Heterometallic complexes and clusters with 2-boratanaphthalene ligands

Article abstract of DOI:10.1039/b101556g

The new lithium (2-boratanaphthalene)tricarbonylmolybdates Li[Mo(RBn)(CO)₃] (Bn = η⁵-C₁₀H₉B; R = NiPr₂, Me) have been prepared and used as nucleophilic reagents for the synthesis of metal-metal bonded complexes and clusters. Dinuclear [(iPr₂NBn)(OC)₃Mo-An(PPh₃)] (7) and trinuclear [Hg{Mo(CO)₃(iPr₂NBn)}₂] (9) and [Ag{Mo(CO)₃(iPr₂NBn)}{Mo(CO)₃[(iPr₂H N)Bn]}] (13) chain complexes have been obtained in which the metalate behaves as an anionic two-electron donor metalloligand. In 13, the other metal carbonyl fragment consists of an N-protonated (2-boratanaphthalene)tricarbonylmolybdenum fragment and acts therefore as a neutral, two-electron donor. In the 58-cluster valence electron planar, triangulated cluster [Mo₂Pd₂(MeBn)₂(CO)₆(PEt₃) ₂] (15), the [Mo(MeBn)(CO)₃]^- fragment is however best viewed as a four-electron donor metalloligand bridging the Pd-Pd bond. These bonding situations are compared with those observed in complexes prepared from the metalate [MoCp(CO)₃]^- (Cp = η⁵-C₅H₅) and this establishes experimentally the isoelectronic and isolobal character of the [Mo(MeBn)(CO)₃]^- and [MoCp(CO)₃]^- fragments. The crystal structures of complexes 7, 9, 13 and 15 have been determined by X-ray diffraction.

Full text of DOI:10.1039/b101556g

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Heterometallic complexes and clusters with 2-boratanaphthalene
ligands†
Pierre Braunstein,*a Elisabeth Curaa and Gerhard E. Herberichb
a Laboratoire de Chimie de Coordination, UMR 7513 CNRS, Université Louis Pasteur,
4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France. E-mail: braunst@chimie.u-strasbg.fr
b Institut für Anorganische Chemie der Rheinisch-Westfälischen Technischen Hochschule,
Professor-Pirlet-Straße 1, D-52056 Aachen, Germany
Received 16th February 2001, Accepted 23rd March 2001
First published as an Advance Article on the web 3rd May 2001
The new lithium (2-boratanaphthalene)tricarbonylmolybdates Li[Mo(RBn)(CO)3] (Bn = η5-C10H9B; R = NiPr2,
Me) have been prepared and used as nucleophilic reagents for the synthesis of metal–metal bonded complexes
and clusters. Dinuclear [(iPr2NBn)(OC)3Mo–Au(PPh3)] (7) and trinuclear [Hg{Mo(CO)3(iPr2NBn)}2] (9) and
[Ag{Mo(CO)3(iPr2NBn)}{Mo(CO)3[(iPr2HN)Bn]}] (13) chain complexes have been obtained in which the metalate
behaves as an anionic two-electron donor metalloligand. In 13, the other metal carbonyl fragment consists of an
N-protonated (2-boratanaphthalene)tricarbonylmolybdenum fragment and acts therefore as a neutral, two-electron
donor. In the 58-cluster valence electron planar, triangulated cluster [Mo2Pd2(MeBn)2(CO)6(PEt3)2] (15), the
[Mo(MeBn)(CO)3]Ϫ fragment is however best viewed as a four-electron donor metalloligand bridging the Pd–Pd
bond. These bonding situations are compared with those observed in complexes prepared from the metalate
[MoCp(CO)3]Ϫ (Cp = η5-C5H5) and this establishes experimentally the isoelectronic and isolobal character of
the [Mo(MeBn)(CO)3]Ϫ and [MoCp(CO)3]Ϫ fragments. The crystal structures of complexes 7, 9, 13 and 15
have been determined by X-ray diffraction.
In organometallic and coordination chemistry, the replacement
of a uninegative, 6π electron cyclopentadienyl ligand with a
dianionic 6π electron ligand may represent a way to obtain
compounds with similar reactivity but with beneficial reduced
Lewis acidity, a desirable feature in homogeneous Ziegler–
Natta olefin polymerization metallocene-type catalysis.1 This
can be achieved e.g. by taking advantage of the isolobal analogy
between CR and BRϪ. In a different context, the isolobal
analogy between the 6π electron borollide dianion (C4H4BR)2Ϫ
(R = Ph) and the cyclopentadienide ion (C5H5)Ϫ has been
recently used to compare the reactivity and bonding proper-
ties of isolobal metal-centred organometallic nucleophiles of
two adjacent columns of the Periodic classification, such as
[WCp(CO)3]Ϫ (1) and [Re(η5-C4H4BR)(CO)3]Ϫ (2).2,3
and bridge the Pd–Pd bond.5,6 A strict analogue of these
clusters does not exist in the borole series since despite its
planar, triangulated metal core, the cluster [Re2Pd2(C4H4-
BPh)2(CO)6] 4 contains only 54 CVE.3
This unusual cluster displays a unique bonding situation for
the borole ligand which not only binds to rhenium in the usual
η5 manner but also to the adjacent palladium via a 2e–3c
B–Cipso–Pd system. These intriguing similarities and differences
led us to extend our studies with borole-containing carbonyl-
metalates to [HFe(η5-C4H4BPh)(CO)2]Ϫ,2,7 [Fe(η5-C4H4BPh)-
(CO)2CN]Ϫ,8 and now to the 2-boratanaphthalene system. Its
boron-containing six-membered aromatic ring should behave
as a neutral five-electron donor, like the five-membered Cp
ligand and in contrast to the five-membered, four-electron
donor borole ligand. This would therefore open the possibility
to make further progress in the systematic comparison of the
behaviour of organometallic building blocks in metal cluster
chemistry9 since one could remain within the same column of
the Periodic classification to form a carbonylmetalate with a
boron-containing π-ligand that is isovalent to its Cp analogue.
