Manipulating the Spin States of Ru₂^V-Based Compounds: A Dual Pathway via Redox Chemistry and Thermal Activation

In this article, a series of M^II-CN-Ru₂^V (M = Fe, Ru) compounds and their one-electron oxidation compounds were synthesized and fully characterized, namely, [Cp⁵(modppe)Fe-(μ-CN)-Ru₂(DiMeOap-4-Me)₃(OAc)][BF₄]_n (1[BF₄]_n), [Cp⁵(modppe)Fe-(μ-CN)-Ru₂(ap-4-Me)₂(OAc)₂(H₂O)][PF₆]_n (2[PF₆]_n), and [Cp⁵(modppe)Ru-(μ-CN)-Ru₂(DiMeOap-4-Me)₃(OAc)][PF₆]_n (3[PF₆]_n) (n = 1, 2; Cp⁵ = 1,2,3,4,5-pentamethyl-cyclopentadienyl, modppe = 1,2-bis(di(4-methoxyphenyl)-phosphino)ethane, DiMeOap-4-Me = 2-(3, 5-dimethoxy)anilino-4-methylpyridine, ap-4-Me = 2-anilino-4-methylpyridine, OAc = CH₃COO). The analysis of data shows that the electron configurations of Ru₂^V in 1[BF₄], 2[PF₆], and 3[PF₆] with the structure of M^II-CN-Ru₂^V (M = Ru, Fe) are high spin (σ²π⁴δ²)π*²δ* (S_Ru2 = 3/2). Upon one-electron oxidation, compound 1[BF₄]₂ exhibits temperature-dependent spin crossover behavior for the Ru₂^V unit from low spin π*³ (S_Ru2 = 1/2) to high spin π*²δ* (S_Ru2 = 3/2), whereas the Ru₂ unit in 2[PF₆]₂ and 3[PF₆]₂ are assigned as high spin π*²δ* (S_Ru2 = 3/2) Ru₂^V and π*² (S_Ru2 = 1) Ru₂^VI, respectively, confirmed by single-crystal X-ray diffraction structure analyses, infrared microspectroscopy, and magnetic analyses and supported by the TDDFT calculations. To the best of our knowledge, the pair of complexes 1[BF₄]/1[BF₄]₂ is the first example of a spin-state transition initiated by the redox process of an organometallic substituent.