Rhodium catalyzed synthesis of isoindolinones via C-H activation of N-benzoylsulfonamides

An efficient approach to a wide range of isoindolinones, including 3-monosubstituted and 3,3-disubstituted isoindolinones, from the annulation of N-benzoylsulfonamides with olefins and diazoacetate has been developed. The transformation is broadly compatible with both terminal and internal olefins. Moreover, diazoacetate is for the first time incorporated into an amide-directed C-H functionalization reaction. Specifically, the rhodium complex [{RhCl₂Cp*}₂] enables the in situ dimerization of diazoacetate in addition to its role in catalyzing C-H functionalization/cross-coupling.     

Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

Heterobimetallic Mn/Co hybrid complexes composed of proximate organometallic and classical coordination sites

A series of highly unsymmetric heterobinuclear Mn/Co complexes is reported, in which an organometallic CpMn(CO)₂ fragment and a classical Werner-type cobalt(II) subunit are arranged in close proximity by means of a bridging pyrazolate. Two ligand scaffolds are employed that differ by the chelate size of the tripodal tetradentate {N4} binding site for cobalt. Molecular structures of three complexes with either nitrate or acetate coligands have been characterized by X-ray crystallography. IR and UV-Vis-spectroelectrochemistry reveals that oxidation of the heterobimetallic systems is highly localized at the organometallic manganese site, while electrochemical reduction occurs at cobalt. Structural and spectroscopic features as well as trends for the redox potentials of the Mn^I/Mn^II couple suggest that changes at the cobalt(II) Werner-type subunit have only minor effects on the properties of the organometallic site.     

The first metal complexes of bis(diisopropylamino)carbene: synthesis, structure and ligand properties

The synthesis of rhodium(I) and iridium(I) complexes of the bis(diisopropylamino)carbene is described for the first time. The formamidinium chloride and the free bis(diisopropylamino)carbene (L) were used as consecutive precursor compounds to form the metal complexes. Spectroscopic and, for LRh(cod)Cl, crystallographic data are presented for the complexes LRh(cod)Cl and LIr(cod)Cl (L=bis(diisopropylamino)carbene). The ligand properties of the acyclic bis(diisopropylamino)carbene are compared with imidazolin-2-ylidenes and imidazolidin-2-ylidenes as ligands in related rhodium(I) carbonyl complexes. Bis(diisopropylamino)carbene is the most basic known carbene ligand to date.     

A simple synthesis of functionalized 3-methyl-1-pyridinyl-1H-imidazolium salts as bidentate N-heterocyclic-carbene precursors and their application in Ir-catalyzed arene borylation

The selective alkylation of functionalized 2-(1H-imidazol-1-yl)pyridines 1 furnishes 3-methyl-1-pyridinyl-1H-imidazolium salts 2, which can be deprotonated to deliver strongly electron-donating bidentate N-heterocyclic carbene ligands (NHC). The synthesis of these ligands and their application in the iridium-catalyzed C-H activated borylation of arenes with its current scope and limitations are reported.     

Photophysical processes and photochemical reactions involved in poly(N-vinylcarbazole) and in copolymers with carbazole units

This paper is devoted to the analysis of the photochemical behaviour of copolymers with carbazole units exposed to long-wavelength radiation. These copolymers are constituted of two types of carbazolylethyl methacrylate units (CEM) with octyl methacrylate moieties (OMA). The exposure of copolymers and PVK to UV light results in dramatic modifications of the physical and photophysical properties of the polymer. These modifications can be correlated with modifications of the chemical structure of the matrix. The photoageing of copolymers and PVK has been analysed by fluorescence, ESR, UV-vis and infrared spectroscopies. The effects of crosslinking and chain scissions were determined by gel fraction measurements and size exclusion chromatography.     

Irreversible cleavage of a carbene-rhodium bond in Rh-N-heterocyclic carbene complexes: implications for catalysis

Despite the generally accepted belief that carbene-metal bonds are strong and do not dissociate, the reaction of Rh-N-heterocyclic carbene complexes with triphenylphosphine in dichloroethane was determined to take place via cleavage of the Rh-carbene bond. The products of this reaction are Wilkinson’s catalyst and a bisimidazolium salt derived from reaction between dichloroethane and two equivalents of the carbene. The implications of this reaction for catalysis are significant since the carbene complex shows lower activity than Wilkinson’s catalyst in hydrogenation reactions. In non-halogenated solvents, the catalyst shows higher stability, such that the rate of exchange with free phosphine could be measured, and was determined to be ca. 10 times slower than in Wilkinson’s catalyst.     

