Synthesis, spectroscopic characterization, crystal structure, DFT and Hirschfeld surface analysis of a manganese(I) complex ([Mn(P-NH-NH-P)(CO)2][BPh4])

Abstract

We report the synthesis of a new Mn—PNNP complex ([Mn(P-NH-NH-P)(CO)2][BPh4]) with an original approach for the synthesis of a previously reported PNNP ligand PPh2(o-C6H4)NHCH2CH2NH(o-C6H4)PPh2 using a new protocol in a less toxic solvent. The PNNP ligand forms a stable mononuclear Mn(I) complex in a low spin state with the additional coordination of two carbonyl groups. This new complex has been characterized by elemental analysis, 1H, 13C and 31P NMR spectroscopy, FTIR spectroscopy and HRMS studies. The molecular structure of the complex was determined by X—ray diffraction analysis, which confirmed its distorted octahedral geometry with the linear tetradentate ligand in a rare cis-α-configuration. Additionally, theoretical calculations were performed on the optimized structure of the complex using the functional-basis-set combination B3PW91/6―311++G (d, p)/SDD which showed good correlation with the experimental data. The frontier molecular orbital analysis revealed a large HOMO to LUMO gap (4.66 eV) as expected for a low spin, d6 octahedral metal complex with the HOMO concentrated on the Mn centre. The Hirschfeld surface analysis signalled the important intermolecular H…H and C…H interactions. A preliminary catalytic study of the complex on transfer hydrogenation of acetophenone was conducted.