New cyclopentenyl-linked [NPN] ligands and their coordination chemistry with zirconium: Synthesis of a dinuclear side-on-bound dinitrogen complex

Article abstract of DOI:10.1021/ic201762r

The synthesis and characterization of two 1,2-cyclopentyl-bridged diiminophosphine proligands, ^CY5[NPN]^DMPH₂ (CY5 = cyclopentylidene; DMP = 2,6-Me₂C₆H₃) and ^CY5[NPN]^DIPP

Full text of DOI:10.1021/ic201762r

ARTICLE
pubs.acs.org/IC
New Cyclopentenyl-Linked [NPN] Ligands and Their Coordination
Chemistry with Zirconium: Synthesis of a Dinuclear Side-On-Bound
Dinitrogen Complex
Ting Zhu, Truman C. Wambach, and Michael D. Fryzuk*
Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver, British Columbia, Canada V6T 1Z1
S Supporting Information
b
ABSTRACT: The synthesis and characterization of two 1,2-cyclopentyl-
bridged diiminophosphine proligands, CY5[NPN]DMPH2 (CY5 = cyclopentyli-
dene; DMP = 2,6-Me2C6H3) and CY5[NPN]DIPPH2 (DIPP = 2,6-iPr2C6H3),
are presented, and tautomerization to the corresponding 1,2-cyclopentenyl-
bridged enamineimine phosphine precursors is reported. These two new
proligands are obtained by deprotonation of N-DMP- or N-DIPP-cyclopentyl-
ideneimine (N-DMP, 2,6-dimethylphenyl; N-DIPP, 2,6-diisopropylphenyl)
and the subsequent addition of 0.5 equiv of dichlorophenylphosphine. Each
ligand precursor exists as a mixture of isomers that consist of the diimine,
enamineimine, and dienamine tautomers and corresponding stereoisomers,
each of which could be identified. The bis(dimethylamido)zirconium com-
plexes CY5[NPN]DMPZr(NMe2)2 and CY5[NPN]DIPPZr(NMe2)2 were pre-
pared directly from the neutral proligands and Zr(NMe2)4 via protonolysis. Exchange of the dimethylamido ligands in the latter
complexes for chlorides and iodides takes place upon reaction with excess Me3SiCl and Me3SiI, respectively. A dinuclear
zirconiumꢀdinitrogen complex, {CY5[NPN]DMPZr(THF)}2(μꢀη2:η2-N2), was obtained via KC8 reduction of CY5[NPN]DMPZrCl2
4ꢀ
under 4 atm of N2. On the basis of single-crystal X-ray analysis, N2 has been reduced to a side-on-bound hydrazido (μ-η2:η2-N2
)
unit. This dinitrogen complex is thermally unstable and decomposes in solution.
Chart 1
’ INTRODUCTION
Amidophosphine hybrid ligands are multidentate ligand scaf-
folds that incorporate hard amido and soft phosphine donors in
various permutations.1ꢀ9 We have already reported10ꢀ19
a
number of combinations with ꢀCH2SiMe2ꢀ linking units, as
shown generically coordinated to metals in Chart 1.
Depending on the charge of the ligand donor set, a variety of
oxidation states and coordination geometries can be accessed. Of
recent interest in our group have been the diamidophosphine
arrays (NPN), which have shown a rich chemistry in small-
molecule activation.6,18,20ꢀ29 We have explored NPN derivatives
with different linker units ranging from the original ꢀCH2SiMe2ꢀ
(A) to o-phenylene (B) and 2,3-thiophene (C), as shown in
Chart 2.
In an effort to simplify the synthesis of these kinds of systems,
we designed a new 1,2-alkenyl-linked NPN ligand framework. In
Scheme 1, the rationale is given graphically. To avoid the
kinetically labile SiꢀN bond found in A, we have explored robust
CꢀN and CꢀP bonds, especially those involving sp2 hybridiza-
tion, as is evident from our studies on the already mentioned
o-phenylene-linked NPN system (B)4,26 and the analogous 2,
3-thiophene-linked system (C),6 both of which use Hartwigꢀ
Buchwald arylamination procedures to generate the CꢀN bond.
Common to both B and C is the dienamidophosphine linker
shown as D, but rather than examine this unsubstituted system, a
more convenient precursor to use was the cyclopentylideneꢀ
ketoimine precursor (E), which ensures that the imine and
phosphine donors have a syn orientation; the use of condensation
chemistry to generate the imine unit also simplifies the formation
of the CꢀN bond. The imine unit has figured prominently
Received: August 13, 2011
Published: October 07, 2011
r
2011 American Chemical Society
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Chart 2
Scheme 2
Scheme 1
we found that this method was not reliable, and so we opted for
the LDA deprotonation protocol instead.
recently with a number of studies on diiminopyridine-type
ligands and their coordination chemistry with a variety of
metals;30ꢀ39 there have also been reports of chelating imino-
phosphine ligands and their coordination chemistry with
iron.40ꢀ43 This paper documents the synthesis of a diimine-
phosphine precursor framework starting from arylimine deriv-
atives of cyclopentanone and its coordination chemistry with
zirconium. We also report the formation of a thermally labile
dinuclear dinitrogen complex of zirconium formed via reduc-
tion using KC8.
From these reactions, one could isolate oily, yellow materials
that were mixtures of products; for both 1a and 1b, five singlets
were initially observed in the 31P NMR spectrum, corresponding
to five different species, in variable amounts (see the Experi-
mental Section). We could purify the oily mixtures to generate
solids by rapid precipitation from a pentane solution; in the case
of 1a, depending on the workup, the solid could be either a
mixture of five species in similar amounts to the crude oily
mixture or just one pure compound. For 1b, a single compound
with δ(31P{1H}) ꢀ8.8 was isolated as a powder in moderate
NMR spectroscopy (1H{31P} NMR), mass spectrometry (EI-
MS), and elemental analysis (EA); that the diimine tautomer of
1b was isolated was ascertained by HSQC spectroscopy because
each proton resonance correlates to a 13C signal and therefore
indicates the absence of NH protons. On the basis of NMR
spectroscopy, we were able to definitively assign this material as a
meso-diimine stereoisomer of 1b, which was confirmed via X-ray
analysis (vide infra).
As was observed for the related bidentate systems, the existence
of isomers is likely due, in part, to a tautomeric equilibrium
between the imine and enamine forms; however, in our case,
because we have two imines linked by a tertiary phosphine, there
exist stereoisomers as well as structural isomers, the latter being
due to the aforementioned equilibrium. This is shown generically
in Scheme 2 and could potentially involve the diimine, en-
amineimine, and dienamine tautomers. As willbe discussed below,
’ RESULT AND DISCUSSION
1
Synthesis of CY5[NPN]DMPH2 (1a) and CY5[NPN]DIPPH2 (1b).
