Cationic chiral-at-metal paddlewheel Diruthenium complexes

A family of cationic heteroleptic diruthenium paddlewheel complexes have 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 Ru Ru bond axis. Coordination of a DMF molecule at one axial site completes the coordination sphere, yielding: [ cis -Ru 2 (DMF)(μ-DPhF) 2 (μ-hmp)(μ-OAc)](BF 4 ) ( RuhmpBF 4 ), [ cis -Ru 2 (DMF)(μ-DPhF) 2 (μ-amp)(μ-OAc)](BF 4 ) ( RuampBF 4 ), [ cis -Ru 2 (DMF)(μ-DAniF) 2 (μ-hmp)(μ-OAc)](BF 4 ) ( Ru’hmpBF 4 ) and [ cis -Ru 2 (DMF)(μ-DAniF) 2 (μ-amp)(μ-OAc)](BF 4 ) ( Ru’ampBF 4 ) (DPhF = N , N ´-diphenylformamidinate, DAniF = N , N ´-bis( p -methoxyphenyl)formamidinate). For RuhmpBF 4 , RuampBF 4 and Ru’ampBF 4 , 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-BF 4 -DMF] + species in the MALDI mass spectra. Variable temperature magnetic susceptibility measurements indicate a S = 3/2 species with a non-negligible orbital contribution and a relatively large axial zero-field splitting ( D = 42.6(8) - 49.2(9) cm −1 ).