The facile chemical oxidation of the binuclear rhodium(I) formamidinate complex [Rh(C8H12)(Form)]2 (Form = [p-CH3C6H4NC(H)NC6H 4CH3-p]-) with AgO2CCF3 (mole ratio 1:4) yields the mixed-ligand Rh2 4+ complex Rh2(Form)2-(O2CCF3) 2(H2O)2. The complex reacts with Lewis bases such as pyridine, dimethyl sulfoxide, piperidine, and 4-methylimidazole to produce stable 1:2 axial adducts. The crystal structure has been determined by X-ray diffraction analysis. The green crystals are triclinic, space group P1, with a = 10.467 (1) Å, b = 13.151 (1) Å, c = 15.470 (2) Å, α = 70.68 (2)°, β = 88.89 (4)°, γ = 79.16 (3)°, V = 1971.6 Å3, Z = 2, Dcalcd = 1.609 g cm-3, R = 0.032, and Rw = 0.034. The molecule consists of two formamidinate and two trifluoroacetate groups symmetrically disposed about the Rh-Rh unit in the conventional fashion. Two water molecules are axially bonded at 2.315 (3) Å from the rhodium atoms. The striking features of the structure are the lengthening of the Rh-Rh (2.425 (1) Å) and Rh-Oeq (2.082 (3) Å) bond distances with respect to the analogous Rh2(O2CCF3)4(H2O) 2·2DTBN and the cisoid arrangement of the formamidinate groups. The Rh-Rh-Oax angles deviate significantly from linearity (167.9 (1) and 169.3 (1)°) as a consequence of steric interactions between the tolyl fragments and the water molecules that participate in hydrogen-bonding interactions throughout the crystal lattice. The electrochemistry in different nonaqueous solvents points out the ability of the title complex to undergo two subsequent one-electron reversible or quasi-reversible anodic processes, attributable to the RhIIRhII/RhIIRhIII and RhIIRhIII/RhIIIRhIII charge transfers, respectively. As expected, these anodic processes are easier than in the case of the corresponding tetracarboxylato species. Of the two electrogenerable anodic products, only the mixed-valence RhIIRhIII derivative is fully stable, and its stability has been quantitatively evaluated and discussed also with respect to that of the other dirhodium complexes.

Chemical oxidation of binuclear rhodium(I) complexes with silver salts. Synthesis, x-ray crystal structure, and electrochemical properties of the rhodium [Rh24+] mixed-ligand complex Rh2(Form)2(O2CCF3)2(H2O)2.0.5C6H6 (Form = N,N'-di-p-tolylformamidinate anion)

PIRAINO, Pasquale;BRUNO, Giuseppe;TRESOLDI, Giuseppe;LO SCHIAVO, Sandra;
1987

Abstract

The facile chemical oxidation of the binuclear rhodium(I) formamidinate complex [Rh(C8H12)(Form)]2 (Form = [p-CH3C6H4NC(H)NC6H 4CH3-p]-) with AgO2CCF3 (mole ratio 1:4) yields the mixed-ligand Rh2 4+ complex Rh2(Form)2-(O2CCF3) 2(H2O)2. The complex reacts with Lewis bases such as pyridine, dimethyl sulfoxide, piperidine, and 4-methylimidazole to produce stable 1:2 axial adducts. The crystal structure has been determined by X-ray diffraction analysis. The green crystals are triclinic, space group P1, with a = 10.467 (1) Å, b = 13.151 (1) Å, c = 15.470 (2) Å, α = 70.68 (2)°, β = 88.89 (4)°, γ = 79.16 (3)°, V = 1971.6 Å3, Z = 2, Dcalcd = 1.609 g cm-3, R = 0.032, and Rw = 0.034. The molecule consists of two formamidinate and two trifluoroacetate groups symmetrically disposed about the Rh-Rh unit in the conventional fashion. Two water molecules are axially bonded at 2.315 (3) Å from the rhodium atoms. The striking features of the structure are the lengthening of the Rh-Rh (2.425 (1) Å) and Rh-Oeq (2.082 (3) Å) bond distances with respect to the analogous Rh2(O2CCF3)4(H2O) 2·2DTBN and the cisoid arrangement of the formamidinate groups. The Rh-Rh-Oax angles deviate significantly from linearity (167.9 (1) and 169.3 (1)°) as a consequence of steric interactions between the tolyl fragments and the water molecules that participate in hydrogen-bonding interactions throughout the crystal lattice. The electrochemistry in different nonaqueous solvents points out the ability of the title complex to undergo two subsequent one-electron reversible or quasi-reversible anodic processes, attributable to the RhIIRhII/RhIIRhIII and RhIIRhIII/RhIIIRhIII charge transfers, respectively. As expected, these anodic processes are easier than in the case of the corresponding tetracarboxylato species. Of the two electrogenerable anodic products, only the mixed-valence RhIIRhIII derivative is fully stable, and its stability has been quantitatively evaluated and discussed also with respect to that of the other dirhodium complexes.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11570/2036496
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