Our short-form descriptors for these ligand precursors use
the linker ring CY5 for the cyclopentylidene unit and either
DMP or DIPP to indicate the substitution pattern of the
N-arylimine moiety, with DMP being 2,6-dimethylphenyl
and DIPP short for 2,6-diisopropylphenyl. These ligands can be
easily assembled using a modification of a literature prepara-
tion.44 The reaction of either cyclopentylideneꢀ2,6-di-
methylaniline or cyclopentylideneꢀ2,6-diisopropylaniline
with lithium diisopropylamide (LDA) at low temperature
followed by quenching with 0.5 equiv of dichlorophenylpho-
sphine results in the formation of the diiminephosphine
derivatives 1a and 1b, as shown in eq 1. The original
literature preparation44 describes the synthesis of bidentate
P,N ligands and reports the use of BuLi as the preferred
method of generating the enamide via deprotonation of an
α-methylene proton of the cyclopentylidene ketoimine. However,
yield and identified as the diiminophosphine proligand by H
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Figure 1. 31P HMBC NMR at 400 MHz taken in C6D6.
1
there could potentially be six isomeric species formed: three
diastereomeric forms of the diimine (two meso and one rac), two
diastereomeric enamineimines, and the dienamine. Given that
we could see five species initially, one of the challenges was to
determine if indeed a sixth species was formed and, if so, to locate
its resonance in the 31P NMR spectrum.
as the α protons of the cyclopentyl unit in the H NMR
spectrum. The two small doublets arise from NꢀH protons of
the enamineimine tautomers, which was determined from the
13C HSQC NMR experiment that showed no correlation of these
two doublets with any carbon atoms in the 13C NMR spectrum.
Thus, the two upfield singlets in the 31P NMR spectrum
(δ ꢀ32.1 and ꢀ36.7) are due to enamineimine tautomers, and
there are two diastereomers that result from the stereogenic
phosphorus and carbon centers in this tautomeric form (Chart 3).
The doublets arise from long-range coupling to the phosphine
(4JNP ∼ 4ꢀ6 Hz).
For the DMP ligand precursor 1a, dissolution of the solid
material obtained from pentane in C6D6 showed five peaks in the
31P NMR spectrum at δ ꢀ5.6 (28%), ꢀ6.0 (6%), ꢀ8.5 (47%),
ꢀ32.1 (6%), and ꢀ36.7 (13%); the actual amounts of each
material vary by a few percent, but the major product is always
the peak at δ ꢀ8.5. By use of a series of 2D NMR experiments,
these resonances could be assigned. In Figure 1, the 31P HMBC
NMR spectrum of the mixture shows that the major peak at δ
At this point, the five species identified consist only of diimine
and enamineimine forms of 1a, with no peaks attributable to the
dienamine tautomer. On the basis of the upfield shift of the
enamineimine form compared to the diimine, we reasoned that
the 31P NMR resonance for the putative dienamine species
would likely be located upfield of the enamineimine form, likely
in the range of δ ꢀ60 to ꢀ70. Upon close examination of this
region, we did find a very small resonance at δ ꢀ63, which
correlated in the 31P HMBC NMR experiment to a shoulder in
the NꢀH region of the 1H NMR spectrum at δ 6.2. This is shown
in Figure 1.
1
ꢀ8.5 only correlates with the triplet at δ 3.9 in the H NMR
spectrum; the other two peaks in this part of the 31P NMR
spectrum (i.e., at δ ꢀ5.6 and ꢀ6.0) also correlate to peaks
between δ 5.0 and 3.6 in the 1H NMR spectrum; as will be shown
below, these 1H NMR peaks are due to the α protons next to the
phosphine in the cyclopentyl substituent and are assigned to the
rac and two meso forms of the dimine tautomer. Another set of
resonances in the 31P NMR spectrum are the upfield peaks at
δ ꢀ32.1 and ꢀ36.7; using 31P HMBC NMR, these two resonances
correlate with two small doublets between δ 6.6 and 6.2, as well
As was already mentioned, the major peak in the 31P NMR
spectrum of 1a occurs at δ ꢀ8.5 and correlates to a single CH
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Chart 3
shown in Figure 2, along with selected bond lengths and angles.
What is clearly evident is that the crystal is the dimine tautomer
and that it is the meso diastereomer, with the SrR absolute
configuration. All of the distances and angles are that expected
for this dimine form with two CdN double bonds and sp3-
hybridized α-carbon centers. One notable feature of the
structure is a short contact, perhaps due to hydrogen bonding,
between the α-CH bond and the distal imine nitrogen, H7 and
N1 [H7
N1, 2.55(3) Å].
3 3 3
X-ray-quality crystals of 1b were obtained by recrystallization
of the crude powder from hexanes; the solid-state structure is
given in the Supporting Information (Figure S3). There were no
indicators of partial oxidation in the solid-state molecular struc-
ture obtained for 1b. It is also the diimine form and is the (SrR)-
meso diastereoisomer. The bond lengths and angles of 1b are very
similar to those of 1a, as expected. No short contacts are
observed between N1 and H7 in this iteration of the ligand,
likely because of the presence of the increased steric bulk of the
2,6-diisopropyl substituents on the arylimines, which prevents a
conformation that orients the imine nitrogen atoms toward those
particular α protons.
Synthesis of Zirconium Complexes of CY5[NPN]DMPH2 (2a)
and CY5[NPN]DIPPH2 (2b). The bis(dimethylamido)zirconium(IV)
complexes CY5[NPN]DMPZr(NMe2)2 (2a) and CY5[NPN]DIPP
-
Zr(NMe2)2 (2b) were obtained starting from Zr(NMe2)4 and
the isolated proligands 1 via a protonolysis process. In the case
of 2a, complete conversion is observed after a toluene solution
of the reactants is kept at 60 °C for 12 h, while prolonged
heating for 2 weeks at 100 °C is required to form the sterically
more congested analogue 2b (see Scheme 3).
