Heterobimetallic cubane-like cluster compounds prepared as the homologous series [(η5-Cp′)3Mo3 S4M′(PPh3)]+ (M′ = Ni, Pd, Pt). Crystal structures show that platinum is smaller than palladium

Article abstract of DOI:10.1021/om010151q

Exchange of the aqua ligands in [(H₂O)₉Mo₃ S₄][pts]₄·9H₂O for Cp′ ligands (Cp′ = methylcyclopentadienyl; pts = p-toluenesulfonate) yielded the novel cluster salt [(η⁵-Cp′)₃-Mo₃ S₄][pts] ([1][pts]). Reactions of [1][pts] in the presence of triphenylphosphane with [Ni-(cod)₂] (cod = 1,5-cyclooctadiene) or [Pd₂(dba)₃] (dba = dibenzylidenacetone) afforded the heterobimetallic cubane-like cluster compounds [(η⁵- Cp′)₃Mo₃S₄M′(PPh₃)] [pts] ([2][pts]: M′ = Ni; [3] [pts]: M′ = Pd). By reaction of [1][pts] with [Pt(nor)₃] (nor = 2-norbornene) at ambient temperature [(η⁵-Cp′)₃Mo₃ S₄Pt(nor)] [pts] ([4][pts]) was isolated and further converted to [(η⁵-Cp′)₃Mo₃S₄ Pt(PPh₃)] [pts] ([5][pts]) at 60°C. A ³¹P{¹H} NMR spectroscopic characterization of [5][pts] revealed a coupling constant ¹J(PtP) of 6656 Hz, whose size supports the view that the platinum atom is Pt⁰-rather than Pt^II-like. Single-crystal X-ray studies of the complete homologous series [2][pts], [3][pts], and [5][pts] demonstrated that the cluster cations are isostructural with M′-P bond lengths in the order Ni < Pt < Pd.

Full text of DOI:10.1021/om010151q

Organometallics 2001, 20, 3655-3660
3655
Heter obim eta llic Cu ba n e-lik e Clu ster Com p ou n d s
P r ep a r ed a s th e Hom ologou s Ser ies
[(η5-Cp ′)3Mo3S4M′(P P h 3)]+ (M′ ) Ni, P d , P t). Cr ysta l
Str u ctu r es Sh ow th a t P la tin u m Is Sm a ller th a n
P a lla d iu m
Konrad Herbst,† Barbara Rink,† Lutz Dahlenburg,‡ and Michael Brorson*,†
Haldor Topsøe A/ S, Nymøllevej 55, DK-2800 Lyngby, Denmark, and Institut fu¨r Anorganische
Chemie, Universita¨t Erlangen-Nu¨rnberg, Egerlandstrasse 1, D-91058 Erlangen, Germany
Received February 26, 2001
Exchange of the aqua ligands in [(H2O)9Mo3S4][pts]4‚9H2O for Cp′ ligands (Cp′ )
methylcyclopentadienyl; pts ) p-toluenesulfonate) yielded the novel cluster salt [(η5-Cp′)3-
Mo3S4][pts] ([1][pts]). Reactions of [1][pts] in the presence of triphenylphosphane with [Ni-
(cod)2] (cod ) 1,5-cyclooctadiene) or [Pd2(dba)3] (dba ) dibenzylidenacetone) afforded the
heterobimetallic cubane-like cluster compounds [(η5-Cp′)3Mo3S4M′(PPh3)][pts] ([2][pts]: M′
) Ni; [3][pts]: M′ ) Pd). By reaction of [1][pts] with [Pt(nor)3] (nor ) 2-norbornene) at
ambient temperature [(η5-Cp′)3Mo3S4Pt(nor)][pts] ([4][pts]) was isolated and further converted
to [(η5-Cp′)3Mo3S4Pt(PPh3)][pts] ([5][pts]) at 60 °C. A 31P{1H} NMR spectroscopic character-
1
ization of [5][pts] revealed a coupling constant J (PtP) of 6656 Hz, whose size supports the
view that the platinum atom is Pt0- rather than PtII-like. Single-crystal X-ray studies of the
complete homologous series [2][pts], [3][pts], and [5][pts] demonstrated that the cluster
cations are isostructural with M′-P bond lengths in the order Ni < Pt < Pd.
In tr od u ction
bimetallic cluster cores thereby formed comprise single
cubes [Mo3S4M′], edge-shared double cubes [(Mo3S4M′)2],
and corner-shared double cubes [(Mo3S4)2M′]. The
Mo3S4M′ cluster motif has attracted interest because of
the bioinorganic importance of metal sulfide clusters
and, in particular, because it provides an unusual
opportunity to study, within a homologous series of
compounds, how metal-metal bonding and electron
density distributions are affected by the nature of M′.20
Our own interest in the system originates from the oil
refinery process of catalytic hydrodesulfurization:21 The
Mo3S4M′ (M′ ) Co, Ni) and Co2Mo2Sx (x ) 3, 4) cluster
cores constitute molecular models for the active sites of
the industrially used heterogeneous CoMo or NiMo
catalysts. 22-25
The incorporation of metals or metal ions into the
geometrically incomplete [Mo3IVS4]4+ cluster core has
been effected for an extended array of elements (Cr,1
Mo,2 W,3 Fe,4 Co,5 Ni,6 Pd,7 Pt,8 Cu,9 Cd,10 Hg,5 Ga,11
In,12 Tl,13 Sn,14 Pb,15,16 As,17 Sb,18 and Bi19). The hetero-
* To whom correspondence should be addressed. Tel: +45 45272653.
Fax: +45 45272999. E-mail: mib@topsoe.dk.
† Haldor Topsøe A/S.
‡ Universita¨t Erlangen-Nu¨rnberg.
(1) Routledge, C. A.; Humanes, M.; Li, Y.-J .; Sykes, A. G. J . Chem.
