Reactions of group 4 amide guanidinates with dioxygen or water. Studies of the formation of oxo products

Article abstract of DOI:10.1021/ic4016965

Reactions of the zirconium amide guanidinates (R₂N) ₂M[ⁱPrNC(NR₂)NⁱPr]₂ (R = Me, M = Zr, 1; M = Hf, 2; R = Et, M = Zr, 3) with O₂ or H ₂O give products that are consistent with the oxo dimers {M(μ-O)[ⁱPrNC(NR₂)NⁱPr]₂} ₂ (R = Me, M = Zr, 4; M = Hf, 5; R = Et, M = Zr, 6) and polymers {M(μ-O)[ⁱPrNC(NR₂)NⁱPr]₂} _n (R = Me, M = Zr, 7; M = Hf, 8; R = Et, M = Zr, 9). Mass spectrometric (MS) analyses of the reactions of water in air with 1 and 2 show formation of the Zr monomer Zr(=O)[ⁱPrNC(NMe₂)N ⁱPr]₂ (10), oxo dimers 4 and 5, and dihydroxyl complexes M(OH)₂[ⁱPrNC(NMe₂)NⁱPr]₂ (M = Zr, 11; Hf, 12). Similar MS analyses of the reaction of diethylamide guanidinate 3 with water in air show the formation of Zr(=O)[ ⁱPrNC(NEt₂)NⁱPr]₂ (13), Zr(OH) ₂[ⁱPrNC(NEt₂)NⁱPr]₂ (14), 6, and {(Et₂N)Zr[ⁱPrNC(NEt₂)N ⁱPr]₂}⁺ (15). Kinetic studies of the reaction between 1 and a continuous flow of 1.0 atm of O₂ at 80-105 C indicate that it follows pseudo-first-order kinetics with ΔH^? = 8.7(1.1) kcal/mol, ΔS^? = -54(3) eu, ΔG ^?_{358 K} = 28(2) kcal/mol, and a half-life of 213(1) min at 85 C.

Full text of DOI:10.1021/ic4016965

Article
pubs.acs.org/IC
Reactions of Group 4 Amide Guanidinates with Dioxygen or Water.
†
Studies of the Formation of Oxo Products
Bhavna Sharma, Tabitha M. Callaway, Adam C. Lamb, Carlos A. Steren, Shu-Jian Chen, and Zi-Ling Xue*
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996, United States
*
S Supporting Information
ABSTRACT: Reactions of the zirconium amide guanidinates
i
i
(
R N) M[ PrNC(NR )N Pr] (R = Me, M = Zr, 1; M = Hf, 2;
2 2 2 2
R = Et, M = Zr, 3) with O or H O give products that are
2
2
i
consistent with the oxo dimers {M(μ-O)[ PrNC(NR )-
N Pr] } (R = Me, M = Zr, 4; M = Hf, 5; R = Et, M = Zr,
) and polymers {M(μ-O)[ PrNC(NR )N Pr] } (R = Me, M
2
i
2
2
i
i
6
2 2 n
=
Zr, 7; M = Hf, 8; R = Et, M = Zr, 9). Mass spectrometric
(
MS) analyses of the reactions of water in air with 1 and 2
i
show formation of the Zr monomer Zr(O)[ PrNC(NMe )-
2
i
N Pr] (10), oxo dimers 4 and 5, and dihydroxyl complexes
2
i
i
M(OH) [ PrNC(NMe )N Pr] (M = Zr, 11; Hf, 12). Similar MS analyses of the reaction of diethylamide guanidinate 3 with
2
2
2
i
i
i
i
water in air show the formation of Zr(O)[ PrNC(NEt )N Pr] (13), Zr(OH) [ PrNC(NEt )N Pr] (14), 6, and
2
2
2
2
2
i
i
+
{
8
2
(Et N)Zr[ PrNC(NEt )N Pr] } (15). Kinetic studies of the reaction between 1 and a continuous flow of 1.0 atm of O at
0−105 °C indicate that it follows pseudo-first-order kinetics with ΔH = 8.7(1.1) kcal/mol, ΔS = −54(3) eu, ΔG
8(2) kcal/mol, and a half-life of 213(1) min at 85 °C.
2
2
2
2
⧧
⧧
⧧
=
3
58 K
INTRODUCTION
in, e.g., PCs, smart phones, and tablets last longer. HfO -based
chips have also been used in car propulsion systems. CVD and
2
■
Many early-transition-metal complexes are sensitive to O and
2
ALD have been used extensively to make metal oxide thin films
H O, and they are usually handled under an inert
2
0
1
−6
through reactions of an oxygen source such O or H O with d
2
2
atmosphere.
Earlier studies of the reactions between O2
10a−o,11b,e,f
1
complexes that include homoleptic amides M(NR )
2
n
and early-transition-metal complexes focused on O insertion
1
0q,r
0
1−5
1
a
and imides.
The high-oxidation-state d complexes show
into the Zr−Si bond in Cp Zr(SiMe )Cl and the M−C bonds
2
3
1
b
1c
reactivities toward O different from those of late-transition-
2
in Cp ZrRCl/Cp ZrR (R = alkyl), (RO) TiMe , (Ar-
2
2
2
2
2
n
6
1
d
1e
metal d complexes. Because O is a diradical, many of its
2
O) TaMe , and (ArN) MoMe . In addition, a bis-
2
3
2
2
reactions are radical in nature. For example, reactions of Group
(
peroxo) complex was isolated as a product in the reaction of
4
M(NMe ) (M = Zr, Hf) with O gave unusual aminoxides
2 4 2
O2 with a zirconium(IV) complex containing redox-active
bis(enediamide) ligands. The reaction between O2 and
7a
2
M (NMe ) (μ-NMe ) (μ -O)(μ -ONMe ) and Me NNMe .
3 2 6 2 3 3 3 2 2 2
Reactions of Group 5 M(NR ) (M = Nb, Ta; R = Me, Et) and
2
5
(
ONHO)ZrCl (THF) (THF = tetrahydrofuran) with a
2
7b,e
+
3−
O led to insertion of O into a M−N bond.
Although homoleptic Groups 4 and 5 amide complexes
M(NR ) have been used as precursors to give metal-based
2
2
redox-active, H -containing ligand {[ONOcat] = bis(3,5-di-
tert-butyl-2-phenoxy)amide} showed that the ligand served as
+
3
2
n
both an electron and H donor. O has also been used in the
2
10a−o,11b,e,f
0
0
materials in CVD and ALD processes,
air sensitivity
preparation of d complexes. For example, d Mo(NMe ) was
2
6
2
4
of these amide precursors makes them difficult to handle.
prepared from d Mo(NMe ) and O . Adventitious O was
2
4
2
2
0
Ancillary ligands such as guanidinates have thus been used to
believed to play a role here in the preparation of d complexes
12
1
2
make precursor compounds more stable. As shown in
from d or d starting materials. Other reports include rapid
5
Scheme 1, bidentate anionic guanidinate ligands provide at
autoxidation of M(CH R) by O . Our recent studies of the
2
4
2
13−15
0
least four electrons to the metal centers.
