Synthesis and structural diversity of ZnCl2 and Zn(C 6F5)2 complexes of a phosphinimine ligand

Article abstract of DOI:10.1002/zaac.201100355

Zinc complexes of the potentially bidentate neutral monophosphinimine ligand 4-(ArN=PPh₂)dibenzofuran were prepared. Two derivatives of this framework were studied, which differ in the steric demand of the N-aryl group (Ar = Dipp, Mes). The ligand interacts with diethylzinc in solution but does not form a tightly bound complex, whereby the degree of association is found to be dependent on temperature. However, isolable complexes are formed upon reaction with the more Lewis acidic precursors ZnCl₂ and Zn(C₆F₅)₂. In this way, the ZnCl₂ complexes 1 and 2 and Zn(C₆F₅)₂ complexes 3 and 4 were prepared and structurally characterized. The nuclearity of 1 and 2 was shown to depend on the bulk of the ligand. Furthermore, the strength of the bonding interaction between the zinc atoms and the dibenzofuran oxygen atoms in 3 and 4 also depends on the choice of ancillary ligand. Attempts to further derivatize these complexes were unsuccessful, and thus, functionalization of the complex LZnEt(OTf) was undertaken instead, resulting in formation of the novel linear trinuclear complex 5. Copyright

Full text of DOI:10.1002/zaac.201100355

ARTICLE
DOI: 10.1002/zaac.201100355
Synthesis and Structural Diversity of ZnCl2 and Zn(C6F5)2 Complexes of a
Phosphinimine Ligand
Craig A. Wheaton,[a] Benjamin J. Ireland,[a] and Paul G. Hayes*[a]
Keywords: Phosphinimine; Zinc; N,O ligands; X-ray diffraction; Dibenzofuran
Abstract. Zinc complexes of the potentially bidentate neutral mono- prepared and structurally characterized. The nuclearity of 1 and 2 was
phosphinimine ligand 4-(ArN=PPh2)dibenzofuran were prepared. Two shown to depend on the bulk of the ligand. Furthermore, the strength
derivatives of this framework were studied, which differ in the steric of the bonding interaction between the zinc atoms and the dibenzofu-
demand of the N-aryl group (Ar = Dipp, Mes). The ligand interacts ran oxygen atoms in 3 and 4 also depends on the choice of ancillary
with diethylzinc in solution but does not form a tightly bound complex, ligand. Attempts to further derivatize these complexes were unsuccess-
whereby the degree of association is found to be dependent on tem-
perature. However, isolable complexes are formed upon reaction with
ful, and thus, functionalization of the complex LZnEt(OTf) was under-
taken instead, resulting in formation of the novel linear trinuclear com-
the more Lewis acidic precursors ZnCl2 and Zn(C6F5)2. In this way, plex 5.
the ZnCl2 complexes 1 and 2 and Zn(C6F5)2 complexes 3 and 4 were
reaction with an appropriate aryl azide under standard Staud-
Introduction
inger conditions.[8] Two derivatives of this architecture have
been utilized, where the choice of N-aryl group was either
2,4,6-trimethylphenyl (Mes), LMes, or 2,6-diisopropylphenyl
(Dipp), LDipp, which vary significantly in steric bulk. The
preparation of LDipp was reported in a previous study,[7e] but
this is the first account of the smaller analogue LMes
(Scheme 1).
Bidentate phosphinimine ligands, which have seen substan-
tially increased use in recent years, were utilized to support a
wide range of metals,[1] including early[2] and late transition
metals,[3] rare-earth metals,[4] main group elements,[5] and a
variety of zinc complexes.[6] The diverse applications found
for these species include olefin polymerization,[2a] ring-open-
ing polymerization of lactones,[4a,4b,6e] and hydroamination.[4d]
We have been studying chemically robust, formally neutral
phosphinimine ligand architectures for stabilizing cationic di-
valent metal atoms.[7] Our motivation for this work was to
study the efficacy of such highly electrophilic complexes to-
ward the ring-opening polymerization of lactones. However,
the fundamental coordination chemistry of these scaffolds has
remained largely unexplored. The presented report details the
synthesis and characterization of several neutral zinc com-
plexes of a monophosphinimine ligand, constructed by instal-
lation of a phosphinimine functionality at the 4-position of a
rigid dibenzofuran (dbf) core. The insight gleaned from these
studies regarding the fundamental properties of this hemilabile,
potentially bidentate ligand framework, is described herein.
Results and Discussion
Ligand Synthesis and Characterization
The neutral ligands employed in this study were synthesized
in one simple step from 4-diphenylphosphino-dibenzofuran by
* Prof. Dr. P. Hayes
Fax: +01-403-329-2057
E-Mail: p.hayes@uleth.ca
[a] Department of Chemistry and Biochemistry
University of Lethbridge
E866 University Hall, 4401 University Drive
Lethbridge, Alberta, Canada
Scheme 1. Preparation of complexes 1–5.
Z. Anorg. Allg. Chem. 2011, 637, (14-15), 2111–2119
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C. A. Wheaton, B. J. Ireland, Paul G. Hayes
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As discussed above, LMes was easily prepared by reaction nance shifted to δ = 29.9 ppm.[6b] Unsurprisingly, attempts to
of the precursor phosphine with mesityl azide. This afforded isolate a metal complex resulted in loss of diethylzinc upon
the ligand in 69% yield as an analytically pure powder that is removal of the solvent in vacuo, giving only the free ligand.