Soc., Dalton Trans. 1994, 1275.
(2) Ooi, B.-L.; Sykes, A. G. Inorg. Chem. 1989, 28, 3799.
(3) Deeg, A.; Keck, H.; Kruse, A.; Kuchen, W.; Wunderlich, H. Z.
Naturforsch., B: Chem. Sci. 1988, 43, 1541.
(4) Shibahara, T.; Akashi, H.; Kuroya, H. J . Am. Chem. Soc. 1986,
108, 1342.
(5) Shibahara, T.; Akashi, H.; Yamasaki, M.; Hashimoto, K. Chem.
Lett. 1991, 689.
(6) Shibahara, T.; Yamasaki, M.; Akashi, H.; Katayama, T. Inorg.
Chem. 1991, 30, 2693.
(7) Murata, T.; Gao, H.; Mizobe, Y.; Nakano F.; Motomura, S.;
Tanase, T.; Yano, S.; Hidai, M. J . Am. Chem. Soc. 1992, 114, 8287.
(8) Masui, D.; Ishii, Y.; Hidai, M. Bull. Chem. Soc. J pn. 2000, 73,
931.
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110, 3313.
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hara, T. Chem. Lett. 1999, 631.
(11) Shibahara, T.; Kobayashi, S.; Tsuji, N.; Sakane, G.; Fukuhara,
M. Inorg. Chem. 1997, 36, 1702.
Most work with the Mo3S4M′ cluster core motif has
been carried out in aqueous solution where heterobi-
metallic clusters can be prepared by reaction of [(H2O)9-
Mo3S4]4+ with either metal powder or metal ions and a
reducing agent (typically NaBH4). The heterobimetallic
(18) Lu, S.-F.; Huang, J .-Q.; Lin, Y.-H.; Huang, J .-L. Acta Chim.
Sin. 1987, 3, 191.
(19) Saysell, D. M.; Sykes, A. G. Inorg. Chem. 1996, 35, 5536.
(20) Bahn, C. S.; Tan, A.; Harris, S. Inorg. Chem. 1998, 37, 2770.
(21) Topsøe, H.; Clausen, B. S.; Massoth, F. E. In Catalysis-Science
and Technology; Anderson, R. R., Boudart, M., Eds.; Springer: Berlin,
1996; Vol 11, pp 1-302.
(12) Sakane, G.; Shibahara, T. Inorg. Chem. 1993, 32, 777.
(13) Varey, J . E.; Sykes, A. G. Polyhedron 1996, 15, 1887.
(14) Akashi, H.; Shibahara, T. Inorg. Chem. 1989, 28, 2906.
(15) Brorson, M.; J acobsen, C. J . H.; Helgesen, H. K. M.; Schmidt,
I. Inorg. Chem. 1996, 35, 4808. Correction: 1997, 36, 264.
(16) Saysell, D. M.; Huang, Z.-X.; Sykes, A. G. J . Chem. Soc., Dalton
Trans. 1996, 2623.
(22) Schmidt, I.; Hyldtoft, J .; Hjortkjær, J .; J acobsen, C. J . H. Acta
Chem. Scand. 1996, 50, 871.
(23) Brorson, M.; King, J . D.; Kiriakidou, K.; Prestopino, F.; Nord-
lander, E. In Metal Clusters in Chemistry; Braunstein, P., Oro, L. A.,
Raithby, P. R., Eds.; Wiley-VCH: Weinheim, 1999; Vol. 2., Chapter
2.6, pp 741-781.
(24) Curtis, M. D.; Williams, P. D. Inorg. Chem. 1983, 22, 2261.
(25) Riaz, U.; Curnow, O.; Curtis, M. D. J . Am. Chem. Soc. 1991,
113, 1416.
(17) Hernandez-Molina, R.; Edwards, A. J .; Clegg, W.; Sykes, A. G.
Inorg. Chem. 1998, 37, 2989.
10.1021/om010151q CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/17/2001

3656 Organometallics, Vol. 20, No. 17, 2001
Herbst et al.
in triethylorthoformate (25 mL), and the mixture was stirred
at room temperature for 16 h. The solution was reduced to
half of its volume in vacuo, by which a green-brown solid
precipitated. Diethyl ether (30 mL) was added and the solid
allowed to settle. The supernatant solution was removed by a
pipet. The addition/removal of diethyl ether was repeated
twice, after which the solid was dried in a vacuum. The brown
powder was dissolved in CH3CN (30 mL), resulting in a green
solution, which was evaporated to dryness after 1 h of stirring.
The solid was redissolved in THF (40 mL) and added to a
solution of TlCp′ (1.25 g, 4.37 mmol) in CH2Cl2 (40 mL). The
brown-green mixture was stirred for 3 h, filtered (P4), and
evaporated to dryness. The crude product was purified by
column chromatography on silica gel using mixtures of CH2-
Cl2/CH3OH with increasing polarity (20/1, 15/1, 10/1) as eluent.
The intensely green 10/1 fraction was collected and evaporated
to dryness. Yield: 520 mg (0.63 mmol, 45%). 1H NMR (CDCl3;
δ/ppm): 2.12 (s, 9 H, Cp′); 2.31 (s, 3 H, pts); 5.88 (t, J ) 2.4
Hz, 6 H, Cp′); 6.21 (t, 6 H, Cp′); 7.10 (d, J ) 7.8 Hz, 2 H, pts);
7.80 (d, 2 H, pts). UV/vis (MeOH, λmax/nm (ꢀ/dm3 mol-1 cm-1)):
397 (4400); 576 (1000); 678 (900). FAB+ mass spectrum (m/z
(% abundance)): 653 (M+ - pts, 95); 574 (M+ - pts - Cp′,
14), 495 (M+ - pts - 2 Cp′, 8). Anal. Calcd for C25H28Mo3O3S5
(824.62): C, 36.41; H, 3.42; S, 19.44. Found: C, 36.92; H, 3.69;
S, 19.67.