Their zwitterionic
reactions between d complexes and O have revealed unusual
2
7
resonance structures also contribute to the stability of the
complexes. Guanidinates have been used as ancillary ligands to
reactivities with surprising findings. Reactions of early-
transition-metal complexes with H O have also been actively
2
12−15
8
stabilize early-transition-metal and lanthanide complexes.
Finding new CVD/ALD precursors has led, in part, to recent
studied.
0
Reactions of d complexes with O or H O have recently
2
2
13
interest in amide guanidinates. Devi and co-workers have
prepared Group 4 amide guanidinate complexes (R N) M-
been used to make metal oxides as a new generation of
microelectronic insulating materials through chemical vapor
deposition (CVD) and atomic layer deposition (ALD)
2
2
9
−11
processes.
Thinner and better-insulating metal oxides
Received: July 2, 2013
make the chips smaller with better performance, and batteries
Published: September 23, 2013
©
2013 American Chemical Society
11409
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Inorganic Chemistry
Article
1
2l,x,16,17
Scheme 1. Common Types of Bidentate N-Containing
Ligands and Zwitterionic Resonance Structures of the
Guanidinate Ligands
modified published procedures.
Devi and co-workers
12x
have reported the crystal structures of 1 and 3. Additional
16
characterization of 1−3 is provided. Detailed NMR studies of
i
i
(
Et N) Zr[ PrNC(NEt )N Pr] (3; Figures S1−S5 in the
2
2
2
2
16
Supporting Information, SI), including those using 2D
NMR techniques, were performed to assign overlapping
peaks in its 13C{ H} NMR spectrum, and the results are
1
16
given in the SI. Devi and co-workers reported variable-
temperature (VT) NMR spectra of 3 at −20 to +80 °C and
its hafnium analogue. We have conducted additional studies
12x
12l
of the dynamic properties of 3 between 5(1) and 110(1) °C,
⧧
⧧
yielding activation parameters ΔH and ΔS for the exchanges
in 3.
Analysis of the structure of 3 reveals that there are four
diastereotopic centers in the compound (Figure 1) when bond
1
rotations are restricted at 278(1) K on the H NMR time scale.
Similar properties have been observed by Devi and co-workers
1
12l
in the H NMR spectra of the hafnium analogue. At 278(1)
1
K, the H NMR spectrum of 3 (Figure 1) shows four sets of
[iPrNC(NR )N Pr] (M = Zr, R = Me , 1; Et , 3; MeEt;
i
12x
M
2
2
2
2
2
doublets for the isopropyl groups CHMe Me and CHMe Me .
E
F
G
H
1
2l
i
=
Hf, R = Me , 2; Et ; MeEt ) through insertion of PrN
The CH H atoms in CN(CH H Me) on the guanidinate
2
2
2
A B A B 2
i
CNPr into M−NR bonds in M(NR ) . We have studied the
ligands were observed as two multiplets at 2.90−3.10 ppm. The
CH H atoms in the amide ligands ZrN(CH H Me) were
2
2 4
reactions of O or H O with the guanidinate complexes 1−3.
2
2
C
D
C
D
2
The kinetics of the reaction between 1 with O has been
observed as multiplets at 3.8−3.9 ppm. A VT NMR study of 3
(Figure 1) illustrates a gradual increase in the rotations of the
restricted bonds. Both CN(CH H Me) and ZrN-
2
investigated, yielding rate constants and activation parameters
⧧
⧧
⧧
ΔH , ΔS , and ΔG 358 K. Our studies are reported here.
A
B
2
(
CH H Me) peaks coalesced around 333(1) K, and then
C D 2
RESULTS AND DISCUSSION
■
each became a quartet at 383(1) K, indicating fast rotations of
Characterization of Group 4 Amide Guanidinate
Complexes 1−3. 1−3 in the current work were prepared by
the N−C bonds. The isopropyl groups CHMe Me and
E
F
CHMe Me coalesced around 338(1) and 333(1) K,
G H
1
Figure 1. VT H NMR spectra of 3 in toluene-d showing its diastereotopic property.
8
1
1410
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Inorganic Chemistry
Article
⧧
respectively, as a result of the fast rotation of the N−C bonds in
the guanidinate ligands. Then, as the temperature increases
further, the molecule undergoes Bailar exchange (Scheme
activation free energy ΔG . For example, for the exchange of
⧧
⧧
H ,H , ΔH = 3.5(8) kcal/mol and ΔS = −39(2) eu. At
A
B
⧧
⧧
⧧
coalescence [338(1) K], ΔG = ΔH − TΔS = 16.7(1.5)
kcal/mol. The large, negative activation entropies in the current
exchanges are consistent with the difficulties in rotating the
bonds and groups in the crowded molecules of 3.
1
8,19
2).
The two enantiomers interconvert rapidly via a trigonal-
Scheme 2. Bailar Twist Mechanism for Exchanges in 3
The assignments of H ,H , H ,H , Me ,Me , and Me ,Me
A
B
C
D
E
F
G
H
are supported by NOESY (nuclear Overhauser effect spectros-
16
1
1
copy) and EXSY (exchange spectroscopy) studies. H− H
COSY (correlation spectroscopy) was also obtained to
16
understand the structural features of 3. A discussion of
16
13
1
these results is given in the SI, along with the C{ H} NMR
spectrum of 3, its peak assignments, and confirmation of the
assignments by HSQC (heteronuclear single quantum
coherence) and HMBC (heteronuclear multiple-bond correla-
tion spectroscopy) experiments.
prismatic intermediate, making the two bonding sites of the
guanidinate ligands equivalent. The two coalesced peaks (from
CHMe Me and CHMe Me ) coalesce again at 363(1) K and
i
i
Reaction of (Me N) Zr[ PrNC(NMe )N Pr] (1) with O .
2
2
2
2
2
E
F
G
H
The zirconium amide guanidinate complex 1 has been found to
eventually become a doublet at 383(1) K.
1
react with O slowly even at 70 °C. H NMR monitoring
2
The kinetics of the exchanges in 3 has been studied. The rate
constants of the interconversions in 3 at various temperatures
showed that it took ca. 44 h to complete the reaction of 1 with
20
1 atm of O
1 gradually decreased. In solution, organic products HNMe
2
2 6
in benzene-d at 70 °C. In the process, the peak of
were calculated from eq 1, and they are listed in Table S1 in
1
6
the SI.
