Syntheses of chromium pentacarbonyl derivatives of arsenic(V) and antimony(V). Contrasting chemical reactivity with organic halogen derivatives

Article abstract of DOI:10.1021/ic0004277

We have synthesized a new series of chromium-group 15 dihydride and hydride complexes [H₂As{Cr(CO)₅}₂]^- (1) and [HE{Cr(CO)₅}₃]^2- (E = As, 2a; E = Sb, 2b), which represent the first examples of group 6 complexes containing E-H fragments. The contrasting chemical reactivity of 2a and 2b with organic halogen derivatives is demonstrated. The reaction of 2a with RBr (R = PhCH₂, HC≡CCH₂) produces the RX addition products [(R)(Br)As{Cr(CO)₅}₂]^- (R = PhCH₂, 3; R = C₃H₃, 4), while the treatment of 2b with RX (RX = PhCH₂Br or HC≡CCH₂Br, CH₃(CH₂)₅C(O)CI) forms the halo-substituted complexes [XSb{Cr(CO)₅}₃]^2- (X = Br, 5; X = Cl, 6). Moreover, the dihaloantimony complexes [XX′Sb{Cr(CO)₅}₂]^- can be obtained from the reaction of 2b with the appropriate organic halides. In this study, a series of organoarsenic and antimony chromium carbonyl complexes have been synthesized and structurally characterized and the role of the main group on the formation of the resultant complexes is also discussed.

Full text of DOI:10.1021/ic0004277

1206
Inorg. Chem. 2001, 40, 1206-1212
Syntheses of Chromium Pentacarbonyl Derivatives of Arsenic(V) and Antimony(V).
Contrasting Chemical Reactivity with Organic Halogen Derivatives
Jiann-Jang Cherng,† Yun-Wen Lai,† Yi-Hung Liu,‡ Shie-Ming Peng,§ Chuen-Her Ueng,† and
Minghuey Shieh*,†
Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan, Republic of China,
and Department of Chemistry and Instrumentation Center, National Taiwan University,
Taipei 107, Taiwan, Republic of China
ReceiVed April 18, 2000
We have synthesized a new series of chromium-group 15 dihydride and hydride complexes [H2As{Cr(CO)5}2]-
(1) and [HE{Cr(CO)5}3]2- (E ) As, 2a; E ) Sb, 2b), which represent the first examples of group 6 complexes
containing E-H fragments. The contrasting chemical reactivity of 2a and 2b with organic halogen derivatives is
demonstrated. The reaction of 2a with RBr (R ) PhCH2, HCtCCH2) produces the RX addition products
[(R)(Br)As{Cr(CO)5}2]- (R ) PhCH2, 3; R ) C3H3, 4), while the treatment of 2b with RX (RX ) PhCH2Br or
HCtCCH2Br, CH3(CH2)5C(O)Cl) forms the halo-substituted complexes [XSb{Cr(CO)5}3]2- (X ) Br, 5; X )
Cl, 6). Moreover, the dihaloantimony complexes [XX′Sb{Cr(CO)5}2]- can be obtained from the reaction of 2b
with the appropriate organic halides. In this study, a series of organoarsenic and antimony chromium carbonyl
complexes have been synthesized and structurally characterized and the role of the main group on the formation
of the resultant complexes is also discussed.
Introduction
MLnE{Cr(CO)5}2 (MLn ) Mn(CO)5, E ) As; MLn ) Cr(CO)5,
Mn(CO)5, MoCp(CO)3, Mo(CO)5, W(CO)5, E ) Sb).4 We have
developed a facile route to a new series of chromium-group
15 dihydride and hydride complexes [H2As{Cr(CO)5}2]- (1)
and [HE{Cr(CO)5}3]2- (E ) As, 2a; E ) Sb, 2b). There are
relatively few well-characterized metal carbonyl complexes
containing E-H (E ) As, Sb) fragments, and the structurally
authenticated examples are limited to (µ-HAs){CpMn(CO)2}2,5
Transition metal carbonyl complexes incorporating main
group fragments have attracted great attention because of their
unusual bonding and versatile reactivity patterns.1 In contrast
to the well-developed iron-group 15 complexes,2 most of the
previously described As-Cr-CO and Sb-Cr-CO complexes
exhibit trigonal-planar structures such as XAs{Cr(CO)5}2
(X ) Br, Cl, I, Ph, OMe, OEt, SC2H5, SC6H11, SeC6H5)3 and
[HAs{Fe(CO)4}3]2- 6,7 and [HSb{Fe(CO)4}3]2-.7 To our knowl-
,
edge, complexes 1, 2a, and 2b represent the first examples of
group 6 complexes containing E-H fragments in which 2a and
2b contain one E-H bond each and 1 possesses two E-H
bonds.
* To whom correspondence should be addressed.
† Department of Chemistry, National Taiwan Normal University.
‡ Instrumentation Center, National Taiwan University.
§ Department of Chemistry, National Taiwan University.
(1) (a) Shriver, D. F.; Kasez, H. D.; Adams, R. D. The Chemistry of Metal
Cluster Complexes; VCH Publishers: New York, 1990. (b) Herrmann,
W. A. Angew. Chem., Int. Ed. Engl. 1986, 25, 56. (c) Scherer, O. J.
Comments Inorg. Chem. 1987, 6, 1. (d) Scherer, O. J. Angew. Chem.,
Int. Ed. Engl. 1985, 24, 924. (e) Whitmire, K. H. J. Coord. Chem.
1988, 17, 95. (f) Huttner, G.; Evertz, K. Acc. Chem. Res. 1986, 19,
406. (g) Vahrenkamp, H. AdV. Organomet. Chem. 1983, 22, 169. (h)
Scherer, O. J. Angew. Chem., Int. Ed. Engl. 1990, 29, 1104. (i) Cowley,
A. H. J. Organomet. Chem. 1990, 400, 71. (j) Dimaio, A.-J.;
Rheingold, A. L. Chem. ReV. 1990, 90, 169. (k) Compton, N. A.;
Errington, R. J.; Norman, N. C. AdV. Organomet. Chem. 1990, 31,
91. (l) Whitmire, K. H. J. Cluster Sci. 1991, 2, 231. (m) Whitmire, K.
H. J. AdV. Organomet. Chem. 1997, 42, 1. (n) Shieh, M. J. Cluster
Sci. 1999, 10, 3.
