Reactions of Hydrogen Sulfide with Singly and Doubly Tucked-in Titanocenes

Reactions of permethyltitanocene tucked-in derivatives with carbon dioxide

Both single tucked-in permethyltitanocene 1 and double tucked-in permethyltitanocene 2 react with excess CO₂ by insertion into their Ti-CH₂ bonds. The former one precipitates instantly a yellow carboxylate-tethered oligomer [3]_n which is insoluble in aprotic solvents and in a vacuum it sublimes as a monomer without decomposition. Computations for n ≤ 4 optimised the structure of the monomer [3] and showed that open chain oligomers bound by dative O → Ti bonds were not sterically hindered. The latter bond dissociates when [3]_n is oxidized by chlorination with CDCl₃ or CD₂Cl₂ to give Ti(IV) chloride 4 or upon metathesis of [3]_n with Me₃SiCl yielding Ti(III) chloride 5. Oxidative addition of MeCN affords a C-C coupled dinuclear titanocene diimine 6. Compound [3]_n also reacts with 1 to give the tethered carbodiolate 8 or with [Cp*₂TiH] (where Cp* = η⁵-C₅Me₅) to give the half-tethered carbodiolate 10. The non-tethered carbodiolate 12 was obtained from [Cp*₂TiH] and CO₂ yielding titanocene formate by reaction of the latter with another equivalent of [Cp*₂TiH]. All these carbodiolates contain Ti(III) metal atoms forming electronic triplet states of axial or orthorhombic symmetry. In contrast to the rapidly reacting 1 compound 2 reacts with excess CO₂ slowly in m-xylene at 100 °C using only one of its two Ti-CH₂ moieties. The structure of the obtained carbodiolate 13 indicates that the primary product analogous to 3 reacts with 2 more rapidly than with CO₂.

Vivid Wording for the Chemistry of Group 4 Metallocene Complexes

Three selected examples for the use of unusual wording to describe the organometallic chemistry of Group 4 metallocenes are explained and discussed. The term "tuck(ed)-in" concerns the behavior of decamethyltitanocene [(C₅ Me₅ )₂ Ti] and similar complexes in which one or two methyl groups form the titanium hydride complex [(C₅ Me₅ )(C₅ Me₄ CH₂ )TiH] or other hydride complexes by C-H activation. In the so-called "merry-go-round reaction" the rearrangement of C atoms bound to titanium in organometallic molecules is described which corresponds to the rotation of two C atoms along with a rotation of the six-membered ring in a dihydroindenyl moiety at titanium. In the third example "migration" or "tobogganing" concerns the "sliding" of titanocene along the chain of a linear polyyne by coordination to one or more triple bonds. In all these reactions changes of the coordination mode of the metal at Cp or substrate ligands by intramolecular dynamics occur.

Hydrosulfide complexes of the transition elements: diverse roles in bioinorganic, cluster, coordination, and organometallic chemistry

Molecules containing transition metal hydrosulfide linkages are diverse, spanning a variety of elements, coordination environments, and redox states, and carrying out multiple roles across several fields of chemistry.

The Reductive Activation of CO2 Across a Ti=Ti Double Bond: Synthetic, Structural, and Mechanistic Studies

The reactivity of the bis(pentalene)dititanium double-sandwich compound Ti2Pn†2 (1) (Pn† = 1,4-{SiiPr3}2C8H4) with CO2 is investigated in detail using spectroscopic, X-ray crystallographic, and computational studies. When the CO2 reaction is performed at -78 °C, the 1:1 adduct 4 is formed, and low-temperature spectroscopic measurements are consistent with a CO2 molecule bound symmetrically to the two Ti centers in a μ:η2,η2 binding mode, a structure also indicated by theory. Upon warming to room temperature the coordinated CO2 is quantitatively reduced over a period of minutes to give the bis(oxo)-bridged dimer 2 and the dicarbonyl complex 3. In situ NMR studies indicated that this decomposition proceeds in a stepwise process via monooxo (5) and monocarbonyl (7) double-sandwich complexes, which have been independently synthesized and structurally characterized. 5 is thermally unstable with respect to a μ-O dimer in which the Ti-Ti bond has been cleaved and one pentalene ligand binds in an η8 fashion to each of the formally TiIII centers. The molecular structure of 7 shows a "side-on" bound carbonyl ligand. Bonding of the double-sandwich species Ti2Pn2 (Pn = C8H6) to other fragments has been investigated by density functional theory calculations and fragment analysis, providing insight into the CO2 reaction pathway consistent with the experimentally observed intermediates. A key step in the proposed mechanism is disproportionation of a mono(oxo) di-TiIII species to yield di-TiII and di-TiIV products. 1 forms a structurally characterized, thermally stable CS2 adduct 8 that shows symmetrical binding to the Ti2 unit and supports the formulation of 4. The reaction of 1 with COS forms a thermally unstable complex 9 that undergoes scission to give mono(μ-S) mono(CO) species 10. Ph3PS is an effective sulfur transfer agent for 1, enabling the synthesis of mono(μ-S) complex 11 with a double-sandwich structure and bis(μ-S) dimer 12 in which the Ti-Ti bond has been cleaved.

Reactivity of uranium(iii) with H2E (E = S, Se, Te): synthesis of a series of mononuclear and dinuclear uranium(iv) hydrochalcogenido complexes

We report the syntheses, electronic properties, and molecular structures of a series of mono- and dinuclear uranium(iv) hydrochalcogenido complexes supported by the sterically demanding but very flexible, single N-anchored tris(aryloxide) ligand (^AdArO)₃N)^3-. The mononuclear complexes [((^AdArO)₃N)U(DME)(EH)] (E = S, Se, Te) can be obtained from the reaction of the uranium(iii) starting material [((^AdArO)₃N)U^III(DME)] in DME via reduction of H₂E and the elimination of 0.5 equivalents of H₂. The dinuclear complexes [{((^AdArO)₃N)U}₂(μ-EH)₂] can be obtained by dissolving their mononuclear counterparts in non-coordinating solvents such as benzene. In order to facilitate the work with the highly toxic gases, we created concentrated THF solutions that can be handled using simple glovebox techniques and can be stored at -35 °C for several weeks.