Cationic zirconium hydrides supported by an nnnn-type macrocyclic ligand: Synthesis, structure, and reactivity

Article abstract of DOI:10.1021/ic301880z

An air- and light-sensitive, but thermally stable tris[(trimethylsilyl) methyl]zirconium complex containing an NNNN-type macrocyclic ligand [Zr(Me ₃TACD)(CH₂SiMe₃)₃] (1; Me ₃TACD = Me₃[12]aneN₄: 1,4,7-trimethyl-1,4,7,10- tetraazacyclododecane) was prepared by reacting [Zr(CH₂SiMe ₃)₄] with (Me₃TACD)H. Reaction of the zirconium tris(alkyl) 1 with a Lewis or Bronsted acid gave a dialkyl cation with a weakly coordinating anion [Zr(Me₃TACD)(CH₂SiMe ₃)₂][A] [A = Al{OC(CF₃)₃} ₄ (2a), B{3,5-C₆H₃(CF₃) ₂}₄ (2b), B(3,5-C₆H₃Cl ₂)₄ (2c), and BPh₄) (2d)]. Hydrogenolysis of 2a-2c resulted in the formation of the dinuclear tetrahydride dication [{Zr(Me₃TACD)(μ-H)₂}₂][A]₂ (3a-3c). Compounds 1-3 were characterized by multinuclear NMR spectroscopy, and the solid-state structures of 1, 2c, and 3b were established by single-crystal X-ray diffraction studies. The dinuclear hydride complex 3b exhibits a quadruply bridged {Zr₂(μ-H)₄} core in solution and in the solid state with a relatively short Zr...Zr distance of 2.8752(11) . Density functional theory computations at the B3PW91 level reproduced this structure (Zr...Zr distance of 2.900 ). The cationic hydride complex 3b reacted with excess carbon monoxide in tetrahydrofuran at room temperature to give ethylene in 25% yield based on 3b. Upon analysis of ¹³C NMR spectra of the reaction mixture using ¹³CO, oxymethylene and enolate complexes were detected as intermediates among other complexes.

Full text of DOI:10.1021/ic301880z

Article
pubs.acs.org/IC
Cationic Zirconium Hydrides Supported by an NNNN-Type
Macrocyclic Ligand: Synthesis, Structure, and Reactivity
Heiko Kulinna,† Thomas P. Spaniol,† Laurent Maron,*,‡ and Jun Okuda*,†
†Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany
S
* Supporting Information
ABSTRACT: An air- and light-sensitive, but thermally stable tris[(trimethylsilyl)-
methyl]zirconium complex containing an NNNN-type macrocyclic ligand [Zr-
(Me3TACD)(CH2SiMe3)3] (1; Me3TACD = Me3[12]aneN4: 1,4,7-trimethyl-1,4,7,10-
tetraazacyclododecane) was prepared by reacting [Zr(CH2SiMe3)4] with (Me3TACD)H.
Reaction of the zirconium tris(alkyl) 1 with a Lewis or Brønsted acid gave a dialkyl cation
with a weakly coordinating anion [Zr(Me3TACD)(CH2SiMe3)2][A] [A = Al{OC-
(CF3)3}4 (2a), B{3,5-C6H3(CF3)2}4 (2b), B(3,5-C6H3Cl2)4 (2c), and BPh4) (2d)].
Hydrogenolysis of 2a−2c resulted in the formation of the dinuclear tetrahydride dication
[{Zr(Me3TACD)(μ-H)2}2][A]2 (3a−3c). Compounds 1−3 were characterized by multinuclear NMR spectroscopy, and the
solid-state structures of 1, 2c, and 3b were established by single-crystal X-ray diffraction studies. The dinuclear hydride complex
3b exhibits a quadruply bridged {Zr2(μ-H)4} core in solution and in the solid state with a relatively short Zr···Zr distance of
2.8752(11) Å. Density functional theory computations at the B3PW91 level reproduced this structure (Zr···Zr distance of 2.900
Å). The cationic hydride complex 3b reacted with excess carbon monoxide in tetrahydrofuran at room temperature to give
ethylene in 25% yield based on 3b. Upon analysis of 13C NMR spectra of the reaction mixture using 13CO, oxymethylene and
enolate complexes were detected as intermediates among other complexes.
Chart 1. Group 4 Metal Complexes with Quadruple Hydride
Bridges
INTRODUCTION
■
The first molecular hydride complex of zirconium was reported
in 1970 by Wailes and Weigold.1 Since then, metallocene
hydride complexes [Zr(η5-C5H4R)2H(μ-H)]2 with R = CH3,2
C(CH3)3,3 and Si(CH3)3 have been intensely studied,
4
including the “latent hydrides” tetrahydridoborate5 and
hydridoaluminate6 complexes. In particular, decamethylzirco-
nocene dihydride [Zr(η5-C5Me5)2H2] introduced by Bercaw et
al. played a pioneering role in elucidating the reactivity patterns
of molecular early-transition-metal hydrides.7 Although cationic
group 4 complexes are thought to be the active species in
homogeneous olefin polymerization and hydrogenation catal-
ysis, only a few cationic hydride complexes, in particular those
without cyclopentadienyl ligands, have been structurally
authenticated so far.5a−c,8−10 Apart from complexes with
terminal8 as well as with a single and a double hydride
bridge,2−4,5a,c,d,8b,9 a number of triply bridged hydride
complexes with a variety of noncyclopentadienyl ancillary
ligands are known.5a,d,10 While only recently has a cationic
triply bridged hydride complex been reported,10b examples of
dinuclear complexes with quadruply bridged hydrides [{Zr{(μ-
H)2BH2}2(PMe3)2}2(μ-H)4]5b and [{(P2N2)M}2(μ-H)4] [P2N2
= PhP(CH2SiMe2NSiMe2CH2)2PPh); M = Zr, Hf] are limited
so far to neutral species (Chart 1).11
stabilize a series of Lewis base-free rare-earth metal alkyl and
hydride compounds12a,c,d as well as some alkaline-earth metal
compounds.12b,e,f We hypothesized that Me3TACD would also
be a suitable ligand to support cationic zirconium alkyl and
hydride fragments. The cationic charge and the absence of
bulky electron-rich cyclopentadienyl ancillary ligands were
surmised to increase the electrophilicity and thus reactivity of
the zirconium hydride.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of [Zr(Me3TACD)-
(CH2SiMe3)3] (1) and [Zr(Me3TACD)(CH2SiMe3)2][A] (2a−
2d). The solvent-free tris[(trimethylsilyl)methyl] complex 1
We report here on the first example of cationic zirconium
complexes with quadruple hydride bridges that are supported
by the monoanionic NNNN-type macrocyclic ligand,
(Me3TACD)− derived from 1,4,7-trimethyl-1,4,7,10-tetraazacy-
clododecane (Me3TACD)H (Me3[12]aneN4).12 This L3+1X-
type or 10-electron-donor ligand has previously been used to
Received: August 28, 2012
Published: October 31, 2012
© 2012 American Chemical Society
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was prepared by reacting thermally stable and air-, moisture-,
and light-sensitive [Zr(CH2SiMe3)4]13 with (Me3TACD)H
(Scheme 1) and isolated as a thermally stable but still air-,
moisture-, and light-sensitive compound. 1 was characterized by
NMR spectroscopy and single-crystal X-ray diffraction.
assigned to the axial and equatorial protons and can be
explained by a slow exchange process between the two
macrocyclic λδδδ and δλλλ ring conformations on the NMR
time scale.12a,d Lowering the temperature to −80 °C results in
the broadening of all resonances.
