Methyllead(IV) Derivatives Stabilized by DAPTSC^2–: Synthesis and Structures of New Diorganolead(IV) Complexes

Abstract

The reaction of the bis(thiosemicarbazone) of dimethyl pyridine‐2,6‐diyl diketone, H2DAPTSC, with PbMe2(OAc)2, PbMePh(OAc)2 or PbPh2(OAc)2 in MeOH afforded the complexes [PbMe2(DAPTSC)], [PbMePh(DAPTSC)] or [PbPh2(DAPTSC)] (in the first two cases together with [Pb(DAPTSC)]). X‐ray crystallography of the Pb(IV) complexes showed that the metal has a pentagonal bipyramidal coordination sphere. The N3,S2‐bound DAPTSC2– anion occupied the equatorial plane and the organic groups were in the apical positions. These compounds retain the same coordination mode in DMSO solution. DAPTSC2– is also N3,S2‐bound in [Pb(DAPTSC)], a complex with a stereochemically active PbII lone pair. The reaction of PbPh2Cl2 with H2DAPTSC, also in methanol at room temperature, afforded [PbPh2(H2DAPTSC)]2[PbPh2Cl4]Cl2·6CH3OH. X‐ray crystallography of this centrosymmetric complex showed it to consist of two [PbPh2(H2DAPTSC)]2+ cations of similar structure to the neutral [PbR2(DAPTSC)] complexes, together with a trans‐octahedral [PbPh2Cl4]2– anion and two Cl– anions. This compound decomposes in DMSO solution, probably evolving to H2DAPTSC and PbPh2Cl2(DMSO)n. In order to evaluate the changes undergone by H2DAPTSC under metallation, the X‐ray structure of the free molecule was also determined.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Effect of the Metal Ion on the Enantioselectivity and Linkage Isomerization of Thiosemicarbazone Helicates

“…As far as the ligands 1 and 2 arrangements are concerned, it must be noted that the donor atoms in both bidentate domains (N3/S1 and N4/S2, Figure 1) are oriented in opposite directions. For this reason, a conformation change is required in order to make the imine nitrogen and the thioamide sulfur atoms point towards the same metal center in a helicate …”

A Conspicuous Deprotonation in Complexes of Diphenyllead(IV) with Ligands Containing Both Semicarbazone and Thiosemicarbazone Chains

“…[9] The orientation of the SC and TSC chains with respect to the pyridine ring (as "open-arm" and "closed-arm", respectively, Figure 1) is similar to that described for the ligand 2,6-diacetylpyridine bis(thiosemicarbazone) methanol solvate [10] and 2,6-diacetylpyridine bis(N-ethyl-thiosemicarbazone). [11] The "closed-arm" orientation of the TSC chain enables the formation of a strong intramolecular hydrogen bond between N(6)-H(6A) and the pyridine nitrogen atom [N(4)] ( Figure 1 and Table 2).…”

“…The interaction with the solvent seemingly induces the evolution www.eurjic.orgof the ligand to a second form [responsible for spectrum (c), Figure 7] in which the N(6)-H···N(4) bond is weakened or even disappears, thus increasing the shielding of the N(6)H proton and bringing the C(4)H and C(6)H doublets in the spectrum closer together. In this second form the TSC arm may adopt an "open" orientation [10] similar to that shown by the SC arm in the solid-state structure. This conformation with both arms in the "open-orientation" has been described for other related molecules.…”

“…Diphenyllead(IV) diacetate was prepared [10] by the reaction of diphenyllead(IV) dichloride with silver(I) acetate in a 1:2 molar ratio in methanol. The silver(I) chloride formed was filtered off, and the solution containing the diphenyllead(IV) diacetate was used immediately in the preparation of the complexes.…”

“…The positions of the signals at δ = 11.94 and 1.90 ppm are rather similar to those observed for acetic acid in dmso solution (δ = 11.91 and 1.91 ppm [21] Pb) coupling constants in these compounds range from 208.6 to 226 Hz, that is, the expected values for a lead coordination number of six or above. [10,22] This suggests that the metal-ligand interactions described in the solid state probably remain in dmso solution.…”