Alkoxy-substituted group 6 allenylidene complexes - Synthesis and properties

Bis(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR′)OR], as well as mono(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR′)Ph], of chromium and tungsten are accessible from propynones [HCCC(O)Ph] or propynoic acid esters [HCCC(O)OR; R = Et, (−)-menthyl, endo-bornyl] by the following reaction sequence: (a) deprotonation of the alkynes, (b) reaction with [(CO)₅M-THF] (M = Cr, W), and (c) alkylation of the resulting alkynyl metallate, [(CO)₅MCCC(O)R], with Meerwein salts. Vinylidene complexes, [(CO)₅MCC(R′)C(O)OR], are formed as a by-product by C_β-alkylation of the alkynyl metallate. Dimethylamine displaces one alkoxy substituent of the bis(alkoxy)allenylidene complexes to give dimethylamino(alkoxy)allenylidene complexes, [(CO)₅MCCC(OR)NMe₂]. The analogous reaction of dimethylamine with a mono(alkoxy)-substituted allenylidene complex affords the aminoallenylidene complex [(CO)₅CrCCC(NMe₂)Ph]. When the amine is used in large excess, the α,β-unsaturated aminocarbene complex [(CO)₅CrC(NMe₂)C(H)C(NMe₂)Ph] is additionally formed by addition of the amine across the C_αC_β-bond of the allenylidene ligand. The reaction of [(CO)₅MCCC(OEt)₂] with dimethyl ethylenediamine offers access to bis(amino)allenylidene complexes, in which C_γ is part of a five-membered heterocycle. Photolysis of bis(alkoxy)allenylidene complexes in the presence of triphenylphosphine yields tetracarbonyl- and tricarbonyl{bis(phosphine)}allenylidene complexes. Diethylaminopropyne inserts into the C_βC_γ bond of [(CO)₅MCCC(OEt)OMethyl] to give alkenylallenylidene complexes. Subsequent acid-catalyzed intramolecular cyclization affords a pyranylidene complex.     

Ferrocenyl-substituted allenylidene complexes of chromium, molybdenum and tungsten: Synthesis, structure and reactivity

Bis(ferrocenyl)-substituted allenylidene complexes, [(CO)₅MCCCFc₂] (1a-c, Fc = (C₅H₄)Fe(C₅H₅), M = Cr (a), Mo (b), W (c)) were obtained by sequential reaction of Fc₂CO with Me₃Si-CCH, KF/MeOH, n-BuLi, and [(CO)₅M(THF)]. For the synthesis of related mono(ferrocenyl)allenylidene chromium complexes, [(CO)₅CrCCC(Fc)R] (R = Ph, NMe₂), three different routes were developed: (a) reaction of the deprotonated propargylic alcohol HCCC(Fc)(Ph)OH with [(CO)₅Cr(THF)] followed by desoxygenation with Cl₂CO, (b) Lewis acid induced alcohol elimination from alkenyl(alkoxy)carbene complexes, [(CO)₅CrC(OR)CHC(NMe₂)Fc], and (c) replacement of OMe in [(CO)₅CrCCC(OMe)NMe₂] by Fc. Complex 1a was also formed when the mono(ferrocenyl)allenylidene complex [(CO)₅CrCCC(Fc)NMe₂] was treated first with Li[Fc] and the resulting adduct then with SiO₂. The replacement route (c) was also applied to the synthesis of an allenylidene complex (7a) with a CC spacer in between the ferrocenyl unit and C_γ of the allenylidene ligand, [(CO)₅CrCCC(NMe₂)-CCFc]. The related complex containing a CHCH spacer (9a) was prepared by condensation of [(CO)₅CrCCC(Me)NMe₂] with formylferrocene in the presence of NEt₃. The bis(ferrocenyl)-substituted allenylidene complexes 1a-c added HNMe₂ across the C_α-C_β bond to give alkenyl(dimethylamino)carbene complexes and reacted with diethylaminopropyne by regioselective insertion of the CC bond into the C_β-C_γ bond to afford alkenyl(diethylamino)allenylidene complexes, [(CO)₅MCCC(NEt₂)CMeCFc₂]. The structures of 5a, 7a, and 9a were established by X-ray diffraction studies.     

