16 research outputs found
C–H Activation on an Oxo-Bridged Dititanium Complex: From Alkyl to μ‑Alkylidene Functionalities
Thermal treatment
of the dinuclear compound [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(μ-O)] (<b>1</b>) provides
the formation of the metallacycle derivatives [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(μ-O)] (<b>2</b>) and [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>(μ-O)] (<b>3</b>) and the μ-alkylidene
complex [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(μ-CHSiMe<sub>3</sub>)(μ-O)] (<b>4</b>) by sequential carbon–hydrogen activation processes.
The reaction of <b>3</b> with <i>tert</i>-butylisocyanide,
in 1:1 and 1:2 ratios, leads to the η<sup>2</sup>-iminoacyl
complexes [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-<i>t</i>BuNCCH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(μ-O)] (<b>5</b>) and [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-<i>t</i>BuNCCH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>(μ-O)]
(<b>6</b>), respectively. The molecular structures of complexes <b>3</b>, <b>4</b>, <b>5</b>, and <b>6</b> have
been determined by single-crystal X-ray diffraction analyses
C–H Activation on an Oxo-Bridged Dititanium Complex: From Alkyl to μ‑Alkylidene Functionalities
Thermal treatment
of the dinuclear compound [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>}<sub>2</sub>(μ-O)] (<b>1</b>) provides
the formation of the metallacycle derivatives [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(μ-O)] (<b>2</b>) and [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>(μ-O)] (<b>3</b>) and the μ-alkylidene
complex [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(μ-CHSiMe<sub>3</sub>)(μ-O)] (<b>4</b>) by sequential carbon–hydrogen activation processes.
The reaction of <b>3</b> with <i>tert</i>-butylisocyanide,
in 1:1 and 1:2 ratios, leads to the η<sup>2</sup>-iminoacyl
complexes [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-<i>t</i>BuNCCH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(μ-CH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)(μ-O)] (<b>5</b>) and [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>2</sub>(μ-<i>t</i>BuNCCH<sub>2</sub>SiMe<sub>2</sub>CH<sub>2</sub>)<sub>2</sub>(μ-O)]
(<b>6</b>), respectively. The molecular structures of complexes <b>3</b>, <b>4</b>, <b>5</b>, and <b>6</b> have
been determined by single-crystal X-ray diffraction analyses
An Effective Route to Dinuclear Niobium and Tantalum Imido Complexes
Thermal treatment
of the trichloro complexes [MCl<sub>3</sub>(NR)py<sub>2</sub>] (R
= <i>t</i>Bu, Xyl; M = Nb, Ta) (Xyl = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) under vacuum affords the dinuclear imido
species [MCl<sub>2</sub>(μ-Cl)(NR)py]<sub>2</sub> (R = <i>t</i>Bu, Xyl; M = Nb <b>1</b>, <b>3</b>; Ta <b>2</b>, <b>4</b>) with loss of pyridine. Complexes <b>1</b>–<b>4</b> can be easily transformed to the mononuclear
starting materials [MCl<sub>3</sub>(NR)py<sub>2</sub>] (R = <i>t</i>Bu, Xyl; M = Nb, Ta) upon reaction with pyridine. While
reactions of compounds <b>1</b> and <b>2</b> with a series
of alkylating reagents render the mononuclear peralkylated imido complexes
[MR<sub>3</sub>(N<i>t</i>Bu)] (R = Me, CH<sub>2</sub>Ph,
CH<sub>2</sub>CMe<sub>3</sub>, CH<sub>2</sub>CMePh, CH<sub>2</sub>SiMe<sub>3</sub>), the analogous treatment with allylmagnesium chloride
results in the formation of the dinuclear niobium(IV) derivative [(N<i>t</i>Bu)(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)M(μ-C<sub>3</sub>H<sub>5</sub>)(μ-Cl)<sub>2</sub>M(N<i>t</i>Bu)py<sub>2</sub>] (<b>5</b>). Additionally, the treatment
of the starting materials <b>1</b> and <b>2</b> with the
organosilicon reductant 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene
