Recoverable Phospha-Michael Additions Catalyzed by a 4-N,N-Dimethylaminopyridinium Saccharinate Salt or a Fluorous Long-Chained Pyridine: Two Types of Reusable Base Catalysts.

Phospha-Michael addition, which is the addition reaction of a phosphorus-based nucleophile to an acceptor-substituted unsaturated bond, certainly represents one of the most versatile and powerful tools for the formation of P-C bonds, since many different electrophiles and P nucleophiles can be combined with each other. This offers the possibility to access many diversely functionalized products. In this work, two kinds of basic pyridine-based organo-catalysts were used to efficiently catalyze phospha-Michael addition reactions, the 4-N,N-dimethylaminopyridinium saccharinate (DMAP·Hsac) salt and a fluorous long-chained pyridine (4-Rf-CH2OCH2-py, where Rf = C11F23). These catalysts have been synthesized and characterized by Lu's group. The phospha-Michael addition of diisopropyl, dimethyl or triethyl phosphites to α, ß-unsaturated malonates in the presence of those catalysts showed very good reactivity with high yield at 80-100 °C in 1-4.5 h with high catalytic recovery and reusability. With regard to significant catalytic recovery, sometimes more than eight cycles were observed for DMAP·Hsac adduct by using non-polar solvents (e.g., ether) to precipitate out the catalyst. In the case of the fluorous long-chained pyridine, the thermomorphic method was used to efficiently recover the catalyst for eight cycles in all the reactions. Thus, the easy separation of the catalysts from the products revealed the outstanding efficacy of our systems. To our knowledge, these are good examples of the application of recoverable organo-catalysts to the DMAP·Hsac adduct by using non-polar solvent and a fluorous long-chained pyridine under the thermomorphic mode in phospha-Michael addition reactions.

Side-chain conformations in the isomorphous polyfluorinated {4,4'-bis[(2,2-difluoroethoxy)methyl]-2,2'-bipyridine-κ2N,N'}dichloridopalladium and -platinum complexes.

The polyfluorinated title compounds, [MCl2(C16H16F4N2O2)] or [4,4'-(HCF2CH2OCH2)2-2,2'-bpy]MCl2 [M = Pd, (1), and M = Pt, (2)], have -C(Hα)2OC(Hß)2CF2H side chains with H-atom donors at the α and ß sites. The structures of (1) and (2) are isomorphous, with the nearly planar (bpy)MCl2 molecules stacked in columns. Within one column, π-dimer pairs alternate between a π-dimer pair reinforced with C-H...Cl hydrogen bonds (α,α) and a π-dimer pair reinforced with C-Hß...F(-C) interactions (abbreviated as C-Hß...F-C,C-Hß...F-C). The compounds [4,4'-(CF3CH2OCH2)2-2,2'-bpy]MCl2 [M = Pd, (3), and M = Pt, (4)] have been reported to be isomorphous [Lu et al. (2012). J. Fluorine Chem. 137, 54-56], yet with disorder in the fluorous regions. The molecules of (3) [or (4)] also form similar stacks, but with alternating π-dimer pairs between the (α,ß; α,ß) and (ß,ß) forms. Through (C-)H...Cl hydrogen-bond interactions, one molecule of (1) [or (2)] is expanded into an aggregate of two inversion-related π-dimer pairs, one pair in the (α,α) form and the other pair in the (C-Hß...F-C,C-Hß...F-C) form, with the plane normals making an interplanar angle of 58.24 (3)°. Due to the demands of maintaining a high coordination number around the metal-bound Cl atoms in molecule (1) [or (2)], the ponytails of molecule (1) [or (2)] bend outward; in contrast, the ponytails of molecule (3) [or (4)] bend inward.