Structure and reactivity of neutral and cationic trans - N, N′-dibenzylcyclam zirconium alkyl complexes

Article abstract of DOI:10.1021/om100465d

Reactions of (Bn₂Cyclam)ZrCl₂ (1) (where Bn ₂Cyclam = trans-N,N′(PhCH₂)₂Cyclam) with appropriate alkylating reagents produced (Bn₂Cyclam)ZrR₂ (R = Me (2), CH₂Ph (3), ⁿBu (4), CCPh (5)). Activation of the ortho C-H bond of the two macrocycle benzyl substituents in complexes 2, 3, and 4 was thermally induced, leading to the formation of a bis(ortho-metalated) complex, ((C₆H₄CH₂)₂Cyclam)Zr (6). This reaction proceeds along with RH elimination and converts the original dianionic tetracoordinated cyclam in a tetraanionic hexacoordinated ligand where two new Zr-C_Ph bonds complete the metal sphere. Treatment of 6 with one equivalent of HC≡CPh led to ((C₆H₄CH ₂)BnCyclam)Zr(CCPh) (7) via protonation of one Zr-C_Ph bond by phenylacethylene. Further reaction of 7 with an excess of HC≡CPh led to 5. The reactions of 2 and 3 with B(C₆F₅)₃ are strongly solvent dependent. Solvent-stabilized cationic species of formula [(Bn₂Cyclam)ZrR(Solv)][RB(C₆F₅)₃] were obtained from reactions of 2 in CD₂Cl₂ (10) or d ₈-THF (12) and from 3 in d₈-THF (9). The reactions of 3 in CD₂Cl₂ or d₈-toluene gave [(Bn ₂Cyclam)Zr(η²-CH₂Ph)][ PhCH ₂B(C₆F₅)₃] (8). Finally, the reaction of 2 in d₈-toluene led to [(Bn₂Cyclam)Zr(C ₆F₅){CH₂B(C₆F₅) ₂}] (14); the precursor of the latter is the zwitterionic [(Bn ₂Cyclam)Zr(CH₃){CH₃B(C₆F ₅)₃}] (11), which then undergoes methane elimination and C₆F₅ migration from boron to zirconium. The mechanism of this reaction was studied by DFT and revealed that (i) methane elimination is assisted by one alpha-agostic C-H bond and (ii) migration of the C ₆F₅ ring is supported by one bridging fluorine bond between the zirconium and one of the C₆F₅ rings that remains bonded to boron.

Full text of DOI:10.1021/om100465d

Organometallics 2010, 29, 3753–3764 3753
DOI: 10.1021/om100465d
Structure and Reactivity of Neutral and Cationic
trans-N,N0-Dibenzylcyclam Zirconium Alkyl Complexes
ꢀ †,‡
Rui F. Munha, M. Augusta Antunes,† Luis G. Alves,† Luis F. Veiros,†
Michael D. Fryzuk,‡ and Ana M. Martins*,†
†
´
ꢀ
Centro de Quımica Estrutural, Instituto Superior Tecnico, Avenida Rovisco Pais, No. 1, 1049-001 Lisboa,
Portugal, and ‡Department of Chemistry, The University of British Columbia, 2036 Main Mall, Vancouver,
British Columbia, Canada, V6T 1Z1
Received May 14, 2010
Reactions of (Bn2Cyclam)ZrCl2 (1) (where Bn2Cyclam = trans-N,N0(PhCH2)2Cyclam) with app-
ropriate alkylating reagents produced (Bn2Cyclam)ZrR2 (R = Me (2), CH2Ph (3), nBu (4), CCPh
(5)). Activation of the ortho C-H bond of the two macrocycle benzyl substituents in complexes 2, 3,
and 4 was thermally induced, leading to the formation of a bis(ortho-metalated) complex,
((C6H4CH2)2Cyclam)Zr (6). This reaction proceeds along with RH elimination and converts the
original dianionic tetracoordinated cyclam in a tetraanionic hexacoordinated ligand where two new
Zr-CPh bonds complete the metal sphere. Treatment of 6 with one equivalent of HCtCPh led to
((C6H4CH2)BnCyclam)Zr(CCPh) (7) via protonation of one Zr-CPh bond by phenylacethylene.
