A new dinitrogen adduct of a homoleptic uranium tris(siloxide) complex, [U{OSi(Mes)3}3]2(μ-η2:η2-N2), is reported. Synthesis of the 15N-labeled isotopomer and Raman spectroscopy confirm the reductive activation of N2 to a (N2)2– dianion. The 15N NMR shift of the 15N2-labeled isotopomer is also reported. Crystallographic characterization shows a side-on (N2)2– coordinated in either an eclipsed or staggered conformation in different crystals. The U–N2–U complex is stable to vacuum and shows high thermal stability, retaining the formally reduced dinitrogen at 100 °C. The parent three-coordinate uranium(III) [U{OSi(Mes)3}3] could not be isolated in our hands, with N2-free syntheses affording only uranium(IV) compounds. The rational synthesis and full characterization of two such U(IV) byproducts, [U{OSi(Mes)3}{N(SiMe3)2}3] and [U{OSi(Mes)3}4], is also reported.

The reactions of f-block silylamido N-heterocyclic carbene (NHC) complexes ([M(L)(N{SiMe(3)}(2))(2)], M = Y, Ce, and U, L = bidentate alkoxy-tethered NHC ligand) with CO and CO(2) have been studied and compared to each other, to those of selected [M(L)(2)(N{SiMe(3)}(2))] complexes, and to those of [M(N{SiMe(3)}(2))(3)] to identify the effect of the labile NHC group on the small molecule activation chemistry. The small molecules COS and N(2)CPh(2) have also been studied.

The natural amide bond found in all biotinylated proteins has been replaced with a triazole through CuAAC reaction of an alkynyl biotin derivative. The resultant triazole-linked adducts are shown to be highly resistant to the ubiquitous hydrolytic enzyme biotinidase and to bind avidin with dissociation constants in the low pM range. Application of this strategy to the production of a series of biotinidase-resistant biotin-Gd-DOTA contrast agents is demonstrated.

A study is reported on the relative stability of trivalent bis(ligand) complexes of the form [M(L(R))(2)N''] for trivalent group 3, lanthanide and actinide cations, using the sterically demanding N-heterocyclic carbene ligand L(R) = [OCMe(2)CH(2){CNCH(2)CH(2)NR}] (R = (i)Pr L(P), Mes L(M), Dipp L(D); N'' = N(SiMe(3))(2)). For the small Y(III) cation (r(6-coord) = 1.040 A) and the smallest L(R), R = (i)Pr, mono, bis, and tris(L(P)) complexes can be made; [Y(L(P))(2)N''] and [Y(L(P))(3)] have been characterised. For the larger ligands, L(M) and L(D), only the mono(L(R)) complexes [Y(L(M))N''(2)] and [Y(L(D))N''(2)] can be made. For the larger Ce(III) (r(6-coord) = 1.15 A), mono(L(R)) and bis(L(R)) complexes [Ce(L(M))N''(2)], [Ce(L(D))N''(2)], [Ce(L(M))(2)N''], and [Ce(L(D))(2)N''] can be made; structural characterisation of the latter two confirm the high degree of steric congestion. The new complex [U(L(M))N''(2)] has also been isolated. Despite the very similar radii of Ce(III) and U(III) (r(6-coord) = 1.165 A), the complexes [U(L(R))(2)N''] cannot be isolated; a surprising display of the difference between the 4f and 5f metal series. However, the six-coordinate, bis(ligand) U(IV) complexes can readily be isolated if smaller ancillary ligands are used; [U(L(M))(2)I(2)] and [U(L(D))(2)I(2)] have been fully, including structurally, characterised.