Reversible skeletal transmetalations of inorganic rings: Isolation of aluminatophosphazenes, a zwitterionic phosphazene, and a donor-stabilized alumazine-phosphazene hybrid cation

Article abstract of DOI:10.1021/ic0509938

Synthesis of the cyclic aluminatophosphazene ring N(PCl₂NMe) ₂AlMeCl (5) has been achieved via a skeletal transmetalation reaction between AlMe₃ and the boratophosphazene N(PCl₂NMe) ₂BCl₂ (1). Reaction of 5 with various halogenated Lewis acids such as GaCl₃ yielded the fully chlorinated aluminum heterocycle N(PCl₂NMe)₂AlCl₂ (8) through a methyl-halogen exchange process. In contrast, treatment of 5 with excess AlMe₃ resulted in complete methylation at aluminum to give N(PCl ₂NMe)₂AlMe₂ (6). Compound 5 was reacted with various Ag⁺ salts with weakly coordinating anions, including Ag[OSO₂CF₃], which afforded the triflate-substituted heterocycle N(PCl₂-NMe)₂AlMe(OSO₂CF ₃) (9). The reaction of 5 with Ag[BF₄] surprisingly produced the previously known fluorinated boratophosphazene N(PCl ₂NMe)₂BF₂ (10). The transformation of 1 to 5 and then to 10 represents a rare, formally reversible, skeletal transmetalation process involving boron and aluminum. Treatment of 5 with Ag[PF₆] led to the insertion of phosphorus in place of aluminum to form the novel zwitterionic fluorinated phosphorus(V) heterocycle N(PCl₂NMe) ₂PF₄ (11). The ethyl-substituted aluminatophosphazene N(PCl₂NMe)₂AlMeEt (14) reacted cleanly with a 1:1 mixture of [Ph₃C][B(C₆F₅)₄] and THF to give the novel donor-stabilized alumazine-phosphazene hybrid cation, [7·THF]⁺, as the [B(C₆F₅) ₄]^- salt [N(PCl₂NMe)₂AlMe· THF][B(C₆F₅)₄] (15).

Full text of DOI:10.1021/ic0509938

Inorg. Chem. 2005, 44, 6789−6798
Reversible Skeletal Transmetalations of Inorganic Rings: Isolation of
Aluminatophosphazenes, a Zwitterionic Phosphazene, and a
Donor-Stabilized Alumazine−Phosphazene Hybrid Cation
Eric Rivard, Paul J. Ragogna,‡ Andrew R. McWilliams,† Alan J. Lough, and Ian Manners*
Department of Chemistry, UniVersity of Toronto,
80 St. George St. Toronto, Ontario, M5S 3H6, Canada
Received June 17, 2005
Synthesis of the cyclic aluminatophosphazene ring N(PCl2NMe)2AlMeCl (5) has been achieved via a skeletal
transmetalation reaction between AlMe3 and the boratophosphazene N(PCl2NMe)2BCl2 (1). Reaction of 5 with various
halogenated Lewis acids such as GaCl3 yielded the fully chlorinated aluminum heterocycle N(PCl2NMe)2AlCl2 (8)
through a methyl−halogen exchange process. In contrast, treatment of 5 with excess AlMe3 resulted in complete
methylation at aluminum to give N(PCl2NMe)2AlMe2 (6). Compound 5 was reacted with various Ag+ salts with
weakly coordinating anions, including Ag[OSO2CF3], which afforded the triflate-substituted heterocycle N(PCl2-
NMe)2AlMe(OSO2CF3) (9). The reaction of 5 with Ag[BF4] surprisingly produced the previously known fluorinated
boratophosphazene N(PCl2NMe)2BF2 (10). The transformation of 1 to 5 and then to 10 represents a rare, formally
reversible, skeletal transmetalation process involving boron and aluminum. Treatment of 5 with Ag[PF6] led to the
insertion of phosphorus in place of aluminum to form the novel zwitterionic fluorinated phosphorus(V) heterocycle
N(PCl2NMe)2PF4 (11). The ethyl-substituted aluminatophosphazene N(PCl2NMe)2AlMeEt (14) reacted cleanly with
a 1:1 mixture of [Ph3C][B(C6F5)4] and THF to give the novel donor-stabilized alumazine
−phosphazene hybrid cation,
[7 THF][B(C6F5)4] (15).
‚
THF]+, as the [B(C6F5)4]- salt [N(PCl2NMe)2AlMe
‚
Introduction
variety of stable coordination numbers and oxidation states
accessible.1 As a reflection of the renewed interest in main
group heterocycles, a series of cationic aluminum-based
catalysts are currently being explored as alternatives to their
ubiquitous transition metal counterparts (e.g., in the Ziegler-
Natta polymerization of olefins).2,3 In addition, the ring-
opening polymerization (ROP) of various perhalogenated
Cyclic compounds of main group elements often exhibit
interesting structural motifs, display novel chemical reactiv-
ity, and pose intriguing bonding questions as a result of the
* To whom correspondence should be addressed. E-mail:
imanners@chem.utoronto.ca.
† Current address: Department of Chemistry and Biology, Ryerson
University, 350 Victoria St., Toronto, Ontario, M5B 2K3, Canada.
‡Current address: Department of Chemistry, University of Western
Ontario, London, Ontario, N6A 5B7, Canada.
(2) For selected examples of aluminum-based heterocyclic catalysts, see:
(a) Coles, M. P.; Jordan, R. F. J. Am. Chem. Soc. 1997, 119, 8125.
(b) Ihara, E.; Young, V. G., Jr.; Jordan, R. F. J. Am. Chem. Soc. 1998,
120, 8277. (c) Bruce, M.; Gibson, V. C.; Redshaw, C.; Solan, G. A.;
White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 2523. (d)
Cameron, P. A.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Bruce, M.
D.; White, A. J. P.; Williams, D. J. Chem. Commun. 1999, 1883. (e)
Duchateau, R.; Meetsma, A.; Teuben, J. H. Chem. Commun. 1996,
223. (f) Korolev, A. V.; Ihara, E.; Guzei, I. A.; Young, V. G., Jr.;
Jordan, R. F. J. Am. Chem. Soc. 2001, 123, 8291. (g) Yu, R.-C.; Hung,
C.-H.; Huang, J.-H.; Lee, H.-Y.; Chen, J.-T. Inorg. Chem. 2002, 41,
6450. (h) Cameron, P. A.; Gibson, V. C.; Irvine, D. J. Angew. Chem.,
Int. Ed. 2000, 39, 2141.
(3) For selected examples of transition metal-based heterocyclic catalysts,
see: (a) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem.
Soc. 1995, 117, 6414. (b) Scollard, J. D.; McConville, D. H. J. Am.
Chem. Soc. 1996, 118, 10008. (c) Baumann, R.; Davis, W. M.;
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vandi, P.; Schrock, R. R. J. Am. Chem. Soc. 2001, 123, 10746. (e)
Hagihara, H.; Shiono, T.; Ikeda, T. Macromolecules 1998, 31, 3184.
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Betley, T. A.; Peters, J. C. Angew. Chem., Int. Ed. 2003, 42, 2385.
(h) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283.
(1) (a) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.; Hao,
H.; Cimpoesu, F. Angew. Chem., Int. Ed. 2000, 39, 4272. (b)
Scheschkewitz, D.; Gornitzka, A. H.; Schoeller, W. W.; Bourissou,
D.; Bertrand, G. Science 2002, 295, 1880. (c) Hardman, N. J.; Power,
P. P.; Gorden, J. D.; Macdonald, C. L. B.; Cowley, A. H. Chem.
Commun. 2001, 1866. (d) Ni, Y.; Lough, A. J.; Rheingold, A. L.;
Manners, I. Angew. Chem., Int. Ed. Engl. 1995, 34, 998. (e) Guo,
C.-Y.; Kirchmeier, R. L.; Shreeve, J. M. J. Am. Chem. Soc. 1991,
113, 9000. (f) Barclay, T. M.; Cordes, A. W.; Goddard, J. D.;
Mawhinney, R. C.; Oakley, R. T.; Preuss, K. E.; Reed, R. W. J. Am.
Chem. Soc. 1997, 119, 12136. (g) Brownridge, S.; Du, H.-B.; Fairhurst,
S. A.; Haddon, R. C.; Oberhammer, H.; Parsons, S.; Passmore, J.;
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Dalton Trans. 2000, 3365. (h) Burford, N.; Cameron, T. S.; Conroy,
K. D.; Ellis, B.; Lumsden, M.; Macdonald, C. L. B.; Phillips, A. D.;
Ragogna, P. J.; Schurko, R. W.; Walsh, D.; Wasylishen, R. E. J. Am.
