The preparation and characterisation of a series of cationic bimetallic linear triphos-bridged complexes of the type [Mo (CO) (L,L′ or L″–P) (η2-RC2R′)Cp] [BF4] {L,L′ or L″= [WI2 (CO){PhP(CH2CH2PPh2)2–P,P′} (η2-RC2R′)] (L,R=R′=Me; L′,R=R′=Ph; L″,R=Me,R′=Ph}

Equimolar quantities of [Mo (CO) (η²-RC₂R′)₂Cp] [BF₄] (R=R′=Me Ph R=Me R′=Ph) and L L′ or L″ {L L′ or L″= [WI₂ (CO){PhP(CH₂CH₂PPh₂)₂-PP′} (η²-RC₂R′)]} (L R=R′=Me L′ R=R′=Ph L″ R=Me R′=Ph) react in CH₂Cl₂ at room temperature to give the new bimetallic complexes[Mo (CO) (L L′ or L″–P) (η²-RC₂R′)Cp] [BF₄] (1–9) via displacement of the alkyne ligand on the molybdenum centre The complexes have been characterised by elemental analysis IR and ¹ H NMR spectroscopy and in selected cases by ³¹ P NMR spectroscopy.     

Synthesis of optically active cobalt(salen) type complexes and their asymmetric reactivity toward propylene oxide

An optically active Co(I)(salen) type complex, lithium N,N′-bis(salicylaldehyde)-1(R), 2(R)-1,2-trans-cyclohexanediiminatocobalt(I), was prepared by reducing the Co^II complex, N,N′-bis(salicylaldehyde)-1(R),2(R)-1,2-trans-cyclohexanediiminatocobalt(II), with LiAlH₄. The structure of the Co^I complex was determined on the basis of the structure of the corresponding Co^II complex and was confirmed by usual physicochemical methods. Furthermore, characteristics of the absorption and circular dichroism(CD) spectra of the Co^I complex were compared with those of the reported structure of Na⁺[Co(I)(salen)]^?. Highly asymmetric selectivity was found in a resolution reaction of DL-propylene oxide by use of the above optically active lithium cobalt(I) complex as a catalyst.     

Asymmetric nitrogen

The¹H NMR spectra ofO-derivatives of 1-hydroxy-2,2-bis(trifluoromethyl)aziridine containing such substituents as EtO₂CCH₂, (R/S)-RO₂CCH(Me) (R=Me, Prⁱ, or Bu^t), (R/S)-H₂NC(O)CH(Me), and (R)-H₂NC(O)CH(Me) were analyzed. Both of the diastereomerically pure amides of the latter type were isolated. The validity of the¹H NMR criteria, which were suggested for the determination of absolute configurations of diastereomers ofN-alkoxyaziridines, was confirmed by X-ray diffraction study of the (R,R)-amide.     

Diastereospecific synthesis of β-heterosubstituted alcohols from 1,2-diols via 1,3,2λ5-dioxaphospholanes

The stereochemistry of the ring opening of (R,S) or (R,R)-4,5-dimethyl-2,2,2-triphenyl-1,3,2λ⁵-dioxaphospholanes (prepared by reaction of (R,S) or (R,R)-butane-2,3-diol with dibromotriphenylphosphorane) by aniline or thiophenol was investigated. The reaction affords stereoselectively the corresponding β-anilino- or β-phenylthioalcohols with a nearly complete inversion of stereochemistry at the stereogenic reaction centre.     

Reactions of 1,4-diaza-3-methylbutadien-2-ylpalladium(II) derivatives with chloro-bridged rhodium(I) complexes

