Thermal Substitution Reactions Research Articles

Photoinduced Self-assembly: An Alternative Strategy for the Construction of Coordination Oligomers and Polymers.

Self-assembled oligonuclear and polynuclear complexes have numerous functionalities and potential applications. Generally, such compounds have been constructed by thermal substitution reactions with bridging ligands. Herein, we report bottom-up and photochemical construction of functional coordination oligomers and polymers by photosubstitution-induced self-assembly. The photosubstitution reactions of a ruthenium precursor complex with bridging ligands having pyrazole moieties afford mono-, di-, tri-, tetra-, and pentanuclear ruthenium complexes, Ru1-Ru5, which have one-dimensional architectures. Intramolecular hydrogen bonding between each bridging ligand is a key to construct the molecular nanowires. All the complexes have been isolated and thoroughly characterized. The photochemically synthesized ruthenium complexes act as synthons for longer metal-complex-based nanowires with a length of the order of tens-of nanometers. The multinuclear complexes are generated by photoinduced self-assembly in the presence of a base, and they undergo photoinduced disassembly in the presence of acid.

Synthesis of Cr2AuC via thermal substitution reaction in Au-covered Cr2GaC and Cr2GeC thin films

Intercalation of noble metals into non-van der Waals solids provides a new avenue to synthesize novel nanolaminated compounds with distinct material properties. Herein, we use solid-state reaction at 400 °C to prepare Cr2AuC from two Cr-based Mn+1AXn phase precursors and demonstrate the formation of Cr2AuC upon full replacement of Ga layers with Au in Cr2GaC thin films via thermal substitution reaction. The resulting Cr2AuC exhibits 2.7% lattice expansion relative to the original Cr2GaC, whereas Ge in a Cr2GeC thin film was sparsely replaced by Au, as revealed by electron microscopy and x-ray diffraction analysis. To explain the observed differences, using ab initio calculations, we consider the bonding properties of Cr2GaC and Cr2GeC, and the energetic driving forces for substitution by evaluating the mixing free energy of Au on both A-sites of the MAX phases, and of both A-elements in the surrounding Au lattice. The results suggest that it is somewhat easier to mix Au on the A-site in Cr2GaC than in Cr2GeC, and substantially easier to mix Ga into the Au-lattice than Ge. Finally, we discuss how the gained insights can be consulted for exploring a wider class of Mn+1AXn phases with intercalated noble metals.

Lead Telluride Through Transformation of Plumbonacrite in Tellurium Atmosphere and Its Behavior as Part of PbTe–Si Photodiode

Plumbonacrite [Pb10(CO3)6O(OH)60] is a versatile material, which can be deposited by a simple solution process and transformed into lead chalcogenides by thermal substitution. This paper is focused on the plumbonacrite film synthesis by photo chemical bath deposition over silicon substrate, its transformation into lead telluride by a thermal substitution reaction using hot tellurium gas and the study of the heterojunction formed between PbTe p-type/Si n-type. The PbTe-p/Si-n device assembled with plumbonacrite and placed under tellurium gas shows the characteristics that can be obtained by direct PbTe synthesis. The photodiode produced by this two-step method shows a photoresponsivity of 0.1 A/W.

Synthesis and characterization of 9-O-alkyl substituted palmatine derivatives

For the establishment of chemical library of protoberberines provided for the bio-activity screening, the target compounds were synthesized by thermal degradation and nucleophilic substitution reactions with the bio-active alkaloid, palmatine (1), as the raw material, and their structures were identified and conformed by 1H-NMR and MS spectra. Among them, 13 compounds were new.

Cadmium selenide film through ammonia free thermal substitution reaction on cadmium oxide hydroxide films by chemical vapor deposition

Polycrystalline CdSe films with hexagonal phase were deposited on glass substrates by thermal substitution reaction in a CVD reactor. The films were prepared in two stages. First, films of cadmium oxide hydroxide Cd(O2)0.88(OH)0.24 were deposited on the glass substrates by chemical bath deposition (CBD), using ammonia free, low temperature process in alkaline aqueous solution. Then the CBD-deposited films were placed in a Chemical Vapor Deposition (CVD) Hot Wall reactor where they acted as precursors in a reaction of substitution of non-metallic film component by Se, thus forming CdSe semiconductor films. The Se gas was transported from the source to the substrate with a nitrogen flux of 0.25l/min. The chalcogen source temperature was 500°C, which is above the melting point (217°C) but below the boiling point of Se (684.9°C). The substrate temperature was adjusted to obtain a hexagonal phase of CdSe.

