Zirconium hydrazides as metallanitrene synthons: Release of molecular N2 from a hydrazinediido complex induced by oxidative N-N bond cleavage

Article abstract of DOI:10.1021/om400337g

The N-N bond in the zirconium hydrazinediido(2-) complex [Zr(N ₂^TBSN_py)(NNPh₂)(py)] (1) is readily cleaved by one-electron oxidation. Reacting [Zr(N₂ ^TBSN_py)(NNPh₂)(py)] (1) with 0.5 molar equiv of iodine led to the release of molecular N₂ and yielded the mixed diphenylamido/iodo complex [Zr(N₂^TBSN_pyNPh ₂)(I)] (2). Exposure of hydrazinediide 1 to an excess of iodine resulted in further oxidation of the diphenylamido ligand, yielding the diiodo complex 3 and tetraphenylhydrazine. Similar reactivity was observed in the reaction of 1 with diphenyl diselenide and diaryl disulfides, which reacted to give the corresponding diphenylamido/arylchalcogenido complexes [Zr(N ₂^TBSN_pyNPh₂)(SePh)] (4a) and [Zr(N₂^TBSN_py)(NPh₂)(SAr)] (Ar = Ph (4b), C₆F₅ (4c)) along with N₂. The reactions were also carried out on an NMR scale with a ¹⁵N_α- labeled hydrazido complex (1-¹⁵N). In all cases a single ¹⁵N NMR resonance at 310.16 ppm, assigned to ¹⁵N ₂, indicated the formation of dinitrogen from the N_α atom in the hydrazide. A crossover labeling experiment employing a 1:1 mixture of 1 and ¹⁵N_α-labeled 1-¹⁵N revealed that the isotope distribution is, as expected, statistical 1:2:1 ( ¹⁴N₂: ^14/15N₂: ¹⁵N ₂), which is consistent with a reaction pathway involving a dinuclear intermediate in the dinitrogen-forming step. Complex 1 reacted with N ₂O to give a mixture of two compounds, the bis(diphenylamido) complex 6 and the doubly bridged μ-oxo complex 7. In contrast, reaction of 1 with 1 molar equiv of pyridinium N-oxide only gave the doubly bridged μ-oxo complex 7 along with 2,2′-bipyridine and diphenylamine.

Full text of DOI:10.1021/om400337g

Article
pubs.acs.org/Organometallics
Zirconium Hydrazides as Metallanitrene Synthons: Release of
Molecular N2 from a Hydrazinediido Complex Induced by Oxidative
N−N Bond Cleavage
Thorsten Gehrmann,† Julio Lloret-Fillol,‡ Heike Herrmann,† Hubert Wadepohl,† and Lutz H. Gade*,†
†Anorganisch-Chemisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
̈
‡Departament de Quimica, QBIS, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
S
* Supporting Information
ABSTRACT: The N−N bond in the zirconium hydrazinedii-
TBS
do(2−) complex [Zr(N2 Npy)(NNPh2)(py)] (1) is readily
TBS
cleaved by one-electron oxidation. Reacting [Zr(N2 Npy)-
(NNPh2)(py)] (1) with 0.5 molar equiv of iodine led to the
release of molecular N2 and yielded the mixed diphenylamido/
TBS
iodo complex [Zr(N2 NpyNPh2)(I)] (2). Exposure of
hydrazinediide 1 to an excess of iodine resulted in further
oxidation of the diphenylamido ligand, yielding the diiodo
complex 3 and tetraphenylhydrazine. Similar reactivity was
observed in the reaction of 1 with diphenyl diselenide and diaryl disulfides, which reacted to give the corresponding
TBS
TBS
diphenylamido/arylchalcogenido complexes [Zr(N2 NpyNPh2)(SePh)] (4a) and [Zr(N2 Npy)(NPh2)(SAr)] (Ar = Ph (4b),
C6F5 (4c)) along with N2. The reactions were also carried out on an NMR scale with a 15Nα-labeled hydrazido complex (1-15N).
In all cases a single 15N NMR resonance at 310.16 ppm, assigned to 15N2, indicated the formation of dinitrogen from the Nα
atom in the hydrazide. A crossover labeling experiment employing a 1:1 mixture of 1 and 15Nα-labeled 1-15N revealed that the
isotope distribution is, as expected, statistical 1:2:1 (14N2: 14/15N2: 15N2), which is consistent with a reaction pathway involving a
dinuclear intermediate in the dinitrogen-forming step. Complex 1 reacted with N2O to give a mixture of two compounds, the
bis(diphenylamido) complex 6 and the doubly bridged μ-oxo complex 7. In contrast, reaction of 1 with 1 molar equiv of
pyridinium N-oxide only gave the doubly bridged μ-oxo complex 7 along with 2,2′-bipyridine and diphenylamine.
oxidatively coupled to form μ-bridging N2 complexes or release
molecular nitrogen.10 Formally such an N−N bond re-
formation step may be coupled to the N−N bond cleavage in
a redox chemical transformation of a metal hydrazinediide (in
the process the oxidation state of the metal is reduced from n to
n − 1):
INTRODUCTION
■
Early-transition-metal hydrazides are thought to be intermedi-
ates in the reductive activation of dinitrogen.1 A key aim has
been the development of molecular catalysts for Haber−Bosch
type chemistry2 as well as the direct activation of N2 for the
synthesis of more complex organic products.3 Proof of principle
for the former has been provided by Schrock and co-workers a
decade ago,4 and the conversion of metal-coordinated
hydrazides to organic nitrogen compounds, in particular N-
heterocycles, was pioneered by the Leigh and Hidai groups.5
Group 4 metal hydrazides have only been studied systematically
during the past decade6 and have been identified as active
species inter alia in catalytic hydrohydrazinations of alkynes.7
These transformations have been further incorporated into
metal-catalyzed domino reactions such as indole cyclization8
and other multicomponent reactions leading to N-hetero-
cycles.9
Whereas research on dinitrogen activation has obviously
focused on the reductive cleavage of the N−N bond, it has been
shown that the nitrido ligands, which may be viewed as
fragments resulting from such a process of reductive N−N
scission, may in turn be oxidatively coupled to regenerate the
N2 unit. In this context, several group 8 metal nitrido
complexes in high oxidation states have been prepared and
We recently studied the reactivity of the zirconium
11,12
TBS
hydrazinediido complex [Zr(N2 Npy)(NNPh2)(py)] (1)
and found that in many of the transformations this
hydrazinediide may be viewed formally as a synthon for a
metallanitrene which readily undergoes coupling reactions with
unsaturated substrates.12 Such metallanitrenes could emerge
from the hydrazinediide A via type C bent structures, as
observed on Lewis acid adducts of the hydrazinediido complex,
leading to a type D species (Chart 1).13
A computational study has shown that such a metallanitrene
D would be a high-energy species, and combined experimental
and computational mechanistic studies of the observed reaction
Received: April 18, 2013
Published: July 8, 2013
© 2013 American Chemical Society
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Chart 1
Chart 2
Scheme 1. Oxidative N−N Bond Cleavage in the Reaction of 1 with Iodine, Phenyl Disulfide, or Diaryl Diselenide To Give the
Complexes 2−5
patterns of complex 1 indicate that such species do not play a
role as intermediates in these reactions, despite their formal
relationship to the observed products (Chart 2).11a,13 Instead,
initial coupling of a substrate with ZrN−NR2 (inter alia as
formal 2 + 2 cycloaddition) appears to induce cleavage of the
N−N bond and migration of the NR2 unit. Nevertheless, the
notion of the hydrazinediido ligand as a synthon for a nitrene
species remains a useful heuristic concept.
