Deprotonated diindolylmethanes as dianionic analogues of scorpionate bis(pyrazolyl)borate ligands: Synthesis and structural characterization of representative titanocene and zirconocene complexes

Article abstract of DOI:10.1016/j.jorganchem.2004.09.003

Deprotonation of di(3-methylindol-2-yl)phenylmethane (L₂H ₂) or 2-methoxyphenyldi(3-methylindol-2-yl)methane(L2′H2) with two equivalents of ⁿBuLi, followed by reactions with Cp ₂TiCl₂ or Cp₂ZrCl₂ yielded complexes Cp2TiL2(1),Cp2TiL2′(2),Cp2ZrL2(3)andCp2ZrL2′(4). Compounds 1-4 were characterized by NMR spectroscopy, and compounds 1, 3, and 4 were further analyzed by X-ray crystallography and elemental analysis. The molecular structures of 1, 3, and 4 illustrate that chelating di(3-methylindol-2-yl) methanes have a structural relationship to coordinated bis(pyrazolyl)borates.

Full text of DOI:10.1016/j.jorganchem.2004.09.003

Journal of Organometallic Chemistry 690 (2005) 157–162
www.elsevier.com/locate/jorganchem
Deprotonated diindolylmethanes as dianionic analogues of
scorpionate bis(pyrazolyl)borate ligands: synthesis and
structural characterization of representative titanocene and
zirconocene complexes
*
Mark R. Mason , Doug Ogrin, Bassam Fneich, Thomas S. Barnard, Kristin Kirschbaum
Department of Chemistry, The University of Toledo, MS 602, Toledo, OH 43606-3390, USA
Received 26 July 2004; accepted 1 September 2004
Available online 28 September 2004
Abstract
Deprotonation of di(3-methylindol-2-yl)phenylmethane (L2H2) or 2-methoxyphenyldið3-methylindol-2-ylÞmethane ðL02H2Þ with
two equivalents of nBuLi, followed by reactions with Cp2TiCl2 or Cp2ZrCl2 yielded complexes Cp2TiL2 ð1Þ, Cp2TiL0 ð2Þ;
2
Cp2ZrL2 ð3Þ and Cp2ZrL02 ð4Þ. Compounds 1–4 were characterized by NMR spectroscopy, and compounds 1, 3, and 4 were further
analyzed by X-ray crystallography and elemental analysis. The molecular structures of 1, 3, and 4 illustrate that chelating di(3-methyl-
indol-2-yl)methanes have a structural relationship to coordinated bis(pyrazolyl)borates.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Diindolylmethanes; Nitrogen-donor ligands; Titanium; Zirconium
1. Introduction
sion of this class of ligands to include dianionic and tri-
anionic analogues useful for metals in higher oxidation
states are desirable [6]. Suitable dianionic and triani-
onic analogues of poly(pyrazolyl)borates can be envi-
sioned via substitution of pyrrolyl [7] or bulkier
indolyl moieties for pyrazolyl substituents in bis- and
tris(pyrazolyl)methanes. In this regard, we recently
demonstrated the utility of trianionic tri(pyrrol-
2-yl)methane and tri(3-methylindol-2-yl)methane for
the preparation of bulky, constrained p-acidic phos-
phines [8,9]. Here, we demonstrate that deprotonated
Anionic poly(pyrazolyl)borates are versatile ligands
for fine-tuning coordination environments in inorganic
and organometallic complexes [1]. Neutral poly(pyraz-
olyl)methanes have similarly been investigated to fur-
ther extend the applications of this valuable family of
ligands [2]. However, analogous and isoelectronic dian-
ionic and trianionic ligands have not been heavily
investigated. Considering that pyrazolyl and related
heterocycles have advantages of reduced tendency for
p-coordination and M–N–M bridging, and reduced
proclivity for N ! M p-donation [3–5], further exten-
di(3-methylindol-2-yl)phenylmethane
(L2H2)
and
2-methoxyphenyldið3-methylindol-2-ylÞmethane ðL02H2Þ
function as dianionic scorpionate chelates to transition
metals. The synthesis and characterization of represent-
*
Corresponding author. Tel.: +1 419 530 1532; fax: +1 419 530
ative transition metal complexes Cp2TiL2 ð1Þ; Cp2TiL0
4033.
2
E-mail address: mmason5@uoft02.utoledo.edu (M.R. Mason).
