En route to zirconium hydrazides(2-)

Article abstract of DOI:10.1039/b800682b

The structures and properties of a series of new zirconium hydrazido(1-) complexes and the possibility of converting them to the respective hydrazido(2-) species are reported. Reaction of complex [Zr(N₂^TBSN _py)Cl₂

Full text of DOI:10.1039/b800682b

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PAPER
www.rsc.org/dalton | Dalton Transactions
En route to zirconium hydrazides(2−)†
Heike Herrmann, Hubert Wadepohl and Lutz H. Gade*
Received 14th January 2008, Accepted 18th February 2008
First published as an Advance Article on the web 13th March 2008
DOI: 10.1039/b800682b
The structures and properties of a series of new zirconium hydrazido(1−) complexes and the possibility
of converting them to the respective hydrazido(2−) species are reported. Reaction of complex
TBS
[Zr(N2 Npy)Cl2] (1) with the monolithiated hydrazide LiNHNMe2 gave the hydrazido(1−) complex
TBS
[Zr(N2 Npy)(NHNMe2)Cl] (2) which exists as two isomeric forms (2a and 2b) in solution. All attempts
to convert a mixture of 2a and 2b to the respective hydrazido(2−) compound by reaction with the bulky
base lithium hexamethyldisilazide or via the alkyl/hydrazido(1−) complex
TBS
[Zr(N2 Npy)(CH2SiMe3)(NHNMe2)] (3) and subsequent thermal alkane elimination failed. Reaction
TBS
of 1 with LiHNNPhMe gave a mixture of stereoisomers of [Zr(N2 Npy)(NHNMePh)Cl] (4a and 4b),
2
in which the hydrazido unit is end-on bound in solution and g -bonded in the solid state. Reaction of
this mixture with lithium hexamethyldisilazide in the presence of pyridine selectively yielded the
TBS
hydrazido(2−) complex [Zr(N2 Npy)(NNPhMe)(py)] (5) which aggregated upon attempts to isolate it.
Reaction of the insoluble precipitate with 4-dimethylaminopyridine (dmap) selectively gave the
TBS
corresponding hydrazido(2−) complex [Zr(N2 Npy)(NNPhMe)(dmap)] (6), which could be obtained
in a one-pot reaction directly from 1 and which was analytically and spectroscopically fully
characterized. It appears that the isolation of stable hydrazido(2−) complexes of zirconium depends on
the type of substituents at the Nb atom as well as the co-ligands coordinated to the metal centre.
reactivity based on N–N bond cleavage and N–E (E = main group
Introduction
element) bond formation. In these transformations the group 4
metal hydrazide reacts as a synthon for a Zr–N “metallanitrene”
fragment.11,12 This has led to the synthesis of, inter alia, a new
class of dinuclear complexes containing dinitridosulfate(IV) and
dinitridoselenate(IV) bridging ligands which were assembled atom
by atom.
Much attention has been devoted to transition metal hydrazides
due to the role they are thought to play in the stoichiometric and
catalytic reduction of dinitrogen to ammonia.1 Most of the work
has been devoted to the group 6 metals.2,3 In contrast a systematic
investigation into the chemistry of group 4 hydrazides has only
recently begun,4 despite Wiberg’s early report of the synthesis
of the titanium hydrazide(2−) complex, [Cp2TiN2(SiMe3)2], in
the late 1970s.5 This resurgent interest is related to the role of
hydrazidotitanium complexes as intermediates in stoichiometric
and catalytic hydrazinations of alkynes6 and related reactions.7
Until very recently, there was only one example of a heavier
group 4 hydrazido complex, [Cp2Zr(N2Ph2)(dmap)] (dmap = 4-
dimethylaminopyridine), which had been reported by Bergman
and co-workers in 1991.8 In a preliminary study into the reactivity
of the compound, a tendency for N–N-bond cleavage in reactions
with alkynes and CO was observed.
TBS
The Zr hydrazide(2−) [Zr(N2 Npy)(NNPh2)] has been pre-
−
pared from the {NHNPh2} precursor by dehydrohalogenation
with lithium hexamethyldisilazide. Crystal structures of such
hydrazido(1−) complexes are known for titanium13–16 but have not
been reported previously for its heavier congeners. It is therefore
the aim of this first study into their chemistry to provide a complete
structural characterization of these species. Furthermore, the way
that the substituents R at the Nb atom of the hydrazide(1−)
influence its convertibility to a hydrazide(2−) will be discussed.
We have recently begun to investigate the structural chemistry
and reactivity of zirconium hydrazides using a tridentate diami-
Results and discussion
R
dopyridyl ligand [N2 Npy]2− as a supporting ligand. This system
Synthesis and structural characterization of the side-on
TBS
hydrazido(1−) zirconium complexes [Zr(N2 Npy)(NHNMe2)Cl]
had been originally developed by us to stabilize complexes contain-
9
(2a and 2b)
=
ing reactive M N bonds and their derivatives, allowing inter alia
the isolation of key intermediates of the catalytic hydroamination
As starting material employed in the synthesis of the
of alkynes.10 This ligand platform allowed the preparation and
hydrazido(1−) zirconium complexes we used the dichloro complex
full structural characterization of [Zr(N2 Npy)(NNPh2)].11 As
TBS
bearing the dianionic tricoordinate ligand [N2 Npy]2−. This
TBS
first study of its reactivity revealed exciting new patterns of
compound is readily available by reaction of the protioligand
TBS
H2N2
N
with an equimolar amount of [Zr(NMe2)4] and
py
the subsequent exchange of the two remaining Me2N− ligands
by reaction with two equivalents of Me3SiCl. The complex
Anorganisch-Chemisches Institut, Universita¨t Heidelberg, Im Neuenheimer
Feld 270, 69120, Heidelberg, Germany. E-mail: lutz.gade@uni-hd.de;
Fax: +49-6221-545609
† CCDC reference numbers 674839–674842. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b800682b
TBS
[Zr(N2 Npy)Cl2] (1) was characterized by CHN analysis and by
1H, 13C, 15N, and 29Si NMR spectroscopy as a trigonal bipyramidal
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pentacoordinate compound in which the two amido and one of
the chloro ligands occupy the equatorial whereas the third neutral
pyridyl “arm” of the tripodal protecting ligand as well as the
second chloride occupy the axial positions. This assignment has
also been confirmed by a single-crystal X-ray structure analysis.
The asymmetric unit of the crystal structure of complex 1 contains
two independent molecules with nearly identical geometries. One
molecule is displayed in Fig. 1, along with selected bond lengths
and angles.
−73 Hz, Me2NNH) and 49.4 (Me2NNH) for complex 2a, the
corresponding 15N nuclei resonated at d 213.1 (1JNH = −71 Hz,
Me2NNH) and 52.6 (Me2NNH) for complex 2b.
Upon storing a saturated solution of this mixture of isomers
in toluene at 10 ◦C one of them crystallized. On redissolution of
the isolated crystals, the equilibrium mixture of 2a and 2b was
re-generated instantaneously. The crystals obtained for 2a were
suitable for X-diffraction. Its molecular structure, determined by
X-ray crystallography, is depicted in Fig. 2 along with the principal
bond lengths and angles.
Fig.
