Supported transition-metal catalysts for the C---C coupling reaction between ethene and diazoalkanes

The preparation of a series of immobilized transition-metal catalysts are reported. The catalysts were obtained by chemisorption of either rhodium(I) or iridium(I) complexes [MX(C₂H₄)₂]_n (M = Rh, Ir; X = Cl, OAc, acac, f₃-acac, f₆-acac) on SiO₂ or MgO supports. The oxides were also activated by SiCl₄ or TiCl₄ to give support materials in which the acidic nature of the surface is substantially increased. The activity of the immobilized catalysts was tested, particularly in the reaction of ethene with diphenyldiazomethane which yields a mixture of 1.1-diphenylpropene (8) and 1.1-diphenylcyclopropane (9). It was found that the most active and most selective (highest ratio 8:9) catalyst B1 was formed support material B (SiO₂ activated by SiCl₄) and [RhCl(C₂H₄)₂]₂ (1) and that both the activity and selectivity of B1 was comparable with that of complex 1 in solution. In contrast, the supported catalysts A2, D2 and A3, D3 obtained from [Rh(OAc)(C₂H₄)₂]₂ (2) and [Rh(acac)(C₂H₄)₂] (3) were less active than compounds 2 and 3 in solution. The immobilized catalysts A6, A7, D7 and E7, which were generated from the chloro- and acetatoiridium(I) complexes [IrCl(C₂H₄)₂]₂ (6) and [Ir(OAc)(C₂H₄)₂]₂ (7), possessed a lower activity than the rhodium counterparts. With diazoalkanes other than Ph₂CN₂, the activity of the supported catalyst B1 was partly higher and partly lower than that of complex 1 in the homogeneous phase.     

Preparation of silyl polyenol ethers by carbonyl olefination of silyl esters

Silyl enol ethers were produced by the carbonyl olefination of silyl esters with titanium carbene complexes generated by the desulfurizative titanation of thioacetals. The regioselective preparation of silyl dienol and trienol ethers has been achieved by using unsaturated silyl esters and thioacetals.     

One-step double reduction of aryl nitro and carbonyl groups using hydrazine

Single-step reduction of aryl nitro and carbonyl groups to the corresponding synthetically useful alkyl-anilines occurs with excellent yields by treatment with hydrazine and a base in a solvent-free reaction. The method has been applied to a broad range of compounds with different properties. Investigations into the mechanism of the reduction reveal that each group is reduced independently. A mechanism is proposed for this novel reduction of aromatic nitro groups.     

Cyclopentadienyl-ruthenium(II) complexes as efficient catalysts for the reduction of carbonyl compounds

This work reports the reduction of a large variety of aldehydes and ketones with the system PhSiH₃/[CpRu(PPh₃)₂Cl] in good to excellent yields and high chemoselectivity. The catalyst [CpRu(PPh₃)₂Cl] can be used in at least 12 catalytic cycles with excellent catalytic activity and several substrates were reduced under solvent free conditions.     

Iridium-catalyzed carbonyl group-directed oxidative coupling of arenes with alkenes

The iridium complex [Cp¹IrCl₂]₂ is a good catalyst for the directed oxidative coupling of arenes with alkenes; a wide range of carbonyl functionalities (NHCOR, CONH₂ and COR) can be employed as the directing group.     

Selective reduction of carbonyl groups in the presence of low-valent titanium reagents

The chemoselective reduction of several structurally diverse compounds containing carbonyl groups was achieved in the presence of low-valent titanium reagents. This novel synthetic method provides easy access to highly selective reduction of carbonyl groups, and possesses several advantages including one-step procedure, convenient manipulation, good to excellent yields, and short reaction times.     

Double Carbonyl Substitution in [BrMn(CO)5]: Reaction with Benzoylhydrazine and Synthesis of fac‐[Mn(Br)(CO)3(BHD)]·2THF (BHD = OC(Ph)—NH—NH2)

