Tetramethylcyclobutadienecobalt(I) complexes containing pyrazolate or tetrazolate ligands with various coordination modes

Article abstract of DOI:10.1016/j.jorganchem.2010.10.046

Treatment of CbCo(CO)₂I (Cb = η⁴-C ₄Me₄) with one equivalent of potassium 3,5-dimethylpyrazolate (Me₂pzK) or potassium 3,5-bis(trifluoromethyl) pyrazolate ((CF₃)₂pzK) in tetrahydrofuran at 0 °C afforded (η⁴-C₄Me₄(Me₂pz))Co(CO) ₂ and CbCo((CF₃)₂pz)(CO)₂ in 90 and 71% yields, respectively. Treatment of CbCo(CO)₂I with one equivalent of Me₂pzH followed by the addition of one equivalent Me ₂pzK in tetrahydrofuran afforded CbCo(Me₂pzH)(Me ₂pz)(CO) in 74% yield. The reaction of CbCo(CO)₂I with one equivalent of potassium phenyl tetrazolate (PhtetzK) in tetrahydrofuran at 0 °C afforded [CbCo(Phtetz)(CO)]₂ in 44% yield. The solid state structure of (η⁴-C₄Me₄(Me ₂pz))Co(CO)₂ revealed nucleophilic addition of a pyrazolate nitrogen atom to a Cb ligand carbon atom to afford a novel tetradentate ligand that bonds to the cobalt ion through an η³- π-allyl interaction and one pyrazolyl nitrogen atom. Two carbonyl ligands are also present. An X-ray crystal structure determination of CbCo((CF ₃)₂pz)(CO)₂ showed η¹- coordination of the (CF₃)₂pz ligand and η⁴-coordination of the Cb ligand. The solid state structure of CbCo(Me₂pz)(Me₂pzH)(CO) is monomeric with one η¹-Me₂pz, one η¹-Me₂pzH, two carbonyl, and one η⁴-Cb ligands. The η¹-Me ₂pz and η¹-Me₂pzH ligands are linked by a hydrogen bond involving the uncoordinated nitrogen atoms. The X-ray crystal structure determination of [CbCo(Phtetz)(CO)]₂ showed a dimeric molecular structure with two μ:η¹,η¹-Phtetz ligands connected to the cobalt ions through the 2- and 3-nitrogen atoms, one η⁴-Cb ligand, and one carbonyl ligand per cobalt center. (η⁴-C₄Me₄(Me₂pz))Co(CO) ₂ is highly volatile and sublimes at 60 °C/0.03 Torr.

Full text of DOI:10.1016/j.jorganchem.2010.10.046

Journal of Organometallic Chemistry 696 (2011) 1975e1981
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Tetramethylcyclobutadienecobalt(I) complexes containing pyrazolate
or tetrazolate ligands with various coordination modes
1
*
Oussama M. El-Kadri , Mary Jane Heeg, Charles H. Winter
Department of Chemistry, Wayne State University, 5101 Cass Avenue, Detroit, MI 48202, USA
a r t i c l e i n f o
a b s t r a c t
Treatment of Cb*Co(CO)2I (Cb*
¼
h
4-C4Me4) with one equivalent of potassium 3,5-dimethylpyrazolate
Article history:
(Me2pzK) or potassium 3,5-bis(trifluoromethyl)pyrazolate ((CF3)2pzK) in tetrahydrofuran at 0 ꢀC afforded
Received 17 August 2010
Received in revised form
19 October 2010
(h
4-C4Me4(Me2pz))Co(CO)2 and Cb*Co((CF3)2pz)(CO)2 in 90 and 71% yields, respectively. Treatment of
Cb*Co(CO)2I with one equivalent of Me2pzH followed by the addition of one equivalent Me2pzK in
tetrahydrofuran afforded Cb*Co(Me2pzH)(Me2pz)(CO) in 74% yield. The reaction of Cb*Co(CO)2I with one
Accepted 20 October 2010
ꢀ
equivalent of potassium phenyl tetrazolate (PhtetzK) in tetrahydrofuran at 0 C afforded [Cb*Co(Phtetz)
Keywords:
Cobalt
(CO)]2 in 44% yield. The solid state structure of (
of a pyrazolate nitrogen atom to a Cb* ligand carbon atom to afford a novel tetradentate ligand that bonds
to the cobalt ion through an h3
-allyl interaction and one pyrazolyl nitrogen atom. Two carbonyl ligands
are also present. An X-ray crystal structure determination of Cb*Co((CF3)2pz)(CO)2 showed 1-coordi-
nation of the (CF3)2pz ligand and h4-coordination of the Cb* ligand. The solid state structure of Cb*Co
(Me2pz)(Me2pzH)(CO) is monomeric with one
1-Me2pz, one 1-Me2pzH, two carbonyl, and one h4-Cb*
ligands. The
1-Me2pz and 1-Me2pzH ligands are linked by a hydrogen bond involving the uncoordi-
nated nitrogen atoms. The X-ray crystal structure determination of [Cb*Co(Phtetz)(CO)]2 showed
h
4-C4Me4(Me2pz))Co(CO)2 revealed nucleophilic addition
Tetramethylcyclobutadienyl ligand
Pyrazolate ligand
Tetrazolate ligand
Nucleophilic addition
Atomic layer deposition
-
p
h
h
h
h
h
a dimeric molecular structure with two m: ,h
h1 1-Phtetz ligands connected to the cobalt ions through the
2- and 3-nitrogen atoms, one h4-Cb* ligand, and one carbonyl ligand per cobalt center. ( 4-C4Me4
h
(Me2pz))Co(CO)2 is highly volatile and sublimes at 60 ꢀC/0.03 Torr.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
Reports by Pauson et al. [5] and Kudinov et al. [6] described
simple synthetic procedures for the preparation of Cb*Co(CO)2I
(Cb* ¼ C4Me4) in high yields. The availability of Cb*Co(CO)2I has
allowed broad access to Cb*Co-containing complexes [5e7]. The
methyl groups on the Cb* ligand make it similar sterically to the Cp*
ligand. The Cp* ligand has found many applications in stabilizing
metal complexes across the periodic table, due to its strong electron
donating character and steric profile imparted by the methyl
groups [8].
