Water as an ideal solvent for the synthesis of easily hydrolyzable compounds: High-yield preparation of 2-pyrrolecarbaldimines and their CVD/ALD-relevant Cu(II) derivatives in H2O

Article abstract of DOI:10.1002/adsc.200404181

Water was found to be an ideal solvent for the remarkably high-yield, fast preparation of easily hydrolyzable 2-pyrrolecarbaldimines. In the presence of Cu²⁺, the reaction afforded, in one step, the corresponding Cu(II) chelates which were demonstrated to meet the initial set of current microelectronics criteria for Cu metal deposition via a CVD/ALD process. Electronic effects of the substituent on the imino nitrogen of the Cu complexes were shown to strongly influence the coordination geometry at the Cu center.

Full text of DOI:10.1002/adsc.200404181

COMMUNICATIONS
Water as an Ideal Solvent for the Synthesis of Easily
Hydrolyzable Compounds: High-Yield Preparation of
2
-Pyrrolecarbaldimines and their CVD/ALD-Relevant Cu(II)
†
Derivatives in H O
2
Vladimir V. Grushin,* William J. Marshall
Central Research & Development, E. I. DuPont de Nemours & Co., Inc., Experimental Station, Wilmington, Delaware
19880-0328, USA
Fax: (þ1)-302-695-8281, e-mail: vlad.grushin-1@usa.dupont.com
Received: June 16, 2004; Accepted: September 10, 2004
Supporting Information for this article is available on the WWW under http://asc.wiley-vch.de.
[
6,7]
Abstract: Water was found to be an ideal solvent for
the remarkably high-yield, fast preparation of easily
hydrolyzable 2-pyrrolecarbaldimines. In the presence
of Cu , the reaction afforded, in one step, the corre-
sponding Cu(II) chelates which were demonstrated to
meet the initial set of current microelectronics criteria
for Cu metal deposition via a CVD/ALD process.
Electronic effects of the substituent on the imino ni-
trogen of the Cu complexes were shown to strongly
influence the coordination geometry at the Cu center.
dry ether to minimize the reverse process, hydrolysis.
Azeotropic distillation of the H O byproduct has also
been employed to maximize the yield.
2
[
10,11]
For aromatic
2
þ
amines, catalysis with acids is often used, which, while
speeding up the reaction, can also cause product decom-
position and coloring. Regardless of the solvent and con-
ditions employed, the yields for isolated, pure 2-pyrrole-
carbaldimines rarely exceed 70% and often are not
specified. Close to quantitative isolated yields for pure,
colorless pyrrolecarbaldimines are seldom reported.
While the above considerations of the equilibrium in
Keywords: chelating agents; chemical vapor deposi-
tion; copper; imines; Schiff bases
Eq. (1) suggested that H O should be avoided as thor-
oughly as possible, we found that water is a superior sol-
vent for the reaction of pyrrole-2-carboxaldehyde with
2
RNH . Running the synthesis in water afforded the de-
2
sired imines in pure form in ꢀ90% isolated yield
[
Eq. (2)]. For alkylamines, the reaction is fast, taking
[
1]
Since the original 1929 report of the first imino deriv- only a few minutes to furnish the products as colorless
atives of pyrrole-2-carboxaldehyde and its Co and Cu or slightly yellow crystalline materials or oils. The less
chelates, numerous 2-pyrrolecarbaldiminato-metal nucleophilic aniline reacted with pyrrole-2-carboxalde-
complexes have been synthesized and have found a hyde in water more slowly to give the imine in 94% iso-
number of important applications. Recent examples of lated yield after 3 days. The observed ca. 100% selectiv-
exciting applications of 2-pyrrolecarbaldiminato com- ity at full conversion eliminated the need for additional
plexes include efficient post-metallocene catalysis of purification of the products. Although the alkylimines
[
2]
[3]
ethylene polymerization with titanium and hafnium
complexes, and facile CÀH activation with platinum de- was performed via extraction with hexanes, followed by
rivatives under mild conditions. Most of the reported filtration through a short Na SO column, evapora-
precipitated out of the aqueous medium, their isolation
[
4]
[12]
2
4
ligands of the type 2-pyrrolyl-CH¼NR are more stable tion, and brief vacuum-drying. This extraction proce-
derivatives of aromatic amines (R¼Ar), whereas dure is preferred to an alternative isolation technique
much more easily hydrolyzable alkyl counterparts are via simple phase separation, washing with water, and
[2,3,5–8]
[9]
scarce.
the preparation of pyrrolecarbaldimines from the alde- the product requires a longer exposure to vacuum which
hyde and a primary amine. can lead to noticeable losses of the volatile products.
