Zirconium complexes of a cross-bridged cyclam

Article abstract of DOI:10.1021/om049469j

The acid-base reaction of tetrabenzylzirconium with 1,4,8,11-tetraazabicyclo[6.6.2]-hexadecane (H₂(CBC), 1) produces (CBC)Zr(CH₂Ph)₂, 2. Similarly, reaction of 2 with phenols yields (CBC)Zr(CH₂Ph)(O-2, 6-C₆H₃Bu ₂^t), 3, and (CBC)Zr(O-2,6-C₆H ₃Me₂)₂, 5. Prolonged heating of 3 leads to the metalated product (CBC)Zr[k²(C,O)-OC₆H ₃(6-Bu^t)(2-CMe₂CH₂)], 4. Reaction of ZrCl₂[N(SiMe₃)₃]₂ with H ₂(CBC) leads to (CBC)ZrCl₂, 6, which subsequently affords (CBC)Zr(X)(Y) by salt metathesis (7, X = Cl, Y = N(SiMe₃) ₂; 8, X = Y = CH₃; 9, X = Y = CH₂Si(CH ₃)₃). Compounds 3 and 7 show restricted rotation about the Zr-O and Zr-N bonds, respectively, on the NMR time scale. For 3, the energy of activation for this process was determined to be 69 ±1 kJ/mol. Neither 6 nor 8 shows ethylene polymerization activity when treated with 500 equiv of MAO. Reaction of 6 with 2 equiv of n-BuLi in the presence of excess diphenylacetylene leads to the zirconacyclopentadiene 10, (CBC)Zr(C ₄Ph₄). The structures of 5, 9, and 10 have been determined by X-ray crystallography, and all three display distorted octahedral geometry.

Full text of DOI:10.1021/om049469j

28
Organometallics 2005, 24, 28-36
Zirconium Complexes of a Cross-Bridged Cyclam
Paul O’Connor,* David J. Berg,* and Brendan Twamley†
Department of Chemistry, University of Victoria, P.O. Box 3065,
Victoria, British Columbia, Canada V8W 3V6
Received July 14, 2004
The acid-base reaction of tetrabenzylzirconium with 1,4,8,11-tetraazabicyclo[6.6.2]-
hexadecane (H2(CBC), 1) produces (CBC)Zr(CH2Ph)2, 2. Similarly, reaction of 2 with phenols
yields (CBC)Zr(CH2Ph)(O-2,6-C6H3But2), 3, and (CBC)Zr(O-2,6-C6H3Me2)2, 5. Prolonged
heating of 3 leads to the metalated product (CBC)Zr[κ2(C,O)-OC6H3(6-But)(2-CMe2CH2)], 4.
Reaction of ZrCl2[N(SiMe3)2]2 with H2(CBC) leads to (CBC)ZrCl2, 6, which subsequently
affords (CBC)Zr(X)(Y) by salt metathesis (7, X ) Cl, Y ) N(SiMe3)2; 8, X ) Y ) CH3; 9, X )
Y ) CH2Si(CH3)3). Compounds 3 and 7 show restricted rotation about the Zr-O and Zr-N
bonds, respectively, on the NMR time scale. For 3, the energy of activation for this process
was determined to be 69 ( 1 kJ/mol. Neither 6 nor 8 shows ethylene polymerization activity
when treated with 500 equiv of MAO. Reaction of 6 with 2 equiv of n-BuLi in the presence
of excess diphenylacetylene leads to the zirconacyclopentadiene 10, (CBC)Zr(C4Ph4). The
structures of 5, 9, and 10 have been determined by X-ray crystallography, and all three
display distorted octahedral geometry.
Introduction
In previous work, we reported a number of zirconium
dialkyls, LZrR2, and their analogous cations, LZrR+,
supported by the macrocycle 4,13-diaza-18-crown-6
(Figure 1, DAC)20 and the “half macrocycle” system
[(C6F5)NHCH2CH2OCH2]2 (NOON).21 The DAC cation
took part in interesting catalytic reactions with alkynes,
while the neutral NOON dibenzyl species underwent
photolytic Zr-C bond cleavage and subsequent C-F
bond activation.22 Both supporting ligands displayed
fluxional behavior in solution; we believe that the high
flexibility of these systems may be contributing to the
decomposition of the alkyl complexes and limiting their
reaction chemistry.
Accordingly, we have turned our attention to the
organometallic chemistry of cross-bridged cyclam
(H2(CBC), 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane).23
This ligand is attractive for two reasons: the cross-
bridge restricts the conformations of the ligand while
it is coordinated to the metal, and the ligand is satu-
rated, precluding the alkyl migrations to the ligand
observed in Schiff base systems.4,5,24,25
Several diamido ligands bearing additional neutral
donors have been explored as alternatives to cyclopen-
tadienyl-based systems for group 4 organometallic
chemistry.1 These include macrocycles such as porphy-
rins,2,3 tetraaza[14]annulenes,4,5 tropocoronand,6 and
7-9
P2N2
rings as well as tripodal10,11 and linear sys-
tems.12,13 These ligands have been exploited in such
diverse areas as olefin polymerization catalysis,11,14,15
unusual insertion chemistry,4,6,16-18 imide reactions,19
and dinitrogen activation.9
* To whom correspondence should be addressed. E-mail:
djberg@uvic.ca.
† Present address: University Research Office, 109 Morrill Hall,
University of Idaho, Moscow, ID 83844-3010.
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The coordination chemistry of protio and N-alkylated
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10.1021/om049469j CCC: $30.25 © 2005 American Chemical Society
Publication on Web 12/03/2004

Zr Complexes of a Cross-Bridged Cyclam
Organometallics, Vol. 24, No. 1, 2005 29
from sodium benzophenone ketyl under argon immediately
prior to use. Tetrabenzylzirconium39 and Zr[N(SiMe3)2]2Cl2
40
were prepared according to literature procedures. N-Butyl-
lithium and MAO (methylaluminoxane) were obtained com-
mercially (Aldrich) and were used as received.
NMR spectra were recorded using a Bruker AMX-360 MHz
spectrometer: 1H (360 MHz), 13C (90.55 MHz), 29Si (71.54
MHz), 11B (115.54 MHz) unless otherwise specified. All deu-
terated solvents were dried over activated 4 Å molecular sieves
except for tetrahydrofuran (THF), which was dried by distil-
lation from sodium benzophenone ketyl under argon and stored
over activated 4 Å molecular sieves. Spectra were recorded
using 5 mm tubes fitted with a Teflon valve (Brunfeldt) at
room temperature unless otherwise specified. 1H and 13C NMR
spectra were referenced to residual solvent resonances. Melting
points were recorded using a Bu¨chi melting point apparatus
in sealed capillary tubes and are not corrected. Elemental
analyses were performed by Canadian Microanalytical, Delta,
BC. Despite the use of co-oxidants such as V2O5 and PbO2,
the analytical data for most complexes were consistently 2-4%
low in carbon, likely due to metal carbide formation. Despite
repeated attempts, satisfactory analyses of 2, 9, and 10 were
not obtained; this may be a result of decomposition of the
compounds during shipping, storage, or handling of the
samples, as they have been observed to slowly decompose in
the solid state at room temperature even when stored in the
glovebox. Mass spectra were recorded on a Kratos Concept H
spectrometer using electron impact (70 eV) ionization.
H2(CBC) (1). Cyclam was prepared via a nickel templated
reaction, which does not require the use of perchlorate salts.41
The free base was then obtained without isolating the nickel
cyclam complex.42 The synthesis of cross-bridged cyclam has
been described previously;28a however, we found it necessary
to sublime the oil obtained after benzene extraction from KOH
and to store a toluene solution of the title compound over
freshly activated molecular sieves for several days to thor-
oughly dry the product.