Low-Temperature N−O Bond Cleavage in Nitrosyl Ligands Induced by the Unsaturated Dimolybdenum Anion [Mo2(η5-C5H5)2(μ-PPh2)(μ-CO)2]−

The unsaturated anion [Mo(2)Cp(2)(mu-PPh(2))(mu-CO)(2)](-) (1) (Na(+) salt) reacts with the nitrosyl complexes [MCp'(CO)(2)(NO)]BF(4) (M = Mn, Re; Cp' = eta(5)-C(5)H(4)Me) rapidly at about 193 K. Upon warming of the resulting mixtures up to 243 K orange solutions are obtained, shown to contain the corresponding oxo- and nitride-bridged tetracarbonyl complexes [Mo(2)MCp(2)Cp'(mu-N)(mu-O)(mu-PPh(2))(CO)(4)] as the major product, which could be isolated only for M = Re. Above 253 K, however, these compounds experience spontaneous decarbonylation to yield the unsaturated tricarbonyl derivatives [Mo(2)MCp(2)Cp'(mu-N)(mu-O)(mu-PPh(2))(CO)(3)] (Mo-Mo = 2.840 A for the Mn compound, according to density functional theory (DFT) calculations). These complexes in turn react rapidly with air to give the corresponding dioxodicarbonyl derivatives [Mo(2)MCp(2)Cp'(mu-N)(mu-O)(mu-PPh(2))(O)(CO)(2)] almost quantitatively. The structure of the latter product (M = Re) was determined by X-ray diffraction methods (Mo-Mo = 2.763(1) A). In contrast with the N-O bond cleavage easily taking place in the above reactions, the direct nitrosylation of 1 with N-methyl-N-nitroso-p-toluenesulfonamide induces no bond cleavage process in the nitrosyl ligand, but just gives the electron-precise tricarbonyl derivative [Mo(2)Cp(2)(mu-PPh(2))(CO)(3)(NO)] or, in the presence of CN(t)Bu, a mixture of the new isocyanide complexes [Mo(2)Cp(2)(mu-PPh(2))(CN(t)Bu)(CO)(2)(NO)] and [Mo(2)Cp(2)(mu-PPh(2))(mu-eta(1):eta(2)-CN(t)Bu)(CO)(NO)]. Separate experiments indicated that these isocyanide complexes cannot be converted one into each other, nor can they be obtained through thermal substitution reactions on the above tricarbonyl product.

Synthesis and electrochemistry of Group 6 tetracarbonyl ( N, N′-bis(ferrocenylmethylene)ethylenediamine)metal(0) complexes

Thermal substitution reaction of Cr(CO) 4(η 2:2-1,5-cyclooctadiene), Mo(CO) 4(η 2:2-norbornadiene), and W(CO) 5(η 2-bis(trimethylsilyl)ethyne) with N, N′-bis(ferrocenylmethylene)ethylenediamine (bfeda) yields M(CO) 4(bfeda) complexes which could be isolated from the reaction solution and characterized by elemental analysis, MS, IR, and NMR spectroscopy. In the case of tungsten, W(CO) 5(bfeda) is formed as intermediate and then undergoes the ring closure reaction yielding the ultimate product W(CO) 4(bfeda). The electrochemical behavior of the M(CO) 4(bfeda) complexes was studied by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in dichloromethane with tetrabutylammonium tetrafluoroborate as electrolyte. Constant potential electrolysis of the complexes was performed successively at their peak potentials at 0 °C in their CH 2Cl 2 solution and the electrolysis was followed by in situ recording the electronic absorption spectra in every 5 mC. In the electrolysis of Cr(CO) 4(bfeda), the central Cr(0) is oxidized first and electrolysis continues with oxidations of two ferrocenyl groups until the end of totally three moles of electron passage per mole of complex. In the electrolysis of Mo(CO) 4(bfeda) and W(CO) 4(bfeda) the first oxidation occurs on the central atom forming a short-lived species which undergoes an intramolecular one-electron transfer and is reduced back to M(0) while one of the ferrocene units is oxidized to the ferrocenium cation at the same time. This indicates that the electron is transferred from iron to the central metal atom.

