Synthesis, structure, and reactions of (acylimino)triaryl-λ5-bismuthanes: First comparative study of the (acylimino)pnictorane series

Article abstract of DOI:10.1021/ja003623l

The synthesis, structure, and reactions of (acylimino)triaryl-λ⁵-bismuthanes and a comparative study of the structure and reactivity of a series of (acylimino)pnictoranes are reported. Treatment of ortho-substituted triarylbismuth dichlorides 1 (Ar₃BiCl₂; Ar = 2-MeC₆H₄, 2-MeOC₆H₄, 2,4,6-Me₃C₆H₂) with amides 2 (H₂-NCOR; R = CF₃, CCl₃, 3,5-(CF₃)₂C₆H₃) in the presence of 2.2 equiv of KO-t-Bu in dichloromethane afforded (acylimino)triaryl-λ⁵-bismuthanes 3 (Ar₃Bi=NCOR) in yields of 77-96%. The ortho-substituted aryl ligands and the electron-withdrawing N-substituents afford kinetic and thermodynamic stabilization, respectively, to the reactive Bi=N bond. The structures and properties of a series of (acylimino)pnictoranes (Ar₃M=NCOR and H₃M=NCOCF₃; M = P, As, Sb, Bi) are compared by IR and ¹³C and ¹⁵N NMR, X-ray crystallography, and ab initio molecular orbital calculations. It was found that the contribution of the M⁺-N=C-O^- canonical form becomes more prominent and the single-bond character of the M=N bond increases progressively as the pnictogen atom becomes heavier. The Bi=N bond of (acylimino)-λ⁵-bismuthanes 3 possesses a highly polarized single-bond character, probably due to the differences in orbital size and electronegativity between the bismuth and nitrogen atoms. Thermal decomposition of (aroylimino)triaryl-λ⁵-bismuthane 3f (o-Tol₃Bi=NCOAr; Ar = 3,5-(CF₃)₂C₆H₃) produces a gel in dry conditions or aniline 12 (ArNH₂) in slightly wet conditions with a good recovery of tris(2-methylphenyl)bismuthane (4a). It is likely that the aryl isocyanate 13 (ArNCO) is produced during the thermolysis via a concerted C → N migration of the Ar group with an elimination of the triarylbismuthonio group as bismuthane 4a. (Acylimino)triaryl-λ⁵-bismuthanes 3 oxidize 1,1,2,2-tetraphenylethanediol, benzenethiol, methanol, and ethanol to benzophenone, diphenyl disulfide, methyl formate, and acetaldehyde, respectively, in two different reaction pathways depending on the structure of the substrates. Compound 3d (o-Tol₃Bi=NCOCCl₃) transfers the nitrenoid moiety to triphenylphosphane, triphenylarsane, and tris(2-methylphenyl)stibane to give the corresponding (acylimino)pnictoranes (Ar₃M=NCOCl₃; M = P, As, Sb) and 4a, suggesting that 3d is thermodynamically much less stable than their lighter pnictogen counterparts. The copper-catalyzed decomposition of 3 (o-Tol₃Bi=NCOR) afforded N-acyl-o-toluidines 18 (o-TolNHCOR) via a Bi → N migration of the tolyl group. The observed reactivities of (acylimino)triaryl-λ⁵-bismuthanes 3 demonstrate a good leaving ability of the bismuthonio group.

Full text of DOI:10.1021/ja003623l

10954
J. Am. Chem. Soc. 2001, 123, 10954-10965
Synthesis, Structure, and Reactions of
(Acylimino)triaryl-λ5-bismuthanes: First Comparative Study of the
(Acylimino)pnictorane Series
Yoshihiro Matano,*,† Hazumi Nomura,† Hitomi Suzuki,†,‡ Motoo Shiro,§ and
Haruyuki Nakano¶
Contribution from the Department of Chemistry, Graduate School of Science, Kyoto UniVersity,
Sakyo-ku, Kyoto 606-8502, Japan, Rigaku Corporation, Akishima-shi, Tokyo 196-8666, Japan, and
Department of Applied Chemistry, Graduate School of Engineering, The UniVersity of Tokyo,
Bunkyo-ku, Tokyo 113-8656, Japan
ReceiVed October 9, 2000
Abstract: The synthesis, structure, and reactions of (acylimino)triaryl-λ5-bismuthanes and a comparative study
of the structure and reactivity of a series of (acylimino)pnictoranes are reported. Treatment of ortho-substituted
triarylbismuth dichlorides 1 (Ar3BiCl2; Ar ) 2-MeC6H4, 2-MeOC6H4, 2,4,6-Me3C6H2) with amides 2 (H2-
NCOR; R ) CF3, CCl3, 3,5-(CF3)2C6H3) in the presence of 2.2 equiv of KO-t-Bu in dichloromethane afforded
(acylimino)triaryl-λ5-bismuthanes 3 (Ar3BidNCOR) in yields of 77-96%. The ortho-substituted aryl ligands
and the electron-withdrawing N-substituents afford kinetic and thermodynamic stabilization, respectively, to
the reactive BidN bond. The structures and properties of a series of (acylimino)pnictoranes (Ar3MdNCOR
and H3MdNCOCF3; M ) P, As, Sb, Bi) are compared by IR and 13C and 15N NMR, X-ray crystallography,
and ab initio molecular orbital calculations. It was found that the contribution of the M+-NdC-O- canonical
form becomes more prominent and the single-bond character of the MdN bond increases progressively as the
pnictogen atom becomes heavier. The BidN bond of (acylimino)-λ5-bismuthanes 3 possesses a highly polarized
single-bond character, probably due to the differences in orbital size and electronegativity between the bismuth
and nitrogen atoms. Thermal decomposition of (aroylimino)triaryl-λ5-bismuthane 3f (o-Tol3BidNCOAr; Ar
) 3,5-(CF3)2C6H3) produces a gel in dry conditions or aniline 12 (ArNH2) in slightly wet conditions with a
good recovery of tris(2-methylphenyl)bismuthane (4a). It is likely that the aryl isocyanate 13 (ArNCO) is
produced during the thermolysis via a concerted C f N migration of the Ar group with an elimination of the
triarylbismuthonio group as bismuthane 4a. (Acylimino)triaryl-λ5-bismuthanes 3 oxidize 1,1,2,2-tetraphenyl-
ethanediol, benzenethiol, methanol, and ethanol to benzophenone, diphenyl disulfide, methyl formate, and
acetaldehyde, respectively, in two different reaction pathways depending on the structure of the substrates.
Compound 3d (o-Tol3BidNCOCCl3) transfers the nitrenoid moiety to triphenylphosphane, triphenylarsane,
and tris(2-methylphenyl)stibane to give the corresponding (acylimino)pnictoranes (Ar3MdNCOCl3; M ) P,
As, Sb) and 4a, suggesting that 3d is thermodynamically much less stable than their lighter pnictogen
counterparts. The copper-catalyzed decomposition of 3 (o-Tol3BidNCOR) afforded N-acyl-o-toluidines 18
(o-TolNHCOR) via a Bi f N migration of the tolyl group. The observed reactivities of (acylimino)triaryl-
λ5-bismuthanes 3 demonstrate a good leaving ability of the bismuthonio group.
Introduction
thesis have been reported for iminophosphoranes (R3PdNR′),
which can convert the CdO group in various carbonyl
compounds to the CdNR′ group (aza-Wittig reaction) by
abstracting carbonyl oxygen atoms as phosphane oxides
Iminopnictoranes (R3MdNR′; M ) P, As, Sb, Bi)1 are a class
of compounds that include a formal double bond between the
pnictogen(V) and nitrogen atoms and are structurally related to
ylides (R3MdCR′R′′) and oxides (R3MdO). The chemistry of
iminopnictoranes has received considerable interest because of
their importance for both organic and inorganic reactions as
they form bonds to nitrogen.2 Since the discovery of the
Staudinger reaction,3 numerous applications for organic syn-
(2) For example, see: (a) Johnson, A. W. Ylid Chemistry; Academic
Press: New York, 1966. (b) Singh, G.; Zimmer, H. Organomet. Chem.
ReV. 1967, 2, 279-348. (c) Abel, E. W.; Mucklejohn, S. A. Phosphorus
Sulfur 1981, 9, 235-266. (d) Gololobov, Y. G.; Zhmurova, I. N.; Kasukhin,
L. F. Tetrahedron 1981, 37, 437-472. (e) Gusar, N. I. Russ. Chem. ReV.
1991, 60, 146-161. (f) Gololobov, Y. G.; Kasukhin, L. F. Tetrahedron
1992, 48, 1353-1406. (g) Johnson, A. W. Ylides and Imines of Phosphorus;
Wiley: New York, 1993. (h) Molina, P.; Vilaplana, M. J. Synthesis 1994,
1197-1218. (i) Dehnicke, K.; Stra¨hle, J. Polyhedron 1989, 8, 707-726.
(j) Lloyd, D.; Gosney, I. In The Chemistry of Organic Arsenic, Antimony
and Bismuth Compounds; Patai, S., Ed.; Wiley: Chichester, U.K., 1994;
Chapter 16, pp 657-693. (k) Matano, Y.; Suzuki, H. Bull. Chem. Soc. Jpn.
1996, 69, 2673-2681. (l) Nugent, W. A.; Mayer, J. M. Metal-Ligand
Multiple Bonds; Wiley: New York, 1988. (m) Matano, Y.; Ikegami, T. In
Organobismuth Chemistry; Suzuki, H.; Matano, Y. Eds.; Elsevier: New
York, 2001; Chapter 3.6, pp 313-319 and references therein.
* Corresponding author. E-mail: matano@kuchem.kyoto-u.ac.jp.
† Kyoto University.
‡ Present address: Department of Chemistry, School of Science, Kwansei
Gakuin University, Uegahara, Nishinomiya 662-0891, Japan.
§ Rigaku Corp.
¶ The University of Tokyo.
(1) Unless otherwise noted, the bonds between the pnictogen and nitrogen
atoms in iminopnictoranes are represented as MdN, irrespective of the actual
nature of the bonds.
(3) Staudinger, H.; Meyer, J. HelV. Chim. Acta 1919, 2, 635-646.
10.1021/ja003623l CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/11/2001

(Acylimino)triaryl-λ5-bismuthanes
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10955
(R3PdO).2a-h Iminophosphoranes also undergo metathesis with
metal-oxo complexes to afford the corresponding metal-imido
complexes.2l,4 Although the number of examples is rather
limited, iminoarsoranes (R3AsdNR′)5 and imino-λ5-stibanes
(R3SbdNR′)6 have been used as alternative nitrene sources for
aza-Wittig type reactions. On the other hand, little is thus far
known about the synthetic utility of imino-λ5-bismuthanes
(R3BidNR′).7
toranes. In 1997, Koketsu and co-workers calculated the
geometry and energy of a series of imaginary iminopnictoranes,
H3MdNH (M ) P, As, Sb, Bi), by ab initio molecular orbital
calculations.12 They concluded that it is hard for n-σ* negative
hyperconjugation in iminopnictoranes with heavier pnictogen
atoms to take place, resulting in smaller double-bond character.
To the best of our knowledge, however, no attempt has been
made to compare the structure and reactivity of iminopnictoranes
on the basis of experimental results. This may largely be due
to a lack of information regarding the final family members,
imino-λ5-bismuthanes (R3BidNR′). Thus, to systematically
understand the nature of the MdN bond in iminopnictoranes,
it is necessary to elucidate the chemistry of imino-λ5-bismuth-
anes so as to complete the iminopnictoranes family list.
Since the first report by Wittig and Hellwinkel in 1964,16
imino-λ5-bismuthanes have been prepared by oxidative nitrene
transfer from Chloramine-T or (tosylimino)phenyl-λ3-iodinane
to triarylbismuthanes7,16 and by a Kirsanov-type reaction17 of
triarylbismuth dihalides with sulfonamides.18,19 Therefore, all
known imino-λ5-bismuthanes are of the type Ar3BidNSO2R and
are thermally stabilized by an electron-withdrawing sulfonyl
group on the imido nitrogen. This means that information of
the structure and reactivity of imino-λ5-bismuthanes is limited
to thermally stabilized N-sulfonyl derivatives.