Figure 1. Polydentate diamido ligands.
dium.34 However, in this contribution we report the
synthesis and structural studies of several coordination
and organometallic zirconium complexes supported by
the cross-bridged cyclam dianion (CBC2-) as well as the
thermal decomposition of one of these compounds.
Additionally, since zirconacycles have a range of uses
in organic chemistry,35 materials chemistry,36 macro-
cycle synthesis,37 and metallacycle transfer reactions,38
we report the synthesis and structure of a zirconcyclo-
pentadiene supported by cross-bridged cyclam.
Experimental Section
General Procedures. All manipulations were carried out
under a nitrogen or argon atmosphere, with the rigorous
exclusion of oxygen and water, using standard glovebox (Braun
MB150-GII) or Schlenk techniques. Tetrahydrofuran (THF),
diethyl ether, hexane, and toluene were dried by distillation
(CBC)Zr(CH2Ph)2 (2). H2(CBC) (0.500 g, 2.21 mmol) was
added to a solution of tetrabenzylzirconium (1.00 g, 2.19 mmol)
in 20 mL of toluene. The solution was protected from light and
stirred at room temperature overnight. Cooling to -30 °C
afforded a yellow powder after decanting the mother liquor
and drying under vacuum. Yield: 0.935 g, 85%. Mp: 171 °C
(dec). NMR (d6-benzene): 1H δ 7.20 (m, 4H, m-arylH), 7.14
(m, 4H, o-arylH), 5.84 (tt, 2H, p-arylH), 4.30 (m, 2H), 3.11 (dd,
(28) (a) Wong, E. H.; Weisman, G. R.; Hill, D. C.; Reed, D. P.; Rogers,
M. E.; Condon, J. S.; Fagan, M. A.; Calabrese, J. C.; Lam, K.-C.; Guzei,
I. A.; Rheingold, A. L. J. Am. Chem. Soc. 2000, 122, 10561. (b) Hubin,
T. J.; McCormick, J. M.; Alcock, N. W.; Clase, H. J.; Busch, D. H. Inorg.
Chem. 1999, 38, 4435. (c) Hubin, T. J.; McCormick, J. M.; Collison, S.
R.; Alcock, N. W.; Busch, D. H. J. Chem. Soc., Chem. Commun. 1998,
1675. (d) Sun, X.; Wuest, M.; Weisman, G. R.; Wong, E. H.; Reed, D.
P.; Boswell, C. A.; Motekaitis, R.; Martell, A. E.; Welch, M. J.;
Andersen, C. J. J. Med. Chem. 2002, 45, 469. (e) Niu, W.; Wong, E.
H.; Weisman, G. R.; Zakharov, L. N.; Incarvito, C. D.; Rheingold, A.
L. Polyhedron 2004, 23, 1019. (f) Boswell, C. A.; Sun, X.; Niu, W.;
Weisman, G. R.; Wong, E. H.; Rheingold, A. L.; Anderson, C. J. J. Med.
Chem. 2004, 47, 1465. (g) Hubin, T. J.; Alcock, N. W.; Busch, D. H.
Acta Crystallogr., Sect. C 2000, C56, 37.
2H), 2.90-2.84 (m, 4H), 2.78 (td, 2H), 2.56 (d, 2H, CHHPh,
2
2JHH ) 10.2 Hz), 2.51 (td, 2H), 2.47 (d, 2H, CHHPh, JHH
)
10.2 Hz), 2.41-2.36 (m, 2H), 1.80 (m, 2H), 1.64-1.54 (dd
and m, 4H), 1.37 (m, 2H), 0.72 (m, 2H); 13C{1H} δ 151.9
(quat-arylC), 128.7 (m-arylC), 126.3 (o-arylC), 120.3 (p-arylC),
(29) Hubin, T. J.; McCormick, J. M.; Collinson, S. R.; Buchalova,
M.; Perkins, C. M.; Alcock, N. W.; Kahol, P. W.; Raghunatan, A.; Busch,
D. H. J. Am. Chem. Soc. 2000, 122, 2512.
1
70.3 (CH2Ph, t in the gated 13C, JCH ) 113 Hz), 60.4, 58.60,
54.2, 54.0, 50.8 (NCH2), 22.2 (CH2CH2CH2). Anal. Calcd for
C26H38N4Zr: C, 62.73; H, 7.69; N, 11.25. Found: C, 57.97; H,
7.19; N, 11.45.
(30) Hubin, T. J.; McCormick, J.; Alcock, N. W.; Busch, D. H. Inorg.
Chem. 2001, 40, 435.
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Rheingold, A. L. Inorg. Chem. Commun. 1999, 2, 361. (b) Niu, W.;
Wong, E. H.; Weisman, G. R.; Peng, Y.; Anderson, C. J.; Zakharova,
L. N.; Golen, J. A.; Rheingold, A. L. Eur, J. Inorg. Chem. 2004, 3310.
(c) Niu, W.; Wong, E. H.; Weisman, G. R.; Zakharova, L. N.; Sommer,
R. D.; Rheingold, A. L. Abstracts of Papers, 234th ACS National
Meeting, Boston, MA, August 18-22, 2002. INOR-659.
(32) Hubin, T. J.; Alcock, N. W.; Clase, H. J.; Busch, D. H. Supramol.
Chem. 2001, 13, 261.
(CBC)Zr(CH2Ph)(O-2,6-C6H3But2) (3). Toluene (5 mL) was
added to an intimate mixture of (CBC)Zr(CH2Ph)2 (0.050 g,
0.10 mmol) and 2,6-di-tert-butylphenol (0.021 g, 0.10 mmol).
The mixture was stirred at room temperature overnight and
the solvent removed under reduced pressure. The powder was
recrystallized by cooling a hot toluene solution to -30 °C to
produce pale yellow microcrystals. Yield: 0.026 g, 43%. Mp:
220-224 °C. NMR (d6-benzene): 1H δ 7.50 (dd, 1H, m-phe-
noxideH), 7.42 (dd, 1H, m-phenoxideH), 7.12 (1H obscured by
d6-benzene, p-benzyl, or p-phenoxide) 6.97 (t, 1H, p-benzyl or
(33) Hubin, T. J.; Alcock, N. W.; Busch, D. H. Acta Crystallogr., Sect.
C 1999, C55, 1404.
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Rheingold, A. L. Inorg. Chem. Chem. 2002, 5, 1.
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2683. (b) Nitschke, J. R.; Zurcher, S.; Tilley, T. D. J. Am. Chem. Soc.
2000, 122, 10345.
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S. Inorg. Synth. 1976, 16, 223.

30 Organometallics, Vol. 24, No. 1, 2005
O’Connor et al.
was washed twice with 5 mL of hexanes and dried at reduced
pressure. Yield: 2.64 g, 90%. Mp: 271-5 °C (dec). NMR (d6-
benzene): 1H δ 4.73 (m, 2H), 3.30 (m, 4H), 2.95 (m, 2H), 2.87
(m, 2H), 2.76 (dd 2H), 2.64 (m 2H), 1.91 (dd 2H), 1.71 (dd 2H),
1.56 (m 2H), 1.34 (m, 2H), 0.80 (m, 2H); 13C{1H} δ 61.8, 60.3,
54.0, 53.3, 52.8, 30.6 (CH2N), 21.7 (CH2CH2CH2). Anal. Calcd
for C12H24N4Cl2Zr: C, 37.29; H, 6.26; N, 14.50. Found: C,
37.33; H, 6.54; N, 13.78.
