Amine olefin rhodium(i) complexes: pKa and NH bond strength

Abstract

A combination of the rigid bis(5H-dibenzo[a,d]cyclohepten-5-yl)amine (trop₂NH) and 5-amino-5H-dibenzo[a,d]cycloheptene (tropNH₂) ligand allowed the synthesis of the stable pentacoordinated 18 electron amine olefin rhodium(I) complex [Rh(trop₂NH)(tropNH₂)]O₃SCF₃ (5); this complex can be cleanly deprotonated [pK_a^DMSO = 20.6(1)] to the corresponding amide [Rh(trop₂N)(tropNH₂)] (6) which is reversibly oxidised at −0.466 V (vs. Fc/Fc⁺). The coordinated NH bond strength in 5 is estimated to be 379 ± 10 kJ mol⁻¹.