The reactions of the organometallic 1,4-diazabutadienes, RN=C(R′)C(Me)=NR″ [R = R″ = p-C₆H₄OMe, R′ = trans-PdCl(PPh₃)₂ (DAB); R = p-C₆H₄OMe, R″ = Me, R′ = trans-PdCl(PPh₃)₂ (DAB^I; R = R″ = p-C₆H₄OMe, R′ = Pd(dmtc)-(PPh₃), dmtc = dimethyldithiocarbamate (DAB^II); R = R″ = p-C₆H₄OMe, R′ = PdCl(diphos), diphos = 1,2-bis(diphenylphosphino)ethane (DAB^III)] with [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene, Pd/Rh ratio = $\text{1}\text{2}$) depend on the nature of the ancillary ligands at the Pd atom in group R′. In the reactions with DAB and DAB^I transfer of one PPh₃ ligand from Pd to Rh occurs yielding [RhCl(COD)(PPh₃)] and the new binuclear complexes [Rh(COD) {RN=C(R?)-C(Me)=NR″}], in which the diazabutadiene moiety acts as a chelating bidentate ligand. Exchange of ligands between the two different metallic centers also occurs in the reaction with DAB^II. In this case, the migration of the bidentate dmtc anion yields [Rh(COD)Pdmtc] and [Rh(COD) {RN=C(R?)C(Me)=NR″}]. In contrast, the reaction with DAB^III leads to the ionic product [Rh(COD)- (DAB^III)][RhCl₂(COD)], with no transfer of ligands. The cationic complex [Rh(COD)(DAB^III)]⁺ can be isolated as the perchlorate salt from the same reaction (Pd/Rh ratio = 1/1) in the presence of an excess of NaClO₄. In all the binuclear complexes the coordinated 1,5-cyclooctadiene can be readily displaced by carbon monoxide to give the corresponding dicarbonyl derivatives. The reaction of [RhCl(CO)₂]₂ with DAB and/or DAB^I yields trinuclear complexes of the type [RhCl(CO)₂]₂(DAB), in which the diazabutadiene group acts as a bridging bidentate ligand. Some reactions of the organic diazabutadiene RN=C(Me)C(Me)=NR (R = p-C₆H₄OMe) are also reported for comparison.     

Luminescence of neutral and ionic gold(I) complexes containing pyrazole or pyrazolate-type ligands

A series of pyrazole (Hpz) and pyrazolate (pz⁻) Au(I) complexes of types [Au(Hpz^2R(n))(PPh₃)]⁺ (I), [Au(Hpz^2R(n))₂]⁺ (II), [Au(μ-pz^R(n))]₃ (III), [Au(pz^R(n)/2R(n))(PPh₃)] (IV), [AuCl(Hpz^R(n)/2R(n))] (V) and [(PPh₃)Au(μ-pz^R(n))Au(PPh₃)]⁺ (VI), R(n) and 2R(n) represent C₆H₄OC_nH_2n+1 substituents at the 3- or 3- and 5-positions of the heterocyclic ring, respectively, have been shown to be luminescent in the solid state at 77 K, independently of the presence or not of inter-metallic Au-Au interactions. The emission spectra of all complexes consist of structured bands in the region 395-500 nm, attributed to ligand-to-metal charge transfer (LMCT) transitions involving the Hpz or pz⁻ ligands, the pattern of bands of compounds being related with the molecular structure and/or the nature of the ligands. The thermal behaviour of several complexes of the types III, IV and V containing long-chain substituents (n ? 12) was examined by polarising light optical microscopy (POM). The derivative [AuCl(Hpz^R(12))] was proved to have liquid crystal properties exhibiting a mesophase SmA but the remaining complexes were not liquid crystal materials. This complex is one of the scarce examples of Au(I) derivatives exhibiting both liquid crystal and luminescent properties.     

Application of the Seth-Paul-Van Duyse equation—I : A simple relation defining new X+(R) substituent constants on the basis of electrophilic σ+ constants

The Seth-Paul-Van Duyse equation (SPVDE) correlating the CO stretching frequencies of a great number of R₁COR₂ molecules with X (R) substituent constants has been reinvestigated. A simple empirical relation defining new X⁺(R) constants on the basis of electrophilic σ constants has been derived: X⁺ (R) = 0·238 σ⁺ + 1·077. The three earlier reported relationships between the X(R) constants and Hammett σ values have been replaced by this single relationships and a set of new X⁺(R) constants has been calculated. The new X⁺(R) constants applied to 287 R₁COR₂ compounds containing the para- or meta-substituted benzene rings fit very well the SPVDE. It has been possible to extend the SPVDE to various aromatic systems.     