(CBC)Zr(Cl)[N(Si(CH3)3)2] (7). Method A: Complex 7 was
isolated as a byproduct in the synthesis of (CBC)ZrCl2 from
ZrCl2[N(Si(CH3)3)2]2, possibly due to the presence of ZrCl-
[N(Si(CH3)3)2]3 as a contaminant in the bis(trimethylsilyla-
mide) complex. Method B: THF (15 mL) was added to a
mixture of (CBC)ZrCl2 (0.200 g, 0.518 mmol) and NaN(Si-
(CH3)3)2 (0.095 g, 0.518 mmol), and the resulting solution was
stirred at room temperature overnight. The solvent was
removed under reduced pressure, and the solid residue was
extracted with toluene (15 mL), then filtered through Celite
to afford a clear solution. The product was isolated as clear
colorless crystals by layering a saturated toluene solution with
hexamethyldisiloxane and storing at -30 °C. The crystals
become opaque when removed from the solvent. Yield: 0.037
g, 14%. Mp: 173-176 °C (dec). NMR (d6-benzene): 1H δ 4.89
(m, 1H), 4.09 (m, 1H), 3.75 (m, 1H), 3.50 (m, 1H), 3.25-2.70
(m, 10H), 1.98 (m, 1H), 1.88 (m, 1H), 1.80-1.55 (m, 4H), 1.30
(m, 1H), 1.16 (m, 1H), 0.99 (m, 1H), 0.88 (m, 1H), 0.79 (s,
9H, CH3), 0.54 (s, 9H, CH3); 13C{1H} δ 61.9, 61.0, 60.0, 58.5,
54.8, 54.6, 54.5, 53.3, 53.0, 52.7 (CH2N), 22.3 (CH2CH2CH2),
21.5 (CH2CH2CH2), 7.4 (CH3), 7.2 (CH3). Anal. Calcd for
C18H42N5ClSi2Zr: C, 42.27; H, 8.28; N, 13.69. Found: C, 41.88;
H, 7.87; N, 13.69.
Figure 2. NMR numbering scheme for 5 (C2 symmetry
in solution). The coupling constants of Ha and Hb reso-
nances are consistent with pseudoaxial and pseudoequa-
torial sites, respectively.
p-phenoxideH), 6.88-6.82 (m, 4H, o- and m-benzylH), 4.64 (m,
1H), 4.03 (m, 1H), 3.13-2.96 (m, 10H), 2.79-2.71 (m, 2H),
2.61-2.54 (m, 3H), 2.54 (d, 1H, CHHPh, 2JHH ) 10.7 Hz), 2.34
(d, 1H, CHHPh, 2JHH ) 10.7 Hz), 2.00 (m, 2H), 1.88-1.67 (m,
t
t
1H), 1.85 (s, 9H, Bu), 1.78 (s, 9H, Bu), 1.38-1.22 (m, 2H),
0.88 (m, 2H); 13C{1H} δ 164.5 (OC), 153.0 (quat-benzylC), 140.5
(CC(CH3)3), 139.4 (CC(CH3)3), 128.7 (o- or m-aryl obscured
by d6-benzene), 126.6 (o- or m-arylC), 126.4 (o- or m-arylC),
125.8 (o- or m-arylC), 120.2 (p-arylC), 118.9 (p-arylC), 64.8
(CH2Ph), 61.6, 60.7, 59.4, 58.1, 55.2, 54.7, 54.6, 52.5, 51.7, 49.7
(NCH2), 36.7, 36.4 (C(CH3)3), 32.9, 32.1 (CH3), 21.9, 21.5
(CH2CH2CH2). Anal. Calcd for C33H52N4OZr: C, 64.76; H, 8.56;
N, 9.15. Found: C, 63.80; H, 8.25; N, 9.03.
(CBC)Zr[K2(C,O)-OC6H3(6-But)(2-CMe2CH2)] (4). A solu-
tion of (CBC)Zr(CH2Ph)(O-2,6-C6H3But2)] (0.140 g, 0.229 mmol)
in 30 mL of toluene was sealed in a Kontes bomb and heated
at 100 °C for 7 days. The solvent was removed and the product
was recrystallized from a minimum volume of hot toluene.
Cooling to -30 °C yielded the product as a pure colorless
powder. Yield: 0.054 g, 39%. Mp: 224-229 °C (dec). NMR
(d6-benzene): 1H δ 7.65 (dd, 1H, m-arylH), 7.39 (dd, 1H,
m-arylH), 7.05 (t, 1H, p-arylH), 4.25 (m 1H), 3.98 (m, 1H), 3.32
(m, 1H), 3.11-2.97 (m, 7H), 2.92-2.73 (m, 4H), 2.17 (m, 1H),
2.00-1.96 (m, 2H), 1.93 (m, 1H), 1.90-1.68 (m, 2H), 1.88 (s,
3H, CH3), 1.81 (s, 3H, CH3), 1.73 (s, 9H, C(CH3)3), 1.40 (dd,
1H), 1.29 (dd, 1H), 1.16 (d, 1H, ZrCHH, 2JHH ) 13.3 Hz), 0.87
(CBC)Zr(CH3)2 (8). MeLi (1.4 M, 1.85 mL, 2.6 mmol) was
added to a suspension of (CBC)ZrCl2 (0.500 g, 1.29 mmol) in
20 mL of THF and stirred at room temperature overnight. The
solvent was removed under reduced pressure, and the solids
were extracted twice with 50 mL of toluene. The extract was
filtered (Celite), and the solvent removed under reduced
pressure. The product was repeatedly recrystallized from
warm toluene to yield colorless or pale yellow microcrystals.
Yield: 0.107 g, 24%. Mp: 175 °C (dec). NMR (d6-benzene): 1H
δ 4.50 (m, 2H), 3.25 (dd, 2H), 3.13-2.96 (m, 6H), 2.80 (m, 2H),
2.47 (m, 2H), 1.99 (m, 2H) 1.83 (dd, 2H), 1.81 (m, 2H), 1.75
(m, 2H), 0.80 (m 2H), 0.60 (s, 6H); 13C{1H} and DEPT δ
60.9, 59.8, 53.9, 53.8, 51.6 (CH2N), 39.3 (CH3, t in the gated
2
(d, 1H, ZrCHH, JHH ) 13.3 Hz), 0.85 (m, 1H), 0.70 (m, 1H);
1
13C, JCH ) 109 Hz), 22.1 (CH2CH2CH2). Anal. Calcd for
13C{1H} and DEPT δ 162.1 (OC), 143.7 (o-arylC), 136.4
(o-arylC), 125.8 (m-arylC), 124.5 (m-arylC), 118.8 (p-arylC),
75.4 (ZrCH2) 62.3, 62.0, 58.8, 58.3, 54.4, 53.2, 53.0, 51.4, 51.2,
51.2 (NCH2), 42.9 (quat-C), 39.8 (quat-C), 35.8 (CH3), 33.4
(CH3), 31.3 (C(CH3)3), 22.0 (overlapping CH2CH2CH2). Anal.
Calcd for C26H44N4OZr: C, 64.76; H, 8.56; N, 9.15. Found: C,
63.80; H, 8.25; N, 9.03.
C14H30N4Zr: C, 48.65; H, 8.75; N, 16.21. Found: C, 48.38; H,
8.54; N, 16.13.
