Synthesis of the New Polydentate Phosphine Ligand 1-[(Diphenylphosphino)methyl]-4-(2-pyridyl)piperazine and Structural Characterization of Its Binuclear Silver(I) and Mononuclear Iron(0) Complexes

Full text of DOI:10.1021/ic9800482

6090
Inorg. Chem. 1998, 37, 6090-6092
Notes
Scheme 1
Synthesis of the New Polydentate Phosphine
Ligand 1-[(Diphenylphosphino)methyl]-4-
(2-pyridyl)piperazine and Structural
Characterization of Its Binuclear Silver(I) and
Mononuclear Iron(0) Complexes
Shan-Ming Kuang,† Zheng-Zhi Zhang,*,‡
Qi-Guang Wang,† and Thomas C. W. Mak*,†
Department of Chemistry, The Chinese University of Hong
Kong, Shatin, New Territories, Hong Kong, and
Elemento-Organic Chemistry Laboratory,
containing a methylene spacer in which the proximal nitrogen
atom is incorporated into the six-membered ring of piperazine.
Nankai University, Tianjin, China
Experimental Section
ReceiVed January 16, 1998
General Procedure, Measurements, and Materials. All reactions
were carried out under a nitrogen atmosphere using standard Schlenk
techniques. The solvents were purified by standard methods. The 1H
NMR and 13C{1H} NMR spectra were recorded on a Bruker-300 NMR
spectrometer using Si(Me4) as the external standard and CDCl3 as
solvent. The 31P{1H} NMR spectra were recorded on a Bruker-500
NMR spectrometer at 202.45 MHz using 85% H3PO4 as the external
standard and CDCl3 as solvent. [Ag(MeCN)4](O3SCF3) was prepared
from the literature procedure.7
Preparation of 1-[(Diphenylphosphino)methyl]-4-(2-pyridyl)pip-
erazine (L1). Diphenylphosphine (1.86 g, 10.00 mmol) was added to
a mixture of 1.63 g (10.00 mmol) of 1-(2-pyridyl)piperazine and 0.45
g (15.00 mmol) of paraformaldehyde in 20 mL of toluene at 70-80
°C. The mixture was stirred until all the solid paraformaldehyde had
completely dissolved (about 5 h). This solution was cooled and then
filtered through Celite. The solvent was removed in a vacuum, leaving
a colorless solid which was recrystallized with dichloromethane/ethanol
to give crystals of L1. Yield: 2.80 g (78%). 31P{1H} NMR: δ 2.40
ppm. 1H NMR: δ 8.19 (t, J ) 0.4 Hz, 1H), 7.47(m, 5H), 7.33 (m,
6H), 3.57 (t, J ) 1.5 Hz, 4H), 3.28 (t, J ) 0.4 Hz, 2H), 2.77 (t, J )
1.1 Hz, 4H). Anal. Calcd for C22H24N3P: C, 73.11; H, 6.69; N, 11.62.
Found: C, 73.05; H, 6.67; N, 11.63.
Preparation of Binuclear Silver(I) Complex [Ag(µ-L1)(O3SCF3)]2,
1. To a solution containing 0.36 g (1.00 mmol) of L1 in 30 mL of
CH3CN was added solid [Ag(MeCN)4](O3SCF3) (0.42 g, 1.00 mmol).
The resulting solution was stirred at room temperature for 1 h.
Subsequent diffusion of diethyl ether into the concentrated solution
gave [Ag(µ-L1)(O3SCF3)]2 as colorless crystals. Yield: 0.52 g (85%).
31P(1H) NMR: δ 21.40 ppm. Anal. Calcd for C46H48Ag2F6N6O6P2S2:
C, 44.67; H, 3.91; N, 6.80. Found: C, 44.57; H, 3.90; N, 6.75. Crystals
of [Ag(µ-L1)(O3SCF3)]2‚MeCN‚1/2H2O suitable for X-ray analysis were
obtained by vapor diffusion of diisopropyl ether into its acetonitrile
solution.
