Cationic chiral-at-metal paddlewheel diruthenium complexes

Abstract

A family of cationic heteroleptic diruthenium paddlewheel complexes has been synthesized and characterized, featuring two formamidinate ligands, one acetate ligand, and one pyridinate-based ligand in the equatorial positions. The incorporation of non-symmetric pyridinate ligands derived from 2-hydroxy-6-methylpyridine (hmp−) or 2-amino-6-methylpyridine (amp−) generates an intrinsically chiral arrangement of donor atoms around the Rusingle bondRu bond axis. Coordination of a DMF molecule at one axial site completes the coordination sphere, yielding: [cis-Ru2(DMF)(μ-DPhF)2(μ-hmp)(μ-OAc)](BF4) (RuhmpBF4), [cis-Ru2(DMF)(μ-DPhF)2(μ-amp)(μ-OAc)](BF4) (RuampBF4), [cis-Ru2(DMF)(μ-DAniF)2(μ-hmp)(μ-OAc)](BF4) (Ru’hmpBF4) and [cis-Ru2(DMF)(μ-DAniF)2(μ-amp)(μ-OAc)](BF4) (Ru’ampBF4) (DPhF = N,N´-diphenylformamidinate, DAniF = N,N´-bis(p-methoxyphenyl)formamidinate). For RuhmpBF4, RuampBF4 and Ru’ampBF4, a racemic mixture is obtained as determined by single crystal X-ray diffraction. The chiral paddlewheel structure is fairly robust, although the axial position, occupied by DMF, is labile as shown the preponderance of the [M-BF4-DMF]+ species in the MALDI mass spectra. Variable temperature magnetic susceptibility measurements indicate a S = 3/2 with a non-negligible orbital contribution and a relatively large axial zero-field splitting (D = 42.6(8) - 49.2(9) cm−1).