(2) (a) Ro¨ttinger, E.; Vahrenkamp, H. Angew. Chem., Int. Ed. Engl. 1978,
17, 273. (b) Luo, S.; Whitmire, K. H. Inorg. Chem. 1989, 28, 1424.
(c) Whitmire, K. H.; Shieh, M.; Lagrone, C. B.; Robinson, B. H.;
Churchill, M. R.; Fettinger, J. C.; See, R. F. Inorg. Chem. 1987, 26,
2798. (d) Whitmire, K. H.; Leigh, J. S.; Luo, S.-F.; Shieh, M.; Fabiano,
M. D. New. J. Chem. 1988, 12, 397. (e) Luo, S.-F.; Whitmire, K. H.
J. Organomet. Chem. 1989, 376, 297. (f) Arnold, L. J.; Mackay, K.
M.; Nicholson, B. K. J. Organomet. Chem. 1990, 387, 197. (g) Shieh,
M.; Liou, Y.; Peng, S.-M.; Lee, G.-H. Inorg. Chem. 1993, 32, 2212.
(h) Shieh, M.; Liou, Y. Jeng. B.-W. Organometallics 1993, 12, 4926.
(i) Shieh, M.; Sheu, C.-M.; Ho, L.-F.; Cherng, J.-J.; Ueng, C.-H.; Peng,
S.-M.; Lee, G.-H. Inorg. Chem. 1996, 35, 5504.
The main group element has been shown to have influence
on the reactivity of the mixed main group-transition metal
complexes in the well-studied E-Fe-CO system.2g-i,8 To
understand the effect of main group elements on this new family
of E-Cr-CO complexes, we extensively investigate the chemi-
cal reactivity of [HE(Cr(CO)5)3]2- (E ) As, 2a; E ) Sb, 2b)
with organic halides. In this paper, we report the contrasting
chemical reactivity of 2a and 2b with organic halogen deriva-
tives, and a series of new organoarsenic and antimony chromium
carbonyl complexes (3-8) has been synthesized and structurally
characterized as well. The syntheses of 2a and 2b have been
communicated.9
(4) Huttner, G.; Weber, U.; Sigwarth, B.; Scheidsteger, O.; Lang, H.;
Zsolnai, L. J. Organomet. Chem. 1985, 282, 331.
(5) Herrmann, W. A.; Koumbouris, B.; Zahn, T.; Ziegler, M. L. Angew.
Chem., Int. Ed. Engl. 1984, 23, 812.
(6) (a) Bachman, R. E.; Miller, S. K.; Whitmire, K. H. Inorg. Chem. 1994,
33, 2075. (b) Bachman, R. E.; Miller, S. K.; Whitmire, K. H.
Organometallics 1995, 14, 796.
(7) Henderson, P.; Rossignoli, M.; Burns, R. C.; Scudder, M. L.; Craig,
D. C. J. Chem. Soc., Dalton Trans. 1994, 1641.
(3) (a) Seyerl, J. V.; Sigwarth, B.; Schmid, H.-G.; Mohr, G.; Frank, A.;
Marsili, M.; Huttner, G. Chem. Ber. 1981, 114, 1392. (b) Huttner, G.;
Schmid, H.-G. Angew. Chem., Int. Ed. Engl. 1975, 14, 433.
(8) Shieh, M.; Ho, L.-F.; Cherng, J.-J.; Ueng, C.-H.; Peng, S.-M.; Lee,
G.-H. J. Organomet. Chem. 1999, 587, 176.
10.1021/ic0004277 CCC: $20.00 © 2001 American Chemical Society
Published on Web 02/16/2001

Syntheses of Ar(V) and Sb(V) Derivatives
Inorganic Chemistry, Vol. 40, No. 6, 2001 1207
(chemical shifts not given for [Et4N]+). Negative ion FABMS: m/z
628.8. Anal. Calcd for [Et4N][3]: C, 39.49; H, 3.58; N, 1.84. Found:
C, 39.26; H, 3.33; N, 1.85. The residue was then extracted with THF,
and the THF extract was recrystallized with hexanes/CH2Cl2 to give
0.11 g (0.273 mmol) of the known compound [Et4N][BrCr(CO)5]11
(24% based on [Et4N]2[2a]). IR (νCO, THF): 2054 w, 1921 vs, 1862
vs cm-1. Anal. Calcd for [Et4N][BrCr(CO)5]: C, 38.82; H, 5.01; N,
3.48. Found: C, 38.76; H, 4.97; N, 3.27.
Experimental Section
All reactions were performed under an atmosphere of pure nitrogen
using standard Schlenk techniques.10 Solvents were purified, dried, and
distilled under nitrogen prior to use. Cr(CO)6 (Strem), As2O3 (WAKO),
and Sb2O3 (Aldrich) were used as received. Infrared spectra were
recorded on a Perkin-Elmer Paragon 500 IR spectrometer as solutions
in CaF2 cells. The 1H and 13C NMR spectra were taken on a JEOL 400
instrument at 399.78 and 100.53 MHz, respectively. FAB mass spectra
were taken on a JEOL SX-102A mass spectrometer. Quantitative
analysis of the organic products was performed on a Shimadzu GC-
9A instrument and GC Hewlett-Packard 6890 instrument equipped with
a Hewlett-Packard 5973 MS selective detector. Elemental analyses of
C, H, and N were performed on a Perkin-Elmer 2400 analyzer at the
NSC Regional Instrumental Center at National Taiwan University,
Taipei, Taiwan.