yields the pyridyl-bridged dinuclear derivatives [M<sub>2</sub>Cl<sub>2</sub>(μ-Cl)<sub>2</sub>(N<i>t</i>Bu)<sub>2</sub>py<sub>2</sub>]<sub>2</sub>(μ-NC<sub>4</sub>H<sub>4</sub>N)<sub>2</sub> (M = Nb <b>6</b>, Ta <b>7</b>). Controlled hydrolysis
reaction of <b>1</b> and <b>2</b> affords the oxo chlorido-bridged
products [MCl(μ-Cl)(N<i>t</i>Bu)py]<sub>2</sub>(μ-O)
(M = Nb <b>8</b>, Ta <b>9</b>) in a quantitative way,
while the treatment of these latter with one more equivalent of pyridine
led to complexes [MCl<sub>2</sub>(N<i>t</i>Bu)py<sub>2</sub>]<sub>2</sub>(μ-O) (M = Nb <b>10</b>, Ta <b>11</b>). Structural study of these dinuclear imido derivatives has been
also performed by X-ray crystallography
Systematic Approach for the Construction of Niobium and Tantalum Sulfide Clusters
Treatment of the
imido complexes [MCl<sub>3</sub>(NR)py<sub>2</sub>] (R = <sup><i>t</i></sup>Bu, 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>;
M = Nb <b>1</b>, <b>3</b>; Ta <b>2</b>, <b>4</b>) (Xyl = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) with (Me<sub>3</sub>Si)<sub>2</sub>S in a 1:1 ratio afforded the new cube-type
sulfide clusters [MCl(NR)py(μ<sub>3</sub>-S)]<sub>4</sub> (R
= <sup><i>t</i></sup>Bu, 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>; M = Nb <b>5</b>, <b>7</b>; Ta <b>6</b>, <b>8</b>) with loss of Me<sub>3</sub>SiCl. Reactions of <b>5</b> and <b>6</b> with cyclopentadienyllithium in 1:4 ratio
resulted in the rupture of the coordinative M–S bonds and the
replacement of a pyridine molecule and a chlorine atom by an η<sup>5</sup>-cyclopentadienyl group in each metal center, affording the
compounds [M(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)(N<sup><i>t</i></sup>Bu)(μ-S)]<sub>4</sub> (M = Nb <b>9</b>, Ta <b>10</b>). These processes may develop through
formation of the complexes [M<sub>4</sub>(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>(μ-Cl)(N<sup><i>t</i></sup>Bu)<sub>4</sub>py<sub>2</sub>(μ<sub>3</sub>-S)<sub>2</sub>(μ-S)<sub>2</sub>](C<sub>5</sub>H<sub>5</sub>) (M = Nb <b>11</b>, Ta <b>12</b>), also obtained
by reaction of <b>5</b> and <b>6</b> with cyclopentadienyllithium
in 1:3 ratio. As further evidence, <b>11</b> and <b>12</b> led to complexes <b>9</b> and <b>10</b> by treatment
with one more equivalent of the lithium reagent. The structural study
of these metal sulfide clusters has been also performed by X-ray crystallography
Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides
The reactivity of
the “tuck-over” species [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(CH<sub>2</sub>Ph)<sub>3</sub>(μ-η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>CH<sub>2</sub>-κ<i>C</i>)(μ-O)]
(<b>1</b>) and [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(CH<sub>2</sub>CMe<sub>3</sub>)(μ-η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>CH<sub>2</sub>-κ<i>C</i>)(μ-CH<sub>2</sub>CMe<sub>2</sub>CH<sub>2</sub>)(μ-O)] (<b>2</b>) toward isocyanides has been
examined both synthetically and theoretically. Treatment of <b>1</b> with the isocyanides RNC, R = Me<sub>3</sub>SiCH<sub>2</sub>, 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>, <i>t</i>Bu, <i>i</i>Pr, leads to a series of η<sup>2</sup>-iminoacyl species (<b>3</b>–<b>6</b>) where the
molecule of isocyanide inserts into one of the terminal metal–alkyl
bonds. The analogous reaction of the “tuck-over” metallacycle
species <b>2</b> with 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NC and <i>t</i>BuNC results in the initial insertion of
one isocyanide into the terminal Ti–alkyl bond to form the
iminoacyl complexes <b>7</b> and <b>8</b>, followed by
a second insertion into the metallacycle moiety to generate <b>9</b>, in the case of <i>tert</i>-butylisocyanide. DFT
calculations support the selective reactivity observed experimentally
with a kinetic and thermodynamic preference for RNC insertion on the
terminal alkyl groups bound to both metallic centers over the alternative
insertion on the “tuck-over” ligand
