Reactions of α-diimine-aluminum complexes with sodium alkynides: versatile structures of aluminum σ-alkynide complexes

Article abstract of DOI:10.1039/c5dt01693b

Reaction of AlCl₃ with the monoanionic α-diimine ligand [NaL] yielded the complex [L^?-Al^IIICl₂^-] (1, L = [(2,6-iPr₂C₆H₃)NC(Me)]₂), and subsequent reduction

Full text of DOI:10.1039/c5dt01693b

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Reactions of α-diimine-aluminum complexes with
sodium alkynides: versatile structures of aluminum
σ-alkynide complexes†
Cite this: Dalton Trans., 2015, 44,
13671
Yanxia Zhao, Yanyan Liu, Biao Wu and Xiao-Juan Yang*
Reaction of AlCl3 with the monoanionic α-diimine ligand [NaL] yielded the complex [L•−AlIIICl2−] (1, L =
[(2,6-iPr2C6H3)NC(Me)]2), and subsequent reduction of 1 by sodium metal afforded the mononuclear
[L2−AlIIICl−(THF)] (2) and binuclear [L2−(THF)AlII−AlII(THF)L2−] (3). Compounds 2 and 3 exhibit interesting
reactivities to sodium alkynides at room temperature. Treatment of dialumane 3 with 1 equiv. of
4-methylphenylacetylene in the presence of sodium metal yielded the asymmetric Al–Al-bonded com-
pound [Na(Et2O)][LAl–Al(CuC(C6H4–Me))L] (4) containing an alkynyl group attached to one of the Al
atoms. The reaction of 2 with 4-methylphenylacetylene and Na (or sodium 4-methylphenylacetylide)
resulted in the mononuclear product [L(THF)Al(CuC–(C6H4–Me))] (5) containing a single terminal acety-
lide ligand. Precursor 2 reacted with 2 equiv. of phenylacetylene (or 4-methylphenylacetylene, trimethyl-
silylacetylene) and Na to give the tweezer “ate” complexes, [Na(THF)(DME)][LAl(CuCR)2] (R = C6H5, 6a;
C6H4–Me, 6b; Si(Me)3, 6c), [Na(THF)]2[LAl(CuCPh)2]2(µ-C7H8) (7), [Na(C7H8)][(µ-Na)][LAl(CuCSi(Me)3)2]2
(8), as well as the polymeric [LAl(CuCPh)2Na]n (9). In the products, two alkynyl groups coordinate termin-
ally to one Al center and a sodium ion is embedded between these two alkynyls. Interestingly, both cyclo-
addition and terminal acetylide coordination of three equiv. of alkyne occurred in the reaction of 2 with
1-hexyne, resulting in the unique dialuminum complex [Na(Et2O)]2[{L(C(C4H9)vCH)}Al(CuC(C4H9))2]2 (10).
Complexes 1–10 have been characterized by NMR (1H, 13C) and IR spectroscopy, elemental analysis, and
X-ray diffraction, and their electronic structures were studied by DFT calculations.
Received 5th May 2015,
Accepted 10th June 2015
DOI: 10.1039/c5dt01693b
www.rsc.org/dalton
state architectures due to the metallophilic interactions. In
contrast, information about main group metal analogues is
Introduction
Owing to the linear structure, π-unsaturation, and the ease of
functionalization of the alkynyl unit, metal alkynide complexes
have very promising electronic and structural properties,
which could provide potential applications in nonlinear
optics, liquid crystals, luminescent materials, molecular wires,
ion sensors, as well as photoconductive materials.1 Further-
more, alkynide complexes have been proposed to play im-
portant roles in many industrial processes including
homogeneous and heterogeneous catalysis.2 To date, most
studies on alkynyl derivatives have been based on transition
metal complexes,3 which can result in various alkynyl bonding
motifs: clusters, multinuclear aggregates, or extended solid-
scarce, and the majority of σ-alkynide complexes adopt mono-
meric or dimeric structures.4
The investigation into the synthesis and reactivity of orga-
noaluminum alkynides has attracted considerable interest
because these compounds can be used as excellent starting
materials in synthetic organic chemistry.5 Although aluminum
acetylide compounds were synthesized in as early as 1960,6 the
first structurally characterized Al complexes with the terminal
alkynide appeared only in 2000 from the reaction of an
aluminumdihydride precursor with excess PhCuCH or
Me3SiCuCH.7 By now a couple of such complexes have been
prepared by metallation of CH-acidic terminal alkynes with
dialkylaluminum hydrides8 or dialkylaluminum halides with
the alkali metal salts of acetylide.9
Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the
Ministry of Education, College of Chemistry and Materials Science, Northwest
We have been exploring the reactivity of metal–metal-
bonded compounds bearing low-valent, low-coordinate metal
centers stabilized by the noninnocent α-diimine ligands in
their radical monoanionic or closed-shell dianionic form.10
University, Xi’an 710069, China. E-mail: yangxiaojuan@nwu.edu.cn
†Electronic supplementary information (ESI) available: X-ray structure of 6b,
EPR spectra of complex 1, structure information and DFT calculations. CCDC
1054517, 1054518, 932639–932646, 1044207–1044567 and 1044568. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/
c5dt01693b
The Al–Al single bond compound, [L2−(THF)AlII−AlII(THF)L2−
]
(L = [(2,6-iPr2C6H3)NC(Me)]2) (3) has proven to exhibit novel
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Scheme 1 Synthesis of complexes 1–10.
activation of unsaturated organic molecules, such as cleavage amount) of the 4-methylphenylacetylene and Na, the expected
of the NvN double bond of azobenzene derivatives via a four- product with two alkynide ligands, each attaching to an Al
electron reduction11 or activation of alkenes.10f Very recently, atom, was not obtained, possibly due to the steric crowding of
we reported the reaction of dialumane 3 with diphenylacety- such a structure.
lene or phenylacetylene, which afforded novel insertion or
Furthermore, reactions of the mononuclear complex 2 with
cycloaddition products.12 In a further study on the reactions of various terminal alkynes under different conditions (e.g.,
α-diimine aluminum complexes with alkynes, we found that solvent, amount of the reactants and Na metal) led to the ver-
both the mononuclear precursor [LAlCl(THF)] (2) and dialu- satile products 5–10. The complex [L(THF)Al(CuC(C6H4–Me))]
mane 3 displayed very good reactivity to alkynides, resulting in (5) was obtained from 2 and 4-methylphenylacetylene with
a rich variety of aluminum alkynide complexes with versatile 1 equiv. of Na metal, and all of the other products were
structures (Scheme 1). Herein we present the synthesis and synthesized by the reaction of 2 and the corresponding alkyne
crystal structures of these complexes and theoretical studies (2 or 3 equiv.) in the presence of 2 equiv. of Na (Scheme 1).
on their electronic structures.
