Reactions of (Me2C)(Me2Si)[(η-C5H3)Mo(CO)3]2 with nitrile and subsequent cleavage of the CN bond by cooperation of molybdenum and ruthenium

Reaction of the doubly bridged dinuclear molybdenum complex (Me₂C)(Me₂Si)[(η⁵-C₅H₃)Mo(CO)₃]₂ (1) with benzonitrile in refluxing xylene afforded complexes (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η²-η²(⊥)-NCPh)] (2) (50%) and (Me₂C)(Me₂Si)[(η⁵-C₅H₃)₂Mo₂(CO)₄(μ-η¹-η²-NCPh)] (3) (6%) with different coordination of nitrile. The corresponding μ-η²-η² acetonitrile and propionitrile complexes 4 and 5 could be obtained from the reactions of (Me₂C)(Me₂Si)(C₅H₄)₂ with (RCN)₃Mo(CO)₃ (R = Me, Et) in refluxing xylene. Reactions of 1 with isonitriles generated μ-η¹-η²-CNR (R = ^tBu, Ph, C₆H₁₁) bridged complexes 6-8 in 53-63% yields. Subsequent reaction of 4 with Ru₃(CO)₁₂ yielded two CN bond cleavaged MoRu clusters (Me₂C)(Me₂Si)(η⁵-C₅H₃)₂Mo₂Ru₃(CO)₁₀(μ-CO)(μ₃-CMe)(μ₄-N) (9) (7%) and [(Me₂C)(Me₂Si)(η⁵-C₅H₃)₂]₂Mo₄Ru₆(CO)₁₆(μ-CO)(μ₄-CO)₂(μ₃-η¹-η²-η²-NCMe)(μ₃-CMe)(μ₅-N) (10) (8%). All the new complexes have been fully characterized. The molecular structures of 2, 4, 6, 9, and 10 have been determined by X-ray diffraction analysis.     

Ruthenium carbene complexes containing bidentate and tridentate PO ligands

Treatment of [Ru(CHR)Cl₂(PCy₃)₂] (Cy = cyclohexyl) with Tl[N(Pr₂ⁱPO)₂] and AgL_OEt (L_OEt⁻ = [CpCo{P(O)(OEt)₂}₃]⁻) afforded the Ru carbene complexes [Ru(CHPh)(PCy₃)Cl{N(Pr₂ⁱPO)₂}] (1) and [L_OEtRu(CHR)(PCy₃)Cl] (2), respectively. Chloride abstraction of complex 2 with TlPF₆ in MeCN afforded [L_OEtRu(CHPh)(PCy₃)(MeCN)][PF₆] (3). Complexes 1 and 2 are capable of catalyzing ring-closing metathesis of diethyl 1,2-diallylmalonate. The crystal structure of complex 2 has been determined.     

Phosphorus-supported multidentate coumarin-containing fluorescence sensors for Cu

Phosphorus hydrazides PhP(O)[N(Me)NH₂]₂, (S)P[N(Me)NH₂]₃, and N₃P₃[N(Me)NH₂]₆ were condensed with 7-diethylaminocoumarin-3-aldehyde (RCHO) to afford the corresponding hydrazones PhP(O)[N(Me)NCHR]₂ (1), (S)P[N(Me)NCHR]₃ (2), and N₃P₃[N(Me)NCHR]₆ (3). The structural characterization of 1-3 was carried out by their HRMS, ¹H and ³¹P{¹H} NMR spectra. The molecular structure of 2 was established by a single-crystal X-ray analysis. Interaction of 1 and 2 with various transition metal ions revealed substantial fluorescence enhancement upon interaction with Cu²⁺ enabling a selective detection mechanism for this metal ion. However, such a fluorescence enhancement was not observed in the case of 3. A 1:1 complex [2·Zn][ClO₄]₂·4CH₂Cl₂ was isolated in the reaction of 2 with Zn(ClO₄)₂·6H₂O. The molecular structure of this complex revealed that the Zn^II is encapsulated by the ligand utilizing a 3N, 3O coordination set.     

