Bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine - A versatile ligand for complexation in Rh^I cationic complexes

The bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine ligand (1) reacts with [Rh(COD)(THF)2][BF4] leading to [Rh(COD)(1)][BF4] ([2][BF4]) in which 1 is κ3 bonded in the solid state. Because of the steric bulk of 1,5-cyclooctadiene, it prefers the κ2 mode of bonding in solution. Substitution of 1,5-cyclooctadiene by carbon monoxide generates [3][BF4] in which 1 is κ3 bonded in solution and solid state. Variable temperature NMR spectroscopic studies give evidence of a κ3 ⇄ κ2 equilibrium in solution. [3][BF4] is easily decarbonylated to [Rh(CO)(1)][BF4] [4][BF4] in which 1 is κ3 bonded; however on bubbling carbon monoxide through, [3][BF4] is regenerated. The single-crystal X-ray structures of [2][BF4], [3][BPh4], and [4][BPh4] are reported.