[BrMn(CO)₅] reacts with benzoylhydrazine in THF occurring substitution of two CO groups by a Metal‐ligand ring to give fac‐[Mn(Br)(CO)₃(BHD)]·2THF (BHD = C₆H₅CONHNH₂). The novel compound shows a distorted octahedral arrangement at the manganese atom, with three nearly linear carbonyl ligands in a fac arrangement, illustrating another example that the CO group in position trans to the bromine ligand in [BrMn(CO)₅] presents the most intensive metal‐CO backbonding effect of all the CO groups of the parent complex, leading to the formation of a facial (and not meridional) isomer, even in the presence of a bidentate ligand like benzydrazide. X‐ray measures of yellow crystals showed that the title complex belong to space group P2₁/c, with the asymmetric unit containing one crystallographically independent [Mn(Br)(CO)₃(BHD)] complex and two tetrahydrofurane solvate molecules. The new compound represents heretofore the unique occurrence of the complexing single bidentate ligand ‐O=C(Ph)‐N(H)‐N(H)₂‐ with an octahedral coordination at the Mn^I atom supported chiefly by carbonyl groups.     

Preparation of hydride complexes of ruthenium with bidentate phosphite ligands

Hydride complex RuH₂(PFFP)₂ (1) [PFFP = (CF₃CH₂O)₂PN(CH₃)N(CH₃)P(OCH₂CF₃)₂] was prepared by allowing the compound RuCl₄(bpy) · H₂O (bpy = 1,2-bipyridine) to react first with the phosphite PFFP and then with NaBH₄. Chloro-complex RuCl₂(PFFP)₂ (2) was also prepared, either by reacting RuCl₄(bpy) · H₂O with PFFP and zinc dust or by substituting triphenylphosphine with PFFP in the precursor complex RuCl₂(PPh₃)₃. Hydride derivative RuH₂(POOP)₂ (3) (POOP = Ph₂POCH₂CH₂OPPh₂) was prepared by reacting compound RuCl₃(AsPh₃)₂(CH₃OH) first with the phosphite POOP and then with NaBH₄. Depending on experimental conditions, treatment of carbonylated solutions of RuCl₃ · 3H₂O with POOP yields either the cis- or trans-RuCl₂(CO)(PHPh₂)(POOP) (4) derivative. Reaction of both cis- and trans-4 with LiAlH₄ in thf affords dihydride complex RuH₂(CO)(PHPh₂)(POOP) (5). Chloro-complex all-trans-RuCl₂(CO)₂(PPh₂OMe)₂ (6) was obtained by reacting carbonylated solutions of RuCl₃ · 3H₂O in methanol with POOP. Treatment of chloro-complex 6 with NaBH₄ in ethanol yielded hydride derivative all-trans-RuH₂(CO)₂(PPh₂OMe)₂ (7). The complexes were characterised spectroscopically and the X-ray crystal structures of complexes 1, 3, cis-4 and 6 were determined.     

Novel and efficient Ni-mediated pinacol coupling of carbonyl compounds

It was firstly found that the Rieke Ni generated in situ was able to promote the pinacol coupling of various carbonyls efficiently. Based on this information, another catalytically effective, cheaper and more convenient NiCl₂(Cat.)/Mg/TMSCl system was designed and developed further successfully. The interesting single-electron transfer (SET) mechanisms for the coupling reactions were proposed. Additionally, the dl/meso diastereoselectivity and some additive effects were also explained in terms of the proposed mechanisms.     

Reaction of enamines with trifluoromethyl containing carbonyl reagents

The reaction of linear push-pull enamines bearing a methyl group at the α-position with a set of trifluoromethylated carbonyl compounds was investigated. It has been found that the reaction proceeds at the methyl group of the enamines. The first computational study of the reaction between push-pull enamines and strong electrophilic reagents was reported. Out of three pathways considered DFT and MP2 calculations support ene-mechanism previously suggested based on experimental results only.     

Photo-allylation and photo-benzylation of carbonyl compounds using organotrifluoroborate reagents

Allyl- and benzyl-trifluoroborates can be applied to the photoreaction of carbonyl compounds to afford the corresponding alcoholic adducts in acceptable yields via a photo-induced single electron transfer pathway. The results were confirmed from the reaction selectivity and the negative free energy change for the electron transfer process.     

Reaction of halothane with carbonyl compounds in the presence of bases

The reaction of halothane, 2-bromo-2-chloro-1,1,1-trifluoroethane (1), with aldehydes and ketones in the presence of bases was found to give 1-alkyl- or 1-aryl-2-bromo-2-chloro-3,3,3-trifluoropropanols (2) or 2-chloro-3,3-difluoro-2-propenols (3) selectively in good to moderate yields depending on the bases and reaction conditions.     