1
Molecular structure of complex 1. Selected bond lengths
◦
˚
(A) and angles ( ) (values in square brackets refer to the second
independent molecule): Zr(1)–N(1) 2.012(3) [2.004(3)], Zr(1)–N(2)
2.006(3) [2.010(4)], Zr(1)–N(3) 2.364(3) [2.368(3)], Zr(1)–Cl(1) 2.461(1)
[2.454(1)], Zr(1)–Cl(2) 2.457(1) [2.543(1)]; N(1)–Zr(1)–N(2) 104.1(1)
[103.4(1)], N(1)–Zr(1)–N(3) 80.3(1) [81.8(1)], N(2)–Zr(1)–N(3) 81.0(1)
[79.9(1)], N(1)–Zr(1)–Cl(1) 124.21(9) [123.65(10)], N(1)–Zr(1)–Cl(2)
101.81(9) [101.72(10)], N(2)–Zr(1)–Cl(1) 126.58(9) [127.96(11)],
N(2)–Zr(1)–Cl(2) 100.74(9) [100.18(11)], N(3)–Zr(1)–Cl(1) 85.62(8)
[85.63(8)], N(3)–Zr(1)–Cl(2) 176.77(8) [176.35(8)], Cl(2)–Zr(1)–Cl(1)
91.15(4) [91.52(5)].
˚
Fig. 2 Molecular structure of complex 2a. Selected bond lengths (A)
and angles (◦): Zr(1)–N(1) 2.058(2), Zr(1)–N(2) 2.073(2), Zr(1)–N(3)
2.438(2), Zr(1)–N(4) 2.044(2), Zr(1)–N(5) 2.334(2), N(4)–N(5) 1.431(2),
Zr(1)–Cl(1) 2.4822(6), N(1)–Zr(1)–N(2) 111.96(6), N(1)–Zr(1)–N(3)
76.78(6), N(1)–Zr(1)–N(4) 108.37(7), N(1)–Zr(1)–N(5) 87.98(6),
N(2)–Zr(1)–N(3) 76.16(6), N(2)–Zr(1)–N(4) 108.42(7), N(2)–Zr(1)–N(5)
88.58(6), N(3)–Zr(1)–N(4) 170.39(6), N(3)–Zr(1)–N(5) 152.20(5),
N(4)–Zr(1)–N(5) 37.41(6), N(5)–N(4)–Zr(1) 82.36(10), N(4)–N(5)–Zr(1)
60.23(9), N(4)–Zr(1)–Cl(1) 87.70(5).
Whilst the metal ligand bond lengths in 1 lie within the
expected range, its distorted trigonal bipyramidal structure is
best characterized by the angle N(3)–Zr(1)–Cl(2) of 176.77(8)◦
(176.35(8)◦ in the second molecule) which thus deviates only
slightly from perfect linearity.
The most remarkable spectroscopic feature of 1 is the low
field 15N NMR chemical shift of the equatorial amido N-donors
of the tripodal ligand (d 220.9, ext. reference NH3) compared
to the {Zr(NMe2)2} precursor (149.9 ppm) as well as all other
complexes bearing anionic N-donor fragments (<200 ppm, vide
infra). This is a general trend which we have observed in other
mixed amidohalide complexes of the group 4 metals.
Complex 2a is the first example of a mononuclear zirconium
2
compound containing a g -bonded hydrazido(1−) ligand. This
type of side-on ligation of the hydrazido unit has been reported
previously for titanium13 as well as several other transition metals
such as cobalt17 and molybdenum.18 Whilst this is the more
−
common bonding mode of a {R2NNH} fragment, there are
also a few examples of end-on coordination in the literature.19,20
It appears that the electron density at the metal along with the
steric bulk of the Nb-substituents as well as the other ligands at
the metal determine the structural arrangement to be found.
The coordination geometry in complex 2a may be described
as pseudo trigonal-bipyramidal if the hydrazido ligand is viewed
as occupying a single coordination site trans to the pyridyl unit
of the tripodal ancillary ligand [N(3)–Zr(1)–N(4) 170.39(6)]. In
the equatorial plane the chloro and amido ligands are arranged
in a very similar way as in complex 1. The Zr(1)–N(3) bond
The reaction of complex 1 with one molar equivalen◦t of the
monolithiated hydrazide LiNHNMe2 in toluene at −78 C gave
TBS
the hydrazido(1−) complex [Zr(N2 Npy)(NHNMe2)Cl] (2) as a
microcrystalline solid. When redissolved in C6D6, two isomeric
forms of this complex, 2a and 2b (Scheme 1), were identified
by observation of two sets of resonances in the 1H, 13C, 15N
and 29Si NMR spectra. Both isomers convert only slowly into
one another on the NMR timescale in solution and could thus
be clearly distinguished. Whereas the characteristic 15N NMR
˚
length of 2.438(2) A may indicate a slightly weaker ligation
of the pyridyl unit than in the dichloro complex 1 (Zr–N
1
˚
2.364(3)/2.368(3) A), although this is not reflected in the H NMR
chemical shifts of the ortho-proton H6 of the pyridyl group [2a: d
9.92 compared to 1: d 9.50] observed in solution.
signals of the hydrazido(1−) unit were observed at d 202.1 (1JNH
=
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Scheme 1 Synthesis of the side-on hydrazido(1−) zirconium complexes 2a and 2b and their attempted conversion to a hydrazide(2−).
The binding of the Na [N(4)] and Nb [N(5)] atoms to the
zirconium centre differs markedly. The former may be viewed as a
formally anionic amido-type donor, as reflected in the Zr(1)–N(4)
carried out. Its result is displayed in Fig. 3 along with the principal
bond lengths and angles. The overall molecular structure of 3 is
very similar to that described in detail for complex 2a and may
likewise be understood as distorted trigonal bipyramidal [N(3)–
˚
distance of 2.044(2) A, which is similar to the amido bonding
˚
of the facially coordinating tripod ligand [Zr(1)–N(1) 2.058(2),
Zr(1)–N(4) 173.55(9) A]. As found for the latter, the hydrazido
˚
Zr(1)–N(2) 2.073(2) A)]. In contrast, the Nb atom displays amine-
ligands is side-on coordinated [Zr(1)–N(4) 2.060(3), Zr(1)–N(5)
◦
˚
type coordination and thus a significantly longer Zr(1)−N(5)
2.385(2), N(4)–N(5) 1.435(3) A, Zr(1)–N(4)–N(5) 84.0(2) ] while
the alkyl fragment occupies one of the equatorial coordination
sites. The metal–ligand atom distances for both of the formally
˚
bond [2.334(2) A]. This value may be compared with the Zr–Nb
bond length in Bergman’s hydrazido-bridged dinuclear complex
[(Cp2Zr)2(l2:g ,g -NNPh2)(l2:g ,g -NNPh2)] [2.446(6) A], which
1
1
2
1
8
˚
displays a slightly longer dative ligand–metal interaction of this
˚
type. The hydrazido N(4)–N(5) distance of 1.431(2) A is similar
2
to the corresponding value in Leigh’s [Ti(C5H5)Cl2(g -NHNMe2)]
13
˚
[1.41(2) A] and only slightly shorter than in hydrazine itself
˚
(ca. 1.47 A). Finally, we note that the M–N–N angles in 2a
[Zr(1)–N(4)–N(5) 82.4(1)◦] and [Ti(C5H5)Cl2(NHNMe2)] [Ti–Na–
Nb 80.0(6)◦] are nearly identical.
