Classically, late transition-metal organometallic compounds promote multielectron processes solely through the change in oxidation state of the metal centre. In contrast, uranium typically undergoes single-electron chemistry. However, using redox-active ligands can engage multielectron reactivity at this metal in analogy to transition metals. Here we show that a redox-flexible pyridine(diimine) ligand can stabilize a series of highly reduced uranium coordination complexes by storing one, two or three electrons in the ligand. These species reduce organoazides easily to form uranium-nitrogen multiple bonds with the release of dinitrogen. The extent of ligand reduction dictates the formation of uranium mono-, bis- and tris(imido) products. Spectroscopic and structural characterization of these compounds supports the idea that electrons are stored in the ligand framework and used in subsequent reactivity. Computational analyses of the uranium imido products probed their molecular and electronic structures, which facilitated a comparison between the bonding in the tris(imido) structure and its tris(oxo) analogue.

A family of cyclopentadienyl uranium complexes supported by the redox-active pyridine(diimine) ligand, (Mes)PDI(Me) ((Mes)PDI(Me) = 2,6-((Mes)N═CMe)2-C5H3N, Mes = 2,4,6-trimethylphenyl), has been synthesized. Using either Cp* or Cp(P) (Cp* = 1,2,3,4,5-pentamethylcyclopentadienide, Cp(P) = 1-(7,7-dimethylbenzyl)cyclopentadienide), uranium complexes of the type Cp(X)UI2((Mes)PDI(Me)) (1-Cp(X); X = * or P), Cp(X)UI((Mes)PDI(Me)) (2-Cp(X)), and Cp(X)U((Mes)PDI(Me))(THF)n (3-Cp(X); *, n = 1; P, n = 0) were isolated and characterized. The series was generated via ligand centered reduction events; thus the extent of (Mes)PDI(Me) reduction varies in each case, but the uranium(IV) oxidation state is maintained. Treating 2-Cp(X), which has a doubly reduced (Mes)PDI(Me), with furfural results in radical coupling between the substrate and (Mes)PDI(Me), leading to C-C bond formation to form Cp(X)UI((Mes)PDI(Me)-CHOC4H3O) (4-Cp(X)). Exposure of 3-Cp* and 3-Cp(P), which contain a triply reduced (Mes)PDI(Me) ligand, to benzaldehyde and benzophenone, respectively, results in the corresponding pinacolate complexes Cp*U(O2C2Ph2H2)((Mes)PDI(Me)) (5-Cp*) and Cp(P)U(O2C2Ph4)((Mes)PDI(Me)) (5-Cp(P)). The reducing equivalents required for this coupling are derived solely from the redox-active ligand, rather than the uranium center. Complexes 1-5 have been characterized by (1)H NMR and electronic absorption spectroscopies, and SQUID magnetometry was employed to confirm the mono(anionic) [(Mes)PDI(Me)](-) ligand in 1-Cp(P) and 5-Cp(P). Structural parameters of complexes 1-Cp(P), 2-Cp(X), 4-Cp*, and 5-Cp(X) have been elucidated by X-ray crystallography.

The electronic structures of a series of highly reduced uranium complexes bearing the redox-active pyridine(diimine) ligand, (Mes)PDI(Me) ((Mes)PDI(Me) = 2,6-(2,4,6-Me3-C6H2-N═CMe)2C5H3N) have been investigated. The complexes, ((Mes)PDI(Me))UI3(THF) (1), ((Mes)PDI(Me))UI2(THF)2 (2), [((Mes)PDI(Me))UI]2 (3), and [((Mes)PDI(Me))U(THF)]2 (4), were examined using electronic and X-ray absorption spectroscopies, magnetometry, and computational analyses. Taken together, these studies suggest that all members of the series contain uranium(IV) centers with 5f (2) configurations and reduced ligand frameworks, specifically [(Mes)PDI(Me)](•/-), [(Mes)PDI(Me)](2-), [(Mes)PDI(Me)](3-) and [(Mes)PDI(Me)](4-), respectively. In the cases of 2, 3, and 4 no unpaired spin density was found on the ligands, indicating a singlet diradical ligand in monomeric 2 and ligand electron spin-pairing through dimerization in 3 and 4. Interaction energies, representing enthalpies of dimerization, of -116.0 and -144.4 kcal mol(-1) were calculated using DFT for the monomers of 3 and 4, respectively, showing there is a large stabilization gained by dimerization through uranium-arene bonds. Highlighted in these studies is compound 4, bearing a previously unobserved pyridine(diimine) tetraanion, that was uniquely stabilized by backbonding between uranium cations and the η(5)-pyridyl ring.