In this work, we describe the synthesis of (2-boratanaph-
thalene)tricarbonylmolybdates and their use for the synthesis
of metal–metal bonded complexes to be compared to those
obtained in the Cp series.
This led inter alia to the synthesis of heterodinuclear com-
plexes with Re–Cu, Re–Ag, Re–Au or Re–Hg bonds in which
the borole-containing carbonylmetalate behaves as a terminal,
two-electron donor metalloligand. This bonding behaviour
is also commonly encountered with the cyclopentadienyl-
containing carbonylmetalates [MCp(CO)3]Ϫ (M = Cr, Mo or
W) in metal–metal bonded complexes.4 In the 58-cluster valence
electron (CVE), planar, triangulated clusters [M2Pd2Cp2(CO)6-
(PEt3)2] (M = Cr, 3a; M = Mo, 3b; M = W, 3c) however, the
latter metalates behave as four-electron donor metalloligands
† Part of the PhD Thesis of E. C. Dedicated to Professor Antonio
Tiripicchio on the occasion of his 65th birthday, with our most sincere
congratulations and warmest wishes.
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J. Chem. Soc., Dalton Trans., 2001, 1754–1760
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b101556g

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Results and discussion
The DME-solvated lithium salts of the (2-boratanaphthalene)-
tricarbonylmolybdates 6a,b were prepared by reaction of
[Mo(CO)6] with the corresponding lithium 2-boratanaphthal-
enes 5a,b.10 The reaction was performed under reflux, using
conditions very similar to those described for the preparation
of Na[MoCp(CO)3)]ؒ2DME [eqn. (1)].11
(1)
Fig. 1 ORTEP view of the molecular structure of 7.
Table 1 Selected bond lengths (Å) and angles (Њ) for 7
Synthesis of heterometallic Mo–Au, Mo–Ag and Mo–Hg
complexes
Au–Mo
Au–P
Au–C19
C19–O1
C20–O2
C21–O3
B–N
2.7248(2)
2.2750(7)
2.485(3)
1.171(3)
1.153(3)
1.163(3)
1.422(4)
2.670(3)
2.379(2)
2.403(2)
2.438(3)
2.419(2)
2.462(2)
Mo–C19
B–C24
B–C25
1.980(2)
1.538(4)
1.566(4)
1.435(4)
1.447(4)
1.456(4)
1.402(4)
166.16(2)
171.5(2)
121.5(2)
123.9(2)
114.5(2)
The reaction of 6a with one equivalent of [AuCl(PPh3)] yielded
the air-stable, orange bimetallic complex [(OC)3(iPr2NBn)Mo–
Au(PPh3)] (7) (Scheme 1). Single crystals suitable for X-ray
C24–C23
C23–C22
C22–C26
C26–C25
Mo–Au–P
Mo–C19–O1
B–N–C32
B–N–C35
C32–N–C35
Mo–B
Mo–C24
Mo–C23
Mo–C22
Mo–C26
Mo–C25
bond is reflected in the distance of 1.422(4) Å,14 and in the
sum of the angles around N being equal to 359.9Њ. A similar
situation was also encountered in the free ligand 5a.10 The B–N
moiety tends to deviate out of the ligand plane and be further
away from molybdenum. Thus, the boron-containing hetero-
cycle is bonded to Mo in a manner that is closer to η5.
It is interesting that despite the isolobal analogy between
[Au(PPh3)]ϩ and Hϩ, their reactions with 6a and [MoCp(CO)3]Ϫ
give very different products. Protonation of 6a (HCl in Et2O
solution at Ϫ80 ЊC or [HNEt3]Cl) did not afford the metal
hydride complex analogous to [HMoCp(CO)3]15 but led to
ligand protonation, metal decoordination and liberation of
8 (Scheme 1). In contrast, the chromium hydrido borole com-
plex [HCr(C5H5B–Me)(CO)3] has been obtained by reaction
of Na[Cr(C5H5B–Me)(CO)3] with Hϩ. This emphasizes the
influence of the substituent at boron (and that of the metal)
on the reactivity of the carbonylmetalate. The hydride [HCr-
(C5H5B–Me)(CO)3] has been reported as sensitive and unstable,
with a tendency to dimerize into [Cr(C5H5B–Me)(CO)3]2.16
The reaction of 6a with HgCl2 in a 2 : 1 ratio in toluene led to
the formation of two orange trinuclear complexes of formula
[Hg{Mo(iPr2NBn)(CO)3}2] (9) in the form of a 50 : 50 diastereo-
meric mixture (NMR spectroscopy) (Scheme 1). This results
from the racemic nature of the molybdenum salt 6a. The
reaction of 6a with excess HgCl2 or of 9 with HgCl2 led to
the heterodinuclear complex [(OC)3(iPr2NBn)MoHgCl] (10).
Recrystallization of the diastereomeric mixture 9 gave rod-like
single crystals which were analysed by X-ray diffraction. The
molecular structure possesses crystallographic centrosymmetry
and, in addition, displays disordered boratanaphthalene
ligands (Fig. 2). The disorder relates to the bonding of the
metal to the two enantiotopic faces of the planar chiral
boratanaphthalene and is illustrated for the meso isomer in
Scheme 2. Superposition of the two alternative dispositions
of the molecule produces apparent lateral symmetry of the
metal-to-ligand bonding. Note that this superposition may
equally well comprise the two racemic isomers. Selected bond
distances and angles are collected in Table 2.
Scheme 1 Reactions of the (2-boratanaphthalene)tricarbonylmolyb-
date 6a.
diffraction were obtained by slow diffusion of pentane in a
toluene solution. A view of the molecular structure is shown
in Fig. 1 and selected bond distances and angles are given in
Table 1.