Synthesis and structural characterization of the alkyl/hydrazido-
TBS
(1−) complex [Zr(N2 Npy)(CH2SiMe3)(NHNMe2)] (3)
In their syntheses of several imidozirconium complexes Bergman
and co-workers successfully employed a synthetic route based
on the thermal methane elimination from the respective RHN−
amido/methyl precursors. A similar method led to the hy-
drazido complex [Cp2Zr(N2Ph2)(dmap)].8 Attempts to con-
vert the hydrazido(1−)/chloro complex 2 to the correspond-
ing linear hydrazido(2−) complex by reaction with MeLi or
MeMgCl in the presence of pyridine as co-ligand did not
lead to well defined isolable products. However, stirring 2a
with one molar equivalent of LiCH2SiMe3 in toluene at
−78 ◦C and subsequent warming to ambient temperature se-
lectively yielded the corresponding alkyl/hydrazido(1−) complex
˚
Fig. 3 Molecular structure of complex 3. Selected bond lengths (A)
and angles (◦): Zr(1)–N(1) 2.081(2), Zr(1)–N(2) 2.081(2), Zr(1)–N(3)
2.452(2), Zr(1)–N(4) 2.060(3), Zr(1)–N(5) 2.385(2), N(4)–N(5) 1.435(3),
Zr(1)–C(24) 2.291(3), N(1)–Zr(1)–N(2) 112.39(9), N(1)–Zr(1)–N(3)
76.23(8), N(1)–Zr(1)–N(4) 107.56(10), N(1)–Zr(1)–N(5) 87.38(9),
N(2)–Zr(1)–N(3) 75.26(8), N(2)–Zr(1)–N(4) 107.41(10), N(2)–Zr(1)–N(5)
88.10(9), N(3)–Zr(1)–N(4) 173.55(9), N(3)–Zr(1)–N(5) 149.66(8),
N(4)–Zr(1)–N(5) 36.76(9), N(5)–N(4)–Zr(1) 84.02(15), N(4)–N(5)–Zr(1)
59.22(13), N(4)–Zr(1)–C(24) 89.56(10), Si(3)–C(24)–Zr(1) 128.28(14).
TBS
[Zr(N2 Npy)(CH2SiMe3)(NHNMe2)] (3).
In order to establish the details of the molecular structure
of complex 3, a single-crystal X-ray structure analysis has been
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1
neutral ligating units, the hydrazido NMe2 fragment [Zr(1)–N(5)
with similar H, 13C and 29Si NMR spectroscopic characteristics
˚
˚
2.385(2) A] and the pyridyl ligand “arm” [Zr(1)–N(3) 2.452(2) A]
are greater than in the dichloro complex 1 as well as compound
2a which we attribute to a combination of steric and electronic
factors: the bulky equatorial alkyl ligand and the replacement of
the electronegative chlorine atoms by less electron withdrawing
substitutents which reduce the Lewis acidity of the metal centre
and thus the donor acceptor bonding.
(Scheme 2).
However, the chemical shifts of the Nb nuclei in 4a and
4b [d(15Nb) 74.3] are different to those of 2a,b [49.4, 52.6,
respectively] which indicated a different preferred bonding
mode. A possible end-on coordination in solution, as ob-
−
served for the previously characterized {NHNPh2} derivative
[Zr(N2 Npy)(NHNPh2)Cl],11 are thought to explain these data as
TBS
All attempts to convert complex
3
to the respective
well as the observed mirror symmetry reflected in the NMR signal
patterns of both 4a and 4b. The chiral centre which is generated
upon a coordination of the Nb-atom, as in 2a,b would render the
two amido ligand “arms” of the tripod diastereotopic. Whereas
the structure of 4 in solution is thus most likely analogous to that
hydrazido(2−) compound at elevated temperatures failed. The
alkyl amido complex proved to be remarkably stable up to ca.
85 ◦C. At higher temperatures only nonselective degradation
was observed. Alternatively, the corresponding transformation
was attempted by reacting the mixture of 2a and 2b with
the bulky base lithium hexamethyldisilazide as has previously
proved to be an efficient preparative method for the synthesis of
TBS
of [Zr(N2 Npy)(NHNPh2)Cl], the solid state structure proved to
be different.
Single crystals suitable for an X-ray diffraction study were ob-
tained from a solution of 4a and 4b in toluene. The asymmetric unit
contains two crystallographically independent but geometrically
quite similar molecules of the isomer 4a. Fig. 4 depicts one of these
molecules structures along with selected bond lengths and angles.
The overall molecular structure of 4a as well as the bonding
pattern of the hydrazido ligand is similar to that established
for complex 2a [Zr(1)–N(4) 2.063(2), Zr(1)–N(5) 2.356(2), N(4)–
TBS
[Zr(N2 Npy)(NNPh2)(py)]. Deprotonation occurred immediately
at low temperatures accompanied by the precipitation of a colour-
less solid. The latter was found to be insoluble in all nonprotic
organic solvents and therefore could not be characterized further.
We assume that a polymeric material has been formed based on
the linkage of Zr centres through bridging hydrazido units.
−
˚
N(5) 1.439(2) A]. A similar coordination of {PhMeNNH} to
a metal centre has been reported for the molybdenum complex
[Mo(g -NHNMePh)(g -NNMePh)(S2CNMe2)2][BPh4] for which
Synthesis and structural characterization of the hydrazido(1−)
2
1
TBS
zirconium complexes [Zr(N2 Npy)(NHNMePh)Cl] (4a and 4b)
˚
the bond lengths Mo–Nb 2.176(9) and Mo–Na 2.070(8) A have
and their conversion to the hydrazido(2−) complex
been reported.18 In this case the difference between amido– and
amine–metal bond lengths is less pronounced than for 4a.
Give the solid-state structure of 4a,b as well as the NMR
spectroscopic data in solution, we assume an equilibrium be-
TBS
[Zr(N2 Npy)(NNMePh)(py)] (5)
The apparent aggregation of complex 2a,b upon the attempted
base-induced dehydrohalogenation which worked well in the
TBS
1
2
synthesis of [Zr(N2 Npy)(NNPh2)(py)], led us to investigate the
tween isomeric species containing the hydrazide in g - and g -
coordination as represented in Scheme 3. The preference for the
more open form in solution is clearly entropy driven, whereas
intermediate case with a methyl/phenyl substitution pattern on
the Nb atom. Reaction of 1 with LiHNNPhMe gave a mixture
TBS
2
of stereoisomers of [Zr(N2 Npy)(NHNMePh)Cl] (4a and 4b)
g -coordination may be slightly enthalpically favoured. Upon
Scheme 2 Synthesis of a (thermally labile) zirconium hydrazide(2−) (5) via the hydrazido(1−) zirconium complexes 4a and 4b. Conversion of the
precipitate derived from 5 to the mononuclear dmap/hydrazido(2−) complex 6.
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resonates at 291.0 ppm while the signal of the two amido groups
of the ancillary ligand appears high field at 140.4 ppm. Whereas
complex 5 could be characterized in solution, thermally induced
aggregation set in upon its isolation which is in contrast to the
TBS
behaviour found for the very stable [Zr(N2 Npy)(NNPh2)(py)].
Its isolation as a pure crystalline solid was therefore precluded,
however, the insoluble aggregated material could be re-dissolved
in C6D6 upon addition of p-dimethylamidopyridine (dmap) giving
complex [Zr(N2 Npy)(NNPhMe)(dmap)] (6). Here again, the 15
N
TBS
NMR signals of the hydrazido(2−) fragment at 291.5 (ZrN) and
156.2 (NMePh) are characteristic of this type of ligation.