ð2Þ; Cp2ZrL2 ð3Þ and Cp2ZrL02 ð4Þ are reported.
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.003

158
M.R. Mason et al. / Journal of Organometallic Chemistry 690 (2005) 157–162
2. Experimental
2.1. General procedures
120.88 (Cp), 119.84 (C5), 118.99 (Cp), 118.34 (C6),
118.14 (C4), 114.53 (C7), 113.63 (C3), 67.96 (CH2O,
THF), 40.23 (CH), 25.61 (THF), 9.65 (CH3). Anal. Calc.
for C35H30N2Ti Æ C4H8O: C, 78.25; H, 6.40; N, 4.68.
Found: C, 76.67; H, 5.90; N, 5.44%.
All reactions were performed under an atmosphere of
purified nitrogen using standard inert atmosphere tech-
niques. Hexanes and toluene were distilled from calcium
hydride and sodium, respectively, prior to use. Tetra-
hydrofuran and diethyl ether were distilled from sodium
benzophenone ketyl. CDCl3 was dried by storage over
activated molecular sieves. Di(3-methylindol-2-yl)phe-
nylmethane (L2H2) [10,11] and 2-methoxyphenyldi-
ð3-methylindol-2-ylÞmethane ðL02H2Þ [11] were prepared
by sulfuric acid-catalyzed reactions of 3-methylindole
with benzaldehyde and 2-anisaldehyde, respectively, as
previously reported. Dichlorobis(g5-cyclopentadienyl)-
titanium and dichlorobis(g5-cyclopentadienyl)zirconium
were obtained from Strem Chemical and used as
received. All other reagents were obtained from Aldrich
Chemical Co. and used as received. Solution NMR spec-
tra were recorded on a Varian Unity 400 spectrometer
using CDCl3 as the solvent. Chemical shifts are reported
relative to tetramethylsilane. Tentative 13C NMR
assignments are based on previously reported NMR
assignments for polyindolylmethanes [11,12] as well as
on NMR assignments of indole derivatives reported by
Park et al. [13]. In the reporting of NMR data, indole
carbons are labeled C2–C7 with C3a and C7a indicating
ring fusion positions. Phenyl carbons of the methine
substituents are labeled Ph-C1–Ph-C6. All 13C{1H}
NMR resonances are singlets. Elemental analyses were
performed by Schwarzkopf Microanalytical Laborato-
ries, Woodside, NY.
2.3. Synthesis of bis(g5-cyclopentadienyl){2-meth-
oxyphenyldi(3-methylindol-2-yl)methane}titanium (2)
n
A solution of BuLi (1.1 ml, 1.6 M in hexanes, 1.8
mmol) was added to
a
oxyphenyldi(3-methylindol-2-yl)methane
solution of 2-meth-
(0.310 g,
0.815 mmol) in THF (15 ml) under nitrogen. After stir-
ring at room temperature for 1 h, the dark green solu-
tion was added slowly via cannula to a solution of
dichlorobis(g5-cyclopentadienyl)titanium (0.203 g,
0.815 mmol) in toluene (20 ml). The resulting mixture
was refluxed for 1.5 h, cooled to room temperature,
and the supernatant separated from precipitated LiCl
by decantation. Volatiles were removed from the sup-
ernatant in vacuo. The resulting residue was dissolved
in toluene (10 ml), the solution was filtered through Cel-
iteꢁ, and volatiles were removed from the filtrate in va-
cuo. Dissolution of the remaining solid in hot
chloroform followed by the addition of hexanes (20
ml) resulted in precipitation of the deep red product,
which was isolated by filtration and dried under vac-
uum. 1H NMR (CDCl3, 400 MHz): d 7.44 (m, 2H,
H7), 7.09 (s, 5H, Cp), 7.06–6.95 (m, 5H, aromatic),
6.84 (d, 1H, aryl), 6.74–6.66 (m, 4H, aromatic), 6.08
(s, 1H, CH), 5.53 (s, 5H, Cp), 3.69 (s, 3H, OCH3),
2.41 (s, 6H, CH3). 13C{1H} NMR (CDCl3, 100.6
MHz): d 156.53 (Ph-C2), 147.44 (C7a), 142.43 (C2),
133.53 (C3a), 132.80 (Ph-C1), 130.15 (Ph-C6), 127.13
(Ph-C4), 120.51 (Cp), 119.79 (Ph-C5), 119.69 (C5),
118.59 (Cp), 118.21 (C6), 117.87 (C4), 115.0 (C7),
113.88 (Ph-C3), 110.46 (C3), 55.17 (OCH3), 36.45
(CH), 9.95 (CH3).
