Employing a template synthesis to access diastereopure Np(iv) and U(iv) complexes and analysis of their 5f orbitals in bonding

Abstract

Development of new synthetic methods to employ with transuranium organometallic complexes will help further the field and may provide a stronger understanding of their distinct reactivity, electronic structures, and chemical bonding. Although the organoneptunium field has grown over the last decade, just a handful of complexes have been synthesized, most of which are found in the trivalent oxidation state. Few reactions with neptunium (Np) have considered the stereochemical outcome, thus we employed a diastereoselective template protocol to synthesize meso (or: C₂) complexes of neptunium(IV). Following previous success with the diastereoselective synthesis of (^(tBu2P)ONO)UCl₂(dtbpy) (1), adaptation to NpCl₄(dme)₂ led to the isolation of diastereopure (^(tBu2P)ONO)NpCl₂(dtbpy) (2), (^(tBu2P)ONO = 2,6-bis((di-tert-butylphosphino)-methanolato)pyridine). The addition of a bulky indenide ligand, derived from the in situ deprotonation of 4,7-dimethyl-1,3-bis(1-methylethyl)-1H-indene (1,3-(ⁱPr)₂-4,7-Me₂-C₉H₃), was pursued to synthesize the organoactinide complexes (^(tBu2P)ONO)U(1,3-(ⁱPr)₂-4,7-Me₂-C₉H₃)Cl (3) and (^(tBu2P)ONO)Np(1,3-(ⁱPr)₂-4,7-Me₂-C₉H₃)Cl (4). Bonding analyses consisting of orbital localization and energy decomposition methods show resemblances in covalent character between uranium (1 and 3) and neptunium (2 and 4) systems. However, an increased orbital overlap was identified in the metal – indenide with respect to the metal–dtbpy interaction, mainly driven by 5f electrons. This was attributed to the better symmetry match between the organic ligand and metal orbitals that allowed the participation of the 5f orbitals.