Recently, it has been found that bismuthonium ylides
(R3BidCR′R′′), isoelectronic analogues of imino-λ5-bismuth-
anes, exhibit a wide range of reactivity depending on the
structure of the alkylidene moiety20 and that observed modes
of reaction differ considerably from those of their lighter
pnictogen counterparts. For instance, monocarbonyl ylides of
the type Ph3MdCHCOR (M ) P, As, Sb) undergo Wittig-type
olefination with a variety of carbonyl compounds,2a,j,20g whereas
the corresponding bismuthonium ylides (Ph3BidCHCOR) un-
dergo Corey-Chaycovsky-type epoxidation, ring expansion, or
acyl transposition, depending on the structure of the carbonyl
compounds.20g,21 These findings have led us to investigate the
properties and reactivities of imino-λ5-bismuthanes bearing an
N-substituent other than the sulfonyl group. Thus, we first set
out to prepare (acylimino)triaryl-λ5-bismuthanes of the type Ar3-
BidNCOR because the acyl group is commonly used as an
N-substituent for lighter iminopnictoranes and it was expected
to reflect the intrinsic properties of the BidN bond.
The bonding properties of the MdN bond in iminopnictoranes
have been a subject of considerable interest. The MdN bond
of iminopnictoranes is often described as a hybrid with the ionic
canonical form M+-N- but with its bonding characteristics such
as bond order, polarization, and energy being strongly dependent
on a relevant pnictogen atom. Until now, much attention has
been paid to iminophosphoranes, in which the observed PdN
bond lengths8 are significantly shorter than an ideal value for
the P-N single bond length.9 This bond shortening has been
explained by the pπ-dπ orbital interaction,10,11 the n-σ*
negative hyperconjugation,12,13 and the electrostatic interac-
tion12,13 between phosphorus and nitrogen atoms. Among them,
the pπ-dπ orbital interaction has become a classical concept
for representing the PdN bond,14 but its contribution, if any,
to the shortened PdN bond is now believed to be very small.12,13
Recent theoretical studies on a parent iminophosphorane (H3Pd
NH)12,13 have concluded that the contribution of an ionic
canonical form P+-N- would be more important than that of
a neutral canonical form PdN with n-σ* negative hypercon-
jugation.15 By contrast, very little information is available about
the bonding properties of the MdN bonds in other iminopnic-
(4) (a) Chatt, J.; Dilworth, J. R. J. Chem. Soc., Chem. Commun. 1972,
549. (b) Alper, H.; Partis, R. A. J. Organomet. Chem. 1972, 35, C40-
C42. (c) Chong, A. O.; Oshima, K.; Sharpless, K. B. J. Am. Chem. Soc.
1977, 99, 3420-3426. (d) Maatta, E. A.; Haymore, B. L.; Wentworth, R.
A. D. Inorg. Chem. 1980, 19, 1055-1059. (e) Maatta, E. A.; Kim, C. Inorg.
Chem. 1989, 28, 623-624.
(5) (a) Frøyen, P. Acta Chem. Scand. 1969, 23, 2935-2938. (b) Frøyen,
P. Acta Chem. Scand. 1971, 25, 2781-2782. (c) Frøyen, P. Acta Chem.
Scand. 1973, 27, 141-145. (d) Kokorev, G. I.; Yambushev, F. D.;
Badrutdinov, S. K. Zh. Obshch. Khim. 1986, 56, 1794-1798. (e) Kokorev,
G. I.; Yambushev, F. D.; Badrutdinov, S. K. Zh. Obshch. Khim. 1989, 59,
1548-1550.
(6) (a) Pinchuk, A. M.; Kuplennik, Z. I.; Belaya, Z. N. Zh. Obshch. Khim.
1976, 46, 2242-2246. (b) Kuplennik, Z. I.; Pinchuk, A. M. Zh. Obshch.
Khim. 1979, 49, 155-160. (c) Kasukhin, L. F.; Ponomarchuk, M. P.;
Kuplennik, Z. I.; Pinchuk, A. M. Zh. Obshch. Khim. 1980, 50, 1032-1034.
(d) Kuplennik, Z. I.; Belaya, Z. N.; Pinchuk, A. M. Zh. Obshch. Khim.
1981, 51, 2711-2715. (e) Kuplennik, Z. I.; Belaya, Z. N.; Pinchuk, A. M.
Zh. Obshch. Khim. 1984, 54, 462-463.
(7) (a) Suzuki, H.; Nakaya, C.; Matano, Y.; Ogawa, T. Chem. Lett. 1991,
105-108. (b) Suzuki, H.; Ikegami, T. J. Chem. Res., Synop. 1996, 24-25.
(8) See Table 13.3 (p 415) in ref 2g and references therein.
(9) Cameron, T. S.; Chan, C.; Chute, W. J. Acta Crystallogr. 1980, B36,
2391-2393. The anion of potassium phosphoramidate (K[H3NO3P]) is
considered to contain an “ideal” P-N single bond [1.800(4) Å], where the
nitrogen atom is sp3 hybridized with no lone pair of electrons.
(10) (a) Albright, T. A.; Freeman, W. J.; Schweizer, E. E. J. Org. Chem.
1976, 41, 2716-2720. (b) Gonbeau, D.; Pfister-Guillouzo, G.; Mazie`res,
M.-R.; Sanchez, M. Can. J. Chem. 1985, 63, 3242-3248. (c) Molina, P.;
Alajar´ın, M.; Leonardo, C. L.; Claramunt, R. M.; Foces-Foces, M. C.; Cano,
F. H.; Catala´n, J.; de Paz, J. L. G.; Elguero, J. J. Am. Chem. Soc. 1989,
111, 355-363.
(11) (a) Claydon, A. P.; Fowell, P. A.; Mortimer, C. T. J. Chem. Soc.
1960, 3284-3287. (b) Singh, G.; Zimmer, H. J. Org. Chem. 1965, 30, 417-
420. (c) Goetz, H. Angew. Chem. 1965, 77, 1021. (d) Goetz, H.; Probst, D.
Liebigs Ann. Chem. 1968, 715, 1-14. (e) Schuster, I. Tetrahedron 1977,
33, 1075-1079.
(12) Koketsu, J.; Ninomiya, Y.; Suzuki, Y.; Koga, N. Inorg. Chem. 1997,
36, 694-702.
(13) Sudhakar, P. V.; Lammertsma, K. J. Am. Chem. Soc. 1991, 113,
1899-1906.
(14) The involvement of the phosphorus d-orbital in the PdO and PdC
bonding of phosphane oxides and phosphorus ylides is now believed to be
slight. For a review, see: Gilheany, D. G. Chem. ReV. 1994, 94, 1339-
1374.
In this paper, we first describe the synthesis of (acylimino)-
triaryl-λ5-bismuthanes, then provide a structural comparison with
other (acylimino)pnictoranes of lighter family members, and
(15) The n(π)-σ* negative hyperconjugation was originally suggested
to rationalize the hypervalent (πAY) bonding of 32-valence-electron species
of the type X3AY: Reed, A. E.; Schleyer, P. v. R. J. Am. Chem. Soc. 1990,
112, 1434-1445.
(16) Wittig, G.; Hellwinkel, D. Chem. Ber. 1964, 97, 789-793.
(17) Kirsanov, A. V. Zh. Obshch. Khim. 1952, 22, 269-273.
(18) Pasenok, S. V.; Kirij, N. V.; Yagupolskii, Y. L.; Naumann, D.; Tyrra,
W. J. Fluorine Chem. 1993, 63, 179-183.
(19) Ikegami, T.; Suzuki, H. Organometallics 1998, 17, 1013-1017.
(20) (a) Lloyd, D.; Singer, M. I. C. J. Chem. Soc., Chem. Commun. 1967,
1042-1043. (b) Barton, D. H. R.; Blazejewski, J.-C.; Charpiot, B.; Finet,
J.-P.; Motherwell, W. B.; Papoula, M. T. B.; Stanforth, S. P. J. Chem. Soc.,
Perkin Trans. 1 1985, 2667-2675. (c) Glidewell, C.; Lloyd, D.; Metcalfe,
S. Synthesis 1988, 319-321. (d) Suzuki, H.; Murafuji, T.; Ogawa, T. Chem.
Lett. 1988, 847-848. (e) Ogawa, T.; Murafuji, T.; Suzuki, H. J. Chem.
Soc., Chem. Commun. 1989, 1749-1751. (f) Kirij, N. V.; Pasenok, S. V.;
Yagupolskii, Y. L.; Naumann, D.; Tyrra, W. J. Fluorine Chem. 1994, 66,
75-78. (g) Matano, Y. J. Chem. Soc., Perkin Trans. 1 1994, 2703-2709.
(21) (a) Matano, Y.; Yoshimune, M.; Suzuki, H. J. Org. Chem. 1995,
60, 4663-4665. (b) Matano, Y.; Suzuki, H. Chem. Commun. 1996, 2697-
2698. (c) Rahman, M. M.; Matano, Y.; Suzuki, H. Synthesis 1999, 395-
397. (d) Rahman, M. M.; Matano, Y.; Suzuki, H. Chem. Commun. 1998,
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J. Org. Chem. 1999, 64, 6924-6927.

10956 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Matano et al.
Scheme 1
Scheme 2
Table 1. Synthesis of (Acylimino)triaryl-λ5-bismuthanes
entry
1
2
(acylimino)triaryl-λ5-bismuthane (3)a yield (%)
1
2
3
4
5
6
7
8
9
1a 2a o-Tol3BidNCOCF3 (3a)
1b 2a o-Ans3BidNCOCF3 (3b)
1c 2a Mes3BidNCOCF3 (3c)
1a 2b o-Tol3BidNCOCCl3 (3d)
1b 2b o-Ans3BidNCOCCl3 (3e)
1a 2c o-Tol3BidNCOC6H3-3,5-(CF3)2 (3f)
1b 2c o-Ans3BidNCOC6H3-3,5-(CF3)2 (3g)
1a 2d o-Tol3BidNCOC6H4-4-NO2 (3h)
1a 2e o-Tol3BidNCOPh (3i)
93
91
86
77
96
95
94
b, c
b, c
b, d
b, d
e, therefore, afford significant kinetic stabilization26 to the
moisture-sensitive BidN bond in imino-λ5-bismuthanes.27
Dichlorides 1a,b also reacted with 3,5-bis(trifluoromethyl)-
benzamide (2c) to yield the corresponding (aroylimino)-λ5-
bismuthanes 3f,g as moderately stable solids (entries 6,7). The
reaction between 1a and p-nitrobenzamide (2d) gave the desired
imino-λ5-bismuthane 3h, but the product gradually decomposed
during recrystallization (entry 8). (Benzoylimino)-λ5-bismuthane
3i prepared from 1a and benzamide (2e) decomposed more
rapidly at room temperature to afford a mixture of tris(2-
methylphenyl)bismuthane (4a), amide 2e, aniline, and others
(entry 9). The formation of aniline suggests the probable
involvement of phenyl isocyanate as an intermediate during the
thermal decomposition of 3i (vide infra). These results revealed
the ability of electron-withdrawing acyl groups to enhance the
thermal stability of (acylimino)triaryl-λ5-bismuthanes.
10
11
1d 2a p-Tol3BidNCOCF3 (3j)
1e 2a Ph3BidNCOCF3 (3k)
a o-Tol ) 2-MeC6H4; o-Ans ) 2-MeOC6H4; Mes ) 2,4,6-Me3C6H2;
p-Tol ) 4-MeC6H4. b Not isolated. c Decomposed thermally at room
temperature. d Hydrolyzed in air.
finally discuss the reactivity of (acylimino)triaryl-λ5-bismuth-
anes.22 The single-bond character of the MdN bond as well as
the contribution of the M+-NdC-O- canonical form becomes
more prominent as the pnictogen atom becomes heavier. The
unique reactivities of (acylimino)triaryl-λ5-bismuthanes observed
demonstrate their potential utility in organic synthesis.
Compounds 3a-g are colorless or pale yellow solids and
soluble in CH2Cl2, CHCl3, and benzene but are insoluble in
hexane. Compounds 3a-e can be stored in the solid state for
over 1 month in a refrigerator, whereas 3f,g decompose over
the course of 1 day, even in a refrigerator (at 4 °C).