The four-legged piano-stool geometry around the Mo centre
is as expected and the Mo–Au distance of 2.7248(2) Å com-
pares with that in [(OC)3(η5-C5H5)Mo–Au(PPh3)] [2.710(1) Å]12
or in [(OC)3(η5-C5H4CHO)Mo–Au(PPh3)] [2.7121(5) Å].13 The
carbonyl ligands are all terminal, including C(19)–O(1) which,
despite a slightly longer C–O distance [1.171(3) Å] is too
far from the Au centre [Au–C(19) = 2.485(3) Å] and makes an
Mo–C(19)–O(1) angle too wide [171.5(2)Њ] to be considered as
even semi-bridging. The double-bond character of the B–N
J. Chem. Soc., Dalton Trans., 2001, 1754–1760
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Table 2 Selected bond lengths (Å) and angles (Њ) for 9
Table 3 Selected bond lengths (Å) and angles (Њ) for 13
Mo–Hg
B1–N1
N1–C9
N1–C12
C1–O1
C2–O2
C3–O3
Mo1–C1
Mo1–C2
Mo1–C3
2.7483(9)
1.425(7)
1.470(8)
1.486(7)
1.140(8)
1.150(8)
1.130(8)
1.990(7)
1.967(6)
1.995(7)
Mo1–B
2.672(6)
2.380(6)
2.388(6)
2.406(6)
2.384(5)
2.401(5)
122.8(5)
115.2(4)
122.0(5)
Ag–Mo1
Ag–Mo2
Mo1–C8
Mo1–B1
B1–N1
Mo2–C27
Mo2–B2
B2–N2
2.8097(4)
2.8395(4)
2.425(3)
2.703(3)
1.437(4)
2.406(3)
2.502(3)
1.570(4)
1.0536
Mo1–Ag–Mo2
B1–N1–C14
B1–N1–C17
C14–N1–C17
B2–N2–C33
B2–N2–C36
C33–N2–C36
C33–N2–H01
C36–N2–H01
174.95(1)
121.8(3)
124.5(3)
113.5(2)
115.8(2)
112.8(2)
114.2(2)
97.25
Mo1–C4
Mo1–C5
Mo1–C6
Mo1–C7
Mo1–C8
B–N–C12
C9–N1–C12
B–N–C9
N2–H01
107.72
Fig. 2 ORTEP view of the molecular structure of 9. The carbon sites
C(18), C(19) and C(20), C(21) have occupancies of 0.5 due to disorder
(see also Scheme 2).
Fig. 3 ORTEP view of the molecular structure of 13.
Scheme 2 Two dispositions of the meso-isomer of 9 resulting in dis-
order in the crystal.
The mercury atom resides on an inversion centre and the
Mo–Hg distance of 2.7481(5) Å is similar to that found
in [Hg{MoCp(CO)3}2] (11a) [2.746(2) Å].17,18 In the latter
complex, the Hg atom is situated on a crystallographic C2 axis.
Similarly, the Re–Hg–Re complex 122 is centrosymmetric
whereas its isolobal analogue 11b processes a C2 axis.
However, its crystal structure was determined by X-ray diffrac-
tion and revealed features of sufficient interest to be reported.
If a metal chain Mo–Ag–Mo was indeed present, the complex
turned out to be neutral and not anionic, as originally antici-
pated. A view of the molecular structure is shown in Fig. 3 and
selected bond distances and angles are given in Table 3.
These differences can be explained on steric grounds since the
bulkier ligands in 9 and 12 prevent a molecular conformation
of the type encountered with the Cp analogues. As in 7, the
iPr2NBn ligand is coordinated in an η5 manner to Mo and the
B–N bond possesses double bond character. By analogy with
the reaction of HgCl2 with two equivalents of 6a, we expected
that a similar reaction with [AgOTf] would afford an anionic
Mo–Ag–Mo chain complex, as observed in the Cp series
with [Ag{MoCp(CO)3}2]Ϫ.19 The reaction turned out to be
more complicated than expected and a mixture was obtained
whose analysis by mass spectrometry suggested the presence of
oligomeric species (see Experimental section). In the course of
purification procedures, one of the complexes present, 13, was
obtained as single crystals from toluene–hexane. The quantity
of pure material was unfortunately too small to allow full
characterization by analytical and spectroscopic methods.
The two iPr2NBnMo fragments are chemically non-equiv-
alent and a proton is bound to N(2), which has clearly become
sp3 hybridized in contrast to N(1) which remains unchanged.
The B(2)–N(2) distance of 1.570(4) Å corresponds to a single
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J. Chem. Soc., Dalton Trans., 2001, 1754–1760

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(2)
yielded a dark green complex whose crystal structure could
Fig. 4 ORTEP view of the molecular structure of 15.
Table 4 Selected bond lengths (Å) and angles (Њ) for 15
be established by X-ray diffraction [eqn. (2)]. This first metal
cluster with a boratanaphthalene ligand, [Mo2Pd2(MeBn)2-
(CO)6(PEt3)2] (15), contains a planar triangulated metal core
with a centre of symmetry in the middle of the Pd–Pd bond.
Selected bond distances and angles are given in Table 4 and a
view of the molecule is shown in Fig. 4.
The Pd–PdЈ distance of 2.5955(4) Å is short relative to the
sum of the covalent radii (2.98 Å) or that in Pd metal (2.751 Å)
or in other complexes.5,28 It is however similar to that found
in the related cluster [Mo2Pd2Cp2(CO)6(PEt3)2] (3b) (2.582(1) Å)
which also contains a linear R3P←Pd–Pd→PR3 moiety bridged
by two MoCp(CO)3 fragments. The disposition of the carbonyl
ligands C(8)–O(2) and C(9)–O(3), which form asymmetric
bridges and C(7)–O(1), which is semi-triply bridging, is similar
to that in [Mo2Pd2Cp2(CO)6(PEt3)2]2. The Mo–Pd distances of
2.8815(4) and 2.8334(3) Å are in the range of those found for
this bond in other dinuclear and cluster complexes.5,29
With the hope of characterizing a 54 CVE cluster, with an
Mo2Pd2 core but no phosphine ligand, that would be related to
cluster 4, we reacted two equivalents of 6a with [PdCl2(NCPh)2]
in toluene. Although a major, deep-blue product displayed νCO
absorptions in KBr at 1956s, 1881m, 1841s, 1808w cmϪ1, it
could not be further characterized owing to decomposition and
formation of paramagnetic species.
