Bis(tert-butylamido)- and bis(arylamido)cyclodiphosph(III)azane complexes of Ti, V, Zr and Hf: Ligand substituent effects and coordination number

Article abstract of DOI:10.1039/b211009a

Syntheses and structures of [{(Bu^tNP)₂(Bu ^tN)₂}MCl₂], M = Zr, Hf, [{(Bu ^tNP)₂(ArN)₂}TiCl₂], Ar = Ph, m-Tol, p-Tol, and of [{(Bu^tNP)₂(P

Full text of DOI:10.1039/b211009a

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Bis(tert-butylamido)- and bis(arylamido)cyclodiphosph(III)azane
complexes of Ti, V, Zr and Hf: ligand substituent effects and
coordination number
Daniel F. Moser,a Luke Grocholl,a Lothar Stahl*a and Richard J. Staplesb
a Department of Chemistry, University of North Dakota, Grand Forks, ND 58202-9024, USA.
E-mail: lstahl@chem.und.edu
b Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138,
USA
Received 8th November 2002, Accepted 11th February 2003
First published as an Advance Article on the web 26th February 2003
Syntheses and structures of [{(ButNP)2(ButN)2}MCl2], M = Zr, Hf, [{(ButNP)2(ArN)2}TiCl2], Ar = Ph, m-Tol, p-Tol,
and of [{(ButNP)2(PhN)2}VClؒTHF], are reported. In the solid-state these compounds are seco-heterocubic metal
complexes featuring one η3-coordinated bis(amido)cyclodiphosphazane ligand. When ZrCl4 and HfCl4 are treated
with {(ButNP)2(PhNLiؒTHF)2}, however, the diligand complexes [{(ButNP)2(PhN)2}2M], M = Zr, Hf are isolated.
Introduction
Amido-complexes of early transition metals are electronically
and often coordinatively unsaturated species,1 that are useful in
the activation of small molecules,2 polymerization catalysis3
and as precursors for metal nitrides.4 Because of this versatility
much effort has gone into tuning the reactivity of such com-
pounds with purpose-specific bulky monodentate5 or multi-
dentate6 ligands. Our interest in the synthesis of nitrogen-
donor complexes of early transition metals was spurred by
reports that certain bis(amido)metal dichloride complexes of
Group 4 metals are highly-active, living homogeneous poly-
olefin catalysts.7 We introduced bis(tert-butylamido)cyclo-
diphosph()azanes as possible variants of chelating diamides,8
because the U-shaped structure of these ligands is conducive to
creating monomeric pseudo-tetrahedral complexes. Some time
ago we communicated syntheses and structures of [{(But-
NP)2(ButN)2}MCl2], M = Zr (1), Hf (2)—the first transition
metal complexes of these ligands.9 Here we report full synthetic
and structural details of these compounds and the extension of
this chemistry to related metals and ligands.
The utility of homogeneous polyolefin catalysts is deter-
mined by both metal and ligand. Thus, titanocenes and
vanadocenes with identical ligands often have very different
properties,10 vanadocenes typically being less active but pro-
ducing polymers of higher molecular weights. Similarly large
effects are observed upon subtle ligand modifications for
catalysts with identical metal centers. To further explore the
structural chemistry of bis(amido)cyclodiphosph()azanes
and their complexes, we expanded our investigations to
vanadium and to ligands with the sterically smaller anilino and
toluidino substituents. Below we report the full synthetic and
structural details of bis(tert-butylamido)- and bis(arylamido)-
cyclodiphosph()azanes and their mono- and diligand com-
plexes of Group 4 and 5 metals.
Scheme 1
data collection and selected bond parameters of these com-
plexes are given in Tables 1 and 2, respectively. The ORTEP
drawing of 1 (Fig. 1) depicts the pseudo-trigonal bipyramidal
coordination of the zirconium atom, while that of 2 (Fig. 2)
emphasizes the deviation of the metal atom from a central
position above the heterocycle. Because both complexes are
isostructural, only the hafnium complex will be discussed in
detail. Although the coordination geometry of the hafnium
atom is close to trigonal-bipyramidal in the solid state, the long
Results and discussion
The reaction of MCl4 (M = Zr, Hf ) with {(ButNP)2(ButNLiؒ
THF)2} (Scheme 1) is highly solvent dependent, affording
[{(ButNP)2(ButN)2}MCl2], M = Zr (1), Hf (2) reproducibly
from hot toluene, but leading to intractable mixtures when
done in THF. Both Group 4 metal complexes were isolated as
moderately moisture-sensitive, light-yellow or cream-colored
solids, respectively.
The compounds crystallize isostructurally as molecular
solids without unusual intermolecular contacts. Listings of the
Fig. 1 Thermal-ellipsoid (35%) plot and partial numbering scheme of
1. Hydrogen atoms have been omitted for clarity.
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 2 Selected bond lengths (Å) and angles (Њ) for 1 and 2
1
2
M–Cl(avg.)
M–N(amido, avg.)
M–N(imido)
P(1,2)–N(1,avg.)
P(1,2)–N(2,avg.)
P(1,2)–N(3,4)
2.377(2)
2.064(3)
2.398(3)
1.785(3)
1.736(3)
1.682(3)
2.368(5)
2.067(9)
2.394(9)
1.787(10)
1.743(10)
1.648(9)
Cl(1)–M–Cl(2)
Cl(1)–M–N(1)
Cl(2)–M–N(1)
N(3)–M–N(4)
104.51(8)
100.82(9)
154.66(10)
124.62(13)
103.7(2)
100.8(2)
155.5(3)
124.8(4)
((2.394(9) Å) and weak N–Hf donor bond makes it more
appropriate to describe the coordination number of the metal
as 4 ϩ 1. The hafnium–chloride and hafnium–amide bonds
have average lengths of 2.368(5) and 2.067(9) Å, respectively
and are thus similar to the corresponding bonds in a 1,2-ben-
zenediamidozirconium dichloride(THF) dimer, which feature
Zr–N and terminal Zr–Cl bonds of 2.049(5) and 2.403(2) Å
length, respectively.11 Because of the planarity of the amido
groups in 1 and 2, it may be assumed that there is at least some
π-bonding between ligand and metal, making these ligands
possible 8 electron donors and raising the electron-count at the
metal to 14 electrons. While the donor bond from the basal
nitrogen atom (N1) creates a Cs-symmetric ground-state, the
equivalence of the ring-tert-butyl substituents in the NMR
spectra supports a time-averaged C2v symmetry in solution.