Molybdenum amido complexes with single Mo-N bonds: synthesis,structure, and reactivity

Reactions of the complex [MoCl(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1) (phen=1,10-phenanthroline) with potassium arylamides were used to synthesize the amido complexes [Mo(N(R)Ar)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (R=H, Ar=Ph, 2 a; R=H, Ar=p-tolyl, 2 b; R=Me, Ar=Ph; 2 c). For 2 b the Mo-N(amido) bond length (2.105(4) A) is consistent with it being a single bond, with which the metal attains an 18-electron configuration. The reaction of 2 b with HOTf affords the amino complex [Mo(eta(3)-C(3)H(4)-Me-2)(NH(2)(p-tol))(CO)(2)(phen)]OTf (3-OTf). Treatment of 3-OTf with nBuLi or KN(SiMe(3))(2) regenerates 2 b. The new amido complexes react with CS(2), arylisothiocyanates and maleic anhydride. A single product corresponding to the formal insertion of the electrophile into the Mo-N(amido) bond is obtained in each case. For maleic anhydride, ring opening accompanied the formation of the insertion product. The reaction of 2 b with maleimide affords [Mo(eta(3)-C(3)H(4)-Me-2)[NC(O)CH=CHC(O)](CO)(2)(phen)] (7), which results from simple acid-base metathesis. The reaction of 2 b with (p-tol)NCO affords [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(eta(2)-MoO(4))] (8), which corresponds to oxidation of one third of the metal atoms to Mo(VI). Complex 8 was also obtained in the reactions of 2 b with CO(2) or the lactide 3,6-dimethyl-1,4-dioxane-2,5-dione. The structures of the compounds 2 b, 3-OTf, [Mo(eta(3)-C(3)H(4)-Me-2)[SC(S)(N(H)Ph)](CO)(2)(phen)] (4), [Mo(eta(3)-C(3)H(4)-Me-2)[SC(N(p-tol))(NH(p-tol))](CO)(2)(phen)] (5 a), and [Mo(eta(3)-C(3)H(4)-Me-2)[OC(O)CH=CHC(O)(NH(p-tol))](CO)(2)(phen)] (6), 7, and 8 (both the free complex and its N,N'-di(p-tolyl)urea adduct) were determined by X-ray diffraction.     

Toward a general method for CCC N-heterocyclic carbene pincer synthesis: Metallation and transmetallation strategies for concurrent activation of three C-H bonds

A general solution to the preparation of pincer complexes that require the formation of two N-heterocyclic carbenes (NHC’s) and the activation of an aryl C-H bond is reported. The reaction of a phenylene-bridged bis(imidazolium) salt with Zr(NMe₂)₄ generated the requisite CCC-NHC Zr pincer complex, which has been characterized by X-ray crystallography. Subsequent manipulation of the Zr coordination sphere by reaction with MeI demonstrated the robustness of the ligand geometry at Zr and led to the isolation and structural characterization of a CCC-NHC Zr triiodide pincer complex. A variation of the methodology has been applied to a saturated NHC analog to produce the corresponding CCC-NHC Zr pincer complex. Importantly, it has been found that CCC-NHC Zr pincer complexes can be generated in situ and transmetallated with an appropriate Rh source to generate CCC-NHC Rh pincer structures. These two methodologies, metallation of CCC-NHC precursors with transition metal amido complexes combined with transmetallation, hold great promise for opening general synthetic pathways to a wide variety of transition metal CCC-NHC pincer complexes.     

Sulfur and oxygen functionalized cyclopentadienyl half-sandwich cobalt complexes with 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolato ligands

Sulfur and oxygen functionalized cyclopentandienyl half-sandwich cobalt dicarbonyl complexes [η⁵-C₅H₄(CH₂)₂SCH₂CH₃]Co(CO)₂ (3) and [η⁵-C₅H₄(CH₂)₂OCH₃]Co(CO)₂ (7) were prepared. Oxidation of 3 or 7 with I₂ led to formation of 18-electron complexes [η⁵-C₅H₄(CH₂)₂SCH₂CH₃]CoI₂ (4) and [η⁵-C₅H₄(CH₂)₂OCH₃]Co(CO)I₂ (8). The reactions of diiodide complex (4) with dilithium 1,2-dicarba-closo-dodecaborane(12)-1,2-dichalcogenolates [(THF)₃LiE₂C₂B₁₀H₁₀Li(THF)]₂ [E=S (1a), Se (1b)] afforded 18-electron mononuclear complexes [η⁵-C₅H₄(CH₂)₂SCH₂CH₃]Co(E₂C₂B₁₀H₁₀) [E=S (5a), Se (5b)] in which sulfur atoms of side-chain were attached via an intramolecular coordination. Complex 7 reacted with 1a and 1b to give the binuclear complexes {[η⁵-C₅H₄(CH₂)₂OCH₃]Co(E₂C₂B₁₀H₁₀)}₂ [E=S (10a), Se (10b)]. The molecular structures of 5a and 10b were determined by X-ray crystallographic analysis. According to the X-ray structure analyses, 10b contains two o-carborane diselenolate bridges, and each Cp^′Co fragment is attached to one terminal and two bridging selenolato ligands. The central Co₂Se₂ four-membered ring is planar, and the direct metal-metal interaction is absent.     

