Development of catalyst-controlled stereoselective olefin metathesis processes1 has been a pivotal recent advance in chemistry. Incorporation of appropriate ligands within molybdenum-2, tungsten3 and ruthenium-based complexes4 has made reactivity and selectivity levels that were formerly inaccessible feasible. Here, we show that molybdenum monoaryloxide chloride (MAC) complexes furnish higher energy (Z) isomers of trifluoromethyl-substituted alkenes through cross-metathesis (CM) reactions with commercially available, inexpensive and typically inert Z-1,1,1,4,4,4-hexafluoro-2-butene. Furthermore, otherwise inefficient and non-stereoselective transformations with Z-1,2-dichloro- and 1,2- dibromoethene can be effected with substantially improved efficiency and Z selectivity. Synthesis of representative biologically active molecules and trifluoromethyl analogues of medicinally relevant compounds underscore the importance of the advance. The origins of activity and selectivity levels, which contradict the previously proposed principles5, are elucidated with the aid of DFT calculations.

Partial bromination or epoxidation has been used to prove the tacticities of several stereoregular polymers made through ROMP methods with well-defined Mo or W initiators. Tacticities were proven for cis,isotactic and cis,syndiotactic poly(norbornene), poly(3-methyl-3phenylcyclopropene), and poly(endo,anti-tetracyclododecene). Various limitations can prevent application of these proofs in general to stereoregular polymers prepared through ROMP.

Generating monovalent pnictogens within NCN pincers has resulted in the isolation of three distinct types of 1,2-azaheteroles, highly aromatic nitrogen analogues like pyrazole-based 5, aromatic yet fluxional P- and As-derived bell-clappers 1 and 2, and hypervalent Sb and Bi derivatives 3 and 4, which are supported by 3-center, 4-electron N–E–N bonds. Careful analysis of the solid-state structures of 1–5/[5-Me]­[OTf] in combination with NICS calculations (at the GIAO/M06/cc-pVTZ­(-PP) level) and other computational methods (NBO) suggest that simpler NC chelates may support new phosphorus- and arsenic-containing heterocycles. Indeed, reduction of ECl2 (E = P or As) derivatives supported by N-Dipp (Dipp = 2,6-diisopropylphenyl) substituted NC bidentate ligands produced 1,2-benzoazaphosphole 11 and 1,2-benzoazaarsole 12. NICS calculations revealed 11 and 12 had aromatic character on par with that of pyrazole-based 5.

The trapping of a phosphinidene (R-P) in an NCN pincer is presented. Stabilized phosphinidene 1 was characterized by P{ H}, H, and C{ H} NMR spectroscopy, exhibiting an averaged C symmetry in solution between -60 and 60 °C. In the solid state, the phosphinidene is coordinated by one adjacent N atom featuring a formal P-N bond (1.757(2) Å) to give a five-membered ring with some aromatic character, confirmed by DFT calculations (B3LYP-D3/6-311G**++) to be the ground-state structure. Equilibration of the two N ligands occurs rapidly in solution via a "bell-clapper"-type process through an associative symmetric transition state calculated to lie 4.0 kcal mol above the ground state.

The concept of using disulfides as an oxidant for Cu(i) is introduced as part of a Cu-catalyzed process leading to the formation of benzothiazole from an iminodisulfide under an inert atmosphere.