1,3-Bis(3'-butylimidazol-1'-yl)benzene diiodide (2a), 1,3-bis(3'-but-3''-enyl-imidazolium-3'-yl)benzene diiodide (2b), 1,3-bis(3'-pent-4''-enyl-imidazolium-3'-yl)benzene diiodide (2c), 1,3-bis(4'-butyl-1',2',4'-triazolium-1'-yl)benzene diiodide (2d), or 1,3-bis(4'-butyl-1',2',4'-triazolium-1'-yl)benzene dibromide (2e) was reacted with Ag2O yielding unprecedented tetra-N-heterocyclic carbene-Ag(I)-X cubane-type clusters. These were characterized by (1)H and (13)C NMR spectroscopy, ESI-TOF MS, elemental analysis, and X-ray crystallography. Results from VT (13)C NMR spectroscopy and cross-over experiments are consistent with intramolecular exchange suggesting that the Ag(I) complexes are molecular rotors.
Four new CCC-NHC pincer Zr complexes have been synthesised, characterised, and used in mechanistic studies in the hydroamination/cyclisation of unactivated amino-alkenes. These Zr pre-catalysts will cyclise a primary amino-alkene, but no reaction was observed for a secondary amino-alkene even in the presence of a primary amine. The empirical rate law, experimentally determined activation parameters, and kinetic isotope effects (KIEs) are reported. Several possible mechanisms, including amido- versus imido-insertion and concerted-insertion versus [2 + 2] cycloaddition mechanisms, were modelled computationally at the PBEPBE level of theory with double-zeta quality basis sets. The formation of a catalytically relevant imido complex via the monoamido complexes was accompanied by in situ formation of ammonium salts of the substrates. The experimental and computational data are consistent with an imido-[2 + 2] cycloaddition mechanism for the CCC-NHC pincer diamido Zr complexes that follow saturation kinetics under catalytically relevant concentrations.
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