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

Abstract

Equivalent amounts of ReOX(3)(OPPh(3))(Me(2)S) (where X = Cl, Br) and L-histidine (L-hisH) in acetonitrile yield ReOX(2)(L-his), in which the amino acid monoanion is N,N,O-tridentate. X-ray diffraction work on both compounds shows that the three donors occupy a face in a distorted octahedron and the carboxylate oxygen is coordinated trans to the Re=O bond. The 2:1 complex [ReO(L-his)(2)]I is obtained by reacting 2 equiv of L-histidine with ReO(2)I(PPh(3))(2) in methanol in the presence of NaOCH(3). (1)H NMR spectroscopy indicates that these complexes contain one N,N,O-tridentate histidine anion coordinated as above and one N,N-bidentate histidine anion, whose carboxylate group is free. By refluxing ReOX(2)(L-his) in methanol, the carboxylic groups esterify and two octahedral units condense into an oxo-bridged dinuclear complex [ReOX(2)(L-hisMe)](2)O containing N,N-bidentate histidine methyl ester. The O=Re-O-Re=O backbone is approximately linear, and the two ReOX(2)(L-hisMe) units are related by a 2-fold axis through the central oxygen. Crystals of [ReOBr(2)(L-hisMe)](2)O consist of an ordered phase containing two of the possible diastereoisomers in a 1:1 ratio. (1)H NMR spectra of these crystals include two sets of signals, consistent with the presence of two isomers with C(2) symmetry, and the spectra of the nonrecrystallized material confirm that these are the only two isomers formed.

<b>Synthesis and crystal structure of an oxorhenium(V) complex containing a tridentate imidazole ligand</b>

“…Another indication of its double bond character is that the Re-O(1)-C(6) angle is splayed to 129.6(3)° when no apparent intramolecular nonbonding contacts exist, which is close to the expected 120° for Re(V)-O double bonds [9]. The Re = O(2) [1.696(3) Å] shows high doublebond character and is within a range that is expected for mononuclear octahedral oxorhenium(V) complexes (Table 3) with an anionic oxygen donor atom trans to the oxo ligand [17][18][19][20]. The Re-Cl(1) distance [2.41(1) Å] is markedly longer than the Re-Cl(2) bond [2.37(1) Å], indicating the greater trans influence of the imidazole ring compared to the sulfur atom.…”

“…The axial Re-O(1) bond [1.911(3) Å] is slightly longer than those found for Re(V)-O (ethoxide) bonds [1.880(6)-1.896(6) Å], where significant multiple bonding has been postulated and is substantially less than the range of 2.00-2.08 Å which is considered to be representative of Re(V)-O single bonds, and it indicates some double-bond character for this bond [9,17,18]. Another indication of its double bond character is that the Re-O(1)-C(6) angle is splayed to 129.6(3)° when no apparent intramolecular nonbonding contacts exist, which is close to the expected 120° for Re(V)-O double bonds [9].…”

“…A similar complex, [ReOCl 2 (ami)] [Hami = 2-(1-ethanolaminomethyl)-1-methylimidazole], has also been isolated and fully characterized, where ami¯ is a tridentate ligand containing an alcoholate oxygen, secondary amino nitrogen and an imidazolyl nitrogen as donor atoms [20]. In addition to the tridentate imidazole ligands, Beauchamp and co-workers have isolated the neutral mononuclear complexes [ReOX 2 (L-his)] (X = Cl, Br), where L-hisH is the non-sulfurcontaining amino acid histidine with a carboxylic oxygen, amino nitrogen and an imidazolyl nitrogen as donor atoms [18]. X-ray structural studies reveal a cis arrangement of the halides and the coordination of the carboxylate oxygen trans to the oxo group.…”

Study of the histidine complex of uranium(IV): synthesis, spectrophotometric, magnetic and electrochemical properties

“…shows the engagement of a tridentate ligand (N, N, O) and a bidentate ligand (N, N) [8]. This chemistry appeared after mixing the 2:1 mole ratio of histidine with ReOX 3 (OPPh 3 )(Me 2 S).…”

Stereospecific π–π stacking interactions between pseudo-enantiomeric sulfur-bridged dinuclear Co(III)–Pd(II) and Co(III)–Pt(II) complexes of optically active penicillaminates

“…From the view point of coordination chemistry, such sulfur-containing amino acids are useful ligands and their metal complexes are recognized not only as model compounds for living body related substances but building-blocks for constructions of various type sulfur-bridged polynuclear structures [3][4][5]9,[12][13][14][15][16]. Among the latter complexes as building-blocks, the six-coordinated octahedral types have been widely investigated so far and shown to give complicated and diversified polynuclear structures in many cases [17].…”