indefinitely stable at ambient temperature when stored in an
Exposure of LMes to diethylzinc in C6D6 caused a more per-
inert atmosphere. The diagnostic 31P{1H} NMR resonance ap- ceptible change, resulting in a 31P{1H} NMR resonance at δ =
pears at δ = –15.3, which is upfield of the corresponding LDipp 8.7 when three equiv. of diethylzinc were used. This represents
resonance by approximately 2 ppm.[7e] While the aromatic re- a 6.6 ppm downfield shift relative to the free ligand. However,
gion of the 1H NMR spectrum is complicated, the mesityl this change is still much smaller than expected for a tightly
groups provide excellent spectroscopic handles, with singlet bound complex, and attempts to isolate this species again re-
signals appearing at δ = 2.30 and 2.21 ppm for the para- and sulted only in liberation of the free ligand. Furthermore, de-
ortho-CH3 groups, respectively. Similarly, the isopropyl spite the fact that three equiv. of the zinc reagent were em-
groups of LDipp provide diagnostic resonances in the aliphatic ployed, only one unique set of resonances attributed to the
1
1
region of the H spectrum. Single crystals of LMes were ob- ethyl groups was observed in the H NMR spectrum (δ = 1.19
tained and the crystal structure was determined (Figure 1), and 0.14 ppm for the CH3 and CH2 groups, respectively). This
which serves to verify the connectivity of the molecule. The suggests an exchange process that is rapid on the NMR times-
P–N bond length is in the expected range for a formal bond cale due to labile metal-ligand bonding. Variable temperature
order of two [P(1)–N(1) = 1.547(3) Å], and is similar to that NMR studies ([D8]toluene) were performed in an attempt to
measured in the previously reported crystal structure of LDipp garner more information about this equilibrium (Figure 2). It
[1.559(2) Å],[7e] as well as other neutral phosphinimines.[9]
was found that the chemical shift of the 31P signal is highly
dependent on temperature, with more downfield shifts ob-
served at lower temperatures (Figure 2). At –80 °C, the reso-
nance appears at δ = 11.2, which is 26.5 ppm downfield of the
free ligand. These observations corroborate the idea that the
system exists in equilibrium between the desired metal com-
plex and the free starting materials. The fact that free ZnEt2
and LMes are greatly favored at ambient temperature suggests
a very weak metal-ligand interaction. Similar lability was
noted for a related diazadiene ligand system.[10]
ZnCl2 Complexes
Due to the inability to access neutral dialkylzinc complexes,
we opted to pursue the preparation of species from much more
electron deficient zinc precursors. All reactions were per-
formed in non-coordinating solvents to prevent formation of
solvent adducts, which could interfere with coordination of the
weakly-binding ligand. Reaction of LDipp with ZnCl2 required
harsh conditions due to the poor solubility of the metal salt,
but at 120 °C in toluene slow and irreversible conversion to a
new species was observed. After 48 h, the reaction was com-
plete and compound 1 was isolated as an analytically pure
white powder in 65% yield. The complex exhibits a single
signal in the 31P{1H} NMR spectrum at δ = 30.5 ppm
Figure 1. Thermal ellipsoid plot of one of two crystallographically
unique molecules of LMes in the crystal lattice, with hydrogen-atoms
and a molecule of toluene omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
Reactivity with Diethylzinc
Our initial motivation for preparing these ligands was to
eventually utilize them for the preparation of cationic hetero-
leptic zinc complexes. To that end, it was our desire to first
prepare the neutral complex of diethylzinc, which would be
converted into the cationic ethylzinc complex via alkide ab-
straction with a Lewis or Brønsted acid. However, reaction of
L
Dipp with diethylzinc did not afford the anticipated result, but
rather, it was discovered that exposure of the ligand to a single
equiv. of diethylzinc resulted in little change in the spectro-
scopic features of the ligand. Specifically, the 31P{1H} NMR
resonance was observed at δ = 12.6 in [D6]benzene, which
only represented a 0.8 ppm downfield shift compared to the
free ligand. This small change does not suggest a tightly bound
complex, as the 31P{1H} NMR shift of phosphinimine moeities
is well established to be much more sensitive to the presence
of a metal atom. For example, a recent report by Mehrkhodav-
andi et al. examined a phosphinimine-imine ligand, which res-
Figure 2. Variable temperature 31P{1H} NMR spectra of a C6D6 solu-
onated at δ = 0.9, and upon complexation of ZnCl2 the reso- tion containing stoichiometric quantities of LMes and ZnEt2.
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ZnCl2 and Zn(C6F5)2 Complexes of a Phosphinimine Ligand
(CD2Cl2), which is indicative of tight ligand coordination. Ad- about zinc is 356.63(5)°. Interestingly, the zinc atom sits sig-
1
ditionally, it was observed in the H NMR spectrum that the nificantly out of the plane defined by the dibenzofuran back-
isopropyl methyl groups were now inequivalent, giving rise to bone (approx. 1.67 Å).
doublets at δ = 1.21 and 0.23 ppm. The complex is only spar-
Complex 2 was prepared using LMes under similar reaction
ingly soluble in aromatic solvents, and as a result some of the conditions as for 1, giving an analytically pure white powder
product crystallized on the walls of the reaction vessel during in approximately 89% yield. This complex is dramatically less
the course of the reaction. From this material, high quality soluble than 1 in common organic solvents and correspond-
single crystals were obtained, and the molecular structure of ingly only 1H and 31P{1H} NMR spectra were obtained. A
complex 1 was determined (Figure 3, Table 1).
single resonance was noted in the 31P{1H} NMR spectrum at
δ = 28.0 ppm, while diagnostic mesityl peaks appear at δ =
2.01 (o-CH3) and δ = 1.87 ppm (p-CH3). Elemental analysis
indicated the same stoichiometry of one ligand per ZnCl2 unit;
however, the limited solubility was suggestive of some degree
of aggregation.
From material that had precipitated during the course of the
reaction, a suitable single crystal of complex 2 was obtained
and its solid-state structure was determined (Figure 4, Table 1).
The structure confirms that aggregation does indeed occur,
with the complex existing as a dimer in the solid state. The
ligand does not adopt an orientation suitable for bidentate co-
ordination, and thus, no interaction was noted between the zinc
atom and the oxygen atom. Instead, the available coordination
site is occupied by a bridging chloride Cl(2), giving rise to
the observed dimeric structure. The two bridging chlorides are
virtually equidistant between the zinc atoms with bond lengths
of approximately 2.34 Å and a Zn(1)–Cl(2)–Zn(1b) angle ap-
proaching 90°. At 2.20 Å the terminal Zn–Cl distance is sub-
Figure 3. Thermal ellipsoid plot of complex 1, with hydrogen atoms
omitted for clarity. Thermal ellipsoids are drawn at the 30% prob-
ability level.
Table 1. Selected bond lengths /Å and angles /° for the crystal struc-
tures of complexes 1 and 2.