Reaction of [Et4N]2[HAs{Cr(CO)5}3] ([Et4N]2[2a]) with HCt
CCH2Br. To a solution of 0.33 g (0.36 mmol) of [Et4N]2[2a] in 20
mL of THF was added 0.04 mL (0.53 mmol) of HCtCCH2Br. The
resulting solution was stirred in an ice/water bath for 20 min, then
warmed to room temperature, and stirred for another 2 days. The ether
extract was recrystallized with hexane/CH2Cl2 to give 0.15 g (0.21
mmol) of the pure compound [Et4N][(Br)(C3H3)As{Cr(CO)5}2] ([Et4N]-
[4]) (58% based on [Et4N]2[2a]). IR (νCO, THF): 2058 m, 2046 m,
1
2038 s, 1972 m, 1943 vs, 1900 s cm-1. H NMR (DMSO-d6, 298 K,
Syntheses of [Et4N][H2As{Cr(CO)5}2] ([Et4N]2[1]) and [Et4N]2-
[HAs{Cr(CO)5}3] ([Et4N]2[2a]). To a mixture of 5.40 g (96.2 mmol)
of KOH, 0.20 g (1.00 mmol) of As2O3, and 1.32 g (6.01 mmol) of
Cr(CO)6 was added 20 mL of MeOH. After being stirred for 3 days at
room temperature, the solution was filtered and an aqueous solution
of 1.35 g (6.40 mmol) of Et4NBr was added, precipitating the orange
product. The product was collected by filtration, washed with H2O,
and dried under vacuum. The residue was washed with hexane and
extracted with ether to give 0.55 g (0.93 mmol) of [Et4N][H2As{Cr-
(CO)5}2] (47% based on As). Crystals suitable for X-ray diffraction
were grown from hexanes/CH2Cl2. IR (νCO, CH2Cl2): 2032 s, 1929
ppm): δ 6.80 (t, 1H, J ) 6.23 Hz), 5.06 (d, 2H, J ) 6.23 Hz) (chemical
shifts not given for [Et4N]+). 13C NMR (DMSO-d6, 298 K, ppm): δ
227.58, 220.21, 204.35, 98.46, 77.92 (chemical shifts not given for
[Et4N]+). Negative ion FABMS: m/z 578.7. Anal. Calcd for [Et4N]-
[4]: C, 35.61; H, 3.27; N, 1.98. Found: C, 35.29; H, 3.40; N, 1.77.
The residue was then extracted with THF, and the THF extract was
recrystallized with hexanes/CH2Cl2 to give the known compound [Et4N]-
[BrCr(CO)5].11
Reaction of [Bu4N]2[HSb{Cr(CO)5}3] ([Bu4N]2[2b]) with PhCH2Br.
To a solution of 0.72 g (0.61 mmol) of [Bu4N]2[2b] in 7.5 mL of THF
was added 0.08 mL (0.67 mmol) of PhCH2Br. The resulting solution
was stirred in an ice/water bath for 20 min, then warmed to room
temperature, and stirred for another 2.5 h. The solvent was removed
under vacuum, and the organic product-toluene (0.373 mmol, 61%
based on [Bu4N]2[2b]) was quantified and identified by GC and GC/
MS. Then the THF extract was recrystallized with ether/THF to give
0.50 g (0.396 mmol) of the pure compound [Bu4N]2[BrSb{Cr(CO)5}3]
([Bu4N]2[5]) (65% based on [Bu4N]2[2b]). IR (νCO, THF): 2012 vs,
1929 vs, 1865 s cm-1. Anal. Calcd for [Bu4N]2[5]: C, 44.71; H, 5.75;
N, 2.22. Found: C, 44.61; H, 5.82; N, 2.05.
1
vs, 1881 s cm-1. H NMR (CD2Cl2, ppm): δ 0.0 (s, 2H) (chemical
shifts not given for [Et4N]+). Negative ion FABMS: m/z 460.8. Anal.
Calcd for [Et4N][1]: C, 36.56; H, 3.75; N, 2.37. Found: C, 36.43; H,
3.66; N, 2.16. The residue was then extracted with THF, and the THF
extract was recrystallized from ether/THF to give 0.32 g (0.35 mmol)
of [Et4N]2[HAs{Cr(CO)5}3] ([Et4N]2[2a]) (18% based on As). IR (νCO
,
THF): 2007 vs, 1914 vs, 1847 s cm-1. H NMR (DMSO-d6, ppm): δ
-2.0 (s, 1H) (chemical shifts not given for [Et4N]+). Anal. Calcd for
[Et4N]2[2a]: C, 40.80; H, 4.53; N, 3.07. Found: C, 40.50; H, 4.45; N,
3.11. Crystals suitable for X-ray diffraction were grown from ether/
CH2Cl2.
1
Reaction of [Et4N]2[HSb{Cr(CO)5}3] ([Et4N]2[2b]) with HCt
CCH2Br. To a solution of 0.52 g (0.54 mmol) of [Et4N]2[2b] in 20
mL of THF was added 0.055 mL (0.73 mmol) of HCtCCH2Br. The
resulting solution was stirred in an ice/water bath for 20 min, then
warmed to room temperature, and stirred for another 4 h. The solvent
was removed under vacuum, and the CH2Cl2 extract was recrystallized
with Et2O/CH2Cl2 to give 0.43 g (0.41 mmol) of the pure compound
[Et4N]2[BrSb{Cr(CO)5}3] ([Et4N]2[5]) (76% based on [Et4N]2[2b]).
Reaction of [Et4N]2[HSb{Cr(CO)5}3] ([Et4N]2[2b]) with CH3-
(CH2)5C(O)Cl. To a solution of 0.63 g (0.66 mmol) of [Et4N]2[2b] in
7.5 mL of THF was added 0.12 mL (0.78 mmol) of CH3(CH2)5C(O)-
Cl. The resulting solution was stirred in an ice/water bath for 20 min,
then the solvent was removed under vacuum. The organic product-
CH3(CH2)5CHO (>0.40 mmol, 61% based on [Et4N]2[2b]) was
quantified and identified by GC and GC/MS. The THF extract was
recrystallized with ether/THF to give 0.55 g (0.55 mmol) of the pure
compound [Et4N]2[ClSb{Cr(CO)5}3] ([Et4N]2[6]) (83% based on [Et4N]2-
[2b]). IR (νCO, THF): 2012 vs, 1930 vs, 1869 s cm-1. Anal. Calcd for
[Et4N]2[6]: C, 37.46; H, 4.06; N, 2.82. Found: C, 37.44; H, 4.01; N,
2.69.
