Photochemical synthesis of (η6-arene)chromium hydrido stannyl and (η6-arene)chromium bis(stannyl) complexes

Article abstract of DOI:10.1021/ic951431z

Photolysis of (η⁶-arene)Cr(CO)₃ complexes and HSnPh₃ in aromatic solvents at room temperature has led to two classes of complexes: hydrido stannyl compounds containing the η²-H-SnPh₃ ligand and bis(stannyl) compounds containing two SnPh₃ ligands. The ratio between the two complexes simultaneously produced depends on the choice of the arene. Complexes with different arenes (mesitylene, toluene, benzene, fluorobenzene, and difluorobenzene) have been obtained and characterized including X-ray structures for (η-⁶C₆H₃(CH₃) ₃)Cr(CO)₂ (H)(SnPh₃) (1a). (η⁶-C₆H₃)₃)(η ⁶CH₃)₃)Cr(CO)₂(SnPhs ₃)₂ (1b), (η-C₆-H₆H₃F)Cr(CO)₂(SnPh ₃)₂ (4b), and (η-C₆C₆H₄ (CO)₂(SnPh₃)₂ (5b). X-ray crystallography of the last three compounds has given the following results: 1b, monoclinic, space group P2₁/c (No. 14), a = 13.905(4) A?, b = 18.499(2) A?, c = 17.708(2) A?, Z = 4, V = 4285(1) A?³; 4b, orthorhombic, space group Pca2₁ (No. 29), a = 16.717(2) A?, b = 18.453(2) A?, c = 25.766(2) A?, Z = 8, V = 7948(2) A?³; 5b, monoclinic, space group P2₁/c (No. 14), a = 13.756(2) A?, b = 18.560(2) A?, c = 17.159(2) A?, Z = 4, V = 4372(2) A?³. The relatively high J(¹¹⁹Sn-Cr-H) and J(¹¹⁷Sn-Cr-H) values as well as the X-ray structural data provide evidence for the existence of three-center two-electron bonds in the hydrido stannyl complexes. The ¹H NMR data of the complexes are compared with chromium-arene bond distances, and a sensible trend is observed and discussed.

Full text of DOI:10.1021/ic951431z

Inorg. Chem. 1996, 35, 3223-3227
3223
Photochemical Synthesis of (η6-Arene)chromium Hydrido Stannyl and (η6-Arene)chromium
Bis(stannyl) Complexes
Abbas Khaleel and Kenneth J. Klabunde*
Department of Chemistry, Kansas State University, Manhattan, Kansas 66506
ReceiVed NoVember 2, 1995X
Photolysis of (η6-arene)Cr(CO)3 complexes and HSnPh3 in aromatic solvents at room temperature has led to two
classes of complexes: hydrido stannyl compounds containing the η2-H-SnPh3 ligand and bis(stannyl) compounds
containing two SnPh3 ligands. The ratio between the two complexes simultaneously produced depends on the
choice of the arene. Complexes with different arenes (mesitylene, toluene, benzene, fluorobenzene, and
difluorobenzene) have been obtained and characterized including X-ray structures for (η6-C6H3(CH3)3)Cr(CO)2-
(H)(SnPh3) (1a), (η6-C6H3(CH3)3)Cr(CO)2(SnPh3)2 (1b), (η6-C6H5F)Cr(CO)2(SnPh3)2 (4b), and (η6-C6H4F2)Cr-
(CO)2(SnPh3)2 (5b). X-ray crystallography of the last three compounds has given the following results: 1b,
monoclinic, space group P21/c (No. 14), a ) 13.905(4) Å, b ) 18.499(2) Å, c ) 17.708(2) Å, Z ) 4, V )
4285(1) Å3; 4b, orthorhombic, space group Pca21 (No. 29), a ) 16.717(2) Å, b ) 18.453(2) Å, c ) 25.766(2)
Å, Z ) 8, V ) 7948(2) Å3; 5b, monoclinic, space group P21/c (No. 14), a ) 13.756(2) Å, b ) 18.560(2) Å, c
) 17.159(2) Å, Z ) 4, V ) 4372(2) Å3. The relatively high J(119Sn-Cr-H) and J(117Sn-Cr-H) values as well
as the X-ray structural data provide evidence for the existence of three-center two-electron bonds in the hydrido
1
stannyl complexes. The H NMR data of the complexes are compared with chromium-arene bond distances,
and a sensible trend is observed and discussed.
Introduction
chemical and spectroscopic evidence for the presence of Mn,
H, Si three-center two-electron bonds has been gathered and
discussed.7,8
The addition of H-M′R3, where M′ is a main group IV metal,
to transition metal fragments (LnM) has been of great interest
in the last 30 years. An extensive work has been carried out
on the addition of HSiR3 (R ) Cl or alkyl group).1-3 Most of
the work has been done on complexes stabilized by Cp or alkyl-
substituted Cp rings, and less work on arene-containing
complexes has been reported. The photochemical decarbon-
ylation of metal tricarbonyl complexes followed by addition of
HSiR3 has led to a variety of Cp and arene-hydride-SiR3
complexes of Mn, Cr, and Fe.1-3 To a lesser extent, the addition
of HSnR3 and HGeR3 has been also studied.4-6 The complete
oxidative addition of HSiR3 to a transition metal complex moiety
(LnM) would totally cleave the H-Si bond giving a hydrido
silyl complex with both M-H and M-Si bonds. After A. G.