Alternatively, products 5–9 can also be obtained by the reaction
of the chloro complex 2 with sodium alkynides, which is similar
to the reaction of aluminum chlorides with lithium/sodium
alkynides.9 Thus, it is possible that sodium alkynides were
firstly formed in the one-pot reaction of 2 or 3 with alkyne and
sodium metal and then the alkynide coordinated to Al upon
NaCl elimination. Complex 5 shows a mononuclear structure
with one alkyne. In contrast, when increased amounts of
alkynes (2 equiv.) were used, a series of aluminum diacetylides
(6a,b,c–9) containing embedded sodium ions between two
alkynyl groups were isolated, which have a common main
“tweezer”-type motif [LAl(CuCR)2Na] but different aggregation
structures (monomeric 6a–6c, dimeric 7 and 8, and even poly-
meric 9). Most interestingly, when the amount of alkyne was
further increased to 3 equiv., the unique centrosymmetric
dimer 10 was obtained, which features both terminally co-
ordinated acetylides and the cycloaddition of 1-hexyne to the
metal−ligand moiety. Compounds 4–10 are highly air- and
moisture-sensitive. In their crystal structures, the Al atoms
reside in a distorted tetrahedral geometry (except for a three-
Results and discussion
Synthesis
As shown in Scheme 1, the dichloro aluminum complex 1 was
prepared by the reaction of anhydrous AlCl3 and [NaL] (in situ
generated from ligand L0 and sodium) in a 1 : 1 stoichiometry.
Reduction of 1 with 1-fold Na afforded the monochloro
complex 2. Both complexes feature a formal AlIII center with
either monoanionic (for 1) or dianionic (for 2) ligand L. Upon
further reduction of 2 by one equiv. of Na, the Al−Al-bonded
complex 3 was obtained, which contains the AlII ion and di-
anionic L2− 11
Reaction of the dialumane 3 with 1 equiv. of
.
4-methylphenylacetylene and Na in Et2O afforded the complex
[Na(Et2O)][LAl–Al(CuC(C6H4–Me))L] (4), which shows an
asymmetric structure with the persistence of the Al−Al single
bond and coordination of only one alkynide ligand. Notably,
with the addition of one more equivalent (or even an excess
13672 | Dalton Trans., 2015, 44, 13671–13680
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coordinate Al atom in 4) with formal oxidation state of +2 (in composition LAlCl2 with related ligands, such as dpp-Bian,
4) or +3 (in 5–10).
β-diketiminate and diiminepyridine, have been reported in the
literature.14a–d In contrast, mono-halide species with an auxi-
liary ligand, such as amino, methyl or solvent molecule, are
relatively rare.14e–g
Crystal structures
The simplified model compounds [L′AlCl2] (1H, L′ =
(PhNCMe)2) and [L′AlCl(THF)] (2H) were used in DFT compu-
tations for complexes 1 and 2 (Fig. S3†). Natural population
analysis (NPA) shows a significant positive charge (1.67 and
1.86 for 1 and 2, respectively) on the Al atom, which displays a
formal oxidation state of +3 (Table S2 in the ESI†). On the
other hand, the L′ fragment accumulates negative partial
charges, from −0.57 (1H) to −1.42 (2H), thus indicating the
reduction of the radical monoanionic α-diimine ligand in 1
into the dianion in 2.
[Na(Et2O)][LAl(CuC(C6H4Me))−AlL] (4). When dialumane 3
was reacted with 1 equiv. of 4-methylphenylacetylene and 1
equiv. of Na, product 4 was obtained as purple-red crystals
(Scheme 1, Fig. 3). Compound 4 shows an asymmetric struc-
ture that differs significantly from 5–10 (obtained with 1−3
equiv. of the alkynes; vide infra). Notably, the Al−Al distance of
2.625(2) Å in 4 remains essentially unchanged relative to that
in 3 (2.658(2) Å). Only one 4-methylphenylacetylene molecule
binds terminally to one of the Al centers, resulting in a tetra-
hedral coordination environment around Al(1). The other
aluminum atom (Al(2)), however, is free of the alkyne molecule
or extra Lewis base donor (such as THF), being coordinated by
one L ligand and Al(1) in a slightly distorted trigonal-planar
geometry. It is known that, due to the Lewis acidic nature of
Al, only a few examples of dialumanes with the general
formula R2Al–AlR2 that are free of Lewis base have been iso-
[LAlCl2] (1) and [LAlCl(THF)] (2). In complex [LAlCl2] (1), the
aluminum atom is coordinated by a chelating ligand L and
two chloride ions in a distorted tetrahedral geometry (Fig. 1),
which is similar to the cationic aluminum dichloride
[LAlCl2]+[AlCl4]− stabilized by neutral α-diimine.13 However,
the ligand in the neutral complex 1 exists as a radical-anion
(and the aluminum displays a formal oxidation state of +3).
The EPR spectra of compound 1 (Fig. S2, ESI†) showed the
expected paramagnetic signals (centered at an average of g =
2.003), which were similar to those reported for metal com-
plexes that contained radical anionic diimine ligands.10c,11
Reduction of 1 with 1 equiv. of Na led to complex 2,
[LAlCl(THF)] (Scheme 1), in which the monoanionic ligand is
further reduced to the dianion, as indicated by the C–N
(1.444(3) and 1.435(3) Å) and C−C (1.346(3)Å) bond lengths of
the C2N2 backbone, while the formal AlIII ion is unchanged
(Fig. 2). Some similar dichloro aluminum complexes of the
Fig. 1 Molecular structure of 1. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and bond angles (°): Al–N 1.875(2), Al–Cl(1) 2.124(2), Al–Cl(2)
2.104(2), N–C(1) 1.354(3), C(1)–C(1A) 1.406(6), N–Al–N(A) 87.1(2), Cl(1)–
Al–Cl(2) 109.1(7). Symmetry code: (A) x, 0.5 − y, z.
Fig. 3 Molecular structure of 4. Thermal ellipsoids are set at the
30% probability level; hydrogen atoms and isopropyl groups of L are
omitted for clarity. Selected bond lengths (Å) and bond angles (°):
Al(1)–Al(2) 2.625(2), Al(1)–N(1) 1.859(3), Al(1)–N(2) 1.844(3), Al(2)–N(3)
1.821(3), Al(2)–N(4) 1.829(3), Al(1)–C(57) 1.978(5), C(57)–C(58) 1.208(5),
Na–O 2.187(6), N(1)–C(1) 1.422(5), N(2)–C(2) 1.431(5), C(1)–C(2) 1.344(5),
N(3)–C(29) 1.417(5), N(4)–C(30) 1.428(5), C(29)–C(30) 1.336(5), N(1)–
Al(1)–N(2) 88.9(2), N(3)–Al(2)–N(4) 89.6(2), Al(2)–Al(1)–C(57) 100.3(1),
Al(1)–C(57)–C(58) 168.4(4), C(57)–C(58)–C(59) 178.7(5).