N−N bond scission of a group 4 metal hydrazinediide with an
oxidation step might lead to the coupling of two of the metal-
bonded nitrogen atoms. We therefore investigated the behavior
of the previously reported zirconium hydrazinediido complex 1
toward oxidizing agents.
RESULTS AND DISCUSSION
■
TBS
Reactions of [Zr(N2 Npy)(NNPh2)(py)] (1) with I2 and
Nitrido and nitrene complexes differ in their metal−nitrogen
bonding but otherwise are closely related.14 Combination of the
Ar−E−E−Ar (E = S, Se). Reacting [Zr(N2 Npy)(NNPh2)-
TBS
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Figure 1. Molecular structures of complexes 2 (a), 4a (b), and 4b (c; only one of the two independent molecules is shown). Hydrogen atoms are
omitted for clarity. Selected bond lengths and angles are given in Table 1.
(py)] (1)11a with 0.5 molar equiv of iodine led to the release of
formation of dinitrogen from the former Nα in the hydrazide
(all 15N chemical shifts relative to 15NH3 as reference). A
crossover labeling experiment (see the Experimental Section)
employing a 1:1 mixture of 1 and 15Nα-labeled 1-15N revealed
that the expected statistical isotope distribution
(14N2:14/15N2:15N2 = 1:2:1) is consistent with a reaction
pathway involving a dinuclear intermediate in the dinitrogen-
forming step (vide infra).
In order to establish the structural details of the complexes 2
and 4a,b, single-crystal X-ray structure analyses were carried
out. Their molecular structures are closely related and depicted
in Figure 1; a comparative listing of the principal bond lengths
and angles is given in Table 1. The coordination geometries in
compounds 2 and 4a,b are best described as distorted trigonal
bipyramidal with the diphenylamido ligand in an equatorial
position and the pyridyl and ER (E = S, Se) groups in axial
sites. This is in contrast to, for instance, the related
carbodiimido complexes prepared from the hydrazinediido
complex 1 and isocyanides represented in Chart 2 (NR′2
axial).11a
The halogenido and aryl chalcogenido ligands are bonded in
the second axial position, in trans disposition to the pyridyl
nitrogen donor atom with bond lengths in the range found in
the literature15 (Zr(1)−I(1) = 2.8889(11) Å (2), Zr(I)−Se(I)
= 2.629(9) Å (3), Zr(I)−S(I) = 2.5711(11) Å (4b)). Although
it was not characterized by X-ray diffraction, we assume that the
fluorido complex 5 possesses the same overall structure. In the
19F NMR spectrum one singlet is observed at δ 95.0, in the
typical range for fluorine nuclei bound terminally to a
zirconium(IV) center.16
molecular N2 (vide infra) and selectively yielded the mixed
TBS
diphenylamido/iodo complex [Zr(N2 NpyNPh2)(I)] (2).
Exposure of hydrazinediide 1 to an excess of iodine resulted
in further oxidation of the diphenylamido ligand, giving the
diiodo complex 3 and tetraphenylhydrazine. Complex 3 is also
obtained on reacting 2 with excess I2. Similar reactivity was
observed in the reaction of 1 with diphenyl diselenide and
diaryl disulfides, which reacted to give the corresponding
diphenylamido/arylchalcogenido complexes [Zr-
TBS
TBS
(N2 NpyNPh2)(SePh)] (4a) and [Zr(N2 Npy)(NPh2)-
(SAr)] (Ar = Ph (4b), C6F5 (4c)) along with N2. However,
oxidation of the diphenylamido ligand was not observed, even
with a 10-fold excess of diaryl dichalcogenide. Evolution of N2
was observed in the reaction of 1 with 1 molar equiv of silver(I)
fluoride, giving the fluorido complex 5 and silver(0) (Scheme
1). Complex 5 was also obtained by electrolysis (10 min, 1 V)
of a thf solution of hydrazinediide 1 in presence of 1 equiv of
the conducting salt tetrabutylammonium hexafluorophosphate,
(n-Bu)4NPF6.
The analytical data as well as the 1H, 13C, 15N, and 29Si NMR
spectra are consistent with the molecular structures as displayed
in Scheme 1. To satisfy the atom and electron count in these
reactions, the extrusion of molecular N2 is required and is
consistent with the observation of gas evolution during the
course of the transformations. To prove the identity of the
evolved gas unambiguously and to establish its origin, the
reactions described above were carried out on an NMR scale
with an 15Nα-labeled hydrazido complex (1-15N). In all cases a
single resonance at 310.1 ppm was observed in the 15N NMR
spectra, which is assigned to 15N2, indicating clearly the
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Table 1. Selected Bond Lengths and Angles of Complexes 2
and 4a,b
Scheme 2. Initial One-Electron Oxidation of 1 by Iodine and
Displacement of Pyridine, Generating the Radical Hydrazide
Intermediate II
bond length (Å) or angle
a
(deg)
2
4a
4b
Zr(1)−N(1)
2.034(2)
2.045(4)
2.034(4),
2.045(4)
Zr(1)−N(3)
Zr(1)−N(4)
2.374(2)
2.133(1)
2.889(1)
2.385(4)
2.138(4)
2.365(4),
2.370(4)
2.146(4),
2.143(4)
Zr(1)−I(1)
Zr(1)−S(1)
Zr(1)−Se(1)
2.571(1)
2.683(2),
2.686(2)
compound II the Zr(1)−N(1) bond is longer (by 0.13 Å) and
the N(1)−N(2) bond shorter (by 0.07 Å) than in 1, indicating
that the oxidation primarily involves the {Zr−N−N} fragment.
Previous NLMO analysis of the electronic structure of the
N(3)−Zr−N(4)
86.59(6)
86.6(1)
86.6(2), 86.5(2)
N(3)−Zr(1)−I(1)
N(3)−Zr(1)−S(1)
N(3)−Zr(1)−Se(1)
174.11(4)
174.83(9)
174.3(1),
173.7(1)
TBS
[Zr(N2 Npy)(NNPh2)(py)] starting complex characterized
Zr(1)−S(1)−C(34)
Zr(1)−Se(1)−C(34)
113.4(2)
the formally dianionic NNPh2 unit as a six-electron-donor
ligand, which bonds to the Zr atom via one σ and two π
nitrogen highly polarized molecular orbitals, one of the π
orbitals of the {Zr(1)−N(1)−N(2)} fragment being the
HOMO.13 Removing one electron from the π-conjugated
HOMO therefore reduces the Zr(1)−N(1) bond and increases
the N(1)−N(2) bond order, which accounts for the structural
changes upon one-electron oxidation (Table 2).
110.1(2),
110.7(2)
a
Two independent molecules.
The complexity of the redox reactions involving the N2 re-
formation resulting from multistep reaction sequences
precluded a complete computational analysis of a mechanism.
However, given the experimental results described above, it is
possible to speculate about a potential mechanistic scheme and
to test the viability of key reaction steps with the aid of
modeling tools. Therefore, the oxidation of zirconium
Table 2. Comparison between Selected Distances (in Å)
Calculated for Compounds 1 and II
TBS
TBS
TBS
[Zr(N2 Npy)(NNPh2)
[Zr(N2 Npy)(NNPh2)
hydrazinediide [Zr(N2 Npy)(NNPh2)(py)] (1) leading to
(py)] (1)
(I)] (II)
the extrusion N2 molecules derived entirely from the Zr-bound
Nα atom of the hydrazinediide was partially modeled using the
ONIOM hybrid DFT(uB3PW91)/UFF computational tool.17
For this study we selected the reaction of zirconium complex
Zr(1)−N(1)
N(1)−N(2)
Zr(1)−N(3)
Zr(1)−N(4)
1.871
1.373
2.152
2.120
1.998
1.299
2.086
2.062
TBS
[Zr(N2 Npy)(NNPh2)(py)] with I2 as oxidant, since it
appeared to involve the least complex sequence of reaction
steps and intermediates, while providing general insight into the
fragmentation of the NNR2 unit and the observed formation of
N2.