2.2. Synthesis of bis(g5-cyclopentadienyl){di(3-methylin-
dol-2-yl)phenylmethane}titanium (1)
n
A solution of BuLi (1.78 ml, 1.6 M in hexanes, 2.85
mmol) was added to a solution of di(3-methylindol-2-
yl)phenylmethane (0.500 g, 1.43 mmol) in THF (10 ml)
under nitrogen. After stirring at room temperature for
1 h, the dark red solution was added dropwise to a solu-
tion of dichlorobis(g5-cyclopentadienyl)titanium (0.355
g, 1.43 mmol) in toluene (10 ml). The resulting mixture
was refluxed for 2 h, cooled to room temperature, and
filtered through Celiteꢁ. Volatiles were removed from
the filtrate in vacuo and the remaining solid was recrys-
tallized from hot THF to afford black crystals. Yield:
0.548 g, 0.915 mmol, 64%. 1H NMR (CDCl3, 400
MHz): d 7.58 (d, 2H, H7), 7.08 (m, 7H, phenyl and
H4), 6.62 (d, 2H, H6), 6.59 (s, 5H, Cp), 6.36 (d, 2H,
H5), 5.78 (s, 5H, Cp), 5.70 (s, 1H, CH), 3.75 (m, 4H,
CH2O, THF), 2.50 (s, 6H, CH3), 1.85 (m, 4H, CH2,
THF). 13C{1H} NMR (CDCl3, 100.6 MHz): d 145.42
(Ph-ipso), 143.69 (C7a), 143.42 (C2), 132.89 (C3a),
128.10 (Ph-meta), 127.16 (Ph-ortho), 125.94 (Ph-para),
2.4. Synthesis of bis(g5-cyclopentadienyl){di(3-methylin-
dol-2-yl)phenylmethane}zirconium (3)
n
A solution of BuLi (1.80 ml, 2.88 mmol, 1.6 M) in
hexane was added to a solution of di(3-methylindol-2-
yl)phenylmethane (0.500 g, 1.43 mmol) in THF (10 ml)
and the resulting dark red solution was stirred at room
temperature for 1 h. This solution was added to a
solution of dichlorobis(g5-cyclopentadienyl)zirconium
(0.420 g, 1.44 mmol) in toluene (10 ml) and the result-
ing mixture was refluxed for 2 h. The reaction mixture
was cooled to room temperature and filtered through
Celiteꢁ to remove lithium chloride. Volatiles were
removed from the filtrate in vacuo to leave a black
residue. Recrystallization from a minimum volume of
hot THF afforded dark, red crystals of 3 that were iso-
lated by filtration and dried in vacuo. Concentration of

M.R. Mason et al. / Journal of Organometallic Chemistry 690 (2005) 157–162
159
SHELXL-93 [15]. All non-hydrogen atoms were refined
anisotropically, except for the carbon and oxygen atoms
of the THF solvate molecule of 4 Æ 0.5C4H8O, which
were refined with isotropic atomic displacement param-
eters. Hydrogen atoms in 1 Æ C4H8O and 3 Æ C4H8O were
located and refined with isotropic displacement parame-
ters, except for some of the hydrogen atoms bonded to
the disordered THF molecules, which were placed in cal-
culated positions and included in the refinement as rid-
ing atoms (2 H atoms in 1 Æ C4H8O; all in 3 Æ C4H8O).
The hydrogen atoms in the room-temperature measure-
ment of 4 Æ 0.5C4H8O were placed in calculated positions
and included in the refinement as riding models. No
hydrogen atoms were added for the disordered THF
molecule. The THF solvent molecules exhibit a similar
disorder in all three structures. One atom in the five-
member ring assumes two different positions in the lat-
tice. The two positions were refined with equal occupan-
cies for 1 Æ C4H8O and 4 Æ 0.5C4H8O, and with
occupancies of 70% and 30% for 3 Æ C4H8O. Details of
data collection and refinement are provided in Table 1.
