are proposed and discussed.     

Nickel nitrosyl complexes with the diphenylphosphinoethane ligand

Summary Four-coordinate nickel nitrosyl complexes of the general formula Ni(NO)X(Dppe) (Dppe=Ph₂PCH₂CH₂PPh₂) have been prepared byin situ formation of Ni(NO₂)X(Dppe), (X= Cl, Br, I or SCN) followed by reduction with triphenylphosphine, or carbon monoxide, and/or DMF. Oxygenation of the nitrosyl complexes gives the corresponding nitro products and as indicated by u.v.-vis spectroscopy involves formation of an intermediate. The oxygenation rate increases markedly in the presence of light or of a catalytic amount of benzoyl peroxide and a tentative explanation is offered for these observations. Ionic adducts are formed in reactions between the nitrosyl complexes and donor molecules.Paper presented in part at the XXth ICCC Conference.     

Ligand controlled dioxygen oxidation of rhenium nitrosyl complexes

The addition of an excess of phenyldiazomethane to chlorobenzene solutions of the cationic dinitrosyl bisphosphine rhenium(-I) complexes [Re(NO)2(PR3)2][BAr(F)4] (R = Cy 1a, R = (i)Pr 1b) gave the corresponding benzylidene complexes [Re{=CH(C6H5)}(NO)2(PR3)2][BAr(F)4] (2a and 2b) in good yields. The treatment of 2b with dioxygen resulted in the oxidation of one of the nitrosyl ligands into the corresponding eta2-nitrito (3b) and nitrato complexes (4b) both in the solid state and in solution. In the case of the tricyclohexylphosphine derivative 2a the analogous conversion was not observed. A mechanism for the reaction of 2b with O2 is proposed which is based on an initial SET to the O2 molecule and subsequent formation of a peroxynitrite complex followed by the formation of a dinuclear mU-N2O4 intermediate. This in turn would undergo fission of the peroxo bond to afford 3b. A related sequence of steps is anticipated for the transformation of 3b to 4b. Furthermore, a similar mechanism seems reasonable for the seemingly topochemical reaction of 2b to 3b and 4b in the solid state. The initial SET to dioxygen and subsequent formation of the peroxynitrite complex is supported by DFT calculations on the trimethylphosphine model complexes [Re=CH{C6H5})(NO)2(PMe3)2]n+ (n = 1 and 2).     

Developing iron nitrosyl complexes as NO donor prodrugs

A novel class of water-soluble iron nitrosyl complexes has been developed for use as NO donor prodrugs. To elaborate these NO prodrugs various water-soluble ligands were used such as P(CH2OH)3, 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane (PTA), 1,2-bis[bis(hydroxymethyl)phosphino]ethane (HMPE), 1,2-bis[bis(hydroxymethyl)phosphino]benzene (TMBz), cysteamine, cysteamine hydrochloride, L-cysteine ethyl ester hydrochloride (LCEE) and pyrimidine-2-thiol (pyrim). The mononuclear complexes Fe(NO)2P(CH2OH)3Cl , Fe(NO)2(P(CH2OH)3)2, Fe(NO)2(PTA)2, Fe(NO)2HMPE , Fe(NO)2TMBz , [Fe(NO)2pyrimI] , [Fe(NO)3P(CH2OH)3][X] (X=PF6, SbF6, BF4) and the dinuclear species [Fe(NO)2S(CH2)2NH3Cl]2, [Fe(NO)2S(CH2)2NH3I2] , [Fe(NO)2LCEE]2 and [Fe(NO)2pyrim]2 were obtained. Complexes , , , , , , and are water-soluble. , and were identified as nitroxyl and , , , and as nitric oxide donors by applying an EPR NO-trap assay. To determine the amount of nitric oxide which was released from the nitric oxide donors, an additional electrochemical methodology was used. The equilibrium release or the trapping concentration of NO was also studied by a UV-vis method, which allowed the rate constant of NO release to be determined.     