The bis(dimethylamido) complexes 2 are obtained as yellow
powders in high yields upon workup. For protonolysis to proceed,
the tautomeric equilibrium shown in Scheme 2 must be partly
operative because this would facilitate the formation of the
dienamido complexes 2 from Zr(NMe2)4 by elimination of
HNMe2. This is supported by the fact that clean conversions
to complexes 2 are observed when the proligands 1 are used as a
mixture of isomers.
resonance at δ 3.9; this identifies it as a meso diastereomer of the
diimine tautomer of the ligand, which has been confirmed by
X-ray crystallography (vide infra). A second diastereomer of the
diimine tautomer of the ligand is assigned to a 31P resonance at
δ ꢀ5.4. This signal correlates with two CH protons, supporting
the assignment of this resonance as the rac stereoisomer of the
diimine tautomer of the ligand. As illustrated in Chart 3, the two
α protons of the rac enantiomers (RR and SS) are not related by
symmetry; therefore, two unique resonances would be expected
in the 1H NMR spectrum. The α protons of both meso diastereo-
mers are related by a mirror plane and thus appear as a single
resonance.
The 31P{1H} NMR spectra of 2a and 2b in C6D6 show singlets
at δ ꢀ38.9 and ꢀ35.5, respectively. Two singlets for the ArCH3
substituents (2a) and four doublets for the Ar[CH(CH3)2]2
methyl groups (2b) are observed in the 1H{31P} NMR spectrum,
indicating that rotation of the N-aryl groups is hindered once the
ligands are coordinated to zirconium. The dimethylamido
ligands are inequivalent as well, which indicates that both
complexes have Cs symmetry in solution.
In the mixture of isomers of 1a, the 31P resonance at δ ꢀ6.0
(∼6ꢀ7% of the mixture) is a second meso diastereomer,
which is predicted to be present due to the pseudochiral
phosphorus center; this signal is very close to the resonances
of the rac- and meso-dimine diastereomers, which is consis-
tent with a diimine framework because the chemical shift is
consistent with sp3 hybridization of both α-carbons of the
cyclopentyl linker that flank the 31P nucleus. A single cross
peak is observed by 31P HMBC NMR in the region of interest;
this 31P resonance correlates with a 1H signal at δ 3.8, which
overlaps with the previously discussed resonances assigned as
α-CH protons.
The single-crystal X-ray structures of the major isomers of
both ligand precursors have been determined. X-ray-quality
crystals of 1a were obtained by dissolving the crude mixture in
boiling methanol followed by slow cooling of the solution. The
crystal selected was partially oxidized at the phosphorus center;
this partial oxidation was modeled as a disordered oxygen atom
with 12.8% occupancy. The solid-state molecular structure is
These findings are consistent with the solid-state structures of
2 determined by single-crystal X-ray diffraction. The molecular
structure of 2a is shown in Figure 3 (2b is given in Figure S4 in
the Supporting Information). Similar to the previously reported
[NPN]*Zr(NMe2)2 species (where [NPN]* = {[N-(2,4,6-
Me3C6H2)(2-N-5-MeC6H3)]2PPh}),4 a distorted trigonal-
bipyramidal geometry is found, with the [NPN] ligand coordi-
nating in a facial fashion. The phosphorus donor and one
of the dimethylamides in 2a and 2b occupy the apical posi-
tions, while the remaining amides form the equatorial plane.
The observed distortion is mainly due to the acute bite angles
of the ligands, which deviate significantly from 90° [2a,
N1ꢀZr1ꢀP1 = 73.78(3)°, N2ꢀZr1ꢀP1 = 72.59(3)°; 2b,
N1ꢀZr1ꢀP1 = 72.26(6)°, N2ꢀZr1ꢀP1 = 71.84(6)°]. All
nitrogen donors are planar (sp2-hybridized) and the phos-
phorus donors pyramidal, with the ZrꢀN and ZrꢀP bond
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Figure 2. ORTEP drawing of the solid-state molecular structure of the (SrR)-meso-diimine form of 1a shown with 50% thermal ellipsoids. The
hydrogen atoms have been excluded for clarity except for H2 and H7, whose positions were determined from the difference map. Selected bond lengths
(Å) and bond angles (deg): N1ꢀC1 1.2767(4), C1ꢀC2 1.5074(3), C2ꢀP1 1.8509(7), P1ꢀC11 1.8399(4), P1ꢀC7 1.8535(5), C7ꢀC6 1.4887(5),
C6ꢀN2 1.2731(4), N1ꢀC17 1.4248(3), N1 H7 2.55(3); C17ꢀN1ꢀC1 119.34(2), N1ꢀC1ꢀC2 122.7(2), C2ꢀP1ꢀC7 102.52(13), P1ꢀC7ꢀC6
3 3 3
114.16(19), C7ꢀC6ꢀN2 122.9(3), C6ꢀN2ꢀC23 121.3(2).
Scheme 3
Me3SiCl or Me3SiI (see Scheme 2). Upon workup, the volatile
byproduct Me3SiNMe2 is removed from the reaction mixture
under vacuum and the products are isolated as orange powders.
Compounds 3 and 4 were fully characterized by NMR spectros-
copy, EI-MS, EA, and single-crystal X-ray diffraction.
Dissolution of 3a and 4a in tetrahydrofuran (THF) results in a
sharp color change from orange to deep red, suggesting that THF
adducts are formed. Compared to samples in C6D6, the phos-
phorus resonances in THF-d8 are shifted downfield from
δ ꢀ31.9 and ꢀ30.1 to δ ꢀ21.4 and ꢀ23.6 for 3a and 4a,
respectively. Interestingly, no change in the 31P{1H} NMR
spectrum is observed when THF is added to 3b, which indicates
that the bulkier N-arylisopropyl substituents prevent coordina-
tion of THF. As in the case of complexes 2, hindered rotation
around the N-aryl bonds is suggested by the observation of
1
inequivalent H NMR signals for the o-methyl and o-isopropyl
groups. Combining all of the collected NMR data, an overall Cs
symmetry is deduced for 3a, 3b, and 4a.
The ORTEP representations of the solid-state molecular
structures of 3a and 4a are shown in Figures 4 and 5, respectively
(the structure of 3b can be found in the Supporting Information).
