New stable cyclopentadienyl iron(II) complexes containing 3,5-dimethylpyrazolyl phosphine: X-ray structure of [FeCp(CO)2PPh2(Me2Pz)]BF4

Article abstract of DOI:10.1016/S0022-328X(03)00261-4

Very stable complexes of general formula [FeCp(CO)_xPh₂P(Me₂Pz)]BF₄, where x=1(1)-2(2) were prepared by room temperature reaction of the 3,5-dimethylpyrazolylphosphine ligand with [Fe₂ (CO)₂(C₅H₅)₂]. When [FeCp(CO)₂Ph₂P(Me₂Pz)]BF₄ (1) was treated with (CH₃)₃ NO·2H₂O, one coordinated CO was lost and complex 2 was formed. ¹H-, ¹³C- and ³¹P-NMR spectra supported a structure of 2 with pyrazolyl ligand chelated to iron forming a four-membered metallocycle.

Full text of DOI:10.1016/S0022-328X(03)00261-4

Journal of Organometallic Chemistry 676 (2003) 38Á42
/
www.elsevier.com/locate/jorganchem
New stable cyclopentadienyl iron(II) complexes containing
3,5-dimethylpyrazolyl phosphine
X-ray structure of [FeCp(CO)2PPh2(Me2Pz)]BF4
Rosa-Mar´ıa Tribo´ a, Josep Ros a, Josefina Pons a, Ramo´n Ya´nez *,
˜
b
Angel Alvarez-Larena , Joan-Francesc Piniella
b
´
a Departament de Qu´ımica, Universitat Auto`noma de Barcelona, 08193 Cerdanyola del Valle`s, Barcelona, Spain
b Departament de Geolog´ıa, Unitat de Cristal lograf´ıa, Universitat Auto´noma de Barcelona, 08193 Cerdanyola del Valle`s, Barcelona, Spain
Received 25 October 2002; received in revised form 12 February 2003; accepted 12 February 2003
Abstract
Very stable complexes of general formula [FeCp(CO)xPh2P(Me2Pz)]BF4, where xꢀ
/
1(1)Á2(2) were prepared by room
/
temperature reaction of the 3,5-dimethylpyrazolylphosphine ligand with [Fe2(CO)2(C5H5)2]. When [FeCp(CO)2Ph2P(Me2Pz)]BF4
1
(1) was treated with (CH3)3NO×
/
2H2O, one coordinated CO was lost and complex 2 was formed. H-, 13C- and 31P-NMR spectra
supported a structure of 2 with pyrazolyl ligand chelated to iron forming a four-membered metallocycle.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Iron complexes; Pyrazole complexes; Crystal structures
1. Introduction
pyrazolylphosphine ligand with [RuCl2(p-cymene)]2 has
shown that the coordination of the ligand was possible
but the PꢀN(pyrazole) bond remained highly reactive
towards ROH molecules, giving a rapid cleavage of Pꢀ
N bond in the same way as free phosphine ligands [3]. In
an attempt to clarify this kind of reaction we have now
prepared a cyclopentadienyl dicarbonyl complex of iron
with the same (PPh2(Me2Pz)) phosphine. The fact that
CO ligands are more p-electron withdrawing than
chlorides could mean that the lone-pair on the nitrogen
The chemistry of metal complexes containing hemi-
labile ligands has received considerable attention in
recent years [1]. Hemilabile ligands are those polyden-
tate chelates which contain at least two types of bonding
groups with different properties in substitution reac-
tions. One of groups could be strongly bonded to one
metal atom while the other could be displaced easily by
others ligands. Interest in such ligands stems from their
potential use in catalysis and organometallic-based
synthetic chemistry. Recently [2], we have been inter-
ested in the synthesis, structural characterization, and
reactivity of 3,5-dimethylpyrazol N-substituted organo-
metallic complexes which show hemilabile ligand beha-
viour. Our observation of the reaction of diphenyl-
/
/
azine less basic and the Pꢀ
/
N bond more resistant to
hydrolysis.