Single crystals suitable for X-ray diffraction studies were
obtained by the slow evaporation of a saturated cyclohexane
solution at room temperature. The coordination geometry
around the seven-coordinate zirconium atom can be described
as capped trigonal prismatic (Figure 2). Three carbon atoms
(C12, C16, and C20) and three nitrogen atoms (N1, N3, and
N4) constitute two faces of the prism, and N2 caps one side.
The Zr1−C distances are similar [Zr1−C12 = 2.3230(15) Å,
Zr1−C16 = 2.2995(14) Å, and Zr1−C20 = 2.3680(15) Å] and
in the expected range of Zr−C bonds [2.215(9)−2.640(5)
Å].14 The Zr1−N1 distance [2.1224(13) Å] is significantly
shorter than the zirconium−amino distances [Zr1−N2 =
2.6639(13) Å, Zr1−N3 = 2.5628(13) Å, and Zr1−N4 =
2.6335(14) Å]. Both are in the expected range of the
corresponding Zr−N distances [2.063−2.192 Å for Zr−
N(amido)15b−d,16 and 2.414−2.977 Å for Zr−N(amine)15]
for polydentate ligands with amine and amido donors. The
Me3TACD ligand is distorted due to the sp2-hybridized amido
nitrogen atom (sum of the C−N1−C and C−N1−Zr1 angles:
359.7°), resulting in a coplanar orientation of the five atoms
a
Scheme 1. Synthesis of 1 and 2a−2d from [Zr(CH2SiMe3)4]
and (Me3TACD)H
a
[Zr(Me3TACD)(CH2SiMe3)2][A], where A = Al{OC(CF3)3}4 (2a),
B{3,5-C6H3(CF3)2}4 (2b), B(3,5-C6H3Cl2)4 (2c), and BPh4 (2d).
[C−C−N(sp2)−C−C] around the amido nitrogen atom.12a,b
17
The 1H NMR spectrum of 1 in a benzene-d6 solution shows
Cs symmetry. Broad resonances for the CH2CH2 groups at
ambient temperature indicate fluxional behavior, which was
studied by variable-temperature 1H NMR spectroscopy in
toluene-d8 (Figure 1). Between −40 and −60 °C, four sharp as
well as two broad resonances for the CH2CH2 groups of
Me3TACD are observed. The four sharp resonances can be
Calculating the available cavity radii [r(H)cavity
]
from the
distances determined crystallographically gives the same size as
that in the hydrochloride salt [(Me3TACD)H]Cl [r(H)cavity
=
1.244 Å].12c The size of the macrocyclic ligand cavity forces the
metal to sit below the macrocyclic ligand. The distance between
Zr1 and the mean plane formed by the nitrogen atoms N1−N4
is 1.4926(7) Å.
Figure 1. Variable-temperature 1H NMR spectra of 1 in toluene-d8: resonances for CH2CH2 protons (*) split into resonances of the axial (×) and
equatorial protons (+); resonances for the methyl groups (#) of Me3TACD; the methyl (§) and CH2 groups ($) of the (trimethylsilyl)methyl
groups.
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(2c), BPh4 (2d); Scheme 1). With the exception of 2d, these
complexes are soluble in polar, aprotic solvents such as
dichloromethane (DCM), 1,2-difluorobenzene, 1,2-dichloro-
benzene, and tetrahydrofuran (THF) but not in hydrocarbons.
2d is only slightly soluble in DCM and THF.
1
The H NMR spectra of the cations show Cs symmetry in
CD2Cl2. The resonances of the CH2CH2 groups of the ligand at
ambient temperature are sharp and allow for discrimination
between the axial and equatorial protons. This indicates a rigid
conformation in solution and a stronger interaction of the
Me3TACD ligand with the metal center than in the neutral
complex 1.
Single crystals of 2c suitable for single-crystal X-ray
diffraction experiments were obtained by diffusion of pentane
into a 1,2-difluorobenzene solution. The crystal structure of 2c
contains disordered ligands within the complex cation. This
disorder was modeled with split positions for each carbon and
nitrogen atom. The occupancy factors for all atoms involved
were close to 0.5. Attempted refinement with anisotropic
displacement parameters led to physically meaningless values,
but these atoms could be refined with isotropic displacement
parameters. Because of disorder in the crystal associated with
low values for Rint and Rσ as well as poor refinement parameters
(Table 1), details on interatomic distances and angles in 2c are
not discussed. 2c crystallizes as a separated ion pair without any
close interaction or coordination of the counterion with the
cationic zirconium center (see the Supporting Information,
SI).18 The zirconium atom in 2c is six-coordinate, bonded to
two carbon atoms and four nitrogen atoms (Figure 3). The
coordination geometry around the metal center can be
described as a distorted trigonal prism. Two nitrogen atoms
and one carbon atom (N1A, N2A, C12A and N3A, N4A,
Figure 2. ORTEP drawing of the molecular structure of 1.
Displacement ellipsoids are drawn at the 50% probability level;
hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and
angles [deg]: Zr1−N1 2.1224(13), Zr1−N2 2.6639(13), Zr1−N3
2.5628(13), Zr1−N4 2.6335(14), N4‑plane···Zr1 1.4926(7), Zr1−C12
2.3230(15), Zr1−C16 2.2995(14), Zr1−C20 2.3680(15); N1−Zr1−
N3 86.12(5), N2−Zr1−N4 120.49(4). r(H)cavity = 1.244 Å; Σ(C−
N1−C/Zr1) = 359.7°.
One of the (trimethylsilyl)methyl groups in 1 can be
abstracted with either [Ph3C][A] or [H(OEt2)2][A] (A =
Al{OC(CF3)3}4, B{3,5-C6H3(CF3)2}4, B(3,5-C6H3Cl2)4, and
BPh4) to give [Zr(Me3TACD)(CH2SiMe3)2][A] (A = Al{OC-
(CF3)3}4 (2a), B{3,5-C6H3(CF3)2}4 (2b), B(3,5-C6H3Cl2)4
a,b
Table 1. Crystallographic and Refinement Data for 1, 2c, 3b, and 4b
1
2c
3b
4b
formula
fw, g/mol
cryst size, mm
cryst syst
space group
T, K
C23H58N4Si3
566.22
C19H47N4Si2Zr·C24H12BCl8
1073.75
C22H54N8Zr2·2C32H12BF24
2339.62
C26H62N8SiZr2·2C32H12BF24·C6H12·C6H4F2
2622.07
0.25 × 0.30 × 0.36
monoclinic
C2/c
0.06 × 0.08 × 0.33
tetragonal
0.01 × 0.03 × 0.35
triclinic
0.15 × 0.28 × 0.32
monoclinic
P 21/c
I 41cd
P1
̅
100
130
100
100
a, Å
12.1670(9)
17.0955(13)
30.775(13)
24.293(2)
13.658(3)
17.059(4)
20.564(3)
94.157(4)
90.002(4)
95.107(5)
4759.6(18)
2
24.6582(17)
18.4059(13)
25.2129(18)
b, Å
c, Å
34.827(3)
α, deg
β, deg
γ, deg
92.2364(11)
106.717(2)
U, Å3
6399.7(8)
8
20553(3)
16
10959.4(13)
4
Z
D
calcd, mg/m3
1.175
1.388
1.633
1.589
F(000)
2448
8864
2344
5296
θ range, deg
1.3−30.8
46831
1.7−24.7
78510
1.0−26.4
56956
0.9−26.4
132363
refns collected
indep reflns (Rint)
reflns obsd [I > 2σ(I)]
data/restraints/params
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
GOF on F2
9432 (0.0550)
8262
8772 (0.1540)
5226
19473 (0.1174)
10385
22449 (0.0997)
13335
9432/0/292
0.0333, 0.0805
0.0390, 0.0869
1.075
8772/114/521
0.0740, 0.1670
0.1179, 0.1875
0.921
19473/0/1333
0.0905, 0.2187
0.1651, 0.2650
1.038
22449/41/1598
0.0730, 0.1972
0.1221, 0.2297
0.995
Δρmax, Δρmin, e/Å3
0.722, −0.542
0.564, −0.329
2.188, −1.326
2.356, −1.072
a
b
2
2
R1 = ∑||Fo| − |Fc||/∑|Fo|. wR2 = {∑w(Fo − Fc2)2/∑w(Fo )2}1/2
.