(CBC)Zr[CH2Si(CH3)3]2 (9). (CBC)ZrCl2 (0.500 g, 1.29
mmol) was suspended in 50 mL of toluene, and LiCH2Si(CH3)3
(0.244 g, 2.59 mmol) was added; the mixture was stirred at
room temperature overnight. Filtration (Celite) of the reac-
tion mixture and removal of the solvent at reduced pres-
sure afforded a white powder. The product was dissolved in
14 mL of 5:2 toluene/hexanes and cooled to -30 °C to yield
clear, colorless, rod-shaped crystals. Yield: 0.399 g, 63%. Mp:
127-128 °C. NMR (d6-benzene): 1H δ 4.30 (m, 2H), 3.22 (m,
2H), 3.02 (m, 4H), 2.95 (m, 2H), 2.75 (m, 2H), 2.50 (m, 2H)
1.97 (m, 2H), 1.81 (m, 2H), 1.78-1.67 (m, 2H), 1.51 (m, 2H),
0.76 (m, 2H) 0.47 (s, 18H, Si(CH3)3), 0.42 (d, 2H, ZrCHH, 2JHH
(CBC)Zr(O-2,6-C6H3Me2)2 (5). (CBC)Zr(CH2Ph)2 (0.930 g,
1.87 mmol) was dissolved in 50 mL of warm toluene, and 2,6-
dimethylphenol (0.456 g, 3.73 mmol) was added. The solution
was stirred at room temperature for 2 h and then stored at
-30 °C, resulting in clear colorless crystals of 5 (two crops).
Yield: 0.89 g, 85%. Mp: 270 °C (dec). NMR (d6-benzene): 1H
δ 7.04 (d, 4H, H9), 6.77 (t, 2H, H10), 4.01 (m, 2H, H5a), 3.65 (m,
2H, H2a), 3.15 (m, 2H, H1b), 3.10-3.02 (m, 4H, H1a, and H3a),
2.99 (m, 2H, H6b), 2.93(m, 2H, H5b), 2.50 (s, 12H, H11), 2.06
(m, 2H, H3b), 1.98 (m, 2H, H2b), 1.79 (m, 2H, H4a), 1.38 (m,
2H, H6a), 0.62 (m, 2H, H4b); 13C{1H} δ 161.0 (C7), 129.2 (C9),
127.3 (C8), 119.3 (C10), 62.7 (C2), 59.7 (C3), 53.3 (C1), 52.9 (C5),
52.3 (C6), 21.7 (C4), 18.6 (C11). Assignments given in Figure 2
are based on 1H-1H and 1H-13C COSY. Anal. Calcd for
C28H42N4O2Zr: C, 60.28; H, 7.59; N, 10.04. Found: C, 60.24;
H, 7.45; N, 10.05. MS (EI): M+ 556.
2
) 12.1 Hz), 0.033 (d, 2H, ZrCHH, JHH ) 12.1 Hz); 13C{1H} δ
60.7, 60.2, 54.0, 54.0 (CH2N), 53.1 (CH2Si, t in the gated 13C,
1JCH ) 102 Hz), 51.4 (CH2N), 22.1 (CH2CH2CH2), 4.3 (Si(CH3)3).
Anal. Calcd for C20H46N4Si2Zr: C, 49.02; H, 9.46; N, 11.43.
Found: C, 48.08; H, 8.75; N, 11.67.
(CBC)Zr(C4Ph4) (10). Diphenylacetylene (0.507 g, 2.84
mmol), (CBC)ZrCl2 (0.500 g, 1.29 mmol), and 50 mL of THF
were cooled in a dry ice-acetone (-78 °C) bath prior to the
addition of n-BuLi (1.6 M, 1.62 mL, 2.6 mmol). The mixture
was stirred at low temperature for 20 min and then transferred
to an ice bath for 2 h. The solvent was removed under reduced
pressure to yield a brown oil. Toluene (40 mL) was added, and
(CBC)ZrCl2 (6). H2(CBC) (1.50 g, 6.63 mmol) and ZrCl2-
[N(Si(CH3)3)2]2 (3.30 g, 6.62 mmol) were sealed in a Kontes
bomb with 20 mL of toluene and heated at 100 °C for 2 days.
The product precipitated from solution as a yellow powder and

Zr Complexes of a Cross-Bridged Cyclam
Organometallics, Vol. 24, No. 1, 2005 31
Table 1. Summary of Crystallographic Dataa
5
9
10
formula
C
28H42N4O2Zr
C20H46N4Si2Zr
490.01
C47H52N4Zr
764.15
fw
557.88
cryst syst
orthorhombic
Pcc2
monoclinic
C2/c
monoclinic
C2/c
space group
a (Å)
11.9203(10)
11.9130(10)
19.4240(16)
90
14.891(3)
18.461(4)
9.4278(19)
101.26(3)
2541.8(9)
4
16.770(3)
12.417(3)
18.247(4)
91.34(3)
b (Å)
c (Å)
â (deg)
V (Å3)
2758.3(4)
4
3798.6(14)
4
Z
density(cald) (Mg/m3)
1.343
1.280
1.336
abs coeff (mm-1
)
0.429
0.539
0.329
F(000)
1176
1048
1608
θ range for data collection (deg)
no. of obsd reflns
1.05 to 28.33
32 772
1.78 to 27.49
31 721
2.04 to 27.50
26 431
no. of unique reflns
6859
2916
4368
[R(int) ) 0.0424]
28.33°, 99.7%
6859/1/321
1.036
R1 ) 0.0329,
wR2 ) 0.0720
R1 ) 0.0402,
wR2 ) 0.0757
[R(int) ) 0.0628]
27.49°, 99.5%
2916/0/126
1.175
R1 ) 0.0386,
wR2 ) 0.0773
R1 ) 0.0431,
wR2 ) 0.0785
[R(int) ) 0.0477]
27.5°, 99.8%
4368/0/268
1.056
R1 ) 0.0395,
wR2 ) 0.0884
R1 ) 0.0534,
wR2 ) 0.0949
completeness to θ
no. of data/restraints/params
goodness of fit on F2
final R indices [I > σ(I)]
R indices (all data)
a All data were collected at 83(2) K using Mo KR radiation λ ) 0.71073 Å. Refinement method was full-matrix least-squares on F2 for
all compounds.
the suspension was filtered through Celite. The volume of the
filtrate was reduced to 10 mL and the solution cooled to -30
°C. The resulting yellow powder was washed twice with 4 mL
of hexanes and dried under reduced pressure. Yield: 0.307 g,
33%. Mp: turns red 135-140 °C, melts 169-173 °C (dec).
NMR (d6-benzene): 1H δ 7.22 (d, 4H, o-arylH, 3JHH ) 6.9 Hz),
7.15 (8H, aryl, obscured by solvent), 6.83 (m, 6H, o- and/or
1.65 (m, 1H, CH2CHHCH2), 1.3-1.4 (m, 4H, two CH2CHHCH2,
NCHH, and ZrCH); 13C{1H} δ 155.2, 145.1, 144.5, 144.4, 142.1,
138.6 (quat-C), 130.7, 128.6, 128.4, 128.2, 127.7, 127.1, 126.4,
125.6, 124.5 (arylCH), 115.4 (p-arylC), 77.9 (ZrCH, correlates
with a δ1.3-1.4 ppm 1H resonance), 75.0 (quat-C), 69.4
1
(NCH2), 67.7 (CdCHPh, correlates with δ5.67 ppm H reso-
nance), 60.7, 60.42, 60.37, 59.5, 55.8, 51.54, 51.36, 51.24
3
m-arylH), 6.62 (t, 2H, p-arylH, JHH ) 7.4 Hz), 4.94 (m, 2H),
(NCH2), 31.9 (CH2CH2CH2), 30.7 (CH2CH2CH2). Assignments
1
1
3.23-3.09 (m, 8H), 2.73 (m, 2H), 2.23 (m, 2H), 1.76-1.62 (m,
6H), 1.11 (m, 2H), 0.7 (m, 2H); 13C{1H} δ 203.1 (ZrC), 151.2
(quat-C), 150.0 (quat-C), 143.8 (quat-C), 128.4 (signals ob-
scured by solvent), 127.1 (o- or m-arylC), 126.7 (o- or m-arylC),
124.9 (p-arylC), 122.4 (p-arylC), 61.3, 57.2, 53.9, 52.9, 50.3
(CH2N), 21.8 (CH2CH2CH2). NMR (d8-THF): 1H δ 6.96 (t, 4H,
o- or m-arylH, 3JHH ) 7.7 Hz), 6.74 (m, 8H, o- and/or m-arylH),
6.63 (m, 6H, o- and/or m-arylH and p-arylH), 6.53 (t, 2H,
are based on DEPT, H-1H, and H-13C COSY. Anal. Calcd
for C40H44N4Zr: C, 71.49; H, 6.60; N, 8.34. Found: C, 66.76;
H, 6.65; N, 6.61. A small sample of 11 in d6-benzene was
hydrolyzed with D2O, and the organic and aqueous phases
were separated. The 1H NMR of the aqueous phase showed
pure CBC ligand, but the integration of one resonance due to
the central CH2 of the three-carbon bridge (δ0.80 ppm) was
decreased substantially. The organic phase contained 1,2,3,4-
tetraphenylbutadiene and 1,2,3,4-tetraphenylbutadiene-d1 by
mass spectroscopy (M+ ) 358 and 359 amu, respectively).