2. Results and discussion
The cationic P-coordinated diphenylpyrazolylpho-
sphino PPh2(Me2Pz) complex [FeCp(CO)2PPh2(Me2-
Pz)]BF4 was prepared in high yield by oxidation of
starting cyclopentadienyl complex [Fe2(CO)2(C5H5)2]
* Corresponding author.
E-mail address: ramon.yanez@uab.es (R. Ya´nez).
˜
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00261-4

R.-M. Tribo´ et al. / Journal of Organometallic Chemistry 676 (2003) 38Á
/42
39
Scheme 1.
([Fp2]) with ferricinium cation in the presence of one
equivalent of PPh2(Me2Pz) (Scheme 1) according to the
reaction
n(Cꢁ
/
C)ꢁ
/
n(Cꢁ
/
N) absorption of pyrazole. This shifting
to high energy of the n(Cꢁ
/
C)ꢁn(CꢁN) band is attri-
/
/
butable of a strained pyrazol [6]. The methyl resonances
of PPh2(Me2Pz) are quite sensitive to complexation. For
the ligand, the higher field resonance is assigned to 5-
methyl group, on the basis of relatively greater para-
magnetic shielding by the phenyl rings. The 5-methyl
group on complex 1 is ‘locked’ in place, in close
proximity to two phenyl rings (Fig. 1) and experiences
a strong shielding effect (1.47 ppm). Moreover the shift
of the 5-methyl group of the pyrazole ring 1H resonance
to low field (2.3 ppm) is attributable to the less
paramagnetic shielding effect of phenyl groups attached
to the phosphorus atom on that methyl, as a result of
coordination of both phosphorus and N atoms forming
12[Fp2]ꢁ[FeCp2]ꢁ ꢁPPh2(Me2Pz)
0 [(Fp)(PPh2(Me2Pz)]ꢁ (1)ꢁFeCp2
In the infrared spectrum, complex 1 exhibited two
bands: 2064, 2021 cmꢂ1 assigned to the n(CO) of the
fragment [CpFe(CO)2]ꢁ and one band at 1568 cmꢂ1
corresponding to the n(Cꢁ
/
C)ꢁ
/
n(Cꢁ
/
N) absorption of
pyrazole. Moreover, the 1H- and 13C-NMR spectra of 1
in CD3Cl solution show the signals corresponding to the
presence of h5-cyclopentadienyl ligand; the two methyl
groups attached to the pyrazole ring appear at 1.47 and
2.30 ppm in the 1H-NMR spectrum. The {1H}31P-NMR
spectrum of 1 shows a signal a 121.2 ppm which is
assigned to the phosphorus atom coordinated to an iron
atom.
a PNNFe metallocyclic structure [5,7Á9]. Efforts to
/
grow crystals from solutions of complex 2 were un-
successful. In order to preclude other possible structures
like, for instance, that corresponding to a dicationic
dimer [CpFe(CO)2PPh2(Me2Pz)]2[BF4]2, electrospray
mass spectra of complexes 1 and 2 in NCMe were
recorded, but not reliable data were obtained.
In conclusion we have shown that the coordination of
PPh2(Me2Pz) ligand can coordinate the ‘CpFe’ centre in
P-monodentate and P,N-bidentate modes. The coordi-
nation of PPh2(Me2Pz) to Fe(II) in complex
[CpFe(CO)2(PPh2(Me2Pz))]ꢁ (1) leads to a significant
It is noticeable that complex 1 did not react at room
temperature or reflux with ROH (RꢀH, CH3,
/
CH3CH2). This behaviour contrasts with that of com-
plex [RuCl2(p-cymene) PPh2(Me2Pz)]ꢁ, which reacts
with ROH molecules resulting in a cleavage of the Pꢀ
/
N
bond [3]. This trend could be explained by the less basic
character of the lone pair over N2 in pyrazol due to the
coordination of phosphorus atom to a more electro-
philic iron metal [4,5].
