The first evidence for a transient stibaallene ArSbCCR2

Dechlorofluorination of ArSb(F)-C(Cl)CR₂ (CR₂ = fluorenylidene, Ar = 2,4,6-tri-tert-butylphenyl) by tert-butyllithium afforded a 3,4-bis(fluorenylidene)-1,2-distibacyclobutane. The formation of the latter probably involves the transient stibaallene ArSbCCR₂ followed by a head-to-head dimerization via two SbC double bonds. Molecular orbital calculations at the ab initio and DFT levels support the head-to-head dimerization of ArSbCCR₂ with the formation of a 1,2-distibacyclobutane.     

Ferrole-type compounds containing thiophenic or thiepinic rings in the 3,4-positions of the metallacycle

The new ferrole Fe₂(CO)₆[μ-η²,η⁴-(Fc)CC{C(H)C(R)S}CC(SiMe₃)] [R = SiMe₃ (1) and R = Fc (2)] and ruthenoles Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(H)}CC(Fc)] 3 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC(SCCFc)C(H)C(Fc)] 4, have been obtained from the reactions of M₃(CO)₁₂ (M = Fe, Ru) and FcCCSCCSiMe₃ through S-C bond activations and C-C coupling reactions. Thermolysis of Ru₂(CO)₆[μ₃-η²,η⁴,η³-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃}Ru(CO)₃}CC(Fc)] alone and in the presence of HCCFc, yielded the compounds Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)}CC(Fc)] 5 and Ru₂(CO)₆[μ-η²,η⁴-(Me₃Si)CC{SC(Fc)C(SCCSiMe₃)C(H)C(Fc)}CC(Fc)] 6, respectively. The crystal structures of the compounds 1, 3, 4 and 6 are reported.     

Protonation of manganese phosphonioallenyl complexes

The addition of phosphines to the manganese allenylidene complexes Cp(CO)₂MnCCC(Ph)R (R = H, Ph) proceeds selectively at the C_α atom to result in the α-phosphonioallenyl complexes Cp(CO)₂Mn⁻-C(⁺PR₃¹)CC(Ph)R. The protonation of the latter affords the η²-(1,2)-phosphonioallenes Cp(CO)₂Mn{η²-(1,2)-HC(⁺PR₃¹)CC(Ph)R}, rather than the phosphoniovinylcarbenes Cp(CO)₂MnC(⁺PR₃¹)-HCC(Ph)R. All complexes obtained are stereochemically rigid and do not isomerize into the η²-(2,3)-phosphonioallene isomers.     

Oxidatively induced reactions of a diimine platinum(IV) tetramethyl complex

The oxidation of the Pt(IV) tetramethyl complex [ArNCHCHNAr]PtMe₄ (Ar = 2,6-Me₂C₆H₃) has been investigated in acetonitrile and dichloromethane. Cyclic voltammetry demonstrates that the irreversible oxidation of [ArNCHCHNAr]PtMe₄ occurs at a slightly less positive oxidation potential than the irreversible oxidation of the analogous Pt(II) species [ArNCHCHNAr]PtMe₂. The product distribution arising from the oxidation depends strongly on the reaction conditions and includes cationic Pt(IV) species (acetonitrile, dichloromethane solvents) and Pt(II) species (dichloromethane only). Evidence is presented that suggests that homolytic cleavage of a weakened PtC bond in is involved in the oxidatively induced reactions.     