Graham et al. isolated and chraracterized a number of complexes
of the general formula Cp(CO)2Mn(H)SiR3, in the early 1970s,
The possibility of a three-center bond involving a SnR3 ligand
has been considered. In 1989, Schubert et al. reported the first
example of a transition metal, hydrogen, tin three-center two-
electron bond in the Mn complex (MeCp)(CO)2Mn(H)SnPh3.4a
Later in 1991 Schubert and co-workers reported the structure
of the complex (η6-C6H3(CH3)3)Cr(CO)2(H)SnPh3 obtained from
the photochemical reaction of HSnPh3 with (η6-C6H3(CH3)3)-
Cr(CO)3.4c Under different reaction conditions we have ob-
tained the same complex and, for the first time under photo-
chemical conditions, the bis(stannyl) complex (η6-C6H3(CH3)3)-
Cr(CO)2(SnPh3)2.
In this paper we report the synthesis, characterization, and
structure of two types of arene-chromium complexes: Hydrido
stannyl complexes which have Cr, hydrogen, tin three-center
two-electron bonds, i.e., an η2-coordination of H-Sn to the Cr
center, and the bis(stannyl) complexes containing two stannyl
ligands (SnPh3). These complexes have been characterized by
1H NMR, IR, elemental analysis, and X-ray crystallography.
This is an extension of previous work to prepare new arene-
metal complexes in unusual oxidation states and study their
arene lability as well as their catalytic potential in different
processes.9 Since the overall goal of our work in this area is to
gain access to compounds with labile η6-arene ligands, we were
particularly interested in the bis(stannyl) complexes and their
structures. This is because the bulky nature of two SnPh3 groups
causes, we have noted, enhanced lability of the η6-arene.
X Abstract published in AdVance ACS Abstracts, May 1, 1996.
(1) (a) Colomer, E.; Corriu, R. J. P.; Vioux, A. Inorg. Chem. 1979, 18,
695. (b) Colomer, E.; Corriu, R. J. P.; Marzin, C.; Vioux, A. Inorg.
Chem. 1982, 21, 368. (c) Schubert, U. AdV. Organomet. Chem. 1990,
30, 151 and references therein. (d) Matarasso-Tchiroukhine, E.; Jaouen,
G. Can. J. Chem. 1988, 66, 2157. (e) Schubert, U.; Ackerman, K.;
Kraft, G.; Worle, B. Z. Naturforsch. 1983, 38b, 1488. (f) Carre, F.;
Colomer, E.; Corriu, R. J. P.; Vioux, A. Organometallics 1984, 3,
971. (g) Schubert, U.; Mu¨ller, J.; Alt, H. G. Organometallics 1987, 6,
469. (h) Knorr, M.; Schubert, U. Transition Met. Chem. 1986, 11,
269. (i) Schubert, U. Transition Met. Chem. 1991, 16, 136.
(2) (a) Schubert, U.; Mayer, B.; RuB, C. Chem. Ber. 1994, 127, 2189.
(b) Gilbert, S.; Knorr, M.; Mock, S.; Schubert, U. J. Organomet. Chem.
1994, 480, 241.
(3) Glavee, G. N.; Jagirdar, B. R.; Schneider, J. J.; Klabunde, K. J.;
Radonovich, L. J.; Dodd, K. Organometallics 1992, 11, 1043.
(4) (a) Schubert, U.; Kunz, E.; Harkers, B.; Willnecker, J.; Meyer, J. J.
Am. Chem. Soc. 1989, 111, 2572. (b) Mock, S.; Schubert, U. Chem.
Ber. 1993, 126, 2591. (c) Piana, H.; Kirchga¨bner. U.; Schubert, U.
Chem. Ber. 1991, 124, 743. (d) Carre, F.; Colomer, E.; Corriu, R. J.
P.; Vioux, A. Organometallics 1984, 3, 1272. (e) Schubert, U.;
Schubert, J. J. Organomet. Chem. 1992, 434, 169.
Results and Discussion
The photochemical reaction of (arene)Cr(CO)3 complexes
with an excess of HSnPh3 in the appropriate arene as a solvent
(5) Zhang, S.; Brown, T. L. Organometallics 1992, 11, 2122.
(6) Latif, L. A.; Eaborn, C.; Pidcock, A. P. J. Organomet. Chem. 1994,
474, 217.
(7) Graham, W. A. G. J. Organomet. Chem. 1986, 300, 81.
(8) Schubert, U.; Scholz, G.; Mu¨ller, J.; Ackerman, K.; Worle, B.;
Stansfield, R. F. D. J. Organomet. Chem. 1986, 306, 303.
