Synthesis of phthalide derivatives using nickel-catalyzed cyclization of o-haloesters with aldehydes

The reaction of o-bromobenzoate (1 b) with benzaldehyde (2 a) in the presence of [NiBr(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) and zinc powder in THF (24 hours, reflux temperature), afforded 3-phenyl-3H-isobenzofuran-1-one (3 a) in an 86 % yield. Similarly, o-iodobenzoate reacts with 2 a to give 3 a, but in a lower yield (50 %). A series of substituted aromatic and aliphatic aldehydes (2 b, 4-MeC(6)H(4)CHO; 2 c, 4-MeOC(6)H(4)CHO; 2 d, 3-MeOC(6)H(4)CHO; 2 e, 2-MeOC(6)H(4)CHO; 2 f, 4-CNC(6)H(4)CHO; 2 g, 4-(Me)(3)CC(6)H(4)CHO; 2 h, 4-C(6)H(5)C(6)H(4)CHO; 2 i, 4-ClC(6)H(4)CHO; 2 j, 4-CF(3)C(6)H(4)CHO; 2 k, CH(3)(CH(2))(5)CHO; 2 l, CH(3)(CH(2))(2)CHO) also underwent cyclization with o-bromobenzoate (1 b) producing the corresponding phthalide derivatives in moderate to excellent yields and with high chemoselectivity. Like 1 b, methyl 2-bromo-4,5-dimethoxybenzoate (1 c) reacts with tolualdehyde (2 b) to give the corresponding substituted phthalide 3 m in a 71 % yield. The methodology can be further applied to the synthesis of six-membered lactones. The reaction of methyl 2-(2-bromophenyl)acetate (1 d) with benzaldehyde under similar reaction conditions afforded six-membered lactone 3 o in a 68 % yield. A possible catalytic mechanism for this cyclization is also proposed.     

Cobalt-catalyzed cross-coupling reactions of alkyl halides with aryl Grignard reagents and their application to sequential radical cyclization/cross-coupling reactions

Reactions of alkyl halides with arylmagnesium bromides in the presence of cobalt(II)(diphosphine) complexes are discussed. Treatment of 1-bromooctane with phenylmagnesium bromide with the aid of a catalytic amount of CoCl₂(dppp) [DPPP=1,3-bis(diphenylphosphino)propane] yielded octylbenzene in good yield. The reaction mechanism would include single electron transfer from an electron-rich cobalt complex to alkyl halide to generate the corresponding alkyl radical. The mechanism was justified by CoCl₂(dppe)-catalyzed [DPPE=1,2-bis(diphenylphosphino)ethane] sequential radical cyclization/cross-coupling reactions of 6-halo-1-hexene derivatives that yielded benzyl-substituted cyclopentane skeletons.     

Structure of a new binuclear complex of tungsten [W2S4Cl2(dppe)2]·2CH3CN

Journal of Structural Chemistry - In the reaction of (Et4N)2[W2S4Cl4] with 1,2-bis(diphenylphosphino)ethane in acetonitrile a new binuclear complex of tungsten(V) [W2S4Cl2(dppe)2]·2CH3CN is...     

Synthesis of aromatic compounds by catalytic C-C bond activation of biphenylene or angular [3]phenylene

Substituted phenanthrenes and picenes were easily prepared by reaction of biphenylene or angular [3]phenylene with various alkynes in the presence of a catalytic amount of [IrCl(cod)](2) /dppe (cod=1,5-cyclooctadiene, dppe=1,2-bis(diphenylphosphino)ethane). The reaction is based on C-C bond activation of the cyclobutane ring. The reaction tolerates the presence of bulky groups on the alkyne, such as the ferrocene moiety. In addition, a catalytic system based on [RhCl(cod)](2)/dppe enabled the, hitherto unreported, reaction of biphenylene with nitriles to provide phenanthridines.     

