Synthesis and characterization of organo-scandium and yttrium complexes stabilized by phosphinoamide ligands

Article abstract of DOI:10.1039/c1dt11501d

Addition of three equivalents of phosphinoamine, (ArNHPⁱPr ₂) [Ar = 3,5-dimethylphenyl] to M(CH₂SiMe ₃)₃(THF)₂ [M = Sc, Y] precursors gives complexes of the form (ArNPⁱPr₂

Full text of DOI:10.1039/c1dt11501d

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PAPER
Synthesis and characterization of organo-scandium and yttrium complexes
stabilized by phosphinoamide ligands†
Nathan R. Halcovitch and Michael D. Fryzuk*
Received 8th August 2011, Accepted 31st October 2011
DOI: 10.1039/c1dt11501d
Addition of three equivalents of phosphinoamine, (ArNHPiPr2) [Ar = 3,5-dimethylphenyl] to
M(CH2SiMe3)3(THF)2 [M = Sc, Y] precursors gives complexes of the form (ArNPiPr2)3M(THF) [M =
Sc, Y]. In the case of scandium, addition of Sc(CH2SiMe3)3(THF)2 to (ArNPiPr2)3Sc(THF) affords
(ArNPiPr2)2Sc(CH2SiMe3)(THF), which has been isolated and structurally characterized. In contrast,
addition of Y(CH2SiMe3)3(THF)2 to (ArNPiPr2)3Y(THF) generates a distribution of phosphinoamide-
containing products consistent with the formulations (ArNPiPr2)2Y(CH2SiMe3)(THF) and
(ArNPiPr2)Y(CH2SiMe3)2(THF), as ascertained using NMR spectroscopy. Attempts to react the
alkyl-containing phosphinoamide complexes with small molecules such as H2 led to disproportionation
type processes.
Introduction
Organo-scandium and yttrium chemistry has been dominated
by the use of bis(cyclopentadienyl) or cyclopentadienyl-amido
supporting frameworks.1,2 In attempts to broaden the chemistry
of these group 3 elements, much effort has been invested in
other ancillary ligand types that involve combinations of different
donors in multidentate arrays.3–6 Most of these modifications
away from cyclopentadienyl ligands have involved nitrogen and/or
oxygen donors, which is not surprising given that N- and O-based
hard donors are well matched with the hard M3+ metal centers of
Fig. 1 Generic complexes of silylmethyl-linked NPN (A),24 arene-linked
NPN (B),25,26 thiophene-linked NPN (C),28 ‘linkerless’ phosphinoamide
(D).
group 3.
linkers, an obvious strategy was to study the effect of having no
linker between the phosphine and amido donors, and therefore
we initiated a study of phosphinoamide systems of the general
formula, RN-PR¢2, which is D in Fig. 1.
Our researchefforts have focusedon ligands thatcombine amido
-
(NR2 ) and phosphine (PR3) donors in chelating, multidentate
arrays. These ligand types have shown the ability to coordinate to
a variety of metals across the periodic table,7 including the group
3 metals and the lanthanides.8–16 Other research groups have also
investigated N and P type donors in chelating arrays with group 3
and 4 metals.17–22 We have had success using a motif involving two
amido donors flanking a central phosphine, generically named
‘NPN’, for early transition metal chemistry.23–27 Recent ligand
designs in our laboratory have been focused on modifying the
nitrogen-phosphorus linkers of the NPN ligand backbone (see
Fig. 1). As can be seen, our original design depicted as A is quite
flexible and can adopt both facial and meridional coordination
modes; replacing the CH2SiMe2 units with o-phenylene linkers as
in B, introduces more rigidity in the system, which is also evident
for the 2,3-thiophene linkers in C. In considering other types of
Recently, these highly tunable phosphinoamide ligands contain-
ing a direct N–P bond have received attention as robust frame-
works for the synthesis of Ti(IV),29,30 Zr(IV)30 and Cr(II)31 com-
plexes. These anionic ligands of the general formula (RNPR¢2)-
have also been shown to be useful for assembling early–late
heterobimetallics,32–36 one system in particular has demonstrated
the stability of these ligands under reducing conditions.37–39
Other researchers have also identified a variety of ligands
containing a P–N bond as good candidates for the synthesis
of group 3 and rare-earth metal complexes, and this work
was recently summarized.40 We report herein the synthesis of
tris(phosphinoamide) complexes of scandium and yttrium, and
the isolation of (ArNPiPr2)2Sc(CH2SiMe3)(THF) (where Ar = 3,5-
dimethylphenyl).
