17 research outputs found
1,10-Phenanthroline Analogue Pyridazine-Based N-Heterocyclic Carbene Ligands
No full textSynthesis of a planar, π-conjugated pyridazine-based
biscarbene
is reported. Starting from 3,6-dimethylpyridazine, the bisimidazolium
salt <b>1</b>*<b>2HPF</b><sub><b>6</b></sub> was
prepared in a four-step synthesis by chlorination, amination, formylation,
and cyclization. The free carbene <b>1</b> can be generated
in situ by addition of base. Despite the rigid annelated tricycle,
the carbene ligand turns out to be highly flexible upon coordination
of transition-metal complexes. With silver(I) oxide or copper(I) oxide
binuclear carbene complexes with a bridging coordination mode of the
ligand are obtained. Transmetalation of both complexes to the respective
gold complex is described. The bridging coordination mode of the carbene
ligand is similar to that of 2,2′-bipyridine. Reaction of the
bisimidazolium salt <b>1*2HPF</b><sub><b>6</b></sub> with
potassium acetate and [RhCl(COD)]<sub>2</sub> leads to a mononuclear
rhodium complex with the chelating binding mode of <b>1</b>,
resembling strongly the coordination properties of 1,10-phenanthroline
Boryl Azides in 1,3-Dipolar Cycloadditions
No full textThe 1,3-dipolar cycloaddition reaction
of boron azides with alkynes
has been investigated experimentally and computationally. At room
temperature pinBN<sub>3</sub> (pin = pinacolato) reacts with the strained
triple bond of cyclooctyne with formation of an oligomeric boryl triazole.
Alcoholysis of the oligomer yields the parent 4,5,6,7,8,9-hexahydro-2<i>H</i>-cyclooctatriazole, which could be characterized as a hydrate
by X-ray crystallography. A computational analysis of the reaction
of tri- and tetracoordinate boron azides R<sub>2</sub>BN<sub>3</sub> (R = H, Me, pin, cat; cat = catecholato) and <i>I</i>Me·H<sub>2</sub>BN<sub>3</sub> (<i>I</i>Me = 2,6-dimethylimidazole-2-ylidene)
reveals significant differences in the reactivity depending on the
coordination number: tricoordinate boron azides behave as type II
1,3-dipoles, while the tetracoordinate <i>I</i>Me·H<sub>2</sub>BN<sub>3</sub> is an electron-rich 1,3-dipole (type I) that
strongly prefers reactions with electron-poor alkynes
Reactivity of Yttrium Methyl Complexes: Hydrido Transfer Capability of Selected Alkylalanes
No full textThe
reactivity of alkylaluminum hydrides HAlMe<sub>2</sub>, HAl(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>, and H<sub>2</sub>AlMes* (Mes*
= C<sub>6</sub>H<sub>2</sub><i>t</i>Bu<sub>3</sub>-2,4,6)
toward yttrium methyl complexes was assessed. From the reaction with
[Cp<sub>2</sub>YMe]<sub>2</sub> the corresponding methylated alkylaluminum
compounds could be isolated and characterized along with [Cp<sub>2</sub>Y(thf)(μ-H)]<sub>2</sub>, obtained upon workup in thf (Cp =
C<sub>5</sub>H<sub>5</sub> = cyclopentadienyl). Structurally characterized
complexes Cp<sub>14</sub>Y<sub>6</sub>H<sub>3</sub>Cl and Cp<sub>15</sub>Y<sub>6</sub>H<sub>3</sub> represent side-products of the transformation.
