Synthesis, characterization, and thermal rearrangement of zirconium tetraazadienyl and pentaazadienyl complexes

Article abstract of DOI:10.1021/om300291b

Reaction of the zirconium dichloro complex [Zr(N₂ ^TBSN_py)Cl₂] (1) with 1 molar equiv of ArNHLi (Ar = Mes, DIPP) yielded the zirconium imido complexes [Zr(N₂ ^TBSN_py)(=N^DIPP)(py)] (2; N₂ ^TBSN_py = [(2-C₅H₄N)C(CH ₃){CH₂NSi(CH₃)₂tBu} ₂]^2-, DIPP = 2,6-diisopropylphenyl) and [Zr(N ₂^TBSN_py)(=N^Mes)(py)] (3; Mes = mesityl). The imido complexes are converted to the tetraazadienido complexes [Zr(N₂^TBSN_py)(N^DIPPN ₂N^Ph)] (4) and Zr(N₂^TBSN _py)(N^MesN₂N^Ph)] (5) by addition of phenyl azide, whereas the reaction of 2 or 3 with mesityl azide gave the alternative product 7, in which the azide is coupled with the CH activated ancillary tripod ligand. Reaction of 1 molar equiv of trimethylsilyl azide or 1-adamantyl azide with the previously reported hydrazinediido complex [Zr(N ₂^TBSN_py)(=NNPh₂)(py)] (9) at ambient temperature resulted in the formation of the five-membered zirconaacacycles [Zr(N₂^TBSN_py)(N^TMSN ₃NPh₂)] (10) and [Zr(N₂^TBSN _py)(N^AdN₃NPh₂)] (11). Complex 11 was thermally converted into the diazenido complex 12 via loss of 1 molar equiv of molecular N₂. The direct formation of the analogous side-on-bonded diazenido analogue 13 was observed upon reaction of 9 with 1 equiv of mesityl azide at ambient temperature. On the basis of ¹⁵N labeling and DFT modeling (DFT(B3PW91/6-31 g(d))) a mechanism for the reaction pathway leading to 12 and 13 is proposed.

Full text of DOI:10.1021/om300291b

Article
pubs.acs.org/Organometallics
Synthesis, Characterization, and Thermal Rearrangement of
Zirconium Tetraazadienyl and Pentaazadienyl Complexes
Thorsten Gehrmann, Julio Lloret Fillol, Hubert Wadepohl, and Lutz H. Gade*
Anorganisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
S
* Supporting Information
ABSTRACT: Reaction of the zirconium dichloro complex
TBS
[Zr(N2 Npy)Cl2] (1) with 1 molar equiv of ArNHLi (Ar =
Mes, DIPP) yielded the zirconium imido complexes [Zr-
(N2 Npy)(NDIPP)(py)] (2; N2
N
= [(2-C5H4N)C-
TBS
TBS
py
(CH3){CH2NSi(CH3)2tBu}2]2−, DIPP = 2,6-diisopropylphen-
yl) and [Zr(N2 Npy)(NMes)(py)] (3; Mes = mesityl). The
TBS
imido complexes are converted to the tetraazadienido
complexes [Zr(N2 Npy)(NDIPPN2NPh)] (4) and Zr-
TBS
(N2 Npy)(NMesN2NPh)] (5) by addition of phenyl azide,
TBS
whereas the reaction of 2 or 3 with mesityl azide gave the
alternative product 7, in which the azide is coupled with the
CH activated ancillary tripod ligand. Reaction of 1 molar equiv
of trimethylsilyl azide or 1-adamantyl azide with the previously
TBS
reported hydrazinediido complex [Zr(N2 Npy)(NNPh2)(py)] (9) at ambient temperature resulted in the formation of the
TBS
TBS
five-membered zirconaacacycles [Zr(N2 Npy)(NTMSN3NPh2)] (10) and [Zr(N2 Npy)(NAdN3NPh2)] (11). Complex 11 was
thermally converted into the diazenido complex 12 via loss of 1 molar equiv of molecular N2. The direct formation of the
analogous side-on-bonded diazenido analogue 13 was observed upon reaction of 9 with 1 equiv of mesityl azide at ambient
temperature. On the basis of 15N labeling and DFT modeling (DFT(B3PW91/6-31 g(d))) a mechanism for the reaction
pathway leading to 12 and 13 is proposed.
may be either isolated starting materials or species generated in
situ by thermal fragmentation of azides at low-valent metal
centers and subsequent reaction with excess azide to give the
cycloaddition product. Furthermore, ruthenium tetrazene
intermediates have been proposed to play a key role in the
catalyst deactivation in ruthenium-catalyzed “click”-azide−
alkyne cycloadditions.6 We also note the insertion of an azide
into a nitrogen−silicon bond to form an N4 species7 as well as
the formation of an iron hexazene complex by reductive
dimerization of two molecules of azide reported by Holland
and co-workers.8
INTRODUCTION
■
Tetraazadiene complexes have been studied for many d-block
metals in different formal oxidation states.1 The bonding within
the N4 fragment has been of special interest. It may be regarded
as a neutral tetraazadiene donor (a), as part of a delocalized π
system including the metal atom (b), or as a dianionic
tetraazene-1,4-diido ligand with an isolated NN double bond
(c).
Bergman and co-workers first reported the synthesis of the
t
zirconium tetraazadienido complex [Cp2Zr(N4 Bu2)] by
reaction of [Cp2Zr(NtBu)(thf)] with tert-butyl azide.9 In
the presence of phenyl azide the N-bonded phenyl and tert-
butyl groups underwent exchange, a process which was
suggested to proceed via cycloreversion of the tetraazene-1,4-
diide (I). The free imide generated in this process was trapped
with norbornene to form a [2 + 2] cycloaddition product (II).
With 2-butyne [2 + 2] cycloaddition of the alkyne and the
thermally generated imide took place, followed by insertion of
the free azide into a Zr−C bond to give a metallabicyclic system
(III) (Scheme 1).9
Evidence for all three cases has been reported in the
literature on the basis of structural data as well as theoretical
studies.2 While the N4 unit coordinated to late transition metals
tends to be best represented by resonance structures a and b,
the bonding situation in early-transition-metal complexes is
adequately represented by resonance form c.
Several preparative routes to tetraazadiene complexes have
been described in the literature, including the coupling of
diazonium cations at the metal center,3 salt metathesis of
dihalides with Li2N4R2,4 andmost commonlythe cyclo-
addition of organic azides with imido complexes.5 The latter
Received: April 15, 2012
Published: June 4, 2012
© 2012 American Chemical Society
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t
Scheme 1. Azide Exchange in [Cp2Zr(N4 Bu2)] via
Cycloreversion and Imide Trapping Reactions9
Figure 1. Molecular structure of the imido complex 2 (H atoms have
been omitted for clarity). Selected bond lengths (Å) and angles (deg):
Zr(1)−N(1) = 2.096(2), Zr(1)−N(5) = 2.371(2), Zr(1)−N(2) =
2.104(2), N(4)−C(22) = 1.374(2), Zr(1)−N(3) = 2.315(2); Zr(1)−
N(4)−C(22) = 169.9(1), Zr(1)−N(4) = 1.913(2), N(3)−Zr(1)−
N(5) = 169.23(5).
We note that Kawaguchi and co-workers recently reported
the synthesis of the zirconium tetraazadienido complex
[(ArRO)2Zr(N4Ad2)] (ArRO = 2,6-diadamantyl-4-methylphe-
nolate).10 In view of the first results of azide cycloaddition to
zirconium hydrazinediido complexes, which generated metal-
bonded N5 units,11 we began to study the chemistry of
zirconium tetraazadienido complexes synthesized from imido
zirconium compounds. The propensity of zirconium hydrazi-
nediido complexes to undergo N−N bond cleavage and
subsequent conversions is now well established. Therefore,
the comparison of the reactivity of their azide cycloaddition
products with that of the metallacyclic species derived from the
corresponding imido complex was of particular interest to us
and is reported in this work.
similar to that of the previously characterized zirconium imido
TMS
complex [Zr(N2 Npy)(NDIPP)(py)] (2a) (in particular, the
ZrN bond length: Zr1−N4 1.9126(17) Å in 2 compared to
1.916(4) Å in 2a).14
Whereas both complexes 2 and 3 are unreactive toward
trimethylsilyl and 1-adamantyl azides, probably due to steric
congestion, they readily form the tetrazenido complexes 4 and
5 by reaction with phenyl azide at ambient temperature
1
(Scheme 1). In the H NMR spectra of both tetrazenido
complexes the signals for the protons adjacent to the pyridyl
nitrogen in the ancillary ligand exhibit a strong high-field shift
(in C6D6: δ 7.09 (4), 7.07 (5)) in comparison to the signals in
the corresponding imido complexes (δ 9.42 (2), 9.37 (3)),
which indicates an orientation of these protons toward the
anisotropy cones of aromatic DIPP or mesityl rings of the
tetraazadienyl unit. The formation of the N4 chains was
supported by the 15N NMR spectra of 4 and 5, which are
shown in Figure 2.