the filtrate similarly yielded a second crop of crystalline
1
product. Yield: 0.463 g, 0.721 mmol, 50%. H NMR
(CDCl3, 400 MHz): d 7.62 (d, 2H, H7), 7.14 (m, 5H,
phenyl), 7.09 (d, 2H, H4), 6.82 (t, 2H, H6), 6.37 (s,
7H, Cp and H5), 5.84 (s, 1H, CH), 5.81 (s, 5H, Cp),
3.75 (m, 4H, CH2O, THF), 2.50 (s, 6H, CH3), 1.86
(m, 4H, THF). 13C{1H} NMR (CDCl3, 100.6 MHz):
d 144.33 (Ph-ipso), 144.13 (C7a), 143.35 (C2), 132.14
(C3a), 127.98 (Ph-meta), 127.38 (Ph-ortho), 126.06
(Ph-para), 120.14 (C5), 118.62 (C6), 118.57 (C4),
116.14 (Cp), 114.89 (Cp), 114.28 (C7), 113.83 (C3),
67.97 (CH2O, THF), 40.17 (CH), 25.63 (THF), 9.62
(CH3). Anal. Calc. for C35H30N2Zr Æ C4H8O: C,
72.97; H, 5.97; N, 4.36. Found: C, 72.31; H, 5.94; N,
4.36%.
2.5. Synthesis of bis(g5-cyclopentadienyl){2-methoxy-
phenyldi(3-methylindol-2-yl)methane}zirconium (4)
n
Compound 4 was prepared from solutions of BuLi
(1.20 ml, 1.92 mmol, 1.6 M) in hexane, 2-meth-
oxyphenyldi(3-methylindol-2-yl)methane (0.310 g, 0.815
mmol) in THF (10 ml), and dichlorobis(g5-cyclopenta-
dienyl)zirconium (0.238 g, 0.815 mmol) in toluene (10
ml) using a procedure analogous to that described for
the synthesis of 3. Recrystallization of the resulting black
residue from a minimum volume of hot THF afforded
dark, red crystals of 4 that were isolated by filtration
and dried in vacuo. Concentration of the filtrate similarly
yielded a second crop of crystalline product. In some
cases a few crystals of unreacted ligand L02H2 were also
3. Results and discussion
Deprotonation of di(3-methylindol-2-yl)phenylmeth-
ane (L2H2) or 2-methoxyphenyldið3-methylindol-2-ylÞ
methane ðL0 H2Þ with nBuLi, followed by reactions
2
with Cp2TiCl2 yielded Cp2TiL2 (1) and Cp2TiL0 ð2Þ
2
as brown-black and deep red crystals, respectively
(Eq. (1)). NH resonances for the free di(3-methylin-
dol-2-yl)methane ligands ðL2H2 : 7:56 ppm; L02H2 :
7:68 ppmÞ [11] are absent in the 1H NMR spectra
for 1 and 2, verifying that deprotonation was success-
ful and that the di(3-methylindol-2-yl)methanes coor-
dinate as dianions.
1
isolated along with 4. H NMR (CDCl3, 400 MHz): d
7.50 (m, 2H, H7), 7.07 (m, 5H, aromatic), 6.91 (s, 5H,
Cp), 6.88 (m, 3H, aromatic), 6.73 (m, 2H, aromatic),
6.19 (s, 1H, CH), 5.47 (s, 5H, Cp), 3.66 (s, 3H, OCH3),
2.43 (s, 6H, CH3). 13C{1H} NMR (CDCl3, 100.6 MHz):
d 156.49 (Ph-C2), 145.70 (C7a), 142.65 (C2), 132.88
(Ph-C1), 132.76 (C3a), 129.71 (Ph-C6), 127.12 (Ph-C4),
119.84 (C5), 119.66 (Ph-C5), 118.58 (C6), 118.29 (C4),
116.03 (Cp), 114.40 (Cp), 114.32 (C7), 113.96 (Ph-C3),
110.40 (C3), 55.23 (OCH3), 36.28 (CH), 9.84 (CH3).