Further reactions of some bis(vinylidene)diruthenium complexes

Whereas {Ru(dppm)Cp*}₂(μ-CCCC) (2) is the only product formed by deprotonation of [{Ru(dppm)Cp*}₂{μ(CCHCHC)}]⁺ with dbu, a mixture of 2 with Ru{CCCHCH(PPh₂)₂[RuCp*]}(dppm)Cp* (3) and {Cp*Ru(PPh₂CHCCH-)}₂ (4) is obtained with KOBu^t. A similar reaction with [{Ru(dppm)Cp*}₂{μ(CCMeCMeC)}]⁺ (5) gave Ru{CCCMeCH(PPh₂)₂[RuCp*]}(dppm)Cp* (6). X-ray structures of 4, 5 and 6 confirm the presence of the 1-ruthena-2,4-diphosphabicyclo[1.1.1]pentane moiety, which is likely formed by an intramolecular attack of the deprotonated dppm ligand on C(1) of the vinylidene ligand. Protonation of {Ru(dppe)Cp*}₂(μ-CCCC) (8-Ru) regenerates its precursor [{Ru(dppe)Cp*}₂{μ(CCHCHC)}]²⁺ (7-Ru). Ready oxidation of the bis(vinylidene) complex affords the cationic carbonyl [Ru(CO)(dppe)Cp*]PF₆ (9) (X-ray structure).     

Nickel alkynyl and allenylidene complexes: Synthesis and properties

Copper-catalyzed reaction of [Cp(PPh₃)NiCl] with the terminal alkynes H-CC-C(O)R (R = O-Menthyl, NMe₂, Ph) yields the alkynyl complexes [Cp(PPh₃)Ni-CC-C(O)R]. Subsequent O-methylation with either [Me₃O]BF₄ or MeSO₃CF₃ affords cationic allenylidene complexes, [Cp(PPh₃)NiCCC(OMe)R]⁺X¯ (X = BF₄, SO₃CF₃). N-Alkylation of Cp(PPh₃)Ni-pyridylethynyl complexes likewise gives cationic allenylidene complexes. [Cp(PPh₃)Ni-CC-C(CH)₄N] adds BF₃ at nitrogen. Modification of the ligand sphere in these nickel allenylidene complexes is possible by replacing PPh₃ by PMe₃ in the alkynyl complex precursors. The first allenylidene(carbene)nickel cation, [Cp(SIMes)NCCC(OMe)NMe₂]⁺, is accessible by successive reaction of [Cp(SIMes)NiCl] with H-CC-C(O)NMe₂ and [Me₃O]BF₄. By the analogous sequence an allenylidene complex containing the chelating (diphenylphosphanyl)ethylcyclopentadienyl ligand can be prepared. DFT Calculations were carried out on the allenylidene complex cation [Cp(PPh₃)NiCCC(OMe)NMe₂]⁺ and on its precursor, the alkynyl complex [Cp(PPh₃)Ni-CC-C(O)NMe₂]. Based on the spectroscopic data and a X-ray structure analysis the bonding in the new nickel allenylidene complexes is best represented by several resonance forms, an alkynyl resonance form considerably contributing to the overall bond.     

Organometallic chemistry and catalysis on gold metal surfaces

As in transition metal complexes, CN-R ligands adsorbed on powdered gold undergo attack by amines to give putative diaminocarbene groups on the gold surface. This reaction forms the basis for the discovery of a gold metal-catalyzed reaction of CN-R, primary amines (R′NH₂) and O₂ to give carbodiimides (R′-NCN-R). An analogous reaction of CO, RNH₂, and O₂ gives isocyanates (R-NCO), which react with additional amine to give urea (RNH)₂CO products. The gold-catalyzed reaction of CN-R with secondary amines (HNR′₂) and O₂ gives mixed ureas RNH(CO)NR′₂. In another type of gold-catalyzed reaction, secondary amines HN(CH₂R)₂ react with O₂ to undergo dehydrogenation to the imine product, RCHN(CH₂R). Of special interest is the high catalytic activity of gold powder, which is otherwise well-known for its poor catalytic properties.     

