Structural and Magnetic Studies of a Quasi-Inverse Sandwich Cyclooctatetraene Complex with Two High-Spin Chromium(II) Ions Bound Anti-Facially

Reaction of K₂COT (COT = 1,3,5,7-cyclooctatetraene, C₈H₈) with the aryl chromium­(II) halide [Ar^{<i>i</i>Pr₄}Cr­(μ-Cl)]₂ (Ar^{<i>i</i>Pr₄} = C₆H₃-2,6-(C₆H₃-2,6-^<i>i</i>Pr₂)₂) gave (CrAr^{<i>i</i>Pr₄})₂(μ₂-η³:η⁴-COT) (<b>1</b>), in which a nonplanar COT ring is complexed between two CrAr^{<i>i</i>Pr₄} moieties, a configuration previously unknown for chromium complexes of COT. One Cr²⁺ ion is bonded primarily to three COT carbons (Cr–C = 2.22–2.30 Å) as well as an ipso carbon (Cr–C ≈ 2.47 Å) from a flanking aryl ring of its terphenyl substituent. The other Cr²⁺ ion bonds to an ipso carbon (Cr–C ≈ 2.53 Å) from its terphenyl substituent as well as four COT carbons (Cr–C = 2.24–2.32 Å). The COT carbon–carbon distances display an alternating pattern, consistent with the nonplanarity and nonaromatic character of the ring. The magnetic properties of <b>1</b> indicate that the Cr²⁺ ions have a high-spin d⁴ configuration with <i>S</i> = 2. The temperature dependence of the magnetism indicates that their behavior is due to zero-field splitting of the <i>S</i> = 2 state. Attempts to prepare <b>1</b> by the direct reaction of quintuple-bonded (CrAr^{<i>i</i>Pr₄})₂ with COT were unsuccessful