Chiral diethylzinc complexes with diamine ligands: synthesis, crystal structure and enantioselective solvent-free alkylation

In search for conglomerates of stereochemically labile organometallic reagents, three new complexes between diethylzinc and diamine ligands have been synthesized and structurally characterized by single-crystal X-ray diffraction methods. Ligands include N,N,N′,N′-tetraethylethylenediamine (teeda), N-isopropyl-N,N′,N′-trimethylethylenediamine (itmeda), and (−)-sparteine (spa). Diethylzinc forms monomeric complexes, exhibiting a distorted tetrahedral coordination geometry around zinc in all three complexes, viz. [ZnEt₂(teeda)] (1), [ZnEt₂(itmeda)] (2), and [ZnEt₂(spa)] (3). Both 1 and 2 are stereochemically labile and exhibit chiral complexes, displaying different types of conformational chirality, but they form racemic crystals. By using the chiral crystals of 3 in a nucleophilic addition to benzaldehyde in the absence of solvent at low temperature, an increase in ee from approximately 8 to 10% was obtained (compared to the same reaction in solution). It thus seems feasible, not only to retain the enantioselectivity obtained in solution, but perhaps even to increase the ee by using solventless reactions.     

Coordination chemistry of ester-functionalized cp ligands: synthesis and catalytic activity of [Rh{CpCO2(CHPh)2OH}(NBD)] and [Rh{CpCO2(CH2)3OH}(NBD)]

Two new sodium hydroxyalkoxycarbonylcyclopentadienide salts Na[rac-CpCO₂(CHPh)₂OH] (1) and Na[(2S,3S)-CpCO₂(CHPh)₂OH] (2) were prepared by reaction of NaCp with the five-membered cyclic carbonates cis-4,5-diphenyl-1,3-dioxolan-2-one and (4S,5S)-4,5-diphenyl-1,3-dioxolan-2-one. The reaction of these salts with [Rh(NBD)Cl]₂ gave [Rh{rac-CpCO₂(CHPh)₂OH}(NBD)] (3) and (−)-[Rh{(2S,3S)-CpCO₂(CHPh)₂OH}(NBD)] (4) whose catalytic activity in the hydroformylation of hex-1-ene and styrene has been investigated and compared with that of the previously reported rhodium complexes [Rh{CpCO₂(CHR)₂OH}(NBD)] (R=H, Me). In addition we also discuss some preliminary results regarding the behavior of these complexes in the hydrogenation of the same substrates. The reactivity of NaCp toward the six-membered cyclic carbonate 1,3-dioxan-2-one has also been studied and it has been found that the reaction leads to two cyclopentadienide anions [CpCO₂(CH₂)₃OH]⁻ (5) and [CpCO₂(CH₂)₃OC(O)O(CH₂)₃OH]⁻ (6) in amounts strictly dependent on the carbonate/NaCp stoichiometric ratio.     

Isolation, synthesis and photochemical properties of almazolone, a new indole alkaloid from a red alga of Senegal

An indole alkaloid bearing an oxazolone ring, christened almazolone, has been isolated from a new collection of Haraldiophyllum sp. from Dakar (Senegal), as an 88:12 mixture of (Z)/(E) stereoisomers. The relative ratio could be modified under controlled photochemical and thermal processes. The product (Z)-3-indolyl-2-(phenyl-propionylamino)-acrylic acid obtained by oxazolone ring opening has also been observed. Its formation has been confirmed by alkaline hydrolysis of (Z)-almazolone available from synthesis, where condensation of indole-3-carboxaldehyde with (3-phenylpropionylamino)-acetic acid represents the key step.     

N,N′-Diisopropyl- and N,N′-dicyclohexylthiourea cadmium(II) complexes as precursors for the synthesis of CdS nanoparticles

Crystals of the cadmium(II) complexes of N,N-diisopropylthiourea and N,N-dicyclohexylthiourea were obtained and their X-ray single crystal structures determined. These complexes are air-stable, easy to prepare and inexpensive and decompose cleanly to give good quality crystalline CdS. The nanoparticles of CdS thus obtained showed quantum confinement effects in their optical spectra, with close to band-edge emission in luminescence experiments. The broad diffraction patterns observed are typical of nanodimensional particles. The variation of concentration of precursor-to-HDA ratio change the isolated materials from spheres to rod-shaped. TEM images showed agglomerates of needle-like plate of particles.     