Fig. 2 Molecular structure of 2. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and bond angles (°): Al–N(1) 1.814(2), Al–N(2) 1.812(2), Al–Cl
2.116(9), Al–O 1.876(2), N(1)–C(1) 1.444(3), C(1)–C(2) 1.346(3), N(2)–C(2)
1.435(3), N–Al–N(A) 94.2(9), Cl–Al–O 101.4(6).
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lated.15 Recently, the first 1,2-dibromodialumane without
coordination of a Lewis base has been isolated.16 In the
current case, the lack of THF coordination on Al(2) may result
in the larger steric exclusion of the 4-methylphenylacetylene
ligand on Al(1). Upon incorporation of the 4-methyl-
phenylacetylene molecule to one Al atom, the two C2N2Al rings
are nearly perpendicular to each other (87.0°), while they are
parallel in the symmetric parent compound 3.11 A similar reac-
tion with phenylacetylene has also been tested and a same
color change of the solution was observed, from which purple-
red microcrystals were isolated. However, analysis of its struc-
ture was unsuccessful due to the poor quality of the crystals.
Furthermore, IR spectrum revealed a band at 2048 cm−1
,
characteristic of the ν(CuC) stretch of acetylide ligands.
Related compounds ([L2M–M(CuCPh)L2]− (M = Ga, In; L = CH-
(SiMe3)2)) with intact Ga–Ga and In–In single bonds were pre-
Fig. 4 Molecular structure of 5. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms and isopropyl groups of L are omitted
for clarity. Selected bond lengths (Å) and bond angles (°): Al–N(1)
pared by similar addition of one alkynide ligand to one of the 1.813(4), Al–N(2) 1.821(4), Al–C(29) 1.920(5), Al–O 1.880(3), C(29)–C(30)
Lewis-acidic central atoms,17 but no such structure has been
reported for the lighter congener aluminum.
1.208(6), N(1)–C(1) 1.431(5), N(2)–C(2) 1.437(5), C(1)–C(2) 1.349(6), N(1)–
Al–N(2) 91.6(2), C(29)–Al–O 98.3(2), C(29)–C(30)–C(31) 176.6(5), Al–C
(29)–C(30) 174.3(4).
The Al–N bond lengths of the four-coordinate Al(1) (1.859
(3) and 1.844(3) Å) in complex 4 are slightly longer than those
of the three-coordinate Al(2) (1.821(3) and 1.829(3) Å). The Al–
CCuC bond length (1.978(5) Å) is comparable to those in 6–10
nuclear mono-acetylide compounds are relatively rare.21 The
(1.963(6)–2.000(6) Å) but is somewhat longer than that in 5
Al–N bond lengths (1.813(4) and 1.821(4) Å) in 5 are close to
those in 4 (av. 1.838 Å). The Al–O distance (1.880(3) Å) is
shorter than that in 3 (1.957(3) Å) and other reported values
for coordinated THF.11 The Al–C distance (1.920(5) Å) is much
shorter than that of 4 (1.978(5) Å), while the alkynyl C(29)–
C(30) distance (1.208(6) Å) is comparable to 4 (1.208(5) Å). The
alkynyl group deviates only slightly from linearity, with Al–
CuC and CuC–C angles of 174.3(4)° and 176.6(5)°, which are
in the normal range of known aluminum acetylides.8,9
DFT calculations (Fig. S3†) reproduced the molecular struc-
ture of 5. The calculated alkynyl C–C bond length (1.225 Å) is
somewhat longer than the X-ray data (1.208(6) Å).
Natural population analysis (NPA) shows significant positive
charges (av. 1.73) on Al atoms. These values are much larger
than those of 3H (1.13) and 4H (1.17, 1.22). On the other
hand, the 4-methylphenylacetylene molecule shows −0.55
charges, while the α-diimine ligand shows almost no change
(Table S2†).
[Na(THF)2][LAl(CuCPh)2] (6a), [Na(THF)(DME)][LAl(CuC-
(C6H4–Me))2] (6b), [Na(THF)(DME)][LAl(CuCSi(Me)3)2] (6c),
[Na(THF)]2[LAl(CuCPh)2]2(µ-C7H8) (7), [Na(C7H8)][(µ-Na)] [LAl-
(CuCSi(Me)3)2]2 (8), and [LAl(CuCPh)2Na]n (9). The reactions
of complex 2 with 2 equiv. of terminal alkynes (phenyl-
acetylene, 4-methylphenylacetylene, or trimethylsilylacetylene)
in the presence of 2.0 equiv. of Na metal in different solvents
afforded the products 6(a,b,c)−9 (Scheme 1, Fig. 5–9 and S1†).
The Al atoms in the compounds reside in a distorted tetra-
hedral geometry, being coordinated by two nitrogen atoms of
one ligand L and the terminal carbon atoms (σ-bonding) of
two alkynide ligands. Interestingly, in all of these complexes a
sodium ion is embedded between the two coordinated alky-
nide groups through η2-coordination to form the tweezer-type
(1.920(5) Å). Moreover, the Al–CuC backbone (168.4(4)°) devi-
ates slightly from linearity compared to those in 5–10 (av.
176.1°). This deviation has been reported for some transition
metal acetylide complexes18 and was also found in analogous
aluminum compounds.7,8a–c In product 4, the C(57)−C(58) dis-
tance (1.212(6) Å) of the alkynyl is typical for a triple carbon−
carbon bond.19 The α-diimine ligands remain dianionic.10
The optimized structure of the model compound [Na(H2O)]-
[L′Al(CuC(C6H4–Me))–AlL′] (4H, L′ = [PhNCMe]2) (Fig. S3 and
S4†) compares well to the X-ray data for 4, except that the
theoretical Al−Al distance (2.586 Å) is somewhat shorter than
the experimental data in 4 (2.625(2) Å). The Wiberg bond index
indicates an Al−Al bond order of 0.91. The bond dissociation
energy E(Al–Al) of 57.47 kcal mol−1 is larger than that in 3H
(46.27 kcal mol−1).11 The CuC triple bond has a bond order of
2.75. The natural charges on Al are +1.17 and +1.22, which are
comparable to 3H (+1.13), and the total negative charges on
the ligand L underwent only slight diminution, from −1.79
(3H) to −1.40 and −1.25 (4H). Meanwhile, the –CuCPh frag-
ment has a negative charge of −0.60.
