"Synthesis, Characterization, and Gas-Phase Fragmentation of Rhenium-Carbonyl Complexes Bearing Imidazol(in)ium-2-dithiocarboxylate Ligands"

Tomás F. Beltrán, Guillermo Zaragoza, and Lionel Delaude

Journal Cover
          source: Dalton Transactions
            year: 2016
          volume: 45
      first page: 18346
       last page: 18355
             doi: 10.1039/c6dt03428d

graphical abstract

Abstract: Five complexes with the generic formula [ReBr(CO)32-S,S'-S2C·NHC)] were obtained by reacting [ReBr(CO)5] 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)5] to afford bimetallic Re(0) species. Depending on the experimental conditions, either octacarbonyl dimers [Re2(CO)821-S1-S'-S2C·NHC)] or hexacarbonyl clusters [Re2(CO)62-S,S'3-S,C,S'-S2C·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·CS2 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 CS2- group by 13C 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.

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