Metal atom synthesis of metallaboron clusters. 4. Direct synthesis of (.eta.6-arene)ferracarborane clusters from alkynes and boranes. Structural characterization of the four-carbon (.eta.6-arene)metallacarboranes 1-[.eta.6-C6Me6]Fe-4,5,7,8-Me4C4B3H3 and 2-[.eta.6-MeC6H5]Fe-6,7,9,10-Me4C4B5H5
Abstract:The reaction of thermally generated iron atoms with pentaborane(9), toluene, and 2-butyne was found to yield as the major product the (x-arene)ferracarborane sandwich complex l-[V-C6(CH3)6]Fe-2,3-(CH3)2C2B4H4, I, along with smaller amounts of the four-carbon metallacarborane complexes 1-[t?6-C6-(CH3)6]Fe-4,5,7,8-(CH3)4C4B3H3, II, l-[^6-CH3C6H6]Fe-4,5,7,8-(CH3)4C4B3H3, III, and 2-["6-CH3C6H5]Fe-6,7,9,10-(CH3)4C4B5H6, IV. Reactions carried out in the absence of toluene also yielded I and II but in reduced yields… Show more
“…However, the only structurally characterized 8-vertex nido-cluster with this geometry is nido - (η-C 5 H 5 ) 2 Co 2 SB 5 H 7 nido -(η 6 -C 6 Me 6 )FeMe 4 C 4 B 3 H 3 , and nido -(η-C 5 H 5 )CoPh 4 C 4 B 3 H 3 , have structures based on a 10-vertex bicapped square antiprism missing two vertices, which is the same geometry expected for 8-vertex arachno-clusters (Figure b). Thus, the question of which is the preferred geometry for 8-vertex nido cages has been a longstanding problem in cluster chemistry. 26,f,, 2 Derivation of open 8-vertex cage frameworks based upon geometrical systematics: (a) removal of a high-coordinated vertex from a 9-vertex tricapped trigonal prism to generate a 5-membered open-face nido geometry; (b) removal of two high-coordinated vertices from a 10-vertex bicapped square antiprism to generate a 6-membered open-face arachno geometry.…”
Synthesis and structural studies, employing combined NMR, X-ray
crystallographic, and ab initio/IGLO/NMR methods, of a variety of new subicosahedral carboranes with adjacent
cage carbons are reported. Acetonitrile-induced cage degradation of
arachno-4,5-C2B7H12
-
gave
nido-4,5-C2B6H9
-
(1
-
) in nearly quantitative yield,
which
can then be protonated to give the neutral carborane
nido-4,5-C2B6H10
(1) in good yield. Both of these nido
electron-count clusters are shown to have an arachno-type geometry, i.e. a
six-membered open face. The
nido-4,5-C2B6H10
(1) hydroborated alkenes or alkynes which following
deprotonation gave
nido-7-R-4,5-C2B6H8
-
(2a
-
−
c
-
)
ions.
Both
nido-4,5-C2B6H9
-
(1
-
) and
nido-4,5-C2B6H10
(1) serve as useful precursors to other adjacent cage-carbon
clusters.
Thus,
nido-4,5-C2B6H9
-
(1
-
) reacted with
BH3·THF to give
arachno-5,6-C2B7H12
-
(3
-
) which a single-crystal
X-ray
diffraction study showed is the first carborane to adopt the
n-B9H15 cage geometry. Thermal
or chemical degradation
of nido-4,5-C2B6H10
(1) gave
closo-2,3-C2B5H7
(5) in good to moderate yields. The
nido-4,5-C2B6H9
-
(1
-
) was
also found prone to lose a cage boron as evidenced by its reactions
with (η-C5H5)Co(CO)I2 and
(η6-C6Me6)2Ru2Cl4
which gave
closo-3,1,2-(η-C5H5)CoC2B5H7
(6) and
closo-3,1,2-(η6-C6Me6)RuC2B5H7
(7), respectively. NMR studies
showed the
nido-4,5-C2B6H10
(1) was converted to
arachno-4,5-C2B6H11
-
by reaction with LiEt3BH, and an alkyl
derivative,
arachno-7-CH3-4,5-C2B6H10
-
(4
-
), was formed by reacting MeLi
with
nido-4,5-C2B6H9
-
(1
-
) followed
by protonation. The
closo-2,3-C2B5H7
(5) was also converted in high yields to the smaller nido
carborane, nido-2,3-C2B4H8, via reaction with
TMEDA/H2O, and to
nido-3,4-C2B5H8
-
(8
-
) by reaction with
LiEt3BH.
“…However, the only structurally characterized 8-vertex nido-cluster with this geometry is nido - (η-C 5 H 5 ) 2 Co 2 SB 5 H 7 nido -(η 6 -C 6 Me 6 )FeMe 4 C 4 B 3 H 3 , and nido -(η-C 5 H 5 )CoPh 4 C 4 B 3 H 3 , have structures based on a 10-vertex bicapped square antiprism missing two vertices, which is the same geometry expected for 8-vertex arachno-clusters (Figure b). Thus, the question of which is the preferred geometry for 8-vertex nido cages has been a longstanding problem in cluster chemistry. 26,f,, 2 Derivation of open 8-vertex cage frameworks based upon geometrical systematics: (a) removal of a high-coordinated vertex from a 9-vertex tricapped trigonal prism to generate a 5-membered open-face nido geometry; (b) removal of two high-coordinated vertices from a 10-vertex bicapped square antiprism to generate a 6-membered open-face arachno geometry.…”
Synthesis and structural studies, employing combined NMR, X-ray
crystallographic, and ab initio/IGLO/NMR methods, of a variety of new subicosahedral carboranes with adjacent
cage carbons are reported. Acetonitrile-induced cage degradation of
arachno-4,5-C2B7H12
-
gave
nido-4,5-C2B6H9
-
(1
-
) in nearly quantitative yield,
which
can then be protonated to give the neutral carborane
nido-4,5-C2B6H10
(1) in good yield. Both of these nido
electron-count clusters are shown to have an arachno-type geometry, i.e. a
six-membered open face. The
nido-4,5-C2B6H10
(1) hydroborated alkenes or alkynes which following
deprotonation gave
nido-7-R-4,5-C2B6H8
-
(2a
-
−
c
-
)
ions.