Untersuchungen zum elektronischen einfluss von organylliganden: IV. 13C-NMR-spektroskopische untersuchung der gegenseitigen beeinflussung von organylliganden in triethylzinnorganylverbindungen

By means of ¹³C NMR spectroscopy, the coupling constants ¹J(¹¹⁹Sn¹³C_Et) of 18 compounds of the SnEt₃R type (R = organo group) have been measured. These coupling constants have been shown to reflect the change induced by R in the s-content of the tin hybrid orbitals of the SnCEt bonds. The series of the influence of R obtained on the basis of the coupling constant mentioned as a parameter is compared with a trans-influence series of R obtained on organo-mercury compounds. Occurring differences are attributed to different modes of bonding of the group R at the central atom.     

Metallacumulenylidene complexes in the [(η5-C5Me5)(η2-dppe)Fe(=C(=C)nR2)]X (n = 0, 1, 2) series: investigations of the iron-carbon bonding by Mössbauer spectroscopy and X-ray analyses

The synthesis of the iron allenylidene complexes [(η⁵-C₅Me₅)(η²-dppe)Fe(=C=C=C(Ph)Ph)][X] (5a, X = PF₆, 95%; 5b, X = BPh₄, 91%; dppe = 1,2-bis(diphenylphosphino)ethane) was achieved by reacting the complex (η⁵-C₅Me₅)(η²-dppe)FeCl (10) with 1 equiv of 1,1-diphenyl-prop-2-yn-1-ol in methanol in the presence of KPF₆ or NaBPh₄. Surprisingly, when the reaction was carried out in the presence of the tetraphenylborate anion, the final product contained both 5b and the hydroxyvinylidene [(η⁵-C₅Me₅)(η²-dppe)Fe(=C=C(H)C(OH)(Ph)₂)][BPh₄] (14b) in the 1:1 ratio. Further treatment of the mixture with Amberlyst 15 in methanol provided the allenylidene 5b as a pure sample. The allenylidene complexes [(η⁵-C₅Me₅)(η²-dppe)Fe(=C=C=C(Me)Ph)][PF₆] (6) and [(η⁵-C₅Me₅)(η²-dppe)Fe(=C=C=C(Me)Et)][PF₆] (7) were prepared according to the same procedure and they were isolated as purple powders in 90% yield. The X-ray crystal structures were determined for the vinylidene complexes [(η⁵-C₅Me₅)(η²-dppe)Fe(=C=CH₂)][PF₆] (3) and [(η⁵-C₅Me₅)(η²-dppe)Fe(=C=C(Ph)H)][PF₆] (4), and the allenylidene derivative 5a. In the homogeneous series of complexes [(η⁵-C₅Me₅)(η²-dppe)Fe(=(C)_n(R)R’)][PF₆], (n = 1, R = H, R′ = Me, X = PF₆, 1; n =1, R = H, R’ = OMe, X = PF₆, 2a; n = 1, R = H, R’ = OMe, X = CF₃OSO₂, 2b; n = 2, R = R′ = H, X = PF₆, 3; n = 2, R = H, R′ = Ph, X = PF₆, 4; n = 3, R = R′ = Ph, X = PF₆, 5a; n = 3, R = R′ = Ph, X = BPh₄, 5b; n = 3, R = Me, R′ = Ph, X = PF₆, 6; n = 3, R = Me, R′ = Et, X = PF₆, 7; n = 3, R = Me, R′ = OMe, X = BPh₄, 8), an empiric relationship between the Mössbauer parameters, δ and QS, was found. This observation would indicate that the positive charge on the iron nucleus decreases with the Fe=C bond order. Moreover, in this series of iron cumulenylidene derivatives, comparison of the variation of the metal–carbon bond distances determined by X-ray analyses with the Mössbauer QS values allows the observation of a linear correlation (R = 0.99). To cite this article: G. Argouarch et al., C. R. Chimie 6 (2003).     