Syn th esis of [(η5-Cp ′)3Mo3S4Ni(P P h 3)][p ts] ([2][p ts]). A
suspension of [Ni(cod)2] (30.0 mg, 0.109 mmol) in THF (5 mL)
was added to a suspension (partially solution) of [1][pts] (90.0
mg, 0.109 mmol) in THF (15 mL). After stirring the brown
solution for 30 min, PPh3 (28.6 mg, 0.109 mmol) was added.
After 2 h a fine precipitate had formed, which was isolated by
filtration. The solid was recrystallized from CH2Cl2/pentane
to yield a black-red powder. Yield: 112 mg (0.097 mmol, 89%).
1H NMR (CDCl3; δ/ppm): 2.02 (s, 9 H, Cp′); 2.27 (s, 3 H, pts);
5.46 (t, J ) 2.1 Hz, 6 H, Cp′); 5.56 (t, 6 H, Cp′); 7.06 (d, J )
8.1 Hz, 2 H, pts); 7.17 (m, 6 H, PPh3); 7.39 (m, 9 H, PPh3);
7.85 (d, 2 H, pts). 31P{1H} NMR (CDCl3; δ/ppm): 34.4 (s). UV/
vis (MeOH; λmax/nm (ꢀ/dm3 mol-1 cm-1)): 286 (24300); 513
(1900); 678 (900). FAB+ mass spectrum (m/z): 974 (M+ - pts);
712 (M+ - pts - PPh3). Anal. Calcd for C43H43Mo3NiO3PS5
(1145.60): C, 45.08; H, 3.78; S, 13.99. Found: C, 45.09; H, 3.78;
S, 13.86.
products have been isolated as aqua complexes or as
complexes with polydentate ligands with N and/or O
ligating atoms. With the exception of a number of
cluster complexes with Mo3S4Pd7,26-29 and Mo3S4Pt8,30
cores, no clusters containing noble metal atoms have
been described. This is probably due to the low reactivity
of these metals in aqueous solution. By avoiding aque-
ous media we have managed to work around this
problem. Recently we described the conversion of [(H2O)9-
Mo3IVS4][pts]4‚9H2O to [(η5-Cp)3Mo3IVS4][pts] (Cp )
cyclopentadienyl; pts ) p-toluenesulfonate) by a series
of ligand substitution reactions.31 This organically
soluble Mo3S4 cluster starting material could be reacted
in tetrahydrofuran with [(CH3CN)3M′(CO)3] to give the
series [(η5-Cp)3Mo3S4M′(CO)3][pts] (M′ ) Cr, Mo, W).
Insertion reactions of group 8 and 9 metal alkene
complexes into the analogous starting material [(η5-
Cp′)3Mo3S4][pts] ([1][pts]; Cp′ ) methylcyclopentadienyl)
resulted in heterobimetallic clusters with cubane-like
Mo3S4M′ cores (M′ ) Ru, Os, Rh, Ir).32
The present paper describes the incorporation of
heterometals into [1][pts] by reactions with group 10
metal(0) alkene complexes. After stabilization of the
heterometallic site by coordination of triphenylphos-
phane (PPh3), the homologous series [(η5-Cp′)3Mo3S4M′-
(PPh3)][pts] ([2][pts], M′ ) Ni; [3][pts], M′ ) Pd; [5][pts],
M′ ) Pt) was isolated.
Exp er im en ta l Section
Gen er a l P r oced u r es, In str u m en ta tion , a n d Ma ter ia ls.
All preparations were carried out under an atmosphere of dry
nitrogen using Schlenk techniques. Solvents were dried and
distilled from standard drying agents prior to use (pentane,
THF: Na/benzophenone; MeOH: Mg; CH2Cl2: P4O10) and
stored under nitrogen. Silica gel (70-230 mesh, Aldrich) was
dried in vacuo at 160 °C for 14 h and stored under nitrogen.
Solvents for column chromatography were degassed before use.
NMR spectra were recorded at room temperature on a Varian
1
UNITY 300 MHz spectrometer (300.1 MHz for H, 121.4 MHz
Syn th esis of [(η5-Cp ′)3Mo3S4P d (P P h 3)][p ts] ([3][p ts]).
A solution of [Pd2(dba)3] (61 mg, 0.067 mmol) in CH2Cl2 (10
mL) was added dropwise to a solution of [1][pts] (110 mg, 0.133
mmol) in CH2Cl2 (20 mL). The dark brown solution was stirred
for 20 min at room temperature. Solid PPh3 (35 mg, 0.133
mmol) was added and the mixture stirred for another 2 h. The
solution was concentrated to approximately 5 mL, and pentane
(20 mL) was added. The dark precipitate was isolated by
filtration, washed with pentane, and dried in vacuo. Yield: 135
mg (0.113 mmol, 85%). 1H NMR (CDCl3; δ/ppm): 2.10 (s, 9 H,
Cp′); 2.29 (s, 3 H, pts); 5.60 (t, J ) 2.4 Hz, 6 H, Cp′); 5.63 (t,
6 H, Cp′); 7.09 (d, J ) 7.8 Hz, 2 H, pts); 7.16 (m, 6 H, PPh3);
7.34 (m, 9 H, PPh3); 7.85 (d, 2 H, pts). 31P{1H} NMR (CDCl3;
δ/ppm): 26.0 (s). UV/vis (MeOH; λmax/nm (ꢀ/dm3 mol-1 cm-1)):
291 (27 700); 472 (5600); 682 (900). FAB+ mass spectrum (m/
z): 1022 (M+ - pts); 760 (M+ - pts - PPh3). Anal. Calcd for
for 31P) and were referenced to the chemical shift of the
nondeuterated part in the deuterated solvents relative to TMS
(downfield positive). Elemental analyses were performed at
DB-Lab, Dansk Bioprotein A/S, Odense, Denmark.