Mo–Pd
Mo–Pd
Pd–PdЈ
Pd–P
2.8815(4)
2.8334(3)
2.5955(4)
2.358(1)
2.547(5)
2.409(4)
2.440(4)
2.446(4)
2.392(4)
2.353(4)
2.066(4)
1.972(4)
1.994(4)
2.442(4)
2.331(3)
2.409(4)
2.367(4)
C7–O1
C8–O2
C9–O3
B–C10
1.169(4)
1.183(5)
1.179(5)
1.517(6)
1.531(6)
1.400(5)
1.453(5)
1.442(6)
1.414(6)
1.577(7)
Mo–B
B–C14
Mo–C10
Mo–C11
Mo–C12
Mo–C13
Mo–C14
Mo–C7
Mo–C8
Mo–C9
Pd–C7
C10–C11
C11–C12
C12–C13
C13–C14
B–C15
Pd–Mo–PdЈ
Mo–Pd–MoЈ
P–Pd–PdЈ
Mo–C7–O1
Mo–C8–O2
Mo–C9–O3
54.01(1)
125.99(1)
176.75(3)
158.7(2)
166.3(3)
158.7(3)
PdЈ–C7
PdЈ–C8
Pd–C9
bond, as observed in amineboranes14,20 and is similar to that of
1.541(4) Å in the 2-pyridine-2-boratanaphthalene complexes 14
where the BC5 ring is hexahapto coordinated to the metal.21,22
Both 3b and 15 are 58 CVE butterfly-type clusters and the
deviation from the 62 CVE count expected on the basis of the
Wade–Mingos rules originates from the 16 electron rather than
18 electron count for the palladium centres. Note however that
a butterfly structure with five metal–metal bonds involving
these metals is not always observed with the 58 CVE count, as
exemplified by the spiked-triangular structure of [Mo2Pd2Cp-
(CO)6(dppe)] (16) whose composition differs from that of 3b
only by the nature of the phosphine ligands.30
Since the vacant orbital on boron is no longer stabilized
through π-bonding with nitrogen, the boron atom comes much
closer to the electron-rich molybdenum atom [Mo(2)–B(2) =
2.502(3) Å]. The heterocycle is now bonded to Mo in an η6
manner. The Mo(1)(iPr2NBn)(CO)3 fragment is, in contrast,
very similar to those in 7 and 9. Its N(1) atom has a trigonal
planar environment and the B(1)–N(1) distance of 1.437(4) Å
indicates a double bond character, with an η5 coordination of
the Bn ligand.
Complex 13 is best viewed as resulting from the combination
of the metalate [Mo(iPr2NBn)(CO)3]Ϫ with the Agϩ cation and
the coordination of the neutral two-electron donor fragment
[Mo(iPr2HNBn)(CO)3] whose HOMO is centred on the metal.
This fragment has never been isolated before and only observed
in 13 as a metalloligand. Note however that protonation of the
nitrogen atom of diisopropylaminoborole complexes was first
observed with Cr, Fe, Ru and Co and afforded stable salts with
no B–N bond dissociation.23 This was then extended to the case
of Zr, Hf 24,25 and Ta26,27 complexes.
Cluster 3b has been adequately described as containing a
[R3P→Pd–Pd←PR3]2ϩ d9–d9 unit bridged by two four-electron
donor [MoCp(CO)3]Ϫ metalates. This emphasized the relation-
ship between cluters 3 and phosphido-, allyl- or halide-bridged
dinuclear Pd() complexes.31 The crystal structures of 7, 9, 13
and 15 now experimentally establish that the terminal (two-
electron donor) or bridging (four-electron donor) bonding
modes observed previously with the metalloligand [MoCp-
Synthesis of the first boratanaphthalene metal cluster
The reaction of two equivalents of 6b with [PdCl2(PEt3)2]
J. Chem. Soc., Dalton Trans., 2001, 1754–1760
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(CO)3]Ϫ can be similarly extended to the isolobal and isovalent
anions of the type [Mo(RBn)(CO)3]Ϫ. Such relationships help
rationalize the synthesis and structures of transition metal
clusters.9
Hz, 1H, 7-H), 6.73 (ddd, J = 8.5, 6.4, 1.2 Hz, 1H, 6-H), 4.80
(d, 4J13 = 1.6 Hz, 1H, 3-H), 4.74 (d, 4J13 = 1.6 Hz, 1H, 1-H), 2.54
(s, 3H, 4-Me), 0.49 (s, 3H, BMe). DME: 3.43 (s, 4H, CH2), 3.27
(s, 6H, Me). 13C NMR (THF-d8): δ 230.7 (CO), 132.2 (C-8),
128.7 (C-5), 125.4 (C-7), 122.5, 117.7 and 104.1 (C-4, C-4a,
C-8a), 119.8 (C-6), 108.0 (br, C-3), 90.1 (br, C-1), 23.8 (4-Me),
2.2 (br, BMe). DME: 72.7 (CH2), 58.9 (Me). 11B NMR (THF-
d8): δ 24. IR (12-crown-4, DME): νCO = 1933s, 1911s, 1808m.