Introduction
Polydentate phosphine ligands with -(CH2)n- spacers be-
tween the donor atoms are useful backbones for the construction
of bi- and polynuclear transition metal complexes.1 Each
additional methylene group provides a predetermined separation
and flexibility between the donor centers so that metal-metal
distances in such complexes can span the range involved in
metal-metal bonding and metal-ligand-metal-bridged bond-
ing.2 Bis(diphenylphosphino)methane (Ph2PCH2PPh2) has been
widely exploited in this fashion,3 while (diphenylarsino)(diphe-
nylphosphino)methane (Ph2PCH2AsPh2) has been used in the
rational synthesis of heterobinuclear complexes.4 However, the
nonrigid PN-phosphine ligand (diphenylphosphino)(diphenyl-
amino)methane (Ph2PCH2NPh2) has only been developed as a
monodentate phosphine ligand to form mononuclear RhI,2 AuI,5
and CuI 6 complexes. The reason that it does not function as a
bidentate ligand is attributed to the nearly planar configuration
around the tertiary amino nitrogen atom, which precludes its
coordination to a metal center, as revealed by the structures of
Rh(Ph2PCH2NPh2)2(CO)Cl,2 Au[(Ph2PCH2NPh2)]2Cl,5 Cu[(Ph2-
PCH2NPh2)]2(NO3), and Cu[(Ph2PCH2NPh2)]2Cl.6 Replacement
of the diphenylamino group by a piperazine ring, as in the newly
designed nonrigid PN-phosphine ligand L1 (see Scheme 1),
ensures that the proximal tertiary amino nitrogen atom has a
pyramidal configuration, and we report here the synthesis and
structure of its binuclear silver(I) complex and mononuclear
iron(0) complex with a new nonrigid PN-phosphine ligand
† The Chinese University of Hong Kong.
Preparation of Mononuclear Iron(0) Complex trans-Fe(CO)3-
(L1)2, 2. To a solution of NaOH (0.10 g, 2.50 mmol) in n-butanol (20
mL) was added Fe(CO)5 (0.15 mL, 1.2 mmol), and the mixture was
stirred for 30 min at room temperature. Then L1 (0.90 g, 2.50 mmol)
was added, and the mixture was refluxed for 2 h. After the solution
was cooled to room temperature, a yellow precipitate appeared. The
precipitate was filtered out and recrystallized from CH2Cl2/MeOH to
give yellow crystals of 2. Yield: 0.63 g (61%). 31P(1H): δ 70.60
ppm. Anal. Calcd for C47H48FeN6O3P2: C, 65.43; H, 5.61; N, 9.24.
Found: C, 64.83; H, 5.58; N, 9.62.
‡ Nankai University.
(1) Balch, A. L. In Homogeneous Catalysis with Metal Phosphine
Complexes; Pignolet, L. H., Ed.; Plenum: New York, 1983; p 17.
(2) Balch, A. L.; Olmstead, M. M.; Rowley, S. P. Inorg. Chim. Acta 1990,
168, 255.
(3) Puddephatt, R. J. Chem. Soc. ReV. 1983, 12, 99.
(4) (a) Guimerans, R. R.; Balch, A. L. Inorg. Chim. Acta 1983, 77, L177.
(b) Balch, A. L.; Guimerans, R. R.; Wood, F. E. Inorg. Chem. 1984,
23, 1307. (c) Balch, A. L.; Guimerans, R. R.; Linehan, J.; Wood, F.
E. Inorg. Chem. 1985, 24, 2021. (d) Balch, A. L.; Guimerans, R. R.;
Linehan, J.; Olmstead, M. M.; Oram, D. E. Organometallics 1985, 4,
1445.
X-ray Crystallography. Intensity data for 1‚MeCN‚1/2H2O were
collected in the variable ω-scan mode on a four-circle diffractometer
(5) Larsonneur, A.-M.; Turpin, R.; Castan, P.; Bernardinelli, G. Inorg.
Chim. Acta 1994, 227, 85.
(6) Larsonneur, A.-M.; Turpin, R.; Ferte, P.; Castan P.; Bernardinelli, G.
Transition Met. Chem. 1994, 19, 548.
(7) Akermark, B.; Vitagliano, A. Organometallics 1985, 4, 1281.
10.1021/ic9800482 CCC: $15.00 © 1998 American Chemical Society
Published on Web 10/24/1998

Notes
Inorganic Chemistry, Vol. 37, No. 23, 1998 6091
Table 1. Crystal Data for 1‚MeCN‚1/2H2O and 2
C46H48Ag2F6N6O6P2S2‚
MeCN‚1/2H2O (1‚MeCN‚ C47H48FeN6O3P2
formula
1/2H2O)
(2)
fw
T, K
1286.77
294
862.76
294
cryst syst
space group
unit-cell dimens
a (Å)
b (Å)
c (Å)
monoclinic
C2/c (No. 15)
monoclinic
P21/c (No. 14)
21.444(3)
15.615(3)
17.370(6)
103.39(1)
5658(3)
4
11.644(2)
11.945(5)
31.875(5)
91.47(1)
4432(2)
4
â (deg)
V (Å3)
Z
F(000)
2604
1.555
1808
1.254
Dc (g cm-3
)
λ, Å (Mo KR)
0.710 73
0.899
3-52
0.93
5576
2846
0.710 73
0.458
4-52
1.39
7571
7132
µ, cm-1
collcn range (2θ, deg)
goodness-of-fit index
no. of unique reflctns
no. of obsd reflctns
(|F| g 4σ(F))
Figure 1. ORTEP drawing (35% thermal ellipsoids) showing the
molecular structure of [Ag(µ-L1)(O3SCF3)]2, 1, in 1‚MeCN‚1/2H2O.