Compound 6 could be directly obtained in a one-pot reaction
starting from 1 (Scheme 4). Stirring the dichloro-complex with
LiHNNPhMe for 36 h and then adding dmap and lithium
hexamethyldisilazide to the reaction mixture selectively gave
the hydrazido(2−) complex 6, which was isolated as a brown
microcrystalline solid and characterized analytically whilst the
NMR spectroscopic data were identical to those of the species
generated in situ as described above.
Fig. 4 Molecular structure of complex 4a. Selected bond lengths
◦
˚
(A) and angles ( ) (values in square brackets refer to the second
independent molecule): Zr(1)–N(1) 2.0499(15) [2.0564(14)], Zr(1)–N(2)
2.0730(14) [2.0648(16)], Zr(1)–N(3) 2.4429(17) [2.4348(17)], Zr(1)–N(4)
2.0626(17) [2.0517(17)], Zr(1)–N(5) 2.3564(17) [2.3796(17)], Zr(1)–Cl(1)
2.4687(7) [2.4859(7)]; N(1)–Zr(1)–N(2) 111.63(6) [109.76(6)], N(1)–Zr(1)–
N(3) 77.15(6) [76.56(6)], N(1)–Zr(1)–N(4) 107.15(7) [106.58(6)],
N(1)–Zr(1)–N(5) 89.93(6) [89.96(6)], N(2)–Zr(1)–N(3) 75.49(5) [76.93(6)],
N(2)–Zr(1)–N(4) 108.92(6) [111.95(6)], N(2)–Zr(1)–N(5) 85.94(6)
[88.25(5)], N(3)–Zr(1)–N(4) 171.46(5) [168.02(5)], N(3)–Zr(1)–N(5)
151.23(5) [154.94(5)], N(4)–Zr(1)–N(5) 37.27(6) [36.78(6)], N(5)–N(4)–
Zr(1) 82.52(9) [84.16(9)], N(4)–N(5)–Zr(1) 60.21(8) [59.06(8)],
N(4)–Zr(1)–Cl(1) 88.40(5) [86.56(5)].
Scheme
4
One pot synthesis of the hydrazido(2−) complex
TBS
[Zr(N2 Npy)(NNPhMe)(dmap)] (6) from 1.
Conclusion
This work has shed light on the structures and properties of a series
of new zirconium hydrazido(1−) complexes and the possibility of
converting them to the respective hydrazido(2−) species. It appears
that the possibility to isolate the latter crucially depends on the
type of substituents at the Nb atom as well as the co-ligands in the
coordination sphere of the group 4 metals. The electron density at
the metal along with the steric bulk of the Nb-substituents as well
as the other ligands at the metal appear to determine the structural
arrangement to be found.
However, thermal instability of the hydrazide for a given Nb
substitution pattern does not necessarily rule out such species
in catalytic processes in which they may play a role as short
lived intermediates. Our current research activities are aimed at
investigating this aspect more closely and extending this zirconium
chemistry to its heavier congener hafnium.
Scheme 3 Proposed equilibrium between the open and side-on bound
forms of the hydrazido(1−) ligand in 4a.
lowering the temperature to 193 K, broadening of all the 1H NMR
signals is observed, however, even further temperature decrease
did not give spectra corresponding to the low-temperature limit.
This indicates that the free enthalpies of the two isomeric forms
are almost identical and that both isomers are separated by an
activation barrier of less than 10 kcal mol−1.
Reaction of the mixture of 4a and 4b with lithium hexa-
methyldisilazide in the presence of pyridine selectively yielded the
Experimental
TBS
hydrazido(2−) complex [Zr(N2 Npy)(NNPhMe)(py)] (5) which is
thought to have a similar bonding mode of the hydrazido ligand as
All manipulations of air- and moisture-sensitive materials were
performed under an inert atmosphere of dry argon using stan-
dard Schlenk techniques or by working in a glove box. Sol-
vents were dried over sodium (toluene), potassium (hexanes) or
sodium/potassium alloy (pentane, diethyl ether), distilled, and
degassed prior to use. Deuterated solvents were dried over potas-
sium (C6D6, toluene-d8), vacuum distilled and stored in Teflon
TBS
previously established for [Zr(N2 Npy)(NNPh2)(py)] (Scheme 2).
1
Whereas the resonance patterns observed in the H, 13C and 29Si
NMR spectra are consistent with the structure represented in
Scheme 2, the 15N NMR spectral data are particularly charac-
teristic. The resonances of the hydrazido(2−) ligand are observed
at d 293.6.1 (Na) and 157.1 (Nb), the pyridyl unit of the tripod
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Dalton Trans., 2008, 2111–2119 | 2115
©

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1
(C6py), 160.3 (C2py); 29Si{ H} NMR (80 MHz, C6D6, 296 K): d
valve ampoules under argon. Samples for NMR spectroscopy
were prepared under argon in 5 mm Wilmad tubes equipped
3.11 (Si(CH3)2 Bu); 15N NMR (60 MHz, C6D6, 296 K): d 220.9
(NSi(CH3)2 Bu), 283.0 (Npy).
t
1
with J. Young Teflon valves. H, 13C, 29Si and 15N NMR spectra
t
were recorded on Bruker Avance 200, 400 and 600 NMR spec-
trometers and were referenced internally, using the residual protio
solvent (1H) or solvent (13C) resonances or externally to SiMe4 and
15NH3. Elemental analyses were recorded by the analytical service
TBS
[Zr(N2 Npy)(NHNMe2)Cl] (2a
+
b).
A
solution of
TBS
[Zr(N2 Npy)Cl2] (1) (1.1 g, 2.0 mmol) in toluene (30 ml) was
cooled to −78 ◦C and LiNHNMe2 (132 mg, 2.0 mmol), dissolved
in toluene (10 ml), was added dropwise over a period of ca.
10 min. The reaction was stirred for one day, the precipitated
LiCl subsequently removed by filtration and the volatiles were
removed under reduced pressure. The crude product was washed
with cold pentane to yield a colourless solid (550 mg, 50%). Single
crystals for X-r◦ay diffraction were grown from a saturated toluene
solution at 10 C (Found: C, 47.69; H, 8.38; N, 12.30. Calc. for
C23H48ClN5Si2Zr: C, 47.83; H, 8.38; N, 12.13%); mmax(Nujol)/cm−1
3319s, 1599m, 1466s, 1384w, 1359w, 1290w, 1248m, 1138w, 1061s,
894m, 865s, 826m, 775m, 658w, 585m; (2a) 1H NMR (400 MHz,
C6D6, 296 K): d −0.13, 0.18 (s, 6H, Si(CH3)2), 0.70 (s, 18H,
SiC(CH3)3), 1.08 (s, 3H, CH3), 2.63 (s, 6H, N(CH3)2), 3.44 (d,
2JHH = 12.9 Hz, 2H, CHH), 3.60 (d, 2JHH = 12.8 Hz, 2H, CHH),
of the Heidelberg Chemistry Department. The diamido-pyridine
TBS
protio-ligand H2N2
N
was prepared according to published
py
procedures.9d All other reagents were obtained from commercial
sources and used as received unless explicitly stated.