Lithium tricarbonyl(2-diisopropylamino-4-methyl-2-borata-
naphthalene)molybdate-bis(1,2-dimethoxyethane) Li[Mo(CO)3-
(iPr2NBn)]ؒ2DME (6a). In a similar manner to 6b, [Li(iPr2-
NBn)] (5a) (2.744 g, 11.1 mmol) was reacted with [Mo(CO)6]
(2.930 g, 11.1 mmol) to give Li[Mo(CO)3(iPr2NBn)]ؒ2DME
(6a). Yield: 5.90 g, 87%. 6a is a yellowish powder, insoluble in
pentane, slightly soluble in toluene and very soluble in DME
or THF. Anal. Calc. for C27H43BLiMoNO7: C, 53.40; H, 7.14;
N, 2.31. Found: C, 53.32; H, 6.96; N, 2.25. 1H NMR (THF-d8):
δ 7.55 (dd, J = 8.8, 0.6 Hz, 1H, 5-H), 7.02 (dd, J = 8.5, 0.6 Hz,
1H, 8-H), 6.76 (ddd, J = 8.5, 6.4, 1.2 Hz, 1H, 7-H), 6.53 (ddd,
J = 8.8, 6.4, 1.2 Hz, 1H, 6-H), 4.60 (d, 4J13 = 2.5 Hz, 1H, 3-H),
4.17 (d, 4J13 = 2.5 Hz, 1H, 1-H), 2.54 (s, 3H, 4-Me). NiPr2: 3.60
(m, 3J = 6.7 Hz, 2H, NCH), 1.22 and 1.20 (d, 3J = 6.8 Hz, 12H,
Me). DME: 3.42 (s, 4H, CH2), 3.27 (s, 6H, Me). 13C NMR
(THF-d8): δ 232.4 (CO), 132.7 (C-8), 129.0 (C-5), 125.2 (C-7),
124.2, 120.1 and 99.8 (C-4, C-4a, C-8a), 117.8 (C-6), 96.4 (br,
C-3), 74.3 (br, C-1), 24.6 (4-Me). NiPr2: 46.3 (NC), 23.2 and
23.1 (Me). DME: 72.7 (CH2), 58.9 (Me). 11B NMR (THF-d8):
δ 23. IR (12-crown-4, DME): νCO = 1904s, 1806s, 1790s.
Experimental
General procedures
All reactions were performed in standard Schlenk-type flasks
under nitrogen. Solvents were dried by conventional methods
and freshly distilled under nitrogen. Deuterated solvents for
NMR spectroscopy were degassed, dried and stored over
molecular sieves (4 Å Merck). The Kieselguhr was heated
overnight at 300 ЊC, cooled under vacuum and kept under N2.
Electron impact mass spectra were recorded on a Finnigan-
MAT 95 spectrometer with a nominal electron energy of 70 eV
(Aachen), or on a Fisons ZAB-HF (Strasbourg). Melting
points were determined in sealed capillaries on a Büchi 510
melting point apparatus and are uncorrected. Elemental
analyses were performed by the analytical laboratories of
Prof. H. Malissa and G. Reuter, D-51789 Lindlar, Germany,
of Prof. M. Veith, Universität des Saarlandes, D-66041
Saarbrücken, Germany and the Service Central de Micro-
analyses du CNRS, Institut de Chimie, F-67008 Strasbourg,
France. The NMR spectra were recorded on a Varian Unity
500 spectrometer (1H, 500 MHz; 13C{1H}, 126 MHz; 11B, 160
MHz), on a FT Bruker AC 300 spectrometer (1H, 300 MHz;
31P{1H}, 121 MHz), or on an FT Bruker 400 spectrometer
(13C{1H}, 100 MHz; 11B, 128 MHz). Chemical shifts are given
in ppm; they were measured at ambient temperature and are
[Tricarbonyl(2-diisopropylamino-4-methyl-2-boratanaphthal-
ene)molybdate](triphenylphosphine)gold [(iPr2NBn)(OC)3Mo-
Au(PPh3)] (7). Li[Mo(CO)3(iPr2NBn)]ؒ2DME (6a) (0.181 g,
0.298 mmol) and [AuCl(PPh3)] (0.148 g, 0.299 mmol) were
stirred in 20 mL toluene for 1 h. After complete evaporation of
the volatiles under reduced pressure, the residue was dissolved
in toluene and filtered through Kieselguhr to give a clear orange
solution. The solvent was then removed in vacuo to give 7 in
quantitative yield as an air stable, yellow powder or large
orange–red crystals, slightly soluble in pentane and very sol-
uble in toluene. Mp: decomposition 125 ЊC. Anal. Calc. for
C37H38AuBMoPNO3: C, 50.54; H, 4.36; N, 1.59. Found: C,
50.89; H, 4.24; N, 1.46. 1H NMR (C6D6): δ 7.57 (d, J = 8.8 Hz,
1H, 5-H), 7.41 and 6.98 (m, 15H, PPh3), 7.25 (d, J = 8.8 Hz, 1H,
8-H), 6.85 (ddd, J = 8.6, 6.5, 0.8 Hz, 1H, 7-H), 6.58 (ddd,
J = 8.8, 6.4, 0.8 Hz, 1H, 6-H), 5.12 (d, 4J13 = 2.4 Hz, 1H, 3-H),
4.93 (d, 4J13 = 2.4 Hz, 1H, 1-H), 2.51 (s, 3H, 4-Me). NiPr2: 3.69
relative to internal TMS for H and 13C{1H} and relative to
1
BF3ؒOEt2 as external reference for 11B. 31P{1H} NMR spectra
were externally referenced to 85% H3PO4 in H2O, with down-
field chemical shift reported as positive. The 1H and 13C
spectra show a fairly constant pattern for the phenyl ring
of boratanaphthalene derivatives. Assignments are based on
numerous H,H-COSY, H,C-COSY (HETCOR, HMQC),
NOE, APT and DEPT spectra which are not detailed here. The
IR spectra were recorded in the region 4000–400 cmϪ1 on a
Perkin-Elmer 1720 X FT-IR or a Bruker IFS66/113 (FT-IR)
instrument. [Li(MeBn)] was prepared as reported in the
literature.10
3
(s br, 2H, NCH), 1.34 (d, J = 5.6 Hz, 12H, Me). 13C NMR
(C6D6): δ 228.3 (CO), 124.1, 122.2 and 100.9 (C-4, C-4a, C-8a),
134.6 (C-8), 130.0 (C-5), 128.2 (C-7), 122.8 (C-6), 96.7 (br, C-3),
76.8 (br, C-1), 25.5 (4-Me). NiPr2: 46.9 (NC), 23.5 and 23.4
(Me). PPh3: 135.1 and 130.0 (d, JPC = 15 and 11 Hz, ortho and
meta), 132.1 (d, JPC = 2 Hz, para), 131.7 (d, JPC = 51 Hz, ipso).