Further reaction of 7 with an excess of HCtCPh led to 5. The reactions of 2 and 3 with B(C6F5)3 are
strongly solvent dependent. Solvent-stabilized cationic species of formula [(Bn2Cyclam)ZrR(Solv)]-
[RB(C6F5)3] were obtained from reactions of 2 in CD2Cl2 (10) or d8-THF (12) and from 3 in d8-THF
(9). The reactions of 3 in CD2Cl2 or d8-toluene gave [(Bn2Cyclam)Zr(η2-CH2Ph)][ PhCH2B(C6F5)3]
(8). Finally, the reaction of 2 in d8-toluene led to [(Bn2Cyclam)Zr(C6F5){CH2B(C6F5)2}] (14); the
precursor of the latter is the zwitterionic [(Bn2Cyclam)Zr(CH3){CH3B(C6F5)3}] (11), which then
undergoes methane elimination and C6F5 migration from boron to zirconium. The mechanism of this
reaction was studied by DFT and revealed that (i) methane elimination is assisted by one alpha-
agostic C-H bond and (ii) migration of the C6F5 ring is supported by one bridging fluorine bond
between the zirconium and one of the C6F5 rings that remains bonded to boron.
Introduction
combinations of donor atoms and ligand frameworks a
perennial research topic in coordination chemistry.3
Studies on the reactivity and stability of group 4 metal-
alkyl species have had a tremendous impact on the discovery,
understanding, and improvement of olefin polymerization
catalysts.1 It is now of general knowledge that generating
active olefin polymerization catalysts requires an acidic metal
species, where a metal-carbon bond and a vacant site occupy
adjacent positions in the metal coordination sphere.2 In
addition, the ancillary ligands modulate the reactivity of the
cationic metal-alkyl species by providing the correct balance
of electronic and steric properties to the metal. However, the
inability to predict the reactivity of a metal complex based on
the choice of an ancillary ligand has made the search for new
Following our own efforts in the study of group 4 metal
complexes supported by nitrogen-based ancillary ligands,4
some of us have recently reported on the preparation of
trans-disubstituted cyclam-based ligand precursors and their
coordination chemistry to zirconium.5 The saturated backbone
(3) (a) Agapie, T.; Henling, L. M.; DiPasquale, A. G.; Rheingold,
A. L.; Bercaw, J. E. Organometallics 2008, 27, 6245–6256. (b) Gibson,
V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–315. (c) Coates, G. W.;
Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236–2257.
(d) Shah, S. A. A.; Dorn, H.; Voigt, A.; Roesky, H. W.; Parisini, E.; Schmidt,
H.-G.; Noltemeyer, M. Organometallics 1996, 15, 3176–3181.
(4) (a) Ferreira, M. J.; Matos, I.; Ascenso, J. R.; Duarte, M. T.;
Marques, M. M.; Wilson, C.; Martins, A. M. Organometallics 2007, 26,
119–127. (b) Ferreira, H.; Dias, A. R.; Duarte, M. T.; Ascenso, J. R.; Martins,
A. M. Inorg. Chem. 2007, 46, 750–755. (c) Ferreira, M. J.; Matos, I.;
Ascenso, J. R.; Duarte, M. T.; Marques, M. M.; Wilson, C.; Martins, A. M.
Organometallics 2006, 26, 119–127. (d) Barroso, S.; Cui, J.; Dias, A. R.;
*To whom correspondence should be addressed. E-mail: ana.martins@
ist.utl.pt.
(1) (a) Jordan, R. F. Adv. Organomet. Chem. 1991, 32, 325–387.
(b) Bochmann, M. J. Organomet. Chem. 2004, 689, 3982–3998. (c) Chen,
E. Y.-X.; Marks, T. J. Chem. Rev. 2000, 100, 1391–1434. (d) Deck, P. A.;
Beswick, C. L.; Marks, T. J. J. Am. Chem. Soc. 1998, 120, 1772–1784.
(e) Brintzinger, H. H.; Fischer, D.; Muelhaupt, R.; Rieger, B.; Waymouth,
R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143–1170.
~
Duarte, M. T.; Ferreira, H.; Henriques, R. T.; Conceic-ao Oliveira, M.;
Ascenso, J. R.; Martins, A. M. Inorg. Chem. 2006, 45, 3532–3537.
(e) Martins, A. M.; Ascenso, J. R.; Costa, S. M. B.; Dias, A. R.; Ferreira,
H.; Ferreira, J. A. B. Inorg. Chem. 2005, 44, 9017–9022.