Synthesis and structural studies of phosphorus carbonyl manganacycles containing the tetraphenyldiselenoimidodiphosphinato ligand

The [Mn(CO)_4−x(L){Ph₂P(Se)NP(Se)Ph₂-κ²Se}] complexes, where x = 1 for L = PPh₃ and PMePh₂, and x = 2 for L = Ph₂PCH₂CH₂PPh₂ (diphos), were synthesized by two routes. The complexes were characterized by IR, mass spectrometry (FAB+), NMR (¹H, ¹³C, ³¹P, ⁷⁷Se) spectroscopy and/or single crystal X-ray diffraction. The X-ray diffraction analysis for [Mn(CO)₃PMePh₂{Ph₂P(Se)NP(Se)Ph₂-κ²Se}] showed that the unit cell contains two independent mononuclear molecules with different MnSePNPSe rings’ conformations.     

Carbonyl complexes of manganese, rhenium and molybdenum with 2-pyridylimino acid ligands

[MBr(CO)₃{κ²(N,O)-pyca}] [M = Mn(1a), Re(1b), pyca = pyridine-2-carboxaldehyde] and [MoCl(η³-C₃H₄Me-2)(CO)₂{κ²(N,O)-pyca}] (1c) react with aminoacid β-alanine to give the corresponding iminopyridine complexes 2a-2c. The same method affords the iminopyridine derivatives from γ-aminobutyric acid (GABA) (3a-3c) and 3-aminobenzoic acid (4a-4c). For complexes 2a-2c, 3a, 3c and 4a, the solid state structures have been determined by X-ray crystallography, revealing interesting differences in their hydrogen-bonding patterns in solid state.     

Photodecomposition of molybdenum(II) and tungsten(II) carbonyl complexes with triazole, benz-imidazole, and oxadiazole acetylinic derivatives

Photodecomposition of 10 different molybdenum and tungsten mixed carbonyl complexes, [M(CO)₃(B)(A)]I₂ where B=o-phenanthroline or bipyridyl, A=3-(2-propynyl)thio-4,5-diphenyl-4H-1,2,4-triazole (TRZA) or S-propynyl-2-thio benz-imidazole (BIMDA) and 2(2-propynyl-thio(5-phenyl)-1,3,4-oxadiazole (OXA). M(CO)₃(TRZA)I₂, [M(CO)₂(PPh₃)_X(TRZA)I_Y]I_Z where M=Mo, X, Y and Z=1 and M=W, X and Z=2, Y=0, have been performed at 365 nm in oxygen saturated chloroform at 25 °C. The absorbance spectrum of these complexes have been recorded with the time of irradiation in order to examine the kinetics of photodecay.

The apparent rate constant (K_d) for the first-order reaction have been calculated and found to be (3.32–4.79)×10⁻⁵ s⁻¹. The primary quantum yields (Φ) has also been calculated and were in the range (8.33–12.1)×10⁻⁴. The mechanism of the photodecomposition has been suggested according to the kinetic, and photoproduct analysis data, and is similar to reaction of photo-oxidative degradation of polluted molecules in the water.     

Synthesis and properties of oligomers of iron-manganese carbonyl complexes with bridging disulfido ligands

The reactions of activated CpFeMn(CO)₇1a and Cp*FeMn(CO)₇1b, Cp=C₅Me₅ with thiirane yielded the new dimeric mixed metal disulfido complexes: [CpFeMn(CO)₅(μ₃-S₂)]₂ (2) and [Cp*FeMn(CO)₅(μ₃-S₂)]₂ (3). Compounds 2 and 3 both contain two triply bridging disulfido ligands. When heated at 40 °C, compound 2 was transformed into a trimeric compound Cp₃Fe₃Mn₃(CO)₁₅(μ₃-S₂)(μ₄-S₂)₂, 4. Compound 4 contains three disulfido ligands, each of which has a different bridging coordination mode in the six atom metal cluster. There are three inequivalent CpFe(CO)₂ groupings linked to a central Mn₃(S₂)₃ core by the disulfido ligands. In solution, compound 4 exhibits a dynamical intramolecular exchange process that interconverts two of the three CpFe(CO)₂ groups on the NMR timescale.     