RESULTS AND DISCUSSION
Synthesis and Structural Characterization of Zirco-
■
nium Tetraazadienide Complexes. The zirconium imido
complexes [Zr(N2 Npy)(NDIPP)(py)] (2; N2
N
= [(2-
TBS
TBS
py
C5H4N)C(CH3){CH2NSi(CH3)2tBu}2]2−, DIPP = 2,6-diiso-
propylphenyl) and [Zr(N2 Npy)(NMes)(py)] (3; Mes =
TBS
mesityl) were synthesized in a one-pot procedure from the
dichloro precursor [Zr(N2 Npy)Cl2)] (1)12 by reaction with 1
TBS
For a complete assignment of the 15N NMR spectra,
chemical shifts were calculated using the DFT-GIAO computa-
tional tool (B3PW91 functional;15 Stuttgart relativistic, small
core ECP basis + f polarized function for the Zr; 6-31G for H
and 6-31++G(d) for C atoms; 6-311++G(2d) for N).16 The
computed data are in good agreement with the experimental
values for the NMR chemical shifts. (Table 1)
molar equiv of the corresponding lithium amide and
subsequent treatment with LiHMDS (HMDS = hexamethyldi-
silazide) and pyridine (Scheme 1).
The analytical and spectroscopic properties of both imido
complexes 2 and 3 are consistent with the structures depicted
in Scheme 2.13 In order to establish the details of the zirconium
imido complexes, an X-ray diffraction study of 2 was carried
out. Its molecular structure is shown in Figure 1 and is very
Single-crystal structure analyses were carried out for
complexes 4 and 5. In both cases, the general features of the
N4 unit were established; however, the quality of the data for
complex 4 did not allow a meaningful discussion of its metric
parameters. Therefore, only the molecular structure of 5, which
is displayed in Figure 3, will be discussed. The coordination
geometry in 5 is best described as distorted trigonal
bipyramidal. The ancillary ligand is facially coordinated to the
metal center, while the tetraazadienido ligand occupies the
remaining axial and equatorial coordination sites. The N6−N7
(double) bond length (N6−N7 = 1.264(2) Å) is reduced
Scheme 2. Formation of the Imido Complexes 2 and 3 from
TBS
[Zr(N2 Npy)Cl2)] (1) and Their Conversion to the
Tetraazadienido Complexes 4 and 5 with Phenyl Azide
(DIPP = 2,6-Diisopropylphenyl)
t
compared to that in [Cp2Zr(N4 Bu2)] (NN = 1.281 Å); on
the other hand, the Zr−N4 (2.172(2) Å) and Zr−N5 (2.157(2)
t
Å) distances are greater than in [Cp2Zr(N4 Bu2)] (2.126(6),
2.117(6) Å).
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complexes. A different course of reaction was observed in the
attempted synthesis of a tetraazadienyl complex by reaction of
the imido complex 2 with mesityl azide, as evidenced by the
1
signal patterns and chemical shifts in the H and 15N NMR
spectra of the reaction product. The 15N NMR spectrum
displayed in Figure 4, along with an inverse 15N−1H COSY,
clearly showed the formation of a N−H bond, while the 1H and
13C DEPT NMR spectra indicated the formation of a third CH2
moiety.
Figure 2. 15N NMR spectra at natural abundance of complexes 4 (top)
and 5 (bottom).
Figure 4. 15N NMR spectrum at natural abundance of complex 7.
Table 1. Experimental and Computed 15N NMR Shifts of
Complexes 5 and 7
To establish the molecular structure of 7, a single-crystal X-
ray structure analysis was carried out. The asymmetric unit
contains two crystallographically independent but structurally
very similar molecules, the molecular structure of one of which
is shown in Figure 5. An amido ligand has been formed (Zr−
N4 = 2.118(2) (2.101(2) Å for the second independent
molecule)) and is bonded in a trans disposition to the amido
atoms N1 and N2 of the tripodal ligand. The mesityl azide is
coupled to a methyl group at a silicon atom of the auxiliary
ligand, forming an altogether pentadentate ligand. The Zr−N
5
7
exptl
theor
exptl
theor
N1/N2
N3
197.4
272.0
278.0
288.5
371.1
387.0
219.2
301.3
308.1
320.2
403.1
420.2
164.0/171.9
287.4
190.8/198
320.6
N4
176.8
200.2
N5
288.6
315.9
N6
502.2
547.0
N7
284.0
307.0
Figure 5. Molecular structure of the C−H bond activation product 7
(only one of the two independent molecules is shown; H atoms are
omitted for clarity, except for the amido H). Selected bond lengths (Å)
and angles (deg) (data for the second molecule are given in brackets):
Zr(1)−N(1) = 2.096(2) [2.108(3)], N(5)−N(6) = 1.323(3)
[1.325(3)], N(6)−N(7) = 1.292(3) [1.302(4)], Zr(1)−N(2) =
2.072(3) [2.075(2)], N(7)−C(10) = 1.456(4) [1.460(4)], Zr(1)−
N(3) = 2.399(2) [2.377(2)], C(10)−N(7)−N(6) = 115.3(2)
[115.0(3)], Zr(1)−N(4) = 2.118(2) [2.101(2)], N(5)−N(6)−N(7)
= 108.0(2) [108.3(2)], Zr(1)−N(5) = 2.338(3) [2.348(3)], N(3)−
Zr(1)−N(7) = 136.65(8) [138.27(9)], Zr(1)−N(7) = 2.286(2)
[2.280(3)], N(3)−Zr(1)−N(5) = 168.70(8) [166.72(8)], N(6)−
N(7) = 1.292(3) [1.302(4)].
Figure 3. Molecular structure of the tetraazadienido complex 5. H
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Zr−N(1) = 2.036(2), Zr−N(2) = 2.044(2), Zr−N(3) =
2.338(2), Zr−N(4) = 2.172(2), Zr−N(5) = 2.157(2), N(4)−N(7) =
1.394(2), N(5)−N(6) = 1.382(2), N(6)−N(7) = 1.264(2), N(4)−
C(22) = 1.439(2), N(5)−C(31) = 1.410(2); N(4)−Zr−N(5) =
68.61(6).
The tetraazadienyl complexes 4 and 5 were found to be
unreactive toward unsaturated substrates at ambient temper-
ature, and heating led to nonselective decomposition for both
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Scheme 3. Formation of the C−H Activation Product 7 from Imido Complex 3 and Mesityl Azide
distances of the azide nitrogen atoms lie between typical bond
lengths for monoanionic and neutral N-donor ligands,
indicating a high degree of electron delocalization in the N3
chain. The N−N distances (N6−N7 = 1.292(3) Å; N5−N6 =
1.323(3) Å) are also consistent with the formulation of the N3
chain as an anionic π-allyl analogue.
precedent for insertions of organoazides in σ-alkyl bonds of
group 4 metal complexes in the literature.9,18
Synthesis and Structural Characterization of Zirco-
nium Pentaazadienyl and Diazenido Complexes. The
reactivity observed for imidozirconium complexes may be
readily extended to the structurally related hydrazinediides.
Reaction of 1 molar equiv of trimethylsilyl azide or 1-adamantyl
azide with the previously reported hydrazinediido complex
A complete assignment of the 15N NMR spectrum in Figure
4 was again achieved by means of a DFT-GIAO computational
study. The calculated chemical shifts are also given in Table 1.
In order to obtain some insight into the reaction pathway
leading to complex 7, the imido compound 3 was reacted with
mesityl azide, which was 15N-labeled in the γ position.