Department of Chemistry, The University of British Columbia, 2036 Main
Mall, Vancouver, BC, V6T 1Z1, Canada. E-mail: fryzuk@chem.ubc.ca;
Fax: +1 604-822-2847; Tel: +1 604-822-2897
Results and discussion
† Electronic supplementary information (ESI) available. CCDC reference
numbers 837086 and 837087. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt11501d
Addition of three equivalents of phosphinoamine, 1, (ArNHPiPr2)
[Ar = 3,5-dimethylphenyl] to M(CH2SiMe3)3(THF)2 (where
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M = Sc, Y) in hexanes produces (ArNPiPr2)3M(THF) (eqn 1).
This alkane-elimination route to rare-earth metal complexes is
well established and has recently been reviewed.41
contained in a chelating array, the reported JPY coupling constants
are typically within the range of 60–85 Hz.12,13,15,16 Notable
exceptions are the ‘PNP’ ligated yttrium complexes from Hou and
co-workers, which exhibit JPY coupling constants between 18 and
37 Hz.21,22 In addition, the 1H NMR spectrum of 2b is indicative
of a highly symmetric structure, with equivalent isopropylmethine
resonances and two unique resonances for the isopropylmethyl
groups. It is likely that the phosphine moieties undergo rapid
intramolecular dissociation and reassociation fast on the NMR
timescale, which would result in the observed high symmetry in
solution.
Monitoring the course of the reaction for the synthesis
of 2b, one can observe several detectable intermediates using
The tris(phosphinoamide)yttrium complex 2b could be isolated
as single crystals by vapour diffusion of pentane into a concen-
trated diethyl ether solution. Fig. 2 shows the solid state molecular
structure of this highly distorted seven-coordinate molecule,
where the metal–amido and metal–phosphine bond lengths are
1
31P{ H} NMR spectroscopy, and attempts to control the sub-
stitution at yttrium resulted in a mixture of products (Scheme
1). The same products are observed when 2b is added to
Y(CH2SiMe3)3(THF)2, which could be called a conpropor-
tionation reaction. In solution we can observe both 2b and
Y(CH2SiMe3)3(THF)2 as well as two new complexes. We have
tentatively assigned the two resulting compounds as the monoalkyl
complex, (ArNPiPr2)2Y(CH2SiMe3)(THF), and the dialkyl com-
plex, (ArNPiPr2)Y(CH2SiMe3)2(THF). Several NMR techniques
have been used to support these assignments, which are shown in
detail in the ESI.† However, these complexes have not otherwise
been characterized, as their solubilities are too similar to be
separated using recrystallization techniques. There is no detectable
change of the mixture in solution (as ascertained by NMR
spectroscopy) over a period of hours, nor is there any detectable
change of the mixtures upon cooling as low as -45 ◦C. Solutions of
these mixtures decompose over several days standing at room tem-
perature, or within minutes of heating the samples to 40 ◦C. De-
composition results in formation of a precipitate and the formation
of tetramethylsilane, which can be detected using 1H NMR spec-
troscopy. Attempts to generate the mixed alkyl-phosphinoamide
yttrium complexes in coordinating solvents such as THF were
unsuccessful using either of the aforementioned methods.