1
2
Zn(1)–N(1)
Zn(1)–O(1)
Zn(1)–Cl(1)
Zn(1)–Cl(2)
1.960(1)
2.381(1)
2.2003(3)
2.1713(4)
1.609(1)
120.87(3)
118.95(3)
116.81(2)
98.59(3)
125.05(6)
–
1.994(2)
–
2.2048(8)
2.3437(9), 2.3450(9)
1.609(2)
P(1)–N(1)
N(1)–Zn(1)–Cl(1)
N(1)–Zn(1)–Cl(2)
Cl(1)–Zn(1)–Cl(2)
Cl(1)–Zn(1)–O(1)
P(1)–N(1)–Zn(1)
Zn(1)–Cl(2)–Zn(1b)
115.86(7)
107.47(7), 115.41(7)
112.18(4), 112.42(4)
–
124.4(1)
89.37(3)
The solid-state structure revealed that 1 is a monomeric
complex, with the ligand bound to the zinc atom in a bidentate
manner. The bond length between the phosphinimine nitrogen
and the zinc atom is in the expected range [Zn(1)–N(1) =
1.960(1) Å], whereas the zinc oxygen contact is notably longer
[Zn(1)–O(1) = 2.381(1) Å], suggesting a much weaker interac-
tion. Furthermore, examination of the bond angles leads to the
conclusion that the coordination is best described as distorted
trigonal pyramidal. N(1), Cl(1), and Cl(2) occupy the equato-
Figure 4. Thermal ellipsoid plot of the dimeric complex 2, with hydro-
gen atoms and a disordered molecule of toluene omitted for clarity.
rial sites with bond angles close to 120°; the sum of the angles Thermal ellipsoids are drawn at the 30% probability level.
Z. Anorg. Allg. Chem. 2011, 2111–2119
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C. A. Wheaton, B. J. Ireland, Paul G. Hayes
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stantially shorter and the Zn–N length is within the normal
range [1.994(2) Å]. In this case, the arrangement at zinc is
most accurately described as four-coordinate tetrahedral.
The electronic properties of the ligands in 1 and 2 are highly
similar; thus, it is reasonable to suggest that the large structural
differences observed in the solid state are predominantly due
to steric effects. In the less crowded 2, dimerization is favored
over the weak Zn–O interaction, whereas in complex 1, the
bulky isopropyl groups appear to prohibit this dimerization,
forcing the zinc atom to interact with the dbf oxygen instead.
Zn(C6F5)2 Complexes
Complexes of Zn(C6F5)2 were more straightforward to pre-
pare due to the higher solubility of the zinc precursor com-
pared with ZnCl2; complexation occurred immediately upon
mixing the reagents in toluene solution. Reaction of LDipp with
Zn(C6F5)2 gave pale yellow crystals of complex 3 in 81%
yield, while the corresponding reaction of LMes afforded 4 in
88% yield. Each complex exhibits a single resonance in the
31P{1H} NMR spectrum, with chemical shifts approximately
2 ppm upfield of the analogous ZnCl2 complexes (3: δ = 28.5;
Figure 6. Thermal ellipsoid plot of complex 4, with hydrogen atoms
and a molecule of pentane omitted for clarity. Thermal ellipsoids are
drawn at the 30% probability level.
Table 2. Selected bond lengths /Å and angles /° in complexes 3 and 4.
1
4: δ = 25.7 ppm). The H NMR spectra are also very similar
3
4
to those observed for complexes 1 and 2. For complex 3, the
isopropyl methyl resonances appear at δ = 1.11 and 0.38 ppm.
In complex 4, the p-CH3 signal is again shifted upfield of the
free ligand, to δ = 1.87 ppm. Both complexes exhibit high solu-
bility in aromatic solvents, suggesting no significant aggrega-
tion. Single crystals of both 3 and 4 were grown from toluene/
pentane solutions at –35 °C. The molecular structures are de-
picted in Figure 5 and Figure 6 for 3 and 4, respectively, and
selected metrical parameters for both complexes are located in
Table 2.
Zn–N
2.016(2)
3.144(2)
2.014(2)
2.012(2)
1.614(2)
125.6(1)
113.22(8)
123.53(8)
122.18(9)
74.39(6)
2.006(2)
2.669(2)
2.014(2)
2.010(3)
1.603(2)
122.1(1)
108.33(9)
119.94(9)
127.5(1)
81.08(7)
Zn–O
Zn–C(x)a)
Zn–C(y)a)
P–N
P–N–Zn
N–Zn–C(x)a)
N–Zn–C(y)a)
C(x)–Zn–C(y)a)
N–Zn–O
a) 3: x = 37, y = 43; 4: x = 34, y = 40.
The solid state crystal structure of complex 3 corroborated
its monomeric nature and revealed monodentate nitrogen coor-
dination of the ligand. There is no meaningful bonding interac-
tion between zinc and the dbf oxygen [Zn(1)–O(1) =
3.144(2) Å]. This bond is likely prevented from forming due
to the sterically demanding C6F5 groups. The coordination ar-
rangement is thus three-coordinate trigonal planar, rendering
the zinc atom coordinatively unsaturated. The phosphinimine–
Zn bond length lies within the usual range, as do the Zn–C
bonds. The bond angles about these sites do not deviate signifi-
cantly from 120°, with their sum totalling 358.9(1)°.
Complex 4 is essentially isostructural with 3, with one no-
table exception being
a significant Zn–O interaction
[2.669(2) Å]. This is likely due to the sterically less demanding
ancillary ligand, which permits a more suitable orientation for
bidentate coordination. However, the steric requirements of the
system remain high, thereby preventing a close contact (i.e. a
typical Zn–O bond length of 2.0 Å). The sum of angles about
zinc is reduced to 355.8(2)°, whereas the zinc atom lies 0.24 Å
out of the plane defined by the coordinated nitrogen and car-
bon atoms (cf. 0.12 Å in 4 and 0.22 Å in 1).
Figure 5. Thermal ellipsoid plot of complex 3, with hydrogen atoms
and solvent molecules omitted for clarity. Thermal ellipsoids are drawn
at the 30% probability level.
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ZnCl2 and Zn(C6F5)2 Complexes of a Phosphinimine Ligand
Other Complexes
The molecular structure of complex 5 is depicted in Fig-
ure 7, and selected bond lengths and angles are given in
Table 3. Two unique zinc atoms are present in the complex,
with the central zinc [Zn(1)] occupying an inversion center.
Each ligand is bound only through the phosphinimine nitrogen
atom to a four-coordinate, tetrahedral zinc atom [Zn(2)], of
which there are two in the complex. Both of these zinc atoms
are also bound to two bridging triflate units and a bridging
methoxide group, which connect to the central octahedral zinc
atom [Zn(1)]. This complex can be considered as two mole-
cules of the targeted complex linked by a Zn(OTf)2 moiety.