[(H2O)9Mo3S4][pts]4‚9H2O33 and [Pt(nor)3]34 (nor ) 2-nor-
bornene) were prepared according to published procedures;
methylcyclopentadienyl thallium (TlCp′) was prepared by
reaction of thallium ethoxide with Cp′H.35 [Pd2(dba)3] (dba )
dibenzylidenacetone) was purchased from Aldrich, and [Ni-
(cod)2] (cod ) 1,5-cyclooctadiene) from Strem Chemicals.
Syn th esis of [(η5-Cp ′)3Mo3S4][p ts] ([1][p ts]). [(H2O)9-
Mo3S4][pts]4‚9H2O (2.0 g, 1.40 mmol) and a catalytic amount
(a few crystals) of p-toluenesulfonic acid (Hpts) were dissolved
(26) Murata, T.; Mizobe, Y.; Gao, H.; Ishii, Y.; Wakabayashi, T.;
Nakano, F.; Tanase, T.; Yano, S.; Hidai, M.; Echizen, I.; Nanikawa,
H.; Motomura, S. J . Am. Chem. Soc. 1994, 116, 3389.
(27) Wakabayashi, T.; Ishii, Y.; Murata, T.; Mizobe, Y.; Hidai, M.
Tetrahedron Lett. 1995, 36, 5585.
(28) Wakabayashi, T.; Ishii, Y.; Ishikawa, K.; Hidai, M. Angew.
Chem. 1996, 108, 2268.
(29) Saysell, D. M.; Lamprecht, G. J .; Darkwa, J .; Sykes A. G. Inorg.
Chem. 1996, 35, 5531.
(30) Saysell, D. M.; Sykes, A. G. J . Cluster Sci. 1995, 6, 449.
(31) Rink, B.; Brorson, M.; Scowen, I. J . Organometallics 1999, 18,
2309.
(32) Herbst, K.; Monari, M.; Brorson, M. Inorg. Chem. 2001, 40,
2979.
(33) Shibahara, T.; Akashi, H. Inorg. Synth. 1992, 29, 260.
(34) Crascall, L. E.; Spencer, J . L. Inorg. Synth. 1990, 28, 126.
(35) Blais, M. S.; Chien, J . W. C.; Rausch, M. D. Organometallics
1998, 17, 3775.
C
43H43Mo3O3PPdS5 (1193.33): C, 43.28; H, 3.63; S, 13.43.
Found: C, 43.02; H, 3.66; S, 13.49.
Syn th esis of [(η5-Cp ′)3Mo3S4P t(n or )][p ts] ([4][p ts]). A
solution of [Pt(nor)3] (93 mg, 0.194 mmol) in CH2Cl2 (3 mL)
was added dropwise to a solution of [1][pts] (160 mg, 0.194
mmol) in CH2Cl2 (20 mL). After stirring the green-brown
solution for 20 min at room temperature it was concentrated
to approximately 5 mL by means of vacuum, and pentane (20
mL) was added. The dark precipitate was isolated by filtration,
washed with pentane, and dried in a vacuum. Yield: 147 mg
1
(0.132 mmol, 68%). H NMR (CDCl3; δ/ppm): 0.27 (d, J ) 9.3
Hz, 1 H, nor); 0.42 (m, 1 H, nor); 0.98 (d, J ) 5.4 Hz, 2 H,
nor); 1.65 (d, J ) 8.1 Hz, 2 H, nor); 2.13 (s, 3 H, Cp′); 2.16 (s,

Heterobimetallic Cubane-like Cluster Compounds
Organometallics, Vol. 20, No. 17, 2001 3657
Ta ble 1. Cr ysta l a n d Refin em en t Da ta for [(η5-Cp ′)3Mo3S4M′(P P h 3)][p ts] ([2][p ts], M′ ) Ni; [3][p ts], M′ ) P d ;
[5][p ts], M′ ) P t)
[2][pts]
[3][pts]
[5][pts]
empirical formula
fw
C
43H43Mo3NiO3PS5
C43H43Mo3O3PPdS5
1193.26
C43H43Mo3O3PPtS5
1281.95
1145.57
cryst syst
space group
a, Å
monoclinic
P21/n (no. 14)
9.4781(7)
monoclinic
P21/n (no. 14)
9.462(2)
monoclinic
P21/n (no. 14)
9.4431(7)
b, Å
10.872(3)
10.826(1)
10.817(2)
c, Å
41.793(3)
42.891(4)
42.723(4)
â, deg
91.889(6)
4304.3(13)
4
1.768
1.604
2296
92.380(10)
4389.9(11)
4
1.805
1.553
2368
92.179(7)
4360.8(10)
4
1.953
4.356
2496
cell volume, Å3
Z
Dc, Mg m-3
µ(Mo KR), mm-1
F(000)
cryst size, mm
θ limits, deg
index ranges
0.50 × 0.18 × 0.06
0.45 × 0.25 × 0.16
0.40 × 0.15 × 0.03
2.22; 23.08
2.23; 25.17
2.23; 22.78
-10 e h e 10; 0 e k e 11;
0 e l e 46
-11 e h e 11; 0 e k e 12;
0 e l e 51
-10 e h e 10; 0 e k e 11;
0 e l e 46
no. of reflns collected
no. of ind reflns
6136
7969
5994
6044 [R(int))0.0254]
6044/0/509
1.127
7860 [R(int))0.0148]
7860/0/509
1.137
5905 [R(int))0.0747]
5905/0/509
1.035
no. of data/restraints/params
goodness of fit on F2
final R indices [I>2σ(I)]
R indices (all data)
R1 ) 0.0366, wR2 ) 0.0631
R1 ) 0.0644, wR2 ) 0.0734
0.756 and -0.456
R1 ) 0.0352, wR2 ) 0.0742
R1 ) 0.0584, wR2 ) 0.0849
0.745 and -0.708
R1 ) 0.0607, wR2 ) 0.1029
R1 ) 0.1461, wR2 ) 0.1292
1.306 and -0.932
largest diff peak and hole, e Å-3
3
6 H, Cp′); 2.30 (s, 3 H, pts); 2.43 (s, J (PtH) ) 17.7 Hz, 2 H,
ORTEP-339) implemented therein. H atoms were included in
the final structural models assuming ideal geometry and using
appropriate riding models. Crystal and refinement data are
given in Table 1.