Diruthenium Carbonyl Complexes Bound to Guaiazulene: Preparation and Thermally Reversible Photoisomerization Studies of Phosphine and Phosphite Derivatives of (μ2,η3:η5-guaiazulene)Ru2(CO)5 and Iron Homologues

Preparation of a series of (μ2,η3:η5-guaiazulene)M2(CO)5-n(L)n (M = Fe, Ru; n = 1, 2; L = phosphines and phosphites) was achieved by photochemical or thermal replacement of CO ligands in (μ2,η3:η5-guaiazulene)M2(CO)5 [M = Fe (1) or Ru (2)], which exist as a mixture of two haptotropic isomers (1-A and 1-B, 2-A and 2-B), by L, and the products were subjected to thermally reversible photoisomerization studies. Phosphine and phosphite derivatives of diiron complexes (μ2,η3:η5-guaiazulene)Fe2(CO)4(L) (3) and (μ2,η3:η5-guaiazulene)Fe2(CO)3(L)2 (4) were prepared in high yields by UV irradiation of 1 in the presence of L. In sharp contrast, (μ2,η3:η5-guaiazulene)Ru2(CO)4(L) (5) was successfully prepared by thermal replacement of a CO ligand in 2 by L. Although these derivatives may be formed as a mixture of two possible haptotropic isomers, only one isomer (3-A, 4-A, and 5-A) was isolated in each reaction. Detailed studies on the thermal substitution reaction of 2 revealed that formation of 5-A from a mixture of ...

Preparation and structural elucidation of novel cis ruthenium(II) bis(bipyridine) sulfoxide complexes †

Four novel cis-ruthenium bis(bipyridine) sulfoxide complexes with the general formula cis-[Ru(A)2(B)(Cl)]X (2, A = 2,2′-bipyridine (bpy), B = dimethyl sulfoxide (DMSO); 3, A = 4,4′-dimethyl-2,2′-bipyridine (dmbpy), B = DMSO; 4, A = bpy, B = tetramethylene sulfoxide (TMSO); and 5, A = dmbpy, B = TMSO; X = Cl–, I–, PF6– or ClO4–) were synthesized from cis-[Ru(bpy)2Cl2] 1 or trans-[Ru(dmbpy)2Cl2] 6 in the substrate sulfoxide solutions at 60–120 °C, i.e. by a thermal process. This cis selectivity is in contrast to previously reported results. However, photoirradiation of 1 in the presence of DMSO selectively produced trans-ruthenium bis(bipyridine) sulfoxide; when 6 was photoirradiated in the presence of DMSO cis-[Ru(dmbpy)2(DMSO)Cl]Cl was the sole product. These complexes were fully characterized by elemental analysis, IR, UV/vis, 1H, 13C and 2-D NMR spectroscopy. The sulfoxide ligands co-ordinate through a Ru–S bond in all cases. The NMR studies of 2 imply that no rotation around the Ru–S bond occurs, in accord with quantum mechanics calculations. Crystallographic structural determinations of 2·PF6– (from acetone–diethyl ether) and 2·I– (from water) showed that both complexes share similar octahedral geometries, but different conformations were found for the sulfoxide ligands with Cl–Ru–S–O dihedral angles of 121.6 and 56.3°, respectively, thus demonstrating that a different energetically favored conformation may exist in low or high dielectric environment. The stability of complexes 2–5 allowed separation into their Δ and Λ enantiomers, and the circular dichroism spectra were obtained. Thermal substitution reactions were also carried out using 2·Cl– which was converted into cis-[Ru(bpy)2Cl2] 1 or cis-[Ru(bpy)2I2] 7. Several examples in which the resolved complex Δ-2·PF6– reacts with bipyridine nucleophiles with nearly complete retention of chirality are also given.

A study of substitution pathways in mononuclear ruthenium organometallic complexes by photochemistry

The photosubstitution reactions of d 8 metal carbonyls usually proceed with a high degree of stereospecificity. These studies aim to elucidate the mechanism of photosubstitution in Ru(CO) 4(C 2H 4) and Ru(CO) 4(PR 3) (R≡Ph, OMe) with CO, ethylene and tertiary phosphines. Research shows that photolysis induces the loss of a carbonyl group rather than an ethylene or phosphine ligand, the reaction taking place by a purely dissociative reaction pathway. In addition, the mechanisms of the thermal substitution reactions of Ru(CO) 4(C 2H 4) with CO and tertiary phosphines are discussed. As a result of these investigations, a number of novel phosphine-containing mononuclear ruthenium complexes are reported. © 1997 Elsevier Science S.A.