varied. This distortion is not observed in solution: in benzene,
1
the 31P{ H} NMR spectrum displays a sharp doublet (1JPY
=
18.3 Hz) indicating equivalent phosphine environments. This
coupling constant is greater than that in the related ‘ate-complex’
[(PhNPPh2)4Y][Li(THF)4], for which a coupling constant of 2JPY
=
5.4 Hz is assigned.42 However, when the phosphine donor is
Fig. 2 ORTEP representation of the solid-state molecular structure
of 2b; ellipsoids are drawn at 50% probability. Hydrogens and iPr
methyl carbons are omitted for clarity, and one methine carbon
attached to atom P(3) is averaged over two positions. Selected bond
◦
˚
lengths (A) and angles ( ): N(1)–P(1) 1.6782(19), N(2)–P(2) 1.6733(19),
N(3)–P(3) 1.6783(19), N(1)–Y(1) 2.2735(18), P(1)–Y(1) 2.8521(6),
N(2)–Y(1) 2.3173(19), P(2)–Y(1) 2.7754(6), N(3)–Y(1) 2.2840(19),
P(3)–Y(1) 2.8912(7), O(1)–Y(1) 2.3821(15), N(1)–Y(1)–P(1) 36.03(5),
N(2)–Y(1)–P(2) 37.00(5), N(3)–Y(1)–P(3) 35.45(5), N(1)–Y(1)–N(2)
103.79(6), N(1)–Y(1)–N(3) 113.49(7), N(2)–Y(1)–N(3) 123.98(7),
P(1)–Y(1)–P(2) 122.549(19), P(1)–Y(1)–P(3) 102.119(19), P(2)–Y(1)–P(3)
128.904(19), N(1)–Y(1)–P(2) 102.16(5), N(2)–Y(1)–P(3) 154.54(5),
N(3)–Y(1)–P(1) 132.55(5), N(3)–Y(1)–P(2) 93.46(5), O(1)–Y(1)–N(1)
127.33(6), O(1)–Y(1)–N(2) 86.32(6), O(1)–Y(1)–N(3) 101.25(6),
O(1)–Y(1)–P(1) 91.37(4), O(1)–Y(1)–P(2) 114.31(4), O(1)–Y(1)–P(3)
85.52(4).
Scheme 1 The observed products formed when ArNHPiPr2 is added to
Y(CH2SiMe3)3(THF)2 (1 : 1) at room temperature in toluene.
While we were unable to cleanly prepare mixed alkyl-
phosphinoamide species of yttrium, the analogous reactions
with scandium were more straightforward. Monoalkyl compound
(ArNPiPr2)2Sc(CH2SiMe3)(THF) 3 can be synthesized cleanly
by addition of phosphinoamine 1 to Sc(CH2SiMe3)(THF)2 at
room temperature when the correct stoichiometry is used and
the reaction is allowed to proceed for 24 h. As well, the
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conproportionation reaction using 2 equivalents of (ArNPiPr2)3-
Sc(THF) with Sc(CH2SiMe3)3(THF)2 yields complex 3, and the
reaction is not limited to non-coordinating solvents (Scheme 2).
The difference in reactivity can likely be attributed due to the
smaller size of the Sc(III) metal ion as compared to Y(III).
Scheme 2 Two synthetic routes to (ArNPiPr2)2Sc(CH2SiMe3)(THF) (3).
Single crystals of 3 suitable for X-ray crystallography were
◦
obtained from a concentrated hexanes solution stored at -35 C
for 3 days. The solid-state molecular structure (Fig. 3) contains
a bound THF molecule in a position cis to the alkyl group. The
phosphorus atoms are non-equivalent in this structure as well,
Fig. 3 ORTEP representation of the solid-state molecular structure of 3;
thermal ellipsoids are drawn at 50% probability. Hydrogen and iPr methyl
1
however at room temperature the31P{ H} NMR spectrum displays
◦
˚
atoms are omitted for clarity. Selected bond lengths (A) and angles ( ):
N(1)–P(1) 1.676(2), N(2)–P(2) 1.672(2), Sc(1)–N(1) 2.099(2), Sc(1)–N(2)
2.100(2), Sc(1)–P(1) 2.7115(9), Sc(1)–P(2) 2.6965(9), Sc(1)–O(1) 2.197(2),
Sc(1)–C(29) 2.243(3), N(1)–Sc(1)–P(1) 38.17(7), N(2)–Sc(1)–P(2)
38.31(7), N(1)–Sc(1)–N(2) 114.15(9), P(1)–Sc(1)–P(2) 132.58(3),
N(1)–Sc(1)–P(2) 114.27(6), N(2)–Sc(1)–P(1) 106.81(7), N(1)–Sc(1)–C(29)
123.79(10), N(2)–Sc(1)–C(29) 111.30(10), P(1)–Sc(1)–C(29) 97.99(8),
P(2)–Sc(1)–C(29) 121.85(8), O(1)–Sc(1)–C(29) 88.29(10), O(1)–Sc(1)–N(1)
88.44(8), O(1)–Sc(1)–N(2) 128.36(9), O(1)–Sc(1)–P(1) 117.46(6),
O(1)–Sc(1)–P(2) 90.42(6).
a sharp singlet indicating that both phosphine environments are
equivalent on the NMR timescale in solution. Cooling samples
of 3 in THF to -95 ◦C results in slight broadening in the 31P
NMR spectrum. At these low temperatures one can begin to see
some additional splitting of the methine and methyl resonances in
the 1H NMR spectrum; however, these resonances remain broad
even at low temperatures indicating that this fluxional process
that renders the phosphinoamide fragments equivalent is still fast
on the NMR timescale. We have included the selected variable
temperature NMR spectra in the ESI.† When comparing the solid-
state structure parameters to recent literature values, the Sc–N,43,44
Sc–C45 and Sc–P17,18 bond lengths are as expected.
production of a significant amount of 2a along with the formation
of some precipitate. This demonstrates that ligand redistribution is
problematic. Placing 3 under an atmosphere of 4 atm of H2 gas in
toluene for 48 h gives the same result as thermolysis – partial
conversion of 3 to 2a is observed accompanied by precipitate
formation.