A research goal in our laboratory is to develop volatile, ther-
mally stable, and reactive cobalt source compounds for the
growth of cobalt-containing thin films by atomic layer deposition
(ALD). Cobalt-based thin films are of particular interest for use in
microelectronics, magnetic information storage, gas sensors, and
catalysis [9]. ALD requires precursors that are volatile, thermally
stable at the film growth temperature, and which are highly
reactive toward a second reagent to afford the desired thin film
material [10]. We have previously established that pyrazole-
derived metal complexes possess enhanced thermal stability,
relative to complexes containing many other classes of ligands,
and can lead to precursors that are useful in ALD [11]. We
The chemistry of complexes containing the CbCo (Cb ¼
h
4-C4H4)
fragment and ring substituted analogs has not been as widely
explored as that of complexes containing CpFe fragments, in spite
of their close chemical resemblance [1,2]. A major obstacle to the
development of CbCo chemistry has been the lack of suitable
starting materials. Tetraaryl-substituted CbCo complexes were
prepared by treatment of Co2(CO)8 with [(C4Ar4)Pd(CO)2X]2
(Ar ¼ Ph, p-tolyl; X ¼ Cl, Br, I) [3], but require a stoichiometric
palladium reagent. Alkyne dimerization at the cobalt centers of
CpCo complexes leads to numerous CpCoCb derivatives, including
those containing aryl substituents attached to the cyclobutadiene
core [4].
* Corresponding author. Tel.: þ1 (313) 577 5224; fax: þ1 (313) 577 8289.
E-mail address: chw@chem.wayne.edu (C.H. Winter).
1
Present address: Department of Biology and Chemistry, American University of
Sharjah, P.O. Box 26666, Sharjah, United Arab Emirates.
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.10.046

1976
O.M. El-Kadri et al. / Journal of Organometallic Chemistry 696 (2011) 1975e1981
therefore sought to prepare cobalt complexes containing pyr-
azolate ligands to assess their suitability for use as ALD precursors.
Herein, we describe the synthesis and characterization of cobalt(I)
complexes containing the Cb*Co(CO)x (x ¼ 1 or 2) fragments along
with a various pyrazolate-derived ligands. A complex containing
a tetrazolate ligand is also described. A surprising result from this
study is nucleophilic attack on the Cb* ligand by the Me2pz frag-
ment. The volatility and thermal stability of the new complexes
are also reported.
2. Results and discussion
(2)
Treatment of Cb*Co(CO)2I [6] with one equivalent of Me2pzK or
(CF3)2pzK in tetrahydrofuran at 0 ꢀC, followed by stirring at room
temperature for 18 h, afforded (
h
4-C4Me4(Me2pz))Co(CO)2 (1, 90%)
The dimeric phenyl tetrazolate complex [Cb*Co(Phtetz)(CO)]2
(4) was prepared in 44% yield by treatment of Cb*Co(CO)2I with one
equivalent of the potassium 5-phenyl tetrazolate in tetrahydro-
furan (eq (3)). The structural assignment for 4 was based upon
spectral and analytical data, as well as an X-ray crystal structure
and Cb*Co((CF3)2pz)(CO)2 (2, 71%) as yellow microcrystalline solids
after workup (eq (1)). The formulations and molecular structures of
1 and 2 were established by a combination of spectral and analyt-
ical data, as well as by X-ray crystal structure determinations.
The solid state structure of 1 revealed nucleophilic addition of
a pyrazolate nitrogen atom to the Cb* ligand to afford a novel tet-
determination. The X-ray crystal structure of
4 established
a dimeric constitution with two
m: ,h
h1 1-phenyl tetrazolate ligands
radentate ligand that bonds to the cobalt ion through a h3
-
p-
connected to the cobalt ions through the 2- and 3-nitrogen atoms,
as well as one h4-Cb* and one carbonyl ligand per cobalt center.