S0020-1669(95)01431-5 CCC: $12.00 © 1996 American Chemical Society

3224 Inorganic Chemistry, Vol. 35, No. 11, 1996
Khaleel and Klabunde
for 4 h led to the formation of two types of complexes, (η6-
arene)Cr(CO)2H(SnPh3) and (η6-arene)Cr(CO)2(SnPh3)2:
hν
(arene)Cr(CO)3 + HSnPh3 sf
(arene)Cr(CO) H(SnPh ) (arene)Cr(CO) (SnPh )
+
2
3
2
3 2
a
b
Previous work on similar reactions has shown that the first step
in such reactions is the loss of CO upon photolysis of the
(arene)Cr(CO)3 followed by the addition of HSnPh3.10 The
second step, to form the bis(stannyl) complex, is less well
understood but most likely involves a second photolytic loss of
CO, a second oxidative addition, H2 loss, and CO scavenging.3,11
HSnPh3
-H2
hν
8
+CO8
Figure 1. Diagram of the structure of (η6-C6H3(CH3)3Cr(CO)2(SnPh3)2.
(arene)Cr(CO)2H(SnPh3) -CO8 Ox addition8
Table 1. Selected Bond Distances (Å) and Bond Angles (deg) for
1b
(arene)Cr(CO)2(SnPh3)2
Bond Distances
The following complexes have been prepared:
Cr-Sn(1)
Cr-C(1)
Cr-C(3)
Cr-C(5)
Cr-C(7)
2.72(2)
1.81(1)
2.27(1)
2.29(2)
2.25(1)
Cr-Sn(2)
Cr-C(2)
Cr-C(4)
Cr-C(6)
Cr-C(8)
2.70(2)
1.83(1)
2.27(1)
2.26(1)
2.23(1)
arene
mesitylene
toluene
hydrido stannyl complex bis(stannyl) complex
1a
2a
3a
4a
5a
1b
2b
3b
4b
5b
benzene
Bond Angles
fluorobenzene
difluorobenzene
C(1)-Cr-C(2)
C(1)-Cr-Sn(2)
C(2)-Cr-Sn(2)
103.5(5)
73.7(4)
73.1(4)
C(1)-Cr-Sn(1)
C(2)-Cr-Sn(1)
Sn(1)-Cr-Sn(2)
72.9(4)
73.5(4)
124.8(7)
Schubert and co-workers have reported the complex (η6-
mesitylene)Cr(CO)2H(SnPh3) from a similar reaction but in
petroleum ether and at -10 °C. Under these conditions they
obtained only the hydrido stannyl complex. They treated the
hydrido stannyl complex with excess HSnPh3 under thermal
conditions in an attempt to obtain the bis(stannyl) complex but
were unsuccessful.4c In mesitylene at room temperature we
were able to synthesize both of these compounds simultaneously,
and separate and purify them by column chromatography.
The major product is the hydrido stannyl complex in the case
of mesitylene, while it is the bis(stannyl) complex in the cases
of other arenes. It may be that steric effects control this ratio
of hydrido stannyl/bis(stannyl); i.e., in the case of mesitylene,
the hydrido stannyl complex is easier to form as compared to
the more bulky bis(stannyl) complex due to steric hindrance
by the two stannyl ligands and the methyl groups on the arene
ring. In the case of fluorobenzene and difluorobenzene,
electronic factors become more important and the more stable
bis(stannyl) complexes are preferred.
and compared with the one reported earlier by Schubert et al.4c
From X-ray structural data, the Sn-H distance is 1.95 Å, which
is only 0.24 Å longer than that in methyl-substituted stannanes12
indicating a bonding interaction between both atoms. Additional
evidence for Sn-H interaction can be obtained from the
geometry of the complex which suggests a delocalized Cr, Sn,
H bond. The Sn-Cr-H angle (45°) is too small to suggest
that Sn and H atoms occupy two coordination sites around the
Cr center. This means that H-SnPh3 must be considered as
one ligand such that the Sn-H bond occupies one coordination
site. The angle between the two cis-CO ligands is 84.4°, which
is smaller than that in the bis(stannyl) complex 1b (104°) which
contains two trans-CO ligands in a four-legged piano stool
geometry. These considerations indicate that an η2-bond type
between the Cr and H-Sn is preferred.
Other evidence for a Sn-Cr-H three-center bond can be
obtained from the 1H NMR spectra of complexes 1a-5a. For
free HSnPh3 1J(119Sn-1H) and 1J(117Sn-1H) are 1936 and 1848
Hz, respectively, while they are in the range 321-338 and 306-
322 Hz in our hydrido stannyl complexes. For cis-(CO)4Os-
(H)SnCl3, where there should be no interaction between the
hydride and SnCl3, J(119Sn-Os-H) and J(117Sn-Os-H) were
found to be 136 and 129.5 Hz, respectively.4a The significantly
higher values of J(Sn-Cr-H) in complexes 1a-5a provide
spectroscopic evidence for Sn-H interaction in these com-
pounds.
Structure of (Arene)Cr(CO)2H(SnPh3) Complexes. The
X-ray structure of (mesitylene)Cr(CO)2H(SnPh3) was obtained
(9) (a) Anderson, B. B.; Behrens, C. L.; Radonovich, L. J.; Klabunde, K.
