A Study on the Coordinative Versatility of the Zwitterionic S,N,S Ligand EtNHC(S)­Ph₂P=NPPh₂C(S)NEt in Its Anionic, Neutral and Cationic Forms – Determination of Absolute pK_a Values in CH₂Cl₂ of Rh^I Complexes

Abstract

The coordination properties of EtNHC(S)Ph2P=NPPh2C(S)NEt (HEtSNS) towards RhI species derived from [Rh(CO)2Cl]2 and [Rh(cod)Cl]2 (cod = 1,5‐cyclooctadiene) were studied. This ligand is an amphoteric zwitterion, which forms the H2EtSNS+ cation upon protonation and the EtSNS– dianion–cation upon deprotonation. All three forms coordinate to metal centers. Their geometrical versatility allows many coordination fashions: S‐monodentate; S,S‐bidentate (with a bite angle spanning from 90 to 180°); S,N,S‐tridentate; N,N,N‐tridentate; and S,S‐bridging, as determined by X‐ray diffraction methods. The [Rh(CO)EtSNS] complex is a biprotic base; its conjugated acids are [Rh(CO)HEtSNS]+ and [Rh(CO)H2EtSNS]2+, and their pKa values were determined in dichloromethane solutions. In this triad of compounds, which are geometrically similar, the RhI metal center features variable charge density as confirmed by the νCO infrared absorption frequency.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Synthesis, characterization, crystal structure, theoretical studies, and antibacterial activities of P-coordinated mercury(II) complexes containing phosphine–phosphonium salts

“…Upon going from complex 1 to 6, the energy gap consistently decrease. It is interesting to note that the energy gap of complexes including Br group (1-3) are significantly higher than the complexes including NO 2 group (4)(5)(6). In this regard, for metal complexes with different halogens, the energy gap increases in this order Cl > Br > I.…”

“…Therefore we launched our investigation on a number of these types of compounds applying density functional theory (DFT) calculations. To the best of our knowledge, the geometries of phosphonium salts (S 1 and S 2 ) and their metal complexes (1)(2)(3)(4)(5)(6) were fully optimized at B3LYP/CEP-121G level of theory. However, the theoretical study of phosphine-phosphonium salts derived from bis(diphenylphosphino)ethane and corresponding complexes have not been reported.…”

“…Zwitterionic metal complexes have wide applications in the catalysis and biochemistry due to their heightened solubility in low-polarity media, increased tolerance to polar coordinating solvents, and the avoidance of counteranion effects [1][2][3][4][5]. On the other hand, phosphonium salts have been extensively studied both as valuable intermediates in organic synthesis and as interesting ligands in coordination chemistry [6][7][8][9][10][11][12][13].…”

“…Selected IR and NMR spectral data for phosphonium salts and their metal complexes(1)(2)(3)(4)(5)(6).…”

Reactivity of the zwitterionic ligand EtNHC(S)Ph2PNPPh2C(S)NEt towards [Ru3(CO)12]. Sulfur transfer and ligand fragmentation leading to the methideylamide [-N(Et)-CH(R)-] μ3-bridging moiety

“…Among them, [Rh(CO)EtSNS] behaves as a biprotic base; its conjugated acids are [Rh(CO)HEtSNS] + and [Rh(CO)H 2 EtSNS] 2+ whose absolute acid constants (pK a ) were determined in dichloromethane solution. 8 In brief, HEtSNS and derivatives show five possible coordination fashions (Scheme 2): S,N,Stridentate (A), 6-8 S,S-bidentate [with a very variable bite angle: 180 • (B), 7 136 • (C) 7 and 90 • (D) 8 ], S-monodentate (E), 8 S,Sbridging (F) 8 and N,N,N interaction (G). 8 The aim of this work was to investigate the reactivity of HEtSNS, towards the electron-rich trinuclear cluster [Ru 3 (CO) 12 ].…”