Kinetics of Schiff base formation between the cholesterol ozonolysis product 3-beta-hydroxy-5-oxo-5,6-secocholestan-6-al and phosphatidylethanolamine

FTIR spectroscopy and fluorescence polarization were used to show that a bacterial dirhamnolipid interacts with phospholipid membranes composed of DPPC, altering both the acyl chain and the interfacial region of the bilayer. Incorporation of increasing amounts of dirhamnolipid into ²H-DPPC membranes broadened the transition and shifted the transition temperature toward lower values, according to the effect on the CD₂ stretching vibration. Examination of the ¹³CO stretching band of ¹³C-DPPC indicated that, both below and above the phase transition, dirhamnolipid produced a shift of the band frequency toward higher values, indicating a strong dehydration of the phospholipid CO groups, and therefore of the interfacial region of the membrane. The effects on DPH and TMA-DPH fluorescence polarization provided additional support to hypothesize on the location of trehalose lipid within the bilayer. The results shown here could help to explain some of the interesting membrane-related biological actions of rhamnolipids reported before.     

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.     

Modification of aminoallenylidene complexes of chromium via exchange of the C3-bound amino group

The aminoallenylidene(pentacarbonyl)chromium complexes [(CO)₅CrCCC(NR¹R²)Ph] (1a-c) react with dimethylamine by addition of the amine to the C1C2 bond of the allenylidene ligand to give alkenyl(amino)carbene complexes [(CO)₅CrC(NMe₂)CHC(NR¹R²)Ph] (2a-c) (R¹ = Me: R² = Me (a), Ph (b); R¹ = Et: R² = Ph (c)). In contrast, addition of a large excess (usually 20 equivalents) of ammonia or primary amines, H₂NR, to solutions of [(CO)₅CrCCC(NMe₂)Ph] (1a) affords the aminoallenylidene complexes [(CO)₅CrCCC(NHR)Ph] (1d-w) in which the dimethylamino group is replaced by NH₂ or NHR, respectively. In addition to simple amines such as methylamine, butylamine, and aniline, amines carrying a functional group (allylamine, propargylamine) and amino acid esters as well as amino terpenes and amino sugars can be used to displace the NMe₂ substituent. Usually the Z isomer (with respect to the partial C3-N double bond) is formed exclusively. Products derived from addition of H₂NR to the C1C2 bond of 1a are not observed. The amino group in 1d-w is rapidly deprotonated by excess of amine to form iminium alkynyl chromates [1d-w]⁻, thus protecting 1d-w from addition of free amine to either C3 or across the C1C2 bond. The iminium alkynyl chromates are readily reprotonated by acids or by chromatography on wet SiO₂ to reform 1d-w.     

Iridium(III)-vinylidene chemistry: Conversion of an iridacyclopentadiene-chlorido complex and terminal alkynes to iridacyclopentadiene-vinyl complexes

The reactions of [κ²(C¹,C⁴)-CRCRCRCR](PPh₃)₂Ir(Cl) (9, R = CO₂Me) with propargyl alcohol derivatives (2-propyn-1-ol, 2-methyl-3-butyn-2-ol, 1-ethynylcyclopentanol, and 1-ethynylcyclooctanol), in the presence of water leads to the formation of iridium(III)-vinyl complexes bearing the general structure [κ²(C¹,C⁴)-CRCRCRCR](PPh₃)₂Ir(CO)(κ¹-vinyl) where vinyl = -CHCH₂, -(E)-CHCHMe, -CHC(CH₂)₄, or -CHC(CH₂)₇. In these, the CO ligand was derived from the terminal carbon of the starting alkyne and the oxygen atom from water. Under anhydrous conditions, 9 undergoes reaction with 2-propyn-1-ol to give trimethyl 1,3-dihydro-3-oxo-4,5,6-isobenzofurantricarboxylate, the result of a cycloaromatization/transesterification involving the buta-1,3-dien-1,4-diyl ligand in 9 and 2-propyn-1-ol.     

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.     