Anal. Calc. for C36H32N2OZr: C, 72.08; H, 5.38; N,
4.67. Found: C, 71.59; H, 5.62; N, 4.39%.
H3C
H3C
1) 2 nBuLi
NH
NH
N
N
2) Cp2MCl2
Cp
Cp
Ar
H
Ar
H
M
3) toluene, THF
∆
H3C
H3C
2.6. X-ray crystallography
Crystals of 1 Æ C4H8O, 3 Æ C4H8O, and 4 Æ 0.5C4H8O
were grown from THF solutions at ꢀ20 ꢂC. X-ray dif-
fraction data were collected on a Siemens CCD diffrac-
M
Ar
C6H5
2-C6H4(OCH3)
C6H5
1
2
3
4
Ti
Ti
Zr
Zr
˚
tometer using Mo Ka radiation (k = 0.710 73 A),
general procedures for which have been previously re-
ported [11]. Data were corrected for decay, Lorentz
and polarization effects, and absorption. The structures
were solved by direct methods (1 Æ C4H8O, 3 Æ C4H8O) or
the Patterson method (4 Æ 0.5C4H8O) using SHELXS-86
[14] and refined by least-squares methods on F2 using
2-C6H4(OCH3)
ð1Þ
NMR spectra (1H, 13C) of 1 and 2 exhibit the ex-
pected resonances for the di(3-methylindol-2-yl)methane
ligands in each complex. The indolyl moieties are

160
M.R. Mason et al. / Journal of Organometallic Chemistry 690 (2005) 157–162
Table 1
Summary of X-ray crystallographic data
1 Æ C4H8O
39H38N2OTi
598.61
3 Æ C4H8O
4 Æ 0.5C4H8O
Formula
C
C39H38N2OZr
641.93
C38H36N2O1.5Zr
635.91
Red
Formula weight
Color
Habit
Brown-black
Block
Dark red
Chunk
Chunk
Crystal size (mm)
Crystal system
Space group
Unit cell dimensions
0.40 · 0.40 · 0.30
Monoclinic
P2(1)
0.35 · 0.30 · 0.15
Monoclinic
P2(1)
0.22 · 0.20 · 0.15
Monoclinic
P2(1)/n
˚
a (A)
9.504 (2)
14.166 (3)
11.620 (3)
103.596 (1)
1520.6 (6)
2
9.5686 (3)
14.2549 (4)
11.5870 (4)
103.544 (1)
1536.51 (8)
2
10.778 (1)
13.275 (2)
22.476 (3)
101.307 (2)
3153.2 (7)
4
˚
b (A)
˚
c (A)
b (ꢂ)
3
˚
V (A )
Z
T (ꢂC)
ꢀ123
ꢀ123
20
3.83
l(Mo Ka) (cmꢀ1
)
3.16
3.92
˚
k (A)
Transmission constants
0.710 73
0.992–0.792
5–59
0.710 73
0.992–0.920
5–59
0.710 73
0.840–0.674
4–57
2h limits (ꢂ)
Total number of data
Number of unique data
Number of observed dataa
Number of parameters
17 170
7518
11 031
6928
18 748
7255
7167
545
6689
517
5153
385
a,b
R1
0.0308
0.0741
0.0214
0.0538
0.0490
0.1134
a,c
wR2
max, min peaks (e/A)
3
˚
0.226, ꢀ0.233
0.261, ꢀ0.198
0.504, ꢀ0.349
a
I > 2r(I).
P
P
b
c
R1 =
||Fo| ꢀ |Fc||/ |Fo|.
P
P
2
2 1=2
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁꢁ
.
1
chemically equivalent, and integration of the H NMR
spectra confirms the presence of two g5-cyclopentadie-
nyl ligands per diindolylmethane. The H NMR spectra
1
exhibit two singlets for the chemically inequivalent
cyclopentadienyl ligands at 6.59 and 5.78 ppm for 1,
and at 7.09 and 5.53 ppm for 2. The 13C NMR spectra
confirm that the two cyclopentadienyl ligands in each
complex are not chemically equivalent. This chemical
inequivalence of the cyclopentadienyl groups is due to
the methine in the backbone of the diindolylmethane lig-
ands that situates the aryl towards one of the cyclopen-
tadienyl rings on titanium, whereas the other
cyclopentadienyl ring is in the vicinity of the methine
hydrogen. The 1H and 13C NMR resonances for the
methoxy group of 2 were observed at 3.69 and 55.17
ppm, respectively, comparable with the chemical shifts
of the methoxy resonances for the free ligand (3.73
and 55.87 ppm) [11]. Thus, the methoxy substituent of
2-methoxyphenyldi(3-methylindol-2-yl)methane is not
coordinated to the titanium atom in 2.
The molecular structure of 1 was further confirmed
by X-ray crystallography (Fig. 1). The structure consists
of a pseudo-tetrahedral titanium atom ligated by two
inequivalent cyclopentadienyl ligands and a chelating,
bidentate diindolylmethane. Both cyclopentadienyl rings
adopt an g5 coordination mode with Ti–C distances
Fig. 1. ORTEP drawing of Cp2TiL2 (1). Thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted for clarity.
