Iminophosphine cycloaddition reactions of a diazaphosphoniaaluminatacyclobutane and a novel intramolecular phosphiridine P→P coordination

Full text of DOI:10.1021/ic9813718

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Inorg. Chem. 1999, 38, 2248-2249
Iminophosphine Cycloaddition Reactions of a Diazaphosphoniaaluminatacyclobutane and a Novel
Intramolecular Phosphiridine PfP Coordination
Neil Burford* and Daren J. LeBlanc
Department of Chemistry, Dalhousie University, Halifax, Nova Scotia B3H 4J3, Canada
ReceiVed December 1, 1998
The chemistry of phosphorus is experiencing a new evolution-
ary phase by virtue of the development and reactivity studies of
low coordinate environments.1 Heterocycle 12 (illustrations are
drawn with omission of SiMe3 substituents on nitrogen for clarity)
contains a particularly interesting phosphorus environment which
exhibits unusual reactivity.3,4 As part of our assessment of the
unusual acceptor capabilities of phosphorus in 1,4 we have
discovered a novel reaction involving two molecules of 1, which
is facilitated by the simple anions Cl- and CN-. The process is
mimicked by a reversible quantitative cycloaddition reaction of
1 with (Me3Si)2NPNSiMe3 featuring a phosphiridine forming
intramolecular cross-ring PfP coordinative interaction.
Equimolar reaction mixtures of 1 with PPh4Cl or PPh4CN
exhibit similar 31P NMR spectra, with the rapid appearance of a
singlet at 190 ppm assigned to anion 2, which has been isolated
as the tetraphenylphosphonium salt.5 The structure of the anion
in the solid state (Figure 1a) is best described as a P2N2
* Corresponding author. E-mail: Burford@is.dal.ca.
(1) Regitz, M.; Scherer, O. J., Eds. Multiple Bonds and Low Coordination
in Phosphorus Chemistry; Georg Thieme Verlag: Stuttgart, Germany,
1990.
Figure 1. Solid-state structure of (a) the anion of [PPh4][2] and (b) 3.
(2) Niecke, E.; Kro¨her, R. Angew. Chem., Int. Ed. Engl. 1976, 15, 692-
Displacement ellipsoids are drawn at the 50% probability level, and
hydrogen atoms have been omitted for clarity.
693. Niecke, E.; Kro¨her, R. Z. Naturforsch. 1979, 34B, 837-842. Pohl,
S. Chem. Ber. 1979, 112, 3159-3165.
(3) Losier, P.; Burford, N.; Mason, S.; Sereda, S. V.; Cameron, T. S.
Phosphorus Sulfur 1994, 93-94, 463-464. Burford, N.; Losier, P.;
Mason, S.; Bakshi, P. K.; Cameron, T. S. Inorg. Chem. 1994, 33, 5613-
5614.
(4) Burford, N.; Losier, P.; Bakshi, P. K.; Cameron, T. S. J. Chem. Soc.,
Chem. Commun. 1996, 307-308.
(5) A mixture of [PPh4]Cl (0.72 g, 1.9 mmol) and KCN (0.13 g, 1.9 mmol)
in CH2Cl2 (30 mL) was stirred at reflux for 20 min and at room-
temperature overnight. The filtered solution was added to a solution of
1 (0.53 g, 1.7 mmol) in toluene (30 mL) and stirred overnight. The
reaction mixture was filtered and reduced in volume to 20 mL, and
pentane (25 mL) was slowly added, giving a mixture of two crystalline
solids, which were Pasteur separated and characterized as [PPh4][2] and
[PPh4][AlCl4]. Selected characterization data for [PPh4][2]: dp: 145-
160 °C; 31P NMR (CH2Cl2) δ 190 (s, 2), 23 (s, PPh4). Crystal data:
C36H56AlCl2N4P3Si4, M ) 848.00, monoclinic, P21/n, a ) 14.6485(3)
Å, b ) 18.6224(4) Å, c ) 17.3207(4) Å, â ) 98.6260(10)°, V )
4671.47(18) Å3, T ) 150(2) K, Z ) 4, µ ) 0.392 mm-1, 46 910 measured
reflections, 9514 independent reflections, 6404 reflections with I > 2σ(I),
463 refined parameters, R[F2 > 2σ(F2)] ) 0.0457, wR(F2) ) 0.1361, S
) 1.022.
phosphetidine (phosphazane) with a diazaaluminate bridge of the
chemically equivalent phosphorus centers, consistent with analo-
gous bridged phosphazanes.6 The identification of [PPh4][AlCl4],
as a coproduct of the reaction, has been confirmed by X-ray
crystallographic analysis,7 and NMR studies of the reaction
mixture imply a quantitative reaction of 1 with PPh4Cl according
(6) Scherer, O. J.; Wolmersha¨user, G.; Conrad, H. Angew. Chem., Int. Ed.