Co-complexation of Lithium Gallates on the Titanium Molecular Oxide {[Ti(η<sup>5</sup>‑C<sub>5</sub>Me<sub>5</sub>)(μ-O)}<sub>3</sub>(μ<sub>3</sub>‑CH)]
Amide and lithium aryloxide gallates [Li<sup>+</sup>{RGaPh<sub>3</sub>}<sup>−</sup>] (R = NMe<sub>2</sub>, O-2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) react with the μ<sub>3</sub>-alkylidyne
oxoderivative ligand [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(μ-O)}<sub>3</sub>(μ<sub>3</sub>-CH)] (<b>1</b>) to afford the gallium–lithium–titanium cubane
complexes [{Ph<sub>3</sub>Ga(μ-R)Li}{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(μ-O)}<sub>3</sub>(μ<sub>3</sub>-CH)] [R = NMe<sub>2</sub> (<b>3</b>), O-2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub> (<b>4</b>)]. The same complexes
can be obtained by treatment of the [Ph<sub>3</sub>Ga(μ<sub>3</sub>-O)<sub>3</sub>{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)}<sub>3</sub>(μ<sub>3</sub>-CH)] (<b>2</b>) adduct
with the corresponding lithium amide or aryloxide, respectively. Complex <b>3</b> evolves with formation of <b>5</b> as a solvent-separated
ion pair constituted by the lithium dicubane cationic species [Li{(μ<sub>3</sub>-O)<sub>3</sub>Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-CH)}<sub>2</sub>]<sup>+</sup> together with the anionic [(GaPh<sub>3</sub>)<sub>2</sub>(μ-NMe<sub>2</sub>)]<sup>−</sup> unit. On the other
hand, the reaction of <b>1</b> with Li(<i>p</i>-MeC<sub>6</sub>H<sub>4</sub>) and GaPh<sub>3</sub> leads to the complex [Li{(μ<sub>3</sub>-O)<sub>3</sub>Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-CH)}<sub>2</sub>][GaLi(<i>p</i>-MeC<sub>6</sub>H<sub>4</sub>)<sub>2</sub>Ph<sub>3</sub>] (<b>6</b>). X-ray diffraction studies were performed on <b>1</b>, <b>2</b>, <b>4</b>, and <b>5</b>, while
trials to obtain crystals of <b>6</b> led to characterization
of [Li{(μ<sub>3</sub>-O)<sub>3</sub>Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ<sub>3</sub>-CH)}<sub>2</sub>][PhLi(μ-C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>Ga(<i>p</i>-MeC<sub>6</sub>H<sub>4</sub>)Ph] <b>6a</b>
Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides
The reactivity of
the “tuck-over” species [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(CH<sub>2</sub>Ph)<sub>3</sub>(μ-η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>CH<sub>2</sub>-κ<i>C</i>)(μ-O)]
(<b>1</b>) and [Ti<sub>2</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(CH<sub>2</sub>CMe<sub>3</sub>)(μ-η<sup>5</sup>-C<sub>5</sub>Me<sub>4</sub>CH<sub>2</sub>-κ<i>C</i>)(μ-CH<sub>2</sub>CMe<sub>2</sub>CH<sub>2</sub>)(μ-O)] (<b>2</b>) toward isocyanides has been
examined both synthetically and theoretically. Treatment of <b>1</b> with the isocyanides RNC, R = Me<sub>3</sub>SiCH<sub>2</sub>, 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>, <i>t</i>Bu, <i>i</i>Pr, leads to a series of η<sup>2</sup>-iminoacyl species (<b>3</b>–<b>6</b>) where the
molecule of isocyanide inserts into one of the terminal metal–alkyl
bonds. The analogous reaction of the “tuck-over” metallacycle
species <b>2</b> with 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>NC and <i>t</i>BuNC results in the initial insertion of
one isocyanide into the terminal Ti–alkyl bond to form the
iminoacyl complexes <b>7</b> and <b>8</b>, followed by
a second insertion into the metallacycle moiety to generate <b>9</b>, in the case of <i>tert</i>-butylisocyanide. DFT
calculations support the selective reactivity observed experimentally
with a kinetic and thermodynamic preference for RNC insertion on the
terminal alkyl groups bound to both metallic centers over the alternative
insertion on the “tuck-over” ligand
Carbon–Nitrogen Bond Construction and Carbon–Oxygen Double Bond Cleavage on a Molecular Titanium Oxonitride: A Combined Experimental and Computational Study
New
carbon–nitrogen bonds were formed on addition of isocyanide