The spin density distribution on the oxidized compound II
depicted in Figure 2 illustrates the way in which the unpaired
First, the thermodynamics of the {ZrN−NPh2} fragment
TBS
oxidation in [Zr(N2 Npy)(NNPh2)(py)] by 0.5 I2 to a
TBS
[Zr(N2 Npy)(NNPh2)(I)] (II) radical species was considered
and found to be highly exothermic. Previous experimental and
TBS
theoretical studies had shown that [Zr(N2 Npy)(NNPh2)] is
energetically accessible by the displacement of the py.8f,g,13
Therefore, coordination of the oxidant (I2) to the vacant
TBS
coordination site in [Zr(N2 Npy)(NNPh2)] should induce an
internal redox process. A similar transformation is thought to
occur in the reactions with other one-electron oxidants, such as
AgF, or by electrochemical oxidation in the presence of an
excess of tetrabutylammonium hexafluorophosphate. We note
that we have not been able to identify the radical species by
EPR spectroscopy, which indicates that it is a rather short-lived
species and rapidly converts to the reaction products. Since
formal two-electron oxidations led to reaction pathways with
unacceptably high activation barriers, only the one-electron
oxidation of the hydrazide is considered: for the oxidation by I2
Figure 2. (left) Spin density distribution on compound II. (right)
Corresponding line drawing of II. The black part represents the QM
description, while the gray part represents the MM.
electron of the {Zr(1)−N(1)−N(2)} fragment is primarily
located on the two nitrogen atoms N(1) and N(2) (possessing
spin densities of 0.5 and 0.33).
The generation of molecular N2 from the metal-bonded
N(1) atom (as shown by the 15N labeling) requires the
interaction of two complex molecules at some stage of the
reaction pathway. Since dimerization of two radicals is usually a
favored process, we considered the dimerization by coupling
the atoms on which the radical is mainly located: namely, at
TBS
the transformation to [Zr(N2 Npy)(NNPh2)(I)] is favored by
−26.1 kcal mol−1 (Scheme 2).
TBS
The electronic structure of [Zr(N2 Npy)(NNPh2)] is
changed significantly by the oxidation, which is clearly reflected
in the altered Zr(1)−N(1) and N(1)−N(2) distances. In
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Scheme 3. Electronic Energy Profile Calculated for the Oxidation of 1 (I) with 0.5 I2 and the Following Sequence of Steps To
a
Form 2 (V) and 0.5 N2
a
Energies (in kcal mol−1) are given from full DFT (uB3PW91) and ONIOM (uB3PW91/UFF, in parentheses).
N(1). Such a coupling may produce dimer IV′ via N−N single-
bond formation (Scheme 3). However, the energy of this
intermediate is 21 kcal mol−1 higher than that of II, probably
due to steric repulsion of the two complex fragments.
Alternatively, a type C bent structure (Chart 1) could give
rise to an intermediate for this transformation but was found
not to correspond to an energy minimum. In fact, the oxidation
of the {Zr(1)−N(1)−N(2)} fragment stabilizes the π
conjugation and thus disfavors a bent hydrazide.
Scheme 4. Initial One-Electron Oxidation of 1 by the
Diphenyl Dichalcogenides (PhE)2 and Displacement of
Pyridine, Generating the Radical Hydrazide Intermediates
IISPh and IISePh
In contrast, a structural arrangement as in intermediate III, in
which the pyridyl unit of the ancillary tripod ligand is
decoordinated, was found to be energetically accessible.
Notably, intermediate III is sterically less encumbered than
its immediate precursor II and, consequently, the N(1)−N(1)
radical dimerization, to form intermediate IV, is now associated
with a considerably lower activation barrier (ΔE(TSIII−IV) =
−12.6 kcal mol−1) and is therefore realistic. Intermediate IV
and the observed final product V (complex 2) are connected
(endothermic by ΔE = 7.7 and 8.7 kcal mol−1, respectively).
We therefore assume a reaction sequence similar to that
detailed above for the reaction with I2.
TBS
Reactions of [Zr(N2 Npy)(NNPh2)(py)] (1) with N2O
through an energetically low lying transition state (ΔE(TSIV−V
)
and C5H5N−O. Reactions of the hydrazinediido complex 1
with the oxygen transfer reagents N2O and pyridine N-oxide
gave rise to diverse results: Bubbling N2O for 5 min through a
solution of 1 in toluene led to a mixture of two compounds, the
bis(diphenylamido) complex 6 and the doubly bridged μ-oxo
= −11.0 kcal mol−1). In the process, two N−N bonds of the N-
NPh2 ligands and the two Zr(1)−N(1) are broken, two Zr−
NPh2 bonds are formed concomitantly, and a NN molecule
is subsequently ejected. The nitrogen atoms of the liberated
dinitrogen molecule would thus originate from the Nα atoms of
the hydrazido unit, in agreement with the results of the 15N
-labeling experiments.
TBS
complex 7 (Scheme 5). In contrast, reaction of [Zr(N2 Npy)-
(NNPh2)(py)] (1) with 1 molar equiv of pyridine N-oxide only
gave the doubly bridged μ-oxo complex 7 along with 2,2′-
bipyridine (Scheme 6).
We note that the dichalcogenide oxidants PhSSPh and
PhSeSePh are closely related to I2 in their potential interaction
with 1. In both cases, the initial step of the reaction, the
The analytical data as well as the 1H, 13C, 15N, and 29Si NMR
spectra are consistent with the molecular structures displayed in
Schemes 5 and 6. These results appear to be in contrast to the
reactivity of complex 1 with the transfer reagents for the heavier
chalcogen atoms sulfur and selenium. As previously reported,
TBS
oxidation of [Zr(N2 Npy)(NNPh2)(py)] with 0.5 Ph−E−E−
TBS
Ph to [Zr(N2 Npy)(NNPh2)(E−Ph)] (E = S, Se) is slightly
exothermic (ΔE = −0.4 and −0.6 kcal mol−1, respectively),
giving rise to the radical Zr intermediates IISPh and IISePh
(Scheme 4). In addition, the dimerization of two [Zr-
TBS
the reaction of [Zr(N2 Npy)(NNPh2)(py)] (1) with
propylene sulfide and triphenylphosphine selenide led to
element−N coupling and transformation of the α-nitrogen
atom in the hydrazide to bridging [μ-EN2]2− units.11 The
TBS
(N2 Npy)(NNPh2)(E−Ph)] radicals (E = S, Se) is
thermodynamically feasible under the reaction conditions
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Scheme 5. Reaction of 1 with N2O Leading Initially to a Proposed Transient Singly Bridged Oxo Dimer Which in Turn
Redistributes to 6 and 7
Scheme 6. Selective Formation of 7 from the Reaction of 1 with Pyridine N-Oxide under Release of 2,2′-Bipyridine
different reaction patterns represented in Schemes 5 and 6, on
the other hand, reflect the pronounced oxophilicity of
zirconium.
5). A precedent for this reaction in the literature is the
dismutation of the ansa-zirconocene [{(Me2Si)cp2ZrCl}2-μ-O]
to the corresponding dichloro complex [(Me2Si)cp2ZrCl2] and
oxo derivatives, described by Royo et al.19
The molecular structures of compounds 6 and 7 were
established by single-crystal X-ray diffraction (Figures 3 and 4).
The tripodal diamido pyridyl ligand coordinates facially,
occupying one axial and two equatorial sites of a distorted-
trigonal-bipyramidal structure in both complexes. In complex 6
the two diphenylamido ligands are bonded in the remaining
axial and equatorial positions. As expected for a trigonal-
bipyramidal coordination geometry we find d(Zr−N(5)ax) >
d(Zr−N(4)eq).
