Actinide Pnictinidene Chemistry: A Terminal Thorium Parent-Arsinidene Complex Stabilised by a Super-Bulky Triamidoamine Ligand.

We report the direct synthesis of the terminal pnictidenes [An(Tren )(PnH)][M(2,2,2-cryptand)] (Tren ={N(CH CH NSiCy ) } ; An/Pn/M=Th/P/Na 5, Th/As/K 6, U/P/Na 7, U/As/K 8) and their conversion to the pnictides [An(Tren )(PnH )] (An/Pn=Th/P 9, Th/As 10, U/P 11, U/As 12). Use of the super-bulky Tren ligand was essential to accessing complete families, and 6 is an unprecedented example of a terminal thorium-arsinidene complex and only the second structurally authenticated parent terminal arsinidene complex of any metal. Comparison of the terminal Th=AsH unit of 6 to the bridging ThAs(H)K linkage in structurally analogous [Th(Tren ){μ-As(H)K(15-crown-5)}] (Tren ={N(CH CH NSiPr ) } ) reveals a stronger Th-As bond in the former compared to the latter, and a large response overall to the nature of the Th=AsH bonding upon removal of the electrostatically-bound K-ion; the σ-bond changes little but the π-bond is significantly perturbed.

Dipnictogen f-Element Chemistry: A Diphosphorus Uranium Complex.

The first isolation and structural characterization of an f-element dinitrogen complex was reported in 1988, but an f-element complex with the first heavier group 15 homologue diphosphorus has to date remained unknown. Here, we report the synthesis of a side-on bound diphosphorus complex of uranium(IV) using a 7λ-(dimethylamino)phosphadibenzonorbornadiene-mediated P atom transfer approach. Experimental and computational characterization reveals that the diphosphorus ligand is activated to its dianionic (P) form and that in-plane U-P π-bonding dominates the bonding of the U(μ-η:η-P)U unit, which is supplemented by a weak U-P interaction of δ symmetry.

Back-bonding between an electron-poor, high-oxidation-state metal and poor π-acceptor ligand in a uranium(V)-dinitrogen complex.

A fundamental bonding model in coordination and organometallic chemistry is the synergic, donor-acceptor interaction between a metal and a neutral π-acceptor ligand, in which the ligand σ donates to the metal, which π back-bonds to the ligand. This interaction typically involves a metal with an electron-rich, mid-, low- or even negative oxidation state and a ligand with a π* orbital. Here, we report that treatment of a uranium-carbene complex with an organoazide produces a uranium(V)-bis(imido)-dinitrogen complex, stabilized by a lithium counterion.