Reaction of [Et4N]2[BrSb{Cr(CO)5}3] ([Et4N]2[5]) with CH3C-
(O)Cl. To a solution of 0.24 g (0.23 mmol) of [Et4N]2[5] in 20 mL of
THF in an ice/water bath was added 0.04 mL (0.56 mmol) of CH3C-
(O)Cl. The mixture was stirred in an ice/water bath for 30 min and
then warmed to room temperature and stirred for 1 day. The resultant
solution was filtered to collect the filtrate, and the solvent was removed
under vacuum. The residue was extracted with mixed solvents of THF/
hexanes ) 2:3; the extract was then recrystallized with hexanes/CH2-
Cl2 to give 0.09 g (0.13 mmol) of the pure compound [Et4N][Cl2Sb-
{Cr(CO)5}2] ([Et4N][7]) (57% based on [Et4N]2[5]). Crystals suitable
Synthesis of [Et4N]2[HSb{Cr(CO)5}3] ([Et4N]2[2b]). To a mixture
of 5.39 g (96.0 mmol) of KOH, 0.27 g (0.93 mmol) of Sb2O3, and
1.25 g (5.67 mmol) of Cr(CO)6 was added 25 mL of MeOH. After
being stirred for 3 days at room temperature, the solution was filtered
and an aqueous solution of 1.53 g (5.95 mmol) of Et4NBr was added,
precipitating the orange product. This product was collected by filtration,
washed with H2O, and dried under vacuum. Recrystallization from Et2O/
THF gave 1.41 g (1.47 mmol) of [Et4N]2[HSb{Cr(CO)5}3] ([Et4N]2-
[2b]) (79% based on Sb). IR (νCO, THF): 2003 vs, 1919 vs, 1860 s
cm-1. 1H NMR (DMSO-d6, ppm): δ -5.5 (s, 1H) (chemical shifts not
given for [Et4N]+). Anal. Calcd for [Et4N]2[2b]: C, 38.81; H, 4.31; N,
2.92. Found: C, 38.51; H, 4.34; N, 2.76. Crystals suitable for X-ray
diffraction were grown from ether/THF.
Reaction of [Et4N]2[HAs{Cr(CO)5}3] ([Et4N]2[2a]) with PhCH2Br.
To a solution of 0.35 g (0.38 mmol) of [Et4N]2[2a] in 5 mL of THF
was added 0.05 mL (0.42 mmol) of PhCH2Br. The resulting solution
was stirred in an ice/water bath for 10 min, then warmed to room
temperature, and stirred for another 20 h. The solvent was removed
under vacuum, and the organic product-toluene (0.239 mmol, 63%
based on [Et4N]2[2a]) was quantified and identified by GC and GC/
MS. The ether extract was recrystallized with hexane/CH2Cl2 to give
0.08 g (0.11 mmol) of the pure compound [Et4N][(Br)(PhCH2)As{Cr-
(CO)5}2] ([Et4N][3]) (29% based on [Et4N]2[2a]). Crystals suitable for
X-ray diffraction were grown from ether/CH2Cl2. IR (νCO, THF): 2056
1
w, 2037 m, 1942 vs, 1933 vs, sh, 1897 s cm-1. H NMR (DMSO-d6,
298 K, ppm): δ 7.42, 7.41, 7.29, 7.27, 7.22, 7.20 (m, 5H), 4.11 (s,
2H) (chemical shifts not given for [Et4N]+). 13C NMR (DMSO-d6, 298
K, ppm): δ 227.69, 220.42, 141.46, 130.84, 128.99, 127.48, 49.18
(9) Cherng, J.-J.; Lee, G.-H.; Peng, S.-M.; Ueng, C.-H.; Shieh, M.
Organometallics 2000, 19, 213.
(11) (a) Abel, E. W.; Butler, I. S.; Reid. J. G. J. Chem. Soc. 1963, 2068.
(b) Fischer, E. O.; O¨ fele, K. Z. Naturforsch. 1959, 14b, 763. (c)
Fischer; E. O.; O¨ fele, K. Chem. Ber. 1960, 93, 1156.
(10) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air SensitiVe
Compounds; Wiley: New York, 1986.

1208 Inorganic Chemistry, Vol. 40, No. 6, 2001
Cherng et al.
Table 1. Crystallographic Data for [Et4N][H2As{Cr(CO)5}2] ([Et4N][1]), [Et4N]2[HSb{Cr(CO)5}3] ([Et4N][2b]), and
[Bu4N][BrISb{Cr(CO)5}2]·0.5CH2Cl2 ([Bu4N][8]‚0.5CH2Cl2)
[Et4N][1]
[Et4N][2b]
[Bu4N][8]‚0.5CH2Cl2
empirical formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
C18H22AsCr2NO10
591.28
triclinic
C31H41Cr3N2O15Sb
959.40
orthorhombic
Pcnb
13.224(5)
23.477(3)
26.754(4)
C26.5H37NO10Cr2SbIBrCl
997.58
monoclinic
P21/n
17.073(3)
14.288(3)
P1h
8.988(5)
12.123(4)
12.4341(21)
79.769(2)
78.60(3)
74.15(4)
1266.6(8)
2
17.074(3)
R, deg
â, deg
110.42(3)
γ, deg
V, Å3
8306(3)
8
1.534
3903.3(13)
4
1.698
Z
D(calcd), g cm-3
µ, cm-1
1.550
22.0
14.7
31.362
diffractometer
radiation λ, Å
temp, °C
2θ range, deg
Nonius (CAD4)
0.709 30
25
18.46-24.18
0.53/0.62
3271
Nonius (CAD4)
0.709 30
25
20.50-27.88
0.58/0.72
3691
Nonius (CAD4)
0.710 73
25
18.40-21.54
0.375/0.503
4104
tmin/tmax
independent reflns (I > 2σ(I))
a
R,a Rw
0.048, 0.041
0.057, 0.048
0.036, 0.038
a Thefunctions minimized during least-squares cycles were R ) ∑|Fo - Fc|/∑Fo and Rw ) [∑w(Fo - Fc)2/∑w(Fo)2]1/2
.
Table 2. Crystallographic Data for [Et4N]2[HAs{Cr(CO)5}3] ([Et4N][2a]), [Et4N][(Br)(PhCH2)As{Cr(CO)5}2] ([Et4N][3]), and
[Et4N][Cl2Sb{Cr(CO)5}2] ([Et4N][7])
[Et4N][2a]
[Et4N][3]
[Et4N][7]
empirical formula
fw
cryst syst
space group
a, Å
b, Å
C31H41AsCr3N2O15
912.58
monoclinic
P21/n
13.4332(3)
13.8294(4)
22.4643(6)
92.410(1)
4169.6(2)
4
1.454
16.18
SMART CCD
0.710 73
22
C25H27AsBrCr2NO10
760.31
monoclinic
C2/c
21.5470(30
12.39990(10)
23.5648(3)
100.1770(10)
6197.00(13)
8
1.630
31.02
SMART CCD
0.710 73
-123
C18H20Cl2Cr2NO10Sb
707.00
orthorhombic
Pna21
11.9041(3)
13.1714(4)
35.6497(7)
c, Å
â, deg
V, Å3
5589.6(2)
8
1.680
Z
D(calcd), g cm-3
µ, cm-1
19.61
diffractometer
radiation λ, Å
temp, °C
SMART CCD
0.710 73
23
θ range, deg
independent reflns
goodness-of-fit on F2
R1a/wR2b [I > 2σ(I)]
R1a/wR2b (all data)
1.73-23.26
5991 (Rint ) 0.0476)
1.050
0.0496/0.1097
0.0878/0.1306
1.76-25.00
5465 (Rint ) 0.0289)
1.041
0.0289/0.0681
0.0437/0.0762
1.14-25.00
4912 (Rint ) 0.0334)
1.146
0.0396/0.0998
0.0451/0.1098
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2
.