The reactions of [YMe<sub>3</sub>]<sub><i>n</i></sub> and
[(C<sub>5</sub>Me<sub>5</sub>)YMe<sub>2</sub>]<sub>3</sub> indicated
occurrence of hydrido transfer for H<sub>2</sub>AlMes* and led to
product mixtures for HAl(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>. Following the reaction of HAlMe<sub>2</sub> with these compounds
as well as the half-sandwich derivatives (C<sub>5</sub>Me<sub>4</sub>R)Y(AlMe<sub>4</sub>)<sub>2</sub> (R = Me, SiMe<sub>3</sub>) indicated
reversible hydrido binding, leading ultimately to the formation of
insoluble hydride clusters. The organoaluminum compounds [HAl(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>]<sub>3</sub>, [(μ-H)(Me)AlMes*]<sub>2</sub>, and Me<sub>2</sub>AlMes* were analyzed by X-ray crystallography
Silylamide Complexes of Chromium(II), Manganese(II), and Cobalt(II) Bearing the Ligands N(SiHMe<sub>2</sub>)<sub>2</sub> and N(SiPhMe<sub>2</sub>)<sub>2</sub>
No full textBis(dimethylsilyl)amide
and bis(dimethylphenylsilyl)amide complexes of the divalent transition
metals chromium, manganese, and cobalt were synthesized. Dimeric,
donor-free {Mn[N(SiHMe<sub>2</sub>)<sub>2</sub>]<sub>2</sub>}<sub>2</sub> could be obtained via two different pathways, a salt metathesis
route (utilizing MnCl<sub>2</sub>(thf)<sub>1.5</sub> and LiN(SiHMe<sub>2</sub>)<sub>2</sub>) and a transsilylamination protocol (utilizing
Mn[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(thf) and HN(SiHMe<sub>2</sub>)<sub>2</sub>). Addition of 1,1,3,3-tetramethylethylendiamine
(tmeda) to {Mn[N(SiHMe<sub>2</sub>)<sub>2</sub>]<sub>2</sub>}<sub>2</sub> yielded the monomeric adduct Mn[N(SiHMe<sub>2</sub>)<sub>2</sub>]<sub>2</sub>(tmeda). The syntheses of Cr[N(SiHMe<sub>2</sub>)<sub>2</sub>]<sub>2</sub>(tmeda), Co[N(SiMe<sub>3</sub>)<sub>2</sub>][N(SiHMe<sub>2</sub>)<sub>2</sub>](tmeda), and Co[N(SiHMe<sub>2</sub>)<sub>2</sub>]<sub>2</sub>(tmeda) were achieved by transsilylamination
from Cr[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(tmeda) and {Co[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>}<sub>2</sub>(μ-tmeda), respectively.
Bis(dimethylphenylsilyl)amide complexes Mn[N(SiMe<sub>2</sub>Ph)<sub>2</sub>]<sub>2</sub>, Cr[N(SiMe<sub>2</sub>Ph)<sub>2</sub>]<sub>2</sub>, and Co[N(SiMe<sub>2</sub>Ph)<sub>2</sub>]<sub>2</sub>(thf) were
obtained via salt metathesis employing MCl<sub>2</sub>(thf)<sub><i>x</i></sub> (M = Cr, Mn, Co) with equimolar amounts of LiN(SiMe<sub>2</sub>Ph)<sub>2</sub> in <i>n</i>-hexane. Treatment of
CrCl<sub>2</sub> with LiN(SiMe<sub>2</sub>Ph)<sub>2</sub> in thf gave
Cr[N(SiMe<sub>2</sub>Ph)<sub>2</sub>]<sub>2</sub>(thf)<sub>2</sub>, featuring an almost square planar <i>trans</i>-coordination.