Fig. 2 Thermal-ellipsoid (35%) plot and partial numbering scheme of
2. Hydrogen atoms have been omitted for clarity.
The regio- and stereoselectivities of homogeneous catalysts
depend largely on ligand effects. Cs- and C2-symmetric metallo-
cenes of identical metals and cocatalalysts, for example,
produce syndiotactic and isotactic polypropylene, respectively.
In order to build symmetry and steric effects into cyclo-
diphosphazane ligands, we began using 2,4-diarylamino-substi-
tuted heterocycles,12 because aromatic amines with a variety
of substituents are commercially available. Although a 1,3-
diphenyl-2,4-dianilino-substituted
cyclodiphosph()azane,
namely, cis-{Ph(H)NP(µ-NPh)2PN(H)Ph} is available in a one-
step synthesis,13 its low solubility makes it an unsuitable ligand.
We had previously described the synthesis of cis-{Ph(H)-
NP(µ-NBut)2PN(H)Ph} (4a) from cis-{ClP(µ-NBut)2PCl}14 (3)
and lithium anilide.12 Here we report the syntheses of the m-
and p-tolylamino analogues, which are outlined in Scheme 2, as
well as the solid-state structure of 4a. This compound, whose
data collection and bond parameters are listed in Tables 1 and
2, crystallizes in the form of colorless rods in the monoclinic
crystal system. The isolated molecules are stacked along the
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
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Scheme 2
Table 3 Selected bond lengths (Å) and angles (Њ) for 4a and 5a
4aa
P(1)–N(1)
P(1)–N(2)
P(1)–N(2A)
1.689(2)
1.730(2)
1.723(2)
N(1)–P(1)–N(2)
N(1)–P(1)–N(2A)
N(2)–P(1)–N(2A)
P(1)–N(2)–P(1A)
104.84(11)
104.83 (11)
80.96(11)
96.86(11)
5a
P–NBut(avg.)
P–NPh(avg.)
Li–NPh(avg.)
Li–NBut(avg.)
Li–O(avg.)
1.763(3)
1.677(3)
2.076(6)
2.094(6)
1.870(6)
NBut–P–NBut(avg.)
NPh–P–NBut(avg.)
Li–NPh–Li(avg.)
NPh–Li–NPh(avg.)
P–NBut–P(avg.)
83.04(13)
98.07(12)
75.1(2)
100.4(3)
96.93(13)
Fig. 3 Thermal-ellipsoid (35%) plot and partial numbering scheme of
4a. Hydrogen atoms have been omitted for clarity.
twofold axes of the space group C2/c, giving them, analogous
to cis-{But(H)NP(µ-NBut)2PN(H)But},8 crystallographic two-
fold-rotation symmetry.
a Symmetry transformations used to generate equivalent atoms for 4a:
Ϫx ϩ 2, y, Ϫz ϩ 1/2.
The thermal-ellipsoid plot of 4a (Fig. 3) emphasizes the
greater span, but comparatively lesser steric bulk of the phenyl
groups, which are in an exo-orientation with respect to the
heterocycle. This highly-puckered central ring has equidistant
P–N bonds (avg. 1.731(2) Å) and bears almost perpendicularly
disposed anilino groups, whose P–N bonds (1.689(2) Å) are
significantly shorter than those of the heterocycle.
Bis(arylamino)cyclodiphosph()azanes, like 4a, 4b and 4c,
are readily converted to their dilithio salts by treatment with
n-butyllithium, as shown in Scheme 2, affording thermally
stable, but air-sensitive, crystalline solids. An X-ray analysis
of 5a, an ORTEP drawing of which is shown in Fig. 4, revealed
the common heterocubic structure that had also been observed
for the tert-butyl analogue.8 Crystal data and selected bond
parameters of 5a are collected in Tables 1 and 3.
The central portion of the molecule is a rhombically-
distorted cube of P, N and Li atoms, which enclose angles
ranging from 75 to 100Њ. While the bond lengths and angles are
unremarkable and similar to those in the tert-butyl analogue,8
the Li–O bonds of 5a are significantly (ca. 0.1 Å) shorter than
those in the tert-butyl analogue, and this may reflect either the
compactness of the phenyl substituents or their lesser electron-
donating ability.
Fig. 4 Thermal-ellipsoid (35%) plot and partial numbering scheme of
5a. The THF molecule coordinated to Li(2) and hydrogen atoms have
been omitted for clarity.
the syntheses of 1 and 2, yielded the off-white, crystalline solids
6 and 7. The NMR spectra of these species showed equally
symmetrical peak patterns as those of 1 and 2, but the negative
Treatment of MCl4, M = Zr, Hf, with {(ButNP)2(PhNLiؒ
THF)2} (Scheme 3), under the same conditions as those used for
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
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Table 4 Selected bond lengths (Å) and angles (Њ) for 6 and 7ؒC6H5CH3
6
7ؒC6H5CH3
M–N(am., avg.)
M–N(im., avg.)
P–N(endoc., avg.)
P–N(exoc., avg.)
2.157(2)
2.393(2)
1.750(2)
1.701(2)
2.125(4)
2.396(4)
1.758(4)
1.700(4)
N–M–N(am., avg.)
N(am.)–M–N(im., avg.)
108.04(8)
134.37(9)
107.86(14)
140.11(12)
chloride-tests were consistent only with diligand complexes of
the formula [{(ButNP)2(PhN)2}2M], M = Zr (6), Hf (7).