(A) Preparation of the complexes
TBS
TBS
[Zr(N2 Npy)Cl2] (1) via [Zr(N2 Npy)(NMe2)2]. (a) Zr-
TBS
(NMe2)4 (2.6 g, 9.7 mmol) and H2N2
N (3.8 g, 9.7 mmol) were
py
dissolved in toluene (60 ml) and placed under partial vacuum.
After stirring the reaction mixture at 95 ◦C for 18 h, the solution
was filtered and the volatiles were removed under reduced pressure
TBS
to yield [Zr(N2 Npy)(NMe2)2] as a yellow solid. Yield 5.1 g
3
3
4.80 (s, 1H, NH), 6.65 (ddd, JH5pyH4py = 7.5 Hz, JH5pyH6py
=
(8.9 mmol, 92%) (Found: C, 52.37; H, 9.26; N, 12.24. Calc. for
C25H53N5Si2Zr: C, 52.58; H, 9.35; N, 12.26%); mmax(Nujol)/cm−1
1599s, 1565w, 1469s, 1383m, 1281w, 1245s, 1150m, 1087m, 1056s,
1004w, 959s, 893s, 868s, 825s, 765m, 662m; 1H NMR (400 MHz,
C6D6, 296 K): d 0.25, 0.28 (s, 6 H, Si(CH3)2), 0.78 (s, 18 H,
SiC(CH3)3), 1.08 (s, 3 H, CH3), 3.16, 3.17 (s, 6 H, N(CH3)2),
3.40 (d, 2JHH = 12.5 Hz, 2 H, CHH), 3.76 (d, 2JHH = 12.4 Hz, 2 H,
5.4 Hz,4JH5pyH3py = 1.3 Hz, 1H, H5py), 6.91 (d, 3JH3pyH4py = 7.9 Hz,
1H, H3py), 7.07 (dt, 3JH4pyH3py/5py = 7.9 Hz, 4JH4pyH6py = 1.9 Hz, 1H,
H4py), 9.92 (ddd, 3JH6pyH5py = 5.4 Hz, 4JH6pyH4py = 1.8 Hz, 5JH6pyH3py
=
0.9 Hz, 1H, H6py); 13C{ H} NMR (100 MHz, C6D6, 296 K): d −4.2,
−4.0 (Si(CH3)2), 20.8 (SiC(CH3)3), 24.7 (CCH3), 27.6 (SiC(CH3)3),
46.7 (CCH3), 52.8 (N(CH3)2), 63.1 (CH2), 120.7 (C3py), 121.2
1
(C5py), 137.8 (C4py), 147.9 (C6py), 160.5 (C2py); 29Si{ H} NMR
1
CHH), 6.56 (ddd, 3JH5pyH4py = 7.4 Hz, 3JH5pyH6py = 5.2 Hz,4JH5pyH3py
=
(80 MHz, C6D6, 296 K): d −0.5 (Si(CH3)2 Bu); 15N NMR (60 MHz,
t
3
1.0 Hz, 1 H, H5py), 6.86 (d, JH3pyH4py = 8.0 Hz, 1 H, H3py), 7.05
t
C6D6, 296 K): d 166.1 (NSi(CH3)2 Bu), 202.1 (1JNH = −73 Hz,
3
4
(dt, JH4pyH3py/5py = 7.8 Hz, JH4pyH6py = 1.8 Hz, 1 H, H4py), 8.21
1
NH), 49.4 (NMe2), 295.6 (Npy); (2b) H NMR (400 MHz, C6D6,
3
4
1
(dd, JH6pyH5py = 5.2 Hz, JH6pyH4py = 0.8 Hz, 1 H, H6py); 13C{ H}
NMR (100 MHz, C6D6, 296 K): d −3.9, −3.8 (Si(CH3)2), 20.1
(SiC(CH3)3), 24.8 (CH3), 27.9 (SiC(CH3)3), 42.1, 45.2 (N(CH3)2),
48.5 (CCH3), 63.3 (CH2), 120.3 (C3py), 121.4 (C5py), 138.3 (C4py),
296 K): d 0.25, 0.39 (s, 6H, Si(CH3)2), 0.84 (s, 18H, SiC(CH3)3),
1.05 (s, 3H, CH3), 2.52 (s, 6H, N(CH3)2), 3.34 (d, 2JHH = 12.7 Hz,
2
2H, CHH), 4.05 (d, JHH = 12.5 Hz, 2H, CHH), 4.73 (s, 1H,
NH), 6.51 (ddd, 3JH5pyH4py = 7.4 Hz, 3JH5pyH6py = 5.4 Hz,4JH5pyH3py
=
147.0 (C6py), 163.0 (C2py); 29Si { H} NMR (80 MHz, C6D6, 296 K):
1
3
1.1 Hz, 1H, H5py), 6.82 (d, JH3pyH4py = 8.0 Hz, 1H, H3py), 7.02
t
d 1.79 (Si(CH3)2 Bu); 15N NMR (60 MHz, C6D6, 296 K): d 142.3,
3
4
(dt, JH4pyH3py/5py = 7.9 Hz, JH4pyH6py = 1.9 Hz, 1H, H4py), 8.66
t
145.4 (NMe2), 149.9 (NSi(CH3)2 Bu), 292.3 (Npy).
3
4
5
(ddd, JH6pyH5py = 5.4 Hz, JH6pyH4py = 1.8 Hz, JH6pyH3py = 0.8 Hz,
TBS
(b) To a stirred solution of [Zr(N2 Npy)(NMe2)2] (3.1 g,
1H, H6py); 13C{ H} NMR (100 MHz, C6D6, 296 K): d −4.3, −3.5
1
5.5 mmol) in diethyl ether (40 ml) trimethylsilyl chloride
(2.1 ml, 16.4 mmol) was added dropwise over a period of
ca. 10 min. During the addition the clear yellow solution
turned cloudy. The reaction was stirred for two days, the sol-
vent subsequently removed by filtration and the crude prod-
uct was washed with pentane (2 × 10 ml) to yield [Zr-
(Si(CH3)2), 20.4 (SiC(CH3)3), 24.3 (CCH3), 27.9 (SiC(CH3)3), 48.1
(C−CH3),52.7 (N(CH3)2), 63.0 (CH2), 120.6 (C3py), 121.2 (C5py),
138.3 (C4py), 147.9 (C6py), 162.0 (C2py); 29Si{ H} NMR (80 MHz,
1
C6D6, 296 K): d 2.8 (Si(CH3)2 Bu); 15N NMR (60 MHz, C6D6,
t
296 K): d 173.4 (NSi(CH3)2 Bu), 213.3 (1JNH = −71 Hz, NH), 52.6
t
(NMe2), 291.4 (Npy).