J. J. Am. Chem. Soc. 1976, 98, 5390. (b) Gastinger, R. G.; Anderson,
B. B.; Klabunde, K. J. J. Am. Chem. Soc. 1980, 102, 4959. (c)
Groshens, T. J.; Klabunde, K. J. Organometallics 1982, 1, 564. (d)
Lin, S. T.; Narske, R. N.; Klabunde, K. J. Organometallics 1985, 3,
571. (e) Brezinski, M. M.; Klabunde, K. J. Organometallics 1983, 2,
1116. (f) Groshens, T. J.; Klabunde, K. J. J. Organomet. Chem. 1983,
259, 337. (g) Klabunde, K. J.; Anderson, B. B.; Neuenschwander, K.
Inorg. Chem. 1980, 19, 3719. (h) Choe, S. B.; Kanai, H.; Klabunde,
K. J. J. Am. Chem. Soc. 1989, 111, 2875. (i) Choe, S. B.; Schneider,
J. J.; Klabunde, K. J.; Radonovich, L. J.; Ballantine, T. A. J.
Organomet. Chem. 1989, 376, 419. (j) Brezinski, M. M.; Schneider,
J. J.; Radonovich, L. J.; Klabunde, K. J. Inorg. Chem. 1989, 28, 2414.
(10) (a) Davis, R.; Kane-Maguire, L. A. P. In ComprehensiVe Organome-
tallic Chemistry; Wilkinson, G., Ed.; Pergamon Press: New York,
1987; Vol. 3, p 1036. (b) Knoll, L.; Reiss, K.; Schafer, J.; Klu¨fers, P.
J. Organomet. Chem. 1980, 193, C40.
Crystal Structure of (η6-Mesitylene)Cr(CO)2(SnPh3)2 (1b).
An ORTEP drawing of the structure is shown in Figure 1.
Selected bond distances and angles are given in Table 1. The
ligands adopt a piano stool arrangement around the Cr center
where the arene ring represents the seat and the two CO ligands
and two stannyl ligands represent the legs. The two CO ligands
are trans to each other with a C(1)-Cr-C(2) angle of of 103.5-
(11) Jagirdar, B. R.; Palmer, R.; Klabunde, K. J.; Radonovich, L. J. Inorg.
Chem. 1995, 34, 278.
(12) (a) Linde, D. R. J. Chem. Phys. 1951, 19, 1605. (b) Beaglay, B.;
McAloon, K.; Freman, J. M. Acta Crystallogr., Sect. B 1974, 30, 444.

(η6-Arene)chromium Complexes
Inorganic Chemistry, Vol. 35, No. 11, 1996 3225
Figure 2. Diagram of the structure of (η6-C6H5F)Cr(CO)2(SnPh3)2
(molecule A).
Figure 3. Diagram of the structure of (η6-C6H4F2)Cr(CO)2(SnPh3)2.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for
4b
Table 3. Selected Bond Distances (Å) and Bond Angles (deg) for
5b
Bond Distances (A)
Cr-Sn(1)
Cr-C(1)
Cr-C(3)
Cr-C(5)
Cr-C(7)
C(5)-F
2.70(3)
1.90(2)
2.16(2)
2.18(2)
2.26(2)
1.38(2)
Cr-Sn(2)
Cr-C(2)
Cr-C(4)
Cr-C(6)
Cr-C(8)
2.68(3)
1.88(2)
2.13(2)
2.23(2)
2.23(2)
Bond Distances
Cr-Sn(1)
Cr-C(1)
Cr-C(3)
Cr-C(5)
Cr-C(7)
C(1)-F(1)
2.70(2)
2.17(1)
2.24(1)
2.25(1)
1.82(1)
1.38(2)
Cr-Sn(2)
Cr-C(2)
Cr-C(4)
Cr-C(6)
Cr-C(8)
C(4)-F(2)
2.71(2)
2.24(1)
2.18(1)
2.27(1)
1.86(1)
1.41(2)
Bond Distances (B)
Cr-Sn(1)
Cr-C(1)
Cr-C(3)
Cr-C(5)
Cr-C(7)
C(5)-F
2.70(3)
1.77(2)
2.31(2)
2.31(2)
2.22(2)
1.32(2)
Cr-Sn(2)
Cr-C(2)
Cr-C(4)
Cr-C(6)
Cr-C(8)
2.70(3)
1.83(2)
2.33(2)
2.22(2)
2.26(2)
Bond Angles
Sn(1)-Cr-Sn(2)
Sn(1)-Cr-C(8)
Sn(2)-Cr-C(8)
Cr-Sn(1)-C(9)
Cr-Sn(1)-C(21)
Cr-Sn(2)-C(39)
C(1)-Cr-C(2)
C(3)-Cr-C(4)
C(5)-Cr-C(6)
C(6)-Cr-C(3)
128.09(8)
75.8(4)
75.5(4)
116.2(4)
113.9(3)
106.8(4)
37.5(6)
36.2(6)
35.9(5)
80.9(6)
Sn(1)-Cr-C(7)
Sn(2)-Cr-C(7)
C(7)-Cr-C(8)
Cr-Sn(1)-C(15)
Cr-Sn(2)-C(33)
Cr-Sn(2)-C(27)
C(2)-Cr-C(3)
C(4)-Cr-C(5)
C(6)-Cr-C(1)
73.3(4)
73.3(4)
104.5(5)
111.9(3)
115.7(4)
117.3(3)
36.5(5)
Bond Angles (A)
C(1)-Cr-C(2)
Sn(1)-Cr-C(1)
Sn(2)-Cr-C(1)
C(3)-Cr-C(4)
C(5)-Cr-C(6)
C(7)-Cr-C(8)
100.1(6)
72.5(5)
75.8(5)
38.5(7)
35.8(7)
37.6(7)
Sn(1)-Cr-Sn(2)
Sn(1)-Cr-C(2)
Sn(2)-Cr-C(2)
C(4)-Cr-C(5)
C(6)-Cr-C(7)
C(8)-Cr-C(3)
127.8(1)
71.4(4)
74.8(4)
37.9(7)
36.7(7)
36.5(7)
37.6(6)
36.1(6)
of 1b, the ligands around the Cr center display a piano stool
arrangement.