Attempted reactivity studies
Synthesis of alkyl complexes of the group 3 metals and their
thermal behaviour remains an actively explored research area.46–49
However, an exciting recent advance in group 3 chemistry has been
the hydrogenolysis of metal alkyl derivatives to form polynuclear
hydride species,22,50–53 which can show remarkable reactivity pat-
terns with small molecules.54 Attempts to examine the reactivity
of the mixed alkyl(phosphinoamide) yttrium complexes in situ
were complicated by the presence of the Y(CH2SiMe3)3(THF)2
starting material. For example, addition of 1 atm of H2 gas or
excess PhSiH3 to the mixtures of yttrium complexes (as shown in
Scheme 1) results in the observation of the tris(phosphinoamide)
derivative 2b; however, there is also precipitate formation and very
broad resonances in the baseline of the 1H NMR spectrum. Thus
our attempts to examine whether ligand redistribution is occurring
were rendered unreliable.
Conclusions
While phosphinoamide ligands have been found to be excellent
scaffolds for certain metal systems, our observation of facile ligand
redistribution with scandium and yttrium has shown that these
complexes are unsuitable for small molecule reactivity studies.
However, given the increased stability expected of chelating
systems, further work will focus on tethered phosphinoamide
systems, which will be reported in due course.
Experimental
General
The scandium monoalkyl complex 3 is stable for days in the
solid state at room temperature. In toluene solution, 3 is relatively
thermally robust, however, heating at 90 ◦C for 18 h results in
Unless otherwise noted all experiments were carried out
using oven-dried glassware cooled under vacuum, and all
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compounds were handled under an atmosphere of dry N2 in a
glovebox or by standard Schlenk technique. Starting materials
M(CH2SiMe3)3(THF)2 where M = Sc or Y were prepared by
previously published procedures.55 Hexanes, toluene and THF
were passed over alumina under a nitrogen atmosphere and were
with 2 ¥ 2 mL hexanes, and was dried in vacuo. (Yields = 2a: 498
mg, 60%; 2b: 319 mg, 92%).
1
For 2a: 31P{ H} NMR (d in ppm, C6D6, 293 K, 162 MHz): 34.4
1
(s); H NMR (d in ppm, C6D6, 293 K, 400 MHz): 6.90 (s, 6H,
o-Ar), 6.50 (s, 3H, p-Ar), 3.74 (br, 4H, O-CH2), 2.63 (d of septets,
collected over activated 4 A molecular sieves. Dichloromethane,
6H, 2JHP = 2.8 Hz, 3JHH = 7.2 Hz, P-CH), 2.25 (s, 18H, Ar-CH3),
˚
triethylamine and 3,5-dimethylaniline were distilled over calcium
1.41 (br, 4H, O-CH2CH2), 1.28 (dd, 18H, 2JHP = 18.4 Hz, 3JHH
=
C
hydride, collected over 4 A molecular sieves and degassed via three
7.2 Hz, CH3-iPr) 1.27 (dd, 18H, 3JHP = 18.4 Hz, 3JHH = 7.2 Hz); 13
˚
2
freeze–pump–thaw cycles. Samples of d6-benzene and d8-toluene
NMR (d in ppm, C6D6, 100.63 MHz): 152.7 (d, JCP = 12.2 Hz,
3
˚
were dried over activated 4 A molecular sieves and degassed via
N-Cipso), 137.9 (s, Me-Cmeta), 121.4 (s, HCpara), 120.4 (d, JCP =
three freeze–pump–thaw cycles. 1H, 13C and 31P NMR spectra were
recorded on either a Bruker Avance 300 or 400 MHz spectrometer.