Pertinent bond lengths (Å) and angles (deg): Ag(1)-Ag(1a) 3.033(1),
Ag(1)-P(1) 2.383(1), Ag(1)-O(1) 2.557(2), Ag(1)-N(1a) 2.279(2);
P(1)-Ag(1)-O(1) 108.2(1), P(1)-Ag(1)-Ag(1a) 84.9(1), P(1)-Ag-
(1)-N(1a) 153.2(1), O(1)-Ag(1)-Ag(1a) 84.9(1), O(1)-Ag(1)-N(1a)
95.3(1), N(1a)-Ag(1)-Ag(1a) 84.6(1). Symmetry code: (a) -x + 1/2,
no. of variables, p
348
0.069
0.136
532
0.059
0.063
a
RF
2 b
RwF
1
b
2
a RF ≡ ∑(|Fo| - |Fc|)/∑ |Fo|. RwF ≡ [{∑w(|Fo| - |Fc|)2}/
-y + /2, -z.
2
{∑w|Fo| }]1/2
.
Scheme 2
(Siemens R3m/V) using Mo KR radiation (λ ) 0.710 73 Å, 50 kV, 25
mA, 2θmin ) 3°, 2θmax ) 52°) at 294 K. The intensity data of 2 were
collected at 294 K on a Rigaku RAXIS IIC imaging-plate diffractometer
using Mo KR radiation (λ ) 0.710 73 Å) from a rotating-anode
generator operating at 50 kV and 90 mA (2θmin ) 4°, 2θmax ) 52°, 36
5° oscillation frames in the range of 0-180°, exposure 8 min/frame).8
A self-consistent semiempirical absorption correction based on Fourier
coefficient fitting of symmetry-equivalent reflections was applied using
the ABSCOR program.9 The crystal structures were determined by
direct methods, and non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were all generated geometrically (C-H bond lengths
fixed at 0.96 Å), assigned appropriate isotropic thermal parameters,
and allowed to ride on their parent carbon atoms. All the H atoms
were held stationary and included in the structure factor calculation in
the final stage of full-matrix least-squares refinement on the F2 data.
All computation were performed on an IBM-compatible 486 PC with
the SHELXL-PC program package.10 Analytic expressions of neutral-
atom scattering factors were employed, and anomalous dispersion
corrections were incorporated.11
Information concerning X-ray data collection and structure refine-
ment of all compounds is summarized in Table 1.
Results and Discussion
Heating a mixture of diphenylphosphine, 1-(2-pyridyl)-
piperazine, and paraformaldehyde in toluene in a manner similar
to that devised by Maier12 yielded a colorless solution, from
which 1-[(diphenylphospino)methyl]-4-(2-pyridyl)piperazine (L1)
was obtained as colorless crystals after evaporation and crystal-
lization from dichlomethane/ethanol (Scheme 1). The 31P{1H}
NMR spectrum gave a singlet at 2.4 ppm. The 1H NMR
spectrum showed characteristic resonances of phenyl and pyridyl
protons as well as three groups of methylene protons. Compared
to (diphenylphosphino)(diphenylamino)methane, this PN-phos-
phine ligand has a pyramidal nitrogen atom seated at the
bridgehead of the piperazine ring, which can readily coordinate
to a metal center with its lone-pair electrons.
(8) (a) Tanner J.; Krause, K. Rigaku J. 1994, 11, 4; 1990, 7, 28. (b) Krause
K. L.; Phillips, G. N., Jr. J. Appl. Crystallogr. 1992, 25, 146. (c) Sato,
M.; Yamamoto, M.; Imada, K.; Katsube, Y.; Tanaka N.; Higashi, T.
J. Appl. Crystallogr. 1992, 25, 348.
(9) Higashi, T. ABSCOR-An Empirical Absorption Correction Based on
Fourier Coefficient Fitting; Rugaku Corp.: Tokyo, 1995.
(10) (a) Sheldrick, G. M. SHELXL PC Manual; Siemens Analytical X-ray
Instruments, Inc.: Madison, WI, 1990. (b) Sheldrick, G. M. In
Computational Crystallography; Sayre, D., Ed.; Oxford University
Press: New York, 1982; pp 506. (c) Sheldrick, G. M. In Crystal-
lographic Computing 3: Data Collection, Structure Determination,
Proteins, and Databases; Oxford University Press: New York, 1985;
p 175.
Reaction of L1 with an equimolar amount of [Ag(CH3CN)4]-
(O3SCF3) in acetonitrile at room temperature leads to rapid
(11) Ibers, J. A.; Hamilton, W. C. In International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974: (a) Vol.
