Low-Coordinate Cobalt Fluoride Complexes: Synthesis, Reactions, and Production from C–F Activation Reactions

Abstract

A cobalt(II) fluoride complex, [L tBuCo(μ-F)]2 [L tBu = 2,2,6,6-tetramethyl-3,5-bis(2,6-diisopropylphenylimido)hept-4-yl], was synthesized from L tBuCo using Me3SnF via homolytic cleavage of the Sn–F bond. L tBuCo also performed the overall binuclear oxidative addition of fluorinated arenes to give [L tBuCo(μ-F)]2 and a cobalt(II) aryl complex of the corresponding fluorobenzene substrate in a 1:2 molar ratio. The C–F activation reaction has a first-order rate dependence on both cobalt and fluorobenzene concentrations. The rate is increased by meta-fluoride substituents, and slowed by ortho-fluoride substituents, suggesting electronic and steric influences on the transition state, respectively. The data are most consistent with a mechanism beginning with rate-limiting oxidative addition of the aryl fluoride to cobalt(I), followed by rapid reduction of the cobalt(III) aryl fluoride intermediate by a second molecule of L tBuCo. [L tBuCo(μ-F)]2 also reacts with Et3SiH to give the hydride complex [L tBuCo(μ-H)]2. This hydride complex has low reactivity toward alkenes and N2, in contrast to an earlier report.

Carbon Dioxide Insertion into Bridging Iron Hydrides: Kinetic and Mechanistic Studies

“…Assuming that this differences arises from the greater bond strength of one or both Fe–(µ‐H) bonds for the hydride being transferred from 1 to CO 2 as compared to the reported monometallic complexes, we surmise that one or more Fe–H bonds is substantially weakened during hydride transfer to CO 2 (Scheme ). We note that a direct hydride transfer from the bridging hydride (Scheme a) in 1 to CO 2 disagrees with the limited reactivity observed for the bis[β‐diketoiminatoiron(II)] di(µ‐hydride) and the absence of reactivity for its cobalt congener . We conclude that an opening of the hydride bridge to an asymmetric or terminal mode likely precedes hydride transfer from 1 to CO 2 .…”

Activation and Formation of Aromatic C–F Bonds

“…LaBerge and J.A. Love (Scheme 14) [79]. Upon reaction with another equivalent of L t BuCo, a bridged fluoro complex (28) is obtained along with a Co-Ph species (29).…”

Аномалии Магнитной Восприимчивости При Фазовых Переходах Второго Рода Вне Точки Кюри

“…Исследованиям фазовых переходов посвящены моно-графии (см., например, [4,5]) и то, что фазовые переходы представляют одно из наиболее распространенных и интересных явлений, отмечено 2 в [6][7][8][9]. Поскольку в последние годы увеличилось количество экспериментальных исследований [10][11][12][13][14][15], связанных с использованием фторида кобальта (CoF 2 ), то в рабо-те [16] изучено состояние фторида кобальта в окрестно-сти критического значения H C продольного магнитного поля H, при котором магнитная подсистема этого кри-сталла переходит в угловую фазу [17,18] вместо обычно наблюдаемого перехода из состояния l A [001] в состояние l ⊥ A (A -ось легчайшего намагничивания, l -вектор антиферромагнетизма).…”