Crystals, suitable for X-ray diffraction studies, were obtained
for both compounds, although those of the hafnium analogue
were isolated only as a toluene solvate, namely [{(ButNP)2-
(PhN)2}2HfؒC6H5CH3]. Crystal and refinement parameters for
6 and 7ؒC6H5CH3 are listed in Table 1 and selected bond lengths
and angles are given in Table 4. The ORTEP drawing of 6
(Fig. 5) emphasizes the crystallographic twofold-rotation sym-
metry of the compound, while that of 7ؒC6H5CH3 (Fig. 6)
depicts the structural relationship of these diligand complexes
to their monoligand counterparts 1 and 2.
Fig. 5 Thermal-ellipsoid (35%) plot and partial numbering scheme of
6, viewed along the crystallographic twofold-rotation axis. Hydrogen
atoms have been omitted for clarity.
Fig. 6 Thermal-ellipsoid (35%) plot and partial numbering scheme of
7ؒC6H5CH3. Hydrogen atoms and toluene moiety have been omitted for
clarity.
Scheme 3
bonds (avg. 2.157(2) Å) are ca. 0.1 Å longer than those in 1 and
2, but they are somewhat shorter than the Zr–N bonds
(2.197(6) Å) in a related pseudo-octahedral bis(aminotropon-
iminato)zirconium dichloride complex.15 Two long (2.393(2) Å)
N–Zr donor bonds complete the coordination sphere of 6.
The appearance of all chemically-equivalent tert-butyl
Complexes 6 and 7 are the first bis(amido)cyclodiphosph()-
azane derivatives in which the central metal atom is sandwiched
between two η3-coordinated bis(amido)cyclodiphosph()-
azanes. The diligand coordination is a strong indication that
the anilido-substituted ligand is sterically less encumbered than
the tert-butyl-substituted analogue, because for the latter ligand
disubstitution has not yet been observed. As was the case for
the monoligand complexes 1 and 2, the coordination environ-
ments about the Group 4 metals cannot be described in terms
of conventional geometries, being neither octahedral nor tri-
gonal prismatic. The four metal–amido bonds are almost tetra-
hedrally-disposed about the metal atom, with N–M–N angles
ranging from 92.44(14) to 140.25(14)Њ. Their zirconium–amide
1
groups as one signal in the low-temperature H and 13C NMR
spectra of 6 and 7 shows that the diligand complexes exhibit
similar fluxionalities as 1 and 2 and with similarly low activ-
ation energies. The disubstitution in 6 and 7 can be rationalized
by the low solubility of MCl4, even in hot toluene, resulting in
the ligation of the much more soluble {(ButNP)2(PhN)2MCl2}
by the second equivalent of ligand, in preference to MCl4. All
attempts at obtaining monoligand complexes in solvents in
which the MCl4 starting materials are more soluble failed, just
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
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Table 5 Selected bond lengths (Å) and angles (Њ) for 8a and 9
8a
9
M–Cl
M–O
M–N(amido, avg.)
M–N(imido)
P–N(endocyc., avg.)
P–N(exocyc., avg.)
2.2460(6)
2.2918(7)
2.1028(14)
1.9429(7)
2.1588(7)
1.7952(8)
1.7088(7)
1.929(2)
2.267(2)
1.744(2)
1.727(2)
Cl(1)–M–O(or Cl2)
Cl(1)–M–N(1)
O(or Cl2)–M–N(1)
N(3)–M–N(4)
100.63(3)
158.76(5)
100.59(5)
114.27(8)
92.38(4)
106.35(5)
161.19(6)
109.49(7)
as it had in the case of 1 and 2. Because their metal atoms are
completely sterically shielded, 6 and 7 are obviously unsuitable
candidates for catalytic applications.
The steric crowding in 6 and 7 caused us to consider the much
smaller titanium (rcov = 1.34 Å) as a candidate for monoligand
derivatives of the more compact aryl-substituted ligands 4a, 4b
and 4c. Treatment of titanium tetrachloride with the corre-
sponding dilithiobis(amido)cyclodiphosphazanes (5a–5c), how-
ever, was accompanied by considerable reduction of the
titanium ion and led to a mixture of products. The target com-
pounds were cleanly synthesized by treating TiCl4ؒ(THF)2 with
4a, 4b or 4c in the presence of triethylamine (Scheme 4); these
reactions afforded diamagnetic orange–red to purple crystalline
solids in good yields. Diligation of titanium was not only
avoided, but it was, in fact, impossible to substitute titanium
with two ligands even when 4a, 4b or 4c were present in large
excess. The solution NMR data of 8a, 8b and 8c are similar to
those of the zirconium and hafnium complexes exhibiting
equivalent aryl and tert-butyl groups and are thus consistent
with symmetrical solution-structures.
Fig. 7 Thermal-ellipsoid (35%) plot and partial numbering scheme of
8a. Hydrogen atoms have been omitted for clarity.
but 8a has a noticeably wider coordination gap, and this may
have implications for metal-centered reactions of these com-
plexes. The titanium–amide (1.929(2) Å) and titanium–chloride
(2.2460(6) Å) bonds are identical to those in the tert-butyl
analogue16 and in related diamido-titanium dichlorides, but the
Ti–amide bonds are slightly longer. For comparison, the Ti–N
and Ti–Cl bonds in [{1,2-(NSiPri3)benzene}TiCl2] are 1.880(4)
and 2.234(2) Å long,17 respectively, while the corresponding
bonds in [{1,3-(N-2,6-PriPh)propyl}TiCl2] are 1.847(5) and
2.248(2) Å long.18 The N–Ti donor bond (2.267(2) Å) of 8a is
of comparable length to those in the zirconium and hafnium
species, when the smaller radius of titanium (1.34 vs. 1.45 Å) is
taken into account.