1H and 13C NMR chemical shifts were referenced to residual
solvents signals from the deuterated solvents. 31P NMR chemical
shifts were referenced to external samples of phosphoric acid
(85%) at d = 0 ppm. Elemental analyses (EA) determinations
were performed under an N2 atmosphere using a Carlo Erba
Elemental Analyzer 1108, and were performed in the Department
of Chemistry at the University of British Columbia by Mr. David
Wong.
8.8 Hz, HCortho), 69.2 (s, O-CH2-CH2), 28.1 (d, 1JCP = 7.2 Hz, HC-
P), 25.7 (s, OCH2-CH2), 21.7 (s, H3C-Ar), 20.7 (br m, H3C-iPr).
C46H77N3O1P3Sc1 EA (% calc.): C, 66.89; H, 9.40; N, 5.09. EA (%,
found): C, 66.59; H, 9.41; N, 5.68.
1
For 2b: 31P{ H} NMR (d in ppm, C6D6, 293 K, 162 MHz): 29.6
(d, JPY = 18.3 Hz); 1H NMR (d in ppm, C6D6, 293 K, 400 MHz):
6.98 (s, 6H, o-Ar), 6.52 (s, 3H, p-Ar), 4.01 (br, 4H, O-CH2), 2.58
2
3
(d of septets, 6H, JHP = 2.0 Hz, JHH = 7.2 Hz, P-CH), 2.32 (s,
2
18H, Ar-CH3), 1.35 (br, 4H, O–CH2CH2), 1.19 (dd, 18H, JHP
=
15.0 Hz, JHH = 7.2 Hz, CH3-iPr) 1.15 (dd, 18H, JHP = 12.2 Hz,
3
3
3JHH = 7.2 Hz); 13C NMR (d in ppm, C6D6, 100.63 MHz): 154.5
2
3
(d, JCP = 11.7 Hz, N-Cipso), 137.4 (s, Me-Cmeta), 121.3 (d, JCP
=
Synthesis of N-bis(diisopropylphosphino)-3,5-dimethylaniline,
8.7 Hz, HCortho), 120.9 (s, HCpara), 72.3 (s, O-CH2-CH2), 28.0 (d,
1JCP = 10.6 Hz, HC-P), 25.7 (s, OCH2-CH2), 21.9 (s, H3C-Ar),
20.8 (d, 2JCP = 16.9 Hz, H3C-iPr), 20.6 (d, 2JCP = 8.2 Hz, H3C-iPr).
C46H77N3O1P3Y1 EA (%, calc.): C, 63.51; H, 8.92; N, 4.83. EA (%,
found): C, 63.80; H, 9.14; N, 4.61.
ArNHPiPr2 (1)
This synthesis is a modified version of a published procedure
for the synthesis of other phosphinoamines.56,57 Triethylamine
(33.5 mL, 0.24 mol) and 3,5-dimethylaniline (15.0 mL, 0.12 mol)
were added via syringe to 250 mL CH2Cl2 in a 500 mL Schlenk
flask equipped with a stir bar. At room temperature chlorodi-
isopropylphosphine (19.1 mL, 0.12 mol) was added dropwise by
syringe over the course of 30 min. The reaction mixture was stirred
at room temperature for 19 h, and the volatiles were removed in
vacuo. The residues were extracted with 3 ¥ 75 mL of hexanes and
filtered through a 1 inch plug of Celite. The hexanes were removed
in vacuo and the solids were recrystallized from 50 mL pentane at
-35 ◦C. The large colourless crystals were collected on a glass frit
Synthesis of (ArNPiPr2)2Sc(CH2SiMe3)(THF) (3)
Method A. To a mixture of solid 1 (949 mg, 4.0 mmol) and
Sc(CH2SiMe3)3(THF)2 (902 mg, 2.0 mmol) was added 10 mL
toluene at room temperature. The mixture was stirred for 24 h
at which point the volatiles were removed in vacuo; the residues
were recrystallized twice from 5 mL hexanes at -35 ◦C to give
colourless crystals of 3 (Yield = 910 mg, 67%).
Method B. To a mixture of solid 2a (33 mg, 0.04 mmol) and
Sc(CH2SiMe3)3(THF)2 (9 mg, 0.02 mmol) was added 2 mL of
THF at room temperature. After stirring for 5 h the volatiles were
removed in vacuo. Conversion to 3 was quantitative as ascertained
by NMR spectroscopy.
