A convenient approach to heterocyclic building blocks: synthesis of novel ring systems containing a [5,6]Pyrano[2,3-c]pyrazol-4(1H)-one moiety

Starting from commercially available educts, a straightforward synthetic route to new heterocyclic building blocks is exemplified with the one- or two-step synthesis of tri-, tetra-, or pentacyclic ring systems. Representatives of the following novel ring systems are prepared from 3-methyl-1-phenyl-2-pyrazolin-5-one and the corresponding o-halo-arenecarbonyl chloride using calcium hydroxide in refluxing 1,4-dioxane: pyrimidino[4',5':5,6]pyrano[2,3-c]pyrazol-4(1H)-one, thieno[3',2':5,6]pyrano[2,3c]pyrazol- 4-(1H)-one, thieno[3',4':5,6]pyrano[2,3-c]pyrazol-4(1H)-one, thieno[3',2':4',5']thieno[2',3':5,6]-pyrano[2,3-c]pyrazol-4(1H)-one, [1,3]dioxolo[5',6'][1]benzothieno[2',3':5,6]pyrano-[2,3-c]- pyrazol-4(1H)-one, pyridazino[4',3':5,6]pyrano[2,3-c]pyrazol-4(1H)-one and pyrazolo-[4',3':5',6']pyrido[3',4':5,6]pyrano[2,3-c]pyrazol-4(1H)-one. While the latter two ring systems are directly obtained due to a spontaneous intramolecular substitution reaction, in the other reactions uncyclised 4-aroylpyrazol-5-ols are produced, which are cyclised into the target heterocycles in a subsequent synthetic step (i.e. treatment with NaH in DMF). Detailed NMR spectroscopic investigations ((1)H-, (13)C-, (15)N-) with the obtained compounds were undertaken to unambiguously prove the new structures.     

Tricalixarenes and pentacalixarenes: synthesis and complexation studies

Tricalix[4]arene 4, tricalix[5]arene 14, and pentacalix[4]arene 10 have been synthesized from O-alkylcalixarene mono- and dialdehydes by a two-step conversion to the corresponding monoethynyl ketones or diethynyl ketones followed by aryne trimerization in refluxing DMF containing a dialkylamine. The tricalixarenes 4 and 14 were converted, in turn, to calixarenes 6 and 16, which carry OH groups on the lower rim and methylenes as the bridging moieties to the benzene ring. Complexation studies with the tricalix[5]arene 16 show that it forms (a) a 1:3 complex with N,N-dimethylethylenediamine in which each calixarene unit contains a molecule of the amine, (b) a 1:1 complex with tris(aminomethyl)amine in which each calixarene unit contains one of the three arms of the guest, and (c) a 1:1 complex with C60 in which the guest presumably resides in the cavity provided by the three calixarene units acting cooperatively.     

New bonding modes for boraamidinate ligands in heavy group 15 complexes: fluxional behavior of the 1:2 complexes, LiM[PhB(NtBu)2]2 (M = As, Sb, Bi)

The reactions of MCl3 with Li2[PhB(NtBu)2] in 1:1, 1:1.5, and 1:2 molar ratios in diethyl ether produced the monoboraamidinates ClM[PhB(NtBu)2] (1a, M = As; 1b, M = Sb; 1c, M = Bi), the novel 2:3 boraamidinate complexes [PhB(NtBu)2]M-micro-N(tBu)B(Ph)N(tBu)M[PhB(NtBu)2] (2b, M = Sb; 2c, M = Bi), and the bisboraamidinates LiM[PhB(NtBu)2]2 (3a, 3a.OEt2, M = As; 3b, M = Sb; 3c.OEt2, M = Bi), respectively. The 2:3 complexes 2b and 2c were also observed in the reactions carried out in a 1:2 molar ratio at room temperature. All complexes have been characterized by multinuclear NMR spectroscopy (1H, 7Li, 11B, and 13C) and by single-crystal X-ray structural determinations. The molecular units of the mono-boraamidinates 1a-c are isostructural, but their crystal packing is distinct as a result of stronger intermolecular close contacts going from 1a to 1c. In the novel 2:3 bam complexes 2b and 2c, each metal center is N,N'-chelated by a bam ligand and these two [M(bam)]+ units are bridged by the third [bam]2- ligand. The structures of the unsolvated bis-boraaminidate complexes 3a and 3b consist of [Li(bam)]- and [M(bam)]+ monomeric units linked by Li-N and M-N bonds to give a tricyclic structure. Solvation of the Li+ ion by diethyl ether results in a bicyclic structure composed of four-membered BN2As and six-membered BN3AsLi rings in 3a.OEt2. In contrast, the analogous bismuth complex 3c.OEt2 exhibits a tetracyclic structure. Variable-temperature NMR studies reveal that the nature of the fluxional behavior of 3a-c in solution is dependent on the group 15 center.     