Results and Discussion
Synthesis. As depicted in Scheme 1, treatment of ortho-
substituted triarylbismuth dichlorides 1a-c with R,R,R-triha-
loacetamides 2a,b in the presence of 2.2 equiv of KO-t-Bu in
CH2Cl2 gave [(trihaloacetyl)imino]triaryl-λ5-bismuthanes 3a-e
as air-stable solids in 77-96% yields (Table 1, entries 1-5).
A similar reaction of tris(4-methylphenyl)bismuth dichloride
(1d) or triphenylbismuth dichloride (1e) with 2a gave the
expected (acylimino)-λ5-bismuthanes 3j,k, but the product was
so sensitive to moisture that it decomposed during attempted
recrystallization under air to give an insoluble substance and
2a (entries 10,11). The insoluble solid obtained from 1d showed
a sharp IR absorption at 625 cm-1, which may be assigned as
an asymmetric Bi-O-Bi stretching mode.23 Its FABMS
spectrum in 3-nitrobenzyl alcohol matrix showed a strong peak
at m/z 634 in accord with a [(4-MeC6H4)3BiOCH2C6H4-3-NO2]+
ion. When treated with aqueous HCl, the substance was
converted to dichloride 1d. These results indicate that the
insoluble solid is a polymeric triarylbismuthane oxide, (Ar3-
BidO)n,23,24 probably derived from hydrolysis of the initially
formed imino-λ5-bismuthane.25 The ortho-substituents in 3a-
To compare the structure of 3 with those of lighter pnictogen
counterparts, an iminophosphorane 6,28 an iminoarsorane 8,29
and imino-λ5-stibanes 10a-c were prepared by the oxidative
condensation30 of triphenylphosphane (5), triphenylarsane (7),
and tris(2,4,6-trimethylphenyl)stibane (11) with 2b in the
presence of diethyl azodicarboxylate and by treating triaryl-
stibane oxides 9a,b with trichloroacetonitrile in CH2Cl2 (Scheme
2). Despite the presence of ortho-substituent groups, compounds
10a,b are extremely moisture sensitive and readily decompose
to give the corresponding oxides 9a,b under ambient conditions.
1
Thus, 10a,b were characterized by H NMR, FABMS, and IR
analyses as well as by chemical transformations to other Sb(V)
(26) Kinetic stabilization afforded by ortho-substituted aryl groups has
been applied for stabilizing highly reactive functionalities. For example,
see: (a) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J.
Am. Chem. Soc. 1981, 103, 4587-4589. (b) West, R.; Fink, M. J.; Michl,
J. Science 1981, 214, 1343-1344. (c) Cowley, A. H.; Kilduff, J. E.;
Newman, T. H.; Pakulski, M. J. Am. Chem. Soc. 1982, 104, 5820-5821.
(d) Tokitoh, N.; Matsumoto, T.; Okazaki, R. Bull. Chem. Soc. Jpn. 1999,
72, 1665-1684.
(27) ortho-Methoxy aryl groups have been shown to stabilize the cationic
heteroatom thermodynamically. For example, see: (a) McEwen, W. E.; Lau,
K. W. J. Org. Chem. 1982, 47, 3595-3596. (b) Wada, M.; Kanzaki, M.;
Fujiwara, M.; Kajihara, K.; Erabi, T. Bull. Chem. Soc. Jpn. 1991, 64, 1782-
1786. (c) Suzuki, H.; Ikegami, T.; Azuma, N. J. Chem. Soc., Perkin Trans.
1 1997, 1609-1616. Thus, in compounds 3b,e, the ortho-methoxyl groups
may also afford thermodynamic stabilization to the BidN bond.
(28) Cristau, H. J.; Manginot, E.; Torreilles, E. Synthesis 1991, 382-
384.
(22) For preliminary results, see: Matano, Y.; Nomura, H.; Shiro, M.;
Suzuki, H. Organometallics 1999, 18, 2580-2582.
(23) A band observed at 625 cm-1 in the IR spectrum of (Ph3BiO)n was
assigned as the Bi-O-Bi asymmetric stretching mode: Goel, R. G.; Prasad,
H. S. J. Organomet. Chem. 1972, 36, 323-332.
(24) (a) Goel, R. G.; Prasad, H. S. J. Organomet. Chem. 1973, 50, 129-
134. (b) Suzuki, H.; Ikegami, T.; Matano, Y. Tetrahedron Lett. 1994, 35,
8197-8200.
(29) Gadreau, C.; Faucaud, A.; Me´rot, P. Synthesis 1981, 73-74.
(30) Bittner, S.; Assaf, Y.; Krief, P.; Pomerantz, M.; Ziemnicka, B. T.;
Smith, C. G. J. Org. Chem. 1985, 50, 1712-1718.
(25) For hydrolysis of a triphenyl(sulfonylimino)-λ5-bismuthane, see ref
18. We did not attempt to isolate phenyl and p-tolyl derivatives of 3.

(Acylimino)triaryl-λ5-bismuthanes
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10957
Table 2. IR and 13C and 15N Spectral Data for
(Acylimino)triarylpnictoranes and 2b
a
νCdO
b
compd
(∆νCdO
)
13Cc
15Nd
o-Ans3BidNCOCCl3 (3e) 1561 (137) 172.2 225.3
Mes3SbdNCOCCl3 (10c) 1583 (115) 171.5 184.3
Ph3AsdNCOCCl3 (8)
Ph3PdNCOCCl3 (6)
H2NCOCCl3 (2b)
1611 (87) 173.0 149.3
1638 (60) 170.1 117.6 (|JPN| ) 41.35 Hz)
1698 163.8 95.3
a IR absorption of the CdO group on KBr pellets, reported in cm-1
.
b Difference in frequency from νCdO of the parent amide 2b (1698
cm-1). c 13C Chemical shifts of the carbonyl carbon atom, referenced
to CDCl3 (77 ppm). d 15N Chemical shifts of the nitrogen atom of the
15N-labeled derivatives. Recorded at 50.55 MHz in CDCl3 (ca. 0.01
M), referenced to NH3(l).
compounds.31 Compound 10c is much more stable toward
atmospheric moisture than 10a,b.
Structural Comparison of (Acylimino)pnictoranes. The
structures of a series of (acylimino)pnictoranes were studied
by means of IR and 13C and 15N NMR, as well as by X-ray
analysis and ab initio molecular orbital calculations.
Figure 1. ORTEP diagram for 3e (30% probability ellipsoids). Selected
bond lengths (Å) and angles (deg): Bi-C(3), 2.198(4); Bi-C(10),
2.204(4); Bi-C(17), 2.196(4); C(3)-Bi-C(10), 109.4(1); C(3)-Bi-
C(17), 109.3(1); C(10)-Bi-C(17), 106.2(1); N-Bi-C(3), 106.9(1);
N-Bi-C(10), 108.8(1); N-Bi-C(17), 116.1(1).
(a) IR and 13C and 15N NMR Spectra. The CdO stretching
13
frequencies (νCdO) and
C
CdO
and 15N chemical shifts of
[(trichloroacetyl)imino]triarylpnictoranes 3e, 6, 8, and 10c are
summarized in Table 2. The CdO absorptions of these
iminopnictoranes were observed at lower frequencies compared
to that of amide 2b. The differences in frequency (∆νCdO) from
2b increase progressively from iminophosphorane 6, imino-
arsorane 8, imino-λ5-stibane 10c, to imino-λ5-bismuthane 3e,
indicating that the double-bond character of the CdO bond
decreases as the pnictogen atom becomes heavier. There are
only slight differences among the 13CCdO chemical shifts of 3e,
6, 8, and 10c. By contrast, the 15N peaks shift significantly
downfield as the pnictogen atom becomes heavier: the 15N
peaks of 2b-15N, 6-15N, 8-15N, 10c-15N, and 3e-15N were
observed at δ 95.3, 117.6, 149.3, 184.3, and 225.3, respectively,
relative to NH3(l).32 The 15N chemical shift and coupling
constant (JPN) of 6 are close to those previously reported for
Ph3PdNCOAr33 (Ar ) p-substituted phenyl). The nitrogen
nucleus is known to be deshielded when the bonding electrons
are in the orbitals of high s character and/or when multiple
bonding to nitrogen is present or enhanced.34 Thus, the low-
field appearance of the 15N peak of 3e-15N suggests that the
Bi+-NdC-O- character makes a greater contribution than that
of Bi+-N--CdO.
(b) X-ray Crystallographic Analyses. The crystal structures
of [(trichloroacetyl)imino]triarylpnictoranes 3e, 6, 8, and 10c
were compared by X-ray crystallography. ORTEP diagrams are
provided in Figures 1-4, crystallographic data are summarized
in Table 3, and selected bond lengths and angles are listed in
Table 4. These iminopnictoranes (Ar3MdNCOCCl3) exist in a
monomeric form, and there is no intermolecular interaction
between the pnictogen center and the neighboring molecules.
The pnictogen atom possesses a distorted tetrahedral geometry
with average C-M-C and N-M-C bond angles of 107.9-
110.7 and 108.0-110.9°, respectively.
Figure 2. ORTEP diagram for 6 (30% probability ellipsoids). Selected
bond lengths (Å) and angles (deg): P-C(3), 1.800(2); P-C(9), 1.796-
(2); P-C(15), 1.799(2); C(3)-P-C(9), 106.9(1); C(3)-P-C(15),
108.1(1); C(9)-P-C(15), 108.8(1); N-P-C(3), 115.1(1); N-P-C(9),
105.2(1); N-P-C(15), 112.3(1).
The observed MdN bond lengths primarily reflect the orbital
size of the respective pnictogen atom.35 Therefore, the multiplic-
ity of the MdN bond in iminopnictoranes is discussed by
comparison with known M-N bond lengths of the correspond-
ing tricoordinate pnictogen(III) amides. The BidN bond length
of 2.125(3) Å in 3e is comparable to that [2.13(1) Å] of (p-
Tol)2ArBidNSO2CF3 [Ar ) 2-(4,4-dimethyl-4,5-dihydrooxazol-
2-yl)phenyl]19 and is slightly shorter than known Bi-N bond
lengths (2.165-2.20 Å) observed for bismuth(III) amides.36 If
we take into account a slight shortening (∼0.04 Å) of the Bi-X
bond, which arises with the quaternization of the bismuth atom,
the BidN bond of 3e is considered to possess an appreciable
single-bond character.37 The PdN bond length of 1.620(2) Å
in 6 is comparable to that [1.626(3) Å] of Ph3PdNCOPh38 and
is much shorter than typical P-N bond lengths (1.68-1.75 Å)
of phosphorus(III) amides39 and an ideal P-N single bond
(31) On treatment with an acid (HX), compounds 10a,b were converted
quantitatively to Ar3SbX2 (X ) Cl or OAc).
(32) The chemical shift relative to NH3(l) was calculated using the
equation δ(NH3) ) δ(MeNO2) + 380.23: Levy, G. C.; Lichter, R. L.
Nitrogen-15 Nuclear Magnetic Resonance Spectroscopy; Wiley: New York,
1979; Chapter 3.
(33) δN ) 119.82-124.91, relative to NH3(l); JPN ) 43.8-44.7 Hz:
Chou, W.-N.; Pomerantz, M.; Witzcak, M. K. J. Org. Chem. 1990, 55,
716-721.
(35) Emsley, J. The Elements, 3rd ed.; Oxford University Press: Oxford,
U.K., 1998. Covalent radii: N, 0.70 Å; P, 1.10 Å; As, 1.21 Å; Sb, 1.41 Å;
Bi, 1.52 Å. van der Waals radii: O, 1.4 Å; P, 1.9 Å; As, 2.0 Å; Sb, 2.2 Å;
Bi, 2.4 Å.
(34) See discussion in pp 7-9 and pp 58-67 in ref 32.

10958 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Matano et al.
