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Due to similar coordination chemistry of palladium and platinum, a large number of palladium compounds as well have been investigated for their anticancer activity. In the present study, we describe synthesis, characterization, and anticancer activity of palladium complex [Bis(1,8-quinolato)palladium (II)], coded as NH3 against seven different cancer cell lines. NH3 is found to have higher antitumor activity than cisplatin against both parent ovarian A2780 cell line and cisplatin-resistant cell lines. Also, NH3 has the lower IC50 value in HT-29 colorectal cancer cell line. The higher antitumor activity of NH3 is due to the presence of bulky 8-Hydroxyquinoline ligand, thus reducing its reactivity. Proteomic study has identified significantly expressed proteins which have been validated through bioinformatics. NH3 has been found to be less toxic than cisplatin at 2.5 mg/kg and 5 mg/kg dosages on mice models. Binary combinations of NH3 with curcumin and epigallocatechin gallate (EGCG) have demonstrated dose and sequence-dependent synergism in ovarian and colorectal cancer models. All of the preclinical studies indicate promising therapeutic potential of NH3 [Bis(1,8-quinolato)palladium (II)] as an anticancer drug.

Chemical investigation of an undescribed Australian fungus, Aspergillus nanangensis, led to the identification of the nanangenines – a family of seven new and three previously reported drimane sesquiterpenoids. The structures of the nanangenines were elucidated by detailed spectroscopic analysis supported by single crystal X-ray diffraction studies. The compounds were assayed for in vitro activity against bacteria, fungi, mammalian cells and plants. Bioinformatics analysis, including comparative analysis with other acyl drimenol-producing Aspergilli, led to the identification of a putative nanangenine biosynthetic gene cluster that corresponds to the proposed biosynthetic pathway for nanangenines.

Ionic liquids (ILs) have been widely promoted as functional replacements of volatile organic solvents; however restricting their use to conventional solvents constrains their potential. One means of enhancing their utility is through the development of dual purpose ILs, capable of acting as both solvent and catalyst. A series of bromozincate ILs was synthesised, and the Lewis acidities probed spectroscopically. Furthermore, the crystal and molecular structure of [C2Py]2[ZnBr4] was determined through single-crystal X-ray diffraction. The ILs were then used in a model reaction, aimed at probing effects of both IL Lewis acidity and structural organisation on the reaction outcome.

Cyclometalation of 2-phenylpyridine with the η5:κS-indenyl-sulfanyl and -sulfinyl rhodium dichloride complexes rac-8, (pR*,RS*)-9, and (pR*,SS*)-9 in the presence of AgSbF6 provided the rhodacyclic complexes 10, 11, and 12, respectively, in yields ranging from 72% to 92%. The complexes were obtained as mixtures of chiral-at-metal epimers, with ratios of the epimer with the phenyl ligand anti to the indenyl benzo-ring [(pR*,SRh*)] to the epimer with the phenyl ligand syn to the benzo-ring [(pR*,RRh*)] of 3:2, 10:1, and 2:5 for complexes 10, 11, and 12, respectively, establishing that sulfoxide chirality has a significant role in stereocontrol of metal-centered chirality in the initially formed complexes. Equilibration of the rhodacyclic complexes takes place at 120 °C in 1,1,2,2-tetrachloroethane-d2 (C2D2Cl4) solution or at 60 °C in C2D2Cl4 solution in the presence of catalytic 4-ethylpyridine. Kinetic studies demonstrate that under the former conditions, epimerization is catalyzed by adventitious water an...

Dual H-bond donors are widely used as recognition motifs in anion receptors. We report the synthesis of a library of dual H-bond receptors, incorporating the deltic and croconic acid derivatives, termed deltamides and croconamides, respectively, and a comparison of their anion binding affinities (for monovalent species) and Brønsted acidities to those of the well-established urea and squaramide dual H-bond donor motifs. For dual H-bonding cores with identical substituents, the trend in Brønsted acidity is croconamides> squaramides>deltamides>ureas, with the croconamides found to be 10–15 pKa units more acidic than the corresponding ureas. In contrast to the trends displayed by ureas, deltamides and squaramides, N,N’-dialkyl croconamides displayed higher binding affinity to chloride than the N,N’-diaryl derivatives, which was attributed to partial deprotonation of the N,N’-diaryl derivatives at neutral pH. A number of differences in anion binding selectivity were observed upon comparison of the dual H-bond cores. Whereas the squaramides display similar affinity for both chloride and acetate ions, the ureas have significantly higher affinity for acetate than chloride ions and the deltamides display higher affinity for dihydrogenphosphate ions than other oxoanions or halides. These inherent differences in binding affinity could be exploited in the design of anion receptors with improved ability to discriminate between monovalent anions.

