Synthesis of Novel Dinuclear N-Substituted 4-(Dimethylamino)benzaldehyde Thiosemicarbazonates of Rhenium(I): Formation of Four- and/or Five-Membered Chelate Rings, Conformational Analysis, and Reactivity

Abstract

The reaction of fac-[ReX­(CH3CN)2(CO)3] (X = Cl, Br) with N-phenyl-[4-(dimethylamino)­benzaldehyde] thiosemicarbazone (HL A ) or N-4-methoxybenzyl-[4-(dimethylamino)­benzaldehyde] thiosemicarbazone (HL B ) under controlled synthetic conditions gave 4 mononuclear [ReX­(HL)­(CO)3] (X = Cl, Br) and 16 dinuclear [Re2L2(CO)6] compounds. These complexes were obtained as single crystals, and their structures were established by X-ray diffraction. The structural study of these dimers showed the formation of several solvates, the presence of linkage isomerism, and the stabilization of four- and/or five-membered chelate rings. The different ligand coordination modes (a new μ-κ2-S,N2:κ-N3 coordination mode for a thiosemicarbazone ligand was observed), the conformation of the thiosemicarbazone chain in each case, the formal symmetry of the dimers, and the role of the synthetic procedure in the stability of the different chelate rings were analyzed and are discussed. Theoretical calculations in the gas phase were performed for the dimers with the HL A ligand in order to identify the thermodynamically most stable species. The behavior and structural stability of dimers in dimethyl sulfoxide and acetone solutions was investigated by 1H NMR spectroscopy. The strength of the ReI–L bond in solution was evidenced by the formation of [Re2(LNO2 )2(CO)6] and [Re­(LA)­(py)­(CO)3] upon reaction of the corresponding dimer with concentrated nitric acid and pyridine, respectively.

Coordination Chemistry of Potentially S,N,Npy-Tridentate Thiosemicarbazones with the {Re(CO)3}+ Fragment and Formation of Hemiaminal Derivatives

“…However, it is also probable that the reorganization of the thiosemicarbazonate ligand may be difficult, especially for the groups involved in coordination. 31 …”

“…Previous studies on these kinds of compounds in solution in DMSO suggest that dissociation occurs with the probable formation of the solvent complex [Re­(solv)­(L)­(CO) 3 ]. However, it is also probable that the reorganization of the thiosemicarbazonate ligand may be difficult, especially for the groups involved in coordination …”

“…Ligands included in Scheme 1 were synthesized by the reaction of the aldehyde or ketone as described before. 31 The details and spectroscopic characterization are included in the Supporting Information .…”

“…However, it is also probable that the reorganization of the thiosemicarbazonate ligand may be difficult, especially for the groups involved in coordination. 31 Structure of the Dinuclear Thiosemicarbazonate [Re 2 (L 13 ) 2 (CO) 6 ] (13f). The structure of the complex 13f is represented in Figure 7 and it consists of a dimer [Re 2 (L 13 ) 2 (CO) 6 ] in which the ligand, in addition to deprotonation, establishes a sulfur bridge between the rhenium centers.…”

Influence of the Reaction Conditions in the Crystal Structures of Zn(II) and Ni(II) Coordination Compounds with a Dissymmetric Bis(Thiosemicarbazone) Ligand

“…This confers to these ligands a huge versatility in terms of coordination modes [1,2]. The most common one is as N,S bidentate chelate [3,4], coordination mode that affords the formation of a very stable five-membered chelate ring, but many others are described in the literature, for example S monodentante [5,6], N,S bidentate chelate and S bridge [7,8] Crystals 2022, 12, 310 2 of 12 or N,S bidentate chelate and N bridge [9]. This, together with the control of protonation/deprotonation and the nature of auxiliary anions, lead to the formation of different structures such as monomers [10][11][12], dimers [13][14][15] or coordination polymers [16][17][18].…”