Figure 3. ORTEP diagram for 8 (30% probability ellipsoids). Selected
bond lengths (Å) and angles (deg): As-C(3), 1.913(2); As-C(9),
1.910(2); As-C(15), 1.909(2); C(3)-As-C(9), 107.18(7); C(3)-As-
C(15), 108.01(8); C(9)-As-C(15), 110.18(8); N-As-C(3), 116.27-
(7); N-As-C(9), 103.16(7); N-As-C(15), 111.78(7).
length (1.80 Å) observed for potassium phosphoramidate.9 On
the basis of a previous discussion of the P-N bonding properties
of phosphorus(III) amides,39 it has been suggested that the back-
bonding from the nitrogen atom to the phosphorus atom causes
a P-N bond-shortening of 0.04-0.12 Å.40 Therefore, the
double-bond character of the PdN bond in 6 is much more
significant than that of the BidN bond in 3e. As is the case
with aminophosphonium salts,41 the positive charge on the
phosphorus atom of 6 would be partially neutralized through
the lone pair of electrons on the nitrogen. The AsdN bond
length of 1.783(2) Å in 8 is slightly longer than that [1.755(3)
Figure 4. ORTEP diagrams for 10c (30% probability ellipsoids). (a)
Selected bond lengths (Å) and angles (deg): Sb(1)-C(3), 2.148(6);
Sb(1)-C(12), 2.145(6); Sb(1)-C(21), 2.134(6); C(3)-Sb(1)-C(12),
115.2(2); C(3)-Sb(1)-C(21), 100.9(2); C(12)-Sb(1)-C(21), 115.9-
(2); N(1)-Sb(1)-C(3), 99.4(2); N(1)-Sb(1)-C(12), 105.0(2); N(1)-
Sb(1)-C(21), 119.5(2). (b) Selected bond lengths (Å) and angles
(deg): Sb(2)-C(32), 2.151(6); Sb(2)-C(41), 2.151(6); Sb(2)-C(50),
2.145(6); C(32)-Sb(2)-C(41), 102.3(2); C(32)-Sb(2)-C(50), 113.3-
(2); C(41)-Sb(2)-C(50), 115.0(2); N(2)-Sb(2)-C(32), 100.9(2);
N(2)-Sb(2)-C(41), 119.6(2); N(2)-Sb(2)-C(50), 105.0(2).
(36) (a) Clegg, W.; Compton, N. A.; Errington, R. J.; Norman, N. C.;
Wishart, N. Polyhedron 1989, 8, 1579-1580. (b) Clegg, W. Compton, N.
A.; Errington, R. J.; Fisher, G. A.; Green, M. E.; Hockless, D. C. R.;
Norman, N. C. Inorg. Chem. 1991, 30, 4680-4682. (c) Wirringra, U.;
Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Inorg. Chem. 1994, 33,
4607-4608. (d) Edwards, A. J.; Beswick, M. A.; Galsworthy, J. R.; Paver,
M. A.; Raithby, P. R.; Rennie, M.-A.; Russell, C. A.; Verhorevoort, K. L.;
Wright, D. S. Inorg. Chim. Acta 1996, 248, 9-14. (e) Burford, N.;
Macdonald, C. L. B.; Robertson, K. N.; Cameron, T. S. Inorg. Chem. 1996,
35, 4013-4016. The values in parentheses are the averaged Bi-N bond
lengths.
Å] of Ph3AsdNSO2Tol42 but shorter than typical As-N bond
lengths (1.84-1.88 Å) of arsenic(III) amides.39g,j,43 Imino-λ5-
stibane 10c consists of two isolated molecules with similar
geometry around the antimony center. The SbdN bond lengths
of 1.989(5)-1.992(5) Å in 10c are slightly longer than those
[1.958(4)-1.962(2) Å] of the N-sulfonyl derivatives, Ar3Sbd
NSO2CF3 (Ar ) o-Tol, o-Ans)44 but somewhat shorter than
known Sb-N bond lengths (2.04-2.08 Å) of antimony(III)
amides.36e,39j,45As expected, the bonding properties of the Asd
N and SbdN bonds are between those of the BidN and PdN
bonds.
(37) The ortho-methoxy groups in 3e were found to lean ca. 5° toward
the bismuth center. This attractive interaction may cause a slight elongation
of the BidN bond.
(38) Bar, I.; Bernstein, J. Acta Crystallogr. 1980, B36, 1962-1964.
2
(39) Typical bond lengths are 1.68-1.69 Å for P-Nsp and 1.74-1.75
3
Å for P-Nsp bonds. For example, see: (a) Muir, K. W. J. Chem. Soc.,
Dalton Trans. 1975, 259-262. (b) Cobbledick, R. E.; Einstein, F. W. B.
Acta Crystallogr. 1975, B31, 2731-2733. (c) Rømming, C.; Songstad, J.
Acta Chem. Scand. 1978, A32, 689-699. (d) Thompson, M. L.; Haltiwanger,
R. C.; Norman, A. D. J. Chem. Soc., Chem. Commun. 1979, 647-648. (e)
Scherer, O. J.; Andres, K.; Kru¨ger, C.; Tsay, Y.-H.; Wolmerha¨user, G.
Angew. Chem., Int. Ed. Engl. 1980, 19, 571-572. (f) Thompson, M. L.;
Tarassoli, A.; Haltiwanger, R. C.; Norman, A. D. J. Am. Chem. Soc. 1981,
103, 6770-6772. (g) Atwood, J. L.; Cowley, A. H.; Hunter, W. E.;
Mehrotra, S. K. Inorg. Chem. 1982, 21, 1354-1356. (h) Chen, H.-J.;
Haltiwanger, R. C.; Hill, T. G.; Thompson, M. L.; Coons, D. E.; Norman,
A. D. Inorg. Chem. 1985, 24, 4725-4730. (i) Nieger, M.; Niecke, E.;
Ga¨rtner-Winkhaus, C. Acta Crystallogr. 1990, C46, 2470-2472. (j) Burford,
N.; Cameron, T. S.; Lam, K.-C.; LeBlanc, D. J.; Macdonald, C. L. B.;
Phillips, A. D.; Rheingold, A. L.; Stark, L.; Walsh, D. Can. J. Chem. 2001,
79, 342-348.
Quite recently, Burford, Cameron, and co-workers compared
the structures of the first homologous series of bis(amido)-
diazadipnictetidines, [DipNMN(H)Dip]2 (M ) P, As, Sb, Bi;
Dip ) 2,6-diisopropylphenyl), with averaged M-N bond lengths
(42) Mai, H.-J.; Weller, F.; Dehnicke, K.; Maichle-Mo¨ssmer, C.; Stra¨hle,
J. Z. Anorg. Allg. Chem. 1994, 620, 851-855.
2
(43) Typical bond lengths are 1.84-1.85 Å for As-Nsp and 1.87-1.88
3
Å for As-Nsp bonds. For example, see: (a) Weiss, J.; Eisenhuth, W. Z.
Anorg. Allg. Chem. 1967, 350, 9-17. (b) Rømming, C.; Songstad, J. Acta
Chem. Scand. 1980, A34, 365-373.
(40) It must be noted that the quaternization of phosphorus atom in the
P(III) to P(V) conversion would cause the additional P-N bond shortening.
(41) (a) Cowley, A. H.; Kemp, R. A.; Lasch, J. G.; Norman, N. C.;
Stewart, C. A. J. Am. Chem. Soc. 1983, 105, 7444-7445. (b) Chiche, L.;
Christol, H. J. Chem. Soc., Perkin Trans. 2 1984, 753-755. (c) Schomburg,
D.; Bettermann, G.; Ernst, L.; Schmutzler, R. Angew. Chem., Int. Ed. Engl.
1985, 24, 975-976. (d) Roesky, H. W.; Mainz, B.; Noltemeyer, M.;
Sheldrick, G. M. Z. Naturforsch. B 1988, 43, 941-944.
(44) Matano, Y.; Nomura, H.; Suzuki, H. Inorg. Chem. 2000, 39, 1340-
1341.
(45) (a) Edwards, A. J.; Paver, M. A.; Raithby, P. R.; Russell, C. A.;
Wright, D. S. J. Chem. Soc., Dalton Trans. 1993, 2257-2258. (b) Edwards,
A. J.; Paver, M. A.; Rennie, M.-A.; Raithby, P. R.; Russell, C. A.; Wright,
D. S. J. Chem. Soc., Dalton Trans. 1994, 2963-2966. The values in
parentheses are the averaged Sb-N bond lengths.

(Acylimino)triaryl-λ5-bismuthanes
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10959
Table 3. Crystallographic Data for (Acylimino)triarylpnictoranes
6
8
10c
3e
empirical formula
fw
cryst dimens (mm)
cryst system
a (Å)
b (Å)
c (Å)
C20H15Cl3NOP
422.68
C20H15AsCl3NO
466.63
C58H66Cl6N2O2Sb2
1279.39
C23H21BiCl3NO4
690.76
0.34 × 0.20 × 0.18
monoclinic
9.469(3)
19.063(4)
10.976(4)
94.90(3)
1973(1)
P21/n
0.20 × 0.20 × 0.20
monoclinic
9.4395(4)
19.098(1)
10.8085(6)
95.312(2)
1940.1(2)
P21/n
0.10 × 0.10 × 0.10
monoclinic
16.6407(7)
13.1648(6)
26.062(1)
92.144(2)
5705.5(4)
P21/c
0.25 × 0.08 × 0.05
monoclinic
8.776(2)
17.577(4)
15.875(4)
96.10(2)
2434.9(10)
P21/n
â (deg)
V (Å3)
space group
Z
D
4
4
4
4
calcd (g cm-3
)
1.422
1.597
1.489
1.884
radiation (λ, Å)
µ(Mo KR) (cm-1
temp (°C)
2θmax (deg)
no. of reflcns measd
total
Mo KR (0.710 69)
Mo KR (0.710 69)
Mo KR (0.710 69)
Mo KR (0.710 70)
)
5.54
21.74
12.69
141.85
25
55.0
-150
54.9
-150
55.0
-130
55.2
4800
18 746
52 765
4787
unique
4735
4735
Ι > 0.00σ(I)
235
0.043, 0.132
1.11
4420
4420
all, 2θ < 54.86°
235
0.025, 0.054
1.00
13 003
13 003
all, 2θ < 54.97°
631
0.049, 0.137
0.95
4786
4342
I > 2.00σ(I)
290
0.025, 0.034
1.11
no. of observns
no. of reflcns
no. of variables
R1, Rw
goodness of fit
Table 4. Selected Bond Lengths and Bond Angles of Ar3MdNCOCCl3
compd
M-N
N-C
C-O
M-Ca
M‚‚‚O
C-M-Ca
N-M-Ca
M-N-C
117.7(2)
110.0(1)
108.2(4)
106.3(4)
104.0(3)
N-C-O
129.9(2)
130.7(2)
129.4(6)
130.8(6)
130.9(4)
6 (M ) P)
8 (M ) As)
10c (M ) Sb)
1.620(2)
1.783(2)
1.989(5)
1.992(5)
2.125(3)
1.333(3)
1.323(2)
1.329(8)
1.330(8)
1.314(5)
1.220(3)
1.234(2)
1.265(7)
1.244(7)
1.255(5)
1.798
1.911
2.142
2.149
2.199
2.912(2)
2.837(1)
2.901(4)
2.872(4)
2.877(3)
107.9
108.5
110.7
110.2
108.3
110.9
110.4
108.0
108.5
110.6
3e (M ) Bi)
a Average values. See captions under Figures 1-4.
Table 5. MdN/M-N Bond-Length Ratios
Scheme 3
M
MdNa
M-Nb
MdN/M-N
P
1.620
1.783
1.991c
2.125
1.709
1.867
2.043
2.165
0.948
0.955
0.975
0.982
As
Sb
Bi
a The MdN bond lengths of 3e, 6, 8, and 10c. b The average M-N
bond lengths of [DipNMN(H)Dip]2, taken from refs 36c and 39j.
c Average value.
of 1.709 Å for P-N, 1.867 Å for As-N, 2.043 Å for Sb-N,
and 2.165 Å for Bi-N.36c,39j These values are within the range
of typical M-N bond lengths of the respective pnictogen(III)
amides (vide supra). To evaluate the multiplicity of the MdN
bonds of a homologous series of (acylimino)triarylpnictoranes,
the ratios of the MdN bond lengths of 6, 8, 11c, and 3e vs the
averaged M-N bond lengths of [DipNMN(H)Dip]2 were
calculated. As shown in Table 5, the MdN/M-N bond-length
ratios increase in the order P (0.948) < As (0.955) < Sb (0.975)
< Bi (0.982).46 This clearly suggests that the single-bond
character of the MdN bond increases progressively as the
pnictogen atom becomes heavier and is the most significant for
3e of all the (acylimino)triarylpnictoranes examined. The
difference in multiplicity of the MdN bonds may reasonably
be attributed to the differences in orbital size and electronega-
tivity among pnictogen atoms. Thus, the larger orbital radii and
the smaller electronegativities of the heavier pnictogen atoms
result in weaker conjugative interactions with nitrogen atoms.