New photochromic xerogels composites based on nitrosyl complexes

New photoswitchable hybrid materials based on mononitrosyl complexes with excellent optical properties have been obtained by sol–gel process. Inclusion in silica matrix prepared from tetramethoxysilane precursor leads to new materials in which the ruthenium complex [RuCl(NO)py₄](PF₆)₂·1/2H₂O (py = pyridine) is stabilized as crystalline nanoparticles with diameters between 2 and 15 nm. Photochromic properties are maintained and have been evidenced by infrared spectroscopy under irradiation (λ = 473 nm) at low temperature (T = 100 K). The reversible transfer from the ground state (GS) to the metastable state (MS1) is about 40% in the composite, which is close to the value observed on the most studied sodium nitroprusside (50% on pure material).     

Direct observation of photoinduced bent nitrosyl excited-state complexes

Ground-state structures with side-on nitrosyl (eta (2)-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited-state structures with bent-NO ligands have been proposed for years but never directly observed. Here, we use picosecond time-resolved infrared spectroscopy and density functional theory (DFT) modeling to study the photochemistry of Co(CO) 3(NO), a model transition-metal-NO compound. Surprisingly, we have observed no evidence for ON and eta (2)-NO structural isomers, but we have observed two bent-NO complexes. DFT modeling of the ground- and excited-state potentials indicates that the bent-NO complexes correspond to triplet excited states. Photolysis of Co(CO) 3(NO) with a 400-nm pump pulse leads to population of a manifold of excited states which decay to form an excited-state triplet bent-NO complex within 1 ps. This structure relaxes to the ground triplet state in ca. 350 ps to form a second bent-NO structure.     

Ruthenium and rhodium nitrosyl complexes containing dichalcogenoimidodiphosphinate ligands

Interaction of [Ru(NO)Cl₃(PPh₃)₂] with K[N(R₂PS)₂] in refluxing N,N-dimethylformamide afforded trans-[Ru(NO)Cl{N(R₂PS)₂}₂] (R = Ph (1), Prⁱ (2)). Reaction of [Ru(NO)Cl₃(PPh₃)₂] with K[N(Ph₂PSe)₂] led to formation of a mixture of trans-[Ru(NO)Cl{N(Ph₂PSe)₂}₂] (3) and trans-[Ru(NO)Cl{N(Ph₂PSe)₂}{Ph₂P(Se)NPPh₂}] (4). Reaction of Ru(NO)Cl₃ · xH₂O with K[N(Ph₂PO)₂] afforded cis-[Ru(NO)(Cl){N(Ph₂PO)₂}₂] (5). Treatment of [Rh(NO)Cl₂(PPh₃)₂] with K[N(R₂PQ)₂] gave Rh(NO){N(R₂PQ)₂}₂] (R = Ph, Q = S (6) or Se (7); R = Prⁱ, Q = S (8) or Se (9)). Protonation of 8 with HBF₄ led to formation of trans-[Rh(NO)Cl{HN(Prⁱ₂PS)₂}₂][BF₄]₂ (10). X-ray diffraction studies revealed that the nitrosyl ligands in 2 and 4 are linear, whereas that in 9 is bent with the Rh–N–O bond angle of 125.7(3)°.     

The reactivity of nitrosyl ruthenium complexes containing polypyridyl ligands

A series of cis nitrosyl complexes containing polypyridyl ligands were prepared and characterized as cis-[RuL(bpy)₂(NO)](PF₆)₃ (L = pyridine, 4-picoline, or 4-acetylpyridine), by elemental analysis, u.v.–vis. and i.r. spectroscopy, and by electrochemical techniques such as cyclic voltammetry, differential pulse voltammetry, spectroelectrochemistry, and coulometry. The complexes exhibit stretching frequencies (NO) at ca. 1950 cm^–1 indicating that nitrosyl group has a sufficiently high degree of nitrosonium ion (NO⁺) character. In non-aqueous solution, the reduction of these complexes induce nitrosyl to nitro conversion. In aqueous solution the reduction product is cis-[RuL(bpy)₂(NH₃)]²⁺ formed by a six electron mechanism. The nitrosyl compounds are susceptible to nucleophilic attack by hydroxide ion. The equilibrium constants were determined.     