1
13
1
and CH (NMe ) (16) were observed in the H and C{ H}
2
2 2
16
2
2
NMR spectra (Figure S10 in the SI ). The soluble, zirconium-
containing product was identified as {Zr(μ-O)[ PrNC(NMe )-
k = π 2(Δv − Δv )
0
(1)
i
2
i
where Δν and Δν are the frequency differences (hertz)
0
N Pr] } (4), the dimer of the oxo compound Zr(
2
2
i
i
between exchange-broadened sites at temperature T and
O)[ PrNC(NMe )N Pr] (10). An insoluble product precipi-
2
2
2
0
i
between the two sites at the slow exchange limit, respectively.
tated from the solution and was identified as {Zr(μ-O)[ PrNC-
NMe )N Pr] } (7), the polymer of the oxo product 10
16
i
Eyring plots (Figures S6−S9 in the SI ) give the activation
parameters of the exchanges listed in Table 1. A common
(
2 2 n
(
Scheme 3). As the reaction progressed, more precipitate
formed, although the peaks of the dimer 4 stayed at about the
1
6
Table 1. Activation Parameters for Interconversions in 3
same intensity.
1
a
The H NMR spectrum of the dimer 4 (Figure S10 in the
exchanges
H ,H
Me ,Me
Me ,MeH MeE−F,MeG−H,
G
A
B
E
F
16
SI, top) shows two doublets at 0.885 and 1.12 ppm for the
⧧
ΔH , kcal/mol
3.5(8)
7.5(1.3)
6.0(8)
7.5(1.2)
methyl groups in the isopropyl moieties on the guanidinate
⧧
ΔS , eu
−39(2)
−27(4)
−31(3)
−26(3)
i
i
−
[
PrNC(NMe )N Pr] ligand. The singlet at 2.64 ppm is
a
2
MeE−F,MeG−H refers to the interconversion between Me ,Me and
Me ,MeH after they each have coalesced, and the interconversion
E
F
assigned to the CNMe methyl groups in the guanidinate
2
G
ligand. The CHMe atom in the isopropyl moieties appear as a
2
eventually coalesces at 353(1) K.
multiplet at 3.30 ppm. These observations, suggesting that the
two guanidinate ligands are chemically equivalent and that
there are two environments for the isopropyl groups on the
guanidinate ligands, are consistent with the structure of the
dimer 4 in Scheme 3. One N atom of each guanidinate
feature among the four sets of activation parameters is that, in
comparison to those in chemical reactions, ΔH are fairly
small, reflecting the fact that no bonds are broken in the
exchanges. ΔS in the current exchanges are, however, much
more negative than those in typical unimolecular chemical
reactions, and TΔS are, in fact, much larger contributors to the
21
⧧
⧧
i
i
−
[ PrNC(NMe )N Pr] ligand is trans to the bridging oxo
2
ligands, and the other N atom is trans to the N atom of the
⧧
13
1
other guanidinate ligand. The C{ H} NMR spectrum of 4
Scheme 3. Reactions of O with 1−3 and H O with 1 and 2
2
2
1
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Inorganic Chemistry
Figure S10 in the SI, bottom) is consistent with the
Article
16
(
Scheme 5. Reactions of M(NMe ) (M = Zr and Hf) with
2
4
7a
structure. Two peaks at 25.66 and 25.70 ppm are assigned to
O2
methyl groups in the isopropyl CHMe moieties, and their CH
2
groups are observed at 46.16 and 47.70 ppm. The peaks at
3
9.69 and 168.97 ppm are assigned to the methyl groups in the
i
i
−
CNMe moiety on the guanidinate [ PrNC(NMe )N Pr]
2
2
ligand and its quaternary C atom, respectively. Attempts to
crystallize the soluble dimer 4 failed because it gradually turned
into the insoluble polymer 7 and precipitated from the solution.
This observation is perhaps not surprising because the dimer
may polymerize into 7, as shown in Scheme 3. The polymer 7,
pathway may operate in the current reaction of 1 with O in
2
however, does not dissolve in pentane, hexanes, benzene, Et O,
2
Scheme 3, giving HNMe and 16.
2
THF, or toluene.
Reaction of 1 with H O. The reaction was initially
2
1
It should be noted that the NMR spectrum of the dimer 4
also fits the structure of the monomer, trimer, or tetramer of 10
or the polymer 7. However, the following observations support
the assignment of the species as the dimer 4: (a) As discussed
below, the dimer 4 has also been observed in the reaction of 1
monitored by H NMR spectroscopy. The addition of 2 equiv
of H O in THF to 1 (15 mg) in benzene-d was found to give
2
6
16
soluble products HNMe and dimer 4 (Figure S11 in the SI ).
2
The reaction was much faster than that of 1 with O and was
2
completed in a few minutes. After the reaction, the product
mixture turned slightly cloudy, presumably as a result of
recipitation of the polymer 7, but the amount of the solid was
too small to be isolated. These observations point to the
reaction in Scheme 3. When the reaction of 1 with water was
with H O and identified by its mass spectrometry (MS)
2
spectrum. No other oligomers were observed. (b) Although
both the monomer 10 and dimer 4 have been observed by MS
in the reaction of 1 with H O, the pentacoordinated monomer
2
10 is coordinatively unsaturated and perhaps less stable than
conducted on a larger scale in THF, a H O/THF mixture (2
2
the hexacoordinated dimer 4. (c) We cannot rule out that the
soluble species is the trimer of 10 (Scheme 4), which is also
hexacoordinated. However, it is unlikely to be the tetramer of
equiv of H O) was added to a solution of 1 in THF at 0 °C.
2
Afterward, the solution was gradually warmed to room
temperature with formation of the polymer solid 7. The
white solid was isolated by filtration and characterized by
elemental analysis and IR and solid-state 13C NMR spectros-
copies. Volatiles in a small amount of filtrate were removed in
10 (Scheme 4) because it is heptacoordinated and more
crowded than the dimer or trimer.
1
13
1
Scheme 4. Hexacoordinated Trimer and Heptacoordinated
Tetramer of 10
vacuo. H and C{ H} NMR analyses of the residue showed
that it was mainly the dimer 4. Attempts to grow crystals from
the filtrate yielded additional insoluble solid of the polymer 7.
13
The solid-state C NMR spectrum of 7 (Figure S12 in the
1
6
SI ) shows peaks at 23.67 ppm for CHMe , 39.93 ppm for C−
2
NMe , 45.65 ppm for CHMe , and 159.17 ppm for CNMe .
2
2
2
These resonances are consistent with the polymeric structure of
. It is noted that one peak at 23.67 ppm is observed for the
methyl groups on the CHMe moieties on the guanidinate
7
2
i
i
−
[
PrNC(NMe )N Pr] ligand. Although we cannot rule out the
2
possibility that two CHMe peaks overlap here, the observation
2
of a single peak is consistent with the structure of the polymer 7
in Scheme 3, in which all four CHMe groups on a Zr center are
chemically equivalent. In comparison, there are two inequiva-
2
Identification of the polymer 7 was based on the solid-state
C NMR spectrum and elemental analysis of samples from the
1
3
lent CHMe groups in the dimer 4 (Scheme 3), as revealed by
2
reaction of 1 with H O, as discussed below. Identification of
its NMR spectrum (Figure S10 in the SI). Similarly, the trimer
of 10 would also have two inequivalent CHMe2 groups
(Scheme 4). In addition, the trimer is expected to have some
solubility in common organic solvents. As analyzed earlier, the
heptacoordinated tetramer of 10 (Scheme 4) is more crowded,
and it is unlikely to be a product. These analyses, including
elemental analysis and the insolubility of 7, support its
assignment as a polymer. The IR spectrum of 7 in a KBr
2
HNMe and 16 as products in the reaction was based on a
2
1
13
1
comparison of the H and C{ H} NMR spectra of the
reaction mixture (Figure S10 in the SI ) with those of pure
16
HNMe and 16. When the volatiles of the reaction mixture
2
were removed in vacuo, condensed, and analyzed by gas
chromatography (GC)−MS, both HNMe and 16 were
2
identified.