In all cases, the geometry around the metal center is best
described as distorted trigonal bipyramidal. Similar to the
bis(dimethylamido) complexes 2, the CY5[NPN] ligands are
bound facially with the NꢀZrꢀP angles deviating significantly
from 90° due to the strain imposed by the cyclopentenyl
linkers. Compared to the previously reported4 zirconium
lengths within the values reported for other zirconium(IV)
complexes.45,46
Starting from the bis(dimethylamido) complexes 2, the diha-
lides CY5[NPN]DMPZrCl2 (3a), CY5[NPN]DIPPZrCl2 (3b), and
CY5[NPN]DMPZrI2 (4a) are obtained by reaction with excess
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Figure 3. ORTEP drawing of the solid-state molecular structure of 2a
(ellipsoids at the 50% probability level). All hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Zr1ꢀN1 2.1727(10), Zr1ꢀN2 2.1740(10), Zr1ꢀP1 2.7756(3), Zr1ꢀ
N3 2.0191(10), Zr1ꢀN4 2.0670(10), C1ꢀC2 1.3618(16), C20ꢀC21
1.3570(16); N1ꢀZr1ꢀN2 123.52(4), N3ꢀZr1ꢀN4 104.88(4),
N1ꢀZr1ꢀP1 73.78(3), N2ꢀZr1ꢀP1 72.59(3), N1ꢀZr1ꢀN3 111.36(4),
P1ꢀZr1ꢀN3 89.90(3), P1ꢀZr1ꢀN4 164.75(3), N1ꢀZr1ꢀN4
103.49(4), N2ꢀZr1ꢀN4 97.75(4), N2ꢀZr1ꢀN3 112.54(4), C2ꢀ
C1ꢀN1 126.20(10), C21ꢀC20ꢀN2 125.67(10), C6ꢀN1ꢀZr1
124.83(7), C25ꢀN2ꢀZr1 118.89(7).
Figure 4. ORTEP drawing of the solid-state molecular structure of 3a
(ellipsoids at the 50% probability level). All hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Zr1ꢀN1 2.0844(11), Zr1ꢀP1 2.7689(8), Zr1ꢀCl1 2.3887(10), Zr1ꢀ
Cl2 2.4088(8), C1ꢀC2 1.3512(16); N1ꢀZr1ꢀN1* 120.12(6), Cl1ꢀ
Zr1ꢀCl2 100.771(19), N1ꢀZr1ꢀP1 73.22(3), N1ꢀZr1ꢀCl1 112.84(3),
P1ꢀZr1ꢀCl1 86.401(16), P1ꢀZr1ꢀCl2 172.828(18), N1ꢀZ1ꢀCl2
103.63(3), C2ꢀC1ꢀN1 124.83(11), C6ꢀN1ꢀZr1 116.55(7).
basis of the assumption that the latter solids are decomposition
products generated by decoordination of THF, we decided to
focus our efforts on the reduction of 4a, which was shown to
form a stable THF adduct (vide supra). Thus, 4a was reacted
with 2.2 equiv of KC8 in THF at ꢀ116 °C under 1 atm of N2
and the reaction mixture slowly warmed to room temperature
(see eq 2).
complex [NPN]*ZrCl2, (where [NPN]* = {[N-(2,4,6-Me3C6H2)-
(2-N-5-MeC6H3)]2PPh}), the C2ꢀC1ꢀN1 angles in 3 are
opened up wider due to geometry imposed by five-membered
cyclopentenyl linkers (C2ꢀC1ꢀN1ꢀ124° in 4 and ∼118° in
[NPN]*ZrCl2).
The structure of 4a (see Figure 3) closely resembles the
structures of 3a and 3b with both iodides cis-disposed. The
ZrꢀI bond lengths are 2.79 Å on average, which agrees well with
related values reported in the literature.47
Synthesis of {CY5[NPN]DMPZr(THF)}2(μ-η2:η2-N2) (5). We
have previously reported that dinuclear side-on-bridging dinitro-
gen complexes of zirconium can be obtained via KC8 reduction of
a variety of amidophosphine-containing precursor complexes.26,48ꢀ52
For example, reduction of [NPN]*ZrCl2 in THF under 4 atm of
N2 at low temperature in THF leads to the formation of
{[NPN]*Zr(THF)}2(μ-η2:η2-N2).26 When the same methodol-
ogy was applied, attempts were made to reduce 3a, 3b, and 4a in
the presence of molecular nitrogen. In each case, deep-green
solutions were initially observed, which decomposed rapidly
upon removal of THF. Analysis of the crude reaction mixtures
by 31P NMR revealed that multiple products formed and that all
starting materials had been consumed. In attempts to separate
the different species by fractional crystallization, pentane was
added to the crude reaction mixtures (after removal of graphite
by filtration over Celite), which resulted in the precipitation of
bluesolids. These solids were found to be insoluble in all common
organic solvents and resisted appropriate characterization. On the
After filtration, slow evaporation of the crude reaction mixture
in a glovebox at room temperature generated black crystals over
the course of several days, which were analyzed by single-crystal
X-ray diffraction. The refined molecular structure revealed that
the dinuclear side-on dinitrogen complex 5 formed with one THF
molecule coordinated to each metal center (see Figure 6). The
Zr2N2 unit in this arrangement is almost planar, with a dihedral
angle of 179.5° between the two ZrN2 planes (see Figure 5).
Similar to the NꢀN bond distance of 1.503(6) Å in
{[NPN]*Zr(THF)}2(μ-η2:η2-N2),26 the NꢀN bond in 5 is
elongated to 1.508(5) Å, corresponding to the hydrazido moiety
(N24ꢀ). This compares well to many of the side-on-bound
dinitrogen complexes reported in the literature, as shown in
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Figure 6. ORTEP drawing of the solid-state molecular structure of 5
(ellipsoids at the 50% probability level). All hydrogen atoms have been
omitted for clarity. Carbons of one of the 2,6-dimethylphenyl substit-
uents (except Cipso) on the N2 donor are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Zr1ꢀP1 2.7136(9), Zr1ꢀN1
2.237(3), Zr1ꢀN2 2.189(3), Zr1ꢀO1 2.348(2), Zr1ꢀN3 2.017(3),
Zr1ꢀN3* 2.073(3), N3ꢀN3* 1.508(5); P1ꢀZr1ꢀN1 74.35(7),
P1ꢀZr1ꢀN2 74.61(7), N3ꢀZr1ꢀN3* 43.25(14), Zr1ꢀN3ꢀZr1*
136.75(14), O1ꢀZr1ꢀP1 152.32(6), P1ꢀZr1ꢀN3 82.54(8).
Figure 5. ORTEP drawing of the solid-state molecular structure of 4a
(ellipsoids at 50% probability level). All hydrogen atoms have been
omitted for clarity. Selected bond length (Å) and angles (°): Zr1ꢀN1
2.0837(19), Zr1ꢀN2 2.0810(19), Zr1ꢀP1 2.7536(8), Zr1ꢀI1 2.7859(17),
Zr1ꢀI2 2.7966(6), C1ꢀC2 1.348(3), C20ꢀC21 1.352(3), N1ꢀZr1ꢀ
N2 120.44(8), I1ꢀZr1ꢀI2 99.59(2), N1ꢀZr1ꢀP1 72.94(5), N2ꢀ
Zr1ꢀP1 72.96(5), N1ꢀZr1ꢀI1 109.59(6), P1ꢀZr1ꢀI1 84.54(3),
P1ꢀZr1ꢀI2 175.773(16), N1ꢀZr1ꢀI2 106.29(5), N2ꢀZr1ꢀI2
104.31(5), N2ꢀZr1ꢀI1 113.98(6), C6ꢀN1ꢀZr1 117.04(14), C25ꢀ
N2ꢀZr1 117.44(14), C2ꢀC1ꢀN1 124.6(2), C21ꢀC20ꢀN2 124.2(2).
