Radical polymerization of 1‐alkenes catalyzed by lithium salts of carboranes

Abstract

Radical polymerization of selected 1‐alkenes, (1‐hexene, 1‐octene and 2‐methyl‐1‐heptene), initiated with classical radical initiators and catalyzed by lithium salts of selected carboranes was studied. In accordance with recently published results it was found that the use of radical initiators under catalysis by “naked” lithium cation of carboranes promotes the radical polymerization of 1‐alkenes, otherwise nonpolymerizable by the radical mechanism. However, although in our experiments relatively high monomers conversions are reached for some of the thermal initiators used, only low‐molecular‐weight oligomers with Mn < 1000 are formed, regardless of the initiator and carborane anion used. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Dual role for alkali metal cations in enhancing the low-temperature radical polymerization of N,N-dimethylacrylamide

“…LiCl induced heterotactic specificity in CF 3 CH 2 OH, which was the same as LiNTf 2 . 59 The addition of an equimolar amount of NaNTf 2 or KNTf 2 also enhanced the polymer yields and molecular weights when the DMAAm polymerization reaction was conducted in polar solvents, except for KNTf 2 in CF 3 CH 2 OH (Table 4, runs [30][31][32][33][34][35]. The r diad content reached up to 65% in THF, which is comparable to the highest r diad content of 69% reported to date for radically prepared poly (DMAAm)s. 58 On the other hand, LiOTf exhibited a different effect to that of LiNTf 2 and LiCl, in that it gave syndiotactic-Scheme 2 Relationship between the stoichiometry of the DMAAm-Li + complex and the stereospecificity of the DMAAm polymerization.…”

“…It was recently reported that "naked" lithium cations, derived from the lithium salt of a carborane anion, were used to catalyze the radical polymerization of propene and other terminal olefins with triplet dioxygen or conventional radical initiators. [30][31][32] In this particular polymerization system, the complexation of Li + to olefins (i.e., cation-π interaction) is considered to be a key interaction in terms of favoring the addition reaction over the competing H-abstraction reaction, as predicted by calculation. 33,34 The second role for the alkali metal would involve the "stabilization of the propagating radical".…”

Metal Complexes with Very Large Dipole Moments: the Anionic Carborane Nitriles 12-NC–CB11X11– (X = H, F, CH3) as Ligands on Pt(II) and Pd(II)

“…Spectral data agreed with those reported. 54 trans-Diiodobis(triethylphosphine)palladium(II) (15). The literature procedure 56 was slightly modified.…”

Isotactic Regulation in the Radical Polymerization of Calcium Methacrylate: Is Multiple Chelation the Key to Stereocontrol?

“…More than 25 years ago, Clark predicted that radical addition to nonpolar alkenes could be catalyzed by coordination of Li + to the CC bond . Michl et al later experimentally verified this prediction, finding that the Li + salts of a noncoordinating carboborane anion could facilitate the radical polymerization of 1‐alkenes by catalyzing propagation over the degenerative hydrogen transfer reactions that otherwise impede the formation of polymer . Clark demonstrated that these rate accelerations are predominantly caused by electrostatic effects and suggested such catalysis does not require covalent interactions between the metal cation and the CC bond .…”

“…In addition to influencing polymer stereochemistry, metal cations can enhance the reactivity of radicals toward CC and CC bonds . Pioneering theoretical work by Clark uncovered the importance of odd‐electron interactions with metal ions in the radical addition reactions of nonpolar alkenes and several radical ring closures (the so‐called “radical‐clock” reactions) .…”