The effective and efficient removal of the BF2 moiety from F-BODIPY derivatives has been achieved using two common Brønsted acids; treatment with trifluoroacetic acid (TFA) or methanolic hydrogen chloride (HCl) followed by work-up with Ambersep® 900 resin (hydroxide form) effects this conversion in near-quantitative yields. Compared to existing methods, these conditions are relatively mild and operationally simple, requiring only reaction at room temperature for six hours (TFA) or overnight (HCl).

An unprecedented diversity of high-order bromine catenates (anionic polybromides) was generated in a tetraalkylphosphonium-based room temperature ionic liquid system. Raman spectroscopy was used to identify polybromide monoanions ranging from [Br5 ](-) to [Br11 ](-) in the bulk solution, while single-crystal X-ray diffraction identified extended networks of linked [Br11 ](-) units, forming a previously unknown polymeric [Br24 ](2-) dianion. This represents the largest polybromide species identified to date. In combination with recent work, this suggests that other, higher order molecular polybromide ions might be isolated.

The synthesis, electronic absorption and 1H NMR spectra of a suite of novel porphyrinoids derived from meso-bromoporphyrins by palladium-catalysed aminations using ethyl and tert-butylcarbazates are reported. Instead of the expected carbazate-substituted porphyrins, a facile oxidative dearomatisation of the porphyrin ring occurs in high yield, especially for the nickel(II) complexes, resulting in high yields of 5,15-diiminoporphodimethenes (DIPDs). The analogous zinc(II) and free base DIPDs were also characterised, the former by X-ray crystallography. The oxidation and reduction reactions of DIPDs and their precursor carbazate porphyrins were studied. Density Functional Theory (DFT) was used to calculate the optimised geometries and frontier molecular orbitals of DIPD Ni8c and bis(azocarboxylate) 19c, and Time Dependent DFT calculations allowed the prediction of electronic absorption spectra, whose characteristics corresponded well with those of the observed solution spectra. In the latter case, the calculated low-energy absorptions were unlike those of a typical porphyrin, due to the near-degeneracy of the highest filled frontier orbitals, and the wide energy separation between the unfilled orbitals. This feature was present in the observed spectrum.

The synthesis and photophysical properties of four squaramide based fluorescent anion sensors (1-4) are described. These luminescent compounds showed selectivity for Cl(-) over various other anions with concomitant changes in both their UV/visible and fluorescence properties upon Cl(-) addition, attributed to initial H-bonding followed by NH deprotonation in the presence of excess Cl(-), signaled by a color change. The nature of the electron withdrawing aryl substituents is directly related to the H-bonding ability/acidity of the squaramide protons and can be used to tune the deprotonation behavior.

The aza-Henry reaction is an efficient route to important chiral, vicinal diamines. Reports of the asymmetric version typically use electron-deficient acyclic imines. We report the first example of a catalytic, asymmetric aza-Henry reaction on an unfunctionalized cyclic imine that gives access to enantiopure diamine derivatives under experimentally straightforward conditions. The stereocentre is established through the initial nitromethane addition to the imine. The scalemic intermediate may be trapped through acylation, then crystallized.

Axially chiral rac-1-(2-methyl-1H-inden-3-yl)-2-(methylsulfanyl)naphthalene (rac-3) was synthesized from methyl 2-(methylsulfanyl)-1-naphthoate through reaction with the di-Grignard reagent derived from 1-bromo-2-(2-bromopropyl)benzene, followed by acid-catalyzed dehydration of the intermediate indanol. Oxidation of rac-3 with m-CPBA gave the diastereomeric sulfoxides (aR*,RS*)-5 and (aR*,SS*)-6, with the relative configuration of 5 established using single-crystal X-ray diffraction. The dichloro[η5:κS-indenyl-sulfanyl and -sulfinyl]rhodium complexes rac-4, (pR*,SS*)-7, and (pR*,RS*)-8 were synthesized through reaction of the ligands rac-3, (aR*,RS*)-5, and (aR*,SS*)-6, respectively, with rhodium trichloride in 9:1 methanol/water solution heated under reflux. The use of water as a cosolvent was found to be critical for obtaining good yields in the complexation reactions. Solid-state structures for the racemic rhodium complexes were determined through single-crystal X-ray diffraction. The enantiomers of th...