stabilisation of the Pꢀ
/N bond towards polar ROH
Treatment of 1 dissolved in CH2Cl2 with Me3NO×
/
2H2O in molar ratio 1:1 gave [FeCp(CO)PPh2Pz]BF4
complex (2) (Scheme 2). The {1H}31P-NMR spectrum of
2 in CDCl3 solution showed a singlet at d 115.6 ppm
slightly shifted to a higher field than phosphorus in
complex 1. The corresponding 1H-NMR spectrum in
CDCl3 also showed a signal a 4.4 ppm which was
assigned to the Cp ligand. The PPh2(Me2Pz) ligand
showed signals at 2.28(CH3), 2.36(CH3) and 5.83(CH)
ppm. In the infrared spectrum, complex 2 exhibited a
band at 1936 assigned to the n(CO) of the fragment
[CpFe(CO)]ꢁ and one band at 1581 corresponding to
Fig. 1. An ORTEP view of the structure of cation [FeCp(CO)2(Ph2P-
(Me2pz))]ꢁ. The thermal ellipsoids enclose 50% probability.
Scheme 2.

40
R.-M. Tribo´ et al. / Journal of Organometallic Chemistry 676 (2003) 38Á42
/
Table 1
Crystal data and structure refinement for 1
meters of the CpFe(CO)2 fragment are very similar to
those found in [FpEPh3]ꢁ Eꢀ
P, As, Sb, Bi) complexes
[10Á12]. The most significant feature of this structure is
the Feꢀ
than in related complexes. This effect could be attrib-
uted to the strong p-acceptor nature of the pyrazole
group [13,14].
/
/
Empirical formula
Formula weight
Temperature (K)
C24H22BF4FeN2O2P
544.074
293(2)
˚
P bond distance of 2.11(1) A, which is shorter
/
˚
Wavelength (A)
Crystal system
0.71069
Triclinic
¯
P1
Space group
˚
/
a (A)
˚
8.9540(20)
10.1840(50)
14.1220(30)
91.42(3)
103.21(2)
91.32(3)
1252.75(73)
2
b (A)
˚
c (A)
3. Experimental
a (8)
b (8)
g (8)
V (A )
Z
rcalc (g cmꢂ3
3.1. General data
3
˚
All reactions were performed under nitrogen by using
standard Schlenk tube techniques. All the solvents were
distilled and dried before use. Infrared spectra were
)
1.4424
0.719
556.0
Absorption coefficient (mmꢂ1
F(000)
)
recorded on a PerkinÁElmer FT 1710 spectrophot-
ometer on KBr disks or with CH2Cl2 solutions. Mass
spectra were obtained on a Hewlett Packard H.P. 2985
/
Crystal size (mm)
0.2ꢃ
1.78Á
4390
2437 [I ꢀ
Least-squares
4390/16/316
0.883
/
0.2ꢃ
24.98
/
0.15
u Range for data collection (8)
Reflections collected
Independent reflections
Refinement method
/
/
2s(I)]
Table 2
Data/parameters
Goodness-of-fit on F2
˚
Selected bond lengths (A) and angles (8) for 1
Final R1 indices [I ꢀ
R indices (all data)
Largest difference peak and hole
/
2s(I)]
R1ꢀ
R1ꢀ
0.275 and ꢂ
/
0.0498, wR2ꢀ
0.1120, wR2ꢀ
0.246
/
0.11
Bond lengths
/
/0.11
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
Feꢀ
C(6)ꢀ
FeꢀC(8)
C(8)ꢀO(8)
Feꢀ
PꢀN(11)
N(11)ꢀ
N(11)ꢀ
N(12)ꢀ
C(13)ꢀ
C(14)ꢀ
C(13)ꢀ
C(15)ꢀ
/
C(1)
C(2)
C(3)
C(4)
C(5)
Cp
2.093(5)
2.083(5)
2.090(5)
2.085(4)
2.086(5)
2.088(5)
1.776(5)
1.131(6)
1.775(5)
1.138(6)
2.211(1)
1.711(4)
1.396(5)
1.380(6)
1.314(6)
1.391(7)
1.343(8)
1.514(8)
1.499(8)
/
/
/
/
molecules. This behaviour differs from that observed in
a previously reported p-cymene-Ru(II) complex and
should be originated by the strong p-acceptor character
of CO ligands coordinated to the metal. The displace-
ment of one CO of complex 1 produces a new
compound [CpFe(CO)(PPh2(Me2Pz))]ꢁ (2) whose ana-
lytical and spectroscopic data are congruent with the
formation of a four membered PNNFe ring. This study
proves that, in spite of results of previously reported
works, the very available PPh2(Me2Pz) can be used, in
some cases, as ancillary ligand to give stable organome-
tallic compounds.