ꢀ
(5) (a) Munha, R. F.; Alves, L. G.; Maulide, N.; Teresa Duarte, M.;
(2) (a) Klamo, S. B.; Wendt, O. F.; Henling, L. M.; Day, M. W.;
Bercaw, J. E. Organometallics 2007, 26, 3018–3030. (b) Britovsek, G. J. P.;
Gibson, V. C.; Wass, D. F. Angew. Chem., Int. Ed. 1999, 38, 428–447.
(c) Beswick, C. L.; Marks, T. J. Organometallics 1999, 18, 2410–2412.
Marko, I. E.; Fryzuk, M. D.; Martins, A. M. Inorg. Chem. Commun.
ꢀ
Duarte, M.; Ascenso, J. R.; Dias, A. R.; Martins, A. M. J. Organomet. Chem.
2006, 691, 3853–3861.
2008, 11, 1174–1176. (b) Munha, R. F.; Namorado, S.; Barroso, S.; Teresa
r
2010 American Chemical Society
Published on Web 08/13/2010
pubs.acs.org/Organometallics

ꢀ
Munha et al.
3754 Organometallics, Vol. 29, No. 17, 2010
Scheme 1a
a Reaction conditions: (i) 2 MgClMe or 2 LiBun in THF; (ii) 2 MgClCH2Ph in THF; (iii) 2 LiCCPh in THF; (iv) 70 °C, benzene, 2 h; (v) reflux, toluene,
72 h; (vi) HCCPh; (vii) HCCPh.
of the macrocyclic ligand confers an enhanced flexibility
when compared to its unsaturated congeners, such as por-
phyrins or tetraazaannulenes.6 Experimental and theoretical
studies on amido, hydrazido, and imido complexes proved
that different ancillary ligand conformations and metal
coordination geometries are attained depending on the steric
properties of the ligands present in the remaining coordina-
tion positions.6
Our interest in further exploring the reactivity of the
zirconium systems led us to prepare the corresponding alkyl
complexes and perform stoichiometric reactivity studies that
are relevant to assess the potential of trans-disubstituted
cyclam zirconium complexes as olefin polymerization cata-
lysts.
to methane is identified at 0.16 ppm, which then increases
over time. Its thermal instability constrains its preparation to
small-scale reactions and hampers its isolation in high yield.
The choice of alkylating agent also appears critical, as the use
of a LiMe solution produces a complex mixture of com-
pounds where only free H2(Bn2Cyclam) could be identified.
Under similar reaction conditions, 3 was prepared in 80%
yield using the appropriate Grignard reagent (MgClCH2Ph).
The rapid conversion of the bright yellow THF suspension of
(Bn2Cyclam)ZrCl2 into an intensely yellow-colored solution
is indicative that the reaction proceeds faster than in the case
of 2; the higher solubility of the resulting complex 3 and the
fact that it is more stable in solution prove to be important for
further reactivity studies.
Reaction of 1 with two equivalents of LinBu gives (Bn2-
Cyclam)Zr(nBu)2 (4) in86% yield. Theformation ofbis(alkyl)
complexes containing β-hydrogens is unusual as they normally
tend to undergo β-elimination reactions to give other products.7
However, in what is becoming a trend in zirconium com-
plexes supported by amido ligands, alkyl complexes of this
type display an unexpected stability.8
(Bn2Cyclam)Zr(CCPh)2 (5) was synthesized on a prepara-
tive scale via salt metathesis; to a cold THF suspension of 1,
two equivalents of LiCCPh was added and 5 was isolated in
52% yield. This reaction is a convenient alternative synthetic
route for the recently reported preparation of 5 via reaction
of (Bn2Cyclam)Zr(N2,6-iPrPh) with an excess of phenylacety-
lene.6
Results and Discussion
Synthesis and Characterization of Zirconium Alkyl Com-
plexes. The zirconium dichloride (Bn2Cyclam)ZrCl2 (1) can
be prepared by a salt metathesis reaction between Li2(Bn2-
Cyclam)(THF)2 and ZrCl4(THF)2 or via a protonolysis reaction
of the neutral ligand precursor with ZrCl2(CH2SiMe3)2(Et2O)2.5
(Bn2Cyclam)ZrCl2 proved a convenient starting material for
the synthesis of a variety of zirconium derivatives, and as
shown in Scheme 1, complexes of general formula (Bn2Cyclam)-
ZrR2 (R = Me (2), CH2Ph (3), nBu (4), CCPh (5)) are readily
obtained by chloride metathesis using Mg or Li compounds
as alkylating agents. Reaction of THF suspensions of (Bn2-
Cyclam)ZrCl2 (1) with two equivalents of MgClR (R = CH3,
CH2Ph) gave the corresponding zirconium dialkyl comp-
lexes (Bn2Cyclam)ZrMe2 (2) and (Bn2Cyclam)Zr(CH2Ph)2
(3). 2 was isolated as an off-white solid in 63% yield upon
extraction in toluene; it has a low solubility in aromatic
solvents, and it is not stable at room temperature in solution,
as attested by the 1H NMR spectrum, where a singlet assigned
The synthesis of mixed alkyl-chloride complexes by reac-
tion of (Bn2Cyclam)ZrCl2 with one equivalent of each of the
above-mentioned alkylating agents was attempted, but it was
not possibletoisolatethe desiredmonosubstituted complexes.