Local molecular environment effects on the rates of ligand exchange at an asymmetric di[dihydroxotin(IV)] bis-porphyrin 5 are examined. The host 5 possesses four non-equivalent tin(IV)-ligand binding sites that are distinguished by their position relative to a shallow cavity, by the steric environment at each binding site and by electronic-structure differences between the constituent porphyrin and quinoxalinoporphyrin macrocycles. These design features of the asymmetric host are confirmed by X-ray crystal structure analysis. Binding experiments with monodentate carboxylic acids and bidentate dicarboxylic acids show significant differences in the rate of ligand exchange at each of the four tin(IV) binding sites. For monodentate carboxylic acids, binding preferentially occurs at the exterior porphyrin site. Further addition of carboxylic acid results in sequential binding at the quinoxalinoporphyrin sites and lastly at the interior site on the porphyrin, with high regioselectivity. These selective binding outcomes are immediately apparent by NMR spectroscopy. A series of 2D NMR spectroscopy experiments allowed identification of the preferred binding sites at the host. This positively identifies that steric hindrance and electron-withdrawing functionality on the porphyrin macrocycle impede ligand exchange. However, these effects are overcome by dicarboxylic acid guests, which form ditopic hydrogen-bond interactions between the intracavity hydroxo ligands in the initial stage of ligand exchange, leading to regioselective binding between the tin(IV) sites within the cavity. It is envisaged that the factors identified herein that define regioselective ligand exchange at host 5 will find wider application in supramolecular systems incorporating tin(IV) porphyrins.

Several chiral amines were investigated for the stereoselective preparation of homophenylalanine derivatives using the Petasis reaction. Chiral secondary amines such as N,α-dimethylbenzylamine and N-benzylphenylglycinol gave the best results in terms of both yield and diastereoselectivity. The use of N-benzylphenylglycinol leads directly to 3-alkenyl-4-benzyl-5-phenyloxazin-2-one products. Intriguing variation was observed in the stereoselectivity of reactions employing para-substituted styrenylboronic acid substrates, where presumably only electronic factors are involved.

The first synthesis of Troger’s base analogues bearing three and four atoms in the apical strap is reported, leading to a dramatic change in the shape of the aromatic scaffold with respect to the Troger’s base framework.

Acetylido methyl ruthenium(II) complexes, trans-Ru(C⋮CR)(CH3)(dmpe)2, were synthesized in a single metathesis reaction from trans-Ru(CH3)2(dmpe)2 at ambient temperature; at elevated temperatures the reaction yields trans-Ru(C⋮CR)2(dmpe)2. Addition of a second terminal acetylene to a methanol solution of trans-Ru(C⋮CR)(CH3)(dmpe)2 results in the formation of trans-Ru(C⋮CR)(C⋮CR‘)(dmpe)2.

The synthesis and characterisation by single crystal X-ray diffraction of 1:2 host-guest assemblies formed between the tetra-amine macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) and diphenylphosphinic acid or 4-tert-butylbenzoic acid are reported. In each case strong hydrogen bonds associated with proton transfer from the acid species to two (trans) amino groups in the cyclen ring are observed. Both adducts are also associated with complex hydrogen bonded networks involving the secondary amines and water molecules, with each crystal structure containing five water molecules per asymmetric unit.

Four platinum(II) metallointercalating complexes of 1,10-phenanthroline (phen) with the chiral ancillary ligands trans-R,R- and trans-S,S-1,2-diaminocyclohexane (R,R- and S,S-dach, respectively), and N,N'-dimethyl-R,R- and N,N'-dimethyl-S,S-1,2-diaminocyclohexane (Me(2)-R,R-dach and Me(2)-S,S-dach, respectively) have been synthesised and characterised. The crystal structure of [Pt(Me(2)-S,S-dach)(phen)](ClO(4))(2)1.5 H(2)O (C(20)H(26)Cl(2)N(4)O(9.5)Pt) has been determined; orthorhombic, space group P2(1)2(1)2(1)(No. 19), a=23.194(8), b=25.131(9), c=8.522(3) A. In vitro cytotoxic assays (IC(50)) in the human bladder cancer cell line 5637 and in the murine leukemia L1210 cell line revealed that [Pt(S,S-dach)(phen)](ClO(4))(2) (0.091 and 0.13 microM, respectively) and [Pt(R,R-dach)(phen)](ClO(4))(2) (0.54 and 1.50 microM, respectively) were more cytotoxic than cisplatin (0.31 and 0.50 microM, respectively) and considerably more cytotoxic than their methylated counterparts, [Pt(Me(2)-R,R-dach)(phen)](ClO(4))(2) and [Pt(Me(2)-S,S-dach)(phen)](ClO(4))(2) (both>23 microM). Chiral discrimination for [Pt(S,S-dach)(phen)](ClO(4))(2) over its R,R-enantiomer was observed in all 13 cancer cell lines investigated. Moreover, [Pt(S,S-dach)(phen)](ClO(4))(2) was more active than cisplatin in all cell lines tested and shows only partial cross-resistance to cisplatin in two cisplatin resistant cell lines.

