Gold(I) and silver(I) metallocryptates based on 2,9-bis(diphenylphosphino)-1,8-naphthyridine

In acetonitrile the rigid diphosphine ligand 2,9-bis(diphenylphosphino)-1,8-naphthyridine (dppn) reacts with (SMe2)AuCl in the presence of NaPF6 to produce a pale-yellow material identified as [Au2Na(mu-dppn)3](PF6)3 (1). In acetonitrile dppn reacts with 2 equiv of (SMe2)AuCl to form the simple Au-Cl adduct of the ligand, Au2Cl2dppn (2). In a fashion analogous to that of the synthesis of 1, the reaction of equimolar AgNO3 with dppn produces the trimetallic species [Ag2(mu-dppn)3Ag](PF6)3 (3) as a bright-yellow material. 1, 2, and 3 were characterized by 31P(1H) NMR spectroscopy, electronic absorption spectroscopy, X-ray crystallography, emission spectroscopy, and elemental analysis. Additionally 1 was further characterized by cyclic voltammetry and mass spectrometry. 1.4.5CH3CN.0.5(C2H5)2O (C107H72Au2F18N10.5NaO) crystallizes in the triclinic space group P1 with a = 15.408(3) A, b = 17.295(3) A, c = 22.425(5) A, alpha = 73.68(1) degrees, beta = 77.32(1) degrees, gamma = 74.18(1) degrees, V = 5451.4(19) A3, and Z = 2. C32H24Au2Cl2N2P2 (2) crystallizes in the monoclinic space group Cc with a = 10.936(2) A, b = 19.860(5) A, c = 20.864(2) A, beta = 118.182(1) degrees, V = 3127.3(8) A3, and Z = 4. Compound 3 crystallizes as the bis-DMSO adduct (C101H84Cl2F18N6O2P9S2) in the monoclinic space group C2/c with a = 28.825(7) A, b = 17.013(3) A, c = 23.916(7) A, beta = 115.23(1) degrees, V = 10609.6(44) A3, and Z = 4. The structures of 1 and 3 contain a three-coordinate metal capping the metallocryptate with an encapsulated ion. The central Ag(I) ion in 3 is positioned off-center to form a short Ag...Ag interaction of 3.145(2) A, while the central Na+ ion of 1 is centrally positioned with long Au...Na interactions of approximately 3.5 A. The solution-state properties of 1 were probed. 1 is emissive, as are the Li, K, and Cs analogues.     

Luminescent gold(I) and silver(I) complexes of 2-(diphenylphosphino)-1-methylimidazole (dpim): characterization of a three-coordinate Au(I)-Ag(I) dimer with a short metal-metal separation

The Au(I) and Ag(I) closed-shell metal dimers of 2-(diphenylphosphino)-1-methylimidazole, dpim, were investigated. dpim formed the discreet binuclear species [Ag2(dpim)2(CH3CN)2](2+) (1) when reacted with appropriate Ag(I) salts. Likewise, [Au2(dpim)2](2+) (3) and [AuAg(dpim)3](2+) (4) were produced via reactions with (tht)AuCl, tht is tetrahydrothiophene, and Ag(I). Compound 3 exhibits an intense blue luminescence (lambdamax=483 nm) in the solid state. However, upon initial formation of 3, a small impurity of Cl- was present giving rise to an orange emission (lambdamax=548 nm). Attempts to form [Au2(dpim)2]Cl2 yielded only (dpim)AuCl (2), which is not visibly emissive. The rare three-coordinate heterobimetallic complex [AuAg(dpim)3](2+) (4) exhibits intense luminescence in the solid-state resembling that of 3. The crystal structures of 1-4 were determined, revealing strong intramolecular aurophilic and argentophilic interactions in the dimeric compounds. Compound 1 has an Ag(I)-Ag(I) separation of 2.9932(9) A, while compound 3 has a Au(I)-Au(I) separation of 2.8174(10) A. Compound 4 represents the first example of a three-coordinate Au(I)-Ag(I) dimer and has a metal-metal separation of 2.8635(15) A. The linear Au(I) monomer, 2, has no intermolecular Au(I)-Au(I) interactions, with the closest separation greater than 6.8 A.     

A Palladium‐Catalyzed Carbonylation Approach to Eight‐Membered Lactam Derivatives with Antitumor Activity

The reactivity of 2‐(2‐alkynylphenoxy)anilines under PdI₂/KI‐catalyzed oxidative carbonylation conditions has been studied. Although a different reaction pathway could have been operating, N‐palladation followed by CO insertion was the favored pathway with all substrates tested, including those containing an internal or terminal triple bond. This led to the formation of a carbamoylpalladium species, the fate of which, as predicted by theoretical calculations, strongly depended on the nature of the substituent on the triple bond. In particular, 8‐endo‐dig cyclization preferentially occurred when the triple bond was terminal, leading to the formation of carbonylated ζ‐lactam derivatives, the structures of which have been confirmed by XRD analysis. These novel medium‐sized heterocyclic compounds showed antitumor activity against both estrogen receptor‐positive (MCF‐7) and triple negative (MDA‐MB‐231) breast cancer cell lines. In particular, ζ‐lactam 3 j′ may represent a novel and promising antitumor agent because biological tests clearly demonstrate that this compound significantly reduces cell viability and motility in both MCF‐7 and MDA‐MB‐231 breast cancer cell lines, without affecting normal breast epithelial cell viability.     