Bond Angles (B)
C(1)-Cr-C(2)
Sn(1)-Cr-C(1)
Sn(2)-Cr-C(1)
C(3)-Cr-C(4)
C(5)-Cr-C(6)
C(7)-Cr-C(8)
107.2(7)
79.4(5)
74.9(5)
35.9(6)
36.5(6)
36.4(7)
Sn(1)-Cr-Sn(2)
Sn(1)-Cr-C(2)
Sn(2)-Cr-C(2)
C(4)-Cr-C(5)
C(6)-Cr-C(7)
C(8)-Cr-C(3)
129.2(1)
76.2(5)
70.8(5)
35.8(6)
36.9(7)
35.8(7)
Crystal Structure of (η6-Difluorobenzene)Cr(CO)2(SnPh3)2
(5b). Figure 3 displays an ORTEP diagram of the molecule.
Again the two CO ligands and the two stannyl ligands are in
trans positions with C(7)-Cr-C(8) and Sn(1)-Cr-Sn(2) angles
of 104.5° and 128.09°, respectively (Table 3). The Cr-Sn
distances are similar to those in 1b and 4b, 2.7 Å. The two
fluorine atoms eclipse the two CO ligands avoiding the steric
effect from the two bulky SnPh3 ligands. The arene ring
undergoes boat distortion where C(1) and C(4) that carry the
two fluorines are each bent up 0.05 Å.
(5)°. The two stannyl ligands are also trans to each other with
a Sn(1)-Cr-Sn(2) angle of 124.8(7)°. The Cr-Sn distances
are 2.72 and 2.70 Å. The distance between the arene ring center
and the Cr is 1.79 Å, which is 0.07 Å longer than that in the
analogous hydrido stannyl complex 1a. This longer distance
is probably a result of larger steric hindrance from the two
stannyl ligands and the methyl groups on the arene ring. C-
(10) almost eclipses Sn(2), and C(9) and C(11) are staggered
with Sn(1) to avoid steric effects. The effect of the steric
hindrance can be seen in the distances of the methyl groups
from the arene plane, which are 0.13 and 0.11 Å for C(9) and
C(11) and 0.26 Å for C(10) as a result of the eclipsed position.
Crystal Structure of (η6-Fluorobenzene)Cr(CO)2)(SnPh3)2
(4b). An ORTEP drawing of the structure is shown in Figure
2. Two independent molecules (A and B) have been found in
an asymmetric unit. Table 2 shows selected bond angles and
distances of the molecule. The two CO ligands as well as the
two stannyl ligands are trans to each other with C(1)-Cr-C(2)
and Sn(1)-Cr-Sn(2) angles of 100.1° (A), 107.2° (B) and
127.8° (A), 129.2° (B), respectively. Similar to the structure
1H NMR Studies and Correlation with Arene-Chromium
Interaction. In (arene)Cr(CO)3 complexes, the more alkyl
(electron-donating) substituents the arene ring has, the stronger
is the arene-chromium interaction and the more stable is the
complex. In the same sense, electronegative substituents on
the arene ring decrease the arene-chromium interaction giving
less stable complexes. In our hydrido stannyl and bis(stannyl)
complexes there are two competing factors: steric and electronic
effects. One of the best parameters to study and compare the
degree of interaction between the arene and the chromium center
1
is the H NMR chemical shift of the arene protons. For free
1
arenes, the H chemical shifts are downfield to around 7 ppm.
