Synthesis, characterization and coordination chemistry of a macrocyclic ligand containing arsenic donors

Article abstract of DOI:10.1039/b415976d

The preparation and characterization of the macrocyclic diamido-diarsine ligand [As₂N₂]Li₂(1,4-dioxane) (1) (where As₂N₂ = PhAs(CH₂SiMe₂NSiMe ₂CH₂)₂AsPh) and a series of early transition metal complexes are presented. The complexes [As₂N ₂]MCl₂ (M = Zr, 2; Ti, 4) and the complex ([As ₂N₂]Y)₂(μ-Cl)₂ (5) can be prepared by reaction of 1 with the corresponding THF adduct of the metal halide. The iodide derivative of 2, [As₂N₂]ZrI₂ (3) can be prepared by reaction with iodotrimethylsilane. The lithium complex 1 displays a very long lithium-arsenic bond distance of 3.162(10) A, and the yttrium complex 5 is the first known complex containing a yttrium-arsenic bond. Reduction of 2, 3 or 4 using C₈K or activated magnesium decomposed the complexes in such a manner that the ligand was separated from the metal centre. Indirect evidence suggests this may be due to reduction of arsenic in the ligand in preference to the metal.

Full text of DOI:10.1039/b415976d

View Article Online / Journal Homepage / Table of Contents for this issue
F U L L P A P E R
Synthesis, characterization and coordination chemistry of a
macrocyclic ligand containing arsenic donors
Christopher D. Carmichael and Michael D. Fryzuk*
Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British
Columbia, Canada V6T 1Z1. E-mail: fryzuk@chem.ubc.ca
Received 5th November 2004, Accepted 11th November 2004
First published as an Advance Article on the web 14th December 2004
The preparation and characterization of the macrocyclic diamido-diarsine ligand [As2N2]Li2(1,4-dioxane) (1) (where
As2N2 = PhAs(CH2SiMe2NSiMe2CH2)2AsPh) and a series of early transition metal complexes are presented. The
complexes [As2N2]MCl2 (M = Zr, 2; Ti, 4) and the complex ([As2N2]Y)2(l-Cl)2 (5) can be prepared by reaction of 1
with the corresponding THF adduct of the metal halide. The iodide derivative of 2, [As2N2]ZrI2 (3) can be prepared
by reaction with iodotrimethylsilane. The lithium complex 1 displays a very long lithium–arsenic bond distance of
˚
3.162(10) A, and the yttrium complex 5 is the first known complex containing a yttrium–arsenic bond. Reduction of
2, 3 or 4 using C8K or activated magnesium decomposed the complexes in such a manner that the ligand was
separated from the metal centre. Indirect evidence suggests this may be due to reduction of arsenic in the ligand in
preference to the metal.
Introduction
Phosphine donors are well suited as ancillary ligands to a wide
range of metal centres across the Periodic Table.1 In contrast,
arsine donors, the next heaviest member of group 15, are much
less common.2–4 While phosphorus-based ligands display strong
r-donor and p-acceptor abilities along with a convenient NMR-
active nucleus, arsenic ligands are known to be modest r-donors
and p-acceptors,5 and 75As (I = 3/2) is not a useful NMR nucleus
due to its quadrupolar nature.6 Thus, it is not surprising that
many arsenic ligands display lower reactivity when compared
to similar phosphorus based systems,7,8 although there are
exceptions.9,10
Previously, the synthesis of mixed-donor macrocyclic
diamido-diphosphine system, [P2 N2 ] (where P2 N2
=
PhP(CH2SiMe2NSiMe2CH2)2PPh)11 and its coordination chem-
istry with the early transition elements, particularly groups 3
and 4, were reported.12,13 While one can fine tune the reactivity
patterns by changing the substituents at phosphorus within
the macrocycle, an alternative approach was to change the
donor atoms from P to As. In this paper, the successful
synthesis of the diamido-diarsine macrocycle, [As2N2] (where
As2N2 = PhAs(CH2SiMe2NSiMe2CH2)2AsPh) is reported and
its coordination chemistry with Zr, Ti and Y is detailed. The
results of attempts to prepare dinitrogen complexes of Zr and
Ti stabilized by the [As2N2] ligand system are also discussed.
Scheme 1
Addition of 1,4-dioxane to a concentrated toluene solution of
the crude product gives 1 as a fine cream coloured powder
isolated in 67% yield by precipitation with hexanes. 1 is sparingly
soluble in hexanes and the need to remove hexanes soluble
impurities from the product contributes to the mediocre yield.
X-Ray quality crystals of 1 can be grown by placing the
concentrated toluene solution in a −40 ◦C freezer overnight,
following 1,4-dioxane addition. The solid-state molecular struc-
ture of 1 is presented in Fig. 1; crystal data are given in Table 6,
and selected bond distances and angles are detailed in Table 1.
The structure is a one-dimensional polymer with the 1,4-dioxane
bridging the lithium atoms of adjacent molecules in a head to tail
fashion. Both arsenic atoms are associated to a single lithium
atom in a syn fashion, like that seen in syn-[P2N2]Li2(THF).11
However, unlike syn-[P2N2]Li2(THF) where the distances are
equal by symmetry, the Li–As distances in 1 differ by half an
Results and discussion
Synthesis of [As2N2] ligand
Following the lithium template synthesis developed for the phos-
phorus based [P2N2]Li2(1,4-dioxane)11 ligand, the synthesis of
[As2N2]Li2(1,4-dioxane) (1) is detailed in Scheme 1. Phenylarsine
is synthesizedin72%yieldbythe reduction of phenylarsonic acid
using zinc dust and hydrochloric acid.14 Updating the procedure
to take advantage of modern Schlenk techniques allows for an
approximate 20% increase in isolated yield over the original
and more recent publications using the same preparation.15
Reaction of two equivalents of LiAsHPh with the disilazane
HN(SiMe2CH2Cl)2 leads to formation of the intermediate di-
arsinosilazane HN(SiMe2CH2AsHPh)2 in virtually quantitative
yield. Further reaction of the diarsinosilazane with another
equivalent of HN(SiMe2CH2Cl)2 in the presence of 4 equivalents
˚
angstrom. The bond distance of 2.658(11) A between Li(1) and
As(1) agrees well with other literature Li–As distances.16–19 It
is more difficult to describe the interaction between Li(1) and
˚
As(2) as a true bonding interaction; the distance of 3.162(10) A is
˚
significantly longer than the longest distance, 2.799 A, reported
in the literature.20 This distance is, however, considerably shorter
than the sum of the van der Waals radii for the two atoms
21
˚
(3.67 A) and suggests that there is a weak interaction present
1
of BuLi leads to a single product by H NMR spectroscopy.
in the solid state.
