Diamidonaphthalene-stabilized N-heterocyclic pnictogenium cations and their cation-cation solid-state interactions

Article abstract of DOI:10.1021/om7004436

The synthesis and comprehensive characterization of a new series of N-heterocyclic phosphine, arsine, and stibine compounds is presented. The diamidochloropnictines ClPn(NR)₂C₁₀H₆ (Pn = P, As, Sb) were prepared via the dehydrohalide coupling reactions of N,N′-diisopropyl-1,8-diaminonaphthalene, (ⁱPrNH) ₂C₁₀H⁶, or N,N′-diphenyl-1,8- diaminonaphthalene, (PhNH)₂C₁₀H₆, with the appropriate pnictogen trichloride. Reaction of these pnictines with appropriate halide abstraction agents yielded the corresponding phosphenium and arsenium salts. These planar pnictogenium cations {Pn(NR)₂C₁₀H ₆}⁺ (Pn = P, As; R = ⁱPr, Ph) display dicoordinate pnictogen centers that are stabilized by an electron-rich diamidonaphthalene framework and represent rare examples of six-membered N-heterocyclic pnictogenium cations possessing a π-conjugated carbon backbone. The related stibenium salts could not be prepared via this route; however, the reaction of the new heteroleptic triamidostibene, (Me ₂N)Sb(ⁱPrN)₂C₁₀H₆, with triflic acid does generate the base-stabilized stibenium cation, [Sb( ⁱPrN)₂C₁₀H₆·(Me ₂NH)]⁺. The phosphenium and arsenium salts exhibit different modes of packing in their solid-state structures depending upon the identity of the nitrogen substituents. The two phenyl substituted compounds display an interaction between the pnictogen center and the π-system of an adjacent naphthyl moiety. In contrast, the isopropyl substituted species undergo metastable dimerization through naphthyl π-stacking. These dimers are bound by strong dipole-dipole and dispersion interactions as revealed through computational studies.

Full text of DOI:10.1021/om7004436

4972
Organometallics 2007, 26, 4972-4982
Diamidonaphthalene-Stabilized N-Heterocyclic Pnictogenium
Cations and Their Cation-Cation Solid-State Interactions
Heather A. Spinney,† Ilia Korobkov,† Gino A. DiLabio,‡ Glen P. A. Yap,§ and
Darrin S. Richeson*,†
Center for Catalysis Research and InnoVation, Department of Chemistry, UniVersity of Ottawa, Ottawa,
Ontario, Canada K1N 6N5, National Institute for Nanotechnology, National Research Council of Canada,
11421 Saskatchewan DriVe, Edmonton, Alberta, Canada T6G 2M9, and Department of Chemistry and
Biochemistry, UniVersity of Delaware, Newark, Delaware 19716
ReceiVed May 4, 2007
The synthesis and comprehensive characterization of a new series of N-heterocyclic phosphine, arsine,
and stibine compounds is presented. The diamidochloropnictines ClPn(NR)2C10H6 (Pn ) P, As, Sb) were
prepared via the dehydrohalide coupling reactions of N,N′-diisopropyl-1,8-diaminonaphthalene, (iPrNH)2C10H6,
or N,N′-diphenyl-1,8-diaminonaphthalene, (PhNH)2C10H6, with the appropriate pnictogen trichloride.
Reaction of these pnictines with appropriate halide abstraction agents yielded the corresponding
phosphenium and arsenium salts. These planar pnictogenium cations {Pn(NR)2C10H6}+ (Pn ) P, As; R
) iPr, Ph) display dicoordinate pnictogen centers that are stabilized by an electron-rich diamidonaphthalene
framework and represent rare examples of six-membered N-heterocyclic pnictogenium cations possessing
a π-conjugated carbon backbone. The related stibenium salts could not be prepared via this route; however,
the reaction of the new heteroleptic triamidostibene, (Me2N)Sb(iPrN)2C10H6, with triflic acid does generate
the base-stabilized stibenium cation, [Sb(iPrN)2C10H6‚(Me2NH)]+. The phosphenium and arsenium salts
exhibit different modes of packing in their solid-state structures depending upon the identity of the nitrogen
substituents. The two phenyl substituted compounds display an interaction between the pnictogen center
and the π-system of an adjacent naphthyl moiety. In contrast, the isopropyl substituted species undergo
metastable dimerization through naphthyl π-stacking. These dimers are bound by strong dipole-dipole
and dispersion interactions as revealed through computational studies.
isolation of a number of N-heterocyclic phosphenium,4-6
arsenium,7-9 and stibenium10-12 cations represented by 2-6.
While some varieties of molecular structures have been reported,
these species are principally dominated by a cyclic five-
membered 1,3,2-diazapnictogenium species (2).
This paper concerns the isolation and characterization of
pnictogenium cations (7) supported by the N,N′-disubstituted
1,8-diamidonaphthalene (R2DAN2-) framework.13-15 These
molecules possess a novel topology and electronic framework
in which the dicoordinate pnictogen center resides in a
π-electron-rich, six-membered heterocyclic ring. The geometric
and electronic features of the R2DAN2- ligand are reminiscent
Introduction
Pnictogenium cations are six-electron, dicoordinate group 15
species containing lone pairs of electrons and vacant p-orbitals
and accordingly display amphoteric properties as Lewis acids
and bases. The electron deficient, coordinatively unsaturated
element centers characteristic of these compounds attract interest
from a fundamental perspective and ultimately provide for their
interesting reactivity and synthetic utility. Like the now
ubiquitous N-heterocyclic carbenes (NHCs), and their heavier
congeners (1), successful isolation of the isoelectronic pnicto-
genium cations relies on heteroatom bonding and charge
delocalization through incorporation of the pnictogen atom into
a conjugated π-electron system.1,2 Following the discovery of
the first stable phosphenium ion some 40 years ago,3 the
sustained interest in related group 15 compounds has led to the
(4) Reviews: (a) Cowley, A. H.; Kemp, R. Chem. ReV. 1985, 85, 367.
(b) Gudat, D. Coord. Chem. ReV. 1997, 173, 71.
(5) Carmalt, C. J.; Lomeli, V.; McBurnett, B. G.; Cowley, A. H. Chem.
Commun. 1997, 2095.
(6) Reeske, G.; Hoberg, C. R.; Hill, N. J.; Cowley, A. H. J. Am. Chem.
Soc. 2006, 128, 2800.
(7) Burford, N.; Parks, T. M.; Royan, B. W.; Borecka, B.; Cameron, T.
S.; Richardson, J. F.; Gabe, E. J.; Haynes, R. J. Am. Chem. Soc. 1992, 114,
8147.
* Corresponding author. E-mail: darrin@uottawa.ca.
† University of Ottawa.
‡ National Research Council of Canada.
§ University of Delaware.
(1) For selected recent examples, see: (a) Hill, N. J.; West, R. J.
Organomet. Chem. 2004, 689, 4165. (b) Kuhl, O. Coord. Chem. ReV. 2004,
248, 411. (c) Fedushkin, I. L.; Skatova, A. A.; Chudakova, V. A.;
Khvoinova, N. M.; Baurin, A. Y.; Deckert, S.; Hummert, M.; Schumann,
H. Organometallics 2004, 23, 3714. (d) Jing, H.; Edulji, S. K.; Gibbs, J.
M.; Stern, C. L.; Zhou, H.; Nguyen, S. T. Inorg. Chem. 2004, 43, 4315. (e)
Hitchcock, P. B.; Hu, J.; Lappert, M. F.; Severn, J. R. Dalton Trans. 2004,
4193. (f) Richards, A. F.; Brynda, M.; Power, P. P. Organometallics 2004,
23, 4009.
(2) Bourissou, D.; Guerret, O.; Gabba¨ı, F. P.; Bertrand, G. Chem. ReV.
2000, 100, 39.
(3) Dimroth, K.; Hoffmann, P. Angew. Chem., Int. Ed. Engl. 1964, 3,
384.
(8) Burford, N.; Macdonald, C. L. B.; Parks, T. M.; Wu, G.; Borecka,
B.; Kwiatkowski, W.; Cameron, T. S. Can. J. Chem. 1996, 74, 2209.
(9) Reeske, G.; Cowley, A. H. Chem. Commun. 2006, 1784.
(10) Gudat, D.; Gans-Eichler, T.; Nieger, M. Chem. Commun. 2004,
2434.
(11) (a) Burck, S.; Daniels, J.; Gans-Eichler, T.; Gudat, D.; Na¨ttinen,
K.; Nieger, M. Z. Anorg. Allg. Chem. 2005, 631, 1403. (b) Gans-Eichler,
T.; Gudat, D.; Nieger, M. Heteroatom. Chem. 2005, 16, 327.
(12) (a) Veith, M.; Bertsch, B.; Huch, V. Z. Anorg. Allg. Chem. 1988,
559, 73. (b) Veith, M.; Bertsch, B. Z. Anorg. Allg. Chem. 1988, 557, 7.
(13) (a) Spinney, H. A.; Yap, G. P. A.; Korobkov, I.; DiLabio, G. A.;
Richeson, D. S. Organometallics 2006, 25, 3541. (b) Spinney, H. A.;
Korobkov, I.; Richeson, D. S. Chem. Commun. 2007, 1647.
10.1021/om7004436 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 08/23/2007

Diamidonaphthalene-Stabilized Pnictogenium Cations
Organometallics, Vol. 26, No. 20, 2007 4973
nitrogen atmosphere. Triethylamine was dried by fractional distil-
lation from KOH and then CaH2. Dichloromethane was distilled
over CaH2 prior to use. All other solvents were sparged with
nitrogen and then dried by passage through a column of activated
alumina using an apparatus purchased from Anhydrous Engineering.