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2b and fully characterized (see the SI). Isolated 4b was slowly
converted to the tetrahydride 3b over a period of 7 days.
Formation of a similar dinuclear μ-benzylidene dihydride
complex [{2,6-CH2 -4-MeC6 H2 OMe(2-t Bu-4-Me-
C6H2O)}2Zr2(μ-H)2(μ-CHPh)] with a bis(phenolate) ancillary
ligand was reported to form upon hydrogenolysis of the
dibenzyl complex [{2,6-CH2-4-MeC6H2OMe(2-tBu-4-
MeC6H2O)}Zr(CH2Ph)2].9t
In the 1H NMR spectra of 3a−3c, the hydrides are observed
as three triplets between δ 6.00 and 6.60 ppm with an integral
ratio of 1:2:1. These three triplets, each with a different
coupling constant (6.56 ppm, 1JHH = 16.6 Hz; 6.30 ppm, 1JHH
=
1
14.7 Hz; 5.98 ppm, JHH = 13.0 Hz), are explained by two
Me3TACD ligands, which are orthogonal to each other in a
dimeric structure (Figure 4). A NOESY experiment shows the
close vicinity of the hydrides to each other and to the methyl
groups of the macrocycle. The chemical shift difference of Δδ =
0.6 ppm between the hydride resonances is small compared to
that of complexes bearing a {ZrH(μ-H)}2 core such as [{Zr(η5-
4
C5H4R)2H(μ-H)}2] [R = CH3,2 C(CH3)3,3 and Si(CH3)3 , and
related complexes.9h,i], where a Δδ(Hterm.,Hbrid.) value between
6.73 and 9.35 ppm is observed. With a decrease in the
temperature to −40 °C, the hydride resonances are broadened
(Figure 5). Above +40 °C, these resonances also become broad,
but three different resonances can still be resolved. All four
hydrides are exchanged against deuterium by treating 3c with
D2 (1 bar) in a THF solution over a period of 48 h. A 1:1
mixture of 3b and the tetradeuteride 3b[D4] does not give any
scrambled products after 14 days at room temperature,
suggesting the high stability of the dimeric structure in solution.
Single crystals of 3b suitable for X-ray diffraction were
obtained directly by treating a solution of 2b in 1,2-
dichlorobenzene with dihydrogen (50 bar). The molecular
structure of 3b was determined by single-crystal X-ray
diffraction analysis (Figure 6). The data set is not good enough
to draw closer conclusions about the hydride positions as
reflected by the Rint value of 0.1174 as well as by the values for
R1 and wR2 (Table 1). The Zr···Zr distance of 2.8752(11) Å is
significantly shorter than that in other zirconium complexes
with bridging hydrides (Figure 7). This compound represents a
rare example for a compound with a {Zr(μ-H)4Zr} core in the
solid state.5b,9s The two macrocyclic ligands are coplanar and
twisted with respect to each other, as expressed by the N1−
Zr1−Zr2−N5 torsion angle of 87.3(4)°, and the nitrogen
atoms are nearly eclipsed. The distance of the four nitrogen
atoms to the zirconium [N4‑plane···Zr = 1.181(3) and 1.200(3)
Å] and the large angles of N1−Zr1−N3 and N5−Z2−N7
[98.5(2)° and 97.0(2)°] are comparable to those in 2c.
The bonding in 3b was investigated using density functional
theory (DFT) methods with focus on the nature of the
hydrides and the Zr···Zr interaction. Geometry optimization of
3b was carried out at the DFT(B3PW91) level. All geometrical
parameters agree well with the structure that was found in the
solid state. In particular, the experimental Zr···Zr distance of
2.8752(11) Å was reproduced with 2.899 Å within 0.024 Å, and
the Zr−N1(amido) distances agree with a maximum deviation
of 0.03 Å. This indicates that this method is suitable for
describing cationic zirconium complexes. All attempts to locate
structures with terminal hydrides failed, and only the structure
with four bridging hydrides was obtained. Notably, the Wiberg
indices (0.89) suggest a significant interaction between the two
zirconium atoms. This interaction is also found at the natural
bond order (NBO) level. The Lewis structure may be written
Figure 3. Ball-and-stick drawing of the molecular structure of the
cationic part of 2c. Only one of the split positions for the carbon and
nitrogen atoms of the disordered ligands are shown. The counterion
and hydrogen atoms are omitted for clarity.
C16A) constitute one face of the prism. The Me3TACD ligand
coordinates as in 1. The structure can be compared to the
isoelectronic, neutral rare-earth metal complexes of this
macrocyclic ligand [M(Me3TACD)(CH2SiMe3)2] (M = Sc,
Y, Lu).12a,d
Synthesis and Characterization of [{Zr(Me3TACD)(μ-
H)2}2][A]2 (3a−3c). When the bis[(trimethylsilyl)methyl]
complexes 2a−2c were treated with 50 bar of dihydrogen in
THF or 1,2-dichlorobenzene at room temperature, the
formation of the hydride complexes 3a−3c were observed
with concomitant formation of SiMe4 (Scheme 2). When high
a
Scheme 2. Synthesis of 3a−3c from 2a−2c
a
A = Al{OC(CF3)3}4 (a), B{3,5-C6H3(CF3)2}4 (b), and B(3,5-
C6H3Cl2)4) (c).
pressure (50 bar) was applied to a solution of 2a−2c, both
(trimethylsilyl)methyl groups were cleaved at room temper-
ature within 24 h and the dinuclear complexes 3a−3c were
obtained in good yield. 1H NMR spectroscopy shows that 3a−
3c are stable in a THF solution for several months at room
temperature.
When a lower hydrogen pressure (≈1 bar) was applied to a
THF solution of 2a−2c, complete conversion to give 3a−3c
took several days. Under these conditions, the dinuclear μ-
alkylidene dihydride [(Me3TACD)Zr(μ-CHSiMe3)(μ-H)2Zr-
(Me3TACD)][B{3,5-C6H3(CF3)2}4]2 (4b) was formed from
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1
○
Figure 4. H NMR spectrum of 3b in THF-d8 at 25 °C: ZrH (§), dihydrogen ( ), CH2CH2 (×), methyl groups (+) of the Me3TACD ligand, B{3,5-
C6H3(CF3)2}4 (#), THF-d8 ($), traces of 1,2-C6H4Cl2 (*), and impurities (&).
1
Figure 5. Variable-temperature H NMR spectra of 3a in THF-d8. The hydride region between +50 and −80 °C is shown.
with four three-center Zr−H−Zr bonds involving bridging
5b in THF-d8 at ambient temperature shows a sharp singlet for
the bridging hydrides at δ 5.28 ppm. As in 2b, the resonances of
the Me3TACD ligand indicate Cs symmetry and a rigid
geometry in solution. The isopropyl groups appear as a septet
and a doublet at δ 4.44 and 1.26 ppm (3JHH = 6.3 Hz). 6b was
2
hydrogen atoms. Thereby, the dz orbital of each zirconium is
partially filled (0.5 electron each), allowing some d−d
interactions to be in agreement with the second-order NBO
analysis. The stabilizing interaction of more than 40 kcal/mol
seems to be crucial for the stability of this dinuclear complex.
