2,6-bis(diphenylphosphino)pyridine-bridged hetero-polynuclear complexes consolidated by Fe→M (M = Ag, Hg) dative bonding

Article abstract of DOI:10.1021/ic010426u

The bridging phosphine ligand 2,6-bis(diphenylphosphino)pyridine (L) was used to synthesize a new, neutral organometallic ligand {Fe(CO)₄)₂(μ-L) 1, which exhibits eclipsed and staggered conformations in two crystalline forms. This Fe,N,Fe-tridentate ligand reacts with silver perchlorate to form the hetero-trinuclear complex [{Fe(CO)₄}₂Ag(μ-L)](ClO₄) 2, in which the central silver(I) atom bridges a pair of iron(0) atoms at Fe - Ag distances of 2.627(3) and 2.652(3) A; the Fe - Ag - Fe angle is 170.98(9)°. The reaction of 1 with mercury(II) chloride gives {Fe(CO)₄}₂Hg₂Cl₄(μ-L), 3. The ligand also reacts with mercury(II) acetate to form a hetero-octanuclear complex [{Fe(CO)₃Hg}₂(μ-L)]₂ 4 and a novel hetero-heptanuclear complex Fe₃(CO)₈Hg₄(μ-L)₂(MeCO ₂)₂ 5. Complex 4 displays a square metallic core in which the iron and mercury atoms occupy the comers and the centers of the edges, respectively. The metal atoms in 5 are linked to form a kinky line with bends at the iron atoms.

Full text of DOI:10.1021/ic010426u

5928
Inorg. Chem. 2001, 40, 5928-5933
2,6-Bis(diphenylphosphino)pyridine-Bridged Hetero-Polynuclear Complexes Consolidated by
FefM (M ) Ag, Hg) Dative Bonding
Hai-Bin Song,† Zheng-Zhi Zhang,‡ and Thomas C. W. Mak*,†
Department of Chemistry, The Chinese University of Hong Kong,
Shatin, New Territories, Hong Kong SAR, P. R. China, and State Key Laboratory of
Elemento-Organic Chemistry, Nankai University, Tianjin, 300071, P. R. China
ReceiVed April 24, 2001
The bridging phosphine ligand 2,6-bis(diphenylphosphino)pyridine (L) was used to synthesize a new, neutral
organometallic ligand {Fe(CO)4}2(µ-L) 1, which exhibits eclipsed and staggered conformations in two crystalline
forms. This Fe,N,Fe-tridentate ligand reacts with silver perchlorate to form the hetero-trinuclear complex [{Fe-
(CO)4}2Ag(µ-L)](ClO4) 2, in which the central silver(I) atom bridges a pair of iron(0) atoms at Fe-Ag distances
of 2.627(3) and 2.652(3) Å; the Fe-Ag-Fe angle is 170.98(9)°. The reaction of 1 with mercury(II) chloride
gives {Fe(CO)4}2Hg2Cl4(µ-L), 3. The ligand also reacts with mercury(II) acetate to form a hetero-octanuclear
complex [{Fe(CO)3Hg}2(µ-L)]2 4 and a novel hetero-heptanuclear complex Fe3(CO)8Hg4(µ-L)2(MeCO2)2 5.
Complex 4 displays a square metallic core in which the iron and mercury atoms occupy the corners and the
centers of the edges, respectively. The metal atoms in 5 are linked to form a kinky line with bends at the iron
atoms.
Introduction
Scheme 1
For many years pyridyl-phosphine ligands have been widely
used to synthesize hetero- or homo-nuclear metal complexes,1
as electronic differentiation associated with the hard (N) and
soft (P) donor atoms dictates their unique reactivities and
coordination modes. One important property of these ligands
is that they can stabilize metal ions in a variety of valence states
and geometries. Hence, a metal-metal bond between an
electron-rich metal (soft base) and a high oxidation-state metal
(Lewis acid) is easy formed, and some homogeneous catalytic
applications, including hydrogenation, hydroformylation, car-
bonylation, and alkene insertion, have been investigated.2 Recent
work from our laboratories has explored the use of bifunctional
pyridyl-phosphine ligands typified by 2-(diphenylphosphino)-
pyridine, Ph2Ppy, for the construction of hetero-binuclear
transition-metal complexes that are consolidated by a donor-
acceptor metal-metal bond (Scheme 1).3
ladium, platinum, rhodium, iridium, silver, gold, copper, rhe-
nium, and molybdenum complexes.5 The rigidity of this ligand
governs the P‚‚‚N‚‚‚P ligand bite distance so that binding a metal
to each donor site places the metal ions in very close proximity
(about 2.6-2.8 Å). This restriction on metal-metal separation
appears to limit the range of complexes that can be generated
from this ligand, and to date only two trinuclear (Pd3Cl6(µ-L)3
and [Ir2Cu(CO)2Cl2(MeCN)(µ-L)2](ClO4)‚2MeCN) and two
tetranuclear ([Rh4(µ-Cl)2Cl2(µ-L)2(µ-CO)(CO)2]‚2CH2Cl2 and
The neutral ligand 2,6-bis(diphenylphosphino)pyridine, (Ph2P)2-
py (L), first synthesized by Newkome and Hager,4 has been
shown to form various novel binuclear and polynuclear pal-
(2) (a) Zhang, Z.-Z.; Cheng, H. Coord. Chem. ReV. 1996, 147, 1. (b)
Newkome, G. R. Chem. ReV. 1993, 93, 2067. (c) Francio`, G.;
Scopelliti, R.; Arena, C. G.; Bruno, G.; Drommi, D.; Faraone, F.
Organometallics 1998, 17, 338. (d) Zhang, Z.-Z.; Xi, H.-P.; Zhao,
W.-J.; Jiang, K.-Y.; Wang, R.-J.; Wang, H.-G.; Wu, Y. J. Organomet.
