C - Cl bond activation of ortho-chlorinated imine with iron complexes in low oxidation states

Article abstract of DOI:10.1021/om801162u

The orthzo-chelated iron(II) complexes [FeC1(PMe₃) ₃((C₆H₃C1-orthzo)CH=N-R)] (R = Me, Ph) (3, 4) and [FeCl(PMe₃)3(C₆H₄-CH=N-R)] (R = Ph, n-Bu) (7, 8) were prepared through oxidat

Full text of DOI:10.1021/om801162u

2206
Organometallics 2009, 28, 2206–2210
C-Cl Bond Activation of ortho-Chlorinated Imine with Iron
Complexes in Low Oxidation States
Yujie Shi, Min Li, Qingping Hu, Xiaoyan Li, and Hongjian Sun*
School of Chemistry and Chemical Engineering, Shandong UniVersity, Shanda Nanlu 27, 250100 Jinan,
People’s Republic of China
ReceiVed December 8, 2008
The ortho-chelated iron(II) complexes [FeCl(PMe3)3((C6H3Cl-ortho)CHdN-R)] (R ) Me, Ph) (3, 4)
and [FeCl(PMe3)3(C6H4-CHdN-R)] (R ) Ph, n-Bu) (7, 8) were prepared through oxidative addition of
the C-Cl bond of ortho-chlorinated imine using iron(0) complexes, [Fe(PMe3)4]. The reactions of 3, 4,
and 8 with CO delivered the carbonyl Fe(II) complexes 9-11. A one-pot reaction of [FeMe2(PMe3)4]
with (C6H3Cl2-2,6)CHdN-Ph in CO atmosphere resulted in carbonyl Fe(II) complexes [FeMe(CO)(PMe3)2-
((C6H3Cl-ortho)CHdN-Ph)] (12). The crystal and molecular structures of complexes 3, 4, 7-9, and 12
were determined by X-ray diffraction.
(eq 2) center with imine as an anchoring group. In the case of
nickel(0) complexes, a series of bis(isoindolinone)s were formed
through carbonylative cyclization and dimerization of phe-
nylimine.
Introduction
In the past few years aromatic carbon-halogen bond activa-
tion at transition metal centers has been proven to be a useful
tool in synthetic organic chemistry. When compared with the
reactive and expensive iodo- and bromoarenes, as well as both
costly and inert fluoroarenes, chloroarenes are certainly the most
attractive aryl halides for synthetic applications on an industrial
scale. Due to the importance of functionalization or dechlori-
nation of aromatic chlorides, there is currently a great deal of
interest in the activation of the C-Cl bond, which has been
found comparatively inert.1 There have been some examples
of catalytic activation of the carbon-chlorine bond and
carbon-carbon coupling of chloroarenes by palladium,2-4
nickel,5 cobalt,6-8 and iron9 complexes such as the Heck
reaction, Suzuki coupling, and Stille coupling.
Recently we have reported cyclometalation reactions involv-
ing C-Cl bond activation at a cobalt(I)6c (eq 1) and nickel(0)5g
* Towhomcorrespondenceshouldbeaddressed.E-mail:hjsun@sdu.edu.cn.
Fax: +86-531-88564464.
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Here we report on our new progress in the direction of
cyclometalation reactions involving C-Cl bond activation at
iron centers with imine as prechelate ligands. The new ortho-
chelated iron complexes formed by oxidative addition of an
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Lett. 1998, 39, 6163. (b) Cahiez, G.; Avedissian, H. Tetrahedron Lett. 1998,
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10.1021/om801162u CCC: $40.75
2009 American Chemical Society
Publication on Web 03/04/2009

C-Cl Bond ActiVation of ortho-Chlorinated Imine
Organometallics, Vol. 28, No. 7, 2009 2207
Figure 1. Molecular structure of 3 (all hydrogen atoms were omitted for clarity). Selected distances (Å) and angles (deg): N1-Fe1 2.024(2),
Fe1-C6 1.951(2), Fe1-P3 2.2435(9), Fe1-P1 2.2504(8), Fe1-P2 2.2647(8), Fe1-Cl2 2.3977(8); C7-N1-Fe1 114.86(16), C8-N1-Fe1
129.31(17), C6-Fe1-N1 81.55(9), C6-Fe1-P3 95.58(7), N1-Fe1-P3 176.96(6), C6-Fe1-P1 93.14(7), N1-Fe1-P1 89.38(6),
P3-Fe1-P1 91.77(3), C6-Fe1-P2 91.95(7), N1-Fe1-P2 88.19(6), P3-Fe1-P2 90.93(3), P1-Fe1-P2 173.99(3), C6-Fe1-Cl2 170.60(7),
N1-Fe1-Cl2 89.10(6), P3-Fe1-Cl2 93.75(3), P1-Fe1-Cl2 87.72(3), P2-Fe1-Cl2 86.74(3).