The title complexes thus share a number of structural simi-
larities with metal derivatives of the diamide {1,2-(NSiPri3)-
benzene}2Ϫ 17
, which afforded diligand complexes for the larger
zirconium, namely, [{1,2-(NSiPri3)benzene}2Zr] (A, shown in
Chart 1), but monoligand species for titanium, namely, [{1,2-
(NSiPri3)benzene}TiCl2] (B). Moreover these 1,2-bis(amido)-
benzene complexes also feature weak, secondary interactions
with the aromatic linker.
Although the bis(amido)cyclodiphosphazane ligands of the
title compounds display η3-coordination in the solid state, the
NMR data on the diamagnetic derivatives are consistent only
with molecules of higher symmetries. In solution, therefore, the
metal atoms cannot be significantly associated with the basal
imido atom even at temperatures as low as Ϫ80 ЊC. It appears
that, as the result of the basket-shaped structure of the bis-
(amido)cyclodiphosphazanes, the metal atoms are forced to be
close to the ring-nitrogen atoms, without significant bond
formation.
This behavior is in contrast to that of the related bis-
(amido)amine zirconium complexes of the type [N2NX]ZrMe2
(C) reported by Schrock et al., which exhibit bis(amido)amino
coordination.19 In these latter compounds the Zr–N(amido)
(2.095(6) Å) and Zr–N(amino) (2.380(6) Å) bonds are almost
identical in length to those in 1 and 2, but with the notable
exception that the donor bond formed by the sp3-hybridized
amine atom is static.
To date no bis(amido)cyclodiphosph()azane compound for
a transition metal from Groups 5 through 9 has been reported.
It was therefore of interest to see if a bis(anilido)cyclodiphos-
phazane complex of vanadium chloride would be accessible.
Treatment of VCl3ؒ(THF)3 with 5a in toluene (Scheme 5)
Scheme 4
Crystal and refinement parameters for 8a are listed in Table 1
and selected bond parameters of 8a are given in Table 5. The
ORTEP view of 8a in Fig. 7 emphasizes the high symmetry of
this seco-heterocubic complex and the lesser steric crowding
about the titanium atom. As expected, most of the bond
parameters are identical to those of the tert-butyl analogue,16
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
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Scheme 5
Chart 1
produced an orange–brown solution from which dark-red
crystals of 9 deposited on cooling. In solution this compound
exhibited an effective magnetic moment of 2.59 Bohr
magnetons, consistent with a vanadium() ion, having two
unpaired electrons.
Lack of NMR-spectroscopic information necessitated an
X-ray structural analysis, the data-collection parameters of
which are listed in Table 1. Selected bond parameters of this
compound are compared with those of the related 8a in Table 5.
The thermal-ellipsoid plot of 9, which is shown in Fig. 8,
emphasizes the seco-heterocubic nature of this complex and its
structural relationship to 1, 2 and 8a. Thus, the vanadium atom
has pseudo trigonal-bipyramidal geometry, being η3-coordin-
ated by the chelating diamide, one chloride ligand and one
molecule of tetrahydrofuran. The metal–amide and metal–
chloride bond lengths of 9 are similar to those of 8a, despite the
smaller covalent radius (1.22 Å) of vanadium. Solely the N–V
donor bond of 9 (2.1588(7) Å) is significantly shorter than that
of 8a (2.267(2) Å). This dative interaction has lengthened the
P–N bonds of the ring nitrogen (N1) atom from 1.735(2) Å in
the pristine ligand 4a to 1.7952(8) Å in the vanadium com-
plex. The V–Cl (2.2918(7) Å), V–N(2, 3) (avg. 1.9429(7) Å)
and V–O (2.1028(14) Å) bonds may be compared to those of
azaatranevanadium() and azaatranevanadium() complexes.
Thus, for example, [{N(CH2CH2NSiMe3)3}VCl] (D, shown in
Chart 2) features vanadium–amide, vanadium–amino and
vanadium–chloride bonds of 1.880(6), 2.238(6) and 2.278(2) Å,
respectively.20 In the corresponding vanadium() species
[{N(CH2CH2NSiMe3)3}V] (E) the amido–vanadium bonds
are almost identical (avg. 1.930(6) Å) to those in 9, but the
lone donor bond is notably shorter (2.08 (6) Å), a feature
which the authors ascribed to the absence of a second axial
substituent.21
Fig. 8 Thermal-ellipsoid (35%) plot and partial numbering scheme of
9. Hydrogen atoms have been omitted for clarity.
When compounds 1 and 2 were tested in polymerization
studies, as outlined in the experimental section, no polymer was
produced. Unexpectedly, however, 8a did produce polyethylene,
although its activity was approximately one order of magnitude
lower than that of the precatalyst Cp2ZrCl2 under identical
conditions. The phosphine odor emanating from the pressure
vessel indicated that these reactions are accompanied by
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Microlit Laboratories, Inc., Madison, NJ, performed the
elemental analyses.
Syntheses
[{(ButNP)2(ButN)2}ZrCl2] (1). Samples of cis-{(But-
NP)2(ButNLiؒTHF)2}, (1.23 g, 2.43 mmol) and zirconium
tetrachloride (0.594 g, 2.56 mmol) were combined in toluene
(30 mL). The ensuing suspension was stirred at 80 ЊC for 1 d,
cooled to 0 ЊC for 3 h, and then filtered through a medium-
porosity frit. The light-yellow solution was concentrated to
10 mL in vacuo and then stored at Ϫ12 ЊC for 3 d. This pro-
duced light-yellow, columnar crystals (0.948 g, 1.86 mmol).
Yield: 72.7%. Mp 215 ЊC. Found: C, 37.55; H, 6.89; N,
10.87. C16H36Cl2N4P2Zr requires C, 37.79; H, 7.13; N, 11.02%.
δH (C6D6) 1.410 (18 H, s, But), 1.267 (18 H, s, But); δC (C6D6)
59.7 (d, J = 16 Hz), 55.26 (t, J = 11 Hz), 33.7 (d, J = 11 Hz),
30.1 (t, J = 6 Hz); δP (C6D6) 101.67; m/z (CI, methane) 509.78
[M ϩ H]ϩ.