(7) (a) Harney, M. B.; Keaton, R. J.; Fettinger, J. C.; Sita, L. R.
J. Am. Chem. Soc. 2006, 128, 3420–3432. (b) Wendt, O. F.; Bercaw, J. E.
Organometallics 2001, 20, 3891–3895.
(8) (a) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics
1998, 17, 308–321. (b) Schattenmann, F. J.; Schrock, R. R.; Davis, W. M.
Organometallics 1998, 17, 989–992.
ꢀ
(6) Munha, R. F.; Veiros, L. F.; Duarte, M. T.; Fryzuk, M. D.;
Martins, A. M. Dalton Trans. 2009, 7494–7508.

Article
Organometallics, Vol. 29, No. 17, 2010 3755
Once the alkyl-chloride complex is formed, the second sub-
stitution is apparently favored, generating a mixture of
mono- and bis(alkyl) complexes that could not be separated.
The NMR spectra of compounds 2-5 display an average
C2 symmetry in solution, similar to the dichloride precursor.
1
Thus, in the room-temperature H NMR spectra 10 reso-
nances can be identified, integrating to two protons each,
assigned to the Hanti and Hsyn methylenic protons of the macro-
cyclic ligand backbone. Given the complexity of the NMR
spectra and the overlap of these resonances, the signals
assigned to the benzylic protons of the ancillary ligand are
generally diagnostic due to the fact that they are shifted to
low field and show as a characteristic AB pattern (2JHH
=
14 Hz). The 13C{1H} NMR spectra confirm the average C2
symmetry in solution of the metal complexes, as six reso-
nances attributed to the ancillary ligand methylenic carbons
and one set of aromatic signals are observed. Two-dimen-
sional NMR experiments, such as COSY, NOESY, HMBC,
and HSQC, were conducted in order to assign all proton and
carbon resonances of the ancillary ligand set.
Figure 1. Solid-state molecular structure (ORTEP representation
shown at 50% thermal ellipsoid probability) of (Bn2Cyclam)-
Zr(nBu)2 (4) as determined by X-ray crystallography. Selected
˚
bond lengths (A) and angles (deg): Zr(1)-C(25) 2.340(5); Zr(1)-
C(29) 2.318(5); Zr(1)-N(1) 2.456(4); Zr(1)-N(2) 2.099(4); Zr(1)-
N(3) 2.474(4); Zr(1)-N(4) 2.093(4); C(25)-Zr(1)-C(29) 82.9(2);
N(2)-Zr(1)-N(4) 117.33(18); N(1)-Zr(1)-N(3) 133.81(13);
C(29)-Zr(1)-N(2) 93.57(18); C(29)-Zr(1)-N(4) 135.61(18);
C(25)-Zr(1)-N(4) 93.55(19); C(25)-Zr(1)-N(2) 136.09(18).
In the C6D6 1H NMR spectrum of (Bn2Cyclam)ZrMe2 (2),
the AB pattern corresponding to the benzylic protons of the
cyclam ligand is observed at 4.54 and 4.35 ppm, whereas the
signal that accounts for the zirconium-bound methyl groups
appears at 0.58 ppm as a singlet. The 13C{1H} NMR of 2
shows a distinct signal at 36.5 ppm that accounts for the two
methyl groups. The 1H NMR spectrum of (Bn2Cyclam)Zr-
(CH2Ph)2 (3) shows two signals at 4.37 and 3.51 ppm that
account for the diastereotopic benzylic protons of the ancil-
lary ligand; another AB system, with each doublet integrat-
The AB system corresponding to the benzylic protons of
the macrocyclic ligand in (Bn2Cyclam)Zr(CCPh)2 (5) shows
at 5.33 and 4.33 ppm. The phenylacetylenyl ligand is char-
acterized by a distinguishable set of aromatic resonances at
7.65 and 7.10-7.00 ppm. In relation to the 13C{1H} NMR
spectrum of the alkynyl ligand, besides one set of ortho, meta,
and para carbons, three signals at 105.5, 127.0, and 149.9
ppm, corresponding to quaternary carbons, are observed.
