Comparative bonding behavior of functional cyclopentadienyl ligands and boron-containing analogues in heterometallic complexes and clusters

Article abstract of DOI:10.1021/ic060318d

The reactivity of isolobal molybdenum carbonylmetalates containing a 2-boratanaphthalene, [Mo(η⁵-2,4-MeC₉H ₆BMe)(CO)₃]^- (5a) and [Mo(η⁵-2, 4-MeC₉H₆BNi-Pr₂)(CO)₃]^- (5b), a 1-boratabenzene, [Mo(η⁵-3,5-Me₂C ₅H₃BNi-Pr₂)(CO)₃]^- (8), or a functionalized cyclopentadienyl ligand, the new metalate [Mo(η⁵-C₅H₄Ph)(CO)₃] ^- (7) and [Mo(η⁵-C₅H₄NMe ₂)(CO)₃]^- (9), toward palladium (I and II) or platinum (I and II) complexes, such as trans-[PdCl₂(NCPh) ₂], [Pd₂(NCMe)₆](BF₄)₂, trans-[PtCl₂(PEt₃)₂], and [N(n-Bu) ₄]₂ [Pt₂Cl₄(CO)₂], has been investigated, and this has allowed an evaluation of the influence of the π-bonded ligands on the structures and unprecedented coordination modes observed in the resulting metal-metal-bonded heterometallic clusters. The new 58 CVE planar-triangulated centrosymmetric clusters, [Mo₂Pd ₂(η⁵-C₅H₄Ph)₂(CO) ₆(PEt₃)₂] (11), [Mo₂Pd ₂(η⁵-2,4-MeC₉H₆BNi-Pr ₂)₂(CO)₆] (12), [Mo₂Pd ₂(η⁵-3,5-Me₂C₅H ₃BNi-Pr₂)₂(CO)₆] (13), [Mo ₂Pd₂(η⁵-C₅H₄NMe ₂)₂(CO)₆(PEt₃)₂] (15), [Mo₂Pt₂(η⁵-C₅H ₄NMe₂)₂(CO)₆(PEt₃) ₂] (16), and [Mo₂Pt₂(η⁵-C ₅H₄NMe₂)₂(CO)₈] (20), have been characterized by single-crystal X-ray diffraction. Their structural features were compared with those of the 54 CVE cluster [Re₂Pd ₂(η⁵-C₄H₄BPh) ₂(CO)₆)] (4), previously obtained from the borole-containing metalate [Re(η⁵-C₄H ₄BPh)(CO)₃]^- (2), in which a 2e-3c B-C _ipso-Pd interaction involving the π-ring was observed. As an extension of what has been observed in 4, clusters 12 and 13 present a direct interaction of the boratanaphthalene (12) and the boratabenzene (13) ligands with palladium. In clusters 11, 15, 16, and 20, the π-ring does not interact with the palladium (11 and 15) or platinum centers (16 and 20), which confers to these clusters a geometry very similar to that of [Mo₂Pd ₂(η⁵-C₅H₅)₂(CO) ₆(PEt₃)₂] (3b). The carbonylmetalates [Mo(π-ring)(CO)₃]^- are thus best viewed as formal four electron donors which bridge a dinuclear d⁹-d⁹ unit. The orientation of this building block in the clusters influences the shape of their metal cores and the bonding mode of the bridging carbonyl ligands. The crystal structure of new centrosymmetric complex [Mo(η⁵-C ₅H₄Ph)(CO)₃]₂ (10) was determined, and it revealed intramolecular contacts of 2.773(4) A between the carbon atoms of carbonyl groups across the metal-metal bond and intermolecular bifurcated interactions between the carbonyl oxygen atoms (2.938(4) and 3.029(4) A), as well as intermolecular C-H...π_Ar(C=C) interactions (2.334-(3) and 2.786(4) A) involving the phenyl substituents.

Full text of DOI:10.1021/ic060318d

Inorg. Chem. 2006, 45, 5852−5866
Comparative Bonding Behavior of Functional Cyclopentadienyl Ligands
and Boron-Containing Analogues in Heterometallic Complexes and
Clusters†
Pierre Croizat,‡ Nicolas Auvray,‡ Pierre Braunstein,*,‡ and Richard Welter§
Laboratoire de Chimie de Coordination, UMR 7177 CNRS, UniVersite´ Louis Pasteur,
67070 Strasbourg Ce´dex, France, and Laboratoire DECOMET, UMR 7177 CNRS, UniVersite´
Louis Pasteur, 67070 Strasbourg Ce´dex, France
Received February 24, 2006
The reactivity of isolobal molybdenum carbonylmetalates containing a 2-boratanaphthalene, [Mo(η
5-2,4-MeC9H6-
BMe)(CO)3]- (5a) and [Mo(
η
5-2,4-MeC9H6BNi-Pr2)(CO)3]- (5b), a 1-boratabenzene, [Mo(
η
5-3,5-Me2C5H3BNi-Pr2)-
(CO)3]- (8), or a functionalized cyclopentadienyl ligand, the new metalate [Mo(
η
5-C5H4Ph)(CO)3]- (7) and [Mo(η5
-
C5H4NMe2)(CO)3]- (9), toward palladium (I and II) or platinum (I and II) complexes, such as trans-[PdCl2(NCPh)2],
[Pd2(NCMe)6](BF4)2, trans-[PtCl2(PEt3)2], and [N(n-Bu)4]2 [Pt2Cl4(CO)2], has been investigated, and this has allowed
an evaluation of the influence of the
observed in the resulting metal metal-bonded heterometallic clusters. The new 58 CVE planar-triangulated
centrosymmetric clusters, [Mo2Pd2(
5-C5H4Ph)2(CO)6(PEt3)2] (11), [Mo2Pd2( 5-2,4-MeC9H6BNi-Pr2)2(CO)6] (12), [Mo2-
Pd2(
5-3,5-Me2C5H3BNi-Pr2)2(CO)6] (13), [Mo2Pd2( 5-C5H4NMe2)2(CO)6(PEt3)2] (15), [Mo2Pt2( 5-C5H4NMe2)2(CO)6-
(PEt3)2] (16), and [Mo2Pt2(
5-C5H4NMe2)2(CO)8] (20), have been characterized by single-crystal X-ray diffraction.
Their structural features were compared with those of the 54 CVE cluster [Re2Pd2(
5-C4H4BPh)2(CO)6)] (4), previously
obtained from the borole-containing metalate [Re( 3c B Cipso Pd interaction
5-C4H4BPh)(CO)3]- (2), in which a 2e
involving the -ring was observed. As an extension of what has been observed in 4, clusters 12 and 13 present
a direct interaction of the boratanaphthalene (12) and the boratabenzene (13) ligands with palladium. In clusters
11, 15, 16, and 20, the -ring does not interact with the palladium (11 and 15) or platinum centers (16 and 20),
which confers to these clusters a geometry very similar to that of [Mo2Pd2(
5-C5H5)2(CO)6(PEt3)2] (3b). The
carbonylmetalates [Mo(
-ring)(CO)3]- are thus best viewed as formal four electron donors which bridge a dinuclear
d9 d9 unit. The orientation of this building block in the clusters influences the shape of their metal cores and the
bonding mode of the bridging carbonyl ligands. The crystal structure of new centrosymmetric complex [Mo(η5
C5H4Ph)(CO)3]2 (10) was determined, and it revealed intramolecular contacts of 2.773(4) Å between the carbon
atoms of carbonyl groups across the metal metal bond and intermolecular bifurcated interactions between the
π-bonded ligands on the structures and unprecedented coordination modes
−
η
η
η
η
η
η
η
η
−
−
−
π
π
η
π
−
-
−
carbonyl oxygen atoms (2.938(4) and 3.029(4) Å), as well as intermolecular C−H‚‚‚πAr(CdC) interactions (2.334-
(3) and 2.786(4) Å) involving the phenyl substituents.
Introduction
for further organometallic synthesis. For example, this was
used for the preparation of the first complex containing a
heterometallic metal-metal bond.1 A considerable number
of dinuclear and cluster complexes have since been obtained
from cyclopentadienyl-containing reagents, such as [M(η5-
C5H5)(CO)3]- (M ) Cr, 1a; M ) Mo, 1b; M ) W, 1c).
We have previously used the isolobal analogy between the
cyclopentadienide anion and the 6π-electron borollide di-
anion (C4H4BR)2- (R ) Ph) to compare the reactivity and
The cyclopentadienide anion, (C5H5)-, is one of the most
important ligands in organometallic chemistry, and it has
been associated with a number of metals to form a wide range
of neutral or anionic reagents that have been used, in turn,
† Part of the PhD Thesis of P.C.
* To whom correspondence should be addressed. E-mail:
braunst@chimie.u-strasbg.fr.
‡ Laboratoire de Chimie de Coordination.
§ Laboratoire DECOMET.
(1) Abel, E. W.; Singh, A.; Wilkinson, G. J. Chem. Soc. 1960, 1321.
5852 Inorganic Chemistry, Vol. 45, No. 15, 2006
10.1021/ic060318d CCC: $33.50
© 2006 American Chemical Society
Published on Web 06/29/2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
bonding behavior of the corresponding metal-centered or-
ganometallic nucleophiles of two adjacent columns of the
Periodic Classification, such as 1 and [Re(η5-C4H4BR)-
(CO)3]- (2).2
Consistently, the first metal cluster with a boratanaphthalene
ligand, [Mo2Pd2(η5-2,4-MeC9H6BMe)2(CO)6(PEt3)2] (6),2 was
prepared from 5a and shown to contain a planar, triangulated
metal core with a center of symmetry in the middle of the
Pd-Pd bond, similar to that in the η5-C5H5 derivatives, 3.3
This was applied to the study of heterometallic metal-
metal-bonded complexes and clusters and led to the discovery
of unprecedented bonding situations. Thus, we found that
the 58 cluster valence electron (CVE), planar, triangulated
[M2Pd2(η5-C5H5)2(CO)6(PEt3)2] (M ) Cr, 3a; M ) Mo, 3b;
M ) W, 3c)3 clusters do not have direct analogues in the
borole series since, despite its planar triangulated metal core
characterized by the presence of 5 metal-metal bonds, the
[Re2Pd2(η5-C4H4BPh)2(CO)6)] (4) cluster contains only 54
CVE.4 In this most unusual cluster, the borole ligand not
only binds to rhenium in the usual η5 manner but also to the
adjacent palladium via a 2e-3c B-Cipso-Pd system.
Although the original reaction of the 1,2-dimethoxyethane
(DME) lithium salt of 5a (Li‚5a‚2DME) with trans-[PdCl2-
(NCPh)2] yielded a product with a deep blue color, charac-
teristic of a metal-metal-bonded complex, perhaps a Mo2Pd2
cluster analogous to borole cluster 4, it was too unstable to
be identified.