TBS
(N2 Npy)Cl2] (1) as a colourless microcrystalline solid. Single
TBS
crystals for X-ray diffraction were grown from a saturated toluene
solution at 10 ◦C. Yield 1.91 g (3.5 mmol, 64%) (Found: C, 45.43;
H, 7.56; N, 7.73. Calc. for C21H41Cl2N3Si2Zr: C, 45.54; H, 7.46;
N, 7.59%); mmax(Nujol)/cm−1 1604w, 1466m, 1262w, 1045w, 912w,
[Zr(N2 Npy)(CH2SiMe3)(NHNMe2)] (3). A solution of [Zr-
TBS
(N2 Npy)(NHNMe2)Cl] (2a + b) (465 mg, 0.8 mmol) in toluene
(20 ml) was cooled to −78 ◦C and LiCH2SiMe3 (76 mg, 0.8 mmol),
dissolved in toluene (5 ml), was added dropwise over a period of
ca. 10 min. The reaction was stirred for 18 h, the precipitated LiCl
subsequently removed by filtration and the solvent was removed
in vacuo. The crude product was washed with cold pentane (3 ×
10 ml) to yield a colourless solid (450 mg, 88%). Single crystals for
X-ray diffraction were grown from a saturated toluene solution at
10 ◦C (Found: C, 51.27; H, 9.53; N, 11.06. Calc. for C27H59N5Si3Zr:
C, 51.53; H, 9.45; N, 11.13%); mmax(Nujol)/cm−1 1598w, 1462s,
1377m, 1257m, 1247m, 1127w, 1056m, 862s, 827w, 769w; 1H
NMR (400 MHz, C6D6, 296 K): d 0.00, 0.06 (s, 6H, Si(CH3)2),
0.24 (s, 2H, CH2Si(CH3)3), 0.50 (s, 9H, CH2Si(CH3)3), 0.60 (s,
1
851m, 672w; H NMR (400 MHz, C6D6, 296 K): d −0.01, 0.54
(s, 6 H, Si(CH3)2), 0.81 (s, 18 H, SiC(CH3)3), 0.92 (s, 3 H, CH3),
2
2
3.18 (d, JHH = 12.8 Hz, 2 H, CHH), 3.98 (d, JHH = 12.7 Hz,
2 H, CHH), 6.50 (ddd, JH5pyH4py = 7.4 Hz, JH5pyH6py = 5.5 Hz,4J
3
3
3
H5pyH3py= 1.1 Hz, 1 H, H5py), 6.77 (d, JH3pyH4py = 8.0 Hz, 1 H,
H3py), 7.01 (dt, JH4pyH3py/5py= 7.8 Hz,4JH4pyH6py = 1.8 Hz, 1 H,
3
3
4
H4py), 9.50 (dd, JH6pyH5py = 5.5 Hz, JH6pyH4py = 1.1 Hz, 1 H,
H6py);13C{ H} NMR (100 MHz, C6D6, 296 K): d −4.9, −3.9
1
(Si(CH3)2), 20.7 (SiC(CH3)3), 23.7 (CH3), 27.4 (SiC(CH3)3), 49.4
(CCH3), 63.0 (CH2), 120.8 (C3py), 122.2 (C5py), 139.4 (C4py), 148.3
2116 | Dalton Trans., 2008, 2111–2119
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©

View Article Online
18H, SiC(CH3)3), 1.11 (s, 3H, CH3), 2.61 (s, 6H, N(CH3)2), 3.45
18H, SiC(CH3)3), 1.15 (s, 3H, CH3), 3.73 (s, 3H, NCH3), 3.56,
3.99 (d, 2JHH = 12.7 Hz, 4H, CH2), 6.40 (ddd, 3JH5pyH4py = 7.4 Hz,
3JH5pyH6py = 5.4 Hz, 4JH5py,H3py = 1.2 Hz, 1H, H5py), 6.52 (br s, 2H, m-
HPy), 6.64 (br s, 1H, p-Hpy), 6.77 (t, 3JmHpH = 7.3 Hz, 1H, p-HPh),
2
(d, JHH = 12.4 Hz, 4H, CH2), 4.64 (s, 1H, NH), 6.61 (ddd,
3
3JH5pyH4py = 7.3 Hz, JH5pyH6py = 5.3 Hz,4JH5pyH3py = 1.1 Hz,
3
1H, H5py), 6.96 (d, JH3pyH4py = 8.1 Hz, 1H, H3py), 7.07 (dt,
4
3
3
3JH4pyH3py/5py = 7.9 Hz, JH4pyH6py = 1.7 Hz, 1H, H4py), 9.22
6.87 (d, JH3pyH4py = 8.0 Hz, 1H, H3py), 7.03 (dt, JH4pyH3py/5py =
3
1
(d, JH6pyH5py = 5.2 Hz, 1H, H6py); 13C{ H} NMR (100 MHz,
C6D6, 296 K): d −4.2, −3.0 (NSi(CH3)2), 4.4 (CH2Si(CH3)3),
20.8 (SiC(CH3)3), 25.5 (CCH3), 27.5 (NSiC(CH3)3), 43.7
(CH2Si(CH3)3), 46.4 (CCH3), 52.8 (N(CH3)2), 63.5 (CH2), 121.0
(C3py), 121.9 (C5py), 137.6 (C4py), 146.2 (C6py), 161.4 (C2py);
7.8 Hz, 4JH4pyH6py = 1.8 Hz, 1H, H4py), 7.44 (dd, 3JmHoH = 8.7 Hz,
3JmHpH = 7.2 Hz, 2H, m-HPh), 7.55 (d, 3JmHoH = 7.9 Hz, 2H, o-HPh),
3
4
9.01 (br s, 2H, o-Hpy), 9.55 (dd, JH6pyH5py = 5.4 Hz, JH6pyH4py
=
1.5 Hz, 1H, H6py); 13C{ H} NMR (100 MHz, C6D6, 296 K):
d −3.5, −2.9 (Si(CH3)2), 20.4 (CCH3), 25.6 (SiC(CH3)3), 27.7
(SiC(CH3)3), 43.6 (NCH3), 46.9 (CCH3), 64.1 (CH2), 110.3 (o-
CPh), 113.9 (C3py); 120.1 (p-CPh), 120.7 (m-Cpy, C5py), 128.7 (m-
CPh), 138.2 (p-Cpy), 138.3 (C4py), 149.3 (NCPh), 152.0, 152.3 (C6py,
1
29Si{ H} NMR (80 MHz, C6D6, 296 K): d −0.6, 0.0 (Si(CH3)2 Bu,
1
t
CH2SiMe3).
TBS
[Zr(N2 Npy)(NHNMePh)Cl] (4a + 4b). To a stirred solution
o-Cpy), 161.2 (C2py); 29Si{ H} NMR (80 MHz, C6D6, 296 K): d
1
TBS
of [Zr(N2 Npy)Cl2] (1) (1.46 g, 2.6 mmol) in toluene (30 ml)
−0.1 (Si(CH3)2 Bu); 15N NMR (60 MHz, C6D6, 296 K): d 140.4
t
a suspension of LiNHNMePh (404 mg, 3.2 mmol, 1.2 eq.)
in toluene (10 ml) was added dropwise over a period of ca.
10 min. The reaction was stirred for 2 days, the precipitated
LiCl subsequently removed by filtration and the volatiles were
removed under reduced pressure. The crude product was washed
with cold pentane (3 × 10 ml) to yield a slightly off-white powder
(850 mg, 50%) (Found: C, 52.41; H, 8.01; N, 11.07. Calc. for
C28H50ClN5Si2Zr: C, 52.58; H, 7.88; N, 10.95%); mmax(Nujol)/cm−1
3308s, 2782m, 1599m, 1487w, 1465s, 1379w, 1303w, 1250m, 1056s,
t
(NSi(CH3)2 Bu), 157.1 (NMePh), 291.0 (L-Npy), 293.6 (ZrN), n.o.
(Npy).