The formation of the oxo complex 7 as only metal-containing
product in the reaction of 1 with pyridine N-oxide is consistent
with O-atom transfer to the metal center and one-electron
oxidation of both the Nα and the Nβ atoms. Similar to the
formation of the diiodo complex 3, one would expect the
generation of tetraphenylhydrazine as the second reaction
product; however, this was not observed. We therefore isolated
and carefully analyzed the organic byproducts by NMR and
high-resolution mass spectroscopy. Comparison with authentic
samples proved the formation of diphenylamine and 2,2′-
bipyridine, which is thought to be formed by oxidative coupling
of two pyridine moieties. The latter was further substantiated
by the same reaction with the equivalent amount of d5-
pyridinium N-oxide. Analysis of the reaction products showed
that diphenylamine and 2,2′-bipyridine exclusively carried the
deuterium label and no dissociated pyridine from reactant 1 is
The oxo complex 7 adopts a dimeric structure. The
molecular halves are related by a crystallographic center of
symmetry, which results in an exactly planar Zr2O2 ring. The
TBS
N2
N ligands on each Zr are arranged in a way which puts
py
the plane of the respective pyridyl substituent at a small angle
to the Zr2O2 ring (interplanar angle 9.55(8)°). Its structure is
closely related to those of other reported μ2-oxo zirconium
complexes.18 The formation of the two products 6 and 7 in the
reaction of 1 with N2O is thought to proceed via a common
intermediate, a singly μ-O-bridged amido/oxo complex. Its
redistribution leads to the isolated product complexes (Scheme
TBS
involved. Accordingly, the complex [Zr(N2 Npy)(NNPh2)-
(py-d5)] (1-d5), bearing a d5-py-labeled pyridine ligand in the
axial position, reacted with nondeuterated pyridine N-oxide,
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The different nature of the oxidant in comparison with I2,
PhSSPh, and PhSeSePh leads to the formation of a diradical
species (Figure 5). Two spin states are expected: a singlet
diradical by antiferromagnetic coupling of the unpaired
electrons and a triplet ground state. All attempts to model
the antiferromagnetically coupled diradical were unsuccessful,
and only the structure corresponding to the closed-shell S = 0
state was found to correspond to a local energy minimum.
As expected, the spin density in the triplet diradical IIOPy is
distributed over the pyridine N-oxide as well as the {Zr(1)−
N(1)−N(2)} fragment (Figure 6). As for the radical
intermediate II in the oxidation with I2, dimerization of IIOPy
may lead to IIIOpy (16.7 kcal mol−1) (Scheme 7). The isomer/
conformer of IIIOpy shown in Scheme 7 only corresponds to
one of many local minima which are of similar or even lower
energy. Complete modeling would require a full conformational
analysis, which was found to be unfeasible for a system of this
complexity. In the dimeric intermediate IIIOPy shown in
Scheme 7 the two pyridine N-oxide units are in close proximity
and therefore a radical coupling between the two ortho carbons
of the pyridine rings leads to the intermediate IVOPy, in which
the 2,2-bipyridine product is preformed. Ejection of N2 and
intramolecular abstraction of the hydrogen atoms at the
coupled ortho carbon atoms of the pyridine N-oxide dimer,
followed by fragmentation and oxygen transfer of the latter,
leads to the observed dinuclear Zr2O2 complex 7 as well as 2,2′-
bipyridine.
Figure 3. Molecular structure of complex 6 (hydrogen atoms are
omitted for clarity). Selected bond lengths (Å) and angles (deg): Zr−
N(1) = 2.069(2), Zr−N(2) = 2.077(2), Zr−N(3) = 2.413(3), Zr−
N(4) = 2.143(2), Zr−N(5) = 2.160(2); N(1)−Zr−N(2) = 101.86(8),
N(1)−Zr−N(3) = 80.90(9), N(1)−Zr−N(4) = 128.93(8), N(1)−
Zr−N(5) = 97.98(10), N(2)−Zr−N(3) = 81.88(7), N(2)−Zr−N(4)
= 122.94(9), N(2)−Zr−N(5) = 105.22(8), N(3)−Zr−N(4) =
82.42(7), N(3)−Zr−N(5) = 172.87(7), N(4)−Zr−N(5) = 92.97(8).
CONCLUSION
■
In this work, we reported the first examples of the oxidative
cleavage of the N−NR2 unit in a group 4 metal
hydrazinediido(2−) complex. The hydrazido(2−) moiety
therefore can be regarded as a one-electron reductant leading
to radical species in which the unpaired electron resides
primarily on the metal-bonded α nitrogen atom. On going
beyond the one-electron-oxidation “trigger”, the N−N scission
and N2 re-formation may be coupled with other trans-
formations such as the coupling of two pyridine molecules
derived from the pyridine N-oxide to a bipyridine unit reported
in this work. Unsurprisingly for the oxophilic zirconium,
oxidations with oxygen transfer reagents lead to hydrazide
fragmentation and the formation of oxo complexes.
EXPERIMENTAL SECTION
■
Figure 4. Molecular structure of complex 7 (hydrogen atoms are
omitted for clarity). Selected bond lengths (Å) and angles (deg):
Zr(1)−N(1) = 2.0975(9), Zr(1)−N(2) = 2.0750(9), Zr(1)−N(3) =
2.3742(8), Zr(1)−O(1) = 2.0615(7), Zr(1)−O(1A) = 1.9490(7);
N(1)−Zr(1)−N(2) = 97.43(3), N(1)−Zr(1)−N(3) = 84.92(3),
N(2)−Zr−N(3) = 84.08(3), N(1)−Zr(1)−O(1) = 134.64(3),
N(2)−Zr−O(1) = 122.14(3), N(3)−Zr(1)−O(1) = 78.70(3),
N(1)−Zr−O(1A) = 105.28(3), N(2)−Zr−O(1A) = 114.16(3),
N(3)−Zr−O(1A) = 157.03(3), O(1)−Zr−O(1A) = 79.62(3).
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), 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 valves. 1H, 13C, 19F, 29Si,
and 15N NMR spectra were recorded on Bruker Avance 400 and 600
NMR spectrometers and were referenced internally, using the residual
solvent (1H) or solvent (13C) resonances, or externally to SiMe4,
CFCl3, and 15NH3. Elemental analyses were recorded by the analytical
service of the Heidelberg Chemistry Department. The hydrazinediido
giving the nonlabeled bipyridine as only observable coupling
product (Scheme 4).
Whereas a detailed and exhaustive theoretical modeling of
the reaction sequences is unrealistic in view of the complexity
of the systems, we suggest that the C−C coupling reaction as
well as hydrogen transfer occur as coupled reactions in the
coordination sphere of the metal complex. First, DFT modeling
TBS
complex [Zr(N2 Npy)(NNPh2)(py)] (1) was prepared as
previously reported.11 All other reagents were obtained from
commercial sources and used as received unless explicitly stated.
TBS
Preparation of [Zr(N2 Npy)(NPh2)I] (2). To a stirred solution of
TBS
TBS
(see above) revealed that the formation of the [Zr(N2 Npy)-
[Zr(N2 Npy)(NNPh2)(py)] (1; 300 mg, 1.08 mmol) in toluene (20
TBS
(NNPh2)(ON2)] and [Zr(N2 Npy)(NNPh2)(OPy)] adducts
mL) was added a solution of iodine (136 mg, 0.54 mmol) in toluene
(5 mL) with a cannula. The reaction mixture was stirred overnight at
by reaction of 1 with N2O and pyO is slightly endothermic.