The resonances at 149.9 and 105.5 ppm are assigned to the
triple-bonded carbon atoms, with the former corresponding
to the zirconium-bonded carbon. The IR spectrum of 5
shows a characteristic band at 2069 cm-1, attributed to the
CtC stretching vibration mode, which is significantly lower
than that of free phenylacetylene (νCtC = 2110 cm-1).
Crystals of 4 were obtained from a cold diethyl ether
solution. An ORTEP representation with selected bond
lengths and angles is depicted in Figure 1. The macrocycle
attains a conformation where the four nitrogens define an
ing to two protons, is observed at 2.72 and 2.63 ppm (2JHH
=
9 Hz), corresponding to the methylenic protons of the benzyl
groups bonded to zirconium. In the 13C{1H} NMR spec-
trum, the latter are characterized by one resonance at 66.1
ppm corresponding to the methylenic carbons and three
distinguishable aromatic resonances at 150.6, 130.1, and
119.7 ppm, accounting for the ipso, ortho, and para carbons,
respectively; the peak for the meta carbons is obscured by the
deuterated solvent resonance. The chemical shifts of the
methylenic and ipso carbons of the benzyl ligand are con-
sistent with an η1-coordination mode.9 This was also con-
firmed by a gated-decoupled 13C NMR experiment, where a
1JCH of 124 Hz for the methylenic carbon was observed.10
The C6D6 1H NMR spectrum of (Bn2Cyclam)Zr(nBu)2 (4)
shows an AB pattern at 4.65 and 4.39 ppm that accounts for
the benzylic protons of the ancillary ligand. The two n-butyl
ligands are equivalent, as attested by the four signals identi-
fied in the 13C{1H} NMR spectrum. The methylene group
bonded to zirconium has two inequivalent protons identified
in the 1H NMR spectrum at 1.05 and 0.60 ppm, whereas the
remaining two methylene and methyl resonances are ob-
served at 2.20, 1.81, and 1.25 ppm, respectively. The 13C{1H}
NMR spectrum shows the broadening of one signal at 55.9
ppm, assigned to the [C3] chain of the macrocycle; this may
hint at a fluxional process and was already observed in
cyclam-based zirconium complexes, but low-temperature
NMR experiments only led to further broadening of the peaks.
˚
average plane with the metal center sitting 1.0280(22) A
above it. The bond distances of the macrocyclic nitrogen
˚
atoms to zirconium—2.093(4) and 2.099(4) A for the Zr-
˚
Namido and 2.456(4) and 2.474(4) A for the Zr-Namine—are
within the expected values11 and compare to previously
described complexes incorporating this macrocyclic ligand.
The geometry around zirconium is best described as trigonal
prismatic with the two n-butyl ligands cis to each other. The
˚
Zr-C bond lengths of 2.318(5) and 2.340(5) A are within the
expected values for alkyl ligands in Zr(IV) metal centers.12
The C(25)-Zr-C(29) angleof82.9(2)° issimilartotheCl(1)-
Zr-Cl(2) angle of the dichloride precursor (84.76(3)°) and
other related zirconium complexes, indicating that there is no
steric hindrance caused by the n-butyl substituents.
Crystals of 3 suitable for X-ray diffraction were obtained
from a concentrated toluene solution, and an ORTEP repre-
sentation is depicted in Figure 2 with selected bond lengths
(9) (a) Kirillov, E.; Lavanant, L.; Thomas, C.; Roisnel, T.; Chi, Y.;
Carpentier, J.-F. Chem.—Eur. J. 2007, 13, 923–935. (b) Chen, Y.-X.;
Marks, T. J. Organometallics 1997, 16, 3649–3657.
(10) (a) Bochmann, M.; Lancaster, S. J. Organometallics 1993, 12,
633–640. (b) Jordan, R. F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D.
Organometallics 1990, 9, 1539–1545. (c) Mintz, E. A.; Moloy, K. G.; Marks,
T. J.; Day, V. W. J. Am. Chem. Soc. 1982, 104, 4692–4695.
(11) (a) Li, Y.; Turnas, A.; Ciszewski, J. T.; Odom, A. L. Inorg. Chem.