4 5 2
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

View Article Online
◦
˚
Unfortunately, reactions performed at lower temperatures or for
shorter periods of time did not go to completion.
Table 1 Selected bond lengths (A) and angles ( ) in [As2N2]Li2(1,4-
dioxane) (1)
N(1)–Li(1)
N(2)–Li(1)
O(1)–Li(1)
As(1)–Li(1)
2.186(13)
2.106(14)
2.080(13)
2.658(11)
N(1)–Li(2)
N(2)–Li(2)
O(2)–Li(2*)
As(2) · · · Li(1)
1.982(17)
2.029(15)
1.998(14)
3.162(10)
Li(1)–N(1)–Li(2)
N(1)–Li(1)–N(2)
O(1)–Li(1)–N(1)
C(13)–As(1)–Li(1)
74.8(5)
99.4(5)
145.9(7)
152.4(4)
Li(1)–N(2)–Li(2)
N(1)–Li(2)–N(2)
O(2*)–Li(2)–N(2)
75.6(6)
109.5(6)
130.4(9)
(1)
X-Ray quality crystals of 2, containing one equivalent of
co-crystallized solvent, were grown from a saturated toluene
solution; the solid-state molecular structure is presented in
Fig. 2; crystal data are given in Table 6, and selected bond
distances and angles are in Table 2. Structurally, 2 assumes
a distorted trigonal prismatic geometry, with the two trigonal
planes described by Cl(1)As(1)N(1) and the crystallographically
related plane Cl(1*)As(1*)N(1*); the chlorides are not located
in the N(1)Zr(1)N(2) plane but are rotated out of this plane by
approximately 45◦. The Zr–N and Zr–Cl bond distances com-
pare favourably to those of the known [P2N2]ZrCl2 complex25
and other similar zirconium complexes.26–28 Very few complexes
containing structurally characterized zirconium arsenic bonds
are known,29–32 and the Zr–As bond length of 2.8812(4) A in
˚
2 is in agreement with recently published zirconium diarsine
complexes.32 A direct result of the longer Zr–As interaction in
2, as compared to the Zr–P distances in [P2N2]ZrCl2 (2.694 and
25
˚
2.707 A), is the position of the arsine phenyl rings; the angle
between the phenyl rings is about 30◦ larger than any observed in
the [P2N2] complexes of zirconium. Like [P2N2]ZrCl2, complex
2 displays a similar C2 twist; however, due to the intrinsically
longer Zr–As bond the degree of twist is much more dramatic,
with the As–Zr–As “bite angle” smaller by 25◦.25 The extreme
C2 twist can also be implicated in the position of the chloride
ligands. Because there is no electronic preference for the orbitals
Fig. 1 Molecular structure (ORTEP) of [As2N2]Li2(1,4-dioxane) (1).
Only the ipso carbons of phenyl rings attached to arsenic are shown.
The solid-state structure in 1 discussed above is not observed
in solution; the ambient temperature 1H NMR spectrum is
more consistent with a C2v symmetric ligand environment, as it
displays resonances due to only two types of silyl methyl protons,
reflecting “top and bottom” asymmetry. The o-protons of the
arsine phenyl ring appear as a distinct multiplet; the CH2 ring
protons appear as a pair of AB doublets. A singlet is observed
for the dioxane protons, integrating to one equivalent, and it
is assumed to coordinate to the lithium not coordinated to
arsenic. The observed symmetry suggests that the [As2N2] ligand
framework is flexible in solution and undergoes a fluxional
process. Variable-temperature NMR experiments performed
on 1 (290–190 K) did not show any decoalescence of the
phenyl, methylene or silyl methyl resonances. Thus, it is not
possible to distinguish between a solution structure with both
arsenic donors coordinated to the lithium ions at all observed
temperatures, or a structure in which the arsenic donors engage
in an associative/dissociative process with Li(1) that is fast on
the NMR timescale. The 1H NMR and 7Li spectra of 1 are both
consistent with a symmetrical structure in solution identical to
that proposed for the syn isomer of [P2N2]Li2(THF).11 Unlike the
phosphine system where two different isomers can be isolated,
no spectral evidence for anti-[As2N2]Li2(dioxane) is observed.
Fig. 2 Molecular structure (ORTEP) of [As2N2]ZrCl2 (2). Only the ipso
carbons of phenyl rings attached to arsenic are shown.
Coordination chemistry of [As2N2]
The coordination chemistry of the [P2N2] ligand has been
extensively explored and documented,12,22–24 particularly with
zirconium.25 In order to study structural and reactivity differ-
ences between [P2N2] and [As2N2] complexes, the coordination
chemistry of [As2N2] with Zr, Ti and Y was investigated.
The synthesis of [As2N2]ZrCl2 (2) is outlined in eqn. (1).
Reaction of 1 with ZrCl4(THF)2 or ZrCl4(THT)2 (THT =
tetrahydrothiophene) in refluxing toluene for 24 h produced the
product in 70% yield. At such elevated reaction temperatures
the product is not stable and decomposes over a period of days.
◦
˚
Table 2 Selected bond lengths (A) and angles ( ) in [As2N2]ZrCl2 (2)
Zr(1)–N(1)
Zr(1)–As(1)
Zr(1)–Cl(1)
2.098(2)
2.8812(4)
2.4810(7)
Zr(1)–N(1*)
Zr(1)–As(1*)
Zr(1)–Cl(1*)
2.098(2)
2.8812(4)
2.4810(7)
N(1)–Zr(1)–N(1*)
Cl(1)–Zr(1)–Cl(1*)
N(1)–Zr(1)–Cl(1*)
111.82(13) As(1)–Zr(1)–As(1*) 128.809(18)
84.02(4)
98.39(6)
N(1)–Zr(1)–Cl(1)
133.39(6)
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9
4 5 3

View Article Online
in a d0 transition metal complex, the deviation from octahedral
coordination about the zirconium centre is steric in nature. The
chloride ligands may be rotated to reduce steric interactions with
the silyl methyl carbons, C(3) and C(3*) in Fig. 2, that due to
the extreme C2 twist are much closer to the metal centre than in
[P2N2] complexes.
In a manner like that of the precursor complex 1, the
dichloride 2 adopts a C2v structure in solution at ambient
temperature; the methylene protons appearing as a pair of AB
doublets, and the silyl methyl protons as two singlets. This
indicates that the solution structure and solid-state structure
differ, and that some fluxional process is occurring such that
on the NMR timescale, an averaged structure is observed. One
possibility is that the complex undergoes a dynamic “rocking”
motion of the disilylamido donors that possesses a twisted
structure at its two extremes and passes through a symmetrical
intermediate, as shown in Scheme 2. Variable-temperature NMR
experiments performed on 2 (290–220 K) were not able to discern
decoalescence of any resonances. The low solubility of 2 in
toluene did not permit data collection at temperatures lower
than 220 K.
