Rearrangement of a Transient Gold Vinylidene into Gold Carbenes

The gold acetylide complex 20 endowed with a biaryl backbone provides opportunities for a study on the formation and fate of gold vinylidenes. Although the formyl group in 20 is not sufficiently electrophilic to get attacked by the acetylide in proximity, its activation with TBSOTf (TBSOTf=tert-butyldimethylsilyl trifluoromethanesulfonate) at low temperature triggered instantaneous formation of a gold vinylidene (21). This metastable species evolved into the cationic gold carbene complex 22 bearing a phenanthrene unit and a hydroxyl group at the aurated center; the recorded data suggest that this product might be better viewed as an acylgold species protonated by triflic acid. The use of [Me3O⋅BF4] as the activating agent led to formation of the analogous Fischer-type carbene 24, whereas replacement of gold by the [CpRu(PPh3)2]+ fragment allowed the ruthenium vinylidene 27 to be isolated, which closely resembles the proposed gold intermediate 21. The starting gold complex 20, the derived products 22 and 24, as well as vinylidene 27 were characterized by X-ray diffraction

An oscillatory plug flow photoreactor facilitates semi-heterogeneous dual nickel/carbon nitride photocatalytic C-N couplings

Carbon nitride materials have emerged as an efficient and sustainable class of heterogeneous photocatalysts, particularly when paired with nickel in dual catalytic cross-coupling reactions. Performing these transformations on larger scales using a continuous process is difficult due to the problems associated with handling solids in flow. By combining an oscillatory pump with a microstructured plug flow photoreactor, a stable suspension of the photocatalyst can be maintained, circumventing clogging of the reactor channels. Through careful tuning of the oscillator properties, the residence time distribution (RTD) was optimized, whilst maintaining a stable catalyst suspension. Short residence times (20 min) were achieved using optimized conditions and the recyclability of the photocatalyst was demonstrated over 10 cycles with no loss of activity. During a stable 4.5 hour scale-out demonstration, the model substrate could be isolated on 12 g scale (90% yield, 2.67 g h-1). Moreover, the method was applied for the gram scale synthesis of an intermediate of the active pharmaceutical ingredient tetracaine

Research challenges at the land-sea interface

The land–sea interface, or Coastal Transition Zone (CTZ), is the area that links terrestrial and marine habitats. We use here the definition of [Schaefer, 1972]: “the sea and the land adjacent to the interface, encompassing that region where terrestrial activities importantly impinge on the marine environment, marine resources and marine activities, and where marine activities importantly impinge on the environment, resources, and activities of the land”. The precise spatial scale and extent of the interface in this definition is (appropriately, we feel) ambiguous, as it depends on both the attributes of the interface at any given location, as well as the processes or features being examined. Like many ecotones, the CTZ is an area of intense interactions and enhanced productivity and biodiversity ([Levin et al., 2001]). The coastal zone is also a “keystone” habitat, providing human and ecosystem services out of proportion to its areal extent (e.g., [Costanza et al., 1997]). The coastal zone represents only 8% of the earth, but provides 20% of the oceanic production ( [Liu et al., 2000. K.K. Liu, K. Iseki and S.Y. Chao, Continental margin carbon fluxes. In: R.B. Hanson, H.W. Ducklow and J.G. Field, Editors, The Changing Ocean Carbon Cycle, Cambridge (2000), pp. 187–239.Liu et al., 2000]). Further, 60% of humans, 3.8 billion people, live within 100 kilometers of the sea ( [Vitousek et al., 1997]). This region is a nexus for transportation, production of energy, and food resources for humans. The importance of this region, both to humans and to terrestrial and aquatic ecosystems, makes it crucial that we understand the processes and interactions in this habitat. The coastal transition zone, however, presents a number of difficult research challenges. While these challenges are qualitatively similar to those faced by scientists in other habitats, they are magnified in the coastal transition zone. The goal of this paper is to describe the difficulties that confront the researcher interested in the CTZ, and to offer some ideas for ways in which we as scientists can approach these challenges more fruitfully

Preparation of tetrasubstituted 3-phosphonopyrroles through hydroamination: scope and limitations

Phosphonylated pyrroles were obtained by a ZnCl2-catalyzed 5-exo-dig hydroamination of propargylic enamines. These starting compounds were obtained in two steps from commercially available beta-ketophosphonates. The method tolerates a wide variety of substituents at the 1,2- and 5-position of the pyrrole, while further derivatization allows for the introduction of substituents at the 4-position via lithiation or halogenation