Interestingly, the 1H NMR spectrum of 4 in toluene-d8 reveals the
presence of two isomers. In toluene-d8, the ratio of these two
isomers was invariant at about 70:30 between ꢁ40 and þ80 ꢀC. At
ꢁ60 and ꢁ80 ꢀC, the ratios changed slightly to 61:39 and 58:42,
respectively. The origin of these isomers is not fully clear. In the
solid state, 4 exists with anti-disposition of the carbonyl and Cb*
ligands within the dimer. It is possible that the isomers correspond
to complexes containing anti- and syn-dispositions of the carbonyl
and Cb* ligands within the dimer.
allyl interaction and one pyrazolyl nitrogen atom. Two carbonyl
ligands are also present. By contrast, 2 contains one h4-Cb*, one
h
1-(CF3)2pz, and two carbonyl ligands. The 1H NMR spectra of 1 and
2 are uniquely consistent with the solid-state structures. At 21 ꢀC in
benzene-d6, the 1H NMR spectrum of 1 consisted of a sharp singlet
at
sharp singlets at
addition, three singlets were observed at
d
5.35 for the pyrazolyl moiety ring hydrogen atom, and two
1.82 and 1.65 for the pyrazolyl methyl groups. In
2.17, 1.36, and 1.06 in
d
d
a 1:2:1 ratio, respectively, for the chemically unique methyl groups
of the h3-Cb*-derived fragment.
(1)
In several syntheses of 1, an additional product was isolated,
which appeared to have the formula Cb*Co(Me2pz)(Me2pzH)(CO)
1
(3) from H NMR analysis. To assess this possibility, Cb*Co(CO)2I
(3)
was treated with an equimolar quantity of Me2pzH in tetrahydro-
furan, followed by one equivalent Me2pzK, to afford 3 in 74% yield
as red crystals after workup (eq (2)). Complex 3 is monomeric in the
solid state with one h4-Cb*, one
h
1-Me2pz, one
h
1-Me2pzH, and one
The crystal structures of 1e4 were determined to establish the
geometry about the metal centers and to assess the bonding modes
of the ligands. Experimental crystallographic data are summarized
in Table 1, selected bond lengths and angles are presented in Tables
2e5, and perspective views are given in Figs. 1e4.
carbonyl ligands. The
h
1-Me2pz and 1-Me2pzH ligands are linked
h
by a hydrogen bond between the uncoordinated nitrogen atoms.
The 1H NMR spectrum of 3 at 21 ꢀC in benzene-d6 solution con-
sisted of a sharp singlet at
ring hydrogen atoms, two singlets at
groups of the
1-Me2pz and 1-Me2pzH ligands, the NeH reso-
nance at 1.96, and a sharp singlet at 0.82 for the methyl groups of
the Cb* ligands. Observation of a single ring hydrogen atom reso-
nance and only two methyl group resonances for the
1-Me2pz and
1-Me2pzH ligands implies that proton transfer between these two
ligands is rapid at 21 ꢀC.
d
5.86 for the
h h
1-Me2pz and 1-Me2pzH
d
2.28 and 2.24 for the methyl
A perspective view of 1 is shown in Fig. 1. The CoeC bond
h
h
distances associated with the h
3-C4Me4 fragment range from 2.002
d
d
(1) to 2.061(1) Å, and the CoeN bond length is 2.027(9) Å. The CeN
bond length formed by the nucleopholic attack of the pyrazolate
nitrogen atom on the Cb* ligand is 1.477(1) Å. Complexes 2e4 share
a common Cb*Co structural fragment (Figs. 2e4). The Cb* ligand in
each of these complexes is coordinated to the Co ion through
h
h

O.M. El-Kadri et al. / Journal of Organometallic Chemistry 696 (2011) 1975e1981
1977
Table 1
Crystal data and data collection parameters for 1e4.
Table 3
Selected bond lengths [Å] and angles [deg] for 2.
1
2
3
4
CoeN(1)
1.993(1)
CoeC(6)
CoeC(7)
CoeC(8)
CoeC(9)
CoeC(10)
CoeC(11)
CoeN(1)eN(2)
C(6)eCoeC(7)
C(6)eCoeN(1)
C(7)eCoeN(1)
1.813(2)
1.808(2)
2.098(2)
2.029(2)
2.002(1)
2.066(2)
115.38(9)
101.34(7)
95.71(6)
104.47(6)
Empirical
formula
Fw
Space group
a (Å)
C15H19Co-
N2O2
318.25
C15H13CoF6N2O2 C19H27Co-
N4O
C
32H34Co2N8O2
426.20
P1
386.38
P21/n
680.53
P21/c
8.5631(2)
C2/c
25.1187(7)
9.5441(3)
15.5266(4)
6.8415(2)
9.5852(3)
14.2602(5)
102.865(2)
8.1635(3)
17.4908(5) 11.6664(3)
13.5892(3) 16.0505(4)
b (Å)
c (Å)
a
b
g
(deg)
(deg)
(deg)
125.8960(10) 103.398(2)
92.654(2)
3015.35(15) 882.12(5)
94.0930(10) 93.0420(10)
V(Å3)
Z
1935.40(10) 1601.19(7)
8
2
4
2
Temp (K)
100(2)
0.71073
1.402
1.140
2.65
100(2)
0.71073
1.605
1.044
3.44
100(2)
0.71073
1.326
0.900
3.28
100(2)
0.71073
1.412
1.078
3.03
l
(Å)
CoeC and CoeN bond energies that would be obtained upon
formation of
5-pyrazolate or 5-tetrazolate ligands, and thus, only
1-azolate ligand coordination is observed in 2e4 and a nucleo-
r
m
calcd (g cmꢁ3
)
h
h
(mmꢁ1
)
h
R(F)(%)
Rw(F2)(%)
6.62
7.46
8.05
7.61
philic addition occurs instead in 1.