When an arene ring binds to a metal in an η6-fashion it loses
its aromaticity as it donates electrons to the metal center and
its protons become less deshielded and their resonances shift
upfield strongly to the region between 3 and 5 ppm. The

3226 Inorganic Chemistry, Vol. 35, No. 11, 1996
Khaleel and Klabunde
Table 4. 1H NMR Data (δ) for Complexes 1-5 in C6D6 at Room
irradiation. Solid transfers were accomplished in a glovebox. Toluene,
hexanes, pentane, benzene, and mesitylene were distilled from sodium
and potassium/benzophenone. Fluorobenzene, CH2Cl2, and difluoro-
benzene were distilled from CaH2 under argon. HSnPh3 was purchased
from Aldrich and used without further purification. (Arene)Cr(CO)3
complexes were prepared by refluxing Cr(CO)6 in the appropriate
aromatic solvent for 3-4 days and then purified after solvent removal
by washing with pentane or sublimation under vacuum at temperatures
between 60 and 70 °C. Infrared spectra were obtained using a Perkin-
Elmer 1330 instrument. The 1H NMR spectra were recorded on a
Varian XL-400 operating at 400 MHz. 1H chemical shifts are reported
relative to tetramethylsilane. 1H NMR data for complexes 1-4 are
given in Table 4. Elemental analyses were obtained from Galbraith
Laboratories.
Synthesis of the Mesitylene Complexes 1a and 1b. A yellow
solution of 0.20 g (0.78 mmol) of (mesitylene)Cr(CO)3 and 1.00 mL
(3.92 mmol) of HSnPh3 in 35 mL of mesitylene was magnetically stirred
under UV irradiation at room temperature for 4 h. Removing the
solvent from the resulting red solution gave about 1/2 mL of an oily
red-brown mixture which was dissolved in 5 mL of toluene and treated
on a silica gel chromatography column using hexanes/toluene as an
eluting solvent. Solutions of hydrido stannyl and bis(stannyl) com-
plexes were collected separately, the hydrido stannyl complex eluting
first. After removing the solvents in vacuo, each product was dissolved
in about 10 mL of CH2Cl2, layered with about 120 mL of pentane, and
stored in the freezer for recrystallization. Needle yellow crystals of
both complexes were obtained within 5 days (about 30% yield of 1a
and about 10% yield of 1b). IR of 1a (cm-1, nujol mull): νCr-H 1945,
νCO 1900, 1840. Anal. Calcd for CrSnO2C29H28 (1a): C, 60.13; H,
4.87. Found: C, 59.78; H, 4.88. IR of 1b (cm-1, nujol mull): νCO
1880, 1832. Anal. Calcd for CrSn2O2C47H42 (1b): C, 60.8; H, 4.56;
Cr, 5.60. Found: C, 58.7; H, 4.52; Cr, 5.59.
Synthesis of Toluene Complexes 2a and 2b. A solution of 0.20 g
(0.88 mmol) of (toluene)Cr(CO)3 and 1.00 mL (3.92 mmol) of HSnPh3
in 45 mL of toluene was stirred under UV light at room temperature
for 4 h. After work-up, purification on the column and recrystallization
from CH2Cl2/pentane, yellow needle crystals of 2a and 2b were obtained
respectively in about 20% and 15% yield. IR of 2a (cm-1, nujol
mull): νCr-H 1918, νCO 1870, 1830. IR of 2b (cm-1, nujol mull): νCO
1883, 1825.
Synthesis of Benzene Complexes 3a and 3b. Both 0.20 g (0.93
mmol) of (benzene)Cr(CO)3 and 1.00 mL (3.92 mmol) of HSnPh3 were
dissolved in 40 mL of benzene. The solution was irradiated with UV
light and stirred at room temperature for 4 h. After filtration, solvent
removal and purification by column chromatography and recrystalli-
zation from CH2Cl2/pentane as previously described, yellow crystals
of 3a and 3b were obtained in about 10% and 20% yield, respectively.
IR of 3a (cm-1, nujol mull): νCr-H 1942, νCO 1895, 1858. IR of 3b
(cm-1, nujol mull): νCO 1895, 1842. Anal. Calcd for CrSn2O2C44H36
(3b): C, 59.64; H, 4.09. Found: C, 58.26; H, 3.94.
Temperature (ppm) and Coupling Constants (Hz)
arene, methyl
hydride
phenyl
J(Sn-H)a
1a 4.37 (s, 3H),
1.54 (s, 9H)
1b 4.82 (s, 3H),
1.48 (s, 9H)
-8.14 (s, 1H) 7.2-7.9 (m, 15H)
7.2-7.9 (m, 30H)
329.2
2a 4.3-4.5 (d, 2H;
t, 2H; t, 1H),
1.48 (s, 3H)
2b 4.1-5.1 (d, 2H;
t, 2H; t, 1H),
1.036 (s, 3H)
3a 4.41 (s, 6H)
3b 4.65 (s, 6H)
4a 3.9-4.6 (m, 5H) -8.52 (s, 1H) 7.2-7.8 (m, 15H)
4b 3.8-5.05 (m, 5H)
5b 4.98 (m, 4H)
-8.72 (s, 1H) 7.3-7.8 (m, 15H)
328.8
338.0
7.2-7.9 (m, 30H)
-8.78 (s, 1H) 7.3-7.8 (m, 15H)
7.2-7.8 (m, 30H)
7.2-7.8 (m, 30H)
7.18-7.8 (m, 30H)
a 1J(119Sn-1H).
stronger the arene binds to the metal, the more deshielded its
protons are and the more upfield their resonance is.
