Selective oxidation of aromatic primary alcohols to aldehydes using molybdenum acetylide oxo-peroxo complex as catalyst

Selective oxidation of various aromatic alcohols to aldehydes has been carried out with very high conversion (90%) and selectivity (90%) for aldehydes using cyclopentadienyl molybdenum acetylide complex, CpMo(CO)₃(CCPh) (1) as catalyst and hydrogen peroxide as environmentally benign oxidant. Water-soluble Mo acetylide oxo-peroxo species is formed in situ after reaction of 1 with aqueous hydrogen peroxide during the course of reaction as catalytically active species. Interestingly even though the catalyst is homogeneous it could be recycled very easily by separating the products in organic phase and catalyst in aqueous phase using separating funnel. Even after five recycles no appreciable loss in alcohol conversion and aldehyde selectivity was observed.     

Stannylation of unsaturated carbon-carbon bonds by tin tetrachloride

The reactions of tin tetrachloride and four terminal alkynes (PhCCH, ^tBuCCH, ⁿBuCCH, HOCH₂CCH), norbornene, and norbornadiene in dichloromethane or chloroform solution lead to the formation of stannylation products, which were characterized by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. Virtually complete α-regioselectivity was obtained in reaction of all four alkynes without any effect of the relative steric bulk of the substituent R at the triple bond of alkyne RC_βC_αH. The reaction of norbornene and norbornadiene with SnCl₄ is stereoselective, giving an exo stannylation product.     

Evolution of lowest singlet and triplet excited states with transition metals in group 10-12 metallaynes containing biphenyl spacer

A new series of thermally stable group 10 platinum(II) and group 12 mercury(II) poly-yne polymers containing biphenyl spacer trans-[-Pt(PBu₃)₂CC(p-C₆H₄)₂CC-]_n and [HgCC(p-C₆H₄)₂CC-]_n were prepared in good yields by Hagihara’s dehydrohalogenation reaction of the corresponding metal chloride precursors with 4,4′-diethynylbiphenyl HCC(p-C₆H₄)₂CCH at room temperature. We report the optical spectroscopy of these polymetallaynes and compare the results with their bimetallic model complexes trans-[Pt(Ph)(PEt₃)₂CC(p-C₆H₄)₂CCPt(Ph)(PEt₃)₂] and [MeHgCC(p-C₆H₄)₂CCHgMe] as well as the group 11 gold(I) counterpart [(PPh₃)AuCC(p-C₆H₄)₂CCAu(PPh₃)]. The structural properties of all model complexes have been studied by X-ray crystallography. The influence of the heavy metal atom in these metal alkynyl systems on the intersystem crossing rate and the spatial extent of lowest singlet and triplet excitons is systematically characterized. Our investigations indicate that the organic triplet emissions can be harvested by the heavy-atom effect of group 10-12 transition metals (viz., Pt, Au, and Hg) which enables efficient intersystem crossing from the S₁ singlet excited state to the T₁ triplet excited state.     

Synthesis, structures and some reactions of Ru(CCCCFc)(PP)Cp (PP = dppm, dppe) and related compounds

The compounds Ru(CCCCFc)(PP)Cp [PP = dppe (1), dppm (2)], have been obtained from reactions between RuCl(PP)Cp and FcCCCCSiMe₃ in the presence of KF (1) or HCCCCFc and K[PF₆] (2), both with added dbu. The dppe complex reacts with Co₂(CO)₆(L₂) [L₂ = (CO)₂, dppm] to give 3, 4 in which the Co₂(CO)₄(L₂) group is attached to the outer CC triple bond. The PPh₃ analogue of 3 (5) has also been characterised. In contrast, tetracyanoethene reacts to give two isomeric complexes 6 and 7, in which the cyano-olefin has added to either CC triple bond. The reaction of RuCl(dppe)Cp with HCCCCFc, carried out in a thf/NEt₃ mixture in the presence of Na[BPh₄], gave [Ru{CCC(NEt₃)CHFc}(dppe)Cp]BPh₄ (8), probably formed by addition of the amine to an (unobserved) intermediate butatrienylidene [Ru(CCCCHFc)(dppe)Cp]⁺. The reaction of I₂ with 8 proceeds via an unusual migration of the alkynyl group to the Cp ring to give [RuI(dppe){η-C₅H₄CCC(NEt₃)CHFc}]I₃ (9). Single-crystal X-ray structural determinations of 1, 2 and 4-9 are reported.     