P
P
P
P
There are several previous reports of nucleophilic additions to
transition metal cyclobutadiene complexes to form cyclobutenyl
ligands. Maitlis described treatment of [MCp(C4Ph4)]þBrꢁ (M ¼ Ni, Fe)
with hydroxide or ethoxide ions to afford the products in which the
oxygen nucleophiles added to the C4Ph4 ligands [13]. These products
were not structurally characterized, but it was proposed that the
nucleophilic additions occurred at the exo-face of the C4Ph4 ligands
[13]. Addition of a range of nucleophiles to the cyclobutadiene ligand
in [Fe(C4H4)(CO)2NO]þ occurs exclusively at the exo-face, and several
products were structurally characterized [14]. Treatment of Cb*NiCl2
R(F) ¼ kFok e kFck/ kFok ; Rw(F) ¼ [ w(Fo2 e Fc2)2/ w(Fo2)2]1/2
.
h
4-bonding, with CoeC bond lengths from 1.981(1) to 2.098(1) Å.
The CeC bond lengths within the Cb* ligands vary from 1.424(10) to
1.554(2) Å. Complexes 1e4 also contain one or two carbonyl
ligands, with CoeC bond distances ranging from 1.775(1) to 1.813
(1) Å. The CoeN bond distance in 2 is 1.993(1) Å. In addition to the
Cb* and carbonyl ligands, 3 contains
ligands that are connected by a hydrogen bond between the
h h
1-Me2pz and 1-Me2pzH
with two equivalents of C5H5Na affords CpNi(h
3-C4Me4(C5H5)) [15],
and an X-ray crystal structure demonstrated that the C5H5 group is
uncoordinated nitrogen atoms. The CoeN bond lengths for the
h
1-Me2pz (CoeN(1)) and 1-Me2pzH (CoeN(3)) ligands are 2.010
h
(1) and 2.029(9) Å, respectively. In 4, a dimeric structure results
situated on the exo-face of the C4Me4 group. The complex 5,7,8-Me3-
h1 1-Phtetz ligands connected to the
11,7,8,10-[
nickel atoms with 2,6-C2B7H11 and 2-butyne [16]. The solid state
structure reveals an
3-C4Me4H ligand with the ring-bound hydrogen
atom residing on the exo-face. X-ray crystal structures were reported
for the exo- and endo- isomers of Pd2Cl2(
3-C4Ph4OEt)2, which
were obtained upon treatment of PdCl2 with diphenylacetylene in
ethanol [17]. CpNi(
3-C4Me4(C5H5)), 5,7,8-Me3-11,7,8,10-[ 3-C4Me4H]
NiC3B7H7, and Pd2Cl2(
3-C4Ph4OEt)2 are likely formed by nucleophilic
attack of C5Hꢁ5 , hydride, and ethoxide, respectively, upon intermediate
cyclobutadiene species. The complex Co(
4-C4(CF3)4(Et2PS))(CO)
(PPh3)containsan
3-cyclobutenylligandinwhichthereisaCePbond
h
3-C4Me4H]NiC3B7H7 was obtained upon treatment of
through adoption of two
m: ,h
cobalt ions through the 2- and 3-nitrogen atoms. The dimer 4
occupies a crystallographic 2-fold axis that relates the two halves of
the molecule. The CoeN bond lengths associated with the Phtetz
ligands are 1.984(1) and 1.996(1) Å.
h
h
Many cobalt(I) complexes containing the Cb*Co fragment have
been structurally characterized. A review gives a comprehensive
list of Cb*Co complexes that also contain halide, cyclopentadienyl,
hydrocarbon, and other anionic donor ligands [2c]. The metrical
parameters associated with the Cb*Co(CO)x (x ¼ 1 or 2) fragments
in 1e4 are similar to those found in related Cb*Co(CO)x complexes
(CoeC (Cb* carbon) ∼1.97 Å, CoeC (carbonyl carbon) ∼1.75 Å)
[2c,6,7]. Complexes containing Cb*Co fragments generally form
metallocene-like sandwich complexes cyclopentadienyl ligands.
h
h
h
h
h
between the uncoordinated cyclobutenyl core C atom and the P atom
oftheEt2PSfragment,aswellasaCoeSbond[18]. Suchaconfiguration
resembles the endo-disposition of the Me2pz fragment in 1. However,
h
5-pyrazolate
Co(h -
4-C4(CF3)4(Et2PS))(CO)(PPh3) was formed by treatment of Co(h2
There was no evidence for the formation of
complexes during the preparations of 1e4, even though the pyr-
Et2PS)(CO)2PPh3 with hexafluoro-2-butyne and did not entail
azolate ligand is similar electronically to cyclopentadienyl ligands
a nucleophilic attack upon a cyclobutadiene ligand. The formation of
and we have previously reported h h
5-pyrazolate and 5-imidazolate
Co(C5H5)(h a-pyrone) upon treatment of Co(h
4-tetraethyl- 4-C4Et4)
(CO)2I with C5Hꢁ5 and ethyl formate was proposed to proceed through
an intermediateresultingfrom nucleophilicattack ofa cyclobutadiene
complexes of ruthenium(II) and osmium(II) [12]. It is likely that the
CoeC bond energies of the carbonyl ligands are higher than the
Table 4
Table 2
Selected bond lengths [Å] and angles [deg] for 3.
Selected bond lengths [Å] and angles [deg] for 1.