16
−1
The formation of HNMe and 16 suggests a radical nature of
pellet (Figure S13 in the SI ) revealed a peak at 1625 cm in
2
22
the reaction between 1 and O (Scheme 3). We earlier
the typical range of the CN stretching frequencies between
2
−1
reported that the reactions of M(NMe ) (M = Zr, Hf) with O
1690 and 1640 cm .
2
4
2
gave aminoxides M (NMe ) (μ-NMe ) (μ -O)(μ -ONMe )
Why is the reaction of 1 with H O here fast? Schwartz and
3
2 6
2 3
3
3
2
2
7a
t
and Me NNMe2 (Scheme 5). Density functional theory
calculations suggest a mechanism involving NMe radicals
co-workers have found that the reactions of Zr(O Bu) with
2
4
•
2
surface OH groups are faster than those of its alkyl analogue
t
8a
t
+
from homoleptic cleavage of newly formed ZrO−NMe
Zr(CH Bu) . Lone-pair electrons on O Bu assist H
2
2 4
7
a
bonds. Several other studies have demonstrated that, once
migration from the OH groups to the alkoxide ligand, removing
•
NMe radicals are formed, their reactions lead to the formation
the latter. The amide ligands NMe in 1 also contain lone-pair
2
2
•
+
of HNMe and 16 involving intermediates such as CH ,
CH NH, H , CH NCH , and (CH ) N−CH . Such a
electrons, and they may help with H migration and removal of
2
3
•
•
22b
the amide ligands (Scheme 6).
2
3
2
3 2
2
1
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Inorganic Chemistry
Article
+
Scheme 6. H Transfer Assisted by Lone-Pair Electrons on
The reaction between 1 and O in Scheme 3 likely follows
second-order kinetics (eq 2)
2
Amide Ligands
−
d[1]/dt = kp [1]
O
(2)
2
where k = rate constant, pO2 = partial pressure of O , and [1] =
2
concentration of 1. Under a constant O pressure, pO = 1 atm,
2
2
the rate law in eq 3 may be simplified to
−
d[1]/dt = k′[1], where k′ = kpO
(3)
2
MS Studies of the Reaction between 1 and H O in Air.
2
Operations of many mass spectrometers require the exposure
of samples to air, albeit briefly (in a few seconds). Thus, they
are usually not appropriate for MS analyses of air-sensitive
compounds, unless the mass spectrometers are operated with
an inert gas apparatus.
The reaction thus follows pseudo-first-order kinetics with rate
constant k′.
The kinetics of the reaction between 1 and 1 atm of O in
2
toluene-d was conducted using a home-designed apparatus
8
16
(Figure S14 in the SI ). Experiments for seven temperatures,
Because the reaction of 1 with H O had already been studied
Scheme 3), it was felt that perhaps the exposure of 1 to air
353−383 K, were conducted. Plots of ln [1]/[1] ([1] = initial
2
0
0
16
(
concentration of 1; Figure S15 in the SI ) yield rate constants
k′ in Table 2. The Eyring plot ln(k′/T) versus 1000/T (Figure
during the MS operations could be utilized to observe reaction
1
6
⧧
products by MS. Even though 21% of air is O , it is unlikely
S15 in the SI ) gives the activation parameters ΔH = 8.7(1.3)
2
⧧
⧧
that there would be a significant degree of the reaction between
kcal/mol, ΔS = −54(4) eu, and ΔG
= 28(3) kcal/mol.
358 K
⧧
1
and O during a few seconds of exposure of 1 to air at 23 °C.
The activation entropy ΔS is large negative, and its
2
⧧
⧧
As discussed earlier, the reaction of 1 with O is probably too
contribution (−TΔS ) to the activation free energy ΔG
2
358 K
⧧
slow at this temperature to be observed.
is more than twice that of the activation enthalpy ΔH . This
90
Zirconium is an element with five stable isotopes [ Zr,
1.45(2)%; Zr, 11.22(2)%; Zr, 17.15(1)%; Zr, 17.38(2)%;
perhaps reflects the following facts: (1) The reaction between 1
91
92
94
5
and O is a dimolecular reaction. (2) Hexacoordinated 1 with
2
9
6
Zr, 2.80(1)%], and MS spectra of zirconium compounds
two bulky guanidinate ligands is a highly crowded molecule, as
12x
containing, e.g., one and two Zr atoms thus each show unique
isotopic patterns. The analysis will help to identify whether the
compound contains a Zr atom or not and how many Zr atoms
are present in the compound.
its crystal structure revealed,
making the metal center
difficult to reach. Although heating does not favor the
dimolecular reaction entropically, increased Zr−N vibrations
at higher temperatures weaken the bonds and their stretching
Molecules of 1 reacted with H O in air, and transient
products [M + H ] (species + H ) were then analyzed by MS.
and bending modes provide opportunities for O to attack the
2
2
+
+
⧧
Zr center. Large negative ΔS have been observed in associative
2
1h,23
In addition to the monomer 10 and dimer 4, the dihydroxyl
reactions that follow second-order kinetics.
The reaction
i
i
complex Zr(OH) [ PrNC(NMe )N Pr] (11) was present
of 1 with O is autoxidation, and such reactions often have
2
6l,24
2
2
2
+
(
4
Scheme 7). The calculated mass for [10 + H ] was m/z
47.23889, and the cation was observed at m/z 447.24075. The
variable initiation periods.
Although we did not observe
such an effect in our studies, the autoxidation may have
isotopic patterns for both calculated and observed [monomer +
contributed to the relatively large errors in the kinetic plots and
the small correlation coefficient R value of 0.975 in the Eyring
plot (Figure S15 in the SI).
+
2
H ] cations are shown in Figure 2. Similarly, the calculated and
+
observed cations of [11 + H ] for the dihydroxyl product 11
were m/z 465.24945 and 465.24985, respectively, and are given
in Figure 3. One pathway to the formation of the monooxo
complex 10 is likely dehydration of the dihydroxyl 11. The
dimer 4, containing two Zr atoms, has a different isotopic
We earlier found that the reactions of M(NMe ) (M = Zr,
2
4
7
a
Hf) with O2 at room temperature were fast, yielding
overnight trinuclear complexes in Scheme 5. The presence of
two guanidinate ligands in 1 significantly reduces the rate of its
+
pattern, as shown Figure 4. The calculated [4 + H ] was m/z
reaction with O , and prolonged heating at >80 °C is required
2
893.46995, and it was observed at m/z 893.48166.
to complete the reaction.