Osmium assisted C-H activation and CN cleavage of N-(2′-hydroxyphenyl) benzaldimines. Synthesis, structure and electrochemical properties of some organoosmium complexes

Reaction of N-(2′-hydroxyphenyl)-4-R-benzaldimines (L-R, R = OCH₃, CH₃, H, Cl and NO₂) with [Os(PPh₃)₃Br₂] in refluxing 2-methoxyethanol in the presence of triethylamine affords two families of organoosmium complexes (1-R and 2-R). In both 1-R and 2-R complexes a benzaldimine ligand is coordinated to the metal center as tridentate C,N,O-donor. In the 1-R complexes, a bidentate N,O-donor imionsemiquinonate ligand, derived from the hydrolysis of another benzaldimine, and a PPh₃ ligand are also coordinated to osmium. In the 2-R complexes, a carbonyl, derived from decarbonylation of 4-R-benzaldehyde (derived from the same hydrolysis stated above), and two PPh₃ ligands take up the remaining coordination sites on osmium. Structures of the 1-Cl and 2-OCH₃ complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the 1-R complexes shows a reversible Os(III)-Os(IV) oxidation within 0.47-0.67 V (vs SCE), followed by an irreversible oxidation of the imionsemiquinonate ligand within 1.10-1.36 V. An irreversible Os(III)-Os(II) reduction is also displayed by the 1-R complexes within −1.02 to −1.14 V. Cyclic voltammetry on the 2-R complexes shows a reversible Os(II)-Os(III) oxidation within 0.29-0.51 V, followed by a quasi-reversible oxidation within 1.04-1.29 V, and an irreversible reduction of the coordinated benzaldimine ligand within −1.16 to −1.31 V.     

Synthesis, structure, and magnetic properties of 2,2′-(buta-1,3-diyne-1,4-diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide 1-oxyl)

An approach to the synthesis of nitronyl nitroxide 2,2′-(buta-1,3-diyne-1,4-diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole 3-oxide 1-oxyl) (4) was developed. Compound 4 is the first diradical with nitronyl nitroxide groups directly linked through a diacetylene fragment. In solid phase the diradicals are arranged in stacks with parallel CC fragments, with the distances between the terminal carbon atoms of the neighboring diacetylene groups (T and d) being 6.170 and 4.466 Å, respectively, and the angle between the translation vector and the median line passing through the CCCC fragment of 45.9°. The values of T and d are outside the range of structural criteria allowing a topochemical reaction. Thus UV irradiation does not initiate solid phase polymerization of 4. After exposure at 373 K for 1 h the crystals of 4 turn dark-brown, become X-ray amorphous and lose the majority of their paramagnetic centers without significantly changing their mass. Upon further heating up to 400-420 K the product explodes, releasing about 360 kJ/mol of heat. A diluted solution of 4 in 1,4-dioxane produces an EPR spectrum typical of a strong exchange (a multiplet of nine broadened lines with A_4N = 0.35 mT), indicating the efficiency of the CCCC fragment as an exchange channel. The character of the experimental μ_eff(T) dependence for 4 indicates a strong intramolecular antiferromagnetic-type exchange interaction (J/k_B ∼ −104 K) and the dominating weak intermolecular ferromagnetic exchange.     

Copper-catalyzed oxidative cleavage of carbon-carbon double bond of enol ethers with molecular oxygen

A novel CC bond cleavage reaction of aromatic enol ethers (1) to give ketones (2) using molecular oxygen as oxidant is described. Among the examined catalysts (Cu(II), Pd(II), Ru(II), and H⁺), CuCl₂ exhibited the highest activity. The reaction proceeded smoothly with several kinds of substrates.     

Chemoselective ring opening of benzoxazaphosphinines

Cyclization of 2-[(4-chloroanilino)methyl]phenol (1) with thiophosphoryl chloride afforded 2-chloro-3-(4-chlorophenyl)-3,4-dihydro-2H-1,3,2λ⁵-benzoxazaphosphinine-2-thione (2). Reaction of 2 with various heterocyclic amines (3) in the presence of Et₃N/NaH gave 3-(4-chlorophenyl)-2-nitrogen heterocyclic substituted-3,4-dihydro-2H-1,3,2λ⁵-benzoxaza-phosphinine-2-thiones (4). Further reaction of 4 with the N-sodium salt of amino heterocyclics in the presence of HCl at 50-60 °C opened the benzoxazaphosphinine ring chemoselectively at the endocyclic P-O bond and yielded 2-[4-chloro(heterocyclic substituted-phosphorothioyl)anilino]methylphenols 5-13.     