All complexes were examined by elemental analyses, DRIFT and UV–vis
spectroscopy, as well as X-ray structure analysis, paying particular
attention to secondary M---SiH β-agostic and M---π(arene)
interactions. Magnetic moments were determined by Evans’ method
Rare-Earth-Metal Allyl Complexes Supported by the [2‑(<i>N</i>,<i>N</i>‑Dimethylamino)ethyl]tetramethylcyclopentadienyl Ligand: Structural Characterization, Reactivity, and Isoprene Polymerization
No full textRare-earth-metal half-sandwich allyl
complexes bearing an amino-functionalized
cyclopentadienyl ligand (Cp<sup>NMe2</sup> = 1-[2-(<i>N</i>,<i>N</i>-dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienyl)
were synthesized in a two-step salt-metathesis reaction. Treatment
of LnCl<sub>3</sub>(THF)<sub><i>x</i></sub> with LiCp<sup>NMe2</sup>, followed by an in situ reaction with the Grignard reagent
C<sub>3</sub>H<sub>5</sub>MgCl, generated the bis(allyl) half-sandwich
complexes Cp<sup>NMe2</sup>Ln(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)<sub>2</sub> only for the smaller rare-earth metals (Ln =
Y, Ho, Lu) in good yields (82–88%). In case of the larger neodymium,
the dimeric mono(allyl) chlorido half-sandwich complex [Cp<sup>NMe2</sup>Nd(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)(μ-Cl)]<sub>2</sub> was obtained in 68% yield. All complexes show moderate to
high activity in isoprene polymerization upon cationization with organoborates
[Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] and [PhNMe<sub>2</sub>H][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], the yttrium,
holmium, and neodymium metal centers yielding mainly 3,4-microstructures
(maximum 79%). Addition of 10 equiv of AlMe<sub>3</sub> to the catalyst
systems Cp<sup>NMe2</sup>Ln(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)<sub>2</sub> (Ln = Y, Ho)/[PhNMe<sub>2</sub>H][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] and [Cp<sup>NMe2</sup>Nd(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)(μ-Cl)]<sub>2</sub>/[PhNMe<sub>2</sub>H][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] switched the
polyisoprene stereoregularity from 3,4-specific to trans-1,4-selective
(maximum 85%). The use of Al<i>i</i>Bu<sub>3</sub> instead
led to polymers with mainly cis-1,4-microstructure for the monomeric
yttrium and holmium complexes (maximum 74%). Treatment of the bis(allyl)
complexes with Et<sub>2</sub>AlCl (as cocatalyst) did not provide
active species for isoprene polymerization but led to [allyl] →
[Cl] exchange and isolation of the hexameric rare-earth-metal clusters
[{(Cp<sup>NMe2AlEt3</sup>)<sub>2</sub>(Cp<sup>NMe2</sup>)Ln<sub>3</sub>(μ<sub>2</sub>-Cl)<sub>3</sub>(μ<sub>3</sub>-Cl)<sub>2</sub>}(μ<sub>2</sub>-Cl)]<sub>2</sub> (Ln = Y, Ho). The complexes
Cp<sup>NMe2</sup>Ln(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)<sub>2</sub> (Ln = Y, Ho, Lu), [Cp<sup>NMe2</sup>Nd(η<sup>3</sup>-C<sub>3</sub>H<sub>5</sub>)(μ-Cl)]<sub>2</sub>, and
[{(Cp<sup>NMe2AlEt3</sup>)<sub>2</sub>(Cp<sup>NMe2</sup>)Ln<sub>3</sub>(μ<sub>2</sub>-Cl)<sub>3</sub>(μ<sub>3</sub>-Cl)<sub>2</sub>}(μ<sub>2</sub>-Cl)]<sub>2</sub> (Ln = Y, Ho) were analyzed
by X-ray crystallography
Versatile Ln<sub>2</sub>(μ-NR)<sub>2</sub>‑Imide Platforms for Ligand Exchange and Isoprene Polymerization
No full textBimetallic rare-earth-metal imide