Crystal Structure and Conformation of a Bilirubin Ester

Summary. Crystal structures determined for three bilirubin analogs with gem-dimethyl groups at C(10) are reported, including the first X-ray structure of a bilirubin dimethyl ester. Conformation-determining torsion angles and key hydrogen bond distances and angles were compared to those from molecular dynamics calculations. Like other rubins, the component dipyrrinones of the three compounds were found to adopt the syn conformation, with Z-configuration double bonds at C(4) and C(15) and bis-lactam tautomeric structures of the end rings. No large differences in bond lengths and bond angles at C(10) were found, and the crystal structures of the two 10,10-dimethyl rubin acids showed considerable similarity to that of bilirubin: both pigments adopt a folded, intramolecularly hydrogen bonded ridge-tile conformation stabilized by six hydrogen bonds, with an interplanar angle in ridge-tile of 98° and 86°. In contrast, the dimethyl ester is intermolecularly hydrogen bonded in the crystal. Each molecule of the ester has its two syn-Z-dipyrrinones rotated into a conformation syn to the gem-dimethyl group, whereas in the acids they are anti.     

Syntheses, structures, and photoisomerization of (E)- and (Z)-2-tert-butyl-9-(2,2,2-triphenylethylidene)fluorene

"Sterically geared" 9-(2,2,2-triphenylethylidene)fluorene (1) is of potential interest as a photoactive moiety in molecular devices, and the 2-tert-butyl derivative (6) has been synthesized to investigate photoisomerization. E and Z stereoisomers of 6 were separated and identified by X-ray crystallography. The tert-butyl group does not introduce additional strain, and its close proximity to the trityl group in the Z isomer suggests an attractive van der Waals interaction. The UV spectra of (E)-6 and (Z)-6 are nearly identical, showing absorption bands that are similar to those of fluorene occurring at wavelengths longer than 240 nm. Photoisomerization of 6 was investigated at 266, 280 and 320 nm. Solutions initially containing only (E)-6 or (Z)-6 were irradiated with pulsed laser light, monitoring isomerization by 1H NMR spectroscopy. Negligible photodecomposition was observed when the solutions were agitated by N2 ebullition. Experimental data were fitted to theoretical curves to obtain photoisomerization quantum yields (phi(ZE) and phi(EZ)) ranging from 0.04 to 0.09. This first photoisomerization study of a dibenzofulvene reveals significant quantum yields, despite theoretical prediction of inefficient or negligible isomerization of the parent hydrocarbon, fulvene. Thermal isomerization of 6 at 270 degrees C (t(1/2) = 120 min) was also followed by 1H NMR spectroscopy, resulting in an estimated activation energy (deltaG(double dagger)) of 43 kcal/mol.     

Molecular recognition studies with a simple dipyrrinone

We present our investigations of 2-ethyl-3-methyl-(10H)-dipyrrin-1-one, its self-association, and anion binding properties. This receptor is easily accessible in a facile single step synthesis with a straightforward workup. An examination of the concentration dependence of the dipyrrinone NH chemical shifts in CDCl₃ and (CDCl₂)₂ over the temperature range from −20 °C to 100 °C determined the self-association constant to be 3850 M⁻¹. Molecular recognition studies have shown that it has a preference for guests with an OH moiety, such as hydrogen sulfate (HSO₄⁻) and carboxylic acids (RCO₂H).     

Cooperative diastereoselectivity of palladium- and platinum-promoted intramolecular [4 + 2] Diels-Alder cycloaddition reactions of 3,4-dimethyl-1-phenylphosphole

The complexes [(DMPP)2M(CH3CN2)]X2 (DMPP = 3,4-dimethyl-1-phenylphosphole; M = Pd, Pt; X = BF4-, NO3-, ClO4-) react with 2 equiv of the dienophiles N,N-dimethylacrylamide (DMAA), 2-vinylpyridine (VyPy), and diphenylvinylphosphine (DPVP) to form bis-[4 + 2] Diels-Alder cycloaddition products. The [M(DMPP)2(DMAA)2]2+ and [M(DMPP)2(VyPy)2]2+ complexes form exclusively as the cis-geometric isomers, whereas for [M(DMPP)2(DPVP)2]2+, both cis- and trans-geometric isomers are formed. The two Diels-Alder cycloadditions occur sequentially, and the absolute configuration of the first reaction influences the absolute configuration of the second. In all cases, recemic mixtures of the (R,R) and (S,S) diastereomers are formed; none of the meso (R,S) diastereomer is observed. New complexes were characterized by elemental analyses, physical properties, infrared spectroscopy, 1H, 1H(31P), 13C(1H), and 31P(1H) NMR spectroscopy, and, in most cases, X-ray crystallography.