Similar interactions between two metals were reported in other
transition-metal complexes, in particular d8···d8 interactions.20
To the best of our knowledge, the compound presented here is
the first example with this interaction between two d0 metal
centers.
1
also obtained from 2b and excess isopropyl alcohol. The H
NMR spectrum of 6b shows broad resonances for the
Me3TACD ligand. The isopropyl groups appear as a septet
and a doublet at δ 4.69 and 1.27 ppm (3JHH = 6.3 Hz). The
methyl groups of the Me3TACD ligand appear at δ 2.70 (s, 3H)
and 2.60 (s, 6H) ppm. Analogous reactions of the deuteride
3b[D4] with acetone confirmed the formation of 5b[D4] and
6b[D2].
Reactivity of 3a−3c toward Acetone and Carbon
Monoxide (CO). According to 1H NMR spectroscopic studies
in THF-d8, 2 equiv of acetone reacted with 3b in THF at room
temperature to form a dimeric isopropoxy hydride 5b. This
complex slowly reacted with more acetone to give 6b. Although
we do not know the nuclearity of both 5b and 6b, plausible
In the past, the reactivity of organometallic hydride
complexes toward CO has been intensely studied in the
context of model reactions for Fischer−Tropsch synthesis.
Late-transition-metal hydrides react with CO to give formyl
species MC(O)H,21 whereas early transition metals includ-
1
structures are shown in Scheme 3. The H NMR spectrum of
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Figure 6. ORTEP drawings of the molecular structure of the cationic part of 3b: (left) side view; (right) top view. Displacement ellipsoids are drawn
at the 50% probability level; the counterions and hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [deg]: Zr1−Zr2
2.8752(11), Zr1−N1 2.109(7), Zr1−N2 2.373(7), Zr1−N3 2.287(6), Zr1−N4 2.382(7), Zr2−N5 2.063(6), Zr2−N6 2.394(6), Zr2−N7 2.350(6),
Zr2−N8 2.369(6), N4‑plane2−Zr2 1.200(3), N4‑plane1−Zr1 1.181(3); N1−Zr1−N3 98.5(2), N5−Zr2−N7 97.0(2); N1−Zr1−Zr2−N5 87.3(4). Σ(C−
N1−C/Zr1) = 358.4°; Σ(C−N5−C/Zr2) = 359.2°.
ing lanthanide and actinide hydrides form more reduced
fragments such as oxymethylenes MOCH2M9e,22 and enedio-
lates MOCHCHOM.22a,23−26 A trimeric (η2-formaldehyde)-
zirconocene complex formed when zirconocene dihydride
[Cp2ZrH2]x was treated with CO.22b More recently,
tetranuclear yttrium dihydride [{Cp′Y(μ-H)2}4(THF)] (Cp′
= C5Me4SiMe3) was reported to react with CO to give ethylene
via oxymethylene, enolate, and oxo hydride intermediates.26
Upon treatment of 3b with excess CO at room temperature,
ethylene (1H NMR, δ 5.36; 13C{1H} NMR, δ 123.4) was
detected as the sole volatile product (0.25 equiv of ethylene per
1
3b). Monitoring this reaction by H and 13C NMR spectros-
copy using either CO or 13CO in THF-d8 at room temperature
suggests the formation of ethylene via an oxymethylene22b and
an enolate24−26 intermediate (Scheme 4). Although the
reaction mixture contained several other species (see the SI),
resonances in the 1H and 13C NMR spectra were observed that
could be assigned to the oxymethylene 7b and an enolate
Figure 7. Plot of Zr···Zr distances against the number of bridging
hydride complex 8b. The oxymethylene intermediate 7b shows
hydrides in dinuclear zirconium hydride complexes.19
a diagnostic triplet in the 13C NMR spectrum at δ 79.3 (t, 1JCH
= 138.7 Hz), and its concentration is at a maximum after 30
Scheme 3. Reactions of 3b with Acetone in THF-d8
min. The NMR resonances of the enolate hydride 8b [1H
NMR, δ 6.75 (dd, 3JHH = 13.9 Hz, 3JHH = 5.8 Hz), 4.31 (d, 3JHH
3
= 13.9 Hz), and 4.14 (d, JHH = 5.8 Hz); 13C{1H} NMR, δ
1
1
153.5 (d, JCC = 78.3 Hz), 95.4 (d, JCC = 78.3 Hz)] are
comparable with those reported for other enolate complexes
such as [(η5-C5Me5)2ZrH(OCHCH2)],24 [(η5-C5H5)2Y-
(OCHCH2)],25 and [(Cp′Y)4(OCHCH2)(μ-O)(μ-
H)5(THF)] (Cp′ = η5-C5Me4SiMe3).26 Apparently, 8b formed
from 7b to give ethylene eventually in a reaction sequence
similar to that established for [(Cp′Y)4(μ-H)8(THF)].26b All
attempts at isolating any of these intermediates or the final oxo
complex 9b in pure form remained unsuccessful.
CONCLUSION
■
Hydrogenolysis of a cationic zirconium dialkyl complex
supported by the macrocyclic ancillary ligand Me3TACD led
to the dicationic dinuclear tetrahydride complex with a {Zr2(μ-
H)4} core featuring a short Zr···Zr distance. The dicationic
tetrahydride reacted with CO to give ethylene, albeit in low
yield. The absence of bulky electron-rich cyclopentadienyl
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27Al, 104.3 MHz). 19F NMR spectra were recorded on a Varian
Mercury NMR spectrometer (19F, 188.1 MHz) or on a Bruker Avance
II spectrometer (19F, 376.5 MHz). Chemical shifts for 1H and 13C{1H}
NMR spectra were referenced internally using the residual solvent
resonances and reported relative to tetramethylsilane. 11B, 19F, and
27Al NMR spectra are referenced externally to a 1 M solution of
NaBH4 in D2O, neat CFCl3, and aqueous Al(NO3)3 solutions,
respectively. Elemental analyses were performed by the microanalytical
laboratory of this department. The analytical data for most complexes
were consistently too low in carbon. This is likely due to metal carbide
formation during combustion, and this phenomenon has been
observed by other workers for related zirconium complexes.15a,16a,35,36
The best values are reported.
Scheme 4. Suggested Formation of Ethylene from CO and
3b
[Zr(Me3TACD)(CH2SiMe3)3] (1). A solution of (Me3TACD)H (700
mg, 3.27 mmol) in 30 mL of pentane was added at −78 °C to a
solution of tetrakis[(trimethylsilyl)methyl]zirconium (1.440 mg, 3.27
mmol) in 30 mL of pentane. The mixture was allowed to warm up and
stirred for 12 h at room temperature. The product was filtered at −78
°C and washed three times with 10 mL of pentane. The crude product
was recrystallized from pentane at −30 °C to afford colorless, light-
sensitive microcrystals; yield 1.027 g (1.81 mmol, 55%). Single crystals
suitable for X-ray diffraction studies were obtained by recrystallization
from a cyclohexane solution.
1H NMR (benzene-d6): δ 3.26 (br s, 2H, NCH2), 2.87 (br s, 2H,
NCH2), 2.75 (br s, 2H, NCH2), 2.14 (s, 6H, NCH3), 1.98 (br s, 5H,
NCH2), 1.80 (br s, 5H, NCH2), 1.80 (s, 3H, NCH3), 0.44 (s, 27H,
SiCH3), 0.38 (s, 6H, ZrCH2). 13C{1H} NMR (benzene-d6): δ 58.16
(br s, NCH2), 57.95 (s, NCH3), 53.31 (br s, NCH2), 52.63 (s,
ZrCH2), 49.24 (br s, NCH2), 45.75 (s, NCH3), 4.46 (s, SiCH3). Anal.