The Schiff reaction [Eq. (1)] is used for drying. To remove the small amounts of water from
ð1Þ
ð2Þ
The condensation of pyrrole-2-carboxaldehyde is com-
[
3,5,8]
monly run in anhydrous alcohols such as EtOH
or
Adv. Synth. Catal. 2004, 346, 1457–1460
DOI: 10.1002/adsc.200404181
ꢀ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1457

COMMUNICATIONS
Vladimir V. Grushin, William J. Marshall
Taking into consideration the equilibrium in Eq. (1), the role-2-carboxaldehydeþCu(OAc) þRNH neat or in
2
2
[
5]
most efficient synthesis of the pyrrolecarbaldimines in EtOH] afforded some of the Cu complexes in satisfac-
water [Eq. (2)] might seem inexplicable. A closer look tory yield but did not work for R¼i-Pr. Once, however,
at the system, however, suggests that both thermody- water was used instead of EtOH, the desired Cu bis-che-
namic and kinetic factors should favor the high-yield for- late was produced in 92% yield. When the reaction with
[
15,16]
mation of the imines in H O. More acidic than MeOH other amines was carried out in water,
a variety of
2
and EtOH, water is a better medium (kinetics) for the pyrrolecarbaldiminato-Cu complexes 1a–m were ob-
synthesis via the Schiff reaction which is known to be tained in considerably better, up to 94% isolated yields
catalyzed by acids. Once formed [Eq. (2)], the water-in- [Eq. (3)].
soluble imines precipitate out, thus shifting the equili-
brium of Eq. (1) to the right. Indeed, good yields (63–
9
0%) from the reaction of pyrrole-2-carboxaldehyde
[
8]
with RNH have been reported only for the selected
2
few pyrrolecarbaldimines that are poorly soluble in
ethanol and hence precipitate upon formation, e.g.,
R¼benzyl, adamantyl. The reaction in EtOH takes
ð3Þ
[8]
hours, whereas in water the condensation is complete
within minutes or even seconds.
Our interest in the imino derivatives of pyrrole-2-car-
boxaldehyde stemmed from their ability to form stable
[
5,8]
Cu(II) bis-chelates
which we considered as candi-
[13,14]
dates for copper metal deposition. Both the CVD
chemical vapor deposition) and ALD (atomic layer Bis-chelates 1a–m were prepared [Eq. (3)] on a 0.5–
deposition) techniques could be used to deposit thin 100 g scale and isolated as analytically pure materials.
copper metal films for semiconductor, flat-panel display, Complexes 1a, 1c, 1g, and 1j (Figure 1) were character-
and other devices. Due to its high conductivity, resist- ized by X-ray diffraction data. Selected geometry
ance to electromigration, and relatively low cost, copper parameters for these and a few previously reported anal-
is currently viewed as the most promising metal for inte- ogous complexes are presented in Table 1.
[
13]
(
[14]
grated circuit interconnects of the future. The modern
microelectronics industrial criteria for a Cu metal pre- formation on the influence of steric and electronic
cursor include sufficient volatility at 0.1–10 torr and
The new structural data (Table 1) provide valuable in-
[
14]
[8] [8,19–
2
1]
factors on the distortion from the square-planar ge-
50–2008C, reducibility with a volatile chemical, and ometry in pyrrolecarbaldiminato bis-chelates of
the lack of halogens and oxygen in all reagents involved. Cu(II). As can be seen from Table 1, the dihedral angle
This set of initial requirements puts most serious limita- between the two chelating NCuN planes varies in a
tions and impediments on the design of molecular pre- broad range of 0 (R¼H) to ca. 608 (R¼t-Bu). While
[
8]
cursors for Cu CVD and ALD processes.
the degree of distortion is believed to be controlled
The synthesis of pyrrolecarbaldiminato-Cu(II) com- mostly by the steric bulk of R, the new X-ray data (Ta-
plexes can be carried out by reacting the ligand, either ble 1) indicate that electronic properties of R are also
pre-made or (more conveniently) generated in situ, very important. Electron-donating groups cause stron-
[
5,8]
with a Cu(II) salt. The Yeh–Barker procedure [pyr- ger distortion, with the dihedral angle increasing in the
Table 1. Selected geometry parameters for Cu complexes 1.
R in 1
CuÀN(pyr) [Š]
CuÀN(im) [Š]
NCuN/NCuN
Interplanar Angle [deg]
Ref.