/
/
/
C(6)
/O(7)
/
/
/
P
/
/
N(12)
C(15)
C(13)
/
/
/
C(14)
C(15)
C(16)
C(17)
/
/
/
Bond angles
2.1. X-ray structure determination of
[FeCp(CO)2PPh2(Me2Pz)]BF4 (1)
C(8)ꢀ
C(6)ꢀ
C(6)ꢀ
FeꢀC(6)ꢀ
FeꢀC(8)ꢀ
Feꢀ
Feꢀ
Feꢀ
N(11)ꢀ
C(21)ꢀPꢀ
C(31)ꢀPꢀ
PꢀN(11)ꢀ
N(11)ꢀN(12)ꢀ
N(12)ꢀC(13)ꢀC(14)
C(13)ꢀC(14)ꢀ
C(14)ꢀC(15)ꢀ
C(15)ꢀN(11)ꢀ
/
Feꢀ
Feꢀ
Feꢀ
/
P
91.61(15)
93.02(15)
95.07(22)
/
/
P
/
/
C(8)
O(7)
O(8)
Suitable single crystals of the [FeCp(CO)2PPh2-
(Me2Pz)]BF4 complex were obtained by slow evapora-
/
/
176.23(42)
176.96(45)
115.12(14)
115.23(13)
111.02(12)
104.49(18)
106.25(18)
103.57(17)
114.61(26)
105.38(35)
111.62(42)
106.55(48)
107.55(42)
108.87(34)
/
/
/
Pꢀ
Pꢀ
Pꢀ
/
C(21)
C(31)
N(11)
tion of a dichloromethaneÁmethanol solution at room
/
/
/
temperature. The structure is composed of complex
cations and [BF4]ꢂ anions held by Coulomb forces.
Final atomic parameters are presented in Table 1.
Significant bond distances and angles are shown in
Table 2.
The structure of the cation [FpFePPh2(Me2Pz)]ꢁ with
the adopted numbering scheme is shown in Fig. 1 and
consists of a [CpFe(CO)2]ꢁ fragment bonded to a
/
/
/
PꢀC(21)
/
/
/
C(31)
/
/
N(11)
/
/N(12)
/
/
C(13)
/
/
/
/
C(15)
/
/
N(11)
PPh2(Me2Pz) ligand through a Feꢀ
/
P bond leading to a
/
/N(12)
classical ‘piano-stool’ configuration. Structural para-

R.-M. Tribo´ et al. / Journal of Organometallic Chemistry 676 (2003) 38Á
/42
41
GC/MS. NMR spectra were recorded on a Bruker AC-
250 (1H, 250 MHz; 13C, 62 MHz) spectrometer in
CDCl3 solutions. Elemental analyses were obtained by
the staff of the Chemical Analysis Service of the
Universitat Autonoma de Barcelona. [Fe2(CO)2Cp2]
was purchased commercially. PPh2(Me2Pz) was pre-
pared by using previously published procedures [15,2].
Crystal structure determination was performed by the
X-ray Diffraction Service of the University Autonoma
de Barcelona.
Anal. Calc. for C24H22BF4FeN2O2P: C, 52.9; H, 4.08;
H, 4.08; N, 5.15. Found: C, 52.18; H, 4.07; N, 4.98%. IR
n(CO) (CDCl3): 2064(s), 2021(s) (cmꢂ1); n(Cꢁ
/
C)ꢁ
N) (KBr): 1568 cmꢂ1. H-NMR (CDCl3): d 1.47
(s, CH3), 2.30 (s, CH3), 5.24 (s, 5H, C5H5), 6.13 (s, CH),
7.4Á
7.6 (m, Ph) ppm. 13C-NMR (CDCl3), except phenyl
resonances: d 13.8Á14.0 (CCH3), 89.1 (C5H5), 113.1
(CH middle pyrazole), 208Á
O) ppm. 31P-
/
1
n(Cꢁ
/
/
/
/
208.6 (Cꢂ
/
NMR (CDCl3): d 121.2 (s, PPh2Pz) ppm.