2
2
for X-ray diffraction were grown from hexanes/CH2Cl2. IR (νCO
,
m/z 712.7. Anal. Calcd for [Bu4N][8]: C, 31.91; H, 3.74; N, 1.40.
Found: C, 31.92; H, 3.68; N, 1.35. The residue was then extracted
with CH2Cl2, and the extract was then recrystallized with hexanes/
THF): 2065 m, 2043 s, 1950 vs cm-1. Negative ion FABMS: m/z
576.6. Anal. Calcd for [Et4N][7]: C, 30.58; H, 2.85; N, 1.98. Found:
C, 30.68; H, 2.87; N, 1.96. The residue was then extracted with CH2-
Cl2, and the CH2Cl2 extract was recrystallized with hexanes/CH2Cl2 to
give 0.05 g (0.11 mmol) of the known compound [Et4N][ClCr(CO)5].11
IR (νCO, THF): 2060 w, 1923 vs, 1856 m cm-1. Anal. Calcd for [Et4N]-
[ClCr(CO)5]: C, 43.65; H, 5.63; N, 3.92. Found: C, 43.65; H, 5.62;
N, 3.80.
CH2Cl2 to give the known compound [Bu4N][ICr(CO)5].11 IR (νCO
,
THF): 2052 w, 1922 vs, 1865 s cm-1. Anal. Calcd for [Bu4N][ICr-
(CO)5]: C, 44.93; H, 6.46; N, 2.49. Found: C, 44.89; H, 6.26; N, 2.53.
X-ray Structural Characterization of Complexes [Et4N][1],
[Et4N]2[2a], [Et4N]2[2b], [Et4N][3], [Et4N][7], and [Bu4N][8]. A
summary of selected crystallographic data for [Et4N][1], [Et4N]2[2a],
[Et4N]2[2b], [Et4N][3], [Et4N][7], and [Bu4N][8] is given in Tables 1
and 2. Data collection for [Et4N][1], [Et4N]2[2b], and [Bu4N][8] was
carried out on a Nonius CAD-4 diffractometer using graphite-
monochromated Mo KR radiation at 25 °C employing the θ/2θ scan
mode. A ψ-scan absorption correction was made.12 Data reduction and
structural refinement were performed using the NRCC-SDP-VAX
packages,13 and atomic scattering factors were taken from ref 14. Data
Reaction of [Bu4N]2[BrSb{Cr(CO)5}3] ([Bu4N]2[5]) with CH2I2.
To a solution of 0.51 g (0.40 mmol) of [Bu4N]2[5] in 20 mL of THF
in an ice/water bath was added 0.1 mL (1.24 mmol) of CH2I2. The
mixture was stirred in an ice/water bath for 10 min and then warmed
to room temperature and stirred for 4 days. The resultant solution was
filtered to collect the filtrate, and the solvent was removed under
vacuum. The residue was extracted with mixed solvents of ether/
hexanes ) 2:1; the extract was then recrystallized with hexanes/CH2-
Cl2 to give 0.23 g (0.24 mmol) of the pure compound [Bu4N][BrISb-
{Cr(CO)5}2] ([Bu4N][8]) (60% based on [Bu4N]2[5]). Crystals suitable
(12) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr. 1968,
A24, 351.
(13) Gabe, E. J.; Le Page, Y.; Charland, J. P.; Lee, F. L.; White, P. S. J.
Appl. Crystallogr. 1989, 22, 384.
for X-ray diffraction were grown from hexanes/CH2Cl2. IR (νCO
,
THF): 2061 m, 2042 s, 1950 vs, 1920 s cm-1. Negative ion FABMS:

Syntheses of Ar(V) and Sb(V) Derivatives
Inorganic Chemistry, Vol. 40, No. 6, 2001 1209
Table 3. Selected Bond Distances (Å) and Bond Angles (deg) for
[Et4N][H2AsCr2{(CO)5}2] ([Et4N][1])
Table 5. Selected Bond Distances (Å) and Bond Angles (deg) for
[Et4N]2[HSbCr3{(CO)5}3] ([Et4N][2b])
(A) Distances
As-Cr(1)
2.518(2)
As-Cr(2)
2.515 (1)
Sb-Cr(1)
Sb-Cr(3)
2.741(2)
(B) Angles
Cr(1)-As-Cr(2)
Cr(1)-As-H(1)
Cr(2)-As-H(1)
133.86(5)
101.87(5)
114.59(5)
H(1)-As-H(2)
Cr(1)-As-H(2)
Cr(2)-As-H(2)
89.56(4)
99.91(5)
107.36(5)
(B) Angles
H(1)-Sb-Cr(1)
H(1)-Sb-Cr(3)
Cr(1)-Sb-Cr(3)
95.42(5)
101.57(5)
116.86(7)
H(1)-Sb-Cr(2)
Cr(1)-Sb-Cr(2)
Cr(2)-Sb-Cr(3)
103.83(5)
116.79(6)
116.98(7)
Table 4. Selected Bond Distances (Å) and Bond Angles (deg) for
[Et4N]2[HAsCr3{(CO)5}3] ([Et4N][2a])
Table 6. Selected Bond Distances (Å) and Bond Angles (deg) for
[Et4N][(Br)(PhCH2))As{Cr(CO)5}2] ([Et4N][3])
(A) Distances
As-H
1.58(4)
2.6151(11)
As-Cr(1)
2.6120(10)
2.6127(11)
As-Cr(2)
As-Cr(3)
As(1)-Cr(1)
As(1)-Br(1)
C(11)-C(12)
2.5115(5)
2.001(3)
(B) Angles
H-As-Cr(1)
H-As-Cr(3)
Cr(1)-As-Cr(3)
100.9(13)
98.0(12)
117.90(4)
H-As-Cr(2)
Cr(1)-As-Cr(2)
Cr(2)-As-Cr(3)
101.2(13)
116.60(4)
116.61(4)
95.11(9)
collection for [Et4N]2[2a], [Et4N][3], and [Et4N][7] was carried out on
a SMART CCD diffractometer. A SADABS scan absorption correction
was made,15 and all calculations were performed using SHELXTL
packages.16
Structures of [Et4N][1], [Et4N]2[2a], [Et4N]2[2b], [Et4N][3], [Et4N]-
[7], and [Bu4N][8]‚0.5CH2Cl2. The crystal of [Et4N][1] chosen for
diffraction measurement was ca. 0.50 mm × 0.15 mm × 0.12 mm.