Kinetic Studies of the Reaction between 1 and O . The
Kinetic Studies of the Reaction of 1 with O in the
Presence of the Radical Initiator Azobis(isobutyronitrile)
2
2
reaction of 1 with O is slow even at elevated temperatures.
2
This offers an opportunity to study the kinetics of the reaction.
(AIBN). O is a diradical in the ground state, and many of its
2
Scheme 7. Reactions of 1−3 with Water in Air; Species Observed by MS
1
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Figure 2. (top) Calculated and (bottom) observed MS for [10 + H+].
Figure 3. (top) Calculated and (bottom) observed MS for [11 + H+].
reactions are radical in nature. Because the reaction of 1 with
reaction between 1 and 1 atm of O is expected to be 453(1)
2
O is slow (Scheme 3), we studied the effect of the radical
min. This reaction with AIBN is thus 5.6 times faster than that
without the radical initiator. The results are consistent with the
2
6
l
initiator AIBN. AIBN, upon heating, decomposes to yield two
radicals, as shown in Scheme 8. Kinetic studies of autoxidation
has often been conducted using a radical initiator such as AIBN
radical nature of the reactions between 1 and O .
2
i
i
Reaction of (Me N) Hf[ PrNC(NMe )N Pr] (2) with O
2
2
2
2
2
24
to provide reproducible reaction rates. It has also been used
to study the kinetics of the reaction between (bipy)PdMe2
or H O. Although zirconium and hafnium compounds often
2
show similar reactivitivies, the reaction of O with 2, the
2
(
bipy = 2,2′-bipyridine) with O to give the methyl peroxide
hafnium analogue of 1, was studied because the formation of
2
6
l
complex (bipy)PdMe(OOMe). Kinetic studies were con-
ducted in solutions containing AIBN and 1 in a 1:1 molar ratio
in toluene-d under 1 atm of O . The reaction at 65(1) °C was
monitored and found to give the dimer 4. Prior to this, a test
reaction of 1 with AIBN was conducted, and the test showed
HfO as microelectronic materials from such reactions is of
2
particular interest.
In a Young’s NMR tube, a solution of 2 in benzene-d under
8
2
6
1 atm of O showed no reaction at room temperature. This
2
solution was then heated at ca. 70 °C for 45 h, and the reaction
1
that they did not react in the absence of O .
was followed by H NMR spectroscopy. Precipitation started
2
16
The kinetic plot (Figure S16 in the SI ) yields the observed
right after the addition of O and increased with heating of the
2
−3
−1
16
rate constant of 8.584(3) × 10 min for the reaction (in the
presence of AIBN) at 65(1) °C. The half-life is 80.75(3) min.
The predicted rate constant of the reaction (without AIBN) at
reaction mixture. The NMR spectra (Figure S17 in the SI )
point to the formation of 16, HNMe , the dimer {Hf(μ-
2
i
i
O)[ PrNC(NMe )N Pr] } (5), and the polymer {Hf(μ-
O)[ PrNC(NMe )N Pr] } (8). In the H NMR spectrum
2 2 n
2
2 2
−3
−1 16
i
i
1
6
5(1) °C is 1.53 × 10 min , and the half-life of the
1
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Figure 4. (top) Calculated and (bottom) observed MS for [4 + H+].
a
Table 2. Rate Constants for the Reaction of 1 with O2
The reaction of 2 with H O was found to be similar to that of
2
its zirconium analogue 1 (Scheme 3), yielding HNMe , the
dimer 5, and the polymer 8 as well.
rate constant k′ (min−1)
2
temperature
−
−
−
−
−
−
3
3
3
3
3
3
353(1)
358(1)
363(1)
368(1)
373(1)
378(1)
2.925(4) × 10
3.253(14) × 10
3.67(11) × 10
4.8(3) × 10
5.84(3) × 10
6.8(2) × 10
MS Studies of the Reaction between 2 and H O in Air.
2
Similar to its zirconium analogue, hafnium is an element with
174
176
177
several stable isotopes [ Hf, 0.16(1)%; Hf, 5.26(7)%; Hf,
178
179
180
1
8.60(9)%;
Hf, 27.28(7)%;
Hf, 13.62(2)%;
Hf,
3
5.08(16)%]. MS spectra of hafnium compounds containing,
for example, one and two Hf atoms thus each showed unique
isotopic patterns. The MS studies here were performed
similarly to those of its zirconium analogue 1. Solid powders
of 2 were kept under nitrogen gas until shortly before MS
a
The total uncertainty δk′/k′ of 0.080 was calculated from δk′ /k′ =
.063 and Δk′ /k′ = 0.050 for the measurements by NMR.
ran
0
sys
Scheme 8. Thermal Decomposition of AIBN Giving Radicals
and Initiation of Autoxidation of Substrates
analysis. Molecules of 2 reacted with H O in air, and transient
2
+
products [M + H ] were then analyzed by MS.
The calculated and observed MS spectra are given in Figures
16
S19 and S20 in the SI. They point to the reaction shown in
Scheme 7 with formation of the dihydroxyl complex
i
i
Hf(OH) [ PrNC(NMe )N Pr] (12) and the dimer 5. The
2
2
2
+
[
M + H ] peak for the dihydroxyl complex 12 was observed at
m/z 551.43002 (calcd m/z 551.28615; Figure S19 in the SI ).
For the dimer 5, its [5 + H ] peak was observed at m/z
16
+
1
067.73474, and the calculated peak was at m/z 1067.54659
16
(
Figure S20 in the SI ).
Reaction of 3 with O . 3 is the diethylamide analogue of
16
(
Figure S17 in the SI, top), two doublets were observed at
2
12x
1
.
In addition to the NEt ligands bound to the Zr atom, the
0
.88 and 1.25 ppm for the CHMe group. The singlet at 2.65
2
2
guanidinate ligands also contain NEt groups. The studies here,
conducted on an NMR scale, offer a comparison with the
ppm and the multiplet at 3.31 ppm were assigned to the
CNMe and CHMe atoms, respectively. In the C{ H} NMR
spectrum (Figure S17 in the SI, bottom), two peaks at 23.65
and 25.69 ppm are assigned to methyl groups in the isopropyl
CHMe moieties, and their CH groups are observed at 46.17
and 47.71 ppm. The peaks at 39.72 and 160.01 ppm are
assigned to the methyl groups in the CNMe moiety on the
guanidinate [ PrNC(NMe )N Pr] ligand and its quaternary C
atom, respectively. The IR spectrum of the insoluble product 8
2
1
3
1
2
2
16
reaction of 1 with O , and the results point to the reaction
2
given in Scheme 3.
