A Rare Low-Spin CoIV Bis(β-silyldiamide) with High Thermal Stability: Steric Enforcement of a Doublet Configuration

Abstract

Attempted preparation of a chelated Co^II β-silylamide resulted in the unprecedented disproportionation to Co⁰ and a spirocyclic cobalt(IV) bis(β-silyldiamide): [Co[(N^t Bu)₂ SiMe₂ ]₂ ] (1). Compound 1 exhibited a room-temperature magnetic moment of 1.8 B.M. and a solid-state axial EPR spectrum diagnostic of a rare S= $1/2$ configuration for tetrahedral Co^IV . Ab initio semicanonical coupled-cluster calculations (DLPNO-CCSD(T)) revealed the doublet state was clearly preferred (-27 kcal mol^-1 ) over higher spin configurations only for the bulky tert-butyl-substituted analogue. Unlike other Co^IV complexes, 1 had remarkable thermal stability, and was demonstrated to form a stable self-limiting monolayer in preliminary atomic layer deposition (ALD) surface saturation experiments. The ease of synthesis and high stability make 1 an attractive starting point to investigate otherwise inaccessible Co^IV intermediates and for synthesizing new materials.

Keywords: EPR spectroscopy; atomic layer deposition; cobalt; coupled-cluster calculations; density functional calculations.