Reactivity of alkynyl Pd(II) azido complexes toward organic isocyanides, isothiocyanates, and nitriles

Alkynyl Pd(II) azido complexes of the type [Pd(N₃)(CCR)L₂] (1-3) were obtained by reactions of aqueous NaN₃ with [Pd(Cl)(CCR)L₂] (R = Ph or C(O)OMe). Treating compounds 1-3 with organic isocyanides (R-NC) afforded novel complexes, trans-[Pd(CCPh)(NCNR)(PMe₃)₂] (R = 2,6-Me₂C₆H₃ (4) or 2,6-Et₂C₆H₃ (5)) and trans-[Pd(CCR)(CN₄-t-Bu)L₂] (6: L = PMe₃, R = Ph; 7: L = PEt₃, R = C(O)OMe; 8: L = PMe₃, R = C(O)OMe), which contain either a carbodiimido or a C-coordinated tetrazolato group. Reactions of compounds 1 and 2 with R-NCS (R = 2,6-Me₂C₆H₃ or CH₂CH₃) and 1,4-phenylene diisothiocyanate (C₆H₄(NCS)₂) smoothly proceeded to give tetrazole-thiolato complexes, trans-[Pd(CCPh)(SCN₄-R)L₂] (L = PMe₃, R = Et (9) or 2,6-Me₂C₆H₃ (10); L = PEt₃, R = 2,6-Me₂C₆H₃ (11)), and a phenylene-bridged dinuclear Pd(II) tetrazole-thiolato complex, [(PEt₃)₂(CCPh)Pd(SCN₄-(μ-C₆H₄)-SCN₄)Pd(CCPh)(PEt₃)₂] (12), respectively. Complexes 9-12 contain the Pd-S bond that is formed by the dipolar cycloaddition of the organic isothiocyanate to the Pd-azido bond. In contrast, the corresponding reactions of compounds 1and 2 with C₆F₅CN and Me₃SiCN (organic nitriles, R-CN) gave an N-coordinated Pd(II)-tetrazolato compound {trans-[Pd(CCPh)(N₄C-C₆F₅)(PMe₃)₂] (13)} and a mixture of Pd(II)-cyano complexes {trans-[Pd(CCPh)(CN)(PEt₃)₂] (14) and [Pd(CN)₂(PEt₃)₂] (15)}, respectively. Bis(phosphine) bis(cyano) complexes of Pd and Ni, [M(CN)₂L₂] (L = PEt₃, PMe₃; L₂ = DEPE), could be obtained independently by the reactions of [M(N₃)₂L₂] with excess Me₃SiCN in organic solvents.     

The course of oxidative addition reactions of haloalkynes and haloalkenes to dimethyl- and dialkynylaurate(I) anions [RAuR]

The reactions of halo-alkynes Cl-CCH, C-lCC-Cl or PhCC-I with solutions of Li⁺[MeAuMe]⁻ in diethylether containing Ph₃P do not give the expected oxidative addition products Me₂(RCC)Au(PPh₃) with R = H, Cl, Ph. A mixture of other complexes is obtained instead which are generated in secondary reactions involving reductive elimination of ethane and/or dialkyne. However, addition of the halo-alkene H(Cl)CCCl₂ to the same substrate solution affords trans-Me₂[trans-H(Cl)CC(Cl)]Au(PPh₃) in good yield. Its molecular structure with pseudo-C_s symmetry has been determined by the solution NMR spectra and a single-crystal X-ray diffraction study. The reaction of methyl iodide with solutions of Li⁺[RCCAuCCR]⁻ in diethylether containing PPh₃ give the quaternary salts Ph₃PMe⁺ [RCCAuCCR]⁻ as the main products and only small amounts of cis-Me₂(RCC)Au(PPh₃) complexes probably formed in a series of oxidative addition, reductive elimination, and substitution reactions. The structure of Ph₃PMe⁺ [PhCCAuCCPh]⁻ has been determined.     

Organometallic π-tweezers incorporating pyrazine- and pyridine-based bridging units

Pyrazine- and pyridine-based π-conjugated σ-donor molecules, such as 4,4′-bipyridine, 1,2-di(4-pyridyl)ethylene, 3,5-dipyridyl-1,2,4-triazole, N,N′-bis(4-pyridylmethylidene)benzene-1,4-diamine, 2,5-di(pyridylmethylidene)cyclopentanone, 2,6-di(4-pyridylmethylidene)cyclohexanone (LL, 2a-2g) can successfully be used to span heterobimetallic π-tweezer units of the type [{[Ti](μ-σ,π-CCSiMe₃)₂}M]⁺ ([Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; M = Cu, Ag). The thus accessible di-cationic species [{[Ti](μ-σ,π-CCSiMe₃)₂}MLLM{(Me₃SiCC-μ-σ,π)₂[Ti]}]²⁺ (4), which are formed via the formation of [{[Ti](μ-σ,π-CCSiMe₃)₂}MLL]⁺ (3) complexes, can be isolated in yields between 66% and 99%.However, when C₅H₄NCHCHC₆H₄CHCHNC₅H₄ (5a) and C₅H₄NCHNC₆H₄CHCHNC₅H₄ (5b), respectively, are reacted with {[Ti](μ-σ,π-CCSiMe₃)₂}AgBF₄(1c) in a 1:1 molar ratio, then the silver(I) ion is released from the organometallic π-tweezer 1c and coordination polymers [AgBF₄ · 5a]_n (6a) and [AgBF₄ · 5b]_n (6b) along with [Ti](CCSiMe₃)₂ (7) are formed in quantitative yield.     