Iridium complex-catalyzed highly selective cross [2 + 2 + 2] cycloaddition of two different monoynes: 2:1 coupling versus 1:2 coupling

[reaction: see text] Highly selective cross [2 + 2 + 2] cycloaddition of two different monoynes is achieved by using a catalytic amount of [Ir(cod)Cl](2) and ligand. The ligand had a considerable effect on the reaction. When 1,2-bis(diphenylphosphino)ethane was used, two molecules of dimethyl acetylenedicarboxylate (DMAD) reacted with one molecule of a monoyne to give the 2:1 coupling product. When 1,2-bis(dipentafluorophenylphosphino)ethane was used instead of dppe, one molecule of DMAD reacted with two molecules of a monoyne to give the 1:2 coupling product.     

Cobalt-catalyzed regioselective carbocyclization reaction of o-iodophenyl ketones and aldehydes with alkynes, acrylates, and acrylonitrile: a facile route to indenols and indenes

An efficient cobalt-catalyzed carbocylization for the synthesis of indenols and indenes and a new method for reductive decyanation are described. 2-Iodophenyl ketones and aldehydes 1a-g undergo carbocyclization with various disubstituted alkynes 2a-k in the presence of Co(dppe)I(2) and zinc powder in acetonitrile at 80 degrees C for 3 h to afford the corresponding indenol derivatives 3a-s and4a-m in good to excellent yields. For some unsymmetrical alkynes, the carbocyclization was remarkably regioselective, affording a single regioisomer. The cobalt-catalyzed carbocyclization reaction was successfully extended to the synthesis of indene derivatives. Thus, the reaction of 2-iodophenyl ketones and aldehydes (1) with acrylates H(2)C=CHCO(2)R (7a-d) and acrylonitrile H(2)C=CHCN (7e) proceeds smoothly in the presence of Co(dppe)Cl(2)/dppe and zinc powder in acetonitrile at 80 degrees C for 24 h to afford the corresponding indenes 8a-k and 9a-c in moderate to good yields. Interestingly, when 7e was employed for the carbocylization, reductive decyanation also occurred to give an indene derivative without the cyano functionality. A possible mechanism for this cobalt-catalyzed carbocyclization reaction is also proposed.     

Functionalised trimethylsilyl reagents in cluster synthesis: reactions of Ph2P(S)SSiMe3 with group 11 salts

A series of complexes, ranging from the small cluster 1/infinity[Ag(Ph2PS2)(dppe)](infinity) [dppe=1,2-bis(diphenylphosphino)ethane] to [Cu48S20(O(t)Bu)2(Ph2PS2)2(dppm-)4(dppm)4][dppm=1,2-bis(diphenylphosphino)methane] (the largest Cu cluster containing phosphinodithioato ligands), has been synthesised. The structural evidence presented here indicates that in these reactions initially small cyclic aggregates or one-dimensional coordination polymers are formed. The growth of these intermediates to larger aggregates can take up to several months and could proceed via cationic intermediates.     

A highly regio- and stereoselective nickel-catalyzed ring-opening reaction of alkyl- and allylzirconium reagents to 7-oxabenzonorbornadienes

[Reaction: see text]. An efficient method for the synthesis of cis-2-alkyl- or allyl-1,2-dihydronaphthalenes via a nickel-catalyzed highly regio- and stereoselective ring-opening addition of alkyl- or allylzirconium reagents to 7-oxabenzonorbornadienes is described. Treatment of 7-oxabenzonorbornadienes 1a-c with various alkylzirconium reagents 2a-j (Cp2ZrClCH2CH2R: R = tert-butyl, n-butyl, n-pentyl, -(CH2)3CH=C(CH3)2, -SiMe3, -CH2SiMe3, -(CH2)3Br, cyclopentyl, cyclohexyl, and benzyl) in the presence of NiBr2(dppe) and Zn powder in dry THF at 50 degrees C afforded the corresponding cis-2-alkyl-1,2-dihydronaphthalene derivatives 3a-m in good yields. In addition, allyl zirconium reagents 4a-c also underwent ring-opening reactions with 1a and 1c to give 5a-d in very good yields. The alkylative ring-opening products from 7-oxabenzonorbornadiene can be further converted to naphthalene derivatives 6a-c, via an acid-mediated dehydration, in good to excellent yields. A possible mechanism for the present catalytic reaction was proposed.     