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10.1021/ic0509938 CCC: $30.25
Published on Web 08/19/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 19, 2005 6789

Rivard et al.
Scheme 1. Synthesis of Aluminatophosphazenes 5, 6, and 8a
main group rings provides a number of previously unknown
inorganic polymeric materials and represents one of the major
avenues of research in inorganic polymer science.4,5
Motivated by the successful use of cyclic perhalogenated
heterophosphazenes such as cyclothionylphosphazenes NS-
(O)X(NPCl2)2 (X ) Cl and F) as polymer precursors via
ROP,6 our group has investigated the chemistry of borato-
phosphazenes. During the unsuccessful attempts to polymer-
ize the cyclic boratophosphazene N(PCl2NMe)2BCl2 (1),
some interesting chemical reactivity was observed. Treatment
of 1 with group 13 halide acceptors (ECl3, E ) B, Al, and
Ga) readily afforded the planar hybrid borazine-phos-
phazene cations [2]+.7 Attempts to generate similar cations
using silver(I) salts with fluorinated counteranions [AsF6]-
and [SbF6]- remarkably led to the insertion of arsenic and
antimony in place of the boron atom in 1 to give the novel
group 15 heterophosphazenes 3 and 4.8,9 Examples of this
a (i) 2 equiv of AlMe3, toluene, 5 h, 20 °C. (ii) 4 equiv of AlMe3, toluene,
16 h, 20 °C. (iii) 1 equiv of either ECl3 (E ) B, Al, and Ga), TaCl5, or
SO2Cl2, CH2Cl2, 24 H, 20 °C.
In this context, we report the successful extension of the
skeletal substitution methodology, which corresponds to a
formal transmetalation process. An unusual example of a
zwitterionic, phosphazene six-membered ring system is
reported in conjunction with the first example of an alumi-
natophosphazene cation, which has potential for a significant
impact in the areas of catalysis and inorganic polymer science
(i.e., as ROP precursors).11
Results and Discussion: Synthesis of
Aluminatophosphazenes
To further explore the scope of the skeletal substitution
chemistry of 1, this species was reacted with a single
equivalent of AlMe3 in toluene. The 31P NMR spectrum of
the resulting solution indicated that the complete consump-
tion of 1 (δ ) 28.8 ppm) had occurred to yield two new
products (ca. 1:1 ratio), as evidenced by the appearance of
upfield-shifted resonances located at δ ) 23.6 and 25.3
ppm.12 Attempts to separate the products by fractional
crystallization were unsuccessful. However, when 2 equiv
of AlMe3 were added, complete conversion of 1 to a single
phosphorus-containing product with the 31P NMR resonance
at δ ) 23.6 ppm occurred. The 11B NMR spectrum of the
reaction mixture identified BMe3 as the only boron-contain-
ing product with a chemical shift of δ ) 85.9 ppm13 (11B
NMR shift of 1: δ ) 5.4 ppm); this observation suggested
that halogen-methyl exchange between a B-Cl group in 1
and AlMe3 had transpired. Removal of the volatiles followed
by recrystallization from toluene afforded highly air- and
moisture-sensitive colorless crystals that did not give a 11B
NMR signal, indicating an absence of boron in the isolated
product. The 1H NMR spectrum contained a sharp singlet at
δ ) -0.57 ppm along with a multiplet resonance at δ )
type of transmetalation reaction, where one atom is selec-
tively replaced by another while retaining the original ring
structure, remain rare.10 The efficient nature of the skeletal
substitution reaction coupled with the facile separation of
the resulting byproducts makes this a valuable synthetic tool
for the construction of new inorganic rings. This process also
highlights interesting issues concerning the structure and
bonding of these main group heterocycles.
(4) Manners, I. Angew. Chem., Int. Ed. Engl. 1996, 35, 1602.
(5) (a) Allcock, H. R.; Kugel, R. L. J. Am. Chem. Soc. 1965, 87, 4216.
(b) Allcock, H. R. J. Inorg. Organomet. Polym. 1992, 2, 197. (c)
Manners, I.; Allcock, H. R.; Renner, G.; Nuyken, O. J. Am. Chem.
Soc. 1989, 111, 5478. (d) Dodge, J. A.; Manners, I.; Allcock, H. R.;
Renner, G.; Nuyken, O. J. Am. Chem. Soc. 1990, 112, 1268. (e) Gates,
D. P.; Manners, I. J. Chem. Soc., Dalton Trans. 1997, 2525.
(6) (a) Gates, D. P.; Edwards, M.; Liable-Sands, L. M.; Rheingold, A.
L.; Manners, I. J. Am. Chem. Soc. 1998, 120, 3249. (b) McWilliams,
A. R.; Gates, D. P.; Edwards, M.; Liable-Sands, L. M.; Guzei, I.;
Rheingold, A. L.; Manners, I. J. Am. Chem. Soc. 2000, 122, 8848. (c)
Liang, M.; Manners, I. J. Am. Chem. Soc. 1991, 113, 4044.
(7) Gates, D. P.; Ziembinski, R.; Rheingold, A. L.; Haggerty, B. S.;
Manners, I. Angew. Chem., Int. Ed. Engl. 1994, 33, 2277.
(8) Gates, D. P.; Liable-Sands, L. M.; Yap, G. P. A.; Rheingold, A. L.;
Manners, I. J. Am. Chem. Soc. 1997, 119, 1125.
(9) Gates, D. P.; McWilliams, A. R.; Ziembinski, R.; Liable-Sands, L.
M.; Guzei, I. A.; Yap, G. P. A.; Rheingold, A. L.; Manners, I. Chem.
Eur. J. 1998, 4, 1489.
(11) For a brief communication on some of this work, see; (a) McWilliams,
A. R.; Rivard, E.; Lough, A. J.; Manners, I. Chem. Commun. 2002,
1102. For an early report on a four-membered N-P zwitterionic ring
system, see: (b) Niecke, E.; Kro¨her, R.; Pohl, S. Angew. Chem., Int.
Ed. 1977, 16, 864.
(10) (a) Fagan, P. J.; Nugent, W. A. J. Am. Chem. Soc. 1988, 110, 2310.
(b) Jolliffe, J. M.; Kelly, P. F.; Woollins, J. D. J. Chem. Soc., Dalton
Trans. 1989, 2179. (c) Kuhn, N.; Kuhn, A.; Lewandowski, J.; Speis,
M. Chem. Ber. 1991, 124, 2197. (d) Breen, T. L.; Stephan, D. W.
Organometallics 1997, 16, 365. (e) Ashe, A. J., III; Fang, X.; Kampf,
J. F. Organometallics 2001, 20, 2109.
(12) The reaction of hexachlorocyclotriphosphazene [Cl2PdN]3 with excess
AlMe3 produces a complex mixture of partially methylated phos-
phazene rings: Harris, P. J.; Jackson, L. A. Organometallics 1983, 2,
1477.
(13) The reported 11B NMR shift for BMe3 in toluene is δ ) 86.6:
Bochmann, M.; Sarsfield, M. J. Organometallics 1998, 17, 5908.
6790 Inorganic Chemistry, Vol. 44, No. 19, 2005

Aluminatophosphazenes: Transmetalation of Inorganic Rings
ppm) along with a broad resonance due to the Al-Me groups
at δ ) -10.6 ppm. The detection of an Al-Me 13C{1H}
NMR resonance for 6 suggested that a more symmetric
electronic environment was present at the aluminum center
when compared to 5, where no 13C{1H} NMR signal was
observed. This is in comparison to the similar 13C{1H} NMR
shift (δ ) -10.6 ppm) that has been reported for the Al-
Me groups within the â-diketiminate complex HC(CMe-
NAr)2AlMe2 (Ar ) 2,6-iPr2C6H3).18
Chemistry of Aluminatophosphazene 5: Discovery of
Novel Skeletal Transmetalations. In previous studies, a
novel class of borazine-phosphazene hybrid cations [2]+
were synthesized from the boratophosphazene 1 using Group
13 Lewis acids (ECl3, E ) B, Al, and Ga) as halide acceptors.
Encouraged by these results and the presence of an apparently
slightly elongated Al-Cl bond within 5 (see below), we
explored the reactions of this aluminum analogue with
various halide acceptors7 with the goal of generating an
alumazine-phosphazene heterocyclic cation [N(PCl2NMe)2-
AlMe]+, [7]+. When 5 was treated with 1 equiv of GaCl3 in
Figure 1. Molecular structure of 5 with thermal ellipsoids at the 50%
probability level. Hydrogen atoms have been removed for clarity. Selected
bond lengths [Å] and angles [deg]: Al(1)-Cl(5), 2.161(1); Al(1)-N(1),
1.889(2); Al(1)-N(3), 1.889(2); P(1)-N(1), 1.575(2); P(1)-N(2), 1.563-
(2); P(2)-N(2), 1.562(2); P(2)-N(3), 1.574(2); N(2)-Al(1)-N(3), 103.3-
(1); Al(1)-N(1)-P(1), 121.1(1); N(1)-P(2)-N(2), 115.1(1); P(1)-N(2)-
P(2), 130.2(2); N(2)-P(2)-N(3), 114.9(1); P(2)-N(2)-Al(1), 121.6(1);
C(1)-Al(1)-Cl(5), 114.0(1).