Kinetische und mechanistische untersuchungen von übergangsmetallkomplex-reaktionen : VI. Kinetik und mechanismus der einschiebung von dimethylcyanamid in die metall—carbenkohlenstoff-bindung von pentacarbonyl(arylphenylcarben)wolfram

Pentacarbonyl(arylphenylcarbene)tungsten complexes, (CO)₅W[C(p-C₆H₄R)C₆H₅] (Ia, R = OCH₃; Ib, R = CH₃; Ic, R = H; Id, R = Br; Ie, R = CF₃) react with dimethylcyanamide (II) via insertion of the CN group into the metalcarbene bond. The formation of pentacarbonyl[dimethylamino(imino)carbene]tungsten(0) (IIIa–IIIe) follows a second-order rate law: d[III]/dt = k[I][II]. Replacement of R = H by electron-withdrawing substituents (Br, CF₃) results in an increase, by electron-donating groups (CH₃, OCH₃) in a decrease of the reaction rate. The rate constants correlate well with Hammett's σ-constants. The activation enthalpies ΔH^≠ are low (37.3–41.6 kJ mol^?1), the activation entropies ΔS^≠ strongly negative (?119 to ?133 J mol^?1 K^?1). The results are discussed on the basis of an associative stepwise mechanism with a nucleophilic attack of the CN group of II at the carbene carbon in the first reaction step.     

Synthese neuer Aminofluorsilane,sowie Alkoxylierung von Bis (trimethylsilyl)-amino-fluorsilanen

The reaction of aminofluorsilanes of the type (R=H,F) (Me ₃Si)₂N?SiF₂R with two moles of ammonia, or of a mono- or dialkylamine, yields the corresponding amino-compounds, e.g. (Me ₃Si)₂N?Si(F)R?NH₂, (Me ₃Si)₂N?Si(F)R?NHR′ and (Me ₃Si)₂N?Si(F)R?NR₂′ (R′=Me, Et). Analogous products are obtained by reaction of the aminofluorosilanes with lithium salts of amines with bulky organic substituents in a 1 : 1 molar ratio. Alkoxy- and aryloxyaminofluorosilanes are prepared by the reaction of sodium alcoholates and sodium phenolate with (Me ₃Si)₂N?Si(F₂)R (R=H, C₂H₃, C₂H₅, C₆H₅). The i.r.-, mass-,¹H- and¹⁹F-NMR spectra of the above compounds are reported.     

Synthesis and coordination chemistry of tetrabutyldithioimidodiphosphinates

Butyl substituted imidodithiophosphinates R₂P(S)NP (S)R′₂ (R=ⁿBuⁱBu^sBuR′=ⁿBuⁱBu^sBu) have been synthesised via an HBr elimination reaction between R₂P(S)NH₂ and R′₂P(S)Br The compounds were characterised spectroscopically Crystallographic and spectroscopic studies reveal ⁿBu₂P(S)NHP(S)ⁿBu₂ and ^sBu₂P(S)NHP(S)ⁱBu₂ to be hydrogen bonded transoid dimers and ⁱBu₂P(S)NHP(S)ⁱBu₂ to be a transoid hydrogen bonded chain Reactions of the imidodithiophosphinates with ZnCl₂ or MCl₂COD gave the coordination complexes M[R₂P(S)NP (S)R′₂]₂ (R=ⁿBuⁱBu^sBuR′=ⁿBuⁱBu^sBuM=ZnPd: R=ⁿBuⁱBu^sBuPt).     

