Mixed-Ligand Rhenium Tricarbonyl Complexes Anchored on a (κ²-H,S) Trihydro(mercaptoimidazolyl)borate: A Missing Binding Motif for Soft Scorpionates

Complex fac-[Re{κ3-H(µ-H)2B(timMe)}(CO)3] (1) (timMe = 2-mercapto-1-methylimidazolyl) promptly reacts with the neutral substrates PPh3, tBuNC and EtOOCCH2NC yielding fac-[Re{κ2-H2(µ-H)B(timMe)}(L)(CO)3] (L = PPh3(2), (tBuNC) (3), (EtOOCCH2NC) (4)). Complexes 2−4 have been fully characterized, including by variable-temperature NMR studies and X-ray diffraction analysis in the case of 2. Unlike 1, complexes 2−4 are fluxional in solution undergoing a dynamic process that accounts for the magnetic equivalence of all the B−H hydrogen atoms at room temperature. Compounds 1 and 2 were studied by DFT methods to explain the different solution behavior of the complexes anchored by (κ2-H,S) and (κ3-H,H′,S) soft scorpionates.