Calcd for C23H58N4Si3Zr: C, 48.79; H, 10.32; N, 9.89. Found: C,
46.89; H, 9.85; N, 9.88.
[Zr(Me3TACD)(CH2SiMe3)2][Al{OC(CF3)3}4] (2a). A solution of
[Ph3C][Al{OC(CF3)3}4] (500 mg, 413.0 μmol) in 10 mL of DCM
was added to 1 (240.0 mg, 423.9 μmol) in 20 mL of DCM and the
reaction mixture stirred for 1 h at room temperature. After removal of
all volatiles under vacuum, the residue was suspended in pentane,
filtered through a pad of glass fiber, and washed with pentane (3 × 25
mL). After drying, an off-white solid was obtained; yield 440.0 mg
(304.3 μmol, 74%).
ligands combined with the cationic charge significantly
enhances the reactivity toward CO, comparable with that
recently reported for rare-earth metal hydride complexes.25,26
Although the insertion reaction of CO into neutral zirconium
hydride complexes has been studied intensely in the past,22−24
the reduction of CO to give ethylene has not been reported
before, to the best of our knowledge. The reduction of CO to
give ethylene is limited to the reaction of CO with [{Cp′Y(μ-
H)2}4(THF)],26 alane (AlH3) reduction of coordinated CO in
[M(CO)n] (M = Cr, Mo, W, Ru),27 and CO hydrogenation on
the surface of ZrO2/Al2O3.28
1H NMR (CD2Cl2): δ 3.69 (td, 3JHH = 12.2 Hz, 3JHH = 6.3 Hz, 2H,
NCH2), 3.40 (dd, 3JHH = 13.9 Hz, 3JHH = 6.2 Hz, 2H, NCH2), 3.30 (m,
3
3
2H, NCH2), 3.20 (m, 4H, NCH2), 3.08 (dd, JHH = 12.8 Hz, JHH
=
5.2 Hz, 2H), 2.88 (s, 6H, NCH3), 2.79 (m, 6H, NCH2), 2.66 (s, 3H,
NCH3), 0.74 (s, 4H, ZrCH2), 0.08 (s, 18H, SiMe3). 13C{1H} NMR
(CD2Cl2): δ 121.7 (q, 1JCF = 292.3 Hz, CF3), 63.5 (s, ZrCH2), 61.5 (s,
NCH2), 56.0 (s, NCH2), 54.3 (s, NCH2), 52.5 (s, NCH2), 51.1 (s,
NCH3), 46.2 (s, NCH3), 3.0 (s, SiMe3). 13C NMR (101 MHz,
CD2Cl2): δ 63.5 (t, 1JCH = 104.0 Hz, ZrCH2). 27Al NMR (CD2Cl2): δ
−34.7. 19F NMR (188.1 MHz, CD2Cl2): δ −73.8. Anal. Calcd for
C35H47AlF36N4O4Si2Zr: C, 29.07; H, 3.28; N, 3.87. Found: C, 28.74;
H, 2.91; N, 4.19.
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed under an
inert atmosphere of argon using a standard Schlenk-line or glovebox
technique but in the dark by covering all glass vessels with aluminum
foil. Hydrogenolysis reactions were performed in a Parr steel reactor
(series 4700) with 50 bar pressure or in J. Young NMR tubes equipped
with a Teflon valve with a maximum pressure of 1 bar. n-Pentane,
tetrahydrofuran (THF), diethyl ether, and dichloromethane (DCM)
were dried using a MBraun SPS-800 solvent purification system.
Benzene-d6 and THF-d8 were distilled from sodium/benzophenone
ketyl. CD2Cl2 and 1,2-C6D4Cl2 as well as the nondeuterated solvents
1,2-difluorobenzene and 1,2-dichlorobenzene were distilled from
CaH2. Acetone was distilled several times from molecular sieves (4
Å). (Me3TACD)H,12c [Zr(CH2SiMe3)4],13 [Ph3C][OTf],29 [Ph3C]-
[B{3,5-C6H3(CF3)2}4],30 [Ph3C][Al{OC(CF3)3}4],31 [Ph3C]-
[BPh4],32 [H(OEt2)2][B{3,5-C6H3(CF3)2}4],33 and Na[B(3,5-
C6H3Cl2)4]34 were synthesized according to literature procedures.
[Ph3C][B(3,5-C6H3Cl2)4] and [H(OEt2)2][B(3,5-C6H3Cl2)4] were
prepared analogously to related compounds.30,33
[Zr(Me3TACD)(CH2SiMe3)2][B{3,5-C6H3(CF3)2}4] (2b). A solution of
trityl tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (1.940 g 1.75
mmol) in 25 mL of DCM was slowly added to a solution of 1
(1.000 g, 1.77 mmol) in 25 mL of DCM. The reaction mixture was
stirred for 3 h at room temperature. After removal of all volatiles under
vacuum, the solid residue was suspended in 80 mL of pentane, filtered
through a pad of glass fiber, washed with pentane, and dried under
reduced pressure for 24 h to give an off-white powder; yield 2.075 g
(1.55 mmol, 87.5%). Alternatively, [H(OEt2)2][B{3,5-C6H3(CF3)2}4]
in CD2Cl2 was used to generate 2b.
1H NMR (CD2Cl2): δ 7.73 (br t, 4JHF = 2.4 Hz, 8H, BPh-2), 7.58 (s,
4H, BPh-4), 3.67 (td, 3JHH = 12.2 Hz, 3JHH = 6.4 Hz, 2H, NCH2), 3.38
(dd, 3JHH = 14.0 Hz, 3JHH = 6.3 Hz, 2H, NCH2), 3.21 (m, 4H, NCH2),
3
3
3.05 (dd, JHH = 12.7 Hz, JHH = 5.2 Hz, 2H, NCH2), 2.86 (s, 6H,
NCH3), 2.75 (m, 6H, NCH2), 2.63 (s, 3H, NCH3), 0.73 (s, 4H,
ZrCH2), 0.08 (s, 18H, SiCH3). 13C{1H} NMR (CD2Cl2): δ 162.2 (q,
1JBC = 50.0 Hz, BPh-1), 135.3 (s, BPh-2), 129.3 (m, BPh-3), 125.1 (q,
1JCF = 273.8 Hz, CF3), 117.9 (m, BPh-4), 63.6 (s, ZrCH2), 61.5 (s,
NMR spectra were recorded on a Bruker Avance II spectrometer at
25 °C (1H, 400.1 MHz; 13C{1H}, 100.1 MHz; 11B{1H}, 128.4 MHz;
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NCH2), 56.0 (s, NCH2), 54.3 (s, NCH2), 52.5 (s, NCH2), 51.1 (s,
NCH3), 46.2 (s, NCH3), 3.0 (s, SiMe3). 11B NMR (CD2Cl2): δ −6.60
(s). 19F NMR (188 MHz, CD2Cl2): δ −60.91 (s). Anal. Calcd for
C51H59BF24N4Si2Zr: C, 45.64; H, 4.43; N, 4.17. Found: C, 43.25; H,
3.64; N, 4.35.