While it was surprising that this linear trinuclear zinc complex
was formed, the structural motif is known in zinc chemistry
and was first reported by Clegg and co-workers in 1985.[12]
There are many examples reported since, although they typi-
cally incorporate acetate bridges.[13] Complex 5 is, to the best
of our knowledge, the first example of a linear trinuclear zinc
complex to incorporate either triflate or simple alkoxide brid-
ges. Although formation of this complex was not the desired
result, it does suggest potential for derivatization of neutral
alkylzinc complexes of this type in the future.
Due to our interest in lactide polymerization catalysis, it was
desirable to prepare a zinc alkoxide or amide species because
such compounds are known to be excellent initiators for this
transformation.[11] However, attempts to functionalize com-
plexes 1–4 have met with little success. In particular, attempted
salt metathesis reactions of the ZnCl2 complexes with alkali
metal amide or alkoxide salts appear to initially give the de-
sired product. However, upon installation of amide or alkoxide
functionalities, aggregation occurs resulting in release of the
free ligand. While the C6F5 substituents of complexes 3 and 4
are not particularly amenable to derivatization, attempts were
made to remove a C6F5 group using the protic salt
[HNMe2][B(C6F5)4]. It was found, however, that upon reaction
of 3 with this reagent, the acidic proton was simply transferred
to the phosphinimine nitrogen with displacement of Zn(C6F5)2,
resulting in formation of the previously reported compound
[LDippH][B(C6F5)4].[7e] Reaction of complex 4 with this same
reagent produced a similar result.
Due to the inability to functionalize complexes 1–4, we have
instead explored derivatization of the previously reported alk-
ylzinc compound LDippZnEt(OTf).[7e,11b] It was anticipated
that selective removal of the ethyl group by alkane elimination
might be possible. In such a scenario, the weakly coordinating
triflate group would be expected to maintain sufficiently high
Lewis acidity at the metal atom to prevent ligand dissociation.
Thus, LDippZnEt(OTf) reacted with one equiv. of dry methanol
in C6D6 and the reaction mixture was monitored by in situ
NMR spectroscopy. Upon heating the solution to 100 °C for 1
1
h, ethane was observed at δ = 0.80 ppm in the H NMR spec-
trum. The reaction mixture contained the free ligand and a new
species which exhibited a broad 31P NMR resonance at δ =
31.7 ppm, in approximately a 1:1 ratio. Within one day at am-
bient temperature, a significant amount of material had crys-
tallized from the reaction mixture. This material proved too
insoluble to characterize spectroscopically, but single crystals
suitable for X-ray diffraction had formed, and so the solid-
state structure was determined, revealing it to be the linear
trinuclear zinc complex 5. In order to give a balanced equation,
complex
5 must arise with concomitant formation of
0.25 equiv. of dimethoxy zinc and 0.5 equiv. of free ligand
(Scheme 2), which accounts for observation of free LDipp in
the reaction mixture.
Figure 7. Thermal ellipsoid plot of complex 5, with hydrogen atoms
and a symmetry equivalent ligand omitted for clarity. Thermal ellip-
soids are drawn at the 30% probability level.
Conclusions
It has been established that neither LDipp nor LMes bind
strongly to diethylzinc, resulting instead in a solution equilib-
rium favoring the free ligand at ambient temperature. How-
ever, when more Lewis acidic zinc precursors were employed
[ZnCl2, Zn(C6F5)2, and EtZnOTf], binding of the ligand was
Scheme 2. Generation of complex 5 by reaction of LDippZnEt(OTf)
with one equiv. of methanol.
Z. Anorg. Allg. Chem. 2011, 2111–2119
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C. A. Wheaton, B. J. Ireland, Paul G. Hayes
ARTICLE
mixture was stirred for 12 h at ambient temperature producing a cloudy
yellow solution. Filtration to remove residual insoluble impurities
yielded a clear yellow solution, which in turn yielded an oily yellow
solid upon removal of toluene in vacuo. Pentane (approx. 60 mL) was
added by vacuum transfer to the crude product and the mixture was
sonicated for approximately 2 min and additionally vigorously stirred
for 2 h. Filtration of the resulting suspension afforded LMes as a white
powder, which was washed three times with 10 mL portions of pentane
and dried in vacuo. Total yield was 69% (0.64 g, 1.3 mmol). 1H NMR
([D6]benzene): δ = 8.02 (dd, 2JHP = 12.1, 3JHH = 6.0 Hz, 1 H, dbf-C3),
Table 3. Selected bond lengths /Å and angles /° in the structure of 5.
Atoms
Distances
Atoms
Angles
P(1)–N(1)
1.618(3)
1.944(2)
2.015(2)
2.023(2)
1.902(2)
2.200(2)
2.212(2)
1.968(2)
N(1)–Zn(2)–O(1)
O(1)–Zn(2)–O(6)
N(1)–Zn(2)–O(2)
O(2)–Zn(2)–O(6)
Zn(2)–O(6)–Zn(1)
O(6)–Zn(1)–O(4)
O(6)–Zn(1)–O(3)
114.1(1)
104.21(9)
106.4(1)
101.65(9)
120.0(1)
90.77(8)
90.14(8)
Zn(2)–N(1)
Zn(2)–O(1)
Zn(2)–O(2)
Zn(2)–O(6)
Zn(1)–O(3)
Zn(1)–O(4)
Zn(1)–O(6)
O(6)–Zn(1)–O(6_b) 180.00(8)
3
3
3
7.91 (dd, JHP = 11.3, JHH = 5.8 Hz, 4 H, o-PPh2), 7.61 (d, JHH
=
6.9 Hz, 1 H, dbf), 7.49 (m, 1 H, dbf), 7.08–6.93 (br. ov m, 10 H, m-
PPh2, p-PPh2, dbf), 6.88 (s, 2 H, m-Mes), 2.30 (s, 6 H, o-Mes), 2.21
(s, 3 H, p-Mes) ppm. 13C{1H} NMR ([D6]benzene): δ = 157.1 (d,
2JCP = 3.0 Hz, dbf-quaternary), 156.8 (s, dbf-quaternary), 145.6 (s, dbf-
quaternary), 134.7 (d, 1JCP = 105 Hz, dbf-C4), 132.8 (d, 2JCP = 9.1 Hz,
stronger and essentially irreversible. Crystallographic studies
demonstrated that the binding mode of the ligand is either η1
or κ2, depending on the steric bulk of the N-aryl group of
the ligand. In the case of ZnCl2, the bulkier ligand prevents
dimerization through bridging chloride groups, thereby pro-
moting a weak Zn–O interaction. Conversely, in the case of
Zn(C6F5)2 complexes, the Zn–O interaction is inhibited by the
bulkier perfluoroaryl moiety. Further functionalization of com-
3
o-PPh2), 132.7 (s, p-Mes CCH3), 132.4 (d, JCP = 6.0 Hz, m-PPh2),
3
131.5 (d, JCP = 3.0 Hz, dbf-C2), 129.7 (s, o-Mes CCH3), 129.5 (s, m-
2
Mes) 128.8 (d, JCP = 12.1 Hz, dbf-C3), 127.7 (s, ipso-Mes), 125.4 (s,
dbf-quaternary), 124.7 (d, 4JCP = 2.4 Hz, p-PPh2), 123.5 (s, dbf), 123.5
1
(s, dbf), 123.4 (s, dbf), 121.2 (s, dbf), 119.3 (d, JCP = 96.6 Hz, ipso-
plexes 1–4 was unsuccessful; however, attempts to derivatize PPh2), 112.4 (s, dbf), 22.0 [s, o-Mes C(CH3)], 21.3 [s, p-Mes C(CH3)]
ppm. 31P{1H} NMR ([D6]benzene): δ = –15.3 (s) ppm. Anal. for
C33H28NOP: calcd. C: 81.65; H: 5.81; N: 2.88%; found: C: 81.16; H:
6.15; N: 2.94%. X-ray quality single crystals of LMes were grown from
a saturated solution in toluene at –35 °C.
