C–H Bond Activation Facilitated by Bis(phosphinoamide) Heterobimetallic Zr/Co Complexes
Nathanael H. Hunter, Elizabeth Lane, Kathryn M. Gramigna, Curtis E. Moore, Christine M. Thomas
Abstract
The activation of C–H bonds using first-row transition metals poses a formidable challenge in the development of sustainable catalytic methods. Early/late heterobimetallic complexes provide a Lewis acidic binding site for directing groups, facilitating the activation of C–H bonds at an appended first-row transition metal center. Herein, the reactivity of the ZrIV/Co–I heterobimetallic complexes (THF)(I)Zr(XylNPiPr2)2Co(PR3) (1-PR3; Xyl = 3,5-dimethylphenyl; PR3 = PMe3, PPh2Me) toward directed C–H bond activation is explored with pyridine and terminal alkyne derivatives. 1-PMe3 reacts reversibly with 4-methylpyridine to afford the C–H activated complex (4-Me-C5H4N)(I)Zr(XylNPiPr2)2(μ-4-Me-C5H3N)Co(PMe3)(H) (3-PMe3). By using the more Lewis basic substrate 4-tert-butylpyridine, (I)Zr(XylNPiPr2)2(μ-4-tBu-C5H3N)Co(PMe3)(H) (4-PMe3) is formed irreversibly. In addition to pyridine derivatives, 1-PPh2Me can activate the C–H bond of terminal alkynes to form (THF)(I)Zr(XylNPiPr2)2(μ-R′C≡C)Co(PPh2Me)(H) (R′ = Ph (5-PPh2Me); R′ = SiMe3 (6-PPh2Me)).