Chart 2
considerable ligand degradation, likely brought on by the
Lewis-acidic cocatalyst.22 This makes it difficult to predict
the true nature of the active species in the reaction mixture of
8a, and we therefore hesitate to draw conclusion based on the
structural differences of 1, 2 and 8a.
Both their instability and the ensuing odor compromise the
use of the title complexes in polyolefin catalysis. Their electron
deficiencies and low coordination numbers (6 and 7 are excep-
tions), however, should render these complexes of interest for
applications outside the realm of polymerization reactions. The
instability of the title compounds may be advantageous for uses
as molecular precursors of solid-state materials. For example,
the ease of ring-opening of cyclodiphosph()azanes, perhaps
in combination with labile SiMe3 nitrogen substituents or
ammonolysis, may lead to metal nitrides (MxNy) or metal
nitride–phosphate compounds, i.e., MxPyNz.23 Attempts of
obtaining the former species from 1 were recently reported by
Roesky et al.24
[{(ButNP)2(ButN)2Hf}Cl2] (2). In a manner identical to that
used for the synthesis of 1, cis-{(ButNP)2(ButNLiؒTHF)2},
(1.26 g, 2.50 mmol) and hafnium tetrachloride (0.863 g,
2.69 mmol) were allowed to react in hot (80 ЊC) toluene (35 mL)
for 2 d. The reaction produced cream-colored, bar-shaped
crystals (1.20 g, 1.94 mmol) in a 72.1% yield. Mp 198 ЊC.
Found: C, 32.34; H, 6.05; N, 9.20. C16H36Cl2N4P2Hf requires C,
32.25; H, 6.09; N, 9.40%. δH (C6D6) 1.398 (18 H, s, But), 1.270
(18 H, s, But); δC (C6D6) 58.4 (d, J = 16 Hz), 55.0 (t, J = 11 Hz),
33.8 (d, J = 9.0 Hz), 29.8 (t, J = 6.0 Hz); δP (C6D6) 99.85.
m/z (CI, methane) 597.1 [M ϩ H]ϩ.
Conclusion
Bis(tert-butylamido)cyclodiphosph()azanes
cis-{ClP(ꢀ-NBut)2PCl} (3). This is a modified version of a
previously-published procedure.14 A 2000 mL three-necked
flask, equipped with addition funnel, magnetic stirbar and two
inlets was charged with PCl3 (27.5 g, 200 mmol), toluene
(50 mL) and triethylamine (30.4 g, 300 mmol). To this cooled
(Ϫ78 ЊC) solution was added via dropping funnel tert-butyl-
amine (21.9 g, 300 mmol) dissolved in toluene (150 mL). The
mixture was allowed to warm to RT, refluxed (3.5 h), stirred at
RT (12 h) and then filtered. Toluene and excess amines were
removed by ambient-pressure and vacuum distillations until a
light-yellow oil remained. This solidified within 24 h to an
off-white crystalline mass. Yield: 25.8 g (94%). Mp 42–46 ЊC.
δH (C6D6) 1.17 (18 H, s, But); δC (C6D6) 54.3 (s), 30.2 (s);
δP (C6D6) 205.8 (s).
react
with
titanium, zirconium and hafnium tetrachlorides to form
η3-coordinated monoligand dichloro complexes, having tri-
gonal-bipyramidally coordinated metal centers. The less bulky
bis(arylamido)cyclodiphosph()azanes form similar mono-
ligand complexes only with the 3d transition metals titanium
and vanadium, while the larger zirconium and hafnium
atoms form homoleptic complexes in which the Group 4 metal
is coordinated by two ligand moieties. Only the bis(anilido)-
cyclodiphosphazanetitanium dichloride compound polymer-
ized ethylene in the presence of MAO, while the zirconium and
hafnium analogues with bis(tert-butyl)cyclodiphosphazane
ligands were inactive.
cis-{m-Tol(H)NP(ꢀ-NBut)2PN(H)m-Tol} (4b). In a cooled
(0 ЊC) 250 mL two-neck flask, m-toluidine (1.34 g, 12.6 mmol),
dissolved in THF (15 mL), was treated with n-butyllithium
(5.03 mL, 12.6 mmol). The solution was allowed to warm to
RT and then treated dropwise with a solution of 3 (1.73 g,
6.30 mmol), dissolved in toluene (12 mL). The ensuing yellow–
orange reaction mixture was stirred at RT for 12 h. All volatile
components were then removed in vacuo, and the solid residue
was extracted with hexanes (20 mL). The extract was filtered
through a medium-porosity frit, and the filtrate was concen-
trated until crystals formed. Upon refrigeration (Ϫ21 ЊC) color-
less, rectangular crystals (1.96 g, 75.0%) separated from the
solution. Mp 106–109 ЊC. Found: C, 63.66; H, 8.55; N, 13.69.
C22H34N4P2 requires C, 63.45; H, 8.23; N, 13.45%. δH (C6D6)
Experimental
All operations were performed under an atmosphere of argon
or pre-purified nitrogen on conventional Schlenk lines or in a
glove box. The hydrocarbon or ethereal solvents were pre-dried
over molecular sieves or CaH2 and distilled under a nitrogen
atmosphere from sodium or potassium benzophenone ketyl
immediately before use. The tetrachlorides of zirconium and
hafnium were purchased from Aldrich and Aesar, respec-
tively, and were used as received. Methylalumoxane (MAO)
was purchased from Aldrich as a 10% wt. toluene solu-
tion. Cis-{But(H)NP(µ-NBut)2PN(H)But},8 cis-{Ph(H)NP-
(µ-NBut)2PN(H)Ph},12 cis-{(ButNP)2(ButNLiؒTHF)2},8 and
cis-{(ButNP)2(PhNLiؒTHF)2}12 were prepared by published
procedures.
