23 research outputs found
Low-Coordinate Cobalt(I) Complexes Stabilized by an Extremely Bulky Amide Ligand
A series of low-coordinate, high-spin,
mono- and dinuclear cobaltĀ(I) complexes bearing an extremely bulky
amide (Lā³ = NĀ(Ar*)Ā(SiPh<sub>3</sub>); Ar* = C<sub>6</sub>H<sub>2</sub>{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>Me-2,6,4) ligand have been
synthesized and characterized. These include the first example of
a neutral two-coordinate cobaltĀ(I) complex, [Lā³CoĀ(IPriMe)]
(IPriMe = :CĀ{NĀ(Pr<sup><i>i</i></sup>)ĀCĀ(Me)}<sub>2</sub>),
which has a near-linear cobalt coordination geometry
Extremely Bulky Amido First Row Transition Metal(II) Halide Complexes: Potential Precursors to Low Coordinate MetalāMetal Bonded Systems
Reactions
of the extremely bulky potassium amide complexes, [KLā²(Ī·<sup>6</sup>-toluene)] or [KLā³] (Lā²/Lā³ = NĀ(Ar*)Ā(SiR<sub>3</sub>), Ar* = C<sub>6</sub>H<sub>2</sub>{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>Me-2,6,4; R = Me (Lā²) or Ph (Lā³)), with a series
of first row transition metalĀ(II) halides have yielded 10 rare examples
of monodentate amido first row transition metalĀ(II) halide complexes,
all of which were crystallographically characterized. They encompass
the dimeric, square-planar chromium complexes, [{CrLā²(THF)Ā(Ī¼-Cl)}<sub>2</sub>] and [{CrLā³(Ī¼-Cl)}<sub>2</sub>], the latter
of which displays intramolecular Ī·<sup>2</sup>-PhĀ·Ā·Ā·Cr
interactions; the dimeric tetrahedral complexes, [{MLā²(THF)Ā(Ī¼-Br)}<sub>2</sub>] (M = Mn or Fe), [{MLā³(THF)Ā(Ī¼-X)}<sub>2</sub>] (M = Mn, Fe or Co; X = Cl or Br) and [{CoLā³(Ī¼-Cl)}<sub>2</sub>] (which displays intramolecular Ī·<sup>2</sup>-PhĀ·Ā·Ā·Co
interactions); and the monomeric zinc amides, [Lā²ZnBrĀ(THF)]
(three-coordinate) and [Lā³ZnBr] (two-coordinate). Solution
state magnetic moment determinations on all but one of the paramagnetic
compounds show them to be high-spin systems. Throughout, comparisons
are made with related bulky terphenyl transition metalĀ(II) halide
complexes, and the potential for the use of the prepared complexes
as precursors to low-valent transition metal systems is discussed
Extremely Bulky Amido First Row Transition Metal(II) Halide Complexes: Potential Precursors to Low Coordinate MetalāMetal Bonded Systems
Reactions
of the extremely bulky potassium amide complexes, [KLā²(Ī·<sup>6</sup>-toluene)] or [KLā³] (Lā²/Lā³ = NĀ(Ar*)Ā(SiR<sub>3</sub>), Ar* = C<sub>6</sub>H<sub>2</sub>{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>Me-2,6,4; R = Me (Lā²) or Ph (Lā³)), with a series
of first row transition metalĀ(II) halides have yielded 10 rare examples
of monodentate amido first row transition metalĀ(II) halide complexes,
all of which were crystallographically characterized. They encompass
the dimeric, square-planar chromium complexes, [{CrLā²(THF)Ā(Ī¼-Cl)}<sub>2</sub>] and [{CrLā³(Ī¼-Cl)}<sub>2</sub>], the latter