aromatic C-Cl bond were isolated and characterized. The
reaction with CO resulted in only substituted carbonyl iron(II)
complexes; no C,C-coupling reactions have been observed in
compration with the case of nickel(0) complex.5g
chelating ligand is coordinated by a N atom and a C atom,
forming a five-membered metallacycle. The sum of internal bond
angles (540°) of this five-membered chelating ring indicates
planarity. Typically, the Cl atom is trans-oriented to the
phenyl-C atom because of mutual trans influence. Two trans-
trimethylphosphine ligands slightly lean toward the Cl atom
because of steric effects. The bulky imino phenyl group of
complex 4 makes the angle P2-Fe1-Cl1 (82.57(3)°) signifi-
cantly smaller than that in complex 3 (P3-Fe1-Cl2 93.75(3)°).
In addition, due to the electron-donating property and the
conjugation effect of the phenyl group, the Fe1-P3 bond
(2.2435(9) Å) in complex 3 is shorter than the Fe1-P2 bond
(2.2771(8) Å) in complex 4.
Results and Discussion
1. Reaction of Fe(PMe3)4 with the Dichlorinated Imine
Ligands Derived from 2,6-Dichlorobenzaldehyde. The reac-
tion of Schiff bases 1 and 2 (R ) CH3, 1; Ph, 2) by reaction
with Fe(PMe3)4 afforded the six-coordinate Fe(II) complex 3
and 4 via C-Cl bond activation (eq 3).
2. Reaction of Fe(PMe3)4 with the Monochlorinated
Imine Ligands Derived from 2-Chlorobenzaldehyde. Treat-
ment of imine ligands 5 and 6 (R ) Ph, 5; R ) n-Bu, 6) with
1 equiv of Fe(PMe3)4 afforded complexes 7 and 8 (eq 4).
Crystallization at -27 °C afforded a wine crystalloid 3 and
purple 4 in pentane, respectively. In the infrared spectra of
complexes 3 and 4, the characteristic ν(CdN) bands are found
at 1564 and 1595 cm-1. Compared with those of the free imine
ligands (ν(CdN) ) 1622-1655 cm-1), the evident red shift
indicates the coordination of the imine N-donor. The expected
five-membered metallocycles have been confirmed by X-ray
crystallography.
Crystallization at -4 °C resulted in purple crystals of 7 in
diethyl ether and dark red crystals of 8 in pentane. In complexes
7 and 8 the iron atom is located at the center of an octahedral
geometry (Figures 3 and 4). The molecular structure of 7 is
close to that of complex 4.
In the crystal structures of complexes 3 and 4 (Figures 1 and
2) the iron atom is centered in an octahedron geometry with
one N atom, one Cl atom, one C atom, and three P atoms. The

2208 Organometallics, Vol. 28, No. 7, 2009
Shi et al.
Figure 2. Molecular structure of 4 (all hydrogen atoms were omitted for clarity). Selected distances (Å) and angles (deg): N1-Fe1 2.050(2),
Fe1-C1 1.957(3), Fe1-P3 2.2435(9), Fe1-P1 2.2710(10), Fe1-P2 2.2771(8), Fe1-Cl1 2.3960(8); C7-N1-Fe1 113.61(18), C8-N1-Fe1
132.61(18), C1-Fe1-N1 81.62(10), C1-Fe1-P3 85.93(9), N1-Fe1-P3 88.50(7), C1-Fe1-P1 87.06(9), N1-Fe1-P1 88.63(7),
P3-Fe1-P1 172.75(3), C1-Fe1-P2 102.61(8), N1-Fe1-P2 175.77(7), P3-Fe1-P2 91.72(3), P1-Fe1-P2 91.63(3), C1-Fe1-Cl1
174.62(8), N1-Fe1-Cl1 93.20(7), P3-Fe1-Cl1 92.48(3), P1-Fe1-Cl1 94.34(3), P2-Fe1-Cl1 82.57(3).
complex 11 was isolated from the reaction of complex 8 with
carbon monoxide (eq 6).