Deuterated benzene and dichloromethane were dried using activated
molecular sieves. Tris(dimethylamido)antimony was purchased from
Strem Chemicals and used as received. All other chemicals were
purchased from Aldrich and used without further purification. N,N′-
Diisopropyl-1,8-diaminonaphthalene and N,N′-diphenyl-1,8-diami-
nonaphthalene were prepared according to previously reported
procedures.14a,19 NMR spectra were run on a Bruker Avance 300
MHz spectrometer with deuterated benzene or dichloromethane as
a solvent and internal standard. Infrared spectra were collected on
samples prepared as Nujol mulls on NaCl plates using a ABB
Bomem MB Series FT-IR spectrometer and are reported in
wavenumbers (cm-1) followed by ranked intensities in parentheses,
where a value of one corresponds to the most intense peak in the
spectrum. Elemental analyses were performed by Guelph Chemical
Laboratories, Guelph, ON, Canada, with the exception of elemental
analyses of 10d and 11b, which were performed by Robertson
Microlit Laboratories, Madison, NJ.
Computational Methods. Calculations were performed using
the Gaussian 03 package of programs.20 To obtain molecular orbitals
for the pnictogenium cations, the positions of the hydrogen atoms
on the crystal structures of the cations were optimized using the
B971/6-31+G(d,p) functional. This functional was chosen because
it can, to some extent, predict interactions in van der Waals
complexes.21 Additional calculations on π-stacked phosphenium
cation dimers were performed using the MP2 approach with various
basis sets.
X-ray. A suitable crystal was selected, mounted on a thin, glass
fiber using viscous oil, and cooled to the data collection temperature.
Data were collected on a Bruker AXS SMART 1k CCD diffrac-
tometer using 0.3° ω-scans at 0, 90, and 180° in æ. Initial unit cell
parameters were determined from 60 data frames collected at
different sections of the Ewald sphere. Semiempirical absorption
corrections based on equivalent reflections were applied. The
structures were solved by direct methods, completed with difference
Fourier synthesis, and refined with full-matrix least-squares pro-
cedures based on F2. All non-hydrogen atoms were refined with
anisotropic displacement parameters. All hydrogen atoms were
treated as idealized contributions. All scattering factors and
anomalous dispersion factors are contained in the SHELXTL 6.1237
program library. Relevant crystal data are reported in Tables 1 and
2, while selected bond distances and angles are reported in Table
3.
of the â-diketiminate scaffold;16 however, among the significant
differences between these two ligand arrays are the dianionic
charge and naphthalene backbone of R2DAN2-. This latter
feature prevents substitution reactions in the ligand backbone,
and as such, we anticipated that R2DAN2- would be a more
robust ligand than â-diketiminate. Interestingly, it is only
recently that the first â-diketiminate supported phosphorus
compound (8), an N,N′-chelated phosphenium cation, was
isolated,17 and computational studies suggest that â-diketiminate
supported pnictogenium cations are inherently unstable.18 The
utilization of the R2DAN2- support structure for group 15
compounds promises to yield novel species with applications
in coordination chemistry and catalysis.
Experimental Procedures
General Methods. Reactions were performed using standard
Schlenk techniques (N2) or, alternatively, in a glove box with a
(14) For applications of R2DAN2- to group 14, see: (a) Bazinet, P. Yap,
G. P. A.; DiLabio, G. A.; Richeson, D. S. Inorg. Chem. 2005, 44, 4616.
(b) Bazinet, P. Yap, G. P. A.; Richeson, D. S. J. Am. Chem. Soc. 2003,
125, 13314. (c) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem.
Soc. 2001, 123, 11162. (d) Ayers, A. G.; Drost, C. D.; Gehrhus, B.;
Hitchcock, P. B.; Lappert, M. F. Z. Anorg. Allg. Chem. 2004, 630, 2090.
(e) Drost, C.; Hitchcock, P. B.; Lappert, M. F. Angew. Chem., Int. Ed. 1999,
38, 1113. (f) Schaeffer, C. D., Jr.; Zuckerman, J. J. J. Am. Chem. Soc.
1974, 96, 7160.
(15) Further applications of R2DAN2- can be found in: (a) Lee, C. H.;
La, Y.-H.; Park, J. W. Organometallics 2000, 19, 344. (b) Lee, C. H.; La,
Y.-H.; Park, J.; Park, J. W. Organometallics 1998, 17, 3648. (c) Nomura,
K.; Naga, N.; Takaoki, K. Macromolecules 1998, 31, 8009. (d) Galka, C.
H.; Tro¨sch, D. J. M.; Ru¨denauer, I.; Gade, L. H.; Scowen, I. J.; McPartlin,
M. Inorg. Chem. 2000, 39, 4615. (e) Hellmann, K. W.; Galka, C. H.;
Ru¨denauer, I.; Gade, L. H.; Scowen, I. J.; McPartlin, M. Angew. Chem.,
Int. Ed. 1998, 37, 1948. (f) Hellmann, K. W.; Galka, C. H.; Gade, L. H.;
Steiner, A., Wright, D. S.; Kottke, T.; Stalke, D. Chem. Commun. 1998,
549.
General Procedure for the Preparation of Diamidochloro-
pnictines 9a-f. To a solution of 1,8-(iPrNH)2C10H6 (0.3-1 g) or
1,8-(PhNH)2C10H6 (0.3-1 g) in 30 mL of toluene was added
(18) Ellis, B. D.; Macdonald, C. L. B. Inorg. Chim. Acta 2007, 360,
329.
(19) Bazinet, P.; Ong, T.-G.; O’Brien, J. S.; Lavoie, N.; Bell, E.; Yap,
G. P. A.; Korobkov, I.; Richeson, D. S. Organometallics 2007, 26, 2885.
(20) Frisch, M. J.; et al. Gaussian 03, revision D.01; Gaussian, Inc.:
Pittsburgh, PA, 2004.
(16) For a recent review of â-diketiminates and their metal complexes,
see: Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031.
(17) Vidovic, D.; Lu, Z.; Reeske, G.; Moore, J. A.; Cowley, A. H. Chem.
Commun. 2006, 3501-3503.
(21) Johnson, E. R.; DiLabio, G. A. Chem. Phys. Lett. 2006, 419, 333-
339.

4974 Organometallics, Vol. 26, No. 20, 2007
Table 1. Crystal Data for Pnictines ClPn(RN)2C10H6 (9a-c,e) and (NMe2)Sb(iPrN)2C10H6 (14)
Spinney et al.
compound
9aa
9b
9cb
9eb,c
14b
formula
C16H20N2PCl
306.76
monoclinic
P21/n
colorless
8.796(2)
16.226(4)
11.612(3)
90
105.817(5)
90
1594.5(7)
4
0.0459
0.1179
C22H16N2PCl
374.79
monoclinic
C2/c
colorless
15.090(4)
9.110(2)
26.584(6)
90
92.548(4)
90
3650.7(15)
8
0.0492
0.1195
C16H20N2AsCl
350.71
monoclinic
P21/n
colorless
8.8383(19)
16.434(3)
11.551(2)
90
106.825(3)
90
1606.0(6)
4
0.0309
0.0763
C37.6H46.4N4Sb2Cl2
868.79
monoclinic
P21/n
C18H26N3Sb
molecular wt (g/mol)
cryst syst
space group
color
a (Å)
b (Å)
406.17
orthorhombic
Pna21
yellow
14.606(3)
9.7332(17)
12.573(2)
90
orange
15.669(4)
11.931(3)
21.118(5)
90
92.125(4)
90
3945.3(15)
4
0.0456
c (Å)
R (deg)
â (deg)
90
90
γ (deg)
V (Å3)
1813.0(5)
4
0.0240
0.0643
1.039
Z
Rd (I > 2σ(I))
wR2e (all data)
GOFf (all data)
∆F max and min (e Å-3
0.1356
1.069
+1.271, -0.596
1.028
+0.317, -0.177
1.058
+0.320, -0.213
1.035
+0.380, -0.247
)
+0.437, -0.394
a Previously reported (see ref 13a). b Previously reported (see ref 13b). c Unit cell contains two independent molecules of 9e and 80% of a disordered
2
2
2
2
2
toluene molecule. d R1 ) (Σ|Fo*| - |Fc|)/(Σ|Fo|). e wR2 ) [(Σw(Fo - Fc )2)/(Σw(Fo )2)]1/2
.
f GOF ) [(Σw(Fo - Fc )/(n - p)]1/2, where n ) number of
reflections and p ) number of parameters.
Table 2. Crystal Data for Pnictogenium Cations [Pn(RN)2C10H6][GaCl4] (10a-d), [P(PhN)2C10H6][OTf] (11b), and
[Sb(iPrN)2C10H6‚NHMe2][OTf] (15)
compound
10aa
10b
10cb,c
10d
11b
15b,d
formula
C16H20N2PGaCl4 C22H16N2PGaCl4 C17.75H22N2AsGaCl4 C22H16N2AsGaCl4 C23H16N2O3F3PS C38H54N6O6F6Sb2S2
molecular wt (g/mol)
cryst syst
space group
color
a (Å)
b (Å)
482.83
triclinic
P1h
550.86
monoclinic
P21/c
549.81
monoclinic
P21/n
594.81
monoclinic
P21/c
488.41
monoclinic
P21/n
1112.49
triclinic
P1h
red-orange
8.12(3)
11.36(4)
11.99(4)
64.86(5)
89.70(6)
78.86(6)
978(6)
red
brown
red
orange
yellow
10.133(3)
10.2962(16)
21.998(5)
90
96.612(9)
90
2279.7(10)
4
0.0335
7.233(2)
17.314(6)
19.580(7)
90
99.501(6)
90
2418.3(14)
4
0.0605
10.106(3)
10.307(3)
21.900(5)
90
95.71(2)
90
2269.8(10)
4
0.0428
0.1146
1.037
11.635(3)
10.954(3)
17.175(4)
90
91.358(3)
90
2188.3(10)
4
0.0447
0.1398
1.045
8.5648(13)
9.7606(15)
27.018(4)
81.973(2)
89.580(2)
81.727(2)
2213.0(6)
2
0.0379
0.0963
1.037
+0.850, -0.472
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
2
Re (I > 2σ(I))
wR2f (all data)
GOFg (all data)
∆F max and min (e Å-3
0.0526
0.1483
1.049
+0.830, -0.452
0.0905
1.037
+0.636, -0.247
0.1550
1.028
+0.875, -0.439
)
+0.722, -0.697
+0.423, 0.253
a Previously reported (see ref 13a). b Previously reported (see ref 13b). c Unit cell contains 25% of a disordered toluene molecule. d Unit cell contains two
independent units of 15. e R1 ) (Σ|Fo*| - |Fc|)/(Σ|Fo|). f wR2 ) [(Σw(Fo2 - Fc )2)/(Σw(Fo )2)]1/2
.
g GOF ) [(Σw(Fo2 - Fc )/(n - p)]1/2, where n ) number
2
2
2
of reflections and p ) number of parameters.