Synthesis and structures of the silyl bridged bis(indenyl) diruthenium complexes and a novel indenyl nonanuclear ruthenium cluster Ru9(μ6-C)(CO)14(μ3-η:η:η-C9H7)2

Thermal treatment of C₉H₇SiMe₂C₉H₇ and C₉H₇Me₂SiOSiMe₂C₉H₇ with Ru₃(CO)₁₂ in refluxing xylene gave the corresponding diruthenium complexes (E)[(η⁵-C₉H₆)Ru(CO)]₂(μ-CO)₂ [E = Me₂Si (1), Me₂SiOSiMe₂ (2)]. A desilylation product [(η⁵-C₉H₇)Ru(CO)]₂(μ-CO)₂ (3) was also obtained in the latter case. Similar treatment of C₉H₇Me₂SiSiMe₂C₉H₇ with Ru₃(CO)₁₂ gave a novel indenyl nonanuclear ruthenium cluster Ru₉(μ₆-C)(CO)₁₄(μ₃-η⁵:η²:η²-C₉H₇)₂ (5) with carbon-centered tricapped trigonal prism geometry, in addition to the diruthenium complex (Me₂SiSiMe₂)[(η⁵-C₉H₆)Ru(CO)]₂(μ-CO)₂ (4) and the desilylation product 3. Complex 4 can undergo a thermal rearrangement to form the product [(Me₂Si)(η⁵-C₉H₆)Ru(CO)₂]₂ (6). The molecular structures of 1, 2, 4, 5, and 6 were determined by X-ray diffraction.     

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.     

The regioselectivity of the formation of 2-pyrazolylthiazoles and their precursors from the reaction of 2-hydrazinothiazoles with 4,4,4-trifluoro-1-hetaryl-1,3-butanediones

Reaction of 2-hydrazinothiazoles 1 with 1-thienyl- and 1-furyl-1,3-butanediones 2a,b in methanol in the presence of hydrochloric acid mainly leads to a mixture of pyrazoles 3 and pyrazolines 4 or pyrazoles 3 and 5 in strong acidic conditions. Isomeric hydrazones 6 and pyrazolines 4 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones 2 with hydrazine 1 is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones 2. Cyclization of hydrazones 6 is shown to occur under milder conditions than dehydration for pyrazolines 4. The new heterocyclic compounds were prepared and fully characterized by NMR spectra and by X-ray analysis for 3c.     

Group 9 complexes of an N-heterocycle carbene bearing a pentafluorobenzyl substituent: attempted dehydrofluorinative coupling of cyclopentadienyl and N-heterocycle carbene ligands

Treatment of N-methylimidazole with pentafluorobenzyl bromide produces 1-pentafluorobenzyl-3-methylimidazolium bromide (1), which reacts with silver(I) oxide to give the N-heterocycle carbene (NHC) complex 1-pentafluorobenzyl-3-methylimidazolin-2-ylidene silver(I) bromide (2). Complex 2 acts as a carbene transfer reagent giving the complexes [(η⁵-C₅Me₅)MCl₂(NHC)] (3a, M = Rh; 3b M = Ir) on reaction with [(η⁵-C₅Me₅)MCl(μ-Cl)]₂. An attempt to use intramolecular dehydrofluorinative coupling methodology to link the carbene and the pentamethylcyclopentadienyl ligands of [(η⁵-C₅Me₅)RhCl(CN^tBu)(NHC)]BF₄ was unsuccessful.     