CoeN(1)
CoeN(3)
CoeC(11)
CoeC(12)
CoeC(13)
CoeC(14)
CoeC(19)
CoeN(1)eN(2)
CoeN(3)eN(4)
N(1)eCoeN(3)
N(1)eCoeC(19)
N(3)eCoeC(19)
2.010(1)
2.029(1)
2.043(1)
1.985(1)
2.028(1)
2.094(1)
1.775(1)
118.61(6)
117.98(7)
93.29(3)
104.39(4)
99.86(4)
CoeN(1)
2.027(1)
1.773(1)
1.767(1)
2.042(1)
2.002(1)
2.061(1)
1.477(1)
106.85(7)
97.67(5)
110.13(4)
114.38(5)
CoeC(1)
CoeC(2)
CoeC(9)
CoeC(10)
CoeC(11)
N(2)eC(8)
CoeN(1)eC(1)
C(1)eCoeC(2)
C(1)eCoeN(1)
C(2)eCoeN(1)

1978
O.M. El-Kadri et al. / Journal of Organometallic Chemistry 696 (2011) 1975e1981
1 sublimed at 60 ꢀC/0.03 Torr over 5 h to afford unchanged 1 in 83%
recovered yield. There was a 4% nonvolatile residue at the comple-
tion of the sublimation. The 1H and 13C{1H} NMR spectrum of
sublimed 1 were identical to the material before sublimation,
demonstrating that no reaction occurred during the sublimation
process. Complexes 2 and 3 did not sublime below 200 ꢀC at
0.03 Torr, and instead decomposed to black, insoluble, nonvolatile
materials. Sublimation studies of 4 were not conducted, due to the
dimeric structure, the high nitrogen content, and attendant risk of
detonation. The thermal stability of 1 was further studied by
measuring its melting point and solid state decomposition temper-
ature. Complex 1 melts from 112 to 114 ꢀC and shows no color change
at this temperature. Upon further heating, 1 changes color from
orange to black at 136e138 ꢀC, indicating decomposition. The 4%
residue observed upon sublimation of 1 and the low decomposition
temperature suggest that 1 does not have enough thermal stability to
serve as an ALD precursor [10]. However, its low sublimation
temperature may allow use of 1 in CVD film growth procedures,
where precursor thermal stability requirements are not as strict.
Table 5
Selected bond lengths [Å] and angles [deg] for 4.
CoeN(1)
1.984(1)
Co0eN(4)
1.996(1)
1.993(1)
1.981(1)
2.097(1)
2.098(1)
1.783(1)
129.91(8)
98.58(4)
97.76(5)
100.47(5)
CoeC(1)
CoeC(2)
CoeC(3)
CoeC(4)
CoeC(16)
CoeN(1)eN(4)
N(1)eCoeN(4)0
N(1)eCoeC(16)
N(4)0eCoeC(16)
carbon atom on the ethyl formate carbonyl group [19]. The resulting
proposed intermediate contains an
4-cyclobutenyl ligand that is
h
bonded to cobalt through three of the cyclobutenyl carbon atoms and
through the resultant alkoxy-like oxygen atom. This proposed
h
4-cyclobutenyl ligand has a chelating structure similar to that of 1.
Treatment of Fe(
h
4-C4R4)(CO)3 (R ¼ H, Me) with tetrafluoroethylene,
hexafluofluoropropene, or hexafluoroacetone led to products in
which the unsaturated bonds inserted into an iron-carbon bond of the
h
4-C4R4 ligandtoaffordcomplexescontaining 4-cyclobutenylligands
h
3. Experimental
with chelating structures similar to that of 1 [20].
3.1. General considerations
In the present study, the pyrazolate moiety in 1 is bonded to the
endo-face of the C4Me4 fragment, suggesting that the Me2pz ion first
displaces the iodide ion in Cb*Co(CO)2I to form intermediate Cb*Co
(CO)2(Me2pz), which then undergoes intramolecular endo-nucleo-
philic addition to afford 1. More complex reaction mechanisms are
also possible that could entail nuclophilic attack on the exo-face of
All reactions were carried out under argon using either glovebox
or Schlenk line techniques. Toluene was distilled from sodium,
tetrahydrofuran was distilled from sodium benzophenone ketyl,
and hexane was distilled from P2O5. Cb*Co(CO)2I [6] and Me2pzK
[21] were prepared by literature procedures. Me2pzH, (CF3)2pzH,
and PhtetzH were purchased from Aldrich Chemical Company and
were used as received.
the Cb* ligand, followed by isomerization of the
p-allyl fragment to
form 1. While exo-attack cannot be ruled out, the proposed endo-
attack is simpler in that it does not require an isomerization step.
The structure of 2 represents an interesting comparison with that of
1H, 13C{1H}, and 19F NMR were obtained in benzene-d6 or
toluene-d8 using 500, 400, or 300 MHz spectrometers. Infrared
spectra were obtained using Nujol as the medium. Elemental anal-
yses were performed by Midwest Microlab, Indianapolis, Indiana,
USA. Melting points were obtained with a Haake-Buchler HBI digital
melting point apparatus and are uncorrected. Preparative sublima-
tions of 1e3 and solid state decomposition studies of 1 were per-
formed according to previously described procedures [11b].
1. In 2, the
h
1-(CF3)2pz ligand has not undergone nucleophilic
addition to the Cb* ligand, presumably due to the lower basicity of
the nitrogen atoms arising from the electron withdrawing tri-
fluoromethyl groups and the greater ability of the (CF3)2pz ligand to
stabilize a negative charge, compared to a p-allyl fragment.