Further chemistry of ruthenium butatrienylidene complexes

Several complexes have been obtained from reactions carried out in early attempts to prepare the diynyl complexes Ru(CCCCR)(dppe)Cp* (R = H, SiMe₃). These have been identified crystallographically as the acyl complex Ru{CCC(O)Me}(dppe)Cp* (3), the cationic imido complex [Ru{CCC(NH₂)Me}(dppe)Cp*]PF₆ (4), the binuclear butenynylallenylidene [{Ru(dppe)Cp*}₂{μ-CCC(OMe)CHCMeCC}]PF₆ (5), and the bis(ethynyl)cyclobutenylidene [{Ru(dppe)Cp*}₂{μ-CCC₄H₂(SiMe₃)CC}]PF₆ (6). NMR studies of 5 have revealed the existence of two isomers. Plausible routes for their formation from the putative butatrienylidene intermediate [Ru(CCCCH₂)(dppe)Cp*]⁺ (A) are discussed.     

Formation of a cyclobutenylidene by cyclo-addition of an alkynyl-ruthenium complex to a cyano(alkynyl)ethene

In contrast to the usual formal [2+2]-cycloaddition reaction, (NC)₂CC{CC(SiPrⁱ₃)}₂, containing bulky alkynyl substituents, reacts with Ru(CCPh)(PPh₃)₂Cp to give the unprecedented cyclobutenylidene complex Ru{C(CN)₂C[CC(SiPrⁱ₃)]CC(SiPrⁱ₃)CPhC}(PPh₃)Cp, formed by addition of one of the CC(SiPrⁱ₃) groups to the Ru-CCPh moiety and subsequent electronic reorganisation.     

Rh(II)-Cp-TsDPEN catalyzed aqueous asymmetric transfer hydrogenation of chromenones into saturated alcohol: CC and CO reduction in one step

As an efficient catalyst for asymmetric transfer hydrogenation reaction (ATH reaction) of α,β-unsaturated ketones, Rh-Cp^∗-TsDPEN (Cp^∗ = 1,2,3,4,5-pentamethylcyclopenta-1,3-diene, TsDPEN = N-(p-toluenesulfonyl)-1,2-diphenyl- ethylenediamine) shows high chemoselectivity on CO and CC reduction. In our method, both CO and CC bonds in a variety of chromenone derivatives were reduced efficiently in aqueous media, resulting in at least 98% ee and up to 99% yields in a convenient way without further purification. The product was a useful intermediate for deriving chiral chroman-4-amine, which was reported as an effective agent against hypotension and inflammatory pain by inhibiting human bradykinin B1 receptor.     

A ruthenium(II) allenylidene complex with a 4,5-diazafluorene functional group: A new building-block for organometallic molecular assemblies

The synthesis of the new ruthenium(II) allenylidene complex [ClRu(dppe)₂CCC₁₁H₆N₂][OTf] (4) (dppe = 1,2-bis(diphenylphosphino)ethane) terminated with a 4,5-diazafluorene ligand is reported. Further coordination of that metal allenylidene to ruthenium and rhenium moieties leads to the bimetallic adducts [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(bpy)₂}][B(C₆F₅)₄]₃ (5a), [ClRu(dppe)₂CCC₁₁H₆N₂{Ru(^tBu-bpy)₂}][PF₆]₃ (5b) and [ClRu(dppe)₂CCC₁₁H₆N₂{Re(CO)₃Cl}][OTf] (6). Their optical and electrochemical properties show that the allenylidene moiety is an attractive molecular clip for the access to larger original redox-active homo/heteronuclear multi-component supramolecular assemblies. The X-ray crystal structure of the allenylidene metal building block is also described.     

Preparation of E-(1,2-difluoro-1,2-ethenediyl)bis(tributylstannane)

Chlorotrifluoroethene is converted in situ to [F₂CCFSiMe₃]. The crude [F₂CCFSiMe₃] solution is reduced with lithium aluminum hydride to (HFCCFSiMe₃), which (without isolation) is converted to (Z)-HFCCFSnBu₃. Subsequent metallation and trapping of the vinyllithium reagent with Bu₃SnCl gives (E)-Bu₃SnCFCFSnBu₃ in 73% overall yield. Only two isolation steps are required and the use of Me₃SiCl and F₂CCFCl provides a cheap, economical route to this useful synthon.     

