3 years ago

Thorium(IV) and Uranium(IV) trans-Calix[2]benzene[2]pyrrolide Alkyl and Alkynyl Complexes: Synthesis, Reactivity, and Electronic Structure

Thorium(IV) and Uranium(IV) trans-Calix[2]benzene[2]pyrrolide Alkyl and Alkynyl Complexes: Synthesis, Reactivity, and Electronic Structure
Nikolas Kaltsoyannis, Polly L. Arnold, Joy H. Farnaby, Jason B. Love, Kieran T. P. O’Brien, Markéta Suvova
The first thorium(IV) and uranium(IV) hydrocarbyl complexes of a trans-calix[2]benzene[2]pyrrolide macrocycle can use ligand noninnocence 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 ThIV and UIV monoalkyl-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 metalated, add C–H bonds of terminal alkynes across the metal and ligand, forming the AnIV-alkynyl complexes [(L)An(C≡CR′)2] (R′ = SiMe3, SiiPr3). This ligand reprotonation from (L–2H)4– to (L)2– is accompanied by a change in coordination mode of the ligand from η5151 to η55. Alternatively, the original alkyl group can be retained if the ligand is reprotonated using [Et3NH][BPh4], affording the ThIV cations [(L)Th(R)][BPh4] (R = CH2Ph, N(SiMe3)2). Here, ligand rearrangement to the κ1616 coordination mode occurs. These complexes provide rare examples of bis(arene) actinide sandwich geometry. The two η1-alkynides in [(L)Th(C≡CSiMe3)2] rearrange upon coordination of [Ni0], forming [(L)Th(C≡CSiMe3)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 κ1616 and η55 coordination modes. A computational study of this conformational change demonstrates the η55 coordination mode to be more stable in the Th/Ni bimetallics (and hypothetical Pt analogues), an observation rationalized by detailed analysis of the Kohn–Sham orbital structure of the κ1616 and η55 conformers. Although remarkably inert to even high pressures of CO2 at room temperature, the bis(alkynyl) complexes [(L)An(C≡CSiMe3)2] completely cleave one CO bond of CO2 when they are heated under 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.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00633

DOI: 10.1021/acs.organomet.7b00633

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