TBS
12,19
[Zr(N2 Npy)(NNPh2)(py)] (9)
at ambient temper-
ature results in the formation of the five-membered zirconaaza-
cycles [Zr(N2 Npy)(NTMSN3NPh2)] (10) and [Zr-
TBS
(N2 Npy)(NAdN3NPh2)] (11). As for the reaction of the
TBS
1
Monitoring the reaction by H and 15N NMR spectroscopy
imido complexes discussed above, the pentaazadienyl units are
formed by formal [2 + 3] cycloaddition of the azide with the
ZrNα double bond of the hydrazinediido unit (Scheme 4).
revealed that, after addition of the azide, the new compound 6
formed immediately (next to unreacted starting material). Its
1H NMR signal patterns were similar to those of the
tetraazadienyl complexes 4 and 5. The 15N NMR spectrum
exhibited the signals of the 15N-labeled nuclei at δ 386.5 and
388.3, respectively, which are assigned to the nitrogen atoms in
the N6 and N7 positions in the tetraazadienyl chain of 6. No
further intermediates were detected in the subsequent
conversion of 6 to the isolated complex 7 (which contained
the 15N label in the N position of the triazaallyl unit adjacent to
the Si−CH2 fragment). Unfortunately, the observation of other
side products, possibly stereoisomers, made this conversion
unsuitable for a detailed kinetic study.
Scheme 4. Formation of the Pentaazadienides 10 and 11
from Hydrazinediide 9 and Organic Azides
We therefore propose that in this multistep reaction complex
6 is formed initially but subsequently undergoes cycloreversion
to form the four-coordinate imido complex A (Scheme 3). The
latter subsequently reacts in a C−H activation step involving
the tBuSiMe2 sustituent of the diamido donor ligand to give
intermediate B. Such reactivity has been well established since
the early pioneering work by Wolczanski and Cummins and has
been observed in several studies since then.17 Finally, the
product complex 7 is formed by insertion of the free mesityl
azide into the zirconium−carbon bond. We note that there is
Both zirconium pentaazadienyl complexes were structurally
characterized. Their molecular structures are depicted in Figure
6, and selected bond lengths and angles are given in Table 2.
The pentaazadienyl units are bound through the N4 and N7
atoms to the zirconium center, with the Zr−N4 and Zr−N5
distances (10, Zr−N4 = 2.139(2) Å, Zr−N7 = 2.159(2) Å; 11,
Zr−N4 = 2.153(2) Å, Zr−N7 = 2.151(2) Å) being in the
typical range for Zr−N bonds of monoanionic N donors. This
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Figure 6. Molecular structures of complexes 10 (left) and 11 (right). H atoms are omitted for clarity. A comparative listing of the principal bond
lengths and angles in provided in Table 2.
Table 2. Selected Bond Lengths (Å) and Angles (deg) of
Complexes 10 and 11
10
11
Zr−N(1)
Zr−N(2)
Zr−N(3)
Zr−N(4)
2.042(2)
2.034(2)
2.326(2)
2.139(2)
2.159(2)
1.397(3)
1.260(3)
1.395(3)
1.415(3)
114.4(2)
114.1(2)
108.7(2)
68.15(7)
2.047(2)
2.046(2)
2.320(2)
2.153(2)
2.151(2)
1.374(3)
1.262(3)
1.398(3)
1.415(3)
114.9(2)
113.9(2)
108.9(2)
67.98(7)
Zr−N(7)
N(4)−N(5)
N(5)−N(6)
N(6)−N(7)
N(7)−N(8)
N(4)−N(5)−N(6)
N(5)−N(6)−N(7)
N(6)−N(7)−N(8)
N(4)−Zr−N(7)
is consistent with the formulation of N4 and N7 as formal
monoanionic donor ligands, similar to the situation found for
the tetraazadienido complex 5.
The newly formed N5 chain was further characterized by 15
N
NMR spectroscopy. To allow full assignment of the spectra, the
15N NMR shifts were calculated using DFT-GIAO methods
and showed good agreement with the experimental values. In
Figure 7 the 15N NMR spectra of 10 and 11 are displayed.
While the signals for the Ph2N atoms could only be detected by
an 1H−15N-HMBC experiment, all other resonances were
detected directly. A comparison of the experimental and
computed NMR shifts is given in Table 3.
Figure 7. 15N NMR spectra at natural abundance of complexes 10
(top) and 11 (bottom).
Table 3. Experimental and Computed 15N NMR Shifts of
Complexes 10 and 11
10
11
Similar to the case for their tetraazadienyl analogues, the
pentaazenido complexes 10 and 11 were found to be unreactive
toward unsaturated substrates but turned out to be thermally
labile. While 10 only showed nonselective degradation by
heating to 70 °C in benzene or thf, 11 was converted selectively
into the new compound 12 upon heating to 70 °C in thf for 10
days. Its spectroscopic and analytical data are consistent with
the loss of 1 molar equiv of molecular N2 and the formation of
a diazenido complex.20,21 The direct formation of the side-on-
bonded diazenido analogue 13 was observed in the reaction of
compound 9 with 1 equiv of mesityl azide at ambient
temperature (Scheme 5).
exptl
theor
exptl
theor
N1/N2
N3
189.9
275.3
293.8
378.6
411.4
291.3
121.4
209.6
304.8
325.8
408.5
446.2
317.3
143.6
189.1
276.4
303.8
374.7
380.8
292.4
122.2
208.3
308.5
334.7
408.3
410.6
312.2
143.9
N4
N5
N6
N7
N8
lengths and angles. The N5 chain of the pentaazenido precursor
has fragmented and the NPh2 unit of the original hydrazido
ligand is bound as an amido ligand in an equatorial position,
while the coordination site in a position trans to the neutral
The molecular structure of 13 was established by X-ray
diffraction and is shown in Figure 8 along with selected bond
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Scheme 5. Formation of Diazenido Complexes 12 and 13
from Hydrazinediide 9 and Organic Azides
Figure 9. 15N NMR spectra at natural abundance of complexes 12
(top) and 13 (bottom).
Table 4. Experimental and Computed 15N NMR Shifts of
Complexes 12 and 13
12
13
exptl
theor
exptl
theor
Figure 8. Molecular structure of diazenide 13 (H atoms have been
omitted for clarity). Selected bond lengths (Å) and angles (deg): Zr−
N(1) = 2.101(3), Zr−N(2) = 2.065(3), Zr−N(3) = 2.377(3), Zr−
N(4) = 2.231(4), Zr−N(5) = 2.223(3), Zr−N(6) = 2.170(3), N(4)−
N(5) = 1.182(5); Zr−N(5)−N(4) = 75.0(3), Zr−N(4)−N(5) =
74.2(3), N(4)−N(5)−C(22) = 119.8(4).
N1/N2
N3
164.3
286.9
804.2
540.1
201.0
186.6
319.9
836.1
542.6
214.9
166.4
284.1
810.9
489.1
186.6
186.6
315.7
897.1
532.8
208.3
N4
N5
N6
Scheme 6. Distribution of Different 15N Labels during the
Formation of Complex 5
pyridyl donor group is occupied by a formally monoanionic,
side-on-bound diazenido ligand.
The diazenides 12 and 13, generated by N2 extrusion, were
also characterized by 15N NMR spectroscopy and the
resonances were again compared to calculated chemical shifts.
The 15N NMR spectra of 12 and 13 are displayed in Figure 9,
and a comparison of the experimental and calculated 15N NMR
shifts is provided in Table 4. Particularly notable is the low-field
resonance assigned to N4, which is observed at 804.2 ppm for
12 and at 810.9 ppm for 13.
DFT Modeling of the Reaction Pathway Leading to
the Diazenido Complexes 12 and 13. The mechanism of
the reaction of 1-adamantyl azide and 1-mesityl azide with
Monitoring the reaction leading to 12 and 13 by 15N NMR
employing both the 15Nα-labeled hydrazinediido complex 9 as
well as 15Nγ-labeled mesityl azide (Scheme 6) revealed that the
extruded N2 exclusively originates from the azide unit, more
precisely, the NβNγ fragment of the latter, whereas the Zr-
bonded Nα atom of the hydrazinediido ligand remains bound to
the metal in the molecule.
In contrast to the observed reactivity for tetraazadienido
complexes 4 and 5, this reactive behavior is reminiscent of
thermal fragmentations of cobalt or chromium tetraazadiene
complexes observed by Trogler and co-workers.22 The clean N2
extrusion reaction obviously is promoted by the substitution of
a carbon at the tetraazadienyl chain by the NPh2 fragment. This
illustrates the significant change in reactivity pattern when
going from imido to hydrazinediido complexes of the group 4
metals observed previously.19
TBS
[Zr(N2 Npy)(N-NPh2)(py)], including the key transition
states, was modeled by DFT methods (B3PW91/6-31g(d)) for
the full molecular structures. The first step of the reaction of
the hydrazinediide I with the azide (Scheme 7) involves an
endergonic pyridine−azide ligand exchange (with 1-adamantyl
azide and 1-mesityl azide) to form complexes IIa (ΔG = 11.2
kcal/mol) and IIb (ΔG = 18.2 kcal/mol), respectively. All
energy/free enthalpy differences represented in Scheme 7 have
been calculated with respect to compound I.