In a Young’s NMR tube, the reaction of 3 with 1 atm of O2
2
(
2 equiv) initially conducted in benzene-d . No reaction was
6
observed at room temperature over several days. At 75 °C, the
2
1
i
i
−
reaction proceeded very slowly and the H NMR peaks
2
corresponding to 3 decreased, and those corresponding to the
16
−1
i
i
(
Figure S18 in the SI ) shows a strong peak at 1628 cm ,
dimer {Zr(μ-O)[ PrNC(NEt
tensity. After heating at 75 °C for 1 week, the volatiles were
removed in vacuo and the residue was redissolved in toluene-d
2 2 2
)N Pr] } (6) increased in in-
indicating the presence of the guanidinate ligand in the solid.
These observations support the assignment of the solid as
polymer 8. The results here are similar to those of the
zirconium analogue 1 and point to the reaction given in
Scheme 3.
.
8
To this solution was then added 1 atm of O , and the mixture
2
1
was heated at 105 °C for 3 weeks. The H NMR peaks of 3 had
disappeared completely.
1
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Figure 5. (top) Calculated and (bottom) observed MS for [13 + H+].
Figure 6. (top) Calculated and (bottom) observed MS for [14 + H+].
1
16
In H NMR spectrum (Figure S21 in the SI ), 6 showed
two doublets at 0.92 and 1.19 ppm, which were assigned to the
CHMe groups. The CN(CH CH ) groups appeared as a
MS Studies of the Reaction between 3 and H O in Air.
These studies were performed similarly to those involving 1
2
and 2. Molecules of 3 reacted with H O in air, and transient
2
2
3 2
2
+
+
triplet at 1.06 ppm. The quartet at 3.11 ppm was assigned to
CN(CH CH ) . Furthermore, the multiplets at 3.31 and 3.39
ppm were assigned to CHMe protons. The main organic
compound in this reaction mixture was HNEt , as confirmed by
MS discussed below. The C{ H} NMR spectrum of 6 (Figure
S22 in the SI ) showed peaks at 12.94 and 43.31 ppm for
CN(CH CH ) and CN(CH CH ) , respectively. The CHMe
products [M + H ] (species + H ) were then analyzed by MS.
The calculated and observed MS spectra are given in Figures
5−8. They point to the reaction shown in Scheme 7. A [M +
2
3 2
2
+
H ] peak at m/z 503.29885 was assigned to the oxo compound
2
1
3
1
i
i
Zr(O)[ PrNC(NEt )N Pr] (13), and its calculated [M +
2
2
1
6
+
+
H ] peak was at m/z 503.30149 (Figure 5). The [M + H ]
peak for the dihydroxyl Zr(OH) [ PrNC(NEt )N Pr] (14) was
2 2 2
i
i
2
3 2
2
3 2
2
groups were observed at 23.76 and 25.51 ppm, and the peaks at
6.20 and 47.73 ppm were assigned to CHMe . Finally, the
observed at m/z 521.30761 (calcd: m/z 521.31205; Figure 6).
+
4
For the dimer 6, its [M + H ] peak was observed at m/z
2
+
CNEt C atom was observed at 168.56 ppm. These assignments
1007.68461, and the calculated [M + H ] peak was at m/z
2
were confirmed by an HSQC experiment (Figure S23 in the
1007.59700 (Figure 7). In addition to these species, {(Et N)-
2
1
6
i
i
+
SI ).
The precipitate, a light-yellow color, was found to be
insoluble in organic solvents. Its IR spectrum (Figure S24 in the
Zr[ PrNC(NEt )N Pr] } (15) was also observed at m/z
2 2
+
558.37429. Its calculated [M + H ] peak was at m/z
558.38007 (Figure 8).
1
6
−1
SI ) revealed a strong peak at 1622 cm , suggesting the
presence of the guanidinate ligand. These observations suggest
that the insoluble solid is a polymeric product 9, an analogue of
Reaction of 1 with 2,2,6,6-Tetramethyl-piperidin-1-
yl)oxyl (TEMPO). TEMPO is an oxygen-containing, stable
25
radical. It has been used as both an oxidant and a radical-
26
7
and 8. Elemental analysis was consistent with 9.
trapping reagent. The radical-trapping technique often refers
1
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We have looked into whether, in the reaction of 1 with O2
here, TEMPO acts as an oxidant or a radical-trapping reagent.
TEMPO reacted with 1 (in the absence of O ) to give the
2
dimeric product 4 (Scheme 10 and Figures S25 and S26 in the
16
SI ). GC−MS analysis of the volatiles from this reaction
showed HNMe , 16, and unreacted TEMPO as the main
2
constituents. The formation of 4 here supports a radical
pathway in the formation of 4.
CONCLUSIONS
■
O and H O are two chemicals in air reacting with early-
2
2
transition-metal compounds, often leading to their decom-
position. They are also two primary oxygen sources in making
metal oxide electronic materials. Our work shows that reactions
of the amide guanidinate complexes here with O or H O
2
2
remove the amide ligands, both yielding oxo dimers that,
observed in the gas phase through MS, then convert into
Figure 7. (top) Calculated and (bottom) observed MS for [6 + H+].
polymers using oxo bridges. In reactions with H O, several
2
additional species, including dihydroxyl guanidinate complexes,
were observed in MS.
The reactions of O with the amide guanidinates are radical
2
in nature. The guanidinate ligands significantly reduce the rates
of reaction with O . Complex 3, with the NEt -containing
2
2
guanidinate and NEt ligands, reacts with O much more slowly
2
2
than 1 and 2 with the NMe -containing guanidinate and NMe
2
2
ligands. The reactions of H O with these amide guanidinate
2
+
complexes are, however, fast even at room temperature. H
transfer from H O to MNR amide ligands is the primary
2
2
pathway in the reactions of the guanidinate amide complexes
with H O. The guanidinate ligands remain after the reactions
2
with O or H O under the current reaction conditions. As a
2
2
protecting group in the complexes, they offer opportunities to
isolate or observe the products in the gas phase and in solution.
EXPERIMENTAL SECTION
Figure 8. (top) Calculated and (bottom) observed MS of 15.
■
All manipulations were performed under a dry nitrogen atmosphere
with the use of either a drybox or standard Schlenk techniques. All
solvents such as pentane, THF, and hexanes were dried over
potassium/benzophenone, distilled, and stored under nitrogen.
Benzene-d and toluene-d were dried over activated molecular sieves
•
to the use of a stable radical to react with a free radical R to
give a diamagnetic product (Scheme 9). The diamagnetic
•
product can then be analyzed to identify the radical R .
6
8
and stored under nitrogen. Toluene-d was used in kinetic studies.
8
Scheme 9. Radical Trapping by TEMPO
NMR spectra were recorded on a Varian 500 MHz Fourier transform
spectrometer unless otherwise noted and were referenced to solvents.
Elemental analyses were conducted via Complete Analysis Labo-
ratories, Inc., Parsippany, NJ. Solid-state NMR spectra were recorded
on a solid-state Varian INOVA 400 MHz spectrometer. MS spectra
were recorded on a JEOL AccuTOF DART mass spectrometer. To
record IR spectra, solid samples were grounded with KBr, which had
been dried at 100 °C and then pressed into pellets. IR spectra were
recorded on a Varian 4100 Excalibur.