Chemistry of thiocarboxylates: synthesis and structures of neutral copper(I) thiocarboxylates with triphenylphosphine

The reactions of Na+ R[O]CS- (R = Me, Ph) with mixtures of CuCl and PPh3 in stoichiometric ratios yielded the compounds [Cu4(SC[O]Me)4(PPh3)4] (1), [Cu4(SC[O]Ph)4(PPh3)3] (2), [Cu2(SC[O]Me)2(PPh3)4] (3), [Cu(SC[O]Ph)(PPh3)2] (4), and [Cu2(SC[O]Ph)2(PPh3)3] (5) quantitatively. Compound 2 was also obtained from mixtures of CuCl, PPh3, and NaSC[O]Ph in the ratio 1:1:1. The analogous thioacetate compound similar to 2 and the thiobenzoate analogue of 1 could not be obtained. Attempts to prepare the unsymmetrical dimer of a thioacetate compound similar to 5 gave a mixture of 1 and 3. The structures of 1-4 have been determined by single-crystal X-ray diffraction methods. Crystal data for 1: triclinic space group Pl, a = 11.5844(3) A, b = 13.2459(3) A, c = 14.3433(3) A, alpha = 64.019(1) degrees, beta = 79.297(1) degrees, gamma = 69.426(1) degrees, V = 1850.98(7) A3, Z = 1, Dcalcd = 1.439 g.cm-3. Crystal data for 2.0.5CH2Cl2.H2O: triclinic space group P1, a = 12.4413(1) A, b = 15.5443(1) A, c = 20.4637(3) A, alpha = 94.974(1) degrees, beta = 95.976(1) degrees, gamma = 100.450(1) degrees, V = 3848.09(7) A3, Z = 2, Dcalcd = 1.416 g.cm-3. Single-crystal data for 3: monoclinic space group P2(1)/n, a = 15.2746(2) A, b = 23.2947(2) A, c = 19.0518(3) A, beta = 96.713(1) degrees, V = 6732.5(2) A3, Z = 4, Dcalcd = 1.309 g.cm-3. Crystal data for 4: triclinic space group P1, a = 10.2524(3) A, b = 12.9826(4) A, c = 14.5340(4) A, alpha = 87.723(1) degrees, beta = 75.322(1) degrees, gamma = 75.978(1) degrees, V = 1815.14(9) A3, Z = 2, Dcalcd = 1.327 g.cm-3. Compound 1, [mu 3-SC[O]Me-S)2(mu-SC[O]Me-S)2(CuPPh3)4], is a tetramer with a distorted stepladder structure in which two copper atoms are trigonally coordinated and the other two are tetrahedrally coordinated. Two bonding modes, namely, mu 3-S and mu 2-S, were observed for the Me[O]CS- anion. The structure of 2 may be described as a highly distorted cubanoid structure and formulated as [(mu 3-SC[O]Ph-S3)(mu 3-SC[O]Ph-S2,O)3(Cu)(CuPPh3)3]. In 2, three copper atoms have tetrahedral coordination geometry and one copper atom is trigonally coordinated. Unprecedented bonding modes, namely, mu 3-S, have been observed for the R[O]CS- anions, in 1 and 2 and mu 3-S2,O in 2. Compound 3, [(mu-SC[O]MeS)(mu-SC[O]Me-S,O)[Cu(PPh3)2]2] is a dimer with mu 2-S and mu 2-S,O bonding modes of Me[O]CS- ligands. Monomeric structure was found in 4 in which the copper atom has trigonal planar geometry with a very weak intramolecular interaction with O. Variable temperature 31P NMR studies in solution show the presence of various species in equilibria.     