Intrigued by the 2e-3c B-Cipso-Pd bonding in cluster
4, we wondered if a phenyl substituent on a π-donor ring
system, other than a borole, could bring about this bonding
behavior. This led us to study the reactivity of the phenyl-
substituted cyclopentadienyl derivative [Mo(η5-C5H4Ph)-
(CO)3]- (7) toward palladium reagents (see below).
The intriguing similarities and differences between clusters
We then considered that a stronger donor substituent than
phenyl, for example, an amino group, on the π-bonded ring
of the molybdate reagent should be more efficient in
providing the adjacent palladium centers with enough
electron density and therefore in confering more stability to
the product. Using the amino-substituted boratanaphthalene
reagent 5b, we have now been able to structurally character-
ize a Mo2Pd2 cluster in which, unexpectedly, the π-system
of the boratanaphthalene ligand interacts with the Pd centers,
rather than the amino group. We also turned our attention
to related aminoboratabenzene and aminocyclopentadienyl
ligands, and the results of our investigations with the
corresponding isoelectronic carbonylmetalates, [Mo(η5-3,5-
Me2C5H3BNi-Pr2)(CO)3]- (8) and [Mo(η5-C5H4NMe2)-
(CO)3]- (9), respectively, are described here.
3 and 4 led us to extend our studies to the borole-containing
5,6
carbonylmetalates, [HFe(η5-C4H4BPh)(CO)2]-
and [Fe-
(η5-C4H4BPh)(CO)2CN]-,7 and then to the 2-boratanaphtha-
lene derivatives 5a and b.2
The boron-containing six-membered ring in 5a and 5b
should behave as monoanionic 6π-electron donors, like the
five-membered anionic (η5-C5H5)- ligand and the five-
membered dianionic 6π-electron donor borollide ligand.
(2) Braunstein, P.; Cura, E.; Herberich, G. E. J. Chem. Soc., Dalton Trans.
2001, 1754.
(3) Bender, R.; Braunstein, P.; Jud, J. M.; Dusausoy, Y. Inorg. Chem.
1983, 22, 3394.
(4) Braunstein, P.; Englert, U.; Herberich, G. E.; Neuschu¨tz, M. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1010.
Inorganic Chemistry, Vol. 45, No. 15, 2006 5853

Croizat et al.
Scheme 1. Complexes and Clusters Containing Anionic 4-Electron Donor Ligands or Metalloligands Bridging a R3P f d9-d9 r PR3 Central Unit
A structural comparison of the bonding of the various
carbonylmetalate fragments in their respective clusters has
also been performed. Since a localized electron count around
each metal center (18e for Cr, Mo, or W and 16e for Pd or
Pt) in clusters 3 and their platinum analogues is not
straightforward, it has been found convenient to consider the
whole anionic bridging moiety µ-[Mo(η5-C5H5)(CO)3]- as
formally donating 4 electrons to the R3P f Pd(I)-Pd(I) r
PR3 or R3P f Pt(I)-Pt(I) r PR3 (R3P f d9-d9 r PR3)
unit. This confers to this 18e anionic fragment a bonding
behavior related to that observed for the 4-electron donor
considered to be anionic 4-electron donors toward the
dinuclear unit R3P f M-M r PR3, where M is an ion with
a d9 electronic configuration (Scheme 1).
The isolobal analogy between these bridging fragments22
encouraged us to explore its extension to other µ-[Mo(π-
ring)(CO)3]- metalloligands in metal clusters, and these
aspects will also be examined here.
Results and Discussion
1. Mixed-Metal Palladium-Molybdenum Clusters. 1.1.
Ph-Substituted Cp Derivatives. Inspired by the fact that
the Re-coordinated phenyl-substituted borole ligand is able
to generate a 2e-3c B-Cipso-Pd system in cluster 4, we
prepared the new metalate [Mo(η5-C5H4Ph)(CO)3]- (7), by
reaction between the sodium phenylcyclopentadienide Na-
(C5H4Ph) and [Mo(CO)6], to determine if its phenyl-
substituted cyclopentadienyl ligand23 could give rise to a
related 2e-3c CipsoCp-CipsoPh-Pd bonding interaction. Un-
fortunately, reactions between 2 equiv of the DME solvated
sodium salt of 7 (Na‚7‚2DME) and trans-[PdCl2(NCPh)2]
or the Pd-Pd complex [Pd2(NCMe)6](BF4)2 24 did not allow
a stable, pure complex to be isolated. Separation of the
reaction mixtures by column chromatography afforded the
new homodinuclear complex [Mo(η5-C5H4Ph)(CO)3]2 (10).
-
bridging phosphido ligands (µ-PR2 ) in some dinuclear
Pd(I)8-11 and Pt(I) complexes12 or in trinuclear heterometallic
platinum-molybdenum13 and platinum-cobalt14 clusters
(Scheme 1). Furthermore, this bridging bonding mode can
also be compared to that of a bridging halide (µ-X-),15-17
an allyl-ene type η3-cyclopentadienide (µ-(η3-C5H5)-),18-20
an η3-allyl (µ-(η3-C3H5)- and µ-(η3-2-MeC3H4)-),17-21 or a
-
carboxylate (µ-RCO2 ) ligand18-20 because they can also be
(5) Braunstein, P.; Englert, U.; Herberich, G. E.; Neuschu¨tz, M.; Schmidt,
M. U. J. Chem. Soc., Dalton Trans. 1999, 2807.
(6) Braunstein, P.; Herberich, G. E.; Neuschu¨tz, M.; Schmidt, M. U.;
Englert, U.; Lecante, P.; Mosset, A. Organometallics 1998, 17, 2177.
(7) Braunstein, P.; Herberich, G. E.; Neuschu¨tz, M.; Schmidt, M. U. J.
Organomet. Chem. 1999, 580, 66.
(8) Arif, A. M.; Heaton, D. E.; Jones, R. A.; Nunn, C. M. Inorg. Chem.
1987, 26, 4228.
(9) Sommovigo, M.; Pasquali, M.; Leoni, P.; Englert, U. Inorg. Chem.
1994, 33, 2686.
(10) Pasquali, M.; Sommovigo, M.; Leoni, P.; Sabatino, P.; Braga, D. J.
Organomet. Chem. 1992, 423, 263.
(11) Leoni, P.; Pasquali, M.; Sommovigo, M.; Albinati, A.; Lianza, F.;
Pregosin, P. S.; Ruegger, H. J. Organomet. Chem. 1995, 488, 39.
(12) Taylor, N. J.; Chieh, P. C.; Carty, A. J. J. Chem. Soc., Chem. Commun.
1975, 448.
(13) Archambault, C.; Bender, R.; Braunstein, P.; Bouaoud, S.-E.; Rouag,
D.; Golhen, S.; Ouahab, L. Chem. Commun. 2001, 849.
(14) Bender, R.; Braunstein, P.; Metz, B.; Lemoine, P. Organometallics
1984, 3, 381.
(15) Vilar, R.; Mingos, D. M. P.; Cardin, C. J. J. Chem. Soc., Dalton Trans.
1996, 4313.
(16) Dura` Vila`, V.; Mingos, D. M. P.; Vilar, R.; White, A. J. P.; Williams,
D. J. J. Organomet. Chem. 2000, 600, 198.
(17) Jolly, P. W.; Krueger, C.; Schick, K. P.; Wilke, G. Z. Naturforsch.
1980, 35B, 926.
The formation of this complex results from a redox
reaction, in agreement with general observations made in
the course of our investigations on the syntheses of the Mo2-
Pd2 clusters containing the Cp ligand.3 An ORTEP view of
the structure of 10 is shown in Figure 1 with the main
distances and angles. The Mo-Mo distance of 3.2134(8) Å
in this centrosymmetric dinuclear complex is close to that
(18) Werner, H.; Thometzek, P.; Kru¨ger, C.; Kraus, H. J. Chem. Ber. 1986,
119, 2777.
(19) Thometzek, P.; Werner, H. Organometallics 1987, 6, 1169.
(20) Werner, H. AdV. Organomet. Chem. 1981, 19, 155.
(21) Krause, J.; Goddard, R.; Mynott, R.; Poerschke, K.-R. Organometallics
2001, 20, 1992.
(22) Hoffmann, R. Angew. Chem., Int. Ed. Engl. 1982, 21, 711.
(23) Riemschneider, R.; Nehring, R. Monatsh. Chem. 1960, 91, 829.
(24) Murahashi, T.; Nagai, T.; Okuno, T.; Matsutani, T.; Kurosawa, H.
Chem. Commun. 2000, 1689.
5854 Inorganic Chemistry, Vol. 45, No. 15, 2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
Figure 1. ORTEP view of the structure 10 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. Selected
bond distances (Å) and angles (deg): Mo-Mo′ ) 3.2134(8), Mo-C(1) )
1.983(3), Mo-C(2) ) 1.987(3), Mo-C(3) ) 1.972(3), C(1)-O(1) ) 1.149-
(3), C(2)-O(2) ) 1.146(3), C(3)-O(3) ) 1.143(3); Mo-C(1)-O(1) )
172.1(3), Mo-C(2)-O(2) ) 173.4(3), Mo-C(3)-O(3) ) 179.1(3).
of 3.235(1) Å in [Mo(η5-C5H5)(CO)3]2.25 The angle between
the mean planes of the cyclopentadienyl ring and its phenyl
substituent is 18.8(1)°. Short intramolecular contacts, C(1)‚
‚‚C(2)′ and C(2)‚‚‚C(1)′, of 2.773(4) Å are observed between
the carbon atoms of carbonyl groups across the metal-metal
bond (Figure 1), which are slightly shorter than those in [Mo-
(η5-C5H5)(CO)3]2 (2.796(4) Å). Furthermore, intermolecular
bifurcated interactions between the carbonyl oxygen atoms
involve three adjacent molecules with O(1)‚‚‚O(2) and O(1)‚
‚‚O(1) separations of 2.938(4) and 3.029(4) Å, respectively
(Figure S-1 of the Supporting Information), while intermo-
lecular C-H‚‚‚πAr(CdC) interactions (2.334(3) and 2.786-
(4) Å) involve the phenyl substituents (Figure S-2).