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TBS
Figure 5. Differences between closed-shell and open-shell computed structures of [Zr(N2 Npy)(NNPh2)] with N2O and pyridine N-oxide,
reflected in the respective ground-state structures.
H4py, p-HPh), 7.20 (t, 3JmHo/pH = 8.0 Hz, 4 H, m-HPh), 7.37 (d, 3JoHmH
3
= 8.0 Hz, 4 H, o-HPh), 8.87 (d, JH6pyH5py = 5.9 Hz, 1 H, H6py).
13C{1H} NMR (150 MHz, C6D6, 296 K): δ −3.4, −3.2 (Si(CH3)2),
20.7 (Si−C(CH3)3), 27.7 (C−CH3), 28.2 (Si−C(CH3)3), 48.5 (C−
CH3), 63.5 (CH2), 121.3 (C3py), 122.0 (C5py), 123.3 (p-CPh), 125.6
(o-CPh), 129.9 (m-CPh), 137.9 (C4py), 148.0 (C6py), 150.3 (N−CPh),
161.2 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 5.09
t
(Si(CH3)2 Bu). 15N NMR (60 MHz, C6D6, 296 K): δ 217.7 (N−
t
Si(CH3)2 Bu), 221.3 (NPh2), 282.1 (L−Npy), IR (Nujol, NaCl): ν
1603 m, 1463 s, 1377 s, 1257 m, 1089 sh, 1018 m, 904 w, 852 s, 847s,
778 m, 742 w, 695 cm−1. Anal. Calcd for C33H51N4ISi2Zr: C, 50.94; H,
6.61; N, 7.20. Found: C, 50.63; H, 6.44; N, 7.54.
Crossover Experiment for the Oxidation with I2 of a 1:1
Mixture of 14Nα and 15Nα Hydrazide 1. A crossover experiment was
carried out in an NMR tube (ca. 0.5 mL of C6D6) using 20 mg of 15Nα-
Figure 6. Spin density distribution on the compound IIOPy (S = 1).
labeled 1 and an equal amount of the unlabeled compound, to which
0.5 equiv of I2 was added (from a stock solution in C6D6). Reaction
conditions were as stated above. Given the established stoichiometry
of the oxidation and the exact 1:1 ratio of 14Nα and 15Nα hydrazide, the
establishment of the ratio of the isotopologues was straightforward:
two 15N NMR signals of equal intensity at δ 310.16 and 310.10 were
observed, which are assigned to 15N15N and 15N14N, respectively (the
difference being due to the isotope effect on the chemical shift). The
1:1 intensity ratio of the two resonances implies a 1:2 ratio of 15N15N
and 15N14N, which evolve, and the stoichiometry between labeled and
nonlabeled starting material as well as the clean and complete
60 °C. The reaction mixture was filtered, and the volatiles were
removed under reduced pressure. The resulting dark gray solid was
washed with pentane (3 × 5 mL) before drying in vacuo to yield 618
mg (74%) of 2 as a gray solid. Single crystals for X-ray diffraction were
1
grown from a saturated toluene solution at 10 °C. H NMR (600
MHz, C6D6, 296 K): δ 0.03, 0.29 (s, 6 H, Si(CH3)2), 0.72 (3 H, CH3),
0.78 (s, 18 H, Si−6(CH3)3), 3.44 (d, 2JHH = 12.7 Hz, 2 H, CHH), 4.06
2
3
(d, JHH = 12.6 Hz, 2 H, CHH), 6.32 (t, JH5pyH4pyH6py = 6.3 Hz, 1 H,
3
H5py), 6.77 (d, JH3pyH4y = 8.0 Hz, 1 H, H3py), 6.90−6.95 (m, 3 H,
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a
Scheme 7. Selected Intermediates in the Proposed Mechanism for the Reaction of 1 with Pyridine N-Oxide
a
DFT (uB3PW91) and ONIOM energies (uB3PW91/UFF, in parentheses) are given in kcal mol−1.
conversion to the reaction product implies a corresponding ratio of 2:1
for 15N14N and 14N14N.
The assignment of the signal for the mixed-labeled species was
Calcd for C21H41I2N3Si2Zr: C, 34.23; H, 5.61; N, 5.70. Found: C,
34.20; H, 5.78; N, 5.62.
TBS
Preparation of [Zr(N2 Npy)(NPh2)(SePh)] (4a). To a stirred
TBS
solution of [Zr(N2 Npy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in
established by combustion of the commercially available monolabeled
−
azide N3 , which gives rise to a mixture of 14N14N and 15N14N, only
toluene (20 mL) was added a solution of diphenyl diselenide (63 mg,
0.20 mmol) in toluene (10 mL) dropwise. The reaction mixture was
stirred for 2 days at 50 °C. The reaction mixture was filtered, and the
volatiles were removed under reduced pressure. The resulting solid
was washed with pentane (2 × 20 mL) before drying in vacuo to yield
230 mg (71%) of 3 as a greenish gray 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 0.04, 0.23 (s, 6H, Si(CH3)2), 0.64
the latter of which is observed by 15N NMR.
TBS
Preparation of [Zr(N2 Npy)I2] (3). To a stirred solution of
TBS
[Zr(N2 Npy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in toluene (10
mL) was added a solution of iodine (130 mg, 0.50 mmol) in toluene
(5 mL) with a cannula. The reaction mixture was stirred overnight at
60 °C. The reaction mixture was filtered, and the volatiles were
removed under reduced pressure. The resulting red solid was washed
with pentane (3 × 5 mL) before drying in vacuo to yield 618 mg
2
(s, 18H, Si−C(CH3)3), 1.07 (s, 3H, CH3), 3.55 (d, JHH = 12.7 Hz,
2H, CHH), 4.16 (d, 2JHH = 12.6 Hz, 2H, CHH), 6.34 (pt, 3JH5pyH4/6py
1
(74%) of 6 as a pale yellow powder. H NMR (600 MHz, C6D6, 296
3
= 6.4 Hz, 1H, H5py), 6.82 (d, JH3pyH5py = 8.2 Hz, 1H, H3py), 6.89−
K): δ 0.26, 0.58 (s, 6 H, Si(CH3)2), 0.72 (3 H, CH3), 0.82 (s, 18 H,
7.04 (sh, 3H, p-HSe‑Ph, p-HPh, H4py), 7.15 (m, 2H, m-HSe‑Ph), 7.21 (t,
2
2
Si−6(CH3)3), 3.17 (d, JHH = 12.6 Hz, 2 H, CHH), 3.88 (d, JHH
=
3JmHo/pH = 7.5 Hz, 4H, m-HPh), 7.36 (d, 3JoHmH = 7.9 Hz, 4H, o-HPh),
12.6 Hz, 2 H, CHH), 6.42 (t, 3JH5pyH4pyH6py = 6.4 Hz,v1 H, H5py), 6.67
(d, 3JH3pyH4y = 8.0 Hz, 1 H, H3py), 6.91 (t, 3JH4pyH5pyH3py = 7.7 Hz, 4 H,
3
3
7.95 (d, JoHmH = 7.5 Hz, 2H, o-HSe‑Ph), 8.86 (d, JH6pyH5py = 5.1 Hz,
1H, H6py). 13C{1H} NMR (C6D6, 100.55 MHz, 296 K): δ −3.8, −2.4
(Si(CH3)2), 20.2 (Si−C(CH3)3), 24.8 (C−CH3), 28.1 (Si−C(CH3)3),
48.8 (C−CH3), 64.1 (CH2N), 121.2 (C3py), 122.2 (C5py),123.0, 123.9
(p-CSe‑Ph, p-CPh), 124.9(o-CPh), 128.4 (m-CSe‑Ph), 129.8 (m-CPh), 135.8
(o-CSe‑Ph), 138.2 (Se-CSe‑Ph), 139.7 (C4py), 148.1 (C6py), 151.0 (N−
CPh), 161.7 (C2py). 29Si{1H} NMR (C6D6, 80 MHz, 296 K): δ 5.52
H4py), 9.80 (d, JH6pyH5py = 5.5 Hz, 1 H, H6py). 13C{1H} NMR (150
3
MHz, C6D6, 296 K): δ −3.7, −3.1 (Si(CH3)2), 20.7 (Si−C(CH3)3),
24.0 (C−CH3), 27.7 (Si−C(CH3)3), 49.3 (C−CH3), 63.1 (CH2),
121.1 (C3py), 122.2 (C5py), 139.4 (C4py), 149.9 (C6py), 159.5 (C2py).