Synthesis, spectroscopy, structures and photophysics of metal alkynyl complexes and polymers containing functionalized carbazole spacers

A new class of soluble and thermally stable group 10 platinum(II) poly-yne polymers functionalized with 9-arylcarbazole moiety trans-[-Pt(PBu₃)₂CCRCC-]_n (R = 9-arylcarbazole-3,6-diyl; aryl = p-methoxyphenyl, p-chlorophenyl) were prepared in good yields by the polycondensation polymerization of trans-[PtCl₂(PBu₃)₂] with HCCRCCH under ambient conditions. The optical absorption and emission properties of these polymetallaynes were investigated and compared with their bimetallic molecular model complexes trans-[Pt(Ph)(PEt₃)₂CCRCCPt(Ph)(PEt₃)₂] as well as their group 11 gold(I) and group 12 mercury(II) neighbors [(PPh₃)AuCCRCCAu(PPh₃)] and [MeHgCCRCCHgMe]. The structures of all the compounds were confirmed by spectroscopic methods and by X-ray crystallography for selected model complexes. The influence of the heavy metal atom and the 9-aryl substituent of carbazole on the evolution of lowest electronic singlet and triplet excited states is critically characterized. It was shown that the organic-localized phosphorescence emission can be triggered readily by the heavy-atom effect of group 10-12 transition metals (viz., Pt, Au, and Hg) with the emission efficiency generally in the order Pt > Au > Hg. These carbazole-based organometallic materials possess high-energy triplet states of 2.68 eV or higher which do not vary much with the substituent of 9-aryl group.     

Highly stereoselective and efficient synthesis of ω-heterofunctional di- and trienoic esters for Horner-Wadsworth-Emmons reaction via alkyne hydrozirconation and Pd-catalyzed alkenylation

In situ OH metalation with ⁱBu₂AlH and hydrozirconation with HZrCp₂Cl of HOCH₂CCH, (E)-HOCH₂CHCHCCH, and HOCH₂CCCH₃ followed by Pd-catalyzed alkenyl-alkenyl coupling with (E)-BrCHCHCO₂Et and (E)-BrCHC(Me)CO₂Et using PEPPSI-IPr (7) as a catalyst provides a highly efficient and selective (?98% all-E) route to ω-hydroxy di- and trienoic acid esters (1a-6a). The corresponding phosphonate esters (1c-4c) of ?98% isomeric purity can be obtained via conventional bromination-phosphonation in >80% yields. As expected, their carbonyl olefination is ca. 85-90% E-selective with alkyl aldehydes but ?98% E-selective with PhCHO and some α,β-unsaturated aldehydes under the conditions used.     

Polymetallation of alkenes: Formation of some complexes containing branched chain carbon-rich ligands

Reactions of {(Ph₃P)AuCC}₂CC{CCAu(PPh₃)}₂ (1b), with Co₃(μ-CBr)(μ-dppm)_n(CO)_9−2n (n = 0, 1) result in complete or partial elimination of AuBr(PPh₃) to give the complexes {(OC)₉Co₃-μ₃-CCC}₂CC{CC-μ₃-CCo₃(CO)₉}₂ (3), trans-{(OC)₇(μ-dppm)Co₃-μ₃-CCC}(HCC)CC{CCAu(PPh₃)}{CC-μ₃-CCo₃(μ-dppm)(CO)₇} (4), {(OC)₇(μ-dppm)Co₃-μ₃-CCC}₂CC(CCH){CC-μ₃-CCo₃(μ-dppm)(CO)₇} (5) and {(OC)₇(μ-dppm)Co₃-μ₃-CCC}₂CC{CCAu(PPh₃)}{CC-μ₃-CCo₃(μ-dppm)(CO)₇} (6), which have been identified by spectroscopic methods and in the cases of 3, 4 and 5, by single-crystal X-ray diffraction methods.     

