An Actinide Complex with a Nucleophilic Allenylidene Ligand.

The reaction of [CpTh(3,3-diphenylcyclopropenyl)] (Cp = η-CH) with 1 equiv of lithium diisopropylamide (LDA) results in cyclopropenyl ring opening and formation of the thorium allenylidene complex, [Li(EtO)][CpTh(CCCPh)] ([Li(EtO)][]), in good yield. Additionally, deprotonation of [CpTh(3,3-diphenylcyclopropenyl)] with 1 equiv of LDA, in the presence of 12-crown-4 or 2.2.2-cryptand, results in the formation of discrete cation/anion pairs, [Li(12-crown-4)(THF)][CpTh(CCCPh)] ([Li(12-crown-4)(THF)][]) and [Li(2.2.2-cryptand)][CpTh(CCCPh)] ([Li(2.2.2-cryptand)][]), respectively. Interestingly, the complex [Li(EtO)][] undergoes dimerization upon standing at room temperature, resulting in the formation of [CpTh(μ:η:η-CCCPh)] (), via loss of LiCp. The reaction of [Li(EtO)][] with MeI results in electrophilic attack at the C carbon atom, leading to the formation of a thorium acetylide complex, [CpTh(C≡CC(Me)Ph)] (), which can be isolated in 83% yield upon workup, whereas the reaction of [Li(EtO)][] with benzophenone results in the formation of 1,1,4,4-tetraphenylbutatriene () in 99% yield, according to integration against an internal standard. Density functional theory (DFT) calculations performed on [] and reveal significant electron delocalization across the allenylidene ligand. Additionally, calculations of the C NMR chemical shifts for the C, C, and C nuclei of the allenylidene ligand were in good agreement with the experimental shifts. The calculations reveal modest deshielding induced by spin-orbital effects originating at Th due to the involvement of the 5f orbitals in the Th-C bonds. According to a DFT analysis, the cyclopropenyl ring-opening reaction proceeds via [CpTh(η-3,3-Ph--C)] (), which features a carbanion character at C.