Figure 2. ORTEP view of the structure 11 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. Selected
bond distances (Å) and angles (deg): Pd-Pd′ ) 2.5836(9), Pd-Mo )
2.8128(9), Pd′-Mo ) 2.8564(8), Pd-P ) 2.328(2), Pd-C(1) ) 2.374(6),
Pd-C(2) ) 2.370(7), Pd-C(3) ) 2.283(6), Pd′-C(3) ) 2.438(6), Mo-
C(1) ) 1.955(6), Mo-C(2) ) 1.953(6), Mo-C(3) ) 2.028(7), C(1)-O(1)
) 1.184(6), C(2)-O(2) ) 1.186(7), C(3)-O(3) ) 1.175(7), C(8)-C(9) )
1.479(8); Pd′-Pd-Mo ) 63.75(4), Mo-Pd-Mo′ ) 125.78(3), Pd-Pd′-
Mo ) 62.03(3), Pd-Mo-Pd′ ) 54.22(3), Pd′-Pd-P ) 175.76(6), Mo-
C(1)-O(1) ) 166.6(5), Mo-C(2)-O(2) ) 159.5(6), Mo-C(3)-O(3) )
158.4(5), Pd-C(1)-O(1) ) 113.0(4), Pd-C(2)-O(2) ) 118.2(5), Pd-
C(3)-O(3) ) 116.4(5), Pd′-C(3)-O(3) ) 118.6(5).
The reaction of Na‚7‚2DME with trans-[PdCl2(PEt3)2] or
with [Pd2(NCMe)6](BF4)2 in the presence of PEt3, led to the
formation of the [Mo2Pd2(η5-C5H4Ph)2(CO)6(PEt3)2] (11)
cluster, X-ray diffraction analysis of which confirmed a
centrosymmetric structure of the type found in 3.
Table 1. Structural Parameters
â (deg)a
γ (deg)b
δ (deg)c
h (Å)d
23
3b
4
6
11
12
13
15
16
20
1.95(10)
3.3(2)
10.7(7)
4.6(1)
2.9(2)
8.7(2)
6.81(7)
5.6(1)
6.5(1)
1.14(1)
0.90(1)
1.01(1)
0.91(1)
0.89(1)
1.06(1)
1.10(1)
0.86(1)
0.83(1)
1.02(1)
74.7(1)
88.4(4)
81.3(1)
78.9(2)
89.3(1)
87.69(5)
82.7(1)
86.8(3)
89.7(2)
87.19(1)
68.33(4)
86.06(1)
87.05(2)
74.72(2)
68.99(1)
85.14(3)
86.54(3)
75.87(1)
7.3(3)
a â ) angle between the metallic plane and the mean plane defined by
the carbon atoms of the π-ring (Scheme 2). b γ ) M(2)-Csym-Cring angle
(Scheme 2). c δ ) angle between the mean plane defined by the carbon
atoms of the π-ring and the plane defined by the carbon atoms of the
carbonyls. d h ) shortest distance between M and the C(1)C(2)C(3) plane
(Scheme 6).
An ORTEP view of the structure of 11 is shown in Figure
2 with the main distances and angles. Each Mo atom is
bonded to two asymmetric doubly bridging and one semi-
triply bridging carbonyls. The mean planes of the C5 rings
are parallel by symmetry and form a dihedral angle, â, of
78.9(2)° with the metallic plane and an angle of 19.9(2)°
with the mean plane of their phenyl substituents (see Table
1 and Scheme 2). A comparison with the η5-C5H5 analogue
3b shows that the presence of the phenyl ring does not
influence the orientation of the π-bonded ligand η5-C5H4Ph
with respect to the metal core, as shown by the values of
the angles â and γ (between the axis passing through the
π-ring centroid (Cring) and the center of symmetry of the
cluster (Csym) and the M(2)M(2)′ axis; see Table 1 and
Scheme 2). Coordination of the phosphine ligands to
palladium is much favored over the formation of a 2e-3c
CipsoCp-CipsoPh-Pd bonding system.
1.2. Boratanaphthalene Derivatives. After studying the
reaction of Li‚5a‚2DME with trans-[PdCl2(NCPh)2] in the
presence of PEt3, which yielded [Mo2Pd2(η5-2,4-MeC9H6-
BMe)2(CO)6(PEt3)2] (6), we examined the reaction of the
amino-substituted reagent Li‚5b‚2DME with the dinuclear
complex [Pd2(NCMe)6](BF4)2 in which the palladium is
already in the +I oxidation state, as in the desired product,
which should limit or suppress undesirable redox side-
reactions. This led to the new cluster [Mo2Pd2(η5-2,4-
MeC9H6BNi-Pr2)2(CO)6] (12) whose structure was deter-
mined by X-ray diffraction. An ORTEP view of the structure
of 12 is shown in Figure 3 with the main distances and
angles. Although we anticipated the presence of a 2e-3c
B-N-Pd bonding, related to the 2e-3c B-C-Pd system
(25) Adams, R. D.; Collins, D. M.; Cotton, F. A. Inorg. Chem. 1974, 13,
1086.
Inorganic Chemistry, Vol. 45, No. 15, 2006 5855

Croizat et al.
Scheme 2. Representation of the Angles â and γ
Scheme 3. Two Dispositions of the meso-Isomer of 12 Resulting in
Disorder in the Crystal
arrangements of the molecule. This superposition may
equally well include the two racemic isomers. The planar
geometry around the nitrogen atom of the BNi-Pr2 group is
shown by the sum of the angles around N of 360(1)°, which
is consistent with a partial boron-nitrogen double bond
(B-N ) 1.413(6) Å).26 There is no interaction between this
group and the Pd centers. Each Mo center is bonded to one
terminal and two semi-bridging carbonyls, as observed for
cluster 4. The mean planes defined by the carbon atoms of
the boratanaphthalene ligands are, by symmetry, parallel to
each other and form a dihedral angle, â, of 89.3(1)° with
the metallic plane (see Table 1). The total valence electron
count of this cluster is 58e, when including the two electrons
donated to each Pd center by the boratanaphthalene π-system.
1.3. Amino-boratabenzene Derivatives. We then con-
sidered it to be of interest to examine a similar reaction using
the amino-substituted boratabenzene analogue of 5b, [Mo-
(η5-3,5-Me2C5H3BNi-Pr2)(CO)3]- (8),27 which is much less
likely to lead to an interaction between the aromatic CdC
system and the Pd centers. The reaction of 2 equiv of the
DME-solvated lithium salt of 8 (Li‚8‚2DME)27 with [Pd2-
(NCMe)6](BF4)2 in toluene produced the tetranuclear cluster
[Mo2Pd2(η5-3,5-Me2C5H3BNi-Pr2)2(CO)6] (13), and its crystal
structure determination established the presence of a 2e-3c
B-N-Pd bonding.
encountered in 4, it is now the π-system of the aromatic
ligand that donates electron density to the palladium centers.
The molecular structure possesses crystallographic cen-
trosymmetry and displays disordered aminoboratanaphthalene
ligands. This disorder relates to the bonding of the metal to
the two enantiotopic faces of the planar chiral boratanaph-
thalene and is illustrated for the meso isomer in Scheme 3.
The apparent lateral symmetry of the metal-to-ligand
bonding results from the superposition of the two alternative
Figure 3. ORTEP view of the structure 12 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. For the
disorder of the aminoboratanaphthalene ligands, see text. Selected bond
distances (Å) and angles (deg): Pd-Pd′ ) 2.892(1), Pd-Mo ) 2.666(1),
Pd′-Mo ) 2.959(10), Pd-C(11) ) 2.407(5), Pd-C(12) ) 2.210(4), Pd-
C(1) ) 2.227(4), Pd-C(2) ) 2.229(5), Mo-C(1) ) 2.010(4), Mo-C(2)
) 2.007(4), Mo-C(3) ) 2.001(5), C(1)-O(1) ) 1.167(5), C(2)-O(2) )
1.170(5), C(3)-O(3) ) 1.135(5), B-N ) 1.413(6); Pd′-Pd-Mo ) 64.19-
(2), Mo-Pd-Mo′ ) 118.38(2), Pd-Pd′-Mo ) 54.20(3), Pd-Mo-Pd′ )
61.62(2), Mo-C(1)-O(1) ) 163.5(4), Mo-C(2)-O(2) ) 163.7(5), Mo-
C(3)-O(3) ) 179.9(5), Pd-C(1)-O(1) ) 118.8(3), Pd-C(2)-O(2) )
118.5(4), B-N-C(16) ) 123.5(3), B-N-C(19) ) 122.2(3), C(16)-N-
C(19) ) 114.3(3).
An ORTEP view of the structure of 13 is shown in Figure
4 with the main distances and angles. The B-Pd distance
of 2.488(2) Å is shorter than the 2.59(2) Å observed in the
5856 Inorganic Chemistry, Vol. 45, No. 15, 2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
Figure 5. ORTEP view of the structure of 15 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. Selected
bond distances (Å) and angles (deg): Pd-Pd′ ) 2.590(2), Pd-Mo )
2.8075(5), Pd′-Mo ) 2.867(1), Pd-P ) 2.320(2), Pd-C(1) ) 2.392(3),
Pd-C(2) ) 2.395(4), Pd-C(3) ) 2.370(4), Pd′-C(3) ) 2.480(4), Mo-
C(1) ) 1.972(4), Mo-C(2) ) 1.977(4), Mo-C(3) ) 2.033(3), C(1)-O(1)
) 1.170(4), C(2)-O(2) ) 1.165(4), C(3)-O(3) ) 1.169(4), C(8)-N )
1.364(5); Pd′-Pd-Mo ) 64.03(4), Mo-Pd-Mo′ ) 125.71(5), Pd-Pd′-
Mo ) 61.68(4), Pd-Mo-Pd′ ) 54.29(5), Pd′-Pd-P ) 173.69(3), Mo-
C(1)-O(1) ) 157.4(3), Mo-C(2)-O(2) ) 164.8(3), Mo-C(3)-O(3) )
159.9(3), Pd-C(1)-O(1) ) 121.0(3), Pd-C(2)-O(2) ) 115.8(3), Pd-
Figure 4. ORTEP view of the structure of 13 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. Selected
bond distances (Å) and angles (deg): Pd-Pd′ ) 3.015(1), Pd′-Mo ) 2.676-
(1), Pd-Mo ) 2.877(2), Pd-N ) 2.304(2), Pd-B ) 2.488(2), Pd-C(1)
) 2.199(2), Pd-C(2) ) 2.186(2), Mo-C(1) ) 2.021(2), Mo-C(2) ) 2.020-
(2), Mo-C(3) ) 1.964(2), C(1)-O(1) ) 1.173(3), C(2)-O(2) ) 1.163(3),
C(3)-O(3) ) 1.175(3), B-N ) 1.470(3); Pd-Pd′-Mo ) 60.39(4), Mo-
Pd-Mo′ ) 114.35(4), Pd′-Pd-Mo ) 53.96(4), Pd-Mo-Pd′ ) 65.65(4),
Mo-C(1)-O(1) ) 164.4(2), Mo-C(2)-O(2) ) 163.3(2), Mo-C(3)-O(3)
) 178.0(2), Pd-C(1)-O(1) ) 117.0(2), Pd-C(2)-O(2) ) 117.8(2),
N-Pd-Mo ) 91.55(6), B-N-Pd ) 79.09(11), B-N-C(11) ) 116.8(2),
B-N-C(12) ) 120.3(2), C(11)-N-C(12) ) 112.8(2).