A DFT study on the mechanism of the gas phase reaction of ground-state Y (4d5s,D) with 2-butyne

The reaction of ground-state Y with 2-butyne has been investigated in detail using B3LYP method. Four pathways for elimination of H₂ were identified. Two isomers, Y(HCCC)CH₃ and Y(H₂CCCCH₂) were assigned to the observed product, YC₄H₄. The calculated PESs suggest that the concerted H₂-elimination leading to Y(H₂CCCCH₂) + H₂ product is the most favorable pathway. For the elimination of CH₃, combining the results of this work with our previous study on Y + propyne reaction, a general mechanism for the reactions of Y with 2-alkynes bearing RCCCH₃ structure was established: Y + RCCCH₃ → π-complex → TS(H-migration) → HY(CH₂CC)R → TS (CC insertion) → (CH₂)HYCCR → TS(H-migration) → H₃CYCCR → CH₃ + YC₂R. Such mechanism was found to be always energetically more favorable than the direct sp–sp³ CC bond insertion mechanism. Further, such mechanism can also be applied to the elimination of CH₄ and it can be described as: Y + CH₃CCCH₃ → π-complex → TS (H-migration) → HY(H₂CCC)CH₃ → TS(CC insertion) → (H₂CCC)HYCH₃ → TS(H-migration) → CH₄ + YC₃H₂.     

Solvent and phosphine dependency in the reaction of cis-RuCl2(P-P)2 (P-P = dppm or dppe) with terminal alkynes

Reaction of cis-[RuCl₂(dppm)₂] (dppm = 1,2-bis(diphenylphosphino)methane) with PhCCH and NaPF₆ utilising methanol as solvent results in the formation of the η³-butenynyl complex [Ru(η³-PhCCCCHPh)(dppm)₂][PF₆] in good yield. Similar reactions with Bu^tCCH and PrⁿCCH resulted in the corresponding alkyl-substituted complexes and all three of these compounds have been characterised by NMR spectroscopy and X-ray crystallography. The mechanism of this reaction has been probed by employing labelling experiments with both PhCCD and PhC¹³CH allowing the identity of possible intermediates in the reaction to be determined. Furthermore, [Ru(η³-PhCCCCHPh)(dppm)₂][PF₆] has been shown to be an effective regio- and stereo-selective catalyst for the dimerisation of PhCCH to Z-PhCCCHCHPh in the absence of solvent. In contrast, no evidence for the formation of alkyne coupling was obtained from the reaction of cis-[RuCl₂(dppe)₂] (dppe = 1,2-bis(diphenylphosphino)ethane) with PhCCH and NaPF₆.     

Cross-coupling reactions of gold(I) alkynyl and polyyndiyl complexes

Gold(I) alkynyl complexes are shown to efficiently couple with aryl iodides under mild conditions in the presence of both Pd(II) and Cu(I) co-catalysts. The reaction is not gold catalysed, but rather the Au(I) centre serves to transfer the alkynyl moiety to Cu(I), which then enters the conventional Sonogashira cycles. Using this method, a small range of 1,4-disubstituted diynes, including examples of differentially substituted compounds ArCCCCAr′, have been prepared directly from [(Ph₃P)AuCCCCAu(PPh₃)] and aryl iodides ArI.     

Some complexes containing Pt-C5-Co3 fragments: Molecular structure of trans-Pt{CCCC-μ3-C[Co3(μ-dppm)(CO)6(PPh3)]}2(PPh3)2 determined using synchrotron radiation

Reactions of platinum(II) chloro-phosphine complexes with Co₃(μ₃-CCCCCSiMe₃)(μ-dppm)(CO)₇ in the presence of NaOMe have given the compounds Pt{CCCC-μ₃-C[Co₃(μ-dppm)(CO)₇]}₂(dppe) (1), trans-Pt{CCCC-μ₃-C[Co₃(μ-dppm)(CO)₇]}₂(PEt₃)₂ (2) and trans-Pt{CCCC-μ₃-C[Co₃(μ-dppm) (CO)₆(PPh₃)]}₂(PPh₃)₂ (3), each of which contains two Co₃ clusters linked by C₅ chains to the Pt centre. Electrochemical studies (CVs) show the presence of both oxidation and reduction processes, the latter probably occurring on the CCo₃ cores. Ready reductive elimination of {Co₃(μ-dppm)(CO)₇}₂(μ₃:μ₃-C₁₀) occurs from 1 upon heating. The X-ray study of 3 was carried out using synchrotron radiation (Advanced Photon Source, Argonne, IL) to confirm its structure.     