Table 3. Selected Bond Lengths (Å), Angles (deg), and 31P NMR Chemical Shifts (ppm) for New Compounds 9a-c, 9e, 10a-d,
11b, 14, and 15
compound
Pn-Xa
Pn-N(1)
Pn-N(2)
N(1)-Cnaph
N(2)-Cnaph
N-Pn-N
bend angleb
δ
31P NMR
ClP(iPrN)2C10H6 (9a)
ClP(PhN)2C10H6 (9b)
ClAs(iPrN)2C10H6 (9c)
ClSb(iPrN)2C10H6d (9e)
2.1723(9)
2.148(1)
2.2820(8)
2.392(2)
2.4141(16)
4.04(1)
3.258(7)
3.49(1)
3.20(1)
2.594(5)
2.056(4)
2.323(4)
2.313(4)
1.670(2)
1.678(2)
1.810(2)
2.021(5)
2.014(4)
1.609(8)
1.633(2)
1.762(7)
1.771(3)
1.635(2)
2.022(3)
1.997(4)
1.988(4)
1.670(2)
1.681(2)
1.812(2)
2.017(4)
2.020(4)
1.629(7)
1.634(2)
1.757(7)
1.765(3)
1.632(2)
2.028(4)
2.000(4)
1.991(4)
1.412(3)
1.422(3)
1.410(3)
1.396(7)
1.411(7)
1.410(9)
1.435(2)
1.437(11)
1.424(4)
1.431(3)
1.382(5)
1.424(6)
1.410(6)
1.409(3)
1.433(3)
1.413(3)
1.394(7)
1.405(6)
1.408(9)
1.434(2)
1.434(11)
1.423(4)
1.430(3)
1.391(6)
1.407(6)
1.419(6)
99.7(1)
98.9(1)
95.61(9)
86.5(2)
87.98(18)
105.4(3)
103.17(8)
101.4(3)
98.8(1)
31.7
32.1
31.9
39.6
34.9
2.2
5.5
3.9
6.4
4.0
102c
99c
[P(iPrN)2C10H6][GaCl4] (10a)
[P(PhN)2C10H6][GaCl4] (10b)
[As(iPrN)2C10H6][GaCl4] (10c)
[As(PhN)2C10H6][GaCl4] (10d)
[P(PhN)2C10H6][OTf] (11b)
(NMe2)Sb(iPrN)2C10H6 (14)
[Sb(iPrN)2C10H6·NHMe2][OTf]d (15)
239e
195e
102.78(11)
86.2(2)
93.0(2)
120c
42.0
26.0
18.1
92.77(17)
a Pnictogen-halogen bond length or closest pnictogen-halogen contact. b Angle between naphthalene plane and N-Pn-N plane. c C6D6. d Two independent
molecules in asymmetric unit. e CD2Cl2.
sequentially PnCl3 (Pn ) P or As: 1.3 equiv; Pn ) Sb: 1 equiv)
followed by NEt3 (2.6 equiv). The reaction mixture was stirred for
4 days, during which time a copious amount of white precipitate
formed, and the solution gradually turned colorless (P), yellow (As),
or orange (Sb). All volatiles were removed under vacuum, toluene
was added to the solid reaction mixture, and the solution was filtered
through a glass frit packed with Celite. After removal of volatiles
from the filtrate, the solid material obtained was recrystallized as
outlined next.
ClP(iPrN)2C10H6 (9a). X-ray quality, colorless crystals of 9a
(0.265 g, 70%) were obtained by placing a concentrated hexane
solution in the freezer at -20 °C overnight. 1H NMR (C6D6): 1.2
(dd, 3JHH ) 7 Hz, 4JP-H ) 2 Hz, 6H, CH3), 1.3 (dd, 3JHH ) 7 Hz,
4JP-H ) 0.5 Hz, 6H, CH3), 3.8 (doublet of septets, 3JP-H ) 18 Hz,

Diamidonaphthalene-Stabilized Pnictogenium Cations
Organometallics, Vol. 26, No. 20, 2007 4975
3JHH ) 7 Hz, 2H, CHMe2), 6.6 (d, 3JHH ) 8 Hz, 2H, HAr), 7.2 (t,
ClSb(PhN)2C10H6 (9f). Yellow-orange, fibrous crystals of 9f
(0.413 g, 67%) were obtained overnight by recrystallization from
a 50:50 toluene/hexane mixture at -20 °C. The crystals were not
3
3JHH ) 8 Hz, 2H, HAr), 7.3 (d, JHH ) 8 Hz, 2H, HAr). 13C{1H}
3
3
NMR (C6D6): 21 (d, JPC ) 15 Hz, CH3), 24 (d, JPC ) 21 Hz,
CH3), 51 (d, 2JPC ) 28 Hz, CHMe2), 109 (s, CHAr), 122 (s, CHAr),
127 (s, CHAr), 130 (s, CAr), 137 (s, CAr), 139 (d, JPC ) 5 Hz,
suitable for X-ray diffraction. 1H NMR (CD2Cl2): 6.5 (dd, 3JHH
)
2
4
3
8 Hz, JHH ) 1 Hz, 2H, HAr), 7.2 (t, JHH ) 8 Hz, 2H, HAr), 7.3
CAr). 31P{1H} NMR (C6D6): 102 (s). IR: 1612(11), 1575(5), 1517-
(16), 1324(13), 1301(12), 1249(16), 1192(15), 1178(12), 1168(11),
1141(8), 1087(8), 1050(9), 967(6), 943(11), 911(14), 895(14), 878-
(10), 815(3), 800(3), 784(4), 761(2), 697(7), 635(1), 586(13), 551-
(5). Anal. Calcd for C16H20N2PCl: C 62.64, H 6.57, N 9.13;
Found: C 62.37, H 6.30, N 9.24.
(d, JHH ) 8 Hz, 6H, HAr), 7.46-7.52 (m, 4H, HAr). 13C{1H}
3
NMR (CD2Cl2): 112 (s, CHAr), 119 (s, CAr), 121 (s, CHAr), 126.8
(s, CHAr), 127.1 (s, CHAr), 128 (s, CHAr), 131 (s, CHAr), 138
(s, CAr), 145.5 (s, CAr), 146.0 (s, CAr). IR: 1590(12), 1578(15),
1557(4), 1484(7), 1344(15), 1283(7), 1272(8), 1257(9), 1205(11),
1166(13), 1037(5), 1025(12), 915(10), 876(14), 810(3), 797(11),
757(1), 739(6), 695(2). Anal. Calcd for C22H16N2SbCl: C 56.75,
H 3.46, N 6.02; Found: C 56.46, H 3.99, N 5.84.
ClP(PhN)2C10H6 (9b). X-ray quality, colorless crystals of 9b
(0.815 g, 67%) were obtained overnight by recrystallization from
1
a 50:50 toluene/hexane mixture at -20 °C. H NMR (C6D6): 6.5
General Procedure for the Preparation of Pnictogenium
Gallate Salts 10a-d. To a solution of the appropriate diamido-
chloropnictine 9a-d (0.2 - 0.3 g) in 5 mL of toluene was added
a solution of GaCl3 (1 equiv) in 5 mL of toluene, causing immediate
precipitation of the corresponding pnictogenium gallate salt as a
powder. The solvent was removed by decantation, and the solid
was washed with 2 × 5 mL portions of hexane and then dried under
vacuum to yield 10a-d.
(d, 3JHH ) 8 Hz, 2H, HAr), 6.9-7.1 (m, 8H, HAr), 7.2 (d, 3JHH
)
3
8 Hz, 2H, HAr), 7.4 (d, JHH ) 8 Hz, 4H, HAr). 13C{1H} NMR
(C6D6): 112 (s, CHAr), 119 (s, CAr) 122 (s, CHAr), 127 (s, CHAr),
128.5 (d, 4JPC ) 3 Hz, CHAr), 129.3 (d, 3JPC ) 9 Hz, CHAr), 131
2
2
(s, CHAr), 136 (s, CAr), 140 (d, JPC ) 5 Hz, CAr), 142 (d, JPC
) 23 Hz, CAr). 31P{1H} NMR (C6D6): 99 (s). IR: 1572(13), 1288-
(14), 1275(14), 1209(15), 1159(15), 1055(14), 967(13), 907(12),
887(13), 860(10), 815(4), 786(5), 763(3), 756(3), 747(2), 727(3),
693(1), 634(8), 627(6), 615(10), 578(11), 540(7), 515(9). Anal.
Calcd for C22H16N2PCl: C 70.50, H 4.30, N 7.47; Found: C 70.43,
H 4.65, N 7.36.