Reaction of [Mo(CO)3(3-azahexane-1,6-diamine)] with formaldehyde and the carbon acid nitroethane leads to cyclisation involving one terminal amine and either the internal secondary amine (minor product) or the other terminal primary amine (major product), with zinc/acid reduction yielding new cyclic tetraamines, also characterised as their cobalt(III) complexes. This is the first example of Mannich-style formation of a pendant-arm triazamacrocycle around a molybdenum(0) template. The unexpected N-(1′-aminopropyl)-6-methyl-1,4-diazacycloheptan-6-amine minor product has been characterised by an X-ray structure as its cis-dichlorocobalt(III) complex.

A range of rhodium(I) and iridium(I) complexes containing bidentate phosphine−pyrazolyl ligands of general formulas [M(R2PyP)(COD)]BPh4 (R = Me, iPr, Ph, M = Ir, 3b−3d and M = Rh, 4b−4d), [Ir(R2PyP)(CO)2]BPh4 (R = Me, iPr, 5b,5c), and [M(R2PyP)(CO)Cl] (R = Me, iPr, Ph, M = Ir, 6b−6d and M = Rh, 7b−7d) were successfully synthesized. A number of these complexes and their analogues with unsubstituted ligands are extremely active as catalysts for the intramolecular hydroamination of alkynes. The air-stable cationic iridium complexes containing 1,5-cyclooctadiene, COD, as co-ligands, [Ir(R2PyP)(COD)]BPh4 (R = H, Me, iPr, and Ph, 3a−3d), are efficient as catalysts for the cyclization of 4-pentyn-1-amine (8) to 2-methyl-1-pyrroline (9) with the turnover rate at 50% conversion (Nt) of up to 3100 h-1, at 60 °C. The cationic iridium complexes containing carbonyl co-ligands, [Ir(R2PyP)(CO)2]BPh4 (R = H, Me, iPr, 5a−5c), are moderately effective in catalyzing this reaction, and the neutral complexes [M(R2PyP)(CO)Cl] ...

The most adhered to strategy in inorganic chemistry for stabilizing reactive functionalities, achieving reaction selectivities, and accessing novel structural motifs is the use of hindered “nonparticipative ligands” to afford protection and/or force unusual/desired behavior.

A series of novel indolyl-imine ligand precursors have been synthesized. In particular, bidentate, tridentate, and potentially tetradentate ligands were prepared, each containing both indolyl sp2-N and imine sp2-N donors. A series of neutral rhodium(I) and iridium(I) complexes of these ligands were synthesized, including monometallic and bimetallic complexes. The X-ray structures of three of the monometallic complexes with bidentate indolyl-imine ligands were determined. In each complex, the metal center was in a square planar conformation, as expected for Rh(I) and Ir(I) complexes. The fiveand six-membered metallocycles formed on complexation of the metal with the ligands were all planar, and the aromaticity of the ligands was maintained. The Rh(I) complex with the tridentate indolyl ligand (L) reacted at room temperature with CH2Cl2 to form the Rh(III) chloromethyl complex [Rh(L)(CO)-(CH2Cl)(Cl)] via oxidative addition of the C-Cl bond of CH2Cl2. The Rh/Ir(I) indolyl-imine complexes are efficient catalysts for the intramolecular cyclization of 4-pentynoic acid to form c-methylene-c-butyrolactone. A dinuclear Rh(I) complex was the most active catalyst, demonstrating a significant degree of bimetallic cooperativity.

Hydrolysis studies of derivatives of molybdocene dichloride in which the two chloride ligands were replaced by 3,5-bis(trifluoromethyl)thiophenol, 3,5-bis(trifluoromethyl)benzyl thiol, and 2,2,2-trifluoroethane thiol ligands confirmed that the electron-withdrawing groups affect the lability of the Mo−S bonds and promote slow generation of the putative biologically active species “Cp2Mo2+”; the trifluoroethane thiol derivative underwent 50% hydrolysis in 14 h in 10% D2O/DMSO-d6. The structure of molybdocene bis(S-3,5-bis(trifluoromethyl)benzyl thiol) was confirmed by X-ray crystal structure analysis.

Ditopic symmetrical bis(pyridyl) ligands incorporating the chiral dibenzobicyclo[b,f][3.3.1]nona-5a,6a-diene-6,12-dione cleft have been synthesised and characterised by NMR spectroscopy, mass spectrometry and X-ray crystallography. The ligands, which incorporate pyridyl groups directly connected to the carbocyclic cleft core or via alkyne or phenyl linkers were accessed from palladium-catalysed coupling reactions of 2,8-dibromodibenzobicyclo[b,f][3.3.1]nona-5a,6a-diene-6,12-dione. X-ray crystal analyses show the interplanar angles between the two cleft aromatic rings in these molecules, which range from 97.80(3) to 109.80(4)°.