L
DippZnEt(OTf) by reaction with methanol afforded a novel
linear trinuclear complex with unusual methoxy and triflate
bridges. Overall, we have observed that variation in metal pre-
cursor and ligand substitution leads to an intriguing diversity
of solution – and solid-state structures, which we hope to ex-
ploit in future studies.
Synthesis of LDippZnCl2 (1): LDipp (100 mg, 0.190 mmol) and ZnCl2
(25.8 mg, 0.190 mmol) were combined in a bomb with toluene (5 mL),
resulting in dissolution of the ligand and a suspension of the zinc di-
chloride. This mixture was heated to 120 °C for 24 h, resulting in a
clear yellow solution with all material dissolved. Allowing the reaction
mixture to cool caused the solution to become cloudy. This solution
was transferred to a vial and left at ambient temperature to crystallize
for 48 h, resulting in the formation of white crystals of the compound.
The supernatant was decanted and the crystals were washed with pen-
tane (3ϫ1 mL) and dried in vacuo, giving complex 1 in 64.8% yield
Experimental Section
General: All manipulations of air-sensitive materials and reagents
were conducted using high-vacuum techniques in a purified argon at-
mosphere or in a glove box (MBraun Labmaster 130). Protio solvents
were purified with an MBraun solvent purification system (MB-SPS),
stored in Teflon-sealed glass vessels over appropriate drying agents,
and vacuum transferred directly to reaction vessels. Deuterated sol-
vents (Cambridge Isotopes) were dried with appropriate drying agents,
vacuum transferred, and stored in an inert atmosphere prior to use.
ZnCl2, Zn(C6F5)2, and ZnEt2 were purchased from commercial sources
in high purity and used without additional purification. LDipp was pre-
pared as previously reported,[7e] while MesN3[14] and 4-(diphenylphos-
phanyl)dibenzofuran[15] were prepared by the standard literature meth-
ods. NMR spectra [1H (300.13 MHz), 13C{1H} (75.47 MHz), 31P{1H}
(121.48 MHz), 19F (282.42 MHz), and 11B (96.29 MHz)] were col-
lected with a Bruker Avance II NMR spectrometer equipped with a
variable-temperature unit. Spectra were collected at ambient tempera-
ture and referenced to residual solvent resonances (1H and 13C{1H}),
or an external standard [triphenylphosphine (31P{1H}), trifluorotoluene
(19F), or boron trifluoride diethyl etherate (11B)]. 1H and 13C NMR
peak assignments were facilitated by DEPT, COSY, and HSQC experi-
ments. X-ray crystal data were collected with a Bruker AXS SMART
APEX II single-crystal X-ray diffractometer [Mo-Kα (λ = 0.71073 Å)].
Elemental analyses were performed with an Elementar Vario Micro-
cube.
1
3
(81.5 mg, 0.123 mmol). H NMR (CD2Cl2): δ = 8.36 (d, 1 H, JHH
=
3
7.7 Hz, 1-dbf), 8.10 (d, 1 H, JHH = 7.7 Hz, 9-dbf), 7.91 (br. s, 1 H,
6-dbf), 7.67–7.58 (ov m, 3 H, p-Ph + 7-dbf), 7.58–7.37 (ov m, 10 H,
o-Ph + m-Ph + 2-dbf + 8-dbf), 7.18–6.94 (ov m, 4 H, m-Dipp + p-
Dipp + 3-dbf), 3.35 [sp, 2 H, 3JHH = 6.8 Hz, CH(CH3)2], 1.21 [d, 6 H,
3JHH = 6.8 Hz, CH(CH3)2], 0.23 [d, 6 H, JHH = 6.8 Hz, CH(CH3)2]
3
ppm. 13C{1H} NMR (CD2Cl2): δ = 158.55 (s, Aromatic C), 156.36 (s,
3
3
Aromatic C), 147.16 (d, JCP = 5.4 Hz, Aromatic C), 138.51 (d, JCP
2
= 7.9 Hz, Aromatic C), 134.72 (d, JCP = 10.0 Hz, o-Ph), 134.18 (d,
2JCP = 11.1 Hz, 3-dbf), 133.90 (d, JCP = 2.6 Hz, p-Ph), 129.68 (s, 8-
dbf), 129.48 (d, JCP = 12.5 Hz, m-Ph), 127.43 (s, 1-dbf), 127.08 (d,
1JCP = 97.1 Hz, ipso-Ph), 126.30 (d, JCP = 3.5 Hz, p-Dipp), 125.23
4
3
5
(s, 7-dbf), 124.71 (d, 3JCP = 2-dbf), 124.62 (d, 4JCP = 5.0 Hz, m-Dipp),
123.00 (s, Aromatic C), 121.63 (s, 9-dbf), 113.53 (s, 6-dbf), 109.74
(d, 1JCP = 112.8 Hz, 4-dbf), 29.39 [s, CH(CH3)2], 25.72 (s, CH(CH3)2],
22.62 (CH(CH3)2] ppm. One quaternary 13C signal was not observed.