X-ray Crystallographic Studies. Crystallographic data
for 5, 9, and 10 are given in Table 1. Crystals of 9 and 10 were
grown from a saturated toluene solution at -30 °C; crystals
of 5 were obtained by cooling a warm (60 °C) toluene solution
to room temperature. The crystals were removed from the flask
and covered with a layer of hydrocarbon oil. A suitable crystal
was selected, attached to a glass fiber, and placed in a low-
temperature nitrogen stream.43 Data for 5, 9, and 10 were
collected at 83(2) K using a Bruker/Siemens SMART APEX
instrument (Mo KR radiation, λ ) 0.71073 Å) equipped with
a Cryocool NeverIce low-temperature device. Data were mea-
sured using omega scans of 0.3° per frame for 30 s, and a full
sphere of data was collected. A total of 2132 frames were
collected with a final resolution of 0.75 Å for 5 and 0.77 Å for
9 and 10. The first 50 frames were re-collected at the end of
data collection to monitor for decay. Cell parameters were
retrieved using SMART44 software and refined using SAINT-
Plus45 on all observed reflections. Data reduction and correc-
tions for Lorentz polarization and decay were performed using
the SAINTPlus software. Absorption corrections were applied
using SADABS.46 The structures were solved by direct methods
3
p-arylH, JHH ) 7.3 Hz), 4.80 (m, 2H), 3.62 (m, 2H) 3.52 (m,
2H), 3.24 (dd, 2H), 3.15 (m, 2H), 3.04 (m, 2H), 2.27-2.17 (m,
8H), 2.09 (m, 2H), 0.95 (m, 2H); 13C{1H} δ 203.5 (ZrC), 152.1
(quat-C), 149.5 (quat-C), 144.1 (quat-C), 131.0 (o- or m-arylC),
128.0 (o- or m-arylC), 126.8 (o- or m-arylC), 126.7 (o- or
m-arylC), 124.4 (p-arylC), 122.1 (p-arylC), 61.9, 57.7, 54.3, 53.7,
50.6 (CH2N), 22.4 (CH2CH2CH2). Anal. Calcd for the toluene
solvate C47H52N4Zr: C, 73.87; H, 6.86; N, 7.33. Found: C,
71.09; H, 6.82; N, 7.33. The yield improves slightly if the
reaction is carried out in toluene (41%).
Red Product (11) from the Thermal Decomposition of
Metallacycle 10. (CBC)Zr(C4Ph4) (0.250 g, 0.372 mol) and 20
mL of toluene were sealed in a bomb. The solution was stirred
at 50 °C for 7 days, and then the solvent was removed under
reduced pressure to yield a brown oily material. Dissolution
of this oil in 3 mL of toluene followed by layering with 1 mL
of hexane and cooling at -30 °C afforded a deep red material
after filtration to remove a small amount of an insoluble tan
solid. Recrystallization of the red solid from 1:1 toluene/hexane
produced a dark red solid that displayed a clean NMR
spectrum. Yield: 0.102 g (41%). Mp: 224-229 °C (dec). NMR
(d6-benzene): 1H δ 7.46 (br s, 1H, arylH), 7.26 (br s, 5H, arylH),
7.14 (br s, 2H, arylH), 7.10-6.98 (m, 7H, arylH), 6.78 (m, 3H,
arylH), 6.46 (br s, 1H, arylH), 6.26 (t, 1H, p-arylH, 3JHH ) 7.2
Hz), 5.67 (s, 1H, CdCHPh), 3.72 (dt, 1H), 3.46 (dd, 1H), 3.14
(td, 1H), 3.02-2.95 (m, 2H), 2.59 (td, 1H), 2.47 (td, 1H), 2.27
(td, 1H, NCHH), 2.23-2.09 (m, 7H, six NCHH and one
CH2CHHCH2), 1.87 (dd, 1H, NCHH), 1.75 (m, 2H, NCHH),
(43) Hope, H. Prog. Inorg. Chem. 1995, 41, 1.
(44) SMART: v.5.626, Bruker Molecular Analysis Research Tool;
Bruker AXS: Madison, WI, 2002.
(45) SAINTPlus: v. 6.22, Data Reduction and Correction Program;
Bruker AXS: Madison, WI, 2001.

32 Organometallics, Vol. 24, No. 1, 2005
O’Connor et al.
Scheme 1
and refined by the least-squares method on F2 using the
SHELXTL program package.47
cleavage due to ambient light,22 we were concerned that
this might again be a possibility. Irradiation of (NOON)-
Zr(CH2Ph)2 for 14 h at 435 nm led to complete trans-
formation of the compound; in contrast, 2 showed minor
degradation when irradiated at 375 nm for 24 h and
bibenzyl was not produced. This suggests that 2 is not
degraded by ambient light.
For compound 5, the structure was solved in the space group
Pcc2 (#116) by analysis of systematic absences. The compound
was refined as a pseudo-merohedral twin using the twin law
0 1 0 1 0 0 0 0 -1. Although the absences suggest a higher
symmetry, i.e., the tetragonal space group P-4c2, refinement
using this solution clearly leads to a twinned structure with a
higher R value. All atoms were refined anisotropically. For
compound 9, the structure was solved in the space group C2/c
(#15) by analysis of systematic absences. All atoms were
refined anisotropically. For compound 10, the structure was
solved in the space group C2/c (#15) by analysis of systematic
absences. There is a half-occupied toluene molecule in the
asymmetric unit that is disordered over the inversion center.
All atoms were refined anisotropically. No decomposition was
observed during data collection for any of these compounds.
Structural plots were drawn with ORTEP3.48 Further details
are provided in the Supporting Information.
We initially encountered difficulties preparing (CBC)-
ZrCl2 (vide infra), so as an alternative, we explored pro-
tonolysis of 2 with phenols, since the resulting phenox-
ides can be used in metathesis reactions as an alterna-
tive to halides with group 3 metals.49 Reaction of 2 with
2 equiv of 2,6-di-tert-butylphenol produces the mono-
substituted product (CBC)Zr(CH2Ph)(O-2,6-C6H3But), 3,
as a pale yellow powder. Presumably steric effects
prevent the introduction of the second phenol at the
metal center, since the less hindered 2,6-dimethylphenol
reacts cleanly to give 5. When the reaction of 2 with 2
equiv of 2,6-di-tert-butylphenol is followed by NMR,
there is no evidence for either reaction of the benzyl
group or the amido groups of the ligand with the second
equivalent of phenol. Given the acidity of the phenol, it
is surprising that the amido groups do not react, but
this may be attributable to the strong chelate effect of
the macrocycle and the steric congestion at the metal
center.