Scheme 10. Reaction of 1 with TEMPO
1
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In the kinetic studies, at least two separate experiments performed
for all temperatures gave the uncertainty. The maximum random
uncertainty in the rate constants was combined with the estimated
systematic uncertainty, ca. 5.0%. The total uncertainties in the rate
0.029 mmol) in benzene-d in a Young’s NMR tube. The progress of
the reaction was followed by H NMR spectroscopy, revealing
formation of the oxo-bridged dimer 4 and HNMe2.
6
1
Reaction Conducted in a Schlenk Flask. 1 (700 mg, 1.35 mmol)
dissolved in toluene was cooled to −78 °C. Water (121 μL, 1.35
mmol) in a H O/THF mixture (20% v/v H O) at −78 °C was added
16
constants were used in the Eyring plots and error propagation
calculations. The estimated uncertainty in the temperature measure-
ments for an NMR probe and an oil bath was 1 K. The uncertainties in
2
2
dropwise to the solution of 1. The solution was gradually warmed to
room temperature. A large amount of white precipitate formed.
Filtration and separation of the insoluble solid of 7 were performed
(isolated 0.41 g, 59% yield). Attempts to grow crystals of the dimer 4
from the filtrate were unsuccessful. Solid-state 13C NMR of 7: δ 159.17
⧧
⧧
ΔH and ΔS were computed from the following error propagation
formulas, which were derived by Girolami and co-workers from the
Eyring equation R ln(kh/k T) = −ΔH /T + ΔS .
⧧
⧧
27
b
σΔH ) = R T 2T /ΔT {(σT/T) [(1 + TminΔL/ΔT)
⧧
2
2
2
2
2
2
(
max min
(
CNMe ), 45.65 (CHMe ), 39.93 (CNMe ), 23.67 (CHMe ). The IR
2 2 2 2
2
2
−1
+
(1 + TmaxΔL/ΔT) ] + 2(σk/k) }
(4)
(5)
spectrum of 7 showed a strong peak at 1625 cm . Anal. Calcd for
C H N OZr (7): C, 48.28; H, 9.00; N, 18.77. Found: C, 48.15; H,
18
40
6
⧧
2
2
2
2
2
2
8.89; N, 18.68.
(
σΔS ) = R /ΔT {(σT/T) [T (1 + T ΔL/ΔT)
max
min
Reaction of 2 with O . O (1 atm, 0.094 mmol) was added to 2
2
2
2
2
2
+
Tmin (1 + T ΔL/ΔT) ] + (σk/k)
(21.8 mg, 0.036 mmol) in benzene-d by the procedure described
max
6
Tmax2 + Tmin2)}
above for the reaction of 1 with O in a Young’s NMR tube. The
2
solution was then heated at 70 °C. After 45 h, the peaks corresponding
to 2 had disappeared, and the solution turned cloudy with solid
(
where
precipitation. In addition to HNMe and 16, new peaks corresponding
2
1
ΔL = [ln(kmax/Tmax) − ln(kmin/Tmin)] and ΔT = Tmax − Tmin
to the dimer product 5 were observed. H NMR of 5 (benzene-d ,
6
4
1
=
99.7 MHz, 25 °C): δ 3.30 (m, 8H, CHMe ), 2.65 (s, 24H, CNMe ),
2
2
Reaction of 1 with O . NMR-Scale Reactions. In a Young’s NMR
3
3
2
.25 (d, 24H, CHMe , J
= 6.16 Hz), 0.88 (d, 24H, CHMe , J
2
H−H
2 H−H
tube, 1 (38.7 mg, 0.0494 mmol) was dissolved in toluene-d . (The
13
1
8
6.4 Hz). C{ H} NMR (benzene-d , 125 MHz, 25 °C): δ 160.01
6
volume of the headspace in the Young’s NMR tube was 2.4 mL.)
(
(
CNMe ), 47.71 (CHMe ), 46.16 (CHMe ), 39.72 (CNMe ), 25.69
2 2 2 2
Before O was added, the solution was frozen in liquid nitrogen and
2
CHMe ), 23.65 (CHMe ). A white insoluble solid 8 (8.8 mg, 40%
2
2
nitrogen gas was removed in vacuo. O (0.5 atm, 0.0494 mmol) was
2
1
yield) was also formed that settled onto the bottom of the NMR tube.
then added. H NMR spectra over a period of time showed no new
−1
In the IR spectrum of 8, a strong peak was observed at 1628 cm .
Reaction of 3 with O . In an NMR-scale reaction, excess O was
peaks at room temperature, indicating no reaction of 1 with O . The
2
2
2
Young’s NMR tube was then heated at ca. 60 °C. The disappearance
1
added to 3 (31.2 mg, 0.0494 mmol) in benzene-d in a Young’s NMR
of 1 began, as revealed by the H NMR spectrum.
6
1
tube. The solution was heated at 75 °C, but the H NMR peaks of 3
In a separate test, O (1 atm, 0.123 mmol) was added to 1 (48.1 mg,
2
were still observed after several days of heating. The volatiles were
0
.0614 mmol) in toluene-d . (The volume of the headspace in the
8
then removed in vacuo, and toluene-d was added as the solvent. The
Young’s NMR tube was 3.0 mL.) Si(SiMe ) (5.0 mg) was used as an
8
3
4
solution was then heated at 105 °C for ca. 3 weeks, after which 3
disappeared and peaks corresponding to the dimer 6 were observed.
In a large-scale test, to 3 (0.62 g, 0.98 mmol) in toluene in a Schlenk
internal standard. The NMR tube was heated at 90 °C. After ca. 40 h,
1
the reaction was quenched in ice water. The H NMR spectrum was
1
recorded. The volatiles were removed in vacuo, and another H NMR
spectrum of the residue was recorded. The spectra clearly showed the
flask was added excess O . The reaction mixture was then heated at
2
disappearance of 1 and appearance of new peaks corresponding to the
105 °C for ca. 3 weeks, yielding a light-yellow solid precipitate. A small
1
oxo-bridged dimer 4. The H NMR spectrum also revealed peaks
portion of the supernatant solution was removed from the Schlenk
1
corresponding to HNMe (0.003 g, 6.23% yield based on NMR) and
flask, and volatiles in the solution were removed. The H NMR
2
1
6 (0.015 g, 31.2% yield based on NMR). The presence of HNMe2
spectrum of the residual solid from the supernatant solution revealed
and 16 was confirmed with GC−MS. A white precipitate formed and
that 3 had completely converted. The light-yellow insoluble precipitate
i
i
was identified as the polymeric product 7 (0.028 g, 58.3% yield). The
of {Zr(μ-O)[ PrNC(NEt )N Pr] } (9, isolated 0.41 g, 66% yield), an
2
2 n
−1
IR spectrum of 7 shows a strong peak at 1624 cm .
The reaction of 1 with O was repeated in benzene-d . H NMR of
analogue of 7, settled at the bottom of the Schlenk flask.
