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Protonation and Electrochemical Properties of Bisphosphide Diiron Hexacarbonyl Complex Bearing Amino Groups on the Bridge

Abstract

A bisphosphide-bridged diiron hexacarbonyl complex 3 with NEt2 groups on the phosphide bridge was synthesized to examine a new proton relay system from the NEt2 group to the bridging hydride between the two iron centers. As a precursor of the bridging moiety, peri-Et2NP—PNEt2-bridged naphthylene 5 was synthesized by a reaction of 1,8-dilithionaphthylene with two equivalents of Cl2PNEt2 followed by reductive P—P bond formation by magnesium. The reaction of the diphosphine ligand 5 with Fe2(CO)9 gave the diironhexacarbonyl complex 3, in which the P—P bond of the ligand was cleaved to form the bisphosphide-bridge. The molecular structure of 3 indicated that the trigonal plane of the NEt2 group was forced to face the Fe-Fe bond to avoid steric congestion with the naphthylene group linking the two phosphide groups. The NEt2 group could be protonated by p-toluenesulfonic acid. Density functional theory (DFT) calculations confirmed that the proton of the N(H)Et2 group adopted a position close the bridging hydride. The DFT results on the ferrocene analog 1, in which the 1,8-naphthylene group of 3 was replaced with a 1,1’-ferrocenylene group, also revealed that the most stable orientation of the protonated NHEt2 group was that in the protonated 3. As a result, electrochemical proton reduction using complexes 1 and 3 proceeded with similar catalytic efficiency. Unfortunately, the catalytic efficiencies (CE) of these complexes were much lower than those of complexes with a proton relay system to the terminal hydrogen, indicating the reactive property of the bridging hydribe in the present proton relay system cannot exceed that of the terminal hydride.

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Publication details

The article was received on 22 Aug 2019, accepted on 10 Oct 2019 and first published on 11 Oct 2019


Article type: Paper
DOI: 10.1039/C9DT03427G
Dalton Trans., 2019, Accepted Manuscript

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    Protonation and Electrochemical Properties of Bisphosphide Diiron Hexacarbonyl Complex Bearing Amino Groups on the Bridge

    T. Shimamura, Y. Maeno, K. Kubo, S. Kume, C. Greco and T. Mizuta, Dalton Trans., 2019, Accepted Manuscript , DOI: 10.1039/C9DT03427G

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