Superoxide reactivity of KatG: insights into isoniazid resistance pathways in TB

To gain insight into the mechanism of INH activation by KatG and to understand how resistance is conferred by the single active-site point mutation of KatG(S315T), we have employed pulse radiolysis as the means to initiate a catalytic pathway capable of mimicking the in vivo oxidation of isoniazid (INH). Radiolysis of a solution containing WT KatG revealed two intermediates: compound III (oxyferrous KatG) [415 (Soret), 545, 580 nm] formed [k1 = (4.47 +/- 0.91) x 105 M-1 s-1] in the absence of INH and compound II (410 (Soret), 540, 575 nm) formed [k1 = (4.43 +/- 0.69) x 105 M-1 s-1] in the presence of INH, with a comparison of the rates suggesting that compound III (rate-limiting) precedes compound II formation. By contrast, radiolysis of KatG(S315T) only led to compound III formation, whether INH was present [k1 = (4.72 +/- 0.99) x 105 M-1 s-1] or not [k1 = (4.51 +/- 1.38) x 105 M-1 s-1]. HPLC studies to determine the rates of INH-NADH adduct formation (an inhibitor of InhA) as catalyzed by KatG were also performed employing various oxidants: air [WT: (7.18 +/- 1.25) x 10-4, S315T: (0.74 +/- 0.39) x 10-4], superoxide (SOTS-1) [WT: (9.22 +/- 1.10) x 10-4, S315T: not detected], and tert-butylhydroperoxide [WT: (20.5 +/- 1.13) x 10-4, S315T: (10.15 +/- 0.19) x 10-4]. Taken together, the results from the pulse radiolysis work as well as the InhA inhibitor studies allow us to propose a mechanism capable of correlating the inability for the oxyferrous intermediate of KatG(S315T) to oxidize ("activate") INH to the suppressed formation of the INH-NADH adduct, thereby leading to INH resistance in Mycobacterium tuberculosis.     

Dynamic [2]catenanes based on a hydrogen bonding-mediated bis-zinc porphyrin foldamer tweezer: a case study

This paper describes the self-assembly of a new class of three-component dynamic [2]catenanes, which are driven or stabilized by intramolecular hydrogen bonding, coordination, and electrostatic interaction. One of the component molecules 2, consisting of an aromatic oligoamide spacer and two peripheral zinc porphyrin units, was designed to adopt a folded preorganized conformation, which is stabilized by consecutive intramolecular three-centered hydrogen bonds. Component molecule 3 is a linear secondary ammonium bearing two peripheral pyridine units, which was designed to form a 1:1 complex with 24-crown-8 (5). The 1H NMR and UV-vis experiments in CDCl3-CD3CN (4:1 v/v) revealed that, due to the preorganized U-shaped feature, 2 could efficiently bind 3 through the cooperative zinc-pyridine coordination to generate highly stable 1:1 complex 2.3. Adding 5 to the 1:1 solution of 2 and 3 led to the formation of dynamic three-component [2]catenane 2.3.5 as a result of the threading of 3 through 5. 1H NMR studies indicated that in the 1:1:1 solution (3 mM) [2]catenane 2.3.5 was generated in 55% yield at 25 degrees C. The yield was increased with the reduction of the temperature and [2]catenane could be produced quantitatively in a 1:1:2 solution ([2]=3 mM) at -13 degrees C. Replacing 3 with 1,2-bis(4,4'-bipyridinium)ethane (4) in the three-component solution could also give rise to similar dynamic [2]catenane 2.4.5 albeit in slightly lower yield.     