complexes Ln<sub>2</sub>(μ<sub>2</sub>-Ndipp)(μ<sub>3</sub>-Ndipp)[(μ<sub>2</sub>-Me)<sub>2</sub>AlMe](AlMe<sub>4</sub>)<sub>2</sub> (<b>3</b>-Ln; Ln
= Y, La, Ce, Nd; dipp = 2,6-diisopropylphenyl) have been obtained
from the reaction of Ln(AlMe<sub>4</sub>)<sub>3</sub> (<b>1</b>-Ln) with Li(NHdipp) (<b>2</b>). X-ray diffraction studies
of toluene-soluble <b>3</b>-Ln revealed an unusual Ln[{(μ<sub>2</sub>-Me)<sub>2</sub>AlMe}(μ<sub>3</sub>-Ndipp)]Ln moiety
as the most striking feature. Facile salt-metathetical exchange of
the tetramethylaluminato ligands in <b>3</b>-Ln with K(L) (L
= N(SiMe<sub>3</sub>)<sub>2</sub>, Cp′) allowed for the isolation
of Ln<sub>2</sub>(Ndipp)<sub>2</sub>[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(AlMe<sub>3</sub>) (<b>4</b>-La), partially exchanged
Ln<sub>2</sub>(Ndipp)<sub>2</sub>(Cp′)(AlMe<sub>4</sub>)(AlMe<sub>3</sub>) (<b>5</b>-La, Cp′ = C<sub>5</sub>Me<sub>4</sub>SiMe<sub>3</sub>), and Ln<sub>2</sub>(Ndipp)<sub>2</sub>(Cp′)<sub>2</sub>(AlMe<sub>3</sub>) (<b>6</b>-La). Attempted cleavage
of the AlMe<sub>3</sub> moiety in <b>3</b>-Ln with THF led to
C–H bond activation of one of the isopropyl methine moieties
to produce Ln<sub>2</sub>(μ<sub>2</sub>-Ndipp)[(μ<sub>3</sub>-NC<sub>6</sub>H<sub>3</sub>-2-CMe<sub>2</sub>-6-<i>i</i>Pr)Al(μ<sub>2</sub>-Me)<sub>2</sub>](AlMe<sub>4</sub>)<sub>2</sub> (<b>7</b>-La). Selective cleavage of the bridging AlMe<sub>3</sub> “cap” was achieved by addition of DMAP (DMAP
= 4-dimethylaminopyridine) to produce [Ln(μ<sub>2</sub>-Ndipp)(AlMe<sub>4</sub>)(DMAP)]<sub><i>n</i></sub> (<b>8</b>-Ln;
Ln = La, Ce) and concomitantly DMAP·AlMe<sub>3</sub>. The organoaluminum-free
compounds [Ln(μ<sub>2</sub>-Ndipp){N(SiMe<sub>3</sub>)<sub>2</sub>}(DMAP)]<sub>2</sub> (<b>9</b>-Ln; Ln = La, Ce), [Ln(μ<sub>2</sub>-Ndipp)(Cp′)(DMAP)]<sub>2</sub> (<b>10</b>-La),
and [Ln(μ<sub>2</sub>-Ndipp)(OAr)(DMAP)]<sub>2</sub> (<b>11</b>-Ln; Ln = La, Ce; Ar = 2,6-di-<i>tert</i>-butyl-4-methylphenyl)
were obtained via reactions of <b>8</b>-Ln with K(L) (L = Cp′,
N(SiMe<sub>3</sub>)<sub>2</sub>, OAr). In the presence of activators
[Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] and [PhNMe<sub>2</sub>H][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>], AlEt<sub>2</sub>Cl complexes <b>3</b>-Ln, <b>5</b>-Ln, and <b>7</b>-Ln initiate the polymerization of isoprene to yield PIPs with narrow
molecular weight distributions, involving new imido-supported bimetallic
catalysts
Half-Sandwich Rare-Earth-Metal Alkylaluminate Complexes Bearing Peripheral Boryl Ligands
No full text[(C<sub>5</sub>Me<sub>5</sub>)LnMe<sub>2</sub>]<sub>3</sub> (Ln = Y, Lu)
dissolve readily in a <i>n</i>-hexane/toluene mixture upon
addition of 3 equiv of the organoaluminum boryl compound [Me<sub>2</sub>Al{B(NDippCH)<sub>2</sub>}]<sub>2</sub> (Dipp = C<sub>6</sub>H<sub>3</sub><i>i</i>Pr<sub>2</sub>-2,6). The half-sandwich complexes
(C<sub>5</sub>Me<sub>5</sub>)Ln[(AlMe<sub>3</sub>){B(NDippCH)<sub>2</sub>}]<sub>2</sub> thus formed display unsymmetrical heteroaluminate
coordination not only in the solid state but also at lower temperatures
in solution, which is distinct from the behavior of the homoaluminate
congeners (C<sub>5</sub>Me<sub>5</sub>)Ln(AlMe<sub>4</sub>)<sub>2</sub>. The effect of homo- versus heteroaluminate coordination is assessed
in the coordinative polymerization of isoprene
A Dimethylgallium Boryl Complex and Its Methyllithium Addition Compound