Electronic structures of tetragonal nitrido and nitrosyl metal complexes

The standard oxidation states of central metal atoms in C _4v nitrido ([M(N)(L)₅] ^z ) complexes are four units higher than those in corresponding nitrosyls ([M(NO)(L)₅] ^z ) (L=CN: z = 3−, M = Mn, Tc, Re; z = 2−, M = Fe, Ru, Os; L = NH₃: z = 2+, M = Mn, Tc, Re; z = 3+, M = Fe, Ru, Os). Recent work has suggested that [Mn(NO)(CN)₅]³⁻ behaves electronically much closer to Mn(V)[b ₂(xy)]², the ground state of [Mn(N)(CN)₅]³⁻, than to Mn(I)[b ₂(xy)]²[e(xz,yz)]⁴. We have employed density functional theory and time-dependent density functional theory to calculate the properties of the ground states and lowest-lying excitations of [M(N)(L)₅] ^z and [M(NO)(L)₅] ^z . Our results show that [M(N)(L)₅] ^z and [M(NO)(L)₅] ^z complexes with the same z value have strikingly similar electronic structures.     

Transition metal nitrosyl compounds,Part XXV1 Studies of some nitrosyl complexes of molybdenum and tungsten

Summary On u.v. irradiation, the dinitrosyldithiocarbamato M(NO)₂ (S2 CNR2 )2 (M = Mo or W) complexes are converted quantitatively into the mononitrosyl M(NO)(S₂CNR₂)₃ complexes. The tungsten complex exhibits nonrigid behaviour at high temperatures; the activation energy for this process has been determined and compared to that of the molybdenum analogue. The M(NO)₂ (MeCOCHCOMe)₂ and M(NO)₂ [(O)SCNR₂]₂ compounds have been prepared; these undergo conversion into uncharacterized nitrosyl derivatives upon irradiation. Cationic complexes of the type [M(NO)₂ (MeCN)₄]2+, [M(NO)₂ (MeCN)₃ X]+ and [M(NO)₂ (MeCN)₂ (MeCOCHCOMe)]+ have been prepared and their exchange with CD₃CN studied. Exchange occursvia a dissociative process and is stereospecific for [M(NO)₂ (MeCN)₄ ]2+ (M = Mo or W) and [M(NO)₂ (MeCN)₃ X]+ (M = MO, X = Cl; M = W, X = Br).     

Electronic structure of ferric heme nitrosyl complexes with thiolate coordination

The effect of trans thiolate ligation on the coordinated nitric oxide in ferric heme nitrosyl complexes as a function of the thiolate donor strength, induced by variation of NH-S(thiolate) hydrogen bonds, is explored. Density functional theory (DFT) calculations (BP86/TZVP) are used to define the electronic structures of corresponding six-coordinate ferric [Fe(P)(SR)(NO)] complexes. In contrast to N-donor-coordinated ferric heme nitrosyls, an additional Fe-N(O) sigma interaction that is mediated by the dz2/dxz orbital of Fe and a sigma*-type orbital of NO is observed in the corresponding complexes with S-donor ligands. Experimentally, this is reflected by lower nu(N-O) and nu(Fe-N) stretching frequencies and a bent Fe-N-O moiety in the thiolate-bound case.     

New nitrosyl(perfluorocarboxylato) complexes of the platinum metals

Perfluorocarboxylic acids (R_FCOOH) (R_F = CF₃,C₂F₅ and (for Rh) C₆F₅) react with the species [M(NO)₂(PPh₃)₂] (M = Ru, Os) and [M′(NO)(PPh₃)₃] (M′ = Rh, Ir) to yield new nitrosyl complexes [Ru(OCOR_F)₃(NO)(PPh₃)₂], [OsH(OCOR_F)₂(NO)(PPh₃)₂], [Os(OCOR_F)(NO)₂(PPh₃)₂][OCOR_F], [Ir(OCOR_F)(NO)(PPh₃)₂][OCOR_F] and [Rh(OCOR_F)₂(NO)(PPh₃)₂].