Preparation and physicochemical characterization of carbamazepine (CBMZ): para-sulfonated calix[n]arene inclusion complexes

The formation of inclusion complexes with para-sulfonated calix[n]arene (PSC[n]A) was studied for carbamazepine (CBMZ), a poorly water soluble anticonvulsant drug. The effect of PSC[4]A and PSC[6]A on aqueous solubility of carbamazepine was studied extensively. The complete complexation of the drug was achieved after 48 h of shaking with PSC[n]A in water and evaporation of water to get solid complex. The interaction between PSC[n]A and CBMZ in solid state inclusion complexes was accomplished by aqueous phase solubility studies, HPLC, DSC, PXRD, FTIR, UV–Vis, and FT-Raman spectroscopy. The solubility of CBMZ increases as a function of PSC[n]A concentration. The results of the two phase solubility experiments are in good conformity to signify the formation of 1:1 (PSC[6]A:CBMZ) and 2:1 PSC[4]A:CBMZ complexes. The order of dissolution rate of CBMZ is inclusion complex > physical mixture > drug alone. The purpose of this study was to enhance solubility resulting in high dissolution rate and bioavailability of this essentially water insoluble drug.     

P=C bonds as building blocks for three- and four-membered heterocyclic cations: synthesis, structures and mechanistic studies

The activation of the P=C bond of phosphaalkenes with electrophiles is investigated as a means to prepare and characterize unusual organophosphorus compounds. Treatment of RP=CHtBu (1a: R=tBu; 1b: R=1-adamantyl) with HOTf (0.5 equiv) affords diphosphiranium salts [RP-CHtBu-PR (CH(2)tBu)]OTf ([2a]OTf and [2b]OTf), each containing a three-membered P(2)C ring. In contrast, the addition of MeOTf (0.5 equiv) to either 1a or 1b affords diphosphetanium salts [RP-CHtBu-P(Me)R-CHtBu]OTf ([3a]OTf and [3b]OTf) containing four-membered P(2)C(2) heterocycles. The phosphenium triflate [tBuP(CH(2)tBu)]OTf ([5a]OTf) and methylenephosphonium triflate [tBu(Me)P=CHtBu]OTf ([7a]OTf) are identified spectroscopically as intermediates in the formation of [2a](+) and [3a](+), respectively. The phosphenium triflate intermediate can be trapped with 2-butyne to afford phosphirenium salt [MeC=CMe-tBuPCH(2)tBu]OTf ([6a]OTf). Treatment of diphosphetanium [3a]OTf with an excess MeOTf affords [Me(2)P-CHtBu-PMetBu-CHtBu](OTf)(2) ([4a](OTf)(2)), a compound containing a diphosphetanium dication. The molecular structures are reported for [2a]OTf, [2b][H(OTf)(2)], [3a]I, [3b]I, [4a](OTf)(2), and [6a]OTf.     

The first ruthenium-based paullones: syntheses, X-ray diffraction structures, and spectroscopic and antiproliferative properties in vitro

Two novel paullone derivatives, namely, 6-(alpha-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L1) and 9-bromo-6-(alpha-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L2), have been prepared. The reaction of cis-[RuCl2(DMSO)4] (DMSO=dimethyl sulfoxide) with L1 and L2 in a 1:1 molar ratio in dry ethanol at 50 degrees C afforded the complexes trans-[RuIICl2(DMSO)2L1] (1a) and trans-[RuIICl2(DMSO)2L2] (1b) in 26 and 30% yield, respectively. The reaction carried out from the same starting compounds in a 1:2 molar ratio at 75 degrees C led to the formation of [RuIICl(DMSO)(L1)2]Cl (2a) and [RuIICl(DMSO)(L2)2]Cl (2b) in 16 and 23% yield, correspondingly. The products were characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, electrospray ionization mass spectrometry, IR spectroscopy, electronic spectra, cyclic voltammetry, and X-ray crystallography (L1, L2, 1a, and 2b). Complexes 2a and 2b exhibit remarkable antiproliferative activity in three human carcinoma cell lines, A549 (non-small cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon carcinoma). The novel complexes show an intercalative mode of interaction with DNA, which may render them attractive alternatives to metal compounds with a coordinative mode of interaction.     