H2O2 and (.)NO scavenging by Mycobacterium leprae truncated hemoglobin O

Kinetics of ferric Mycobacterium leprae truncated hemoglobin O (trHbOFe(III)) oxidation by H₂O₂ and of trHbOFe(IV)O reduction by NO and NO₂⁻ are reported. The value of the second-order rate constant for H₂O₂-mediated oxidation of trHbOFe(III) is 2.4 × 10³ M⁻¹ s⁻¹. The value of the second-order rate constant for NO-mediated reduction of trHbOFe(IV)O is 7.8 × 10⁶ M⁻¹ s⁻¹. The value of the first-order rate constant for trHbOFe(III)ONO decay to the resting form trHbOFe(III) is 2.1 × 10¹ s⁻¹. The value of the second-order rate constant for NO₂⁻-mediated reduction of trHbOFe(IV)O is 3.1 × 10³ M⁻¹ s⁻¹. As a whole, trHbOFe(IV)O, generated upon reaction with H₂O₂, catalyzes NO reduction to NO₂⁻. In turn, NO and NO₂⁻ act as antioxidants of trHbOFe(IV)O, which could be responsible for the oxidative damage of the mycobacterium. Therefore, Mycobacterium leprae trHbO could be involved in both H₂O₂ and NO scavenging, protecting from nitrosative and oxidative stress, and sustaining mycobacterial respiration.     

Gas-phase molecular structures of substituted 1,3-bisketenes: A challenge for theory and experiment

Molecular structures of dimethylbis(trimethylsilylketyl)silane (Me₂Si[C(SiMe₃)CO]₂), dimethylbis(trimethylgermylketyl)silane (Me₂Si[C(GeMe₃)CO]₂), and dimethylbis(trimethylstannylketyl)germane (Me₂Ge[C(SnMe₃)CO]₂) have been studied in the gas phase by electron diffraction accompanied by high level ab initio and DFT calculations. Extensive theoretical conformational analyses of the molecules in the vapour predicted a possibility of existence of two types of conformers with small energy differences. The first type had gauche-gauche arrangements of the ketenyl groups in the central C(CO)XC(CO) fragments directed away from each other. The second type had nearly syn-gauche arrangements of the ketenyl groups. In addition, the energy differences were found to depend on the level of computations used. The experimental analysis, in turn, was unable to distinguish between different conformers due to the large number of similar overlapping distances. The experimental data were fitted by an averaged single-conformer model, which nevertheless allowed reliable determination of bonds and bonded angles in the molecules. Main experimental (r_h1) structural parameters for Me₂Si[C(SiMe₃)CO]₂, Me₂Si[C(GeMe₃)CO]₂, and Me₂Ge[C(SnMe₃)CO]₂, i.e. Me₂X[C(YMe₃)CO]₂ (X,Y = Si, Ge, Sn), are (X-C)_mean 187.7(1) pm, 194.6(2) pm, 216.1(3) pm; (Y-C)_mean, 187.7(1) pm, 188.8(8) pm, 194.6(4) pm; (CC)_mean, 135.3(5) pm, 131.6(5) pm, 131.5(13) pm; (CO)_mean, 117.0(7) pm, 117.4(7) pm, 119.0(11) pm; (C-H)_mean, 110.6(7) pm, 110.0(4) pm, 109.1(13) pm; (X(Y)-CC)_mean, 114.4(2)°, 115.6(1)°, 115.6(2)°; (C-X(Y)-C_Me)_mean, 108.3(3)°, 108.4(3)°, 108.9(13)°; C(2)-C(1)-Y(4)-C(10), −19(6)°, 5(4)°, −9(10)°; C(7)-C(6)-Y(9)-C(38),−22(7)°, −32(3)°, −9(10)°; C(2)-C(1)-X(5)-C(6), 128(4)°, 142(1)°, 108(9)°; C(7)-C(6)-X(5)-C(1), 92(6)°, 115(2)°, 108(9)°, respectively.     

Melatonin strongly interacts with zwitterionic model membranes—evidence from Fourier transform infrared spectroscopy and differential scanning calorimetry

Interactions of melatonin with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes (MLVs) were investigated as a function of temperature and melatonin concentration (1-30 mol%) by using two noninvasive techniques, namely Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The investigation of the C-H, CO, and PO₂⁻ antisymmetric double stretching modes in FTIR spectra and DSC studies reveal that melatonin changes the physical properties of the DPPC bilayers by decreasing the main phase transition temperature, abolishing the pretransition, ordering the system in the gel phase, and increasing the dynamics of the system both in the gel and liquid crystalline phases. It also causes significant decrease in the wavenumber for the CO stretching and PO₂⁻ antisymmetric double bond stretching bands, which indicates strong hydrogen bonding The results imply that melatonin locates in the interfacial region of the membrane. Furthermore, in the DSC curve, more than one signal is observed at high melatonin concentrations (24 and 30 mol%), which indicates melatonin-induced phase separation in DPPC membranes.     