[L(THF)Al(CuC(C6H4–Me))] (5). When one equivalent of
4-methylphenylacetylene was used to react with 2 in the pres-
ence of 1 equiv. of Na in THF, the mononuclear compound
[L(THF)Al(CuC(C6H4–Me))] (5) was formed (Fig. 4). In complex
5, one alkynyl group coordinates terminally to the aluminum
center, and the remaining coordination site is occupied by a
THF molecule to complete a distorted tetrahedral geometry
(bond angles: N–Al–N, 91.6(2)°; C–Al–O, 98.3(2)°). In the litera-
ture reports, aluminum compounds with terminal alkynyl
groups, (R2Al–CuC–R′)2 (R = alkyl; R′ = aryl, alkyl), usually give
dimeric or trimeric formula units with the α-C atoms of the
alkynides in the bridging positions.20 In contrast, mono-
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Fig. 7 Molecular structure of 7. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms and isopropyl groups of L are omitted
for clarity. Selected bond lengths (Å) and bond angles (°): Al–N(1) 1.835(5),
Al–N(2) 1.777(6), Al–C(29) 1.963(6), Al–C(37) 1.969(7), C(29)–C(30) 1.229(9),
C(37)–C(38) 1.228(8), N(1)–C(1) 1.432(8), N(2)–C(2) 1.419(8), C(1)–C(2)
1.341(8), N(1)–Al–N(2) 90.7(2), C(29)–Al–C(37) 101.0(3), C(31)–C(30)–
C(29) 174.0(7), C(39)–C(38)–C(37) 173.6(7), Al–C(29)–C(30) 177.1(0), Al–
C(37)–C(38) 176.9(6). Symmetry code: (A) 1 − x, 2 − y, −z.
Fig. 5 Molecular structure of 6a. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms and isopropyl groups of L are omitted
for clarity. Selected bond lengths (Å) and bond angles (°): Al–N(1) 1.831
(4), Al–N(2) 1.831(4), Al–C(29) 1.975(5), Al–C(37) 1.975(5), C(29)–C(30)
1.203(6), C(37)–C(38) 1.202(6), N(1)–C(1) 1.433(5), N(2)–C(2) 1.435(5),
C(1)–C(2) 1.342(6), N(1)–Al–N(2) 90.8(2), C(29)–Al–C(37) 100.8(2),
Al–C(29)–C(30) 177.5(5), Al–C(37)–C(38) 179.2(5).
Fig. 8 Molecular structure of 8. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms and isopropyl groups of L are omitted
for clarity. Selected bond lengths (Å) and bond angles (°): Al(1)–N(1)
1.833(4), Al(1)–N(2) 1.841(4), Al(1)–C(57) 1.978(5), Al(1)–C(62) 2.000(6),
C≠C 1.214 (av.), Na–C 2.794 (av.), N(1)–C(1) 1.420(6), N(2)–C(2) 1.428(6),
C(1)–C(2) 1.343(7), Al(2)–N(3) 1.843(4), Al(2)–N(4) 1.839(4), Al(2)–C(67)
1.982(5), Al(2)–C(72) 1.993(6), N(3)–C(29) 1.419(6), N(4)–C(30) 1.434(6),
C(29)–C(30) 1.342(7), N(1)–Al(1)–N(2) 89.1(2), C(57)–Al(1)–C(62)
100.5(2), Si(1)–C(58)–C(57) 173.6(5), Al(1)–C(57)–C(58) 178.0(4), Al(1)–
C(62)–C(63) 177.6(5), N(3)–Al(2)–N(4) 89.1(2), C(67)–Al(2)–C(72)
100.2(2), Si(3)–C(68)–C(67) 174.6(5), Al(2)–C(67)–C(68) 177.6(5), Al(2)–
C(72)–C(73) 177.3(4).
Fig. 6 Molecular structure of 6c. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms and isopropyl groups of L are omitted
for clarity. Selected bond lengths (Å) and bond angles (°): Al–N(1) 1.834
(3), Al–N(2) 1.827(3), Al–C(29) 1.980(4), Al–C(34) 1.987(4), C(29)–C(30)
1.223(5), C(34)–C(35) 1.211(5), N(1)–C(1) 1.418(4), N(2)–C(2) 1.424(4),
C(1)–C(2) 1.356(5), N(1)–Al–N(2) 89.3(1), C(29)–Al–C(34) 100.3(2), Si(1)–
C(30)–C(29) 175.0(3), Si(2)–C(35)–C(34) 176.6(4), Al–C(29)–C(30)
176.1(3), Al–C(34)–C(35) 176.2(3).
structure, and this sodium ion is also encapsulated by four Al center is coordinated by three terminal phenylethynyl
alkynide groups from two [LAl(CuCSi(Me)3)2] units (in 8). It is groups and a sodium ion is π-coordinated by four CuC
known that a transition metal or alkali metal ion can be groups, has been reported.24 However, no structurally charac-
embedded through η2-coordination between two terminal terized tweezer-like Al complex with Na+ embedded by two
alkynyl groups in tweezer-shaped transition metal alkyne com- alkynyl ligands is known.
plexes,22 which merit increasing interest regarding non-linear
Notably, the solvent used in the reaction has an important
optical properties.23 The first aluminum alkynide compound influence on the structure of products 6–9 (Scheme 1). In the
in which the alkynyl group interacts with an alkali metal ion coordinating solvents THF and DME, mononuclear acetylide
was reported in 2002 by Roesky et al.24 To date there are only complexes (6a–6c) were isolated, in which the Na atom is sol-
very few examples of aluminum alkynides with alkali metal vated by THF and DME molecules, leading to the discrete
ions.21b,c,24,25 A dinuclear aluminum alkynide, in which each structures. However, when toluene was used as the solvent,
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The interaction between the sodium ion and the CuC bonds
makes the two alkynyl groups much closer in space (bite angle
of C–Al–C: 100.8(2)−101.0(3)°) than those observed in the ana-
logues without alkali metal ions (107.7–116.7°).7,8a,d In con-
trast, these C–Al–C angles are much wider than the lithium
alkynyl aluminum compounds (av. 96.2°).25 An almost ideal
linear environment is detected for the alkynyl groups with
Al–CuC and CuC–C angles of 176.2° (av.) and 175.9° (av.),
respectively. The bond lengths between the alkynyl carbon
atom and the sodium ion in 6–9 are in the range of 2.68−2.87
(av.) Å, which are similar to the reported values (Na−CCuC
:
2.65–3.36 Å) for ([Na(THF)][LAl(CuCPh)3])2 (L = 2,6-iPr2C6H3N–
(SiMe3)).24 The C–Na–C angles are in the range 23.7–25.7°,
which are also comparable to the only other example of the
sodium alkynyl aluminum compound (20.6–24.8°).24
Fig. 9 (a) Molecular structure of 9. Thermal ellipsoids are set at the 30%
probability level; hydrogen atoms and isopropyl groups of L are omitted
for clarity. (b) The linear chain along the a axis formed by intermolecular
Na–C bonds. Selected bond lengths (Å) and bond angles (°): Al–N(1)
1.827(3), Al–N(2) 1.831(3), Al–C(29) 1.968(3), Al–C(37) 1.974(4), C(1)–N(1)
1.432(3), C(2)–N(2) 1.422(4), C(1)–C(2) 1.336(4), C(29)–C(30) 1.207(4),
C(37)–C(38) 1.207(4), N(1)–Al–N(2) 89.7(1), C(29)–Al–C(37) 100.6(1),
C(31)–C(30)–C(29) 178.1(4), C(39)–C(38)–C(37) 174.7(4), Al–C(29)–
C(30) 171.6(3), Al–C(37)–C(38) 171.5(3).