C(3)-O(3) ) 117.5(3), Pd′-C(3)-O(3)
118.5(3), C(8)-N-C(9) )
)
119.0(3), C(8)-N-C(10) ) 117.8(4), C(9)-N-C(10) ) 117.0(3).
[Mo(η5-C5H4NMe2)(CO)3]2 (14) (IR (CH2Cl2) ν(CO): 1938s,
1898s cm-1).
case of 4. The N-Pd distance is 2.304(2) Å. The angle, â,
between the mean plane defined by the carbon atoms of the
boratabenzene ring and the metal plane is 87.69(5)° (see
Table 1). Because of its coordination to palladium, the
environment of the nitrogen atom is not planar (sum of the
angles around N ) 349.9(4)°). Each molybdenum is bonded
to a terminal carbonyl ligand and to two doubly bridging
carbonyls. When the ligand η5-3,5-Me2C5H3BNi-Pr2 is
considered as a neutral moiety, it formally donates 5 electrons
to the Mo and 2 to the adjacent Pd centers. This provides a
total electron count of 58 for this cluster, similar to that in
3 but in contrast to the situation in 4.
However, when the reaction was performed in the presence
of 2 equiv of PEt3, the reaction mixture became violet
instantaneously, characteristic of a cluster of type 3. Indeed,
the new cluster isolated, [Mo2Pd2(η5-C5H4NMe2)2(CO)6-
(PEt3)2] (15), was shown by X-ray diffraction to adopt a
centrosymmetric structure.
1.4. Amino-Cp Derivatives. For comparison with the
amino-boratabenzene reagent 8 and to compare the bonding
of the phenyl-borole ligand in 4 with that of a related Cp
derivative, we used the metalate Li[Mo(η5-C5H4NMe2)-
(CO)3]‚2DME (Li‚9‚2DME).27 It was prepared by reaction
of Li(C5H4NMe2) with [Mo(CO)6] in refluxing DME and
reacted with [Pd2(NCMe)6](BF4)2 in THF at -78 °C. A deep-
blue solution was instantaneously formed, suggesting the
formation of a mixed-metal complex, but unfortunately,
various workup procedures only led to the formation of
palladium (black) and of some red homodinuclear complex
An ORTEP view of the structure of 15 is shown in Figure
5 with the main distances and angles. The angle, â, between
the mean plane of the amino-cyclopentadienyl ligand and
the metal plane is 82.7(1)° (see Table 1). The sum of the
angles around N is 353.8(10)°.
(26) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A.
G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(27) Auvray, N.; Baul, T. B.; Braunstein, P.; Croizat, P.; Englert, U.;
Herberich, G. E.; Welter, R. Dalton Trans. 2006, 2950.
Inorganic Chemistry, Vol. 45, No. 15, 2006 5857

Croizat et al.
2. Mixed-Metal Platinum-Molybdenum Clusters
In view of the difficulty or impossibility of isolating some
of the desired palladium-containing clusters because of their
high lability or instability, we decided to explore the behavior
of platinum analogues since platinum complexes and clusters
are generally more stable than their palladium counterparts.
By analogy with the successful use of [Pd2(NCMe)6](BF4)2
in the synthesis of heterometallic palladium clusters (see
above), we decided first to prepare an analogous homodi-
nuclear Pt(I) complex and explore its reactivity with the
carbonylmetalates. The selective reduction of a Pt(II) precur-
sor into a Pt(I) complex often remains an interesting
challenge. Although homodinuclear Pt(I) complexes contain-
ing phosphine or isonitrile ligands are known,28,29 we did
not consider them to be suitable candidates since the strong
phosphorus-platinum or carbon-platinum bonds, respec-
tively, would not allow coordination of a weaker donor
function in the final cluster. Preliminary experiments using
[N(n-Bu)4]2[Pt2Cl4(CO)2]30 and Li‚9‚2DME were unsuccess-
ful (see below). A desirable precursor with labile ligands
coordinated to the metals would be [Pt2(NCMe)6](BF4)2 but
this complex has not been described in the literature. We
attempted to synthesize it by the reaction between [Pt2(dba)3]
and [Pt(NCMe)4](BF4)2, following a procedure similar to that
described for the synthesis of [Pd2(NCMe)6](BF4)2.24 How-
ever, no reaction occurred at room temperature and decom-
position to platinum metal was observed upon heating (even
upon changing reaction conditions, solvents, temperature,
etc.). Although SmI2 is a convenient and mild one-electron
reducing agent which changes color from purple to yellow
upon oxidation to Sm(III),31,32 its reactions with trans-[PtCl2-
(NCPh)2] or trans-[PtCl2(NCMe)2] in the corresponding
organonitrile as a solvent at -20 °C, followed by the addition
of NH4PF6, did not lead to the desired Pt(I)-Pt(I) complex.
Decomposition to Pt metal was again observed at room
temperature.
When the complex [N(n-Bu)4]2[Pt2Cl4(CO)2] was reacted
with Li‚9‚2DME in THF at -78 °C, a deep-blue solution
was obtained (ca. 1 h), but at higher temperature, rapid
formation of platinum black and of 14 was observed. This
color change suggests, like in the reaction of [Pd2(NCMe)6]-
(BF4)2 with Li‚9‚2DME in the absence of phosphine, that
cluster formation occurs but we cannot determine if it is
accompanied by coordination of the amino-Cp ligand to the
d9 metal centers. Possible reaction intermediates are discussed
below.
When trans-[PtCl2(PEt3)2] was reacted with 2 equiv of Li‚
9‚2DME in THF at room temperature, the stable cluster
[Mo2Pt2(η5-C5H4NMe2)2(CO)6(PEt3)2] (16) was obtained and
characterized by X-ray diffraction. An ORTEP view of the
structure of 16 is shown in Figure 6 with the main distances
Figure 6. ORTEP view of the structure of 16 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. Selected
bond distances (Å) and angles (deg): Pt-Pt′ ) 2.650(2), Pt-Mo ) 2.7739-
(8), Pt′-Mo ) 2.826(2), Pt-P ) 2.275(3), Pt-C(1) ) 2.243(9), Pt-C(2)
) 2.324(9), Pt-C(3) ) 2.43(1), Mo-C(1) ) 2.00(1), Mo-C(2) ) 1.97-
(1), Mo-C(3) ) 2.032(9), C(1)-O(1) ) 1.16(1), C(2)-O(2) ) 1.18(1),
C(3)-O(3) ) 1.16(1), C(8)-N(2) ) 1.35(1); Pt′-Pt-Mo ) 62.76(4), Mo-
Pt-Mo′ ) 123.52(6), Pt-Pt′-Mo ) 60.76(4), Pt-Mo-Pt′ ) 56.48(6),
Pt′-Pt-P ) 172.28(6), Mo-C(1)-O(1) ) 149.3(8), Mo-C(2)-O(2) )
162.9(8), Mo-C(3)-O(3) ) 164.7(8), Pt-C(1)-O(1) ) 127.4(8), Pt-
C(2)-O(2) ) 116.7(7), Pt-C(3)-O(3) ) 116.4(7), C(8)-N-C(9) ) 118.6-
(10), C(8)-N-C(10) ) 119.7(10), C(9)-N-C(10) ) 115.6(10).
and angles. This cluster adopts a centrosymmetric structure,
similar to that of its palladium analogue 15 and to that of
the 58 CVE, planar, triangulated cluster [Mo2Pt2(η5-C5H5)2-
(CO)6(PEt3)2].33 Each Mo atom is bonded to three asym-
metrically doubly bridging carbonyls, whereas two asym-
metrically doubly bridging and one semi-triply bridging
carbonyls were observed in 15 and [Mo2Pt2(η5-C5H5)2(CO)6-
(PEt3)2].33 The coordination environment around the nitrogen
atom is almost planar (sum of the angles around N of 354-
(3)°).
These results show that coordination of the phosphine
ligands to palladium is much favored over a 2e-3c CipsoCp
-
N-Pd bonding situation.
3. Suggested Mechanism for the Formation of the
Heterometallic Clusters. Formation of the heterotetranuclear
clusters by reactions of the dinuclear precursor complexes
[Pd2(NCMe)6](BF4)2 and [N(n-Bu)4]2[Pt2Cl4(CO)2] (in which
the d9-d9 bond present in the product already exists) with
the various carbonylmetalates could occur according to
Scheme 4. Substitution of the MeCN or Cl ligands, respec-
tively, would lead to deeply colored and reactive linear
[m]-d9-d9-[m] intermediates ([m] ) Cr(η5-C5H5)(CO)3,
Mo(η5-C5H5)(CO)3, or W(η5-C5H5)(CO)3). These would
rearrange upon addition of phosphine (3b, 6, 11, 15, and
16) or through direct coordination of the metalate ring (12
(28) Mu¨ller, T. E.; Ingold, F.; Menzer, S.; Mingos, D. M. P.; Williams, D.
J. J. Organomet. Chem. 1997, 528, 163.
(29) Garrou, P. E. Chem. ReV. 1985, 85, 171.
(30) Goggin, P. L.; Goodfellow, R. J. J. Chem. Soc., Dalton Trans. 1973,
2355.
(31) Ogoshi, S.; Morita, M.; Inoue, K.; Kurosawa, H. J. Organomet. Chem.
2004, 689, 662.
(32) Molander, G. A.; Harris, C. R. Chem. ReV. 1996, 96, 307.
(33) Bender, R.; Braunstein, P.; Jud, J.-M.; Dusausoy, Y. Inorg. Chem.
1984, 23, 4489.
5858 Inorganic Chemistry, Vol. 45, No. 15, 2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
Scheme 4. Suggested Mechanism for the Formation of the Heterotetranuclear Clusters
and 13) and lead to the stable tetranuclear clusters (Scheme
4). It is interesting to note that similar deeply colored
intermediates have also been observed in the reactions
between carbonylmetalates [m]- and the d9-d9 precursor
complex [Pd2(µ-dppm)2Cl2] and were suggested to have a
linear metal core, [m]-d9-d9-[m], which rearranges into a
spike-triangular structure by insertion of the fragment [m]
into a Pd-P bond.34,35
synthesize it from [Pd2(dba)3] and [Pt(NCMe)4](BF4)2 and
from [Pt2(dba)3] and [Pd(NCMe)4](BF4)2, but no reaction was
observed.
However, when the stronger tert-butylisocyanide was used
in place of the acetonitrile ligands, the reaction between 2
equiv of [Pt(CNt-Bu)4][PF6]2 and [Pd2(dba)3], followed by
the addition of 4 equiv of t-BuNC in CH2Cl2, produced the
new heterobimetallic complex [PdPt(CNt-Bu)6](PF6)2 (17).
