Bonding Properties of a Novel Inorganometallic Complex, Ru(SnPh3)2(CO)2(iPr-DAB) (iPr-DAB = N,N‘-Diisopropyl-1,4-diaza-1,3-butadiene), and its Stable Radical-Anion, Studied by UV−Vis, IR, and EPR Spectroscopy, (Spectro-) Electrochemistry, and Density Functional Calculations

• Published in: Inorganic chemistry 1996-09, Vol.35 (19), p.5468-5477
• Main Authors: Aarnts, Maxim P, Wilms, Maikel P, Peelen, Karin, Fraanje, Jan, Goubitz, Kees, Hartl, František, Stufkens, Derk J, Baerends, Evert Jan, Vlček, Antonín
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic960042h

Ru(SnPh3)2(CO)2(iPr-DAB) was synthesized and characterized by UV−vis, IR, 1H NMR, 13C NMR, 119Sn NMR, and mass (FAB+) spectroscopies and by single-crystal X-ray diffraction, which proved the presence of a nearly linear Sn−Ru−Sn unit. Crystals of Ru(SnPh3)2(CO)2(iPr-DAB)·3.5C6H6 form in the triclinic space group P1̄ in a unit cell of dimensions a = 11.662(6) Å, b = 13.902(3) Å, c = 19.643(2) Å, α = 71.24(2)°, β = 86.91(4)°, γ = 77.89(3)°, and V = 2946(3) Å3. One-electron reduction of Ru(SnPh3)2(CO)2(iPr-DAB) produces the stable radical-anion [Ru(SnPh3)2(CO)2(iPr-DAB)]•- that was characterized by IR, and UV−vis spectroelectrochemistry. Its EPR spectrum shows a signal at g = 1.9960 with well resolved Sn, Ru, and iPr-DAB (H, N) hyperfine couplings. DFT-MO calculations on the model compound Ru(SnH3)2(CO)2(H-DAB) reveal that the HOMO is mainly of σ(Sn−Ru−Sn) character mixed strongly with the lowest π* orbital of the H-DAB ligand. The LUMO (SOMO in the reduced complex) should be viewed as predominantly π*(H-DAB) with an admixture of the σ(Sn−Ru−Sn) orbital. Accordingly, the lowest-energy absorption band of the neutral species will mainly belong to the σ(Sn−Ru−Sn)→π*(iPr-DAB) charge transfer transition. The intrinsic strength of the Ru−Sn bond and the delocalized character of the three-center four-electron Sn−Ru−Sn σ-bond account for the inherent stability of the radical anion.