The optimized structures of the model compounds [Na-
(H2O)2][L′Al(CuCPh)2] (6aH), [L′Al(CuC(C6H4–Me)2][Na(DME)-
(THF)] (6bH), [Na(H2O)3][LAl(CuCSi(Me)3)2] (6cH), and [Na]-
[(µ-Na)][L′Al(CuCSi(Me)3)2]2 (8H) (Fig. S3†) are in good agree-
ment with the X-ray data. The theoretical CuC bond lengths
(av. 1.233 Å) are slightly longer than the experimental data (av.
1.214 Å), and all of them fall in the range of typical CuC triple
bond. The Al–CCuC (av. 1.982 Å) distances and C–Al–C (av.
103.8°) angles are close to the experimental values (av. 1.985 Å
and 100.5°), and the geometrical parameters within the NCCN
fragment of ligand L are also very similar to the experimental
data. NBO analysis gives charges (av. 1.74) on Al, which are
comparable to 2H (1.86). The charge of the dianionic ligand L
is −1.38 (av.). Moreover, the NBO results reveal considerable
covalent bonding between Al and the acetylide ligands, with
an average bond order of 0.52.
two dimeric complexes (7 and 8) were isolated (Fig. 7 and 8).
In the centrosymmetric compound 7, a toluene molecule func-
tions as a bridge between two tweezer-shaped [LAl(CuCPh)2]
units through bonding to the embedded Na+ ions, forming a
“triple-decker” sandwich structure. In contrast to the mono-
meric complexes 6a–6c and the dimeric 7, the other dimerized
compound 8 contains two sodium ions with different coordi-
nation modes. One of the Na+ ions (Na(1)) is η2-coordinated by
four (instead of two) phenylethynyl groups. Thus in this case
the alkali metal cation acts as a bridge to link the two [LAl-
(CuCPh)2] units. The other sodium ion (Na(2)), on the other
hand, is η4-bonded by the C2N2 moiety of one ligand L and
π-coordinated by a toluene molecule, thereby resulting in the
asymmetric dimer 8. Finally, product 9, which was isolated
from the non-coordinating solvent n-hexane, features a one-
dimensional coordination polymer structure linked by inter-
molecular interactions between the embedded Na atom and
an aryl ring of the ligand L (Fig. 9). Such a variation of
the aggregation status of complexes crystallized from different
solvents has also been observed previously.25
[Na(Et2O)]2[{L(C(C4H9)vCH)}Al(CuC(C4H9))2]2
(10). The
reaction of 2 with 3 equiv. of 1-hexyne followed by treat-
ment with 2 equiv. of Na proceeded smoothly, affording the
unique centrosymmetric dimer 10 that is bridged by two
sodium ions (Fig. 10). Most remarkably, six molecules of
Despite the difference in the solvation or further contacting
mode of the embedded sodium ion in 6–9, the main structural
parameters of the [LAl(alkynyl)2Na] fragment in the six com-
plexes (6–9) are quite similar. The CuC bond lengths (1.196(7)
to 1.229(9) Å) are in the expected range and correspond well to
the standard triple bond length of 1.20 Å.19 The Al–C bond
lengths in the Al–CuCPh moieties are within the range of
1.963(6)–2.002(6) Å, close to those found in 4 (1.978(5) Å) and
in related complexes.24,25 However, they are somewhat longer
than those in 5 (1.920(5) Å) and [(3,5-tBu2pz)(μ4-Al(CuCPh)2)]2
(1.913(3)–1.929(3) Å) without the embedded alkali metal ion.7
Fig. 10 Molecular structure of 10. The acetylenic hydrogen atoms are
presented, while the other ones as well as isopropyl groups of L are
omitted for clarity. Selected bond lengths (Å) and bond angles (°): Al–
N(1) 1.834(2), Al–C(29) 1.965(3), Al–C(35) 1.969(3), Al–C(41) 1.984(3),
C(29)–C(30) 1.338(4), N(1)–C(1) 1.498(3), N(2)–C(2) 1.276(3), C(1)–C(2)
1.552(4), C(1)–C(30) 1.542(4), C(35)–C(36) 1.199(4), C(41)–C(42) 1.207(4),
Na⋯Na 3.796, N(1)–Al–C(29) 90.64(12), C(35)–Al–C(41) 103.53(13),
C(36)–C(35)–Al 171.1(3), C(42)–C(41)–Al 175.6(3), N(1)–C(1)–C(2)–N(2)
(torsion) = 116.28°. Symmetry code: (A) −x, −y, −z.
13676 | Dalton Trans., 2015, 44, 13671–13680
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1-hexyne are incorporated, which show two completely same aluminum atom) further proves the versatile reactivity of
different coordination patterns. Four hexynide anions coordi- compound 2.
nate terminally to the two Al atoms to form the tweezer struc-
ture as in compounds 6a–c, while the other two 1-hexyne
molecules add to the metal−ligand moieties as previously
Conclusions
observed for the phenylacetylene complexes12,26 and related Al
and Ga complexes27 reported in the literature. We propose that The aluminum compounds 2 and 3 show interesting reactiv-
an intermediate like 6a–c might have formed in the first reac- ities toward sodium alkynides. By varying the amounts of the
tion step. In comparison, the aluminum with three terminal reactants and reaction conditions, a rich variety of products
alkynide ligands was not isolated as in some previously with terminal alkynes have been obtained. Product 4 rep-
reported complexes,8b,9b,24 when an excess of 1-hexyne was resents a unique monoalkynyl dialuminum compound with an
added.
intact AlII–AlII single bond. Moreover, a series of novel tweezer-
Another noticeable feature of product 10 is the coordination shaped aluminum alkynide complexes (6–9) were isolated,
mode of the α-diimine ligand L, which has a largely twisted including monomeric, dimeric, and polymeric structures with
conformation (torsion angle of N(1)–C(1)–C(2)–N(2): 116.3°). a sodium ion embedded between two alkynyl groups. Most
And the two nitrogen atoms are oriented to opposite sides. As interestingly, compound 10 incorporates six molecules of
a result, the ligand shows an unusual monodentate coordi- 1-hexyne, which show two different coordination patterns
nation in the amido-imine form, with the N(1) atom bonding (cycloaddition and terminal acetylide coordination). Possible
to Al and N(2) free from metal coordination. Chang and co- activation of other small molecules by these aluminum com-
workers reported the formation of alkynyl magnesium amides plexes is currently being studied in this laboratory.