The crystal of [Et4N]2[2a] had dimensions 0.38 mm × 0.25 mm ×
0.05 mm. The crystal of [Et4N]2[2b] had dimensions 0.35 mm × 0.30
mm × 0.30 mm. The crystal of [Et4N][3] had dimensions 0.25 mm ×
0.20 mm × 0.20 mm. The crystal of [Et4N][7] had dimensions 0.40
mm × 0.35 mm × 0.30 mm, and the crystal of [Bu4N][8]‚0.5CH2Cl2
had dimensions 0.40 mm × 0.30 mm × 0.20 mm. Cell parameters
were obtained from 25 reflections with 2θ angle in the range 18.46-
24.18° for [Et4N][1], 20.5° < 2θ < 27.88° for [Et4N]2[2b], 18.4° <
2θ < 21.54° for [Bu4N][8]‚0.5CH2Cl2, 1.73° < θ < 23.26° for [Et4N]2-
[2a], 1.76° < θ < 25.00° for [Et4N][3], and 1.14° < θ < 25.00° for
[Et4N][7]. A total of 3271 reflections with I > 2.5σ(I) for [Et4N][1]
(5991 reflections with I > 2.0σ(I) for [Et4N]2[2a], 3691 reflections with
I > 2.0σ(I) for [Et4N]2[2b], 5163 reflections with I > 2.0σ(I) for [Et4N]-
[3], 4827 reflections with I > 2.0σ(I) for [Et4N][7], and 4104 reflections
with I > 2.0σ(I) for [Bu4N][8]‚0.5CH2Cl2) were refined by least-squares
cycles. All the non-hydrogen atoms were refined with anisotropic
temperature factors. For [Et4N][1], the dihydrides were found from
Fourier difference maps, approximately 1.600 Å from the As atom,
but not refined in the least-squares cycle. For [Et4N][2a], the hydride
was located crystallographically and refined isotropically, while for
[Et4N][2b], the hydride was found from Fourier difference maps,
approximately 1.799 Å from the Sb atom, but not refined in the least-
squares cycle. Full-matrix least-squares refinement led to convergence
with R ) 4.9% and Rw ) 4.2% for [Et4N][1], with R1 ) 4.96% and
wR2 ) 10.97% for [Et4N]2[2a], with R ) 5.6% and Rw ) 4.7% for
[Et4N]2[2b], with R1 ) 2.89% and wR2 ) 6.81% for [Et4N][3], with
R1 ) 3.69% and wR2 ) 9.98% for [Et4N][7], and with R ) 3.6% and
Rw ) 3.8% for [Bu4N][8]‚0.5CH2Cl2.
Sb(1)-Cl(1)
Sb(1)-Cr(1)
2.441(4)
2.582(2)
Sb(1)-Cl(2)
2.419(4)
2.587(2)
Sb(1)-Cr(2)
(B) Angles
Cr(1)-Sb(1)-Cr(2) 129.01(6) Cl(1)-Sb(1)-Cl(2)
Cl(1)-Sb(1)-Cr(1) 107.2(1)
Cl(2)-Sb(1)-Cl(1) 107.1(1)
93.7(2)
Cl(1)-Sb(1)-Cr(2) 107.7 (1)
Cl(2)-Sb(1)-Cr(2) 106.5(1)
Table 8. Selected Bond Distances (Å) and Bond Angles (deg) for
[Bu4N][BrISb{Cr(CO)5}2]‚0.5CH2Cl2 ([Bu4N][8]‚0.5CH2Cl2)
(A) Distances
2.697(1)
2.621 (1)
Sb-Br
Sb-Cr(1)
Sb-I
Sb-Cr(2)
2.7974(8)
2.627(1)
(B) Angles
132.96(4)
104.11(4)
106.23(3)
Cr(1)-Sb-Cr(2)
Br-Sb-Cr(1)
I-Sb-Cr(1)
I-Sb-Br
Br-Sb-Cr(2)
I-Sb-Cr(2)
93.02(3)
105.90(4)
107.44(3)
dihydrido complex [H2As{Cr(CO)5}2]- (1) as the major product
and the monohydrido complex [HAs{Cr(CO)5}3]2- (2a) as the
minor product. Under similar conditions, the reaction with Sb2O3
only yields the monohydrido complex [HSb{Cr(CO)5}3]2- (2b);
however, the dihydrido complex [H2Sb{Cr(CO)5}2]- is not
observed. This can be rationalized that the larger size of Sb
could favor the three chromium substituents to bind more than
for As where two chromium substituents may be accommodated
easily but three are sterically less favorable. The anionic
complexes 1, 2a, and 2b can be isolated as the [Et4N]+ salts by
metathesis, and they are fully characterized by single-crystal
X-ray analyses and/or spectroscopic methods. Complex 1 can
The selected bond distances and angles for [Et4N][1], [Et4N]2[2a],
[Et4N]2[2b], [Et4N][3], [Et4N][7], and [Bu4N][8]‚0.5CH2Cl2 are repre-
sented in Tables 3-8, respectively. Additional crystallographic data
are available as Supporting Information.
2-
be viewed as a central As(V) ion coordinated to two Cr(CO)5
groups and two hydrides. Similarly, complexes 2 and 3 are
described as a central As(V) or Sb(V) ion each bonded to three
2-
Cr(CO)5 groups and one hydride.
Results and Discussion
The most interesting feature of 1, 2a, and 2b is the presence
of the hydrides bound to the main group atom. They can be
located from the difference maps of the X-ray analyses and are
also inferred on the basis of electron-counting considerations,
and, most importantly, from H NMR data analysis. The H
NMR spectra exhibit singlets at δ 0.0 for [H2As{Cr(CO)5}2]-
(1), δ -2.0 for [HAs{Cr(CO)5}3]2- (2a), and δ -5.5 for
[HSb{Cr(CO)5}3]2- (2b). These results indicate that the hydridic
character of the hydrogens increases in the order of 1 < 2a <
2b attributable to the increased negative charge of the complexes
Syntheses of the Hydrido Complexes 1, 2a, and 2b.
