Preparation and Protonation Studies of trans-Dioxorhenium(V) Complexes with Imidazoles

Abstract

Reacting ReO 2 I(PPh 3 ) 2 with imidazole (ImH) and its methylated derivatives 1-MeIm, 1,2-Me 2 Im, 2-MeImH, and 4(5)-MeImH yielded salts of the trans-dioxo cation [ReO 2 L 4 ] + . Pure stable compounds were isolated for X -) Iand L ) ImH, 1,2-Me 2 Im, and 1-MeIm and X -) B(C 6 H 5 ) 4 -and L ) 1-MeIm, 2-MeImH and 5-MeImH. The ν as (OdRedO) IR bands were observed between 765 and 794 cm -1 , whereas the ν s Raman band appeared in the 900-925 cm -1 range. The compounds were also characterized by 1 H and 13 C NMR and UV-vis spectroscopies. Crystal structures were determined for three compounds:The complexes adopt the trans-dioxo geometry, and the octahedra are remarkably regular. Protonation of [ReO 2 L 4 ]I was studied in methanol and in water. Acid dissociation constants were determined in aqueous solution for the [ReO(OH)L 4 ] 2+ (K a1 ) and [ReO(OH 2 )L 4 ] 3+ (K a2 ) species of 1-MeIm (pK a1 ) 2.0, pK a2 ) ∼-4.0) and 1,2-Me 2 Im (pK a1 ) ∼3.8, pK a2 ) ∼-4.1). Iodide salts of [ReO(OH)L 4 ] 2+ were not stable enough to be isolated, but the B(C 6 H 5 ) 4 -salt of [ReO(OH)(1,2-Me 2 Im) 4 ] 2+ was obtained in pure form. The crystal structure of [ReO(OH)(1,2-Me 2 Im) 4 ](I 3 ) 0.5 -(ReO 4 ) 1.5 (monoclinic, I2/a, a ) 23.290(8) Å, b ) 10.863(7) Å, c ) 25.709(8) Å, β ) 94.36(3)°, Z ) 8, R ) 0.060) showed the presence of octahedral dications in which the oxo and hydroxo groups are trans to one another and the Re-N bonds are displaced to the Re-OH side by the steric effect of the multiple Re-oxo bond. The σ-donor ability of imidazole, greater than that of pyridine, leads to more stable [ReO 2 L 4 ] + compounds in which the Re)O double bond character is lower and the oxo groups are better nucleophiles.

PRESSURE-INDUCED CHANGE OFd-dLUMINESCENCE ENERGIES, VIBRONIC STRUCTURE AND BAND INTENSITIES IN TRANSITION METAL COMPLEXES

“…[38][39][40][41][42][43][44] Many complexes with different ancillary ligands show almost identical rhenium-oxo bond lengths of 1.765 Å , varying by only 0.001 Å for trans-dioxo complexes of rhenium(V) with ethylenediamine, pyridine and 1-methylimidazole ligands in the xy plane. [45,46] Figure 3 shows the pressure-dependent luminescence spectra of trans-ReO 2 (py) 4 I and trans-ReO 2 (tmen) 2 Cl at room temperature. [47][48][49] The abbreviations py and tmen denote pyridine and tetramethylethylenediamine ligands, respectively.…”

Oxorhenium(V) Complexes with the Non-Sulfur-Containing Amino Acid Histidine

“…57 The Re-NH 2 bond is ∼0.05 Å longer than the Re-N(Im) bond, in agreement with the literature data for complexes with amino acids (mean Re V -N ) 2.188 Å, σ ) 0.032 Å, 20 data) 15,17,18,58 and imidazoles (mean Re V -N ) 2.124 Å, σ ) 0.016 Å, 35 data). [59][60][61][62][63][64] The angles listed in Table S-5 (Supporting Information) show that the octahedron is severely distorted. The general displacement of the "equatorial" ligands away from the RedO bond opens all the cis OdRe-L angles (mean 98.0°), reducing the trans angles below 180°and the cis angles below 90°in this plane.…”

Pressure-Induced Change of d-d Luminescence Energies, Vibronic Structure, and Band Intensities in Transition Metal Complexes

“…[39][40][41][42][43][44][45] Many complexes with different ancillary ligands in the xy plane show almost identical rhenium-oxo bond lengths of 1.765 Å, varying by only 0.001 Å for trans-dioxo complexes of rhenium(V) with ethylenediamine, pyridine or 1-methylimidazole ligands in the xy plane. [47,48] Figure 3 shows the pressure-dependent luminescence spectra of trans-ReO 2 (py) 4 I and trans-ReO 2 (tmen) 2 Cl at room temperature. [49][50][51] The abbreviations py and tmen denote pyridine and tetramethylethylenediamine ligands, respectively.…”