Selective Endo and Exo Binding of Mono‐ and Ditopic Ligands to a Rhomboidal Diporphyrin Prism

Copper(I) can preferentially form heteroleptic complexes containing two phosphine and two nitrogen donors due to steric factors. This preference was employed to direct the self‐assembly of a porphyrin‐faced rhomboidal prism having two parallel tetrakis(4‐iminopyridyl)porphyrinatozinc(II) faces linked by eight 1,4‐bis(diphenylphosphino)benzene pillars. The coordination preferences of the Cu^I ions and geometries of the ligands come together to generate a slipped‐cofacial orientation of the porphyrinatozinc(II) faces. This orientation enables selective encapsulation of 3,3′‐bipyridine (bipy), which bridges the Zn^II ions of the parallel porphyrins, whereas 4,4′‐bipy exhibits weaker external coordination to the porphyrin faces. Reaction with 2,2′‐bipy, by contrast, results in the displacement of the tetratopic porphyrin ligand and formation of [{(2,2′‐bipy)Cu^I}₂(diphosphine)₂]. The differing strengths of interactions of bipyridine isomers with the system allows for a hierarchy to be deciphered, whereby 4,4′‐bipy may be displaced by 3,3′‐bipy, which in turn is displaced by 2,2′‐bipy.     

Different Modes of Anion Response Cause Circulatory Phase Transfer of a Coordination Cage with Controlled Directionality

Controlled directional transport of molecules is essential to complex natural systems, from cellular transport up to organismal circulatory systems. In contrast to these natural systems, synthetic systems that enable transport of molecules between several spatial locations on the macroscopic scale, when external stimuli are applied, remain to be explored. Now, the transfer of a supramolecular cage is reported with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different anions. Notably, circulatory phase transfer of the cage was demonstrated based on a system where the three layers of solvent are arranged within a circular track. The direction of circulation between solvent phases depended upon the order of addition of anions.     

Ruthenium‐Catalyzed Reductive Arylation of N‐(2‐Pyridinyl)amides with Isopropanol and Arylboronate Esters

A new three‐component reductive arylation of amides with stable reactants (iPrOH and arylboronate esters), making use of a 2‐pyridinyl (Py) directing group, is described. The N‐Py‐amide substrates are readily prepared from carboxylic acids and PyNH₂, and the resulting N‐Py‐1‐arylalkanamine reaction products are easily transformed into the corresponding chlorides by substitution of the HN‐Py group with HCl. The 1‐aryl‐1‐chloroalkane products allow substitution and cross‐coupling reactions. Therefore, a general protocol for the transformation of carboxylic acids into a variety of functionalities is obtained. The Py‐NH₂ by‐product can be recycled.     

Synthesis and structures of cadmium(II) complexes of a series of multinucleating N/S donor ligands

The coordination chemistry of a series of bis-bidentate ligands with cadmium(II) ions has been investigated. The ligands, containing two N,S-donor chelating (pyrazolyl/thioether) fragments, have afforded complexes of a variety of structural types (dinuclear M₂L₂ ‘mesocate’ complexes, a one-dimensional chain coordination polymer and a simple mononuclear complex) according to whether the bis-bidentate ligands act as bridges spanning two metal ions, or a tetradentate chelate to a single metal ion. The p-phenylene and m-biphenyl spaced ligands L¹ and L³ form dinuclear M₂L₂ complexes where the ligands are arranged in a ‘side-by-side’ fashion. In contrast the m-phenylene spaced ligand L² forms a one-dimensional coordination polymer where the ligands adopt a highly folded conformation. The 1,8-naphthalene spaced ligand L⁴ adopts a tetradendate chelating mode and affords a simple mononuclear complex.     

Peripheral Templation Generates an MII6L4 Guest‐Binding Capsule

Pseudo‐octahedral M^II₆L₄ capsules result from the subcomponent self‐assembly of 2‐formylphenanthroline, threefold‐symmetric triamines, and octahedral metal ions. Whereas neutral tetrahedral guests and most of the anions investigated were observed to bind within the central cavity, tetraphenylborate anions bound on the outside, with one phenyl ring pointing into the cavity. This binding configuration is promoted by the complementary arrangement of the phenyl rings of the intercalated guest between the phenanthroline units of the host. The peripherally bound, rapidly exchanging tetraphenylborate anions were found to template an otherwise inaccessible capsular structure in a manner usually associated with slow‐exchanging, centrally bound agents. Once formed, this cage was able to bind guests in its central cavity.     

Selective Encapsulation and Sequential Release of Guests Within a Self‐Sorting Mixture of Three Tetrahedral Cages

A mixture of two triamines, one diamine, 2‐formylpyridine and a Zn^II salt was found to self‐sort, cleanly producing a mixture of three different tetrahedral cages. Each cage bound one of three guests selectively. These guests could be released in a specific sequence following the addition of 4‐methoxyaniline, which reacted with the cages, opening each in turn and releasing its guest. The system here described thus behaved in an organized way in three distinct contexts: cage formation, guest encapsulation, and guest release. Such behavior could be used in the context of a more complex system, where released guests serve as signals to other chemical actors.     

Pellet freezing of in vitro produced bovine embryos using dry ice

In vitro produced bovine embryos were frozen by pellet freezing or vitrification method. In the pellet freezing method, the embryos were cooled on the dry ice and then frozen as pellets. At warming, the pellets were immersed directly into 0.5 M sucrose. The survival rates of blastocysts frozen by the pellet freezing method were higher (P<0.01) in 40% ethylene glycol (EG) than those in the lower concentrations (20 and 30% EG). Higher survival rates of blastocysts frozen by the pellet freezing method were obtained but the development rates did not differ, as compared with those by the vitrification method. There were no significant differences between the pellet freezing and vitrification method in the frequencies of post-thaw survival of hatched blastocysts. These results demonstrate that the pellet freezing method using dry ice can be used successfully for the cryopreservation of blastocysts.     

Total Synthesis and Stereochemical Revision of Phacelocarpus 2‐Pyrone A

The first total synthesis of phacelocarpus 2‐pyrone A is reported. The original natural compound was tentatively assigned (by NMR spectroscopy) as containing two cis‐alkenes and a trans‐vinyl ether connected to a 2‐pyrone ring motif. Our computational predictions indicated that a cis‐vinyl ether motif was equally feasible. Attempts to prepare the trans‐vinyl ether were met with no success. The all cis‐target compound was synthesised in nine steps, employing key regio‐ and stereoselective reactions including Au^I‐catalysed vinyl etherification, Wittig alkenylation and end‐game Stille macrocyclisation. Analysis of the NMR data enabled identification and confirmation of the correct structure of phacelocarpus 2‐pyrone A, containing a cis‐vinyl ether. Our studies pave the way for future development of methodologies to these structurally distinct pyrone skipped‐polyenyne natural products.