Table 1. Selected Dinuclear Zirconium Dinitrogen Com-
plexes with Side-On-Bound Dinitrogen
Table 1.26,48ꢀ55 With respect to 5, a 2-fold rotation axis bisects
the NꢀN bond perpendicular to the Zr2N2 plane, resulting in an
overall C2 symmetry (Figure 7). The ZrꢀN bond lengths of
the N2 core are slightly different from each other [Zr1ꢀN3 =
2.017(3) Å and Zr1ꢀN3* = 2.073(3) Å] and significantly shorter
than the ZrꢀN(ligand) bonds [Zr1ꢀN1 = 2.237(3) Å and
Zr1ꢀN2 = 2.189(3) Å]; the Zr1ꢀP1 [2.7136(9) Å] and
Zr1ꢀO1 [2.348(2) Å] bond lengths are unexceptional.
NꢀN bond
compound
([PNP]ZrCl)2(μ-η2:η2-N2)a
([PNP]Zr(O-2,6-Me2C6H3))2(μ-η2:η2-N2)
([P2N2]Zr)2(μ-η2:η2-N2)b
{[NPN]Zr(THF)}2(μ-η2:η2-N2)c
{[NPN]*Zr(THF)}2(μ-η2:η2-N2)d
[η5-C5Me4H)2Zr]2(μ-η2:η2-N2)
(rac-BpZr)2(μ-η2:η2-N2)e
length (Å)
1.587(7)49
1.528(7)48
1.465(19)51
1.503(3)52
1.503(6)26
1.377(3)55
1.241(2)53
1.47(3)54
Despite several efforts, well-resolved NMR spectra of 5 in
THF-d8 or C6D6 were not obtained. Upon isolation of the black
crystals from a THF solution, rapid decomposition to the already
mentioned blue solids is observed, which prevented the acquisi-
tion of other spectroscopic and analytical data.
[Cp002Zr]2(μ-η2:η2-N2)f
((η5-C5Me5)Zr(iPrNC(NMe2)NiPr))2(μ-η2:η2-N2)
1.518(2)50
{
CY5[NPN]DMPZr(THF)}2(μ-η2:η2-N2)g
1.508(5)
a [PNP] = N(SiMe2CH2PPri2)2. b [P2N2 = PhP(CH2SiMe2NSiMe2-
CH2)2PPh. c [NPN] = PhP(CH2SiMe2NPh)2. d [NPN]* = {[N-(2,4,
6-Me3C6H2)(2-N-5-MeC6H3)]2PPh}. e rac-Bp = rac-Me2Si(η5-C5H2-
2-SiMe3-4-CMe3)2. f Cp00 = η5-1,3-C5H3(SiMe3)2. g 5 (Figure 6).
’ CONCLUSIONS
In this paper, two new diiminophosphine proligands 1 and
their zirconium complexes 2ꢀ4 were prepared and fully char-
acterized. The proligands exist as a mixture of isomers because of
the presence of tautomers and stereoisomers. Nevertheless, the
various isomers of both 1a and 1b are cleanly deprotonated upon
reaction with Zr(NMe2)4 to form the dienamido compounds 2a
and 2b, respectively. The potential of the new zirconium NPN
complexes 3 and 4 to activate dinitrogen upon reduction was
explored and the THF-solvated side-on dinitrogen complex 5
obtained. The latter compound is unstable, presumably because
of desolvation, which prevented full characterization as well
as reactivity studies. Attempts to reduce complex 3b, which
incorporates the bulkier DIPP-substituted ligand, did not pro-
duce any isolable dinitrogen-containing products.
’ EXPERIMENTAL SECTION
General Considerations. Unless otherwise stated, all manipula-
tions were performed under an atmosphere of dry, oxygen-free N2 or Ar
by means of standard Schlenk or glovebox techniques. Hexanes, toluene,
THF, and diethyl ether were purchased anhydrous from Aldrich, sparged
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Inorganic Chemistry
ARTICLE
(t, 0.21H, 7 Hz, o-PPh), 7.85 (dd, 1.15H, 4.25 and 10.25 Hz, o-PPh),
7.72 (m, 2.42H, o-PPh), 6.87ꢀ7.29 (m, 20H, m-NAr and o-NAr), 6.47
(d, 0.12H, 4 Hz, NꢀH), 6.11 (d, 0.27H, 6 Hz, NꢀH), 4.62 (t, 0.58H, 7
Hz, α-CH rac), 4.21 (t, 0.58H, 9 Hz, α-CH rac), 3.89 (t, 2H, 8 Hz, α-CH
meso), 3.73 (t, 0.41H, 8 Hz, α-CH enamineimine), 3.64 (dd, 0.31H, 6
and 10 Hz, α-CH enamineimine), 2.28 (s, 0.72H, ArCH3), 2.26 (s, 2H,
ArCH3), 2.17 (s, 6H, ArCH3), 2.15 (s, 2H, ArCH3), 2.14 (s, 1H,
ArCH3), 2.12 (s, 3H, ArCH3), 2.09 (s, 2H, ArCH3), 2.08 (s, 1H,
ArCH3), 2.07 (s, 6H, ArCH3), 1.88ꢀ2.06 (m, 7H, CH2), 1.85 (s, 2H,
ArCH3), 1.19ꢀ1.83 (m, 22H, CH2).
1H NMR of Pure meso-1a (C6D6, 300 MHz): δ 7.74 (m, 2H, o-PPh),
7.18 (m, 3H, m- and p-PPh), 7.05 (d, 4H, 6 Hz, m-NAr), 6.94 (t, 2H, 6
Hz, p-NAr), 3.88 (t, 2H, 6 Hz, CH), 2.19 (s, 6H, ArCH3), 2.09 (s, 6H,
ArCH3), 2.05 (m, 2H, CH2), 1.68 (m, 6H, CH2), 1.45 (m, 2H, CH2),
1.30 (m, 2H, CH2). 31P{1H} NMR (C6D6, 161 MHz): δ ꢀ9.4 (s).
