2017) Thorium(IV) and uranium(IV) transcalix[2]benzene[2]pyrrolide alkyl and alkynyl complexes: synthesis, reactivity, and electronic structure. ABSTRACT: The first thorium(IV) and uranium(IV) hydrocarbyl complexes of a trans-calix[2]benzene[2]pyrrolide macrocycle can use ligand non-innocence to enable multiple C-H bond activation reactions at the metal. Both alkyl and alkynyl complexes supported by the (L) dianion and (L -2H ) tetraanion are reported. The Th IV and U IV mono-alkyl -ate complexes [M(L -2H )An(R)] (M = K for R = CH2Ph, M = Li for R = Me, CH2SiMe3), in which the ligand aryl groups are metallated, add the C-H bonds of terminal alkynes across the metal and ligand, forming the An IV -alkynyl complexes [(L)An(C≡CR')2] (R' = SiMe 3 , Si i Pr 3 ). This ligand reprotonation from (L -2H ) 4to (L) 2is accompanied by a change in coordination mode of the ligand from η 5 :η 5 to η 5 :η 1 :η 5 :η 1 . Alternatively, the original alkyl group can be retained if the ligand is reprotonated using [Et3NH][BPh4], affording the Th IV cations [(L)Th(R)][BPh4] (R = CH2Ph, N(SiMe3)2). Again, ligand rearrangement to the κ 1 :η 6 :κ 1 :η 6 coordination mode occurs. These complexes provide rare examples of bis(arene) actinide sandwich geometry. The two η 1 -alkynides in [(L)Th(C≡CSiMe 3 ) 2 ] rearrange upon coordination of [Ni 0 ], forming [(L)Th(C≡CSiMe 3 ) 2 ·Ni(PR'' 3 )] (R'' = phenyl, cyclohexyl) -featuring the shortest yet reported distance between Th and Ni, and giving unprecedented insight into the changes in macrocyclic ligand coordination between κ 1 :η 6 :κ 1 :η 6 and η 5 :η 5 coordination modes. A computational study of this conformational change demonstrates the η 5 :η 5 coordination mode to be the more stable in the Th/Ni bimetallics (and hypothetical Pt analogues), an observation rationalised by detailed analysis of the Kohn-Sham orbital structure of the κ 1 :η 6 :κ 1 :η 6 and η 5 :η 5 conformers. Although remarkably inert to even high-pressures of CO 2 at room temperature, the bis(alkynyl) complexes [(L)An(C≡CSiMe 3 ) 2 ] completely cleave one CO bond of CO 2 when heated under a 1 bar pressure, resulting in the formation, and elimination from the metal, of a new, CO-inserted, bicyclic, carbonylated macrocycle with complete control over the C-C and C-N bond forming reactions. Scheme 2. Syntheses of [M(L -2H )Th(R)] (R = Me (2), CH 2 SiMe 3 (3), CH 2 Ph (4) and [M(L -2H )U(R)] (R = Me (5), CH 2 SiMe 3 (6), CH 2 Ph (7)).

Good correlations are found between QTAIM BCP and EDA data for a range of Th(iv)- and Th(iii)-p element bonds.

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