In situ synthesized homochiral dysprosium-oxo clusters with threonine Schiff bases

Chiral high-nuclearity lanthanide (4f) clusters have shown fantastic properties in various fields. However, their synthesis is still of great challenge. Herein, we report two pairs of enantiomers of high-nuclearity Dy-oxo clusters synthesized through in situ strategy. They are [Dy₁₈(^R/SHftp)₄ (^R/SH₂btp)₄(μ₂-OH)₈(μ₃-OH)₂₀(μ₆-O)(NO₃)₄(μ-H₂O)₈]·[solvents] (1R and 1S) and [Dy₉(^R/SHftp)₂ (^R/SH₂btp)₂(OAc)₆(μ₃-OH)₁₀(H₂O)₆](OAc)·[solvents] (2R and 2S), where ^R/SHftp²⁻ and ^R/SH₂btp³⁻ represent in situ formed 2-formyl-6-[N-(threonine)iminomethyl]-4-methylphenol and 2,6-bis[N-(threonine)iminomethyl]-4-methylphenol anions, respectively. These in situ formed clusters were endowed with not only homochirality via introducing ^R/SHftp²⁻ and ^R/SH₂btp³⁻ ligands, but also rich oxo-bridges by controlling the hydrolysis of Dy^III ions. Different anions from Dy^III salts further induced structural variation between two sets of clusters. 1R and 1S feature an unprecedent four-blade propeller shaped {Dy₁₈} core, whose centered octahedral {Dy₆} unit are surrounded by four triangular {Dy₃} units. Strikingly, they represent the second largest chiral 4f cluster species so far. 2R and 2S display a sandglass-like {Dy₉} skeleton that consist of two square pyramid {Dy₅} units sharing a Dy^III vertex. Magnetic investigation revealed possible antiferromagnetic interactions between the Dy^III centers in these clusters.     

5-Bromo- and 3,5-dibromo-2-hydroxy-N-phenylbenzamides — inhibitors of photosynthesis

5-Bromo-(Br-PBA) and 3,5-dibromo-2-hydroxy-N-phenylbenzamides (Br₂-PBA) inhibited photosynthetic electron transport (PET) and their inhibitory efficiency depended on the compound lipophilicity as well as on the electronic properties of the R substituent in the N-phenyl moiety. Br-PBA showed higher PET inhibiting activity than Br₂-PBA with the same R substituent. The most effective inhibitors in the tested series were the derivatives with R = 3-F (Br-PBA; IC₅₀ = 4.3 μmol dm^?3) and R = 3-Cl (Br₂-PBA; IC₅₀ = 8.6 μmol dm^?3). Bilinear dependence of the PET inhibiting activity on the lipophilicity of the compounds as well as on the Hammett constant, σ, of the R substituent was observed for both investigated series. Using EPR spectroscopy it was found that the site of action of the tested compounds in the photosynthetic apparatus is situated on the donor side of PS 2, in D^· or in the Z^·/D^· intermediates. Interaction of the studied compounds with chlorophyll a and aromatic amino acids present in the pigment-protein complexes mainly in photosystem 2 was documented by fluorescence spectroscopy.     

29Si and 13C NMR Studies of organofunctional di- and trisilanes

A series of di- and trisilanes of general structure Ph₃SiSiMe₂R and (Ph₃Si)₂SiR′R″ were synthesized, and the ²⁹Si and ¹³C chemical shifts and one-bond siliconsilicon coupling constants (¹J_SiSi) were measured. The coupling constants of the disilanes were found to be primarily dependent upon the inductive effect of the alkyl group, R, as measured by the Taft o^★ constant. In both series of compounds, increasing alkyl substitution at silicon led to a decrease in ¹J_SiSi.     

Preparation of some 4- and 5-fluoromethylated 1,3-dioxans

Difficulties associated with the successful preparation of 4- and 5-fluoromethylated 1,3-dioxans (III)(⁵′R = ⁵R = H) and (IV)(⁵R = Me; ²R = H or Me) are reported. Claisen condensation between ethyl monofluoroacetate and methyl ketones afforded furan derivatives (e.g. compound (V)).Attempts to dialkylate fluorinated 1,3-diketones by classical procedures did not yield the corresponding 2,2-gem-alkylated 1,3-diketones but rather asymmetric ketones by β-diketone degradation, the fluorinated moiety being lost.     