˚
Selected distances (A) and angles (ꢂ): Ti(1)–N(1) 2.090(1), Ti(1)–N(2)
2.084(1), Ti(1)–C(31) 2.425(2), Ti(1)–C(32) 2.415(2), Ti(1)–C(33)
2.427(2), Ti(1)–C(34) 2.406(2), Ti(1)–C(35) 2.422(2), Ti(1)–C(41)
2.465(2), Ti(1)–C(42) 2.439(2), Ti(1)–C(43) 2.377(2), Ti(1)–C(44)
2.377(2), Ti(1)–C(45) 2.442(2), N(1)–Ti(1)–N(2) 95.15(5).
5
˚
ranging from 2.377(2) to 2.465(2) A, typical of bis(g -

M.R. Mason et al. / Journal of Organometallic Chemistry 690 (2005) 157–162
161
cyclopentadienyl)titanium(IV) complexes [16]. The di(3-
methylindol-2-yl)phenylmethane ligand is coordinated
to titanium via the two g1-indolyl nitrogen atoms to
form a six-member chelate ring. The chelate ring adopts
a slight chair conformation and an N–Ti–N angle of
95.15(5)ꢂ. The Ti–N distances of 2.090(1) and 2.084(1)
˚
A are comparable with the distances of 2.100(4) and
˚
2.070(5) A reported for Cp2Ti(pyrrolyl)2 [16]. The Ti–
N distances in 1 are longer than those for strong
p-donating dimethylamido groups in Cp*Ti(NMe2)3
˚
˚
(1.912(9) A, 1.923(14) A) [17], consistent with the
reduced tendency for p-donation by g1-N-indolyl lig-
ands. We were unable to obtain X-ray quality crystals
of compound 2.
Deprotonation of L2H2 or L02H2 with nBuLi, followed
by reactions with Cp2ZrCl2, yielded dark red crystals of
Cp2ZrL2 (3) and Cp2ZrL02 ð4Þ, respectively (Eq. (1)).
Yields of 4 were somewhat variable and the purity of
4 was often plagued by 1–2% of free diindolylmethane,
L02H2, based on integration of methyl resonances in
the 1H NMR spectrum. This impurity could be removed
by multiple recrystallizations from toluene.
Fig. 2. ORTEP drawing of Cp2ZrL2 (3). Thermal ellipsoids are drawn
at the 40% probability level. Hydrogen atoms are omitted for clarity.
˚
Selected distances (A) and angles (ꢂ): Zr(1)–N(1) 2.155(1), Zr(1)–N(2)
2.167(1), Zr(1)–C(31) 2.535(2), Zr(1)–C(32) 2.517(2), Zr(1)–C(33)
2.527(2), Zr(1)–C(34) 2.523(2), Zr(1)–C(35) 2.540(2), Zr(1)–C(41)
2.556(2), Zr(1)–C(42) 2.545(2), Zr(1)–C(43) 2.497(2), Zr(1)–C(44)
2.498(2), Zr(1)–C(45) 2.541(2), N(1)–Zr(1)–N(2) 93.54(5).
Spectral data for 3 and 4 are similar to those obtained
1
for titanium analogues 1 and 2. Integration of the H
NMR resonances for each compound confirms the pres-
ence of two g5-cyclopentadienyl ligands per diindolyl-
methane. Singlet resonances for the chemically
inequivalent cyclopentadienyl ligands are observed in
1
the H NMR spectra at 6.37 and 5.81 ppm for 3 and
6.91 and 5.47 ppm for 4. Corresponding cyclopentadie-
nyl resonances are observed in the 13C NMR spectra at
116.14 and 114.89 ppm for 3 and 116.03 and 114.40 ppm
for 4. The 1H and 13C NMR resonances for the methoxy
group of 4 are observed at 3.66 and 55.23 ppm, respec-
tively, and confirm that the methoxy substituent of the
diindolylmethane ligand does not coordinate to the zir-
conium atom.
The molecular structures of 3 and 4 were confirmed
by X-ray crystallography (Figs. 2 and 3). Each structure
consists of a pseudo-tetrahedral zirconium atom ligated
by two inequivalent cyclopentadienyl ligands and a
chelating, bidentate diindolylmethane. Each cyclopenta-
dienyl ring coordinates g5 with Zr–C distances ranging
Fig. 3. ORTEP drawing of Cp2ZrL20 ð4Þ. Thermal ellipsoids are drawn
˚
from 2.497(2) to 2.556(2) A, comparable with distances
˚
of 2.49(2)–2.59(2) A observed in Cp2Zr(pyrrolyl)2 and
at the 40% probability level. Hydrogen atoms are omitted for clarity.