When the heterotetranuclear clusters discussed here are
prepared from the d8 mononuclear precursor complexes,
trans-[PtCl2L2] and trans-[PdCl2L2] (L ) PR3, PhCN), it has
been previously envisioned that a trans-[m]-Pt(or Pd)L2-
[m] chain complex is formed first.3,33 When L ) phosphine
ligands, its instability resulting from the steric bulk of L (flat
or rodlike L ligands give stable chain complexes), would
result in homolytic cleavage of a [m]-Pt (or Pd) metal-
metal bond and lead to two radical fragments [m]• and {-
[m]-Pt (or Pd)}•. Their homocoupling yields the [m]-[m]
dinuclear complex and the [m]2(Pd or Pt)2 clusters.3,33
4. Syntheses of Mixed-Metal Complexes and Clusters
from Heterodinuclear Precursors. We also envisioned the
synthesis of heteropolymetallic Mo2PdPt clusters with the
hope of increasing the stability of the products by introducing
Pt while maintaining the high reactivity characteristic of Pd
derivatives.
The reaction between Li‚9‚2DME and 17 in THF at -78
°C, after the reaction mixture was stirred overnight and the
temperature brought to ambient, yielded a black precipitate
of palladium metal and an orange compound that was isolated
from the solution. It was not the expected tetranuclear cluster
but the linear trinuclear complex trans-[(η5-C5H4NMe2)2(OC)6-
Mo2Pt(CNt-Bu)2] (Mo-Pt-Mo) (18).27
Therefore, we examined the use of different mixed-metal
Pd(I)-Pt(I) complexes as building blocks for cluster syn-
thesis. A dinuclear complex such as [PdPt(NCMe)6](BF4)2,
which has not yet been described, would represent an
excellent candidate, by analogy with its dipalladium analogue
which led to the Mo2Pd2 structures. We attempted to
(34) Braunstein, P.; Guarino, N.; de Me´ric de Bellefon, C.; Richert, J. L.
Angew. Chem. 1987, 99, 77; Angew. Chem., Int. Ed. Engl. 1987, 26,
88.
Isolation of this complex indicates that cleavage of the Pt-
Pd bond in the precursor complex has occurred.
(35) Braunstein, P.; de Me´ric de Bellefon, C.; Ries, M. Inorg. Chem. 1988,
27, 1338.
Inorganic Chemistry, Vol. 45, No. 15, 2006 5859

Croizat et al.
The formation of this complex prompted us to use trans-
[PtCl2(NCPh)2] as a precursor, with the hope that displace-
ment of the labile PhCN ligand could lead to a 2e-3c
CipsoCp-N-Pt interaction. However, the heterometallic linear
complex obtained as the major product, trans-[(η5-C5H4-
NMe2)2(OC)6Mo2Pt(NCPh)2] (Mo-Pt-Mo) (19), did not
show any interaction between the Cp-bound amino group
and Pt.
Figure 7. ORTEP view of the structure of 20 with the atom-numbering
scheme. Thermal ellipsoids enclose 50% of the electron density. Selected
bond distances (Å) and angles (deg): Pt-Pt′ ) 2.6649(5), Pt-Mo ) 2.7448-
(6), Pt′-Mo ) 2.8388(6), Pt-C(11) ) 1.865(7), Pt-C(1) ) 2.452(7), Pt-
C(2) ) 2.319(7), Mo-C(1) ) 2.009(8), Mo-C(2) ) 2.041(7), Mo-C(3)
) 2.024(7), C(1)-O(1) ) 1.160(9), C(2)-O(2) ) 1.155(8), C(3)-O(3) )
1.135(8), C(11)-O(4) ) 1.127(8), C(8)-N ) 1.357(9); Pt′-Pt-Mo )
63.28(2), Mo-Pt-Mo′ ) 123.02(1), Pt-Pt′-Mo ) 59.73(2), Pt-Mo-Pt′
) 56.99(1), Pt′-Pt-C(11) ) 160.0(2), Mo-C(1)-O(1) ) 167.6(6), Mo-
C(2)-O(2) ) 163.7(6), Mo-C(3)-O(3) ) 176.2(6), Pt-C(1)-O(1) )
116.9(6), Pt-C(2)-O(2) ) 118.2(5), Pt-C(11)-O(4) ) 178.4(7), C(8)-
N-C(9) ) 119.9(6), C(8)-N-C(10) ) 119.3(7), C(9)-N-C(10) ) 117.4-
(6).
Formation of this complex was associated with smaller
quantities of [Mo2Pt2(η5-C5H4NMe2)2(CO)8] (20), [(η5-
C5H4NMe2)(OC)3MoPt(NCPh)Cl] (Mo-Pt) (21), and [Mo-
(η5-C5H4NMe2)(CO)3Cl] (22).
5. Structural Comparison of the Clusters Containing
a Mo(π-ring)(CO)3 Fragment. 5.1. Metal Cores. In all the
clusters discussed here, the centrosymmetric metal core has
the shape of a parallelogram. It is closest to a lozenge in
3b,3 6,2 11, 15, 16, and 20 with the Mo-M(2) and Mo-
M(2)′ bond lengths being almost equal and longer than the
M(2)-M(2)′ distance. For 3b, 6,2 11 and 15, the Pd-Pd′
distance ranges from 2.582(1) (in 3b) to 2.5955(4) Å (in 6),
and the Mo-Pd distances range from 2.8075(5) (in 15) to
2.8815(4) Å (in 6). In 16 and 20, the Pt-Pt′ distances are
similar (2.650(2) and 2.6649(5) Å, respectively), while their
Mo-Pt distances reflect a more regular rhombus in 16
(2.7739(8) and 2.826(2) Å) than in 20 (2.7448(6) and 2.8388-
(6) Å). The partial coordination of the Mo-bound π-ring to
the palladium centers in clusters 12 and 13 results in a
significant elongation of the Mo-Pd-bridged bond and in a
shortening of the other Mo-Pd bond: the Mo-Pd bond
lengths are 2.666(1) and 2.959(10) Å in 12 and 2.676(1) and
2.877(2) Å in 13. These two clusters are therefore best
described as adopting a parallelogram geometry. The nature
of their π-ring significantly affects the Pd-Pd distances
(2.892(1) and 3.015(1) Å, respectively). All these metal-
metal distances are in the range found for the corresponding
bonds in the literature.36 Interestingly, the shape of the Re2-
Pd2 metal core of cluster 4, which contains a “bridging”
phenylborole ligand, is also closer to a parallelogram than
to a lozenge, with Re-Pd distances of 2.666(1) and 2.866-
(1) Å. Its Pd-Pd′ distance of 2.899(2) Å is similar to that
in 12.4
The synthesis of these compounds and the crystal structures
of 19, 21, and 22 will be detailed elsewhere.27
The crystal structure of the 58 CVE cluster 20 was also
determined by X-ray diffraction. It adopts a planar triangu-
lated geometry. Even if it is not a major product of the
reaction, 20 is very interesting because it is the first Cp-
containing cluster in this family to adopt such a geometry
without any phosphine coordinated to platinum. The origin
of the carbonyl ligands coordinated to platinum is to be found
in the decomposition of some Mo(η5-C5H4NMe2)(CO)3
fragments.
An ORTEP view of the structure of 20 is shown in Figure
7 with the main distances and angles. Its geometry differs
from that of [Mo2Pt2(η5-C5H5)2(CO)6(PEt3)2],33 each molyb-
denum being bonded to one terminal and two doubly bridging
carbonyls. This arrangement is however similar to that of
the carbonyls in clusters 4, 12, and 13. The angle, â, between
the mean plane of the amino-Cp and the metal plane is 89.7-
(2)° (see Table 1). The sum of the angles around N is 357-
(1)°.
5.2. Bonding and Orientation of the Mo(π-ring)(CO)3
Fragments. The various tricarbonylmetalates [Mo(π-ring)-
(CO)3]- 1b, 5a, 5b, 7, 8, and 9 used to prepare clusters are
related to each other by the isolobal analogy (Scheme 5).
(36) Burrows, A. D.; Mingos, D. M. P. Transition Met. Chem. 1993, 18,
129.
5860 Inorganic Chemistry, Vol. 45, No. 15, 2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
Inorganic Chemistry, Vol. 45, No. 15, 2006 5861

Croizat et al.
Scheme 6. Distance, h, between the Mo Atom and the Plane Defined
by the Carbonyl C Atoms
Because the Mo(π-ring)(CO)3 building block is a recurrent
entity in both the precursors and the products, a comparison
of its bonding mode in the clusters is justified. In all these
clusters, it adopts a bridging position toward a L f Pd-Pd
r L or L f Pt-Pt r L central fragment, which involves
the metal and the carbonyl ligands. Since a localized electron
count around the metal atoms cannot be performed in these
58e clusters, we will consider the whole bridging moiety
µ-[Mo(π-ring)(CO)3]-, as an anionic 18e moiety formally
donating 4 electrons to the L f Pd(I)-Pd(I) r L or L f
Pt(I)-Pt(I) r L (L f d9-d9 r L) central unit (L ) PEt3,
CO) in 3b, 6, 11, 15, 16, and 20. This is reminiscent of the
situation encountered in a number of complexes containing
a L f d9-d9 r L unit bridged by more conventional 4e
donor ligands (see Scheme 1). This provides the Mo and Pd
or Pt centers with their usual electron count of 18e and 16e,
respectively. In 12 and 13, the anionic bridging building
block µ-[Mo(π-ring)(CO)3]- donates six electrons to the
central Pd(I)-Pd(I) unit when the two additional electrons
given by the pendant functional group of the π-ring are taken
into account. The presence of five metal-metal bonds in all
these clusters is consistent with their VEC of 58. The
presence of isolobal Mo(π-ring)(CO)3 building blocks in the
Mo2Pd2 clusters facilitates a comparison of their orientation
toward the central d9-d9 entity.