A structural feature around the N-acyl group is also note-
worthy. The observed N-C bond lengths [1.314(5)-1.333(3)
Å] are shorter than the typical N-C single bond length (1.38
Å), whereas the observed CdO bond lengths [1.220(3)-1.265-
(7) Å] are longer than the typical CdO double bond length (1.21
Å).47 The M, N, C, and O atoms are almost on the same plane
for all iminopnictoranes, with torsion angles of -4.8(3) to
4.2(5)°, indicating an extensive delocalization of the anionic
charge of the nitrogen through the carbonyl group. It is likely
that the canonical structures Y and Z contribute significantly
to the actual bonding of (acylimino)pnictoranes (Scheme 3).
Among them, 3e bears the shortest N-C bond [1.314(5) Å]
and the longest CdO bond [1.255(5) Å].48 These data is
indicative of the largest double-bond character of the N-C bond
and the largest single-bond character of the CdO bond of 3e.
Thus, the contribution of the canonical structure Z would be
(47) March, J. AdVanced Organic Chemistry, 4th ed.; Wiley: New York,
1992; Table 1.5, p 21. The values for the sp2 carbon, nitrogen, and oxygen
atoms are used.
(48) The difference in the CdO bond of the two molecules of 10c might
be caused by the different configuration of the aryl groups and the
trichloroacetyl group.
(46) One of the reviewers gave us valuable comments regarding the
evaluation of the multiplicity of the MdN bonds. If we use an “ideal” P-N
single bond length of 1.800 Å (ref 9), the PdN/P-N bond-length ratio is
calculated to be 0.900.

10960 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Matano et al.
Table 6. Calculated Parameters of H3MdNCOCF3 (M ) P, As, Sb, Bi)a
M
P
MdNb
MdN/ M-Nc
BOd
N-C1 C1dO M-N-C1 M‚‚‚O
Me
Ne
Oe
M-H1 M-H2
1.656 (1.601)
0.929
0.937
0.962
0.959
1.289
1.170
1.036
0.943
1.363
1.357
1.338
1.342
1.246
1.253
1.279
1.271
105.6
102.5
94.7
2.634
2.606
2.433
2.566
1.136 -1.000 -0.641
1.296 -0.979 -0.665
1.672 -0.929 -0.728
1.545 -0.876 -0.714
1.418
1.506
1.685
1.738
1.410
1.502
1.697
1.750
As 1.781 (1.715)
Sb
Bi
2.014 (1.899)
2.081 (1.977)
96.3
a At MP2 level. All bond lengths in angstroms and bond angles in degrees. b Values in parentheses are those of H3MdNH, taken from ref 12.
c Bond-length ratio of MdN in H3MdNCOCF3 vs M-N in H2M-NHCOCF3 (1.783 Å for M ) P, 1.900 Å for M ) As, 2.093 Å for M ) Sb,
2.170 Å for M ) Bi), calculated at the same level. d Mayer-Mulliken natural bond order (NBO) of MdN at the MP2 level. e Natural charges on
M, N, and O atoms.
most significant for (acylimino)-λ5-bismuthane 3e, as inferred
from the IR observations. All intramolecular M‚‚‚O distances
are within the sum of their van der Waals radii,35 and the
M-N-C bond angle decreases in the order P-N-C [117.7-
(2)°] > As-N-C [110.0(1)°] > Sb-N-C [106.3(4)-108.2-
(4)°] > Bi-N-C [104.0(3)°]. It is apparent that the electrostatic
The large negative charge on the oxygen atom is indicative
of the effective delocalization of the negative charge from
nitrogen through the adjacent carbonyl group. The calculated
natural charges on M, N, and O atoms, the N-C bond lengths,
and the CdO bond lengths indicate that the contribution of the
M+-NdC-O- canonical structure becomes more significant
in the order P < As < Bi e Sb.51 The inverted order of H3-
SbdNCOCF3 and H3BidNCOCF3 is not accordance with the
experimentally observed order P < As < Sb < Bi. This
discrepancy may arise from the absence of a crystal environment
and/or relativistic effects not included in the effective core
potential.52
It should be noted that the heavier iminopnictoranes (M )
Sb, Bi) possess much shorter M‚‚‚O distances and smaller
M-N-C1 bond angles compared to the lighter iminopnic-
toranes (M ) P, As). Also noteworthy is that M-H2 bond
lengths are longer than the M-H1 bond lengths in the heavier
iminopnictoranes. These data suggest that the intramolecular
coordination from the oxygen atom to the pnictogen center
becomes important in H3SbdNCOCF3 and H3BidNCOCF3.53
Reaction of (Acylimino)triaryl-λ5-bismuthanes. The chemi-
cal behavior of (acylimino)triaryl-λ5-bismuthanes 3 was inves-
tigated and compared with those of lighter (acylimino)triaryl-
pnictoranes.
interaction between the positively charged pnictogen atom (Mδ+
)
and the negatively charged carbonyl oxygen atom (Oδ-
)
becomes increasingly important as the pnictogen becomes
heavier.
(c) Ab initio Molecular Orbital Calculations. To obtain a
greater insight into the nature of the MdN bond of (acylimino)-
pnictoranes, ab initio molecular orbital calculations were carried
out for a series of [(trifluoroacetyl)imino]pnictoranes, H3Md
NCOCF3 (M ) P, As, Sb, Bi), by replacing all aryl groups on
pnictogen atoms with hydrogen. These imaginary compounds
are considered to be suitable models for discussing the structures
and properties of some (acylimino)triarylpnictoranes that have
been well characterized by X-ray crystallography. The calcula-
tions were performed at a level of second-order Møller-Plesset
perturbation theory with a relativistic effective core potential
and a valence double-ú plus a polarization-quality basis set,
which is the same as that used for the calculation of the
geometries of H3MdNH (M ) P, As, Sb, Bi)12 and H3Md
CH2.49 Selected geometrical data for H3MdNCOCF3 are listed
in Table 6.50 In all compounds examined, the pnictogen center
possesses a distorted tetrahedral geometry, and the M, N, C,
and O atoms are on the same plane.
The calculated MdN bond lengths of H3MdNCOCF3 are
slightly longer than those of the parent H3MdNH,12 suggesting
that replacement of the N-hydrogen atom by a trifluoroacetyl
group increases the single-bond character of the MdN bond.
This phenomenon is probably due to the high electron-
withdrawing ability of the trifluoroacetyl group. To compare
the multiplicity of the MdN bond, the M-N bond lengths of
H2M-NHCOCF3 (M ) P, As, Sb, Bi) were also calculated.
As shown in Table 6, the bond-length ratio of BidN/Bi-N
(0.959) is close to that of SbdN/Sb-N (0.962) and much larger
than those of PdN/P-N (0.929) and AsdN/As-N (0.937).
Additionally, the calculated MdN bond order decreases pro-
gressively in the order PdN (1.289) > AsdN (1.170) > SbdN
(1.036) > BidN (0.943). These results indicate that the single-
bond character of the MdN bond becomes more prominent as
the pnictogen atom becomes heavier.
(a) Thermal Decomposition. The thermal stability of imino-
λ5-bismuthanes is strongly dependent on the N-substituents.
When heated in absolutely dry and deaerated benzene-d6 at 60
°C for 1 week in a sealed NMR tube, 3a was recovered mostly
unchanged.54 By contrast, 3f decomposed within 15 h under
the same conditions to give bismuthane 4a quantitatively (eq
1
1). The H NMR spectrum of the reaction mixture showed
broad, ill-resolved peak patterns, excepting those peaks attribut-
able to 4a. Exposure to air produced a gel that was insoluble in
organic solvents such as CH2Cl2, CHCl3, benzene, and DMSO.
(51) A similar trend, P < As < Bi e Sb, was observed for another basis
set (the Stevens-Basch-Krauss-Jasien-Cundari relativistic ECP plus
valence double-ú polarization basis set) and/or calculation method (density
functional theory with the B3LYP hybrid functional).
(52) It is known that the orbital size and energy of pnictogen atoms do
not vary in a linear manner due to the relativistic effect and the d-orbital
contraction. See: Nagase, S. In The Chemistry of Organic Arsenic, Antimony
and Bismuth Compounds; Patai, S., Ed.; Wiley: Chichester, U.K., 1994;
Chapter 1, pp 1-24.
(53) The n orbital of the oxygen atom may interact with the σ* orbitals
of the Sb-H2 and Bi-H2 bonds to lengthen these bonds and shorten the
Sb‚‚‚O and Bi‚‚‚O distances.
(54) In a previous communication (ref 22), we reported that 3a
decomposed by heating for 48 h at 60 °C in benzene to give bismuthane
4a in a 61% yield together with 2a. Later, it was found that the
decomposition was caused by adventitious moisture present in the reaction
system.
(49) Naito, T.; Nagase, S.; Yamataka, H. J. Am. Chem. Soc. 1994, 116,
10080-10088.
(50) All geometrical parameters are summarized in Supporting Informa-
tion.

(Acylimino)triaryl-λ5-bismuthanes
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10961
Scheme 4
was cleaved oxidatively by 1 equiv of 3a or 3f at room
temperature to give benzophenone in 74-84% yields (eq 3).
Benzenethiol was also oxidized by 0.5 equiv of 3a to give
diphenyl disulfide in 80% yield (eq 4). In these reactions,
bismuthane 4a was recovered in good yields.
Interestingly, when the thermolysis of 3f was carried out in
benzene in a flask, 3,5-bis(trifluoromethyl)aniline (12) and
amide 2c were obtained with a good recovery of 4a (eq 2). The
formation of 12 strongly suggested the intermediary formation
of 3,5-bis(trifluoromethyl)phenyl isocyanate (13) during ther-
molysis.
Ethanol and methanol were oxidized by 3f at room temper-
ature. Treatment of 3f with 5 equiv of ethanol in CDCl3 for 5
h afforded acetaldehyde in 90% NMR yield (based on 3f)
together with toluene (99%), amide 2c (76%), and bismuth(III)
compounds 14 of the type o-Tol2BiX (ca. 90% yield) (eq 5).60
Methanol was oxidized to methyl formate (76% based on 3f)
with good recovery of toluene (94%), 2c (70%), and 14 (ca.
90%) (eq 6). Formaldehyde, a putative initial product, could
not be detected during the reaction, suggesting that the second
oxidation step (H2CO f HCO2Me) proceeded much more
rapidly than the first (CH3OH f H2CO). In this oxidation, the
R-hydrogen is abstracted by the tolyl group. When the reaction
was carried out using CD3OH, deuterated toluene was formed
(detected by GCMS).
There are two possible pathways that may lead to 13 from
3f, a concerted pathway via 1,2-migration and a stepwise
pathway via free nitrene. When the thermolysis of 3f was carried
out in the presence of an excess (5-20 equiv) of a trapping
agent or a hydrogen source such as cyclohexene, styrene,
cyclohexane, or 9,10-dihydroanthracene, 12 and 2c were
obtained in a combined yield of 56-77%. Although the ratio
12/2c varied slightly, the products trapped by the additive could
1
not be detected by H NMR in all cases examined. Thus, it is
unlikely that a free nitrene species is involved as the primary
intermediate. Although no direct evidence is available for the
formation of 13,55 it is likely that the 3,5-bis(trifluoromethyl)-
phenyl group of 3f migrates from the acyl carbon to the imido
nitrogen concertedly with the elimination of a triarylbismuthonio
group, leading to 13 and 4a as the initial products (Scheme 4).
