Synthesis and reactivity of binuclear pyrazolate-bridged ruthenium(I) complexes. Crystal structures of bis[µ-(3,5-dimethylpyrazolato-NN′)-tricarbonylruthenium(I)](Ru–Ru) and bis[µ-(3,5-dimethylpyrazolato-NN′)]-µ-iodo-bis[tricarbonylruthenium(II)]tri-iodide

Abstract

The complexes [Ru₂(µ-L)₂(CO)₆][HL = 3,5-dimethylpyrazole (Hdmpz)(1), pyrazole (Hpz)(2), 3-methylpyrazole (3), or indazole (4)] have been obtained by reaction of RuCl₃·nH₂O with carbon monoxide in refluxing 2-methoxyethanol followed by reduction with zinc in the presence of HL and CO. This synthetic route provides an easy method to prepare turhenium(I)compounds in high yield. Complexes (1) and (2) react with iodine to afford [Ru₂(µ-I)(µ-L)₂(CO)₆]I₃[L = dmpz (5) or pz (6)] or [Ru₂I₂(µ-L)₂(CO)₆][L = dmpz(7) or pz (8)] depending on the Ru: I ratio used. Complex (1) reacts with an excess of acetonitrile at 56 °C to give the C₁ monosubstituted product [Ru₂(µ-dmpz)₂(CO)₅(NCMe)](9), whereas with excess of pyridine (py) it affords the C_s monosubstituted product [Ru₂(µ-dmpz)₂(CO)₅(py)](10). However, it reacts with an excess of PPh₃, P(C₆H₁₁)₃, or bis(diphenylphosphino)methane (dppm) at 20 °C to give the C1 monosubstituted products [Ru₂(µ-dmpz)₂(CO)₅(PR₃)][PR₃= PPh₃(11), P(C₆H₁₁)₃(12), or dppm (13)]. Infrared and ¹H and ³¹P-{¹H} n.m.r. spectra of all the compounds are presented and discussed in relation to their structures. The crystal structures of complexes (1) and (5) have been determined by X-ray diffraction methods. Crystals of (1) are monoclinic, space group P2₁/n, with a= 15.388(7), b= 10.497(5), c= 13.706(5)Å, β= 110.32(2)°, and Z= 4. Crystals of (5) are triclinic, space group P, with a= 10.970(5), b= 12.393(6), c= 10.522(6)Å, α= 98.22(2), β= 103.94(3), γ= 74.29(2)°, and Z= 2. The structures were solved from diffractomer data by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.056(1) and 0.043(5) for 1 987 (1) and 3 348 (5) observed reflections. In complex (1) the two Ru atoms are doubly bridged by two dmpz ligands with a Ru–Ru distance, 2.705(2)Å, consistent with a metal–metal bond. In (5) an iodine atom has been inserted between the two Ru atoms, Ru–I 2.699(2) and 2.707(2)Å, and the Ru–Ru distance is increased to 3.636(2)Å.