The preparation, characterization, and interconversion reactions of a series of novel O- and N-bonded acetamide and deprotonated N- and N,O-bonded acetamido derivatives of platinum(II)-terpy (terpy = 2,2′:6′,2″-terpyridine) are described. The X-ray structures of the mononuclear N-acetamido and an unusual di-nuclear N,O-acetamido species are also reported.

The outcome of aerial oxidation of the glucocortico-steroid side-chain (as exemplified by dexamethasone) has been shown to be subject to strict pH control. At pH 7.4 the glyoxal is the only product; at pH values of 8 and 9.2 the etioacid is formed, and at pH values of 13 or above the epimeric glycolic acids are produced. The glycolic acid epimer that predominates by a factor of 2 and is more stable has been shown by an X-ray crystal structural analysis to be the 20R compound. The presence of arsenite changes the course of the reaction and only the glycolic acids are yielded at pH values of 8 and above.

Novel porphyrinoids with interrupted conjugation (di-iminoporphodimethenes) result from the Pd-catalyzed coupling of meso-bromo porphyrins and their metal complexes with carbazates and hydrazones, followed by aerial oxidation. X-Ray crystallography revealed a saddle shape for molecules of the nickel(II) complex of a di-iminoporphodimethene.

Cationic Rh(I) and Ir(I) complexes of the form [M(PC)(COD)]BPh4 (M = Rh (4), Ir (5); PC = 3-[2-(diphenylphosphino)ethyl]-1-methylimidazol-2-ylidene) were synthesized by the addition of 3-[2-(diphenylphosphino)ethyl]-1-methylimidazolium (3) to [M(μ-OEt)(COD)]2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) in the presence of base. COD was successfully displaced from [Rh(PC)(COD)]BPh4 (4) by addition of carbon monoxide to a methanol/hexane suspension to form [Rh(PC)(CO)2]BPh4 (6). The analogous addition of CO to the iridium compound 5 resulted in the formation of the five-coordinate Ir(I) complex [Ir(PC)(COD)(CO)]BPh4 (7). The single-crystal X-ray structures of 4, 5, and 7 were determined. The metal centers of 4 and 5 are square planar, and the metal center of 7 is a distorted trigonal bipyramid. Complexes 4−7 are effective as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. Complete conversion (>97%) of 4-pentyn-1-amine was observed using complexes 4−7 as catalysts, in b...

[structures: see text] Penta-1,3-dienyl acrylates undergo kinetically controlled intramolecular Diels-Alder (IMDA) reactions and DFT calculations (B3LYP/6-31+G(d)) predict stereoselectivities that are in very good agreement with the experimental values. The nature of the diene C1 substituent has virtually no influence upon reactivity or trans/cis-stereoselectivity whereas terminal C9 dienophile substituents have a substantial effect on both the reactivity and stereoselectivity of these IMDA reactions. The TSs highlight contributions from strain in the developing tether-containing ring, and steric and electronic effects between tether and dienophile substituents, thus providing insight into the origins of IMDA reactivity and stereoselectivity.

The stereochemical outcome phile. The stereochemical outcomes of structures. New insights into the conof the intramolecular Diels-Alder reac- these reactions are explained by refer- formational preferences of allylic alcotion of ester-linked 1,3,8-nonatrienes ence to B3LYP/6-31G(d) transition hol derivatives are reported, results can be controlled by substituents about which allow an explanation of the difa stereogenic center attached to Cl. fering levels of π-diastereofacial selecThe scope and limitations of this ap- tivity and cis/trans (i.e. endo/exo) selecproach have been investigated, with tivity from the reaction. variation in substrate structure about the allylic stereocenter and the dieno.

The cyclization of small peptides which do not incorporate turn inducers is often difficult. We have developed a method involving the use of removable turn inducers, in the form of pseudoprolines, for the cyclization of difficult peptide sequences. The pseudoprolines induce a cisoid amide bond in the peptide backbone which facilitates cyclization. They are then readily removed to yield a cyclic peptide that does not contain any turn inducers.

Ansa-zirconocene dichloride complexes containing a 9-fluorenyl group at the 1-position of naphthalene and a 2-indenyl 12, 1-indenyl 13, or cyclopentadienyl 14 group at the 2-position of the naphthalene were synthesised and characterised. The molecular structures of the complexes have been determined by single crystal X-ray diffraction studies. After activation with excess methylalumoxane (MAO), the complexes were used as homogeneous catalysts for the homopolymerisation of ethylene and propylene.

