Identification of new N-Sb topologies: Understanding the sequential dehydrochloride coupling of primary amines and trichloropnictines

Article abstract of DOI:10.1039/b509481j

Subtle steric strain imposed by 2,6-dimethylphenyl substituents on N-Sb frameworks has enabled identification of the first acyclic dipnictadiazane and the first six-membered cyclotristibatriazane providing insight into the dehydrohalide coupling reaction

Full text of DOI:10.1039/b509481j

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Identification of new N–Sb topologies: understanding the sequential
dehydrochloride coupling of primary amines and trichloropnictines
Neil Burford,*a Ezra Edelstein,a Jeff C. Landry,a Michael J. Fergusonb and Robert McDonaldb
Received (in Berkeley, CA, USA) 4th July 2005, Accepted 17th August 2005
First published as an Advance Article on the web 13th September 2005
DOI: 10.1039/b509481j
The mechanism of these reactions is not known, but likely
begins with the formation of an N–P adduct 1P followed by
deprotonation at nitrogen and subsequent elimination of chloride.
While specific examples of the consequential aminodichlorophos-
phines 2P,5,6 diphosphinoamines 3P6,7 and diaminophosphines
5P5 have been isolated, the intramolecular dehydrochloride
cyclization to 7P is highly favored and acyclic diphosphadiazanes,
such as 6P have not been observed. Dehydrochloride coupling
Subtle steric strain imposed by 2,6-dimethylphenyl substituents
on N–Sb frameworks has enabled identification of the first
acyclic dipnictadiazane and the first six-membered cyclotristi-
batriazane providing insight into the dehydrohalide coupling
reaction of amines with halopnictines.
Polymers with inorganic backbones exhibit new and diverse
properties,1 however examples are limited and development of
preparative procedures represents a prominent research focus. The
versatility of ring opening polymerization prompts the search for
appropriate heterocyclic frameworks to provide new polymer
backbone compositions. We are targeting nitrogen–pnictogen
(Pn 5 P, As, Sb, Bi) systems as precursors to the, as yet unknown,
polypnictazanes. Dehydrochloride coupling reactions of chloro-
phosphines and primary amines are well established to give cyclo-
2,4-diphospha-1,3-diazanes 7P and 9P2–4 (Scheme 1).
reactions have been reported for AsCl3 and SbCl3,9 but not for
8
BiCl3, although reactions of alkali metal amides with PnCl3 have
been generally applied to prepare 2,4-substituted cyclo-2,4-
dipnicta-1,3-diazanes (Pn 5 As,10–14 Pn 5 Sb,9,14–22 Pn 5 Bi14,22,23).
Cyclotripnictatriazanes 8Pn are rare,24–26 but recently we have
realized that the presence of the medium sized substituents 2,6-
dimethylphenyl- (Dmp) or 2,6-diisopropylphenyl- (Dipp) at
nitrogen facilitates transformation of the dimer 7 to the trimer 8
for Pn 5 P27 or As.28 Imposition of this subtle substituent steric
strain on the stibazane system has now allowed for the
identification of the amine–stibine adduct 1Sb, the bisamine–
stibine adduct 4Sb, the first acyclic dipnictadiazane 6Sb and the
first six-membered cyclotristibatriazane 8Sb.
Mixtures of DmpNH2 with SbCl3 in toluene give a co-crystalline
mixture of 1Sb and 4Sb that has been crystallographically
characterized.{ One signal corresponding to the methyl groups
1
of the Dmp substituents is observed in the H NMR spectrum.
Structural parameters for 1Sb and 4Sb compare with those for 1Sb
(R 5 Ph),29 the only previously reported example of a primary
amine–stibine adduct. Antimony adopts a predictable disphenoidal
environment in 1Sb and a square pyramidal environment in 4Sb.
˚
The N–Sb distances in 4Sb [2.614(2); 2.799(2) A] are longer than
˚
that in 1Sb [2.596(2) A] due to crowding imposed by the higher
coordination number at antimony. A variety of products are
apparent in the 1H NMR spectrum when NEt3 is present in
mixtures of DmpNH2 and SbCl3. Two types of crystal have been
isolated in small quantities and have been identified as 6Sb (Fig. 1)
and 8Sb (Fig. 2) by X-ray crystallography.
The alternating N–Sb backbone of 6Sb is terminated by two
Sb–Cl bonds and an N–H bond, but a close intra-molecular
interaction occurs between these sites (N1 to Sb2) imposing a
conformation that is reminiscent of a cyclodistibadiazane (7Sb and
9Sb).20 The N1–Sb distances are significantly longer than N2–Sb,