11B NMR (C6D6): δ 24. 31P NMR (C6D6): δ 47.8. IR (KBr):
νCO = 1948s, 1869m, 1835s.
Syntheses
Lithium tricarbonyl(2,4-dimethyl-2-boratanaphthalene)molyb-
date-bis(1,2-dimethoxyethane)
Li[Mo(CO)3(MeBn)]ؒ2DME
(6b). A solution of [Li(MeBn)] (5b) (3.498 g, 21.7 mmol) in 60
mL of DME was added to a suspension of [Mo(CO)6] (5.73 g,
21.7 mmol) in 100 mL of DME. The mixture which turned
orange was refluxed for 24 h with constant stirring. The dis-
appearance of [Mo(CO)6] was followed by IR spectroscopy.
The solution was filtered through Kieselguhr. After concen-
tration of the solution and precipitation with pentane (200
mL), compound Li[Mo(CO)3(MeBn)]ؒ2DME (6b) was isolated
by filtration, washed with pentane (3 × 50 mL) and dried
in vacuo. Yield: 10.2 g, 90%. 6b is a bright yellow powder,
insoluble in pentane but soluble in toluene, DME or THF.
Anal. Calc. for C22H32BLiMoO7: C, 50.60; H, 6.18. Found: C,
Tricarbonyl(chloromercury)(2-diisopropylamino-4-methyl-2-
boratanaphthalene)molybdenum
[(iPr2NBn)(OC)3MoHgCl]
(10). Solid HgCl2 (large excess, 0.150 g, 0.552 mmol) was added
to a suspension of Li[Mo(CO)3(iPr2NBn)]ؒ2DME (6a) (0.254 g,
0.418 mmol) in 30 mL of toluene. The mixture was stirred for
1 h and the resulting greenish suspension was filtered through
Kieselguhr. The yellow filtrate was then concentrated under
reduced pressure. The product 10, [(iPr2NBn)(OC)3MoHgCl]
was obtained in quantitative yield after precipitation with
pentane. 10 is a yellow, air stable powder, light-sensitive in
solution, slightly soluble in pentane and very soluble in toluene.
Mp: 132 ЊC. Anal. Calc. for C19H23BClHgMoNO3: C, 34.78;
1
1
50.33; H, 5.98. H NMR (THF-d8): δ 7.68 (d, J = 8.8 Hz, 1H,
H, 3.53; N, 2.13. Found: C, 35.07; H, 3.51; N, 1.94. H NMR
5-H), 7.11 (d, J = 8.5 Hz, 1H, 8-H), 6.89 (ddd, J = 8.5, 6.4, 1.2
(C6D6): δ 7.19 (d, J = 9.0 Hz, 1H, 5-H), 6.73 and 6.59 (m, 3H,
1758
J. Chem. Soc., Dalton Trans., 2001, 1754–1760

View Article Online
Table 5 Summary of the crystallographic details
7
9
13
15
Empirical formula
Formula weight
C37H38AuBMoNO3P
879.41
C38H46B2HgMo2N2O6
1040.89
C38H47AgB2Mo2N2O6ؒC7H8
1041.32
C40H54B2Mo2O6P2Pd2
1119.12
Crystal system
Space group
Monoclinic
P21/c
Triclinic
P1
Monoclinic
P21/n
Monoclinic
P21/n
¯
a/Å
b/Å
c/Å
α/Њ
17.8519(8)
10.3946(6)
19.1659(8)
9.2428(6)
9.7821(6)
12.3798(5)
78.225(5)
87.103(5)
67.449(5)
1011.5(1)
1
12.0187(2)
18.5098(6)
20.4035(6)
8.8882(4)
20.8012(8)
11.9776(6)
β/Њ
100.148(8)
98.989(5)
103.372(5)
γ/Њ
V/Å3
3500.9(6)
4
4483.3(4)
4
2154.4(3)
2
Z
Crystal size/mm
0.18 × 0.15 × 0.12
1.67
0.20 × 0.16 × 0.02
1.71
0.20 × 0.08 × 0.06
1.54
0.10 × 0.04 × 0.02
1.73
D/g cmϪ3
F(000)
1728
4.625
510
4.440
2112
1.031
1116
1.508
µ/mmϪ1
Temperature/K
θ limits/Њ
Reflns. collected
No. of variables
R
294
2.5/27.48
8427
406
0.022
173
2.5/27.50
6602
250
0.037
173
173
2.5/27.50
8976
244
0.029
2.5/27.47
19098
523
0.029
Rw
GOF
0.031
1.031
0.050
1.021
0.031
1.053
0.043
1.004
Largest peak in final diff.
0.611
1.182
0.429
0.621
map/e ÅϪ3
No. of data with I > 3σ(I)
Weighting scheme
6860
3395
6353
3678
2
2
4
2
2
4
2
2
4
2
2
4
4Fo /(σ2(Fo ) ϩ 0.0016Fo )
4Fo /(σ2(Fo ) ϩ 0.0049Fo )
4Fo /(σ2(Fo ) ϩ 0.0001Fo )
4Fo /(σ2(Fo ) ϩ 0.0025Fo )
6-H, 7-H, 8-H), 4.80 (d, J = 1.8 Hz, 1H, 3-H), 4.56 (d, J = 2.4
Hz, 1H, 1-H), 1.94 (s, 3H, 4-Me). NiPr2: 3.46 and 3.26 (sept,
3J = 7.2 and 6.6 Hz, 2H, NCH), 1.18 (m br, 12H, Me). 13C
NMR (C6D6): δ 227.8, 223.2 and 219.4 (CO), 134.1, 128.2,
127.3 and 126.6 (C-5, C-6, C-7, C-8), 119.3, 116.3 and 101.2
(C-4, C-4a, C-8a), 91.1 (br, C-3), 75.8 (br, C-1), 22.7 (4-Me).