[17]
–
[10]
[8]
H
Ph (1j)
p-tolyl
1.950(8)
1.972(9)
0
20
26
[a]
1.952(3), 1.954(3)
1.940(6), 1.956(8)
1.959(2)
2.035(2), 2.054(3)
2.020(7), 2.020(7)
2.038(2)
Ph CH
29
2
PhCH (1i)
1.951(2)
2.024(2)
33
[8]
2
[
b]
[a]
Me (1a)
n-Pr (1c)
1.936(2) – 1.940(2)
1.930(3) – 1.947(3)
1.937(2)
2.007(2) – 2.016(2)
1.974(3) – 2.006(3)
2.057(2)
32–33
42–45
57
–
–
–
[c]
[a]
[a]
t-Bu (1 g)
t-Bu (1 g)
1.939(8)
2.054(8)
61
[18]
[
[
[
a]
b]
c]
This work.
Three structurally similar molecules in asymmetric unit.
Four structurally similar molecules in asymmetric unit.
1458
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asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 1457–1460

Water as Solvent for the Synthesis of Easily Hydrolyzable Compounds
COMMUNICATIONS
a thin film of Cu metal at 160–1708C. Most unexpected-
ly, slow reduction to Cu metal was observed for 1a, b
upon treatment with a 1:1 mixture of NH and H at
3
2
1
808C and above. Ammonia or H alone were not as re-
2
active. In one experiment with 1a, white needle-shaped
crystals condensed from the hot gaseous mixture coming
from the reduction zone. These crystals were collected
and identified by NMR as 2-pyrrolecarbaldmethyli-
mine, the free ligand that would form upon hydrogenol-
ysis of the pyrrole NÀCu bond in 1a. The role of ammo-
nia and mechanism of reduction remain unknown.
Nonetheless, these preliminary results obtained with a
simple glass apparatus identify complexes 1 as candi-
dates for a Cu CVD or ALD process.
In conclusion, the most efficient synthesis of easily hy-
drolyzable alkyliminoderivatives of pyrrole-2-carboxal-
dehyde in water has been demonstrated. The Cu(II)
complexes of 2-pyrrolecarbaldimines have been shown
Figure 1. Molecular structure of bis(2-pyrrolecarbaldphenyli-
minato)copper(II) species 1j.
order H<Ph<p-tolyl<Ph CH<PhCH ꢁ Me<n- to meet the modern microelectronics criteria for Cu
2
2
Pr<t-Bu (Table 1). The aryls are less electron-rich metal CVD/ALD precursors.
than simple alkyls or aralkyls, resulting in smaller dihe-
dral angles. Within the two aryls, the angle is 208 for R¼
Ph (Figure 1) and 268 for the more electron-donating p-
Experimental Section
[10]
tolyl. The derivatives of the smallest methyl and bulk-
ier PhCH exhibit very similar angles of 32–338, where-
2
General Remarks
as the even more cumbersome yet less electron-donat-
[
8]
ing Ph CH group leads to a smaller angle of 298. Small
2
All synthetic procedures were performed in air. Amines, pyr-
role-2-carboxaldehyde, Cu salts, and other chemicals were ob-
but electron-rich n-propyl gives one of the largest angles
observed (42–458). Steric effects, however, should not tained from Aldrich and used as received. A Bruker Avance
be neglected. Thus, the dihedral angle increases when DRX 400 instrument was used for recording NMR data in
going from R¼Me (1a; 32–338) to more electron-rich CD
Cl . Selected representative procedures are given below.
A detailed description of the imine and Cu chelate synthesis
is presented in the Supporting Information.
2 2
n-Pr (1c; 42–458) and further to t-Bu (1g; 57–618). At
the same time, the CuÀN(im) bond first shortens from
2.01 to 1.99 Š but then elongates to 2.06 Š (Table 1),
likely due to steric effects. Also, crystal packing forces
may dictate a certain orientation of a substituent, possi-
bly leading to some deviation from the actual dihedral
2
-Pyrrolecarbaldmethylimine
Aqueous methylamine (40%, 10 mL) was added to a stirring
suspension of pyrrole-2-carboxaldehyde (5.22 g) in hexanes
[8]
angle in solution.