and ketone reagents to the oxonitride species [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(μ-O)}<sub>3</sub>(μ<sub>3</sub>-N)] (<b>1</b>). Reaction of <b>1</b> with XylNC
(Xyl = 2,6-Me<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) in a 1:3 molar
ratio at room temperature leads to compound [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(μ-O)}<sub>3</sub>(μ-XylNCCNXyl)(NCNXyl)]
(<b>2</b>), after the addition of the nitrido group to one coordinated
isocyanide and the carbon–carbon coupling of the other two
isocyanide molecules have taken place. Thermolysis of <b>2</b> gives [{Ti(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)(μ-O)}<sub>3</sub>(XylNCNXyl)(CN)] (<b>3</b>) where the heterocumulene
[XylNCCNXyl] moiety and the carbodiimido [NCNXyl] fragment in <b>2</b> have undergone net transformations. Similarly, <i>tert</i>-butyl isocyanide (<i>t</i>BuNC) reacts with the starting
material <b>1</b> under mild conditions to give the paramagnetic
derivative [{Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ-O)<sub>3</sub>(NCN<i>t</i>Bu)}<sub>2</sub>(μ-CN)<sub>2</sub>] (<b>4</b>). However, compound <b>1</b> provides the oxo ketimide
derivatives [{Ti<sub>3</sub>(η<sup>5</sup>-C<sub>5</sub>Me<sub>5</sub>)<sub>3</sub>(μ-O)<sub>4</sub>}(NCRPh)]
[R = Ph (<b>5</b>), <i>p</i>-Me(C<sub>6</sub>H<sub>4</sub>) (<b>6</b>), <i>o</i>-Me(C<sub>6</sub>H<sub>4</sub>) (<b>7</b>)] upon reaction with benzophenone, <i>p</i>-methylbenzophenone, and <i>o</i>-methylbenzophenone,
respectively. In these reactions, the carbon–oxygen double
bond is completely ruptured, leading to the formation of a carbon–nitrogen
and two metal–oxygen bonds. The molecular structures of complexes <b>2</b>–<b>4</b>, <b>6</b>, and <b>7</b> were determined by single-crystal X-ray diffraction analyses. Density
functional theory calculations were performed on the incorporation
of isocyanides and ketones to the model complex [{Ti(η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)(μ-O)}<sub>3</sub>(μ<sub>3</sub>-N)] (<b>1H</b>). The mechanism involves the coordination
of the substrates to one of the titanium metal centers, followed by
an isomerization to place those substrates cis with respect to the
apical nitrogen of <b>1H</b>, where carbon–nitrogen bond
formation occurs with a low-energy barrier. In the case of aryl isocyanides,
the resulting complex incorporates additional isocyanide molecules
leading to a carbon–carbon coupling. With ketones, the high
oxophilicity of titanium promotes the unusual total cleavage of the
carbon–oxygen double bond
Ultrafast Dynamics of Nile Red Interacting with Metal Doped Mesoporous Materials
We
report on ultrafast studies of Nile Red (NR) interacting with
MCM41 mesoporous materials doped by Al, Ga, Zr, and Ti in dichloromethane
suspensions. The steady-state results showed a significant red shift
and broadening of the diffuse transmittance and the emission spectra
upon interaction with the MCM41-based materials. These findings are
explained in terms of H-bonds with the host, different Brønsted/Lewis
interactions with the matrix and formation of H- and J-aggregates,
in addition to weakly and strongly adsorbed monomers. The pico- to
nanosecond time-resolved data support this explanation, showing a
significant shortening in the emission lifetimes where NR is interacting
with metal-doped MCM41. The femtosecond dynamics of NR loaded into
X-MCM41 (X = Si, Al, Ga) indicate that the charge-separated state
(CS) is formed at the S<sub>1</sub> state in ∼350 fs. For Zr-
and Ti- MCM41 hosts the intramolecular charge transfer (ICT) occurs
in less than 200 fs, and a subsequent electron injection to Ti or
Zr trap states happens in ∼250 fs. Our studies reveal a strong
interaction between the NR species and the framework of MCM41 materials
at both the S<sub>0</sub> and S<sub>1</sub> states