Chem. 1993, 454, 221. (e) Braunstein, P.; Durand, J.; Knorr, M.;
Strohmann, C. J. Chem. Soc., Chem Commun. 2001, 211. (f)
Braunstein, P.; Rose´, J. In Metal Clusters in Chemistry; Braunstein,
P., Ora, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, 1999;
Vol. 2, pp 616-677.
(3) (a) Kuang, S.-M.; Cheng, H.; Sun, L.-J.; Zhang, Z.-Z.; Zhou, Z.-Y.;
Wu, B.-M.; Mak, T. C. W. Polyhedron 1996, 15, 3417. (b) Li, S.-L.;
Mak, T. C. W.; Zhang, Z.-Z. J. Chem. Soc., Dalton Trans. 1996, 3475.
(c) Zhang, Z.-Z.; Cheng, H.; Kuang, S.-M.; Zhou, Y.-Q.; Liu, Z.-X.;
Zhang, J.-K.; Wang, H.-G. J. Organomet. Chem. 1996, 516, 1. (d)
Kuang, S.-M.; Xue, F.; C. Duan, Y.; Mak, T. C. W.; Zhang, Z.-Z. J.
Organomet. Chem. 1997, 534, 15. (e) Kuang, S.-M.; Zhang, Z.-Z.;
Wu, B.-M.; Mak, T. C. W.; Zhang, Z.-Z. J. Organomet. Chem. 1997,
540, 55. (f) Kuang, S.-M.; Xue, F.; Mak, T. C. W.; Zhang, Z.-Z. Inorg.
Chim. Acta 1999, 284, 119;
* To whom correspondence should be addressed. E-mail: tcwmak@
cuhk.edu.hk. Fax: (852) 2603 5057.
† The Chinese University of Hong Kong.
‡ Nankai University.
(1) See, for example: (a) Farr, J. P.; Olmstead, M. M.; Balch, A. L. J.
Am. Chem. Soc. 1980, 102, 6654. (b) Barder, T. J.; Cotton, F. A.;
Powell, G. L.; Tetrick, S. M.; Walton, R. A. J. Am. Chem. Soc. 1984,
106, 1323. (c) Arena, C. G.; Rotondo, E.; Faraone, F.; Lanfranchi,
M.; Tiripicchio, A. Organometallics 1991, 10, 3877. (d) Arena, C.
G.; Bruno, G.; Munno, G. De; Rotondo, E.; Drommi, D.; Faraone, F.
Inorg. Chem. 1993, 32, 1601. (e) Chan, W.-H.; Zhang, Z.-Z.; Mak,
T. C. W.; Che, C. M. J. Chem. Soc., Dalton Trans. 1998, 803. (f)
Jones, N. D.; MacFarlane, K. S.; Smith, M. B.; Schutte, R. P.; Rettig,
S. J.; James, B. R. Inorg. Chem. 1999, 38, 3956. (g) Barloy, L.;
Ramdeehul, S.; Osborn, J. A.; Carlotti, C.; Taulelle, F.; Cian, A. D.;
Fisher, J. Eur. J. Inorg. Chem. 2000, 2535. (h) Coles, S. J.; Durran,
S. E.; Hursthouse, M. B.; Slawin, A. M. Z.; Smith, M. B. New J.
Chem. 2001, 25, 416. (i) Catalano, V. J.; Bennett, B. L.; Muratidis,
S.; Noll, B. C. J. Am. Chem. Soc. 2001, 123, 173.
(4) Newkome, G. R.; Hager, D. C. J. Org. Chem. 1978, 43, 947.
10.1021/ic010426u CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/11/2001

Hetero-Polynuclear Complexes Consolidated by Dative Bonding
Inorganic Chemistry, Vol. 40, No. 23, 2001 5929
Table 1. X-ray Crystallographic Data and Refinement Parameters of the Complexes
complex
formula
1a
1b
2
4‚2THF
5‚2THF
C37H23Fe2NO8P2
C37H23Fe2NO8P2
C37H23AgClFe2NO12P2
C70H46Fe4Hg4N2-
O12P4‚2THF
2400.94
C70H52Fe3Hg4N2-
O12P4‚2THF
2351.13
M
783.2
783.2
990.52
cryst syst
space group
cryst size/
mm
a/Å
b/Å
monoclinic
monoclinic
monoclinic
monoclinic
monoclinic
P21/c (No.14)
0.44 × 0.19 × 0.11
P21/c (No.14)
0.36 × 0.27 × 0.25
P21/c (No.14)
0.36 × 0.20 × 0.08
P21/c (No.14)
0.20 × 0.12 × 0.10
C2/c(No. 15)
0.60 × 0.40 × 0.40
14.4593(6)
11.1013(5)
23.1378(10)
101.1260(10)
3644.2(3)
4
1.428
1592
0.935
13.364(2)
14.852(3)
18.063(3)
98.363(4)
3547.2(11)
4
1.467
1592
0.961
18.194(5)
11.920(4)
18.205(6)
95.474(6)
3930(2)
4
1.674
1976
1.434
15.606(2)
14.677(2)
18.830(3)
111.445(3)
4014.4(10)
2
1.986
2280
8.461
22.244(3)
14.429(2)
25.380(3)
106.590(2)
7801.5(16)
4
2.002
4480
8.529
c/Å
â/°
U/Å3
Z
Dc/g cm-3
F (000)
µ (Mo KR)/
mm-1
GOF
no. unique
reflns
0.867
8811
0.910
8607
1.052
5139
0.774
9689
0.957
9368
(Rint)
0.0937
3149
451
0.0539, 0.1150
0.0792
3782
452
0.0522, 0.1097
0.0964
2825
446
0.0742
5032
479
0.0385
6970
474
no. obs reflns
no. variables, p
R1, wR2
[I > 2σ(I)]a
R1, wR2
(all data)
0.0935, 0.2370
0.0380, 0.0537
0.0318, 0.0683
0.1808, 0.1557
0.1488, 0.1425
0.1600, 0.2919
0.0982, 0.0627
0.0519, 0.0738
2
a R1 ) ∑(|Fo| - |Fc|/∑|Fo|. wR2 ) {w[∑(|Fo| - |Fc|)2]/∑|Fo| }1/2
.
min. The yellow precipitate was collected and dried under vacuum.