TBS
NMR tube reaction of (5) to [Zr(N2 Npy)(NNMePh)(dmap)]
(6). To the polymeric material formed by thermal degradation of
(5) a solution of 4-dimethylaminopyridine (9.8 mg, 0.08 mmol) in
C6D6 (0.5 ml) was added. The reaction mixture was heated to 75 ◦C
for 18 h. The yellow solid dissolved and the colourless solution
became dark brown. The reaction product 6 was characterized by
1
1
850s, 827s, 769s, 696w, 665w; (4a) H NMR (400 MHz, C6D6,
NMR spectroscopy. H NMR (400 MHz, C6D6, 296 K): d 0.10,
296 K): d −0.15, 0.00 (s, 12H, Si(CH3)2), 0.59 (s, 18H, SiC(CH3)3),
1.10 (s, 3H, CH3), 3.07 (s, 3H, NCH3), 3.41 (d, 2JHH = 13.1 Hz, 2H,
CHH), 3.74 (d, 2JHH = 13.1 Hz, 2H, CHH), 5.29 (s, 1H, NH), 6.64
(ddd, 3JH5pyH4py = 7.4 Hz, 3JH5pyH6py = 5.4 Hz,4JH5pyH3py = 1.2 Hz, 1H,
H5py), 6.91 (d, 3JH3pyH4py = 8.0 Hz, 1 H, H3py), 6.95 (m, 1H, m-HPh),
7.06 (dt, 3JH4pyH3py/5py = 7.8 Hz,4JH4pyH6py = 1.8 Hz, 1 H, H4py), 7.20
(m, 2H, m-HPh), 7.30 (m, 2H, o-HPh), 9.86 (dd, 3JH6pyH5py = 5.4 Hz,
0.23 (s, 12H, Si(CH3)2), 0.86 (s, 18H, SiC(CH3)3), 1.28 (s, 3H,
CH3), 2.10 (s, 6H, N(CH3)2), 3.75 (s, 3H, NNCH3), 3.61, 4.07 (d,
2JHH = 12.6 Hz, 4H, CH2), 5.86 (br s, 2H, m-Hdmap), 6.52 (br s, 1H,
3
3
H5py), 6.68 (t, JpHmH = 7.0 Hz, 1H, p-HPh), 6.98 (d, JH3pyH4py
=
8.2 Hz, 1H, H3py) 7.15 (m, 1H, H4py, C6D6), 7.38 (m, 2H, m-HPh),
7.52 (d, 3JoHmH = 8.3 Hz, 2H, o-HPh), 8.69 (br s, 2H, o-Hdmap), 9.58
1
(d, 3JH6pyH5py = 5.2 Hz, 1H, H6py); 13C{ H} NMR (100 MHz, C6D6,
1
4JH6pyH4py = 1.8 Hz, 1H, H6py); 13C{ H} NMR (100 MHz, C6D6,
296 K): d −3.3, −2.6 (Si(CH3)2), 20.7 (CCH3), 25.7 (SiC(CH3)3),
28.0 (SiC(CH3)3), 38.3 (N(CH3)2), 43.7 (NNCH3), 47.4 (CCH3),
64.5 (CH2), 105.6 (m-Cdmap), 110.3 (o-CPh), 113.5 (p-CPh), 120.1
(C3py), 120.8 (C5py), 128.8 (m-CPh), 138.1 (C4py), 149.5 (NCPh),
296 K): d −4.7, −3.9 (Si(CH3)2), 20.8 (CCH3), 24.8 (SiC(CH3)3),
27.6 (SiC(CH3)3), 47.1 (CCH3), 53.5 (NCH3), 63.4 (CH2), 120.1
(o-CPh), 121.4, 121.5 (p-CPh, C3py), 123.8 (C5py), 128.7 (m-CPh),
1
138.1 (C4py), 148.2 (C6py), 156.5, 160.8 (C2py, CPh); 29Si{ H} NMR
1
152.0 (o-Cdmap), 152.5 (C6py), 154.1 (p-Cdmap), 161.7 (C2py); 29Si{ H}
(80 MHz, C6D6, 296 K): d 0.0 (Si(CH3)2 Bu); 15N NMR (60 MHz,
t
NMR (80 MHz, C6D6, 296 K): d −0.5 (Si(CH3)2 Bu); 15N NMR
t
t
t
C6D6, 296 K): d 74.3 (NMePh), 173.5 (NSi(CH3)2 Bu), 191.7
(60 MHz, C6D6, 296 K): d 62.7 (py-NMe2), 135.5 (NSi(CH3)2 Bu),
(1JNH = −75 Hz, NH), 294.0 (Npy); (4b) 1H NMR (400 MHz, C6D6,
156.2 (NMePh), 242.7 (Npy-NMe2), 291.5 (ZrN), 292.8 (L-Npy).
296 K): d 0.10, 0.40 (s, 12H, Si(CH3)2), 0.87 (s, 18H, SiC(CH3)3),
TBS
2
One-pot synthesis and isolation of [Zr(N2 Npy)(NNMePh)-
1.02 (s, 3H, CH3), 3.15 (s, 3H, NCH3), 3.31 (d, JHH = 12.5 Hz,
TBS
2H, CHH), 4.06 (d, 2JHH = 12.5 Hz, 2H, CHH), 5.46 (s, 1H, NH),
6.43 (m, 1H, H5py), 6.78 (d, 3JH3pyH4py = 7.9 Hz, 1H, H3py), 8.51 (d,
(dmap)] (6). To a stirred solution of [Zr(N2 Npy)Cl2] (1) (0.50 g,
0.9 mmol) in toluene (20 ml) a suspension of LiNHNMePh
(113 mg, 0.9 mmol) in toluene (10 ml) was added dropwise over a
period of ca. 5 min. The reaction was stirred for 36 h and a solution
of 4-dimethylaminopyridine (110 mg, 0.9 mmol) in toluene (5 ml)
and a solution of lithium hexamethyldisilazide (160 mg, 0.9 mmol)
in toluene (10 ml) were added subsequently. The mixture was
stirred for another 36 h. The precipitated LiCl was removed by
filtration and the solvent removed under reduced pressure. The
crude product was washed with pentane (3 × 10 ml) to yield 6
as a yellow–brown microcrystalline solid (411 mg, 57%) (Found:
C, 57.44; H, 8.01; N, 13.32. Calc. for C35H59N7Si2Zr: C, 57.96; H,
8.20; N, 13.52%).
1
3JH6pyH5py = 5.5 Hz, 1H, H6py); 13C{ H} NMR (100 MHz, C6D6,
296 K): d −4.0 (Si(CH3)2), 24.3 (SiC(CH3)3), 28.0 (SiC(CH3)3),
48.5 (C−CH3), 50.9 (NCH3), 63.3 (CH2), 120.7 (o-CPh), 121.0 (p-
CPh, C3py), 122.9 (C5py), 128.4 (m-CPh), 138.6 (C4py), 147.6 (C6py),
1
155.7, 161.8 (C2py, CPh); 29Si{ H} NMR (80 MHz, C6D6, 296 K):
d 2.5 (Si(CH3)2 Bu); 15N NMR (60 MHz, C6D6, 296 K): d 74.3
t
(NMePh), 183.0 (NSi(CH3)2 Bu), 209.5 (1JNH = −69 Hz, NH),
t
289.0 (Npy).
TBS
NMR tube reaction of (4a + 4b) to [Zr(N2 Npy)(NNMePh)(py)]
(5). To a solution of (4a + 4b) (54 mg, 0.08 mmol) and pyridine
(6.9 ll, 0.08 mmol) in C6D6 (0.4 ml) a solution of lithium
hexamethyldisilazide (14.2 mg, 0.08 mmol) in C6D6 (0.1 ml) was
added. The colourless solution turned dark green immediately.