Non-aromatic stabilised form of 3,4-difluoropyrrole at triosmium clusters: N-H and C-H versus C-F activation

Reaction of 3,4-difluoropyrrole with the labile triosmium cluster [Os₃(CO)₁₀(CH₃CN)₂] affords products in which C-H, N-H and C-F bonds are cleaved under mild conditions. C-H and N-H bonds are cleaved to give [Os₃H(NCCFCFCH₂)(CO)₁₀] (1) a non-aromatic stabilised form of 3,4-difluoropyrrole. Thermolysis of 1 affords in moderate yields the compounds [Os₃H₂(CCCFCHNH)(CO)₉] (2) and [Os₃H₂(NCHCFCFC)(CO)₉] (3). For compound 3, C-H and N-H bonds are cleaved with concomitant migration of H atoms to the metal framework. In contrast, for compound 2 activation of C-H and C-F bonds leads to coordination of the ligand through the carbon atoms, acting as a four-electron donating species.     

Oxidovanadium(IV) complexes containing ligands derived from dithiocarbazates - Models for the interaction of VO with thiofunctional ligands

The tetragonal-pyramidal VO²⁺ complexes [VO{(RSC-S)N-NX}₂] (1-6) were synthesised by the reactions of VO(OCHMe₂)₃ with the dithiocarbazate ligands RSC(S)-NH-NX, where X = cyclo-pentyl, cyclo-hexyl or 4-Me₂N-C₆H₄-CH, and R = CH₃ or CH₂C₆H₅. The compounds were characterised by elemental analysis, IR- and mass spectrometries, and in cases of compounds 1, 3, 4 and 5, by X-ray diffraction. The chiral compound 4 (X = cyclo-hexyl, R = CH₂C₆H₅) crystallises in the C configuration. In compound 5, the VO moiety is disordered (83.3:16.7%) with respect to the plane spanned by the four equatorial ligand functions.     

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*).     

Evidence for a pathway that facilitates nitric oxide diffusion in the brain

Nitric oxide (NO) is a diffusible messenger that conveys information based on its concentration dynamics, which is dictated by the interplay between its synthesis, inactivation and diffusion. Here, we characterized NO diffusion in the rat brain in vivo. By direct sub-second measurement of NO, we determined the diffusion coefficient of NO in the rat brain cortex. The value of 2.2 × 10⁻⁵ cm²/s obtained in vivo was only 14% lower than that obtained in agarose gel (used to evaluate NO free diffusion). These results reinforce the view of NO as a fast diffusing messenger but, noticeably, the data indicates that neither NO diffusion through the brain extracellular space nor homogeneous diffusion in the tissue through brain cells can account for the similarity between NO free diffusion coefficient and that obtained in the brain. Overall, the results support that NO diffusion in brain tissue is heterogeneous, pointing to the existence of a pathway that facilitates NO diffusion, such as cell membranes and other hydrophobic structures.     

A closer look at the phosphorus-phosphorus double bond lengths in meta-terphenyl substituted diphosphenes

The single crystal X-ray structure of DmpPPDmp (1, Dmp = 2,6-Mes₂C₆H₃), which was previously reported to have a relatively short PP bond distance of 1.985(2) Å at room temperature, has been reexamined at variable temperatures. Crystallographic analyses of 1 at 100 K allow for resolution of disorder of the two phosphorus atoms (which is unresolvable from room temperature diffraction data), and for determination of a more conventional PP bond length of 2.029(1) Å. Single crystals of the closely related diphosphene DxpPPDxp (2, Dxp = 2,6-(2,6-Me₂C₆H₃)₂C₆H₃) show similar disorder in one of two crystallographically independent molecules in the unit cell. A value of 2.0276(4) Å is found for the non-disordered PP bonds at 100 K for 2. A new diphosphene Ar′PPAr′ (3, Ar′ = 2,6-Mes₂-4-OMe-C₆H₃) has been prepared and its structure has also been examined. The PP bond length for 3 was determined to be 2.0326(9) Å and relatively free of the effects of disorder.     