31P{1H} NMR (CD2Cl2):
δ
=
30.46 (s) ppm. Anal. for
C36H34Cl2NOPZn: calcd. C: 65.12; H: 5.16; N: 2.11%; found: C:
64.82; H: 4.94; N: 2.44%.
Synthesis of 4-(Mes–N=PPh2)dbf (LMes): A two-neck 100 mL
Synthesis of LMesZnCl2 (2): LMes (200 mg, 0.412 mmol) and ZnCl2
round–bottom flask attached to a swivel frit apparatus was charged
(56.1 mg, 0.412 mmol) were combined in a bomb with toluene
with 4-(diphenylphosphanyl)dibenzofuran (0.67 g, 1.9 mmol). Toluene (20 mL). The resulting suspension was heated to 120 °C with stirring
(approx. 35 mL) was added by vacuum transfer followed by injection
of excess MesN3 (0.4634 g, 2.279 mmol). Within minutes of initiating
the reaction, evolution of a colorless gas was observed. The reaction
for a period of 48 h. During this time, ZnCl2 was observed to eventu-
ally dissolve, followed by gradual formation of a white precipitate.
The volume of toluene was reduced to 10 mL in vacuo, and an equiva-
2116
www.zaac.wiley-vch.de
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2011, 2111–2119

ZnCl2 and Zn(C6F5)2 Complexes of a Phosphinimine Ligand
lent amount of pentane was added to encourage complete precipitation 6.6 Hz, Aromatic C), 123.86 (s, 8-dbf), 122.89 (d, JCP = 11.3 Hz, 2-
3
2
of the product. The solvent was decanted and the resulting white solid
dbf), 122.11 (t, JCF = 67 Hz, ipso-C6F5), 122.08 (s, Aromatic C),
1
was dried in a vacuum, giving complex 2 in 88.6% yield (227 mg,
120.48 (s, 9-dbf), 112.95 (s, 6-dbf), 111.17 (d, JCP = 99.0 Hz, 4-dbf),
1
3
6
0.365 mmol). H NMR (CD2Cl2): δ = 8.19 (d, 1 H, JHH = 7.7 Hz, 1- 20.70 (br. s, o-CH3Mes), 20.10 (d, JCP = 1.4 Hz, p-CH3Mes) ppm.
3
3
dbf), 7.93 (d, 1 H, JHH = 7.7 Hz, 9-dbf), 7.75 (dd, 4 H, JPH = 12.7,
19F{1H} NMR (C6D6): δ = –114.53 (m, 4F, o-C6F5), –157.07 (t, 2F,
3JHH = 7.7 Hz, o-Ph), 7.67 (tq, 2 H, JHH = 7.7, JHH = 1.8, JPH
=
p-C6F5), –161.27 (m, 4F, m-C6F5) ppm. 31P{1H} NMR (C6D6): δ =
3
4
5
3
4
1.8 Hz, p-Ph), 7.51 (td, 4 H, JHH = 7.7, JPH = 3.5 Hz, m-Ph), 7.45 25.7 (s) ppm. Anal. for C45H28F10NOPZn·C5H12: calcd. C: 62.74; H:
–7.23 (ov m, 5 H, 2-dbf + 3-dbf + 6-dbf + 7-dbf + 8-dbf), 6.45 (s, 2
4.21; N: 1.46%; found: C: 62.67; H: 3.96; N: 1.43%.
H, m-Mes), 2.01 (s, 6 H, o-CH3Mes), 1.87 (s, 3 H, p-CH3Mes) ppm.
31P{1H} NMR (CD2Cl2):
C33H28Cl2NOPZn: calcd. C: 63.74; H: 4.54; N: 2.25%; found: C:
64.16; H: 4.75; N: 2.18%.
δ
=
28.0 (s) ppm. Anal. for
Synthesis of LDipp2Zn3(μ-SO3CF3)4(μ-OCH3)2 (5): In a 20 mL Tef-
lon-sealed vial, a stoichiometric amount of dry methanol (5.2 μL,
0.13 mmol) was added to a suspension of LDippZnEt(OTf) (100 mg,
0.130 mmol) in benzene (3 mL). The vial was sealed, heated to 100 °C
for 1 h, and afterwards cooled to ambient temperature and left to stand
for a period of 48 h. A significant amount of material crystallized
during that time. The mother liquor was decanted, and the colorless
crystals were washed with benzene (2ϫ1 mL) and pentane (2ϫ1 mL)
and dried in vacuo, affording 5 as a white crystalline material in 92.4%
yield (57.2 mg, 0.0300 mmol). The compound is essentially insoluble
in non-coordinating solvents, thus precluding characterization by NMR
spectroscopy. Anal. for C78H74F12N2O16P2S4Zn3: calcd. C: 49.05; H:
3.91; N: 1.47; S: 6.72%; found: C: 49.25; H: 4.07; N: 1.52; S: 6.68%.