Both
nido-4,5-C2B6H9
-
(1
-
) and
nido-4,5-C2B6H10
(1) serve as useful precursors to other adjacent cage-carbon
clusters.
Thus,
nido-4,5-C2B6H9
-
(1
-
) reacted with
BH3·THF to give
arachno-5,6-C2B7H12
-
(3
-
) which a single-crystal
X-ray
diffraction study showed is the first carborane to adopt the
n-B9H15 cage geometry. Thermal
or chemical degradation
of nido-4,5-C2B6H10
(1) gave
closo-2,3-C2B5H7
(5) in good to moderate yields. The
nido-4,5-C2B6H9
-
(1
-
) was
also found prone to lose a cage boron as evidenced by its reactions
with (η-C5H5)Co(CO)I2 and
(η6-C6Me6)2Ru2Cl4
which gave
closo-3,1,2-(η-C5H5)CoC2B5H7
(6) and
closo-3,1,2-(η6-C6Me6)RuC2B5H7
(7), respectively. NMR studies
showed the
nido-4,5-C2B6H10
(1) was converted to
arachno-4,5-C2B6H11
-
by reaction with LiEt3BH, and an alkyl
derivative,
arachno-7-CH3-4,5-C2B6H10
-
(4
-
), was formed by reacting MeLi
with
nido-4,5-C2B6H9
-
(1
-
) followed
by protonation. The
closo-2,3-C2B5H7
(5) was also converted in high yields to the smaller nido
carborane, nido-2,3-C2B4H8, via reaction with
TMEDA/H2O, and to
nido-3,4-C2B5H8
-
(8
-
) by reaction with
LiEt3BH.
“…The structure of 2 comprises a 10 skeletal electron pair (sep) nido‐ tetracarbon metallacarborane (Figure 113 and Scheme ). This structure has novel composition but is of a known structural type, which has been discussed in the literature 14–16…”
Materials with the ability to harness multiple sources of energy from the ambient environment could lead to new types of energy-harvesting systems. It is demonstrated that nanocomposite films consisting of zinc oxide nanostructures embedded in a common paper matrix can be directly used as energy-conversion devices to transform mechanical and thermal energies to electric power. These mechanically robust and flexible devices can be fabricated over large areas and are capable of producing an output voltage and power up to 80 mV and 50 nW cm(-2) , respectively. Furthermore, it is shown that by integrating a certain number of devices (in series and parallel) the output voltage and the concomitant output power can be significantly increased. Also, the output voltage and power can be enhanced by scaling the size of the device. This multisource energy-harvesting system based on ZnO nanostructures embedded in a flexible paper matrix provides a simplified and cost-effective platform for capturing trace amounts of energy for practical applications.
“…A limited number of other nido-8-vertex electron-count clusters have also been structurally characterized via X-ray crystallography. The following have been shown to have the same ni-8〈VI〉 configuration: nido -(η 6 -C 6 Me 6 )Fe(Me) 4 C 4 B 3 H 3 , nido -(η 5 -C 5 H 5 )Co(Ph) 4 C 4 B 3 H 3 , and nido -4,5-C 2 B 6 H 9 - .…”
An extensive investigation of boranes, carboranes, and heteroboranes falling into the nido-8-vertex electron-count class has been carried out using ab initio methods. The results of this study indicate a nido six-membered open face geometry, ni-8, is usually the preferred configuration over a nido five-membered open face geometry, ni-8. In only two systems, B(8)H(9)(3)(-) and OB(7)H(7)(2)(-), is a ni-8 geometry calculated to be of lowest energy. Attempts to test empirical carbon placement rules along with the skeletal bridge and endo-hydrogen location preferences were also evaluated. The results indicate the nido-8-vertex family is not ideally suited for the application of these empirical rules alone. This is probably due to the open face of these clusters not having homogeneous vertexes and/or not being "rigid". The ab initio/IGLO/NMR method was applied to the disputed B(8)H(10).L and C(4)B(4)H(8) systems. The known nido-B(8)H(10).NEt(3) was found to have a ni-8 geometry with a fluxional bridge hydrogen. The calculations confirmed that the known alkylated derivatives of the nido-C(4)B(4)H(8) carboranes have ni-8 configurations in solution. In an investigation of B(8)H(12), a previously unreported isomer of C(2) symmetry was found which high-level G2MP2 calculations indicate is only 1.6 kcal/mol higher in energy than the lowest energy C(s)() symmetry isomer. This C(2) symmetry isomer is likely the higher energy intermediate in the degenerate interconversion of B(8)H(12) into its mirror image. The transition state for the conversion of the C(s)() to the C(2) symmetry isomer has C(1) symmetry with a barrier of 2.1 kcal/mol at the MP2/6-31G level of ab initio theory.
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