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.     

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.     

Ruthenium hydride and vinyl complexes supported by nitrogen-oxygen mixed-donor ligands

The Schiff base, 2-chlorophenylsalicylaldimine (HL₁), is formed readily from salicylaldehyde and 2-chloroaniline. After deprotonation, this ligand is found to react as a bidentate mixed-donor chelate with the complexes [RuRCl(CO)(BTD)(PPh₃)₂] (R = H, CHCHC₆H₅, CHCHC₆H₄Me-4, CHCH^tBu, CCCPhCHPh; BTD = 2,1,3-benzothiadiazole) to form the compounds [RuR(L₁)(CO)(PPh₃)₂] through displacement of the chloride and BTD ligands. An analogous reaction occurs with the osmium complex [OsHCl(CO)(BTD)(PPh₃)₂] to provide [OsH(L₁)(CO)(PPh₃)₂]. The compound [Ru(CHCHC₆H₄Me-4)(L₂)(CO)(PPh₃)₂] is formed through reaction of salicylaldehyde (HL₂) with [Ru(CHCHC₆H₄Me-4)Cl(CO)(BTD)(PPh₃)₂] in the presence of base. Two further ligands were investigated to extend the study to encompass 5- and 4-membered chelates; 8-hydroxyquinoline (HL₃) and 2-hydroxy-4-methylquinoline (HL₄) react with [Ru(CHCHPh)Cl(CO)(BTD)(PPh₃)₂] and [Ru(CHCHC₆H₄Me-4)Cl(CO)(BTD)(PPh₃)₂] in the presence of base to yield the complexes [Ru(CHCHPh)(L₃)(CO)(PPh₃)₂] and [Ru(CHCHC₆H₄Me-4)(L₄)(CO)(PPh₃)₂], respectively. The crystal structure of [Ru(CHCHC₆H₄Me-4)(L₁)(CO)(PPh₃)₂] is reported.     

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.     

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.     

Polyunsaturated fatty acid-cholesterol interactions: Domain formation in membranes

Polyunsaturated fatty acids (PUFA) constitute an influential group of molecules that promote health by an as yet unknown mechanism. They are structurally distinguished from less unsaturated fatty acids by the presence of a repeating CH-CH₂-CH unit that produces an extremely flexible chain rapidly reorienting through conformational states. The most highly unsaturated case in point is docosahexaenoic acid (DHA) with 6 double bonds. This review will summarize how the high disorder of DHA affects the properties of the membrane phospholipids into which the PUFA incorporates, focusing upon the profound impact on the interaction with cholesterol. Results obtained with model membranes using an array of biophysical techniques will be presented. They demonstrate DHA and the sterol possesses a mutual aversion that drives the lateral segregation of DHA-containing phospholipids into highly disordered domains away from cholesterol. These domains are compositionally and organizationally the opposite of lipid rafts, the ordered domain enriched in predominantly saturated sphingolipids “glued” together by cholesterol that is believed to serve as the platform for signaling proteins. We hypothesize that DHA-rich domains also form in the plasma membrane and are responsible, in part, for the diverse range of health benefits associated with DHA.     

Switching between penta- and hexacoordination with salen-silicon-complexes

The reaction between phenyltrichlorosilane and the tetradentate ligands o-HO-C₆H₄-C(CH₃)N-(CH₂)_n-NC(CH₃)-o-C₆H₄-OH (n = 2, 3, 4), supported by an amine base, yields pentacoordinate silicon complexes (C₆H₅)Si-[o-O-C₆H₄-C(CH₃)N-(CH₂)_n-N-C(CH₂)-o-C₆H₄-O] with enamine functionalized ligands. This reaction pattern can be transferred onto various ligands of 2-iminomethylphenolate-type. The resulting pentacoordinate silicon complexes react with a variety of Brønsted acids HY to yield hexacoordinate salen silicon complexes (C₆H₅)(Y)Si-[o-O-C₆H₄-C(CH₃)N-(CH₂)_n-NC(CH₃)-o-C₆H₄-O] (Y = benzoate, picrate, 8-oxyquinolinate, 2-oxy-1,4-naphthoquinonate, p-tert-butylphenolate, (5-phenyltetrazol)-2-ide, fluoride, tetrafluoroborate). Hexacoordination of their Si-atoms was confirmed by ²⁹Si NMR spectroscopy and, in some cases, by X-ray crystal structure analysis. Examples for similarities and differences in the coordination behavior of the silicon atom and its heavier congeners (Ge, Sn) in the salen-type coordination sphere as well as data regarding the nucleophilicity of some of these novel enamine complexes are presented.     