[P(iPrN)2C10H6]GaCl4 (10a). The gallate salt 10a was obtained
as a dark purple powder (0.276 g, 86%). X-ray quality crystals
were obtained by placing a concentrated CH2Cl2 solution of 10a
1
in the freezer at -20 °C for 1 week. H NMR (CD2Cl2): 1.7 (dd,
ClAs(iPrN)2C10H6 (9c). X-ray quality, yellow crystals of 9c (0.80
3JHH ) 7 Hz, 4JPH ) 3 Hz, 12H, CH3) 4.5 (doublet of septets, 3JPH
3
3
g, 55%) were obtained overnight by recrystallization from a 50:50
) 11 Hz, JHH ) 7 Hz, 2H, CHMe2), 6.9 (d, JHH ) 8 Hz, 2H,
1
3
3
3
toluene/hexane mixture at -20 °C. H NMR (C6D6): 1.1 (d, JHH
) 7 Hz, 6H, CH3), 1.3 (d, 3JHH ) 6 Hz, 6H, CH3), 3.9 (septet, 3JHH
) 7 Hz, 2H, CHMe2), 6.6 (d, 3JHH ) 8 Hz, 2H, HAr), 7.2 (t, 3JHH
HAr), 7.4 (t, JHH ) 8 Hz, 2H, HAr), 7.6 (d, JHH ) 8 Hz, 2H,
HAr). 13C{1H} NMR (CD2Cl2): 23 (d, 3JPC ) 19 Hz, CH3), 56 (d,
2JPC ) 22 Hz, CHMe2), 111 (d, 3JPC ) 3 Hz, CHAr), 124 (d, 3JPC
) 5 Hz, CAr), 127 (s, CHAr), 128 (s, CHAr), 134 (d, 2JPC ) 8 Hz,
CAr), 137 (s, CAr). 31P{1H} NMR (CD2Cl2): 239 (s). IR: 1626-
(14), 1606(17), 1577(9), 1316(12), 1294(6), 1252(16), 1178(8),
1145(4), 1111(7), 1076(5), 1054(11), 1047(10), 1019(3), 975(15),
943(17), 918(13), 819(2), 809(6), 762(1), 621(12). Anal. Calcd for
C16H20N2PCl4Ga: C 39.80, H 4.17, N 5.80; Found: C 40.22, H
4.52, N 5.86.
3
4
) 8 Hz, 2H, HAr), 7.3 (dd, JHH ) 8 Hz, JHH ) 0.9 Hz, 2H,
HAr). 13C{1H} NMR (C6D6): 22 (s, CH3), 25 (s, CH3), 50 (s,
CHMe2), 108 (s, CHAr), 120.7 (s, CAr), 121.4 (s, CHAr), 127 (s,
CHAr), 138 (s, CAr), 142 (s, CAr). IR : 1923(13), 1821(18), 1740-
(15), 1727(14), 1640(18), 1606(9), 1569(8), 1519(14), 1297(12),
1249(16), 1331(12), 1129(8), 1165(10), 1104(10), 1081(10), 1048-
(7), 955(4), 878(6), 812(3), 870(4), 784(5), 762(1), 668(17), 632-
(2), 565(11), 520(8). Anal. Calcd for C16H20N2AsCl: C 54.79, H
5.75, N 7.99; Found: C 55.15, H 6.15, N 8.02.
[P(PhN)2C10H6]GaCl4 (10b). The gallate salt 10b was obtained
as a brown powder (0.434 g, 98%). X-ray quality crystals were
obtained by placing a concentrated CH2Cl2 solution of 10b in the
ClAs(PhN)2C10H6 (9d). Yellow, fibrous crystals of 9d (0.712
g, 70%) were obtained overnight by recrystallization from a 50:50
toluene/hexane mixture at -20 °C. The crystals were not suitable
1
freezer at -20 °C for 1 week. H NMR (CD2Cl2): 6.2 (broad s,
2H, HAr), 7.2 (broad s, 2H, HAr), 7.5 (broad s, 2H, HAr), 7.7
(broad s, 10H, HAr). 13C{1H} NMR: the fluxionality of this
compound, combined with its low solubility, prevented collection
of a 13C NMR spectrum with a good enough signal-to-noise ratio
to report a listing of peaks. 31P{1H} NMR (CD2Cl2): 195 (broad
singlet). IR: 1630(15), 1598(11), 1588(10), 1576(6), 1485(6), 1290-
(13), 1271(10), 1219(12), 1196(8), 1165(7), 1130(6), 1107(8), 1075-
(5), 1040(4), 999(10), 857(15), 845(14), 820(3), 754(2), 693(1),
545(7), 526(14), 513(9). Anal. Calcd for C22H16N2PCl4Ga: C 47.97,
H 2.93, N 5.09; Found: C 47.76, H 3.26, N 5.09.
1
3
for X-ray diffraction. H NMR (CD2Cl2): 6.4 (d, JHH ) 8 Hz,
2H, HAr), 7.2 (t, 3JHH ) 8 Hz, 2H, HAr), 7.3 (d, 3JHH ) 8 Hz, 2H,
HAr), 7.4-7.6 (m, 10H, HAr). 13C{1H} NMR (CD2Cl2): 111 (s,
CHAr), 119 (s, CAr), 122 (s, CHAr), 127 (s, CHAr), 128.6 (s,
CHAr), 129.0 (s, CHAr), 131 (s, CHAr), 137 (s, CAr), 142 (s, CAr),
143 (s, CAr). IR : 1613(18), 1590(13), 1567(7), 1486(10), 1289-
(12), 1273(14), 1256(15), 1210(14), 1165(11), 1073(18), 1047(9),
943(13), 932(7), 894(7), 862(18), 816(1), 808(6), 786(17), 759(5),
744(3), 727(4), 706(8), 697(2), 629(16), 622(10), 614(10). Anal.
Calcd for C22H16N2AsCl: C 63.10, H 3.85, N 6.69; Found: C 62.94,
H 4.11, N 6.45.
[As(iPrN)2C10H6]GaCl4 (10c). The gallate salt 10c was obtained
as a dark blue powder. As much of the solid as possible was
dissolved in 15 mL of CH2Cl2, and the solution was filtered and
placed in the freezer at -20 °C to yield dark blue crystals of 10c
after 1 week (0.17 g, 37%). X-ray quality crystals were obtained
by dissolving a very small amount of 10c in toluene and placing
ClSb(iPrN)2C10H6 (9e). X-ray quality, orange crystals of 9e (0.63
g, 38%) were obtained overnight by recrystallization from a 50:50
1
3
toluene/hexane mixture at -20 °C. H NMR (C6D6): 1.1 (d, JHH
) 6 Hz, 6H, CH3), 1.2 (d, 3JHH ) 6 Hz, 6H, CH3), 4.1 (septet, 3JHH
) 6 Hz, 2H, CHMe2), 6.7 (d, 3JHH ) 8 Hz, 2H, HAr), 7.3 (t, 3JHH
) 8 Hz, 2H, HAr), 7.4 (d, 3JHH ) 7 Hz, 2H, HAr). 13C{1H} NMR
(C6D6): 25 (s, CH3), 26 (s, CH3), 50 (s, CHMe2), 109 (s, CHAr),
121 (s, CHAr), 122 (s, CAr), 127 (s, CHAr), 138 (s, CAr), 145 (s,
CAr). IR: 2725(16), 1708(16), 1586(14), 1558(3), 1316(3), 1292-
(1), 1242(11), 1162(6), 1134(4), 1106(8), 1072(5), 1045(9), 958-
(10), 944(8), 930(10), 873(13), 854(13), 808(3), 780(12), 762(7),
753(2), 740(7), 630(15). Anal. Calcd for C16H20N2SbCl: C 48.34,
H 5.07, N 7.05; Found: C 47.77, H 5.47, N 6.68.
1
the solution in the freezer (-20 °C) for 2 weeks. H NMR (CD2-
Cl2): 1.7 (d, 3JHH ) 4 Hz, 12H, CH3) 4.5 (broad, 2H, CHMe2), 6.7
(broad, 2H, HAr), 7.3 (broad, 4H, HAr). 13C{1H} NMR: the
fluxionality of this compound, combined with its low solubility,
prevented collection of a 13C NMR spectrum with a good enough
signal-to-noise ratio to report a listing of peaks. IR: 2725(13), 2670-
(14), 1618(18), 1569(12), 1311(5), 1284(3), 1215(15), 1169(11),
1138(6), 1111(8), 1067(9), 1049(17), 961(10), 937(7), 811(4), 786-
(13), 777(16), 754(2), 734(1), 697(18), 613(14). Anal. Calcd for

4976 Organometallics, Vol. 26, No. 20, 2007
Spinney et al.
C16H20N2AsCl4Ga: C 36.48, H 3.83, N 5.32; Found: C 36.37, H
4.13, N 5.28.
and placed in the freezer at -20 °C overnight to yield yellow
1
3
crystals of 14 (1.82 g, 54%). H NMR (C6D6): 1.2 (d, JHH ) 7
Hz, 6H, CH3), 1.3 (d, 3JHH ) 7 Hz, 6H, CH3), 2.4 (s, 6H, NCH3),
[As(PhN)2C10H6]GaCl4 (10d). The gallate salt 10d was obtained
a purple powder (0.352 g, 83%). X-ray quality crystals were
obtained by placing a concentrated CH2Cl2 solution of 10d in the
freezer at -20 °C for 1 week. 1H NMR (CD2Cl2): one broad peak
in aryl region from 7.4 to 7.9 ppm. 13C{1H} NMR: the fluxionality
of this compound, combined with its low solubility, prevented
collection of a 13C NMR spectrum with a good enough signal-to-
noise ratio to report a listing of peaks. IR: 1619(13), 1589(12),
1569(8), 1482(6), 1341(13), 1285(14), 1272(8), 1223(16), 1200-
(12), 1167(10), 1125(11), 1073(14), 1046(4), 1025(15), 1003(15),
959(5), 819(2), 807(8), 768(7), 763(6), 757(9), 748(3), 693(1). Calcd
for C22H16N2AsCl4Ga: C 44.42, H 2.71, N 4.71; Found: C 44.10,
H 2.59, N 4.50.
