Synthesis, characterization, and gas-phase fragmentation of rhenium–carbonyl complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands

Abstract

Five complexes with the generic formula [ReBr(CO)(κ-S,S'-SC·NHC)] were obtained by reacting [ReBr(CO)] with a set of representative imidazol(in)ium-2-dithiocarboxylate zwitterions. These ligands are the adducts of N-heterocyclic carbenes (NHCs) and carbon disulfide. The monometallic Re(i) compounds were further coupled with Na[Re(CO)] to afford bimetallic Re(0) species. Depending on the experimental conditions, either octacarbonyl dimers [Re(CO)(μ-κ-S,κ-S'-SC·NHC)] or hexacarbonyl clusters [Re(CO)(κ-S,S'-κ-S,C,S'-SC·NHC)] were isolated. All the products were fully characterized using various analytical techniques. Single crystal XRD analysis helped establish with certainty the various binding modes exhibited by the NHC·CS ligands. With bite angles ranging from ca. 104 to 130°, these zwitterions displayed a remarkable flexibility, which also permitted significant twists of the thiometallated rings to preserve a staggered arrangement of the carbonyl groups in the bimetallic systems. Monitoring the chemical shift of the CS moiety by C NMR spectroscopy was most useful to detect its change of hapticity upon decarbonylation of the octacarbonyl compounds into hexacarbonyl derivatives. IR spectroscopy was another very convenient tool to identify the type of complex formed in a reaction, based on the pattern of its carbonyl vibration bands. Advanced mass spectrometry techniques showed that all the compounds underwent partial or total decarbonylation in the gas phase with no concomitant fragmentation of the bimetallic assemblies into monometallic ions.

Imidazol(in)ium-2-Thiocarboxylate Zwitterion Ligands: Structural Aspects in Coordination Complexes

“…In all the examples, the metal center shows a distorted octahedral geometry with a bidentate NHC•CS 2 zwitterion ligand, a bromide, and three carbonyl ligands (Figures 7 and 8) [16,17]. Table 4 summarizes the most significant distances and angles.…”

“…There are only three examples of rhenium complexes bearing azolium-2-thiocarboxylate zwitterionic ligands as a bidentate bridge, which are 35-37 (Figure 14) [16]. In this case, the complexes are dimers where two cis-tetracarbonyl rhenium fragments are connected via a metal-metal bond and a CS 2 − bridge.…”

Homoleptic ruthenium(ii) complexes bearing imidazol(in)ium-2-dithiocarboxylate ligands: synthesis, characterization, and redox properties

“…7 In the late 1980s, Borer et al showed that 1,3-dimethylimidazolium-2-dithiocarboxylate (IMe·CS 2 ) formed stable complexes with a range of transition metal halides or nitrates, but the exact nature of the products obtained remained highly speculative. 8 Since the new millennium, we and others have investigated in more detail the various binding modes of NHC·CS 2 zwitterions with diverse metals, such as manganese, 9 rhenium, 10,11 ruthenium, 11–15 osmium, 14 palladium, 16 copper, 17–19 or gold 20 (see Chart 1 for a few selected examples). In most cases, heteroleptic complexes were targeted for their physicochemical properties or catalytic potentials.…”

Aldiminium and 1,2,3-triazolium dithiocarboxylate zwitterions derived from cyclic (alkyl)(amino) and mesoionic carbenes

“…These 1,1-dithiolate inner salts strongly bind main group elements and transition metals through various coordination modes. Indeed, we and others have already reported the synthesis of diverse metallic complexes featuring monodentate [ 44 – 45 ], chelating bidentate [ 46 – 55 ], or bridging bidentate NHC·CS 2 ligands [ 45 , 51 – 52 ]. Small bimetallic clusters [ 51 – 52 56 ], coordination polymers [ 57 ], self-assembled monolayers [ 58 ], and nanoparticles [ 45 ] based on these zwitterions were also prepared, while a few reports disclosed the formation of polynuclear clusters, in which the dithiocarboxylate unit underwent further chemical transformations [ 59 – 61 ].…”