7.09 (2 H, t, JHH = 7.6 Hz), 6.97 (2 H, s), 6.93 (2 H, d, JHH
=
8.2 Hz), 6.68 (2 H, d, JHH = 7.3 Hz), 4.77 (2 H, s, NH), 2.15
(6 H, s, Me), 1.31 (18 H, s, NBut); δC (C6D6) 143.5 (s), 139.0 (s),
129.3 (s), 122.1 (s), 119.4 (s), 119.4 (br s), 51.7 (t, JPC = 13.6 Hz),
31.1 (t, JPC = 6.3 Hz), 21.6 (s); δP (C6D6) 99.6 (s).
Mass spectra were recorded on a Finnigan MAT 95 in the
chemical ionization mode, using methane as the reacting gas.
NMR spectra were recorded on Varian VXR-300 and Bruker
1
Avance-500 spectrometers. H, 13C and 31P NMR spectra are
referenced relative to C6D5H (7.15 ppm) C6H6 (128.0 ppm) and
P(OEt)3 (ϩ 137.0), respectively. Melting points were recorded
on a Mel-Temp melting point apparatus; they are uncorrected.
E & R Microanalytical Services, Parsippany, NJ, and Robertson
cis-{p-Tol(H)NP(ꢀ-NBut)2PN(H)p-Tol} (4c). In a 200 mL
two-necked flask, p-toluidine (0.771 g, 7.20 mmol) and tri-
ethylamine (1.00 mL, 7.20 mmol) were dissolved in 10 mL of
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
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toluene. When this mixture was treated with a toluene solution
(10 mL) of 3 (0.990 g, 3.60 mmol) a white precipitate formed.
The reaction mixture was kept at 35 ЊC for 12 h, filtered through
a medium-porosity frit and concentrated until crystals formed.
The flask was stored in a freezer for 1 d to afford 1.10 g (73.0%)
of colorless needles. Mp 162–164 ЊC. Found: C, 63.27; H, 8.52;
N, 13.08. C22H34N4P2 requires C, 63.45; H, 8.23; N, 13.45%.
[{(ButNP)2(m-TolN)2}TiCl2] (8b). The compound was pre-
pared by combining 0.370 mL (2.67 mmol) of triethylamine,
1.30 mL (1.30 mmol) of a 1.0 M solution of TiCl4 and 0.557 g
(1.34 mmol) of 4b in a manner identical to that used for the
synthesis of 8a. Overall yield: 0.501g (70.0%). Mp 139–141 ЊC.
Found: C, 49.34; H, 6.22; N, 10.51. C22H32Cl2N4P2Ti requires C,
49.55; H, 6.05; N, 10.51%. δH (C6D6) 7.40 (s, 2 H); 7.29 (d, 2 H,
δH (C6D6) 7.03 (4 H, d, JHH = 8.4 Hz), 6.97 (4 H, d, JHH
=
JHH = 7.9 Hz), 7.07 (t, 2 H, JHH = 7.7 Hz), 6.72 (d, 2 H, JHH =
8.4 Hz), 4.69 (2 H, s, NH), 2.12 (6 H, s, Me), 1.31 (18 H, s,
NBut); δC (C6D6) 141.3 (s), 130.3 (s), 129.7 (s), 119.7 (br s), 52.0
(t, JPC = 13.6 Hz), 31.5 (t, JPC = 6.4 Hz), 21.1 (s); δP (C6D6) 100.4
(s).
7.3 Hz), 2.09 (s, 6 H), 1.16 (s, 18 H, NtBu); δC (C6D6) 151.0 (m),
138.9 (s), 128.9 (s), 126.1 (s), 122.5 (m), 118.1 (m), 54.7 (t,
JPC = 8.8 Hz), 28.1 (t, JPC = 6.9 Hz); δP 127.6 (s).
[{(ButNP)2(p-TolN)2}TiCl2] (8c). In a manner identical to that
used for the synthesis of 8a, 0.400 mL (2.90 mmol) of triethyl-
amine, 1.50 mL of a titanium tetrachloride stock solution and
0.604 g (1.45 mmol) of 4c were allowed to react. Dark-red,
rod-shaped crystals were recovered for an overall yield of
0.617 g (79.8%). Mp 170–172 ЊC. Found: C, 49.64; H,
6.31; N, 10.24. C22H32Cl2N4P2Ti requires C, 49.55; H, 6.05;
N, 10.51%. δH (C6D6) 7.39 (d, 4 H, JHH = 8.3 Hz); 6.92 (d,
4 H, JHH = 8.2 Hz), 2.04 (s, 6 H, Me), 1.15 (s, 18 H, NtBu);
δC (C6D6) 151.5 (s); 134.8 (s), 129.6 (s), 121.4 (d, JPC = 10.5 Hz),
54.7 (t, JPC = 8.6 Hz), 28.1 (t, JPC = 6.8 Hz), 20.7 (s); δP (C6D6)
128.2 (s).
{(ButNP)2(m-TolNLiؒTHF)2} (5b). A 100 mL two-necked
flask, equipped with inlet, stirbar and funnel was charged with
4b (0.534 g, 1.28 mmol) and THF (15 mL). The flask was
immersed in an ice bath and the solution was treated dropwise
with n-butyllithium (1.10 mL, 2.75 mmol). The solution was
refluxed (12 h) and then concentrated until crystals formed.
