Kinetics and Mechanism Study of the Substitution Reactions of the Chloride Ligand in Dichloro(5,10,15,20)‐tetraphenyl‐21H,23H‐porphinato)tin(IV) by Organic Bases in Dimethylformamide Solvent

Substitution reactions of a Cl⁻ ligand in [SnCl₂(tpp)] (tpp=5,10,15,20‐tetraphenyl‐21H,23H‐porphinato(2−)) by five organic bases i.e., butylamine (BuNH₂), sec‐butylamine (^sBuNH₂), tert‐butylamine (^tBuNH₂), dibutylamine (Bu₂NH), and tributylamine (Bu₃N), as entering nucleophile in dimethylformamide at I=0.1M (NaNO₃) and 30–55° were studied. The second‐order rate constants for the substitution of a Cl⁻ ligand were found to be (36.86±1.14)⋅10⁻³, (32.91±0.79)⋅10⁻³, (22.21±0.58)⋅10⁻³, (19.09±0.66)⋅10⁻³, and (1.36±0.08)⋅10⁻³ M ⁻¹s⁻¹ at 40° for BuNH₂, ^tBuNH₂, ^sBuNH₂, Bu₂NH, and Bu₃N, respectively. In a temperature‐dependence study, the activation parameters ΔH^≠ and ΔS^≠ for the reaction of [SnCl₂(tpp)] with the organic bases were determined as 38.61±4.79 kJ mol⁻¹ and −150.40±15.46 J K⁻¹mol⁻¹ for BuNH₂, 40.95±4.79 kJ mol⁻¹ and −143.75±15.46 J K⁻¹mol⁻¹ for ^tBuNH₂, 30.88±2.43 kJ mol⁻¹ and −179.00±7.82 J K⁻¹mol⁻¹ for ^sBuNH₂, 26.56±2.97 kJ mol⁻¹ and −194.05±9.39 J K⁻¹mol⁻¹ for Bu₂NH, and 39.37±2.25 kJ mol⁻¹ and −174.68±7.07 J K⁻¹ mol⁻¹ for Bu₃N. From the linear rate dependence on the concentration of the bases, the span of k₂ values, and the large negative values of the activation entropy, an associative (A) mechanism is deduced for the ligand substitution.