No full textThe three-coordinate complex Me<sub>2</sub>Ga[B(NArCH)<sub>2</sub>] (Ar = C<sub>6</sub>H<sub>3</sub><i>i</i>Pr<sub>2</sub>-2,6) is accessible via a tandem Lewis acid–base metathesis protocol employing (THF)<sub>2</sub>Li[B(NArCH)<sub>2</sub>] and GaMe<sub>3</sub>. It features
a very
short Ga–B bond of 2.067(3) Å, which was further investigated
by DFT calculations and the analysis of the electron density. Reaction
of MeLi with Me<sub>2</sub>Ga[B(NArCH)<sub>2</sub>] forms tetrameric
[LiMe<sub>3</sub>Ga{B(NArCH)<sub>2</sub>}]<sub>4</sub> with a “nanowheel”
structure
Half-Sandwich Rare-Earth-Metal Alkylaluminate Complexes Bearing Peripheral Boryl Ligands
No full text[(C<sub>5</sub>Me<sub>5</sub>)LnMe<sub>2</sub>]<sub>3</sub> (Ln = Y, Lu)
dissolve readily in a <i>n</i>-hexane/toluene mixture upon
addition of 3 equiv of the organoaluminum boryl compound [Me<sub>2</sub>Al{B(NDippCH)<sub>2</sub>}]<sub>2</sub> (Dipp = C<sub>6</sub>H<sub>3</sub><i>i</i>Pr<sub>2</sub>-2,6). The half-sandwich complexes
(C<sub>5</sub>Me<sub>5</sub>)Ln[(AlMe<sub>3</sub>){B(NDippCH)<sub>2</sub>}]<sub>2</sub> thus formed display unsymmetrical heteroaluminate
coordination not only in the solid state but also at lower temperatures
in solution, which is distinct from the behavior of the homoaluminate
congeners (C<sub>5</sub>Me<sub>5</sub>)Ln(AlMe<sub>4</sub>)<sub>2</sub>. The effect of homo- versus heteroaluminate coordination is assessed
in the coordinative polymerization of isoprene
Tris(pyrazolyl)borate Complexes of the Alkaline-Earth Metals: Alkylaluminate Precursors and Schlenk-Type Rearrangements
No full textA series of 3,5-substituted tris(pyrazolyl)borate (Tp<sup>R,Me</sup>; R = Me, Ph, <i>t</i>Bu) complexes of the alkaline-earth
metals (Mg, Ca, Ba) was synthesized by salt metathesis reactions.
The influence of different organometallic precursors on Schlenk-type
rearrangement reactions was studied, putting emphasis on the metal
size and the steric encumbrance of the Tp ligands. Magnesium alkyls
MgR<sub>2</sub> (R = AlMe<sub>4</sub>, CH<sub>3</sub>) react with
KTp<sup>R,Me</sup> to form the heteroleptic complexes (Tp<sup>Me,Me</sup>)Mg(CH<sub>3</sub>), (Tp<sup><i>t</i>Bu,Me</sup>)Mg(CH<sub>3</sub>), and (Tp<sup>Me,Me</sup>)Mg(AlMe<sub>4</sub>). The latter
tetramethylaluminate complex can also be obtained by treatment of
Tp<sup>Me,Me</sup>Mg(CH<sub>3</sub>) with an excess of trimethylaluminum.
The formally six-coordinate cyclopentadienyl derivative (C<sub>5</sub>Me<sub>5</sub>)Mg(Me)(thf)<sub>2</sub> is synthesized from MeMgBr
and 1 equiv of K(C<sub>5</sub>Me<sub>5</sub>). Equimolar reactions
of the tetraethylaluminates [M(AlEt<sub>4</sub>)<sub>2</sub>]<sub><i>n</i></sub> of the heavier alkaline-earth metals calcium
and barium with KTp<sup>R,Me</sup> give the homoleptic complexes of
Ca(Tp<sup>R,Ph</sup>)<sub>2</sub> and Ba(Tp<sup>R,Me</sup>)<sub>2</sub>. Heterotrimetallic [BaK(AlEt<sub>4</sub>)<sub>3</sub>]<sub><i>n</i></sub> is identified as a ligand rearrangement product
and can be independently obtained by adding [K(AlEt<sub>4</sub>)]<sub><i>n</i></sub> to [Ba(AlEt<sub>4</sub>)<sub>2</sub>]<sub><i>n</i></sub>. Treatment of Ba[N(SiMe<sub>3</sub>)<sub>2</sub>]<sub>2</sub>(thf)<sub>2</sub> with KTp<sup>Me,Me</sup> generates
the heteroleptic complex (Tp<sup>Me,Me</sup>)Ba[N(SiMe<sub>3</sub>)<sub>2</sub>](thf)<sub>2</sub>. All complexes are fully characterized
including X-ray structure analyses