13C{1H} NMR (C6D6, 101 MHz): δ 181.2 (d, 9 Hz), 151.0, 135.7, 135.6
(d, 36 Hz), 129.3, 128.5, 128.3, 128.1, 127.8, 125.5 (d, 23 Hz), 122.9,
42.4 (d, 19 Hz), 32.6, 28.4 (d, 6 Hz), 23.6 (d, 5 Hz), 18.9, 18.3 (ArCH3).
EI-MS (m/z): 480 ([M]+). Anal. Calcd for C32H37N2P: C, 79.97; H,
7.76; N, 5.83. Found: C, 80.06; H, 7.88; N, 5.70.
Figure 7. Side view of the stereochemistry around the Zr2(η2:η2-N2)
core in 5.
with N2, and passed through columns containing activated alumina and
Ridox catalyst. C6D6 was dried by distillation from sodium/benzophe-
none onto activated 4 Å molecular sieves and freezeꢀpumpꢀthaw
degassed three times. Pentane and benzene were dried over sodium/
Synthesis of 1b. In a round-bottomed flask, LDA was prepared by
the slow addition of 1.6 M n-butyllithium (7.04 mL, 11.5 mmol) to
diisopropylamine (1.62 mL, 11.5 mmol) in 20 mL of diethyl ether at
ꢀ78 °C. The resulting mixture was stirred for 30 min during warming to
ꢀ50 °C. The solution was cooled to ꢀ78 °C again, and neat N-
cyclopentylidene-2,6-diisopropylaniline (2.81 g, 11.5 mmol) was added
dropwise. Thereafter, the reaction mixture was warmed to ꢀ40 °C over
1 h. The mixture was cooled to ꢀ78 °C again, and a solution of
dichlorophenylphosphine (0.78 mL, 5.75 mmol) in 80 mL of diethyl
ether was added over 1 h. The colorless solution gradually changed to
pale yellow. Upon completion, the reaction vessel was warmed to room
temperature and stirred overnight. The volatiles were then removed in
vacuo, and 20 mL of toluene was added to the mixture, which was filtered
through Celite using a glass frit. Toluene was removed in vacuo to give a
yellow oil, which consists of a mixture of isomers (31P{1H} NMR signals
at δ ꢀ2.9, ꢀ3.8, ꢀ8.8, ꢀ28.5, and ꢀ37.2 in toluene). A total of 10 mL of
pentane was added to the residue, which resulted in the formation of a
white precipitate. The suspension was cooled to ꢀ40 °C overnight, and
the precipitate was collected on a glass frit and dried in vacuo. Yield: 1.64
1
benzophenone and distilled prior to use. Unless otherwise noted, H,
31P{1H}, and 13C{1H} NMR spectra were recorded on a Bruker AV-300
or a Bruker AV-400 spectrometer, operating at 300.1 and 400.0 MHz for
1H NMR spectra, respectively. All spectra were recorded at room
1
temperature. H NMR spectra were referenced to residual protons in
the deuterated solvent C6D6 (δ 7.16). 31P{1H} NMR spectra were
referenced to external P(OMe)3 (δ 141.0 with respect to 85% H3PO4 at
δ 0.0). 13C{1H} NMR spectra were referenced to the residual solvent
C6D6 (δ 128.0). Chemical shifts (δ) listed are in parts per million, and
absolute values of the coupling constants are in hertz. EI-MS, EA (C, H,
and N), and X-ray crystallography were all performed at the Department
of Chemistry, University of British Columbia.
Dichlorophenylphosphine was purified by distillation. Diisopropyla-
mine was dried over CaH2 and distilled prior to use. n-Butyllithium was
purchased from Aldrich, and the molarity was determined via direct
titration with diphenylcarboxylic acid.56 KC8 was prepared according to
a literature procedure.57 All other compounds were purchased from
commercial suppliers and used as received.
g, 48%. 1H NMR (C6D6, 400 MHz): δ 7.71 (dd, 2H, JHP = 8 Hz, JHH
=
8 Hz, o-PPh), 7.19ꢀ7.09 (m, overlap with the solvent peak), 3.83 (t, 2H,
8 Hz, CH), 3.05 (sept, 4H, 4 Hz, CH), 2.10 (m, 2H, CH2), 1.89 (m, 2H,
CH2), 1.70 (m, 4H, CH2), 1.46 (m, 2H, CH2), 1.35 (m, 2H, CH2), 1.29
(d, 6H, 4 Hz, CH3), 1.24 (d, 6H, 4 Hz, CH3), 1.16 (d, 6H, 4 Hz, CH3), 1.15
(d, 6H, 4 Hz, CH3). 31P{1H} NMR (C6D6, 161 MHz): δ ꢀ8.8 (s).
13C{1H} NMR (C6D6, 75 MHz): δ 181.3 (d, 8 Hz), 148.2, 136.2, 136.0,
135.8, 135.6, 135.4 (d, 26 Hz), 129.3, 128.0, 123.5 (d, 25 Hz), 123.2, 42.8 (d,
20 Hz), 33.0, 28.4, 28.2 (d, 6 Hz), 27.8, 24.6, 23.7 (d, 5 Hz), 23.4, 23.1, 22.9.
EI-MS (m/z): 592 ([M]+), 549 ([M ꢀ CH(CH3)2]+). Anal. Calcd for
C40H53N2P: C, 81.04; H, 9.01; N, 4.73. Found: C, 81.16; H, 8.86; N, 4.85.
Synthesis of 2a. Zr(NMe2)4 (1.463 g, 3.05 mmol) and 1a (0.815 g,
3.05 mmol) were combined and dissolved in toluene (20 mL). The
reaction mixture was then transferred to a 100-mL Kontes-sealed
reaction vessel (bomb) and stirred in an oil bath at 60 °C for 12 h.
The resulting yellow solution was taken to dryness to obtain a yellow
residue. Upon the addition of pentane (10 mL), a light-yellow pre-
cipitate formed and was collected on a frit and dried (1.71 g, 2.60 mmol,
85%). Yellow single crystals of 2a suitable for X-ray diffraction were
grown by the slow evaporation of a pentane solution of the compound.