Importantly, all solid complexes 1 were found to be (150 mL). After 15 min of stirring, the upper organic layer
was separated and filtered through a short column filled with
anhydrous sodium sulfate. The column was washed with hex-
anes. The combined hexane filtrates were evaporated to leave
the crude product as slightly yellowish crystals; yield: 5.75 g
sublimable under vacuum without decomposition. Con-
ditions for vacuum deposition of the complexes vary de-
pending on the nature of R on the ligand. Thus, in the
pressure range of 0.02–1 torr, 1a–e (R¼Me, Et, Pr, i-
Pr, Bu) sublimed cleanly at 85–1308C, whereas 1j
(
97%). The latter was sublimed under vacuum to produce
pure, white 2-pyrrolecarbaldmethylimine (identical with an
authentic sample); yield: 5.35 g (90%). The compound turns
yellow and eventually dark brown even if stored under nitro-
gen.
(
R¼Ph) sublimed at 150–1608C. An oil at ambient
temperature, 1h could be distilled under reduced pres-
sure.
Complexes 1 are robust materials that are chemically
inert, probably for kinetic reasons. The highly stable 5-
membered chelate rings do not open up easily to gener- 2-Pyrrolecarbaldisobutylimine
ate a vacant coordination site that is presumably needed
for reactivity. Nonetheless, reducing agents were found
to produce Cu metal from 1 at elevated temperatures.
Isobutylamine (4.8 mL, 3.5 g, 4.8 mmol) was added to pyrrole-
2
2
-carboxaldehyde (2.3 g, 2.4 mmol) in water (4 mL). After
min of stirring, water (15 mL) and hexanes (25 mL) were
When 1a – g (R¼alkyl) were exposed to vapors of Et
2
added, and the stirring continued for 15 min. The organic layer
was filtered through a short column filled with anhydrous Na2
SiH no Cu metal formation was observed in the temper-
2
ature range of 100–2108C. Under similar conditions, SO . The aqueous layer was washed with hexanes (3ꢂ15 mL),
4
however, 1j (R¼Ph) underwent reduction to produce and the combined extracts were filtered through the same
Adv. Synth. Catal. 2004, 346, 1457–1460
asc.wiley-vch.de
ꢀ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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COMMUNICATIONS
Vladimir V. Grushin, William J. Marshall
Na SO column. The combined hexanefiltrates were evaporated Acknowledgements
2
4
(
N ) to leave spectroscopically and analytically pure 2-(N-iso-
2
butylformimidoyl)pyrrole as white crystals; yield: 3.6 g (99%).
Anal.: calcd. (%) for C H N : C 72.0, H 9.4, N18.6; found:
We thank Drs. David Thorn and Vsevolod Rostovtsev for a
fruitful discussion, and Mr. Gary A. Halliday for technical assis-
tance with some sublimation and reduction experiments.
9
1
14
2
C 72.4, H 9.1, N18.8; H NMR (CD Cl , 208C): d¼0.95 (d,
2
2
6
H, J¼6.7 Hz, CH ), 1.9 (sept, 1H, J¼6.7 Hz, Me CH), 3.45
3
2
(m, 2H, NCH ), 6.2 (m, 1H, pyrr-H), 6.5 (m, 1H, pyrr-H), 6.9
2
(
m, 1H, pyrr-H), 8.1 (s, 1H, N¼CH), 10.0 (br s, 1H, NH);
References
1
3
C NMR (CD Cl , 208C): d¼20.7; 30.2; 69.3; 109.7; 114.2;
2
2
†
122.0; 130.8; 152.4.
Contribution No. 8545.
[
[
1] B. Emmert, K. Diehl, F. Gollwitzer, Ber. Dtsch. Chem.
Ges. 1929, 62B, 1733.
2] Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, T. Nakano,
H. Tanaka, N. Kashiwa, T. Fujita, Organometallics
Bis(2-pyrrolecarbaldethyliminato)copper(II) (1b)
To a vigorously stirring mixture of pyrrole-2-carboxaldehyde
2
001, 20, 4793.
(
45.4 g), CuCl ·2 H O (44.7 g), and water (450 mL) were add-
2 2
[
[
3] S. Matsui, T. P. Spaniol, Y. Takagi, Y. Yoshida, J. Okuda,
J. Chem. Soc. Dalton Trans. 2002, 4529.
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J. A. Labinger, J. E. Bercaw, J. Am. Chem. Soc. 2003, 125,
ed 70% aqueous ethylamine (50 mL) and then a solution of
NaOH (24.0 g) in water (100 mL). After the mixture was stir-
red for 3 hours, the black-brown product was separated by fil-
tration, washed with water, and dried. The crude product was
dissolved in dichloromethane (500 mL), and the solution was
filtered through a short silica gel plug which was then washed
with dichloromethane. The combined filtrate and washings
were evaporated to a thick paste of the complex in a small
amount of dichloromethane, and treated with hexanes
1
2674.