In the first intermediate IIa,b the organic azide bonds to the
zirconium atom with the nitrogen bearing the organic
substituent. Intermediates IIa,b are linked to two types of
transition states for each azide. The transition state which is
lower in energy/free enthalpy, TSII‑IIIa (ΔG⧧ = 22.8 kcal/mol)
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Scheme 7. General Scheme of the Reactions of the Hydrazinediido Complex [Zr(N2 Npy)(NNPh2)(py)] with 1-Adamantyl
Azide and 1-Mesityl Azide (Computed using DFT(B3PW91/6-31g(d))
and TSII‑IIIb (ΔG⧧ = 19.8 kcal/mol), leads to the formation of
hydrazinediido complex 9. For this class of compounds the
directly detected 15N NMR spectra recorded at natural 15N
abundance, combined with DFT modeling of the chemical
shifts, provided significant structural information.
While the tetraazadienyl complex undergoes retrocycloaddi-
tion and subsequent transformation, the hydrazinediido ligand
fragments, liberating N2 and transferring a nitrogen atom to an
electronically unsaturated ligand fragment. Here again, the
propensity of the Zr-bonded hydrazide to undergo N−N bond
cleavage defines the pattern of reactivity and leads to unusual
structural motifs.
TBS
the corresponding five-membered metallacycles [Zr(N2 Npy)-
(NRN3NPh2)] (IIIa,b with R = adamantyl (IIIa corresponding
to compound 11), mesityl (IIIb)). For both transition states,
TSII‑IIIa and TSII‑IIIb, the activation barriers allow the formation
of intermediates IIIa,b at room temperature but only the
formation of compound IIIa is clearly exergonic (ΔG = −5.1
kcal/mol) and is, in fact, observed experimentally. The
computed ΔG value of −0.2 kcal/mol for the reaction of
TBS
[Zr(N2 Npy)(NNPh2)(py)] with 1-mesityl azide, for which
an error of around 2 kcal/mol is to be assumed, may account
for the fact that intermediate IIIb is not observed in solution.
Intermediates IIa,b also connect with the highly stabilized
IVa (ΔG = −23.9 kcal/mol) and IVb (ΔG = −32.2 kcal/mol)
intermediates via the transition states TSII‑IVa and TSII‑IVb, in
which the extrusion of the dinitrogen molecule takes place.
Intermediates IVa,b are subsequently converted via the cyclic
triazenido species Va,b to give the diazenides VIa,b,
corresponding to complexes 12 and 13. The energies of
transition states TSII‑IVa (ΔG⧧ = 34.3 kcal/mol) and TSII‑IVb
(ΔG⧧ = 28.9 kcal/mol) are in agreement with the observed
reactivity (prolonged heating at 70 °C): the transition state for
the 1-mesityl azide (TSII‑IVb) is the system that more rapidly
reacts to give the diazenide, as observed experimentally.
EXPERIMENTAL SECTION
■
All manipulations of air- and moisture-sensitive materials were
performed under an inert atmosphere of dry argon using standard
Schlenk techniques or by working in a glovebox. Solvents were dried
over sodium (toluene), potassium (hexanes, thf), or sodium/
potassium alloy (pentane, diethyl ether), distilled, and degassed
prior to use. Deuterated solvents were dried over potassium (C6D6,
thf-d8, toluene-d8), vacuum-distilled, and stored in Teflon valve
ampules under argon. Samples for NMR spectroscopy were prepared
under argon in 5 mm Wilmad tubes equipped with J. Young Teflon
1
valves. H, 13C, 29Si, and 15N NMR spectra were recorded on Bruker
Avance 400 and 600 NMR spectrometers and were referenced
internally, using the residual protio solvent (1H) or solvent (13C)
resonances, or externally to SiMe4 and 15NH3. We obtained good-
quality 15N NMR spectra by direct detection of the heteronuclei
without isotope enrichment and with “normal” sample concentrations
(20−30 mg in 0.5 mL deuterated solvent in 5 mm NMR tubes) with
the aid of a cryogenically cooled direct detection probe (Bruker QNP-
cryoprobe) on the 600 MHz NMR spectrometer.
CONCLUSION
■
In this work we have explored the different thermal reactivities
of tetraazadienyl and pentaazadienyl complexes which were
generated by formal [2 + 3] cycloaddition of azides to the
ZrN bonds of the imido complexes 2 and 3 and the
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Elemental analyses were recorded by the analytical service of the
Preparation of [Zr(N2 Npy)(NPhN2NDIPP)] (4). To a stirred
TBS
chemistry department of the Universitat Heidelberg. The dichloro
solution of [Zr(N2 Npy)(NDIPP)(py)] (2; 300 mg, 0.41 mmol) in
̈
TBS
complex [Zr(N2 Npy)Cl2] and the hydrazinediido complex [Zr-
toluene (20 mL) was added a solution of phenyl azide (48 mg, 0.41
mmol) in 5 mL of toluene. The reaction mixture was stirred for 16 h at
room temperature and filtered, and the volatiles were removed in
vacuo. The crude product was washed with hexane (3 × 5 mL) and
dried to yield 220 mg (0.30 mmol, 72%) of 4 as a bright yellow solid.
1H NMR (600 MHz, THF-d8, 296 K): δ −0.06, 0.12 (s, 6 H,
Si(CH3)2), 0.70 (s, 18 H, Si−C(CH3)3), 1.07, 1,23 (d, 3JHH = 6.7 Hz, 6
12
TBS
(N2 Npy(NNPh2)(py)] (9) were prepared as already reported;
phenyl azide, mesityl azide, and 15Nγ-mesityl azide were prepared
according to published procedures.23 All other reagents were obtained
from commercial sources and used as received unless explicitly stated.
TBS
Preparation of [Zr(N2 Npy)(NDIPP)(py)] (2). To a stirred
TBS
solution of [Zr(N2 Npy)Cl2] (1.00 g, 1.8 mmol) in toluene (40 mL)
3
was added a suspension of lithium 2,6-diisopropylaniline (331 mg, 1.8
mmol) in 5 mL of toluene. The reaction mixture was stirred for 2 days
at 60 °C. Then pyridine (150 μL, 1.8 mmol) and a solution of lithium
hexamethyldisilazide (303 mg, 1.8 mmol) in 5 mL of toluene was
added and the mixture was stirred for 2 days at 80 °C. The reaction
mixture was filtered from lithium chloride, and the volatiles were
removed in vacuo. The remaining solid was washed with hexane (3 ×
5 mL) and dried to yield 800 mg (1.50 mmol, 61%) of 2 as a light
orange solid. Single crystals for X-ray diffraction were grown from a
H, CH(CH3)2), 1.73 (s, 3 H, CH3), 3.51 (sep, JHH = 6.7 Hz, 2 H,
CH(CH3)2), 3.63 (d, 2JHH = 12.7 Hz, 2 H, CHH), 4.24 (d, 2JHH = 12.7
Hz, 2 H, CHH), 6.79 (t, 3Jp‑HPhm‑HPh= 0.7.6 Hz, 1H, p-HPh), 7.05−7.10
(m, 2 H, H6py, H5py), 7.73 (t, 3Jm‑HPho‑HPh/m‑HPh = 7.6 Hz, 2 H, m-HPh),
7.28 − 7.34 (m, 3 H, p-HDIPP, m-HDIPP), 7.54 (d, 3Jo‑HPhm‑HPh = 7.6 Hz,
2 H, o-HPh), 7.90 (d, 3JH3pyH4py = 8.1 Hz, H3py), 8.11 (t, 3JH4pyH5py/H3py
= 8.1 Hz, 1 H, H4py). 13C{1H} NMR (150 MHz, THF-d8, 296 K): δ
−4.1, −3.5 (Si(CH3)2), 20.2 (Si−C(CH3)3), 23.9, 26.7 (CH(CH3)),
27.5 (C−CH3), 28.5 (Si−C(CH3)3), 48.6 (C−CH3), 63.1 (CH2),
119.2 (o-CPh), 120.6 (p-CPh), 123.7 (C3py, C5py), 124.4, 127.3 (m-
CDIPP, p-CDIPP), 129.0 (m-CPh), 143.1 (C4py), 146.9 (i-CDIPP), 147.0
(o-CDIPP), 147.7 (C6py), 152.9 (i-CPh), 162.3 (C2py). 29Si {1H} NMR
(80 MHz, THF-d8, 296 K): δ 6.86 (Si(CH3)3). 15N NMR (60 MHz,
1
saturated toluene solution at room temperature. H NMR (600 MHz,
C6D6, 296 K): δ −0.10, 0.21 (s, 6 H, Si(CH3)2), 0.79 (s, 18 H, Si−
3
C(CH3)3), 1.13 (s, 3 H, CH3), 1.43 (d, JHH = 6.7 Hz, 12 H,
CH(CH3)2), 3.49 (d, 2JHH = 12.1 Hz, 2 H, CHH), 3.96 (d, 2JHH = 12.1
3
t
Hz, 2 H, CHH), 4.65 (sep, JHH = 6.7 Hz, 2 H, CH(CH3)2), 6.50, (t,
THF-d8, 296 K): δ 198.5 (N-Si(CH3)2 Bu), 270.8 (L−Npy), 273.9
3
3JH5H6/H4 = 6.6 Hz, 1H, H5py), 6.59 (t, JmHpH/oH = 6.7 Hz, 2 H, m-
(N−DIPP), 290.2 (N−Ph), 369.4, 390.5 (NN). IR (Nujol, NaCl): ν
2724 w, 1592 w, 1462 s, 1377 s, 1305 w, 1257 m, 1152 w, 1088 w,
1028 m, 1016 m, 935 w, 850 w, 828 w, 802 m, 772 w, 722 s cm−1.