The isocyanate 13 would readily be hydrolyzed by moisture in
the solvent or from the atmosphere to give aniline 12.56
Previously, Furukawa and Oae reported a similar type of thermal
decomposition of N-acylsulfilimines (Ph2SdNCOR), where
diphenyl sulfide and isocyanates (RNCO) are eliminated at much
higher temperatures (ca. 200 °C).57 The decomposition mode
of (aroylimino)triaryl-λ5-bismuthane 3f contrasts to that of
(benzoylimino)triphenylphosphorane (Ph3PdNCOPh) and (ben-
zoylimino)triphenylarsorane (Ph3AsdNCOPh), which thermally
decompose to afford benzonitrile and the corresponding oxides
(Ph3PdO and Ph3AsdO), presumably via enolate intermedi-
ates.5a,58
Plausible reaction pathways for these oxidations are depicted
in Scheme 5.61 1,1,2,2-Tetraphenylethanediol reacts with 3f to
form a cyclic intermediate 15, which undergoes ligand cleavage
to give benzophenone (path a). On the other hand, methanol
and ethanol react with 3f to form an acyclic intermediate 16,
which undergoes an intramolecular R-hydrogen abstraction by
the adjacent tolyl group to form an aldehyde and o-Tol2Bi-
NHCOAr 14a (path b). The bismuth(III) amide 14a is hygro-
scopic and slowly undergoes hydrolysis to generate amide 2c
and compound 14b. The lighter pnictogen counterparts 6, 8,
and 10a did not oxidize these alcohols under the same reaction
conditions, demonstrating a remarkable oxidizing ability of
(acylimino)triaryl-λ5-bismuthanes 3.
There exists a great difference in thermal stability between
(sulfonylimino)-λ5-bismuthane and (acylimino)-λ5-bismuthane;
(tosylimino)tris(2-methoxyphenyl)-λ5-bismuthane [(2-MeOC6H4)3-
BidNSO2C6H4-4-Me]59 remained intact even after heating for
1 week at 60 °C in benzene-d6.
(c) Other Reactions. Compound 3d reacted with 5, 7, and
tris(2-methylphenyl)stibane in benzene-d6 at 60 °C to yield 6,
8, and 10a, respectively, with a quantitative recovery of 4a (eq
7). These results suggest that the (acylimino)triaryl-λ5-bismuth-
(b) Oxidation. (Acylimino)triaryl-λ5-bismuthanes 3 possess
a mild oxidizing ability (eqs 3-6). 1,1,2,2-Tetraphenylethanediol
(60) The X group in compound 14 was assigned as OBi(o-Tol)2,
NHCOC6H3-3,5-(CF3)2, or OR (R ) Et or Me) by comparison with the
authentic sample or by analysis of the 1H NMR data. See the Experimental
Section.
(55) This isocyanate 12 was found to polymerize in rigorously dried
benzene-d6 in the presence of a catalytic amount of 4a to give a gel, which
1
showed only broadened H NMR signals.
(56) Amide 2c may be formed by direct hydrolysis of 3f.
(57) (a) Furukawa, N.; Nishio, T.; Fukumura, M.; Oae, S. Chem. Lett.
1978, 209-210. (b) Furukawa, N.; Fukumura, M.; Nishio, T.; Oae, S. Bull.
Chem. Soc. Jpn. 1978, 51, 3599-3605.
(58) Staudinger, H.; Hauser, E. HelV. Chim. Acta 1921, 4, 861-886.
(59) Matano, Y.; Nomura, H.; Suzuki, H. Manuscript in preparation.
(61) Similar Bi(V)-alkoxo intermediates were proposed by Barton et al.
for the oxidation of alcohols with organobismuth(V) compounds. See: (a)
Barton, D. H. R.; Kitchin, J. P.; Lester, D. J.; Motherwell, W. B.; Papoula,
M. T. B. Tetrahedron 1981, 37, Supplement 9, 73-79. (b) Barton, D. H.
R.; Lester, D. J.; Motherwell, W. B.; Papoula, M. T. B. J. Chem. Soc.,
Chem. Commun. 1980, 246-247.

10962 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Matano et al.
Scheme 5
have revealed that the single-bond character of the MdN
bond as well as the contribution of the canonical form
M+-NdC-O- becomes increasingly prominent as pnictogen
atoms become heavier. This apparently is owing to the differ-
ences in orbital size and electronegativity among pnictogen
atoms. (Acylimino)triaryl-λ5-bismuthanes have been found to
possess remarkable oxidizing and nitrene-transfer abilities and
nucleophilicity, which appear to be largely attributable to the
good leaving ability of the bismuthonio group as well as to the
highly polarized character of the BidN bonding. The observed
reactivities of (acylimino)triaryl-λ5-bismuthanes differ consider-
ably from those of the lighter pnictogen counterparts and
demonstrate their potential utility in organic synthesis.
Experimental Section
ane 3 is thermodynamically much less stable than their lighter
pnictogen counterparts.
General Methods. All reactions were carried out under an argon
atmosphere unless otherwise noted. All melting points were determined
on a Yanagimoto hot-stage apparatus and are uncorrected. 1H and 13
C
NMR spectra were recorded on a Varian Gemini-200 or a JEOL FX400
spectrometer using CDCl3 as the solvent unless otherwise noted.
Chemical shifts are reported as the relative value vs tetramethylsilane.15N
NMR spectra were measured on a JEOL R-500 spectrometer and the
chemical shifts referenced to NH3(l).32 19F NMR spectra were measured
on a JEOL JNM-LA500 spectrometer in CDCl3 with neat CF3COOH
as an external standard. Unless otherwise noted, IR spectra were
observed as KBr pellets on a Shimadzu FTIR-8100S spectrophotometer.
EIMS, CIMS, and GCMS spectra were recorded on a Shimadzu QP5000
or QP2000 mass spectrometer. FABMS spectra were measured on a
JEOL JMS-HS100 spectrometer using m-nitrophenyl octyl ether as a
matrix. Elemental analyses were performed at the Microanalytical
Laboratory of Kyoto University. Column chromatography was per-
formed on silica gel (Wakogel C200). Dichloromethane (CH2Cl2) was
distilled from CaH2 before use. Tetrahydrofuran (THF) and diethyl ether
(Et2O) were distilled from sodium benzophenone ketyl before use.
Hexane, pentane, and CDCl3 were distilled from CaH2 and stored over
4 Å molecular sieves. Benzenes (C6H6 and C6D6) were distilled from
sodium and stored over 4 Å molecular sieves. Sealed NMR samples
were prepared by using a vacuum line with rigorously dried and
deaerated solvents. Triarylbismuth dichlorides 1 were prepared from
the corresponding triarylbismuthanes and sulfuryl chloride according
to Barton’s procedure.63 Triarylstibane oxides 964 and tris(2,4,6-
trimethylphenyl)stibane (11)65 were prepared according to reported
methods. Trichloroacetamide-15N (2b-15N) was prepared from trichlo-
roacetyl chloride and 15NH3, generated in situ from 15NH4Cl and KOH.66
Other reagents used were of commercial grade.
Treatment of 3a with aqueous HCl in CH2Cl2 gave dichloride
1a and amide 2a quantitatively (eq 8). Similar acidolysis was
observed for the reaction of 3b with acetic acid, in which
diacetate 17 was formed in 98% yield (eq 9). In the presence
of a catalytic amount of copper(II) triflate, both 3a,f underwent
aryl migration to give the N-acyltoluidines 18a,b, respectively,
with a moderate recovery of 4a and 2a,c (eq 10). The yield of
18 was not affected by the presence or absence of styrene, ruling
out the possible involvement of a nitrenoid species therein.
Although 3a did not react with benzaldehyde in boiling benzene,
3a,f were found to react with dimethyl acetylenedicarboxylate
(DMAD) to afford highly stabilized bismuthonium ylides.62 This
indicates that the (acylimino)triaryl-λ5-bismuthanes 3 possess
nucleophilicity and undergo the Michael addition to the acety-
lenic carbon of DMAD. In contrast, the lighter pnictogen
counterparts 6, 8, and 10a did not react with DMAD under the
same reaction conditions (in CDCl3, 50 °C, 15 h).
Triarylbismuth Dichlorides. 1a: 1H NMR δ 2.75 (s, 9H), 7.44-
7.57 (m, 9H), 8.04 (d, 3H, J ) 7.2 Hz). 1b: 1H NMR δ 3.87 (s, 9H),
7.19-7.27 (m, 6H), 7.45-7.54 (m, 3H), 8.13 (d, 3H, J ) 8.2 Hz). 1c:
1H NMR δ 2.31 (s, 9H), 2.72 (s, 18H), 7.14 (s, 6H). 1d: 1H NMR δ
2.41 (s, 9H), 7.45 (d, 6H, J ) 8.2 Hz), 8.37 (d, 6H, J ) 8.2 Hz). 1e:
1H NMR δ 7.52-7.56 (m, 3H), 7.64-7.69 (m, 6H), 8.53 (d, 6H, J )
7.6 Hz).
Triarylstibane Oxides. 9a: mp 261-265 °C (dec); 1H NMR δ 2.14
(s, 9H), 7.03-7.21 (m, 9H), 7.89 (d, 3H, J ) 7.4 Hz). Anal. Calcd for
C21H21OSb: C, 61.35; H, 5.15. Found: C, 61.48; H, 5.17. 9b: 1H NMR
δ 3.24 (s, 9H), 6.71 (d, 3H, J ) 8.1 Hz), 6.85-6.93 (m, 3H), 7.18-
7.25 (m, 3H), 7.83 (dd, 3H, J ) 7.3, 1.6 Hz).
Summary
(Acylimino)triaryl-λ5-bismuthanes have been prepared by the
base-promoted reaction of triarylbismuth dichlorides with
amides. The ortho-substituted aryl ligands have been found to
afford kinetic stabilization to the reactive BidN bond. The
thermal stabilities of (acylimino)triaryl-λ5-bismuthanes are
strongly dependent on the acyl group, with the less electron-
withdrawing acyl groups making them more thermally labile.
Experimental as well as theoretical comparisons of the structures
have been made for a series of (acylimino)pnictoranes, which
Tris(2,4,6-trimethylphenyl)stibane (11): 1H NMR δ 2.29 (s, 9H),
2.33 (s, 18H), 6.86 (s, 6H).
Synthesis of (Acylimino)triaryl-λ5-bismuthanes 3. General Pro-
cedure. KO-t-Bu (998 mg, 8.89 mmol) was added to a mixture of
(63) Barton, D. H. R.; Bhatnagar, N. Y.; Finet, J.-P.; Motherwell, W. B.
Tetrahedron 1986, 42, 3111-3122.
(64) Westhoff, T.; Huber, F.; Ru¨ther, R.; Preut, H. J. Organomet. Chem.
1988, 352, 107-113.
(65) Ates, M.; Breunig, H. J.; Soltani-Neshan, A.; Tegeler, M. Z.
Naturforsch. B 1986, 41, 321-326.
(62) Matano, Y.; Nomura, H.; Suzuki, H. J. Organomet. Chem. 2000,
611, 89-99.
(66) Clusius, K.; Effenberger, E. HelV. Chim. Acta 1955, 38, 1834-
1843.

(Acylimino)triaryl-λ5-bismuthanes
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10963
triarylbismuth dichloride 1 (4.00 mmol), amide 2 (4.05 mmol), and
CH2Cl2 (80 mL) at -50 °C. The resulting mixture was allowed to warm
gradually to room temperature with stirring. The insoluble solid was
filtered out through Celite and the filtrate concentrated under reduced
pressure to leave an oily residue that was then crystallized from CH2-
Cl2/hexane to give (acylimino)triaryl-λ5-bismuthane 3. Compounds 3f,g
were isolated as solids in a high state of purity but gradually
decomposed upon standing even at 4 °C. Due to thermal instability
(3h,i) or moisture sensitivity (3j,k), compounds 3h-k could not be
isolated, but the formation of these compounds in a high yield was
(3JPC ) 12.4 Hz), 132.9 (4JPC ) 3.0 Hz), 133.1 (2JPC ) 10.2 Hz), 170.1
(2JPC ) 5.6 Hz, CdO); IR νCdO 1638; FABMS m/z 422 ([M + H]+;
35Cl × 3).