Calix[6]pyrrole and hybrid calix[n]furan[m]pyrroles (n+m=6): syntheses and host-guest chemistry

Calix[6]pyrrole 2 and the "hybrid systems" calix[3]furan[3]pyrrole 12, calix[2]furan[4]pyrrole 13, and calix[1]furan[5]pyrrole 14, have been synthesized by increasing conversion of the furan units present in the readily accessible calix[6]furan 3 to pyrroles. The host-guest chemistry of these novel macrocycles towards a number of anions, including halogen ions, dihydrogen phosphate, hydrogen sulfate, nitrate, and cyanide has been investigated in solution by (1)H NMR titration techniques and/or phase transfer experiments. The solid-state structures of the free receptors 2, 12, and 13, the 1:1 complexes of calix[6]pyrrole 2 with chloride and bromide, and the 1:1 complex of 14 with chloride are also reported.     

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.     

New Solid Forms of Nitrofurantoin and 4-Aminopyridine Salt: Influence of Salt Hydration Level on Crystal Packing and Physicochemical Properties

The crystallization of the poorly soluble drug nitrofurantoin (NFT) with 4-aminopyridine (4AmPy) resulted in three multicomponent solid forms with different hydration levels: anhydrous salt [NFT+4AmPy] (1:1), salt monohydrate [NFT+4AmPy+H₂O] (1:1:1), and salt tetrahydrate [NFT+4AmPy+H₂O] (1:1:4). Each salt was selectively prepared by liquid-assisted grinding in the presence of acetonitrile or ethanol/water mixture at a specific composition. The NFT hydrated salts were characterized using single crystal X-ray diffraction. The [NFT+4AmPy+H₂O] salt (1:1:1) crystallized as an isolated site hydrate, while the [NFT+4AmPy+H₂O] salt (1:1:4) crystallized as a channel hydrate. The dehydration processes of the NFT salt hydrates were investigated using differential scanning calorimetry and thermogravimetric analysis. A powder dissolution experiment was carried out for all NFT multicomponent solid forms in pH 7.4 phosphate buffer solution at 37 °C.     

Triphenylantimony(v) catecholates and o-amidophenolates: reversible binding of molecular oxygen

Novel neutral antimony(V) complexes were isolated as crystalline materials and characterized by IR and NMR spectroscopy: o-amidophenolate complexes [4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-amidophenolato]triphenylantimony(V) (Ph3Sb[AP-Me], 1) and [4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolato]triphenylantimony(v) (Ph3Sb[AP-iPr], 2); catecholate complexes (3,6-di-tert-butyl-4-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)Cat], 3), its methanol solvate 3CH3OH (4); (3,6-di-tert-butyl-4,5-di-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)2Cat], 5) and its acetonitrile solvate 5CH3CN (6). Complexes 1-7 were synthesized by oxidative addition of the corresponding o-iminobenzoquinones or o-benzoquinones to Ph3Sb. In the case of the phenanthrene-9,10-diolate (PhenCat) ligand, two different complexes were isolated: Ph3Sb[PhenCat] (7) and [Ph4Sb]+[Ph2Sb(PhenCat)2]- (8). Complexes 7 and 8 were found to be in equilibrium in solution. Molecular structures of 2, 4, 6, and 8 were determined by X-ray crystallography. Complexes 1-7 reversibly bind molecular oxygen to yield Ph3Sb[L-Me]O2 (9), Ph3Sb[L-iPr]O2 (10), Ph3Sb[(MeO)L']O2 (11), Ph3Sb[(MeO)2L']O2 (12) and Ph3Sb[PhenL']O2 (13), which contain five-membered trioxastibolane species (where L is the O,O',N-coordinated derivative of a 1-hydroperoxy-6-(N-aryl)-iminocyclohexa-2,4-dienol, and L' the O,O',O'-coordinated derivative of 6-hydroperoxy-6-hydroxycyclohexa-2,4-dienone). Complexes 9-13 were characterized by IR and 1H NMR spectroscopy and X-ray crystallography.     

