Synthesis and reactivity of low-coordinate diamagnetic Rh and Ir complexes and paramagnetic Rh(II) complexes
Low-coordinate complexes generally show high reactivity and the lower the coordination number is, the higher the reactivity would be. Oxidative addition of C-H and X-H bonds is one of the most important and basic steps in organometallic catalysis. In this work, oxidative addition of Si-H, Sn-H and B-H bonds (E-H) at low-coordinate Rh and Ir β-diiminate (BDI) complexes to form dihydride and trihydride complexes are described. In addition, ligand functionalization via a cleavage of an Sn-C bond was obtained by the treatment of (MeBDI)Rh(COE)(N2) (MeBDI = (2,6-Me2C6H3N=CMe)2CH) with SnMe4 and H2. Steric effects are significant controlling the reactions with EH substrates. To explore the limits of steric hindrance, reaction of (MeBDI)Rh(COE)(N2) with bulky PPh3 was tested, leading to a complex containing a tautomerized BDI ligand. Paramagnetic complexes of platinum group metals often show high and radical-like reactivity. They have one or more single electrons which typically show wide and broad peaks on NMR and they are usually characterized by EPR. Starting from [(MeBDI)Rh]2(μ-Br)2, low-coordinate monomeric Rh(II) complex (MeBDI)Rh(2,6-iPr2C6H3NH) was successfully isolated through reaction with lithium 2,6-diisopropylanilide. Reactions with less hindered anilides resulted in eventual formation of diamagnetic final products. Reactions of [(MeBDI)Rh]2(μ-Br)2 with lithium 2,6-dimethylanilide involves benzylic C-H activation while C-N coupling is observed with unsubstituted lithium anilide.