Selective hydrogenation of chloronitrobenzenes with an MCM-41 supported platinum allyl complex derived catalyst

Abstract

A platinum precatalyst (1) has been prepared by reacting [(η³-C₃H₅)₄Pt₄Cl₄] with surface functionalized MCM-41 with pendant -(CH₂)₃NH(CH₂)₂NH₂ groups. For the hydrogenation of o-, m- and p-chloronitrobenzenes to the corresponding chloroanilines, 1 is found to be a highly active catalyst with good selectivities for the m- and p-isomers. Its performance is superior to that of its palladium analogue and far superior to that of commercial (5%) Pt/C or (5%) Pt/Al₂O₃. Comparison of solid state and solution NMR data and other evidences indicate that on treatment with the functionalized MCM-41 support; [(η³-C₃H₅)₄Pt₄Cl₄] loses the allyl ligand. XPS data show that in the fresh catalyst Pt is present in the 2+ oxidation state. Based on these and analytical data, co-ordination by surface diamine and hydroxo groups to Pt²⁺ in 1 is suggested. In the used catalyst both Pt²⁺ and Pt⁰ are present but the amount of metallic platinum is ~16% of the total.