Heterolytic activation of hydrogen as a trigger for iridium complex promoted activation of carbon-fluorine bonds

The cationic iridium(III) complex [IrCF(3)(CO)(dppe)(DIB)][BARF](2) where DIB = o-diiodobenzene, dppe = 1,2-bis(diphenylphosphino)ethane, and BARF = B(3,5-(CF(3))(2)C(6)H(3))(4)(-) undergoes reaction in the presence of dihydrogen to form [IrH(2)(CO)(2)(dppe)](+) as the major product. Through labeling studies and (1)H and (31)P[(1)H] NMR spectroscopies including parahydrogen measurements, it is shown that the reaction involves conversion of the coordinated CF(3) ligand into carbonyl. In this reaction sequence, the initial step is the heterolytic activation of dihydrogen, leading to proton generation which promotes alpha-C-F bond cleavage. Polarization occurs in the final [IrH(2)(CO)(2)(dppe)](+) product by the reaction of H(2) with the Ir(I) species [Ir(CO)(2)(dppe)](+) that is generated in the course of the CF(3) --> CO conversion.     

Synthesis, molecular and electronic structure of an incomplete cuboidal Re3S4 cluster with an unusual quadruplet ground state

A Re(IV) cluster complex [Re(3)(μ(3)-S)(μ-S)(3)(dppe)(3)Br(3)](+) with nine cluster skeletal electrons (CSE) and a quadruplet ground state has been prepared by treatment of [Re(3)S(7)Br(6)]Br with 1,2-bis(diphenylphosphino)ethane (dppe) in MeCN.     

Oxygenation of Ruthenium Carbene Complexes Containing Naphthothiophene or Naphthofuran: Spectroscopic and DFT Studies

The aryl propargylic alcohol 1‐[2‐(thiophen‐3‐yl)phenyl]prop‐2‐yn‐1‐ol ( 1a ) is readily prepared from 2‐(thiophen‐3‐yl)benzaldehyde. In the presence of visible light, treatment of 1a with one‐half mole equivalent of [Ru]Cl ([Ru]?Cp(dppe)Ru) (dppe=1,2‐bis(diphenylphosphino)ethane) and NH₄PF₆ in O₂ affords the naphtha[2,1‐b]thiophene‐4‐carbaldehyde ( 4a ) in high yields. The cyclization reaction of 1a proceeds through the formation of the carbene complex 2a that contains the naphtha[2,1‐b]thiophene ring, which is isolated in a 1:1 stoichiometric reaction. The C? C bond formation between the inner carbon of the terminal triple bond and the heterocyclic ring is confirmed by structure determination of 2a using single‐crystal X‐ray diffraction analysis. Facile oxygenation of 2a by O₂ yields the aldehyde product 4a accompanied by the formation of phosphine oxide of dppe. Oxygen is most likely activated by coordination to the ruthenium center when one PPh₂ unit of the dppe ligand dissociates. This dissociated PPh₂ unit then reacts with the coordinated oxygen nearby to generate half‐oxidized dppe ligand and an unobserved oxo–carbene intermediate. Coupling of the oxo/carbene ligands followed by demetalation then yields 4a . Presumably the resulting complex with the half‐oxidized dppe ligand continuously promotes cyclization/oxygenation of 1a to yield the second aldehyde molecule. In alcohol such as MeOH or EtOH, the oxygenation reaction affords a mixture of 4a and the corresponding esters 5a or 5a' . Four other aryl propargylic alcohols 1b , 1c , 1d , 1e , which contain thiophen‐2‐yl, isopropenyl, fur‐3‐yl, and fur‐2‐yl, respectively, on the aryl ring are also prepared. Analogous aldehydes 4b , 4c , 4d , 4e are similarly prepared from 1b , 1c , 1d , 1e , respectively. For oxygenations of 1b , 1d , and 1e in alcohol, mixtures of aldehyde 4 , ester 5 , and acetal 8 are obtained. The carbene complex 2b obtained from 1b was also characterized by single‐crystal X‐ray diffraction analysis. The UV/Vis spectra of 2a and 2b consist of absorption bands with a high extinction coefficient. From DFT calculations on 2a and 2b , the visible light is found to populate the LUMO antibonding orbital of mainly Ru?C bonds, thereby weakening the Ru?C bond and promoting the oxygenation/demetalation reactions of 2 .     