3.23 ppm (1:2 integration ratio). On the basis of the observed
integration ratio of these signals and the fact that the
boratophosphazene 1 has a similar 1H NMR resonance at δ
) 3.10 ppm (multiplet) due to the N-Me groups within the
heterocycle, we assigned the product as the novel methyl-
substituted aluminatophosphazene heterocycle N(PCl2N-
Me)2AlMeCl (5) (Scheme 1). 13C{1H} NMR spectroscopy
supported the formation of 5, as the N-Me group was
detected as a singlet at δ ) 31.1 ppm (c.f. the N-Me 13C
NMR resonance for 1 is at δ ) 33.3 ppm). However, no
signal could be detected for the Al-Me moiety within 5
because of quadrupolar broadening of this resonance by the
neighboring aluminum center (27Al; I ) 5/2).14 To unequivo-
cally identify 5 as the reaction product, we performed a
single-crystal X-ray diffraction study (Figure 1) on the
isolated crystalline material.15
In an attempt to synthesize a tetramethylated aluminato-
phosphazene, compound 5 was reacted with additional
equivalents of AlMe3 in toluene. When 1 equiv of AlMe3
was added to 5, two signals (1:1 ratio) were observed by
31P NMR spectroscopy. One signal corresponded to unreacted
5 (δ ) 23.6 ppm), whereas a new upfield-shifted resonance
was also noted at δ ) 21.5 ppm. Addition of excess AlMe3
to the reaction mixture converted all remaining 5 to the
species with the 31P NMR resonance at δ ) 21.5 ppm. A
tacky, white solid was subsequently isolated and identified
as the methylated heterocycle, N(PCl2NMe)2AlMe2 (6),17 on
the basis of NMR spectroscopy and mass spectrometry
(Scheme 1). Analysis of 6 by 1H NMR spectroscopy revealed
a singlet resonance at δ ) -0.82 ppm which was assigned
to the aluminum-bound methyl groups in addition to the
expected multiplet for the N-Me group at δ ) 2.76 ppm.
Each of these signals integrated to six protons, confirming
the presence of two Al-Me groups in 6. The 13C{1H} NMR
spectrum showed the anticipated N-Me resonance (δ ) 31.0
CH2Cl2, we observed quantitative formation of a new product
after 16 h, as indicated by a new resonance at δ ) 25.3 ppm
in the 31P NMR spectrum of a sample of the reaction mixture;
interestingly, a species with the same chemical shift was also
observed as a component of the reaction mixture when the
boratophosphazene 1 was reacted with 1 equiv of AlMe3. A
white solid was subsequently isolated, and large, colorless
plates were then obtained from a 1:1 CH2Cl2/hexanes mixture
at -30 °C. Single-crystal X-ray diffraction identified the
product as the chlorinated heterocycle N(PCl2NMe)2AlCl2
(8), unfortunately the low quality of the data (R1 > 10%)
precludes any detailed discussion of the bonding within this
compound. 1H NMR spectroscopy provided additional
evidence for the formation of 8, as a multiplet was detected
at δ ) 2.92 ppm for the N-bonded methyl groups, while no
Al-Me resonance was observed. Moreover, the molecular
ion for 8 (m/z ) 373) was detected by mass spectrometry
and the product gave satisfactory elemental analyses. When
5 was reacted with the related chlorinated Lewis acids AlCl3,
BCl3, TaCl5, and SO2Cl2, similar methyl-halogen exchange
reactions occurred to give 8. It is possible that formation of
the perhalogenated aluminum ring 8 proceeds via a transient
aluminatophosphazene cation such as [7]+.19
As the chlorination of 5 occurred in the presence of Lewis
acidic chlorides, we explored the reactivity of this alumi-
natophosphazene toward various silver(I) salts containing
(14) Cocco, L.; Eyman, D. P. J. Organomet. Chem. 1979, 179, 1.
(15) For related Al-N-P heterocycles, see: (a) Hasselbring, R.; Roesky,
H. W.; Heine, A.; Stalke, D.; Sheldrick, G. M. Z. Naturforsch. 1994,
49B, 43. (b) Burford, N.; LeBlanc, D. J. Inorg. Chem. 1999, 38, 2248.
(c) Lawson, G. T.; Jacob, C.; Steiner, A. Eur. J. Inorg. Chem. 1999,
1881.
(16) Burrow, R. A.; Farrar, D. H.; Honeyman, C. H. Acta Crystallogr. 1994,
C50, 681.
(17) Compound 6 can also be synthesized by the reaction of boratophos-
phazene 1 with excess AlMe3 (4-10 equiv).
(18) Qian, B.; Ward, D. L.; Smith, M. R., III. Organometallics 1998, 17,
3070.
Inorganic Chemistry, Vol. 44, No. 19, 2005 6791

Rivard et al.
Scheme 2. Generation of the Fluorinated Heterocycles 10 and 11 via
Skeletal Substitution Chemistry
weakly coordinating anions as an alternative path to a
cationic aluminatophosphazene ring. As previously noted,
in the case of the boron analogue 1, this strategy led to the
discovery of a series of unusual skeletal substitution reac-
tions.8,9
Figure 2. Experimental (a) and simulated (b) 31P NMR spectra of the
hexacoordinated phosphorus atom within 11 (CDCl3, 121.5 MHz, 20 °C).
The reaction of 5 with a slight excess of Ag[OSO2CF3] in
dichloromethane led to the isolation of a highly moisture-
sensitive, colorless oil. The 31P NMR spectrum of this
product in CDCl3 consisted of a singlet at δ ) 25.7 ppm,
which was shifted downfield from the 31P NMR resonance
of 5 (δ ) 23.6 ppm). A 19F NMR chemical shift attributed
to a triflate (OSO2CF3) group was observed at δ ) -77.6
ppm; a similar resonance was observed for triflate-substituted
boratophosphazene, N(PCl2NMe)B(OSO2CF3)2 (δ ) -77.4
ppm), and this suggests that the interaction between the
triflate group and the aluminum center in the product is
mainly covalent in nature.18 A quartet resonance due to the
-
BF4 salt) by halide abstraction followed by fluoride ion
-
transfer from BF4 to [7]+ and the formal replacement of a
MeClAl fragment by a BF2 group. Unfortunately, no
intermediates (including the MeAlF2 byproduct) could be
detected spectroscopically during the course of this unusual
skeletal substitution reaction. The ability to exchange atoms
within a cyclic heterophosphazene in a selective and revers-
ible manner, while retaining the initial ring framework,
remains a rarely investigated, yet potentially useful, reaction
in inorganic chemistry.20 As a consequence, we extended
our studies of the reactivity of 5 to include other silver salts.
It is known that the hexafluorophosphate anion, [PF6]-,
coordinates more weakly to cationic substrates than the
tetrafluoroborate anion [BF4]-.21 Reaction of Ag[PF6] with
5 in dichloromethane, followed by analysis of the reaction
mixture by 31P NMR spectroscopy indicated that the PF6
ion was consumed. Two new signals were detected at δ )
CF3 group of the triflate was located at δ ) 118.9 (1JCF
)
316 Hz) in the 13C{1H} NMR spectrum, while the nitrogen-
and aluminum-bound methyl groups appeared at δ ) 31.1
and -15.1 ppm, respectively (the associated 1H NMR
resonances were observed at δ ) 2.86 and -0.52 ppm).
These data were consistent with formation of the aluminato-
phosphazene N(PCl2NMe)2AlMe(OSO2CF3) (9).
