Bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine -: A versatile ligand for complexation in RhI 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 kappa (3) bonded in the solid state. Because of the steric bulk of 1,5-cyclooctadiene, it prefers the kappa (2) mode of bonding in solution. Substitution of 1,5-cyclooctadiene by carbon monoxide generates [3] [BF4] in which 1 is kappa (3) bonded in solution and solid state. Variable temperature NMR spectroscopic studies give evidence of a kappa (3) reversible arrow kappa (2) equilibrium in solution. [3][BF4] is easily decarbonylated to [Rh(CO)(1)][BF4] [4][BF4] in which 1 is kappa (3) 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.