Synthesis and redox chemistry of 1,1′-bis(diphenylphosphino)ferrocene derivatives of R 2C 2Co 2(CO) 6 (R  MeO 2C, CF 3)

Fe(C 5H 4PPh 2) 2 (dppf) undergoes facile thermal substitution reactions with R 2C 2Co 2(CO) 6 (R  MeO 2C, CF 3) to yield a variety of products. When R  MeO 2C, initial coordination gives μ 2-(MeO 2C 2) 2C 2Co 2(CO) 5( η 1-dppf); its crystal and molecular structure, monoclinic, P2 1/c, a = 8.954(3), b = 20.211(2) c = 23.836(5) A ̊ , β = 100.55(2)°, Z = 4, R1 = 0.0345 for 5764 reflections 1 > 2 σ(1), confirms the monodentate coordination mode for dppf. At low dppf/alkyne-complex ratios, oligomeric products with dppf ligands linking up to five (μ 2-MeO 2C) 2C 2Co 2 modules have been characterised but, as the proportion of the phosphine ligand increases. unstable products, which include a η 1- μ- η 1 dppf configuration, are obtained as well. In contrast, for R  CF 3, only [(CF 3) 2C 2]Co 2(CO) 4( η 2-dppf) is found in significant yield. A molecule with two different reduction centres, [ μ 2-(MeO 2C) 2C 2Co 2(CO) 5]( μ-dppf)[Co 3( μ 3-CPh)(CO) 8], was also characterised. Electrochemistry of the dppf complexes was characterised by fast ligand dissociation upon reduction of the (μ-alkyne)Co 2 redox centre and oxidation of coordinated dppf. There was no evidence for communication between redox centres.

Thermal substitution reactions of the heterodinuclear complex CpFe(CO)2Co(CO)4 with phosphorus ligands

Abstract The thermal reactions of CpFe(CO) 2 Co(CO) 4 with phosphorus ligands (L = P( n -Bu) 3 , P( c -Hx) 3 , PPh 3 , P(OPh) 3 , PMePh 2 ) lead to formation of both ionic disproportionation products, [CpFe(CO) 2 L] + [Co(CO) 4 ] − , via a radical chain path, and neutral monosubstitution products, CpFe(CO) 2 Co(CO) 3 L, via a CO-dissociative pathway. Reaction with PPh( o -CH 3 Ph) 2 results in forming only the monosubstituted product and no reactions were observed with the two bulkiest ligands, P( o -CH 3 Ph) 3 and P(C 6 F 5 ) 3 . The slow CO-dissociative pathway is always in effect in these reactions, and the product distribution is therefore determined by the rate of radical chain process. The steric and electronic requirements on the ligand for the radical chain process to dominate are much milder than that for other homodinuclear and heterodinuclear complexes that have been studied.

Photochemistry of macromolecular metal complexes. II. Synthesis, thermal, and photochemistry of some polypyridyl complexes of chromium (III) bound to macromolecules

AbstractPolymer coordinated chromium(III) complexes [Cr(bpy)2(PAA)2]+, 1, [Cr(bpy)2‐(PMA)2]+, 2, [Cr(phen)2(PAA)2]+, 3, and [Cr(phen)2(PMA)2]+, 4, [where bpy, phen, PAA and PMA are, respectively, 2,2′‐bipyridine, 1,10‐phenanthroline, poly(acrylic acid), and poly(methacrylic acid)] were synthesized. The polymer–chromium(III) complexes were characterized by elemental and spectroscopic analyses. Thermal substitution reactions of these macromolecular chromium(III) complexes in basic solutions lead to the replacement of the polypyridyl ligand by hydroxide ion while in strong acidic solutions the polymer complexes precipitate out. The photochemical reactions are qualitatively similar to that of the thermal reactions and the quantum yields are dependant on the pH of the medium. Further, lower quantum yields were observed for the aquation of the polymer complexes in comparison with the monomeric chromium(III) complexes and the results are discussed in terms of the effect of the polymer environment. Flash photolysis of 1 and 3 results in the formation of transients with maxima at 480 nm for 1 and 470 nm, 580 nm for 3. The decay of the transients were found to obey first order kinetics and the rate constants were determined. The transients were suggested to be the alkyl‐chromium complexes. Flash photolysis of 2 and 4 does not produce transients which is interpreted to be due to the presence of a methyl group in the ligand which hinders the formation of the carbonchromium bond.

Pressure as mechanistic indicator in organometallic photochemistry

We have recently undertaken a systematic study of the effect of pressure on photosubstitution reactions of organometallic, mostly carbonyl, complexes of the type M(CO) 6, M(CO) 5L and M(CO) 4L⌢L, where M = Cr, Mo and W. In some systems it was possible to measure the effect of pressure on both the photosubstitution quantum yield and the lifetime of the lowest excited state, whereas in others it was only possible to measure the former. The results are discussed in reference to data available for thermal substitution and photo-induced substitution reactions of related complexes. The results demonstrate that pressure is a key parameter, and therefore a mechanistic indicator, to distinguish between associative and dissociative photosubstitution processes of carbonyl complexes, and to discriminate between different pathways that originate from different electronic states.