-
2
33.8 (d, JPP ) 40 Hz) and -149.0 ppm (m). The latter
When 5 was allowed to react with Ag[BF4], the quantita-
tive formation of a new product was detected by the presence
of a downfield-shifted 31P NMR resonance at δ ) 28.8 ppm
resonance has a similar chemical shift as that in the
previously reported arsenic(V) heterophosphazene ring N(PCl2-
NMe)2AsF4 (3) (δ ) 34.1 ppm),8,9 while the highly upfield-
shifted multiplet is consistent with the presence of a
hexacoordinate phosphorus center (c.f. free PF6- anion δ )
-144.1 ppm (heptet)).22 A simulation of the upfield portion
of the 31P NMR spectra (Figure 2) revealed the presence of
(pseudoquartet) and a singlet at δ ) -147.5 ppm in the 19
F
NMR spectrum of the reaction mixture. These signals, along
1
with the accompanying H and 11B NMR spectra, matched
those of the previously known fluorinated boratophosphazene
heterocycle, N(PCl2NMe)2BF2, 10.9 This reaction represents
part of a formally reversible skeletal atom substitution
process involving boron and aluminum (Scheme 2). A
possible mechanism of this transformation includes the initial
formation of the alumazine-phosphazene cation [7]+ (as the
(20) For examples of the use of skeletal substitution chemistry in organic
synthesis, see: (a) Nakamoto, M.; Tilley, T. D. Organometallics 2001,
20, 5515. (b) Nitschke, J. R.; Tilley, T. D. J. Organomet. Chem. 2002,
666, 15. (c) Takahashi, T.; Ishikawa, M.; Huo, S. J. Am. Chem. Soc.
2002, 124, 388.
(19) We also explored the reactivity of 8 towards GaCl3, AlCl3, and TaCl5
(21) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; Wiley-Interscience: Toronto, 1999; p
392.
(22) Cyr, P. W.; Rettig, S. J.; Patrick, B. O.; James, B. R. Organometallics
2002, 21, 4672.
and in all instances obtained dark red oils with downfield-shifted 31
P
NMR resonances (26-28 ppm). All attempts to isolate pure products
from these reactions have been frustrated by the extreme reactivity of
the possibly cationic aluminum product.
6792 Inorganic Chemistry, Vol. 44, No. 19, 2005

Aluminatophosphazenes: Transmetalation of Inorganic Rings
Figure 4. Molecular structure of 12 with thermal ellipsoids at the 50%
probability level. Hydrogen atoms omitted. Selected bond lengths [Å] and
angles [deg]: Al(1)-C(1), 1.956(2); Al(1)-O(1), 1.712(1), Al(1)-N(1),
1.918(2); Al(1)-N(2), 1.921(2); N(1)-P(1), 1.572(2); P(1)-N(2), 1.570(2);
P(2)-N(1), 1.575(2); P(2)-N(3), 1.559(2); O(1)-C(4), 1.362(2); Al(1)-
O(1)-C(4), 175.0(1); O(1)-Al(1)-C(1), 120.5(1); N(1)-Al(1)-N(2),
103.7(8); Al(1)-N(1)-P(1), 122.9(1); N(1)-P(1)-N(3), 114.9(1); P(1)-
N(3)-P(2), 127.6(1); N(3)-P(2)-N(2), 115.6(1); P(2)-N(2)-Al(1), 124.9(1).
Figure 3. Molecular structure of 11 with thermal ellipsoids at the 50%
probability level. Hydrogen atoms omitted for clarity. Selected bond lengths
[Å] and angles [deg]: F-P(1), avg 1.602(3); P(1)-N(1), 1.814(2); P(1)-
N(2), 1.819(2); P(2)-N(1), 1.599(2); P(2)-N(3), 1.569(2); P(3)-N(2),
1.603(2); P(3)-N(3), 1.561(2); F(1)-P(1)-F(2), 89.4(1); F(3)-P(1)-F(4),
179.2(1); N(1)-P(1)-N(2), 92.4(1); P(1)-N(1)-P(2), 123.0(1); N(1)-
P(2)-N(3), 114.7(1); P(2)-N(3)-P(3), 121.8(1); N(3)-P(3)-N(2), 114.5(1);
P(3)-N(2)-P(1), 122.3(1).
resonance at δ ) 24.0 ppm was observed in the 31P NMR
spectrum of the reaction mixture. The 1H NMR spectrum of
the isolated product displayed the anticipated signals for the
t
Mes*O group with the Bu groups appearing as a set of
an overlapping triplet of triplet of triplets [1JPF ) ca. 800
singlet resonances (δ ) 1.33 and 1.46 ppm for the para and
ortho groups, respectively), with the aromatic protons
resonating at δ ) 7.28 ppm. Additional signals belonging
to N-Me and Al-Me methyl protons were located at δ )
2.83 (m) and -0.46 (s) ppm, respectively. The successful
preparation of the monosubstituted aluminatophosphazene
N(PCl2NMe)2AlMe(OMes*) (12) was confirmed by a single-
crystal X-ray diffraction study (Figure 4).
2
Hz (to equatorial F) and ca. 765 Hz (to axial F); JPP ) 40
Hz],23 and suggested that the incorporation of a phosphorus
atom in place of the aluminum had occurred to give the
zwitterionic cyclophosphazene, N(PCl2NMe)2PF4 (11).
Confirmation of the assigned structure was obtained when
a single-crystal X-ray diffraction study was performed on
large, colorless, rod-shaped crystals of 11, which were grown
from toluene (-30 °C) (Figure 3). To our knowledge,
compound 11 represents the only structurally characterized
phosphazene heterocycle to contain both formally anionic
and cationic phosphorus environments within a ring frame-
work.24
In a similar vein, a clean reaction was observed between
LiN(SiMe3)2 and 5 to give the silylated amide derivative
N(PCl2NMe)2AlMe[N(SiMe3)2] (13) as a colorless oil.
Compound 13 gave a downfield 31P NMR signal (δ ) 21.3
ppm) compared to that for 5 (δ ) 23.6 ppm), and signals
attributable to the SiMe3, Al-Me and N-Me groups were
observed in the anticipated integration ratio by 1H NMR. A
1:1 stoichiometric reaction of MeLi with 5 cleanly yielded
the methylated analogue 6. This route proved to be advanta-
geous over the previously discussed methylation strategy
involving the reaction of 5 with excess AlMe3, as purification
of 6 was rendered much simpler. Using a similar strategy,
the ethyl-substituted derivative N(PCl2NMe)2AlMeEt (14)
Nucleophilic Substitution Chemistry of Aluminato-
phosphazenes. One advantage of halogenated inorganic rings
stems from an increased degree of tunability due to the
availability of many types of halide replacement reactions,
thus providing control over the electrophilicity and subse-
quent reactivity of the ring. Consequently, we decided to
perform further reactivity studies involving 5 and selected
oxygen-, nitrogen-, and carbon-based nucleophiles.
When 5 was to reacted with Mes*OLi‚OEt2 (Mes* )
2,4,6-tBu3C6H2) in toluene, a downfield-shifted singlet
(23) 31P coupling constants were estimated by simulating the 31P NMR
spectra of 11 assuming an AM2X2Y2 spin system.
(24) For related work, see: (a) Well, M.; Jones, P. G.; Schmutzler, R. J.
Fluorine Chem. 1991, 53, 261. (b) Kaukorat, T.; Jones, P. G.;
Schmutzler, R. Heteratom. Chem. 1991, 2, 8129. (c) Schlak, O.;
Schmutzler, R.; Schiebel, H.-M.; Wazeer, M. I. M.; Harris, R. K. J.
Chem. Soc., Dalton Trans. 1974, 2153. (d) Hahn, H.; Toifl, E.; Meindl,
W.; Utvary, K. Monatsh. Chem. 1984, 115, 881. (e) Galle, K.; Utvary,
K. Monatsh. Chem. 1988, 119, 174.
was readily prepared from EtMgCl and 5 and was obtained
Inorganic Chemistry, Vol. 44, No. 19, 2005 6793

Rivard et al.
as a colorless oil.30 The 1H and 13C{1H} NMR spectra of 14
were quite similar to those observed for the related tetra-
methylated aluminatophosphazene 6 except for the presence
of the expected additional resonances arising from the ethyl
group.