Anal. Calcd for C39H63N7Si2Zr: C, 60.26; H, 8.17; N, 12.61. Found: C,
59.97; H, 8.18; N, 12.54.
Hpy), 6.81 − 6.90 (m, 2 H, H3py, p-Hpy), 7.00−7.08 (m, 2 H, H4py, p-
HDIPP), 7.35 (d, 3JmHpH = 7.4 Hz, 2 H, mHDIPP), 9.01 (d, 3JoHmH = 5.1
3
Hz, 2 H, o-Hpy), 9.42 (d, JH6pyH5py = 5.0 Hz, H6py). 13C{1H} NMR
(150 MHz, C6D6, 296 K): δ −4.3, −2.4 (Si(CH3)2), 20.3 (Si-−
(CH3)3), 25.6 (C−CH3), 26.0 (CH(CH3)2), 27.3 (CH(CH3)2), 27.8
(Si−C(CH3)3), 47.3 (C−CH3), 64.3 (CH2), 116.2 (p-CDIPP), 120.5
(C3py), 121.0 (C5py), 123.3 (m-CDIPP), 124.0 (m-Cpy), 139.0 (C4py),
139.2 (p-Cpy), 140.0 (o-CDIPP), 151.3 (C6py), 152.3 (o-Cpy), 154.8 (i-
CDIPP) 161.0 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 0.80
(Si(CH3)3). 15N NMR (60 MHz, C6D6, 296 K): δ 146.0 (N−
TBS
Preparation of [Zr(N2 Npy)(NPhN2NMes)] (5). To a stirred
TBS
solution of [Zr(N2 Npy)(NMes)(py)] (3; 300 mg, 0.43 mmol) in
toluene (20 mL) was added a solution of phenyl azide (52 mg, 0.43
mmol) in 5 mL of toluene. The reaction mixture was stirred for 16 h at
room temperature and filtered, and the volatiles were removed in
vacuo. The crude product was washed with hexane (3 × 5 mL) and
dried to yield 240 mg (0.33 mmol, 76%) of 5 as a bright yellow solid.
Single crystals for X-ray diffraction were grown from a saturated
t
Si(CH3)2 Bu), 278.9 (Npy), 288.8 (L−Npy), 323.0 (ZrN). IR (Nujol,
NaCl): ν 1601 m, 1462 s, 1410 m, 1377 m, 1225 m, 1273 s, 1254 sh,
1085 w, 1061 m, 1010 w, 935 w, 890 s, 867 s, 826 w, 772 w, 700 w,
663 w cm−1. Anal. Calcd: C, 61.90; H, 8.61; N, 9.50. Found: C, 61.67;
H, 8.69; N, 9.63.
1
toluene solution at room temperature. H NMR (600 MHz, THF-d8,
296 K): δ −0.07, 0.01 (s, 6 H, Si(CH3)2), 0.58 (s, 18 H, Si−C(CH3)3),
1.68 (s, 3 H, CH3), 2.28 (s, 6 H, o-CH3), 2.34 (s, 3 H, p-CH3), 3.63
(d, 2JHH = 12.6 Hz, 2 H, CHH), 4.17 (d, 2JHH = 12.7 Hz, 2 H, CHH),
TBS
Preparation of [Zr(N2 Npy)(NMes)(py)] (3). To a stirred
TBS
3
3
solution of [Zr(N2 Npy)Cl2] (1.00 mg, 1.8 mmol) in toluene (40
6.73 (t, Jp‑HPhm‑HPh= 0.7.5 Hz, 1 H, p-HPh), 6.94 (d, JH6pyH5py = 5.6
Hz, 1 H, H6py), 6.96 (s, 3 H, m-Hmes), 7.08 (t, 3JH5pyH4py/H6py = 5.9 Hz,
mL) was added a suspension of lithium 2,4,6-trimethylaniline (255 mg,
1.8 mmol) in 5 mL of toluene. The reaction mixture was stirred for 2
days at 60 °C, and then pyridine (150 μL, 1.8 mmol) and a solution of
lithium hexamethyldisilazide (303 mg, 1.8 mmol) in 5 mL of toluene
was added and the mixture was stirred for 2 days at 80 °C. The
reaction mixture was filtered from lithium chloride, and the volatiles
were removed in vacuo. The remaining solid was washed with hexane
(3 × 5 mL) and dried to yield 800 mg (1.15 mmol, 64%) of 3 as a
bright orange solid. 1H NMR (600 MHz, C6D6, 296 K): δ −0.09, 0.25
(s, 6 H, Si(CH3)2), 0.80 (s, 18 H, Si−C(CH3)3), 1.13 (s, 3 H, CH3),
2.45 (s, 3 H, p-CH3), 2.83 (s, 6 H, o-CH3), 3.50 (d, 2JHH = 12.5 Hz, 2
H, CHH), 3.99 (d, 2JHH = 12.5 Hz, 2 H, CHH), 6.43 (t, 3JH5pyH6py/Hpy4
3
1 H, H5py), 7.15 (t, Jm‑Hpho‑HPh/m‑HPh = 7.6 Hz, 2 H, m-HPh), 7.42 (d,
3Jo‑HPhm‑HPh = 7.6 Hz, 2 H, o-HPh), 7.86 (d, 3JH3pyH4py = 8.0 Hz, H3py),
8.08 (t, JH4pyH5py/H3py = 8.0 Hz, 1 H, H4py). 13C{1H} NMR (150
3
MHz, THF-d8, 296 K): δ −3.7 (Si(CH3)2), 20.4 (Si−C(CH3)3), 21.2
(p-CH3), 21.2 (o-CH3), 27.4 (C−CH3), 28.3 (Si−C(CH3)3), 48.3 (C−
CH3), 63.1 (CH2), 118.6 (o-CPh), 120.4 (p-CPh), 123.7 (C3py), 124.0
(C5py), 129.0 (m-CPh), 130.1 (m-Cmes), 135.5 (p-Cmes), 135.9 (o-Cmes),
143.0 (C4py), 145.9 (i-Cmes), 147.2 (C6py), 153.1 (i-CPh), 162.2 (C2py).
29Si{1H} NMR (80 MHz, THF-d8, 296 K): δ 6.16 (Si(CH3)3). 15N
t
NMR (60 MHz, THF-d8, 296 K): δ 197.4 (N−Si(CH3)2 Bu), 272.0
(L−Npy), 278.0 (N−Mes), 288.5 (N−Ph), 371.1, 387.0 (NN). IR
(Nujol, NaCl): ν 1594 s, 1560 w 1462 s, 1377 s, 1300 w, 1258 s, 171
m, 1133 w, 1084 m, 1037 s, 1017 sh, 992 m, 957 w, 932 m, 905 w, 889
w, 853 s, 825 m, 770 s, 723 m, 693 w, 666 m cm−1. Anal. Calcd for
C36H57N7Si2Zr: C, 58.81; H, 7.81; N, 13.33. Found: C, 58.82; H, 7.86;
N, 13.28.
3
= 6.0 Hz, 1H, H5py), 6.50 (t, Jm‑Hpyo‑Hpy/p‑Hpy = 6.0 Hz, 2 H, m-Hpy),
3
6.80−6.86 (m, 2 H, H3py, p-Hpy), 7.03 (dt, JH4pyH3py/5py = 7.9 Hz,
4JH4pyH6py = 1.7 Hz, 1 H, H4py), 7.20 (s, 2 H, m-Hmes), 8.98 (d,
3
3Jo‑Hpym‑Hpy = 6 Hz, 2H, o-Hpy), 9.37 (d, JH6pyH5py = 5.8 Hz, H6py).
