A Comparative Study of Cyclometallated Palladium(II) Compounds with Terdentate [C,N,S] Pincer Ligands − Crystal and Molecular Structure of [Pd{4-MeC6H3C(Me)=NNC(=S)NHMe}(PPh3)] and [Pd{4-MeOC6H3C(H)=N[2-(SMe)C6H4]}(Cl)]

Abstract

Treatment of the thiosemicarbazone ligands 4‐MeC6H4C(Me)=NN(H)C(=S)NHMe (a), 4‐MeC6H4C(Me)=NN(H)C(=S)NHEt (b), and 4‐MeC6H4C(Me)=NN(H)C(=S)NHPh (c) with K2[PdCl4] produced the tetranuclear palladium(II) compounds [Pd{4‐MeC6H3C(Me)=NNC(=S)NHMe}]4 (1a), [Pd{4‐MeC6H3C(Me)=NNC(=S)NHEt}]4 (1b), and [Pd{4‐MeC6H3C(Me)=NNC(=S)NHPh}]4 (1c) with deprotonation of the NH group. Treatment of thiosemicarbazones 4‐MeOC6H4C(H)=NN(Me)C(=S)NH2 (d) and 3‐MeOC6H4C(H)=NN(Me)C(=S)NH2 (e) with K2[PdCl4] gave the mononuclear palladium(II) compounds [Pd{4‐MeOC6H3C(H)=NN(Me)C(=S)NH2}(Cl)] (1d) and [Pd{3‐MeOC6H3C(H)=NN(Me)C(=S)NH2}(Cl)] (1e). Treatment of the Schiff base 4‐MeOC6H4C(H)=N[2‐(SMe)C6H4] (f) with Li2[PdCl4] afforded [Pd{4‐MeOC6H3C(H)=N[2‐(SMe)C6H4]}(Cl)] (1f). All the ligands are terdentate through the [C,N,S] atoms and the Pd−S bond formed is sufficiently strong to tolerate treatment with nucleophiles without bond cleavage. Treatment of 1a, 1b, and 1c with triphenylphosphane gave the mononuclear species 2a, 2b, and 2c, which upon treatment with hydrochloric acid resulted in the 1:1 electrolytes 3a, 3b, and 3c, with NH and C=S groups. Coordination of PPh3 to Pd in 1f was achieved by treatment of the compound with sodium perchlorate, followed by the nucleophile in a 1:1 molar ratio, to yield 2f. The crystal structures of compounds 2a and 1f are described.

Synthesis, characterization and structural studies of palladium(II) complexes with N-(aroyl)-N′-(2,4-dimethoxybenzylidene)hydrazines

“…This up-field shift is consistent with the weakening of the C@N bond due to the N-coordination and the trans disposition of the Pd and the proton around the C@N [7,[19][20][21][22]. However, unlike the free Schiff bases it appears as a doublet due to the coupling with the 31 P nucleus which is trans (vide infra) to the N-atom [4,7,21,22]. Two doublets observed in the ranges d 6.82-7.28 and 7.85-7.91 correspond to the aroyl ring protons.…”

“…Thiosemicarbazones and semicarbazones of aromatic aldehydes are known to act as tridentate ligands for Pd(II) and Pt(II) via ortho-metallation and can yield cyclometallated complexes having two fused five-membered chelate rings at the metal centre [1][2][3][4]. Thiosemicarbazones can coordinate the metal ion as mono-or bianionic C,N,Sdonor ligand.…”

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

“…The phenyl rings at C 2 carbon involve metallation in the dinuclear complexes [Pd 2 L 2 (dppm)]·CH 3 COCH 3 212 [103] (dppm = Ph 2 PCH 2 PPh 2 ), and [Pd 2 LCl 2 (dppm)] 213 [241]. The former has bridging dppm and the latter has both sulfur and dppm as bridging moieties.…”

“…Tetranuclear complexes [Pd 4 L 4 ] 217 and 218 involve binding via C, N 3 , and S-donor atoms [103,244] and complex 219 binds via N 4 , N 3 , S-donor atoms [245]. The coordinate sulfur bridges Pd centres, and the central core Pd 4 S 4 is an eight-membered twisted ring of alternate Pd and S atoms.…”

Rotation of a double C=N bond driven by palladium

“…These examples show the tendency to form links between palladium centers, when the ligand acts is in the thiolate form due to deprotonation of the thiol form in semicarbazone group [9]. By avoiding this deprotonation is possible to form mononuclear complexes [10]. Ligand structure factors conditioning the coordination modes [C, N,S] and [N,S] were previously described [11].…”