Photochemical reactions of 1-ferrocenyl-4-phenyl-1,3-butadiyne with Fe(CO)5 and CO

Photolysis of a hexane solution containing ironpentacarbonyl, 1-ferrocenyl-4-phenyl-1,3-butadiyne at low temperature yields six new products: [Fe(CO)₂{η²:η²-PhCCCC(Fc)C(CCPh)C(Fc)Fe(CO)₃}-μ-CO] (1), [Fe₂(CO)₆{μ-η¹:η¹:η²:η²-PhCCCC(Fc)-C(O)-C(Fc)CCCPh}] (2), [Fe₂(CO)₆{μ-η¹:η¹:η²:η²-FcCC(CC Ph)-C(O)-C(Fc)CCCPh}] (3), [Fe₂(CO)₆{μ-η¹:η¹:η²:η²-FcCCCC(Fc)-C(O)-C(Fc)CCCPh}] (4), [Fe(CO)₃{μ-η²: η²-[FcCC(CCPh)C(CCPh)C(Fc)}CO] (5) and [Fe(CO)₃{μ-η²: η²-[FcCC(CCPh)C(CCPh)C(Fc)}CO] (6) formed by coupling of acetylenic moieties with CO insertion on metal carbonyl support. In presence of CO, formation of another new product 2,5-bis(ferrocenyl)-3,6-bis(tetracarbonylphenylmaleoyliron)quinone (7) was observed which on further reaction with ferrocenylacetyene gave the quinone, 2,5-bis(ferrocenyl)-3,6-bis(ethynylphenyl)quinone (8). Structures of 1-5 and 8 were established crystallographically.     

Synthesis of a novel one-handed helical poly(phenylacetylene) bearing poly(l-lactide) side chains

The living ring-opening polymerization of l-lactide was carried out by using organocatalyst to synthesize the molecular weight controlled poly(l-lactide) with an phenylacetylenyl end group (HCCPLLA), then the homopolymerization of HCCPLLA was performed by using two different rhodium catalysts. Low molecular weight poly-PLLA₆-1 (M_w,SEC-MALLS = 46,700) was synthesized by using Rh(nbd)BPh₄ as the catalyst, and higher molecular weight poly-PLLA₆-2 (M_w,SEC-MALLS = 471,000) was synthesized by using the [Rh(nbd)Cl]₂/Et₃N catalyst system. Then high molecular weight poly-PLLA₂₀, poly-PLLA₂₉, and poly-PLLA₆₈ were successfully synthesized by using the [Rh(nbd)Cl]₂/Et₃N catalyst system. The α values of the poly-PLLAs using [Rh(nbd)Cl]₂/Et₃N catalyst system were all in the range of 0.6–0.8, this means that these polymers possess linear flexible chain. It is concluded that [Rh(nbd)Cl]₂/Et₃N was more suitable for the synthesis of the cylindrical polymer brush, poly-PLLA with high molecular weight. The analyses of the CD spectra indicated that poly-PLLA possesses a predominantly one-handed helical conformation, temperature and solvents had significant influences on the helical structure of poly-PLLA.     

The syntheses and structures of mono- and di-bromovinylidenes

Reactions of metal acetylide complexes M(CCAr)(PP)Cp′ (M = Fe, Ru; Ar = C₆H₅, C₆H₄Me-4; PP = (PPh₃)₂, dppe; Cp′ = Cp, Cp*; not all combinations), or the analogous vinylidene, with cyanogen bromide yield monobromovinylidene complexes [M{CC(Br)Ar}(PP)Cp′]⁺, isolated as PF₆⁻ salts. The trimethylsilyl-capped acetylides M(CCSiMe₃)(PP)Cp′ react with cyanogen bromide to give [M(CCBr₂)(PP)Cp′]⁺, the first examples of metal complexes containing a terminal dihalovinylidene ligand, which can be isolated as the BF₄⁻ salts. Molecular structures of representative mono- and di-bromovinylidene complexes are reported, together with those of Ru(CCSiMe₃)(PPh₃)₂Cp and Ru(CCSiMe₃)(dppe)Cp*.     