[{Zr(Me3TACD)(μ-H)2}2][B{3,5-C6H3(CF3)2}4]2 (3b). A solution of 2b
(1.000 g, 745 μmol) in 3 mL of THF was treated with 50 bar of
hydrogen in a microreactor for 24 h. The solution was filtered,
carefully dried (p ∼ 1 × 10−1 mbar), and washed with pentane to give
a yellow oil. The addition of 2 mL of benzene led to precipitation of a
yellow solid, which was washed with pentane and dried briefly to give
yellow microcrystals; yield 650 mg (262 μmol, 70%). Alternative
method: A solution of 2b (600 mg, 447 μmol) in 3 mL of 1,2-
dichlorobenzene was treated with 50 bar of hydrogen in a microreactor
for 24 h. A total of 5 mL of pentane was added to the reaction mixture.
The solvent was decanted, and the yellow residue was dried under an
argon atmosphere in the glovebox to afford a yellow powder; yield
499.7 mg (213.6 μmol, 96%).
[Zr(Me3TACD)(CH2SiMe3)2][B(3,5-C6H3Cl2)4] (2c). A solution of
trityl tetrakis(3,5-dichlorophenyl)borate (1.470 g 1.75 mmol) in 25
mL of DCM was slowly added to a solution of 1 (1.000 g 1.77 mmol)
in 25 mL of DCM. The reaction mixture was stirred at room
temperature for 3 h. All volatiles were removed under reduced
pressure, and the resulting solid residue was suspended in pentane,
filtered, and washed with pentane (3 × 40 mL). The crude product
was dried under reduced pressure for 72 h to remove traces of
pentane. An off-white powder was obtained; yield 1.660 g (1.55 mmol,
87.6%). Single crystals suitable for X-ray analysis were obtained by
diffusion of pentane into a 1,2-difluorobenzene solution of the
compound.
1H NMR (THF-d8): δ 7.80 (br t, 4JHF = 2.5 Hz, 16H, BPh-2), 7.59
1
1
(br s, 8H, BPh-4), 6.56 (t, JHH = 16.6 Hz, 1H, ZrH), 6.31 (t, JHH
=
1
14.5 Hz, 2H, ZrH), 5.99 (t, JHH = 13.1 Hz, 1H, ZrH), 3.66 (m, 8H,
NCH2), 3.38 (m, 6H, NCH2), 3.15 (m, 12H, NCH2), 3.06 (s, 6H,
NCH3), 2.98 (s, 6H, NCH3), 2.88 (s, 6H, NCH3), 2.76 (m, 6H,
NCH2). 13C{1H} NMR (THF-d8): δ 162.9 (q, 1JBC = 49.9 Hz, BPh-1),
1H NMR (CD2Cl2): δ 7.04 (m, 8H, BPh-2), 7.02 (m, 4H, BPh-4),
3.60 (td, 3JHH = 12.3 Hz, 3JHH = 6.3 Hz, 2H, NCH2), 3.32 (dd, 3JHH
=
3
2
3
14.0 Hz, JHH = 6.3 Hz, 2H, NCH2), 3.19 (m, 2H, NCH2), 3.03 (m,
135.7 (s, BPh-2), 130.1 (qq, JCF = 31.4 Hz, JBC = 2.6 Hz, BPh-3),
3
3
1
3
4
3H, NCH2), 2.98 (dd, JHH = 12.7 Hz, JHH = 5.2 Hz, 2H, NCH2),
2.79 (s, 6H, NCH3), 2.62 (m, 5H, NCH2), 2.54 (s, 3H, NCH3), 0.68
(s, 4H, ZrCH2), 0.07 (s, 18H, SiCH3). 13C{1H} NMR (CD2Cl2): δ
125.6 (q, JCF = 273.6 Hz, CF3), 118.3 (dt, JCF = 7.7 Hz, JBC = 3.8
Hz, BPh-4), 71.4 (s, NCH2), 63.7 (s, NCH2), 63.4 (s, NCH2), 57.7 (s,
NCH2), 56.0 (s, NCH2), 55.7 (s, NCH2), 54.9 (s, NCH3), 54.2 (s,
NCH2), 53.9 (s, NCH3), 53.6 (s, NCH2), 49.1 (s, NCH2), 47.9 (s,
NCH2), 47.7 (s, NCH2), 47.5 (s, NCH3). 11B NMR (THF-d8): δ
−8.36 (s). 19F NMR (188 MHz, THF-d8): δ −59.76 (s). Anal. Calcd
for C86H78B2F48N8Zr2: C, 44.15; H, 3.36; N, 4.79. Found: C, 43.23; H,
3.16; N, 4.54.
1
2
165.1 (q, JBC = 48.9 Hz, BPh-1), 133.5 (d, JBC = 1.8 Hz, BPh-2),
133.4 (q, 3JBC = 4.0 Hz, BPh-3), 123.6 (s, Ph-4), 63.1 (s, ZrCH2), 61.4
(s, NCH2), 55.9 (s, NCH2), 54.2 (s, NCH2), 52.4 (s, NCH2), 51.0 (s,
NCH3), 46.1 (s, NCH3), 3.1 (s, SiCH3). 11B NMR (CD2Cl2): δ −6.95
(s). Anal. Calcd for C43H59BCl8N4Si2Zr: C, 48.10; H, 5.54; N, 5.22.
Found: C, 45.93; H, 4.75; N, 5.21.
[{Zr(Me3TACD)(μ-H)2}2][B(3,5-C6H3Cl2)4]2 (3c). A solution of 2c
(250 mg, 233 μmol) in 3 mL of THF was treated with 50 bar of
hydrogen in a microreactor for 24 h. The reaction mixture was filtered.
Diethyl ether was allowed to diffuse into the THF solution to give
yellow crystals; yield 146 mg (75.0 μmol, 64.4%). Solvent-free crystals
were obtained by diffusion of diethyl ether into a THF/diglyme
solution.
[Zr(Me3TACD)(CH2SiMe3)2][BPh4] (2d). A solution of trityl
tetraphenylborate (250.0 mg 0.444 mmol) in 20 mL of DCM was
slowly added to a solution of 1 (252.0 mg, 0.445 mmol) in 20 mL of
DCM. The mixture was stirred at room temperature for 3 h. All
volatiles were removed under vacuum, and the resulting solid residue
was suspended in pentane, filtered through a glass fiber, and washed
with pentane (3 × 40 mL). After drying, a colorless solid was obtained;
yield 281.0 mg (0.352 mmol, 79%).
1H NMR (THF-d8): δ 7.04 (m, 16H, BPh-2), 7.01 (t, 4JHH = 2.0 Hz,
1
1
8H, BPh-4), 6.47 (t, JHH = 16.4 Hz, 1H, ZrH), 6.23 (t, JHH = 14.7
1H NMR (CD2Cl2): δ 7.32 (br d, 3JHH = 1.5 Hz, 8 H, BPh-2), 7.04
(t, 3JHH = 7.4 Hz, 8H, BPh-3), 6.90 (t, 3JHH = 7.2 Hz, 4H, BPh-4), 3.50
(td, 3JHH = 12.3 Hz, 3JHH = 6.4 Hz, 2H, NCH2), 3.26 (dd, 3JHH = 14.0
Hz, 2H, ZrH), 5.92 (t, JHH = 12.6 Hz, 1H, ZrH), 3.52 (m, 10H,
1
NCH2), 3.31 (m, 6H, NCH2), 3.04 (m, 8H, NCH2), 3.97 (s, 6H,
NCH3), 2.91 (s, 6H, CH3), 2.75 (s, 6H, CH3), 2.65 (m, 8H, NCH2).