2002, 41, 6298–6306. (b) O'Connor, P. E.; Morrison, D. J.; Steeves, S.;
Burrage, K.; Berg, D. J. Organometallics 2001, 20, 1153–1160.
(12) (a) Tonzetich, Z. J.; Lu, C. C.; Schrock, R. R.; Hock, A. S.;
Bonitatebus, P. J., Jr. Organometallics 2004, 23, 4362–4372. (b) Mehr-
khodavandi, P.; Schrock, R. R.; Bonitatebus, P. J., Jr. Organometallics 2002,
21, 5785–5798.

ꢀ
Munha et al.
3756 Organometallics, Vol. 29, No. 17, 2010
conformations to be attained, depending on the ligands that
occupy the remaining coordination positions.
Reactivity of the Zirconium Alkyl Complexes. The afore-
mentioned instability of (Bn2Cyclam)ZrMe2 (2) in solution
led us to investigate this reaction further. Heating a C6D6
solution of 2 at 70 °C over a two-hour period gave a new C2-
symmetric species for which the 1H NMR spectrum does not
show any resonance attributed to the zirconium-bound methyl
groups and also displays a singlet at 0.16 ppm corresponding
to dissolved methane. The 10 resonances, integrating to two
protons each, assigned to the ligand backbone methylenic
protons display a distinct pattern from starting complex 2. In
addition, the signals corresponding to the benzylic protons
of the ligand appear at 4.81 and 3.60 ppm as an AB system
(4.54 and 4.35 ppm in 2). Integration of the aromatic region
of the spectrum shows only eight protons, including a new
resonance at 8.20 ppm that integrates to two protons. On the
basis of the loss of methane and the observation of only eight
aromatic protons, the new species was assigned as ((C6H4CH2)2-
Cyclam)Zr (6) (Scheme 1), resulting from C-H activation of
the ortho protons of the benzyl groups of the ancillary
ligand.15 Ortho-metalation was confirmed by the 13C{1H}
NMR spectrum; the signal attributed to the aromatic carbon
bound to zirconium is observed at 188.5 ppm, and as
expected, C(2) and C(6) are shifted to a lower field at 151.1
and 140.8 ppm, respectively (see Scheme 1 for labeling). In
addition, six resonances corresponding to the methylenic
carbons are observed between 63.3 and 26.4 ppm. Full NMR
characterization of 6 was based on 13C APT, HSQC, HMBC,
and COSY experiments.
Figure 2. Solid-state molecular structure (ORTEP representation
shown at 50% thermal ellipsoid probability) of (Bn2Cyclam)Zr-
(CH2Ph)2 (3) as determined by X-ray crystallography. Selected
˚
bond lengths (A) and angles (deg): Zr(1)-C(25) 2.3606(19);
Zr(1)-C(32) 2.3902(17); Zr(1)-N(1) 2.4465(15); Zr(1)-N(2)
2.1144(15); Zr(1)-N(3) 2.4611(15); Zr(1)-N(4) 2.0951(16); C(25)-
Zr(1)-C(32) 86.47(7); C(26)-C(25)-Zr(1) 106.90(12); C(33)-
C(32)-Zr(1) 103.18(11); N(2)-Zr(1)-N(4) 106.23(6); N(1)-
Zr(1)-N(3) 156.28(5); C(32)-Zr(1)-N(2) 151.29(6); C(32)-
Zr(1)-N(4) 89.70(6); C(25)-Zr(1)-N(4) 148.93(6); C(25)-
Zr(1)-N(2) 91.15(6).
and angles. The solid-state structure shows the expected cis
coordination of the two benzyl ligands and the metal center
perched on the macrocyclic cavity, as observed in all cyclam-
based zirconium complexes reported to date. However, in 3
the geometry around the metal center is best described as
distorted octahedral, with N(1), N(3), N(4), and C(25)
occupying a slightly twisted square plane displaying a com-
bined equatorial angle of 364.1° and N(2) and C(32) occupy-
ing the axial positions, with an N(2)-Zr-C(32) angle of
151.29(6)°. This result contrasts with previously described
complexes incorporating this ligand set, as hitherto we have
observed that the coordination geometries around the metal
center vary between trigonal prismatic and tetrahedral.
An increase in the N(1)-Zr-N(3) angle from 133.81(13)°
in 4 to 156.28(5)° in 3 is observed; this change is accompanied
by a decrease in the N(2)-Zr-N(4) angle from 117.33(18)°
in 4 to 106.23(6)° in 3. Thus, in the case of 3 the macrocycle
has such a conformational twist that it is not possible to
define an average plane containing the four nitrogen donors.