Ind-N-alkylation of rutaecarpine and synthesis of two novel related heterocyclic ring systems: Indolo[1′,2′:3,4]pyrazo[1,2-α]quinazoline and indolo[1′,2′:3,4] [1,4] diazepino[ 1,2-α]quinazoline

The failure to obtain the N-(13)alkylrutaecarpines ( 1d,e,f ) by heating rutaecarpine ( 1a ) with neat alkyl halides at 120° is discussed in comparison with the facile reaction with methyl iodide. In contrast, with alkyl halide-potassium carbonate in acetone, the corresponding N-(13)alkyl-rutaeearpines ( 1d-l ) are obtained in good yield. By use of 1,3-diiodopropane and 1,2-dibromo-ethane, this reaction provides a facile route to 12a and 13 which are derivatives of the heretofore unknown indolo[1,2′:3,4]pyrazo[1,2-α]quinazoline and indolo[1,2 :3,4][1,4]diazepino[1,2-α]quinazoline ring systems.     

Electrophilic cyclization of o-acetoxy- and o-benzyloxyalkynylpyridines: an easy entry into 2,3-disubstituted furopyridines

[reaction: see text] 2,3-Disubstituted furo[3,2-b]pyridines, 2,3-disubstituted furo[2,3-b]pyridines, and 2,3-disubstituted furo[2,3-c]pyridines are readily prepared under mild conditions via the palladium-catalyzed cross-coupling of 1-alkynes with o-iodoacetoxy- or o-iodobenzyloxypyridines, followed by electrophilic cyclization by I(2) or by PdCl(2) under a balloon of carbon monoxide.     

Synthesis of 4-methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridine

4-Methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridine ( 3 ) was synthetized from 2-acetylfuro[3,2-f]benzo[b]furan ( 4 ) or from 2-acetyl-5,6-dihydrofuro[3,2-f]benzo[b]furan ( 10 ). The key step involves a rearrangement-cyclization of azides 6 and 12 to form 4-methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridin-1(2H) one ( 7 ) and 8,9-dihydro-4-methylfuro[3′,2′:5,6]benzofuro[3,2c]pyridin-1(2H)-one ( 13 ). Introduction of an aminoalkyl chain on carbon 1 was effected by substitution of 1-chloro-4-methylfuro[3′,2′:5,6]benzofuro[3,2-c]pyridine ( 8 ).     

A two-dimensional octacyanomolybdate(V)-based ferrimagnet: {[Mn(II)(DMF)4]3[Mo(V)(CN)8]2}n

Treatment of [HNBu3]3[Mo(V)(CN)8] with manganese(II) p-toluenesulfonate in N,N'-dimethylformamide (DMF) affords {[Mn(II)(DMF)4]3[Mo(V)(CN)8]2}n (1) as a two-dimensional network. The structure of 1 consists of [cis-Mn(II)(DMF)4(mu-NC)2]2+ and [trans-Mn(II)(DMF)4(mu-NC)2]2+ units that are linked via cyanides to three-connected [Mo(V)(CN)5(mu-CN)3]3- centers in a 4:2:6 ratio, forming 12-membered rings. Magnetic measurements indicate that 1 is a ferrimagnet (TN = 8 K) that exhibits frequency-dependent behavior in chi". Heating of 1 affords an additional magnetic phase (TN = 21 K) that is absent of linkage isomerism.     

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.     

From Packed “Sandwich” to “Russian Doll”: Assembly by Charge‐Transfer Interactions in Cucurbit[10]uril

As the host possessing the largest cavity in the cucurbit[n]uril (CB[n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron‐rich guests and detail the influence of encapsulation on the charge‐transfer interactions between guests. For the mono‐bipyridinium guest (methylviologen, MV ²⁺), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge‐transfer interactions between methylviologen and dihydroxynaphthalene ( HN ) by mainly forming the 1:2:1 packed “sandwich” complex (CB[10] ? 2 MV ²⁺ ?HN ). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to “U” shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane‐blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X‐ray crystal structure. Finally, a supramolecular “Russian doll” was built up by threading a guest through the cavities of both blue box and CB[10].     