Biotransformation of the neonicotinoid insecticides imidacloprid and thiamethoxam by Pseudomonas sp. 1G

We report the isolation of a Pseudomonas sp. which is able to transform imidacloprid and thiamethoxam under microaerophilic conditions in the presence of an alternate carbon source. This bacterium, Pseudomonas sp. 1G, was isolated from soil with a history of repeated exposure to imidacloprid. Both insecticides were transformed to nitrosoguanidine (NNO), desnitro (NH), and urea (O) metabolites and a transformation pathway is proposed. This is the first conclusive report of bacterial transformation of the ‘magic nitro’ group which is responsible for the insect selectivity of neonicotinoid insecticides.     

EPR investigation of Cu(II)-complexes with nitrogen derivatives of dialdehyde starch

Dialdehyde starch obtained by periodate oxidation from potato starch was converted into its disemicarbazone (DSC), dithiosemicarbazone (DTSC), dihydrazone (DHZ) and dioxime (DOX). The Cu(II) complexes of these compounds were prepared and characterized by Raman and EPR spectra, as well as by the measurements of magnetic susceptibility. EPR investigations showed that two types of complexes with different surroundings of copper centres existed in each starch derivative. Besides nitrogen atoms of the CN moiety and sulphur atoms of the CS moiety, also oxygen atoms from starch hydroxyl groups and/or water molecule were proposed as the coordination sites for the central copper ions.     

Synthesis and structures of bimetallic silicon-containing imido alkylidene complexes of molybdenum Me2Si[CHMo(NAr)(ORF3)2]2 and PhVinSi[CHMo(NAr)(ORF3)2]2

Bimetallic alkylidene complexes of molybdenum (R_F3O)₂(ArN)MoCH-SiMe₂-CHMo(NAr)(OR_F3)₂ (1) and (R_F3O)₂(ArN)MoCH-SiPhVin-CHMo(NAr)(OR_F3)₂ (2) (Ar = 2,6-C₆H₃; R_F3 = CMe₂CF₃) have been prepared by the reactions of vinyl silicon reagents Me₂Si(CHCH₂)₂ and PhSi(CHCH₂)₃ with known alkylidene compound PhMe₂C-CHMo(NAr)(OR_F3)₂. Complexes 1 and 2 were structurally characterized. Ring opening metathesis polymerization (ROMP) of cyclooctene using compounds 1 and 2 as initiators led to the formation of high molecular weight polyoctenamers with predominant trans-units content in the case of 1 and predominant cis-units content in the case of 2.     

Synthesis and characterization of triphenylphosphine stabilized silver α,β-unsaturated carboxylate: Crystal structure of [Ag(O2CCHC(CH3)2)(PPh3)2]

A series of triphenylphosphine coordinated silver α,β-unsaturated carboxylates of type [Ag(O₂CR)(PPh₃)_n: n = 1, R = CH₃CHCH (2a), (CH₃)₂CCH (2b), CH₃CH₂CHCH (2c), CH₃CH₂CH₂CHCH (2d), PhCHCH (2e), CH₂CH (2f); n = 2, CH₃CHCH (3a), (CH₃)₂CCH (3b), CH₃CH₂CHCH (3c), CH₃CH₂CH₂CHCH (3d)] were prepared by reaction of relative silver carboxylates (1a-1f) with triphenylphosphine in chloroform. These complexes were obtained in high yields and characterized by elemental analysis, ¹H NMR, ¹³C NMR, ³¹P NMR and IR spectroscopy. Thermal stability of the complexes has been determined by TG analysis. The molecular structure of [Ag((O₂CCHC(CH₃)₂))(PPh₃)₂] (3b) shows that the senecioato ligand is chelated with silver atom and generate, a distorted tetrahedron.     

