Experimental and computational studies on a three-membered diphosphido thorium metallaheterocycle [η5-1,3-(Me3C)2C5H3]2Th[η2-P2(2,4,6-iPr3C6H2)2]

Abstract

A three-membered thorium metallaheterocycle [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th[η²-P₂(2,4,6-ⁱPr₃C₆H₂)₂] (4) is readily prepared besides H₂ from [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th(PH-2,4,6-ⁱPr₃C₆H₂)₂ (3) upon heating in toluene solution. Density functional theory (DFT) studies were performed to elucidate the 5f orbital contribution to the bonding within Th-(η²-P-P) revealing more covalent bonds between the [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th²⁺ and [η²-P₂(2,4,6-ⁱPr₃C₆H₂)₂]²⁻ fragments than those in the related thorium metallacyclopropene. Consequently, distinctively different reactivity patterns emerge, e.g., while 4 reacts with pyridine derivatives such as 4-dimethyaminopyridnie (DMAP) and forms the DMAP adduct [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th[η²-P₂(2,4,6-ⁱPr₃C₆H₂)₂](DMAP) (5), it may also act as a [η⁵-1,3-(Me₃C)₂C₅H₃]₂Th(II) synthon when reacted with bipy, Ph₂S₂ or Ph₂Se₂. Nevertheless, no reaction of complex 4 with alkynes is observed, but it reacts as a nucleophile towards nitriles and aldehydes resulting in five- or seven-membered metallaheterocycles, respectively. DFT computations provide some additional insights into the experimental observations.