Chromium hexacarbonyl can react with As2O3 in concentrated
methanolic KOH solution to give the chromium-arsenic
1
1
(14) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, England, 1974; Vol. IV.
(15) Sheldrick, G. M. SADABS, Siemens Area Detector Absorption Cor-
rection Program; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(16) Sheldrick, G. M. SHELXTL, Program for Crystal Structure Detection;
Siemens Analytical X-ray Instruments Inc.: Madison, WI, 1994.

1210 Inorganic Chemistry, Vol. 40, No. 6, 2001
Cherng et al.
Scheme 1
Scheme 3
Scheme 4
Complexes 3 and 4 were shown to have the tetrahedral (R)-
(X)AsCr2 core geometry based on spectroscopic data, and the
structure of 3 was further characterized by the single-crystal
X-ray diffraction method. Note that the C3H3 ligand of 4 in
solution is of the η1-allenyl type of ligation according to the 1H
NMR data (two resonances at 6.80 (t, 1H, J ) 6.23 Hz) and
5.06 (d, 2H, J ) 6.23 Hz)) (Scheme 3).19
Scheme 2
In the Sb-Cr system, the reactions of 2b with RX (RX )
PhCH2Br or HCtCCH2Br, CH3(CH2)5C(O)Cl), however, gave
the haloantimony complexes [XSb{Cr(CO)5}3]2- (X ) Br, 5;
X ) Cl, 6). The corresponding hydrogen-transferred organic
products RH (R ) PhCH2, CH3(CH2)5C(O)) have been char-
acterized and quantified by GC and GC/MS spectroscopy
(Scheme 4). Note that the yields of the hydrogen-transferred
product RH in both cases are around 60% based on 2b, close
to that found in the As-Cr system and indicative of the
comparable hydrogen-transferring efficiency of 2a and 2b.
From the above-mentioned results, the contrasting chemical
reactivity of complexes 2a and 2b toward organic halides is
evident. While complex 2a produces the RX addition products,
complex 2b gives the X-substituted products. The size effect
of As and Sb could be taken into account in terms of toleration
of the negative charge of the resultant complexes. The RX
addition products 3 and 4 each bear only one negative charge,
which can be stabilized by the smaller As atom, whereas the
haloantimony complexes 5 and 6 each possess two negative
charges that are better stabilized by the larger Sb atom. However,
on the basis of the yields of formation of R-H, the hydrogen
transferring efficiency of 2a and 2b is about the same and cannot
be distinguishable under our conditions, although the 1H NMR
chemical shifts indicate that the hydrogen atom of 2b is more
hydridic than that of 2a.
Mixed Dihaloantimony Complexes. Different halides can
be introduced into 2b. The bromoantimony complex 5 can be
produced from 2b with PhCH2Br. The mixed dihaloantimony
complex [BrISb{Cr(CO)5}2]- (8) can be obtained from the
further reaction of complex 5 with CH2I2. These dihaloantimony
complexes may form via the formation of the intermediate
halostibinidene complex [XSb{Cr(CO)5}2] followed by the
attack of the incoming halide. This assumption is consistent with
the fact that the chloroarsinidene complex [ClAs{Cr(CO)5}2]
can be attacked by Lewis bases to form the adduct.20 However,
if complex 5 were treated with CH3C(O)Cl, a dichloroantimony
complex [Cl2Sb{Cr(CO)5}2]- (7) would be obtained instead of
the expected mixed bromochloroantimony complex. The results
and the increased acidity from As to Sb. Moreover, the values
for the monohydrido complexes (2a and 2b) are different from
those in the isoelectronic iron complexes [HAs{Fe(CO)4}3]2-
(δ 1.34) and [HSb{Fe(CO)4}3]2- (δ -1.39).7 This implies that
these hydrogens in chromium-containing complexes 2a and 2b
are more hydridic than those in the corresponding iron com-
plexes because of the more electropositive character of Cr.
General Reactivity of 1, 2a, and 2b. Is the dihydrido
complex 1 an intermediate for the formation of the monohydrido
complex 2a? To answer this, we treated 1 with Cr(CO)6/KOH
under controlled conditions. However, 1 was not transformed
into 2a. Therefore, complexes 1 and 2a result from different
reaction pathways. Interestingly, while the hydridoantimony
complex 2b was found to form the chloroantimony complex
[ClSb{{Cr(CO)5}3]2- (6) in CH2Cl2 solutions, the hydrido-
arsenic complex 2a was not transformed to the corresponding
chloroarsenic complex in CH2Cl2 solutions (Scheme 1).
Reactions of 2a and 2b with RX. Knowing that the hydride
atom of 2b, but not 2a, can be easily replaced by chloride in
CH2Cl2 solutions, we systematically compared the chemical
reactivity of 2a and 2b with organic halogen derivatives.
In the As-Cr system, surprisingly, complex 2a was found
to react with RBr (R ) PhCH2, HCtCCH2), via the formation
of the As-R and As-Br bonds, to give the RX addition
products [(R)(Br)As{Cr(CO)5}2]- (R ) PhCH2, 3; R ) C3H3,
4) along with [BrCr(CO)5]- (Scheme 2). In the former case,
the hydrogen-transferred organic product RH-toluene was also
detected and identified by GC and GC/MS. The yield of RH is
around 60% based on 2a. However, the detailed mechanism
for the formation of R-H is not clear and may occur via hydride
transfer17 or single electron-transfer processes.18 Further study
is required to understand the mechanistic details.
(17) (a) Kao, S. C.; Darensbourg, M. Y. Organometallics 1984, 3, 646.
(b) Kao, S. C.; Gaus, P. L.; Youngdahl, K.; Darensbourg, M. Y.
Organometallics 1984, 3, 1601.
(18) Kochi, J. K. Organometallic Mechanisms and Catalysis; Academic
Press: New York, 1978.
(19) Keng, R.-S.; Lin, Y.-C. Organometallics 1990, 9, 289 and references
therein.
(20) von Seyerl, J.; Huttner, G. Angew. Chem., Int. Ed. Engl. 1979, 18,
233.

Syntheses of Ar(V) and Sb(V) Derivatives
Inorganic Chemistry, Vol. 40, No. 6, 2001 1211
Figure 1. ORTEP diagram showing the structure and atom labeling
for the anion 1.
Figure 3. ORTEP diagram Showing the structure and atom labeling
for the dianion 2b.
Figure 2. ORTEP diagram showing the structure and atom labeling
for the dianion 2a.