Organometallic complexes for nonlinear optics. Part 36. Quadratic and cubic optical nonlinearities of 4-fluorophenylethynyl- and 4-nitro-(E)-stilbenylethynylruthenium complexes

The complexes trans-[Ru(CC-4-C₆H₄F)X(dppe)₂] [X = Cl (1), CCPh (2), CC-4-C₆H₄NO₂ (3)], trans-[Ru{CC-4-C₆H₄-(E)-CHCH-4-C₆H₄NO₂}X(dppe)₂] [X = CCPh (4), CC-4-C₆H₄CCPh (5)], and [C₆H₃-1,3-{CC-trans-[RuCl(dppe)₂]}₂-5-(CC-4-C₆H₄F)] (6) have been synthesized and the identity of 1 confirmed by a single-crystal X-ray diffraction study. Cyclic voltammetry reveals a metal-centered oxidation, the potential of which is largely invariant on alkynyl ligand replacement across the series 1-5; the diruthenium complex 6 shows two oxidation processes, consistent with weakly interacting metal centers. Hyper-Rayleigh scattering (HRS) studies at 1064 nm using ns pulses suggest quadratic nonlinearities for 3-5 that are amongst the largest thus far for organometallic complexes, a trend maintained with the two-level-corrected data. HRS studies at 800 nm using fs pulses and amplitude modulation to remove multi-photon fluorescence contributions reveal significant fluorescence-free nonlinearities for 3-5; the frequency-independent nonlinearities calculated from the 800 nm results are suggestive of fluorescence contributions to the 1064 nm data. Z-scan studies at 820 nm reveal cubic nonlinearities that increase with the size of the π-system, although error margins are significant.     

Reaction of N-hydroxyguanidine with the ferrous-oxy state of a heme peroxidase cavity mutant: A model for the reactions of nitric oxide synthase

Yeast cytochrome c peroxidase was used to construct a model for the reactions catalyzed by the second cycle of nitric oxide synthase. The R48A/W191F mutant introduced a binding site for N-hydroxyguanidine near the distal heme face and removed the redox active Trp-191 radical site. Both the R48A and R48A/W191F mutants catalyzed the H₂O₂ dependent conversion of N-hydroxyguanidine to N-nitrosoguanidine. It is proposed that these reactions proceed by direct one-electron oxidation of NHG by the Fe⁺⁴O center of either Compound I (Fe⁺⁴O, porph⁺) or Compound ES (Fe⁺⁴O, Trp⁺). R48A/W191F formed a Fe⁺²O₂ complex upon photolysis of Fe⁺²CO in the presence of O₂, and N-hydroxyguanidine was observed to react with this species to produce products, distinct from N-nitrosoguanidine, that gave a positive Griess reaction for nitrate + nitrite, a positive Berthelot reaction for urea, and no evidence for formation of NO. It is proposed that HNO and urea are produced in analogy with reactions of nitric oxide synthase in the pterin-free state.     

Orthomercurated and cycloaurated derivatives of the iminophosphorane Ph3PNPh

Ortho-lithiation of Ph₃PNPh followed by reaction with HgCl₂ gave good yields of [Hg{C₆H₄(PPh₂NPh)-2}Cl], 3, which was characterised spectroscopically and by an X-ray crystal structure determination. This is an isomer of the product of direct mercuration of Ph₃PNPh which occurs on the N-bonded phenyl ring [J. Vicente, J.A. Abad, R. Clemente, J. Lopez-Serrano, M.C. Ramirez de Arellano, P.G. Jones, D. Bautista, Organometallics, 22 (2003) 4248]. Transmetallation of 3 with [AuCl₄]⁻ gave the corresponding cycloaurated complex [Au{κ²-C,N-C₆H₄(PPh₂NPh)-2}Cl₂], with a five-membered metallocyclic ring incorporating four different elements.     

Exploring a series of monoethynylfluorenes as alkynylating reagents for mercuric ion: Synthesis, spectroscopy, photophysics and potential use in mercury speciation

New luminescent mononuclear mercury(II) mono- and dialkynylated complexes containing substituted fluorene and fluorenone units [R-CC-HgCH₃] and [R-CC-Hg-CC-R] (R = 9,9-dialkylfluorene-2-yl and fluoren-9-one-2-yl; alkyl = H, ethyl, hexyl, octyl, hexadecyl) were prepared in good yields by mercuration of terminal acetylene R-CCH with CH₃HgCl and HgCl₂ at room temperature via the dehydrohalogenation reaction. The structures of these organomercurial compounds were characterized by IR and NMR spectroscopies, elemental analysis and FAB mass spectrometry. Their optical and photoluminescence spectra were also studied. The structural features of one complex was elucidated by X-ray crystallography in which there is an indication of weak mercuriophicity among the molecules in the solid state. A new protocol is developed for derivatization of inorganic mercury(II) ion into dialkynyl mercury(II) compounds followed by the ready extraction into dichloromethane, which can be analyzed by HPLC technique using UV detection. These results have important implications in the development of analytical procedures for the determination of mercuric ion in aqueous solutions.