Hz, 3JHH = 6.4 Hz, 2H, NCH2), 3.14 (m, 2H, NCH2), 2.89 (dd, 3JHH
=
1
13C{1H} NMR (THF-d8): δ 165.7 (q, JBC = 49.5 Hz, BPh-1), 134.1
12.6 Hz, 3JHH = 5.3 Hz, 4H, NCH2), 2.76 (m, 4H, NCH2), 2.70 (s, 6H,
NCH3), 2.40 (m, 2H, NCH2), 2.36 (s, 3H, NCH3), 0.58 (s, 4H,
ZrCH2), 0.04 (s, 18H, SiCH3). 13C{1H} NMR (MHz, CD2Cl2): δ
2
(d, JBC = 1.3 Hz, BPh-2), 133.9 (m, BPh-4), 124.0 (s, BPh-3), 63.8
(br s, NCH2), 63.4 (br s, NCH2), 60.9 (s, NCH2), 57.7 (s, NCH2),
57.1 (s, NCH2), 55.7 (s, NCH2), 55.0 (s, NCH3), 54.2 (s, NCH2),
54.0 (s, NCH2), 53.9 (s, NCH3), 53.7 (s, NCH2), 53.6 (s, NCH2),
47.7 (s, NCH3). 11B NMR (THF-d8): δ −6.91 (s). Anal. Calcd for
C78H94B2Cl16N8O2Zr2: C, 48.12; H, 4.87; N, 5.76. Found: C, 48.15; H,
4.47; N, 5.64.
1
2
164.4 (q, JBC = 49.1 Hz, BPh-1), 136.4 (d, JBC = 1.5 Hz, BPh-2),
126.1 (q, 3JBC = 2.8 Hz, BPh-3), 122.3 (s, Ph-4), 62.1 (s, ZrCH2), 61.2
(s, NCH2), 55.6 (s, NCH2), 52.4 (s, NCH2), 50.9 (s, NCH3), 45.9 (s,
NCH3), 3.1 (s, SiCH3). 11B NMR (CD2Cl2): δ −6.65 (s). Anal. Calcd
for C43H67BN4Si2Zr: C, 64.70; H, 8.46; N, 7.02. Found: C, 60.18; H,
7.46; N, 7.55.
[{Zr(Me3TACD)(OCH(CH3)(μ-H)}2][B{3,5-C6H3(CF3)2}4]2 (5b). A sol-
ution of 3b (30 mg, 12.8 μmol) in 0.6 mL of THF-d8 was treated with
a solution of acetone in THF-d8 (62 μL, c = 0.413 mol/L, 2.0 equiv). A
1H NMR spectrum was recorded 1 h after the addition.
[{Zr(Me3TACD)(μ-H)2}2][Al{OC(CF3)3}4]2 (3a). A solution of 2a (500
mg, 0.346 μmol) in 3 mL of THF was treated with 50 bar of hydrogen
in a microreactor for 72 h. The yellow solution was filtered, all volatiles
were removed under reduced pressure, and the residue was washed
with pentane (2 × 5 mL) and dried for 10 min. The crude product was
suspended in 20 mL of benzene for 20 min, filtered, washed with
pentane (4 × 10 mL), and gently dried for 10 min. Yellow
microcrystals were obtained; yield 240 mg (0.0942 μmol, 54.5%).
4
1H NMR (THF): δ 7.80 (t, JHF = 2.4 Hz, 16H, BPh-2), 7.58 (s,
3
8H, BPh-4), 5.28 (s, 2H, Zr(μ-H)), 4.44 (sept, JHH = 6.3 Hz, 2H,
3
3
OCH(CH3)2), 3.72 (td, JHH = 11.6 Hz, JHH = 5.9 Hz, 4H, NCH2),
3
3
3.43 (m, 8H, NCH2), 3.29 (dd, JHH = 13.7 Hz, JHH = 5.8 Hz, 4H,
NCH2), 3.07 (m, 8H, NCH2), 3.00 (m, 8H, NCH2), 2.92 (s, 12H,
3
NCH3), 2.82 (s, 6H, NCH3), 1.26 (d, JHH = 6.3 Hz, 12H,
1
1H NMR (THF-d8): δ 6.55 (t, JHH = 16.3 Hz, 1H, ZrH), 6.32 (t,
1
OCH(CH3)2). 13C{1H} NMR (THF-d8): δ 162.9 (q, JBC = 50.9
1JHH = 14.4 Hz, 2H, ZrH), 5.99 (t, 1JHH = 14.0 Hz, 1H, ZrH), 3.71 (m,
5H, NCH2), 3.60 (m, 5H, NCH2), 3.40 (m, 7H, NCH2), 3.19 (m,
10H, NCH2), 3.07 (s, 6H, NCH3), 3.04 (m, 5H, NCH2), 2.99 (s, 6H,
NCH3), 2.86 (s, 6H, NCH3). 13C{1H} NMR (THF-d8): δ 122.3 (q,
1JCF = 290.8 Hz, CF3), 63.8 (s, NCH2), 63.5 (s, NCH2), 57.7 (s,
NCH2), 55.7 (s, NCH2), 54.9 (s, NCH3), 54.2 (s, NCH2), 53.9 (s,
NCH2), 53.7 (s, NCH3), 47.5 (s, NCH3). 27Al NMR (THF): δ 32.71
(s). 19F NMR (188 MHz, THF-d8): δ −72.27 (s). Anal. Calcd for
C62H70Al2F72N8O10Zr2: C, 27.67; H, 2.62; N, 4.16. Found: C, 26.15;
H, 2.39; N, 4.42.
Hz, BPh-1), 135.7 (s, BPh-2), 130.1 (qq, 2JCF = 31.2 Hz, 3JBC = 2.7 Hz,
BPh-3), 125.6 (q, 1JCF = 271.0 Hz, CF3), 118.3 (t, 3JCF = 3.8 Hz, BPh-
4), 72.5 (s, OCH(CH3)2), 94.0 (s, NCH2), 56.8 (s, NCH2), 55.8 (s,
NCH2), 53.5 (s, NCH2), 49.9 (s, NCH3), 49.1 (s, NCH3), 26.9
(OCH(CH3)2).
[{Zr(Me3TACD)(OCD(CH3)(μ-D)}2][B{3,5-C6H3(CF3)2}4]2 (5b[D4]). A
solution of [{Zr(Me3TACD)(μ-D)2}2][B{3,5-C6H3(CF3)2}4]2
(3b[D4]) (30 mg, 12.8 μmol) in 0.6 mL of THF-d8 was treated
with a solution of acetone in THF-d8 (62 μL, c = 0.413 mol/L, 2.0
1
equiv). A H NMR spectrum was recorded 1 h after the addition.
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Inorganic Chemistry
Article
1H NMR (THF-d8): δ 7.80 (t, 4JHF = 2.4 Hz, 16H, BPh-2), 7.58 (s,
8H, BPh-4), 3.72 (td, 3JHH = 11.6 Hz, 3JHH = 5.9 Hz, 4H, NCH2), 3.43
(m, 8H, NCH2), 3.29 (dd, 3JHH = 13.7 Hz, 3JHH = 5.8 Hz, 4H, NCH2),
3.07 (m, 8H, NCH2), 3.00 (m, 8H, NCH2), 2.92 (s, 12H, NCH3), 2.82
(s, 6H, NCH3), 1.26 (s, 12H, OCD(CH3)2). 13C{1H} NMR (THF-
disordered, but the disorder could be modeled with split positions for
these atoms. The occupancy factors for all atoms that are involved
were close to 0.5. Because attempted refinement with anisotropic
displacement parameters led to physically meaningless values, these
atoms were refined with isotropic displacement parameters. The non-
hydrogen atoms except those of the disordered Me3TACD ligand in
2c were refined anisotropically; all hydrogen atoms were placed in
calculated positions except for the hydrides in 3b and 4b. For both
structures, the positions of these hydrides were localized in a difference
Fourier map with peaks of 0.59, 0.63, 0.74, and 0.78 e/Å3 (3b) as well
as 0.68 and 0.88 e/Å3 (4b). We are aware that these positions must
not be overinterpreted, especially because both structures contain
higher peaks of residual electron density in a distance of ca. 1 Å from
zirconium. However, these positions are consistent with the results
from NMR spectroscopy and match the metal−metal distance
together with the DFT calculations. Distance restraints on C−C,
C−N, and C−Si bonds were used in the refinement of 2c and also on
C−C and C−N distances within the disordered part of the Me3TACD
ligand in 4b. Experimental details are given in Table 1.