Prolonged heating of 3 in aromatic solvents leads
to the loss of toluene and the formation of a six-
membered metallacycle (CBC)Zr[κ2(C,O)-OC6H3(6-But)-
(2-CMe2CH2)] (4, Scheme 1). This has been observed
previously with a related aniline species.50 Presumably
the methyl group of the phenoxide can more readily
adopt the correct orientation for the metalation to occur
than any of the methylene groups of the cross-bridged
cyclam ligand.
Results and Discussion
Synthesis and Reactivity. The reaction of cross-
bridged cyclam (H2(CBC): 1,4,8,11-tetraazabicyclo[6.6.2]-
hexadecane) with tetrabenzylzirconium yields (CBC)-
Zr(CH2Ph)2, 2, efficiently, provided the amine has been
suitably dried (Scheme 1). Compound 2 is a yellow
powder that is soluble in aromatic solvents and spar-
ingly soluble in aliphatic ones.
Compound 2 is thermally robust in solution: heating
at 80 °C for 96 h causes 50% decomposition (compared
1
to an internal standard by H NMR); the process does
not follow first-order kinetics and ultimately results in
disappearance of ligand resonances into the baseline.
The compound does degrade over the course of several
weeks when stored at room temperature in a glovebox,
as do all the bis(alkyls) described in this report. Given
our previous observations of photolytic benzyl-Zr bond
The reaction of (CBC)Zr(CH2Ph)2 with 2 equiv of 2,6-
dimethylphenol yields the diphenoxide 5 in good yield.
(46) Sheldrick, G. M. SADABS: v.2.01, An Empirical Absorption
Correction Program; Bruker AXS Inc.: Madison, WI, 2001.
(47) Sheldrick, G. M. SHELXTL: v. 6.10, Structure Determination
Software Suite; Bruker AXS Inc.: Madison, WI, 2001.
(49) Schaverien, C. J.; Orpen, A. G. Inorg. Chem. 1991, 30, 4968.
(50) Zuckerman, R. L.; Bergman, R. G. Organometallics 2000, 19,
4795.
(48) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.

Zr Complexes of a Cross-Bridged Cyclam
Organometallics, Vol. 24, No. 1, 2005 33
Scheme 2
However, attempts to carry out metathesis reactions
with MeLi or LiCH2SiMe3 and 5 were unsuccessful, and
only the starting material was recovered. Consequently,
we returned to (CBC)ZrCl2, 6, as a precursor to a range
of organometallic compounds. Unfortunately, to date we
have been unable to cleanly isolate the Li, Na, or K salts
of cross-bridged cyclam for metathesis with zirconium
tetrachloride. Likewise, we initially experienced low
yields in the direct protonolysis of ZrCl2[N(SiMe3)2]2
with H2(CBC). Due to its extremely low solubility in
toluene, 6 precipitates directly from the reaction mix-
ture; investigation of the supernate led to the isolation
of (CBC)Zr(Cl)[N(Si(CH3)3)2], 7, as the other product.
Its identity has been confirmed by the synthesis of 7
from 6 and NaN(Si(CH3)3)2.
The initial batch of ZrCl2[N(Si(CH3)3)2]2 had been
prepared from zirconium tetrachloride and NaN(Si-
(CH3)3)2. This likely resulted in the contamination of
ZrCl2[N(Si(CH3)3)2]2 with ZrCl[N(Si(CH3)3)2]3 and the
subsequent low yield of 6.51 If LiN(Si(CH3)3)2 is used in
the preparation of ZrCl2[N(Si(CH3)3)2]2, this problem
does not occur and the subsequent yield of 6 is 90%.
(CBC)ZrCl2 is only sparingly soluble in aromatic sol-
vents and does not dissolve under our standard ethylene
polymerization conditions21 (50 °C toluene, 500 equiv
of MAO). Accordingly, we wished to prepare the dimeth-
yl analogue 8. Metathesis reactions of (CBC)ZrCl2 with
methylating reagents have been investigated. The di-
methyl species 8 can be produced in modest yield with
the use of MeLi (Scheme 2), while use of MeMgBr
results in even lower yields and contamination with the
starting dichloride. Unlike the dichloride 6, the dimethyl
compound 8 does dissolve in toluene; however, when it
was treated with 500 equiv of MAO, we found no
evidence of polyethylene production.
nulene is related to CBC in that it is an N4 macrocycle
of the same size, but in contrast, it has two delocalized
anionic subunits rather than localized amido and amino
donors.
Figure 3. Dibenzotetraazaannulene zirconium cation with
a noncoordinating pendant alkene.
Perhaps a better comparison is our previous zirco-
nium diamido NOON2- system, which showed low eth-
ylene polymerization activity.21 The difference in activ-
ity can be understood in the context of Schrock’s work
on M(NON)R2 systems. The cationic M(NON)R+ com-
plexes were found to insert hexene or ethylene; however,
addition of 1 equiv of diethyl ether inhibited insertion.52
In our earlier work with NOON, the neutral donors were
hemilabile, and this allowed for low polymerization
activity. In the present work, it is unlikely that the
amino donors are labile, thus precluding polymerization.
Consequently, the CBC systems described here are
better suited for other types of chemistry.
Zirconacycles are a class of compounds we are inter-
ested in. Since metalation of the tert-butyl moiety in 3
results in zirconacycle 4, we wondered if hydrocarbon
elimination might be a general route to zirconacycles
in this system (Scheme 2). To test this, we prepared
(CBC)Zr[CH2Si(CH3)3]2, 9, via metathesis with 6 and
LiCH2SiMe3. When a solution of 9 was heated, we did
observe the production of tetramethylsilane; however,
we have been unable to isolate any organometallic
products from this reaction.
The lack of ethylene polymerization activity shown
by 8, while disappointing, is not entirely surprising
given previous reports. The octamethyldibenzotet-
raazaannulene zirconium cationic systems were found
to have low ethylene polymerization activity. This was
thought to be a result of the metal center being insuf-
ficiently electrophilic to coordinate alkenes, even pen-
dant ones (Figure 3).5 The octamethyldibenzotetraazaan-
We investigated another route to prepare zircona-
cycles. By treating (CBC)ZrCl2 with n-BuLi in the
(52) Aizenberg, M.; Turculet, L.; Davis, W. M.; Schattenmann, F.
J.; Schrock, R. R. Organometallics 2001, 20, 1153.
(51) Andersen, R. A. Inorg. Chem. 1979, 18, 2928.

34 Organometallics, Vol. 24, No. 1, 2005
O’Connor et al.
annulenes, where the four nitrogens are equivalent and
coplanar.
The largest distortion from octahedral is the average
amide-Zr-amide angle of 145.2° (the asymmetric unit
contains two half-molecules). The small amide-Zr-
amide angle may be caused by the amido nitrogens
trying to achieve the most planar geometry possible in
order to maximize donation to zirconium. This would
force the metal out of the cleft of the CBC ligand, thus
narrowing the amide-Zr-amide angle.54 Evidence for
this proposal includes the observation that the
amide-M-amide angle is much larger (160-170°) in
six-coordinate complexes of Zn(II) even though this
metal has an ionic radius very similar to Zr(IV).31,54 The
average amine-Zr-amine angle is constrained by the
ethyl cross-bridge to 76.5°; accordingly, the O-Zr-O
angle expands to an average 99.5°.
Figure 4. Possible structure of the thermal metalation
product of 10.