Cationic rhodium(I) and iridium(I) complexes of the general formula [M(N−N)(CO)2]+[X]-, incorporating the bidentate heterocyclic nitrogen donor ligands (N−N) bis(1-methylimidazol-2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm), are efficient catalysts for hydroamination. The cyclization of an aliphatic aminoalkyne to the corresponding five-membered imine heterocycle was achieved in good yield with excellent regioselectivity using both rhodium and iridium catalysts. The nature of the counterion to the cationic catalysts has a significant effect on the rate of the hydroamination reaction and interionic contacts between the metal complexes and their counterions in solution were clearly visible by NMR spectroscopy using the nuclear Overhauser effect, indicating a strong anion/cation interaction in solution. The nature of the coligands also had a significant effect on the efficiency of the metal complexes as catalysts, and complexes containing phosphine coligands were less effective catalysts compared to ...

We describe the successful synthesis of the porphyrin [2]catenanes, which completes a set of six structures where the length of the polyethylene glycol strap over the porphyrin is regularly increased from diethylene to triethylene to tetraethylene, and the central electron-donor component is either hydroquinol- or naphthoquinol-based. In the synthetic route to the strapped porphyrin precursors, co-formation of “straight” and “twisted” atropisomers in the longer strapped derivatives, and dimeric and higher oligomeric structures for the shorter straps, has been observed. Catenation results in only a single [2]catenane in each case. X-ray crystal structures of two representative strapped porphyrins are described. For each of the untwisted singly-strapped porphyrins, there is significant binding of paraquat within the cavity formed by the strap, and the binding constants range over about two orders of magnitude. For the catenanes, in each case the overall structural motif is similar to that previously observed for related members of the series. The temperature-dependent dynamic properties of the catenanes have been examined by 1H NMR methods, and the rates of rotation increase from 50 to 25 000 to 340 000 s−1 at room temperature as the length of the strap increases by one ethylene glycol unit on each side. For the similarly sized naphthoquinol derivatives, the rotation rates are reduced by many orders of magnitude, ranging from essentially zero to 10 to 100 times per second at 25 °C through the same increase in chain length as for the hydroquinol analogues. The rates for a second process described as “out, turn around and in again”, range from 2 to 400 to 110 000 s−1 at 25 °C in this naphthoquinol porphyrin series. The electronic spectra of the catenanes themselves do not show any significantly enhanced charge-transfer bands over the hydroquinol counterparts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The mononuclear cationic RhI complexes [Rh(cod)(mdd)]+X− and [Rh(CO)2(mdd)]+X− (X = BPh4, PF6) containing the chelating bidentate N-heterocyclic carbene ligand 1,1′-methylene-3,3′-dimethyldiimidazoline-2,2′-diylidene (mdd) have been synthesised and spectroscopically characterised. The complexes [Rh(cod)(mdd)]+BPh4− and [Rh(CO)2(mdd)]+PF6− have also been characterised by X-ray crystallography. The dicarbonyl complexes catalyse the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The synthesis of tetraoxygenated bromonaphthoquinones 6a , 6b , 6c , 6d , key intermediates for a synthesis of the 3C protease inhibitor, thysanone, were investigated. Addition of 1-methoxy-1,3-bis(trimethylsilyloxy)-1,3-butadiene 8 to 2,6-dibromo-1,4-benzoquinone 10 in benzene afforded a mixture of naphthoquinone 6a , arising from Diels–Alder addition followed by aromatisation, and Michael adduct 12 . The Michael adduct 12 predominated when THF was used as solvent whereas 6a predominated when benzene was used. Naphthoquinone 6a underwent benzylation to naphthoquinone 6c . Addition of 1,1-dimethoxy-3-trimethylsilyloxy-1,3-butadiene 9 to 2,6-dibromo-1,4-benzoquinone 10 followed by benzylation failed to afford the desired bromonaphthoquinone 6d yet methylation did afford naphthoquinone 6b . Bromonaphthoquinone 6d was finally prepared from naphthol 18 , obtained from addition of diene 9 to 1,4-benzoquinone 17 , followed by ortho-bromination and oxidation. Attempted Sakurai allylation of bromonaphthoquinone 6d afforded naphthodihydrofuran 21 . A similar observation was observed for 2-carbomethoxy-1,4-naphthoquinone 22 that also underwent Sakurai allylation to afford naphthodihydrofuran 23 . The structure of Michael adduct 12 was confirmed by X-ray crystallography.