1H NMR (C6D6, 400 MHz): δ 7.58 (dd, 2H, JHP = 8 Hz, JHH = 8 Hz,
o-PPh), 7.25 (t, 2H, 8 Hz, m-PPh), 7.11 (t, 1H, 8 Hz, p-PPh), 7.05
(d, 2H, 8 Hz, m-NAr), 7.03 (d, 2H, 8 Hz, m-NAr), 6.92 (t, 2H, 8 Hz, p-
NAr), 2.90 (s, 6H, N(CH3)2), 2.74 (m, 2H), 2.53 (m, 2H), 2.34 (s, 6H,
ArCH3), 2.33 (s, 6H, ArCH3), 2.24 (s, 6H, N(CH3)2), 2.08 (m, 2H),
Synthesis of 1a. In a round-bottomed flask, LDA was prepared by
the slow addition of 1.63 M n-butyllithium (8.72 mL, 14.2 mmol) to
diisopropylamine (2.00 mL, 14.2 mmol) in 20 mL of diethyl ether
at ꢀ78 °C. The resulting mixture was stirred for 30 min during warming
to ꢀ50 °C. The solution was cooled to ꢀ78 °C again, and neat
N-cyclopentylidene-2,6-dimethylaniline (2.66 g, 14.2 mmol) was added
dropwise. Thereafter, the reaction mixture was warmed to ꢀ40 °C over
1 h. Afterward, the mixture was cooled again to ꢀ78 °C, and a solution of
dichlorophenylphosphine (0.96 mL, 7.10 mmol) in 80 mL of diethyl
ether was added over 1 h. The colorless solution gradually changed to
pale yellow. Upon completion, the reaction vessel was warmed to room
temperature and stirred overnight. The volatiles were then removed in
vacuo, and 20 mL of toluene was added to the mixture, which was filtered
through Celite using a glass frit. Toluene was removed in vacuo, giving
a yellow oil consisting of a mixture of isomers (31P{1H} NMR signals at
δ ꢀ5.6, ꢀ6.0, ꢀ8.5, ꢀ12.1, ꢀ32.1, and ꢀ36.7 in toluene). To the mixture
was added 10 mL of pentane to generate a white precipitate. The
suspension was cooled to ꢀ40 °C overnight, and the solid was collected
on a glass frit and dried in vacuo. Yield: 1.62 g, 41%.
1H NMR (C6D6, 600 MHz). Several structural and stereoisomers exist
in various amounts. The number of protons is based on integration of
each of these resonances relative to the α protons of the meso-diimine
tautomer at δ 3.86 (t, 2H, 8 Hz): δ 8.12 (t, 0.53H, o-PPh), 7.99
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Inorganic Chemistry
ARTICLE
1.90 (m, 6H). 31P{1H} NMR (C6D6, 162 MHz): δ ꢀ38.9 (s). 13C{1H}
NMR (C6D6, 101 MHz): δ 173.1 (d, 37 Hz), 148.9, 135.7, 134.7, 133.9 (d,
32 Hz), 131.2 (d, 12 Hz), 128.7, 128.6, 128.1, 127.8, 124.3, 93.5 (d, 32 Hz),
42.8, 42.2, 34.2 (d, 11 Hz), 31.0 (d, 3 Hz), 24.3 (d, 6 Hz), 19.5, 19.4. EI-MS
(m/z): 656 ([M]+), 612 ([M ꢀ NMe2]+). Anal. Calcd for C36H47N4PZr:
C, 65.71; H, 7.20; N, 8.51. Found: C, 65.36; H, 7.30; N, 8.24.
Synthesis of 3a. To a stirred yellow toluene solution (30 mL) of 2a
(1.53 g, 2.33 mmol) was added chlorotrimethylsilane (2.53 g, 23.3 mmol)
dropwise. The solution was stirred overnight. An orange precipitate
gradually formed. The reaction mixture was taken to dryness to obtain
an orange powder, which was collected on a frit, washed with pentane
(3 ꢁ 5 mL), and dried (1.42 g, 2.22 mmol, 95%). X-ray-quality orange
crystals of 3a were grown by the slow evaporation of a benzene solution
of the compound.
Synthesis of 3b. To a stirred yellow toluene solution (10 mL) of 2b
(0.601 g, 0.782 mmol) was added trimethylsilane chloride (0.845 g, 7.82
mmol) dropwise. The solution was stirred overnight. An orange
precipitate gradually formed. The reaction mixture was taken to dryness
to obtain an orange powder, which was collected on a frit, washed
with pentane (3 ꢁ 2 mL), and dried (0.563 g, 0.751 mmol, 96%).
X-ray-quality orange crystals of 3b were grown by the slow evapora-
tion of a benzene solution of the compound.
1H NMR (C6D6, 300 MHz): δ 7.63 (dd, 2H, JHP = 6 Hz, JHH = 6 Hz, o-
PPh), 7.19ꢀ7.14 (m, overlap with the solvent peak), 7.08 (m, 3H), 3,68
(sept, 2H, 6 Hz, CH), 3.44 (sept, 2H, 6 Hz, CH), 2.60 (m, 2H), 2.49 (m,
2H), 2.14 (m, 2H), 1.78 (m, 4H), 1.64 (m, 2H), 1.53 (d, 6H, 6 Hz,
CH3), 1.42 (d, 6H, 6 Hz, CH3), 1.19 (d, 6H, 6 Hz, CH3), 1.09 (d, 6H, 6
Hz, CH3). 31P{1H} NMR (C6D6, 121 MHz): δ ꢀ32.3 (s). 13C{1H}
NMR (C6D6, 101 MHz): δ 172.3 (d, 48 Hz), 146.3, 145.0, 141.9, 131.2
(d, 16 Hz), 129.9, 128.9 (d, 13 Hz), 128.0, 127.7, 124.9, 124.4, 102.4
(d, 50 Hz), 34.1 (d, 17 Hz), 31.0 (d, 4 Hz), 29.0, 28.5, 25.7, 25.6, 24.4, 24.3
(d, 8 Hz), 24.0. EI-MS (m/z): 752 ([M]+). Anal. Calcd for C40H51-
Cl2N2PZr: C, 63.81; H, 6.83; N, 3.72. Found: C, 63.54; H, 6.63; N, 3.72.
General Procedure for the Reduction Reactions. Compound
3a (0.296 g, 0.463 mmol) and KC8 (0.137 g, 1.02 mmol) were added to a
200-mL thick-walled Kontes-sealed reaction vessel (bomb) and shaken
to mix thoroughly. THF (10 mL) was vacuum-transferred to the solid
mixture at ꢀ196 °C. The flask was filled with dinitrogen at ꢀ196 °C,
sealed, and warmed slowly to room temperature in a liquid-dinitrogen/dry
ice/EtOH slurry behind a blast shield. After the mixture had gradually
melted over 1 h, it was stirred vigorously. The solution was stirred over-
night. The next day the bomb was depressurized by first cooling to
ꢀ196 °C, opening the seal to dinitrogen, and allowing the bomb to
warm to room temperature. The green solution was filtered through
Celite to remove all of the residual graphite and salt. The filtrate was
concentrated to about 3 mL, and pentane (5 mL) was added. Some blue
solid quickly precipitated out. Crystals of 6 suitable for X-ray analysis were
grown in an NMR tube by the slow evaporation of the THF solution.