Cumulated double bond systems as ligands : IV. 1H and 13C NMR studies of the intra- and inter-molecular exchange processes of cationic dialkylsulfurdiimine compounds of RhI,IrI and PtII

The preparation and properties are described of trans-[(Ph₃P)₂(CO)M(RNSNR)] [ClO₄] (M  Rh^I, Ir^I; R  Me, Et, i-Pr, t-Bu) and of cis- or trans-[L₂Pt(RNSNR)X] [ClO₄] (X  Cl^?, L  Et₂S, PhMe₂As, PhMe₂P, R  Me, t-Bu; X  CH₃, L  PhMe₂P, R  Me).¹H and ¹³C NMR data show the existence of various isomers in solution which may interconvert via intra- and inter-molecular exchange processes. A general reaction scheme for the intramolecular exchange processes is discussed.     

Secondary reactions in controlled potential coulometry: Part V. Reversal coulometric study of the reduction of cis- and trans-thioindigo in the presence of carbon dioxide,cinnamonitrile and acrylonitrile

Controlled potential reversal coulometry was applied to the following systems: (I) C+neR; R+C → RC; RC+ne → products. (II) as in (I) except RC not electroactive. (III) C+neR; R+X → RX; RX+ne → products. Equations for these e.c.e. and e.c. mechanisms were obtained and solved numerically. Working curves are presented for the calculation of the rate constants of the homogeneous reactions. This treatment was applied to studies of the reduction of thioindigo (TI) alone and in the presence of several reactants. For TI alone the reaction mechanism involves reaction of the radical anion (TI^?_·) with parent molecule followed by a second electron transfer. In the presence of excess dissolved CO₂, acrylonitrile (AN), or cinnamonitrile (CN), reaction of TI^?_· with these followed by a second electron transfer was proposed. Rate constants for the TI?TI^?_· coupling reaction were 82 (cis-thioindigo), and 323 (trans-thioindigo) l mol^?1 s^?1; pseudo-first-order reactions of TI^?_· were 0.016 (trans-) and 0.047 (cis-) s^?1 with CO₂; 0.023 (trans-) and 0.033 (cis-) s^?1 with CN; 0.022 (trans-) and 0.032 (cis-) s^?1 with AN.     

Synthesis and structure of fluorosilicic acid compounds with 4-aminobenzoic acid and with 4-aminobenzenesulfonamide: The role of H-bonding in crystal structure formation

Preparation and characterization of the ammonium hexafluorosilicate salts, 2[R]⁺[SiF₆]²⁻ (R = 4-(aminosulfonyl)benzenammonium) (1), and 2[R]⁺[SiF₆]²⁻.4H₂O (R = 4-carboxybenzenammonium), (2), are described. These salts, prepared from the reaction of the 4-aminobenzenesulfonamide or the 4-aminobenzoic acid with fluorosilicic acid, were characterized by IR, mass spectrometry and X-ray diffraction. 1 and 2 crystallize in monoclinic crystal system (space group P2₁/c and P2₁/n, respectively), with Z = 2 in both cases. Compounds exhibit an extensive system of hydrogen bonding.     

Methyl- and phenyl-bis(tertiary phosphine) N-bonded carboxamido complexes of platinum(II)

Methyl- or phenylN-carboxamido-complexes of platinum(II) Pt(NHCOR')RL₂ (L = PEt₃, R = Me, R′ = Me, CH = CH₂; L = PEt₃, R = Ph, R′ = Me; L = PMe₂Ph, R = Ph, R′ = Me, Ph; L = PMePh₂, R = Ph, R′ =₃, R = Ph, R′ = Me) have been prepared by the reaction of KOH with cationic nitrile complexes [PtR(NCR′)L₂]BF₄. Thermally unstable hydrido-N-carboxamido-complexes could be detected spectroscopically. IR and NMR (¹H, ³¹P) spectra of some of the complexes indicate the existence of a solvent- and temperature-dependent equilibrium between syn-and anti-isomers arising from restricted rotation about the NC bond of the carboxamido-group. The anti-isomer is favoured by nonpolar solvents and by increasing bulk of L. In the complex [PtH(NCCH CH₂)(PEt₃)₂]BF₄, IR and NMR spectra show acrlonitrile to be bound through nitrogen, not through the olefinic CC bond.