of which displays intramolecular Ī·<sup>2</sup>-PhĀ·Ā·Ā·Cr
interactions; the dimeric tetrahedral complexes, [{MLā²(THF)Ā(Ī¼-Br)}<sub>2</sub>] (M = Mn or Fe), [{MLā³(THF)Ā(Ī¼-X)}<sub>2</sub>] (M = Mn, Fe or Co; X = Cl or Br) and [{CoLā³(Ī¼-Cl)}<sub>2</sub>] (which displays intramolecular Ī·<sup>2</sup>-PhĀ·Ā·Ā·Co
interactions); and the monomeric zinc amides, [Lā²ZnBrĀ(THF)]
(three-coordinate) and [Lā³ZnBr] (two-coordinate). Solution
state magnetic moment determinations on all but one of the paramagnetic
compounds show them to be high-spin systems. Throughout, comparisons
are made with related bulky terphenyl transition metalĀ(II) halide
complexes, and the potential for the use of the prepared complexes
as precursors to low-valent transition metal systems is discussed
Reaction Pathways for Addition of H<sub>2</sub> to Amido-Ditetrylynes R<sub>2</sub>NāEEāNR<sub>2</sub> (E = Si, Ge, Sn). A Theoretical Study
Quantum
chemical calculations of the reaction profiles for addition
of one and two H<sub>2</sub> molecules to amido-substituted ditetrylynes
have been carried using density functional theory at the BP86/def2-TZVPP//BP86/def2-TZVPP
level of theory for the model systems Lā²EELā² and BP86/def2-TZVPP//BP86/def-SVP
for the real compounds. The hydrogenation of the digermyne LGeGeL
(L = NĀ(SiMe<sub>3</sub>)ĀAr*; Ar* = C<sub>6</sub>H<sub>2</sub>MeĀ{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>-4,2,6) follows a stepwise reaction course. The
addition of the first H<sub>2</sub> gives the singly bridged species
LGeĀ(Ī¼-H)ĀGeHL, which rearranges with very low activation barriers
to the symmetrically hydrogenated compound LHGeGeHL and to the most
stable isomer LGeGeĀ(H)<sub>2</sub>L, which is experimentally observed.
The addition of the second H<sub>2</sub> proceeds with a higher activation
energy under rupture of the GeāGe bond, yielding LGeH and LGeH<sub>3</sub> as reaction products. Energy calculations which consider
dispersion interactions using Grimmeās D3 term suggest that
the latter reaction is thermodynamically unfavorable. The second hydrogenation
reaction LGeGeĀ(H)<sub>2</sub>L ā LĀ(H)<sub>2</sub>GeGeĀ(H)<sub>2</sub>L possesses an even higher activation barrier than the bond-breaking
hydrogenation step. Further calculations which consider solvent effects
change the theoretically predicted reaction profile very little. The
calculations of the model system Lā²GeGeLā² (Lā²
= NMe<sub>2</sub>) give a very similar reaction profile. Calculations
of the model disilyne and distannyne homologues Lā²SiSiLā²
and Lā²SnSnLā² suggest that the reactivity of the amido-substituted
ditetrylynes always has the order Si > Ge > Sn. The most stable
product
of the addition of one H<sub>2</sub> to the distannyne Lā²SnSnLā²
is the doubly bridged species Lā²SnĀ(Ī¼-H)<sub>2</sub>SnLā²,
which has been experimentally observed when bulky groups are employed.
