Heterodinuclear Arene Ruthenium Complexes Containing a Glycine-Derived Phosphinoferrocene Carboxamide: Synthesis, Molecular Structure, Electrochemistry, and Catalytic Oxidation Activity in Aqueous Media

Three series of heterodinuclear Ru-Fe complexes were synthesized from (?6-arene)ruthenium dichloride dimers and phosphinoferrocene ligands contg. glycine-based carboxamido substituents. The neutral complexes [(?6-arene)RuCl2(Ph2PfcCONHCH2CO2Me-?P)] (4, arene = benzene (a), p-cymene (b), hexamethylbenzene (c); fc = ferrocene-1,1'-diyl) were obtained by the bridge cleavage reaction of [(?6-arene)RuCl2]2 with Ph2PfcCONHCH2CO2Me (1) in CHCl3 soln. [(?6-P-cymene)RuCl2(Ph2PfcCONHCH2CONH2-?P)] (6b) was synthesized in the same way from Ph2PfcCONHCH2CONH2 (3); the prepn. of [(?6-p-cymene)RuCl2(Ph2PfcCONHCH2CO2H-?P)] (5b), featuring the ferrocene ligand in the free acid form (2), failed due to side reactions and isolation problems. [(?6-Arene)RuCl(MeCN)(1-?P)][PF6] (7a-c) and [(?6-arene)Ru(MeCN)2(1-?P)][PF6]2 (8a-c) were prepd. from 1 and the MeCN precursors [(?6-arene)RuCl(MeCN)2][PF6] and from 4a-c via halide removal with Ag[PF6] in MeCN soln., resp. Alternative synthetic routes to 7b and 8b were also studied. The compds. were fully characterized by elemental anal., multinuclear NMR, IR, and electrospray ionization mass spectra, and their electrochem. properties were studied by cyclic voltammetry at a Pt-disk electrode. The single-crystal x-ray analyses of two representatives (4b and 8b) revealed a pseudotetrahedral coordination geometry at the Ru centers and eclipsed conformations of the ferrocene moieties, with the substituents at the two cyclopentadienyl rings being anti with respect to each other. All complexes showed high activity for the catalytic oxidn. of secondary alcs. with tert-Bu hydroperoxide to give ketones in aq. media. The most active catalyst was obtained from the neutral p-cymene complex 4b, showing a catalytic turnover frequency of 13,200 h-1 at room temp. for the oxidn. of 1-phenylethanol at a substrate/catalyst ratio of 100,000. [on SciFinder(R)]