Reactions of β-alkoxyvinyl trihalogenomethyl ketones with triethyl phosphite

The Perkow reaction of triethyl phosphite and β-alkoxyvinyl trihalogenomethyl ketones, which have common acyclic or cyclic structural fragment: -O-CC-C(O)CX₂Cl, yielded dienyl phosphates: -O-CC-C[OP(O)(OEt)₂]CX₂ where X = F or Cl, whereas γ-bromo-β-methoxy-α,β-unsaturated trifluoromethyl ketone CF₃C(O)CHC(OMe)CH₂Br gave diene CF₃C[OP(O)(OEt)₂]CH-C(OMe)CH₂.     

Thermal gas-phase reaction of perfluorobuta-1,3-diene with NO2

The reaction of NO₂ with perfluorobuta-1,3-diene, CF₂CFCFCF₂ (C₄F₆), has been studied at 312.9, 323.0, 333.4, 396.0 and 418.0 K, using a conventional static system. The products formed in the temperature range 312.9-333.4 K were CF₂CFCF(NO₂)CF₂(NO₂) (I), CF₂(NO₂)CFCFCF₂(NO₂) (II), CF₂CFCF(NO₂)C(O)F (III) and CF₂(NO₂)CFCFC(O)F (IV) and FNO. The formation of these compounds was detected performing infrared and Raman spectra. The infrared spectrum shows a band at 1785 cm⁻¹, characteristic to the terminal -CFCF₂ group and the Raman spectrum shows a band located at 1733 cm⁻¹, corresponding to -CFCF- group. It indicates, that in this temperature range, NO₂ attacks initially only one double bound of CF₂CFCFCF₂. Since the intermediate radical CF₂CFCFCF₂(NO₂) formed in this process is allylic in nature, so there is no isomerization involved in this process, but rather the allylic radical is able to add the second NO₂ either to CF₂ or CFCF₂(NO₂) end, forming the corresponding products. At 396.0 and 418.0 K different products were observed: CF₂(NO₂)CF(NO₂)C(O)F (V), NO, CF₃C(O)F, C(O)F₂ and traces of epoxide of tetrafluoroethene, showing that, at these temperatures, both double bonds are attacked by NO₂ and detachment of CF₂ group is produced. The mechanisms consistent with experimental results in the temperature range 312.9-333.4 and at 396.0 and 418 K are proposed.     

Synthesis and properties of conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains

A versatile synthetic route to conjugated bimetallic ruthenium complexes with σ,σ-bridging azobenzene chains was developed, and new ruthenium complexes with various ligands were synthesized and characterized. These bimetallic complexes showed a remarkable absorption in the visible region (λ_max: 452-483 nm), and undergo trans-to-cis isomerization under UV light irradiation for short time. Electrochemical study showed that the metal centers in bimetallic complexes containing the CHCHC₆H₄NNC₆H₄CHCH bridge interact with each other.     

Towards understanding monomer coordination in atom transfer radical polymerization: synthesis of [Cu(PMDETA)(π-M)][BPh4] (M = methyl acrylate, styrene, 1-octene, and methyl methacrylate) and structural studies by FT-IR and H NMR spectroscopy and X-ray crystallography

