Coordination Chemistry of Highly Hemilabile Bidentate Sulfoxide N‐Heterocyclic Carbenes with Palladium(II)

Abstract

Imidazolium salts, [RS(O)-CH2 (C3 H3 N2 )Mes]Cl (R=Me (L1a), Ph (L1b)); Mes=mesityl), make convenient carbene precursors. Palladation of L1a affords the monodentate dinuclear complex, [(PdCl2 {MeS(O)CH2 (C3 H2 N2 )Mes})2 ] (2a), which is converted into trans-[PdCl2 (NHC)2] (trans-4a; N-heterocyclic carbene) with two rotamers in anti and syn configurations. Complex trans-4a can isomerize into cis-4a(anti) at reflux in acetonitrile. Abstraction of chlorides from 4a or 4b leads to the formation of a new dication: trans-[Pd{RS(O)CH2(C3H2N2)Mes}2](PF6)2 (R=Me (5a), Ph (5b)). The X-ray structure of 5a provides evidence that the two bidentate SO-NHC ligands at palladium(II) are in square-planar geometry. Two sulfoxides are sulfur- and oxygen-bound, and constitute five- and six-membered chelate rings with the metal center, respectively. In acetonitrile, complexes 5a or 5b spontaneously transform into cis-[Pd(NHC)2(NCMe)2](PF6)2. Similar studies of thioether-NHCs have also been examined for comparison. The results indicate that sulfoxides are more labile than thioethers.

Anticancer Gold N‐Heterocyclic Carbene Complexes: A Comparative in vitro and ex vivo Study

“…The nature of the isomers can be better elucidated through 13 C NMR spectrum (Figure S9). It suggests the presence of the two rotamers trans–syn and trans–anti as frequently observed for nickel(II) and palladium(II) complexes of two unsymmetrical NHC ligands . As a matter of fact, only one carbenic carbon signal at chemical shift typical of trans ‐bis(NHCs)PtX 2 complexes is present ( δ =167.3 ppm) .…”

“…It suggestst he presence of the two rotamers trans-syn and trans-anti as frequently observed forn ickel(II) and palladium(II) complexes of two unsymmetrical NHC ligands. [49][50][51] As am atter of fact, only one carbenic carbon signal at chemical shift typical of trans-bis(NHCs)PtX 2 complexes is present( d = 167.3 ppm). [48] The formation of the cis isomer can therefore be excluded, as it would have given ac arbenic carbon signal at significantly upfield shiftedc hemical shift as reported for similar compounds (d % 132-150 ppm).…”

Smart N-Heterocyclic Carbene Ligands in Catalysis

“…Since the recent review published by Fliedel and Braunstein in 2014, 127 very few S-functionalized NHC ligands have been reported. 208,209 An interesting example was described by Liu and Chen and co-workers, 209 who prepared a series of palladium(II) complexes with bidentate sulfoxide-NHC ligands Albrecht and co-workers 153 described in 2014 the preparation of the pincer type NHC-carboxylate complex 121. The coordination and decoordination of the carboxylate arm of the ligand is triggered by addition of a base or acid, respectively.…”

“…Since the recent review published by Fliedel and Braunstein in 2014, very few S-functionalized NHC ligands have been reported. , An interesting example was described by Liu and Chen and co-workers, who prepared a series of palladium­(II) complexes with bidentate sulfoxide-NHC ligands ( 113 – 118 , Scheme ). These authors also studied the behavior of an analogous thioether-functionalized NHC complex for comparison.…”

Recent Advances in Catalysis Involving Bidentate N-Heterocyclic Carbene Ligands

“…There are several review articles reported in the past decade, which are dedicated to NHC ligands bearing one additional donor group [ 7 , 8 , 9 , 10 ]. Included in these review articles are bidentate NHC ligands with phosphorous tether [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ], nitrogen [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ], and oxygen tethers [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ,…”