From four to five and six coordinated sparteine and α-isosparteine mononuclear Cu(II) complexes through the carboxylate donors

Cu[(C₁₅H₂₆N₂)(OCOR)₂] complexes, where OCO is a fragment of either formato or acetato group and C₁₅H₂₆N₂ is sparteine or α-isosparteine have been synthesized and structurally characterized. The bis-formato complexes (1 and 2) display a distorted 4 + 1 coordination resulting from variable metal binding stereochemistry and function of the two formato units. The syn formato group acts as a pseudochelating bidentate while the anti conformer as a monodentate ligand. This inequivalence of the two formate ligands seems deliberate for it allows formation of the stabilizing intramolecular hydrogen bond between the CH donor belonging to the monodentate formate ligand and equatorially coordinated oxygen atom belonging to the pseudo-chelating formate ligand. At variance, the C₂ symmetrical bis-acetato complex (3) displays tetragonally elongated octahedral geometry of the CuN₂O₂O′O′ with long off-axis coordination of the second O atom from each acetate ligand in the axial position.Complexes 1-3 have been also characterized by elemental analysis, IR, UV-Vis and MS spectroscopy.     

Logistic flexibility in the preparation of isomeric halopyridinecarboxylic acids

Although there are many conceivable ways to funtionalize, and specifically carboxylate, 2-chloro-4-(trifluoromethyl)pyridine optionally at all three vacant positions, it is more straightforward to prepare only the 2-chloro-4-(trifluoromethyl)pyridine-3-carboxylic acid (1) from this precursor and the other 6-chloro-4-(trifluoromethyl)pyridine-2- and -3-carboxylic acids (2 and 3) from a different one, viz. 5-bromo-2-chloro-4-(trifluoromethyl)pyridine. In the same manner, it proved more convenient to convert 5-chloro-2-(trifluoromethyl)pyridine in only two of the corresponding acids (6 and 7) and to make the third one (8) from 3-bromo-5-chloro-2-(trifluoromethyl)pyridine as an alternative starting material. All model substrates for functionalization were readily accessible from the correspondingly substituted chloroiodopyridine through heavy halogen displacement by in situ generated (trifluoromethyl)copper.     

Claisen rearrangements based on vinyl fluorides

2-Fluoroalk-1-en-3-ols (4), available from terminal alkenes (1) by bromofluorination, subsequent dehydrobromination of the 1-bromo-2-fluoroalkanes (2) to form 2-fluoroalkenes (3) and selenium dioxide mediated allylic oxidation with tert-butylhydroperoxide, undergo Johnson-Claisen rearrangement on treatment with trimethyl orthoacetate to give methyl 4-fluoroalk-4-enoates (7) in high yields. In contrast Ireland-Claisen rearrangement of 3-acetoxy-2-fluorodec-1-ene (9b) with triethylamine and TMSOTf in ether failed. Instead of the expected formation of a carboxylic acid, selective C-silylation of the α-position to the carboxyl group to form 14 occurred. However, Ireland-Claisen rearrangement was successful with corresponding chloroacetates 10 and propionates 11 of four 2-fluoroalk-1-en-3-ols (4) to give 2-chloro-4-fluoroalk-4-enecarboxylic acids (15) or its 2-methyl derivatives 16, respectively, in moderate yields. These [3,3]-sigmatropic rearrangements are diastereoselective giving trans-configured double bonds, exclusively. Corresponding esters derived from (Z)-2-fluorocyclododec-2-enol (22), did rearrange to yield mixtures of diastereomers much less selectively. Also 2-fluorodec-2-enol (6), which was prepared by rearrangement of 2-fluoro-2-octyloxirane (5) with TMSOTf and triethylamine, was successfully applied as a starting material for [3,3]-sigmatropic rearrangements. The corresponding 3-(1-fluoroethenyl)alkanoic acid derivatives 17 and 18 were formed in moderate yield.     