2
nor); 4.49 (s, J (PtH) ) 97.2 Hz, 2 H, nor); 5.60 (m, 6 H, Cp′);
5.66 (m, 6 H, Cp′); 7.09 (d, J ) 8.4 Hz, 2 H, pts); 7.85 (d, 2 H,
pts). UV/vis (MeOH; λmax/nm (ꢀ/dm3 mol-1 cm-1)): 424 (2300);
652 (700). FAB+ mass spectrum (m/z (% abundance)): 943 (M+
- pts, 57); 849 (M+ - pts - nor, 100). Anal. Calcd for C32H38
-
Resu lts a n d Discu ssion
Mo3O3PtS5‚CH2Cl2 (1198.79): C, 33.06; H, 3.36; S, 13.37.
The purification of heterobimetallic derivatives of [(η5-
Cp)3Mo3S4][pts]31 by column chromatography proved to
be difficult due to their low solubility even in polar
organic solvents. We therefore decided to enhance the
solubility of the [Mo3IVS4]4+ cluster and its heterobi-
metallic derivatives by introducing cyclopentadienyl
ligands with aliphatic side chains. For the present
study, we have prepared the new homonuclear methyl-
cyclopentadienyl cluster compound [(η5-Cp′)3Mo3S4][pts]
([1][pts]). The preparative route is very similar to that
for the Cp cluster complex:31 A conversion of [(H2O)9-
Mo3S4][pts]4‚9H2O to a water-free thf complex followed
by the reaction with methylcyclopentadienyl thallium
(TlCp′) yielded [1][pts]. After purification by column
chromatography, [1][pts] was isolated in 45% yield as
an intensely green solid.
Found: C, 33.10; H, 3.37; S, 13.94.
Syn th esis of [(η5-Cp ′)3Mo3S4P t(P P h 3)][p ts] ([5][p ts]). A
solution of PPh3 (50 mg, 0.191 mmol) in MeOH (3 mL) was
dropped to a solution of [4][pts] (150 mg, 0.135 mmol) in MeOH
(10 mL). The mixture was stirred at 60 °C for 3 h. After
evaporation of the solvent in a vacuum, the residue was
dissolved in CH2Cl2 (5 mL). Addition of pentane (20 mL) caused
a green-brown solid to precipitate, which was isolated by
filtration, washed with pentane, and dried in a vacuum.
Yield: 159 mg (0.124 mmol, 92%). 1H NMR (CDCl3; δ/ppm):
2.13 (s, 9 H, Cp′); 2.29 (s, 3 H, pts); 5.49 (t, J ) 2.1 Hz, 6 H,
Cp′); 5.61 (t, 6 H, Cp′); 7.08 (d, J ) 8.1 Hz, 2 H, pts); 7.20 (m,
6 H, PPh3); 7.35 (m, 9 H, PPh3); 7.86 (d, 2 H, pts). 31P{1H}
NMR (CDCl3; δ/ppm): 15.4 (s, 1J (PtP) ) 6656 Hz). UV/vis
(MeOH; λmax/nm (ꢀ/dm3 mol-1 cm-1)): 287 (23 600); 451 (3900);
652 (700). FAB+ mass spectrum (m/z (% abundance)): 1111
(M+ - pts, 50); 849 (M+ - pts - PPh3, 24). Anal. Calcd for
C
43H43Mo3O3PPtS5 (1281.99): C, 40.29; H, 3.38; S, 12.50.
Found: C, 39.88; H, 3.84; S, 12.44.
X-r a y Cr ysta llogr a p h y. X-ray data for [2][pts], [3][pts],
and [5][pts] were collected at 293(2) K on a Nonius MACH 3
diffractometer using graphite-monochromated Mo KR radia-
tion (0.71073 Å). The structures were solved by direct methods
(SIR-97)36 and subsequently refined by full matrix least-
squares procedures on F2 with allowance for anisotropic
thermal motion of all non-hydrogen atoms employing the
WinGX37 package and the relevant programs (SHELXL-97,38
(36) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Moliterni, A. G. G.; Burla, M. C.; Polidori, G.; Camalli, M.; Spagna, R.
SIR-97-A Package for Crystal Structure Solution by Direct Methods
and Refinement; IRMEC: Bari, Perugia, and Rome, Italy, 1997.
(37) Farrugia, L. J . WinGX (Version 1.63.01)-An Integrated System
of Windows Programs for the Solution, Refinement and Analysis of
Single-Crystal X-ray Diffraction Data; University of Glasgow, 1999;
J . Appl. Crystallogr. 1999, 32, 837.
For the preparation of heterobimetallic cubane-like
clusters, [1][pts] was reacted with π-alkene complexes
(38) Sheldrick, G. M. SHELXL-97-A Program for the Refinement
of Crystal Structures from Diffraction Data (Release 97-2); Universita¨t
Go¨ttingen, 1997.
(39) Farrugia, L. J . ORTEP-3 for Windows (Version 1.062); Univer-
sity of Glasgow, 1997/2000; J . Appl. Crystallogr. 1997, 30, 565.