Synthesis of LDippZn(C6F5)2 (3): LDipp (100 mg, 0.190 mmol) and
Zn(C6F5)2 (76.0 mg, 0.190 mmol) were combined in a scintillation vial
and dissolved in toluene (1 mL), giving a clear yellow solution. This
solution was layered with pentane (3 mL) and placed in a –35 °C
freezer. White crystals of the compound formed after four days. The
supernatant was decanted, the crystals were washed with pentane
(3ϫ1 mL) and dried in vacuo, giving complex 3 in 81.1% yield
(143 mg, 0.154 mmol). 1H NMR (C6D6): δ = 7.59 (d, 1 H, JHH
=
3
8.0 Hz, 9-dbf), 7.56–7.48 (ov m, 2 H, 6-dbf + 1-dbf), 7.32 (br. m, 4
H, o-Ph), 7.22–7.12 (m, 1 H, obscured by solvent, 8-dbf), 7.12–6.87
3
(ov m, 6 H, 7-dbf + p-Dipp + m-Dipp + p-Ph), 6.80 (td, 4 H, JHH
=
X-ray Crystallography: Crystals were grown from hot toluene during
the course of the reaction for 1 and 2, from toluene solutions layered
with pentane at –35 °C for LMes, 3 and 4, and from benzene solution
of the reaction mixture at ambient temperature for 5. X-ray intensities
were measured with a Bruker SMART APEX II instrument (Mo-Kα
radiation; λ = 0.71073 Å) at a temperature of 173(2) K. Unit cell pa-
rameters were determined and refined on all reflections and data were
integrated with APEX2 software.[16] Data reduction and correction for
Lorentz polarization were performed using Saint-plus,[17] and scaling
and absorption correction were performed using the SADABS software
package.[18] Structure solution by direct methods and least-squares re-
finement on F2 were performed using the SHELXTL software suite.[19]
Non-hydrogen atoms were refined with anisotropic displacement pa-
rameters, while hydrogen atoms were placed in calculated positions
and refined with a riding model. The SQUEEZE subroutine of the
PLATON software package[20] was used to model disordered solvent
molecules in 3 and 5 and these solvent molecules are included in the
respective formulae. Multi-scan absorption correction was employed
3
7.7, JPH = 3.0 Hz, m-Ph), 6.76–6.68 (ov m, 2 H, 2-dbf + 3-dbf), 3.84
3
3
[sp, 2 H, JHH = 6.7 Hz, CH(CH3)2], 1.11 [d, 6 H, JHH = 6.7 Hz,
3
CH(CH3)2] 0.38 [d, 6 H, JHH = 6.7 Hz, CH(CH3)2] ppm. 13C{1H}
NMR (C6D6): δ = 158.23 (s, Aromatic C), 156.88 (s, Aromatic C),
1
2
148.58 (br. dd, JCF = 226, JCF = 28 Hz, o-C6F5), 147.41 (d, JCP
=
5.8 Hz, Aromatic C), 140.34 (br. d, 1JCF = 238 Hz, p-C6F5), 139.74 (d,
1
JCP = 8.2 Hz, Aromatic C), 137.04 (br. d, JCF = 248 Hz, m-C6F5),
2
4
134.32 (d, JPC = 9.7 Hz, o-Ph), 133.88 (d, JCP = 2.4 Hz, p-Ph),
3
133.76 (s, 3-dbf), 129.39 (s, 7-dbf), 129.33 (d, JCP = 12.4 Hz, m-Ph),
4
5
126.89 (d, JCP = 2.7 Hz, 1-dbf), 126.66 (d, JCP = 3.6 Hz, p-Dipp),
1
126.64 (br. d, JPC = 101.5 Hz, ipso-Ph), 126.30 (d, JCP = 6.8 Hz,
4
Aromatic C), 125.18 (d, JCP = 3.4 Hz, m-Dipp), 124.61 (s, 8-dbf),
3
2
123.68 (d, JPC = 11.3 Hz, 2-dbf), 123.31 (br. t, JCF = 70 Hz, ipso-
C6F5), 122.69 (d, JCP = 0.9 Hz, Aromatic C), 121.04 (s, 9-dbf), 113.31
1
(s, 6-dbf), 111.10 (d, JPC = 100.6 Hz, 4-dbf), 29.04 [s, CH(CH3)2],
25.28 [s, CH(CH3)2], 23.96 [s, CH(CH3)2] ppm. 19F{1H} NMR
(C6D6): δ = –114.51 (m, 4F, o-C6F5), –156.83 (t, 2F, p-C6F5), –160.82
(m, 4F, m-C6F5) ppm. 31P{1H} NMR (C6D6): δ = 28.5 (s) ppm. Anal.
for C48H34F10NOPZn: calcd. C: 62.18; H: 3.70; N: 1.51%; found: C:
62.27; H: 3.92; N: 1.95%.
in all cases. Structural figures were generated with ORTEP-3.[21]
A
summary of the crystallographic data and structure refinement results
for LMes and complexes 1–5 are listed in Table 4
Synthesis of LMesZn(C6F5)2 (4): Complex 4 was prepared similarly
to 3 using LMes (100 mg, 0.206 mmol) and Zn(C6F5)2 (82.3 mg,
0.206 mmol), affording pale yellow crystals of 4 in 87.8% yield
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-833316, -833317, -833318, -833319, -833320, and
-833321 (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk,
http://www.ccdc.cam.ac.uk).
1
(160 mg, 0.181 mmol). H NMR (C6D6): δ = 7.60–7.45 (ov m, 3 H,
3
3
1-dbf + 6-dbf + 9-dbf), 7.38 (dd, 4 H, JPH = 12.5, JHH = 7.9 Hz, o-
Ph), 7.20–7.10 (ov m, 1 H, 7-dbf, obscured by solvent signal), 7.06
(td, 1 H, 3JHH = 7.5, 4JHH = 1.1 Hz, 8-dbf), 6.94 (tq, 2 H, 3JHH = 7.7,
5
4JHH = 1.5, JPH = 1.5 Hz, p-Ph), 6.86–6.72 (ov m, 6 H, m-Ph + 2-dbf
+ 3-dbf), 6.39 (s, 2 H, m-Mes), 2.12 (s, 6 H, o-CH3Mes), 1.84 (s, 3
H, p-CH3Mes) ppm. 13C{1H} NMR (C6D6): δ = 157.67 (s, Aromatic
1
2
Acknowledgement
C), 156.29 (s, Aromatic C), 148.03 (br. dd, JCF = 222, JCF = 28 Hz,
1
o-C6F5), 140.03 (d, JCP = 7.6 Hz, Aromatic C), 139.60 (br. d, JCF
=
1
240 Hz, p-C6F5), 136.27 (br. d, JCF = 250 Hz, m-C6F5), 136.10 (d,
P.G.H. thanks NSERC, Canada Foundation for Innovation, Canada
JCP = 5.7 Hz, Aromatic C), 133.80 (d, JCP = 3.9 Hz, Aromatic C), School of Energy and Environment and GreenCentre Canada for finan-
2
4
133.49 (d, JCP = 9.9 Hz, o-Ph), 133.20 (d, JCP = 2.9 Hz, p-Ph),
cial support. C.A.W. acknowledges NSERC, the Alberta Ingenuity Fund
3
4
131.95 (d, JCP = 8.4 Hz, 3-dbf), 129.40 (d, JCP = 3.3 Hz, m-Mes), (Alberta Innovates) and the Alberta Heritage Fund for student awards.
