Transition metal complexes of N, N-BIS (dialkylphosphinomethyl) aminomethane derivatives: a DFT study

Abstract

Aminomethylphosphine complexes are used as catalysts in various organic reactions which involve heterogeneous and homogenous processes. Some examples in which aminomethylphosphine complexes are used as catalysts are hydrogenation reactions, hydroformylation reactions and Heck reactions. Some of these studies involve attempts to obtain asymmetric catalysis by making chiral complexes and some involve aminomethylphosphine complexes attached to a solid support in which modifications on the aminomethylphosphine complexes were done. The effect of these modifications, if any, on the structure of the aminomethylphosphine complexes may play an important role for both their reactivities and selectivities. Though papers of experimental studies on these complexes exist in the literature, we have not encountered a computational study. The aim of this study is to understand the effect of different R groups and find a trend for different metal and/or halogen complexes if any. In this work, various transition metal complexes of aminomethylphosphines have been studied by using DFT method. A systematic approach altering the metal M, the halogen X and the substituent R on the phosphorus atom was taken. The transition metals Ni, Pd, Pt which lie on the same group on the periodic table and Rh, which lies on the same period with Pd have been used for complexation. The R groups on the phosphorous atoms utilized are methyl, cyclohexyl and phenyl groups. The halogens Cl, Br and I were used as the coligands. Electronic and structural properties of each complex have been examined. It was found that, phenyl group, which is capable of making-bonding with P and N atoms by resonance, has significant electron withdrawing effect, that halogen atoms with varying electronegativities and metal centers with different electronegativities and sizes also affect the structure of the complex and the charge distribution on it.