and N1–Sb2 is comparable to those in 1Sb, 1Sb (R 5 Ph)29 and
4Sb. Samples of 6Sb decay slowly in solution, precluding attempts
to purify bulk samples.
Scheme 1 Potential outcomes for dehydrochloride coupling of RNH2
and PnCl3 (Pn 5 P, As, Sb, Bi; R 5 Dmp for Pn 5 Sb).
aDepartment of Chemistry, Dalhousie University, Halifax, Nova Scotia,
B3H 4J3, Canada. E-mail: Neil.Burford@dal.ca; Fax: 1-902-494-1310;
Tel: 1-902-494-3190
The solid state structure of 8Sb is disordered as a 55 : 45 mixture
of an envelope conformer (Fig. 2) and a boat conformer. The
chlorine substituents adopt a syn,anti configuration consistent with
bX-ray Crystallography Laboratory, Chemistry Department, University
of Alberta, Edmonton, AB, T6G 2G2, Canada
5074 | Chem. Commun., 2005, 5074–5076
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Notes and references
{ Experimental
Isolation of 1Sb/4Sb: DmpNH2 (2.40 mL, 19.5 mmol) added to SbCl3
(1.78 g, 7.81 mmol) in toluene, filtered and removal of solvent under
reduced pressure gave a precipitate that was dissolved in minimal CH2Cl2
and vapour diffusion of pentane over 2 days gave crystals (1.23 g) of
empirical formula (DmpNH2)3Sb2Cl6?0.5CH2Cl2: mp 81–82 uC; Anal.
Calcd. for C24H33N3Cl6Sb2 (Found): C 35.16 (33.01), H 4.06 (4.04), N 5.13
(5.97); IR (order of intensities): 280(1), 326(5), 436(9), 494(14), 543(11),
670(13), 770(2), 769(3), 928(11), 1027(15), 1098(12), 1139(19), 1154(20),
1211(6), 1262(7), 1577(10), 1598(8), 3295(17), 3357(16), 3374(18); NMR: 1H
(CDCl3): 2.18 (s), 3.86 (s), 6.69 (t), 6.94 (d); Crystal Data:
˚
C
24.5H34Cl7N3Sb2, M 5 862.20 g mol21, triclinic, P-1, a 5 9.9556(7) A,
˚
˚
b 5 10.4211(7) A, c 5 16.9114(12) A, a 5 85.8918(10)u, b 5 84.9494(10)u,
3
˚
c 5 73.7057(9)u, V 5 1675.5(2) A , T 5 193(2) K, Z 5 2, m(MoKa)
˚
0.71073 (A), Reflections; 6811 unique, 6180 observed, R (for 6180
reflections with (I . 2s(I))) 5 0.0220; wR(all) 5 0.0600.
Fig. 1 Solid state molecular structure of 6Sb. Ellipsoids drawn at 50%
probability and hydrogen atoms omitted for clarity. Selected bond
˚
lengths (A): N1–Sb1 2.108(2), N1–Sb2 2.521(2), N2–Sb1 2.023(2), N2–Sb2
Isolation of 6Sb and 8Sb: DmpNH2 (4.94 mL, 39.3 mmol) added to
NEt3 (5.71 mL, 39.6 mmol) and SbCl3 (6.23 g, 27.3 mmol) in toluene
(110 mL) at 0 uC, stirred for 1.5 h at RT. Filtered and the solvent was
removed in vacuo to 5 mL, addition of pentane (5 mL) gave a yellow
precipitate after 4 days at 224 uC, which was dissolved in minimal CH2Cl2
and vapour diffusion of pentane gave a mixture of crystals (0.13 g) with
two distinct morphologies and colours, manually separated. Pale yellow
2.039(2), Sb1–Cl1 2.409(1), Sb2–Cl2 2.425(1), Sb2–Cl3 2.450(1).
(, 0.02 g) 6Sb; Crystal Data: C16H19Cl3N2Sb2, M 5 589.18 g mol21
,
Monoclinic, P21/c, a 5 13.0005(9) A, b 5 20.8528(14) A, c 5 15.5863(10) A,
˚
˚
˚
3
˚
b 5 108.9580(10)u, V 5 3996.2(5) A , T 5 193(2) K, Z 5 8, m(MoKa)
˚
0.71073 (A), Reflections; 8121 unique, 7448 observed, R (for 7448
reflections with (I . 2s(I))) 5 0.0211; wR(all) 5 0.0555. Colourless
(y0.10 g) 8Sb, mp 269–271 uC; Anal. Calcd. for C24H27N3Cl3Sb3 (Found):
C 34.77 (31.52), H 3.28 (3.45), N 5.07 (5.25); IR: 229(5), 325(9), 373(11),
486(15), 522(8), 690(10), 707(7), 790(3), 811(2), 839(4), 901(16), 984(12),
1023(13), 1097(6), 1164(1), 1252(14), 1586(17), 1799(19), 1867(20), 1934(18);
1
NMR: H (CDCl3): 2.60 (s, 3H), 2.66 (s, 6H), 2.69 (s, 3H), 2.74 (s, 6H),
7.02–7.17 (m, 9H); Crystal Data: C24H27Cl3N3Sb3, M 5 829.09 g mol21
,
Monoclinic, P21/c, a 5 16.376(3) A, b 5 8.9041(14) A, c 5 19.122(3) A,
˚
˚
˚
˚
3
b 5 96.817(3)u, V 5 2768.6(7) A , T 5 193(2) K, Z 5 4, m(MoKa)
˚
0.71073 (A), Reflections; 5572 unique, 4468 observed, R (for 4468
reflections with (I . 2s(I))) 5 0.0687; wR(all) 5 0.1960. CCDC 271559–
271561. See http://dx.doi.org/10.1039/b509481j for crystallographic data in
CIF or other electronic format.
Fig. 2 Solid state molecular structure of one conformer of 8Sb.
Ellipsoids drawn at 50% probability and hydrogen atoms omitted for
˚
clarity. Selected bond lengths (A): Sb–N 2.012(8)–2.071(8), Sb–Cl
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We thank the Natural Sciences and Engineering Research
Council of Canada, the Killam Foundation, the Canada Research
Chairs Program, and the Sumner Foundation for funding.
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