Single crystals of 2, which were obtained by slow diffusion of benzene
into a solution in THF, were thin plates of poor quality that were barely
acceptable for X-ray analysis. Yield 85%. Found: C, 44.90; H, 2.48;
N, 1.34. Calcd for 2, C37H23O12NP2ClAgFe2: C, 44.86; H, 2.34; N,
[Rh2Sn(SnCl3)Cl3(CO)2(µ-L)2]‚2CH2Cl2 ) complexes have had
their structures established by X-ray crystallography.5a,k,l Herein,
we report the synthesis and structure of four new hetero-
polynuclear complexes containing the FefM (M ) Ag, Hg)
dative bond.
1.41. IR(νCO): 2055s, 2000s, 1970s, 1950s cm-1 31P{1H}NMR: δ
.
73.6, 73.8 ppm.
Experimental Section
{Fe(CO)4}2Hg2Cl4(µ-L), 3. To a solution of compound 1 (0.10 g,
0.13 mmol) in dichloromethane (5 mL) was added HgCl2 (0.071 g,
0.26 mmol). The mixture was stirred for 3 h and filtered. The solu-
tion was precipitated by addition of hexane (10 mL) to give [Fe-
(CO)4]2Hg2Cl4(µ-L) as a pale yellow powder. Yield 65%. Found: C,
33.10; H, 1.85; N, 0.90. Calcd for 3, C37H23O8NP2Cl4Fe2Hg2: C, 33.51;
Synthesis of Compounds. Unless otherwise stated, all reactions were
performed under a nitrogen atmosphere using standard Schlenk
techniques. The solvents were purified by standard methods. The ligand
(Ph2P)2py (L) was prepared by the published method.4,5l
{Fe(CO)4}2(µ-L), 1. This compound was prepared according to the
published procedure for Fe(CO)4(Ph2Ppy),3a except that excess Fe(CO)5
and a mixed dichloromethane/ethanol solvent were used. (Ph2P)2py (2.23
g, 5 mmol) was dissolved in 10 mL of CH2Cl2 and mixed with a solution
of Fe(CO)5 (25 mmol) in EtOH (10 mL). Me3NO (10 mmol) dissolved
in EtOH (10 mL) was then added dropwise, and the solution stirred
for 2 h, yielding 1 as a yellow precipitate. Yield 50%. Found: C, 56.93;
H, 3.21; N, 1.69. Calcd for 1, C37H23Fe2NO8P2: C, 56.74; H, 2.96; N,
H, 1.75; N, 1.06. IR(νCO): 2077w, 2030s, 1982m, 1940s, 1930s cm-1
31P{1H}NMR: δ 69.0 ppm.
.
[{Fe(CO)3Hg}2(µ-L)]2, 4. To a solution of compound 1 (0.1 g, 0.13
mmol) in THF (5 mL) was added Hg(MeCO2)2 (0.083 g, 0.26 mmol).
The mixture was stirred for a few hours and then filtered to remove
the insoluble material. The filtrate was allowed to stand for two weeks,
and the well-developed orange crystals of 4‚2THF that appeared were
collected by filtration and used in subsequent X-ray crystal analysis.
The product was then dried in a vacuum and used for elemental analysis.
Yield 60%. Found: C, 37.28, H, 2.46, N, 1.09. Calcd for 4, C70H46-
Fe4Hg4N2O12P4: C, 37.26, H, 2.05, N, 1.24. IR(νCO): 1972s, 1908s
1.79. IR(νCO): 2040m, 1987m, 1945s, 1934s cm-1 31P{1H}NMR: δ
.
75.6 ppm. Single crystals of 1a and 1b were obtained from diffusion
of EtOH and hexane, respectively, into a solution of 1 in CH2Cl2.
[{Fe(CO)4}2Ag(µ-L)](ClO4), 2. A solution of AgClO4 (0.053 g, 0.13
mmol) in benzene (5 mL) was added to a solution of compound 1 (0.10
g, 0.13 mmol) in benzene (5 mL), and the mixture was stirred for 10
cm-1
.
Fe3(CO)8Hg4(µ-L)2(µ-MeCO2)2, 5. To a solution of compound 1
(0.1 g, 0.13 mmol) in THF (5 mL) was added Hg(MeCO2)2 (0.083 g,
0.26 mmol) and Ag2CO3 (0.018 g, 0.065 mmol). The mixture was stirred
for 1 day, during which time the Ag2CO3 was slowly dissolved by
acetic acid formed in the reaction of compound 1 and Hg(MeCO2)2,
and the color changed from yellow to orange. The solution was allowed
to stand for 2 weeks, and a small quantity of black metallic silver
appeared. After removal of the precipitate by filtration, hexane was
layered on top of the filtrate. After 2 days, dark-red diffraction-quality
crystals of 5‚2THF were obtained. The product was then dried in a
vacuum and used for elemental analysis. Yield 30%. Found: C, 38.50,
H, 2.45, N, 1.26. Calcd for 5, C70H52N2O12P4Fe3Hg4: C, 38.10, H, 2.37,
(5) (a) Wood, F.; Olmstead, M. M.; Balch, A. L. J. Am. Chem. Soc. 1983,
105, 6332. (b) Wood, F. E.; Hvoslef, J.; Hope, H.; Balch, A. L. Inorg.
Chem. 1984, 23, 4309. (c) Wood, F. E.; Hvoslef, J.; Balch, A. L. J.
Am. Chem. Soc. 1983, 105, 6986. (d) Shieh, S.-J.; Li, D.; Peng, S.-
M.; Che, C.-M. J. Chem. Soc., Dalton Trans. 1993, 195. (e) Shieh,
S.-J.; Hong, X.; Peng, S.-M.; Che, C.-M. J. Chem. Soc., Dalton Trans.