[(Trichloroacetyl)imino]triphenylarsorane (8): mp 218-219 °C
1
(lit.29 mp 216 °C); H NMR δ 7.49-7.67 (m, 9H), 7.77 (d, 6H, J )
7.7 Hz); 13C NMR δ 127.5, 129.7, 132.5, 132.6, 173.0 (CdO); IR νCdO
1611; FABMS m/z 466 ([M + H]+; 35Cl × 3).
Synthesis of Imino-λ5-stibanes 10a-c. Method A. A mixture of
triarylstibane oxides 9a,b (0.63 mmol), trichloroacetonitrile (0.25 mL,
2.5 mmol), and CH2Cl2 (15 mL) was stirred at room temperature for 1
h. The resulting mixture was evaporated in vacuo to leave an oily
residue that contained (acylimino)triaryl-λ5-stibanes 10a,b in a high
state of purity. Compounds 10a,b were extremely moisture sensitive
and readily decomposed to give the corresponding oxides 9a,b under
ambient conditions.
1
confirmed by H NMR and FABMS.
[(Trifluoroacetyl)imino]tris(2-methylphenyl)-λ5-bismuthane (3a):
1
mp 108-116 °C (dec); H NMR δ 2.46 (s, 9H), 7.32-7.49 (m, 9H),
7.68-7.73 (m, 3H); 19F NMR δ 9.92; IR νCdO 1561; FABMS m/z 594
([M + H]+). Anal. Calcd for C23H21BiF3NO: C, 46.55; H, 3.57; N,
2.36. Found: C, 46.59; H, 3.47; N, 2.09.
Method B. Diethyl azodicarboxylate (40% in toluene, 1.5 mL, ca.
3.3 mmol) was added to a mixture of tris(2,4,6-trimethylphenyl)stibane
(11) (1.438 g, 3.00 mmol), 2b (487 mg, 3.00 mmol), and Et2O (30
mL) at 0 °C. The resulting mixture was stirred for 30 h and worked up
as described for the synthesis of 6 to give 10c as a moderately moisture-
sensitive solid.
[(Trifluoroacetyl)imino]tris(2-methoxyphenyl)-λ5-bismuthane (3b):
1
mp 136-143 °C (dec); H NMR δ 3.64 (s, 9H), 7.05-7.17 (m, 6H),
7.41-7.50 (m, 3H), 7.83-7.87 (m, 3H); 19F NMR δ 10.14; IR νCdO
1566; FABMS m/z 642 ([M + H]+). Anal. Calcd for C23H21BiF3NO4:
C, 43.07; H, 3.30; N, 2.18. Found: C, 42.86; H, 3.33; N, 1.91.
[(Trifluoroacetyl)imino]tris(2,4,6-trimethylphenyl)-λ5-bismuth-
[(Trichloroacetyl)imino]tris(2-methylphenyl)-λ5-stibane (10a): 1H
NMR δ 2.46 (s, 9H), 7.28-7.38 (m, 6H), 7.44-7.52 (m, 3H), 7.57 (d,
3H, J ) 7.7 Hz); 13C NMR δ 23.6, 127.3, 128.9, 131.7, 132.3, 135.1,
144.0, 173.7 (CdO); IR (in CH2Cl2) νCdO 1582; FABMS m/z 556
([M + H]+; 35Cl × 3, 123Sb; 35Cl × 2,37Cl, 121Sb).
1
ane (3c): mp 133-134 °C; H NMR δ 2.27 (s, 9H), 2.48 (s, 18H),
7.01 (s, 6H); IR νCdO 1576; FABMS m/z 678 ([M + H]+). Anal. Calcd
for C29H33BiF3NO: C, 51.41; H, 4.91; N, 2.07. Found: C, 51.24; H,
4.90; N, 2.12.
[(Trichloroacetyl)imino]tris(2-methylphenyl)-λ5-bismuthane (3d):
[(Trichloroacetyl)imino]tris(2-methoxyphenyl)-λ5-stibane (10b):
1H NMR δ 3.62 (s, 9H), 6.94 (d, 3H, J ) 8.2 Hz), 7.05-7.12 (m, 3H),
7.44-7.52 (m, 3H), 7.65 (d, 3H, J ) 7.4 Hz); IR (in CH2Cl2) νCdO
1581; FABMS m/z 604 ([M + H]+; 35Cl × 3, 123Sb; 35Cl × 2,
37Cl, 121Sb).
1
mp 113-115 °C (dec); H NMR δ 2.51 (s, 9H), 7.35 (t, 3H, J ) 7.4
Hz), 7.41-7.49 (m, 6H); 7.67-7.69 (m, 3H); IR νCdO 1593; FABMS
m/z 642 ([M + H]+; 35Cl × 3). Anal. Calcd for C23H21BiCl3NO: C,
42.98; H, 3.29; N, 2.18. Found: C, 42.81; H, 3.21; N, 2.19.
[(Trichloroacetyl)imino]tris(2-methoxyphenyl)-λ5-bismuthane (3e):
[(Trichloroacetyl)imino]tris(2,4,6-trimethylphenyl)-λ5-stibane (10c):
1H NMR δ 2.27 (s, 9H), 2.49 (s, 18H), 6.91 (s, 6H); 13C NMR δ 21.0,
23.3, 130.5, 133.0, 141.4, 143.6, 171.5 (CdO); IR νCdO 1583; FABMS
m/z 640 ([M + H]+; 35Cl × 3, 123Sb; 35Cl × 2,37Cl, 121Sb).
15N NMR Spectra of 15N-Labeled (Acylimino)triarylpnictoranes.
15N-labeled compounds 3e-15N, 6-15N, 8-15N, and 10c-15N were prepared
according to the procedures described above using 2b-15N. Compound
1
mp 112-114 °C (dec); H NMR δ 3.66 (s, 9H), 7.05-7.17 (m, 6H),
7.40-7.49 (m, 3H), 7.85-7.89 (m, 3H); 13C NMR δ 56.1, 111.8, 123.6,
132.2, 135.4, 136.6, 160.4, 172.2 (CdO); IR νCdO 1561; FABMS m/z
690 ([M + H]+; 35Cl × 3). Anal. Calcd for C23H21BiCl3NO4: C, 39.99;
H, 3.06; N, 2.03. Found: C, 39.81; H, 3.02; N, 2.11.
[(3,5-Bis(trifluoromethyl)benzoyl)imino]tris(2-methylphenyl)-λ5-
bismuthane (3f): 1H NMR δ 2.51 (s, 9H), 7.31-7.49 (m, 9H), 7.73-
7.81 (m, 3H), 7.88 (s, 1H), 8.62 (s, 2H); FABMS m/z 738 ([M + H]+).
[(3,5-Bis(trifluoromethyl)benzoyl)imino]tris(2-methoxyphenyl)-
λ5-bismuthane (3g): 1H NMR δ 3.62 (s, 9H), 7.05-7.17 (m, 6H),
7.40-7.49 (m, 3H), 7.85-7.93 (m, 4H), 8.65 (s, 2H); FABMS m/z
786 ([M + H]+).
2b-15N: 1H NMR δ 5.72 (d, 1H, JHN ) 91.2 Hz), 6.57 (d, 1H, JHN
)
91.9 Hz); IR ν 3363 (m), 3312 (m), 3242 (m), 3179 (m), 1692 (s, CdO),
1613 (m), 1379 (m), 1349 (m), 1102 (m), 927 (w), 831 (s), 824 (s),
751 (m), 668 (w), 640 (m), 619 (m), 437 (w). The incorporation of the
15N atom was confirmed by FABMS and 15N NMR. Compound 3e-
15N: FABMS m/z 691 ([M + H]+; 35Cl × 3). Compound 6-15N:
FABMS m/z 423 ([M + H]+; 35Cl × 3). Compound 8-15N: FABMS
m/z 467 ([M + H]+; 35Cl × 3). The 15N NMR spectra of the samples
(ca. 0.01 M in CDCl3) were obtained at room temperature using gated,
broad-band proton decoupling, a pulse angle of approximately 30°, and
a postacquisition delay of 20 s. Nitromethane was used as an external
standard. Chemical shifts relative to NH3(l) were calculated using the
equation δ(NH3) ) δ(MeNO2) + 380.23,32 and data are listed in
Table 2.
Thermal Decomposition of (Acylimino)triaryl-λ5-bismuthanes 3.
(a) In a Sealed Tube. Compound 3f (10.2 mg, 14 µmol) was placed
in a sealable NMR tube that was thoroughly evacuated using a vacuum
line. Benzene-d6, dried over sodium, was vacuum transferred into the
tube. After three freeze-pump-thaw cycles, the tube was evacuated
and sealed. The thermal decomposition of 3f was monitored at several
intervals by 1H NMR. After 15 h at 60 °C, the only peaks observed on
the spectrum were those of tris(2-methylphenyl)bismuthane (4a). The
yield of 4a was quantitative. When 3a was similarly reacted in a sealed
tube under the same conditions, no decomposition was observed even
after 1 week.
[(4-Nitrobenzoyl)imino]tris(2-methylphenyl)-λ5-bismuthane (3h):
1H NMR δ 2.51 (s, 9H), 7.30-7.49 (m, 9H), 7.75-7.78 (m, 3H), 8.19
(d, 2H, J ) 9.1 Hz), 8.27 (d, 2H, J ) 9.1 Hz); FABMS m/z 647
([M + H]+).
(Benzoylimino)tris(2-methylphenyl)-λ5-bismuthane (3i): 1H NMR
δ 2.52 (s, 9H), 7.28-7.45 (m, 12H), 7.76-7.80 (m, 3H), 8.10-8.15
(m, 2H); FABMS m/z 602 ([M + H]+).
[(Trifluoroacetyl)imino]tris(4-methylphenyl)-λ5-bismuthane (3j):
1H NMR δ 2.40 (s, 9H), 7.39 (d, 6H, J ) 7.7 Hz), 7.71 (d, 6H, J ) 7.7
Hz); FABMS m/z 594 ([M + H]+).
[(Trifluoroacetyl)imino]triphenyl-λ5-bismuthane (3k): 1H NMR
δ 7.60-7.71 (m, 9H), 7.84 (d, 6H, J ) 7.0 Hz); FABMS m/z 552
([M + H]+).
Synthesis of Iminophosphorane 6 and Iminoarsorane 8. These
compounds were prepared according to Bittner’s method.30 Diethyl
azodicarboxylate (40% in toluene, 0.50 mL, ca. 1.1 mmol) was added
to a mixture of triphenylphosphane (5) (262 mg, 1.00 mmol), 2b (163
mg, 1.00 mmol), and Et2O (10 mL) at 0 °C. The resulting mixture was
stirred for 12 h, during which time the mixture was allowed to warm
to room temperature. The volatiles were removed under reduced
pressure to leave an oily residue that was then washed with Et2O and
THF and crystallized from CH2Cl2/hexane to yield iminophosphorane
6 as a colorless solid (314 mg, 74%). Iminoarsorane 8 was prepared
similarly from arsane 7.
(b) In a Flask. A flask containing a benzene solution (20 mL) of 3f
(0.8-1.0 mmol) was heated at 60 °C for 15 h. The mixture was then
concentrated under reduced pressure to leave an oily residue that was
1
examined by H NMR. 3,5-Bis(trifluoromethyl)aniline (12) and 3,5-
bis(trifluoromethyl)benzamide (2c) were formed in 22-75% and 15-
76% yields, respectively, together with a good recovery of bismuthane
4a. Aniline 12 was characterized by comparison with the authentic
specimen. The residue was chromatographed on silica gel with hexane/
[(Trichloroacetyl)imino]triphenylphosphorane (6): mp 184-186
°C (lit.28 mp 183-184 °C); 1H NMR δ 7.46-7.66 (m, 9H), 7.79
(dd, 6H, J ) 12.5, 7.7 Hz); 13C NMR δ 126.4 (1JPC ) 100.3 Hz), 128.9

10964 J. Am. Chem. Soc., Vol. 123, No. 44, 2001
Matano et al.
ethyl acetate as the eluent to afford 4a: mp 132-136 °C (lit.67 mp
to leave an oily residue that was recrystallized from CH2Cl2/hexane to
1
130-131 °C); H NMR δ 2.44 (s, 9H), 7.03-7.11 (m, 3H), 7.23-
yield 1a (111 mg, 100%): mp 182-185 °C (dec) (lit.70 mp 172 °C).