Bidentates versus monodentates in asymmetric hydrogenation catalysis: synergic effects on rate and allosteric effects on enantioselectivity

C 1-Symmetric phosphino/phosphonite ligands are prepared by the reactions of Ph 2P(CH 2) 2P(NMe 2) 2 with ( S)-1,1'-bi-2-naphthol (to give L A ) or ( S)-10,10'-bi-9-phenanthrol (to give L B ). Racemic 10,10'-bi-9-phenanthrol is synthesized in three steps from phenanthrene in 44% overall yield. The complexes [PdCl 2( L A,B )] ( 1a, b), [PtCl 2( L A,B )] ( 2a, b), [Rh(cod)( L A,B )]BF 4 ( 3a, b) and [Rh( L A,B ) 2]BF 4 ( 4a, b) are reported and the crystal structure of 1a has been determined. A (31)P NMR study shows that M, a 1:1 mixture of the monodentates, PMePh 2 and methyl monophosphonite L 1a (based on ( S)-1,1 '-bi-2-naphthol), reacts with 1 equiv of [Rh(cod) 2]BF 4 to give the heteroligand complex [Rh(cod)(PMePh 2)( L 1a )]BF 4 ( 5) and homoligand complexes [Rh(cod)(PMePh 2) 2]BF 4 ( 6) and [Rh(cod)( L 1a ) 2]BF 4 ( 7) in the ratio 2:1:1. The same mixture of 5- 7 is obtained upon mixing the isolated homoligand complexes 6 and 7 although the equilibrium is only established rapidly in the presence of an excess of PMePh 2. The predominant species 5 is a monodentate ligand complex analogue of the chelate 3a. When the mixture of 5- 7 is exposed to 5 atm H 2 for 1 h (the conditions used for catalyst preactivation in the asymmetric hydrogenation studies), the products are identified as the solvento species [Rh(PMePh 2)( L 1a )(S) 2]BF 4 ( 5'), [Rh(S) 2(PMePh 2) 2]BF 4 ( 6') and [Rh(S) 2( L 1a ) 2]BF 4 ( 7') and are formed in the same 2:1:1 ratio. The reaction of M with 0.5 equiv of [Rh(cod) 2]BF 4 gives exclusively the heteroligand complex cis-[Rh(PMePh 2) 2( L 1a ) 2]BF 4 ( 8), an analogue of 4a. The asymmetric hydrogenation of dehydroamino acid derivatives catalyzed by 3a, b is reported, and the enantioselectivities are compared with those obtained with (a) chelate catalysts derived from analogous diphosphonite ligands L 2a and L 2b , (b) catalysts based on methyl monophosphonites L 1a and L 1b , and (c) catalysts derived from mixture M. For the cinnamate and acrylate substrates studied, the catalysts derived from the phosphino/phosphonite bidentates L A,B generally give superior enantioselectivities to the analogous diphosphonites L 2a and L 2b ; these results are rationalized in terms of delta/lambda-chelate conformations and allosteric effects of the substrates. The rate of hydrogenation of acrylate substrate A with heterochelate 3a is significantly faster than with the homochelate analogues [Rh( L 2a )(cod)]BF 4 and [Rh(dppe)(cod)]BF 4. A synergic effect on the rate is also observed with the monodentate analogues: the rate of hydrogenation with the mixture containing predominantly heteroligand complex 5 is faster than with the monophosphine complex 6 or monophosphonite complex 7. Thus the hydrogenation catalysis carried out with M and [Rh(cod) 2]BF 4 is controlled by the dominant and most efficient heteroligand complex 5. In this study, the heterodiphos chelate 3a is shown to be more efficient and gives the opposite sense of optical induction to the heteromonophos analogue 5.