1993, 3067. (f) Field, J. S.; Haines, R. J.; Warwick, B.; Zulu, M. M.
Polyhedron 1996, 15, 3471. (g) Kuang, S.-M.; Zhang, L.-M.; Zhang,
Z.-Z.; Wu, B.-M.; Mak, T. C. W. Inorg. Chim. Acta 1999, 284, 278.
(h) Kuang, S.-M.; Zhang, Z.-Z.; Wang, Q.-G.; Mak, T. C. W. J. Chem.
Soc., Chem. Commun. 1998, 581. (i) Balch, A. L.; Fossett, L. A.;
Olmstead, M. M. Inorg. Chem. 1986, 25, 4526. (j) Cotton, F. A.;
Dikarev, E. V.; Jordan, G. T., IV; Murillo, C. A.; Petrukhina, M. A.
Inorg. Chem. 1998, 37, 4611. (k) Balch, A. L.; Hope, H.; Wood, F.
E. J. Am. Chem. Soc. 1985, 107, 6936. (l) Kuang, S.-M.; Zhang, Z.-
Z.; Wang, Q.-G.; Mak, T. C. W. Polyhedron 1998, 18, 493.
N, 1.27. IR(νCO): 1983m, 1958s, 1920s, 1904s cm-1
.
X-ray Crystallography. Intensity data for complexes 1a, 1b, 2, 4‚
2THF, and 5‚2THF were collected at 293 K on a Bruker Smart CCD

5930 Inorganic Chemistry, Vol. 40, No. 23, 2001
Song et al.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1A, 1B,
2, 4‚2THF, and 5‚2THF
Scheme 2
Complex 1a
Complex 1b
Fe(1)-P(1)
2.237(2)
2.236(2)
1.782(6)
1.765(7)
1.779(6)
1.760(6)
1.772(8)
1.774(8)
1.746(7)
1.765(7)
87.2(2)
91.4(2)
90.0(2)
175.8(2)
88.8(2)
89.0(2)
Fe(1)-P(1)
2.243(1)
2.240(1)
1.748(6)
1.782(5)
1.768(6)
1.765(6)
1.779(6)
1.782(6)
1.770(6)
1.770(6)
88.7(2)
92.5(2)
90.0(2)
176.9(2)
87.5(2)
92.8(2)
Fe(2)-P(2)
Fe(2)-P(2)
Fe(1)-C(1)
Fe(1)-C(1)
Fe(1)-C(2)
Fe(1)-C(2)
Fe(1)-C(3)
Fe(1)-C(3)
Fe(1)-C(4)
Fe(1)-C(4)
Fe(2)-C(5)
Fe(2)-C(5)
Fe(2)-C(6)
Fe(2)-C(6)
Fe(2)-C(7)
Fe(2)-C(7)
Fe(2)-C(8)
Fe(2)-C(8)
P(1)-Fe(1)-C(1)
P(1)-Fe(1)-C(2)
P(1)-Fe(1)-C(3)
P(1)-Fe(1)-C(4)
P(2)-Fe(2)-C(5)
P(2)-Fe(2)-C(6)
P(2)-Fe(2)-C(7)
P(2)-Fe(2)-C(8)
C(1)-Fe(1)-C(2)
C(1)-Fe(1)-C(3)
C(1)-Fe(1)-C(4)
C(2)-Fe(1)-C(3)
C(2)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
C(5)-Fe(2)-C(6)
C(5)-Fe(2)-C(7)
C(5)-Fe(2)-C(8)
C(6)-Fe(2)-C(7)
C(6)-Fe(2)-C(8)
C(7)-Fe(2)-C(8)
P(1)-Fe(1)-C(1)
P(1)-Fe(1)-C(2)
P(1)-Fe(1)-C(3)
P(1)-Fe(1)-C(4)
P(2)-Fe(2)-C(5)
P(2)-Fe(2)-C(6)
P(2)-Fe(2)-C(7)
P(2)-Fe(2)-C(8)
C(1)-Fe(1)-C(2)
C(1)-Fe(1)-C(3)
C(1)-Fe(1)-C(4)
C(2)-Fe(1)-C(3)
C(2)-Fe(1)-C(4)
C(3)-Fe(1)-C(4)
C(5)-Fe(2)-C(6)
C(5)-Fe(2)-C(7)
C(5)-Fe(2)-C(8)
C(6)-Fe(2)-C(7)
C(7)-Fe(2)-C(8)
C(7)-Fe(2)-C(8)
atoms were subjected to anisotropic refinement. The phenyl groups in
2 were refined as hexagons (C-C bond length and C-C-C angle fixed
at 1.39 Å and 120°, respectively) due to the low data-to-parameter
ratio. All hydrogen atoms were generated geometrically (C-H bond
lengths fixed at 0.96 Å), assigned appropriate isotropic thermal
parameters, and included in structure factor calculations in the final
stage of F2 refinement. A summary of crystal data is given in Table 1.
Selected bond lengths and bond angles are listed in Table 2. Further
details are given in the Supporting Information.
Spectroscopic Measurements. Infrared spectra were recorded on a
Shimadzu 435 spectrometer as KBr disks. 31P{1H} NMR spectra were
recorded on an AC-P200 spectrometer at 81.03 MHz using H3PO4 as
the external standard and CDCl3 as solvent.
89.1(2)
88.1(2)
178.6(2)
120.1(3)
118.0(2)
88.9(2)
121.9(3)
91.9(3)
176.4(2)
120.1(2)
124.8(3)
89.0(3)
115.0(3)
90.5(2)
90.4(3)
89.5(3)
116.2(3)
120.6(3)
92.6(3)
123.1(3)
90.1(3)
120.4(3)
119.6(3)
92.4(2)
120.0(2)
90.3(3)
Result and Discussion
The ligand 2,6-bis(diphenylphosphino)pyridine, (Ph2P)2py
(L), is closely related to diphenylphosphinopyridine, Ph2Ppy,
which has been used extensively in constructing many binuclear
complexes (Scheme 1). To date, four modes of coordination
for ligand L have been established by means of X-ray crystal-
lography, all are bridging modes, as illustrated in Scheme 2.