˚
Selected distances (A) and angles (ꢂ): Zr(1)–N(1) 2.175(3), Zr(1)–N(2)
2.186(2), Zr(1)–C(31) 2.509(4), Zr(1)–C(32) 2.519(3), Zr(1)–C(33)
2.507(4), Zr(1)–C(34) 2.512(4), Zr(1)–C(35) 2.514(4), Zr(1)–C(41)
2.517(3), Zr(1)–C(42) 2.499(3), Zr(1)–C(43) 2.524(4), Zr(1)–C(44)
2.543(3), Zr(1)–C(45) 2.539(3), N(1)–Zr(1)–N(2) 91.86(9).
Cp2Zr(2,5-Me2pyrrolyl)2 [16,18]. The diindolylmethane
ligands each coordinate to zirconium via two g1-N-ind-
olyl moieties to form a six-member chelate ring. The
chelate rings adopt a slight chair conformation and N–
Zr–N angles of 93.54(5) and 91.86(9)ꢂ for 3 and 4,
respectively. The Zr–N distances in
3
(2.155(1),
amido groups in zirconium complexes such as Zr(pyrro-
˚
˚
˚
lyl)(NMe2)3(HNMe2) (2.019(3), 2.053(3), 2.079(3) A)
[20], Zr(2,5-Ph2pyrrolyl)(NMe2)3 (2.023(4), 2.025(4),
˚
2.050(4) A) [20], and Zr(carbazolyl)2-(NMe2)2(HNMe2)
˚
(2.022(4), 2.034(4) A) [5]. The longer Zr–Nindolyl
distances are consistent with the reduced tendency for
2.167(1) A) and 4 (2.175(3), 2.186(2) A) are in the range
observed for representative g1-N-pyrrolyl [3b,7c,16,18–
20] and g1-N-carbazolyl [5] complexes of zirconium
˚
(2.07–2.33 A). The Zr–N distances in 3 and 4 are longer
than those observed for strong p-donating dimethyl-

162
M.R. Mason et al. / Journal of Organometallic Chemistry 690 (2005) 157–162
p-donation by g1-N-indolyl ligands compared with that
for dialkylamido ligands.
References
[1] (a) S. Trofimenko, Chem. Rev. 93 (1993) 943;
(b) S. Trofimenko, Scorpionates, The Coordination Chemistry
of Poly(pyrazolyl)borate Ligands, Imperial College, London,
1999.
Another interesting feature in the molecular struc-
tures of 1, 3, and 4 is the orientation of the di(3-methy-
lindol-2-yl)methane aryl group. This orientation is
reminiscent of the scorpionate bis(pyrazolyl)borates [1]
in that the aryl group is poised for coordination to the
metal in the event that additional ligation were required.
For example, 2-methoxyphenyldið3-methylindol-2-ylÞ-
methane ðL02H2Þ is a potentially tridentate ligand,
although its methoxy substituent does not coordinate
to titanium or zirconium in 2 or 4, respectively.
In summary, we have demonstrated that di(3-methy-
lindol-2-yl)methanes function as dianionic, bidentate
ligands to transition metals. The different anionic charge
of deprotonated diindolylmethanes (ꢀ2) relative to
bis(pyrazolyl)borates (ꢀ1) and bis(pyrazolyl)methanes
(0) makes diindolylmethanes, and their potentially tri-
dentate derivatives, an excellent complement to scorp-
ionate bis(pyrazolyl)borates as ligands for inorganic
and organometallic chemistry. As part of our continuing
effort to explore this new class of ligands [6], the synthe-
sis, characterization, and ethylene polymerization activ-
ity of amido complexes of titanium and zirconium
ligated by di(3-methylindol-2-yl)methanes will be re-
ported elsewhere [4a].
[2] D.L. Reger, T.C. Grattan, K.J. Brown, C.A. Little, J.J.S. Lamba,
A.L. Rheingold, R.D. Sommer, J. Organomet. Chem. 607 (2000)
120, and references therein.