Preparation of [P(iPrN)2C10H6]OTf (11a). ClP(iPrN)2C10H6 (9a)
(0.298 g, 0.97 mmol) and AgSO3CF3 (0.275 g, 1.1 mmol) were
weighed in the same vial. and 10 mL of toluene was added to the
solid mixture. After 1 h of stirring, the reaction mixture was filtered
through a glass frit packed with Celite. The filtrate was concentrated
and placed in the freezer at -20 °C overnight to yield bright red
crystals of 11a (0.274 g, 67%). The crystals were not suitable for
3
3
4.1 (septet, JHH ) 6 Hz, 2H, CHMe2), 6.7 (t, JHH ) 5 Hz, 2H,
HAr), 7.3 (d, JHH ) 5 Hz, 4H, HAr). 13C{1H} NMR (C6D6): 25
3
(s, CH3), 26 (s, CH3), 42 (s, NCH3), 50 (s, CHMe2), 107 (s, CHAr),
119 (s, CHAr), 122 (s, CAr), 127 (s, CHAr), 138 (s, CAr), 148 (s,
CAr). IR : 2373(16), 1893(17), 1692(18), 1563(1), 1387(2), 1321-
(3), 1296(4), 1171(5), 1138(5), 1108(9), 1073(6), 1047(10), 930-
(8), 868(12), 807(9), 781(11), 762(9), 748(7), 641(15), 631(14),
554(13). Anal. Calcd for C18H26N3Sb: C 53.23, H 6.45, N 10.35;
Found: C 53.44, H 6.33, N 10.03.
Preparation of [Sb(iPrN)2C10H6‚NHMe2]OTf (15). A Schlenk
flask containing a solution of (NMe2)Sb(iPrN)2C10H6 (14) (0.50 g,
1.2 mmol) in 20 mL of toluene was cooled in a dry ice/acetone
bath to -78 °C. A solution of triflic acid (0.11 mL, 1.2 mmol) in
5 mL of toluene was transferred into the flask via cannula, causing
an immediate color change from light to dark orange. The reaction
mixture was stirred at low temperature for an additional 20 min,
during which time a yellow solid precipitated. As the reaction
warmed to room temperature, the solid dissolved, returning the
reaction mixture to dark orange. All volatiles were removed,
resulting in an orange oil. The oil was dissolved in a 50:50 toluene/
hexane mixture and placed in the freezer at -20 °C overnight to
1
4
X-ray diffraction. H NMR (C6D6): 1.2 (dd, 3JHH ) 7 Hz, JPH
)
3
3
2 Hz, 12H, CH3) 3.8 (doublet of septets, JPH ) 14 Hz, JHH ) 7
Hz, 2H, CHMe2), 6.4 (d, 3JHH ) 8 Hz, 2H, HAr), 7.1 (t, 3JHH ) 8
1
yield yellow crystals of 15 (0.47 g, 68%). H NMR (C6D6): 1.4
3
(broad, 12H, CH3), 1.9 (s, 6H, NCH3), 4.0 (septet, JHH ) 6 Hz,
Hz, 2H, HAr), 7.2 (d, JHH ) 8 Hz, 2H, HAr) 13C{1H} NMR
3
2H, CHMe2), 6.3 (broad, 1H, NH), 6.5 (d, 3JHH ) 8 Hz, 2H, HAr),
(C6D6): 22 (d, 3JPC ) 19 Hz, CH3), 52 (d, 2JPC ) 28 Hz, CHMe2),
3
3
7.1 (t, JHH ) 8 Hz, 2H, HAr), 7.2 (d, JHH ) 8 Hz, 2H, HAr).
3
3
110 (d, JPC ) 2 Hz, CHAr), 120 (d, JPC ) 3 Hz, CAr), 120 (q,
13C{1H} NMR (C6D6): 25 (s, CH3), 38 (s, NCH3), 53 (s, CHMe2),
110 (s, CHAr), 121.2 (s, CHAr), 121.5 (s, CAr), 122 (q, JFC
1JFC ) 319 Hz, CF3), 123 (s, CHAr), 127 (s, CHAr), 136 (d, JPC
2
1
)
) 5 Hz, CAr), 137 (s, CAr). 31P{1H} NMR (C6D6): 142 (s). 19F
NMR (CH2Cl2): -78.3 (s). IR: 1625(17), 1577(5), 1391(10), 1324-
(15), 1291(7), 1232(7), 1213(8), 1193(11), 1173(8), 1145(9), 1133-
(12), 1114(13), 1075(13), 1013(6), 947(16), 916(16), 819(4),
810(11), 767(3), 635(1), 572(14), 559(13), 515(2). Anal. Calcd for
C17H20N2O3F3PS: C 48.57, H 4.80, N 6.66; Found: C 48.30, H
5.12, N 6.57.
320 Hz, CF3), 127 (s, CHAr), 138 (s, CAr), 145 (s, CAr). 19F NMR
(CH2Cl2): -78.8 (s).IR : 3167(19), 1912(14), 1832(17), 1807-
(16), 1723(15), 1603(11), 1559(1), 1510(12), 1405(18), 1329(9),
1317(8), 1291(7), 1218(6), 1113(6), 1158(6), 1062(5), 1021(4), 961-
(5), 943(6), 930(7), 876(4), 812(3), 780(10), 757(2), 636(8), 574-
(13). Anal. Calcd for C19H27N3O3F3SSb: C 41.02, H 4.89, N 7.55;
Found: C 40.45, H 4.54, N 7.27.
Preparation of [P(PhN)2C10H6]OTf (11b). ClP(PhN)2C10H6
(9b) (0.300 g, 0.80 mmol) and AgSO3CF3 (0.226 g, 0.88 mmol)
were weighed in the same vial, and 15 mL of toluene was added
to the solid mixture. After 3 h of stirring, the reaction mixture was
filtered through a glass frit packed with Celite. The filtrate was
concentrated and placed in the freezer at -20 °C overnight to yield
Results and Discussion
The diamidochloropnictines ClPn(RN)2C10H6 (9a-f) serve
as precursors for pnictogenium cation synthesis and are readily
available from the dehydrohalide coupling reactions of N,N′-
diisopropyl-1,8-diaminonaphthalene or N,N′-diphenyl-1,8-di-
aminonaphthalene with the appropriate pnictogen trichloride (eq
1). Triethylamine was used as an acid scavenger in all reactions,
and the colorless diamidochlorophosphines (9a,b), yellow
diamidochloroarsines (9c,d), and orange diamidochlorostibines
(9e-f) were obtained in good yields after stirring for 4 days at
room temperature. Formation of the diamidochloropnictines was
accompanied by a loss of symmetry for the bis(amido)-
1
bright red crystals of 11b (0.182 g, 47%). H NMR (C6D6): 6.4
(d, 3JHH ) 5 Hz, 2H, HAr), 6.9 (t, 3JHH ) 5 Hz, 2H, HAr), 7.0 (m,
3
3
2H, HAr), 7.07 (t, JHH ) 5 Hz, 4H, HAr), 7.14 (d, JHH ) 5 Hz,
3
2H, HAr), 7.4 (d, JHH ) 5 Hz, 4H, HAr). 13C{1H} NMR (C6D6):
112 (s, CHAr), 119 (s, CAr), 120 (q, 1JFC ) 320 Hz, CF3), 123 (s,
CHAr), 127 (s, CHAr), 128.7 (s, CHAr), 129.2 (s, CHAr), 130 (d,
3JPC ) 7 Hz, CHAr), 131 (s, CHAr), 136 (s, CAr), 138 (d, 2JPC
)
5 Hz, CAr), 140 (d, JPC ) 23 Hz, CAr). 31P{1H} NMR (C6D6):
118 (s). 19F NMR (CH2Cl2): -78.6 (s). IR: 1630(16), 1601(15),
1576(5), 1490(6), 1334(16), 1282(6), 1224(6), 1176(9), 1156(6),
1130(10), 1108(7), 1075(8), 1022(5), 997(12), 972(14), 848(17),
832(17), 814(4), 763(11), 754(2), 696(1), 637(3), 608(14), 547-
(13). Anal. Calcd for C23H16N2O3F3PS: C 56.56, H 3.30, N 5.74;
Found: C 55.70, H 3.43, N 5.53.
2
1
naphthalene framework in the H NMR spectra, which show
two distinct sets of resonances for the N-bound substituents as
expected for these rigid pyramidal species. For example, the
i
NMR spectra of the Pr compounds display two inequivalent
methyl groups, which are coupled to the methine CH groups,
and in the case of 9a with phosphorus. The structural details of
9a-c and 9e were further confirmed by single-crystal X-ray
analyses. Crystallographic data are listed in Table 1, and
structural views of 9a,c,e are presented in Figure 1. Selected
structural parameters and 31P NMR chemical shifts are detailed
in Table 3.
Preparation of (NMe2)Sb(iPrN)2C10H6 (14). A Schlenk flask
containing a solution of tris(dimethylamido)antimony (2.10 g, 8.3
mmol) in 30 mL of toluene was cooled in a dry ice/acetone bath to
-78 °C. A solution of 1,8-(iPrNH)2C10H6 (2.00 g, 8.3 mmol) in 10
mL of toluene was transferred into the flask via cannula, producing
a purple solution. The reaction mixture was stirred at low
temperature for an additional 30 min and then slowly allowed to
warm to room temperature, during which time the reaction mixture
turned from purple to orange, and NH(CH3)2 gas evolved. After
stirring for an additional 2 h, all volatiles were removed to give an
orange oil. The oil was dissolved in a 50:50 toluene/hexane mixture
The solid-state structures of ClP(iPrN)2C10H6 (9a) and ClP-
(PhN)2C10H6 (9b)22 exhibit nearly identical bond lengths and
(22) Thermal ellipsoid plot for this compound is provided in the
Supporting Information.