To assess their initial viability as ALD precursors, sublimation
studies were carried out on 1e3. Inpreparative sublimations (∼0.5 g),
3.2. Preparation of (h
4-C4Me4(Me2pz))Co(CO)2 (1)
A 100-mL Schlenk flask, equipped with a magnetic stir bar and
a rubber septum, was charged with Cb*CoI(CO)2 (0.501 g,1.42 mmol)
and tetrahydrofuran (20 mL) and was cooled to ꢁ78 ꢀC. To this
solution was added Me2pzK (0.191 g, 1.44 mmol) that was dissolved
in tetrahydrofuran (20 mL). The resultant orange solution was
allowed to warm to room temperature and was stirred for 18 h. The
solvent was then removed under reduced pressure to yield a yellow
crystalline solid. This solid was extracted with hexane (40 mL) and
the resultant solution was filtered through a 2-cm pad of Celite on
a coarse glass frit. Removal of the solvent under reduced pressure
afforded 1 as a yellow crystalline solid (0.410 g, 90%): m.p.
114e116 ꢀC; IR (Nujol, cmꢁ1) 1976 (nCO, s), 1911 (nCO, s); 1H NMR
(benzene-d6, 21 ꢀC,
h
h
d
) 5.35 (s, 1H, pz ring CH), 2.17 (s, 3H, CH3 of
3-C4Me4),1.82 (s, 3H, pz CH3),1.65 (s, 3H, pz CH3),1.34 (s, 6H, 2CH3 of
3-C4Me4),1.06 (s, 3H, CH3 of 3-C4Me4); 13C{1H} (benzene-d6, 21 ꢀC,
h
ppm)207.24 (s, CO),149.82 (s, pzCeCH3),137.72 (s, pzCeCH3),106.98
(s, pz ring CH),102.99 (s, carbon atom on the C4 ring that is connected
to the pz ligand), 103.00 (s, CeN of
3-C4Me4), 75.33 (s, CeCH3 of 3-C4Me4), 19.89 (s, CH3), 14.22 (s,
CH3), 14.15 (s, CH3), 11.92 (s, CH3), 10.80 (s, 2CH3 of
3-C4Me4).
h
3-C4Me4), 89.67 (s, 2CeCH3 of
h
h
h
Anal. Calcd for C15H19CoN2O2: C, 56.61; H, 6.02; N, 8.80. Found:
C, 56.76; H, 6.08; N, 8.92.
Fig. 1. Perspective view of 1 with thermal ellipsoids at the 50% probability level.

O.M. El-Kadri et al. / Journal of Organometallic Chemistry 696 (2011) 1975e1981
1979
Fig. 2. Perspective view of 2 with thermal ellipsoids at the 50% probability level.
Fig. 3. Perspective view of 3 with thermal ellipsoids at the 50% probability level.

1980
O.M. El-Kadri et al. / Journal of Organometallic Chemistry 696 (2011) 1975e1981
Fig. 4. Perspective view of 4 with thermal ellipsoids at the 50% probability level.
3.3. Preparation of Cb*Co((CF3)2pz)(CO)2 (2)
Anal. Calcd for C19H27CoN4O: C, 59.06; H, 7.04; N, 14.50. Found:
C, 58.96; H, 6.92; N, 14.47.
In a fashion similar to the preparation of 1, treatment of Cb*Co
(CO)2I (0.508 g, 1.45 mmol) with (CF3)2pzK (0.360 g, 1.49 mmol)
afforded 2 as a yellow crystalline solid (0.431 g, 71%): m.p.
73e75 ꢀC; IR (Nujol, cmꢁ1) 2053(nCO, s), 2016 (nCO, s); 1H NMR
3.5. Preparation of [Cb*Co(Phtetz)(CO)]2 (4)
In a fashion similar to the preparation of 1, treatment of Cb*Co
(CO)2I (0.351 g, 1.00 mmol) with potassium phenyl tetrazolate
(PhtetzK) (0.186 g, 1.00 mmol) afforded 3 as red-colored crystals
(0.151 g, 44%): m.p. 270e272 ꢀC (dec); IR (Nujol, cmꢁ1) 1977 (nCO, s);
(benzene-d6, 21 ꢀC, ) 6.87 (s, 1H, pz CH), 0.78 (s, 12H, Cb* CH3); 13C
d
{1H} (benzene-d6, 22 ꢀC, ppm) 202.35 (s, CO),145.20 (q, JCCF ¼ 36 Hz,
CeCF3), 142.99 (q, JCCF ¼ 35 Hz, CeCF3), 123.12 (q, JCF ¼ 266 Hz, CF3),
122.52 (q, JCF ¼ 266 Hz, CF3), 106.08 (s, pz CH), 95.05 (s, Cb* CeCH3),
1H NMR (benzene-d6, 21 ꢀC,
d) major isomer (78%): 8.45 (d,
8.08 (s, Cb* CH3); 19F NMR (benzene-d6, 21 ꢀC,
120.91 (s, CF3 ).
d) 123.58 (s, CF3),
J ¼ 7.0 Hz, 4H, o-C6H2H02H00), 7.27 (t, J ¼ 7.5 Hz, m-C6H2H02H00), 7.15
(d, J ¼ 8.0 Hz, p-C6H2H02H00), 1.01 (s, 12H, Cb* CH3), minor isomer
(22%): 8.44 (d, J ¼ 7.0 Hz, 4H, o-C6H2H02H00), 7.18 (t, J ¼ 7.5 Hz,
m-C6H2H02H00), 7.16 (d, J ¼ 8.0 Hz, p-C6H2H02H00), 1.09 (s, 12H, Cb*
CH3); 13C{1H} (benzene-d6, 21 ꢀC, ppm) major isomer only: 204.36
(s, CO), 166.95 (s, CeC6H5), 130.38 (s, ipso-C of Ph ring), 128.93 (s,
ortho-CH of Ph ring), 128.18 (s, meta-CH of Ph ring), 126.57 (s, para-
CH of Ph ring), 88.49 (s, Cb* CeCH3), 8.94 (s, Cb* CCH3).