Nickel-catalyzed, cascade cycloadditions of 1-ethynyl-8-halonaphthalenes with nitriles: synthesis, structure, and physical properties of new pyrroloarenes

The reaction of 1-ethynyl-8-halonaphthalenes 1 with nitriles in the presence of the catalytic system [NiBr(2)(dppe)]/Zn (dppe=1,2-bis(diphenylphosphino)ethane) is found to produce unusual pyrroloarenes 2. The carbon-nitrogen triple bond in nitrile is activated twice, and five new bonds are formed in a one-pot transformation, which causes a pyrrole and two six-membered rings to be generated simultaneously. The scope and limitations of this reaction are examined. Similarly, alkyl-bridged diynes also furnish the corresponding polycycles. Diaryl-substituted cycloadducts 2 (R(1)=Ar) are fluxional, because of the restriction in rotation of the aryl groups. The rotational barrier is studied by performing (1)H NMR experiments at various temperatures. The structures of several compounds are determined by X-ray crystallographic analysis. The photophysical and electrochemical properties of the pyrroloarenes are also investigated.     

Sulfido-bridged dinuclear molybdenum-copper complexes related to the active site of CO dehydrogenase: [(dithiolate)Mo(O)S2Cu(SAr)]2- (dithiolate = 1,2-S2C6H4, 1,2-S2C6H2-3,6-Cl2, 1,2-S2C2H4)

The [MoCu] carbon monoxide dehydrogenase (CODH) is a Cu-containing molybdo-flavoprotein, the active site of which contains a pterin-dithiolene cofactor bound to a sulfido-bridged dinuclear Mo-Cu complex. In this paper, the synthesis and characterization of dinuclear Mo-Cu complexes relevant to the active site of [MoCu]-CODH are described. Reaction of [MoO2S2]2- with CuCN affords the dinuclear complex [O2MoS2Cu(CN)]2- (1), in which the CN- ligand can be replaced with various aryl thiolates to give rise to a series of dinuclear complexes [O2MoS2Cu(SAr)]2- (Ar = Ph (2), o-Tol (3), and p-Tol (4)). An alternative synthesis of complex 2 is the reaction of [MoO2S2]2- with [Cu(SPh)3]2-. Similarly, [O2MoS2Cu(PPh3)]- (5), [O2MoS2Cu(dppe)]- (dppe = 1,2-bis(diphenylphosphino)ethane) (6), and [O2MoS2Cu(triphos)]- (triphos = 1,1,1-tris[(diphenylphosphino)methyl]ethane) (7) were prepared from the reactions of [MoO2S2]2- with the Cu(I) phosphine complexes. Treatment of 1, 2, 4, or 5 with dithiols (1,2-(SH)2C6H4, 1,2-(SH)2C6H2-3,6-Cl2, and 1,2-(SH)2C2H4), in acetonitrile, leads to the replacement of a molybdenum-bound oxo ligand to yield [(dithiolate)Mo(O)S2CuL]2- (L = CN, SAr; dithiolate = 1,2-S2C6H4, 1,2-S2C6H2-3,6-Cl2, or 1,2-S2C2H4) (8-13) or [(1,2-S2C6H4)Mo(O)S2Cu(PPh3)]- (14) complexes.     