The product was characterized by NMR spectroscopy. 1H NMR
(400 MHz, C6D6, 296 K): d 0.01, 0.17 (s, 12H, Si(CH3)2), 0.84 (s,
(B) Crystal structure determinations
Crystal data and details of the structure determinations are listed
in Table 1. Intensity data were collected at low temperature with
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 2111–2119 | 2117
©

View Article Online
Table 1 Details of the crystal structure determinations of the complexes, 1, 2a, 3 and 4a
1
2a
3
4a
Formula
Mr
C21H41Cl2N3Si2Zr
553.87
Monoclinic
C23H48ClN5Si2Zr
577.51
Monoclinic
P21/c
9.583(3)
15.613(4)
20.578(6)
C27H59N5Si3Zr
629.28
Monoclinic
C28H50ClN5Si2Zr
639.58
Triclinic
¯
P1
Crystal system
Space group
P21/c
P21/c
˚
a/A
15.056(2)
21.423(3)
18.016(3)
16.7739(9)
12.2454(7)
18.3510(11)
13.360(3)
15.968(3)
16.930(3)
70.93(3)
85.85(3)
74.74(3)
3292.8(11)
4
1.290
1352
0.513
0.9044, 0.8212
170(2)
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90.690(3)
93.439(6)
111.567(1)
3
˚
V/A
5810.5(14)
8
1.266
2320
0.657
0.7464, 0.6838
150(2)
1.4–27.9
3073.5(14)
4
1.248
1224
0.541
0.8923, 0.8760
100(2)
1.6–32.1
3505.5(3)
4
1.192
1352
0.439
0.9574, 0.8982
100(2)
2.1–27.1
Z
Dc/Mg m−3
F000
l(Mo-Ka)/mm−1
Max., min. transmission factors
T/K
h Range/◦
1.4–27.8
Index ranges (indep. set) h,k,l
Reflections measured
Unique, Rint
−19 to 19, 0 to 28, 0 to 23 −14 to 14, 0 to 22, 0 to 30 −21 to 19, 0 to 15, 0 to 23 −17 to 17, −19 to 20, 0 to 22
120143
13856, 0.0903
9446
77762
24978
61069
10414, 0.0606
7730
306
7742, 0.0555
5499
345
15160, 0.0353
13082
699
Observed [I ≥ 2r(I)]
Parameters refined
545
R Indices [F > 4r(F)] R(F), wR(F2) 0.0527, 0.1396
0.0379, 0.0877
0.0598, 0.0956
1.07
0.0421, 0.0961
0.0699, 0.1068
1.04
0.0292, 0.0752
0.0372, 0.0784
1.11
R Indices (all data) R(F), wR(F2)
0.0804, 0.1507
1.10
GooF on F2
Largest residual peaks/e A
−3
˚
0.560, −0.852
0.622, −0.548
0.669, −0.468
0.365, −0.758
Bruker AXS Smart 1000 CCD (complexes 1, 2a and 3) and
Enraf-Nonius Kappa CCD (complex 4a) diffractometers (Mo-
Trans., 1998, 1229; (b) S. Kahlal, J. Saillard, J. Hamon, C. Manzur and
D. Carrillo, New J. Chem., 2001, 25, 231.
4 (a) Ti–hydrazides(2−): A. J. Blake, J. M. McInnes, P. Mountford, G. I.
Nikonov, D. Swallow and D. J. Watkin, J. Chem. Soc., Dalton Trans.,
1999, 379; (b) J. L. Thormann and L. K. Woo, Inorg. Chem., 2000, 39,
1301; (c) Y. Li, Y. Shi and A. L. Odom, J. Am. Chem. Soc., 2004, 126,
1794; (d) T. B. Parsons, N. Hazari, A. R. Cowley, J. C. Green and P.
Mountford, Inorg. Chem., 2005, 44, 8442; (e) S. Patel, Y. Li and A. L.
Odom, Inorg. Chem., 2007, 46, 6373; (f) J. D. Selby, C. D. Manley,
M. Feliz, A. D. Schwarz, E. Clot and P. Mountford, Chem. Commun.,
2007, 4937.
˚
Ka radiation, graphite monochromator, k = 0.71073 A). Data
were corrected for Lorentz, polarization and absorption effects
(semiempirical, SADABS).21
The structures were solved by the heavy-atom method combined
with structure expansion by direct methods applied to difference
structure factors (DIRDIF)22 and refined by full-matrix least
squares methods based on F2.23 All non-hydrogen atoms were
given anisotropic displacement parameters. Hydrogen atoms were
generally placed at calculated positions and refined with a riding
model. The hydrogen atoms on N-a of the hydrazido ligands were
taken from difference Fourier syntheses and refined.
CCDC reference numbers 674839–674842.
5 N. Wiberg, H.-W. Haring, G. Huttner and P. Friedrich, Chem. Ber.,
1978, 111, 2708.
6 (a) J. S. Johnson and R. G. Bergmann, J. Am. Chem. Soc., 2001, 123,
2923; (b) C. Cao, Y. Shi and A. L. Odom, Org. Lett., 2002, 4, 2853;
(c) V. Khedkar, A. Tillack, M. Michalik and M. Beller, Tetrahedron
Lett., 2004, 45, 3123; (d) L. Ackermann and R. Born, Tetrahedron
Lett., 2004, 45, 9541.
7 (a) A. Tillack, H. Jiao, I. Garcia Castro, C. G. Hartung and M. Beller,
Chem.–Eur. J., 2004, 10, 2410; (b) iminohydrazination: S. Banerjee,
Y. Shi, C. Cao and A. L. Odom, J. Organomet. Chem., 2005, 690,
5066; (c) S. Banerjee and A. L. Odom, Organometallics, 2006, 25,
3099.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b800682b
Acknowledgements
8 P. J. Walsh, M. J. Carney and R. G. Bergman, J. Am. Chem. Soc., 1991,
113, 6343.
We thank the Deutsche Forschungsgemeinschaft for funding
and Dr Markus Enders for expert advice concerning 15N NMR
spectroscopy.
9 (a) S. Friedrich, M. Schubart, L. H. Gade, I. J. Scowen, A. J. Edwards
and M. McPartlin, Chem. Ber., 1997, 130, 1751; (b) A. J. Blake, P. E.
Collier, L. H. Gade, M. McPartlin, P. Mountford, M. Schubart and
I. J. Scowen, Chem. Commun., 1997, 1555; (c) A. Bashall, P. E. Collier,
L. H. Gade, M. McPartlin, P. Mountford, S. M; Pugh, S. Radojevic,
M. Schubart, I. J. Scowen and D. J. M. Tro¨sch, Organometallics, 2000,
19, 4784; (d) A. J. Blake, P. E. Collier, L. H. Gade, P. Mountford, S. E.
Pugh, M. Schubart and D. J. M. Tro¨sch, Inorg. Chem., 2001, 40, 870;
(e) D. J. M. Tro¨sch, A. Bashall, P. E. Collier, L. H. Gade, M. McPartlin
and P. Mountford, Organometallics, 2001, 20, 3308; (f) Reviews:L. H.
Gade, Chem. Commun., 2000, 173; (g) L. H. Gade and P. Mountford,
Coord. Chem. Rev., 2001, 216/217, 65.
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