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) in [As2N2]ZrI2 (3)
Zr(1)–N(1)
Zr(1)–As(1)
Zr(1)–I(1)
2.112(3)
2.8326(5)
2.8638(5)
Zr(1)–N(2)
Zr(1)–As(2)
Zr(1)–I(2)
2.090(3)
2.8719(5)
2.9265(4)
N(1)–Zr(1)–N(2) 110.95(12)
I(1)–Zr(1)–I(2)
N(1)–Zr(1)–I(1)
As(1)–Zr(1)–As(2)
83.888(13) N(1)–Zr(1)–I(2)
102.45(8)
135.745(16)
140.02(9)
Fig. 3 Molecular structure (ORTEP) of [As2N2]ZrI2 (3). Only the ipso
carbons of phenyl rings attached to arsenic are shown.
Scheme 2
Work with [P2N2]Hf complexes has shown that the iodide
complex can be a more productive starting material than the
chloride.33 The synthesis of [As2N2]ZrI2 (3) is outlined in eqn. (2).
Reaction of 2 with an excess (10 equiv.) of iodiotrimethylsilane
produced the desired product as a pale yellow solid in 55%
silyl methyl protons are observed as a coincidental singlet in d8-
THF, or two singlets if the spectrum is acquired in d6-benzene.
Reactions of 2 and 3 with various alkylating agents such
as methyllithium or benzyl magnesium chloride resulted in
decomposition. 1H NMR spectra of the isolated materials
showed many silyl methyl environments, multiple methylene
resonances, and broad resonances that could be due to N–H
protons. This evidence suggests that the ligand decomposes and
potentially becomes separated from the metal centre. How this
occurs is unknown but it is possible that an open coordination
site on zirconium, created by partial dissociation of one or both
arsine donors, could promote complex decomposition.
1
yield after washing with small amounts of benzene. H NMR
spectra of these washings showed a large number of silyl methyl
resonances, indicating that a portion of 2 decomposed. If the
reaction is conducted using a smaller excess of iodotrimethylsi-
lane, resonances of a new material, presumed to be the mixed
iodide chloride species [As2N2]Zr(I)Cl, can be observed in the
1H NMR spectrum.
An investigation of titanium coordination chemistry was
prompted by the smaller size of titanium compared to zirconium
and the possibilities derived from a greater size mismatch
between the arsenic donors and the titanium centre. The
synthesis of [As2N2]TiCl2 (4), is outlined in eqn. (3). Reaction of
1 with TiCl4(THF)2 in toluene for five days produces the desired
product in 84% yield.
(2)
The diiodide complex 3 was crystallized from a saturated
THF solution; the solid-state molecular structure is shown in
Fig. 3 with crystal data and selected bond lengths and angles
described in Table 6 and Table 3 respectively. Like the dichloride
2, 3 assumes a trigonal prismatic geometry about the zirconium
centre; the trigonal planes are described by I(1)As(1)N(1) and
I(2)As(2)N(2), and the iodides are rotated out of the zirconium
amido plane by about 45◦. The Zr–N distances are comparable
to 2; however, the Zr–As distances are shorter by approximately
(3)
˚
0.05 A, suggesting that the presence of the iodide ligands
makes the zirconium more electronegative. The Zr–I bonds
X-Ray quality crystals of 4, containing 2.5 equivalents of
co-crystallized solvent, were grown from a saturated benzene
solution. The solid-state molecular structure is shown in Fig. 4
with crystal data and selected bond lengths and angles described
in Table 6 and Table 4, respectively. The titanium centre adopts a
five-coordinate trigonal bipyramidal structure that includes only
are comparable to other zirconium diiodide complexes.34,35
3
displays a less extreme C2 twist than 2, the As(1)–Zr(1)–
As(2) “bite angle” is 135.7◦, but still much more extreme
than [P2N2]ZrCl2.25 In solution, 3 assumes C2v symmetry; the
methylene protons appearing as a pair of AB doublets, and the
4 5 4
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9

View Article Online
◦
˚
yield. Like 2, 5 is not stable at elevated temperatures, however due
to the increased solubility of YCl3(THF)3 in toluene the reaction
was facilitated at a lower temperature, reducing decomposition
of the product.
Table 4 Selected bond lengths (A) and angles ( ) in [As2N2]TiCl2 (4)
Ti(1)–N(1)
Ti(1)–As(1)
Ti(1)–Cl(1)
1.885(4)
Ti(1)–N(2)
1.935(4)
4.186(1)
2.2960(13)
2.6865(9)
2.3248(13)
Ti(1) · · · As(2)
Ti(1)–Cl(2)
N(1)–Ti(1)–N(2)
Cl(1)–Ti(1)–Cl(2)
111.04(15)
92.53(5)
N(1)–Ti(1)–Cl(1)
N(1)–Ti(1)–Cl(2)
110.44(11)
107.14(12)
one titanium arsenic bond. Such a five-coordinate bonding motif
36
has been observed before in the complex anti-[P2N2]TiCl2 and
the four-coordinate complexes anti-[P2N2]MCl (M = Al, Ga).37
In those cases, the second phosphine is unable to bind because
the lone pair is oriented away from the metal centre. Complexes
with only one coordinated neutral donor have not been observed
in the syn-[P2N2] system; however, the significant size differential
and orbital mismatch between titanium and arsenic are likely
rationales for the lack of coordination. Unlike complex 2, where
the Zr–As bonds are elongated, the single Ti–As bond length
in 4 agrees well with literature values.38–40 The Ti–N and Ti–Cl
bond distances compare favourably to those of similar titanium
complexes.41–44
(4)
Crystals of 5 suitable for X-ray diffraction experiments were
grown from a saturated hexanes solution. The solid-state molec-
ular structure is shown in Fig. 5, with crystal data and selected
bond lengths and angles described in Table 6 and Table 5,
respectively. Unlike the previously reported ([P2N2]Y)2(l-Cl)2
structure, where the yttrium centres are structurally different,12
both yttrium centres assume distorted trigonal prismatic ge-
ometries; the planes for Y(1) are described by Cl(1)As(1)N(2)
and Cl(2)N(1)As(2). The Y–Cl and Y–N bond lengths and
the angles of the halide bridge core compare well with those
of ([P2N2]Y)2(l-Cl)2.12 5 is the first example of a coordination
complex containing a Y–As bond.47 The literature contains only
five examples of complexes where arsenic is coordinated to any
group 3 or lanthanide metal, four complexes of samarium48–50
and one of lutetium.51 As expected, the bond lengths between the
◦
˚
Table 5 Selected bond lengths (A) and angles ( ) in ([As2N2]Y)2(l-Cl)2
(5)
Y(1)–N(1)
Y(1)–As(1)
Y(2)–N(3)
Y(2)–As(3)
Y(1)–Cl(1)
Y(2)–Cl(1)
2.361(4)
2.9644(7)
2.320(4)
2.9545(7)
2.8119(13)
2.7226(13)
Y(1)–N(2)
Y(1)–As(2)
Y(2)–N(4)
Y(2)–As(4)
Y(1)–Cl(2)
Y(2)–Cl(2)
2.288(4)
2.9591(7)
2.283(4)
2.9968(7)
2.7152(13)
2.8135(13)
Fig. 4 Molecular structure (ORTEP) of [As2N2]TiCl2 (4). Silyl methyl
groups are omitted for clarity and only the ipso carbons of phenyl rings
attached to arsenic are shown.