t
29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 4.52 (Si(CH3)2 Bu). 15N
t
t
(Si(CH3)2 Bu). 15N NMR (C6D6, 60 MHz, 296 K): δ 209.6 (N−
NMR (60 MHz, C6D6, 296 K): δ 247.4 (N-Si(CH3)2 Bu), 280.1 (L−
t
Si(CH3)2 Bu), 221.9 (NPh2), 282.1 (L−Npy). 77Se NMR (C6D6, 76
Npy). IR (Nujol, NaCl): ν 2727w, 1463 s, 1377 s, 1299 w, 1261 m,
1164 m, 1089 w, 1040 m, 908 w, 843 s, 770 w, 722 s 674 cm−1. Anal.
MHz, 296 K): δ 481.8 (SePh). IR (Nujol, NaCl): ν 1583 m, 1465 s,
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3
1377 m, 1292 w, 1248 m, 1187 m, 1137 w, 1087 w, 1019m, 904 m,
862 m, 847 m, 778 m, 730 w, 694 w, 665 w. Anal. Calcd for
C39H56N4SeSi2Zr: C, 58.03; H, 6.99; N, 6.94. Found: C, 57.88; H,
6.99; N, 7.08.
3JH5pyH4pyH6py = 7.0 Hz, 1 H, H5py), 6.84 (d, JH3pyH4y = 8.0 Hz, 1 H,
H3py), 6.93 (t, 3Jp‑pho‑Hph = Hz, 2 H, p-HPh) 7.09 (t, 3JH4pyH3pyH5py = 8.0
Hz, 1 H, H4py), 7.34 (t, 3JmHo/pH = 7.7 Hz, 4 H, m-HPh), 7.59 (bs, 4 H,
o-HPh), 9.08 (d, JH6pyH5py = 3.0 Hz, 1 H, H6py). 13C{1H} NMR (150
3
TBS
Preparation of [Zr(N2 Npy)(NPh2)(SPh)] (4b). To a stirred
MHz, C6D6, 296 K): δ −5.8, −5.2 (Si(CH3)2), 19.8 (Si−C(CH3)3),
23.4 (C−CH3), 27.2 (Si−C(CH3)3), 49.0 (C−CH3), 63.4 (CH2),
120.6 (C3py), 121.0 (p-CPh), 121.9 (C5py), 123.8 (o-CPh), 129.2 (m-
CPh), 138.8 (C4py), 145.4 (2JN−F = 12.6 Hz, C6py), 155.4 (N−CPh),
160.7 (C2py). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 0.93
TBS
solution of [Zr(N2 Npy)(NNPh2)(py)] (1; 500 mg, 0.68 mmol) in
toluene (20 mL) was added a solution of diphenyl disulfide (73 mg, 34
mmol) in toluene (5 mL) dropwise. The reaction mixture was stirred
overnight at 80 °C. The reaction mixture was filtered, and the volatiles
were removed under reduced pressure. The resulting pale yellow solid
was washed with pentane (3 × 5 mL) before drying in vacuo to yield
320 mg (62%) of 4a as a colorless 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 0.04, 0.20 (s, 6 H, Si(CH3)2), 0.64
(s, 18 H, Si−6(CH3)3), 1.07 (3 H, CH3), 3.55 (d, 2JHH = 12.6 Hz, 2 H,
t
(Si(CH3)2 Bu). 15N NMR (60 MHz, C6D6, 296 K): δ 185.7 (N-−
t
i(CH3)2 Bu), 193.3 (NPh2), 290.2 (L−Npy). IR (Nujol, NaCl): ν 2361
m, 1602 w, 1492 m, 1464 s, 1377 w, 1260 s, 1089 ssh, 1029 s, 853 s,
820 m, 800 s, 728 s, 694 cm−1. Anal. Calcd for C33H51N4FSi2Zr: C,
59.14; H, 7.67; N, 8.36. Found: C, 58.87; H, 7.57; N, 8.15.
TBS
Alternative Preparation of [Zr(N2 Npy)(NPh2)F] (5) by
CHH), 4.15 (d, 2JHH = 12.6 Hz, 2 H, CHH), 6.35 (dt, 3JH5pyH4pyH6py
=
Electrolysis. In the glovebox 100 mg (0.14 mmol) of [Zr(N2TBSNpy)-
(NNPh2)(py)] (1) was dissolved in 2 mL of thf-d8 which contained
0.14 mmol of tetrabutylammonium hexafluorophosphate. The solution
was placed in a 10 mL round-bottom flask which was equipped with a
septum and two platinum electrodes. The reaction mixture was
subjected to electrolysis for 10 min at 1 V. After 10 min 0.5 mL of the
reaction mixture was removed by syringe and NMR spectra were
recorded. The formation of 5 was confirmed by its identical 1H NMR
signals in comparison to those of the compound prepared from 1 and
AgF.
4
3
6.5 Hz, JH5H3 = 1.0 Hz,1 H, H5py), 6.82 (d, JH3pyH4y = 8.1 Hz, 1 H,
3
H3py), 6.92 (d, JpH/mH = 7.3 Hz p-HPh), 6.95−7.01 (m, 2H, H4py, p-
HPhS), 7.20 (t, 3JmHo/pH = 7.7 Hz, 2H, m-HPhS), 7.23 (t, 3JmHo/pH = 8.0
3
4
Hz, 4 H, m-HPh), 7.39 (dd, JoHmH = 8.0 Hz, JoHpH = 1.0 Hz, 4 H, o-
HPh), 7.79 (d, 3JoHmH = 8.7 Hz, 2H, o-HPhS), 8.92 (dd, 3JH6pyH5py = 5.5
Hz, JH6pyH4py = 1.0 Hz, 1H, H6py). 13C{1H} NMR (150 MHz, C6D6,
4
296 K): δ −3.8, −2.8 (Si(CH3)2), 20.2 (Si−C(CH3)3), 24.8(C−CH3),
28.1 (Si−C(CH3)3), 48.3 (C−CH3), 64.0 (CH2), 121.1 (C3py), 122.2
(C5py), 123.0 (p-CPh), 123.3 (p-CS‑Ph), 124.9 (o-CPh), 128.3 (m-CS‑Ph),
129.8 (m-CPh), 133.3 (o-CS‑Ph), 139.8 (C4py), 145.7 (S-CS‑Ph), 148.3
(C6py), 151.1 (N−CPh), 161.8 (C2py). 29Si{1H} NMR (80 MHz, C6D6,
TBS
Preparation of [Zr(N2 Npy)(NPh2)2] (6). N2O was bubbled for 5
min through a solution of [Zr(N2 Npy)(NNPh2)(py)] (1; 400 mg,
TBS
t
296 K): δ 5.60 (Si(CH3)2 Bu). 15N NMR (60 MHz, C6D6, 296 K): δ
0.54 mmol) in toluene (20 mL). The reaction mixture turned orange
and was stirred for 2 h at room temperature. Then it was cooled and
filtered, and the volatiles were removed under reduced pressure. The
resulting pale yellow solid was washed with pentane (3 × 5 mL) before
drying in vacuo to yield 204 mg (46%) of 7 as a colorless solid. Single
crystals for X-ray diffraction were grown from a saturated toluene
t
206.3 (N−Si(CH3)2 Bu), 219.3 (NPh2), 282.7 (L−Npy). IR (Nujol,
NaCl): ν 1584 m, 1482 s, 1464 s, 1377 w, 1252 s, 1192 w, 1021 s, 904
w, 852 s, 847 s, 778 m, 742 w, 695 cm−1. Anal. Calcd for
C39H56N4SSi2Zr: C, 61.61; H, 7.42; N, 7.37. Found: C, 61.63; H, 7.55;
N, 7.43.