3658 Organometallics, Vol. 20, No. 17, 2001
Herbst et al.
of group 10 transition metals. Due to an immediate
decomposition of [Ni(cod)2] in halogen-containing sol-
vents, the reaction of [1][pts] with [Ni(cod)2] had to be
carried out in THF. Both starting materials showed only
a low solubility in THF, but mixing of two suspensions
containing equimolar amounts of [1][pts] and [Ni(cod)2]
resulted in a rapid color change from green to brown
and the formation of a solution. By addition of 1 equiv
of PPh3, a fine precipitate was obtained; recrystalliza-
tion from CH2Cl2/pentane gave [(η5-Cp′)3Mo3S4Ni(PPh3)]-
[pts] ([2][pts]) as a dark red powder. A similar procedure
using CH2Cl2 as solvent was applied for the reaction of
[1][pts] with [Pd2(dba)3]. After combination of two CH2-
Cl2 solutions of [1][pts] and [Pd2(dba)3] with a Mo:Pd
stoichiometry of 3:1, the instant formation of a nontur-
bid, dark brown solution was observed. As for the
synthesis of [2][pts], the Pd site in the cluster was
stabilized by the addition of PPh3, resulting in the
isolation of [(η5-Cp′)3Mo3S4Pd(PPh3)][pts] ([3][pts]) as a
dark brown powder.
While the reactions of [1][pts] with [Ni(cod)2] and [Pd2-
(dba)3] apparently led to a rapid scission of the metal
alkene bonds, the analogous procedure applied for the
reaction of [1][pts] and [Pt(nor)3] resulted in the dis-
placement of only two norbornene ligands. [(η5-Cp′)3-
Mo3S4Pt(nor)][pts] ([4][pts]) was isolated as an analyti-
cally pure green-brown powder after precipitation from
pentane. Coordination of alkene ligands to the hetero-
metallic site in Mo3S4M′ clusters was earlier reported
for both Mo3S4Ni40 and Mo3S4Pd7,26 cores, which took
up ethene (or ethene derivatives) in acidic aqueous
solution. No reactivity of the norbornene cluster complex
[4]+ toward PPh3 was observed at room temperature.
However at 60 °C in MeOH, a complete substitution of
the norbornene ligand in [4]+ for PPh3 was achieved
within a reaction time of 3 h. The reaction was indicated
by only a slight color change to olive, and the isolated
product, [(η5-Cp′)3Mo3S4Pt(PPh3)][pts] ([5][pts]), virtu-
ally had the same color in the solid state as the starting
material [4][pts].
F igu r e 1. UV/vis spectra of [(η5-Cp′)3Mo3S4]+ ([1]+) and
[(η5-Cp′)3Mo3S4M′(PPh3)]+ ([2]+, M′ ) Ni; [3]+, M′ ) Pd;
[5]+, M′ ) Pt) in methanol.
Mo3S4Pt(dppe)4]Cl (dppe ) 1,2-(diphenylphosphanyl)-
ethane).8 Sykes and co-workers42 observed an unusually
high stretching frequency (2060 cm-1) for the carbonyl
ligand in [(H2O)9Mo3S4Ni(CO)][pts]4, and this incited a
discussion in the literature about the true oxidation
state of the heterometal in Mo3S4M′ cluster cores.
Originally the high CO stretching frequency was inter-
preted to have its origin in a metal oxidation state
“probably appreciably closer to NiII” than to Ni0.42 Later,
Harris and co-workers20 on the basis of Fenske-Hall
molecular orbital calculations explained the appearance
of high carbonyl wavenumbers by the ratio of the orbital
energy levels of the Mo3 fragment, the heterometal
atom, and the carbonyl ligand and concluded that the
nickel atom was not oxidized. Since the range for
1J (PtIIP) coupling constants is reported43 to be 1400-
1
5000 Hz, whereas J (Pt0P) couplings range up to 9000
Hz, the observation of a 1J (PtP) coupling constant of
6656 Hz for [5][pts] supports the view that its platinum
atom is Pt0- rather than PtII-like.
The colors of the phosphane cluster complexes [2]+
(red), [3]+ (brown), and [5]+ (green-brown) in MeOH
solution were reflected in the presence of charge-
transfer bands in the visible region of the UV/Vis
spectra (Figure 1). A blue-shift of the dominating
absorption band from 513 ([2]+) to 472 ([3]+) and 451
nm ([5]+) was observed when going down the Ni triad.
Bands at low wavelengths seem to be due to intraligand
transitions, as they show only minor shifts.
The proton NMR spectra of the PPh3 cluster com-
plexes [2]+, [3]+, and [5]+ displayed almost identical
chemical shifts. Compared to the resonances in [1]+, the
Cp′ signals were slightly shifted to higher field. The
PPh3 protons resonated at approximately 7.18 and 7.36
ppm. In the 1H NMR spectrum of [4]+, well-resolved
signals for the norbornene ligand were found. Compared
to the data of the starting material [Pt(nor)3],41 the
alkene protons were shifted from 3.36 to 4.49 ppm,
thereby indicating a decrease in electron density at the
Pt atom after incorporation in the cluster core. The
tertiary norbornene protons at δ ) 2.43, reported as a
singlet at δ )2.96 in [Pt(nor)3], displayed a 3J (PtH)
coupling constant of 17.7 Hz. The methylene protons
were found as AB doublets at higher field in accordance
with the reported shifts for [Pt(nor)3].
Cr ysta llogr a p h ic Stu d y. Since the triphenylphos-
phane-containing clusters [2][pts], [3][pts], and [5][pts]
differ only in the nature of the heterometal, X-ray
crystal structure data would allow the influence of the
heterometal on the cluster core to be studied within a
complete transition metal group. It was therefore one
of our particular aims to obtain X-ray structural infor-
mation of all three cluster compounds. Single crystals
were grown by slow diffusion of pentane into CH2Cl2
solutions of [2][pts], [3][pts], and [5][pts]. Since the three
cluster cations proved to be isostructural, Figure 2
shows the ORTEP plot only of [2]+. Selected bond
distances and angles are collected in Table 2.