4, pp 55, 99, 149; (b) Vol. 3, p 278.
(12) Maier, L. HelV. Chim. Acta 1965, 110, 1034.

6092 Inorganic Chemistry, Vol. 37, No. 23, 1998
Notes
formation of [Ag(µ-L1)(O3SCF3)]2 (Scheme 2). Slow diffusion
of diisopropyl ether into an acetonitrile solution afforded
colorless crystals of [Ag(µ-L1)(O3SCF3)]2‚MeCN‚1/2H2O, the
structure of which was determined by single-crystal X-ray
analysis.
A perspective view of the binuclear complex 1, [Ag(µ-L1)(O3-
SCF3)]2, which has molecular symmetry 1h, is displayed in Figure
1 with atom numbering. The silver atoms are bridged by a pair
of polydentate phosphine ligands in the head-to-tail configura-
tion. The coordination geometry at each silver atom is highly
distorted tetrahedral with the largest bond angle P(1)-Ag(1)-
N(1a) ) 153.2(1)°, and further stabilization was accomplished
by the coordination of an anionic trifluoromethanesulfonate
ligand. The Ag‚‚‚Ag separation of 3.033(1) Å is in agreement
with those (2.943(2)-3.014(2) Å) in [Ag3(dppp)2 (MeCN)2-
(ClO4)2](ClO4)
[dppp
)
bis(diphenylphosphino)phe-
Figure 2. ORTEP drawing (35% thermal ellipsoids) showing the
molecular structure of 2, trans-Fe(CO)3(L1)2. Pertinent bond lengths
(Å) and angles (deg): Fe(1)-P(1) 2.209(1), Fe(1)-P(2) 2.215(1), Fe-
(1)-C(1) 1.753(3), Fe(1)-C(2) 1.758(3), Fe(1)-C(3) 1.767(3); P(1)-
Fe(1)-P(2) 175.7(1), C(1)-Fe(1)-C(2) 120.2(2), C(1)-Fe(1)-C(3)
117.6(1), C(2)-Fe(1)-C(3) 122.2(2).
nylphosphine],13 those (3.005(2), 3.184(2) Å) in {[Ag2(MeCN)2-
(µ-L2)]}n(ClO4)2n (L2 ) 3,6-bis(diphenylphosphino)pyridazine),14
(3.162(1)-3.223(1) Å) in [Ag{HC(PPh2)3}2Cl](ClO4)2‚2MeCN,15
and that those (3.085 Å) in [Ag2(dppm)2 (NO3)2],16 indicating
the possibility of weak metal-metal interaction in this binuclear
complex. The Ag-N bond length of 2.274(7) Å is much shorter
than those (2.456(5), 2.478(6) Å) in [(OC)3Fe(µ-dppy)2Ag-
(dppy)](ClO4)‚MeOH (dppy ) 2-(diphenylphosphino) pyri-
dine.17
in trans-Fe(CO)3(Ph2Ppy)2.19 The three C-Fe-C angles
(120.2(2), 117.6(1), and 122.2(2)°) are not far from the ideal
value of 120°. One noteworthy feature of this structure is that
the mean planes of the outstretched (pyridyl)piperazine groups
are virtually orthogonal to each other (Figure 2).
In summary, we have taken advantage of the coordination
ability of the pyramidal nitrogen atom of the piperazine ring in
the new nonrigid PN ligand to generate the binuclear silver(I)
complex [Ag(µ-L1)(O3SCF3)]2, in which weak metal-metal
interaction is imposed by simultaneous tight binding of the P
and N ligand atoms to two metal centers. Ligand L1 was also
shown to function as a monodentate ligand in forming the
mononuclear iron(0) complex trans-Fe(CO)3(L1)2.
Reactions of L1 with Fe(CO)5 and NaOH in refluxing
n-butanol afforded a yellow precipitate formulated as trans-Fe-
(CO)3(L1)2. The IR spectrum showed an intense carbonyl
absorption at 1874 cm-1, which implies that the local symmetry
about the Fe atom is near D3h.
The molecular structure of 2, trans-Fe(CO)3(L1)2, is depicted
in Figure 2 with atom numbering. The coordination environ-
ment about the iron atom may be best described as an FeP2C3
trigonal bipyramid with two phosphine ligands occupying axial
positions and three carbonyl groups lying on the equatorial
plane. The P-Fe-P angle of 175.7(1)° is comparable to that
(174.2(1)°) in trans-Fe(CO)3(Ph2Ppym)218 and that (177.1(1)°)
Acknowledgment. This work is supported by Hong Kong
Research Grants Council Earmarked Grant Ref. No. CUHK
4179/97P.
Supporting Information Available: Tables of atomic parameters
and bond lengths and angles for 1‚MeCN‚1/2H2O and 2 (12 pages).
Ordering information is given on any current masthead page.
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