TBS
Preparation of [Zr(N2 Npy)(NPh2)(SC6F5)] (4c). To a stirred
1
solution at room temperature. H NMR (600 MHz, C6D6, 296 K): δ
TBS
solution of [Zr(N2 Npy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in
−0.10, 0.19 (s, 6 H, Si(CH3)2), 0.71 (s, 18 H, Si−6(CH3)3), 1.13 (3 H,
CH3), 3.56 (d, 2JHH = 12.4 Hz, 2 H, CHH), 4.03 (d, 2JHH = 12.4 Hz, 2
H, CHH), 6.28 (t, 3JH5pyH4pyH6py = 6.6 Hz, 1 H, H5py), 6.66 (d, 3Jo‑Hm‑H
= 8.0 Hz, 1 H, o-HPh‑A), 6.84−6.90 (m, 3 H, p-HPh‑A, H3py), 6.92 (d,
toluene (10 mL) was added a solution of bis(pentafluorophenyl)
disulfide (80 mg, 0.20 mmol) in toluene (3 mL) dropwise. The
reaction mixture was stirred overnight at 80 °C. The reaction mixture
was filtered, and the volatiles were removed under reduced pressure.
The resulting brown solid was washed with pentane (3 × 5 mL) before
drying in vacuo to yield 270 mg (80%) of 4b as a light brown solid. 1H
NMR (600 MHz, C6D6, 296 K): δ −0.04, 0.00 (s, 6 H, Si(CH3)2),
0.62 (s, 18 H, Si−6(CH3)3), 0.98 (3 H, CH3), 3.23 (d, 2JHH = 12.5 Hz,
3JpH/mH = 7.3 Hz p-HPh), 6.96 (dt, 3JH4pyH5pyH3py = 7.7 Hz, dt, 4JH4pyH6
=
,
1.8 Hz, 1 H, H4py), 7.16−7.34 (bm, 14 H, m-HPh‑A, o-HPh‑B, m-HPh‑B
p-HPh‑B), 9.03 (dd, 3JH6pyH5py = 5.6 Hz, 4JH6pyH4py = 1.6 Hz, 1H, H6py).
13C{1H} NMR (150 MHz, C6D6, 296 K): δ −4.08, −2.7 (Si(CH3)2),
20.0 (Si−C(CH3)3), 25.0(C−CH3), 28.6 (Si−C(CH3)3), 48.8 (C−
CH3), 64.2 (CH2), 120.7 (C3py), 121.9 (C5py), 122.3 (p-CPh‑A, p-
CPh‑A), 123.2(o-CPh‑A), 128.9, 129.4 (o-CPh‑B, m-CPh‑B), 129.9 (m-CPh),
139.3 (C4py), 149.2 (C6py), 151.1 (N−CPh‑A), 162.5 (C2py), n.o. (N−
2
2 H, CHH), 4.18 (d, JHH = 12.5 Hz, 2 H, CHH), 6.33 (t,
3
3JH5pyH4pyH6py = 6.5 Hz, 1 H, H5py), 6.79 (d, JH3pyH4y = 8.2 Hz, 1 H,
3
3
H3py), 6.92 (d, JpH/mH = 7.0 Hz p-HPh), 6.97 (t, JH4pyH3pyH5py,1H,
3
3
H4py), 7.20 (t, JmHo/pH = 7.7 Hz, 4 H, m-HPh), 7.34 (d, JoHmH = 7.9
t
3
CPh‑B). 29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 5.28 (Si(CH3)2 Bu).
Hz, 4 H, o-HPh), 8.84 (d, JH6pyH5py = 5.1 Hz, 1H, H6py). 13C{1H}
t
15N NMR (60 MHz, C6D6, 296 K): δ 191.6 (N−Si(CH3)2 Bu), 200.9
NMR (150 MHz, C6D6, 296 K): δ −4.2, −3.4 (Si(CH3)2), 20.2 (Si−
C(CH3)3), 24.7 (C−CH3), 27.5 (Si−C(CH3)3), 48.3 (C−CH3), 63.6
(CH2), 121.3 (C3py), 122.2 (C5py), 123.4 (p-CPh), 125.2 (o-CPh), 129.8
(m-CPh), 139.9 (C4py), 148.1 (C6py), 150.6 (N−CPh), 161.4 (C2py).
(NPh2-A), 212.3 (NPh2-B), 284.8 (L−Npy). IR (Nujol, NaCl): ν 1594
m, 1482 ssh, 1464 s, 1377 s, 1261 s, 1188 w, 1024 m, 908 w, 850 s, 798
m, 752 w, 697 cm−1. Anal. Calcd for C45H61N5Si2Zr: C, 65.96; H, 7.50;
N, 8.55. Found: C, 65.90; H, 7.50; N, 8.55.
t
29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 4.97 (Si(CH3)2 Bu). 19F
TBS
3
Preparation of [Zr(N2 Npy)(μ-O)]2 (7). To a stirred solution of
[Zr(N2 Npy)(NNPh2)(py)] (1; 300 mg, 0.40 mmol) in toluene (20
NMR (380 MHz, C6D6, 296 K): −165.4 (t, J = 22 Hz, 2 F, m-F),
TBS
−164.5 (t, 3J = 22 Hz, 1 F, p-F), −133.6 (d, 3J = 22 Hz, 2 F, o-F). 15
N
t
mL) was added pyridine N-oxide (39 mg, 0.40 mmol). The reaction
mixture was stirred overnight at at room temperature. The reaction
mixture was filtered, and the volatiles were removed under reduced
pressure. The resulting brown solid was washed with pentane (3 × 5
mL) before drying in vacuo to yield 96 mg (24%) of 8 as a colorless
solid. Single crystals for X-ray diffraction were grown from a saturated
toluene solution at room temperature. 1H NMR (600 MHz, C6D6, 296
K): δ 0.28, 0.50 (s, 6 H, Si(CH3)2), 1.14 (s, 18 H, Si−6(CH3)3), 1.15
(3 H, CH3), 3.47 (d, 2JHH = 12.4 Hz, 2 H, CHH), 3.93 (d, 2JHH = 12.6
NMR (60 MHz, C6D6, 296 K): δ 214.8 (N−Si(CH3)2 Bu), 221.4
(NPh2), 282.1 (L−Npy). IR (Nujol, NaCl): ν 1594 w, 1502 m, 1664 s,
1377 s, 1553 m, 1084 w, 1019 w, 972 w, 858 m, 764 w, 742 w cm−1.
Anal. Calcd for C39H51F5N4SSi2Zr: C, 55.09; H, 6.05; N, 6.59. Found:
C, 55.00; H, 6.25; N, 6.82.
TBS
Preparation of [Zr(N2 Npy)(NPh2)F] (5). To a stirred solution
TBS
of [Zr(N2 Npy)(NNPh2)(py)] (1; 200 mg, 0.27 mmol) in toluene
(20 mL) was added solid silver(I) fluoride (34 mg, 0.27 mmol). The
reaction mixture was stirred overnight at 60 °C. The reaction mixture
was filtered, and the volatiles were removed under reduced pressure.