ChemInform Abstract: Synthesis and Coordination Properties of Bis(bis(pentafluoroethyl)phosphino)ethane.

AbstractThe title diphosphine (III) is prepared according to the scheme.

Synthesis and coordination properties of bis(bis(pentafluoroethyl)phosphino)ethane

The efficient synthesis of (C 2 F 5 ) 2 PCH 2 CH 2 P(C 2 F 5 ) 2 (dfepe) by direct alkylation of Cl 2 PCH 2 CH 2 PCl 2 with C 2 F 5 Li at -95˚C is described. Thermal substitution reactions of dfepe and (C 6 F 5 ) 2 PCH 2 CH 2 P(C 6 F 5 ) 2 (dfppe) with M(CO) 6 (M=Cr, Mo, W) gave high yields of the corresponding tetracarbonyls (P P)M(CO) 4 (P P=dfppe, M=Cr, Mo, W; P P=dfepe, M=Cr, Mo). The reaction of dfpe with fac-Mo(EtCN) 3 (CO) 3 afforded fac-Mo(dfepe)(EtCN)(CO) 3

Dimethylplatinum(IV) Complexes With Cyanide: Thermal and Photoassisted Substitution Reactions, and Characterization of Products by N.M.R.

Reactions of cyanide with the dimethylplatinum (IV) complexes, [PtMe2(OH) (H20)1.5 n, [PtMe2Br2]n and fac-PtMe2Br(H2O)3+, have been studied, principally by 1H, 13C and 195Pt n.m.r. Cyanide rapidly displaces the ligands trans to the methyl groups. Subsequent reactions cis to the methyl groups occur more slowly with heating, or, for bromo complexes, on ultraviolet irradiation. These substitution reactions compete with reductive elimination of groups from the platinum(IV) compounds to produce platinum(II) products. All attempts to prepare solutions of fac-PtMe2(CN)(H2O)3+ were unsuccessful. Oxidative addition of ICN to cis-PtMe2( py )2 ( py = pyridine) gave PtMe2I(CN)( py )2, from which a solution of fac-PtMe2(CN)( MeOH )3+ in methanol could be obtained. Addition of water or aqueous acid to this solution gave a very insoluble precipitate of [PtMe2(CN)(OH)n. The cis and trans influences on Jpt -C and δC of the cyanide ligands have been evaluated.

A new method for indole functionalization. Nucleophilic displacement reactions of [η6-(4- or 5-chloroindole)](η5-cyclopentadienyl)ruthenium(II) hexafluorophosphates

New cyclopentadienylruthenium complexes of 4- or 5-chloroindole prepared by a thermal substitution reaction of (cyclopentadienyltrisacetonitrile)ruthenium with 4- or 5-chloroindole undergo smooth nucleophilic aromatic substitution with various nucleophiles.

Mechanistic Information from the Effect of Pressure on Thermal and Photochemical Substitution Reactions

Abstract The effect of pressure on some typical thermal and photochemical substitution reactions is discussed to illustrate the general applicability of this method in the elucidation of reaction mechanisms. The selected examples include square planar solvolysis, octahedral complex formation, base hydrolysis and photosolvolysis reactions. A critical evaluation is given and general trends are discussed.

ChemInform Abstract: STERIC AND STEREOCHEMICAL LIMITATIONS IN THE SUBSTITUTION REACTIONS OF MANGANESE AND RHENIUM CARBONYL BROMIDE WITH DIASTEREOMERIC DIAZAPHOSPHOLE LIGANDS

Abstract Thermal substitution reactions of M(CO)5Br (M=Mn, Re) with cis (L c ) and trans (L t ) diazaphosphole ligands (L=3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole) have been studied. It has been found that L c behaves as generally found for bulky phosphines affording to cis-M(CO)4(Lc)Br, mer-M(CO)3(L c )2Br and fac-Re(CO)3(L c )2Br which has been thermally isomerized to mer-Re(CO)3(L c )2Br. In contrast the corresponding reaction with the bulkier trans diazaphosphole isomer L t have only afforded cis-M(CO)4(L t )Br and mer-M(CO)3(L t )2Br. All the different stereochemical results are rationalized on the basis of the size of the central metals and of the steric demand of the ligands. The nature of the complexes has been established essentially by IR spectra which, in the case of cis-Re(CO)4(L c )Br presents in cyclohexane solution a doubling of all the characteristic v(CO) bands expected for the C 2v local symmetry. This unexpected result has been tentatively discussed also on the light of a...