Interestingly, the C(25)-Zr-C(32) angle of 86.47(7)° shows
that the new conformation of the ancillary ligand is not
accompanied by a change of the relative positions of the two
benzyl ligands, as this value compares to both 4 and the
dichloride precursor. The Zr-CH2-Cipso angles at 106.90(12)°
and 103.18(11)° are in accordance with an η1-coordination of
the benzyl ligands, although the values are lower than expec-
ted for an sp3-hybridized carbon, suggesting a weak Zr-Cipso
Under the same reaction conditions, (Bn2Cyclam)Zr(nBu)2
(4) gives 6 and n-butane, which is identified in the 1H NMR
spectrum by two resonances at 1.25 and 0.85 ppm. Con-
versely, heating at 70 °C a C6D6 solution of (Bn2Cyclam)-
Zr(CH2Ph)2 (3) over a period of 12 h gives only a small
amount of 6; however, mild reflux of the benzene solution of
3 for 72 h resulted in complete conversion to 6. The ortho-
metalation reaction was not observed for (Bn2Cyclam)-
Zr(CCPh)2 (5) upon reflux in C6D6. This result is consistent
with the higher acidity of sp-hybridized carbons when com-
pared to sp3-carbon ligands.
The reaction of (Bn2Cyclam)ZrMe2 (2) with two equiva-
lents of HCtCPh was studied by NMR in C6D6 solution. At
room temperature the reaction proceeds slowly with a yield
of about 50% of 5 after 18 h. Heating the solution at 50 °C
leads to the quantitative formation of 5 in 4 h. Under these
reaction conditions, its formation may result from the direct
reaction of 2 with HCtCPh or, alternatively, from the re-
action of 6, formed in situ from the ortho-metalation reaction
described above, with HCtCPh. To evaluate whether this
reaction may be considered an alternative path for the
formation of 5, the reaction of 6 with HCtCPh in C6D6
was performed. The addition of one equivalent of HCtCPh
at room temperature led to the formation of 5 alongside a
new species that was identified as 7 (Scheme 1) in a 1:2.5
ratio. The addition of a second equivalent of HCtCPh to a
solution containing 5, 6, and 7 results in the quantitative
formation of 5 after heating at 50 °C for 4 h. The proton
NMR spectrum of 7 reveals a C1-symmetric species. The
macrocyclic protons give rise to 20 resonances ranging from
interaction.13 The Zr-Namido (2.0915(16) and 2.1144(15) A)
˚
˚
and the Zr-C bond lengths (2.3606(19) and 2.3902(17) A)
are within the observed values for other benzyl zirconium
complexes.14 Although the Zr-Namine bonds at 2.4465(15)
and 2.4611(15) A are somewhat elongated, they are compar-
˚
able to previously reported hexacoordinated zirconium com-
plexes incorporating this ligand.
Overall, the analysis of the solid-state molecular structures
of 3 and 4 confirm what had been postulated before: the
saturated ancillary ligand backbone allows for different
(13) (a) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Organometallics 1998,
17, 846–853. (b) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T. R.; Floriani,
C.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1995, 117, 5801–5811.
(14) Kirillov, E.; Roisnel, T.; Razavi, A.; Carpentier, J.-F. Organo-
metallics 2009, 28, 5036–5051.
(15) (a) Boehme, U.; Thiele, K. H. Z. Anorg. Allg. Chem. 1993, 619,
1488–1490. (b) Chmielewski, P. J.; Durlej, B.; Siczek, M.; Szterenberg, L.
Angew. Chem., Int. Ed. 2009, 48, 8736–8739.

Article
Organometallics, Vol. 29, No. 17, 2010 3757
Scheme 2
4.23 to 0.82 ppm. The methylenic protons of the macrocyclic
benzyl substituents appear as two sets of AB systems, corres-
ponding to a zirconium-bound benzyl group and to the non-
ortho-metalated benzyl. The coordination of the aromatic
ring to the metal is confirmed by a doublet at 8.97 ppm assi-
gned to the new ortho proton and by the 13C resonances at
188.3, 150.0, and 142.2 ppm, corresponding to C(1), C(2),
and C(6), respectively (see Scheme 1 for labeling).