Characterization of the three major polymorphic forms and liquid state of tristearin by Raman spectroscopy

Raman spectroscopy was used to distinguish the differences in the molecular organization of the α, β′ and β polymorphs, as well as the liquid state, of tristearin with focus placed on the CO, CH and CC Raman-active stretching regions. The ester carbonyl stretching region permitted polymorphic discrimination due to significant differences in the number of modes, their relative frequencies and their full-widths at half-maximum. In the liquid state, the absence of obvious signatures in this region indicated that many local micro-environments likely exist about the ester carbonyl of molten tristearin. The ratio between the symmetrical and asymmetrical CH stretching modes was linearly correlated with the enthalpy of fusion for each polymorph. The CC stretching modes, which provided insight into the trans/gauche content, were polymorph independent, but changed significantly upon transition into the liquid state (p < 0.05). Overall, Raman spectroscopy allowed for the quick discrimination of tristearin polymorphs from a conformational and thermodynamic perspective.     

A new cumulene diiron complex related to the active site of Fe-only hydrogenases and its phosphine substituted derivatives: synthesis, electrochemistry and structural characterization

A new cumulene diiron complex related to the Fe-only hydrogenase active site [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₆] (1) was obtained by treatment of (μ-LiS)₂Fe₂(CO)₆ with excess 1,4-dichloro-2-butyne. By controllable CO displacement of 1 with PPh₃ and bis(diphenylphosphino)methane (dppm), mono- and di-substituted complexes, namely [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₅L] (2: L = PPh₃; 3: L = dppm) and [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₄L₂] (4: L = PPh₃; 5: L = dppm) could be prepared in moderate yields. Treatment of 1 with bis(diphenylphosphino)ethane (dppe) afforded a double butterfly complex [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₅]₂(μ-dppe) (7). With dppm in refluxing toluene, a dppm-bridged complex [(μ-SCH₂C(S)CCH₂)Fe₂(CO)₄(μ-dppm)] (6) was obtained. These model complexes were characterized by IR, ¹H, ³¹P NMR spectra and the molecular structures of 1, 2 and 5-7 were determined by single crystal X-ray analyses. The electrochemistry of 1-3 was studied and the electrocatalytic property of 1 was investigated for proton reduction in the presence of HOAc.     

Synthesis and characterisation of isomeric cycloaurated complexes derived from the iminophosphorane Ph3PNC(O)Ph

Using different organomercury substrates, two isomeric cycloaurated complexes derived from the stabilised iminophosphorane Ph₃PNC(O)Ph were prepared. Reaction of Ph₃PNC(O)Ph with PhCH₂Mn(CO)₅ gave the manganated precursor (CO)₄Mn(2-C₆H₄C(O)NPPh₃), metallated on the C(O)Ph substituent, which yielded the organomercury complex ClHg(2-C₆H₄C(O)NPPh₃) by reaction with HgCl₂ in methanol. Transmetallation of the mercurated derivative with Me₄N[AuCl₄] gave the cycloaurated iminophosphorane AuCl₂(2-C₆H₄C(O)NPPh₃) with an exo PPh₃ substituent. The endo isomer AuCl₂(2-C₆H₄Ph₂PNC(O)Ph) [aurated on a PPh₃ ring] was obtained by an independent reaction sequence, involving reaction of the diarylmercury precursor Hg(2-C₆H₄P(NC(O)Ph)Ph₂)₂ [prepared from the known compound Hg(2-C₆H₄PPh₂)₂ and PhC(O)N₃] with Me₄N[AuCl₄]. Both of the isomeric iminophosphorane derivatives were structurally characterised, together with the precursors (2-HgClC₆H₄)C(O)NPPh₃ and (CO)₄Mn(2-C₆H₄C(O)NPPh₃). The utility of ³¹P NMR spectroscopy in monitoring reaction chemistry in this system is described.     

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.