Isomerization Reactions in Anionic Mesoionic Carbene‐Borates and Control of Properties and Reactivities in the resulting CoII Complexes through Agostic Interactions

MCLELLAN, ROSS; BEERHUES, JULIA; NEUMAN, NICOLAS; NÖßLER, MAITE; SARKAR, BIPRAJIT; STUBBE, JESSICA; SOMMER, MICHAEL; MULVEY, ROBERT

Angewandte Chemie

WILEY-V C H VERLAG GMBH

Año: 2020

1433-7851

We present here anionic borate based bi‐mesoionic carbene compounds of the 1,2,3‐triazol‐4‐ylidene type (with additional cyclohexyl or phenyl substituents on borate) that undergo C‐N isomerization reactions. The isomerized compounds are excellent ligands for Co II centers. Strong agostic interactions with the ?C‐H?‐groups of the cyclohexyl substituents result in an unusual low spin square planar Co II complex, which is unreactive towards external substrates. Such agostic interactions are absent in the complex with phenyl substituents on the borate backbone. That complex displays a high spin tetrahedral Co II center, which is reactive towards external substrates including dioxygen. A combined synthetic, crystallographic, spectroscopic and theoretical approach is used to investigate the compounds. We conclusively show here that the structure and properties of these Co II complexes can be strongly influenced through interactions in the secondary coordination sphere. Additionally, we unravel a unique ligand rearrangement for these classes of anionic mesoionic carbene based ligands.