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Near‐Infrared‐Absorbing Organometallic Diruthenium Complex Intermediates: Evidence for Bridging Anthrasemiquinone Formation and against Mixed Valency
Author(s) -
Kamatchi Thangavel Sathiya,
Mondal Sudipta,
Scherer Thomas,
Bubrin Martina,
Natarajan Karuppannan,
Kaim Wolfgang
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201703888
Subject(s) - chemistry , electron paramagnetic resonance , ruthenium , crystallography , hyperfine structure , bridging ligand , ligand (biochemistry) , valency , photochemistry , crystal structure , nuclear magnetic resonance , catalysis , linguistics , philosophy , biochemistry , physics , receptor , quantum mechanics
The new redox‐active complexes [RuH(CO)(EPh 3 ) 2 (μ‐Q 2− )RuH(CO)(EPh 3 ) 2 ], E=P ( 1 ) and E=As ( 2 ) with the bis‐chelate bridging ligand Q 2− =1,4‐dioxido‐9,10‐anthraquinone were prepared and characterised. The related compound [RuCl(CO)(PPh 3 ) 2 (μ‐Q x 2− )RuCl(CO)(PPh 3 ) 2 ] ( 4 ) with E=P and Q x 2− =5,8‐dioxido‐1,4‐naphthoquinone 4 revealed trans ‐positioned PPh 3 groups. The electrogenerated one‐electron oxidised states 1 + and 2 + were examined using spectroelectrochemical techniques (EPR, IR and UV/Vis/NIR). In situ EPR studies gave spectra with 31 P or 75 As hyperfine splitting of about 16 Gauss, small 99, 101 Ru coupling and small g‐ anisotropy in the frozen solution state. The 31 P and 75 As hyperfine values reflect axial positioning of the four Ru−E bonds relative to the plane of an anthrasemiquinone bridge. Single CO stretching bands around 1910 cm −1 of the precursors 1 and 2 shift by about 25 cm −1 to higher energies on oxidation. The direction, uniformity and the extent of the shifts confirm ligand bridge‐based oxidation. Absorbance by the cations in the near infrared region is thus assigned to intra‐ligand transitions of ruthenium(II)‐bonded anthrasemiquinones and not to intervalence charge transfer of mixed‐valent species. Ruthenium(II) stabilisation by CO and EPh 3 is made responsible for the anthrasemiquinone formation instead of metal‐centered oxidation.