[{Mg(RCuC)(μ-NiPr2)(THF)}2] (R = Ph, SiMe3) through amine
elimination within the stoichiometric reaction between [Mg-
(iPr2N)2] and HCuCR in THF.28 In compound 10, it can be
viewed as that one of the N atoms of the bidentate ligand L is
Experimental section
General procedures
“freed” from the coordination sphere of Al and is replaced by
an alkynide. Consequently, the tetrahedral environment about All of the reactions and manipulations of air- and moisture-
the Al atom is completed by one N atom from a ligand, two sensitive compounds were carried out under argon or nitrogen
terminal alkynyls, and the terminal carbon of the alkyne mole- with standard Schlenk or dry box techniques. The solvents
cule from the cycloaddition.
The Al–N(1) bond (symmetry-related) lengths (1.834(2) Å), methods and were distilled under argon prior to use. [D6]-
and the Al–C bond lengths (Al–CCvC: 1.965(3) Å, Al–CCuC Benzene was dried over the Na/K alloy. The α-diimine ligand L
(toluene, THF, Et2O and DME) were dried using appropriate
:
1.976 Å (av.)) are similar to the corresponding values in other was prepared according to a literature procedure.29 Sodium
compounds. The CvC (1.338(4) Å) and CuC (1.203 Å (av.)) dis- metal, anhydrous aluminum chloride (AlCl3), phenylacetylene,
tances are indicative of double and triple bonds, while the Al– 4-methylphenylacetylene and trimethylsilylacetylene were
CHvC (107.5°) and Al–CuC (173.3° (av.)) angles are credited purchased from Alfa Aesar. NMR spectra were recorded on
to their sp2 and sp nature, respectively. 1H and 13C NMR a Mercury Plus-400 spectrometer in [D6]benzene. The solubility
spectra of 10 confirm the presence of CHvC and CuC groups of the dimeric or polymeric compounds 7–9 is too low to allow
at the Al center (δ = 6.33 ppm for the Al–CHvC moiety). for spectroscopic studies. The EPR spectra of paramagnetic
Notably, the newly formed C(1)–C(30) bond (1.542(4) Å) is compound 1 were recorded on a Bruker EMX-10/12 spectro-
typical of a single C–C bond.
meter at room temperature. Elemental analyses were per-
The simplified model compound [Na(H2O)]2[{L(C(C4H9)v formed with an Elementar Vario EL III instrument. IR spectra
CH)}Al(CuC(C4H9))2]2 (10H) was used to evaluate the elec- were recorded using a Nicolet Avatar 360 FT-IR spectrometer.
tronic structure of 10 (Fig. S3†). The computed Al−C (av.
[LAlCl2] (1). A solution of AlCl3 (0.133 g, 1.0 mmol) in THF
1.990 Å) bond distances compare well with the experimental (20 mL) was added to a rigorously stirred solution of LNa (pre-
values (av. 1.973 Å), with an average σ-bond order of 0.63. The pared in situ from L (0.404 g, 1.0 mmol) and sodium (0.0230 g,
erstwhile C(29)–C(30) triple bonds now display the double 1.0 mmol) in 20 mL THF). The mixture was stirred for 4 h
bond order of 1.39 with a bond distance of 1.353 Å. Mean- at room temperature. It was then filtered and the filtrate was
while, the (CHvC(C4H9)) and (CuC(C4H9)) fragments concentrated to about 5 mL. Slow evaporation of the solution
accumulate negative partial charges of −0.56 and −0.58 (av.), at ca. −20 °C for several days yielded the product as purple
which are comparable to the other compounds (Table S2†). crystals (0.340 g, 67%). EPR: g = 2.003.
The NPA charge on Al (1.63) is somewhat smaller than that of
[LAlCl(THF)] (2). Sodium (0.0230 g, 1.0 mmol) was added to
2H (1.86), and the negative partial charge on the ligand a suspension of 1 (0.502 g, 1.0 mmol) in THF (30 mL). The
decreases from −1.42 (in 2H) to −0.68 (in 10H), corresponding mixture was stirred for 1 d at room temperature and filtered.
to the change of the oxidation states of L2− to L−. Moreover, The filtrate was concentrated to about 5 mL and stored at
the formation of product 10 (with two terminal alkynide ca. −20 °C for several days to yield the product as purple
1
groups and one alkenediyl unit of cycloaddition bound to the crystals (0.303 g, 56%). H NMR (400 MHz, C6D6, 25 °C, TMS):
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δ = 1.05 (d, 24H, J = 7.2 Hz, CH(CH3)2), 1.39 (THF), 1.70 (s, 6H, 2067, 1959, 1900, 1876, 1735, 1603, 1522, 1494, 1460, 1356,
CCH3), 3.19 (m, 4H, CH(CH3)2), 3.50 (THF), 6.96–7.15 ppm 1257, 1209, 1105, 1080, 895, 728; elemental analysis calcd (%)
(m, 6H, m, p-ArH); 13C NMR (100.6 MHz, C6D6, 25 °C, TMS): for C52H66AlN2NaO2·C4H8O (873.17): C, 77.03; H, 8.54; N, 3.21.
δ = 15.7 (N–CCH3), 23.6 (CH(CH3)2), 26.0 (CH(CH3)2), 27.4 Found: C, 76.82; H, 8.42; N, 3.16.
(CH(CH3)2), 28.9 (THF), 68.6 (THF), 123.9 (m-C6H3), 124.2
(p-C6H3), 126.1 (o-C6H3), 142.4 (i-C6H3), 146.8 ppm (N–CCH3).
[Na(THF)(DME)][L2−AlIII(CuC(C6H4–Me))2] (6b). 4-Methyl-
phenylacetylene (0.232 g, 2.0 mmol) was added to a solution of
[Na(Et2O)][LAl–Al(CuC(C6H4Me))L] (4). 4-Methylphenylace- [LAlCl(THF)] (2) (1.0 mmol) in 30 mL of DME/THF (9 : 1 v : v).
tylene (0.058 g, 0.5 mmol) was added to a solution of After 2 hours, 2.0 equiv. of Na (0.046 g, 2.0 mmol) was added
[LAlII(THF)]2 (3)11 (0.5 mmol) in 30 mL of toluene in the pres- and the solution was stirred for 6 days at ambient temperature.
