Twisting and Tilting l,l'-Bis(dialkylphosphino)ferrocene Bound to Low Valent Tricarbonylmaganese(I to -I). [corrected]

• Published in: Inorganic chemistry Vol. 56; no. 23; pp. 14688 - 14696
• Main Authors: Schäfer, K Michael, Reinders, Leonie, Fiedler, Jan, Ringenberg, Mark R
• Format: Journal Article
• Language: English
• Published: 04.12.2017
• ISSN: 1520-510X
• DOI: 10.1021/acs.inorgchem.7b02627

Recently we had reported the noninnocent behavior of 1,1'-bis(diphenylphosphino)ferrocene (dppf) in Fe(CO)3dppf [Ringenberg et al., Inorg. Chem., 2017, 56, 7501]. Moving to the left in the periodic table, HMn(CO)3(dRpf) where dRpf = dppf (1H) and 1,1'-bis(diisopropylphosphino)ferrocene (dippf) (2H) were synthesized. The hydride ligand was removed by protonation with [(Et2O)2H][B(ArF)4] ([B(ArF)4]- = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate), resulting in the rapid evolution of H2 followed by the formation of an Fe→Mn interaction. The reaction mechanism was determined by in situ IR experiments which show that directly following protonation both [1]+ and [2]+ offer an open manganese coordination site that allows for the formation of an intramolecular Fe→Mn dative bond. This process is significantly faster for [2]+ than for [1]+. The reduction chemistry as studied by cyclic voltammetry (CV) reveals that both complexes change from a distorted octahedral coordination with an Fe→Mn interaction to an open square-pyramidal configuration which is more stable for [1]0 than [2]0. Reoxidation of this square-pyramidal species proceeds more reversibly for 2 versus 1 due to the faster ferrocene ligand reorganization. The electrochemical mechanism was studied by in situ spectroscopic techniques, e.g., IR, UV-vis-NIR (near IR), and EPR spectroelectrochemistry (SEC) as well as by CV simulation. The new complexes described offer an exciting platform for the development of electrocatalysts for the reduction of CO2 to CO, or for proton reduction (2H+ + 2e- → H2).