13C{1H} NMR (150 MHz, C6D6, 296 K): δ −4.0, −2.3 (Si(CH3)2),
20.5 (Si−C(CH3)3), 21.2 (p-CH3), 21.7 (o-CH3), 25.8 (C−CH3), 27.8
(Si−C(CH3)3), 47.2 (C−CH3), 64.4 (CH2), 120.4, (C3py), 121.0
(C5py), 123.0 (p-Cmes), 124.0 (m-Cpy), 128.6 (o-Cmes), 128.6 (m-Cmes),
138.7 (p-Cpy), 138.5 (C4py), 151.2 (C6py), 152.2 (o-Cpy), 156.4 (i-
Cmes), 161.2 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 0.62
(Si(CH3)3). 15N NMR (60 MHz, C6D6, 296 K): δ 144.1 (N−
NMR-Scale Detection of [Zr(N2 Npy)(NMesN2NMes)] (6). To a
TBS
TBS
solution of [Zr(N2 Npy)(NMes)(py)] (3) in C6D6 (10 mg, 0.014
mmol) was added 15Nγ-mesityl azide (2 mg, 0.014 mmol). The NMR
tube was transferred immediately to the spectrometer, and a set of 1H
and 15N NMR spectra were recorded. 1H NMR (600 MHz, C6D6, 296
K): δ −0.10, 0.28 (s, 6 H, Si(CH3)2), 0.69 (s, 18 H, Si−C(CH3)3),
0.92 (s, 3 H, CH3), 2.28 (s, 3 H, p-CH3), 2.30 (s, 3 H, p-CH3), 2.58 (s,
t
Si(CH3)2 Bu), 279.1 (Npy), 289.3 (L−Npy), 330.5 (ZrN). IR (Nujol,
2
NaCl): ν 1601 m, 1463 s, 1377 s, 1311 m, 1253 w, 1210 w, 1161 w,
1088 w, 1054 m, 1010 w, 889 m, 874 s, 824 m, 801 w, 767 w 722 m
cm−1. Anal. Calcd for C35H57N5Si2Zr: , 60.46; H, 8.26; N, 10.07.
Found: C, 59.98; H, 8.17; N, 9.81.
6 H, o-CH3), 2.79 (s, 6 H, o-CH3), 3.22 (d, JHH = 12.5 Hz, 2 H,
CHH), 3.87 (d, 2JHH = 12.7 Hz, 2 H, CHH), 6.21 (t, 3JH5pyH4py/H6py
=
6.7 Hz, 1 H, H5py), 6.69 (d, 3JH3pyH4py = 7.8 Hz, H3py), 6.92 (s, 2 H, m-
Hmes), 6.94−6.99 (m, 3 H, H4py, m-Hmes), 7.54 (d, 3JH6pyH5py = 5.6 Hz,
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2
1 H, H6py). 15N NMR (60 MHz, C6D6, 296 K): δ 386.5, 388.3 (N
N).
Ad−CHH), 1.79 (d, JHH = 12.1 Hz, 3 H, Ad−CHH), 2.12 (bs, 3H,
2
Ad−CH), 2.21 (bs, 6H, Ad−CH2), 3.57 (d, JHH = 13.5 Hz, 2 H,
TBS
Preparation of [Zr(κN,N,N,N,C-N2 Npy)(HNMesN2NMes)] (7).
CHH), 4.03 (d, 2JHH3 = 13.5 Hz, 2 H, CHH), 6.89 (t, 3JpHmH = 7.6 Hz 2
TBS
3
To a stirred solution of [Zr(N2 Npy)(NMes)(py)] (3; 300 mg, 0.43
H, p-HPh), 7.15 (t, JmHo/pH = 7.6 Hz, 4 H, m-HPh), 7.26 (d, JoHmH
=
3
mmol) in toluene (15 mL) was added a solution of mesityl azide (70
mg, 0.43 mmol) in 5 mL of toluene. The reaction mixture was stirred
for 16 h at 80 °C and filtered, and the volatiles were removed in vacuo.
The crude product was washed with hexane (3 × 5 mL) and dried in
vacuo to yield 200 mg (0.26 mmol, 60%) of 7 as a pale yellow solid.
Single crystals for X-ray diffraction were grown from a saturated
7.6 Hz, 4 H, o-HPh), 7.47 (t, JH5pyH6/H4py = 7.3 Hz, 1 H, H5py), 7.82
(d, 3JH3pyH4py = 7.3 Hz, 1 H, H3py), 8.10 (t, 3JH5pyH6/H4py = 7.3 Hz, 1 H,
H4py), 9.66 (d, JH6pyH5py = 7.3 Hz, H6py). 13C{1H} NMR (150 MHz,
3
THF-d8, 296 K): δ −3.2 (Si(CH3)2), 20.4 (Si−C(CH3)3), 26.5 (C−
CH3), 28.1 (Si−C(CH3)3), 31.3 (Ad−CH), 37.9 (Ad−CH2), 43.7
(Ad−CH2), 47.5 (C−CH3), 59.0 (Ad−CN), 63.4 (CH2), 122.9 (p-
CPh), 123.2 (o-CPh), 123.4 (C3py), 123.8 (C5py), 129.2 (m-CPh), 141.9
(C4py), 148.4 (C6py), 151.5 (N−CPh), 161.2 (C2py). 29Si{1H} NMR
1
toluene solution at room temperature. H NMR (600 MHz, THF-d8,
296 K): δ −0.33, 0.24, −0.04 (s, 3 H, Si(CH3)2), 0.85 (s, 3 H, CH3),
1.00 (s, 9 H, Si−C(CH3)3), 2.19 (m, 9 H, o-CH3, m-CH3), 2.22−2.42
(s, 3 H, p-CH3, o-CH3, o-CH3), 3.14 (d, 2JHH = 11.9 Hz, 1 H, CHH),
(80 MHz, THF-d8, 296 K): δ 4.32 (Si(CH3)2 Bu). 15N NMR (60
t
t
MHz, THF-d8, 296 K): δ 122.2 (NPh2), 189.1 (N−Si(CH3)2 Bu),
2
3.43 (d, JHH = 12.9 Hz, 1 H, CHH), 3.54−3.60 (m, 2 H, CHH,
276.4 (L−Npy), 292.4 (ZrN), 303.8 (N−C10H15), 374.7 (NN),
380.8 (NN). IR (Nujol, NaCl): ν 3109 w, 2361 w, 1606 w, 1588 w,
1462 s, 1377 s, 1304 w, 1259 m, 1174 w, 1105 w, 1089 w, 1031 m, 936
m, 866 s, 827 m, 775 m, 752 w cm−1. Anal. Calcd for C43H66N8Si2Zr:
C, 61.31; H, 7.90; N, 13.30. Found: C, 61.25; H, 7.79; N, 12.87.