1H NMR (C6D6, 400 MHz): δ 7.58 (dd, 2H, JHP = 8 Hz, JHH = 8 Hz,
o-PPh), 7.16 (t, 2H, 8 Hz, m-PPh), 7.06 (t, 1H, 8 Hz, p-PPh), 6.96
(m, 6H), 2.64 (m, 2H), 2.48 (s, 6H, ArCH3), 2.50 (m, 2H), 2.43 (s, 6H,
ArCH3), 1.91 (m, 2H), 1.78 (m, 2H), 1.69 (m, 4H). 31P{1H} NMR
(C6D6, 162 MHz): δ ꢀ31.9 (s). 13C{1H} NMR (C6D6, 101 MHz): δ
172.4 (d, 51 Hz), 143.5, 135.8 (d, 35 Hz), 130.7 (d, 15 Hz), 129.7, 129.4,
129.2, 129.1, 128.7, 128.4, 127.4, 103.6 (d, 53 Hz), 32.5 (d, 18 Hz),
30.6 (d, 5 Hz), 24.0 (d, 9 Hz), 19.7, 19.0. EI-MS (m/z): 640 ([M]+), 532
([M ꢀ PPh]+). Anal. Calcd for C32H35Cl2N2PZr 0.73 toluene: C,
3
62.93; H, 5.82; N, 3.96. Found: C, 62.58; H, 5.79; N, 3.88.
Synthesis of 4a. To a stirred yellow toluene solution (5 mL) of 2a
(0.276 g, 0.421 mmol) was added trimethylsilane iodide (0.842 g,
4.21 mmol) dropwise. The solution was stirred overnight. An orange
precipitate gradually formed. The reaction mixture was taken to dryness
to give a deep-orange powder, which was collected on a frit, washed with
pentane (3 ꢁ 1 mL), and dried (0.318 g, 0.387 mmol, 92%). X-ray-
quality crystals of 4a were grown by the slow diffusion of pentane into a
benzene solution of the compound.
1H NMR (C6D6, 400 MHz): δ 7.49 (dd, 2H, JHP = 8 Hz, JHH = 8 Hz,
o-PPh), 7.18 (t, 2H, 8 Hz, m-PPh), 7.07 (t, 1H, 8 Hz, p-PPh), 7.05 (t, 2H,
8 Hz, p-NAr), 6.98 (m, 4H, m-NAr), 2.63 (s, 6H, ArCH3), 2.58 (m, 2H),
2.39 (m, 2H), 2.36 (s, 6H), 1.92 (m, 2H), 1.74 (m, 6H). 31P{1H} NMR
(C6D6, 162 MHz): δ ꢀ30.1 (s). 13C{1H} NMR (C6D6, 101 MHz): δ
172.8 (d, 36 Hz), 142.8, 136.2 (d, 30 Hz), 130.6 (d, 10 Hz), 129.8, 129.7,
129.2, 129.1, 129.0, 128.0, 127.8, 105.7 (d, 38 Hz), 32.9 (d, 12 Hz), 31.1
(d, 3 Hz), 24.30 (d, 6 Hz), 21.1, 20.8. EI-MS (m/z): 822 ([M]+), 695
([M ꢀ I]+). Anal. Calcd for C32H35I2N2PZr: C, 46.66; H, 4.28; N, 3.40.
Found: C, 46.64; H, 4.58; N, 3.27.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic data in CIF
b
format for 1ꢀ5 and details on X-ray structure refinement, ORTEP
diagrams for 1b, 2b, and 3b, and 1H NMR and 13C HSQC NMR
spectra of the mixture of compounds of 1a. This material is available
free of charge via the Internet at http://pubs.acs.org.
Synthesis of 2b. Zr(NMe2)4 (0.186 g, 0.699 mmol) and 1b (0.414
g, 0.699 mmol) were mixed together and dissolved in toluene (10 mL).
The reaction mixture was then transferred to a 100-mL Kontes-sealed
reaction vessel (bomb) and stirred in an oil bath at 100 °C for 10 days.
The resulting yellow solution was taken to dryness to obtain a yellow
residue. Upon the addition of pentane (5 mL), a light-yellow precipitate
formed and was collected on a frit and dried (0.435 g, 0.566 mmol, 81%).
Yellow single crystals of 2b suitable for X-ray diffraction were grown by
the slow evaporation of a pentane solution of the compound.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: fryzuk@chem.ubc.ca.
’ ACKNOWLEDGMENT
We thank NSERC of Canada for funding (Discovery Grant
to M.D.F.). We also thank Nathan Halcovitch and Dr. Brian
O. Patrick for help with the X-ray structures.
1H NMR (C6D6, 400 MHz): δ 7.58 (dd, 2H, JHP = 8 Hz, JHH = 8 Hz,
o-PPh), 7.28 (t, 2H, 8 Hz, m-PPh), 7.18 (t, 2H, 8 Hz, p-NAr), 7.16 (t, 2H,
8 Hz, p-PPh), 7.10 (m, 4H, m-NAr), 3.60 (sept, 4H, 4 Hz, CH), 2.71
(s, 6H, N(CH3)2), 2.70 (m, 2H), 2.51 (s, 6H, N(CH3)2), 2.49 (m, 2H),
2.17 (m, 4H, CH2), 1.88 (m, 2H, CH2), 1.76 (m, 2H, CH2), 1.32 (d, 6H,
4 Hz, CCH3), 1.30 (d, 6H, 4 Hz, CCH3), 1.21 (d, 6H, 4 Hz, CCH3), 1.10
(d, 6H, 4 Hz, CCH3). 31P{1H} NMR (C6D6, 162 MHz): δ ꢀ35.5 (s).
13C{1H} NMR (C6D6, 101 MHz): δ 173.9 (d, 33 Hz), 146.3, 144.9,
134.2, 131.4 (d, 13), 128.6 (d, 9 Hz), 128.1, 127.8, 125.3, 123.8, 123.4,
90.6 (d, 35), 42.3, 40.5, 34.8 (d, 9 Hz), 31.3 (d, 3 Hz), 27.9, 27.7, 25.7,
25.2, 24.6 (d, 5 Hz), 23.7. EI-MS (m/z): 768 ([M]+), 725 ([M ꢀ
CH(CH3)2]+). Anal. Calcd for C44H63N4PZr: C, 68.62; H, 8.24; N,
7.27. Found: C, 68.37; H, 7.86; N, 6.94.
’ REFERENCES
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tallics 2004, 23, 4700.
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