Engl. 1983, 22, 404-405. Scherer, O. J.; Anselmann, R.; Sheldrick, W.
S. J. Organomet. Chem. 1984, 263, C26-C29. Kumravel, S. S.;
Krishnamurthy, S. S.; Cameron, T. S.; Linden, A. Inorg. Chem. 1988,
27, 4546-4550. Linti, G.; No¨th, H.; Schneider, E.; Storch, W. Chem.
Ber. 1993, 126, 619-629. Scherer, O. J.; Ju¨rgen, K.; Ziegler, M. L.
Angew. Chem., Int. Ed. Engl. 1983, 22, 503-504. Reddy, V. S.;
Krishnamurthy, S. S.; Nethaji, M. J. J. Chem. Soc., Dalton Trans. 1995,
1933-1938.
(7) Burford, N.; LeBlanc, D. J.; Lough, A. J. Acta Crystallogr. 1998, C54,
IUC9800040.
10.1021/ic9813718 CCC: $18.00 © 1999 American Chemical Society
Published on Web 05/17/1999

Communications
Inorganic Chemistry, Vol. 38, No. 10, 1999 2249
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
[PPh4][2] and 3
solution (with ring contraction to give 1) above RT according to
eq 2, and only at -63 °C are the two doublets assigned to 3
observed independently, indicating quantitative association. The
new heterocycle can be interpreted in terms of two resonance
structures: a phosphine (P1) phosphonium (P2) aluminate 3a or
a phosphenium (P1) aluminate with an intramolecular phosphine
(P2) coordination 3b representing a new contribution to the
developing coordination chemistry of phosphorus as an acceptor.
[PPh4][2]
3
P1-P2
2.5553(11)
1.681(2)
1.738(2)
1.731(2)
1.672(2)
1.730(3)
1.723(2)
104.03(11)
102.97(12)
82.94(11)
104.82(12)
102.76(12)
83.40(12)
95.43(11)
94.95(12)
-
2.1051(13)
1.673(3)
P1-N1
P1-N3
-
P1-N4
1.874(3)
1.626(3)
1.640(3)
1.637(3)
P2-N2
P2-N3
P2-N4
N1-P1-N3
N1-P1-N4
N3-P1-N4
N2-P2-N3
N2-P2-N4
N3-P2-N4
P1-N4-P2
P1-N3-P2
N4-P1-P2
N4-P2-P1
-
The donor or ligand label for electron rich sites such as
phosphines is becoming somewhat of a misnomer with the
realization of NfP,10 PfP,11 OfP,12 and SfP13 coordination
complexes as well as π-arene complexes14 and examples of halide
ion addition to halophosphines to give [PX4]- salts.15 Compound
3 is a new dramatic illustration of such an interaction, effecting
a fold in the six-membered ring and planarization of the phosphine
donor.
108.33(14)
-
116.42(15)
114.63(15)
118.25(15)
73.34(12)
-
48.15(9)
58.51(10)
-
to reaction eq 1. We speculate that the smaller (sterically
2 1 + 2Ph4PCl f Ph4P[2] + Ph4P[AlCl4] (1)
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada and the Killam Trust
of Dalhousie University for funding, the Atlantic Region Magnetic
Resonance Centre for the use of instrumentation, and Dr. Alan
Lough of the University of Toronto for collecting the X-ray data.
unrestricted) chloride or cyanide anions attack the more electro-
philic and Lewis acidic aluminum center of 1, in contrast to the
observations for reactions of 1 with quinuclidine and N,N-
tetramethylethylenediamine, which involve NfP coordinative
interactions.4 The result is formal abstraction of AlCl2+ (ultimately
as [AlCl4]-) from 1, formally releasing the [Me3SiNPNSiMe3]-
anion which ultimately inserts into a second molecule of 1
effecting ring expansion.