0
Anal. Calcd for C15H13CoF6N2O2: C, 42.27; H, 3.07; N, 6.57. Found:
C, 41.98; H, 3.17; N, 6.34.
3.4. Preparation of Cb*Co(Me2pz)(Me2pzH)(CO) (3)
Anal. Calcd for C32H34Co2N8O2: C, 56.48; H, 5.04; N, 16.47.
Found: C, 56.74; H, 5.15; N, 16.01.
A 100-mL Schlenk flask, equipped with a magnetic stir bar and
rubber septum, was charged with Cb*Co(CO)2I (0.310 g,
a
0.89 mmol), 3,5-dimethylpyrazole (0.845 g, 0.89 mmol), and
tetrahydrofuran (20 mL). The resultant red solution was refluxed
for 2 h and was then allowed to cool to room temperature. To this
solution was added Me2pzK (0.118 g, 0.89 mmol) that was dissolved
in THF (20 mL). The resultant red solution was stirred at ambient
temperature for 18 h. The solvent was then removed under reduced
pressure to yield red crystalline solid. This solid was extracted with
hexane (40 mL) and the resultant solution was filtered through
a 2-cm pad of Celite on a coarse glass frit. Removal of the solvent
under reduced pressure afforded 3 as a afforded yellow crystalline
solid (0.39 g, 84%): m.p. 148e150 ꢀC; IR (Nujol, cmꢁ1) 3201 (w, nNH),
3.6. X-ray crystal structure determinations
Diffraction data were measured on a Bruker X8 APEX-II kappa
geometry diffractometer with Mo radiation and a graphite mono-
chromator. Frames were collected at 100 K for 5e10 s/frame as
a series of sweeps with the detector at 40 mm and 0.3ꢀ between
each frame. APEX-II [22] and SHELX-97 [23] software were used in
the collection and refinement of the models.
Crystals of 1 were obtained as yellow rods, and a sample
measuring approximately 0.2 ꢂ 0.2 ꢂ 0.11 mm3 was used for the
data collection. 27187 reflections were integrated, of which 4858
were independent. Hydrogen positions were placed in observed
positions and refined. The asymmetric unit contains one neutral
molecule without solvent. Complex 2 crystallized as yellow rods
and a crystal of dimensions 0.14 ꢂ 0.12 ꢂ 0.10 mm3 was mounted
and measured. 19827 reflections were integrated, yielding 5425
1952 (nCO, s); 1H NMR (benzene-d6, 21 ꢀC,
d) 5.86 (s, 2H, pz and pzH
CH), 2.28 (s, 6H, pz and pzH CH3), 2.24 (s, 6H, pz and pzH CH3), 1.96
(s, 1H, NeH), 0.82 (s, 12H, Cb* CH3); 13C{1H} (benzene-d6, 22 ꢀC,
ppm) 208.60 (s, CO), 151.16 (s, pz and pzH CCH3), 144.84 (s, pz and
pzH CCH3), 105.53 (s, pz and pzH CH), 85.08 (s, Cb* CCH3), 14.68 (s,
pz and pzH CH3), 12.39 (s, pz and pzH CH3), 8.73 (s, Cb* CH3).

O.M. El-Kadri et al. / Journal of Organometallic Chemistry 696 (2011) 1975e1981
1981
ꢀ
[5] M.R. Cook, P. Härter, P.L. Pauson, J. Sraga, J. Chem. Soc. Dalton Trans. (1987)
2757e2760.
independent data. Hydrogen density was placed according to maps
and refined. The asymmetric unit contains one neutral complex
without solvent. Complex 3 formed red plates, and a cut fragment
measuring 0.39 ꢂ 0.14 ꢂ 0.12 mm3 was chosen for the diffraction
experiment. 49433 spots were measured and averaged into 8316
independent reflections. Hydrogen atoms were placed in observed
or calculated positions. The asymmetric unit contains one neutral
molecule. Complex 4 crystallized as red rhomboids. The data crystal
dimensions were 0.22 ꢂ 0.20 ꢂ 0.12 mm3. 30942 data points were
counted yielding 5321 independent observations. Hydrogen atoms
were placed in observed or calculated positions. The complex exists
as a dimer in the crystal and the asymmetric unit contains 1/2 of
this dimer.
[6] (a) M.V. Butovskii, V. Englert, A.A. Fil’chikov, G.E. Herberich, U. Koelle,
A.R. Kudinov, Eur. J. Inorg. Chem. (2002) 2656e2663;
(b) E.V. Mutseneck, D.A. Loginov, D.S. Pereklin, Z.A. Starikova, D.G. Golovanov,
P.V. Petroviskii, P. Zanello, C. Maddalena, F. Laschi, A.R. Kudinov, Organome-
tallics 23 (2004) 5944e5957.