Scheme 7. R ) (d2 - d1)/d1
0.1 e R e 0.6 ) semi-bridging carbonyl; R e 0.1 ) bridging carbonyl;
R g 0.6 ) terminal carbonyl.
in this work. The angle â indicates the orientation of this
fragment with respect to the metal core (Scheme 2). For the
palladium clusters 3b, 6, 11, and 15, its value ranges from
74.7(1) (for 3b) to 82.7(1)° (for 15). In platinum cluster 16
the value of â is 86.3(3)°, which is slightly larger than those
for 3b, 6, 11, and 15 and close to 90°. This indicates that 16
is more symmetrical than these other phosphine-substituted
clusters. These values are slightly smaller than in clusters
12, 13, and 20, in which there is no phosphine coordinated
to palladium or platinum (see below). The mean planes
defined by the carbon atoms of the ring and the carbon atoms
of the three carbonyls are almost parallel. The average value
of the angle, δ, between these two planes is 4.6(1)°, which
is close to the δ value of 1.95(10)° in 23 (see Table 1). This
is also consistent with a conservation of the whole Mo(π-
ring)(CO)3 building block, since the parallelism between
these two planes in the starting metalates is maintained in
the final geometries. The angle, γ, between the axis passing
through Cring and Csym and the M(2)M(2)′ axis (Scheme 2)
reflects the tilt of the Mo(π-ring)(CO)3 fragment with respect
to the d9-d9 axis. The average value of 86.40(2)° for 3b, 6,
11, 15, and 16 indicates a highly symmetrical structure. The
orientation of the Mo(π-ring)(CO)3 fragment with respect
to the d9-d9 unit determines the bonding mode of the
carbonyl ligands in the clusters. It results in two semi-doubly
bridging modes and one semi-triply bridging mode for the
CO ligands for 3b, 6, 11, and 15 and three semi-doubly
bridging carbonyls for 16. This is consistent with the values
of the asymmetry parameter, R (Scheme 7),38,39 ranging from
0.12 to 0.24. Consequently, the Mo-C(1)-O(1), Mo-C(2)-
O(2), and Mo-C(3)-O(3) angles, which are much smaller
than 180° (between 149.3(8) and 166.6(5)°), reflect the
interactions between the palladium or platinum atoms and
C(1)O(1), C(2)O(2), and C(3)O(3), respectively. The geom-
etry of the [Mo(π-ring)(CO)3] fragment in 3b, 6, 11, 15, and
16 is therefore best described as being of the three-legged
piano stool type.
In the three-legged piano stool-type metalate [Nn-Bu4]-
[Mo(η5-C5H5)(CO)3] (23),37 the Mo(CO)3 moiety is charac-
terized by an almost perfect C3 local symmetry axis, collinear
with the C5 axis Cring-Mo.
The three-legged piano stool environment observed in the
Mo(π-ring)(CO)3 building block is retained in 3b, 6,2 11,
15, and 16 but with a marked increase of the C-Mo-C
angles corresponding to an opening of the “umbrella” formed
by the three carbonyl ligands, which allows the Mo center
to interact with both Pd or Pt atoms in an almost symmetrical
fashion. The Mo-M(2) and the Mo-M(2)′ bonds are
situated inside the cone defined by the three carbonyl legs
of the piano stool. The average sum of the C(1)-Mo-C(2),
C(1)-Mo-C(3), and C(2)-Mo-C(3) angles for these clusters
(304(2)°) is much larger than the value calculated for 23
(264.2°). Consistently, the shortest average distance, h
(Scheme 6), between the molybdenum atom and the plane
defined by the carbon atoms of the three carbonyls is 0.88-
(1) Å against 1.14(1) Å in 23.
Two geometrical parameters, â and γ, have been chosen
to describe and compare the orientation of the whole bridging
fragment, µ-[Mo(π-ring)(CO)3], with respect to the metal
core and the central d9-d9 axis in all the clusters described
For clusters 4, 12, and 13, the orientation of the M(1)(π-
ring)(CO)3 (M(1) ) Mo, Re) fragment with respect to the
(38) Klingler, R. J.; Butler, W. M.; Curtis, M. D. J. Am. Chem. Soc. 1978,
100, 5034.
(39) Curtis, M. D.; Butler, W. M. J. Organomet. Chem. 1978, 155, 131.
(37) Crotty, D. E.; Corey, E. R.; Anderson, T. J.; Glick, M. D.; Oliver, J.
P. Inorg. Chem. 1977, 16, 920.
5862 Inorganic Chemistry, Vol. 45, No. 15, 2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
d9-d9 axis is very different from that in 3b, 6, 11, 15, and
16 because of the interaction of the π-ring, or its substituent,
with palladium. This is best illustrated by a decrease of the
γ angle (between 68.33(4) and 74.72(2)° for 4, 12, and 13
versus 85.14(3) and 87.19(1)° for 3b, 6, 11, 15, and 16).
There is an opening of the “umbrella” formed by the three
carbonyl ligands, as observed in clusters 3b, 6, 11, 15, and
16. Consistently, the distance h in clusters 12 and 13 is 1.08-
(1) Å (versus 1.14(1) Å in 23; Scheme 6 and Table 1).
Contrary to the observation made for 3b, 6, 11, 15, and 16,
the three-legged piano stool environment in the M(1)(π-ring)-
(CO)3 building block is not retained in 4, 12, and 13. The
M(1)-Pd′ bond is situated inside the cone defined by the
three carbonyls legs of the piano stool, whereas the M(1)-
Pd bond is situated outside the cone. This confers to these
M(1) atoms a four-legged piano stool environment formed
by the carbonyls and the Pd atom. The orientation of the
M(1)-Cring axis, with respect to the Pd-Pd bond, confers a
semi-doubly bridging bonding mode to two of the carbonyls
and a terminal position to the third carbonyl. As a conse-
quence, the M(1)-C(1)-O(1) and M(1)-C(2)-O(2) angles
are smaller than 180° (between 161(1) and 163.7(5)°), sign
of interactions between the palladium atoms and C(1)O(1)
and C(2)O(2), respectively. Moreover, the R parameter
(Scheme 4) for C(1)O(1) and C(2)O(2), between 0.11 and
0.15, is consistent with their semi-doubly bridging bonding
mode in 4 and 12. For 13, R is smaller than 0.1 for both
carbonyls (0.08 and 0.09), consistent with their doubly
bridging bonding mode. The geometry of the M(1)(π-ring)-
(CO)3 fragment in 4, 12, and 13 is therefore best described
as being of the four-legged piano stool type.
Conclusion
In this work, we have provided an overview of the bonding
behavior of isolobal tricarbonylmetalates building blocks
containing boratanaphthalene (5a and 5b), boratabenzene (8),
and cyclopentadienyl (7 and 9) π-bonded ligands, toward a
central dinuclear d9-d9 fragment in the 58 CVE tetranuclear
clusters 3b, 6, 11, 12, 13, 15, 16, and 20. These relationships
are summarized in Scheme 5 which shows some obvious
similarities but also significant differences between the
structures of the resulting heterotetranuclear clusters. Similar
to cluster 3b, the new clusters 11, 15, 16, and 20 contain a
substituted cyclopentadienyl ring, whose pendant functional
group does not interact with the neighboring palladium or
platinum centers, even with the good electron-donor amino
group. Each Mo(π-ring)(CO)3 building block behaves as an
anionic 4-electron donor toward the central d9-d9 fragment,
and the coordination sphere around the palladium or platinum
is completed by phosphine (11, 15, and 16) or carbonyl
ligands (20). The amino-boratanaphthalene ring in cluster
12 is connected to the palladium through the π-system of
the aromatic ligand and not through the amino group,
whereas in 13, the coordination of the amino-boratabenzene
group with palladium takes place through a 2e-3c B-N-
Pd interaction. In 12 and 13, each 18e anionic [Mo(π-ring)-
(CO)3]- structural entity brings 4 electrons to the central d9-
d9 fragment and two additional electrons through the
coordination of the functional group of the π-ring with
palladium. Geometry differences have been observed and
discussed for this family of heterometallic clusters, dependent
on the presence or absence of coordination between the
π-ring and the d9 center.
Under similar reaction conditions, the isolobal boratanaph-
thalene-, boratabenzene-, and cyclopentadienyl-containing
metalates lead to similar tetranuclear triangulated clusters.
Except in the case of the boratanaphthalene cluster 6, of
which the geometry is very similar to that of the Cp-
containing clusters (3b, 11, 15, 16, and 20), the presence of
a boron atom in the π-bonded ligand tends to result in
additional ligand interactions with the adjacent metal center
(12 and 13). Related coordination modes with the Cp-
containing metalloligands were not found.
These studies, aimed at a systematic comparison between
organometallic building blocks used in heterometallic cluster
synthesis, provide a better understanding of the relationship
between the cluster total electron count, the nature of the
building blocks, and the molecular structures. When the
applications of the planar M2Pd2 clusters in homogeneous
catalysis (hydrogenation of alkenes and alkynes, oligomer-
ization of butadiene, photochemical hydrosilations of alkenes,
and very recently, cross-coupling reactions of aryl halides
and triflates with 13-metal alkylating reagents)40-42 and in
heterogeneous catalysis (carbonylation of organic nitro
Although the metal core of cluster 20 is similar to that of
3b, 6, 11, 15, and 16, the orientation of the Mo(π-ring)-
(CO)3 fragment with respect to the d9-d9 axis (Pt-Pt) (γ )
75.87(1)°) is intermediate between that in 3b, 6, 11, 15, and
16 (γ average value of 86.40(2)) and that in 4, 12, and 13
(γ average value of 70.68(2)°). Such differences in orienta-
tion appear to be associated to the value of the L-Pd-Pd
or L-Pt-Pt angle, which is itself function of the steric bulk
of L. The reasons for a value of only 160.0(2)° in 20 are not
clear at this point. The π-ring mean plane in 20 is almost
orthogonal to the metal plane (â ) 89.7(2)°). The opening
of the umbrella formed by the carbonyls is also observed
for this cluster, and the distance h in this case is 1.02(1) Å,
which is close to the values reported for clusters 4, 12, and
13. The orientation of the Mo-Cring axis, with respect to
the Pt-Pt bond, results in two semi-doubly bridging and one
terminal carbonyls. As a consequence, the angles Mo-C(1)-
O(1) (167.6(6)°) and Mo-C(2)-O(2) (163.7(6)°) are smaller
than 180°, and the values of the parameter R (Scheme 4),
0.22 for C(1)O(1) and 0.14 for C(2)O(2), are consistent with
their semi-doubly bridging bonding mode. In 20, the
geometry around the molybdenum is best described as a four-
legged piano stool, similar to the geometries observed for
4, 12, and 13.
(40) Braunstein, P.; Rose´, J. In Metal Clusters in Chemistry; Braunstein,
P., Oro, L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, Germany,
1999; Vol. 2, p 616.
(41) Pittman, C. U., Jr.; Honnick, W.; Absi-Halabi, M. m.; Richmond, M.
G.; Bender, R.; Braunstein, P. J. Mol. Catal. 1985, 32, 177.
(42) Shenglof, M.; Molander, G. A.; Blum, J. Synthesis 2006, 1, 111.
Inorganic Chemistry, Vol. 45, No. 15, 2006 5863

Croizat et al.
was stirred for 0.5 h at -78 °C. The mixture was evaporated to
dryness at room temperature; meanwhile, it became dark brown.
The black residue was chromatographed on an alumina column.