A robust and rapid manganese formic acid (FA) dehydrogenation catalyst is reported. The manganese is supported by the recently developed, hybrid backbone chelate ligand tBuPNNOP (tBuPNNOP=2,6‐(di‐tert‐butylphosphinito)(di‐tert‐butylphosphinamine)pyridine) (1) and the catalyst is readily prepared with MnBrCO5 to form [(tBuPNNOP)Mn(CO)2][Br] (2). Dehydrohalogenation of 2 generated the neutral five coordinate complex (tBuPNNOP)Mn(CO)2 (3). Dehydrogenation of FA by 2 and 3 was found to be highly efficient, exhibiting turnover frequencies (TOFs) exceeding 8500 h−1, rivaling many noble metal systems. The parent chelate, tBuPONOP (tBuPONOP=2,6‐bis(di‐tert‐butylphosphinito)pyridine) or tBuPNNNP (tBuPNNNP=2,6‐bis (di‐tert‐butylphosphinamine)pyridine), coordination complexes of Mn were synthesized, respectively affording [(tBuPONOP)Mn(CO)2][Br] (4) and [(tBuPNNNP)Mn(CO)2][Br] (5). FA dehydrogenation with the hybrid‐ligand supported 2 exhibits superior catalysis to 4 and 5.

Solvent exchange of NpCl4(DME)2 with THF proceeds simply to yield NpCl4(THF)3, whereas PuCl4(DME)2 is unstable in THF, partially decomposing to the mixed valent [PuIIICl2(THF)5][PuIVCl5(THF)] salt. Reduction of NpCl4(THF)3 with CsC8 ultimately afforded NpCl3(py)4, the only example of a structurally characterized solvated Np(iii) halide. The method demonstrates a route to a well-defined Np(iii) starting material without the need to employ scarcely available Np metal.

Herein we describe the synthesis of a series of nickel complexes, including the formation of [( iPr PN H P)Ni-(PMe 3 )][BPh 4 ] ( iPr PN H P = HN(CH 2 CH 2 (PiPr 2 )) 2 ). The ability of this phosphine complex to perform the 1,2-addition of H 2 O to produce the Ni−OH species [( iPr PN H P)NiOH]-[BPh 4 ] has been investigated. The nucleophilicity of the hydroxide moiety of both [( iPr PN H P)NiOH][BPh 4 ] and the previously reported ( iPr PN H P)MnOH(CO) 2 was investigated through the hydration of aryl and alkyl nitriles, leading to the formation of a number of metal carboxamide (RC(O)NH − ) bonds. This reactivity generated complexes with the general structures of [( iPr PN H P)Ni(NHC(O)R)][BPh 4 ] for nickel and ( iPr PN H P)Mn(NHC(O)R)(CO) 2 for manganese. Under catalytic conditions, the hydration of nitriles using nickel complexes yielded only a single turnover. However, ( iPr PN H P)MnOH(CO) 2 produced several turnovers, and the reaction conditions were probed for optimization.

Actinyl species, [AnO], are well-known derivatives of the f-block because of their natural occurrence and essential roles in the nuclear fuel cycle. Along with their nitrogen analogues, [An(NR)], actinyls are characterized by their two strong trans-An-element multiple bonds, a consequence of the inverse trans influence. We report that these robust bonds can be weakened significantly by increasing the number of multiple bonds to uranium, as demonstrated by a family of uranium(VI) dianions bearing four U-N multiple bonds, [M][U(NR)] (M = Li, Na, K, Rb, Cs). Their geometry is dictated by cation coordination and sterics rather than by electronic factors. Multiple bond weakening by the addition of strong π donors has the potential for applications in the processing of high-valent actinyls, commonly found in environmental pollutants and spent nuclear fuels.

The first uranium(III) charge separated ketyl radical complex, Tp*2U(OC·Ph2), has been isolated and characterized by infrared, (1)H NMR, and electronic absorption spectroscopies, along with X-ray crystallography. Tp*2U(OC·Ph2) is a potent two-electron reductant towards N3Mes (Mes = 2,4,6-trimethylphenyl) and (2,2,6,6-tetramethyl-piperidin-1-yl)oxyl (TEMPO), with reducing equivalents derived from the metal centre and the redox-active benzophenone.