There are a number of structurally characterized complexes
that contain the L ligand bonded in mode A, including Pd3Cl6-
(µ-L)3,5a Pt2Cl4(µ-L)2‚6CH2Cl2,5b Pt2I4(µ-L)2‚2CH2Cl2,5b [Rh2-
(µ-L)2(CO)2(CH3OH)Cl](PF6)‚2CH2Cl2,5c [Au2(µ-L)3](ClO4)2,5d
[Au2(CtCPh)(µ-L)]∞,5e [Cu2(µ-L)3](PF6)2,5f [Ag2(µ-L)3](ClO4)2‚
2CH2Cl2,5g and [Ag(MeCN)2(µ-L)]∞.5h There exists only one
example of a complex that contains the ligand coordinated in
mode B, namely [Rh2(µ-I)(µ-L)2(µ-CO)](PF6)‚2CH2Cl2.5i There
exist three examples that contain the ligand coordinated in mode
C, namely [Mo2Cl4(µ-L)2]‚2CH2Cl2, [Re2Cl4(µ-L)2], and [(n-
Bu)4N]‚[Re2Cl7(µ-L)]‚CH2Cl2;5j in all these cases, the metal-
metal separations (2.15-2.28 Å) are shorter than those found
in mode A, B, and D. The complex [Rh4(µ-Cl)2Cl2(µ-L)2(µ-
CO)(CO)2]‚2CH2Cl2 has a molecular symmetry of C2, with each
L ligand coordinated in mode D to three metal centers from
either end of an approximately linear array of four rhodium
atoms.5a The only two structurally characterized species that
contains the L ligand bonded to different metal types are [Rh2-
Sn(SnCl3)Cl3(CO)2(µ-L)2]‚2CH2Cl25k and [Ir2Cu(CO)2Cl2(MeCN)-
(µ-L)2](ClO4)‚2MeCN5l in which the ligands adopt coordination
mode D with their outer P atoms coordinated to the same metals
and the middle N atoms bonded to the other metal.
90.5(3)
88.9(2)
Complex 2
Ag(1)-N(1)
2.42(1)
2.627(3)
2.652(3)
91.8(3)
92.9(3)
Fe(1)-P(1)
2.284(4)
2.287(4)
Ag(1)-Fe(1)
Fe(2)-P(2)
Ag(1)-Fe(2)
N(1)-Ag(1)-Fe(1)
N(1)-Ag(1)-Fe(2)
P(1)-Fe(1)-C(4)
P(2)-Fe(2)-Ag(1) 87.0(1)
175.9(6)
Fe(1)-Ag(1)-Fe(2) 170.98(9) P(2)-Fe(2)-C(8)
176.8(7)
P(1)-Fe(1)-Ag(1)
88.6(1)
Complex 4‚2THFa
2.211(1) Fe(2)-P(2)
2.5886(9) Fe(2)-Hg(1)
2.555(1) Fe(2)-Hg(2A)
3.4083(5) Hg(1)-N(1)
95.60(5) P(2)-Fe(2)-Hg(1)
175.07(7) P(2)-Fe(2)-Hg(2A)
Fe(1)-P(1)
2.219(2)
2.5760(9)
2.565(1)
2.650(5)
91.66(5)
177.11(7)
Fe(1)-Hg(1)
Fe(1)-Hg(2)
Hg(1)-Hg(2)
P(1)-Fe(1)-Hg(1)
P(1)-Fe(1)-Hg(2)
Hg(1)-Fe(1)-Hg(2) 83.00(3) Hg(1)-Fe(2)-Hg(2A) 86.43(3)
Fe(1)-Hg(1)-N(1) 85.9(1) Fe(2)-Hg(1)-N(1) 88.5(1)
Fe(1)-Hg(1)-Fe(2) 170.80(4) Fe(1)-Hg(2)-Fe(2A) 172.80(3)
Complex 5‚2THFb
Fe(1)-P(1)
2.225(1) Fe(2)-P(2)
2.243(1) Fe(1)-Hg(1)
2.4839(7) Fe(2)-Hg(1)
2.5491(6) Hg(1)-N(1)
3.3348(4) Hg(2)-O(5)
2.487(5)
2.243(1)
2.6560(7)
2.5491(6)
2.571(3)
2.339(4)
Fe(2)-P(2A)
Fe(1)-Hg(2)
Fe(2)-Hg(1A)
Hg(1)-Hg(1A)
Hg(2)-O(6)
P(1)-Fe(1)-Hg(1)
P(1)-Fe(1)-Hg(2)
93.40(4) P(2)-Fe(2)-P(2A)
166.74(7)
91.66(5)
81.60(3)
173.80(4) P(2)-Fe(2)-Hg(1)
Hg(1)-Fe(1)-Hg(2) 89.45(2) P(2)-Fe(2)-Hg(1A)
Fe(1)-Hg(1)-N(1) 87.36(8) Hg(1)-Fe(2)-Hg(1A) 81.71(3)
Fe(2)-Hg(1)-N(1) 88.5(1) Fe(1)-Hg(1)-Fe(2) 93.82(8)
In view of the insolubility of L in ethanol, a mixed solvent
of dichloromethane and ethanol was used to synthesize [Fe-
(CO)4]2(µ-L) by analogy to the synthesis of Fe(CO)4(µ-Ph2py).3a
However, when equal stoichiometric amounts of Fe(CO)5 and
L were used, the yield of the product was low (<10%).
Therefore a large excess of Fe(CO)5 (5 equiv of Fe(CO)5 and
1 equiv of L) was employed, and a higher yield of the product
a Symmetry code: A 1 - x, -y, 1 - z. b Symmetry code: A -x,
y, 1/2 - z.