Rhenium carbonyl complexes with monodentate-coordinated diphosphines: activation of terminal phosphino groups towards amine-oxide oxidation

Terminal phosphino groups of [Re₂(CO)₉(η¹-P-P)] (P-P = diphosphines) are activated towards oxidation by Me₃NO. The respective reactions of Me₃NO with [Re₂(CO)₉{η¹-P(o-anisyl)₂(CH₂)₃PPh₂}], [Re₂(CO)₉{η¹-PPh₂(CH₂)₃P(o-anisyl)₂}] and [Re₂(CO)₉(η¹-trans-PPh₂CHCHPPh₂)] were studied to investigate the mechanism of this oxidation. The results are consistent with an intramolecular pathway involving a cyclic intermediate, without exchange of the coordinated and terminal phosphino groups. A mechanism which involves an interaction of the terminal phosphino group with a carbonyl ligand is proposed. In sharp contrast to eq-[Re₂(CO)₉(η¹-P-P)] (P-P = Ph₂P(CH₂)_nPPh₂, n = 1-6), eq-[Re₂(CO)₉(η¹-trans-PPh₂CHCHPPh₂)] appears to be indefinitely stable towards equatorial → axial isomerization at room temperature, thus, allowing its crystal structure to be determined.     

Reaction profiles and substituent effects for the reduction of carbonyl compounds with monomer and dimer simple metal hydride reagents

Reaction profiles and energetics for the reactions of substituted benzaldehydes with a series of different simple metal hydrides (BH(3), BMeH(2), BMe(2)H, AlH(3), and AlMe(2)H) are examined computationally. B3LYP/6-31G optimizations and MP2/6-311G single point energy calculations revealed that the Al reagents are more reactive than B reagents. Replacement of H with Me on BH(3) or AlH(3) makes the reduction transition state (TS) less stable. Accordingly the overall reactivity is in the order AlH(3) > AlMe(2)H > BH(3) > BMe(2)H. The Hammett rho value for substituted benzaldehydes (BAs) is negative for the initial complex formation and positive for the hydride-transfer step. The size and the sign of the apparent rho value depend on the relative stabilities of the separated reactants and the complex. The TS structures vary according to the Hammond postulate for substituted BAs and the variation is reflected in carbonyl-carbon and aldehyde-deuterium isotope effects. Comparison of the reaction profiles of the monomer and dimer reagents reveals that the real reacting species is the monomer in the gas phase for BH(3) but the dimer for BMe(2)H.     

Chemistry of vinylidene complexes. XX. Intramolecular carbonylation of vinylidene on the MnFe center: Spectroscopic and structural study. X-ray structure of the new trimethylenemethane type MnFe complex

Reactions of Fe₂(CO)₉ with Cp(CO)₂MnCCHPh (1) and Cp(CO)(PPh₃)MnCCHPh (3) gave the heterometallic trimethylenemethane complexes η⁴-{C[Mn(CO)₂Cp](CO)CHPh}Fe(CO)₃ (2) and η⁴-{C[Mn(CO)(PPh₃)Cp](CO)CHPh}Fe(CO)₃ (4), respectively. The formation of the benzylideneketene [PhHCCCO] fragment included in complexes 2 and 4 occurs via intramolecular coupling of the carbonyl and vinylidene ligands. The structures of 3 and 4 were determined by single crystal XRD methods. The influence of the nature of the L ligands at the Mn atom on the structural and spectroscopic characteristics of η⁴-{C[Mn(CO)(L)Cp](CO)CHPh}Fe(CO)₃ (L = CO (2), PPh₃ (4)) is considered. According to the VT ¹H and ¹³C NMR spectra, complex 2 reversibly transforms in solution into μ-η¹:η¹-vinylidene isomer Cp(CO)₂MnFe(μ-CCHPh)(CO)₄ (2a), whereas complex 4 containing the PPh₃ ligand is not able to a similar transformation.     

Reaction of Grignard reagents with carbonyl compounds under continuous flow conditions

This contribution details how a continuous flow reactor was used to react carbonyl compounds with Grignard reagents at room temperature in an efficient and safe manner. Flow rate, residence time and temperature were optimized for the preparation of a small collection of secondary and tertiary alcohols. Excellent yields and general applicability were observed using the set-up protocol. The procedure was also applied for the preparation of Tramadol, an analgesic drug belonging to the opioid group. The developed conditions allowed the selective addition of Grignard reagents to aldehydes and ketones in the presence of a nitrile function.