Cationic iridium(I), rhodium(I) complexes containing bis(1-methylimidazol-2-yl)methane, bim, [M(bim)(CO)2]BPh4 (M = Ir (1), Rh (2)); bis(pyrazol-1-yl)methane, bpm, [M(bpm)(CO)2]BPh4 (M = Ir (3), Rh (4)) have been shown to be effective in catalysing the regioselective addition of thiophenol to a series of alkynes. Analogous cationic and neutral Ir(I), Rh(I) complexes with the novel mixed P,N-donor bidentate ligand 1-(2-diphenylphosphino)ethylpyrazole, PyP (5), [M(PyP)(COD)]BPh4 (M = Ir (6), Rh (7), COD = 1,5-cyclooctadiene); [Rh(PyP)(COD)]BF4 (8); [Ir(PyP)(CO)2]BPh4 (9); [Rh(PyP)(CO)2]BF4 (10); [M(PyP)(CO)Cl] (M = Ir (11), Rh (12)) have also been synthesised, and characterised by NMR. The solid-state structures of (6), (7), (11) and (12) have been determined by single-crystal X-ray diffraction analysis. The metal complexes (9)–(12) with the mixed P,N-donor ligand, PyP are in most cases more effective in promoting the hydrothiolation of alkynes in comparison with the analogous complexes (1)–(4) with N,N-donor ligands. The iridium complexes were significantly more effective than their rhodium analogues in promoting the hydrothioloation of alkynes. The cationic complexes (9) and (10) are more effective as catalysts for the hydrothiolation of alkynes than their neutral analogues (11) and (12).

A number of iron(II) compounds containing the poly(1-pyrazolyl)methane ligands bis(1-pyrazoyl)methane (BPM, 3), bis(3,5-dimethyl-1-pyrazolyl)methane (dmBPM, 4), and tris(1-pyrazolyl)methane (TPM, 2), were synthesised and characterised: cis-[Fe(BPM)2Cl2] (5), trans-[Fe(BPM)2(NCS)2] (9), [Fe(BPM)2Cl]+(BPh4)− (7), [Fe(dmBPM)2Cl2] (6), [Fe(dmBPM)2Cl]+(BPh4)− (8), [Fe(TPM)2]2+(Cl−)2 (10), and [Fe(TPM)(NCS)2] (11). The solid-state structures of cis-[Fe(BPM)2Cl2] (5) and trans-[Fe(BPM)2(NCS)2] (9) were determined by single crystal X-ray diffraction analysis. The compound cis-[Fe(BPM)2Cl2] (5) crystallises as colourless prisms from ethanol and trans-[Fe(BPM)2(NCS)2] (9) crystallises as colourless plates from methanol. All complexes were characterised by 1H- and 13C-NMR spectroscopy, infrared and far infrared spectroscopy, and mass spectroscopy. All of the iron(II) poly(1-pyrazolyl)methane compounds display temperature-dependent paramagnetism.

Experimental conditions for the intramolecular cycloaddition of four related pentadienyl acrylates 3, 4, 5 and 6 are reported. In contrast with several previous reports, pentadienyl acrylates do undergo synthetically useful intramolecular Diels-Alder reactions: 3, 4, 5 and 6 cyclise at reasonable rates at temperatures of 132-180 degrees C at atmospheric pressure in moderate to good yields. The stereochemical outcome of each of these reactions was accurately measured and the results are in good agreement with transition structure populations predicted using B3LYP/6-31+G(d) theory. The parent system 3 cyclises with moderate endo selectivity; the presence of either a C5-methyl substituent or a C3-bromine atom results in a slight shift towards the trans-fused exo stereoisomer but--overall--a less selective reaction. The presence of both C3-Br and C5-CH3 substituents results in a marked improvement in stereoselectivity with the exo,lk-product predominating. Interpretation of B3LYP/6-31+G(d) transition structures allows insights into the improvement in stereoselectivity obtained by incorporating a removable "steric directing group" into a 5-methyl-1,3,8-nonatriene precursor.

The X-ray crystal structure of a ternary complex of copper(II)-nitrilotriacetic acid (NTA, 2) and bis(N-methylimidazol-2-yl)ketone 3 is reported. This structure provides information about the nature of the interaction of metal complexes of NTA with polyhistidine peptides.

A supramolecular assembly formed between phthalimide and 2-guanidinobenzimidazole, containing a short 2.692(4)AR N-H…N hydrogen bond, is reported. The crystal structure of this species was determined by both X-ray and neutron diffraction. The diffraction data reveal that the proton involved in the short hydrogen bond has been transferred from the phthalimide to the guanidinobenzimidazole to form an ion pair. There is also an interesting stacking interaction between the atoms involved in the short hydrogen bond and the π system of a phthalimide molecule that is approximately 3.3 A away. The structure is compared with the structure of a similar assembly formed between 4-nitrophthalimide and 2-guanidinobenzimidazole.