After the flask had been stored in a freezer (Ϫ12 ЊC), colorless,
block-shaped crystals (0.606 g, 82.8%) deposited. Mp 159–
162 ЊC. Found: C, 62.77; H, 8.70; N, 9.59. C30H48N4Li2O2P2
requires C, 62.93; H, 8.45; N, 9.79%. δH (C6D6) 7.25 (4 H, t,
JHH = 7.6 Hz), 7.04 (2 H, d, JHH = 8.0 Hz), 6.62 (2 H, d, JHH
=
7.2 Hz), 3.42 (8 H, m, THF), 2.34 (6 H, s, Me), 1.45 (18 H, s),
1.19 (8 H, m, THF); δC (C6D6) 156. 0 (d, JPC = 24.3 Hz), 138.2
(s), 129.2 (s), 119.9 (d, JPC = 24.3 Hz), 117.1 (d, JPC = 19.8 Hz),
[{(ButNP)2(PhN)2}VClؒTHF] (9). At Ϫ78 ЊC a suspension of
VCl3(THF)3 (0.364 g, 0.973 mmol) in toluene was treated with a
suspension of 5a (0.530g, 0.973 mmol) in toluene (10 mL). The
reaction mixture was stirred for 12 h while it slowly warmed to
RT. The ensuing orange–brown solution was filtered, then con-
centrated to about half its volume and stored at RT. Yield:
0.382 g (72.2%) of dark-red, octahedral crystals. Mp 163–166
ЊC. Found: C, 52.70; H, 6.72; N, 10.21. C24H36ClN4OP2V
requires C, 52.90; H, 6.66; N, 10.28%. µeff = 2.59µB.
116.2 (s), 68.3 (s, THF), 52.3 (t, JPC = 15.5 Hz), 30.1 (t, JPC
7.3 Hz), 25.4 (s), 22.1 (s, THF); δP (C6D6) 162.6 (s).
=
[{(ButNP)2(PhN)2}2Zr] (6). In a 100 mL two-necked flask,
equipped with stirbar and inlet, ZrCl4 (0.447 g, 1.92 mmol) and
5a (1.04 g, 1.92 mmol) were dissolved in 25 mL of toluene,
resulting in a bright-yellow suspension. The reaction mixture
was stirred at 75 ЊC for 1 d, then cooled to 0 ЊC and filtered
through a medium-porosity frit. The bright-yellow filtrate was
concentrated in vacuo and kept at Ϫ12 ЊC for 3 d to afford 0.581
g (70.7%) of product. Mp 250 ЊC (dec.). Found: C, 55.60; H,
6.73; N, 12.85. C40H56N8P4Zr requires C, 55.60; H, 6.53; N,
12.97%. δH (C6D6) 7.40 (4 H, d, JHH = 7.8 Hz), 6.99 (4 H, t,
JHH = 7.7 Hz), 6.72 (2 H, t, JHH = 6.8 Hz), 1.22 (18 H, s, But);
Polymerization studies
Compounds 1, 2 and 8a were tested for their activity as poly-
olefin catalysts in triplicate reactions. The tests were done in a
nitrogen-flushed, 250 mL, mechanically-stirred, stainless-steel
Parr pressure vessel, equipped with a 200 mL glass liner. In a
typical experiment, micromolar amounts of catalyst (30–50
µmol), dissolved in toluene (40 mL), were injected. Then 100
molar equivalents of a standard MAO solution were added by
syringe and the vessel was pressurized (1.5 × 106 Pa) with ethyl-
ene. The mechanically-stirred reaction mixture was then heated
(60 ЊC) for 1 h. After completion of the reaction, the vessel was
vented and examined for the presence of polymer. Compounds
1 and 2 produced no polymer, but 8a had an activity of 2.0 ×
103 g PE (mol catalyst)Ϫ1 hϪ1 barϪ1. Under these conditions
Cp2ZrCl2 exhibited an activity of 1.2 × 104 g PE (mol catalyst)Ϫ1
δC (C6D6) 129.4 (d, JPC = 17.6 Hz), 129.0 (s), 123.4 (d, JPC
=
14.5 Hz), 122.1 (s), 54.4 (t, JPC = 11.3 Hz), 29.4 (t, JPC = 7.7 Hz);
δP (C6D6) 143.1 (s).
[{(ButNP)2(PhN)2}2Hf] (7). In a manner identical to that
used for the synthesis of 6, HfCl4 (0.890 g, 2.78 mmol) and 5a
(3.03 g, 5.56 mmol) were combined and heated. The bright-
yellow filtrate was concentrated in vacuo and kept at Ϫ12 ЊC for
12 h to afford 1.71 g (65.0%) of pale-yellow crystals. Mp 238–
240 ЊC. Found: C, 50.30; H, 6.09; N, 11.58. C40H56N8P4Hf
requires C, 50.50; H, 5.93; N, 11.78%. δH (C6D6) 7.41 (4 H, d,
JHH = 7.8 Hz, arom. H), 6.99 (4 H, t, JHH = 7.7 Hz, arom. H),
6.71 (2 H, t, JHH = 6.9 Hz, arom. H), 1.22 (18 H, s, But);
δC (C6D6) 129.4 (d, JPC = 17.8 Hz), 129.0 (s), 123.7 (d, JPC = 15.1
Hz), 122.1 (s), 54.4 (t, JPC = 11.4 Hz), 29.4 (t, JPC = 7.7 Hz); δP
(C6D6) 146.1 (s).
h
Ϫ1 barϪ1
.
X-Ray crystallography
Compounds 1, 2, 4a, 5a, 6, 8a and 9. All crystals were grown
from supersaturated toluene or THF solutions at the indicated
temperatures. Suitable, single crystals were coated with oil,
affixed to a glass capillary, and centered on the diffractometer
in a stream of cold nitrogen. Reflection intensities were col-
lected with a Bruker SMART CCD diffractometer, equipped
with an LT-2 low-temperature apparatus, operating at 213 K.
Data were measured using ω scans of 0.3Њ per frame for 30 s
until a complete hemisphere had been collected. The first 50
frames were recollected at the end of the data collection to
monitor for decay. Cell parameters were retrieved using
SMART25 software and refined with SAINT26 on all observed
reflections. Data were reduced with SAINT, which corrects for
Lorentz and polarization factors and decay. An empirical
absorption correction was applied with SADABS.27 The struc-
tures were solved by direct methods with the SHELXS-9028
[{(ButNP)2(PhN)2}TiCl2] (8a). In a 100 mL two-necked flask,
triethylamine (0.430 mL, 3.08 mmol), 1.5 mL of a titanium
tetrachloride stock solution and 4a of were combined. After the
flask had been stored at Ϫ21 ЊC for 24 h, 0.408 g (52.4%) of
dark-red crystals were recovered. This and subsequent fractions
yielded a total of 0.599 g (77.0%) of product. Mp 198–200 ЊC.