Diamidonaphthalene-Stabilized Pnictogenium Cations
Organometallics, Vol. 26, No. 20, 2007 4977
Figure 1. Thermal ellipsoid plots showing the molecular structures and partial atom numbering schemes for (a) ClP(iPrN)2C10H6 (9a), (b)
ClAs(iPrN)2C10H6 (9c), and (c) ClSb(iPrN)2C10H6 (9e).27 Hydrogen atoms have been omitted for clarity.
t
angles. Both compounds have relatively short P-Cl bonds (9a
P-Cl ) 2.1723(9) Å; 9b 2.148(1) Å), which are only slightly
longer than the P-Cl bond distance observed in phosphorus
trichloride (2.04 Å).23 There is no evidence for spontaneous
P-Cl bond heterolysis in solution to generate the corresponding
phosphenium cations, and the 31P NMR chemical shifts of 9a
(δ 31P ) 102 ppm) and 9b (δ 31P ) 99 ppm) are similar to
those reported for other diamidochlorophosphines.24 Both spe-
cies have pyramidal phosphorus centers (Σ P angles 9a ) 300.5-
(1)°; 9b ) 301.2(1)°) that are out of the plane formed by the
bis(amido)naphthalene ligand (bend angle 9a ) 31.7°; 9b )
32.1°).25 Nevertheless, the P-N bond lengths in 9a (P-N(1)
) P-N(2) ) 1.670(2) Å) and 9b (P-N(1) ) 1.678(2) Å;
P-N(2) ) 1.681(2) Å) are shorter than the benchmark P-N
single bond (1.800(4) Å)26 observed in H3NPO3-, indicating
that some degree of N-P π-overlap is present in these
compounds.
diazaarsolene (2-Cl, R) Bu, Pn )As; As-N ) 1.8045(12),
1.8057(12) Å).11b Similarly, the Sb-N bonds in 9e (Sb-N(1)
) 2.021(5) Å; Sb-N(2) ) 2.017(4) Å) are relatively short and
comparable to those in 2-chloro-1,3-di-t-butyl-1,3,2-diaza-
stibolene (2-Cl, R ) tBu, Pn )Sb; Sb-N ) 1.998(4), 2.000(4)
Å)11b and in cyclo-[Me2Si(NtBu)2SbCl] (3-Cl, R ) Bu, Pn )
t
Sb; Sb-N ) 1.995(5) Å).12
In a series of diamidochloropnictines reported by Gudat and
co-workers (2-Cl, R ) tBu, Pn ) P, As, Sb), the Pn-Cl bonds
in the compounds actually decrease in length with an increase
in the size of the pnictogen atom (P-Cl ) 2.6915(4) Å; As-
Cl ) 2.6527(4) Å; Sb-Cl 2.6460(15) Å).11b While this trend
is counter to that expected based on the respective atomic radii
of the atoms, it was justified by suggesting that the stibenium
cation is the best chloride acceptor of the series, while the
phosphenium cation is the poorest. The reverse trend is observed
in the diamidonaphthalene-based series ClPn(iPrN)2C10H6 (9a,c,e),
where the Pn-Cl bond lengths increase with the size of the
pnictogen atom (P-Cl ) 2.1723(9) Å; As-Cl ) 2.2820(8) Å;
Sb-Cl ) 2.392(2) Å). Combining this observation with the
previous explanation leads to a reversal of the chloride acceptor
ordering in this series with the stibenium cation as the poorest
chloride acceptor, while the phosphenium cation appears to be
the better chloride acceptor. As discussed next, this proposition
contradicts the respective reactivities of the diamidochloro-
pnictines, ClPn(RN)2C10H6 (9a-f). Also of note, the Sb atoms
t
in the 1,3,2-diazastibolene (2-Cl, R ) Bu, Pn ) Sb) display
intermolecular contacts between the Sb center and the halogen
atom of a neighboring molecule, forming zigzag chains of pairs
of Sb and Cl atoms in the solid state. No intermolecular contacts
within the sum of the van der Waals radii are present to the Sb
atom in ClSb(iPrN)2C10H6 (9e).
The diamidochloroarsine ClAs(iPrN)2C10H6 (9c) and the
diamidochlorostibine ClSb(iPrN)2C10H6 (9e)27 are structurally
similar to the analoguous phosphine 9a; however, with the
increasing size of the pnictogen center, the N(1)-Pn-N(2) angle
(P 99.7(1)°; As 95.61(9)°; Sb 86.5(2)°) becomes more acute,
and the Pn-Cl moiety moves further out of the plane of the
bis(amido)naphthalene ligand (bend angle: P 31.7°; As 31.9°;
Sb 39.6°). The As-N bonds in 9c (As-N(1) ) 1.810(2) Å;
As-N(2) ) 1.812(2) Å) lie at the lower end of the known range
of As-N bond distances in diamidochloroarsines (1.84 ( 0.04
Å)8 and compare well with those in 2-chloro-1,3-di-t-butyl-1,3,2-
(23) Corbridge, D. E. C. The Structural Chemistry of Phosphorus;
Elsevier: Amsterdam, 1974.
(24) Burford, N.; Cameron, T. S.; Conroy, K. D.; Ellis, B.; MacDonald,
C. L. B.; Ovans, R.; Phillips, A. D.; Ragogna, P. J.; Walsh, D. Can. J.
Chem. 2002, 80, 1404.
(25) Bend angle is measured between the plane of the naphthalene group
and the N-Pn-N plane.
(26) Cameron, T. S.; Chan, C.; Chute, W. J. Acta Crystallogr., Sect. B:
Struct. Sci. 1980, 36, 2391.
(27) For simplicity, discussion has been limited to only one of the two
independent units of 9e in the unit cell. There are no significant differences
in the bond lengths and angles between these two species.
The phosphenium salts [P(RN)2C10H6][GaCl4] (10a,b) and
arsenium salts [As(RN)2C10H6][GaCl4] (10c,d) are readily
accessible from pnictogen-chlorine bond heterolysis of 9a-d

4978 Organometallics, Vol. 26, No. 20, 2007
Spinney et al.
Figure 2. Thermal ellipsoid plot showing the molecular structures and partial atom numbering schemes for the phosphenium cations in (a)
[P(iPrN)2C10H6]GaCl4 (10a) and (b) [P(PhN)2C10H6]GaCl4 (10b) and arsenium cations in (c) [As(iPrN)2C10H6]GaCl4 (10c) and (d) [As-
-
(PhN)2C10H6]GaCl4 (10d). GaCl4 anions and H atoms have been omitted for clarity.
using gallium trichloride (eq 2). Addition of GaCl3 to a toluene
solution of ClP(iPrN)2C10H6 (9a) or ClP(PhN)2C10H6 (9b) caused
immediate precipitation of a dark purple (10a) or brown solid
(10b), which when dissolved in CH2Cl2 exhibited 31P NMR
chemical shifts of 235 and 195 ppm, respectively. These values
are similar to those reported for other N-heterocyclic phosphe-
nium cations.4 Similarly, the addition of GaCl3 to toluene
solutions of ClAs(iPrN)2C10H6 (9c) and ClAs(PhN)2C10H6 (9d)
resulted in immediate precipitation of the respective arsenium
salts, [As(iPrN)2C10H6][GaCl4] (10c) and [As(PhN)2C10H6]-
[GaCl4] (10d), as dark blue and purple solids, respectively. The
arsenium salts are somewhat more soluble than their phosphe-
nium counterparts, and 10c can be recrystallized from toluene.
Toluene solutions of the phosphines 9a,b also react rapidly
with 1 equiv of silver triflate (AgOTf, OTf ) triflate or
CF3SO3-) to generate the triflate salts [P(iPrN)2C10H6][OTf]
(11a) and [P(PhN)2C10H6][OTf] (11b). The dark red compounds
are soluble in arene solvents and have 31P NMR chemical shifts
of 142 ppm (11a) and 119 ppm (11b) in C6D6. The 31P NMR
resonances of 11a (179 ppm) and 11b (130 ppm) appear at lower
fields in CD2Cl2, suggesting that significant contact occurs
between the phosphorus cations and the triflate anions in less
polar solvents. In contrast, the diamidochloroarsines 9c,d are
slow to react with both silver triflate and trimethylsilyltriflate,
and the reactions produced mixtures of products that could not
be separated. Reaction of 9c with silver tetrafluoroborate also
produced multiple products, but purple crystals of the tetrafluo-
roborate salt [As(iPrN)2C10H6][BF4] (12) could be isolated from
the reaction mixture.
at low temperatures. Trimethylsilyltriflate did not react with 9e
at room temperature, and heating 9e with Me3SiOTf in toluene
at 100 °C for 12 h produced a mixture of products that could
not be separated. Attempts to prepare the desired stibenium
cations with the silver salts AgOTf and AgBF4 were also
unsuccessful.
The cations in salts 10a-d represent rare examples of six-
membered N-heterocyclic phosphenium and arsenium cations
possessing π-conjugated carbon backbones.17 The solid-state
structures of the pnictogenium salts [Pn(RN)2C10H6][GaCl4]
10a,b (Pn ) P, R ) iPr, Ph) and 10c,d (Pn ) As, R ) iPr, Ph)
were determined by X-ray crystallography, and the respective
cations are depicted in Figure 2. Crystallographic data are listed
in Table 2, and selected structural parameters and 31P NMR
chemical shifts are detailed in Table 3. In [P(iPrN)2C10H6]-
[GaCl4] (10a), the closest contacts between the dicoordinate
phosphorus atom and the chlorine atoms of the anion are greater
than 4 Å in length, well outside the sum of the van der Waals
radii for phosphorus and chlorine (3.6 Å).28 The gallate anion
is in closer proximity to the phosphenium cation in [P(PhN)2-
C10H6][GaCl4] (10b), with the shortest P-Cl contact being
3.258(7) Å. This difference in cation-anion interaction is likely
a result of the less basic aryl substituted ligand framework of
10b, which should provide less effective stabilization of the low-
coordinate, cationic phosphorus center. Similar features were
observed with the arsenium cations: the ion pair is further
separated in [As(iPrN)2C10H6][GaCl4] (10c) (closest As-Cl
contact 3.49(1) Å) than in the aryl substituted analogue [As-
(PhN)2C10H6][GaCl4] (10d) (As-Cl ) 3.201(6) Å). The closer
approach of the gallate anions to the arsenium cations (10c,d)
Unexpectedly, the addition of GaCl3 or AlCl3 to toluene
solutions of the diamidochlorostibine species 9e,f resulted in
the precipitation of metallic antimony from the reaction, even
(28) Bondi, A. J. Phys. Chem. 1964, 68, 441.