1000 diffractometer system using Mo KR radiation (λ ) 0.71073 Å;
frames of oscillation range 0.3°; 50 kV, 30 mA; 2θmax ) 45° for 2;
2θmax ) 56° for all others). An empirical absorption correction
(SADABS) was applied to the raw intensities. The crystal structures
were determined by direct methods and refined by full-matrix least
squares using the SHELXTL-PC program package.6 Non-hydrogen
(6) Sheldrick, G. M. SHELXTL97, Program for crystal refinement and
crystal structure solution; University of Go¨ttingen: Germany, 1997.

Hetero-Polynuclear Complexes Consolidated by Dative Bonding
Inorganic Chemistry, Vol. 40, No. 23, 2001 5931
Figure 2. Perspective view (35% thermal ellipsoids) of the two
conformations of 1 in form 1a (eclipsed, left) and 1b (staggered, right).
For clarity the carbonyl groups and ipso carbon atoms of the phenyl
rings have been omitted.
Figure 1. Perspective view (35% thermal ellipsoids) of {Fe(CO)4}2-
(µ-L) 1 in crystalline form 1a (top) and 1b (bottom). L ) 2,6-bis-
(diphenylphosphino)pyridine, (Ph2P)2py.
Figure 3. Perspective view (35% thermal ellipsoids) of the [{Fe-
(CO)4}2Ag(µ-L] cation in 2.
was obtained (about 50%). The IR spectrum of 1 shows four
peaks in the range of 1900-2050 cm-1. The 31P{1H} NMR
spectrum of 1 shows a singlet at δ 75.6 ppm, which indicates
the two phosphorus atoms are in the same chemical environ-
ment.
+
spectrum of polynuclear complex 2 shifts to higher frequencies,
which is consistent with both a change in stereochemistry and
a decrease in electron density on the iron(0) atom.
When different solvents (EtOH and hexane) were used to
diffuse into a solution of {Fe(CO)4}2(µ-L) 1 in CH2Cl2, two
crystalline solvates that display allomorphism were obtained.
Different conformations of the molecule exist in the two
allomorphic forms 1a and b, as shown in Figure 1. Selected
bond lengths and angles are listed in Table 2. In both
conformations, the ligand L coordinates to the metal centers in
mode A. The coordination environment about each iron atom
may be described as a trigonal bipyramid, with three carbonyl
groups lying in the equatorial plane (the sum of the three
C-Fe-C angles is nearly 360°) and a phosphorus atom and
the remaining carbonyl group occupying the axial positions (the
P-Fe-C angle is nearly 180°). Figure 2 clearly shows that the
conformation of 1, when viewed as a Newman projection along
the line P(1)‚‚‚P(2), is eclipsed in 1a and staggered in 1b.
The reaction of 1 with AgClO4 and HgCl2 in molar ratio of
1:1 and 1:2 in benzene and dichloromethane gave compound
[{Fe(CO)4}2Ag(µ-L)](ClO4) 2 and 3, respectively, which were
fully characterized by IR and 31P{1H} NMR. The 31P{1H} NMR
spectrum of complex 2 consists of a doublet, which is attributed
to the sum of 2J(P-Ag) and 3J(P-Ag) coupling via the Fe atom
and via pyridine group, respectively. The silver atom bridges
two iron centers, so the two phosphorus atoms are in equivalent
chemical environments. On the other hand, the abundance ratio
An ORTEP drawing with atom numbering for the cation in
[{Fe(CO)4}2Ag(µ-L)](ClO4) 2 is shown in Figure 3. Selected
bond lengths and angles are listed in Table 2. The iron and
silver centers are linked by the bridging ligand L. A distorted
octahedral geometry is adopted by each of the two Fe atoms,
in which the angles P(1)-Fe(1)-C(4) and P(2)-Fe(2)-C(8)
are 175.9(6) and 176.8(7)°, respectively, and the other three
CO moieties of the each iron and the silver metal lie in a plane
perpendicular to the P-Fe-C axis. In this complex, the silver
atom is only three coordinated, with two Fe-Ag distances of
2.627(3) and 2.652(3) Å, which are comparable to those of the
Fe-Ag clusters containing the Fe(CO)42- fragment in [Fe8(CO)32-
Ag13]4- (2.695-2.762 Å),7a [Fe4(CO)16Ag4]4- (2.570-2.600 Å),
[Fe4(CO)16Ag5]3- (2.585-2.727 Å),7b Fe4(CO)16Ag8(dppm)2
(2.608-2.666 Å), and Fe4(CO)16Ag4Au4(dppe)2 (2.643-2.711
Å),7c but shorter than that (2.760(1) Å) in Fe(CO)3(µ-Ph2-
Ppy)2Ag(Ph2Ppy)ClO4.3b The three metal atoms in complex 2
are approximately colinear with an Fe-Ag-Fe angle of
170.98(9)°, and the Fe-Ag-N angles are close to 90°. The
weak interactions of the (CO)1 and (CO)5 ligands with the Ag+
center (Ag(1)-C(1) 2.63(2) Å and Ag(1)-C(5) 2.65(2) Å) are
(7) (a) Albano, V. G.; Grossi, L.; Longoni, G.; Monari, M.; Mulley, S.;
Sironi, A. J. Am. Chem. Soc. 1992, 114, 5708. (b) Albano, V. G.;
Azzaroni, F.; Iapalucci, M. C.; Longoni, G.; Monari, M.; Mulley, S.;
Proserpio, D. M.; Sironi, A. Inorg. Chem. 1994, 33, 5320. (c) Albano,
V. G.; Iapalucci, M. C.; Longoni, G.; Monari, M.; Paselli, A.; Zacchini,
S. Organometallics 1998, 17, 4438.
2
3
of 107Ag and 109Ag is close to 50%, and J(P-Ag) and J(P-
Ag) coupling via the Fe atom and pyridine group generates a
doublet with J(P-Ag) ) 12 Hz. Compared to 1, the IR ν(CO)

5932 Inorganic Chemistry, Vol. 40, No. 23, 2001
Song et al.