7.37 (m, 6H), 7.55 (dd, 3H, J ) 7.3, 1.3 Hz). Aniline 12: 1H NMR δ
4.07 (br-s, 2H), 7.03 (s, 2H), 7.21 (s, 1H). When a benzene solution of
3a was heated at 60 °C for 48 h under N2 or Ar in a flask, 4a was
obtained in 61% yield together with amide 2a. When the thermolysis
of 3f was carried out in the presence of an excess (5-20 equiv) of a
trapping agent or a hydrogen source such as cyclohexene, styrene,
cyclohexane, or 9,10-dihydroanthracene, 12 and 2c were obtained in a
combined yield of 56-77%. Products trapped by the additive could
Reaction of 3b with Acetic Acid. A mixture of 3b (194 mg, 0.303
mmol), acetic acid (0.19 mL, 3.3 mmol), and Et2O (10 mL) was stirred
at room temperature for 4 h. The mixture was evaporated under reduced
pressure to leave an oily residue that was then extracted with Et2O (10
mL). The Et2O extract was dried over MgSO4 and evaporated under
reduced pressure to leave an oily residue that was recrystallized from
CH2Cl2/hexane to yield tris(2-methoxyphenyl)bismuth diacetate (17)
as a crystalline solid (188 mg, 98%): mp 143-145 °C (dec) (lit.71 mp
1
1
not be detected by H NMR.
147 °C); H NMR δ 1.67 (s, 6H), 3.86 (s, 9H), 7.15-7.23 (m, 6H),
Oxidation of 1,1,2,2-Tetraphenylethanediol. A mixture of 3a (121
mg, 0.204 mmol), 1,1,2,2-tetraphenylethanediol (78 mg, 0.21 mmol),
and CH2Cl2 (10 mL) was stirred at room temperature for 24 h.
Evaporation of the solvent under reduced pressure left an oily residue
that was then chromatographed on silica gel (hexane/EtOAc) to give
4a (89 mg, 91%), benzophenone (65.3 mg, 84%), and unchanged diol.
The products were identified by comparison with the authentic
7.37-7.45 (m, 3H), 8.20 (d, 3H, J ) 7 Hz).
Copper(II) Trifluoromethanesulfonate-Catalyzed Aryl Migration
of 3. A mixture of 3a (147 mg, 0.247 mmol), Cu(OTf)2 (4.9 mg, 0.014
mmol), and CH2Cl2 (10 mL) was stirred at room temperature for 24 h.
Evaporation of the mixture under reduced pressure left an oily residue
that was then chromatographed on silica gel (hexane/EtOAc) to give
bismuthane 4a (45 mg, 38%) and N-trifluoroacetyl-o-toluidine (18a)
(17.7 mg, 35%): mp 79-81 °C (lit.72 mp 81-82 °C); 1H NMR δ 2.31
(s, 3H), 7.16-7.32 (m, 3H), 7.45-7.85 (br-s, 1H, NH), 7.78 (d, 1H,
J ) 6.6 Hz); CIMS m/z 204 ([M + H]+), 134, 107. The yield of 18a
was not affected by the presence or absence of an excess amount of
styrene. A similar treatment of 3f with Cu(OTf)2 afforded 18b (33%),
2c (68%), and 4a (15%). N-[3,5-Bis(trifluoromethyl)benzoyl]-o-tolui-
dine (18b): 1H NMR δ 2.35 (s, 3H), 7.15-7.33 (m, 3H), 7.66-7.71
(br-s, 1H, NH), 7.77 (d, 1H, J ) 8.6 Hz), 8.07 (s, 1H), 8.32 (s, 2H);
EIMS m/z 347 (M+), 328, 241, 213, 106.
1
specimens. The presence of 2a in the residue was confirmed by H
NMR and MS. When 3f was used instead of 3a, benzophenone and 4a
were formed in 74% and 83% yield, respectively.
Oxidation of Benzenethiol. A mixture of 3a (178 mg, 0.300 mmol),
benzenethiol (62 µL, 0.60 mmol), and benzene (10 mL) was stirred at
room temperature for 3 h. Concentration of the mixture under reduced
pressure left an oily residue that was chromatographed on silica gel
(hexane/EtOAc) to give 4a (148 mg, 100%) and diphenyl disulfide
(53 mg, 80%). The products were identified by comparison with the
authentic specimens.
Ab initio Molecular Orbital Calculations of Iminopnictorane
Structures, H3MdNCOCF3 (M ) P, As, Sb, Bi). The molecular
structures of imaginary iminopnictoranes, H3MdNCOCF3 (M ) P, As,
Sb, Bi), were predicted by ab initio calculations. The geometry
optimization and bond-order and charge-distribution analyses were made
using the Gaussian 98 program system.73 The basis set was at the
valence double-ú plus polarization function level with the relativistic
effective core potential (ECP). For pnictogen atoms, the Los Alamos
effective core potential plus the valence double-ú basis functions74
augmented with the d-polarization function were used, where the
exponents of the d functions were 0.340 (P), 0.293 (As), 0.211 (Sb),
and 0.185 (Bi). The functions for carbon, nitrogen, oxygen, fluorine,
and hydrogen were the (9s5p/4s)/[3s2p/2s] valence double-ú basis
functions by Dunning and Hay.75 In addition, the d-polarization
functions were placed on carbon, nitrogen, and oxygen atoms, where
the exponents of the d functions were 0.600 (C), 0.864 (N), and 1.154
(O). No polarization functions were placed on the hydrogen and fluorine
atoms. The molecular structures were optimized at the second-order
Møller-Plesset (MP2) perturbation theory level using the analytical
gradient method. All the geometrical parameters were optimized without
any symmetry constraints. The stationary structures were confirmed
by vibrational analysis. The Mayer-Mulliken natural bond order of
the MdN bond and the natural charges76 on the pnictogen, nitrogen,
Oxidation of Ethanol and Methanol. A mixture of 3f (13 mg, 18
µmol), ethanol (5 µL, 89 µmol), and CDCl3 (0.50 mL) was allowed to
stand in an NMR tube at room temperature. The progress of the reaction
1
was monitored by H NMR. After 5 h, acetaldehyde (90%), toluene
(99%), amide 2c (76%), and compounds 14 of the type o-Tol2BiX
(92%) were formed. Methanol was similarly oxidized by 3f to afford
methyl formate (76%), toluene (94%), 2c (70%), and 14 (90%) after 5
h. The oxidation products (acetaldehyde and methyl formate) and
toluene were identified by comparison with the authentic specimens.
The spectral data for the major component (>70%) of 14 was identical
to that of a bismuth compound obtained from the reaction of bis(2-
methylphenyl)bismuth trifluoromethanesulfonate68 with aqueous NaOH.
On the basis of spectral data as well as by comparison with a previous
result with Mes2BiOBiMes2,69 we identified the major component of
14 as tetrakis(2-methylphenyl)dibismuth oxide (14b) (o-Tol2BiOBio-
Tol2): 1H NMR 2.15 (s, 12H), 7.22-7.32 (m, 8H), 7.38-7.42 (m, 4H),
8.20 (d, 4H, J ) 7.2 Hz). Two minor components were tentatively
assigned as bis(2-methylphenyl)bismuth 3,5-bis(trifluoromethyl)ben-
zamide and bis(2-methylphenyl)bismuth alkoxide, but only on the basis
of the 1H NMR spectra of the crude products, and attempts to prepare
these samples independently failed. We speculate that the amide 14a
formed initially, o-Tol2BiNHCOAr (Ar ) 3,5-(CF3)2C6H3), would have
been hydrolyzed by moisture from the solvent or atmosphere to produce
14b and amide 2c.
(70) Fedorov, A.; Combes, S.; Finet, J.-P.Tetrahedron 1999, 55, 1341-
1352.
(71) Combes, S.; Finet, J.-P. Synth. Commun. 1996, 26, 4569-4575.
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Soc., Perkin Trans. 2 1998, 629-634.
Reaction of 3d with 5, 7, and Triarylstibane. A mixture of 3d
(10.6 mg, 16.5 µmol), 5 (11.6 mg, 44.2 µmol), and C6D6 (0.75 mL)
was heated at 60 °C for 7 h. Iminophosphorane 6 was formed with a
quantitative recovery of 4a. Triphenylarsane (7) and tris(2-methylphen-
yl)stibane also reacted with 3d under similar conditions to generate 8
and 10a, respectively, together with 4a.
(73) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M.
W.; Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A.; Gaussian 98, ReVision
A.5; Gaussian, Inc.: Pittsburgh, PA, 1998.
Reaction of 3a with Aqueous HCl. To a CH2Cl2 solution (3 mL)
of 3a (118 mg, 0.199 mmol) was added aqueous HCl (ca. 12 N, 0.2
mL), and the resulting mixture was vigorously stirred at room
temperature. After 1 h, the organic phase was separated and the aqueous
phase was extracted with CH2Cl2 (5 mL × 2). The combined organic
phase was dried over MgSO4 and concentrated under reduced pressure
(67) Nesmeyanov, A. N.; Tolstaya, T. P.; Isaeva, L. S. Dokl. Akad. Nauk
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(Acylimino)triaryl-λ5-bismuthanes
J. Am. Chem. Soc., Vol. 123, No. 44, 2001 10965
and oxygen atoms were calculated. The bond order and the natural
charges were computed at the MP2 level.
Molecular Structure Corp. Further details of the X-ray crystallography
are provided in the Supporting Information.
X-ray Crystallographic Analyses of 3e, 6, 8, and 10c. Single
crystals of compounds 3e, 6, 8, and 10c were grown from CH2Cl2/
hexane (3e, 6, 8) or Et2O/pentane (10c) at 4 °C. Data were recorded
on a Rigaku AFC7S diffractometer (6), a Rigaku RAXIS-IV imaging
plate diffractometer (3e), or a Rigaku RAXIS-RAPID imaging plate
diffractometer (8, 10c), with graphite-monochromated Mo KR radiation.
The data were corrected for Lorentz and polarization effects. The
structures were solved by the direct method77 and were expanded using
Fourier techniques.78 Non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included but not refined. Neutral atom-scattering
factors were taken from Cromer and Waber.79 Anomalous dispersion
Acknowledgment. This work was supported by Grants-in-
Aid (No. 11120224 and 12640516) from the Ministry of
Education, Science, Sports, and Culture of Japan. We thank Mr.
Akira Saito for his assistance with the X-ray crystallography
and Professor Keiji Maruoka for his encouragement.
Note Added after ASAP: An incorrect formula was
published on Page 4 in the version posted October 11, 2001.
The corrected version was reposted October 16, 2001.
Supporting Information Available: Text providing full IR
data for 3a-e, 6, 8, and 10c, tables of all the bond lengths and
angles obtained by ab initio molecular orbital calculations on
the structures of H3MdNCOCF3, and X-ray crystallographic
data (tables and figures) for the structures of 3e, 6, 8, and 10c.
This material is available free of charge via the Internet at
http://pubs.acs.org.
effects were included in Fcalc;
80 the values for ∆f ′ and ∆f ′′ were those
of Creagh and McAuley.81 The values for the mass-attenuation
coefficients are those of Creagh and Hubbel.82 All calculations were
performed using a teXsan83 crystallographic software package of the
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system; Technical Report of the Crystallography Laboratory, University of
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(79) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, England, 1974; Vol.
IV, Table 2.2A.
(81) Creagh, D. C.; McAuley, W. J. International Tables for Crystal-
lography; Wilson, A. J. C., Ed.; Kluwer Academic Publishers: Boston,
MA, 1992; Vol. C, Table 4.2.6.8, pp 219-222.
(82) Creagh, D. C.; Hubbell, J. H. International Tables for Crystal-
lography; Wilson, A. J. C., Ed.; Kluwer Academic Publishers: Boston,
MA, 1992; Vol. C, Table 4.2.4.3, pp 200-206.
(83) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corp: The Woodlands, TX, 1985, 1999.
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