Scheme 3. Preparation of the Cationic Aluminatophosphazene
[7‚THF]+a
Isolation of the Alumazine-Phosphazene Hybrid Cat-
ion [N(PCl2NMe)2AlMe‚THF]+, [7‚THF]+. The generation
of cationic aluminum complexes by the interaction of
alkylated aluminum centers with the methide abstractors
B(C6F5)3 and [Ph3C][B(C6F5)4] has been reported.2,31 Our
investigations in this regard began with a study of the
reactivity of 5 toward the methyl abstractor, B(C6F5)3. The
reaction was monitored by NMR (in CD2Cl2), and evidence
for rapid (<20 min) methyl abstraction from the aluminum
center was observed as the formation of the contact-free
[MeB(C6F5)3]- anion was detected by 1H [δ ) 0.45 (s) ppm]
and 19F [δ ) -133.2 (br), -165.5 (t), and -167.7 (t) ppm]
NMR spectroscopy.32 However, we also observed simulta-
neous Me/C6F5 exchange, presumably between the initially
formed cationic aluminum species [7]+ and the [MeB(C6F5)3]-
counterion, as the methylated borane, MeB(C6F5)2 [1H
NMR: δ ) 1.70 (s) ppm], was also present in the reaction
mixture.33 Consistent with the formation of a complicated
mixture of products was the observation of many signals
(>20) in the 19F NMR spectrum and the appearance of a
series of downfield-shifted 31P NMR resonances (δ ) 25-
27 ppm) due to the generation of either cationic and/or C6F5-
substituted aluminum centers. The abstraction of a perfluo-
rophenyl ring from the generally unreactive [MeB(C6F5)3]-
anion has been observed previously in related cationic
aluminum systems34 and suggests that the initial formation
of the desired cation, [7]+, did occur. However, the high
reactivity of this species resulted in an undesired functional
group scrambling reaction with the counterion.
a (i) Ph3C[B(C6F5)4], THF (1 equiv), CH2Cl2, 30 min.
We were encouraged by recent reports by Lappert31b and
Gibson35 concerning the use of coordinating THF to stabilize
highly reactive cationic aluminum centers. Compound 14 was
reacted with 1 equiv of [Ph3C][B(C6F5)4] in the presence of
THF (in CD2Cl2, 1 h). Analysis of the resulting yellow
solution by 31P NMR revealed a single resonance at δ )
27.3 ppm which was considerably downfield-shifted from
the 31P NMR resonance of the starting material, 14 (δ )
20.2 ppm). The 19F NMR spectrum was also clean, with the
[B(C6F5)4]- counterion as the sole detectable fluorinated
species. The 1H NMR spectrum indicated that the complete
conversion of the [Ph3C]+ cation [δ ) 7.66 (d), 7.88 (t),
and 8.27 ppm (t)] to triphenylmethane, Ph3CH [δ ) 7.1-
7.3 (m, Ph) and 5.55 (s, CH) ppm] had taken place, and
therefore, the desired â-hydride abstraction reaction involving
the aluminum-bound ethyl group in 14 was successful. The
signals associated with the presence of an Al-Et moiety were
no longer present, and a new Al-Me resonance was now
1
detected at δ ) -0.39 ppm; by comparison, the H NMR
resonance (in CD2Cl2) of the Al-Me group in 14 occurs at
δ ) -0.70 ppm. A molecule of THF was clearly coordinated
to the aluminum center, as illustrated by the presence of a
set of broad resonances at δ ) 2.88 and 4.23 ppm, which
1
were located downfield relative to the H NMR resonance
(25) Rivard, E.; McWilliams, A. R.; Lough, A. J.; Manners, I. Acta
Crystallogr. 2002, 58C, 114 and references therein.
(26) Kitashita, K.; Hagiwara, R.; Ito, Y.; Tamada, O. Solid State Sci. 2000,
2, 237.
(27) Klapo¨tke, T. M. J. Chem. Soc., Dalton Trans. 1997, 553.
(28) For salient discussions involving the nature of Al-O-C bonding,
see: (a) Barron, A. R. Polyhedron 1995, 22, 3197. (b) Burford, N.
Coord. Chem. ReV. 1992, 112, 1.
of free THF [δ ) 1.85 and 3.76 ppm]. All of the above data
convincingly support the formation the novel donor-stabilized
alumazine-phosphazene hybrid cation [N(PCl2NMe)2AlMe‚
THF][B(C6F5)4], [7‚THF][B(C6F5)4], (15) (Scheme 3). Re-
moval of the Ph3CH byproduct was accomplished by
repeatedly washing the isolated orange oil with hexanes to
give a yellow solid. Rigorous exclusion of moisture is
required in order to prevent the hydrolysis of 15, as evidenced
by the appearance of a new 31P NMR resonance at δ ) 20.5
ppm. Compound 15 can be stored in the solid state for
indefinite periods of time in a glovebox freezer (-30 °C)
without significant decomposition. All attempts to obtain a
crystalline sample of 15 of suitable quality for single-crystal
X-ray diffraction have been unsuccessful.36 In addition, the
(29) An unusually short Al-O bond (1.659(3) Å) involving a tetracoor-
dinate Al center has recently been reported. The exact nature of this
bond is still under investigation: Neculai, D.; Roesky, H. W.; Neculai,
A. M.; Magull, J.; Walfort, B.; Stalke, D. Angew. Chem., Int. Ed. 2002,
41, 4294.
(30) Use of EtMgBr in THF cleanly produces 14 in situ (by 31P NMR);
however, the similar solubilities of the THF solvated MgBrCl
byproduct and 14 prevented the isolation of the latter in pure form by
this route. Pure 14 was alternatively obtained using a solution of
EtMgCl in Et2O as the ethylating reagent.
(31) For cationic aluminum heterocycles, see: (a) Radzewicz, C. E.; Coles,
M. P.; Jordan, R. F. J. Am. Chem. Soc. 1998, 120, 9384. (b) Cosle´dan,
F.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1999, 705. (c)
Dagorne, S.; Guzei, I. A.; Coles, M. P.; Jordan, R. F. J. Am. Chem.
Soc. 2000, 122, 274. (d) Cameron, P. A.; Gibson, V. C.; Redsahw,
C.; Segal, J. A.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton
Trans. 2002, 415. (e) Schmidt, J. A. R.; Arnold, J. Organometallics
2002, 21, 2306.
1
continual presence of trace (ca. 5% by H NMR) amounts
of unidentified byproducts precluded the accurate charac-
terization of 15 by elemental analysis.
(32) Klosin, J.; Roof, G. R.; Chen, E. Y.-X.; Abboud, K. A. Organome-
tallics 2000, 19, 4684.
(33) Spitzmesser, S. K.; Gibson, V. C. J. Organomet. Chem. 2003, 673,
95.
(34) (a) Pappalardo, D.; Tedesco, C.; Pellecchia, C. Eur. J. Inorg. Chem.
2002, 621. (b) see refs 18 and 33.
(35) Cameron, P. A.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Solan, G.
A.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 2001,
1472.
(36) Salts containing the [B(C6F5)4]- anion are notoriously difficult to
crystallize as they tend to form “clathrate”-type oils.
6794 Inorganic Chemistry, Vol. 44, No. 19, 2005

Aluminatophosphazenes: Transmetalation of Inorganic Rings
Table 1. Crystallographic Data and Structure Refinement for 5,
11, and 12a
considerably with the longest P-N bonds involving the
hexacoordinate P(1) (1.816(2) Å avg), while the remaining
phosphorus atoms [P(2) and P(3)] form much shorter bonds
with the neighboring nitrogen atoms (range from 1.561(2)
to 1.603(2) Å). The shorter P-N bonds suggest some
π-bonding occurs within the P2N3 unit as these P-N
distances approach those within the [Cl3PdNdPCl3]+ cation
(1.51-1.56 Å).25 The elongated P-N bonds involving P(1)
are of similar length to those observed in related fluorinated
phosphazene heterocycles (ca. 1.7-1.8 Å)24a,b and implies a
weaker bonding interaction is present when compared to the
remaining, shorter, P-N bonds within the ring. The P-F
bond distances within 11 are similar (1.597(2)-1.610(2) Å)
5
11
12
formula
fw
C3H9Al1Cl5N3P2
353.30
C2H6Cl4F4N3P3
382.81
C
21H38Al1Cl4N3O1P2
579.26
crystal color
and habit
cryst syst
space group
a (Å)
b (Å)
c (Å)
colorless block
colorless rod
colorless block
monoclinic
P21/c
9.6405(6)
7.8844(5)
19.100(1)
90
105.851(3)
90
1415.4(2)
4
monoclinic
P21/c
6.3250(1)
12.2720(3)
15.9610(4)
90
96.027(1)
90
1232.1(1)
4
monoclinic
P21/c
10.2001(2)
14.9237(3)
18.8602(3)
90
97.967(1)
90
2843.3(1)
4
R (°)
â (°)
γ (°)
V (Å3)
Z
- 26
F
(calc) (g/cm)
1.658
1.282
2.064
1.374
1.353
0.579
and comparable to those within PF6 .