Scheme 5
Figure 4. ORTEP diagram showing the structure and atom labeling
for the anion 3.
indicate that the formation of mixed dihaloantimony complexes
could result from other complicated pathways and that the
outcome strongly depends on the reactivity of the incoming
organic halides (Scheme 5).
Complexes 1-8. All the new complexes 1-8 are fully
characterized by spectroscopic methods and/or by X-ray analy-
sis. The structures of [Et4N][1] (Figure 1), [Et4N]2[2a] (Figure
2), [Et4N]2[2b] (Figure 3), [Et4N][3] (Figure 4), [Et4N][7]
(Figure 5), and [Bu4N][8] (Figure 6) are further determined by
single-crystal X-ray diffraction in which the central atoms (As
or Sb) are all in distorted tetrahedral environments. The analyses
show that the dianionic complexes 2a, 2b, 5, and 6 each consist
of a central antimony(V) or arsenic(V) ion tetrahedrally
Figure 5. ORTEP diagram showing the structure and atom labeling
for the anion 7.
is replaced by another hydride or halide, respectively. Similarly,
the monoanions 3 and 4 each display a central arsenic(V) ion
bonded to two Cr(CO)5 groups, one organic R- group, and
2-
one bromide moiety.
2-
coordinated to one hydride (or halide) and three Cr(CO)5
For comparison, the average Cr-E-Cr angle and the E-Cr
distance in these tetrahedral complexes are listed in Table 9.
Of the As-Cr complexes 1, 2a, and 3, the average As-Cr
groups. The monoanions 1 and 7 (or 8) are structurally similar
to the dianionic 2a or 6 (or 5) except that one Cr(CO)52- group

1212 Inorganic Chemistry, Vol. 40, No. 6, 2001
Cherng et al.
by the steric crowding of the three chromium carbonyl frag-
ments. On the other hand, the Cr-As-Cr bond angle increases
as the number of the Cr(CO)5 fragments decreases.
Similarly, of the Sb-Cr complexes 2b, 7, and 8, the Sb-Cr
distance is the greatest in 2b and similar to those in 7 and 8.
The average Sb-Cr bond length in [Et4N]2[2b] is 2.735(2) Å,
which is larger than those of the Sb-Cr multiple bonds in
[Sb{Cr(CO)5}3]- (av 2.630(3) Å)4 and that in [SbFe3Cr(CO)17]-
(2.6382(9) Å).23 However, the Sb-Cr distances in 7 and 8
(2.585(2), 2.624(1) Å) are normal. The lengthening of these
Sb-Cr bonds in 2b is again influenced by the steric crowding
of the three chromium carbonyl fragments. As shown, the steric
effect of the substituents on the Sb atoms is also reflected in
the trends of the Cr-Sb-Cr angles.
Conclusion
Figure 6. ORTEP diagram showing the structure and atom labeling
for the anion 8.
We have developed a facile route to a new series of group
15-chromium carbonyl hydrido complexes [H2As{Cr(CO)5}2]-
and [HE{Cr(CO)5}3]2- (E ) As, Sb). The contrasting reactivity
patterns of the dianionic hydrido complexes [HE(Cr(CO)5)3]2-
(E ) As, Sb) toward organic halogen derivatives are demon-
strated. While the reaction of [HAs{Cr(CO)5}3]2- with RX
yields the RX addition products [(R)(X)As{Cr(CO)5}2]-, the
treatment of [HSb{Cr(CO)5}3]2- with RX forms the halo-
substituted complexes [XSb{Cr(CO)5}3]2- probably because of
the greater ease of toleration of the higher negative charge of
the resultant complexes by the larger Sb atom. The hydrogen-
transferring efficiency of [HE(Cr(CO)5)3]2- (E ) As, Sb) with
RX to form R-H is comparable under our conditions. Ad-
ditionally, the interesting dihaloantimony complexes [XX′Sb-
{Cr(CO)5}2]- can be obtained from the reaction of [HSb(Cr-
(CO)5)3]2- with the appropriate organic halides.
Table 9. Comparison of the Average Cr-E-Cr Angles and the
Average E-Cr Distances in 1, 2a, 2b, 3, 7, and 8
complex
Cr-E-Cr, deg
E-Cr, Å
[H2As{Cr(CO)5}2]- (1)
[HAs{Cr(CO)5}3]2- (2a)
[(Br)(PhCH2)As{Cr(CO)5}2]- (3)
[HSb{Cr(CO)5}3]2- (2b)
[Cl2Sb{Cr(CO)5}2]- (7)
[BrISb{Cr(CO)5}2]- (8)
133.86
117.04
124.00
116.88
129.01
132.96
2.516
2.613
2.509
2.735
2.585
2.624
distance in 2a is the greatest because of the steric effect of the
Cr(CO)5 group. The average As-Cr bond length in 2a is 2.613-
(1) Å, which is not only significantly longer than those of the
As-Cr multiple bonds in ClAs{Cr(CO)5}2 (av 2.324(2) Å),3
PhAs{Cr(CO)5}2 (av 2.385(3) Å),3 Mn(CO)5As{Cr(CO)5}2 (av
2.429(4) Å),4 Mn(CO)5As(µ-CO){Cr(CO)4}2 (av 2.349(5) Å),4
and (tBu)As{Cr(CO)5}2 (av 2.345(1) Å)21 but also greater than
those of the As-Cr single bonds in [Et4N]2[1] (av 2.516(2) Å)
and As2Cr3Co2(CO)20 (av 2.422(2) Å).22 For 1 and 3, the average
As-Cr bond lengths are 2.516 and 2.509 Å, respectively, and
are close to those of the reported As-Cr single bonds. The
lengthening of the As-Cr bonds in 2a is evident and caused
Acknowledgment. We thank the National Science Council
of the Republic of China for financial support (Grant NSC 88-
2113-M-003-013)
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes [Et4N][1], [Et4N]2[2a], [Et4N]2[2b], [Et4N]-
[3], [Et4N][7], and [Bu4N][8]‚0.5CH2Cl2. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC0004277
(21) Jones, R. A.; Whittlesey, B. R. Organometallics 1984, 3, 469.
(22) Lang, H.; Huttner, G.; Sigwarth, B.; Jibril, I.; Zsolnai, L.; Orama, O.
J. Organomet. Chem. 1986, 304, 137.
(23) Whitmire, K. H.; Shieh, M.; Cassidy, J. Inorg. Chem. 1989, 28, 3164.