[7] E.V. Mutseneck, D.S. Perekalin, J. Holub, Z.A. Starikova, P.V. Petrovskii,
P. Zanello, M. Corsini, B. Stibr, A.R. Kudinov, Organometallics 25 (2006)
2419e2426.
[8] R.B. King, Coord. Chem. Rev. 20 (1976) 155e169.
[9] (a) B.S. Lim, A. Rahtu, R.G. Gordon, Nat. Mater. 2 (2003) 749e754;
(b) N. Koshizaki, A. Narazaki, T. Sasaki, Scr. Mater. 44 (2001) 1925e1928;
(c) S. Haukka, E. Lakomaa, T. Suntola, Stud. Surf. Sci. Catal. 120 (1999)
715e750.
[10] (a) M. Leskelä, M. Ritala, Angew. Chem. Int. Ed. 42 (2003) 5548e5554;
(b) L. Niinistö, J. Päiväsaari, J. Niinistö, M. Putkonen, M. Nieminen, Phys. Status
Solidi A 201 (2004) 1443e1452;
(c) M. Putkonen, L. Niinistö, Top. Organomet. Chem. 9 (2005) 125e145.
[11] (a) C.L. Dezelah IV, M.K. Wiedmann, K. Mizohata, R.J. Baird, L. Niinistö,
C.H. Winter, J. Am. Chem. Soc. 129 (2007) 12370e12371;
(b) M.J. Saly, M.J. Heeg, C.H. Winter, Inorg. Chem. 48 (2009) 5303e5312;
(c) M.J. Saly, F. Munnik, R.J. Baird, C.H. Winter, Chem. Mater. 21 (2009)
3742e3744.
Acknowledgements
We are grateful to the U.S. National Science Foundation (Grant
Nos. CHE-0314615, CHE-0910475) for support of this research. The
American University of Sharjah is acknowledged for a Faculty
Research Grant (FRG09-02-28187) that paid for the travel of
O.M.E.-K.
[12] (a) J.R. Perera, M.J. Heeg, H.B. Schlegel, C.H. Winter, J. Am. Chem. Soc.
121 (1999) 4536e4537;
(b) J.R. Perera, M.J. Heeg, C.H. Winter, Organometallics 19 (2000) 5263e5265;
(c) S.M. Arachchige, M.J. Heeg, C.H. Winter, J. Organomet. Chem. 690 (2005)
4356e4365.
Appendix A. Supplementary material
[13] P.M. Maitlis, A. Efraty, M.L. Games, J. Am. Chem. Soc. 87 (1965) 719e724.
[14] (a) L.A.P. Kane-Maguire, E.D. Honig, D.A. Sweigart, Chem. Rev. 84 (1984)
525e543;
CCDC 789466e789469 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Center via www.
ccdc.cam.ac.uk/data_request/cif.
(b) J.C. Calabrese, S.D. Ittel, H.S. Choi, S.G. Davis, D.A. Sweigart, Organome-
tallics 2 (1983) 226e229;
(c) H.S. Choi, D.A. Sweigart, Organometallics 1 (1982) 60e64;
(d) J.A. Potenza, R. Johnson, D. Williams, B.H. Toby, R.A. Lalancette, A. Efraty,
Acta Crystallogr. Sect. B. Struct. Sci. 37 (1981) 442e444.
[15] W. Oberhansli, L.F. Dahl, Inorg. Chem. 2 (1965) 150e157.
[16] J.J. Briguglio, L.G. Sneddon, Organometallics 5 (1986) 327e336.
[17] L.F. Dahl, W.E. Oberhansli, Inorg. Chem. 4 (1965) 629e637.
[18] E. Lindner, T. Schlenker, R. Fawzi, M. Steimann, Chem. Ber 126 (1993)
2433e2435.
[19] P. O’Donohue, S.A. Brusey, C.M. Seward, Y. Ortin, B.C. Molloy, H. Müller-Bunz,
A.R. Manning, M.J. McGlinchey, J. Organomet. Chem. 694 (2009) 2536e2547.
[20] A. Bond, M. Green, J. Chem. Soc. Dalton Trans. (1972) 763e768.
[21] C. Yélamos, M.J. Heeg, C.H. Winter, Inorg. Chem. 37 (1998) 3892e3894.
[22] APEX-II collection and processing programs are distributed by the manufac-
turer, Bruker AXS Inc., Madison, Wisconsin, USA.
References
[1] R. Gleiter, H. Schimanke, S.J. Silverio, M. Buchner, G. Huttner, Organometallics
15 (1996) 5635e5640.
[2] (a) P.M. Maitlis, Adv. Organomet. Chem. 4 (1966) 95e143;
(b) D. Seyferth, Organometallics 22 (2003) 2e20;
(c) A.R. Kudinov, E.V. Mutseneck, D.A. Loginov, Coord. Chem. Rev. 248 (2004)
571e585.
[3] A. Efraty, P.M. Maitlis, J. Am. Chem. Soc. 89 (1967) 3744e3750.
[4] (a) A. Nakamura, N. Hagihara, Bull. Chem. Soc. Jpn 34 (1961) 452e453;
(b) M.D. Rausch, R.A. Genetti, J. Am. Chem. Soc. 89 (1967) 5502e5503.
[23] G. Sheldrick, SHELX-97. University of Göttingen, Germany, 1997.