In solution, 4 assumes C2v symmetry; the silylmethyl protons
Cl(1)–Y(1)–Cl(2)
Cl(1)–Y(1)–As(2)
Cl(1)–Y(1)–N(2)
Cl(2)–Y(1)–As(2)
Cl(2)–Y(1)–N(2)
As(1)–Y(1)–As(2)
Cl(1)–Y(2)–Cl(2)
Cl(1)–Y(2)–As(4)
Cl(2)–Y(2)–As(4)
Cl(2)–Y(2)–N(4)
As(3)–Y(2)–As(4)
78.10(4)
133.62(3)
98.40(12)
83.27(3)
142.82(12)
135.43(2)
77.95(4)
Cl(1)–Y(1)–As(1)
Cl(1)–Y(1)–N(1)
Cl(2)–Y(1)–As(1)
Cl(2)–Y(1)–N(1)
N(1)–Y(1)–N(2)
Cl(1)–Y(2)–N(4)
Cl(1)–Y(2)–As(3)
Cl(1)–Y(2)–N(3)
Cl(2)–Y(2)–As(3)
Cl(2)–Y(2)–N(3)
N(3)–Y(2)–N(4)
85.69(3)
143.20(12)
132.67(4)
95.68(11)
107.18(16)
146.28(11)
124.86(3)
97.27(11)
85.43(3)
appear as a singlet and the methylene protons appear as a
1
pair of AB doublets in the H NMR spectrum, indicating the
complex is not five-coordinate in solution, but not whether
the complex is four-coordinate or six-coordinate. The absence
of additional resonances in the spectrum indicates that slow
ligand dissociation is not occuring, in contrast to similar six-
coordinate and eight-coordinate arsine complexes of titanium.40
Linewidths do not indicate fluxionality at room temperature,
but the obvious differences between the solution and solid-
state structures prompted a variable-temperature 1H NMR
investigation of 4 in the range 290–180 K. Signal broadening and
decoalescence indicating a loss of symmetry occurs, however, no
low temperature limiting spectrum was observed. If 4 is six-
coordinate in solution it is possible that the complex undergoes
a fluxional process similar to that described for complex 2 above.
Attempts to synthesize various [As2N2]Ti dialkyl complexes such
methyl, benzyl and neosilyl from 4 resulted in reduction to Ti(III)
or mixtures of unidentifiable products.
85.00(3)
124.61(3)
95.05(11)
143.55(2)
150.57(11)
103.76(15)
Previous work in our group using yttrium and lanthanide met-
als with the [P2N2] ligand has led to intriguing carbon–carbon
bond formation upon reaction of halide precursors with aryl-
lithium reagents.12,45,46 The biphenyldiide complex ([P2N2]Y)2{l-
ꢀ
6
6
g :g -(C6H5)2} can be synthesized from the neosilyl complex
and benzene or by direct reaction with phenyllithium; the
naphthalene and anthracene complexes can be synthesized by
reduction of ([P2N2]Y)2(l-Cl)2 with C8K in the presence of the
appropriate polycyclic aromatic compound. Eqn. (4) outlines
the synthesis of the halide precursor ([As2N2]Y)2(l-Cl)2 (5).
Reaction of 1 with YCl3(THF)3 in hot toluene produced 5 in 75%
Fig. 5 Molecular structure (ORTEP) of ([As2N2]Y)2(l-Cl)2 (5). Silyl
methyl groups are omitted for clarity, and only the ipso carbons of
phenyl rings attached to arsenic are shown.
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9
4 5 5

View Article Online
smaller yttrium and arsenic are shorter than known lanthanide
arsenic bonds. In solution, the molecule behaves in a similar
fashion to ([P2N2]Y)2(l-Cl)2,12 1H NMR spectra indicate that
both ends of the molecule are equivalent, the flexibility of the
[As2N2] ligand framework allows the complex to approximate
C2v symmetry; all methylene protons appear as a pair of AB
doublets and the silyl methyl protons appear as two singlets.
Reaction of 5 with various alkyl reagents such as Me3SiCH2Li
produced a mixture of products from which the expected alkyl
could not be cleanly isolated. Attempts to produce and isolate
a p-arene complex from 5 have not been successful. Reaction
of 5 with C8K in the presence of anthracene yielded intensely
blue solutions; however, examination of the isolated solids by 1H
NMR showed they were comprised mostly of anthracene and
unreacted 5. Small resonances, comprising less than 2% of the
sample by integration, were observed that could be tentatively
Mass spectral analysis of the products derived from reductions
of 2 and 3 did show similarities in the fragmentation patterns.
Many fragments could be observed that retained the Si–N
bond, the most common fragment observed was [N(SiMe2)2]+.
However, no common fragments containing As–C bonds could
be assigned. These results suggest that the cleavage of arsenic
carbon bonds could be involved in decomposition of the
complexes. This also suggests that it may be impossible to cleanly
reduce 2 or 3 because of the larger difference in reduction
potential between arsenic and zirconium compared to the
difference between phosphorus and zirconium.
Conclusions
In this report, the synthesis of a mixed donor diamido-diarsine
macrocycle [As2N2], and our attempts to utilize this ligand
in dinitrogen activation and aromatic coupling reactions are
described. The lithium complex [As2N2]Li2(1,4-dioxane) (1) is
a useful reagent to generate the chlorides [As2N2]ZrCl2 (2),
[As2N2]TiCl2 (4) and ([As2N2]Y)2(l-Cl)2 (5) through metathesis
type procedures. The related iodide complex [As2N2]ZrI2 (3) can
be prepared through the reaction of 2 with iodotrimethylsilane.
Attempts to produce coordinated dinitrogen complexes through
the reduction of 2, 3 and 4 with C8K, activated magnesium
and Mg(anthracene)(THF)3 resulted in decomposition of the
parent complex. This same outcome was observed in attempted
reduction reactions of the yttrium complex 5 in the presence
of polycyclic aromatic hydrocarbons. Evidence links this de-
composition to arsenic reduction in the macrocyclic ligand.