ence of 1.0 equiv. of Na (0.012 g, 0.5 mmol), upon which the Single crystals were obtained from a DME solution at −20 °C
red color of 1 changed to green within 0.5 h. The solution was (0.507 g, 54%) after several days. 1H NMR (400 MHz, C6D6,
stirred for 6 days at ambient temperature. X-ray quality crystals 25 °C, TMS): δ = 1.44 (d, 12H, J = 7.2 Hz, CH(CH3)2), 1.67 (d,
of 4 were obtained from ether at −20 °C (0.242 g, 45%) after 12H, J = 7.2 Hz, CH(CH3)2), 1.99 (THF), 2.10 (s, 6H, CCH3),
1
several days. H NMR (400 MHz, C6D6, 25 °C, TMS): δ = 1.11 2.67 (s, C6H4–CH3), 2.72 (OCH3, DME), 3.47 (THF), 3.47 (OCH2,
(d, 24H, J = 7.2 Hz, CH(CH3)2), 1.17 (d, 24H, J = 7.2 Hz, CH- DME), 4.56 (m, 4H, CH(CH3)2), 6.72–7.31 (m, 22H, Ar–H, Ph–
(CH3)2), 1.13 (Et2O), 2.11 (s, 12H, CCH3), 2.92 (s, 3H, C6H4– H); 13C NMR (100.6 MHz, C6D6, 25 °C, TMS): δ = 14.2
CH3), 3.25 (Et2O), 3.37 (m, 8H, CH(CH3)2), 7.00–7.15 (m, Ar–H, (N–CCH3), 20.0 (CH(CH3)2), 23.8 (C6H4–CH3), (24.3 (THF), 26.8
Ph–H); 13C NMR (100.6 MHz, C6D6, 25 °C, TMS): δ = 14.3 (CH(CH3)2), 57.4 (OCH3, DME), 66.6 (THF), 69.6 (OCH2, DME),
(N–CCH3), 21.3 (CH(CH3)2), 23.9 (C6H4–CH3), 25.5 (Et2O), 28.1 121.6, 122.2, 124.3, 127.9, 130.3, 135.9, 136.5 (Ph–C, Ar–C),
(CH(CH3)2), 65.8 (Et2O), 123.4, 125.6, 127.7, 128.1, 128.4, 146.3 (N–CCH3), 147.8 (Al–Cu); IR (KBr, ν/cm−1): 2109, 1905,
129.2, 137.7 (Ph–C, Ar–C), 142.0 (N–CCH3), 146.3 (Al–Cu); IR 1639, 1506, 1459, 1438, 1381, 1322, 1256, 1120, 1084, 1025,
(KBr, ν/cm−1): 2051, 1942, 1858, 1803, 1735, 1643, 1504, 1461, 817, 734; elemental analysis calcd (%) for C54H72AlN2-
1437, 1382, 1255, 1121, 1039, 892, 792; elemental analysis NaO3·C7H8 (939.24): C, 78.00; H, 8.58; N, 2.98. Found:
calcd (%) for C69H97Al2N4NaO (1075.46): C, 77.06; H, 9.09; C, 78.02; H, 8.44; N, 3.24.
N, 5.21. Found: C, 77.12; H, 8.74; N, 5.70.
[Na(THF)(DME)][LAl(CuCSi(Me)3)2] (6c). Complex 6c was
[L(THF)Al(CuC(C6H4–Me))] (5). 4-Methylphenylacetylene prepared by a similar procedure to that employed for 6b by
(0.116 g, 1.0 mmol) was added to a solution of [LAlCl(THF)] (2) using trimethylsilylacetylene (0.196 g, 2.0 mmol). Yield:
1
(1.0 mmol) in 30 mL of toluene. After 2 hours, 1.0 equiv. of Na 0.403 g, 47%. H NMR (400 MHz, C6D6, 25 °C, TMS): δ = 0.03
(0.023 g, 1.0 mmol) was added, upon which the red color of 2 (s, 18H Si(CH3)3), 1.25 (THF), 1.32 (d, 12H, J = 7.2 Hz, CH-
changed to gray-green. The solution was stirred for 6 days at (CH3)2), 1.48 (d, 12H, J = 7.2 Hz, CH(CH3)2), 1.82 (s, 6H, CCH3),
ambient temperature. Single crystals of 5 were grown from 2.61 (OCH3, DME), 3.15 (THF), 3.33 (OCH2, DME), 4.26 (m, 4H,
THF at −20 °C (0.341 g, 52%). 1H NMR (400 MHz, C6D6, 25 °C, CH(CH3)2), 6.90–7.18 (m, 22H, Ar–H, Ph–H); 13C NMR
TMS): δ = 1.10 (d, 12H, J = 7.2 Hz, CH(CH3)2), 1.41 (d, 12H, J = (100.6 MHz, C6D6, 25 °C, TMS): δ = 0.60 (SiMe3), 15.2
7.2 Hz, CH(CH3)2), 1.64 (THF), 1.90 (s, 6H, CCH3), 2.12 (s, 3H (N–CCH3), 25.3 (CH(CH3)2), 25.8 (C6H4–CH3), 26.5 (THF), 27.7
C6H4–CH3), 3.25 (THF), 3.70 (m, 4H, CH(CH3)2), 6.69–7.31 (m, (CH(CH3)2), 59.2 (OCH3, DME), 68.4 (THF), 71.0 (OCH2, DME),
Ar–H, Ph–H); 13C NMR (100.6 MHz, C6D6, 25 °C, TMS): δ = 14.4 118.9, 123.1, 125.8, 127.9, 128.1, 128.6, 129.5 (Al–CuC, Ar–C),
(N–CCH3), 21.1 (CH(CH3)2), 25.8 (C6H4–CH3), 24.8 (THF), 28.1 146.4 (N–CCH3), 149.2 (Al–Cu); IR (KBr, ν/cm−1): 2050, 1943,
(CH(CH3)2), 65.7 (THF), 119.1, 124.5, 127.7, 128.1, 129.0, 131.9, 1858, 1802, 1735, 1603, 1494, 1459, 1380, 1322, 1254,
137.7 (Ph–C, Ar–C), 143.8 (N–CCH3), 146.5 (Al–Cu); IR (KBr, 1122, 1080, 1034, 843, 729, 694; elemental analysis calcd (%)
ν/cm−1): 2128, 1943, 1858, 1803, 1736, 1604, 1461, 1380, 1319, for C46H76AlN2NaO3Si2·0.5C7H8 (857.30): C, 69.35; H, 9.41;
1252, 1178, 1079, 1033, 791, 728, 695; elemental analysis calcd N, 3.27. Found: C, 70.00; H, 9.46; N, 3.25.
(%) for C41H55AlN2O·0.5THF (654.90): C, 78.86; H, 9.08;
N, 4.28. Found: C, 78.62; H, 8.86; N, 4.28.
[L2−AlIII(CuCPh)2Na(THF)]2(µ-C7H8) (7). Complex
prepared by a similar procedure to that employed for 6b. Na
7 was
[Na(THF)2][L2−Al(CuCPh)2] (6a). Phenylacetylene (0.204 g, (0.046 g, 2.0 mmol) was added to a rigorously stirred solution
2.0 mmol) was added to a solution of [LAlCl(THF)] (2) containing the in situ prepared [LAlCl(THF)] (2) (1.0 mmol)
(1.0 mmol) in THF (30 mL) and the color changed from red to and phenylacetylene (0.204 g, 2.0 mmol) in toluene. X-ray
blue-green. After 2 hours, 2.0 equiv. of Na (0.046 g, 2.0 mmol) quality crystals of 7 were grown from a toluene solution cooled
was added and the solution was stirred for 6 days at ambient at −20 °C (0.337 g, 41%); IR (KBr, ν/cm−1): 2011, 1964, 1857,
temperature. Single crystals were obtained from a THF solu- 1802, 1640, 1572, 1465, 1381, 1256, 1209, 1156, 1105, 841, 788,
tion cooled to −20 °C (0.419 g, 48%). 1H NMR (400 MHz, C6D6, 728; elemental analysis calcd (%) for C48H58AlN2NaO·C7H8
25 °C, TMS): δ = 1.03 (d, 24H, J = 7.2 Hz, CH(CH3)2), 1.23 (821.1): C, 80.45; H, 8.10; N, 3.41. Found: C, 80.52; H, 7.65;
(THF), 1.89 (s, 6H, CCH3), 3.33 (THF), 3.96 (m, 4H, CH(CH3)2), N, 3.13.