The reactions between cis-Fe(dmpe)2H2 (dmpe = Me2PCH2CH2PMe2) (1) or cis-Fe(PP3)H2 (PP3 = P(CH2CH2PMe2)3) (2) and phenyl isothiocyanate (PhNCS), ethyl isothiocyanate (EtNCS), and phenyl isocyanate (PhNCO) were investigated. PhNCS reacts with 1 to form a variety of insertion products at low temperature, and the thermodynamic product hydridoiron N-phenylthioformimidate trans-Fe(dmpe)2(SCHNPh)H (3a) at 300 K. Addition of an excess of PhNCS to 1 produces the bis(insertion) product trans-Fe(dmpe)2(SCHNPh)2 (3c). EtNCS inserts into the iron−hydride bond of 1 to form a mixture of trans-Fe(dmpe)2(SCHNEt)H (4a, thermodynamic product) and cis-Fe(dmpe)2(SCHNEt)H (4b, kinetic product). Addition of an excess of EtNCS does not result in a second insertion but rather attack at the thioformimidato ligand to form trans-Fe(dmpe)2(SCHN+(Et)C(S)N-Et)H (4c). PhNCO reacts rapidly with 1 to form trans-Fe(dmpe)2(OCHNPh)H (5a) and higher oligomeric products. The addition of PhNCS, EtNCS, and PhNCO to 2 permits the formation of th...

The synthesis of optically pure functionalized cleft molecules derived from dibenzobicyclo[b,f][3.3.1]nona-5a,6a-diene-6,12-dione is reported. These clefts are reminiscent of Tröger's base but contain clefts with different dimensions and additional carbonyl (or alcohol) groups that may be utilized in molecular recognition studies. The 2,8-dimethyl and 2,8-dibromo derivatives were synthesized via an intramolecular Friedel-Crafts acylation and were resolved by chiral HPLC. The 2,8-dinitro derivative was prepared by regiospecific nitration of dibenzobicyclo[b,f][3.3.1]nona-5a, 6a-diene-6,12-dione. The dibromo and dinitro derivatives allow direct access to a range of functionalized molecular clefts. Palladium-catalyzed coupling of the dibromo derivative afforded the disubstituted phenyl, anisole, and acetylene derivatives, while reduction of the dinitro derivative and acetylation provided amino-dione and amide-hydroxyl derivatives. X-ray crystal structures of the dimethyl 12, dibromo 13, di(p-methoxyphenyl) 16, dinitro 18, and dimethyl dinitro 22 derivatives show cleft angles between the planes between the aromatic rings of 84-104 degrees. The synthetic route, structural features, and potential for molecular recognition studies of this class of clefts are compared with those of the more widely studied Tröger's base cleft molecules.

The methylene-bridged Rh(I) dicarbonyl complex, [ Rh(bim) (CO) 2 + BPh 4 - ] (1) (bim = bis(N-methylimidazol-2-yl)methane), is an effective catalyst for the intramolecular hydroamination of selected ortho-alkynylanilines to give a range of benzo(dipyrroles).

The preparation and characterisation of square planar cationic rhodium(I) dicarbonyl complexes {[Rh((mim) 2 CO)(CO) 2 ] + BPh 4 − ] ( 1 ),{[Rh((mim) 2 CH 2 )(CO) 2 ] + BPh 4 − } ( 2 ) and{[Rh((mBnzim) 2 CH 2 )(CO) 2 ] + BPh 4 − } ( 3 ) [mim= N -methylimidazol-2-yl, mBnzim= N -methylbenzimidazol-2-yl] is reported. The carbonyl ligands in 2 and 3 are readily exchanged for triphenylphosphine to form{[Rh((mim) 2 CH 2 )(PPh 3 ) 2 ] + BPh 4 − } ( 7 ) and {[Rh((mBnzim) 2 CH 2 )(PPh 3 ) 2 ] + BPh 4 − } ( 8 ). Complexes 2 and 3 were characterised by multinuclear NMR spectroscopy as well as by X-ray crystallography. Structural characterisation by X-ray analysis confirmed that complexes 2 and 3 are essentially square planar.

Irradiation of the dinitrogen complex W(N2)2(dppe)2 1 [dppe=bis-1,2-(diphenylphosphino)ethane] in the presence of diphenylphosphine results in P–H bond activation to give the phosphido complex WH(PPh2)(dppe)2 2. The X-ray crystal structure of the phosphido complex 2 indicates a W–P bond length of 2.28 A that is consistent with a W–P double bond.

Oxidative rearrangement of dihydronaphthofuran 5 with aqueous ceric ammonium nitrate afforded the cage compound 7 which decomposed to diol 8 upon standing at room temperature. An X-ray structure obtained for diol 8 confirmed the formation of this novel cage structure.