[3] (a) For advantages and examples of g1-N-pyrrolyl moieties,
see: K.G. Moloy, J.L. Petersen, J. Am. Chem. Soc. 117 (1995)
7696;
(b) Y. Li, A. Turnas, J.T. Ciszewski, A.L. Odom, Inorg.
Chem. 41 (2002) 6298;
(c) S.A. Harris, J.T. Ciszewski, A.L. Odom, Inorg. Chem. 40
(2001) 1987;
(d) I. Korobkov, S. Gambarotta, G.P.A. Yap, Organometallics
20 (2001) 2552;
(e) M. Ganesan, M.P. Lalonde, S. Gambarotta, G.P.A. Yap,
Organometallics 20 (2001) 2443;
(f) T. Dube, S. Gambarotta, G. Yap, Organometallics 19
(2000) 121;
(g) T. Dube, S. Gambarotta, G.P.A. Yap, Organometallics 19
(2000) 817;
(h) T. Dube, S. Gambarotta, G.P.A. Yap, Organometallics 19
(2000) 115.
[4] (a) For advantages of g1-N-indolyl moieties, see: M.R. Mason,
B.N. Fneich, K. Kirschbaum, Inorg. Chem. 42 (2003) 6592;
(b) J.M. Tanski, G. Parkin, Inorg. Chem. 42 (2003) 264.
[5] For advantages of g1-N-carbazolyl moieties, see: P.N. Riley, P.E.
Fanwick, I.P. Rothwell, J. Chem. Soc., Dalton Trans. (2001) 181.
[6] M.R. Mason, Chemtracts 16 (2003) 272.
[7] (a) For examples of di(pyrrol-2-yl)methane complexes of transi-
tion metals, see: J.B. Love, P.A. Salyer, A.S. Bailey, C. Wilson,
A.J. Blake, E.S. Davies, D.J. Evans, Chem. Commun. (2003)
1390;
4. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC 245763 for compound 1 Æ C4H8O,
CCDC 245764 for compound 3 Æ C4H8O, and CCDC
245765 for compound 4 Æ 0.5 C4H8O. Copies of available
materials can be obtained, free of charge, on application
to The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44-1223-336-033; e-mail: depos-
it@ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk.
(b) Y. Shi, C. Hall, J.T. Ciszewski, C. Cao, A.L. Odom, Chem.
Commun. (2003) 586;
(c) A. Novak, A.J. Blake, C. Wilson, J.B. Love, Chem. Commun.
(2002) 2796.
[8] T.S. Barnard, M.R. Mason, Organometallics 20 (2001) 206.
[9] T.S. Barnard, M.R. Mason, Inorg. Chem. 40 (2001) 5001.
[10] V. Dostal, Chem. Listy 32 (1938) 13;
V. Dostal, Chem. Abstr. 32 (1938) 5399.
[11] M.R. Mason, T.S. Barnard, M.F. Segla, B. Xie, K. Kirschbaum,
J. Chem. Crystallogr. 33 (2003) 531.
[12] K. Dittmann, U. Pindur, Arch. Pharm. 318 (1985) 340.
[13] K.H. Park, G.A. Gray, G.D. Daves Jr., J. Am. Chem. Soc. 100
(1978) 7475.
[14] G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467.
[15] G.M. Sheldrick, SHELXL-93: Program for Refinement of Crystal
Structures, University of Go¨ttingen, Go¨ttingen, Germany, 1993.
[16] R.V. Bynum, W.E. Hunter, R.D. Rogers, J.L. Atwood, Inorg.
Chem. 19 (1980) 2368.
Acknowledgements
Acknowledgement is made to the donors of the
Petroleum Research Fund, administered by the Ameri-
can Chemical Society (Grant 37172-AC3), for partial
support of this research. Partial funding was also pro-
vided by The University of Toledo Research Challenge
Fund. The CCD facility of the Ohio Crystallography
Consortium located at the University of Toledo was
established with grants from the Ohio Board of Regents.
[17] A. Martin, M. Mena, C. Yelamos, R. Serrano, P.R. Raithby, J.
Organomet. Chem. 467 (1994) 79.
[18] R.V. Bynum, H.-M. Zhang, W.E. Hunter, J.L. Atwood, Can. J.
Chem. 64 (1986) 1304.
[19] J.-H. Huang, P.-C. Kuo, G.-H. Lee, S.-M. Peng, J. Chin. Chem.
Soc. 47 (2000) 1191.
[20] J.M. Tanski, G. Parkin, Organometallics 21 (2002) 587.