Oxygen‐Promoted C?H Bond Activation at Palladium

[Pd(P(Ar)(tBu)₂)₂] ( 1 , Ar=naphthyl) reacts with molecular oxygen to form Pd^II hydroxide dimers in which the naphthyl ring is cyclometalated and one equivalent of phosphine per palladium atom is released. This reaction involves the cleavage of both C H and O O bonds, two transformations central to catalytic aerobic oxidizations of hydrocarbons. Observations at low temperature suggest the initial formation of a superoxo complex, which then generates a peroxo complex prior to the C H activation step. A transition state for energetically viable C H activation across a Pd peroxo bond was located computationally.     

Divalent osmium complexes: synthesis,characterization, strong red phosphorescence,and electrophosphorescence

We report new divalent osmium complexes that feature strong red metal-to-ligand-charge-transfer (MLCT) phosphorescence and electrophosphorescence. The general formula of the complexes is Os(II)(N-N)(2)L-L, where N-N is either a bipyridine or a phenanthroline and L-L is either a phosphine or an arsine. New polypyridyl ligands synthesized are 4,4'-di(biphenyl)-2,2'-bipyridine (15) and 4,4'-di(diphenyl ether)-2,2'-bipyridine (16), and the 1,10-phenanthroline derivatives synthesized are 4,7-bis(p-methoxyphenyl)-1,10-phenanthroline (17), 4,7-bis(p-bromophenyl)-1,10-phenanthroline (18), 4,7-bis(4'-phenoxybiphen-4-yl)-1,10-phenanthroline (19), and 4,7-bis(4-naphth-2-ylphenyl)-1,10-phenanthroline (20). 4,4'-Diphenyl-2,2'-bipyridine (21) and 4,7-diphenyl-1,10-phenanthroline (22) were also used in these studies. Strong pi-acid ligands used were 1,2-bis(diphenylarseno)ethane (23), cis-1,2-bis(diphenylphosphino)ethylene (24), and cis-1,2-vinylenebis(diphenylarsine) (25). Ligand 25 is used for the first time in these types of luminescent osmium complexes. These compounds feature strong MLCT absorption bands in the visible region and strong red phosphorescent emission ranging from 611 to 651 nm, with quantum efficiency up to 45% in ethanol solution at room temperature. Red organic light-emitting diodes (OLEDs) were successfully fabricated by doping the Os(II) complexes into blend of poly(N-vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD). Brightness over 1400 cd/m(2) for a double-layer device has been reached, with a turn-on voltage of 8 V. The maximum external quantum efficiency was 0.64%. Commission Internationale de l'Eclairage (CIE) chromaticity coordinates (x, y) of the red electrophosphorescence from the complexes are (0.65, 0.34), which indicates pure red emission.     

Ascosalipyrrolidinone A, an antimicrobial alkaloid, from the obligate marine fungus Ascochyta salicorniae

From the green alga Ulva sp., the endophytic and obligate marine fungus Ascochyta salicorniae was isolated. A. salicorniae was mass cultivated and found to produce the unprecedented and structurally unusual tetramic acid containing metabolites ascosalipyrrolidinones A (1) and B (2). Additionally, the new natural product ascosalipyrone (3) and the known metabolites 4 and 5 were obtained. Ascosalipyrrolidinone A (1) has antiplasmodial activity toward Plasmodium falciparum strains K1 and NF 54, as well as showing antimicrobial activity and inhibiting tyrosine kinase p56lck.     

Cyclopentadienyl Complexes of IrIII for Attempted C−D Bond Activation

The complexes Cp(MeIm)IrI₂ and Cp^Me4(MeIm)IrCl₂ have been prepared and subsequently methylated to form Cp(MeIm)IrMe₂ and Cp^Me4(MeIm)IrMe₂ (Cp=η⁵-C₅H₅, Cp^Me4=η⁵-C₅HMe₄, MeIm=1,3-dimethylimidazol-2-ylidene). We attempted unsuccessfully to use the dimethyl complexes to study C−D bond activation via methyl-group abstraction. Protonation with one equivalent of a weak acid, such as 2,6-dimethylpyridinium chloride, affords methane and Ir^III methyl chloride complexes. ¹H-NMR experiments show addition of pyridinium [BArF₂₀]⁻ (BArF₂₀=[B(C₆F₅)₄]⁻) to the dimethyl species forms [Cp(MeIm)IrMe(py)]⁺[BArF₂₀]⁻ (py=pyridine) or [Cp^Me4(MeIm)IrMe(py)]⁺[BArF₂₀]⁻ respectively, alongside methane, while use of the [BArF₂₀]⁻ salts of more bulky 2,6-dimethylpyridinium and 2,6-di-tert-butylpyridinium gave an intractable mixture. Likewise, the generation of 16 e⁻ species [Cp^Me4(MeIm)IrMe]⁺[BArF₂₀]⁻ or [Cp(MeIm)IrMe]⁺[BarF₂₀]⁻ at low temperature using 2,6-dimethylpyridinium or 2,6-di-tert-butylpyridinium in thawing C₆D₆ or toluene-d₈ formed an intractable mixture and did not lead to C−D bond activation. X-ray structures of several Ir^III complexes show similar sterics as that found for the previously reported Cp* analogue.     

Optical rotation of achiral compounds

Oriented achiral molecules and crystals with D(2d) symmetry or one of its non-enantiomorphous subgroups, S(4), C(2v), or C(s), can rotate the plane of transmitted polarized light incident in a general direction. This well-established fact of crystal optics is contrary to the teaching of optical activity to students of organic chemistry. This Minireview gives an overview of the measurement and calculation of the chiroptical properties of some achiral compounds and crystals. Methane derivatives with four identical ligands related by reflection symmetry are quintessential optically inactive compounds according to the logic of van't Hoff. Analysis of the optical activity of simple achiral compounds such as H(2)O and NH(3) provides general aspects of chiroptics that are not readily broached when considering chiral compounds exclusively. We show here, through the use of group theoretical arguments, the transformation properties of tensors, and diagrams, why some achiral, acentric compounds are optically active while others are not.