Figure 4. Possible structures of {Fe(CO)4}2Hg2Cl4(µ-L), 3.
presumably responsible for the nonlinearity of the edge Fe-
Ag-Fe. It has been found that the silver ion can act as a single-
electron transfer reagent that oxidizes Fe(CO)3(R3P)2 to form
[Fe(CO)3(R3P)2]+,8a which is more reactive and easily decom-
posed. On the other hand, compared with Collman’s reagent
2-
Fe(CO)4 , the coordination ability of a neutral iron carbonyl
is weak, and examples of its complexes with silver(I) are rare.3b
It has been reported that a silver salt becomes less exoergic in
THF than in CH2Cl2,8b so THF was used to recrystallize
compound 2. In this complex, the bridging ligand L plays an
important role in stabilizing the FefAg dative bond.
When compound 1 was reacted with HgCl2 in an equimolar
ratio, the IR and 31P{1H} NMR spectra showed that the reaction
did not proceed to completion, and half of the starting materials
remained. However, when the molar ratio of compound 1 and
HgCl2 reached 1:2, all starting materials were consumed, and
compound 3 was obtained. Unfortunately, single crystals of
compound 3 could not be obtained using a variety of solvents.
Compared to compound 1, the IR ν(CO) spectrum of compound
3 exhibits splitting and a shift to higher wavenumber. The 31P-
{1H} NMR spectrum shows a singlet shifted from δ 75.6 to
69.0 ppm, which indicates that the two phosphorus atoms in 3
have the same chemical environment and the electron density
on the iron(0) atoms decreases. The spectral data suggest that
FefHg dative bonds are formed in 3, whose two possible
structures are shown in Figure 4.
Figure 5. Perspective view (35% thermal ellipsoids) of [{Fe(CO)3Hg}2-
(µ-L)]2, 4.
mercury clusters containing an Fe(CO)42- fragment and a linear
Fe-Hg-Fe free system,10 but shorter than those in the binuclear
complexes Fe(CO)3(R3P)2HgX2 (X ) Cl, Br, I, SCN).3c,3d,11 On
the other hand, the long Hg(1)‚‚‚Hg(2) distance of 3.4083(5) Å
can be taken to be a weak interaction when compared with the
Hg-Hg covalent bond length of 2.89 Å in [{(η5-CH3C5H4)Mn-
(CO)2Hg}4].12a Similar weak bonding interactions are found in
[HgPBut]4 (Hg‚‚‚Hg 3.330(1)-3.564(1) Å)12b and [{Fe-
(CO)4}5Hg7(SBut)3Cl] (Hg‚‚‚Hg 3.294(2)-3.731(2) Å).10a This
weak interaction also decreases the Hg-Fe-Hg angle. Compar-
The reaction of Hg(MeCO2)2 with [Fe(CO)4]2(µ-L) in a 2:1
molar ratio in THF, for two weeks at room temperature, yielded
[{Fe(CO)3Hg}2(µ-L)]2 4, whose octanuclear structure is similar
ing the square metallic cores in the series of complexes [Fe-
4-
(CO)4Cd]4, [Fe(CO)4Ag]4
, [Fe(CO)4Au]44-, and 4, the
M-Fe-M and Fe-M-Fe angles in the silver (72-80° and
161-169°) and gold (65-70° and 156-158°) complexes are
much smaller than the corresponding values in the mercury (83-
86° and 171-173°) and cadmium (88-89° and 170-171°)
complexes, which is attributed to argentophilic and aurophilic
interactions. The average Ag-Ag and Au-Au distances of
about 3.0 Å, though weak, cause an inward bending of the Fe-
M-Fe linear sequences.
4-
to those of [Fe(CO)4Cd]4, [Fe(CO)4Ag]44-, and [Fe(CO)4Au]4
.
7b,9
The IR ν(CO) spectrum of complex 4 shows two peaks,
which indicates that the three CO group are in two distinct
environments.
An ORTEP drawing with atom numbering for complex 4 is
shown in Figure 5. Selected bond lengths and angles are listed
in Table 2. The eight metals are alternately arranged in a square
with iron atoms at its corners and a mercury atom located at
the center of each edge. Although this configuration was
assumed for [Fe(CO)4Hg]4, no direct evidence was provided.9a
Each iron atom is in a distorted octahedral environment, being
coordinated by three CO ligands, two cis positioned mercury
atoms (Hg-Fe-Hg angle: 83.00(3)° and 86.43(3)°), which are
comparable with those in [Fe(CO)4(HgCl)2] and [{Fe(CO)4}5Hg7-
(SBut)3Cl],10 and one phosphorus atom of ligand L. The angles
P(1)-Fe(1)-Hg(2) and P(2)-Fe(2)-Hg(2a) are 175.07(7) and
177.11(7)°, respectively, and the other three CO moieties of
the each iron and the Hg(1) metal lie in a plane perpendicular
to the P-Fe-Hg(2) axis. The Fe-Hg distances fall in the range
of 2.555(1)-2.589(1) Å, which are similar to those in iron-
Since the size of the Fe4Hg4 square in complex 4 is about
5.2 × 5.2 Å, we attempted to insert a silver(I) atom into the
central cavity. It is known that a silver ion can be positioned at
the center of [Fe(CO)4Ag]44- to form [Fe4(CO)16Ag5]3- 7b
, and
(10) (a) Fenske, D.; Bettenhausen, M. Angew. Chem., Int. Ed. Engl. 1998,
37, 1291. (b) Eisenmann, J.; Fenske, D.; Hezel, F. Z. Anorg. Allg.
Chem. 1998, 624, 1095. (c) Hezel, F.; Fenske, D.; Eisenmann, J.;
Wetzel, T. Z. Anorg. Allg. Chem. 2000, 626, 290. (d) Sosinsky, B.
A.; Shong, R. G.; Fitzgerald, B. J.; O’Rourke, C. Inorg. Chem. 1983,
22, 3124. (e) Ferrer, M.; Perales, A.; Rossell, O.; Seco, M. J. Chem.