Figure 3. Molecular structure of 7 (all hydrogen atoms were omitted
for clarity). Selected distances (Å) and angles (deg): Fe-C1
1.957(3), Fe-N1 2.058(2), Fe-P3 2.2563(9), Fe-P1 2.2698(9),
Fe-P2 2.2822(9), Fe-Cl 2.3938(8), N1-C7 1.298(4), N1-C8
1.440(4); C1-Fe-N1 81.56(11), C1-Fe-P3 86.25(9), N1-Fe-P3
88.37(7), C1-Fe-P1 86.60(9), N1-Fe-P1 88.20(7), P3-Fe-P1
In the molecular structure of complex 9 (Figure 5), the iron
172.46(4), C1-Fe-P2 102.95(9), N1-Fe-P2 175.49(7), P3-Fe-P2
atom is coordinated with one five-membered chelating [C,N]-
92.04(4), P1-Fe-P2 91.90(4), C1-Fe-Cl 173.93(9), N1-Fe-Cl
ligand, two trimethylphosphine molecules, one chlorine atom,
and one carbonyl ligand in a disordered octahedron. Complexes
9 and 10 are very stable in air. In comparison with the reaction
of Ni(PMe3)4 with analogous Schiff base complexes,5g only the
substituted products were produced instead of the coupling
products.
4. One-Pot Reaction of FeMe2(PMe3)4 with Ligand 5 in
CO Atmosphere. Reactions of Fe(Me2)(PMe3)4 with ligand 5
in a CO atmosphere did not afford the expected complex 13
via C-Cl activation according to Scheme 1, but formed complex
12 through C-H activation and cyclometalation. At the same
time, an expected insertion of CO into the Fe-Me bond did
not occur; only a simple substitution of a trimethylphosphine
ligand by CO was observed. Although the bond energy of the
C-H bond (435 kJ mol-1) is significantly higher than that of
the C-Cl bond (351 kJ mol-1), complex 12 was obtained as a
92.60(7), P3-Fe-Cl 91.99(4), P1-Fe-Cl 94.88(4), P2-Fe-Cl
82.91(3).
A conceivable reaction pathway may be described as
follows: The first step is the substitution of one trimeth-
ylphosphine by the imine N atom. The C-Cl bond activation
is realized through oxidative addition with the support of a
chelating effect. The reaction in eq 4 is slower than the
reaction in eq 3 because the strong electron-withdrawing
ability of the second Cl atom weakens the first C-Cl bond.
3. Reaction of Complexes 3, 4, and 8 with CO. Stirring a
solution of 3 or 4 in CO atmosphere gave rise to complex 9
or 10 (eq 5). The reactions was complete within a few
minutes. The crystals of complex 9 could be obtained with
evaporation of solvent in air. Under the same conditions

C-Cl Bond ActiVation of ortho-Chlorinated Imine
Organometallics, Vol. 28, No. 7, 2009 2209
Figure 6. Molecular structure of 12 (all hydrogen atoms were
omitted for clarity). Selected distances (Å) and angles (deg):
Fe1-C1 1.726(3), Fe1-C8 1.979(3), Fe1-C21 2.183(3), Fe1-P2
2.2446(9), Fe1-P1 2.2500(9), O1-C1 1.154(4), N1-C14 1.300(4),
N1-C15 1.443(3), N1-Fe1 2.063(2); C1-Fe1-C8 94.57(14),
C8-Fe1-N1 80.83(10), N1-Fe1-C21 95.84(10), C1-Fe1-C21
88.77(14), C1-Fe1-P1 91.90(10), C8-Fe1-P1 90.91(7), O1-C1-Fe1
178.5(3),N1-C14-C13118.3(2),C8-C13-C14112.7(2),C13-C8-Fe1
114.42(19), C14-N1-Fe1 113.80(17).