Diamidonaphthalene-Stabilized Pnictogenium Cations
Organometallics, Vol. 26, No. 20, 2007 4979
as compared to the phosphenium cations (10a,b) can be
accounted for by the less effective π-overlap between As and
N, as compared to P and N, leaving the arsenic centers in 10c,d
more electron deficient than the corresponding phosphorus
centers in 10a,b.
Structural features that are associated with the formation of
the pnictogenium cations are a contraction of the Pn-N bonds
and the formation of a more planar heterocyclic framework,
indicating the presence of increased Pn-N π-bonding in the
coordinatively unsaturated species. The P-N bonds in the
phosphenium salts [P(iPrN)2C10H6]GaCl4 (10a) (P-N(1) )
1.609(8) Å; P-N(2) ) 1.629(7) Å) and [P(PhN)2C10H6]GaCl4
(10b) (P-N(1) ) 1.633(2) Å; P-N(2) ) 1.634(2) Å) are shorter
than those in the respective phosphines 9a (P-N(1) ) P-N(2)
) 1.670(2) Å) and 9b (P-N(1) )1.678(2) Å; P-N(2) ) 1.681-
(2) Å) and those in the five-membered aromatic phosphenium
cation 2 (R ) tBu, Pn ) P; P-N ) 1.660(2)Å).29 The decrease
of the P-N bonds in 10a,b is not accompanied by any
significant changes in the N-C and C-C bonds in the PN2C3
heterocyclic ring (Table 3), but the N(1)-P-N(2) angles in the
phosphenium cations (10a 105.4(3)°; 10b 103.17(8)°) are several
degrees wider than those in the corresponding chlorophosphines
(9a 99.7(1)°; 9b 98.9(1)°), perhaps reflecting a modified
hybridization (sp2 vs sp3) of the dicoordinate phosphorus atoms.
The N-isopropyl substituted phosphenium cation 10a is es-
sentially planar (bend angle ) 2.2°), while the N-phenyl
substituted compound is slightly distorted from planarity (bend
angle ) 5.5°). This is likely only a consequence of crystal
packing as all of the other metrical parameters in the two
structures are nearly identical. The structure of the phophenium
triflate salt [P(PhN)2C10H6]OTf (11b) was also determined by
X-ray crystallography and demonstrates that the identity of the
anion does not greatly affect the structural features of the
corresponding cation.22 The phosphenium cation in the triflate
salt (11b) is essentially identical to that in the gallate salt (10b)
and actually exhibits a greater degree of planarity (bend angle
) 4.0°) despite the closer approach of the triflate anion to the
low-coordinate phosphorus center (P-O ) 2.594(5) Å).
Likewise, the As-N bonds in the arsenium salts [As-
(iPrN)2C10H6]GaCl4 (10c) (As-N(1) ) 1.762(7) Å; As-N(2)
) 1.757(7) Å) and [As(PhN)2C10H6]GaCl4 (10d) (As-N(1) )
1.771(3) Å; As-N(2) ) 1.765(3) Å) are shorter than those in
the starting arsine 9c (As-N(1) ) 1.810(2) Å; As-N(2) )
1.812(2) Å) and those in the five-membered aromatic arsenium
cation 2 (R ) tBu, Pn ) As; As-N ) 1.8377(14), 1.8271(13)
Å).11b This suggests that the bis(amido)naphthalene frameworks
are more electron-rich than the corresponding bis(amido)alkene
frameworks; however, it could also be a consequence of a
change in ring size. Like the phosphorus analogues, the
N-isopropyl substituted arsenium cation 10c exhibits a greater
degree of planarity (bend angle ) 3.9°) than its N-phenyl
substituted counterpart 10d (bend angle ) 6.4°).
Figure 3. Thermal ellipsoid plot showing the molecular structure
and partial atom numbering scheme of (Me2N)Sb(iPrN)2C10H6 (14).
H atoms have been omitted for clarity.
good yield as a yellow crystalline solid. Like the chloro analogue
1
9e, the H NMR spectrum of 14 exhibited two signals for the
iPr methyl groups consistent with the proposed pyramidal Sb
center. The structural details of 14 were further confirmed with
single-crystal X-ray analysis, and the results are shown in Figure
3. Compound 14 exhibits nearly identical metrical parameters
to those observed in the structure of 9e, with the Sb-Cl group
replaced with an Sb-NMe2 bond (Sb-N(3) ) 2.056(4) Å)
(Table 3). Compounds 9e,f and 14 represent the first reported
examples of six-membered N-heterocyclic stibines.
We anticipated that the addition of triflic acid (HOTf) to 14
would protonate the dimethylamido group, liberate NHMe2, and
generate a stibenium triflate salt; however, no gas evolution was
observed in the reaction of 9 with HOTf.30 The 1H NMR
spectrum of the yellow crystalline product 15 indicated the
presence of NHMe2, which we anticipated to be coordinated to
the stibenium center. Prolonged exposure of solid samples of
15 to vacuum at room temperature did not remove the NHMe2
ligand. In contrast to our NMR observations for 9e and 14, the
iPr substituents of 15 gave only a single resonance for the methyl
groups in both the 1H and 13C NMR spectra of this compound,
suggesting either a symmetrical or a fluxional structure for this
compound.
The inability to generate the stibenium analogue of 10a-d
using halide abstraction reactions of 9e,f with Lewis acids such
as GaCl3, AlCl3, Me3SiOTf, or silver salts prompted the
exploration of an alternative synthetic strategy summarized in
eq 3.13b For the transamination reaction, Sb(NMe2)3 and 1,8-
bis(isopropylamino)naphthalene were combined at -78 °C and
then slowly allowed to warm to room temperature. During this
reaction, the initial purple solution gradually turned orange, and
evolution of NHMe2 gas was apparent. The new heteroleptic
triamidostibene, (Me2N)Sb(iPrN)2C10H6 (14) was isolated in
The identity of 15 was further confirmed by X-ray crystal-
lography (Figure 4).31 The structural changes that are observed
with the formation of the dimethylamine-stabilized stibenium
(30) An example of this approach employed for generation of a
phosphenium cation can be found in: Dahl, O. Tetrahedron Lett. 1982,
23, 1493.
(31) For simplicity, discussion has been limited to only one of the two
independent units of 15 in the unit cell. There are no significant differences
in the bond lengths and angles between these two species.
(29) Burck, S.; Gudat, D.; Nieger, M.; Du Mont, W.-W. J. Am. Chem.
Soc. 2006, 128, 3946.

4980 Organometallics, Vol. 26, No. 20, 2007
Spinney et al.
Both N-heterocyclic phosphenium and arsenium cations
display interesting cation-cation interactions in the solid state,
which appear to be primarily dependent on the identity of the
nitrogen substituents rather than the identity of the group 15
element. As illustrated in Figure 6, the extended structures of
the N-isopropyl substituted phosphenium and arsenium cations
consist of dimers of π-stacked, antiparallel oriented cations. In
the case of 10a, the phosphenium center and gallate counterion
are well-separated, whereas in the As analogue, 10c, the
pnictogenium center displays two long contacts between the
arsenium center and two chlorine atoms located on a single
tetrachlorogallate anion. The π-stacking, cation-cation contacts
in the arsenium dimer are 3.35(1) Å in length (indicated in
yellow in Figure 6b), whereas those in the phosphenium system
are somewhat longer (3.47(1) Å). Cation-cation interactions
between pnictogenium cations (16) have previously been
observed by Burford and co-workers in dimers of the five-
membered arsenium cation 4 (R ) Me, Pn ) As);7 however,
this dimerization occurs through As-N σ-bonds rather than
through π-interactions. Interestingly, the related six-membered
arsenium cations 5 (R ) Me, Pn ) As) do not form similar
dimers.8
Figure 4. Thermal ellipsoid plot showing the molecular structure
and partial atom numbering scheme of [Sb(iPrN)2C10H6‚NHMe2]-
OTf (15) (only one of the two independent cations in the unit cell
is shown). H atoms and triflate anion have been omitted for clarity.
cation 15 from 14 parallel those observed in the formation of
10a-d and support our protonation approach to stibenium cation
generation. Specifically, protonation of the dimethylamido
nitrogen leads to a substantial increase in the Sb-N(3) bond
length to 2.323(4) Å. Concomitant with this is a slight decrease
in the Sb-N (napthalene) bond lengths (Sb-N(1) ) 1.997(4)
Å; Sb-N(2) ) 2.000(4) Å) to values that are directly compa-
rable to the those in the two previously reported examples of
N-heterocyclic stibenium cations: [H2C2(NtBu)2Sb] SbCl4 (2Sb,
t
R ) Bu, av. Sb-N ) 2.024(2) Å)11b and [Me2Si(NtBu)2Sb]-
AlCl4 (3Sb, R ) tBu, av. Sb-N ) 2.00(2) Å).12 The Sb-N(3)
bond length in 15 is significantly shorter than that observed in
the NHMe2 adduct of the neutral diamidochlorostibine [SbCl-
(µ-NtBu)]2 (Sb-N ) 2.524(3) Å),32 supporting the existence
of a more electron-deficient cationic Sb center in [Sb-
(iPrN)2C10H6‚NHMe2]OSO2CF3.
Consistent with the NMR observations, and as anticipated,
the Sb(iPrN)2C10H6 framework adopted a more planar geometry
as compared to 9e or 14. As well, the N(1)-Sb-N(2) angle
observed in 15 (93.0(2)°) has increased by several degrees from
that observed in the trisamidostibine 14 (86.2(2)°) and 9e
(86.5(2)°). This observation parallels the change in the N-Pn-N
(Pn ) P, As) angle that was observed with the conversion of
diamidochloropnictines to the pnictogenium cations. It should
be noted that the base-stabilized stibenium cation in 15 is well-
separated from the triflate anion, the closest Sb-O contact being
2.823(9) Å in length.
