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Herein we report the first example of a mononuclear uranium complex, [U4+(NP(pip)3)4] (1-U), that selectively reduces dioxygen to produce a terminal oxo complex, [U6+O(NP(pip)3)4] (2-U; [NP(pip)3]1− is tris(piperidinyl)imidophosphorane). Reactions between 1-U and the heavier elemental chalcogens, S8 or Se0, result in six-coordinate U(VI) complexes, [U6+(κ2-E3)(NP(pip)3)4] (E = S (3-U) or Se (4-U)).

Reaction of the complexes [Fe2(μ2-NP(pip)3)2(NP(pip)3)2] (1-Fe) and [Co2(μ2-NP(pip)3)2(NP(pip)3)2] (1-Co), where [NP(pip)3]1- is tris(piperidinyl)imidophosphorane, with nitrous oxide, S8, or Se0 results in divergent reactivity. With nitrous oxide, 1-Fe forms [Fe2(μ2-O)(μ2-NP(pip)3)2(NP(pip)3)2] (2-Fe), with a very short Fe3+-Fe3+ distance. Reactions of 1-Fe with S8 or Se0 result in the bridging, side-on coordination (μ-κ1:κ1-E22-) of the heavy chalcogens in complexes [Fe2(μ-κ1:κ1-E2)(μ2-NP(pip)3)2(NP(pip)3)2] (E = S, 3-Fe, or Se, 4-Fe). In all cases, the complex 1-Co is inert.

We report the synthesis of a new potassium tris(piperdino)imidophosphorane N,N′-dicyclohexylguanidinate, K[CyGNP(pip)3], and describe the synthesis and characterization of the tris-homoleptic compounds, [Ce(CyGNP(pip)3)3], 1-Ce, and [Ce(CyGNP(pip)3)3][BPh4], 2-Ce. The latter is an unusual cationic tetravalent cerium complex. Cyclic voltammetry studies of 1-Ce and 2-Ce revealed Epc potentials of −1.56 V and −1.81 V, and Epa potentials of −0.78 V and −0.66 V (200 mV s−1; THF, vs. Fc0/+), respectively. Compounds 1-Ce and 2-Ce were studied by L3-edge X-ray absorption near-edge spectroscopy (XANES), and the fit of the spectrum of 2-Ce revealed a white-line multiplet with an nf value of 0.50(2).

We report the synthesis of tetrameric Cu(i) and Ag(i) homoleptic complexes supported by the tris(piperidinyl)imidophosphorane [NP(pip)3]1- and [NP(1,2-bis-tBu-diamidoethane)(NEt2)]1- ligands. These complexes demonstrate the redox stability of the imidophosphorane ligands to oxidizing salts, and the silver complexes can, in turn, serve as oxidative transmetallation reagents for the isolation of tetravalent cerium complexes from cerium metal or trivalent cerium precursors.

The synthesis and structural characterization of the first molecular complexes of lanthanide iodides supported by the weak-base, diethyl ether, are reported. Single-crystal diffraction studies reveal a conserved [LnI3(mer-Et2O)3] structure (Ln = Ce, Pr, Nd, Sm, Gd, Tb, and Tm). These precursors are prepared from lanthanide metal and iodine in diethyl ether for all lanthanides La to Tm (excluding Pm and Eu) and provide the THF adducts in good to excellent (60-91%) yield in a two-step process.

Significance The discovery of efficient hydrogen evolution catalysts for solar fuels production continues to be an active research field. Catalyst optimization depends on detailed knowledge of the elementary chemical reaction steps involved in catalysis. Isolation of intermediates in catalytic processes is uncommon owing to their necessarily low stability. By using weak acids, we have isolated and characterized an intermediate in the 2 e − + 2H + → H 2 reaction catalyzed by η 5 -pentamethylcyclopentadienyl (Cp*) Rh(κ 2 -2,2′-bipyridyl) [Rh(bpy)]. We find that the preferred site of Cp*Rh(bpy) protonation is not the metal center but is the Cp* ligand. Despite the reputation of Cp* as a stable ligand in organometallic chemistry, these results suggest an important role for close metal–ligand cooperation in promoting hydrogen–evolution catalysis.