In the 31P{1H} NMR spectra, the PPh3 ligands in [2]+,
[3]+, and [5]+ resonated as singlets in a range 35-15
ppm, the latter flanked by Pt satellites with a coupling
constant 1J (PtP) of 6656 Hz. A similar high 1J (PtP)
coupling constant of 6133 Hz was reported for [Cl3-
(42) Saysell D. M.; Borman C. D.; Kwak C.-H.; Sykes A. G. Inorg.
Chem. 1996, 35, 173.
(43) Verkade J . G.; Mosbo J . A. In Methods in Stereochemical
Analysis; Marchand A. P., Ed.; VCH Publishers: Deerfield Beach, FL,
1987; Vol. 8, Chapter 13, pp 425-464.
(40) Shibahara, T.; Sakane, G.; Maeyama, M.; Kobashi, H.; Yama-
moto, T.; Watase, T. Inorg. Chim. Acta 1996, 251, 207-225.
(41) Green M.; Howard J . A. K.; Spencer J . L.; Stone F. G. A. J .
Chem. Soc., Chem. Commun. 1975, 449.

Heterobimetallic Cubane-like Cluster Compounds
Organometallics, Vol. 20, No. 17, 2001 3659
for Pt than for Pd (Pt(1)-P(1) ) 2.232(4) Å). The same
trend is seen for the Mo-M′ bond lengths (Mo-Niav
)
2.718 Å; Mo-Pdav ) 2.864 Å; Mo-Ptav ) 2.861 Å); these
bond lengths are consistent with single bonds between
each molybdenum and heterometal atom. With six
metal-metal bonds in each cluster core, the cations [2]+,
[3]+, and [5]+ represent electron-precise 60 VE clusters
according to the Wade-Mingos rules for electron-
counting in polyhedra.44
The tendency of 5d transition metals to form metal-
to-ligand bonds of equal or even shorter distance than
their 4d counterparts is a well-known phenomenon
categorized under the heading of the “lanthanide con-
traction”. Traditionally this has been explained as a
contraction of the valence electron shells due to the poor
ability of the 4f electron shell to screen the nuclear
charge.45 Recently, it has been realized that this shell
structure explanation is too simplistic and that relativ-
istic effects play a role in the picture.45-47 Calculations
showed this to be most pronounced for the group 10 and
11 elements Pt and Au, but few experimental data exist
against which comparisons can be made. As pointed out
by Schmidbaur,48 complexes that can be compared must
have identical coordination spheres (in terms of both
ligands and counterions) and must crystallize in iso-
morphous lattices determined at identical experimental
conditions. These strict requirements were fulfilled only
in a few cases, a prominent example being the bis-
(trimesitylphosphane)silver(I) and -gold(I) complexes
[M(PMes3)2][BF4], which indeed revealed that the co-
valent radius of two-coordinated AuI is more than 0.08
Å smaller than that of the corresponding AgI.48 In
isomorphous group 10 metal complexes, the size differ-
ences between Pd and Pt covalent radii are less
pronounced. For linear two-coordinated complexes
[M(PhPtBu2)2] (M ) Pd, Pt) a size difference of 0.033 Å
was recorded,49 and the tetracoordinated planar dioxy-
gen adducts [M(O2)(PhPtBu2)2] (M ) Pd, Pt) showed a
Pd-P/Pt-P bond length difference of 0.068 Å.50
The isomorphously crystallizing cluster cations [2]+,
[3]+, and [5]+ open the possibility to calculate covalent
radius differences for (quasi)tetrahedrally coordinated
Ni0, Pd0, and Pt0 atoms. These calculations focus on
metal-phosphorus distances, since the coordinating
sulfido ligands as a part of the rigid cluster core can
hardly be used for comparable studies. In all three
clusters, the monodentate PPh3 ligand faces weak
interactions with two of the Cp′ methyl groups pointing
toward the phenyl groups (closest distance in all clusters
found in [5]+: H12B-H36 2.262 Å). This results in a
slight misdirection of the heterometal-P(1) vector with
respect to the 3-fold axis of the cubane-like cluster core.
