Rational Synthesis and Characterization of Dimolybdenum(II) Compounds Bearing Ferrocenyl-Containing Ligands toward Modulation of Electronic Coupling

Three novel cis-to-trans-converted dimolybdenum­(II) complexes, trans-[Mo2(O2C-Fc)2(DPPX)2]­[BF4]2 {2a–2c; DPPX = DPPA [N,N-bis­(diphenylphosphino)­amine], DPPM [1,1-bis­(diphenylphosphino)­methane], and DPPE [1,2-bis­(diphenylphosphino)­ethane], respectively}, were synthesized through the insertion of bulky diphosphine ligands, which force a permanent trans arrangement, as evidenced by X-ray crystallography and density functional theory calculations. All compounds were characterized by means of NMR, UV–vis, and IR spectroscopy as well as thermogravimetry–mass spectrometry measurements. Interestingly, uncommon UV–vis transitions and oxidation sequences were observed compared to previously reported ones. As verified by electrochemical measurements, all synthesized complexes show two separate one-electron-redox processes assigned to subsequent oxidations of the two redox-active ferrocenecarboxylate ligands, with a split of ca. 70 mV. This behavior reveals electronic interaction between the two equatorially trans-positioned ferrocenyl units. The presented work provides new insights into the rational synthesis of electronically coupled trans-coordinated Mo2 systems, paving the way toward the design of linear multicenter redox-active oligomers.