Rhenium(I)-Induced Cyclization of Thiosemicarbazones Derived from β-Keto Esters

Abstract

The reactions of methylacetoacetate and ethyl 2-methylacetoacetate thiosemicarbazones (H(2)L(A) and H(2)L(B), respectively) with [ReX(CO)(5)] and [ReX(CO)(3)(CH(3)CN)(2)] (X = Cl, Br) were explored under various experimental conditions. Besides the adducts fac-[ReX(CO)(3)(H(2)L)], in which the rhenium is coordinated to three carbonyl groups, the X anion, and the N,S-bidentate thiosemicarbazone ligand, the following complexes were also isolated: fac-[ReBr(CO)(3)(Hpyz(B))], the tetrameric complexes fac-[Re(pyz(A))(CO)(3)](4) and fac-[Re(pyz(B))(CO)(3)](4), and fac-[Re(pyz(B))(CO)(3)(H(2)O)] (where Hpyz(A) and Hpyz(B) are pyrazolones derived by cyclization of H(2)L(A) and H(2)L(B), respectively). The cyclization reactions were monitored by (1)H NMR spectroscopy and the complexes isolated were identified by elemental analysis, mass spectrometry, IR and (1)H NMR spectroscopy, and in some cases by X-ray diffractometry. The isolation and the full structural identification of the rather unusual fac-[ReBr(CO)(3)(Hpyz(B))], which contains the enol form of the pyrazolone ligand, affords new insight into the cyclization of thiosemicarbazones derived from beta-keto esters.

Bonding and structure trends of thiosemicarbazone derivatives of metals—An overview

“…For molybdenum, MoO 2 (acac) 2 is used as a starting material, the acac anion is replaced by the thiosemicarbazone ligand during complexation [77][78][79]. For W, Tc and Re complexes, metal carbonyls, W(CO) 6 [80,81], (NEt 4 ) 2 Tc(CO) 3 Cl 3 [82], and ReX(CO) 3 (CH 3 CN) 2 [83,84], have been used as precursors. For example, tungsten complexes were prepared by the reaction of a thiosemicarbazone with W(CO) 6 in presence of trimethyl amine-N-oxide in acetone [80,81].…”

Tricarbonyl Rhenium(I) and Technetium(I) Complexes with Hydrazones Derived from 4,5‐Diazafluoren‐9‐one and 1,10‐Phenanthroline‐5,6‐dione

“…[45] This behaviour seems to be a general feature, and it has also been observed in thiosemicarbazone analogs. [46][47][48][49][50] The corresponding signals are only slightly deshielded (0.2-0.30 ppm) for the complexes of the ligands L 3 and L 4 or they are completely unaffected, as in the rhenium complexes of L 5 and L 6 . These findings strongly support the conclusion that the observed solid-state structures with non-coordinated hydrazone groups are also present in solution.…”

Coordination modes of 5-pyrazolones: A solid-state overview

“…All these carbothioamide-5-pyrazolones were obtained by elimination-cyclization processes involving ␤-keto ester or ␤-keto amide thiosemicarbazones (H␤TSCs) in the presence of a metal cation (although other factors such as pH, temperature and the nature of the solvent may influence the process) [109][110][111][112][113][114] (see Scheme 15).…”

“…48) in which the pyrazolonate coordinates to one rhenium atom through its S and N2 atoms, forming a five-membered chelate ring, and to a second metal atom through the oxygen atom (O1). However, [ReBr(CO) 3 (HL 55 )] is a monomer [109] (Fig. 49) [110,112] have also been prepared, as was indicated in Scheme 15, by reaction of Zn(OAc) 2 and the corresponding thiosemicarbazone ligand in MeOH (at room temperature or under reflux).…”

“…with methyl acetoacetate and ethyl 2-methylacetoacetate thiosemicarbazone in toluene under reflux afforded crystals of [Re(L 51 )(CO) 3 ] 4 ·PhCH 3 and [ReBr(CO) 3 (HL 55 )], respectively[109]. In the former case, four fac-Re(CO)3 and four bridgingScheme 14.…”