Found: C, 47.75; H, 5.68; N, 10.98. C20H28Cl2N4P2Ti requires C,
47.55; H, 5.59; N, 11.09%. δH (C6D6) 7.45 (4 H, d, JHH = 7.9 Hz),
7.11 (4 H, t, JHH = 7.7 Hz), 6.85 (2 H, t, JHH = 7.6 Hz), 1.11
(18 H, s, NBut). δC (C6D6) 153.4 (m), 129.1 (s), 125.2 (s),
121.3 (m), 54.7 (t, JPC = 8.7 Hz), 28.1 (t, JPC = 6.9 Hz). δP (C6D6)
127.6 (s).
D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
1409

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program and refined by full-matrix least squares methods on F 2
5 D. C. Bradley, M. B. Hursthouse, C. W. Newing and A. J. Welch,
J. Chem. Soc., Chem. Commun., 1972, 567; C. Airoldi, D. C. Bradley,
H. Chudzynska, M. B. Hursthouse, K. M. Abdul Malik and P. R.
Raithby, J. Chem. Soc., Dalton Trans., 1980, 2010; R. A. Andersen,
Inorg. Chem., 1979, 18, 1507; R. A. Andersen, Inorg. Chem., 1979,
18, 1724.
6 G. D. Whitener, J. R. Hagadorn and J. Arnold, J. Chem. Soc.,
Dalton Trans., 1999, 1249; J. R. Hagadorn and J. Arnold,
Organometallics, 1998, 17, 1355; A. A. Naiini, W. M. P. B. Menge
and J. G. Verkade, Inorg. Chem., 1991, 30, 5009; W. M. P. B. Menge
and J. G. Verkade, Inorg. Chem., 1991, 30, 4628; C. Morton,
P. O’Shaughnessy and P. Scott, Chem. Commun., 2000, 2099;
P. J. Stewart, A. J. Blake and P. Mountford, Organometallics, 1998,
17, 3271; S. Danièle, P. H. Hitchcock, M. F. Lappert and P. G. Merle,
J. Chem. Soc., Dalton Trans., 2002, 13.
with SHELXL-97,29 incorporated in SHELXTL Version 5.10.30
Compound 7ؒC6H5CH3. The crystal was sealed inside an
argon-filled glass capillary, and the intensity data were collected
on a Bruker P4 diffractometer. Three reflections were moni-
tored after every 97 reflections, and the appropriate intensity
corrections were applied during data reduction. Reflection data
were reduced with XDISK of the SHELXTL-PC program
suite, Version 4.1,30 and the structure was solved by direct-
methods with SHELXL-NT, Version 5.10,31 and refined as
described above.
CCDC reference numbers 197168–197175.
7 J. D. Scollard and D. H. McConville, J. Am. Chem. Soc., 1996, 118,
10008; J. D. Scollard, D. H. McConville and S. J. Rettig,
Organometallics, 1997, 16, 1810; J. D. Scollard, D. H. McConville,
N. C. Payne and J. J. Vittal, Macromolecules, 1996, 29, 5241.
8 H. J. Chen, R. C. Haltiwanger, T. G. Hill, M. L. Thompson, D. E.
Coons and A. D. Norman, Inorg. Chem., 1985, 24, 4725; I. Schranz,
L. Stahl and R. J. Staples, Inorg. Chem., 1998, 37, 1493; R. R.
Holmes and J. A. Forstner, Inorg. Chem., 1963, 2, 380.
9 L. Grocholl, L. Stahl and R. J. Staples, J. Chem. Soc.,
Chem. Commun., 1997, 1465.
See http://www.rsc.org/suppdata/dt/b2/b211009a/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the Chevron Phillips Chemical Company for
Research Assistantships to D. F. M. and L. G. and Mr. Ingo
Schranz for doing the polymerization tests.
10 Ziegler Catalysts, ed. G. Fink, R. Mülhaupt and H. H. Brintzinger,
Springer, Berlin, 1995; Applied Homogeneous Catalysis with
Organometallic Compounds, ed. B. Cornils and W. A. Herrmann,
Verlag Chemie, Weinheim, Germany, 1996.
11 S. Danièle, P. H. Hitchcock, M. F. Lappert and P. G. Merle, J. Chem.
Soc., Dalton Trans., 2002, 13.
12 I. Schranz, D. F. Moser, L. Stahl and R. J. Staples, Inorg. Chem.,
1999, 38, 5814.
13 Y. G. Trishin, V. N. Christokletov, A. A. Petrov and V. V. Kosovtsev,
J. Org. Chem. USSR (Engl. Trans.), 1975, 11, 1747.
14 O. J. Scherer and P. Klusmann, Angew. Chem., Int. Ed. Engl., 1969,
8, 752.
15 H. V. Rasika Dias, W. Jin and Z. Wang, Inorg. Chem., 1996, 35, 6074.
16 D. F. Moser, C. C. Carrow, L. Stahl and R. J. Staples, J. Chem. Soc.,
Dalton Trans., 2001, 1246.
17 K. Aoyagi, P. K. Gantzel, K. Kalai and T. D. Tilley,
Organometallics, 1996, 15, 923.
18 J. D. Scollard, D. H. McConville, N. C. Payne and J. J. Vittal,
Macromolecules, 1996, 29, 5241.
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31 SHELXTL 5.10 NT Version, Program Library for Structure
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D a l t o n T r a n s . , 2 0 0 3 , 1 4 0 2 – 1 4 1 0
1410