3
4
128.66 (s, 7-dbf), 128.52 (d, JCP = 12.5 Hz, m-Ph), 126.13 (d, JCP
2.7 Hz, 1-dbf), 126.03 (d, JCP = 103.0 Hz, ipso-Ph), 125.79 (d, JCP
=
=
Mr. Tony Montina of the University of Lethbridge is acknowledged for
expert technical assistance.
1
Z. Anorg. Allg. Chem. 2011, 2111–2119
© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
2117

C. A. Wheaton, B. J. Ireland, Paul G. Hayes
ARTICLE
Table 4. Crystal data and refinement details for LMes and complexes 1–5.
LMes
1
2
3
4
5
Empirical for- C33H28NOP·0.5C7H8 C36H34Cl2NOPZn
mula
C66H56Cl4N2O2P2Zn2·C7H8 C48H34F10NOPZn·C7H8 C45H28F10NOPZn·C5H12 C78H74F12N2O16P2S4Zn3
Formula
weight
Temperature / 173(2)
K
Wavelength /
Å
Crystal system triclinic
Space group
a /Å
b /Å
c /Å
α /°
531.60
663.88
173(2)
1335.7
173(2)
1019.24
173(2)
957.17
173(2)
0.71073
1909.68
173(2)
0.71073
0.71073
triclinic
0.71073
triclinic
0.71073
triclinic
0.71073
triclinic
monoclinic
P21/n
15.274(1)
14.196(1)
21.311(2)
90
98.317(1)
90
4572.3(7)
4
¯
¯
¯
¯
¯
P1
P1
P1
P1
P1
9.1830(5)
14.4232(7)
11.2504(6)
86.958(1)
82.190(1)
75.102(1)
1426.4(1)
2
9.3247(4)
10.7683(4)
16.9837(7)
78.32
83.58
75.89
9.5777(5)
13.5073(7)
14.889(1)
114.568(1)
92.957(1)
108.823(1)
1619.1(2)
2
12.3644(7)
13.2795(7)
17.704(1)
70.327(1)
70.849(1)
71.903(1)
2519.4(2)
2
12.729(2)
13.861(2)
14.226(2)
86.308(1)
89.135(1)
84.456(1)
2492.9(5)
2
β /°
γ /°
Volume /Å3
Z
1616.1(1)
2
ρ calcd. /
Mg·m–3
μ /mm–1
F(000)
Crystal size /
mm
1.238
1.364
1.370
1.344
1.390
1.272
0.126
562
0.46ϫ0.24ϫ0.12
1.004
688
0.39ϫ0.32ϫ0.25
1.003
690
0.24ϫ0.17ϫ0.12
0.595
1044
0.30ϫ0.26ϫ0.24
0.651
1960
0.30ϫ0.26ϫ0.18
0.908
976
0.28ϫ0.26ϫ0.13
θ range /°
Reflections
collected
Independent
reflections
2.31 to 25.03
13790
2.64 to 26.37
17389
2.60 to 26.37
21637
2.56 to 25.03
24263
2.62 to 25.03°.
43393
2.59 to 25.03
23701
5017 [R(int) =
0.0156]
6576 [R(int) =
0.0115]
99.2%
6586 [R(int) = 0.0283]
99.5%
8863 [R(int) = 0.0219]
99.6%
8076 [R(int) = 0.0310]
99.9%
8770 [R(int) = 0.0381]
99.6%
Completeness 99.6%
to θ = 25.03°
Data / re-
5017 / 4 / 380
6576 / 0 / 383
6586 / 99 / 407
8863 / 0 / 615
8076 / 0 / 582
8770 / 0 / 534
straints / pa-
rameters
Goodness-of- 1.028
fit (GOF)
1.068
1.034
1.045
1.025
1.023
R indices [I Ͼ R1 = 0.0333,
2σ(I)]
R1 = 0.0223,
R1 = 0.0377,
R1 = 0.0366,
R1 = 0.0365,
R1 = 0.0408,
wR2 = 0.0845
wR2 = 0.0612
R1 = 0.0238,
wR2 = 0.0979
R1 = 0.0495,
wR2 = 0.0998
R1 = 0.0433,
wR2 = 0.0883
R1 = 0.0513,
wR2 = 0.1026
R1 = 0.0664,
R indices (all
R1 = 0.0378,
data)
wR2 = 0.0876
wR2 = 0.0620
wR2 = 0.1051
wR2 = 0.1033
wR2 = 0.0972
wR2 = 0.1102
Largest diff.
peak/hole /
e·Å–3
0.291 and –0.350
0.394 and –0.251
1.531 and –0.359
0.553 and –0.479
0.482 and –0.304
0.645 and –0.329
[5] See for example: a) S. Courtenay, D. Walsh, S. Hawkeswood,
P. R. Wei, A. K. Das, D. W. Stephan, Inorg. Chem. 2007, 46,
3623–3631; b) G. C. Welch, W. E. Piers, M. Parvez, R. McDon-
ald, Organometallics 2004, 23, 1811–1818; c) P. R. Wei, D. W.
Stephan, Organometallics 2003, 22, 601–604.
[6] See for example: a) C. V. Cárdenas, M. A. M. Hernández, J.-M.
Grévy, Dalton Trans. 2010, 39, 6441–6448; b) C. J. Wallis, I. L.
Kraft, B. O. Patrick, P. Mehrkhodavandi, Dalton Trans. 2010, 39,
541–547; c) S. Marks, T. K. Panda, P. W. Roesky, Dalton Trans.
2010, 39, 7230–7235; d) A. Murso, D. Stalke, Eur. J. Inorg.
Chem. 2004, 4272–4277; e) M. S. Hill, P. B. Hitchcock, J. Chem.
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[7] a) C. A. Wheaton, P. G. Hayes, Organometallics submitted; b)
B. J. Ireland, C. A. Wheaton, P. G. Hayes, Organometallics 2010,
29, 1079–1084; c) C. A. Wheaton, P. G. Hayes, Dalton Trans.
2010, 39, 3861–3869; d) C. A. Wheaton, P. G. Hayes, Chem.
Commun. 2010, 46, 8404–8406; e) C. A. Wheaton, B. J. Ireland,
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[8] a) A. Charafeddine, W. Dayoub, H. Chapuis, P. Strazewski, Chem.
Eur. J. 2007, 13, 5566–5584; b) S. Bräse, C. Gil, K. Knepper, V.
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Received: August 03, 2011
Published Online: September 13, 2011
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