The N-phenyl substituted phosphenium and arsenium cations,
10b,d, exhibit a different form of cation-cation interaction in
the solid state, forming an extended network of zigzag chains
as shown in Figure 7. In these head-to-tail chains, the cations
are oriented in a perpendicular fashion with the pnictogenium
center in one cation directed toward the centroid of a naphtha-
lene ring on an adjacent cation. In the structure of 10b (Figure
7a), the P-centroid distance of 3.426(7) Å is just beyond the
sum of the van der Waals radii for phosphorus and carbon. As
was the case with the N-isopropyl substituted cations, the
arsenium cations of 10d approach each other more closely with
an As-centroid separation of 3.228(6) Å. Similar π-interactions
with low-coordinate phosphorus centers are rare but not
unprecedented in the literature; the phosphadiazonium cation,
17, forms π-complexes with several arene solvents, where the
length of the P-arene contact is dependent on the π-donor
ability of the arene.34 These interactions are analogous to those
reported between tricoordinate As(III) centers and arenes.35
To examine the energetics of the interactions between the
phosphenium cations in the stacked dimers of 10a, full geometry
optimizations were performed at the MP2/3-21G(d) level. These
calculations revealed that the cation dimer exists in a minimum
with a nominal separation between naphthalene rings of 3.25
Å (cf. 3.47(1) Å exptl). A detailed potential energy curve was
Computational Studies. The results of density functional
theory calculations on the pnictogenium components of 10a-
i
d, [E(RN)2C10H6]+ (E ) P or As, R ) Pr or Ph) indicate that
the nitrogen lone pairs are delocalized into the pnictogen pz-
orbital, forming strong π-bonding interactions in the heterocyclic
ring. For the two isopropyl-based species, 10a,c, the P/As lone
pair of electrons is localized on the group 15 center and resides
in a low-energy (HOMO - 4) orbital that is composed of
substantial s-character and is oriented in the molecular plane
and points away from the ring (Figure 5). An analogous bonding
situation was revealed for the compounds 10b,d with phenyl
substitutents. In these two cations, the in-plane lone pairs were
found to reside in a slightly lower HOMO - 9 level.33
(33) Figures of the LUMO and pnictogenium lone pair orbitals for 10a,
10b, and 10d are provided in the Supporting Information.
(34) (a) Burford, N.; Clyburne, J. A. C.; Bakshi, P. K.; Cameron, T. S.
Organometallics 1995, 14, 1578. (b) Burford, N.; Clyburne, J. A. C.; Bakshi,
P. K.; Cameron, T. S. J. Am. Chem. Soc. 1993, 115, 8829.
(35) (a) Schmidbaur, H.; Bublak, W.; Huber, B.; Mu¨ller, G. Angew.
Chem., Int. Ed. Engl. 1987, 26, 234. (b) Probst, T.; Steigelmann, O.; Riede,
H.; Schmidbaur, H. Chem. Ber. 1991, 124, 1089. (c) Schmidbaur, H.;
Nowak, R.; Steigelmann, O.; Mu¨ller, G. Chem. Ber. 1990, 123, 1221.
(32) Edwards, A. J.; Leadbeater, N. E.; Paver, M. A.; Raithby, P. R.;
Russell, C. A.; Wright, D. S. J. Chem. Soc., Dalton Trans. 1994, 1479.

Diamidonaphthalene-Stabilized Pnictogenium Cations
Organometallics, Vol. 26, No. 20, 2007 4981
Figure 5. Orbital contour plots of As(iPrN)2C10H6]GaCl4 (10c) showing the LUMO (left) and As-centered lone pair HOMO-4 (right)
obtained from DFT calculations. Colors in these representations indicate the relative orbital phases. Compounds 10a,b,d displayed analogous
orbitals with similar configurations.33
Figure 6. Representations of the π-stacked cation-cation interactions (dimers) that form in extended structures of (a) P(iPrN)2C10H6]-
GaCl4 (10a) and (b) As(iPrN)2C10H6]GaCl4 (10c). H atoms on the isopropyl groups have been eliminated for clarity. Short contacts (less
than sum of van der Waals radii) are shown in yellow.
Figure 7. Representations of a portion of the extended, head-to-tail cation chains observed for (a) [P(PhN)2C10H6]GaCl4 (10b) and (b)
[As(PhN)2C10H6]GaCl4 (10d). H atoms have been omitted for clarity. Short contacts (less than sum of van der Waals radii) are shown in
yellow.
also calculated at the MP2/6-31G(d) level by incrementing the
separation between rigid cation monomers along a vector
perpendicular to the naphthalene rings (see Figure 6a). The
calculated energies obtained from the scan are plotted in Figure
8. These calculations revealed that the stacked cation dimer of
complex 10a exists in a metastable minimum 22.5 kcal/mol

4982 Organometallics, Vol. 26, No. 20, 2007
Spinney et al.
chlorogallate anion was present, the stabilities were reversed
with the T-shaped structure approximately 11.4 kcal/mol more
stable than the π-stacked dimer. In this case, the structures are
stable with respect to dissociation as a result of the counterion
simultaneously stabilizing two arsenium cations.
From this analysis, we conclude that the different cation-
cation interactions observed in the crystal structures for the two
substituents arise principally from the steric differences between
the isopropyl groups in 10a,c and the phenyl groups in 10b,d.
The phenyl substituents do not allow a close enough approach
of the cations along the π-stacking direction, thus reducing the
stability provided by charge transfer and resulting in the
alternative T-shaped head-to-tail structure with Pn‚‚‚π interac-
tions that was observed.
Conclusion
In conclusion, the library of known N-heterocyclic phos-
phenium, arsenium, and stibenium cations has been expanded
to include examples supported by N,N′-disubstituted-1,8-dia-
midonaphthalene (R2DAN2-) ligation. These differ from the
previously reported cations 2-6 in that the dicoordinate
pnictogen atom is included in a six-membered ring forming part
of an extended π-conjugated framework. The N-heterocyclic
phosphenium and arsenium cations are readily prepared via
pnictogen-chlorine bond heterolysis from the corresponding
diamidochloropnictines 9a-d; however, this procedure could
not be extended to the heavier pnictogen antimony. Circumvent-
ing the usual halide abstraction route, the base-stabilized
stibenium cation 15 was generated using a novel synthetic route
involving protonation of an amido substituent. This reaction
should be generally applicable to the synthesis of other low-
coordinate pnictogen compounds.
The novel topology and electronic framework of the phos-
phenium and arsenium cations 10a-d results in interesting
substitution-dependent cation-cation interactions in the solid
state. The N-isopropyl substituted cations 10a,c form dimers
through naphthyl π-stacking, while the N-phenyl substituted
cations 10b,d form extended zigzag chains through pnictogen-
naphthalene π-interactions. Computational studies indicate that
the π-stacked conformation, bound by dipole-dipole and
dispersion interactions, is actually more energetically favorable
than the chain structure; however, the steric demand of the
phenyl ligands in 10b,d impedes dimer formation. The Lewis
amphoterism exhibited by the pnictogenium cations make them
interesting ligands for transition metal coordination chemistry,
and investigations in this area are currently underway.
Figure 8. Potential energy curve showing the dissociation of
phosphenium cation dimer in 10a along the vector perpendicular
to the naphthalene rings. Energies are relative to twice the monomer
energy.
higher in energy relative to the separated cation monomers. The
barrier to dissociation is 12.1 kcal/mol and occurs at a maximum
separation of 5.25 Å. Additional calculations at selected points
along the potential curve using MP2/6-311G(d) verified the
smaller basis set results. The stacked cations are bound by
dipole-dipole and dispersion interactions, and the metastability
in the dimer complex can be understood as arising from the
contribution of charge transfer states to the wavefunction of
the dimer. The repulsive Coulombic interactions of the cation
dimer complex, C+-C+, which occur at large separations, are
overcome by a highly attractive charge transfer C2+-C state at
short separations. This combination of attractive and repulsive
forces results in a minimum in the potential energy curve (Figure
8) and creates a metastable system.
To make a more direct comparison between the cation
structures bearing isopropyl and phenyl substituents, an opti-
mized arsenium cation bearing N-methyl groups, [As(MeN)2-
C10H6]+, was used as a starting point. The goal was to employ
a single, small substituent in an effort to reduce the role of sterics
in this analysis. This species was then placed in the relative
positions observed in the crystal structures of 10b,d.36 Single-
point energies were then calculated for the π-stacked structure
observed for 10b and for the head-to-tail, T-shaped structure
of 10d both with and without one GaCl4- counterion. The results
indicated that, in the absence of the tetrachlorogallate anion,
the π-stacked structure is more stable than the T-shaped structure
by approximately 10.3 kcal/mol. This suggests that in terms of
cation-cation interactions, the charge transfer states that allow
formation of the metastable π-stacked structure contribute more
to the cation-cation binding than does the pnictogen interaction
with the naphthalene π-orbitals. In contrast, when the tetra-
Acknowledgment. This work was supported by the NSERC.
H.A.S. is the recipient of an NSERC Postdoctoral Fellowship.
G.A.D. thanks the Centre of Excellence in Integrated Nanotools
for access to computational resources.
Supporting Information Available: CIF files for 9a-c, 9e,
10a-d, 11b, 14, and 15. LUMO and pnictogenium lone pair orbitals
for 10a,b,d. Results of HOMO-LUMO transition calculations for
π-stacked pnictogenium complexes. Thermal ellipsoid plots for 9b
and 11b. NMR data for N,N′-diphenyl-1,8-diaminonaphthalene. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(36) Cation model used for these calculations was positioned to give
the best fit with the cation positions in the crystal structures. This fitting
procedure placed the atoms of the model structures within 0.1 Å of the
corresponding atoms in the crystal structure. The single-point energy
calculations were performed using MP2/6-31+G(d).
(37) Sheldrick, G. M. SHELXTL 6.12; Bruker AXS: Madison, WI, 2001.
OM7004436