An interaction of phenyl protons with the sulfido ligands
F igu r e 2. ORTEP plot of the cluster cation [(η5-Cp′)3-
Mo3S4Ni(PPh3)]+ ([2]+) representing the isostructural series
[2]+, [3]+, and [5]+. Atoms are drawn at the 30% probability
level. Hydrogen atoms have been omitted for clarity.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [(η5-Cp ′)3Mo3S4M′(P P h 3)][p ts] ([2][p ts],
M′ ) Ni; [3][p ts], M′ ) P d ; [5][p ts], M′ ) P t)
[2][pts]:
M′ ) Ni
[3][pts]:
M′ ) Pd
[5][pts]:
M′ ) Pt
Mo(1)-M′
Mo(2)-M′
Mo(3)-M′
M′-S(2)
M′-S(3)
M′-S(4)
M′-P(1)
2.7215(9)
2.7237(9)
2.7088(8)
2.199(2)
2.206(2)
2.211(2)
2.160(2)
2.8731(6)
2.8623(6)
2.8565(7)
2.382(1)
2.381(1)
2.390(1)
2.277(1)
2.869(2)
2.861(2)
2.853(1)
2.363(4)
2.379(5)
2.372(5)
2.232(4)
Mo(1)-M′-Mo(2)
Mo(1)-M′-Mo(3)
Mo(2)-M′-Mo(3)
Mo(1)-M′-P(1)
Mo(2)-M′-P(1)
Mo(3)-M′-P(1)
S(2)-M′-S(3)
S(2)-M′-S(4)
S(3)-M′-S(4)
S(2)-M′-P(1)
S(3)-M′-P(1)
S(4)-M′-P(1)
62.71(3)
62.72(2)
62.86(2)
59.24(2)
59.26(2)
59.58(2)
59.35(5)
59.38(4)
59.60(4)
143.3(1)
152.6(1)
138.2(1)
101.9(2)
102.7(2)
102.7(2)
122.1(2)
108.5(2)
116.5(2)
141.20(6)
150.48(6)
136.31(5)
107.46(7)
107.53(7)
108.24(6)
117.35(6)
103.74(7)
112.08(7)
143.24(4)
152.82(4)
138.00(4)
101.54(5)
102.09(5)
102.12(5)
122.64(5)
108.55(5)
117.10(5)
The X-ray structures show that each of the cluster
cores [2]+, [3]+, and [5]+ are formed by a single cubane-
like Mo3S4M′ array, in which the metal atoms occupy
the vertexes of a slightly distorted tetrahedron. Each
tetrahedral face is capped by a µ3-coordinated sulfido
ligand, thus generating a cubane-like structure. The
Mo-Mo distances (average for [2]+ 2.831 Å; for [3]+
2.836 Å; for [5]+ 2.837 Å) are consistent with single
bonds between the metal atoms and are only slightly
affected by the nature of M′. They are, however,
significantly shorter than the average Mo-Mo distance
of 2.877 Å in the earlier reported cluster [(η5-Cp)3-
Mo3S4W(CO)3][pts].31 The most interesting differences
between [2]+, [3]+, and [5]+ are found in the M′-S and
M′-P bond lengths. These distances generally expand
when going from Ni to Pd (e.g., Ni(1)-P(1) ) 2.160(2)
Å; Pd(1)-P(1) ) 2.277(1) Å), but are slightly smaller
(44) Mingos, D. M. P.; Wales, D. J . In Introduction to Cluster
Chemistry; Grimes, R. N., Ed.; Prentice Hall Inorganic and Organo-
metallic Chemistry Series; Prentice Hall: Englewood Cliffs, NJ , 1990;
Chapters 1 and 2.
(45) Kaltsoyannis, N. J . Chem. Soc., Dalton Trans. 1997, 1.
(46) Pyykko¨, P. Chem. Rev. 1988, 88, 563.
(47) Li, J .; Schreckenbach, G.; Ziegler, T. Inorg. Chem. 1995, 34,
3245.
(48) Bayler, A.; Schier, A.; Bowmaker, G. A.; Schmidbaur, H. J . Am.
Chem. Soc. 1996, 118, 7006.
(49) Otsuka, S.; Yoshida, T.; Matsumoto, M.; Nakatsu, K. J . Am.
Chem. Soc. 1976, 98, 5850.
(50) Yoshida, T.; Tatsumi, K.; Matsumoto, M.; Nakatsu, K.; Naka-
mura, A.; Fueno, T.; Otsuka, S. Nouv. J . Chem. 1979, 3, 761.

3660 Organometallics, Vol. 20, No. 17, 2001
Herbst et al.
can be excluded (closest S-Hphenyl distance g 3.0 Å in
all clusters). While the metal-phosphorus bond as
expected expands (by 0.117 Å) when going from Ni to
Pd, the Pt-P bond shows a significant 0.045 Å shorten-
ing relative to the corresponding Pd-P bond. Taking
rP ) 1.11 Å51 as a constant value for the covalent radius
of tetrahedral phosphorus, the metal atoms contribute
to the metal-phosphorus bond length by 1.05 Å (Ni),
1.17 Å (Pd), and 1.12 Å (Pt). This represents a 4%
reduction of the Pt as compared to the Pd size.
However, for two reasons the bond length differences
in each of the above-mentioned Pd/Pt systems cannot
be compared outside their specific isomorphously crys-
tallizing complex pairs: First, a change in metal atom
coordination geometry (linear, planar, tetrahedral) af-
fects the orbital energy levels and thereby possibly the
metal-to-ligand bond length differences. Second, the
geometric and electronic features of the cubane-like
cluster core, which partially encapsulates the hetero-
metal, also influence the metal-phosphorus bond length.
This fact becomes evident when the Ni-P bond length
of 2.160(2) Å in [2]+ is compared to the Ni-P bond
length of 2.143(3) Å in the isomorphously crystallizing
cluster [(η5-Cp′)3W3S4Ni(PPh3)]+.52 The shorter Ni-P
bond in the tungsten-nickel cluster is most likely
explained by the electronic influence of the tungsten-
based cluster core. A broadening of the data basis would
be possible by crystal structure determinations of the
[(η5-Cp′)3W3S4M′(PPh3)]+ (M′ ) Pd, Pt) clusters; this
work is currently in progress.
Ack n ow led gm en t. This work was supported by the
European Commission (TMR Network “Metal Clusters
in Catalysis and Organic Synthesis”; Contract FMRX-
CT96-0091; postdoctoral grants to B.R. and K.H.). We
thank our TMR partner at the University of Lund,
Sweden, for access to their Varian UNITY 300 MHz
NMR spectrometer. We also thank Mrs. A. Nielsen for
the preparation of [(H2O)9Mo3S4][pts]4‚9H2O.
Su p p or tin g In for m a tion Ava ila ble: ORTEP plots for the
cluster cations [3]+ and [5]+; tables on atomic coordinates,
thermal parameters, bond lengths and angles, and unit cell
packing diagrams for [2][pts], [3][pts], and [5][pts]; data are
also available in electronic form in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM010151Q
(51) Corbridge, D. E. C. Phosphorus. An Outline of its Chemistry,
Biochemistry and Technology; Elsevier: Amsterdam, 1978; pp 440-
442.
(52) Herbst, K.; Dahlenburg, L.; Brorson, M. Inorg. Chem. 2001, 40,
1989.