Figure 4. Molecular structure of 8 (all hydrogen atoms were omitted
for clarity). Selected distances (Å) and angles (deg): Fe1-C1
1.9590(18), Fe1-N1 2.0075(15), Fe1-P3 2.0075(15), Fe1-P3
2.2543(7), Fe1-P1 2.2661(7), Fe1-P2 2.2714(7), Fe1-Cl1 2.4208(7),
N1-C71.277(2),N1-C81.480(2);C1-Fe1-N181.77(7),C1-Fe1-P3
86.02(6), N1-Fe1-P3 87.62(5), P3-Fe1-P1 171.05(2), C1-Fe1-P2
104.13(6), N1-Fe1-P2 174.09(5), P3-Fe1-P2 92.62(3), P1-Fe1-P2
91.90(3),C1-Fe1-Cl1173.45(5),N1-Fe1-Cl191.70(5),P2-Fe1-Cl1
82.40(2), P3-Fe1-Cl1 94.30(3), C7-N1-C8 119.90(16), C7-N1-Fe1
114.89(13).
Scheme 1
choring group forms a five-membered metallacyle where the
sum of internal bond angles (540.05°) indicates planarity.
Conclusion
Reactions of mono- and di-ortho-cholorinated compounds (1,
2, 5, and 6) containing imine as anchoring groups with
Fe(PMe3)4 delivered cyclometalated complexes (3, 4, 7, and 8)
in octahedral coordination geometry via the C-Cl bond
activation. The novel stable ortho-chelated iron complexes were
characterized by spectroscopic methods. Only simple substitu-
tion products 9-11 were observed in the reactions of complexes
3, 4, and 8 with CO. No insertion and/or reductive elimination
were found in these reactions. The one-pot reaction of prechelate
ligand 5 with FeMe2(PMe3)4 in CO atmosphere interestingly
afforded the C-H activation product 12 instead of the C-Cl
bond activation product. The structures of complexes 3, 4, 7-9,
and 12 were determined by X-ray diffraction.
Figure 5. Molecular structure of 9 (all hydrogen atoms were omitted
for clarity). Selected distances (Å) and angles (deg): Fe1-C1
1.759(12), Fe1-C2 1.967(8), Fe1-N1 1.999(8), Fe1-P2 2.234(3),
Fe1-P1 2.272(3), Fe1-Cl1 2.384(2), O1-C1 1.086(13), C8-N1
1.318(12), C9-N1 1.478(10); C1-Fe1-C2 95.6(4), C2-Fe1-N1
81.7(3), N1-Fe1-Cl1 93.0(2), C1-Fe1-Cl1 89.8(3), P2-Fe1-P1
176.82(12),C2-Fe1-Cl1174.0(3),C1-Fe1-N1176.2(4),P1-Fe1-Cl1
87.23(10), C9-N1-Fe1 127.1(6).
kinetic product of C-H activation. An attempt to isolate the
possible intermediate 14 was not successful.
In the infrared spectra of complex 12, the characteristic
ν(Ct O) band is found at 1907 cm-1. The proton resonances of
the Fe-CH3 were recorded at -0.77 ppm.
The iron atom has an octahedral geometry and is coordinated
with the carbonyl ligand trans-oriented to the imine N atom
(Figure 6). The chelating ligand with the N atom as the an-
Experimental Section
General Procedures and Materials. Standard vacuum techniques
were used in manipulations of volatile and air-sensitive material.

2210 Organometallics, Vol. 28, No. 7, 2009
Shi et al.