Synthesis and characterization of chiral mono N-heterocyclic carbene-substituted rhodium complexes and their catalytic properties in hydrosilylation reactions

Different chiral mono-substituted N-heterocyclic carbene complexes of rhodium were prepared, starting from [Rh(COD)Cl]₂ (COD = cyclooctadiene) by addition of free N-heterocyclic carbenes (NHC), or an in-situ deprotonation of the corresponding iminium salt. All new complexes were characterized by spectroscopy methods. In addition, the structures of chloro(η⁴-1,5-cyclooctadiene)(1,3-di-[(1R,2R,3R,5S)-2,6,6-trimethylbicyclo[3.1.1]hept-3-yl] imidazolin-2-ylidene)rhodium(I) (5a), chloro(η⁴-1,5-cyclooctadiene)(1,3-di-[(1R,2S,5R)-2-isopropyl-5-menthylcyclohex-1-yl]imidazol-2-ylidene)rhodium(I) (5b) and chloro(η⁴-1,5-cyclooctadiene)(1,3-di-[(2R,4S,5S)-2-methyl-4-phenyl-1,3-dioxacyclohex-5-yl]imidazolin-2-ylidene)rhodium(I) (5i) were analyzed by DFT-calculations. The enantioselective hydrosilylation of acetophenone, ethylpyruvate and n-propylpyruvate with diphenylsilane and hydrolysis was carried out with chiral C₂-symmetrical mono-substituted N-heterocyclic carbene rhodium complexes giving for the first time an enantioselective excess of up to 74% ee in the case of the n-propylpyruvate.     

Synthesis and characterization of new Rh complexes bearing CO, PPh3 and chelating P,O- or Se,Se-ligands: Application to hydroformylation of styrene

The complexes [Rh(CO)(PPh₃){Ph₂PNP(O)Ph₂-P,O}] (3), [Rh(CO)₂{Ph₂P(Se)NP(Se)Ph₂-Se,Se′}] (5), and [Rh(CO)(PPh₃){Ph₂P(Se)NP(Se)Ph₂-Se,Se′}] (6), were synthesised by stepwise reactions of CO and PPh₃ with [Rh(cod){Ph₂PNP(O)Ph₂-P,O}] (2) and [Rh(cod){Ph₂P(Se)NP(Se)Ph₂-Se,Se′}] (4), respectively. The complexes 3, 5 and 6 have been studied by IR, as well as ¹H and ³¹P NMR spectroscopy. The ν(CO) bands of complexes 3 and 6 appear at approximately 1960 cm⁻¹, indicating high electron density at the Rh^I centre. The structure of complexes 3 and 6 has been determined by X-ray crystallography, and the ³¹P NMR chemical shifts have been resolved via low temperature NMR experiments. Both complexes exhibit square planar geometry around the metal centre, with the five-membered ring of complex 3 being almost planar, and the six-membered ring of complex 6 adopting a slightly distorted boat conformation. The C-O bond of the carbonyl ligand is relatively weak in both complexes, due to strong π-back donation from the electron rich Rh^I centre. The catalytic activity of the complexes 2, 3 and 6 in the hydroformylation of styrene has been investigated. Complexes 2 and 3 showed satisfactory catalytic properties, whereas complex 6 had effectively no catalytic activity.     

Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) tetrafluoroborate, an unsymmetrical Rh-homoazallylcarbene: synthesis, X-ray structure and reactivity in carbonyl arylation and hydrosilylation reactions

The synthesis of novel Rh(1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene)(COD) tetrafluoroborate (1, COD = η⁴-1,5-cyclooctadiene) is described. The N-heterocyclic carbene acts as a bidentate ligand with the carbene coordinating to the Rh(I) center and an arene group acting as a homoazallyl ligand. 1 was used in various carbonyl arylation and hydrosilylation reactions allowing the formation of the desired products with unprecedented selectivity and efficiency. Thus, turn-over numbers (TONs) up to 2000 were achieved.     

N-Phenanthroline glycosylamines: synthesis and copper(II) complexes

A series of novel N-(1,10-phenanthrolin-5-yl)-β-glycopyranosylamines was obtained with excellent stereoselectivity and synthetically useful yields by treatment of 5-amino-1,10-phenanthroline with different unprotected monosaccharides, using (NH₄)₂SO₄ as an efficient promoter. Copper(II) complexes having a 2:1 mole ratio of the bidentate ligand phenanthroline N-glycoside and the metal were also prepared.     

Facile synthesis of acyclic azanucleosides from N-pivaloyloxymethyl amides and sulfonamides: synthesis of aza-analogues of Ganciclovir

N-Pivaloyloxymethyl amides and sulfonamides, readily available from N-alkylation of both amides and sulfonamides with commercial chloromethyl pivaloate, were converted into acyclic azanucleosides via a one-pot base silylation/nucleoside coupling procedure.     

Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.