Effect of Axial Ligands on the Oxidation State, Structure, and Electronic Configuration of Diruthenium Complexes. Synthesis and Characterization of Ru₂(dpf)₄Cl, Ru₂(dpf)₄(C⋮CC₆H₅), Ru₂(dpf)₄(C⋮CC₆H₅)₂, and Ru₂(dpf)₄(CN)₂ (dpf = N,N‘-Diphenylformamidinate)

Abstract

The effect of axial ligands on the structure, oxidation state, and electronic configuration of two diruthenium(II,III) and two diruthenium(III,III) complexes is reported. The investigated compounds are represented by Ru2(dpf)4Cl (1), Ru2(dpf)4(C⋮CC6H5) (2), Ru2(dpf)4(C⋮CC6H5)2 (3), and Ru2(dpf)4(CN)2 (4), where dpf is the N,N‘-diphenylformamidinate ion. The chloro and mono(phenylacetylide) complexes, which contain a Ru2 5+ core, are paramagnetic and contain three unpaired electrons, while the bis(phenylacetylide) and bis(cyano) species, which contain a Ru2 6+ core, are diamagnetic. Compound 1, Ru2(dpf)4Cl, was prepared by heating Ru2(CH3COO)4Cl and excess molten N,N‘-diphenylformamidine (Hdpf) for 10 h at 130 °C under an argon atmosphere. Compound 2, Ru2(dpf)4(C⋮CC6H5), was prepared by reaction of purified Ru2(dpf)4Cl with LiC⋮CC6H5 (in a 1:5 ratio) in THF at room temperature (2 h). Compound 3, Ru2(dpf)4(C⋮CC6H5)2, was also obtained from Ru2(dpf)4Cl by using excess LiC⋮CC6H5. A related diruthenium(III,III) complex, Ru2(dpf)4(CN)2 (4), was also synthesized in order to determine whether the observed octahedral distortion in 3 was due to electronic or steric effects. Ru2(dpf)4(CN)2 was prepared by reaction of Ru2(dpf)4Cl and a large excess of NaCN in THF at room temperature (10 h). All four compounds were isolated and characterized by single-crystal X-ray diffraction, 1H NMR, 13C NMR, IR, and UV−visible spectroscopy, and mass spectrometry, as well as by electrochemistry. Compound 1 crystallizes in the tetragonal space group P4/ncc, with a = 14.837(2) Å, c = 21.599(5) Å, and Z = 4, while compound 2 belongs to the monoclinic space group I2/c, with a = 18.590(5) Å, b = 30.913(12) Å, c = 17.360(4) Å, β = 93.61(2)°, and Z = 8. The magnetic moments of the two diruthenium(II,III) species, 1 and 2, are 3.89 and 3.87 μB, respectively, in the solid state at 297 K, consistent with three unpaired electrons and an electronic configuration of (σ)2(π)4(δ)2(δ*π*)3. Compounds 3 and 4 are diamagnetic in their neutral form but paramagnetic upon controlled-potential reduction by one electron. The two reduced RuIIRuIII species, [Ru2(dpf)4(C⋮CC6H5)2]- and [Ru2(dpf)4(CN)2]-, were characterized by ESR spectroscopy after electrochemical generation and display a rhombic signal whose shape is consistent with the presence of only a single unpaired electron. Compound 2, which contains three unpaired electrons, gives a bis adduct Ru2(dpf)4(C⋮CC6H5)(CNCH2C6H5) upon addition of excess CNCH2C6H5 to the solution of Ru2(dpf)4(C⋮CC6H5). The bis adduct species has only one single unpaired electron and shows an ESR spectrum similar to that of electroreduced [Ru2(dpf)4(C⋮CC6H5)2]- and [Ru2(dpf)4(CN)2]-. Crystals of 3 and 4 belong to the monoclinic space groups C2/c and P21, with a = 35.322(7) Å, b = 15.163(3) Å, c = 31.820(9) Å, β = 93.59(2)°, and Z = 12 (compound 3) and with a = 16.184(4) Å, b = 15.784(3) Å, c = 12.896(3) Å, β = 112.29 (2)°, and Z = 2 (compound 4). The Ru−Ru bond distances of 1 and 2 are in the expected range for diruthenium(II,III) co...

Tuning the Magnetic Moment of [Ru2(DPhF)3(O2CMe)L]+ Complexes (DPhF=N,N′‐Diphenylformamidinate): A Theoretical Explanation of the Axial Ligand Influence

“…A more complex and interesting situation was found in the formamidinato Ru 2 5 + complexes. [17][18][19][20][21] Although the tetrakis(formamidinato) complexes containing a Ru 2 5 + unit usually present the S = 3 = 2 spin system, the oxidation of these species leads to diamagnetic compounds [17,19,21] [23] carried out on bisA C H T U N G T R E N N U N G (alkynil) Ru 2 6 + compounds question that simple explanation. The results above for diruthenium derivatives indicate the influence of the nature of the equatorial bridged ligands on the metal-metal energy levels.…”

The First Open‐Paddlewheel Structures in Diruthenium Chemistry: Examples of Intermediate Magnetic Behaviour between Low and High Spin in Ru25+ Species

“…[2] Two different profiles are obtained in the electronic spectra of these high-spin complexes (both in dichloromethane and in the solid state): i) One absorption in the range 512-531 nm with or without significant shoulders at lower energy [3,4,10] (profile a). ii) Two absorptions in the ranges 462-494 and 601-706 nm, sometimes with a small absorption between them [11,12] (profile b).…”

“…83 [a] 465, 569, 704 [a,c] 3.83 [12] 465, 570, 666 [d,12] 3.89 [11] 462, 576, 666 11] 472, 583, 656 11] 475, 633 11] 473, 622 11] 489, 610 11] 494, 601…”

“…Chemicals, including the hydracids HCl (35 %), HBr (48 %) and HI (47 %), and solvents were purchased from commercial sources and used without further purification. [Ru 2 Cl- [6] [Ru 2 (CN)- 4 ], [3] [Ru 2 ClA C H T U N G T R E N N U N G (DPhF) 4 ], [12] and [7] were prepared by following reported procedures. The reactions with silver salts were carried out under exclusion of light.…”

“…[18] The distances Cu À F in those examples are very long (2.502(5)-2.693(2) ) and, therefore, the BF 4 À groups are considered as semicoordinated. However, in complex 4·THF the RuÀF bond lengths are very short (2.069(11) and 2.099 (12) ) and comparable to the length found in several ruthenium complexes in which the fluoride is a terminal ligand: 2.069(2) in [RuF(CO)A C H T U N G T R E N N U N G (dppp) 2 ]PF 6 , 2.069(3) and 2.056(3) in [Ru 2 F 2 A C H T U N G T R E N N U N G (dppp) 2 ] (dppp = 1,3-bis(diphenylphosphino)propane), [19] or 2.065 (1) …”