[
[
5] K.-N. Yeh, R. H. Barker, Inorg. Chem. 1967, 6, 830.
6] G. C. Van Stein, G. Van Koten, H. Passenier, O. Steine-
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1999, 121, 3065.
[
(
300 mL). After 2 h at þ58C the black crystals were separated,
washed with hexanes (3ꢂ50 mL), and dried under vacuum.
The yield of the analytically pure complex was 68.0 g (94%).
Anal.: calcd. (%) for C H CuN : C 55.0, H 5.9, N18.3; found:
[8] C. M. Wansapura, C. Juyoung, J. L. Simpson, D. Szyman-
ski, G. R. Eaton, S. S. Eaton, S. Fox, J. Coord. Chem.
2003, 56, 975.
1
4
18
4
C 55.1, H 5.9, N18.2.
[
9] First reported 140 years ago by the then 30-year old
Hugo Schiff, see: H. Schiff, Ann. 1864/1865, Suppl. 3, 353.
Bis(2-pyrrolecarbaldisopropyliminato)copper(II) (1d)
[10] J. A. Castro, J. Romero, J. A. Garcia-Vazquez, A. Casti-
neiras, M. L. Duran, A. Sousa, Z. Anorg. Allg. Chem.
Isopropylamine (2.0 mL) was added, under stirring, to a mix-
ture of pyrrole-2-carboxaldehyde (1.06 g) and water (10 mL).
1
992, 615, 155.
[
11] M. A. Nesterov, L. G. Menchikov, V. G. Sharf, Koord.
Khim. 1988, 14, 685.
After 2 min, Cu(OAc) (1.20 g) was added. The mixture was
2
stirred at room temperature in air for 1.5 h, then water
[
12] a) It is noteworthy that unlike acidic solids such as the
(
50 mL) was added and the stirring continued for 2 more hours.
[12b]
alumina,
neutral Na SO did not catalyze the Schiff
2 4
The resulting brown solid was filtered, washed with water, air-
dried, and dissolved in dichloromethane. The dark-green solu-
tion was filtered and evaporated to leave well-shaped black
crystals. The product was recrystallized by dissolving it in boil-
ing heptane and then cooling the solution to þ58C. The large
black crystals were washed quickly with cold hexanes (3ꢂ
reaction and was used exclusively for drying; b) F. Texi-
er-Boullet, Synthesis 1985, 679.
[
[
13] J. Rickerby, J. H. G. Steinke, Chem. Rev. 2002, 102, 1525.
14] L. Chen, M. Chang, PCT Int. Appl. 03/044242, 2003.
[15] Our work was completed in 2002 (V. Grushin, PCT Int.
Appl. 2004/015164, 2004), before the recent similar syn-
thesis of pyrrolecarbaldiminato-Cu complexes in water
3
mL), and dried under vacuum. The yield was 1.71 g (92%),
[5]
mp 124–1258C.
[8]
was reported.
[
16] P. Pfeiffer, T. Hesse, H. Pfitzner, W. Scholl, H. Thielert, J.
Prakt. Chem. 1937, 149, 217.
X-ray CrystallographicStudy
[
[
[
17] R. Tewari, R. C. Srivastava, Acta Cryst. B 1971, 27, 1644.
18] C. H. Wei, Inorg. Chem. 1972, 11, 2315.
19] R. H. Holm, A. Chakravorty, L. J. Theriot, Inorg. Chem.
Single crystal X-ray analyses were carried out with a Bruker
SMART 1K CCD system. Crystallographic data (excluding
structure factors) for the structures reported in this paper
have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications CCDC-241927
1
966, 5, 625.
[
[
20] H. Yokoi, A. W. Addison, Inorg. Chem. 1977, 16, 1341.
21] A. W. Addison, J. H. Stenhouse, Inorg. Chem. 1978, 17,
(
(
1a; R¼Me), CCDC-241810 (1c; R¼Pr), CCDC-241811
2
161.
1 g; R¼t-Bu), and CCDC-241809 (1j; R¼Ph). Copies of the
data can be obtained free of charge on application to CCDC,
1
4
2 Union Road, Cambridge CB2 1EZ, UK [Fax: int. code (þ
4)-1223-336-033, e-mail: deposit@ccdc.cam.ac.uk].
1460
ꢀ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 1457–1460