Sodium dithionite initiated addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to β-pinene: Synthesis of CF3-substituted terpenoids

Sodium dithionite effectively promotes the addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to the exocyclic double bond of β-pinene. The reaction proceeded in an MeCN/H₂O system to give almost quantitatively a 1:1 mixture of diastereoisomers of 4-(2-bromoisopropyl)-1-(2-chloro-3,3,3-trifluoropropyl)-cyclohexene (1). Dehydrobromination of 1 with pyridine gave a mixture of regioisomeric dienes 2 and 3, while treatment with DBU at elevated temperature resulted in total dehydrohalogenation to give trienes 4 and 5. Reduction of 1 with Bu₃SnH gave 1-(2-chloro-3,3,3-trifluoropropyl)-4-(isopropyl)cyclohexene (6) which on dehydrochlorination with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded conjugated diene, 4-isopropyl-1-(trans-3,3,3-trifluoropropenyl)-cyclohexene (7), with 50% overall yield. All the transformations proceeded with the retention of configuration at the carbon atom C-4 and the final compound 7 exhibited high optical activity.     

Ligand substitution in HC(O)CCo3(CO)9 with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): Diphosphine ligand fluxionality, decarbonylation of the formyl moiety and competitive P-Ph bond cleavage reactivity

The reaction of the formyl-capped cluster HC(O)CCo₃(CO)₉ (1) with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the presence of added Me₃NO leads to the production of the disubstituted cluster HC(O)CCo₃(CO)₇(bpcd) (2). Thermolysis of 2 in toluene at 60 °C gives the methylidyne-capped cluster HCCo₃(CO)₇(bpcd) (4) and the phosphido-bridged cluster Co₃(CO)₇[μ₂,η²,η¹-P(Ph)CC(PPh₂)C(O)CH₂C(O)] (5). Cluster 4 has been independently prepared from HCCo₃(CO)₉ and bpcd and shown to serve as the precursor to 5. The new clusters 2, 4, and 5 have been isolated and characterized in solution by IR and NMR (¹H and ³¹P) spectroscopies and their solid-state structures have been established by X-ray diffraction analyses. Both clusters 2 and 4 contain 48e- and exhibit triangular Co₃ cores with a chelating and bridging bpcd ligand in the solid state, respectively. The structure of 5 provides unequivocal support for the loss of the methylidyne capping ligand and P-Ph bond cleavage attendant in the activation of 4 and confirms the presence of the face capping seven-electron μ₂,η²,η¹-P(Ph)CC(PPh₂)C(O)CH₂C(O) ligand in the final product. The fluxionality displayed by the bpcd ligand in clusters 2 and 4 and the decarbonylation behavior of the formyl moiety in the former cluster are discussed relative to related alkylidyne-capped Co₃ derivatives.     

Pentamethylcyclopentadienyl rhodium(III) trifluorovinyl phosphine complexes and attempted intramolecular dehydrofluorinative coupling of pentamethylcyclopentadienyl and trifluorovinyl phosphine ligands

The trifluorovinyl phosphine complexes [Cp*RhCl₂{PR_3−x(CFCF₂)_x}] (1x = 1, a R = Ph, b Prⁱ, c Et; 2x = 2, R = Ph) have been prepared by treatment of [Cp*RhCl(μ-Cl)]₂ with the relevant phosphine. The salt [Cp*RhCl(CNBu^t){PPh₂(CFCF₂)}]BF₄, 3, was prepared by addition of Bu^tNC to 1a in the presence of NaBF₄. The salt [Cp*RhCl{κP,κS-(CF₂CF)PPh(C₆H₄SMe-2)}]BF₄ was prepared as a mixture of cis (5a) and trans (5b) isomers by treatment of [Cp*RhCl(μ-Cl)]₂ with the phosphine-thioether (CF₂CF)PPh(C₆H₄SMe-2), 4, in the presence of NaBF₄. The structures of 1a-c and 5a have been determined by single-crystal X-ray diffraction. Intramolecular dehydrofluorinative carbon-carbon coupling between pentamethylcyclopentadienyl and trifluorovinylphosphine ligands of 1a, 3 and 5 has been attempted. No reaction was observed on treatment of the neutral complex [Cp*RhCl₂{PPh₂(CFCF₂)}], 1a, with proton sponge, however, 5a underwent dehydrofluorinative coupling to yield [{η⁵,κP,κS-(C₅Me₄CH₂CFCF)PPh(C₆H₄SMe-2)}RhCl]BF₄, 6. Other reactions, in particular addition of HF across the vinyl bonds of 5, occurred leading to a mixture of products. The cation of 3 underwent similar reactions.