Elution with toluene gave a red compound, which was crystallized
from toluene/pentane and identified as [Mo(η5-C5H4Ph)(CO)3]2 (10)
(0.28 g, 0.44 mmol, 41%). It has been characterized by IR, X-ray
crystallography, and elemental analysis. Anal. Calcd for C28H18-
Mo2O6: C, 52.36; H, 2.82. Found: C, 52.55 H, 2.95%. IR (KBr):
ν(CO) 1950s, 1920sh, 1899sh, 1886s cm-1. IR (CH2Cl2): ν(CO)
2012w, 1958s, 1912br m cm-1. Further elution with toluene and
THF produced no other compounds leaving an important amount
of dark residue on the top of the column.
derivatives into isocyanates, catalytic reduction of NO, and
olefin hydrogenation)40,43-47 are considered, the new related
clusters described in this work may also reveal an interesting
potential for applications.
Experimental Section
General Procedures. Reactions were carried out under a nitrogen
atmosphere using conventional Schlenk techniques. Solvents were
dried according to standard procedures. Elemental analyses were
performed by the Service de Microanalyses, Universite´ Louis
Pasteur, Strasbourg, France.
NMR spectra were recorded on a Bruker Avance 400 (11B,
128.34 MHz; 15N, 40.56 MHz) and a Bruker Avance 300 (1H, 300
MHz; 13C{1H}, 75.47 MHz; 31P{1H}, 121.49 MHz). Chemical shifts
(in ppm) were measured at ambient temperature and are referenced
to external TMS for 1H and 13C, NaBH4 for 11B, H3PO4 (84%) for
31P, and DMF for 15N. The spectra were measured at 298 K.
Preparation of [Mo2Pd2(η5-C5H4Ph)2(CO)6(PEt3)2] (11). Method
A. Solid trans-[PdCl2(PEt3)2] (0.50 g, 1.21 mmol) was added to a
stirred solution of Na‚7‚2DME (1.27 g, 2.42 mmol) in toluene (50
mL) at room temperature. The solution turned dark blue im-
mediately, stirring was maintained for 1 h, and the solvent was
evaporated to dryness. The black residue was chromatographed on
a alumina column. Elution with toluene/pentane (1:1) gave a red
compound identified by IR as 10. Elution with toluene afforded a
dark-blue compound, recrystallized from toluene/pentane and
identified as [Mo2Pd2(η5-C5H4Ph)2(CO)6(PEt3)2] (11) (0.28 g, 0.26
1
1
Assignments are based on APT and DEPT spectra and H, H-
COSY, and 1H,13C-HMQC experiments. The IR spectra were
recorded in the region of 4000-400 cm-1 on a FT-IR IFS66 Bruker
spectrometer. ESI mass spectra were recorded on an Bruker
micrOTOF mass spectrometer.
1
mmol, 43% based on Pd). It has been characterized by IR, H,
The following compounds were synthesized according to litera-
ture procedures or improved syntheses: C5H5Ph,23 trans-[PdCl2-
(NCPh)2],48 [Pd2(NCMe)6](BF4)2,24 trans-[PdCl2(PEt3)2],48 trans-
[PtCl2(PEt3)2],48 [Pt(CNt-Bu)4](PF6)2,49 [Pd2(dba)3]‚CHCl3, trans-
[PtCl2(NCPh)2],48 Li[Mo(η5-2,4-MeC9H6BNi-Pr2)(CO)3],2 Li[Mo(η5-
C5H4NMe2)(CO)3],27 and Li[Mo(η5-C5H3Me2BNi-Pr2)(CO)3].27
Preparation of Na[Mo(η5-C5H4Ph)(CO)3]‚2DME (7). Freshly
distilled phenylcyclopentadiene (2.50 g, 17.6 mmol) was dissolved
into 100 mL of dry ice-cold THF and added slowly to a stirred
suspension of an excess of sodium hydride (0.50 g, 20.8 mmol) in
50 mL THF kept at -78 °C. This solution was stirred at -30 °C
until disappearance of the hydrogen bubbles. The mixture was
filtered through Celite, giving a light orange solution of Na(C5H4-
Ph). Solid [Mo(CO)6] (4.64 g, 17.6 mmol) was added to this
solution, and the mixture was kept at reflux overnight, cooled to
room temperature, concentrated to 50 mL, and precipitated by the
addition of cold pentane (200 mL). The supernatant was removed
by filtration, leaving a brown powder which was washed twice with
pentane (50 mL) and dried in vacuo for 4 h. Yield of Na‚7‚
(2DME): 6.62 g, 72% (12.6 mmol). The product is sensitive to air
and humidity, insoluble in hexane and pentane and soluble in THF.
It has been characterized by IR spectroscopy. IR (DME): ν(CO)
13C{1H}, and 31P{1H} NMR, X-ray crystallography, and elemental
analysis. Anal. Calcd. for C40H48Mo2O6P2Pd2: C, 44.02; H, 4.43.
Found: C, 43.78; H, 4.06%. IR (KBr): ν(CO) 1840s, 1807m,
1793sh, 1761m cm-1. IR (CH2Cl2): ν(CO) 1832s, 1795sh, 1775m
1
cm-1. H NMR(CD2Cl2): δ 7.44-7.16 (m, 10H, C6H5), AA′XX′
spin system 5.64 and 5.27 (2 pseudotriplets, 8H, Cp), 1.49 (m, 12H,
PCH2CH3), 0.81 (m, 18H, PCH2CH3). 13C{1H} NMR (CD2Cl2): δ
241.6 (CO), 133.7-125.9 (Ph), 109.3 (1-C, π-C5H4), 90.3 (2-C,
1
π-C5H4) 89.1 (3-C, π-C5H4), 16.9 (virtual t, PCH2CH3, | J(PC) +
4J(PC)| ) 20 Hz), 8.2 (s, PCH2CH3). 31P{1H} NMR (CD2Cl2): δ
20.9.
Method B. Solid [Pd2(NCMe)6](BF4)2 (0.38 g, 0.60 mmol) was
added to a stirred solution of Na‚7‚2DME (0.66 g, 1.25 mmol) in
toluene (50 mL) cooled with dry ice (-78 °C). The solution turned
dark blue within 1 h, and PEt3 (180 µl, 1.22 mmol) was added to
the cold mixture. The solution turned dark violet immediately; it
was stirred for 15 min and filtered through a Celite pad until the
solution was light blue. The solution was concentrated, and the
dark crystals obtained from pentane were identified as 11 (0.59 g,
0.54 mmol, 90% based on Pd).
Preparation of [Mo2Pd2(η5-2,4-MeC9H6BNi-Pr2)2(CO)6] (12).
Solid [Pd2(NCMe)6](BF4)2 (0.63 g, 1.0 mmol) was added to a stirred
solution of Li‚5b‚2DME (1.21 g, 2.0 mmol) in toluene (50 mL)
cooled with dry ice (-78 °C). The solution turned dark blue; then
it was stirred for 1 h and filtered through a Celite pad which had
been prewashed with toluene. The solution was concentrated and
chromatographed on an alumina column. Elution with toluene/
pentane (1:1) produced two close bands. First, a violet band gave
the meso (R,S) diastereoisomer, identified notably by single-crystal
X-ray diffraction as 12 (0.32 g, 0.30 mmol, 30% based on Pd).
Anal. Calcd for C38H46B2Mo2N2O6Pd2: C, 43.34; H, 4.40; N, 2.66.
Found: C, 43.08; H, 4.16; N, 2.94%. IR (CH2Cl2): ν(CO) 1961s,
1880w, 1842s cm-1. Clear NMR spectra could not be successfully
recorded because of the presence of paramagnetic residues. The
second, a dark blue band, has been identified only by IR since the
1898s, 1792s, 1755m cm-1
.
Reaction of Na‚7‚2DME with trans-[PdCl2(NCPh)2] and
Formation of [Mo(η5-C5H4Ph)(CO)3]2 (10). Solid trans-[PdCl2-
(NCPh)2] (0.41 g, 1.08 mmol) was added to a stirred solution of
Na‚7‚2DME (1.13 g, 2.15 mmol) in toluene (50 mL) cooled with
dry ice (-78 °C). The solution immediately turned dark blue and
(43) Braunstein, P.; Bender, R.; Kervennal, J. Organometallics 1982, 1,
1236.
(44) Kawi, S.; Alexeev, O.; Shelef, M.; Gates, B. C. J. Phys. Chem. B
1995, 99, 6926.
(45) Hoost, T. E.; Graham, G. W.; Shelef, M.; Alexeev, O.; Gates, B. C.
Catal. Lett. 1996, 38, 57.
(46) Kervennal, J.; Cognion, J.-M.; Braunstein, P. French Patent 2 515 640,
1981; U.S. Patent 4478,757, 1982; Chem. Abstr. 1982, 99, 139487.
(47) Carrion, M. C.; Manzano, B. R.; Jalon, F. A.; Maireles-Torres, P.;
Rodriguez-Castellon, E.; Jimenez-Lopez, A. J. Mol. Catal. A 2006,
252, 31.
1
compound decomposed quickly, and H NMR spectra could not
(48) Hartley, F. R. Organomet. Chem. ReV. A 1970, 6, 119.
(49) Lai, S.-W.; Chan, M. C. W.; Wang, Y.; Lam, H. W.; Peng, S. M.;
Che, C. M. J. Organomet. Chem. 2001, 617-618, 133.
be successfully recorded. IR (CH2Cl2): ν(CO) 1935s, 1877sh, 1845s
cm-1
.
5864 Inorganic Chemistry, Vol. 45, No. 15, 2006

Cyclopentadienyl Ligands and Boron-Containing Analogues
Preparation of [Mo2Pd2(η5-3,5-Me2C5H3BNi-Pr2)2(CO)6] (13).
