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. 2023 Sep 11;62(36):14590-14603.
doi: 10.1021/acs.inorgchem.3c01711. Epub 2023 Aug 30.

Highly Reduced Ruthenium Carbide Carbonyl Clusters: Synthesis, Molecular Structure, Reactivity, Electrochemistry, and Computational Investigation of [Ru6C(CO)15]4

Cristiana Cesari  1 , Marco Bortoluzzi  2 , Tiziana Funaioli  3 , Cristina Femoni  1 , Maria Carmela Iapalucci  1 , Stefano Zacchini  1
Affiliations

Highly Reduced Ruthenium Carbide Carbonyl Clusters: Synthesis, Molecular Structure, Reactivity, Electrochemistry, and Computational Investigation of [Ru6C(CO)15]4

Cristiana Cesari et al. Inorg Chem. .

Abstract

The reaction of [Ru6C(CO)16]2- (1) with NaOH in DMSO resulted in the formation of a highly reduced [Ru6C(CO)15]4- (2), which was readily protonated by acids, such as HBF4·Et2O, to [HRu6C(CO)15]3- (3). Oxidation of 2 with [Cp2Fe][PF6] or [C7H7][BF4] in CH3CN resulted in [Ru6C(CO)15(CH3CN)]2- (5), which was quantitatively converted into 1 after exposure to CO atmosphere. The reaction of 2 with a mild methylating agent such as CH3,I afforded the purported [Ru6C(CO)14(COCH3)]3- (6). By employing a stronger reagent, that is, CF3SO3CH3, a mixture of [HRu6C(CO)16]- (4), [H3Ru6C(CO)15]- (7), and [Ru6C(CO)15(CH3CNCH3)]- (8) was obtained. The molecular structures of 2-5, 7, and 8 were determined by single-crystal X-ray diffraction as their [NEt4]4[2]·CH3CN, [NEt4]3[3], [NEt4][4], [NEt4]2[5], [NEt4][7], and [NEt4][8]·solv salts. The carbyne-carbide cluster 6 was partially characterized by IR spectroscopy and ESI-MS, and its structure was computationally predicted using DFT methods. The redox behavior of 2 and 3 was investigated by electrochemical and IR spectroelectrochemical methods. Computational studies were performed in order to unravel structural and thermodynamic aspects of these octahedral Ru-carbide carbonyl clusters displaying miscellaneous ligands and charges in comparison with related iron derivatives.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Synthesis of [Ru6C(CO)15]4– (2) and [HRu6C(CO)15]3– (3)
Figure 1
Figure 1
Reaction of 2 with HBF4·Et2O in CH3CN monitored by IR spectroscopy. IR spectra were recorded after the addition of 0.30 equiv each time.
Figure 2
Figure 2
Molecular structures of (a) [Ru6C(CO)15]4– (2) and (b) [HRu6C(CO)15]3– (3) (orange Ru; red O; gray C; white H).
Scheme 2
Scheme 2. Oxidation Reactions of [Ru6C(CO)15]4– (2) in CH3CN.
All the species have been structurally characterized by SC-XRD except [Ru6C(CO)14(COCH3)]3– (6), which was identified by spectroscopic methods (IR and ESI-MS) and its structure computationally determined.
Figure 3
Figure 3
Molecular structure of [Ru6C(CO)15(CH3CN)]2– (5) (orange Ru; red O; blue N; gray C; white H). Main bond distances (Å): Ru–Ru 2.7901(7)–2.9702(7), average 2.888(2); Ru–Ccarbide 2.019(6)–2.056(6), average 2.042(15); Ru–NCH3CN 2.075(6); C–NCH3CN 1.126(9).
Figure 4
Figure 4
Hydride region of the 1H NMR spectrum of [H3Ru6(CO)15]− (7) in CD2Cl2 at 298 K in the presence of minor traces of [HRu6(CO)16]− (4).
Figure 5
Figure 5
Molecular structures of (a) [H3Ru6C(CO)15]− (7) and (b) [HRu6C(CO)16]− (4) (orange Ru; red O; gray C; white H).
Figure 6
Figure 6
Hydride region of the VT 1H NMR spectra of [H3Ru6(CO)15]− (7) in CD2Cl2. The sharp resonance at ca. δH −19.0 ppm is due to traces of 4.
Figure 7
Figure 7
Molecular structure of [Ru6C(CO)15(CH3CNCH3)]− (8) (orange Ru; red O; blue N; gray C; white H). Main bond distances (Å): Ru–Ru 2.831(2)–2.948(2), average 2.873(7); Ru–Ccarbide 2.017(19)–2.042(18), average 2.03(4); Ru–Nimidoyl 2.067(18); Ru–Cimidoyl 2.07(2); C–Nimidoyl 1.23(3).
Figure 8
Figure 8
Cyclic voltammetry response of [Ru6C(CO)15]4– (2) at a Pt electrode in CH3CN solution between −2.3 and +1.2 V, black line; between −0.8 and −0.2 V, red line; between −0.8 and −0.5 V blue line. [NnBu4][PF6] (0.1 mol dm–3) supporting electrolyte, scan rate: 0.1 V s–1.
Figure 9
Figure 9
Differential pulse voltammetry (blue line) and cyclic voltammetry response of [HRu6C(CO)15]3– (3) at a Pt electrode in CH3CN solution of [NnBu4][PF6] (0.1 mol dm–3) supporting electrolyte: between −0.7 and +0.8 V (black line), scan rate: 0.1 V s–1; between −0.7 and −0.2 V (red line), scan rate: 0.2 V s–1.
Figure 10
Figure 10
IR spectra of a CH3CN solution of [Ru6C(CO)15]4– (4) recorded in an OTTLE cell during the progressive increase of the potential from −0.2 to +0.2 V (vs Ag pseudoreference electrode, scan rate 1 mV s–1). [NnBu4][PF6] (0.1 mol dm–3) as the supporting electrolyte. The absorptions of the solvent and supporting electrolyte have been subtracted.
Figure 11
Figure 11
IR spectra of a solution of [HRu6C(CO)15]3– (3) in CH3CN recorded in an OTTLE cell during (a) progressive increase of the WE potential from −0.1 to +0.7 V (vs Ag pseudoreference electrode; scan rate 1 mV s–1) and (b) during the reduction back-scan from +0.7 to −0.6 V (vs Ag pseudoreference electrode) [NnBu4][PF6] (0.1 mol dm–3) as the supporting electrolyte. The absorptions of the solvent and supporting electrolyte have been subtracted.
Figure 12
Figure 12
DFT-optimized geometries and relative Gibbs energy values of (from top to bottom) [M6C(CO)16]2–, [M6C(COOH)(CO)15]3–, [HM6C(CO)15]3– and [M6C(CO)15]4– (M = Fe, Ru). Color map: orange Ru; green Fe; red O; gray C; white H. Carbonyl ligands are omitted for clarity.
Figure 13
Figure 13
DFT-optimized structure of [Ru6C(CO)14(COCH3)]3– (6) and simulated IR spectra of 6 and 2 (Lorentzian-broadening functions, fwhm = 8 cm–1). Color map: orange Ru; red O; gray C; white H.
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