Supporting Information Available: Complete crystallographic
details, in CIF format, for [PPh4][2] and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC9813718
To obtain a better understanding of eq 1, we have examined
the reaction of 1 with (Me3Si)2NPNSiMe3, which analogously
results in the insertion of the iminophosphine (NdP) unit into
the N-P bond or N-Al bond (considering the precedent for
lability of the N-Al bond)3 of 1 to give cycloadduct 3 (eq 2).8
(9) Niecke, E.; Gudat, D.; Symalla, E. Angew. Chem., Int. Ed. Engl. 1986,
25, 834-835. Niecke, E.; Nickloweit-Lu¨ke, A.; Ru¨ger, R. Angew. Chem.,
Int. Ed. Engl. 1981, 20, 385-386. Roques, C.; Mazieres, M. R.; Majoral,
J. P.; Sanchez, M. Tetrahedron Lett. 1988, 29, 4547-4550. Niecke, E.;
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1986, 40, 202-205. Niecke, E.; Kramer, B.; Nieger, M.; Severin, H.
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(Me3Si)2NPNSiMe3 + 1 h 3
(2)
The solid-state structure of 3 (Figure 1b) reveals a bicyclic
arrangement imposed by a cross-ring P-P interaction that defines
an azadiphosphiridine (PPN) heterocycle.
(10) Bouhadir, G.; Reed, R. W.; Reau, R.; Bertrand, G. Heteroatom Chem.
1995, 6, 371-375. Reed, R.; Reau, R.; Dahan, F.; Bertrand, G. Angew.
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drasekaran, A.; Day, R. O.; Holmes, R. R. Inorg. Chem. 1998, 37, 4945-
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As documented by the comparative structural parameters in
Table 1, adduct 3 can be considered as the formal addition of a
[SiMe3]+ unit at N3 of anion 2 which results in significant
structural changes, including opening of the phosphetidine
heterocycle, contraction of all three P2-N bonds, close to
planarisation of P2 within the N2, N3, N4 triangle [sum of the
N-P2-N angles is 349.30(15)°], an extension of the P1-N4
bond, acute reduction of the P1-N4-P2 angle, and substantial
shortening of the P-P vector. The P1-P2 bond distance
[2.1051(13) Å] and P1-N4-P2 angle [73.34(12)°] of 3 are the
smallest yet observed for crystallographically characterized aza-
diphosphiridines.9
(11) Burford, N.; Cameron, T. S.; LeBlanc, D. J.; Losier, P.; Wu, G.
Organometallics 1997, 16, 4712-4717. Burford, N.; Cameron, T. S.;
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The cluster-like cycloadduct 3 results from an unprecedented
ring-opening and three bond forming cycloaddition. 31P NMR
spectra reveal that 3 achieves retro-dissociation equilibrium in
(8) (Me3Si)2NPNSiMe3 (2.74 g, 9.84 mmol) in toluene (30 mL) was added
to 1 (2.80 g, 9.23 mmol) in toluene (30 mL) and stirred for 1 h. The
volume was reduced to 15 mL, and pentane (20 mL) was slowly added,
giving a white crystalline material characterized as 3 (yield ) 1.40 g,
24%). Anal. Calcd: C, 30.97; H, 7.80; N, 9.63; Cl, 12.19. Found: C,
30.98; H, 7.88; N, 9.68; Cl, 12.11. Mp 98-105 °C; 31P NMR (CH2Cl2),
37 °C, δ 380 [s, 1], 327 [s, (Me3Si)2NPNSiMe3], 14 (d, JP-P ) 94 Hz),
-9 (d, JP-P unresolved); -63 °C: δ 11 (d, JP-P ) 91 Hz), -10 (d, JP-P
) 91 Hz). Crystal data: C15H45AlCl2N4P2Si5, M ) 581.82, monoclinic,
Cc, a ) 22.2416(14) Å, b ) 8.9070(7) Å, c ) 18.5029(13) Å, â )
119.5280(10)°, V ) 3189.4(4) Å3, T ) 150(2) K, Z ) 4, µ ) 0.531
mm-1, 11 799 measured reflections, 6229 independent reflections, 4795
reflections with I > 2σI, 295 refined parameters, R[F2 > 2σ(F2)] )
0.0414, wR(F2) ) 0.0910, S ) 0.979.
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