Method A. Solid trans-[PdCl2(NCPh)2] (0.23 g, 0.61 mmol) was
added to a stirred solution of Li‚8‚2DME (0.74 g, 1.23 mmol) in
toluene (30 mL) cooled with dry ice (-78 °C). The solution
immediately turned dark blue; then it was stirred for 1 h and
evaporated to dryness. The black residue was chromatographed on
an alumina column. Elution with toluene gave a dark blue
compound, which was recrystallized from toluene/pentane and
identified as [Mo2Pd2(η5-3,5-Me2C5H3BNi-Pr2)2(CO)6] (13) (0.13
g, 0.13 mmol, 43% based on Pd). It has been characterized by IR,
1H, 11B, and 15N (inverse detection) NMR, X-ray crystallography,
and elemental analysis. Anal. Calcd for C32H46B2Mo2N2O6Pd2: C,
39.18; H, 4.73. Found: C, 39.47; H, 4.82%. IR (KBr): ν(CO)
Table 2. Crystallographic Data, Data Collection Parameters, and
Refinement Results
10
11
12
13
formula
C
28H18Mo2O6
C
40H48Mo2- C38H46B2Mo2- C32H46B2 -
O6P2Pd2 N2O6Pd2 Mo2N2O6Pd2
1091.40 1053.07 981.01
orthorhombic monoclinic triclinic
fw
642.30
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
monoclinic
P21/n
Pbca
P21/c
P1h
7.577(5)
12.608(5)
25.024(5)
90.00
90.00
90.00
10.9789(10) 8.833(2)
14.453(2) 10.101(4)
13.274(2) 12.733(5)
90.00
105.73(5) 89.467(5)
90.00 67.042(5)
2027.4(7) 1007.5(6)
8.352(5)
20.035(5)
10.811(5)
90.00
75.444(5)
103.05(5)
90.00
2390.6(19)
4
1762.3(14)
2
2
1
1
1922s, 1850s cm-1. IR (CH2Cl2): ν(CO) 1925s, 1841s cm-1. H
cryst size (mm3) 0.08 × 0.07 0.10 × 0.09 0.11 × 0.10 0.08 × 0.07
NMR (CD2Cl2): δ 5.82 (br s (couplings have not been observed),
× 0.06
red
1.785
1.092
173(2)
1272
× 0.08
violet
1.788
1.600
173(2)
1084
× 0.09
green
× 0.06
green
color
2H, 4-H), 4.23 (br s (couplings have not been observed), 4H, 2-/
D
calcd (g cm-3
)
1.736
1.532
173(2)
522
1.849
1.744
173(2)
972
3
6-H), 3.62 (sept, J ) 6.6 Hz, 4H, NCH), 2.10 (s, 12H, 3-/5-Me),
µ (mm-1
T (K)
F(000)
)
1.41 (d, 3J ) 6.6 Hz, Me-iPr), 1.33 (d, 3J ) 6.6 Hz, Me-iPr). 11B-
{1H} NMR: δ 48.72. 15N NMR (inverse detection): δ -308.5.
Method B. Solid [Pd2(NCMe)6](BF4)2 (0.39 g, 0.62 mmol) was
added to a stirred solution of Li‚8‚2DME (0.74 g, 1.23 mmol) in
toluene (30 mL) cooled with dry ice (-78 °C). The solution turned
dark blue; then it was stirred for 1 h and then filtered through a
Celite pad. The solution was concentrated and crystallized from
pentane to obtain dark crystals of 13 (0.54 g, 0.55 mmol, 89% based
on Pd).
Θ limits (deg)
no. of data
measured
no. of data
(I > 2σ(I))
no. of params
R1
2.29/27.47
2732
2.39/29.95 3.15/33.16
2.81/50.44
18 127
5865
7646
1771
3259
5167
12226
163
235
251
208
0.0271
0.0719
0.672
0.0866
0.1087
1.100
1.125/
0.0516
0.1207
0.929
0.973/
0.0444
0.1410
1.078
1.166/
-1.504
wR2
GOF
max/min residual 0.690/
Preparation of [Mo2Pd2(η5-C5H4NMe2)2(CO)6(PEt3)2] (15). A
suspension of [Pd2(NCMe)6][BF4]2 (0.21 g, 0.33 mmol) in THF (5
mL) was added to a stirred solution of Li‚9‚2DME (0.31 g, 0.66
mmol) in THF (20 mL) at -78 °C. The solution immediately turned
dark blue. Triethylphosphine (98 µl, 0.66 mmol, d ) 0.802) was
added to the solution, which then turned violet. Under constant
stirring, the temperature was slowly increased to room temperature
in 3 h. The resulting dark violet mixture was evaporated to dryness,
washed with pentane, and purified by crystallization from a CH2-
Cl2/heptane mixture. Dark violet crystals of 15 were obtained and
characterized by single-crystal X-ray diffraction. Purification by
column chromatography (silica gel pretreated with NEt3, toluene,
and then THF/pentane) led to lower yields because of the retention
of the cluster on the support. Yield: 0.14 g, 41% based on Pd after
recrystallization from CH2Cl2/heptane. It has been characterized
by IR, 1H, 31P, and 13C NMR, X-ray crystallography, electrospray
mass spectrometry, and elemental analysis. Anal. Calcd for C32H50-
Mo2N2O6P2Pd2: C, 37.48; H, 4.91; N, 2.73. Found: C, 37.26; H,
density (e Å-3
)
-0.946
-1.559
-1.818
15
16
20
formula
C
32H50Mo2-
C
32H50Mo2N2-
O6P2Pt2
C
22H20Mo2N2-
N2O6P2Pd2
O8Pt2
fw
1025.36
triclinic
P1h
1202.74
triclinic
P1h
1022.46
triclinic
P1h
cryst syst
space group
a (Å)
b (Å)
c (Å)
9.208(1)
9.938(1)
11.061(1)
106.08(5)
99.15(5)
102.49(5)
923.35(16)
1
0.12 × 0.10
× 0.08
violet
1.844
1.752
8.9590(10)
10.1280(10)
11.0770(10)
108.28(5)
97.83(5)
101.97(5)
911.43(16)
1
0.07 × 0.07
× 0.07
violet
2.191
8.454
8.1580(2)
8.6250(3)
9.9960(3)
78.1200(15)
67.7900(12)
74.370(2)
622.80(3)
1
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
cryst size (mm3)
0.09 × 0.09
× 0.09
color
orange
D
calcd (g cm-3
)
2.726
12.229
173(2)
470
µ (mm-1
T (K)
)
173(2)
510
173(2)
574
F(000)
4.84, N, 2.58%. IR (KBr): ν(CO) 1875vw, 1826vs, 1750s cm-1
.
Θ limits (deg)
no. of data measured
no. of data (I > 2σ(I))
no. of params
R1
2.33/30.05
5185
4039
3.26/30.18
5286
4338
208
0.0623
2.22/30.06
3650
2911
163
0.0420
1H NMR (C6D6): δ AA′MM′ system 4.88 and 4.37 (2 pseudo-
triplets, 8H, Cp), 2.36 (s, 12H, NMe2), 1.71 (m, 12H, PCH2), 0.99
(m, 18H, PCH2CH3). 13C{1H} NMR (C6D6): δ 242.9 (CO), 83.2
208
0.0355
0.1016
1.044
1
(Cp), 70.3 (Cp), 39.7 (CpNMe2), 17.2 (virtual t, PCH2CH3, | J(PC)
wR2
GOF
0.1465
1.050
0.0961
0.982
+ 4J(PC)| ) 20 Hz), 8.1 (s, PCH2CH3) (Cipso was not observed).31P-
{1H} NMR (C6D6): δ 18.9. MS (ES): m/z (Irel) 1287 (M+- 2CO,
50%).
max/min residual
1.053/-1.480
2.228/-2.855
2.509/-3.237
density (e Å-3
)
Preparation of [Mo2Pt2(η5-C5H4NMe2)2(CO)6(PEt3)2] (16). A
suspension of trans-[PtCl2(PEt3)2] (0.28 g, 0.56 mmol) in THF (10
mL) was added to a stirred solution of Li‚9‚2DME (0.53 g, 1.12
mmol) in THF (20 mL) at room temperature. After it was stirred
for 2 h, the mixture was filtered, and the solvent was removed in
vacuo. The residue was chromatographed on an alumina column.
Elution with toluene gave a red solution of 14 (trace amount),
followed by an orange solution (trace amount) which was not
identified. Cluster 14 was identified by IR spectroscopy and by
comparison with the corresponding compound with the Cp ligand
in place of CpNMe2. Elution with a THF/pentane mixture (1:5)
gave a violet solution of 16 (0.026 g, 0.022 mmol). Violet crystals
were obtained from THF/pentane. Yield: 8%. It has been character-
ized by IR, 1H and 31P NMR, X-ray crystallography, and elemental
analysis. Anal. Calcd for C32H50Mo2N2O6P2Pt2: C, 31.96; H, 4.19;
N, 2.33. Found: C, 31.21; H, 4.01; N, 2.30%. IR (KBr): ν(CO)
1
1832sh, 1798s, 1706s br cm-1. H NMR (CDCl3): δ AA′MM′
system 4.97 and 4.43 (2 pseudo triplets, 8H, Cp), 2.63 (s, 12H,
Me), 1.88 (m, 12H, PCH2), 0.99 (m, 18H, PCH2CH3). 31P{1H}
NMR (CDCl3): δ 39.0 (s with 195Pt satellites, 1J(PtP) ) 4323 Hz).
Preparation of [PdPt(CNt-Bu)6](PF6-)2 (17). [Pd2(dba)3]‚CHCl3
(0.24 g, 0.23 mmol) in CH2Cl2 (20 mL) and t-BuNC (0.076 g, 104
Inorganic Chemistry, Vol. 45, No. 15, 2006 5865

Croizat et al.
µl, d ) 0.735, 0.92 mmol) were added to a solution of [Pt(CNt-
Bu)4](PF6)2 (0.37 g, 0.46 mmol) in CH3CN (20 mL). After the
reaction mixture was stirred for 1 h, the yellow solution was
evaporated under reduced pressure, and a yellow solid 17 was
precipitated with ether (100 mL), filtered, and washed with ether
parameters. The hydrogen atoms were included in their calculated
positions and refined with a riding model in SHELXL97.
Acknowledgment. Dedicated to Prof. F. Mathey on the
occasion of his 65th birthday, with our warmest wishes. The
work was supported by the Ministery of Research (PhD
grants to N.A. and P.C.), the CNRS and the Franco-German
Research Training Group (GRK 532 of the DFG). We are
grateful to Prof. G. E. Herberich (Aachen, German) for
samples of Li[Mo(η5-C5H3Me2BNi-Pr2)(CO)3] and Li[Mo-
(η5-2,4-MeC9H6BNi-Pr2)(CO)3] and to Dr. A. DeCian for the
collection of the X-ray data.
1
(3 × 10 mL) (0.47 g, 94%). It has been characterized by IR, H
NMR, and elemental analysis. Anal. Calcd for C30H54F12N6P2-
PdPt: C, 33.05; H, 4.99; N, 7.71. Found: C, 33.32; H, 4.94; N,
8.03%. IR (KBr): ν(NC) 2202 vs. 1H NMR (CD3CN): δ 1.62 (s),
1.57 (s).
Crystal Structure Determinations. The data collections were
performed on a Nonius Kappa-CCD area detector diffractometer
(Mo KR, λ ) 0.71070 Å, æ scan). The relevant data are summarized
in Table 2. The cell parameters were determined from reflections
taken from one set of 10 frames (1.0° steps in æ angle), each at a
20 s exposure. The structures were solved using direct methods
(SHELXS97) and refined against F2 using the SHELXL97 software.
The absorption was corrected empirically (with Sortav) for the area-
detector data. All non-hydrogen atoms were refined with anisotropic
Supporting Information Available: X-ray crystallographic files
in CIF format and ORTEP views of the structures. This material is
available free of charge via the Internet at http://pubs.acs.org.
Crystallographic data can be obtained from the Cambridge Crystal-
lographic Data Centre (CCDC606696-606702).
IC060318D
5866 Inorganic Chemistry, Vol. 45, No. 15, 2006