NiPr2: 46.7 and 45.5 (NC), 22.4, 22.2, 21.7 and 21.3 (Me).
11B NMR (C6D6): δ 23. IR (KBr): νCO = 2007s, 1946m, 1919s.
MS: m/z (Irel): 656 (Mϩ, 32%); 642 (Mϩ Ϫ CH3, 8%); 422
([Mo(CO)3(iPr2NBn)]ϩ, 94%).
123.0 (C-5, C-6, C-7, C-8), 121.3, 116.7 and 100.8 (C-4, C-4a,
C-8a), 93.6 (br, C-3), 76.0 (br, C-1), 23.0 (4-Me). NiPr2: 44.8
(NC), 21.2 (br, Me). 11B NMR (C6D6): δ 24. IR (KBr):
νCO = 1970s, 1915m, 1889s, 1820vw, 1800vw. MS: m/z (Irel): 1041
(Mϩ, 12%); 422 ([Mo(CO)3(iPr2NBn)]ϩ, 100%).
[Tricarbonyl(2-diisopropylamino-4-methyl-2-boratanaphthal-
ene)molybdenum][tricarbonyl(2-diisopropylamine-4-methyl-2-
boranaphthalene)molybdenum]silver [Ag{Mo(CO)3(iPr2NBn)}-
{Mo(CO)3[(iPr2HN)Bn]}] (13). The reaction of one equiv-
alent of 6a with AgOTf in toluene afforded a mixture of
products whose analysis by mass spectrometry suggested the
formation of oligomeric compounds with:
Bis[tricarbonyl(2-diisopropylamino-4-methyl-2-boratanaph-
thalene)molybdenum]mercury [Hg{Mo(CO)3(iPr2NBn)}2] (9).
Solid HgCl2 (0.135 g, 0.497 mmol) was added to a suspension
of Li[Mo(CO)3(iPr2NBn)]ؒ2DME (6a) (0.630 g, 1.037 mmol) in
30 mL of toluene. The mixture was stirred for 1 h, the volatiles
were removed under reduced pressure to give a brown residue
which was dissolved in toluene and filtered twice through
Kieselguhr. The resulting red solution was concentrated
in vacuo. After precipitation with pentane, 9 was isolated as a
mixture of two diastereomers. Yield: varying from 70 to 98%.
Slow diffusion of pentane into a solution of the isomeric
mixture in toluene afforded orange crystals suitable for X-ray
diffraction. The product is an orange air stable powder,
light-sensitive in solution, slightly soluble in pentane and very
soluble in toluene. Mp: decomposition 190 ЊC. Anal. Calc. for
C38H46B2HgMo2N2O6: C, 43.85; H, 4.45; N, 2.69. Found: C,
44.24; H, 4.34; N, 2.70.
m/z (Irel): 1584 (22%): [{AgMo(CO)3(iPr2NBn)}3]ϩ
m/z (Irel): 1165 (99%): [{AgMo(CO)3(iPr2NBn)}2 ϩ Ag ϩ H]ϩ
m/z (Irel): 1056 (22%): [{AgMo(CO)3(iPr2NBn)}2]ϩ
m/z (Irel): 950 (16%): [{Ag[Mo(CO)3(iPr2NBn)]2} ϩ H]ϩ
m/z (Irel): 530 (51%): [AgMo(CO)3(iPr2NBn)]ϩ
During attempts of purification, one of them, 13, could be
isolated in the crystalline form from a mixture toluene–hexane
(Mϩ = 950) and studied by X-ray diffraction.
Hexacarbonyl-bis(ꢀ6-2,4-dimethyl-2-boratanaphthalene)-bis-
(triethylphosphine)-dimolybdenumdipalladium
[Pd2Mo2(Me-
Bn)2(CO)6(PEt3)2] (15). A mixture of 6b (0.205 g, 0.392 mmol)
and [PdCl2(PEt3)2] (0.081 g, 0.196 mmol) in 30 mL of toluene
was stirred for 2 days. A dark green solution with a black pre-
cipitate was formed. The solid was removed by filtration
through Kieselguhr whereas the filtrate was cooled at Ϫ30 ЊC
for crystallization. Cluster 15 was obtained as green crystals
(suitable crystals for X-ray diffraction were obtained by diffu-
sion from hexane in a toluene solution). Yield: 0.022 g, 20%. 15
forms air stable, dark green–red dichroic crystals, insoluble in
pentane and diethyl ether, moderately soluble in toluene and
very soluble in THF. Anal. Calc. for C40H54B2Mo2O6Pd2P2:
C, 42.93; H, 4.86. Found: C, 42.72; H, 4.89. 1H NMR (THF-d8):
δ 7.67 (d, J = 8.5 Hz, 2H, 5-H), 7.36 (d, J = 8.3 Hz, 2H, 8-H),
7.27 (dd, J = 8.4, 6.5 Hz, 2H, 7-H), 7.15 (ddd, J = 8.1, 7.7, 0.8
Hz, 2H, 6-H), 4.95 (d, J = 1.6 Hz, 2H, 3-H), 4.74 (d, J = 2.1 Hz,
2H, 1-H), 2.48 (s, 6H, 4-Me), 0.66 (s, 6H, BMe). PEt3: 1.50 (dm,
2JPH = 48.5 Hz, 12H, CH2), 0.84 (m, 18H, Me). 11B NMR
1
NMR data for the first diastereoisomer: H NMR (C6D6):
δ 7.38 (d, J = 8.4 Hz, 1H, 5-H), 6.85 (m, 3H, 6-H, 7-H, 8-H),
4.65 (d, 4J13 = 2.5 Hz, 1H, 3-H), 4.55 (d, 4J13 = 2.5 Hz, 1H, 1-H),
2.19 (s, 3H, 4-Me). NiPr2: 3.5 (br, 2H, NCH), 1.21 (m br, 12H,
Me). 13C NMR (C6D6): δ 225 (vbr, CO), 133.6, 127.2, 126.2 and
123.4 (C-5, C-6, C-7, C-8), 121.6, 116.9 and 100.5 (C-4, C-4a,
C-8a), 93.6 (br, C-3), 76.0 (br, C-1), 23.0 (4-Me). NiPr2: 44.8
(NC), 21.2 (br, Me). 11B NMR (C6D6): δ 24.