Soc., Chem. Commun. 1990, 1447. (f) Bianchini, A.; Farrugia, L. J.
Organometallics 1992, 11, 540. (g) White, J. P., III; Deng, H.; Boyd,
E. P.; Gallucci, J.; Shore, S. G. Inorg. Chem. 1994, 33, 1685. (h)
Benard, M.; Bodensieck, U.; Braunstein, P.; Knorr, M.; Strampfer,
M.; Strohmann, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2758. (i)
Anderson, S.; Hill, A. F.; White, A. J. P.; Williams, D. J. Organo-
metallics 1998, 17, 2665.
(8) (a) MacNeil, J. H.; Chiverton, A. C.; Fortier, S.; Baird, M. C.; Hynes,
R. C.; Williams, A. J.; Preston, K. F.; Ziegler T. J. Am. Chem. Soc.
1991, 113, 9384. (b) Song, L.; Trogler, W. C. Angew. Chem., Int. Ed.
Engl. 1992, 31, 770.
(11) Song, H.-B.; Wang, Q.-M.; Zhang,, Z.-Z.; Mak, T. C. W. J. Organomet.
Chem. 2000, 605, 15.
(9) (a) Ernst, R. D.; Marks, T. J.; Ibers, J. A. J. Am. Chem. Soc. 1977,
99, 2090. (b) Albano, V. G.; Calderoni, F.; Iapalucci, M. C.; Longoni,
G.; Monari, M. J. Chem. Soc., Chem. Commun. 1995, 433.
(12) (a) Ga¨de, W.; Weiss, E. Angew. Chem., Int. Ed. Engl. 1981, 20, 803.
(b) Ahlrichs, R.; Arnim, M. von; Eisenmann, J.; Fenske, D. Angew.
Chem., Int. Ed. Engl. 1997, 36, 233

Hetero-Polynuclear Complexes Consolidated by Dative Bonding
Inorganic Chemistry, Vol. 40, No. 23, 2001 5933
Scheme 3
Figure 6. Perspective view (35% thermal ellipsoids) of Fe3(CO)8Hg4-
(µ-L)2(MeCO2)2, 5. For each phenyl ring in a Ph2P group, only the
ipso carbon atom is shown.
some complexes containing a Hg-Ag bond have been re-
ported.13 We also took note of the fact that in the synthesis of
complex 4, acetic acid is formed. Therefore, a reaction was
carried out by mixing Ag2CO3, Hg(MeCO2)2 and compound 1
in molar ratio 1:4:2 in THF, with a view to effect a gradual
release of silver ions, but the product obtained, namely
compound 5, was not the intended one that would feature a
nine atom Fe4Hg4Ag square grid.
angles are 173.80(4) and 166.74(7)°, respectively. The
Hg(1)‚‚‚Hg(1A) contact of 3.3348(4) Å is suggestive of a weak
interaction between the two metal centers. The angle Hg(1)-
Fe(2)-Hg(1A) (81.60(3)°) is significantly smaller than Hg(1)-
Fe(1)-Hg(2) (89.45(2)°), which is not affected by the Hg‚‚‚
Hg interaction. On the other hand, the Hg-N bond distance of
2.571(3) Å in 5 is slightly shorter than that of 2.650(5) Å in 4,
and both are comparable to those in Fe(CO)3(µ-Ph2Ppy)2HgX2
(X ) Cl, Br, I, SCN).3c,3d The Fe-Hg distances in 5 fall in the
range of 2.4839(7)-2.6560(7) Å, which is similar to those in 4
and other iron-mercury clusters.10
An ORTEP drawing with atom numbering for Fe3(CO)8Hg4-
(µ-L)2(MeCO2)2 5 is shown in Figure 6. Selected bond lengths
and angles are listed in Table 2. The complex lies on a
crystallographic two-fold axis; the middle iron atom is coordi-
nated by two trans phosphine ligands, two cis CO ligands, and
two cis Hg atoms. In the proposed mechanism shown in Scheme
3, one Fe(CO)3 group in 4 is oxidized and cleaved by a silver-
(I) ion, generating an empty phosphine site on one L ligand.
Next, a pair of acetate ligands each chelates an exposed Hg
atom, freeing a pyridyl site on the same L ligand. A Berry
pseudorotation about the proximal Fe atom then positions the
η1-L ligand and the HgO2CMe group trans to each other. Finally,
nucleophilic attachment of the dangling pyridyl and phosphine
sites to the adjacent Hg and Fe(CO)3 centers, respectively,
dislodges a CO ligand and causes another Berry rearrangement
at the middle Fe atom, such that the bulky PPh2 groups occupy
trans positions around it. In the resulting molecular structure
of 5, the seven metal atoms form a kinky wire with bends at
the three iron centers, and the CO groups are approximately
coplanar. Both independent iron atoms are in distorted octahedral
environments, the P(1)-Fe(1)-Hg(2) and P(2)-Fe(2)-P(2A)
Conclusion
In summary, we have taken advantage of the coordination
ability of the rigid P,N,P-tridentate ligand 2,6-bis(diphenyl-
phosphino)pyridine (L) to synthesize a new organometallic
Fe,N,Fe-tridentate ligand {Fe(CO)4}2(µ-L), which proved to be
quite versatile for the generation of hetero-polynuclear com-
plexes consolidated by FefM (M ) Ag, Hg) dative bonding.
Acknowledgment. This work is supported by Hong Kong
Research Grants Council Earmarked Grant Ref. No. CUHK
4022/98P.
Supporting Information Available: An X-ray crystallographic file
in CIF format for compounds 1a, 1b, 2, 4‚2THF, and 5‚2THF. This
material is available free of charge via the Internet at http://pubs.acs.org.
(13) (a) Knoepfler, A.; Wurst, K.; Peringer, P. J. Chem. Soc., Chem
Commun.1995, 131. (b) Laguna, M.; Villacampa, M. D. Inorg. Chem.
1998, 37, 133.
IC010426U