µ (mm-1
)
Heterocycle 12 exists in a twist chair conformation with
a distorted tetrahedral aluminum center (Figure 4). The
internal heterocyclic N(1)-Al-N(2) angle is 103.7(2)°, and
an almost linear Al-O-C(Mes*) angle of 175.0(1)° is
observed. The presence of such a wide Al-O-C angle is
not surprising, as this unit has been known to adopt angles
from 130° to near 180°, and this effect has been explained
in terms of a low energy barrier required to deform the Al-
O-C unit, rather than the presence of π-bonding; thus,
crystal packing forces largely dictate which geometry is
adopted in the solid state.28 Consistent with the above
explanation, the Al-O and C-O bond distances within 12
(1.712(2) and 1.362(2) Å, respectively) show little multiple-
bond character and compare well with established values for
single bonds.29 The Al-N (1.918(2) and 1.921(2) Å) and
P-N distances within 12 (1.559(2)-1.575(2) Å) are similar
to those observed in the precursor, 5; thus, the bonding within
the aluminatophosphazene ring framework appears to be
largely insensitive to the nature of the substitutents at the
aluminum center.
cryst size
θ range (°)
total reflns
0.40 × 0.30 × 0.30 0.28 × 0.23 × 0.20 0.35 × 0.35 × 0.32
2.72-27.53
3433
2.57-27.44
9415
2.57-27.55
35 483
Rint ) 0.0220
Rint ) 0.0447
Rint ) 0.0440
independent
reflns
3200
2788
6539
R1b (I > 2σ(I)) 0.0365
0.0353
0.0866
0.0354
0.0903
wR2c (all data) 0.0795
a Data collection temperature 150(1) K. b R ) Σ||Fo| -|Fc||/Σ|Fo|. c Rw
2
2
2
) {Σ[w(Fo - Fc )2]/Σ[w(Fo )2]}1/2
.
Single-Crystal X-Ray Diffraction Studies of Cyclic
Heterophosphazenes 5, 11, and 12. The crystallographic
data for compounds 5, 11, and 12 are summarized in Table
1. In the solid state, aluminatophosphazene 5 adopts a boat
conformation with the aluminum atom and two coordinate
nitrogen atom [N(2)] displaced 0.532(2) and 0.265(2) Å
above the remaining P2N2 plane (Figure 1). The aluminum
center has a distorted tetrahedral geometry with identical
Al-N bond lengths of 1.889(2) Å and are of similar value
as typical Al-N single bonds within four-coordinate alu-
minum complexes.15 The P-N bond lengths within 5 vary
from the short bonds involving N(2) [1.563(2) Å avg] to
the slightly longer P-N bonds involving the methylated
nitrogen atoms N(1) and N(3) [1.575(2) avg]; these bond
distances are considerably shorter than those of typical P-N
single bonds (1.69-1.72 Å)16 and suggest some multiple-
bond character is present within 5. The axially positioned
Al-Cl bond appeared to be somewhat elongated [2.161(1)
Å] when compared to the Al-Cl distances within most four-
coordinate aluminum species (e.g., Al-Cl lengths within the
Fluxionality of the Zwitterionic Phosphazene (11)
Probed by Variable-Temperature 19F NMR Spectroscopy.
The 19F NMR of 11 in CD2Cl2 at room temperature consisted
of one set of resolved signals centered at δ ) -65.5 ppm
(doublet of triplets), accompanied by significantly broadened
resonances centered at δ ) -25 and -68 ppm.
As broadened signals have been observed in the room
temperature 19F NMR spectrum of the related arsenic
heterocycle, N(PCl2NMe)2AsF4 (3),9 we decided to perform
a variable-temperature NMR study on 11 in order to better
understand its behavior in solution. Upon cooling the sample,
progressive sharpening of the signals was observed until three
sets of well-defined resonances (1:2:1 integration ratio) could
be discerned (Figure 5). On the basis of the 19F NMR
spectrum of the arsenic analogue, we assigned the doublet
of triplets at δ ) -26.0 ppm to the axial fluorine F(3) atom
(1JFP ) 776 Hz; 2JFF (cis) ) 55.0 Hz; no trans F-F coupling
was observed).27 The doublet of triplets at δ ) -64.6 ppm
-
AlCl4 anion usually range from 2.12 to 2.14 Å).
As shown in Figure 3, the zwitterionic phosphazene
heterocycle 11 also adopts a boat conformation, with the
formally anionic phosphorus atom [P(1)] lying considerably
above the plane created by the central P-N ring atoms [0.84-
(2) Å]; the two-coordinate nitrogen atom [N(3)] is also
buckled away from the internal P2N2 plane and resides at a
distance of 0.29(2) Å above this plane. The geometry about
P(1) is very close to a perfect octahedron, with an axial F(3)-
P(1)-F(4) bond angle of 179.2(1)° and adjacent F-P-F
angles all close to 90° (range from 89.4(1)° to 90.8(1)°).
Furthermore, the equatorial fluorine [F(1) and F(2)] and
nitrogen [N(1) and N(2)] atoms are also coplanar (equatorial
angle sum about P(1): 360.0(2)°) with a N(1)-P(1)-N(2)
bite angle of 92.4(1)°. The P-N bond lengths within 11 vary
2
(1JFP ) 815 Hz; JFF (cis) ) 56.9 Hz) was subsequently
assigned to the equatorial fluorine atoms [F(1) and F(2)] on
the basis of the observed integration ratio. Surprisingly, the
resonance due to the remaining axial fluorine atom F(4) (δ
) -68.2 ppm) displayed a complex doublet of multiplets
(1JFP ) 812 Hz). This complex resonance suggests further
Inorganic Chemistry, Vol. 44, No. 19, 2005 6795

Rivard et al.
Scheme 4. Proposed Pathway for Ring Fluxionality (Boat-Chair-Boat) within 11
coupling between this atom and two magnetically inequiva-
lent phosphorus atoms within the phosphazene ring occurs
due to the closer proximity of F(4) compared to F(3)
(assuming that no trans F-F coupling occurs). Above -40
°C, the resonances due to the axial F atoms broaden,
presumably due to a ring inversion process (Scheme 4) which
exchanges the positions of the axial fluorine atoms, while
the equatorial F atoms remain in a similar chemical environ-
ment throughout the ring inversion; thus, the resonances
associated with the equatorial fluorine atoms (dt, δ ) -64.6
ppm) remain unchanged during the course of the variable-
temperature experiment. At room temperature, the resonances
due to the axial fluorine atoms are still discernible (yet
broad), indicating that the exchange process is still slow on
the NMR time scale.
Conclusions
The aluminum-containing heterophosphazene N(PCl2-
NMe)2AlMeCl (5) has been prepared via a rare skeletal
transmetalation reaction involving the boratophosphazene
N(PCl2NMe)2BCl2 (1) and AlMe3. The successful synthesis
of methylated 6 and chlorinated derivatives 8 was also
achieved. A series of halide replacement reactions involving
5 and various nucleophiles was described, and in all cases,
selective replacement of the aluminum-bound chlorine atom
transpired. Treatment of 5 with Ag[BF4] and Ag[PF6] resulted
in novel skeletal substitution reactions, whereby the alumi-
num atom was replaced by boron and phosphorus to give
the fluorinated heterophosphazenes 10 and 11, respectively.
Heterocycle 11 represents the first structurally characterized
zwitterionic phosphazene ring, and the fluxionality of 11 in
solution was studied using variable-temperature 19F NMR
spectroscopy. Furthermore, the preparation of the first
example of a stable alumazine-phosphazene hybrid cation
[N(PCl2NMe)2AlMe‚THF]+, [7‚THF]+, was described. This
species and its analogues are possible candidates for catalysis
and as precursors to novel inorganic polymers via ROP
strategies.
Experimental Section
Figure 5. Variable-temperature 19F NMR spectra of compound 11 in
General. All reactions and manipulations were carried out strictly
CD2Cl2.
under an atmosphere of prepurified argon or nitrogen (BOC) using
6796 Inorganic Chemistry, Vol. 44, No. 19, 2005

Aluminatophosphazenes: Transmetalation of Inorganic Rings
either Schlenk techniques or an inert-atmosphere glovebox (M-
Braun). Solvents were dried and collected using a Grubbs-type37
solvent system manufactured by M-Braun. H NMR spectra were
to a colorless solution of 5 (0.20 g, 0.56 mmol) in 15 mL of toluene
at 0 °C. After the reaction was warmed to room temperature and
stirred for 3 h, the solvent was removed in vacuo, leaving a colorless
oil that gradually solidified into a waxy white solid (0.15 g, 80%).