Analysis of the H<sub>2</sub>āLā²EELā² interactions
in the transition state for the addition of the first H<sub>2</sub> with the EDA-NOCV method reveals that the HOMOāLUMO and LUMOāHOMO
interactions have similar magnitudes
A Spatial Approach to Mereology
When do several objects compose a further object? The last twenty years have seen a great deal of discussion of this question. According to the most popular view on the market, there is a physical object composed of your brain and Jeremy Benthamās body. According to the second-most popular view on the market, there are no such objects as human brains or human bodies, and there are also no atoms, rocks, tables, or stars. And according to the third-ranked view, there are human bodies, but still no brains, atoms, rocks, tables, or stars. Although itās pleasant to have so many crazy-sounding views around, I think it would also be nice to have a commonsense option available. The aim of this paper is to offer such an option. The approach I offer begins by considering a mereological question other than the standard one that has been the focus of most discussions in the literature. I try to show that the road to mereological sanity begins with giving the most straightforward and commonsensical answer to this other question, and then extending that answer to further questions about the mereology of physical objects. On the approach I am recommending, it turns out that all of the mereological properties and relations of physical objects are determined by their spatial properties and relations
Efficient Reduction of Carbon Dioxide to Methanol Equivalents Catalyzed by Two-Coordinate AmidoāGermanium(II) and āTin(II) Hydride Complexes
The
bulky amidoāgermaniumĀ(II) and ātinĀ(II) hydride
complexes, L<sup>ā </sup>EH [E = Ge or Sn; L<sup>ā </sup> = -NĀ(Ar<sup>ā </sup>) (SiPr<sup><i>i</i></sup><sub>3</sub>); Ar<sup>ā </sup> = C<sub>6</sub>H<sub>2</sub>Pr<sup><i>i</i></sup>{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>-4,2,6],
which are two-coordinate in solution, are shown to be efficient and
highly selective āsingle-siteā catalysts for the reduction
of CO<sub>2</sub> to methanol equivalents (MeOBR<sub>2</sub>), using
HBpin or HBcat as the hydrogen source. L<sup>ā </sup>SnH is
the most active non-transition metal catalyst yet reported for such
reductions, yielding turnover frequencies of up to 1188 h<sup>ā1</sup> at room temperature. Computational studies have identified two thermodynamically
and kinetically viable catalytic pathways by which these reductions
may operate. Spectroscopic investigations have identified several
reaction intermediates, which leads to the conclusion that one of
these reaction pathways predominates in the experimental situation.
Stoichiometric reactivity studies have shed further light on the reaction
mechanisms in operation and indicate that the involvement of the second
reaction pathway cannot be ruled out. This study highlights the potential
of relatively cheap, main group complexes as viable alternatives to
transition metal-based systems in the catalytic transformation of
small molecules
Monomeric Group 13 Metal(I) Amides: Enforcing One-Coordination Through Extreme Ligand Steric Bulk
Reactions of the extremely bulky amido alkali metal complexes,
[KLā²(Ī·<sup>6</sup>-toluene)], or in situ generated [LiLā²]
or [LiLā³] {Lā²/ Lā³ = NĀ(Ar*)Ā(SiR<sub>3</sub>),
where Ar* = C<sub>6</sub>H<sub>2</sub>Ā{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>ĀMe-2,6,4 and R = Me (Lā²) or Ph (Lā³)}
with group 13 metalĀ(I) halides have yielded a series of monomeric
metalĀ(I) amide complexes, [MLā²] (M = Ga, In, or Tl) and [MLā³]
(M = Ga or Tl), all but one of which have been crystallographically
characterized. The results of the crystallographic studies, in combination
with computational analyses, reveal that the metal centers in these
compounds are one coordinate and do not exhibit any significant intra-
or intermolecular interactions, other than their N-M linkages. One
of the complexes, [InLā²], represents the first example of a
one-coordinate indiumĀ(I) amide. Attempts to extend this study to the
preparation of the analogous aluminumĀ(I) amide, [AlLā²], were
not successful. Despite this, a range of novel and potentially synthetically