Attempts to synthesize various alkyl complexes from 2, 3, 4
and 5 resulted in decomposition of the ligand, possibly through
an open coordination site on the metal centre created by partial
dissociation of one or both arsine donors.
assigned to a biphenyldiide complex based upon the resonances
ꢀ
6
6
observed for ([P2N2]Y)2{l-g :g -(C14H10)}.46
Group 4 reduction chemistry
One strategy to prepare early transition metal dinitrogen com-
plexes that has proven useful in the [P2N2] ligand system is to
reduce a chloride precursor with an alkali metal reagent, such as
potassium graphite (C8K) under dinitrogen.13,52 Reductive path-
ways to dinitrogen complexes of hafnium have shown that the
use of a diiodide precursor can give coordinated dinitrogen com-
plexes where reduction of a dichloride species fails to do so.33,53
If these reductions are performed in the absence of dinitrogen,
phosphorus–phenyl activation occurs, giving rise to a highly acti-
vated arene bridged dimer.54 Reduction pathways have also been
used in the preparation of dinitrogen complexes of titanium.55,56
Reaction of 2 or 3 with two equivalents of C8K under
dinitrogen did not produce the desired coordinated dinitrogen
complex. Reactions conducted under a variety of conditions
produced pale hexanes insoluble solids, in contrast to the
Experimental
2
intense blue color of ([P2N2]Zr)2(l-g -N2).13 Mass spectral
General procedures
analysis of the isolated solids did not find any mass peak
compatible with a dimeric complex. H NMR spectra of the
All manipulations were performed under an atmosphere of
dry oxygen-free dinitrogen by means of standard Schlenk or
glovebox techniques (Vacuum Atmospheres HE-553-2 glovebox
equipped with a MO-40-2H purification system and a −40 C
1
isolated materials showed many silyl methyl environments and
multiple methylene resonances, evidence that suggests the ligand
decomposes and potentially becomes separated from the metal
centre much like that observed for the alkylation reactions
described previously. Reductions performed under argon did
not yield an activated arene-bridged dimer, only decomposition
products were observed, none of which could be assigned to
an activated arene bridged dimer. Reductions performed under
argon using diphenylacetylene as a trap molecule produced
only decomposition products and unreacted diphenylacetylene,
suggesting that the decomposition pathway is intramolecular.
The reduction of arsenic(III) to arsenic metal (E◦ = −0.608 V)
occurs at lower potential than the same reduction for phospho-
rus (E◦ = −0.87 V) and both are significantly easier to reduce
than zirconium (E◦ = −1.45 V).57 Potassium reducing agents are
known to be strongly reduc◦ing, with potentials approaching that
of free potassium metal (E = −2.931 V).57 With the possibility
that C8K could reduce the arsenic atoms in the macrocycle,
milder reducing agents were investigated. The THF adduct of
magnesium anthracene is a readily synthesized material with
a reduction potential of approximately 2 V.58,59 Reaction of 2
or 3 with one or two equivalents of Mg(anthracene)(THF)3
under a dinitrogen atmosphere produced a dark olive green
solid. Examination of these solids by 1H NMR indicated
the presence of anthracene, varying amounts of the starting
materials and what appeared to be decomposition products.
Mass spectral analysis confirmed the absence of any high mass
peaks attributable to a dinitrogen complex. Reductions of 2, 3
and 4 using activated magnesium yielded intensely coloured red-
brown products; analysis indicated a mixture of products, none
of which could be assigned to a dinitrogen complex.
◦
freezer). Hexanes and toluene were purchased anhydrous from
Aldrich and further dried by passage through a tower of silica
and degassed by passage through a tower of Q-5 catalyst
under positive pressure of nitrogen.60 Anhydrous diethyl ether
and THF were stored over sieves and distilled from sodium
benzophenone ketyl under argon. Nitrogen and argon were
dried and deoxygenated by passing the gases through a column
containing molecular sieves and MnO. Deuterated benzene
was dried by refluxing with molten sodium/potassium alloy
in a sealed vessel under partial pressure, then trap-to-trap dis-
tilled, and freeze–pump–thaw-degassed three times. Deuterated
tetrahydrofuran and toluene were dried by refluxing molten
potassium metal in a sealed vessel under vacuum, then trap-
to-trap distilled, and freeze–pump–thaw-degassed three times.
NMR spectra were recorded on either a Bruker AMX-500
1
instrument operating at 500.13 MHz for H spectra, a Bruker
AVA-400 instrument operating at 400.13 MHz for 1H spectra, or
a Bruker AVA-300 instrument operating at 300.13 MHz for 1H
spectra. 1H NMR spectra were referenced to residual protons in
7
the deuterated solvent and Li NMR spectra were referenced
to external LiCl (1.0 M in D2O). Elemental analyses were
performed by Mr P. Borda or Mr M. Lakha of this department;
mass spectra were measured by Mr M. Lapawa, also of this
department.
Materials
The compounds C8K,61 Mg(anthracene)(THF)3,62 YCl3-
(THF)3,63 TiCl4(THF)2,64 ZrCl4(THF)2,64 and ZrCl4(THT)2,65
4 5 6
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9

View Article Online
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9
4 5 7

View Article Online
were prepared according to literature procedures. Magnesium
powder was activated using 1,2-dibromoethane. Phenylarsonic
acid and 1.6 M solutions of BuLi in hexanes were purchased
from Acros Chemicals and used as received. Iodotrimethylsilane
was purchased from Aldrich and used without further purifica-
tion. All other reagents were obtained from a commercial source
and purified by appropriate methods.66
0.702 mmol) in toluene (100 mL) at −78 ◦C. The resulting
solution was warmed to room temperature and stirred for 18 h
during which a yellow colour developed. Removal of the solvent
under vacuum produced a bright yellow solid. Washing the solid
with benzene (∼10 mL) gave 3 as a pale yellow solid. Yield:
0.390 g (55%). X-Ray quality crystals of 3 were grown fro◦m a
saturated solution of THF. 1H NMR (300 MHz, C4D8O, 25 C):
d 8.04 (m, 4H, o-Ph), 7.45 (m, m/p-Ph), 1.53 (AB d, 2J = 13.1 Hz,
4H, ring CH2), 1.38 (AB d, 2J = 13.1 Hz, 4H, ring CH2), 0.39 (s,
24H, ring SiCH3). 1H NMR (300 MHz, C6D6, 25 C): d 8.12 (m,
4H, o-Ph), 7.29 (m, m/p-Ph), 1.25 (AB d, 2J = 13.1 Hz, 4H, ring
Synthesis of AsNAs intermediate HN(SiMe2CH2AsHPh)2.