Cu^I complexes of the form [Cu^I(PMDETA)(π-M)][BPh₄] (where PMDETA = N,N,N′,N″,N″-pentamethyldiethylenetriamine, and M = vinyl monomer) were synthesized and isolated from solution as crystals with methyl acrylate (MA), styrene (Sty), and 1-octene (Oct). The interaction of the CC double bond of the vinyl monomer with Cu^I was characterized via FT-IR and ¹H NMR spectroscopy and single crystal X-ray crystallography. A fourth complex with methyl methacrylate (MMA) was synthesized and characterized spectroscopically, but no crystals suitable for X-ray structure analysis could be obtained. In all complexes, PMDETA acts as a tridentate ligand, while the pseudotetrahedral coordination geometry around Cu^I is completed by a π-interaction with the CC double bond of M in the presence of a non-coordinating counter-ion. A decrease in CC IR stretching frequencies of Δν(CC) = −110, −80, −109, and −127 cm⁻¹ for complexes with MA, Sty, Oct, and MMA, respectively, was observed upon coordination. No significant change in CC bond length was seen in the crystal structure for complexes with MA and Oct while a slight lengthening was observed for the Sty complex. The upfield shift of the vinyl proton resonances indicated the presence of significant π-back-bonding.     

Differentiation of isomeric allylic alkenyl methyl ethers by Raman spectroscopy

The Raman spectra of several pairs of alkenyl methyl ethers of general structure R¹R²CCR⁵C(R³R⁴)OCH₃ and R¹R²C(OCH₃)C(R⁵)CR³R⁴ (R¹, R², R³, R⁴, R⁵ = H or C_nH_2n+1, n = 1-3) are reported and discussed, with a view to establishing whether Raman spectroscopy offers a viable means of distinguishing between these isomeric unsaturated species. Key bands associated with the ν(sp₂CH) and ν(CC) stretching modes are found to be particularly useful in this connection: R¹R²CCHCH₂OCH₃ and R¹R²C(OCH₃)CHCH₂ ethers (R¹, R² = CH₃, C₂H₅) are easily distinguished on this basis. Differentiation of their lower homologues, R¹CHCHCH₂OCH₃ and R¹CH(OCH₃)CHCH₂ (R¹ = CH₃, C₂H₅, C₃H₇), by similar means is also quite straightforward, even in cases where cis and trans isomers are possible. Pairs of isomeric ethers, such as CH₃CHC(CH₃)CH₂OCH₃ and CH₃CH(OCH₃)C(CH₃)CH₂, in which the structural differences are more subtle, may also be distinguished with care. Deductions based on bands ascribed to the stretching vibrations are usually confirmed by consideration of the signals associated with the corresponding δ(sp₂CH) deformation vibrations. Even C₂H₅CHCHCH(C₃H₇)OCH₃ and C₃H₇CHCHCH(C₂H₅)OCH₃ are found to have distinctive Raman spectra, but differentiation of these closely related isomers requires additional consideration of the low wavenumber region.     

Bis(amino)allenylidene complexes by displacement of the MeO group in methoxy allenylidene complexes of chromium and tungsten. Synthesis, DFT calculations and solid-state structures of new bis(amino)allenylidene complexes

Pentacarbonyl dimethylamino(methoxy)allenylidene tungsten, [(CO)₅WCCC(OMe)NMe₂] (1b), reacts with one equivalent of primary amines, H₂NR, by selectively replacing the methoxy group to give dimethylamino(amino)allenylidene complexes, [(CO)₅WCCC(NHR)NMe₂]. When the amine is used in excess both terminal groups, OMe as well as NMe₂, are replaced by the primary amino group giving [(CO)₅WCCC(NHR)₂ ]. The NHR substituent in these complexes may be modified by deprotonation with LDA followed by alkylation. The replacement of the methoxy group in 1b by a secondary amino group, NR₂, can be achieved by a stepwise process. Addition of Li[NR₂] to the C_γ atom of 1b affords an alkynyl tungstate. Subsequent OMe⁻ elimination induced by TMS-Cl/SiO₂ yields the allenylidene complexes [(CO)₅WCCC(NR₂)NMe₂]. When bidentate diamines are used instead of monoamines both substituents, OMe and NMe₂, are replaced and allenylidene complexes are formed in which C_γ constitutes part of a 5-, 6-, or 7-membered heterocycle. The reaction of [(CO)₅CrCCC(OMe)NMe₂] (1a) with diethylene triamine affords an allenylidene complex with a heterocyclic endgroup carrying a dangling CH₂CH₂NH₂ substituent. All reactions follow a strict regioselective attack of the nucleophile at C_γ and proceed with good to excellent yields. The addition of N-H to the C_αC_β bond is not observed. By applying either one of these routes nearly any substitution pattern in bis(amino)allenylidene complex can be realized.     