Rhodium-catalyzed α-methylthiolation reaction of unactivated ketones using 1,2-diphenyl-2-methylthio-1-ethanone for the methylthio transfer reagent

In the presence of catalytic amounts of RhH(PPh₃)₄, 1,2-bis(diphenylphosphino)ethane (dppe), and dimethyl disulfide, ketones without α-activating groups were α-methylthiolated with 1,2-diphenyl-2-methylthio-1-ethanone giving α-methylthio ketones. The reaction of unsymmetrical ketones proceeded at the more substituted carbons. The initial formation of kinetic α-methylthiolated products followed by their rearrangement to thermodynamic products was observed in the reaction of α-phenyl ketones. Aldehydes, phenylacetate, and phenylacetonitrile were also α-methylthiolated under these conditions.     

Formation of ammonia in the reactions of a tungsten dinitrogen with ruthenium dihydrogen complexes under mild reaction conditions

Treatment of cis-[W(N2)2(PMe2Ph)4] (5) with an equilibrium mixture of trans-[RuCl(eta 2-H2)(dppp)2]X (3) with pKa = 4.4 and [RuCl(dppp)2]X (4) [X = PF6, BF4, or OTf; dppp = 1,3-bis(diphenylphosphino)propane] containing 10 equiv of the Ru atom based on tungsten in benzene-dichloroethane at 55 degrees C for 24 h under 1 atm of H2 gave NH3 in 45-55% total yields based on tungsten, together with the formation of trans-[RuHCl(dppp)2] (6). Free NH3 in 9-16% yields was observed in the reaction mixture, and further NH3 in 36-45% yields was released after base distillation. Detailed studies on the reaction of 5 with numerous Ru(eta 2-H2) complexes showed that the yield of NH3 produced critically depended upon the pKa value of the employed Ru(eta 2-H2) complexes. When 5 was treated with 10 equiv of trans-[RuCl(eta 2-H2)(dppe)2]X (8) with pKa = 6.0 [X = PF6, BF4, or OTf; dppe = 1,2-bis(diphenylphosphino)ethane] under 1 atm of H2, NH3 was formed in higher yields (up to 79% total yield) compared with the reaction with an equilibrium mixture of 3 and 4. If the pKa value of a Ru(eta 2-H2) complex was increased up to about 10, the yield of NH3 was remarkably decreased. In these reactions, heterolytic cleavage of H2 seems to occur at the Ru center via nucleophilic attack of the coordinated N2 on the coordinated H2 where a proton (H+) is used for the protonation of the coordinated N2 and a hydride (H-) remains at the Ru atom. Treatment of 5, trans-[W(N2)2(PMePh2)4] (14), or trans-[M(N2)2(dppe)2] [M = Mo (1), W (2)] with Ru(eta 2-H2) complexes at room temperature led to isolation of intermediate hydrazido(2-) complexes such as trans-[W(OTf)(NNH2)(PMe2Ph)4]OTf (19), trans-[W(OTf)(NNH2)(PMePh2)4]OTf (20), and trans-[WX(NNH2)(dppe)2]+ [X = OTf (15), F (16)]. The molecular structure of 19 was determined by X-ray analysis. Further ruthenium-assisted protonation of hydrazido(2-) intermediates such as 19 with H2 at 55 degrees C was considered to result in the formation of NH3, concurrent with the generation of W(VI) species. All of the electrons required for the reduction of N2 are provided by the zerovalent tungsten.     

Synthesis of Aromatic Compounds by Catalytic C?C Bond Activation of Biphenylene or Angular [3]Phenylene

Substituted phenanthrenes and picenes were easily prepared by reaction of biphenylene or angular [3]phenylene with various alkynes in the presence of a catalytic amount of [IrCl(cod)]₂/dppe (cod=1,5‐cyclooctadiene, dppe=1,2‐bis(diphenylphosphino)ethane). The reaction is based on C? C bond activation of the cyclobutane ring. The reaction tolerates the presence of bulky groups on the alkyne, such as the ferrocene moiety. In addition, a catalytic system based on [RhCl(cod)]₂/dppe enabled the, hitherto unreported, reaction of biphenylene with nitriles to provide phenanthridines.     