To a solution of PhAsH2 (14.06 g, 91.2 mmol) in 150 mL Et2O
was added a 1.6 M solution of BuLi in hexanes (57.0 mL,
91.2 mmol) dropwise at −78 ◦C. The solution was warmed
2
CH2), 1.04 (AB d, J = 13.1 Hz, 4H, ring CH2), 0.36 (s, 12H,
◦
to ambient temperature, stirred for 30 min, cooled to −78 C
ring SiCH3), 0.24 (s, 12H, ring SiCH3). MS (EI) m/z, (%): 837,
(30) [M+ − I]. Anal. Calc. for C24H42As2I2N2Si4Zr: C, 29.85; H,
4.38; N, 2.90. Found: C, 29.46; H, 4.62; N, 3.03%.
and added dropwise to a solution of 1,3-bis(chloromethyl)-
1,1,3,3-tetramethyldisilazane (10.50 g, 45.6 mmol) in Et2O
at −78 ◦C. The resulting solution was warmed to ambient
temperature, stirred 12 h then evaporated to dryness. The residue
was extracted into toluene (50 mL), filtered through Celite and
the toluene was removed to yield HN(SiMe2CH2AsHPh)2 as
Synthesis of [As2N2]TiCl2 (4). A solution of 1 (1.08 g,
1.50 mmol) in toluene (10 mL) was added dropwise to a solution
of TiCl4(THF)2 (0.50 g, 1.50 mmol) in toluene (10 mL). The
resulting orange solution was stirred for 5 days followed by
filtration through Celite. Removal of the solvent under vacuum
yielded 4 as an orange solid. Yield: 0.99 g (84%). Dark orange
X-ray quality crystals of 4 were grown from a saturated benzene
1
a yellow oil, that was pure by H NMR spectroscopy. Yield:
◦
1
20.67 g (97%). H NMR (500 MHz, C6D6, 25 C): d 7.50 (dd,
4J = 1.5 Hz, J = 7.6 Hz, 4H, o-Ph), 7.09 (m, 6H, m/p-Ph),
3
3.79 (dd, 3J = 10.0 Hz. 3J = 5.3 Hz, 2H, AsH), 1.06 (dd, 2J =
3
2
3
13.2 Hz, J = 5.3 Hz, 2H, CH2), 0.81 (dd, J = 13.2 Hz, J =
solution. H NMR (300 MHz, C6D6, 25 ◦C): d 7.85 (dd, 4H,
1
1
10.0 Hz, 2H, CH2), 0.23 (d, H, NH), 0.11 (s, 12H, SiCH3).
2
o-Ph), 7.23 (m, m/p-Ph), 1.58 (AB d, J = 13.3 Hz, 4H, ring
Elemental analysis was not attempted because the product was
an air-sensitive oil.
2
CH2), 1.06 (AB d, J = 13.3 Hz, 4H, ring CH2), 0.68 (s, 12H,
ring SiCH3), 0.26 (s, 12H, ring SiCH3). MS (EI) m/z, (%): 738,
(35) [M]+. Anal. Calc. for C24H42As2Cl2N2Si4Ti: C, 38.98; H,
5.72; N, 3.79. Found: C, 38.89; H, 5.91; N, 3.98%.
Synthesis of [As2N2]Li2(1,4-dioxane) (1). A solution of
1.6 M BuLi in hexanes (111 mL, 177.6 mmol) was added
dropwise to a stirred solution of HN(SiMe2CH2AsHPh)2
(20.67 g, 44.4 mmol) and 1,3-bis(chloromethyl)-1,1,3,3-
tetramethyldisilazane (10.23 g, 44.4 mmol) in 500 mL Et2O at
−78 ◦C. The solution was warmed to 25 ◦C, stirred for 12 h,
then evaporated to dryness. The resulting solid was extracted
into 100 mL of toluene, filtered through Celite, and the volume
reduced to ca. 30 mL. 1,4-dioxane (4.01 g, 88.1 mmol) was
added, and the solution reduced to a viscous oil. Addition
of 100 mL hexanes precipitated a colourless solid that was
collected and dried under vacuum. X-Ray quality crystals of
1 were grown by cooling the concentrated toluene solution to
−40 ◦C following addition of 1,4-dioxane. Yield: 21.33 g (67%).
1H NMR (500 MHz, C6D6, 25 ◦C): d 7.55 (m, 4H, o-Ph), 7.14 (m,
6H, m/p-Ph), 3.45 (s, 8H, 1,4-dioxane), 1.12 (AB d, 2J = 13.6 Hz,
4H, ring CH2), 1.04 (AB d, 2J = 13.6 Hz, ring CH2), 0.40 (s, 12H,
Synthesis of ([As2N2]Y)2(l-Cl)2 (5). To an intimate mixture
of 1 (2.000 g, 2.77 mmol) and YCl3(THF)3 (1.140 g, 2.77 mmol)
was added toluene (100 mL). The solution was heated at 90 ◦C
for 16 h followed by a hot (∼50 ◦C) filtration through Celite.
Removal of the solvent afforded a yellow residue. Washing the
residue with pentane gave a colourless solid that was collected
and dried under vacuum. Yield: 1.54 g (75%). X-Ray quality
crystals of 5 were grown by slow evaporation of a filtered hexanes
solution. 1H NMR (400 MHz, C6D6, 25 ◦C): d 7.80 (m, 8H, o-
2
Ph), 7.01 (m, 12H, m/p-Ph), 1.47 (AB d, J = 13.0 Hz, 8H,
2
ring CH2), 1.10 (AB d, J = 13.0 Hz, 8H, ring CH2), 0.38 (s,
24H, ring SiCH3), 0.33 (s, 24H, ring SiCH3). MS (EI) m/z,
(%): 1488, (5) [M]+; 744, (100) [M+ − [As2N2]YCl]. Anal. Calc.
for C48H84As4Cl2N4Si8Y2: C, 38.68; H, 5.68; N, 3.76. Found: C,
39.18; H, 5.89; N, 3.74%.
7
ring SiCH3), 0.22 (s, 12H, ring SiCH3). Li NMR (500 MHz,
C6D6, 25 ◦C) d 0.36 (s, 1Li), −1.48 (s, 1Li). MS (EI) m/z, (%): 634,
(100) [M+ − 1,4-dioxane]. Anal. Calc. for C28H50As2N2O2Si4Li2:
C, 46.53; H, 6.97; N, 3.88. Found: C, 45.35; H, 7.08; N, 4.38%.
Repeated attempts to obtain satisfactory elemental analysis,
even with use of added oxidant, were unsuccessful.
Crystallography
In all cases, suitable crystals were selected and mounted on
a glass fibre using Paratone-N oil or an acceptable substitute
and freezing to −100 ◦C. All measurements were made on a
Rigaku/ADSC CCD area detector with graphite monochro-
mated Mo-Ka radiation. Crystallographic data appear in
Table 6. Data was processed using the d*TREK67 module, part
of the CrystalClear software package, version 1.3.6 SP0,68 and
corrected for Lorentz and polarization effects and absorption.