1
and were dried in vacuo. (Yield: 23.1 g, 81%). 31P{ H} NMR (d
1
in ppm, C6D6, 293 K, 162 MHz): 47.1 (s); H NMR (d in ppm,
C6D6, 293 K, 400 MHz): 6.67 (s, 2H, o-Ar), 6.39 (s, 1H, p-Ar),
3.32 (d, 1H, 2JHP = 10.8 Hz, N-H), 2.16 (s, 6H, Ar-CH3), 1.48 (d
of septets, 2H, 2JHP = 2.4 Hz, 3JHH = 7.0 Hz, P-CH), 0.98 (dd, 6H,
1
31P{ H} NMR (d in ppm, C6D6, 293 K, 162 MHz): 26.6 (s); 1H
3JHP = 16.2 Hz, 3JHH = 7.0 Hz), 0.96 (dd, 6H, 3JHP = 10.4 Hz, 3JHH
=
NMR (d in ppm, C6D6, 293 K, 400 MHz): 6.87 (s, 4H, o-Ar), 6.50
7.0 Hz); 13C NMR (d in ppm, C6D6, 293 K, 100.63 MHz): 149.4
(d, 2JCP = 21.5 Hz, N-Cipso), 138.6 (s, Me-Cmeta), 120.9 (s, H-Cpara),
114.4 (d, 3JCP = 11.6 Hz, H-Cortho), 27.1 (d, 1JCP = 12.9 Hz, HC-P),
(s, 2H, p-Ar), 4.01 (br, 4H, O-CH2), 2.59 (d of septets, 4H, 2JHP
=
3
3.2 Hz, JHH = 7.0 Hz, P-CH), 2.29 (s, 12H, Ar-CH3), 1.24 (br,
4H, O-CH2CH2), 1.19 (br ov, 24H, CH3-iPr), 0.43 (s, 9H, CH3-
Si), 0.09 (s, 2H, Sc-CH2-Si); 13C NMR (d in ppm, C6D6, 100.63
MHz): 152.7 (d, 2JCP = 10.0 Hz, N-Cipso), 137.7 (s, Me-Cmeta), 121.7
21.6 (s, H3C-Ar), 19.1 (d, 2JCP = 20.6 Hz, H3C-iPr), 17.3 (d, 2JCP
=
8.2 Hz, H3C-iPr). For C14H24N1P1: EA (%, calc.): C, 70.85; H,
10.19; N, 5.90. EA (%, found): C, 70.71; H, 9.88; N, 5.90.
3
(s, HCpara), 120.1 and 120.0 (ov d, JCP = 4.6 Hz, HCpara), 72.9 (s,
O-CH2-CH2), 37.7 (br and weak, Sc-CH2), 28.0 (d, 1JCP = 10.6 Hz,
HC-P), 25.4 (s, OCH2-CH2), 21.8 (s, H3C-Ar), 20.8 (br, H3C-iPr),
4.8 (s, H3C-Si). For C36H65N2O1P2Sc1Si1 EA (%, calc.): C, 63.88;
H, 9.68; N, 4.14. EA (%, found): C, 63.83; H, 9.70; N, 4.18.
Synthesis (ArNPiPr2)3M(THF) (M = Sc (2a), Y (2b))
In
a 50 mL Schlenk flask equipped with a stir bar
M(CH2SiMe3)3(THF)2 (2a = 451 mg, 1.0 mmol; 2b = 197 mg,
0.40 mmol) was dissolved in (2a: 3 mL; 2b: 2 mL) hexanes. At
room temperature ArNHPiPr2 (2a: 712 mg, 3.0 mmol; 2b: 284 mg,
1.20 mmol) dissolved in (2a: 5 mL; 2b: 2 mL) hexanes was added
dropwise. The solution was stirred for (2a: 3 h, 2b: 24 h), at which
point a white precipitate was collected on a glass frit, was washed
Acknowledgements
We thank the Natural Sciences and Engineering Research Council
of Canada (NSERC) for funding this work. NRH is grateful for
fellowships from NSERC, The University of British Columbia
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(Laird Fellowship), Mountain Equipment Co-op, and the Walter
C. Sumner Foundation.
28 G. Menard, H. Jong and M. D. Fryzuk, Organometallics, 2009, 28,
5253.
29 C. H. Qi, S. B. Zhang and J. H. Sun, J. Organomet. Chem., 2005, 690,
2941.
30 C. H. Qi, S. B. Zhang and J. H. Sun, Appl. Organomet. Chem., 2006,
20, 138.
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1528 | Dalton Trans., 2012, 41, 1524–1528
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