1H NMR (CDCl3): δ ) -0.82 (s, Al-Me, 6H) and 2.76 (m,
N-Me, 6H). 13C{1H} NMR (CDCl3): δ ) -10.6 (br, Al-Me)
and 31.0 (m, N-Me). 31P NMR (CDCl3): δ ) 21.5 (s). MS EI
(70 ev, m/z, %): 318 (M+ - Me, 13), 298 (M+ - Cl, 5), 283 (M+
- Me - Cl, 1), 262 (M+ - 2Cl, 5), 227 (M+ - 3Cl, 2). Anal.
Calcd for C4H12Al1Cl4N3P3: C, 14.43; H, 3.63; N, 12.62. Found:
C, 14.79; H, 3.58; N, 11.81.
Alternatively, MeLi (1.6 M solution in Et2O, 0.90 mL, 1.4 mmol)
was added dropwise to a solution of 5 (0.50 g, 1.4 mmol) in toluene
at -78 °C. The reaction was warmed to room temperature and
stirred for 16 h to give a cloudy mixture. Filtration followed by
removal of the volatiles gave a colorless oil that slowly solidified
to a white solid which gave identical NMR data as that reported
above (0.33 g, 70%).
Preparation of N(PCl2NMe)2AlCl2 (8). A solution of GaCl3 (0.14
g, 0.80 mmol) in 5 mL of CH2Cl2 was added dropwise to a solution
of 5 (0.27 g, 0.76 mmol) in 10 mL of CH2Cl2 at room temperature.
After 8 h, the volatiles were then removed from the colorless
solution to give a white powder, which was recrystallized from a
1:1 hexanes/CH2Cl2 mixture (-30 °C, 24 h) to give colorless blocks
(0.28 g, 98%).
1H NMR (CDCl3): δ ) 2.92 (m, N-Me). 13C{1H} NMR
(CDCl3): δ ) 31.2 (m, N-Me). 31P NMR (CDCl3): δ ) 25.3 (s).
MS EI, 70 eV (m/z, %): 373 (M+, 87), 338 (M+ - Cl, 80), 288
(M+ - 2Cl - Me, 88). Anal. Calcd for C2H6Al1Cl6N3P2: C, 6.43;
H, 1.62. N, 11.24. Found: C, 6.24; H, 1.69; N, 10.74.
Preparation of N(PCl2NMe)2AlMe(OSO2CF3) (9). In the absence
of light, 5 (0.26 g, 0.73 mmol) in 2 mL of CH2Cl2 was added to a
suspension of Ag[OSO2CF3] (0.20 g, 0.79 mmol) in 5 mL of CH2-
Cl2. The immediate formation of a pale purple precipitate was
observed, and the reaction was stirred for 16 h. Filtration of this
mixture followed by removal of the volatiles in vacuo gave a
colorless oil (0.29 g, 85%).
1H NMR (CDCl3): δ ) -0.52 (s, Al-Me, 3H) and 2.86 (m,
N-Me, 6H). 13C{1H} NMR (CDCl3): δ ) -15.1 (br, Al-Me),
31.1 (s, N-Me) and 118.9 (q, 1JCF ) 316 Hz, OSO2CF3). 19F NMR
(CDCl3): δ ) -77.6 (s). 31P NMR (CDCl3): δ ) 25.7 (s).
Preparation of N(PCl2NMe)2BF2 (10) from the Reaction of 5
with Ag[BF4]. In the absence of light, 5 (0.094 g, 0.27 mmol) in 1
mL of CH2Cl2 was added to a suspension of Ag[BF4] (0.054 g,
0.28 mmol) in 3 mL of CH2Cl2. The immediate formation of a
white precipitate was observed, and the reaction was stirred for 16
h. The mixture was filtered, and removal of the volatiles provided
a white solid (0.050 g, 58%), which was identified as 10 on the
basis of NMR spectroscopy.9
1H NMR (CDCl3): δ ) 2.85 (m, N-Me). 11B NMR (CDCl3):
δ ) 0.06 (s). 19F NMR (CDCl3): δ ) -147.5 (m). 31P NMR
(CDCl3): δ ) 28.8 (pseudoquartet). MS EI, 70 eV (m/z, %): 324
(M+ - H, 26), 288 (M+ - 2F, 15), 259 (M+ - BF2Me, 26).
Preparation of N(PCl2NMe)2PF4 (11). In the absence of light, a
solution of 5 (0.34 g, 0.96 mmol) in 1 mL of CH2Cl2 was added to
a suspension of Ag[PF6] (0.25 g, 0.99 mmol) in 10 mL of CH2Cl2.
The immediate formation of a pale purple precipitate was observed,
and the reaction was stirred for 16 h. Filtration of this mixture
afforded a pale yellow solution from which a light beige solid was
isolated when the volatiles were removed in vacuo (0.21 g, 56%).
Crystals (large colorless rods) suitable for single-crystal X-ray
diffraction were obtained from a toluene solution at -30 °C (2
weeks).
1
obtained on a Varian Gemini 300 spectrometer (300.1 MHz) and
referenced to protio impurities in the NMR solvent. 11B, 13C{1H},
19F{1H}, and 31P{1H} NMR spectra were also obtained using a
Varian Gemini 300 spectrometer (96.0, 75.5, 282.2, and 121.5 MHz
respectively) and were referenced externally to BF3‚OEt2, SiMe4
(TMS), CFCl3/CDCl3, and 85% H3PO4 in either CDCl3, CD2Cl2,
or D2O (insert). Variable-temperature 19F NMR spectra were
recorded on a Varian Unity 500 spectrometer (470.2 MHz). Mass
spectra were obtained with the use of a VG 70-250S mass
spectrometer using a 70 eV electron impact ionization source.
Elemental analyses were performed either by Quantitative Tech-
nologies, Inc., Whitehouse, NJ, or at the University of Toronto using
a Perkin-Elmer Series 2400 CHN Analyzer. GaCl3 and AlCl3 were
purchased from Aldrich and sublimed prior to use. TaCl5 was
obtained from Strem and sublimed prior to use. SO2Cl2 (BDH) was
distilled under an atmosphere of nitrogen within 24 h of being used.
BCl3 (1.0 M solution in hexanes), AlMe3 (2.0 M solution of
toluene), EtMgCl (2.0 M solution in diethyl ether), LiN(SiMe3)2,
and B(C6F5)3 were also purchased from Aldrich and used as
received. Ag[OSO2CF3] (Aldrich), Ag[BF4] (Aldrich), and Ag[PF6]
(Aldrich) were dried in vacuo (ca. 120 °C, 10-3 mmHg) prior to
use. Boratophosphazene 1 was prepared according to a literature
procedure9 and was purified by recrystallization from a 1:1 CH2-
Cl2/hexanes mixture at -30 °C. 2,4,6-tBu3C6H2OLi‚OEt2 (Mes*OLi‚
OEt2)38 and [Ph3C][B(C6F5)4]2b were prepared according to literature
procedures.
X-Ray Crystallography. Diffraction data were collected on a
Nonius Kappa-CCD difractometer using graphite-monochromated
Mo KR radiation (λ ) 0.71073 Å). A combination of 1° φ and ω
(with κ offsets) scans were integrated and scaled using the Denzo-
SMN package.39 The structures were solved and refined with the
SHELXTL-PC v6.12 software package.40 Refinement was by full-
matrix least squares on F2 using data (including negative intensities)
with hydrogen atoms bonded to carbon atoms included in calculated
positions and treated as riding atoms. The methyl groups within
11 were disordered and modeled with a 50/50 occupancy related
by a 60° rotation about the N-C bond axis.
Preparative Details. Preparation of N(PCl2NMe)2AlClMe (5).
AlMe3 (10.3 mL, 20.6 mmol, 2.0 M solution in toluene) was added
dropwise to 1 (3.66 g, 10.2 mmol) in 100 mL of toluene at 0 °C to
give a colorless solution. The mixture was allowed to warm to room
temperature and stirred for 5 h; removal of the volatiles in vacuo
afforded a white residue. Recrystallization from toluene (2 mL, -30
°C, 12 h) produced large colorless blocks of 5 (2.14 g, 59%).
1H NMR (CDCl3): δ ) -0.57 (s, Al-Me, 3H) and 2.85 (m,
N-Me, 6H). 11B NMR (CDCl3): no signal detected. 13C{1H} NMR
(CDCl3): δ ) 31.1 (m, N-Me); no Al-Me resonance was
observed. 31P NMR (CDCl3): δ ) 23.6 (s). MS EI, 70 eV (m/z,
%): 355 (M+ + 2H, 20), 338 (M+ - Me, 5), 319 (M+ - Cl, 100).