CHH), 3.91 (d, 2JHH = 13.5 Hz, 1 H, CHH), 4.17 (d, 2JHH = 12.9 Hz, 1
H, CHH), 6.52 (s, 1 H, Mes-NH), 6.70−6.84 (m, 4 H, H-Mes), 7.20
3
3
(t, JH5pyH4py/H6py = 6.5 Hz, 1 H, H5py), 7.68 (d, JH3pyH4py = 8.0 Hz,
H3py), 7.93 (t, 3JH4pyH5py/H3py = 7.7 Hz, 1 H, H4py), 8.53 (d, 3JH6pyH5
=
5.4 Hz, 1 H, H4py). 13C{1H} NMR (150 MHz, THF-d8, 296 K): δ
−5.8, −4.1, −3.3 (Si(CH3)2), 19.8, 20.9 (Mes−CH3), 21.1, 21.2 (Si−
C(CH3)3), 21.3, 22.8 (Mes−CH3), 24.6 (o-CH3), 27.8 (C-CH3), 28.2,
28.3 (Si−C(CH3)3), 47.0 (CH2−Si), 51.1 (C−CH3), 61.6, 63.2 (CH2),
122.5 (C3py), 123.0 (C5py), 126.4 (Mes-Cq), 129.3, 130.4 (Mes-CH),
135.3 (Mes-Cq), 140.8 (C4py), 147.3 (Mes-Cq), 148.7 (C6py), 150.6
(Mes-Cq), 163.3 (C2py). 29Si{1H} NMR (80 MHz, THF-d8, 296 K): δ
0.84, 6.42 (Si(CH3)3). 15N NMR (60 MHz, THF-d8, 296 K): δ 164.0
Preparation of [Zr(N2 Npy)(NNAdNPh2)] (12). A solution of
TBS
TBS
[Zr(N2 Npy)(NAdN3NPh2)] (11; 800 mg, 0.95 mmol) in THF (20
mL) was strirred for 10 days at 70 °C. The reaction mixture was
filtered, and the volatiles were removed in vacuo. The crude product
was recrystallized from cold pentane (−78 °C) to yield 220 mg (0.27
1
mmol, 28%) of 12 as a red solid. H NMR (600 MHz, THF-d8, 296
K): δ 0.00, 0.13 (s, 6 H, Si(CH3)2), 0.66 (s, 18 H, Si−C(CH3)3), 1.51
(s, 3 H, CH3), 1.56−1.63 (m, 6 H, Ad−CH2), 1.66 (bs, 6 H, Ad−
t
2
(N−Si(CH3)2 Bu), 171.9 (N−SiCH2), 176.8 (Mes−NH), 284.0
CH2), 2.06 (bs, 3 H Ad−CH), 3.34 (d, JHH = 12.1 Hz, 2 H, CHH),
(H2C−NN), 287.4 (L−Npy), 288.6 (NN−Mes), 502.2 (NNN). IR
(Nujol, NaCl): ν 3286 w, 1602 m, 1464 s, 1377 s, 1303 m, 1252 s,
1162 w, 1090 w, 1069 w, 1040 w, 1014 w, 955 w, 864 s, 852 s, 825 s,
776 m, 727 m. Anal. Calcd for C39H63N7Si2Zr: C, 60.26; H, 8.17; N,
12.61. Found: C, 60.36; H, 8.44; N, 12.15.
4.02 (d, 2JHH = 12.1 Hz, 2 H, CHH), 6.70 (t, 3JpHmH = 7.3 Hz 2 H, p-
3
HPh), 6.77 (d, JoHmH = 7.6 Hz, 4 H, o-HPh), 7.02−7.06 (m, 5H, m-
HPh, H5py), 7.17−7.23 (m, 1 H, H3py), 7.89 (t, 3JH4pyH5py/H6py = 7.6 Hz,
H4py), 8.87 (d, JH6pyH5py = 5.0 Hz, 1 H, H6py). 13C{1H} NMR (150
3
MHz, THF-d8, 296 K): δ −3.2, −3.7 (Si(CH3)2), 20.9 (Si−C(CH3)3),
25.2 (C−CH3), 28.6 (Si−C(CH3)3), 31.0 (Ad−CH), 37.4 (Ad−CH2),
40.2 (Ad−CH2), 50.1 (C−CH3), 64.0 (CH2), 76.9 (Ad−CN), 120.8
(p-CPh), 122.2 (C5py), 122.6 (C3py), 126.1 (o-CPh), 129.1 (m-CPh),
140.3 (C4py), 147.3 (C6py), 156.8 (N-CPh), 164.1 (C2py). 29Si{1H}
TBS
Preparation of [Zr(N2 Npy)(NTMSN3NPh2)] (10). To a stirred
TBS
solution of [Zr(N2 Npy)(NNPh2)(py)] (9; 800 mg, 0.84 mmol) in
toluene (20 mL) was added trimethylsilyl azide (178 μL, 0.84 mmol)
dropwise. The reaction mixture was stirred overnight at room
temperature. The volatiles were removed under reduced pressure,
and the resulting yellow solid was washed with pentane (3 × 5 mL)
before drying in vacuo to yield 606 mg (65%) of 10 as a pale yellow
solid. Single crystals for X-ray diffraction were grown from a saturated
toluene solution at 10 °C. 1H NMR (600 MHz, C6D6, 296 K): δ 0.07,
0.19 (s, 6 H, Si(CH3)2), 0.62 (s, 18 H, Si−C(CH3)3), 0.66 (s, 9 H,
t
NMR (80 MHz, THF-d8, 296 K): δ 2.06 (Si(CH3)2 Bu). 15N NMR
t
(60 MHz, THF-d8, 296 K): δ 164.3 (N−Si(CH3)2 Bu), 201.0 (NPh2),
286.9 (L−Npy), 540.1 (N−C10H15), 804.2 (ZrN). IR (Nujol, NaCl): ν
2735 w, 1585 w, 1486 sh, 1464 s, 1377 m, 1302 w, 1246 m, 1193 w
1089 m, 1050 s, 858 s, 828 m, 798 w, 751 w, 699 w cm−1. Anal. Calcd
for C43H66N6Si2Zr: C, 63.41; H, 8.17; N, 10.32. Found: C, 63.24; H,
8.03; N, 9.83.
2
Si(CH3)3), 0.96 (s, 3 H, CH3), 3.39 (d, JHH = 13.0 Hz, 2 H, CHH),
TBS
3.84 (d, 2JHH = 13.0 Hz, 2 H, CHH), 6.47 (m, 1 H, H5py), 6.83−6.92
Preparation of [Zr(N2 Npy)(NNMesNPh2)] (13). To a solution of
3
TBS
(m, 3 H, H3, p-HPh), 7.06 (t, JH4pyH3py/5py = 7.1 Hz, 1 H, H4py), 7.16
[Zr(N2 Npy)(NNPh2)(py)] (9; 500 mg, 0.67 mmol) in toluene (20
(t, 3JmHo/pH = 8.0 Hz, 4 H, m-HPh), 7.56 (d, 3JoHmH = 8.0 Hz, 4JoHpH
=
mL) was added mesityl azide (107 μL, 0.67 mmol). The reaction
mixture was stirred for 1 h at room temperature and filtered, and the
volatiles were removed under reduced pressure. The crude product
was washed with pentane (3 × 5 mL) and dried in vacuo to yield 310
mg (0.39 mmol, 58%) of 13 as a pink solid. Single crystals for X-ray
diffraction were grown from a saturated toluene solution at 10 °C. 1H
NMR (600 MHz, THF-d8, 296 K): δ −0.39, −0.13 (s, 6 H, Si(CH3)2),
0.63 (s, 18 H, Si−C(CH3)3), 1.56 (s, 3 H, CH3), 2.17 (s, 6 H, o-Mes−
1.1 Hz, 4 H, o-HPh), 9.69 (d, 3JH6pyH5py = 5.1 Hz, H6py). 13C{1H} NMR
(150 MHz, C6D6, 296 K): δ −3.8, −3.2 (Si(CH3)2), 1.5 (Si(CH3)3),
19.9 (Si−C(CH3)3), 26.1 (C−CH3), 27.8 (Si−C(CH3)3), 46.9 (C−
CH3), 62.6 (CH2), 121.3 (C3py), 122.8 (o-CPh, p-CPh, C5py), 140.5
(C4py), 147.9 (C6py), 151.0 (N−CPh), 160.5 (C2py). 29Si{1H} NMR
t
(80 MHz, C6D6, 296 K): δ 0.47 (Si(CH3)3), 5.01 (Si(CH3)2 Bu). 15N
NMR (60 MHz, C6D6, 296 K): δ 121.4 (NPh2), 189.9 (N−
t
2
Si(CH3)2 Bu), 275.3 (L−Npy), 291.3 (ZrN), 293.8 (N−Si(CH3)3),
CH3), 2.29 (s, 3 H, p-Mes−CH3), 3.57 (d, JHH = 12.4 Hz, 2 H,
378.6 (NN), 411.4 (NN). IR (Nujol, NaCl): ν 1603 m, 1490 m,
1463 s, 1377 m, 1244 m 1169 w, 1088 w, 1042 m 917 m, 864 s, 825 m,
800 m, 752 m, 694 m, 666 w cm−1. Anal. Calcd for C36H60N8Si3Zr: C,
55.41; H, 7.75; N, 14.36. Found: C, 55.42; H, 7.87; N, 13.91.