Table 1. Crystallographic Data for Complexes 3, 4, 7, 8, 9, and 12
3
4
7
8
9
12
empirical formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
C17H34Cl2FeNP3
472.13
monoclinic
P2(1)/n
8.6000(17)
28.838(6)
9.1660(18)
90
93.01(3)
90
2270.1(8)
4
1.381
10 050
5206
0.0403
31.79
0.0356
0.1358
C22H36Cl2FeNP3
534.2
C22H37ClFeNP3
499.8
C20H41ClFeNP3
481.8
C15H25Cl2FeNOP2
424.06
orthorhombic
Pna2 (1)
30.994(6)
8.5930(17)
29.837(6)
90
90
90
7947(3)
16
1.424
34 481
14 372
0.0765
27.11
0.0858
0.2173
C21H31ClFeNOP2
466.71
noclinic
P2(1)/n
8.6390(17)
34.588 (7)
9.5210(19)
90
98.14(3)
90
2816.3(10)
4
1.373
13 744
5952
0.0543
27.14
0.0532
0.1595
monoclinic
P2(1)/n
8.9303(10)
33.154(3)
9.7044(9)
90
99.450(6)
90
2834.3(5)
4
1.251
22 090
5944
0.0235
27.55
0.0443
0.1469
monoclinic
P2(1)/n
897(2)
9.878(8)
9.545(3)
90
96.349(4)
90
2521.6(12)
2
2.065
14 874
5645
0.0430
27.53
0.0323
0.0760
triclinic
j
P1
8.8720(18)
9.0070(18)
15.555(3)
86.41(3)
75.14(3)
74.43(3)
1157.3(4)
2
1.339
4253
3424
0.0411
27.02
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
Dc, g cm-3
no. of rflns collec
no. of indep rflns
Rint
θ
max, deg
R1 (I > 2σ (I))
0.0385
0.1243
wR2 (all data)
Solvents were dried by known procedures and distilled under nitrogen
before use. Corresponding Schiff base complexes of 2,6-dichloroben-
zaldehyde and 2-chlorobenzaldehyde were prepared by refluxing
mixtures of chlorobenzaldehyde and amine in alcohol solution. Infrared
spectra (4000-400 cm-1), as obtained from Nujol mulls between KBr
Synthesis of 10. 4 (0.30 g, 0.56 mmol) was dissolved in pentane.
Stirring the solution in an atmosphere of CO resulted in a green
solution after 1 h. The filtrate was kept at -27 °C to afford purple
crystals of 10. Yield: 0.16 g (60%). IR (Nujol, cm-1): 1917 ν(Ct O).
1H NMR (300 MHz, C6D6, 298 K, ppm): δ 0.98 (m, 18H, PCH3),
6.64-7.85 (m, 8H, Ar-H), 9.05 (s, 1H, CHdN). 31P NMR (121
MHz, C6D6, 298 K, ppm): δ 25.3 (s).
Synthesis of 11. A solution of complex 8 (0.50 g 1.04 mmol) in
50 mL of pentane was stirred in an atmosphere of CO for 12 h.
The filtrate was kept at -27 °C to afford red crystals of 11. Yield:
0.26 g (58%). IR (Nujol, cm-1): 1903 ν(Ct O), 1599 ν(CdN), 1577
ν(CdC), 947 ν(PMe3). 1H NMR (300 MHz, C6D6, 298 K, ppm): δ
1.37 (m, 2H, CH2), 1.68 (m, 2H, CH2), 3.84 (m, 2H, N-CH2),
6.73-7.47 (m, 4H, Ar-H), 8.46 (s, br, 1H, CHdN).
Synthesis of 12. A solution of FeMe2(PMe3)4 (1.00 g, 4.47 mmol)
in 30 mL of pentane was combined with a solution of 7 (0.97 g, 4.50
mmol) in pentane (30 mL) at -80 °C. The reaction mixture was allowed
to warm to room temperature. The reaction mixture turned blue after a
few minutes. After 5 h, stirring the solution in an atmosphere of CO
resulted in a green solution in a few minutes. Crystallization at -27 °C
afforded green microcrystals of 12. Yield: 0.21 g (10%). IR (Nujol, cm-1):
1907 ν(Ct O), 1566 ν(CdC), 946 ν(PMe3). 1H NMR (300 MHz, CDCl3,
298 K, ppm): δ -0.76 (m, 3H, Fe-CH3), 0.89 (m, 18H, PCH3), 6.73-7.90
(m, 8H, Ar-H), 8.75 (s, br, 1H, CHdN). 31P NMR (121 MHz, CDCl3,
294 K, ppm): δ 19.4 (s).
X-ray Structure Determinations. Intensity data were collected on
a Bruker SMART diffractometer with graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å). Crystallographic data for complexes 3, 4, 7-9,
and 12 are summarized in Table 1. The structures were solved by direct
methods and refined with full-matrix least-squares on all F2 (SHELXL-
97) with non-hydrogen atoms anisotropic.