Anal. Calcd for C3H9Al1Cl5N3P2: C, 10.20; H, 2.57; N, 11.89.
Found: C, 9.58; H, 2.43; N, 11.51.
Preparation of N(PCl2NMe)2AlMe2 (6). A solution of AlMe3
(0.60 mL, 1.2 mmol, 2.0 M solution in toluene) was added dropwise
(37) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(38) Bartlett, R. A.; Rasika Dias, H. V.; Flynn, K. M.; Olmstead, M. M.;
Power, P. P. J. Am. Chem. Soc. 1987, 109, 5699.
(39) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(40) Sheldrick, G. M. SHELXTL-Windows NT. V.6.12, Bruker Analytical
X-ray Systems, Inc.: Madison, WI, 2001.
Inorganic Chemistry, Vol. 44, No. 19, 2005 6797

Rivard et al.
1H NMR (CDCl3): δ ) 2.82 (m, N-Me). 13C{1H} NMR
(CDCl3): δ ) 34.0 (s). 19F NMR (470.2 MHz, CD2Cl2, -80 °C):
δ ) -26.0 (dt, F(3)-axial, JFP ) 776 Hz; JFF(cis) ) 55.0 Hz),
-64.6 (dt, F(1,2)-equatorial, 1JFP ) 815 Hz; 2JFF(cis) ) 56.9 Hz),
and -68.2 (dm, F(4)-axial, 1JFP ) 812 Hz). 31P NMR (CDCl3, 20
a white suspension was observed. The reaction was stirred for 5 h,
and filtration of the mixture gave a colorless solution. A colorless
oil was obtained after the volatiles were removed in vacuo (0.53
g, 57%).
1H NMR (CDCl3): δ ) -0.81 (s, Al-Me, 3H), -0.14 (q, 3JHH
) 8.1 Hz, Al-CH2-CH3, 2H), 0.99 (t, 3JHH ) 8.1 Hz, Al-CH2-
CH3, 3H), and 2.80 (m, N-Me, 6H). 13C{1H} NMR (CDCl3): δ )
-12.7 (v br, Al-CH2-CH3), -0.2 (br, Al-Me), 8.8 (s, Al-CH2-
CH3), and 30.7 (m, N-Me). 31P NMR (CDCl3): δ ) 20.2 (s). MS
EI, 70 eV (m/z, %): 318 (M+ - Et, 318, 45), 304 (M+ - Et -
Me, 10), 282 (M+ - Et - Cl, 5). Anal. Calcd for C5H14Al1-
Cl4N3P2: C, 17.31; H, 4.07; N, 12.11. Found: C, 16.51; H, 4.10;
N, 11.61.
1
2
2
1
°C): δ ) 33.8 (d, PCl2, JPP ) 40 Hz) and -149.0 (ttt, PF4, JPF
1
2
(equatorial) ) ∼800 Hz; JPF (axial) ) ∼765 Hz; JPP ) 41 Hz).
MS EI, 70 eV (m/z, %): 382 (M+ - H, 7), 364 (M+ - F, 20), 346
(M+ - 2F, 10), 276 (M+ - PF4, 45), 107 (PF4+, 90). Anal. Calcd
for C2H6Cl4F4N3P3: C, 6.27; H, 1.58; N, 10.98. Found: C, 6.41;
H, 1.50; N, 10.99.
Preparation of N(PCl2NMe)2AlMe(OMes*) (12). A solution of
Mes*OLi‚(OEt2) (0.35 g, 1.0 mmol) in 5 mL of toluene was added
to a solution of 5 (0.35 g, 0.99 mmol) in 5 mL of toluene. After 16
h, a white slurry was observed. Filtration of the mixture followed
by removal of the volatiles gave a white solid, which was
recrystallized from toluene (-30 °C, 16 h) to give large colorless
blocks of 12 (0.36 g, 62%).
1H NMR (CDCl3): δ ) -0.46 (s, Al-Me, 3H), 1.33 (s, para-
tBu (Mes*O), 9H), 1.46 (s, ortho-tBu (Mes*O), 18H), 2.83 (m,
N-Me, 6H), and 7.28 (s, Ar-H (Mes*O), 2H). 13C{1H} NMR
Preparation of [N(PCl2NMe)2AlMe‚THF][B(C6F5)4] (15). Alu-
minatophosphazene 14 (28 mg, 0.081 mmol) and THF (6.5 mg,
0.090 mmol) were dissolved in 0.5 mL of CD2Cl2, and this solution
was then added quickly to [Ph3C][B(C6F5)4] (75 mg, 0.081 mmol)
in 0.5 mL of CD2Cl2. After 1 h, the volatiles from the resulting
bright yellow solution were removed to afford an orange oil. The
residue was washed with hexanes (2 × 10 mL) and dried in vacuo
to give a bright yellow solid (54 mg, 62%). 1H NMR (CD2Cl2): δ
) -0.39 (s, Al-Me, 3H), 2.17 (br, CH2-CH2-O, 4H), 2.88 (m,
N-Me, 6H), 4.23 (br, CH2-CH2-O, 4H). 11B{1H} NMR (CD2-
Cl2): -16.2 (br). 13C{1H} NMR (CD2Cl2): δ ) 13.9 (s, Al-Me),
25.4 (s, CH2-CH2-O), 31.6 (s, N-Me), and 73.9 (s, CH2-CH2-
O). 19F NMR (CD2Cl2): -133.0 (br, 8F, ortho-C6F5), -163.5 (t,
3JFF ) 20.5, 4F, para-C6F5), and -167.4 (t, 3JFF ) 17.8, 8F, meta-
C6F5). 31P NMR (CD2Cl2): δ ) 27.3 (s). Despite numerous attempts
to purify 15, material of purity greater than 95% could not be
obtained (by 1H NMR), thus precluding accurate elemental analysis.
t
t
(CDCl3): δ ) 31.1 (s, Bu), 31.5 (br, N-Me), 32.0 (s, Bu), 34.6
t
t
(s, Bu), 35.4 (s, Bu), 122.5 (s, Caryl), 137.9 (s, Caryl), 139.1 (s,
C
aryl), and 153.8 (s, Caryl); no Al-Me resonance was observed. 31
P
NMR (CDCl3): δ ) 24.0 (s). MS EI, 70 eV (m/z, %): 544 (M+ -
Cl, 3), 320 (M+ - Mes*OH, 36), 262 (Mes*OH, 17), 247 (Mes*OH
- Me, 100). Anal. Calcd for C21H38Al1Cl4N3O1P2: C, 43.54; H,
6.61; N, 7.25. Found: C, 44.02; H, 6.91; N, 7.09.
Preparation of N(PCl2NMe)2AlMe[N(SiMe3)2] (13). A pale
yellow solution of LiN(SiMe3)2 (0.17 g, 1.0 mmol) in 1 mL of
toluene was added dropwise to a solution of 5 (0.35 g, 0.99 mmol)
in 5 mL of toluene. The reaction was stirred for 16 h and filtered
to give a colorless solution. Removal of the volatiles afforded a
colorless oil (0.30 g, 65%).
Acknowledgment. We are thankful to the Natural Science
and Engineering Research Council (NSERC) of Canada for
research funding (I.M.), an NSERC Postgraduate Scholarship
(E.R.) and an NSERC Postdoctoral Fellowship (P.J.R.). We
would like to thank Dr. Tim Burrow for assistance in
acquiring the variable-temperature 19F NMR spectra of
compound 11.
1H NMR (CDCl3): δ ) -0.69 (s, Al-Me, 3H), 0.14 (s,
N(SiMe3)2, 18H), and 2.81 (m, N-Me, 6H). 13C{1H} NMR
(CDCl3): δ ) 5.54 (s, SiMe3) and 30.8 (br, N-Me); no Al-Me
resonance was observed. 31P NMR (CDCl3): δ ) 21.3 (s). MS EI,
70 ev (m/z, %): 314 (M+ - HN(SiMe3)2, 35), 260 (M+
-
2ClSiMe3, 20).
Supporting Information Available: X-ray crystallographic
structures in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
Preparation of N(PCl2NMe)2AlMeEt (14). To a solution of 5
(0.95 g, 2.7 mmol) in 20 mL of toluene was added dropwise a
solution of EtMgCl (2.0 M solution in Et2O, 1.35 mL, 2.7 mmol)
at ambient temperature. Upon the addition of the Grignard reagent,
IC0509938
6798 Inorganic Chemistry, Vol. 44, No. 19, 2005