3.2.3. Synthesis of complex
[FeCp(CO)PPh2(Me2Pz)]BF4 (2)
3.2. X-ray crystal structure determination of 1
The solid compound (CH3)3NO×/2H2O (0.04 g, 0.36
mmol) was added to a solution of 1 (0.1 g, 0.37 mmol) in
dichloromethane (15 ml). The reaction was monitored
by IR spectroscopy (nCO region), and after nearly 2 h of
stirring at room temperature, the solution was filtered
off and evaporated to dryness. The residual solid was
3.2.1. Data collection and processing
Data collected on an EnrafÁ
ometer using graphite-monochromated MoÁ
tion (lꢀ0.71069 A) and an v Á2u scan, v scan widthꢀ
0.80ꢁ0.35tan u. v Scan speed 1.3Á5.58. Reflection
ranges for the data collection: 1BuB 25, ꢂ10BhB
10, ꢂ12BkB 12, 0Bl B16. Lp and empirical absorp-
tion corrections were applied, Tmin 0.817, Tmax
1.000. Four thousand six hundred and ninety-nine
reflections were measured in the range 1.78Bu B
24.988. Four thousand four hundred and twenty with
Iꢀ 2(s(I)). The structure was solved by direct methods
SHELXS-86) [16] and refined by full-matrix least-squares
/
Nonius CAD4 diffract-
/
Ka radia-
/
/
/
/
/
extracted with hexane (3ꢃ10 ml), and the resulting
/
/
/
/
/
/
solution was evaporated to dryness. The residual
product was loaded on a silica gel column. After elution
/
/
/
/
/
ꢀ
/
ꢀ
/
with CH2Cl2 a red complex that eluted with CH2Cl2Á
/
methanol (10/1) was collected and dried in vacuo to give
a red powder of 2. 35% yield.
Anal. Calc. for C23H22BF4FeN2O2P: C, 53.47; H,
4.30; N, 5.43. Found: C, 53.90; H, 4.50; N, 5.51%. IR
/
/
/
(
n(CO) (CH2Cl2): 1936(s) (cmꢂ1); n(Cꢁ
/
C)ꢁ
1H-NMR (CDCl3): d 2.28 (s,
CH3), 2.36 (s, CH3), 4.41 (s, 5H, C5H5), 5.86 (s, CH),
6.7Á
7.8 (m, Ph) ppm. 13C-NMR (CDCl3) except phenyl
resonances: d 11.8Á15.8 (CCH3), 84.4 (C5H5), 107.7
O) ppm. 31P-NMR
/
n(Cꢁ
/
N)
procedures on F2 for all reflections (SHELXL-97) [17]. All
non-hydrogen atoms of 1 were refined anisotropically,
hydrogen atoms bonded to carbon atoms were placed in
calculated positions with isotropic temperature factors
1.5 (methyl hydrogens) or 1.2 times (the rest). The Ueq
values of corresponding carbons, and hydrogen atoms
bonded to oxygen or nitrogen atoms were localized in a
difference electron density map and refined with iso-
tropic temperature factors 1.5 times the Ueq values of
corresponding oxygen or nitrogen atoms. The weighting
(KBr): 1581 cmꢂ1
.
/
/
(CH middle pyrazole), 222.0 (Cꢂ
/
(CDCl3): d 121.2 (s, PPh2Pz) ppm.
Acknowledgements
scheme
whereꢀ
values were 0.0498 and 0.11 for reflections with I ꢀ
was
wꢀ1=[s2(Fo2)ꢁ(0:0580P)2 ꢁ0:000P]
/
[max(Fo2; 0)ꢁ2Fc2]=3: Final R(F) and Rw(F2)
We gratefully acknowledge support from the Minis-
terio de Educacio´n y Cultura of Spain, project PB96-
1146 and BQU2000-0238.
/
2s(I).
3.2.2. Synthesis of complex
[FeCp(CO)2PPh2(Me2Pz)]BF4 (1)
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resulting solution was stirred for 5 h at room tempera-
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ml. Addition of hexane (5 ml) afforded precipitation of a
brown solid, which was then washed with three portions
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