Synthesis, structure, and reactivity of doubly trans-spanning bis(dialkyl selenide) complexes; a new route to diselenamacrocycles via alkene metathesis in metal coordination spheres

Macrocyclic Sulfur Ligand Stabilized Trans-Palladium Dichloride Complex: Syntheses, Structure, Chlorine Rotation, and Application in α-Olefination of Nitriles by Primary Alcohols

Herein, we have reported the synthesis of a macrocyclic organosulfur ligand (L1) having a seventeen-membered macrocyclic ring. Subsequently, the corresponding trans-palladium complex (C1) of bulky macrocyclic organosulfur ligand (L1) was synthesized by reacting it with PdCl2 (CH3 CN)2 salt. The newly synthesized ligand and complex were characterized using various analytical and spectroscopic techniques. The complex showed a square planar geometry with trans orientation of two ligands around the palladium center. The complex possesses intramolecular SCH…Cl interactions of 2.648 Å between the macrocyclic ligand and palladium dichloride. The potential energy surface (PES) for the rotational process of C1 suggested a barrier of ~23.81 kcal/mol for chlorine rotation. Furthermore, the bulky macrocyclic organosulfur ligand stabilized palladium complex (C1) was used as a catalyst (2.5 mol %) for α-olefination of nitriles by primary alcohols. The α,β-unsaturated nitrile compounds were found to be the major product of the reaction (57-78 % yield) with broad substrate scope and large functional group tolerance. Notably, the saturated nitrile product was not observed during the reaction. The mechanistic studies suggested the formation of H2 and H2 O as only by-products of the reaction, thereby making the protocol greener and sustainable.

Bulky selenium ligand stabilized trans-palladium dichloride complexes as catalyst for silver-free decarboxylative coupling of coumarin-3-carboxylic acids

This report describes synthesis of three new trans -palladium dichloride complexes of bulky selenium ligands. These complexes possess a Cl-Pd-Cl rotor spoke attached to a Se-Pd-Se axle. The new ligands and palladium complexes ( C1 - C3 ) were characterized with the help of NMR, HRMS, UV-Vis., IR, and elemental analysis. The single crystal structure of metal complex C2 confirmed a square planer geometry of complex with trans -orientation. The X-ray structure revealed intramolecular secondary interactions (SeCH---Cl) between chlorine of PdCl 2 and CH 2 proton of selenium ligand. Variable temperature NMR data shows coalescence of diastereotopic protons, which indicates pyramidal inversion of selenium atom at elevated temperature. The relaxed potential energy scan of C2 suggests a rotational barrier of ~12.5 kcal/mol for rotation of chlorine atom through Cl-Pd-Cl rotor. The complex C3 possess dual intramolecular secondary interactions (OCH 2 ---Cl and SeCH 2 ---Cl) with stator ligand. Molecular rotor C2 was found to be most efficient catalyst for the decarboxylative Heck-coupling under mild reaction conditions. The protocol is applicable to a broad range of substrates with large functional group tolerance and low catalyst loading (2.5 mol %). The mechanism of decarboxylative Heck-coupling reaction was investigated through experimental and computational studies. Importantly the reaction works under silver-free conditions which reduces the cost of overall protocol. Further, the catalyst also worked for decarboxylative arylation and decarboxylative Suzuki-Miyaura coupling reactions with good yields of the coupled products.

A selenium-coordinated palladium(ii) trans-dichloride molecular rotor as a catalyst for site-selective annulation of 2-arylimidazo[1,2-a]pyridines

This report describes the synthesis of a new class of secondary interaction (SeCHCl)-controlled molecular rotor having a Cl-Pd-Cl rotor spoke attached onto a Se-Pd-Se axle. NMR data acquired at various temperatures established ΔG/ΔG values of 15.5 and 17.2 kcal mol^-1 for a roughly 4.5 Å-long rotor. The molecular rotor showed excellent catalytic activity with reverse regioselectivity for annulation of 2-arylimidazo[1,2-a]pyridines (yields: ∼53-78%) with only 1.5 mol% catalyst loading.

Organophosphorus chemistry based on elemental phosphorus: advances and horizons

The results of studies on the application of elemental phosphorus for the synthesis of important organophosphorus compounds are surveyed and summarized. Currently, this trend represents a synthetically, environmentally and technologically attractive alternative to classical organophosphorus chemistry based on toxic and corrosive phosphorus chlorides. Direct phosphination and phosphinylation of organic compounds with elemental phosphorus (discussed in the first part of the review) basically extend the range of available phosphines, phosphine chalcogenides and phosphinic acids and provides further development of their synthetic potential (discussed in the second part of the review). It is shown that the breakthrough in this area is largely due to the discovery of reactions of elemental phosphorus (white and red) with various electrophiles in superbasic suspensions and emulsions derived from alkali metal hydroxides and to the development of electrochemical, electrocatalytic and catalytic activation of white phosphorus.

The bibliography includes 299 references.