The amido-Zr bond lengths (2.094(4), 2.125(4) Å) in
5 are within the normal range (2.063-2.192 Å)8,10,21,55
for polydentate ligands with amido donors, and the
amino-Zr bonds (2.377(4), 2.394(4) Å) are short com-
pared to the normal range (2.414-2.604 Å)10,13,55c for
polydentate ligands with amino and amido donors in a
six-coordinate environment. The oxygen bond lengths
(1.997(3), 1.994(4) Å) and Zr-O-C angles (163.8(3)° and
164.2(3)°) are consistent with the range found for 2,6-
dimethylphenoxide in other systems containing tris-
(pyrazolylborate), Cp, Cp*, and PNP supporting ligation
(1.948-2.020 Å).56 The Zr-O-C angles in these systems
span a very large range (145.8-176.8°) that has been
attributed to steric factors, meaning this angle is not a
good indication of the extent of M-O π interactions.56c
Compound 9 has been characterized by X-ray crystal-
lography (Table 1), and the structure is depicted in
Figure 6. The significant bond lengths and angles are
given in Table 2. The gross features of the complex are
comparable to 5, with the exception that the Zr-amine
distance in 9 (2.452(2) Å) is longer and more typical of
the usual range. The Zr-C bond length and C-Zr-C
angle are within the typical range.57 The Zr-C
bond length (2.290(2) Å) and Zr-C-Si bond angle
(120.69(12)°) do not suggest that an agostic interaction
is present.57b
Figure 5. ORTEP3 drawing48 (50% probability thermal
ellipsoids) of complex 5. Only one molecule of the asym-
metric unit is shown, and hydrogen atoms have been
removed for clarity.
presence of diphenylacetylene in a route analogous to
that described by Negishi we obtained zirconcyclopen-
tadiene 10 as a pale yellow powder with limited solubil-
ity in toluene.53 Metallacycle 10 is stable in solution at
room temperature in the absence of air, but heating it
at 50 °C results in slow (days) conversion to a deep red
product (11) that displays a 1H NMR spectrum sugges-
tive of a terminal butadienyl unit (CdCHPh resonance
at δ 5.67 ppm). Hydrolysis of this red product with D2O
shows incorporation of D into the macrocycle at the
central methylene carbon of one of the three carbon
bridges and mass spectral evidence for the production
of 1,2,3,4-tetraphenylbutadiene-d1. Although we have
been unable to establish the structure of 11 unequivo-
cally, the results obtained so far seem to suggest that
it is a CBC-metalated butadienyl of structure similar
to that shown in Figure 4.
Attempts to isolate the tetramethyl analogue of 10
by reaction with 2-butyne have been unsuccessful thus
far. Since the tetraphenyl zirconacyclopentadiene de-
composes under relatively mild conditions, and it seems
likely that both steric and electronic factors in the
tetramethyl analogue would make it more prone to
decomposition, it is unsurprising that this compound
has not been isolated.
Solid State Structures. The solid state structure of
the bis(phenoxide) (CBC)Zr(O-2,6-C6H3Me2)2, 5, was
determined by X-ray crystallography (Table 1). The
structure is depicted in Figure 5, and important bond
distances and angles are given in Table 2. The zirconium
center is six-coordinate and best described as distorted
octahedral. The ligand can be thought of as saddle
shaped, with the amido nitrogens trans to one another
and the amino nitrogens adopting a cis geometry,
constrained by the cross-bridge to the points where the
saddle is at its narrowest. The oxygen atoms are trans
to the amino nitrogens and cis to one another. This is
in contrast to the saddle shape of the tetraaza[14]-
Of the over 30 zirconacyclopentadiene structures in
the Cambridge Crystallographic Database, all contain
(54) The authors are indebted to one reviewer for pointing out this
explanation. (a) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(55) (a) Mehrkhodavandi, P.; Schrock, R. R.; Bonitatebus, P. J., Jr.
Organometallics 2002, 21, 5785. (b) Rogers, A. J.; Solari, E.; Floriani,
C.; Chiesi-Villa, A.; Corrado, R. J. Chem. Soc., Dalton Trans. 1997,
2385. (c) Giesbrecht, G. R.; Shafir, A.; Arnold, J. Chem. Commun. 2000,
2135.
(56) (a) Kresinski, R. A.; Isam, L.; Hamor, T. A.; Jones, C. J.;
McCleverty, J. A. J. Chem. Soc., Dalton Trans. 1991, 1835. (b)
Benetollo, F.; Cavinato, G.; Crosara, L.; Milani, F.; Rossetto, G.; Scelza,
C.; Zanella, P. J. Organomet. Chem. 1998, 555, 177. (c) Antinolo, A.;
Carrillo-Hermosilla, F.; Corrochano, A.; Fernandez-Baeza, J.; Lara-
Sanchez, A.; Ribeiro, M. R.; Lanfranchi, M.; Otero, A.; Pellinghelli, M.
A.; Portela, M. F.; Santos, J. V. Organometallics 2000, 19, 2837. (d)
Cohen, J. D.; Fryzuk, M. D.; Loehr, T. M.; Mylvaganam, M.; Rettig, S.
J. Inorg. Chem. 1998, 37, 112.
(57) (a) Jeffery, J.; Lappert, M. F.; Luong-Thi, N. T.; Webb, M.;
Atwood, J. L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1981, 1593.
(b) Cayias, J. Z.; Babaian, E. A.; Hrncir, D. C.; Bott, S. G.; Atwood, J.
L. J. Chem. Soc., Dalton Trans. 1986, 2743. (c) Brand, H.; Arnold, J.
J. Am. Chem. Soc. 1992, 114, 2266. (d) Okuda, J.; Schattenmann, F.
J.; Wocadlo, S.; Massa, W. Organometallics 1995, 14, 789. (e) Dias, H.
V. R.; Wang, Z. J. Organomet. Chem. 1997, 539, 77. (f) Scott, M. J.;
Lippard, S. J. Inorg. Chim. Acta 1997, 263, 287. (g) Gentil, S.; Pirio,
N.; Meunier, P.; Gallucci, J. C.; Schloss, J. D.; Paquette, L. A.
Organometallics 2000, 19, 4169.
(53) Negishi, E.; Cederbaum, F. E.; Takahashi, T. Tetrahedron Lett.
1986, 27, 2829.

Zr Complexes of a Cross-Bridged Cyclam
Organometallics, Vol. 24, No. 1, 2005 35
Table 2. Selected Bond Distances (Å) and Angles (deg) for Complexes 5, 9, and 10
5a
9
10
Bond Distances
Zr-amide
Zr-amine
Zr-X
2.125(4) (Zr1-N2)
2.094(4) (Zr2-N4)
2.377(4) (Zr1-N1)
2.394(4) (Zr2-N3)
1.997(3) (Zr1-O1)
1.994(4) (Zr2-O2)
2.103(2) (Zr1-N3)
2.452(2) (Zr1-N6)
2.290(2) (Zr1-C9)
2.0820(19) (Zr1-N3)
2.4269(19) (Zr1-N6)
2.313(2) (Zr1-C9)
Bond Angles
amide-Zr-amide
amine-Zr-amine
X-Zr-X
145.1(3) (N2-Zr1-N2)
145.3(3) (N4-Zr2-N4)
76.6(2) (N1-Zr1-N1)
76.4(2) (N3-Zr2-N3)
98.4(2) (O1-Zr1-O1)
100.6(2) (O2-Zr2-O2)
352.8 (N2)
142.3(11) (N3-Zr1-N3)
74.78(10) (N6-Zr1-N6)
99.61(12) (C9-Zr1-C9)
353.8 (N3)
142.4(10) (N3-Zr1-N3)
76.81(9) (N6-Zr1-N6)
77.19(11) (C9-Zr1-C9)
354.4 (N3)
sum of angles
at amido N
353.3 (N4)
a The asymmetric unit contains two half-molecules.