All structures were solved by direct methods using the program
SIR97.69 All non-hydrogen atoms were refined anisotropically by
least squares procedures on F2 using SHELXL-97.70 Hydrogen
atoms were included but not refined; their positional parameters
Synthesis of [As2N2]ZrCl2 (2). To an intimate mixture of
1 (0.500 g, 0.69 mmol) and ZrCl4(THF)2 (0.29 g, 0.76 mmol)
was added toluene (100 mL). The solution was refluxed for
24 h followed by a hot (∼50 ◦C) filtration through Celite.
Removal of the solvent afforded a cream solid that was collected,
washed with minimal hexanes and vacuum dried to give a
colourless solid. Yield: 0.44 g (70%). The isolated solid con-
tained approximately 0.75 equivalents of toluene. X-Ray quality
crystals of 2 containing one equivalent of co-crystallised toluene
were grown by slow vacuum evaporation of a toluene solution
without agitation. The synthesis of 2 can also be ◦performed
˚
were calculated with fixed C–H bond distances of 0.99 A for
2
3
˚
˚
sp C, 0.98 A for sp C, and 0.95 A for aromatic sp C, with
Uiso set to 1.2 times the Ueq of the attached sp or sp2 C and
1.5 times the Ueq values of the attached sp3 C atom. Methyl
hydrogen torsion angles were determined by electron density.
Structure solution and refinements were conducted using the
WinGX software package, version 1.64.05.71
1
using ZrCl4(THT)2. H NMR (500 MHz, C6D6, 25 C): d 8.08
(dd, 4H, o-Ph), 7.10 (m, m/p-Ph), 1.20 (AB d, 2J = 13.1 Hz, 4H,
2
ring CH2), 0.92 (AB d, J = 13.1 Hz, 4H, ring CH2), 0.38 (s,
12H, ring SiCH3), 0.17 (s, 12H, ring SiCH3). MS (EI) m/z, (%):
780, (40) [M]+. Anal. Calc. for C24H42As2Cl2N2Si4Zr·0.75C7H8:
C, 41.23; H, 5.68; N, 3.30. Found: C, 41.67; H, 5.75; N, 3.44%.
CCDC reference numbers 250322–250326.
Synthesis of [As2N2]ZrI2 (3). Iodotrimethylsilane (1.0 mL,
7.03 mmol) was added dropwise to a solution of 2 (0.582 g,
See http://www.rsc.org/suppdata/dt/b4/b415976d/ for cry-
stallographic data in CIF or other electronic format.
4 5 8
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9

View Article Online
34 Z. Hou, T. L. Breen and D. W. Stephan, Organometallics, 1993, 12,
3158–3167.
Acknowledgements
Dr B. O. Patrick is gratefully thanked for crystallography
assistance and the data collection for complex 2. We thank the
NSERC of Canada for generous financial support.
35 W. A. King, S. D. Bella, A. Gulino, G. Lanza, I. L. Fragala, C. L.
Stern and T. J. Marks, J. Am. Chem. Soc., 1999, 121, 355–366.
36 G. R. Giesbrecht, PhD Thesis, University of British Columbia, 1998.
37 M. D. Fryzuk, G. R. Giesbrecht and S. J. Rettig, Inorg. Chem., 1998,
37, 6928–6934.
38 R. A. Jones, S. T. Schwab and B. R. Whittlesey, Polyhedron, 1984, 3,
References
505–507.
1 J. Emsley and D. Hall, in The Chemistry of Phosphorus, Harper &
Row, London, 1976, pp. 177–207.
39 P. Mercado, A.-J. DiMaio and A. L. Rheingold, Angew. Chem., Int.
Ed., 1987, 26, 244–245.
2 H. Butenschon, Chem. Rev., 2000, 100, 1527–1564.
3 O. J. Scherer, Acc. Chem. Res., 1999, 32, 751–762.
4 A.-J. DiMaio and A. L. Rheingold, Chem. Rev., 1990, 90, 169–190.
5 N. N. Greenwood and A. Earnshaw, in Chemistry of the Elements,
Butterworth-Hienemann, Oxford, 2nd edn., 1997, pp. 547–599.
6 R. K. Harris, in NMR and the Periodic Table, ed. R. K. Harris and
B. E. Mann, Academic Press, London, 1978, pp. 379–382.
7 J. T. Mague and G. Wilkinson, J. Chem. Soc. A, 1966, 1736–1740.
8 J. T. Carlock, Tetrahedron, 1984, 40, 185–187.
9 A. Kojima, C. D. J. Boden and M. Shibasaki, Tetrahedron Lett., 1997,
38, 3459–3460.
10 L. A. v. d. Veen, P. K. Keeven, P. C. J. Kamer and P. W. N. M. v.
Leeuwen, J. Chem. Soc., Dalton Trans., 2000, 2105–2112.
11 M. D. Fryzuk, J. B. Love and S. J. Rettig, Chem. Commun., 1996,
2783–2784.
40 R. Hart, W. Levason, B. Patel and G. Reid, Eur. J. Inorg. Chem., 2001,
2927–2933.
41 G. Jimenez, P. Royo, T. Cuenca and E. Herdtweck, Organometallics,
2002, 21, 2189–2195.
42 A. Shafir, M. P. Power, G. D. Whitener and J. Arnold,
Organometallics, 2001, 20, 1365–1369.
43 R. M. Porter, S. Winston, A. A. Danopoulos and M. B. Hursthouse,
J. Chem. Soc., Dalton Trans., 2002, 3290–3299.
44 D. W. Stephan, J. C. Stewart, F. Guerin, S. Courtney, J. Kickham, E.
Hollink, C. Beddie, A. Hoskin, T. Graham, P. Wei, R. E. v. H. Spence,
W. Xu, L. Koch, X. Gao and D. G. Harrison, Organometallics, 2003,
22, 1937–1947.
45 M. D. Fryzuk, J. B. Love and S. J. Rettig, J. Am. Chem. Soc., 1997,
119, 9071–9072.
46 M. D. Fryzuk, L. Jafarpour, F. M. Kerton, J. B. Love and S. J. Rettig,
Angew. Chem., Int. Ed., 2000, 39, 767–770.
47 A search of the Cambridge Crystallographic Data Centre, July 2004
update, did not produce any complexes containing a Y–As bond.
48 W. J. Evans, J. T. Leman, J. W. Ziller and S. I. Khan, Inorg. Chem.,
1996, 35, 4283–4291.
49 F. Nief and L. Ricard, J. Organomet. Chem., 1997, 529, 357–360.
50 F. Nief and L. Ricard, Organometallics, 2001, 20, 3884–3890.
51 H. Schumann, E. Palamidis, J. Loebel and J. Pickardt,
Organometallics, 1988, 7, 1008–1010.
