Binding Small Molecules to a cis-Dicarbonyl 99^{\text{99}}TcITc^{\text{I}}-PNP Complex via Metal–Ligand Cooperativity

Metal–ligand cooperativity is a powerful tool for the activation of various bonds but has rarely, if ever, been studied with the radioactive transition metal $^{\text{99}}$Tc. In this work, we explore this bond activation pathway with the dearomatized PNP complex cis-[99TcI(PyrPNPtBu*)(CO)2] (4), which was synthesized by deprotonation of trans-[99TcI(PyrPNPtBu)(CO)2Cl] with KOtBu. Analogous to its rhenium congener, the dearomatized compound reacts with CO2 to form the carboxy complex cis-[99TcI(PyrPNPtBu–COO)(CO)2] and with H2 to form the mono-hydride complex cis-[99TcI(PyrPNPtBu)(CO)2H] (7). Substrates with weakly acidic protons are deprotonated by the Brønsted basic pincer backbone of 4, yielding a variety of intriguing complexes. Reactions with terminal alkynes enable the isolation of acetylide complexes. The deprotonation of an imidazolium salt results in the in situ formation and coordination of a carbene ligand. Furthermore, a study with heterocyclic substrates allowed for the isolation of pyrrolide and pyrazolide complexes, which is uncommon for Tc. The spectroscopic analyses and their solid-state structures are reported

Electron spin resonance spectra of some paramagnetic hydride complexes of niobium(IV) and tantalum(IV)

Frozen solution electron spin resonance spectra show that the unpaired electron is in a dx2-y2 orbital on the metal in the complexes TaCl2H2(drnpe)2, TaCl2H2(PMe3)4 and NbCl2 H2 (dmpe)2, (dmpe = Me2- PCH2CH2PMe2).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26235/1/0000315.pd

Synthesis and characterization of binuclear tantalum hydride complexes

Reduction of the quadruply-bridged (2Cl, 2H) tantalum(IV) dimer, Ta2Cl6 (PMe3)4H2 (2) with sodium amalgam in glyme or THF at 0[deg]C provides deep green Ta2Cl4(PMe3)4H2 (3) in 70% yield. Dimer 3 has a D2d Ta2Cl4(PMe3)4 substructure which closely resembles that of the quadruply metal-metal-bonded dimer W2Cl4(PMe3)4. The hydride ligands of 3 are located on a diagonal plane, bridging the two tantalum atoms and the Ta-Ta separation is 2.545(1) A. 3 reacts cleanly with Cl2, HCl and H2 in diethyl ether to provide the quadruply-bridged dimers 2, Ta2Cl5(PMe3)4H3 (4), and Ta2Cl4(PMe3)4H4 (5), respectively, in high yield. Dimer 5 can also be prepared in high yield via thermolysis of the tantalum(IV) hydride TaCl2H2(PMe3)4 (6) in refluxing methylcyclohexane. The X-ray structure of 5 shows that the ([mu]-H)4 group is staggered by 45[deg] with respect to the eclipsed pyramidal TaCl2(PMe3)2 end groups. The molecular symmetry of 5 is D2d and the Ta-Ta separation is 2.511(2)A. Multiple-scattering X[alpha] calculations on the model compounds Ta2Cl4(PH3)4H2 and Ta2Cl4(PH3)4 are used to elucidate the ground-state electronic structures of 3 and 5, and to probe the question of ([mu]-H)x rotation about the metal-metal bonds in these complexes. Crystal data (at 160[deg]C) are as follows: for 3, monoclinic space group C2/c, a = 18.371(5) A, b = 9.520(3) A, c = 18.942(6) A, [beta] = 125.36(2)[deg], V = 2701.8 A3, Z = 4,dcalc. = 1.991 g cm-3; for 5, tetragonal space group P4/nbm, a = b = 12.579(2) A, c = 10.205(2) A, V = 1614.7 A3, Z = 2, dcalc. = 1.670 g cm-3.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26987/1/0000554.pd

Transuranic organometallics: The next generation

Neptunium and plutonium metal react cleanly with 3/2 equiv. I{sub 2} in aprotic ligating solvents, L, such as tetrahydrofuran (THF), pyridine (Py), and dimethylsulfoxide (DMSO) to give the triiodide complexes as tetrasolvates, AnI{sub 3}(L){sub 4} (An = Np, L = THF (1)); An = Pu, L = THF (2a), Py (2b), and DMSO (2c). These triiodide complexes are convenient precursors to new transuranic compounds. Reaction of the triiodide complexes 1 and 2a hexane with 3 equiv. of sodium bis(trimethylsilyl)amide give the volatile, solvate-free tris(silylamide) complexes, An(N(SiMe{sub 3}){sub 2}){sub 3} (An = Np, 3; An = Pu, 4). The silylamide complexes 3 and 4 undergo rapid reaction in hexane upon stoichiometric addition of HO-2,6-(t-C{sub 4}H{sub 9}){sub 2}C{sub 6}H{sub 3} to give the aryl oxide complexes An(O-2,6-(t-C{sub 4}H{sub 9}){sub 2}C{sub 6}H{sub 3}){sub 3} (An = Np, 5; An = Pu, 6). Preliminary investigations suggest that the aryl oxide complexes 5 and 6 react with lithium bis(trimethylsilyl)methanide, Li{sup +} CH(SiMe{sub 3}){sub 2}, in hexane to give the homoleptic alkyl complexes An(CH(SiMe{sub 3}){sub 2}){sub 3} (An = Np, 7; An = Pu, 8). The homoleptic silylamide, aryl oxide, and alkyl complexes are the first to be reported for transuranic elements. 17 refs

Multiconfigurational Theoretical Study of the Octamethyldimetalates of Cr(II), Mo(II), W(II), and Re(III): Revisiting the Correlation between the M-M Bond Length and the δ → δ* Transition Energy

Four compounds containing metal−metal quadruple bonds, the [M2(CH3)8]n- ions (M = Cr, Mo, W, Re and n = 4, 4, 4, 2, respectively), have been studied theoretically using multiconfigurational quantum-chemical methods. The molecular structure of the ground state of these compounds has been determined and the energy of the δ → δ* transition has been calculated and compared with previous experimental measurements. The high negative charges on the Cr, Mo, and W complexes lead to difficulties in the successful modeling of the ground-state structures, a problem that has been addressed by the explicit inclusion of four Li+ ions in these calculations. The ground-state geometries of the complexes and the δ → δ* transition have been modeled with either excellent agreement with experiment (Re) or satisfactory agreement (Cr, Mo, and W)