6.14–7.29 (m, Ar–H, Ph–H); 13C NMR (100.6 MHz, C6D6, 25 °C,
[Na(C7H8)][(µ-Na)][LAl(CuCSi(Me)3)2]2 (8). Complex 8 was
TMS): δ = 15.3 (N–CCH3), 24.6 (CH(CH3)2), 29.9 (THF), 31.4 prepared by a similar procedure to that employed for 6c, from
(CH(CH3)2), 66.8 (THF), 123.6, 125.5, 127.8, 131.5, 132.2, 142.3 trimethylsilylacetylene (0.196 g, 2.0 mmol), [LAlCl(THF)] (2)
(Ph–C, Ar–C), 144.6 (N–CCH3), 147.4 (Al–Cu); IR (KBr, ν/cm−1): (1.0 mmol) in 30 mL of toluene, and the additional 2.0 equiv.
13678 | Dalton Trans., 2015, 44, 13671–13680
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of Na (0.046 g, 2.0 mmol). Single crystals were grown from a molecules in compounds 6a, 7 and 8, and the SQUEEZE
toluene solution at −20 °C (0.355 g, 48%); IR (KBr, ν/cm−1): command was employed in the refinement of their structures
2048, 1943, 1858, 1802, 1735, 1603, 1495, 1461, 1380, 1322, (one THF in 6a, 0.5 toluene in 7, and one toluene in 8). Crystal-
1254, 1179, 1081, 1036, 843, 730, 694; elemental analysis calcd lographic data and refinement details for complexes 1, 2 and
(%) for C83H124Al2N4Na2Si4·C7H8 (1482.38): C, 72.92; H, 8.98; 4–10 are given in Table S1.† CCDC 1054517 (1), 1054518 (2),
N, 3.78. Found: C, 72.83; H, 9.14; N, 3.31.
932639–932646 (4–9) and 1044207 (10) contain the crystallo-
[LAl(CuCPh)2Na]n (9). Complex 9 was prepared by a similar graphic data for the complexes reported in this work.
procedure to that employed for 7, from Na (0.046 g, 2.0 mmol),
Density functional theory (DFT) studies
[LAlCl(THF)] (2) (1.0 mmol), and phenylacetylene (0.204 g,
2.0 mmol) in n-hexane. Single crystals were grown from
n-hexane at −20 °C (0.374 g, 57%). IR (KBr, ν/cm−1): 2055,
1959, 1905, 1639, 1505, 1459, 1438, 1381, 1256, 1186, 1120,
1084, 1025, 817, 792, 734; elemental analysis calcd (%) for
C44H50AlN2Na (656.83): C, 80.46; H, 7.67; N, 4.26. Found:
C, 79.83; H, 7.64; N, 4.14.
[Na(Et2O)]2[{L(C(C4H9)vCH)}Al(CuC(C4H9))2]2 (10). Three
equiv. of 1-hexyne (0.246 g, 3.0 mmol) was added to a solution
of [LAlCl(THF)] (2) (1.0 mmol) in toluene (30 mL). The color of
the solution changed from red to blue-green. After 2 hours, 2
equiv. of Na (0.046 g, 2.0 mmol) was added and the solution
was stirred for 6 days at ambient temperature. The mixture was
filtered and the reddish filtrate was concentrated to about
5 mL and stored at ca. −20 °C to yield colorless crystals of
product 10 (0.546 g, 63%) after 1 week. 1H NMR (400 MHz,
C6D6, 25 °C, TMS): δ = 0.70 (t, 3H, CHvC(CH2)3CH3), 0.80 (t,
3H, CuC(CH2)3CH3), 0.87 (t, 3H, CuC(CH2)3CH3), 0.91 (2H,
CHvCCH2(CH2)2CH3), 0.95 (t, 6H, Et2O), 1.03–1.10 (m, 8H,
Structure optimization and NBO bonding analysis of com-
plexes 4–6, 8 and 10 have been performed using the B3LYP
method with the basis set 6-31G* by Gaussian 09 program.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21273170 and 21402151) and the Special
Science Research Foundation of Education Committee of
Shanxi Province (14JK1736).
Notes and references
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(CuCCH2(CH2)2CH3)2), 1.17–1.42 (m, 24H,
J = 7.2 Hz,
CH(CH3)2), 1.46 (m, 4H, CHvCCH2(CH2)2CH3)), 1.68 (m, 4H,
2(CuCCH2(CH2)2CH3)), 1.99 (s, 6H, CCH3), 2.27 (m, 1H,
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3.69 (m, 1H, CH(CH3)2), 4.04 (m, 1H, CH(CH3)2), 6.33 (s,
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(100.6 MHz, C6D6, 25 °C, TMS): δ = 13.8 (CuC(CH2)3CH3), 14.5
(N–CCH3), 15.3 (Et2O), 18.9–34.5 (CuC(CH2)3CH3), 25.2 (CH-
(CH3)2), 28.0 (CH(CH3)2), 29.4 (CH(CH3)2), 65.8 (Et2O), 122.9,
123.5, 122.3, 129.1, 137.7 (Ar–C), 124.0(AlCuC(CH2)3CH3),
125.5 (AlCHvC(CH2)3CH3), 138.2 (AlCHvC(CH2)3CH3), 145.8
(N–CCH3), 149.6 (Al–CuC(CH2)3CH3)); IR (KBr ν/cm−1): 3301,
1958, 1637, 1582, 1435, 1381, 1022, 904, 792, 750, 690, 530,
468, 402; elemental analysis calcd (%) for C100H156Al2N4-
Na2O2·2C7H8 (1730.50): C, 79.12; H, 10.02; N, 3.24. Found:
C, 79.03; H, 10.35; N, 3.65.
X-ray crystal structure determination
Diffraction data for complexes 1–10 (sealed in thin glass tubes)
were collected on a Bruker SMART APEX II diffractometer with
graphite-monochromated Mo Kα radiation (λ = 0.71073 Å).
An empirical absorption correction using SADABS was applied
for all data.30 The structures were solved by direct methods
using the SHELXS program.31 All non-hydrogen atoms were
refined anisotropically by full-matrix least squares on F2 by the
use of the program SHELXL.31 Hydrogen atoms bonded to
carbon were included at idealized geometric positions with
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