1
d8): δ 162.9 (q, JBC = 50.9 Hz, BPh-1), 135.7 (s, BPh-2), 130.1 (qq,
2JCF = 31.2 Hz, 3JBC = 2.7 Hz, BPh-3), 125.6 (q, 1JCF = 271.0 Hz, CF3),
118.3 (t, 3JCF = 3.8 Hz, BPh-4), 94.0 (s, NCH2), 56.8 (s, NCH2), 55.8
(s, NCH2), 53.5 (s, NCH2), 49.9 (s, NCH3), 49.1 (s, NCH3), 26.9
(OCD(CH3)2). The resonance for OCD(CH3)2 is not detected.
[Zr(Me3TACD)(OCH(CH3)2][B{3,5-C6H3(CF3)2}4] (6b). A solution of
3b (30 mg, 12.8 μmol) in 0.6 mL of THF-d8 was treated with a
solution of acetone in THF-d8 (124 μL, c = 0.413 mol/L, 4.0 equiv). A
1H NMR spectrum was recorded 30 min after the addition. Full
conversion was achieved after 24 h. Alternative method: 2b (30.0 mg,
22.4 μmol) in 0.6 mL of THF-d8 was treated with a solution of
isopropyl alcohol in THF-d8 (83 μL, c = 0.540 mmol/L, 44.9 μmol, 2.0
1
equiv). A H NMR spectrum was recorded after 1 h.
1H NMR (THF-d8): δ 7.80 (m, 8H, BPh-2), 7.58 (s, 4H, BPh-4),
3
4.70 (sept, JHH = 6.1 Hz, 2H, OCH(CH3)2), 3.39 (m, 1H, NCH2),
ASSOCIATED CONTENT
3.07 (m, 3H, NCH2), 2.80 (m, 10H, NCH2), 2.70 (s, 3H, NCH3), 2.65
■
3
S
* Supporting Information
(m, 2H, NCH2), 2.60 (s, 6H, NCH3), 1.28 (d, JHH = 6.1 Hz, 12H,
1
OCH(CH3)2). 13C{1H} NMR (THF-d8): δ 162.9 (q, JBC = 49.5 Hz,
CIF file giving crystallographic data for compounds 1, 2c, 3b,
2
3
and 4b, ORTEP drawing of 2c, H−1H NOESY spectrum of
1
BPh-1), 135.7 (s, BPh-2), 130.1 (qq, JCF = 31.1 Hz, JBC = 2.6 Hz,
BPh-3), 125.6 (q, 1JCF = 272.7 Hz, CF3), 118.3 (t, 3JCF = 3.8 Hz, Ph-4),
72.9 (s, OCH(CH3)2), 61.2 (s, NCH2), 57.4 (s, NCH2), 55.4 (s,
NCH2), 54.1 (s, NCH2), 54.0 (s, NCH2), 50.5 (s, NCH3), 49.4 (s,
NCH3), 48.4 (s, NCH3), 45.9 (s, NCH2), 27.5 (s, OCH(CH3)2).
[Zr(Me3TACD)(OCD(CH3)2][B{3,5-C6H3(CF3)2}4] (6b[D2]). A solution
of 5b[D4] (12.8 μmol) in 0.6 mL of THF-d8 was treated with a
solution of acetone in THF-d8 (62 μL, c = 0.413 mol/L, 2.0 equiv).
1H NMR (THF-d8): δ 7.80 (m, 8H, BPh-2), 7.58 (s, 4H, BPh-4),
3.39 (m, 1H, NCH2), 3.07 (m, 3H, NCH2), 2.80 (m, 10H, NCH2),
1
3a, H−1H COSY spectrum of 3b, synthesis and character-
ization of 4b, reaction of 3b with CO, and computational
details and optimized structures. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jun.okuda@ac.rwth-aachen.de. Fax: +49 241 92644.
■
2.70 (s, 3H, NCH3), 2.65 (m, 2H, NCH2), 2.60 (s, 6H, NCH3), 1.27
Present Address
1
(s, 12H, OCD(CH3)2). 13C{1H} NMR (THF-d8): δ 162.9 (q, JBC
=
=
‡Universite
́
de Toulouse et CNRS INSA, UPS, CNRS, UMR,
2
3
49.5 Hz, BPh-1), 135.7 (s, BPh-2), 130.1 (qq, JCF = 31.1 Hz, JBC
5215 LPCNO, 135 Avenue de Rangueil, F-31077 Toulouse,
France.
1
3
2.6 Hz, BPh-3), 125.6 (q, JCF = 272.7 Hz, CF3), 118.3 (t, JCF = 3.8
Hz, BPh-4), 61.2 (s, NCH2), 57.4 (s, NCH2), 55.4 (s, NCH2), 54.1 (s,
NCH2), 54.0 (s, NCH2), 50.5 (s, NCH3), 49.4 (s, NCH3), 48.4 (s,
NCH3), 45.9 (s, NCH2), 27.4 (s, OCD(CH3)2). The resonance for
OCD(CH3)2 is not detected.
Notes
The authors declare no competing financial interest.
Hydrogenolysis of CO. A solution of 3b (40 mg, 0.017 μmol) in
ACKNOWLEDGMENTS
■
0.7 mL of THF-d8 was treated with 1.0 bar of CO (either 12CO or
We thank the Fonds der Chemischen Industrie and the Cluster
of Excellence “Tailor-Made Fuels from Biomass” for financial
support. L.M. is a member of the Institut Universitaire de
France. Calmip and CINES are acknowledged for a generous
grant of computing time.
1
13CO). The yellow solution became nearly colorless within 5 min. H
NMR and 13C{1H} spectra were recorded at regular intervals.
1
Ethylene. H NMR (THF-d8): δ 5.36 (s, CH2). 13C{1H} NMR
(THF-d8): δ 123.4 (s, CH2).
Oxymethylene Complex 7b. 1H NMR (THF-d8): δ 3.31 (s,
ZrH2CO). 13C{1H} NMR (THF-d8): δ 79.3 (s, ZrH2CO).13C NMR
1
REFERENCES
(THF-d8): δ 79.3 (t, JCH = 138.7 Hz, ZrH2CO).
■
Enolate Complex 8b. 1H NMR (THF-d8): δ 6.75 (dd, 3JHH = 13.9
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Single-Crystal X-ray Structure Analysis of 1, 2c, 3b, and 4b.
X-ray diffraction data were collected on a Bruker CCD area-detector
diffractometer at 130 K (1) and 100 K (2c, 3b, and 4b) with Mo Kα
radiation (monolayer optics, λ = 0.71073 Å) using ω scans. The
SMART program package was used for data collection and unit cell
determination; processing of the raw frame data was performed using
SAINT,36a absorption corrections were applied with MULABS36b (1
and 2c) or SADABS36c (3b and 4b). The structures were solved by
direct methods.36d Compound 4b crystallizes as a solvate. Refinement
was performed against F2 using all reflections with the program
SHELXL-97, as implemented in the program system WinGX.36e,f The
carbon and nitrogen atoms of the Me3TACD ligand in 2c are
12470
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Inorganic Chemistry
Article
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