NMR data for the second diastereoisomer: 1H NMR (C6D6):
δ 7.51 (d, J = 8.6 Hz, 1H, 5-H), 6.85 (m, 3H, 6-H, 7-H, 8-H),
4.70 (d, 4J13 = 2.6 Hz, 1H, 3-H), 4.50 (d, 4J13 = 2.6 Hz, 1H, 1-H),
2.27 (s, 3H, 4-Me). NiPr2: 3.5 (br, 2H, NCH), 1.21 (m br, 12H,
Me). 13C NMR (C6D6): δ 225 (vbr, CO), 133.6, 126.9, 126.3 and
J. Chem. Soc., Dalton Trans., 2001, 1754–1760
1759

View Article Online
(THF-d8): δ 26. 31P NMR (C6D6): δ 18.3. IR (KBr): νCO = 1856s,
1821(sh), 1806s, 1793(sh).
9 Metal Clusters in Chemistry, eds. P. Braunstein, L. A. Oro and P. R.
Raithby, Weinheim, 1999, vol. 1.
10 G. E. Herberich, E. Cura and J. Ni, Inorg. Chem. Commun., 1999, 2,
503.
Crystal structure determinations
11 P. Braunstein, R. Bender and J.-M. Jud, Inorg. Synth., 1989, 26, 341.
12 J. Pethe, C. Maichle-Mössmer and J. Strähle, Z. Anorg. All. Chem.,
1997, 623, 1413.
13 B. N. Strunin, K. I. Grandberg, V. G. Andrianov, V. N. Setkina,
E. G. Perevalova, Y. T. Struchkov and D. N. Kursanov, Dokl. Akad.
Nauk SSSR, 1985, 281, 599.
14 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen
and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, S1.
15 E. O. Fischer, Inorg. Synth., 1963, 7, 136.
16 G. E. Herberich and D. Söhnen, J. Organomet. Chem., 1983, 254, 143.
17 R. D. Fischer and K. Noak, J. Organomet. Chem., 1969, 16, 125.
18 M. M. Mickiewicz, C. L. Raston, A. H. White and S. B. Wild, Aust.
J. Chem., 1977, 30, 1685.
The X-ray data for all structures were collected on a Kappa
CCD diffractometer, using graphite-monochromated Mo-Kα
radiation (0.71073 Å) and ψ-scan mode. The structures were
solved using direct methods and refined against |F |. For all
computations the Nonius OpenMoleN package was used.32
The hydrogen atoms were introduced as fixed contributors
(dC–H = 0.95 Å, B(H) = 1.3Bequiv(C) Å2). Crystallographic details
are given in Table 5.
CCDC reference numbers 153364–153367.
See http://www.rsc.org/suppdata/dt/b1/b101556g/ for crystal-
lographic data in CIF or other electronic format.
19 P. Hackett and A. R. Manning, J. Chem. Soc., Chem. Comm., 1973,
71.
20 A. Moezzi, R. A. Bartlett and P. P. Power, Angew. Chem., Int. Ed.
Engl., 1992, 31, 1082.
21 R. Boese, N. Finke, T. Keil, P. Paetzold and G. Schmid,
Z. Naturforsch., Teil B, 1985, 40, 1327.
22 R. Boese, N. Finke, J. Henkelmann, G. Maier, P. Paetzold, H. P.
Reisenauer and G. Schmid, Chem. Ber., 1985, 118, 1644.
23 G. E. Herberich, M. Negele and H. Ohst, Chem. Ber., 1991,
124, 25.
Acknowledgements
We are grateful to the Ministère de l’Education Nationale, de la
Recherche et de la Technologie and the Centre National de
la Recherche Scientifique (Paris) for financial support, and
Johnson Matthey PLC for a generous loan of PdCl2.
24 R. W. Quan, G. C. Bazan, A. F. Kiely, W. P. Schaefer and J. E.
Bercaw, J. Am. Chem. Soc., 1994, 116, 4489.
25 A. F. Kiely, C. M. Nelson, A. Pastor, L. M. Henling, M. W. Day and
J. E. Bercaw, Organometallics, 1998, 17, 1324.
26 G. C. Bazan, S. J. Donnelly and G. Rodriguez, J. Am. Chem. Soc.,
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27 C. K. Sperry, W. D. Cotter, R. A. Lee, R. J. Lachicotte and G. C.
Bazan, J. Am. Chem. Soc., 1998, 120, 7791.
28 R. Vilar, D. M. P. Mingos and C. J. Cardin, J. Chem. Soc., Dalton
Trans., 1996, 4313.
29 P. Braunstein, B. Oswald, A. DeCian and J. Fischer, J. Chem. Soc.,
Dalton Trans., 1991, 2685.
30 P. Braunstein, J.-M. Jud, Y. Dusausoy and J. Fischer,
Organometallics, 1983, 2, 180.
31 (a) P. Braunstein, C. de Bellefon, S.-E. Bouaoud, D. Grandjean,
J.-F. Halet and J.-Y. Saillard, J. Am. Chem. Soc., 1991, 113, 5282;
(b) C. Archambault, R. Bender, P. Braunstein, S.-E. Bouaoud,
D. Rouag, S. Golhen and L. Ouahab, Chem. Commun., 2001, 849.
32 Open MoleN, Interactive Structure Solution, Nonius B. V., The
Netherlands, 1997.
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J. Chem. Soc., Dalton Trans., 2001, 1754–1760