1
disks, were recorded on a Nicolet 5700. H and 31P NMR (300 and
121 MHz, respectively) spectra were recorded on a Bruker Avance
300 spectrometer. 31P NMR resonances were obtained with broadband
proton decoupling. X-ray crystallography was performed with a Bruker
Smart 1000 diffractometer.
Synthesis of 3. A solution of Fe(PMe3)4 (1.35 g, 3.75 mmol) in
30 mL of pentane was combined with a solution of 1 (0.7 g, 3.72
mmol) in pentane (20 mL) at -80 °C. The reaction mixture was
allowed to warm to room temperature and stirred for 5 h. During this
period, the reaction mixture turned black-red. At this point the solution
was filtered. Crystallization at -27 °C afforded black-red microcrystals
of 3: yield 0.54 g (30.0%). IR (Nujol, cm-1): 1564 ν(CdN), 1578
ν(CdC), 942 ν(PMe3). 31P NMR (C6D6, 297 K, ppm): δ 11.4 (d, 2J(PP)
) 58 Hz, 2P), 14.7 (t, 2J(PP) ) 52 Hz, 1P).
Synthesis of 4. A sample of 1.07 g (2.97 mmol) of Fe(PMe3)4
and 0.74 g (2.96 mmol) of 2 in 50 mL of pentane after 6 h at room
temperature formed a purple solution. Then the solution was filtered.
Crystallization at -27 °C afforded black-red microcrystals of 5.
Yield: 0.63 g (40%). IR (Nujol, cm-1): 1565 ν(CdC), 1595
ν(CdN), 944 ν(PMe3).
Synthesis of 7. A solution of 0.80 g (2.22 mmol) of Fe(PMe3)4
in 30 mL of diethyl ether was combined with a solution of complex
5 (0.48 g, 2.23 mmol) in 30 mL of diethyl ether at -80 °C. The
mixture was allowed to warm to room temperature and stirred for
12 h. Dark purple crystals of 7 were afforded at -27 °C after
filtering. Yield: 0.75 g (67%). IR (Nujol, cm-1): 1574 ν(CdN),
1558 ν(CdC), 940 ν(PMe3).
Synthesis of 8. Fe(PMe3)4 (0.80 g, 2.22 mmol) dissolved in 30
mL of pentane was combined with a solution of complex 6 (0.44 g,
2.25 mmol) in 40 mL of pentane at room temperature and stirred for
12 h. The filtrate was kept at -27 °C to afford red crystals of 10.
Yield: 0.64 g (60%). IR (Nujol, cm-1): 1596 ν(CdN), 1572 ν(CdC),
941 ν(PMe3). 1H NMR (C6D6, 298 K, ppm): δ 0.96 (m, 27H, PCH3),
1.25 (m, 3H, CH3), 1.37 (m, 2H, CH2), 1.70 (m, 2H, CH2), 3.79 (m,
2H, CH2), 6.90-7.55 (m, 4H, Ar-H), 7.97 (s, 1H, CHdN). 31P NMR
(121 MHz, C6D6, 298 K, ppm): δ 12.8 (s).
Synthesis of 9. 3 (0.20 g, 0.42 mmol) was dissolved in pentane.
Stirring the solution in an atmosphere of CO resulted in a red solution
in a few minutes. The solution was filtered after 2 h. Crystallization at
-27 °C afforded a red deposition of 9. Yield: 0.17 g (98%). IR (Nujol,
cm-1): 1912 ν(Ct O), 1567 ν(CdC), 1593 ν(C)N), 944 ν(PMe3).
1H NMR (300 MHz, C6D6, 298 K, ppm): δ 0.90 (m, 18H, PCH3),
3.48 (s, 3H, CH3), 6.63-7.75 (m, 3H, Ar-H), 8.70 (s, 1H, CHdN).
31P NMR (121 MHz, C6D6, 298 K, ppm): δ 27.2 (s).
CCDC-11783 (3), CCDC-11784(4), CCDC-679219(7), CCDC-
679220 (8), CCDC-679221 (9), and CCDC-702986 (12) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB21EZ, UK (fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Acknowledgment. We gratefully acknowledge the support
by NSF China No. 20872080/20772072. We also thank the kind
assistance from Prof. Dieter Fenske for the X-ray diffraction
analysis.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
OM801162U