Synthesis of di-, tri- and tetranuclear platinum(II) and copper(I) acetylide complexes

Heterobimetallic {cis-[Pt](μ-σ,π-CCPh)₂}[Cu(NCMe)]BF₄ (3a: [Pt] = (bipy)Pt, bipy = 2,2′-bipyridine; 3b: [Pt] = (bipy′)Pt, bipy′ = 4,4′-dimethyl-2,2′-bipyridine) is accessible by the reaction of cis-[Pt](CCPh)₂ (1a: [Pt] = (bipy)Pt, 1b: [Pt] = (bipy′)Pt]) with [Cu(NCMe)₄]BF₄ (2). Substitution of NCMe by PPh₃ (4) can be realized by the reaction of 3a with 4, whereby [{cis-[Pt](μ-σ,π-CCPh)₂}Cu(PPh₃)]BF₄ (5) is formed. On prolonged stirring of 3 and 5, respectively, NCMe and PPh₃ are eliminated and tetrametallic {[{cis-[Pt](η²-CCPh)₂}Cu]₂}(BF₄)₂ (6) is produced. Addition of an excess of NCMe to 6 gives heterobimetallic 3a.When instead of NCMe or PPh₃ chelating molecules such as bipy (7) are reacted with 3a then the heterobimetallic π-tweezer molecule [{cis-[Pt](μ-σ,π-CCPh)₂}Cu(bipy)]BF₄ (8) is formed. Treatment of 8 with another equivalent of 7 produced [Cu(bipy₂)]BF₄ (9) along with [Pt](CCPh)₂. However, when 3b is reacted with 1b in a 1:1 molar ratio then 10 and 11 of general composition [{[Pt](CCPh)₂}₂Cu]BF₄ are formed. These species are isomers and only differ in the binding of the PhCC units to copper(I). A possible mechanism for the formation of 10 and 11 is presented.The solid state structures of 6, 10 and 11 are reported. In 11 the [{cis-[Pt](μ-σ,π-CCPh)₂}₂Cu]⁺ building block is set-up by two nearly orthogonal positioned bis(alkynyl) platinum units which are connected by a Cu(I) ion, whereby the four carbon-carbon triple bonds are unsymmetrical coordinated to Cu(I). In trimetallic 10 two cis-[Pt](CCPh)₂ units are bridged by a copper(I) center, however, only one of the two PhCC ligands of individual cis-[Pt](CCPh)₂ fragments is η²-coordinated to Cu(I) giving rise to the formation of a [(η²-CCPh)₂Cu]⁺ moiety with a linear alkyne-copper-alkyne arrangement (alkyne = midpoint of the CC triple bond). In 6 two almost parallel oriented [Pt](CCPh)₂ planes are linked by two copper(I) ions, whereby two individual PhCC units, one associated with each Pt building block, are symmetrically π-coordinated to Cu.     

Carbon-carbon and carbon-chlorine bond formation on reaction of iodine(III) reagents with the bis(alkynyl)palladium(II) motif, and structural chemistry of trans-Pd(CC-o-Tol)2(PMe2Ph)2] and trans-[PdCl(CC-o-Tol)(PMe2Ph)2]

Trans-di(ortho-tolylethynyl)bis(dimethylphenylphosphine)palladium(II) reacts above −20 °C with the iodonium reagent IPhCl₂ to give predominantly o-Tol-CC-Cl, above 15 °C with IPh₂(OTf) (OTf = triflate) to give o-Tol-CC-Ph and (o-Tol-CC)₂ in ca. 3:1 ratio, and above 10 °C with IPh(CCR)(OTf) (R = Bu^t, SiMe₃) to give predominantly o-Tol-CC-CC-R and (o-Tol-CC)₂. ³¹P NMR spectra provide evidence for detection of intermediates. The complexes trans-[Pd(CC-o-Tol)₂(PMe₂Ph)₂] and trans-[PdCl(CC-o-Tol)(PMe₂Ph)₂] are obtained on reaction of trans-[PdCl₂(PMe₂Ph)₂] with Li(CC-o-Tol) and o-Tol-CCH/Et₃N, respectively, and have been characterised by X-ray crystallography.