The amount of this shift can be used as a parameter to study
and compare arene-chromium bond interaction in complexes
1-5. We will compare the differences of chemical shifts
between the free and the bonded arene protons. The smaller
the difference supposedly the less the arene-chromium interac-
tion. The chemical shifts for the arene protons of the complexes
are given in Table 4, and the differences from the free arenes
are given in Table 5. It is clear that for the same arene
complexes, the arene proton chemical shifts go downfield (closer
to the free arene region) as we go from the tricarbonyl to the
hydrido stannyl to the bis(stannyl) complex. This indeed
suggests that for the same arene the arene metal strength of
interaction increases as follows: bis(stannyl) complexes <
hydrido stannyl complexes < tricarbonyl complexes The
chromium-arene distances obtained from the X-ray structural
analysis support this trend. The chromium-arene distance is
1.79 Å for 1b and 1.72 Å for 1a.
In the same way, complexes with different arenes can be
compared. As shown in Table 5, two different trends are
observed for the methyl-substituted and the fluorine-substituted
arene complexes. The difference in the chemical shifts of arene
protons between the free arene and the bonded arene increases
by going from mesitylene to the less methyl-substituted arene
(toluene and benzene) complexes. In these complexes, steric
effects seem to control the extent of interaction with the
chromium center. The difference between the free and bonded
arene proton chemical shifts increase as follows: mesitylene
complexes < toluene complexes < benzene complexes (Table
5). In the fluorine-substituted arene complexes, electronic
factors seem to become more important. More fluorine sub-
stituents lead to a more electron-demanding arene and a weaker
chromium-arene interaction.
Synthesis of Fluorobenzene Complexes 4a and 4b. A solution of
0.20 g (0.86 mmol) of (fluorobenzene)Cr(CO)3 and 1.00 mL of HSnPh3
in 45 mL of fluorobenzene was stirred under UV irradiation at room
temperature for 4.5 h. The same previous work-up and purification
methods led to mainly the bis(stannyl) complex 4b (about 15% yield)
and a small amount of the hydrido stannyl complex 4a (about 3% yield).
IR of 4a (cm-1, nujol mull): νCr-H 1950 and νCO 1889, 1839. IR of
4b (cm-1, nujol mull): νCO 1890 and 1838. Anal. Calcd for CrSn2-
FO2C44H35 (4b): C, 58.45; H, 3.90. Found: C, 59.15; H, 3.85.
Synthesis of Difluorobenzene Complexes 5a and 5b. Both 0.20
g (0.80 mmol) of (difluorobenzene)Cr(CO)3 and 1.00 mL of HSnPh3
were dissolved in 50 mL of difluorobenzene. The solution was stirred
and irradiated with UV light at room temperature for 4.5 h. Following
the same previous work-up and purification techniques, the bis(stannyl)
complex 5b was mainly obtained (10-15% yield) and only small traces
of the hydrido stannyl complex were obtained for which purification
and recrystallization attempts failed. Anal. Calcd for CrSn2F2O2C44H34
(5b): C, 57.3; H, 3.72. Found: C, 58.7; H, 4.32.
In conclusion, we have found that the (η6-arene)Cr(CO)2H-
(SnPh3) complexes, 1a-4a, possess a three-center Cr-H-Sn
bond, which is in contrast to similar (η6-arene)Cr(CO)(H)2-
(SiCl3)2 derivatives.11 The (η6-arene)Cr(CO)2(SnPh3)2 com-
pounds have stronger chromium-arene interaction when the
arene is less sterically encumbered. Finally, we have noted that
1H NMR chemical shift data correlate roughly with X-ray
determined chromium-(arene center) distances.
Experimental Section
(13) (a) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air SensitiVe
Compounds, 2nd ed.; Wiley: New York, 1986. (b) Herzog, S.;
Dehnert, J.; Luhder, K. In Technique of Inorganic Chemistry;
Johnassen, H. B., Ed.; Interscience: New York, 1969; Vol. VII.
All reactions were carried out under Ar using standard Schlenk
techniques.13 Photochemical reactions were carried out in a quartz tube
equipped with a water-cooled probe. A 450-W UV lamp was used for

(η6-Arene)chromium Complexes
Inorganic Chemistry, Vol. 35, No. 11, 1996 3227
Table 5. Arene Proton Chemical Shifts (ppm) (Differences between Free Arene and Complexed Arene Proton Chemical Shifts in Parentheses)
mesitylene
toluene
7.0-7.1
4.2-4.5 (2.68)
4.3-4.6 (2.58)
4.1-5.1 (2.48)
benzene
7.16
4.27 (2.89)
4.41 (2.75)
4.65 (2.50)
fluorobenzene
difluorobenzene
free arene
Cr-TCa
6.72
6.8-6.9
6.5
4.27 (2.23)
4.08 (2.65)
4.37 (2.36)
4.82 (1.90)
3.6-4.3 (2.89)
3.9-4.6 (2.58)
3.8-5.1 (2.33)
Cr-hydb
Cr-bis(stn)c
4.98 (1.52)
a (arene)Cr(CO)3. b (arene)Cr(CO)2H(SnPh3). c (arene)Cr(CO2)(SnPh3)2.