CHH), 3.71 (d, 2JHH = 12.4 Hz, 2 H, CHH), 6.71 (t, 3JpHmH = 7.2 Hz 2
H, p-HPh), 6.89 (d, 3JoHmH = 8.0 Hz, 4 H, o-HPh), 6.91 (s, 2 H, o-HMes),
7.06 (t, 3JmHo/pH = 4 H, 7.4 Hz), 7.27 (d, 3JH5pyH4py/H6py = 6.7 Hz, 1H,
H5py), 7.72 (d, 3JH3pyH4py = 8.0 Hz, 1 H, H3py), 7.99 (t, 3JH4pyH5py/H6py
=
TBS
Preparation of [Zr(N2 Npy)(NAdN3NPh2)] (11). To a stirred
7.4 Hz, H4py), 9.11 (d, 3JH6pyH5py = 5.6 Hz, 1 H, H6py). 13C{1H} NMR
(150 MHz, THF-d8, 296 K): δ −3.9, −3.3 (Si(CH3)2), 19.2 (o-Mes−
CH3), 21.1 (Si−C(CH3)3), 21.3 (p-Mes−CH3), 25.8 (C−CH3), 28.6
(Si−C(CH3)3), 49.4 (C−CH3), 64.3 (CH2), 120.4 (p-CPh), 122.2
(C3py), 123.2 (C5py), 124.4 (o-CPh), 129.7 (m-CPh), 130.8 (m-C−
Mes), 138.9 (Mes−CCH3), 141.1 (C4py), 150.3 (C6py), 150.8 (Cq−
Mes), 155.1 (N−CPh), 164.0 (C2py). 29Si{1H} NMR (80 MHz, THF-
TBS
solution of [Zr(N2 Npy)(NNPh2)(py)] (9; 800 mg, 0.84 mmol) in
toluene (20 mL) was added a solution of 1-adamantyl azide (211 mg,
0.84 mmol) in 5 mL of toluene dropwise. The reaction mixture was
stirred at room temperature for 10 h. The volatiles were removed
under reduced pressure, and the resulting yellow solid was washed
with pentane (3 × 5 mL) before drying in vacuo to yield 710 mg
(71%) of 11 as a yellow solid. Single crystals for X-ray diffraction were
t
d8, 296 K): δ 3.09 (Si(CH3)2 Bu). 15N NMR (60 MHz, THF-d8, 296
1
t
grown from a saturated toluene solution at 10 °C. H NMR (600
K): δ 166.4 (N−Si(CH3)2 Bu), 186.6 (NPh2), 284.1 (L−Npy), 489.1
MHz, THF-d8, 296 K): δ −0.22, 0.03 (s, 6 H, Si(CH3)2), 0.57 (s, 18
(N−Mes), 810.9 (ZrN). IR (Nujol, NaCl): ν 2728 w, 1602 w, 1583 w,
2
H, Si−C(CH3)3), 1.59 (s, 3 H, CH3), 1.72 (d, JHH = 12.1 Hz, 3 H,
1464 s, 1377 s, 1260 s, 1260 m, 1184 w, 1163 w, 1087 w, 1031 m, 907
4512
dx.doi.org/10.1021/om300291b | Organometallics 2012, 31, 4504−4515

Organometallics
Article
Table 5. Details of the Crystal Structure Determinations of 2, 5, 7, 10, 11, and 13
2
5
7
10
11
13
formula
Mr
C41H70N5Si2Zr
780.42
C36H57N7Si2Zr
735.29
C42H70N7Si2Zr
820.45
C50H76N8SiZr
964.68
C53.50H78N8Si2Zr
980.64
C42H62N6Si2Zr
798.38
cryst syst
space group
a/Å
monoclinic
P21/c
monoclinic
P21/n
triclinic
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/c
P1
̅
16.110(9)
14.099(8)
19.575(12)
11.902(6)
19.455(9)
17.797(10)
14.881(6)
15.938(7)
22.278(11)
71.86(1)
75.37(1)
67.36(1)
4581(4)
4
12.089(1)
24.999(2)
16.865(1)
12.184(2)
26.096(4)
16.732(3)
14.713(2)
10.081(2)
28.870(4)
b/Å
c/Å
α/deg
β/deg
100.81(1)
108.790(8)
97.037(2)
97.041(3)
98.683(3)
γ/deg
V/Å3
4367(4)
4
3901(4)
4
5058.4(7)
4
5280(1)
4
4233(1)
4
Z
F000
1676
1560
1756
2056
2092
1696
dc/Mg m−3
μ(Mo Kα)/mm−1
1.187
1.252
1.190
1.267
1.234
1.253
0.339
0.377
0.328
0.330
0.296
0.352
max, min transmissn
factors
1.0000, 0.8980
0.7464, 0.6887
0.7461, 0.6222
0.7464, 0.6786
0.7458, 0.6850
0.7464, 0.6637
θ range/deg
1.9−30.5
2.1−30.5
1.0−28.3
1.9−25.0
1.9−28.7
2.1−30.0
index ranges (indep set)
−23 to +22, 0−20, −16 to +16, 0− 27, −19 to +19, −19 to
−14 to +14, 0−29, −16 to +16, 0−35,
−20 to +20, 0−14,
h,k,l
0−27
0−25
+21, 0−29
95 644
0−20
0−22
0−40
no. of rflns measd
105 978
95 286
85 154
114 872
79 980
no. of unique rflns (Rint)
13 321 (0.0721)
9832
11 898 (0.0719)
9072
22 728 (0.0666)
15 574
8898 (0.0454)
7469
13 644 (0.0782)
9902
12 354 (0.0537)
8709
no. of obsd rflns (I ≥
2σ(I))
no. of params refined
GooF on F2
517
429
967
511
645
552
1.016
1.029
1.057
1.075
1.053
1.111
R indices (F > 4σ(F)):
R(F), Rw(F2)
0.0386, 0.0748
0.0376, 0.0791
0.0533, 0.1350
0.0346, 0.0868
0.0452, 0.0997
0.0665, 0.1776
R indices (all data): R(F), 0.0672, 0.0852
0.0604, 0.0894
0.0890, 0.1500
0.0453, 0.0932
0.0791, 0.1203
0.0937, 0.1923
Rw(F2)
largest residual peaks/e Å−3 0.682, −0.362
0.984, −0.545
2.089, −0.952
1.668, −0.529
1.053, −0.717
2.797, −1.262
w, 799 m, 776 m, 748 w, 722 w, 697 m cm−1. Anal. Calcd for
C42H62N6Si2Zr: C, 63.18; H, 7.83; N, 10.53. Found: C, 62.98; H, 7.81;
N, 10.14.
Theoretical 15N NMR Shifts. NMR calculations have been carried
out with the GIAO-B3PW91 hybrid functional36 with a 6-311+
+g(2d,2p) basis set for N, 6-31++g(d) basis set37 for C and Si, 6-31g
for H, and SDD + f function effective core potential basis set for Zr.36
X-ray Crystal Structure Determinations,. Crystal data and
details of the structure determinations are given in Table 5.
Preliminary accounts of the structures of 10, 11, and 13 have
appeared.11 Full shells of intensity data were collected at low
temperature with a Bruker AXS Smart 1000 CCD diffractometer (T
= 100 K, Mo Kα radiation, graphite monochromator, λ = 0.710 73 Å).
Data were corrected for air and detector absorption, Lorentz, and
polarization effects;24 absorption by the crystal was treated by
numerical means25 or with a semiempirical multiscan method.25,26
The structures were solved by the charge flip procedure27 (complexes
2, 5, and 7), by conventional direct methods28,29 (complex 11), by
direct methods with dual-space recycling29,30 (complex 10), or by the
heavy-atom method combined with structure expansion by direct
methods applied to difference structure factors31 (complex 13) and
refined by full-matrix least-squares methods based on F2 against all
unique reflections.29,32 All non-hydrogen atoms were given anisotropic
displacement parameters. Hydrogen atoms were placed at calculated
positions and refined with a riding model.29 When found necessary,
disordered groups and/or solvent molecules where subjected to
suitable geometry and adp restraints. Due to severe disorder and
fractional occupancy, electron density attributed to the solvent of
crystallization was removed from the structures (and the correspond-
ing Fo values) of 7 (hexane) and 10 (toluene) with the BYPASS
procedure,33 as implemented in PLATON (SQUEEZE).34
ASSOCIATED CONTENT
■
S
* Supporting Information
Tables giving Cartesian coordinates of all stationary points and
CIF files giving crystallographic data for compounds 2, 5, 7, 10,
11, and 13. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*Fax: (+49) 6221-545609. E-mail: lutz.gade@uni-hd.de.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the University of Heidelberg and the Deutsche
Forschungsgemeinschaft for funding (SFB 623, TP A7) as well
as the EU for a Marie Curie postdoctoral fellowship (to J.L.F.).
Computational Studies. The B3PW91 hybrid functional15 has
been employed to model all the systems by DFT using a 6-31g(d)
basis set for C, N, and H atoms and an SDD + f function effective core
potential basis set for Zr.16,35 All the calculations have been carried out
with the GAUSSIAN0936 program package. Stationary points were
verified by frequency analysis.
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Organometallics
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