Oanh P. Lam

Activation of elemental S, Se and Te with uranium(III): bridging U–E–U (E = S, Se) and diamond-core complexes U–(E)2–U (E = O, S, Se, Te)

Trivalent uranium complexes supported by tris(aryloxide) chelating ligands, [((t-BuArO)3tacn)U] and [((AdArO)3N)U], undergo activation of sulfur and selenium in their elemental forms, generating the mid-valent U(IV)/(U(IV) complexes of the type [{((t-BuArO)3tacn)U}2(μ-E)] and [{((AdArO)3N)U}2(μ-E)] (E = S, Se). Under reducing conditions, [((AdArO)3N)U] reacts with elemental sulfur, selenium and tellurium to yield the mid-valent dinuclear bis-μ-chalcogenide complexes [Na(DME)3]2[{((AdArO)3N)U}2(μ-E)2] (E = S, Se, Te) with the diamond-core structural motif and rare inorganic chalcogenide bridging ligands. For comparison, a unique high-valent U(V)/U(V) dinuclear complex [{((AdArO)3N)U}2(μ-O)2] was also synthesized. A short uranium–uranium distance in this complex with a U(μ-O)2U diamond-core may account for the unusual temperature-dependent magnetic behavior.

Charge-separation in uranium diazomethane complexes leading to C-H activation and chemical transformation.

The reaction of diphenyldiazomethane with [((t-BuArO)3tacn)UIII] (1) results in an eta(2)-bound diphenyldiazomethane uranium complex. This complex exhibits unusual electronic properties as a charge-separated species with a radical anionic open-shell ligand, [((t-BuArO)3tacn)UIV(eta2-NNCPh2)] (2). Treating Ph2CN2 with a uranium complex that contains a sterically more demanding adamantane functionalized ligand, [((AdArO)3tacn)UIII] (3) results in an unprecedented C-H activation and nitrogen insertion to produce a five-membered heterocyclic indazole complex, [((AdArO)3tacn)UIV(eta(2)-3-phen(Ind))] (5). X-ray crystallography and spectroscopic characterization of these two compounds show that the [((t-BuArO)3tacn)UIV(eta(2)-NNCPh2)] compound is a U(IV) complex with a radical anionic ligand, whereas [((AdArO)3tacn)UIV(eta(2)-3-phen(Ind))] is a U(IV) f (2) species with a closed-shell ligand.

Observation of the inverse trans influence (ITI) in a uranium(V) imide coordination complex: an experimental study and theoretical evaluation.

An inverse trans influence has been observed in a high-valent U(V) imide complex, [(((Ad)ArO)(3)N)U(NMes)]. A thorough theoretical evaluation has been employed in order to corroborate the ITI in this unusual complex. Computations on the target complex, [(((Ad)ArO)(3)N)U(NMes)], and the model complexes [(((Me)ArO)(3)N)U(NMes)] and [(NMe(3))(OMe(2))(OMe)(3)U(NPh)] are discussed along with synthetic details and supporting spectroscopic data. Additionally, the syntheses and full characterization data of the related U(V) trimethylsilylimide complex [(((Ad)ArO)(3)N)U(NTMS)] and U(IV) azide complex [(((Ad)ArO)(3)N)U(N(3))] are also presented for comparison.

Reactivity of U–E–U (E = S, Se) Toward CO2, CS2, and COS: New Mixed-Carbonate Complexes of the Types U–CO2E–U (E = S, Se), U–CS2E–U (E = O, Se), and U–COSSe–U

We recently reported the formation of a bridging carbonate complex [{(((Ad)ArO)(3)N)U}(2)(μ-η(1):κ(2)-CO(3))] via reductive cleavage of CO(2), yielding a μ-oxo bridged complex, followed by the insertion of another molecule of CO(2). In a similar strategy, we were able to isolate and characterize a series of mixed carbonate complexes U-CO(2)E-U, U-CS(2)E-U, and even U-OC(S)Se-U, by reacting bridged chalcogenide complexes [{(((Ad)ArO)(3)N)U}(2)(μ-E)] (E = S, Se) with CO(2), CS(2), and COS. These chalcogenido mixed-carbonate complexes represent the first of their kind.

Formation of a Uranium Trithiocarbonate Complex via the Nucleophilic Addition of a Sulfide-Bridged Uranium Complex to CS2

The uranium(IV)/uranium(IV) μ-sulfide complex [{(((Ad)ArO)(3)N)U}(2)(μ-S)] reacts with CS(2) to form the trithiocarbonate-bridged complex [{(((Ad)ArO)(3)N)U}(2)(μ-κ(2):κ(2)-CS(3))]. The trithiocarbonate complex can alternatively be formed in low yields from low-valent [(((Ad)ArO)(3)N)U(DME)] through the reductive cleavage of CS(2).

Reactivity Studies of a Masked Three-Coordinate Vanadium(II) Complex†

Dedicated to Professor Herbert W. RoeskyThe ability of vanadium to exist in various oxidation statesrenders this ion ideal for multielectron reactions, and there-fore, a suitable metal for incorporation into novel ligandframeworks. An archetypal example of a low-valent vana-dium species is vanadocene, [V(Cp)

Molybdenum and Tungsten Structural Differences are Dependent on ndz2/(n + 1)s Mixing : Comparisons of (silox)3MX/R (M = Mo, W; silox = tBu3SiO)

Treatment of trans-(Et 2O) 2MoCl 4 with 2 or 3 equiv of Na(silox) (i.e., NaOSi (t) Bu 3) afforded (silox) 3MoCl 2 ( 1-Mo) or (silox) 3MoCl ( 2-Mo). Purification of 2-Mo was accomplished via addition of PMe 3 to precipitate (silox) 3ClMoPMe 3 ( 2-MoPMe 3), followed by thermolysis to remove phosphine. Use of MoCl 3(THF) 3 with various amounts of Na(silox) produced (silox) 2ClMoMoCl(silox) 2 ( 3-Mo). Alkylation of 2-Mo with MeMgBr or EtMgBr afforded (silox) 3MoR (R = Me, 2-MoMe; Et, 2-MoEt). 2-MoEt was also synthesized from C 2H 4 and (silox) 3MoH, which was prepared from 2-Mo and NaBEt 3H. Thermolysis of WCl 6 with HOSi ( t )Bu 3 afforded (silox) 2WCl 4 ( 4-W), and sequential treatment of 4-W with Na/Hg and Na(silox) provided (silox) 3WCl 2 ( 1-W, tbp, X-ray), which was alternatively prepared from trans-(Et 2S) 2WCl 4 and 3 equiv of Tl(silox). Na/Hg reduction of 1-W generated (silox) 3WCl ( 2-W). Alkylation of 2-W with MeMgBr produced (silox) 3WMe ( 2-WMe), which dehydrogenated to (silox) 3WCH ( 6-W) with Delta H (double dagger) = 14.9(9) kcal/mol and Delta S (double dagger) = -26(2) eu. Magnetism and structural studies revealed that 2-Mo and 2-MoEt have triplet ground states (GS) and distorted trigonal monopyramid (tmp) and tmp structures, respectively. In contrast, 2-W and 2-WMe possess squashed-T d (distorted square planar) structures, and the former has a singlet GS. Quantum mechanics/molecular mechanics studies of the S = 0 and S = 1 states for full models of 2-Mo, 2-MoEt, 2-W, and 2-WMe corroborate the experimental findings and are consistent with the greater nd z (2) /( n + 1)s mixing in the third-row transition-metal species being the dominant feature in determining the structural disparity between molybdenum and tungsten.