The reactions of some σ-alkynylnickel complexes with 7,7,8,8-tetracyanoquinodimethane

The σ-alkynyl complexes Ni(η⁵-C₅H₅)(PPh₃)-CC-R (1), Ni(η⁵-C₅H₅)(PPh₃)-CC-X-CCH (2) and Ni(η⁵-C₅H₅)(PPh₃)-CC-X-CC-Ni(η⁵-C₅H₅)(PPh₃) (3), reactwith 7,7,8,8-tetracyanoquinodimethane, TCNQ, at 30 °C by insertion of the alkyne CC into a CC(CN)₂ bond to give Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}-C{C(CN)₂}-R (4), from 1, Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}-C{C(CN)₂}-X-CCH (5), from 2, and Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}-C{C(CN)₂}-X-CC-Ni(η⁵-C₅H₅)(PPh₃) (6),and Ni(η⁵-C₅H₅)(PPh₃)-C{C₆H₄C(CN)₂}- C{C(CN)₂}-X-C{C(CN)₂}-C{C₆H₄C(CN)₂}-Ni(η⁵-C₅H₅)(PPh₃) (7),from 3 {R = (a) C₆H₅, (b) 4-PhC₆H₄, (c) 4-Me₂NC₆H₄, (d) 1-C₁₀H₇ (1-naphthyl), (e) 2-C₁₀H₇ (2-naphthyl), (f) 9-C₁₄H₉ (9-phenanthryl), (g) 9-C₁₄H₉ (9-anthryl), (h) 3-C₁₆H₉ (3-pyrenyl), (i) 1-C₂₀H₁₁ (1-perylenyl), (j) 2-C₄H₃S (2-thienyl), (k) C₁₀H₉Fe (ferrocenyl = Fc) and (l) H; X = (a) nothing, (b) 1,4-C₆H₄, (c) 1,3-C₆H₄ and (d) 4,4′-C₆H₄-C₆H₄}. The reaction is regiospecificand the other possible insertion product, R-C{C₆H₄C(CN)₂}-C{C(CN)₂}-Ni(η⁵-C₅H₅)(PPh₃) etc., is not formed. Under the same conditions, there is no evidencefor the reaction of TCNQ with the -CCH of 2, PhCCH, 1,4-C₆H₄(CCH)₂ or FcCCH, or for the reaction of more than one CC(CN)₂ of TCNQ with a Ni-alkynyl moiety. Complexes 4-7 are all air-stable, purple solids which have been characterised by elemental analysis and spectroscopy (IR, UV-Vis, ¹H NMR and ¹³C NMR),and by X-ray diffraction for 4a, 4b and 4l. The UV-Vis spectra of 4-7 are very similar. This implies that all contain the same active chromophore which, it is suggested, is Ni-C(5)C₆H₄C(CN)₂ and not R-C(4)C(CN)₂. This isconsistent with the molecular structures of 4a, 4b and 4l which show that the first of these potentially chromophoric fragments is planar or close to it with an in-built potential for delocalisation, whilst in the second the aryl group R is almost orthogonal to the CC(CN)₂ plane. The molecular structures of 4a, 4b and 4l also reveal a short Ni?C(4) separation, indicative of a Ni → C(4) donor-acceptor interaction. The electrochemistry of 4a shows aquasi reversible oxidation at ca. 1 V and complicated reduction processes. It is typical of most 4, but 4l is different in that it shows the same quasi reversible oxidation at ca. 1 V but two reversible reductions at −0.26 and −0.47 V (vs. [Fe(η⁵-C₅Me₅)₂]^+/0 0.0 V).