The resulting dark gray solid was washed with hexane (3 × 5 mL)
before drying in vacuo to yield 120 mg (73%) of 5 as a brown solid. 1H
NMR (600 MHz, C6D6, 296 K): δ −0.23, 0.06 (s, 6 H, Si(CH3)2),
0.67 (s, 18 H, Si−6(CH3)3), 1.02 (3 H, CH3), 3.28 (d, 2JHH = 12.4 Hz,
3
Hz, 2 H, CHH), 6.09 (t, JH5pyH4pyH6py = 6.7 Hz, 1 H, H5py), 7.01 (d,
3JH3pyH4y = 8.0 Hz, 1 H, H3py), 7.09 (d, JH4pyH3/H5py = 7.6 Hz, 1 H,
3
H4py), 9.80 (dd, JH6pyH5py = 5.1 Hz, 1 H, H6py). 13C{1H} NMR (150
3
MHz, C6D6, 296 K): δ −3.5, −1.4 (Si(CH3)2), 20.5 (Si−C(CH3)3),
25.2(C−CH3), 28.3 (Si−C(CH3)3), 50.5 (C−CH3), 61.8 (CH2), 119.1
(C3py), 120.9 (C5py), 139.4 (C4py), 148.0 (C6py), 163.6 (C2py).
2
2 H, CHH), 4.05 (d, JHH = 12.4 Hz, 2 H, CHH), 6.52 (t,
3886
dx.doi.org/10.1021/om400337g | Organometallics 2013, 32, 3877−3889

Organometallics
Article
t
29Si{1H} NMR (80 MHz, C6D6, 296 K): δ 1.09 (Si(CH3)2 Bu). 15N
basis set used for the optimization. Additionally, dispersion effects,
neglected in uB3PW91, were thought to give significant contributions
and therefore have been taken into account by the simple DFT-D2
correction developed by Grimme.26
X-ray Crystal Structure Determinations. Crystal data and
details of the structure determinations are given in Table 3. Full shells
of intensity data were collected at low temperature (100 K) with a
Bruker AXS Smart 1000 CCD diffractometer (Mo Kα radiation, sealed
tube, graphite monochromator). Data were corrected for air and
detector absorption, Lorentz, and polarization effects;27 absorption by
the crystal was treated by a numeric method28 or with a semiempirical
multiscan method.28,29
The structures were solved by the heavy-atom method combined
with structure expansion by direct methods applied to difference
structure factors30 (complexes 4a,b and 7), by direct methods with
dual-space recycling31 (complex 2), or by the charge-flip procedure32
(complex 6) and refined by full-matrix least-squares methods based on
F2 against all unique reflections.33 All non-hydrogen atoms were given
anisotropic displacement parameters. Hydrogen atoms were placed at
calculated positions and refined with a riding model.
t
NMR (60 MHz, C6D6, 296 K): δ 149.5 (N−Si(CH3)2 Bu), 283.2 (L−
Npy). IR (Nujol, NaCl): ν 1594 s, 1495 s, 1458 s, 1377 m, 1311 m,
1090 w, 1040 w, 908 w, 876 w, 753 m, 746 m, 691 w cm−1. Anal. Calcd
for C42H82N6O2Si4Zr2: C, 50.25; H, 8.28; N, 8.42. Found: C, 49.84; H,
8.20; N, 8.04.
Computational Studies. A two-shell ONIOM Hybrid QM/MM
computational tool17 of the GAUSSIAN09 package20 was employed to
model all the systems. For all calculations the spin-unrestricted
formalism was applied. For the inner shell (QM), the uB3PW9121
hybrid functional with 6-31g(d) basis set for C, N, H, S, and O22 and
SDD+f function effective core potential basis set23 for Zr, Se, and I24
were employed, while (MM) UFF force field calculations were applied
to the outer shell.25 The quantum mechanically (QM) and the force
field (MM) modeled sectors of the molecule in the ONIOM
calculations are defined in Figure 7. Stationary points were verified
Crystals of 4a were twinned; after detwinning (approximately twin
fractions 0.53:0.47) refinement was carried out against all observations
involving both domains.28b
ASSOCIATED CONTENT
■
Figure 7. Black part representing the QM description and the gray
S
* Supporting Information
part representing the MM.
Tables giving Cartesian coordinates for the calculated structures
and CIF files giving crystallographic data for compounds 2,
4a,b, 6, and 7. This material is available free of charge via the
Internet at http://pubs.acs.org.
by frequency analyses. Energies were refined by single-point
calculations with the full DFT(uB3PW91) model with the same
Table 3. Details of the Crystal Structure Determinations of 2, 4a,b, 6, and 7
2
4a
4b
6
7
formula
Mr
C33H51IN4Si2Zr
778.08
C39H56N4SSi2Zr
760.34
C39H56N4SeSi2Zr
807.24
C45H61N5Si2Zr
819.39
C21H41N3OSi2Zr
498.97
cryst syst
space group
a/Å
triclinic
triclinic
orthorhombic
Pca21
monoclinic
P21/c
triclinic
P1
̅
P1
̅
P1
̅
9.783(5)
10.379(5)
19.010(9)
91.185(8)
99.16(1)
102.47(1)
1858(2)
2
9.582(5)
10.413(5)
20.309(10)
86.117(6)
87.819(6)
77.450(13)
1973(2)
2
20.184(12)
9.634(6)
19.48(2)
11.45(1)
20.76(2)
10.4274(7)
10.7564(7)
13.5613(9)
66.651(1)
82.552(1)
68.117(1)
1295.6(2)
2
b/Å
c/Å
40.76(2)
α/deg
β/deg
γ/deg
V/Å3
110.73(2)
7926(8)
8
4330(6)
4
Z
F000
796
804
3360
1736
528
dc/Mg m−3
μ/mm−1
1.391
1.280
1.353
1.257
1.279
1.218
0.424
1.288
0.346
0.532
max, min transmission factors 0.9823, 0.6824
θ range/deg 2.0−32.2
0.7457, 0.6156
2.0−28.5
0.7454, 0.6104
2.0−25.7
1.0000, 0.8769
1.1−28.3
0.7464, 0.6618
2.1−32.2
index ranges (indep set) h,k,l −14 to +13, −1 to +15, −1 to +12, −13 to +13, −24 to 0, 0−11, −49 to −25 to +24, 0−15,
−14 to +15, −14 to +16,
0−27
0−27
+49
0−27
0−20
no. of measd rflns
45971
58995
134015
71257
27185
no. of unique rflns (Rint)
12121 (0.0353)
17175 (0.0864)
13483
15051 (0.1112)
12547
10741 (0.0984)
7745
8477 (0.0266)
7910
no. of obsd rflns (I ≥ 2σ(I)) 10379
no. of params refined
GOF on F2
381
436
869
489
264
1.042
1.091
1.040
1.005
1.030
R indices (F > 4σ(F)): R(F), 0.0287, 0.0673
Rw(F2)
0.0562, 0.1412
0.0424, 0.0773
0.0440, 0.0786
0.0220, 0.0595
R indices (all data): R(F),
Rw(F2)
0.0378, 0.0713
0.0795, 0.1580
0.0596, 0.0829
0.0787, 0.0891
0.0241, 0.0606
absolute structure param
largest residual peaks/e Å−3
0.072(7)
1.473, −0.752
0.798, −0.759
0.620, −0.504
0.474, −0.870
0.756, −0.414
3887
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Organometallics
Article
(8) (a) Alex, K.; Tillack, A.; Schwarz, N.; Beller, M. Angew. Chem., Int.
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AUTHOR INFORMATION
Corresponding Author
*L.H.G.: 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).
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