Kinetics and mechanisms of homogeneous catalytic reactions: Part 15. Regio-specific hydroformylation of limonene catalysed by rhodium complexes of phosphine ligands

Limonene hydroformylation was studied in the presence of Rh-based catalytic systems, which were prepared in situ by addition of three equivalents of PPh₃, one of 1,2-bis(diphenylphosphino)ethane (dppe), or one of 1,1,1-tris(diphenylphosphino)ethane (triphos) to Rh(CO)₂(acac) (1). These systems were efficient precatalysts for the target reaction, generating limonenal regio-specifically under mild reaction conditions (80 °C and 20 atm of syngas). The found activity order was: (1)/3 PPh₃?>?(1)/triphos?>?(1)/dppe. The active catalytic species are proposed to be square planar hydrido-carbonyl complexes containing two phosphorus atoms coordinated at the rhodium centre. A kinetic study of this reaction catalysed by (1)/3 PPh₃, the most active catalytic system, allowed us to propose that the mechanism of hydroformylation of limonene is similar to those reported for other olefins using RhH(CO)(PPh₃)₃ or Rh systems containing either dppe or triphos as precatalysts.     

Bis(alkoxycarbonyl) complexes of platinum: preparation,reactivity and their role in carbonylation reactions

bis(alkoxycarbonyl) complexes of platinum of the type [Pt(COOR)₂L] [L = 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), l,4-bis(diphenylphosphino)butane (dppb), 1,1'-bis(diphenylphosphino)ferrocene (dppf) or 1,2-bis-(diphenylphosphino)benzene (dpb); R = CH₃, C₆H₅ or C₂H₅] were obtained by reaction of [PtCl₂L] with carbon monoxide and alkoxides. Palladium and nickel complexes gave only carbonyl complexes of the type [M(CO)L] or [M(CO)₂L]. The new complexes were characterized by chemical and spectroscopic means. The X-ray structure of [Pt(COOCH₃)₂(dppf] · CH₃OH is also reported. The reactivity of some alkoxycarbonyl complexes was also investigated.     

Rhodium-catalyzed phenylthiolation reaction of heteroaromatic compounds using α-(phenylthio)isobutyrophenone

In the presence of catalytic amounts of RhH(PPh₃)₄ and 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-benzothiazoles, 1,3-benzoxazoles, and benzothiophene reacted with α-(phenylthio)isobutyrophenone giving 2-phenylthio derivatives. Reactive monocyclic heteroaromatics, 1-methyl-1,2,3,4-tetrazole and 2-cyanothiophene were also converted into the 5-phenylthio derivatives. The use of an appropriate phenylthio transfer reagent is crucial for the efficient catalyzed conversion of heteroaromatic C-H bonds into C-S bonds.     

Selective reduction of aromatic nitro compounds affording aromatic amines under CO/H2O conditions catalyzed by phosphine-added rhodium and ruthenium carbonyl complexes

High catalytic activities for the selective reduction of aromatic nitro compounds to the corresponding amines under the mild reaction conditions of room temperature and 1 atm of CO were found to be exhibited by chelatephosphine (dppe, dppm, etc.; dppe: 1,2-bis(diphenylphosphino)ethane, dppm: bis(diphenylphosphino)methane)-added rhodium and ruthenium carbonyl complexes in a 5 N NAOH aqueous solution. The reduction proceeded not only with high catalytic activities, but also with remarkably high nitro group selectivities; for example, 1-nitroanthraquinone afforded 1-aminoanthraquinone without other unsaturated groups (such as CO) being reduced. PR₃-added Rh(CO)₂(acac) complexes (PR₃: PEtPh₂, PEt₂Ph, PEt₃, etc.; acac: acetylacetonato) in diglyme in a 5 N NaOH aqueous solution were also found to show significant catalytic activities for the reduction of aromatic nitro compounds under mild CO/H₂O conditions. Both electronic and steric factors of phosphine ligands are important in making this reaction proceed at such remarkable rates.