Table 3. Structural Comparison of (CBC)ZrX2 and
Cp2ZrX2
X
CBC
Cp2
2,6-C6H3Me2O
Zr-O (Å)
1.994(4)
1.997(3)
98.4(2)
1.996(5)56b
1.997(5)
98.6(2)
O-Zr-O (deg)
100.6(2)
Me3SiCH2
Zr-C (Å)
2.290(2)
99.61(12)
2.313(2)
77.19(11)
2.278(4)57a
2.281(4)
97.8(1)
C-Zr-C (deg)
X2 ) C4Ph4
Zr-C (Å)
Figure 6. ORTEP3 drawing48 (50% probability thermal
ellipsoids) of complex 9. The hydrogen atoms have been
omitted for clarity.
2.250(5)60a
2.265(6)
77.5(2)
C-Zr-C (deg)
Overall, the similarities between the solid state
structures of (CBC)ZrX2 and Cp2ZrX256b,57a,60a are strik-
ing, as illustrated in Table 3. The CBC system shows
slightly longer bond lengths on average (0.02 Å). The
average difference in bond angle between the substit-
uents in the two systems is slightly more than 1°,
remarkable given that, for example, the C-Zr-C angle
for L2Zr(CH2Si(CH3)3)2 systems ranges over 25°. This
leads us to postulate that CBC and two Cp groups are
sterically very similar.
Figure 7. ORTEP3 drawing48 (50% probability thermal
ellipsoids) of complex 10. The hydrogen atoms and toluene
of solvation have been omitted for clarity.
at least one cyclopentadienyl ligand, albeit one is a
phosphacyclopentadienyl ligand58 (a metallacycle sup-
ported by benzamidinate ligands59 has been reported,
but its solid state structure has not been determined).
To the best of our knowledge, compound 10 is the first
zirconacyclopentadiene without a cyclopentadienyl ligand
characterized by X-ray crystallography (Tables 1 and
2, Figure 7). The Zr-C bond lengths typically range
from 2.172 to 2.324 Å for zirconacyclopentadienes; thus,
at 2.313(2) Å, 10 falls at the long end of this range.36,60
Accordingly, the C-Zr-C angle is reduced to 77.19(11)°,
falling at the short end of the range 76.4-98.5°. The
geometry of the cross-bridged cyclam moiety in 10 is
remarkably similar to that of the bis(alkyl) 9, especially
given the large difference in the C-Zr-C angles (9,
99.61(12)°; 10, 77.19(11)°). We take this to mean that
the geometry of the ligand about the metal is con-
strained by the cross-bridge and largely invariant,
regardless of the other substituents on the metal center.
Behavior in Solution. As might be expected, the 1H
and 13C NMR of the cross-bridged cyclam moiety in
compounds 2, 5, 6, and 8-10 show effective C2 sym-
metry in solution, with a complicated pattern of 12
resonances for six pairs of diasterotopic protons and six
carbon resonances. In contrast, since compounds 3, 4,
and 7 have two different groups in addition to the cross-
bridged cyclam, the C2 axis is lost, leading to 24 proton
resonances and 12 carbon resonances.
Consistent with C2 symmetry, the benzylic protons
in 2 appear as AB doublets. Compound 2 does not
display the features normally associated with η2-benzyl
coordination; namely, the ortho protons are downfield
1
of 6.7 ppm (7.14 ppm) and the JCH coupling con-
stant for the CH2Ph groups are less than 130 Hz (113
Hz).61 Likewise, the geminal coupling constant of the
CH2SiMe3 group in 9 (12 Hz) is slightly larger than in
(60) (a) Hunter, W. E.; Atwood, J. L. J. Organomet. Chem. 1981,
204, 67. (b) Metzler, N.; Noth, H.; Thomann, M. Organometallics 1993,
12, 2423. (c) Erker, G.; Zwettler, R.; Kruger, C.; Hyla-Kryspin, I.;
Gleiter, R. Organometallics 1990, 9, 524. (d) Wieistra, Y.; Gambarotta,
S.; Meetama, A.; de Boer, J. L. Organometallics 1989, 8, 2696.
(58) Buzin, F.; Nief, F.; Ricard, L.; Mathey, F. Organometallics 2002,
21, 259.
(59) Hagadorn, J. R.; Arnold, J. Organometallics 1994, 13, 4670.

36 Organometallics, Vol. 24, No. 1, 2005
O’Connor et al.
In 7, the N(Si(CH3)3)2 group shows two Si(CH3)3
resonances. Since the geometry of this group is usually
trigonal planar,50,64 this implies that the rotation about
the Zr-N bond is hindered. Heating did result in
broadening of the signals, but the coalescence temper-
ature was greater than the boiling point of toluene.
Future Work. We look forward to studying the
insertion and metallacycle transfer chemistry of these
zirconium complexes to further compare and contrast
their behavior with that of cyclopentadienyl and other
tetraazamacrocycles. In addition, we are investigating
the use of cross-bridged cyclam as a ligand for the group
3 metals and lanthanides.
Figure 8. Variable-temperature 1H NMR (d8-toluene)
spectrum of the meta proton region of 3.
similar species57d and does not indicate any agostic
interactions,57e consistent with the solid state structure.
The observation of two resonances each for the ortho
tert-butyl groups and meta protons of the phenoxide in
(CBC)Zr(CH2Ph)(O-2,6-C6H3But2) at room temperature
suggests that the rotation about the O-C linkage is
hindered. Increasing the temperature of 3 results in a
coalescence of both the tert-butyl and meta protons
(Figure 8) of the phenoxide. From the coalescence
temperature for the two-site exchange of the t-Bu
signals, the activation energy for this process is calcu-
lated to be 69 ( 1 kJ/mol at 325 K.62,63 In contrast,
(CBC)Zr(O-2,6-C6H3Me2)2 shows only one resonance for
the methyl groups, suggesting that steric interactions
hinder the rotation around the Zr-O bond in 3 because
of the large steric size of the tert-butyl groups.
Acknowledgment. D.J.B. (Discovery Grant) and
P.O. (PGS Fellowship) gratefully acknowledge the sup-
port of the Natural Sciences and Engineering Research
Council of Canada.
Supporting Information Available: Tables of atomic
coordinates, bond distances and angles, and anisotropic ther-
1
mal parameters for 5, 9, and 10 and the H NMR spectrum
for 5 are available free of charge via the Internet at
http://pubs.acs.org.
OM049469J
(62) (a) Bradley, D. C.; Chudzynska, H.; Backer-Dirks, J. D. J.;
Hursthouse, M. B.; Ibrahim, A. A.; Motevalli, M.; Sullivan, A. C.
Polyhedron 1990, 9, 1423. (b) Airoldi, C.; Bradley, D. C.; Chudzynska,
H.; Hursthouse, M. B.; Malik, K. M. A.; Raithby, P. R. J. Chem. Soc.,
Dalton Trans. 1980, 2010.
(63) The free energy of activation was calculated from the coales-
cence temperature (Tc) using the equal population, two-site exchange
equation: G ) (1.914 × 10-2)Tc)[9.972 + log(Tc/υ)] in kJ mol-1 where
υ is the separation of the resonances in Hz (25.2 Hz for the t-Bu
resonances) and Tc is in K (325 K). The error in G was estimated to be
1 kJ mol-1 assuming an error of 3 K in Tc.
(61) (a) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell,
I. P.; Huffman, J. C. Organometallics 1985, 4, 902. (b) Bochmann, M.;
Lancaster, S. J. Organometallics 1993, 12, 633. (c) Bochmann, M.;
Lancaster, S. J.; Hursthouse, M. B.; Malik, K. M. A. Organometallics
1994, 13, 2235. (d) Jordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echolls,
S. F.; Willet, R. J. Am. Chem. Soc. 1987, 109, 4111.
(64) Sandstrom, J. Dynamic NMR Spectroscopy; Pergamon: London,
1982.