Thorium(IV) Diphosphazide Complexes: CO2 Insertion into Th–C and Th–N Bonds

A thorium­(IV) trialkyl complex, LPN3Th­(CH2SiMe3)3 (LPN3 = κ5-2,5-[(4-iPrC6H4)­N3PiPr2]2N­(C4H2)−), readily inserts carbon dioxide into the three Th–C bonds to afford LPN3Th­(κ2-O2CCH2SiMe3)3 (1). A new thorium triamido complex, LPN3Th­(NHAd)3 (2) was synthesized and inserts CO2 into the Th–N bonds to form the tricarbamate species LPN3Th­(κ2-O2CNHAd)3 (3). In situ heating experiments revealed that the supporting diphosphazide ligands in complexes 1 and 3 liberate 2 equiv of N2 to form the corresponding diphosphinimine-supported complexes LP=NTh­(κ2-O2CCH2SiMe3)3 (4, LP=N = κ3-2,5-[(4-iPrC6H4)­NPiPr2]2N­(C4H2)−), and 5, LP=NTh­(κ2-O2CNHAd)3, respectively). Conversely, only one unit of N2 was released from 2, affording the asymmetric phosphazide/phosphinimine LP=N/PN3Th­(NHAd)3 (6, LP=N/PN3 = κ3-2-[(4-iPrC6H4)­NPiPr2]-5-[(4-iPrC6H4)­N3PiPr2]­N­(C4H2)−). The addition of 3 equiv of either ClSiMe3 or LiI to complex 1 generated LPN3ThX3 (X = Cl and I) and the carboxylate byproducts Me3SiO2CCH2SiMe3 and LiO2CCHSiMe3, respectively. Addition of LiCH2SiMe3 completed the stepwise synthetic cycle of thorium-mediated CO2 functionalization.