1
1
2
6
H NMR of 6 (benzene-d , 499.7 MHz, 25 °C): δ 3.30−3.39 (m,
6
3
4
(benzene-d , 499.7 MHz, 25 °C): δ 3.30 (m, 8H, CHMe ), 2.64 (s,
6
2
8H, CHMe ), 3.12 [q, 16H, CN(CH CH ) , J
(d, 24H, CHMe , J
JH−H = 6.99 Hz], 0.92 (d, 24H, CHMe , J
= 6.96 Hz], 1.18
2
2
3
2
H−H
3
24H, CNMe ), 1.24 (d, 24H, CHMe , J
= 6.16 Hz), 0.88 (d, 24H,
3
2
2
H−H
= 6.12 Hz), 1.06 [t, 24H, CN(CH CH ) ,
H−H 2 3 2
2
3
13
1
CHMe , J
= 6.39 Hz). C{ H} NMR (benzene-d , 125 MHz, 25
3
3
13
1
2
H−H
6
= 6.37 Hz). C{ H}
H−H
2
°
C): δ 168.97 (CNMe ), 47.70 (CHMe ), 46.16 (CHMe ), 39.69
2 2 2
NMR (benzene-d , 125 MHz, 25 °C): δ 168.56 (CNEt ), 47.73 and
6
2
(
CNMe ), 25.70 (CHMe ), 23.66 (CHMe ).
2 2 2
4
6.20 (CHMe ), 43.31 [CN(CH CH ) ], 25.51 and 23.76 (CHMe ),
2 2 3 2 2
Reaction Conducted in a Schlenk Flask. In another experiment,
1
2.94 [CN(CH CH ) ]. The IR spectral peak of the white insoluble
2
3 2
O (1 atm, 1.895 mmol) was added to 1 (0.7427 g, 0.9472 mmol) in
−1
2
solid 9 was observed at 1622 cm . Anal. Calcd for C H N OZr (9):
22
48
6
toluene in a Schlenk flask. The headspace of the Schlenk flask was
C, 52.44; H, 9.60; N, 16.68. Found: C, 52.33; H, 9.47; N, 16.59.
4
6.33 mL. The solution was heated at 90 °C for ca. 40 h. A white solid
Kinetic Studies of the Reaction between 1 and O . MeSiPh
2
3
precipitated from the solution. Volatiles were removed in vacuo, and
(internal standard, 6.0 mg, 0.022 mmol) and 1 (20.0 mg, 0.0385
Et O was added. The solution was concentrated in an attempt to grow
2
mmol) were dissolved in toluene-d8 in a Young’s NMR tube. A
crystals. No crystals could be isolated from the mixture. Removal of all
of the volatiles yielded a white product of 7 (0.46 g, 62% isolated
yield), which was insoluble in the solvents tested, including pentane,
1
6
homemade setup (Figure S14 in the SI ) was used to provide a
constant pressure of O throughout the kinetic experiment. The NMR
2
tube was then heated in an oil bath at the set temperature with a
hexanes, benzene, Et O, THF, and toluene.
2
1
6
constant O flow (1 atm). At regular intervals, the NMR tube was
This reaction in toluene was repeated at 95 °C (1:O = 1:2), 100 °C
2 2
8 h. In all three instances, formation of the white insoluble solid 7 was
2
2
removed from the oil bath and placed in ice water to quench the
(
1
1:O = 1:2), and once with a continuous flow of O at ca. 90 °C for
1
reaction. H NMR spectra were recorded. The ZrNMe peak in 1 at
2
observed, which was filtered off from the solution. The filtrate was
then concentrated and left in a freezer for several days. Repeated
attempts to grow crystals failed to yield crystalline materials.
Reaction of 1 with Water. NMR-Scale Reaction. Water in THF
3.27 ppm was integrated with respect to the MeSiPh peak at 0.72 ppm
3
1
for each H NMR spectrum. These integrals were then plotted versus
time (min). Kinetic studies were conducted at 80, 85, 90, 95, 100, 105,
and 110 °C, and the test at each temperature was repeated at least
once.
(
20% v/v, 5.2 μL, 0.058 mmol) was added dropwise to 1 (15 mg,
1
1418
dx.doi.org/10.1021/ic4016965 | Inorg. Chem. 2013, 52, 11409−11421

Inorganic Chemistry
Article
Goldberg, D. P. J. Am. Chem. Soc. 2012, 134, 8014. (k) Scheuermann,
M. L.; Fekl, U.; Kaminsky, W.; Goldberg, K. I. Organometallics 2010,
ASSOCIATED CONTENT
Supporting Information
Additional results and discussion, NMR and IR spectra, kinetic
plots, an experimental apparatus for kinetic studies of the
■
*
S
2
9, 4749. (l) Boisvert, L.; Denney, M. C.; Kloek Hanson, S.; Goldberg,
K. I. J. Am. Chem. Soc. 2009, 131, 15802. and references cited therein.
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(
reaction between 1 and O , and an additional experimental
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2
section. This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
E-mail: xue@utk.edu.
■
*
4
2
8, 7017. (q) Mukherjee, D.; Ellern, A.; Sadow, A. D. J. Am. Chem. Soc.
012, 134, 13018. (r) Jana, S.; Berger, R. J. F.; Frohlich, R.; Pape, T.;
̈
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H.; Chen, C.-H.; Hu, C.-C.; Chiang, M.-H.; Tseng, Y.-J.; Hu, C.-H.;
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The work is supported by the U.S. National Science
Foundation (Grant CHE-1012173). The authors thank
Stephen C. Gibson and Dr. Liguo Song for assistance with
MS studies and Matthew D. Dembo for help with the solid-
state NMR work.
(7) (a) Wang, R.; Zhang, X.; Chen, S.; Yu, X.; Wang, C.; Beach, D.
B.; Wu, Y.; Xue, Z. J. Am. Chem. Soc. 2005, 127, 5204. (b) Chen, S.;
Zhang, X.; Yu, X.; Qiu, H.; Yap, G. P. A.; Guzei, I. A.; Lin, Z.; Wu, Y.;
Xue, Z. J. Am. Chem. Soc. 2007, 129, 14408. (c) Chen, S.-J.; Zhang, X.-
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583. (e) Chen, S.; Zhang, J.; Yu, X.; Bu, X.; Chen, X.; Xue, Z. Inorg.
DEDICATION
■
Chem. 2010, 49, 4017. (f) Chen, T.-N.; Zhang, X.-H.; Wang, C.-S.;
Chen, S.-J.; Wu, Z.-Z.; Li, L.-T.; Sorasaenee, K. R.; Diminnie, J. B.;
Pan, H.-J.; Guzei, I. A.; Rheingold, A. L.; Wu, Y.-D.; Xue, Z.-L.
Organometallics 2005, 24, 1214. (g) Qiu, H.; Chen, S.-J.; Wang, C.-S.;
Wu, Y.-D.; Guzei, I. A.; Chen, X.-T.; Xue, Z.-L. Inorg. Chem. 2009, 48,
†
This paper is dedicated to Professor Xiao-Zeng You on the
occasion of his 80th birthday.
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