useful aluminumĀ(III) halide and hydride complexes were prepared en
route to [AlLā²], the majority of which were crystallographically
characterized. These include the alkali metal aluminate complexes,
[Lā²AlH<sub>2</sub>Ā(Ī¼-H)ĀLiĀ(OEt<sub>2</sub>)<sub>2</sub>Ā(THF)] and [{Lā²AlĀ(Ī¼-H)<sub>3</sub>K}<sub>2</sub>], the neutral amido-aluminum hydride complex,
[{Lā²AlHĀ(Ī¼-H)}<sub>2</sub>], and the aluminum halide complexes,
[Lā²AlBr<sub>2</sub>(THF)] and [Lā²AlI<sub>2</sub>]. Reaction
of the latter two systems with a variety of reducing agents led only
to intractable product mixtures
Low Coordinate Germanium(II) and Tin(II) Hydride Complexes: Efficient Catalysts for the Hydroboration of Carbonyl Compounds
This study details the first use
of well-defined low-valent p-block
metal hydrides as catalysts in organic synthesis. That is, the bulky,
two-coordinate germaniumĀ(II) and tinĀ(II) hydride complexes, L<sup>ā </sup>(H)ĀM: (M = Ge or Sn, L<sup>ā </sup> = āNĀ(Ar<sup>ā </sup>)Ā(SiPr<sup>i</sup><sub>3</sub>), Ar<sup>ā </sup> = C<sub>6</sub>H<sub>2</sub>{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>Pr<sup><i>i</i></sup>-2,6,4), are shown to act as efficient catalysts
for the hydroboration (with HBpin, pin = pinacolato) of a variety
of unactivated, and sometimes very bulky, carbonyl compounds. Catalyst
loadings as low as 0.05 mol % are required to achieve quantitative
conversions, with turnover frequencies in excess of 13ā300
h<sup>ā1</sup> in some cases. This activity rivals that of
currently available catalysts used for such reactions
Low Coordinate Germanium(II) and Tin(II) Hydride Complexes: Efficient Catalysts for the Hydroboration of Carbonyl Compounds
This study details the first use
of well-defined low-valent p-block
metal hydrides as catalysts in organic synthesis. That is, the bulky,
two-coordinate germaniumĀ(II) and tinĀ(II) hydride complexes, L<sup>ā </sup>(H)ĀM: (M = Ge or Sn, L<sup>ā </sup> = āNĀ(Ar<sup>ā </sup>)Ā(SiPr<sup>i</sup><sub>3</sub>), Ar<sup>ā </sup> = C<sub>6</sub>H<sub>2</sub>{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>Pr<sup><i>i</i></sup>-2,6,4), are shown to act as efficient catalysts
for the hydroboration (with HBpin, pin = pinacolato) of a variety
of unactivated, and sometimes very bulky, carbonyl compounds. Catalyst
loadings as low as 0.05 mol % are required to achieve quantitative
conversions, with turnover frequencies in excess of 13ā300
h<sup>ā1</sup> in some cases. This activity rivals that of
currently available catalysts used for such reactions
Monomeric Group 13 Metal(I) Amides: Enforcing One-Coordination Through Extreme Ligand Steric Bulk
Reactions of the extremely bulky amido alkali metal complexes,
[KLā²(Ī·<sup>6</sup>-toluene)], or in situ generated [LiLā²]
or [LiLā³] {Lā²/ Lā³ = NĀ(Ar*)Ā(SiR<sub>3</sub>),
where Ar* = C<sub>6</sub>H<sub>2</sub>Ā{CĀ(H)ĀPh<sub>2</sub>}<sub>2</sub>ĀMe-2,6,4 and R = Me (Lā²) or Ph (Lā³)}
with group 13 metalĀ(I) halides have yielded a series of monomeric
metalĀ(I) amide complexes, [MLā²] (M = Ga, In, or Tl) and [MLā³]
(M = Ga or Tl), all but one of which have been crystallographically
characterized. The results of the crystallographic studies, in combination
with computational analyses, reveal that the metal centers in these
compounds are one coordinate and do not exhibit any significant intra-
or intermolecular interactions, other than their N-M linkages. One
of the complexes, [InLā²], represents the first example of a
one-coordinate indiumĀ(I) amide. Attempts to extend this study to the
preparation of the analogous aluminumĀ(I) amide, [AlLā²], were
not successful. Despite this, a range of novel and potentially synthetically
useful aluminumĀ(III) halide and hydride complexes were prepared en
route to [AlLā²], the majority of which were crystallographically
characterized. These include the alkali metal aluminate complexes,
[Lā²AlH<sub>2</sub>Ā(Ī¼-H)ĀLiĀ(OEt<sub>2</sub>)<sub>2</sub>Ā(THF)] and [{Lā²AlĀ(Ī¼-H)<sub>3</sub>K}<sub>2</sub>], the neutral amido-aluminum hydride complex,
[{Lā²AlHĀ(Ī¼-H)}<sub>2</sub>], and the aluminum halide complexes,
[Lā²AlBr<sub>2</sub>(THF)] and [Lā²AlI<sub>2</sub>]. Reaction
of the latter two systems with a variety of reducing agents led only
to intractable product mixtures