12 M. D. Fryzuk, L. Jafarpour, F. M. Kerton, J. B. Love, B. O. Patrick
and S. J. Rettig, Organometallics, 2001, 20, 1387–1396.
13 M. D. Fryzuk, J. B. Love, S. J. Rettig and V. G. Young, Science, 1997,
275, 1445–1447.
14 C. S. Palmer and R. Adams, J. Am. Chem. Soc., 1922, 44, 1356–
1382.
15 M. A. Beswick, Y. G. Lawson, P. R. Raithby, J. A. Wood and D. S.
Wright, J. Chem. Soc., Dalton Trans., 1999, 1921–1922.
16 A. Bashall, A. D. Bond, A. D. Hopkins, S. J. Kidd, M. McPartlin,
A. Steiner, R. Wolf, A. D. Woods and D. S. Wright, J. Chem. Soc.,
Dalton Trans., 2002, 343–351.
17 M. Driess, U. Hoffmanns, S. Martin, K. Merz and H. Pritzkow,
Angew. Chem., Int. Ed., 1999, 38, 2733–2736.
52 M. D. Fryzuk, C. M. Kozak, M. R. Bowdridge, B. O. Patrick and
S. J. Rettig, J. Am. Chem. Soc., 2002, 124, 8389–8397.
53 D. M. Roddick, M. D. Fryzuk, P. F. Seidler, G. L. Hillhouse and J. E.
Bercaw, Organometallics, 1985, 4, 97–104.
18 A. Bashall, M. A. Beswick, N. Choi, A. D. Hopkins, S. J. Kidd, Y. G.
Lawson, M. E. G. Mosquera, M. McPartlin, P. R. Raithby, A. E. H.
Wheatley, J. A. Wood and D. S. Wright, J. Chem. Soc., Dalton Trans.,
2000, 479–486.
54 M. D. Fryzuk, C. Kozak, P. Mehrkhodavandi, L. Morello, B. O.
Patrick and S. J. Rettig, J. Am. Chem. Soc., 2002, 124, 516–517.
55 S. M. Mullins, A. P. Duncan, R. G. Bergman and J. Arnold, Inorg.
Chem., 2001, 40, 6952–6963.
56 T. E. Hanna, I. Keresztes, E. Lobkovsky, W. H. Bernskoetter and P. J.
Chirik, Organometallics, 2004, 23, 3448–3458.
57 P. Vanysek, in CRC Handbook of Chemistry and Physics, ed.
D. R. Lide, CRC Press, Boca Raton, FL, 84th edn. [Online], 2003.
58 B. Bogdanovic, Acc. Chem. Res., 1988, 21, 261–267.
59 J. D. Protasiewicz, P. A. Bianconi, I. D. Williams, S. Liu, C. P. Rao
and S. J. Lippard, Inorg. Chem., 1992, 31, 4134–4142.
60 A. B. Pangborn, M. A. Giardello, R. H. Grubbs, R. K. Rosen and
F. J. Timmers, Organometallics, 1996, 15, 1518–1520.
61 D. E. Bergbreiter and J. M. Killough, J. Am. Chem. Soc., 1978, 100,
2126–2134.
19 A. Bashall, F. Garcia, A. A. Hopkins, J. A. Wood, M. McPartlin,
A. D. Woods and D. S. Wright, Dalton Trans., 2003, 1143–1147.
20 M. Driess, S. Kuntz, K. Merz and H. Pritzkow, Chem. Eur. J., 1998,
4, 1628–1632.
21 A. Bondi, J. Phys. Chem., 1964, 68, 441–451.
22 M. D. Fryzuk, C. M. Kozak, M. R. Bowdridge, W. Jin, D. Tung,
B. O. Patrick and S. J. Rettig, Organometallics, 2001, 20, 3752–3761.
23 M. D. Fryzuk, S. A. Johnson, B. O. Patrick, A. Albinati, S. A. Mason
and T. F. Koetzle, J. Am. Chem. Soc., 2001, 123, 3960–3973.
24 M. D. Fryzuk, G. R. Giesbrecht, S. J. Rettig and G. P. A. Yap,
J. Organomet. Chem., 1999, 591, 63–70.
25 M. D. Fryzuk, J. B. Love and S. J. Rettig, Organometallics, 1998, 17,
846–853.
26 R. R. Schrock, S. W. Seidel, Y. Schrodi and W. M. Davis,
Organometallics, 1999, 18, 428–437.
27 M. D. Fryzuk, A. Carter and S. J. Rettig, Organometallics, 1992, 11,
469–472.
62 B. Bogdanovic, S. Liao, R. Mynott, K. Schlichte and U. Westeppe,
Chem. Ber., 1984, 117, 1378–1392.
63 K. H. D. Haan, J. L. d. Boer, J. H. Teuben, A. L. Spek, B. Kojic-
Prodic, G. R. Hays and R. Huis, Organometallics, 1986, 5, 1726–1733.
64 L. E. Manzer, Inorg. Synth., 1982, 21, 135–140.
65 H. Brand and J. Arnold, Organometallics, 1993, 12, 3655–3665.
66 D. D. Perrin and W. L. F. Amarego, in Purification of Laboratory
Chemicals, Butterworth-Heinemann, Oxford, 3rd edn., 1994.
67 J. W. Pflugrath, Acta Crystallogr., Sect. D, 1999, 55, 1718–1725.
68 CrystalClear: An Integrated Program for the Collection and Process-
ing of Area Detector Data, Rigaku Corporation, 2002–2004.
69 A. Altomare, M. C. Burla, G. Cammali, M. Cascarano, C. Giacov-
azzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and A. Spagna,
J. Appl. Crystallogr., 1999, 32, 115–119.
28 M. D. Fryzuk, D. J. Berg and T. S. Haddad, Coord. Chem. Rev., 1990,
99, 137–212.
29 E. Hey-Hawkins and F. Lindenberg, Organometallics, 1994, 13, 4643–
4644.
30 L. Chen and F. A. Cotton, J. Cluster Sci., 1998, 9, 63–91.
31 M. Driess, H. Ackermann, J. Aust, K. Merz and C. v. Wullen, Angew.
Chem., Int. Ed., 2002, 41, 450–453.
32 W. Levason, M. L. Matthews, B. Patel, G. Reid and M. Webster,
Dalton Trans., 2004, 3305–3312.
33 M. D. Fryzuk, J. R. Corkin and B. O. Patrick, Can. J. Chem., 2003,
81, 1376–1387.
70 G. M. Sheldrick, SHELX97: Programs for Crystal Structure Analysis
(Release 97-2), University of G
o¨ttingen, Germany, 1998.
71 J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
D a l t o n T r a n s . , 2 0 0 5 , 4 5 2 – 4 5 9
4 5 9