Table 6. Crystallographic Data for Complexes 1b, 4b, and 5b
1b
4b
5b
formula
formula weight
crystal system
a (Å)
b (Å)
c (Å)
CrSn2O2C47H42
928.22
CrSn2FO2C44H35
904.14
CrSn2F2O2C44H34
922.13
monoclinic
13.756(2)
18.560(2)
17.159(2)
monoclinic
13.905(4)
18.499(2)
17.708(2)
109.84(1)
4285(1)
P21/c (No. 14)
4
1.467
117.92
1.54178
6.0
16.0
orthorhombic
16.717(2)
18.453(2)
25.766(2)
93.69(1)
7948(2)
Pca21 (No. 29)
8
1.663
140.28
1.54178
6.0
8.0
b (deg)
V (Å3)
4372(2)
P21/c (No. 14)
4
space group
Z
D
calc (g/cm3)
1.510
µ(Cu KR) (cm-1
λ (Å)
)
116.60
1.54178
6.0
16.0
0.79-1.06
3801
take-off-angle (deg)
scan rate (deg/min)
trans. factor s
0.83-1.29
4845
481
0.082; 0.091
0.89-1.02
4626
474
0.049; 0.073
no. of observations
no. of variables
514
0.064; 0.060
a
R; Rw
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [(∑w(|Fo| - |Fc|)2/∑wFo )]1/2
.
X-ray Structural Analysis. Yellow crystals of complexes 1a-4a
and 1b-5b were obtained by slow recrystallization from CH2Cl2/
pentane at low temperature. All measurements were carried out on a
Rigaku AFC5R diffractometer with graphite-monochromated Cu KR
radiation and a 12-kW rotating anode generator. The calculations were
performed using the TEXSAN crystallographic software package of
Molecular Structure Corporation. An empirical absorption correction
using the program DIFABS was applied. The data were corrected for
Lorentz and polarization effects. Crystal data for 1b, 4b, and 5b are
given in Table 6.
was determined to be Pca21 (No. 29). The data were collected at -160
°C using the ω-2θ scan technique to a maximum 2θ value of 112.3°.
A total of 5895 reflections was collected. The intensities of three
representative reflections which were measured after every 150
reflections remained constant throughout data collection. The structure
was solved by direct methods. The final cycle of full-matrix least-
squares refinement gave residuals of R ) 0.049 and Rw ) 0.073.
X-ray Structural Analysis of (η6-C6H4F2)Cr(CO)2(SnPh3)2 (5b).
A yellow plate crystal having approximate dimensions of 0.50 × 0.30
× 0.03 mm was mounted on a glass fiber. Cell constants and an
orientation matrix for data collection were obtained from a least-squares
refinement using the setting angles of 25 carefully centered reflections
in the range 63.86° < 2θ < 68.68°. The space group was determined
to be P21/c (No. 14). The data were collected at 23 °C using the ω-2θ
scan technique to a maximum 2θ value of 112.7°. Of the 6253
reflections which were collected, 5962 were unique (Rint ) 0.03). The
intensities of three representative reflections which were measured after
every 150 reflections remained constant throughout data collection. The
structure was solved by direct methods. Anisotropic refinement on
non-hydrogen atoms gave R ) 0.064 and Rw ) 0.060.
X-ray Structural Analysis of (η6-C6H3(CH3)3)Cr(CO)2(SnPh3)2
(1b). A yellow needle crystal having approximate dimensions of 0.20
× 0.10 × 0.30 mm was mounted in a glass capillary. Cell constants
and an orientation matrix for data collection were obtained from 25
carefully centered reflections in the range 50.50 < 2θ < 61.49°. On
the basis of the systematic absences and the successful solution and
refinement of the structure the space group was determined to be P21/c
(No. 14). The data were collected at a temperature of 23 °C using the
ω-2θ scan technique: 6122 reflections were collected, 5844 of them
were unique (Rint ) 0.045). The intensities of three representative
reflections which were measured after every 150 reflections remained
constant throughout data collection. The structure was solved by
combination of the Patterson method and direct methods. The non-
hydrogen atoms were refined anisotropically. The final cycle of full-
matrix least-squares refinement produced R ) 0.082 and Rw ) 0.091.
X-ray Structural Analysis of (η6-C6H5F)Cr(CO)2(SnPh3)2 (4b).
A yellow plate crystal of approximate dimensions of 0.50 × 0.30 ×
0.10 mm was mounted on a glass fiber. A total of 25 carefully centered
reflections in the range 64.59° < 2θ < 69.10° was used to obtain cell
constants and an orientation matrix for data collection. The space group
Acknowledgment. The support of National Science Founda-
tion is acknowledged with gratitude. We also thank Dr. Zhengui
Yao for helpful discussions.
Supporting Information Available: Tables of thermal parameters,
least-squares-planes, and complete tables of bond distances and angles
for complexes 1b, 4b, and 5b (38 pages). Ordering information is
given on any current masthead page.
IC951431Z