Organic molecules with heavy main-group elements frequently form supramolecular links to electron-rich centres. One particular case of such interactions is halogen bonding. Most studies of this phenomenon have been concerned with either dimers or infinitely extended structures (polymers and lattices) but well-defined cyclic structures remain elusive. Here we present oligomeric aggregates of heterocycles that are linked by chalcogen-centered interactions and behave as genuine macrocyclic species. The molecules of 3-methyl-5-phenyl-1,2-tellurazole 2-oxide assemble a variety of supramolecular aggregates that includes cyclic tetramers and hexamers, as well as a helical polymer. In all these aggregates, the building blocks are connected by Te…O–N bridges. Nuclear magnetic resonance spectroscopic experiments demonstrate that the two types of annular aggregates are persistent in solution. These self-assembled structures form coordination complexes with transition-metal ions, act as fullerene receptors and host small molecules in a crystal.

Alkyl and hydrido scandium complexes of the dianionic pentadentate ligand B2Pz4Py are reported. The key starting material (B2Pz4Py)ScCl is readily prepared and alkylated with organolithium reagents RLi (R = CH3, CH2SiMe3, CH2SiMe2Ph, CH2CH2CH3 and CH2CHMe2) to form alkyl derivatives in 61-93% yields. These compounds are very thermally stable and do not undergo sigma bond metathesis reactions with dihydrogen. The hydrido complex was prepared from (B2Pz4Py)ScCl and NaHBEt3 in 80% yield and was found to be more stable by 28 kcal mol-1 as a dimer, rather than a monomeric hydrido complex. However, the monomer is accessible through dissociation of the dimer at 80 °C. All of the compounds (B2Pz4Py)ScR react with water to form the bridging oxo dimer (B2Pz4Py)ScOSc(B2Pz4Py). The reactivity of the hydrido and methyl complexes towards carbon dioxide was explored; heating to 80 °C results in the formation of κ2 formato and acetate complexes, respectively. The mechanisms were studied via density functional theory and distinct transition states for insertion of CO2 into the Sc-R (R = H, CH3) were found, with the insertion into Sc-CH3 being more enthalpically difficult (by 18 kcal mol-1) than insertion into Sc-H. The slow rate of reaction between [(B2Pz4Py)ScH]2 and CO2 is attributed to the barrier associated with dimer dissociation. In both insertion reactions, the kinetic products are κ1 formato or acetate complexes that are only slightly less stable than the observed κ2 derivatives. The κ1 compounds can therefore be trapped by treating the κ2 isomers with tris-pentafluorophenyl borane.

A rigidified PCalkylP ligand allowed for the synthesis and characterization of cationic and radical PCCarbeneP nickel complexes in which the carbene anchor of the pincer framework is electrophilic rather than nucleophilic.

The synthesis of a p-conjugated organophosphorus species with bridging P-P unit is reported. Because of the pyramidal geometry of the phosphorus centers, the molecular scaffold provides intriguing electronic communication throughout the three-dimensional structure via p-s-p conjugation in stepwise fashion. The dimeric species was serendipitously found to be accessible via a reaction of the corresponding P-amino-phosphole precursor through mediation with the hard Lewis acid BF 3 . We provide detailed mechanistic studies toward a suitable reaction mechanism that was also verified via computational means. Moreover, we elaborate the utility of the biphosphole via phosphorus functionalization that lends further proof for the step conjugation provided by the unique phosphorus-based molecular architecture.

The reactions of K[HC(PPh2NSiMe3)2] (K[1]) and MI3 (M = As, Sb) or TeI4 gave as the major products the complexes [{MI n }{C(PPh2NSiMe3)(PPh2NHSiMe3)}] (MI n = trans-AsI2, trans- or cis-SbI2, TeI3), which feature the ligand [C(PPh2NSiMe3)(PPh2NHSiMe3)]− (2). This anion, the NH tautomer of [HC(PPh2NSiMe3)2]−, is formally generated by a 1,3-hydrogen shift to give complexes in which the ligand is N,C-chelated to the main-group-metalloid center. The M–C distances are slightly longer than the sum of the covalent radii for M and C in the case of the group 15 metalloids but significantly shorter for M = Te. The arsenic derivative [{t-AsI2}2] is monomeric in the solid state, with As–I distances that differ by ca. 0.55 Å, whereas the antimony analogues [{t-SbI2}2] and [{c-SbI2}2] are dimeric through bridging iodide ligands and the disparity in Sb–I distances of the SbI2 units is 0.10 and 0.33 Å, respectively. The tellurium derivative [{TeI3}2] is monomeric with a distorted-square-pyramidal geometry at the Te center and Te–I distances in the narrow range 2.9142(4)–3.0337(4) Å. In contrast to the lighter pnictogens, the bismuth complex [{t-BiI2}1] is comprised of the methanide 1 coordinated in a tridentate (N,C,N) mode to a BiI2 + cation. In the case of arsenic triiodide, the metathesis is accompanied by Si–N bond cleavage to give [{AsI2}{CH2(PPh2N)(PPh2NSiMe3)}] (3), which was characterized by 31P NMR spectroscopy, and conversion to the corresponding salt [{AsI}{CH2(PPh2N)(PPh2NSiMe3)}][SbF6] (3A) by treatment with AgSbF6. The As–N distances in the six-membered CP2N2As ring in 3A differ by 0.20 Å due to the different coordination numbers (2 and 3) of the two N atoms in the novel N,N′-chelated [CH2(PPh2N)(PPh2NSiMe3)]− anion. In contrast, reaction of [{t-SbI2}2] with AgSbF6 gives the expected salt as the dimer {[{SbI}2][SbF6]}2. The two hydrolysis products [CH2(PPh2NSiMe3)(PPh2NHSiMe3)][SbF6] (4A) and [CH2(PPh2NSiMe3) (PPh2NHSiMe3)]2[Te2I6] (4B) were also structurally characterized and shown to contain the same cation. DFT calculations indicate that the N–H tautomer 2 is stabilized by strong M–N and M–C bonding interactions which include a small degree of π character. Weaker bonds, as in the Bi complex, favor the C–H tautomer 1 as the ligand.