A Domino Fusion of an Organic Ligand Depended on Metal-Induced and Oxygen Insertion, Unraveled by Crystallography, Mass Spectrometry, and DFT Calculations

Herein, the reaction of (1-methyl-1 H-benzo[d]imidazol-2-yl)methanamine (L1) with Co(H2O)(6)Cl-2, in CH3CN at 120 degrees C, leading to the 2,3,5,6-tetrakis(1-methyl-1 H-benzo[d]imidazol-2-yl)pyrazine (3), isolated as a dimeric cluster {[Co-2(II)(3)Cl-4].2 CH3CN} (2), is reported. When O-2 and H2O are present, (1-methyl-1 H-benzo[d]imidazole-2-carbonyl)amide (HL1 ') is first formed and crystallized as [Co-III(L1)(2)(L1 ')]Cl-2.2 H2O (4) before fusion of HL1 ' with L1, giving 1-methyl-N-(1-methyl-1 H-benzo[d]imidazol-2-carbonyl)-1 H-benzo[d]imidazol-2-carboxamide (HL2 '') forming a one-dimensional (1D) chain of [Co-3(II)(L2 '')(2)Cl-4](n) (5). The combination of crystallography and mass spectrometry (ESI-MS) of isolated crystals and the solutions taken from the reaction as a function time reveal seven intermediate steps leading to 2, but six steps for 5, for which a different sequence takes place. Control and isotope labeling experiments confirm the two carbonyl oxygen atoms in 5 originate from both air and water. The dependence on the metals, compared with FeCl3.6 H2O leading to a stable triheteroarylmethyl radical, is quite astounding, which could be attributed to the different oxidation states of the metals and coordination modes confirmed by DFT calculations. This metal and valence dependent process is a very useful way for selectively obtaining these large molecules, which are unachievable by common organic synthesis.

Automated summary

This study reports a series of reactions conducted in CH3CN under specific conditions, resulting in the formation of two imine compounds containing 1-methyl-1 H-benzo[d]imidazol-2-yl. Analysis using crystallography and mass spectrometry reveals the intermediate products and reaction mechanisms.