The reaction of (Bn2Cyclam)Zr(CH2Ph)2 (3) with one
equivalent of B(C6F5)3 in d2-dichloromethane affords a cationic
species with a coordinated η2-benzyl, [(Bn2Cyclam)Zr(η2-
CH2Ph)][PhCH2B(C6F5)3] (8) (Scheme 2). The presence of a
established through the Cipso and not the aromatic CdC
bond.17b,c,19 The macrocycle proton and carbon NMR
resonances are consistent with an average C2 symmetry,
suggesting an exchange processes between two possible
conformations (Scheme 2). Low-temperature NMR studies
did not slow the fluxional process, and only broadening of all
proton resonances was observed.
The role of the solvent was investigated, and while carry-
ing out the reaction on a noncoordinating solvent such as d8-
toluene produced the same outcome, the change to d8-THF
gives the solvent-stabilized cation [(Bn2Cyclam)Zr(CH2Ph)-
(THF)][PhCH2B(C6F5)3] (9) (Scheme 2). The proton and
carbon NMR spectra of 9 at room temperature are consis-
tent with an average C2-symmetry complex, implying a rapid
exchange between coordinated and free solvent. The 11B
and 19F NMR spectra confirm the formation of a cationic
species; however in 9, the zirconium-bound benzyl group is
η1-coordinated, as attested by the chemical shift of the ipso
carbon at 147.1 ppm (similar to 3) and a 1JCH of 125 Hz corr-
esponding to the resonance of the methylenic carbon.
The reaction of one equivalent of B(C6F5)3 with 2 was
carried out at room temperature in CD2Cl2. The 19F NMR
spectrum reveals a set of signals with a Δ(δFpara - δFmeta) of
2.7 ppm and a resonance at -14.9 ppm in the 11B NMR
spectrum, suggesting the formation of the cationic complex [(Bn2-
Cyclam)ZrMe(CD2Cl2)][B(C6F5)3(CH3)] (10) (Scheme 3).16a
Abstraction of a methyl group from 2 by B(C6F5)3 is also
based on the observation of a singlet in the 1H NMR
spectrum at 0.49 ppm that shows a correlation to a carbon
resonance at 11.0 ppm in the HSQC spectrum and is assigned
to CH3B. These data and a peak in the mass spectrum with
m/z of 526.9 confirm the formation of [B(C6F5)3(CH3)]-,
supporting the formulation of 10. The AB system due to the
methylenic protons of the cyclam benzyl substituents is
shifted to high field (4.03 and 3.77 ppm) in comparison to
the parent complex (4.54 and 4.26 ppm). This effect is
symptomatic of a cationic complex, as it is observed in all
cations regardless of the solvent that stabilizes the metal
center. Compound 10 is highly stable in CD2Cl2 solution, as
the NMR spectra do not reveal any decomposition over
several weeks at room temperature. The proton and carbon
NMR spectra of 10 at room temperature are consistent with
a metal complex with an average C2 symmetry resulting from
an exchange between free and coordinated solvent. On cooling
the solution, broadening and overlapping of the resonances
free tetrahedral boron anion is supported by a Δ(δFpara
-
δFmeta) lower than 3 ppm (2.9 ppm) in the 19F NMR spectrum
and a single resonance at -12.9 ppm in the 11B spectrum.16 In
the 1H NMR spectrum, the signals corresponding to Zr-CH2Ph
appear as an AB system shifted downfield in comparison to
its precursor (3.08 and 2.70 ppm in 8 vs 2.41 and 2.35 ppm in
3), as reported for other cationic species.17 The methylene
protons bonded to boron give rise to one singlet at 2.86 ppm.
The assignment of this resonance was confirmed by a 19F-
1H HOESY experiment that showed a cross-peak with the
ortho-F resonance of the C6F5 groups. The B-CH2Ph carbon
resonance was not observed in the 13C spectrum but was
identified through a 1H-13C HSQC experiment at 32.0 ppm.
The identification of η2-benzyl coordination in 8 is based on
a gated-decoupled 13C NMR spectrum, where an increase of
1
the JCH of the resonance corresponding to the methylenic
carbon from 124 Hz in 3 to 139 Hz is observed.18 Moreover,
the high-field shift observed for the ipso carbon of the benzyl
group (139.4 ppm in 8 vs 150.8 ppm in 3) suggests that the
interaction between the zirconium and the aromatic ring is
(16) (a) Horton, A. D.; de With, J. Chem. Commun. 1996, 1375–1376.
(b) Shafir, A.; Arnold, J. Organometallics 2003, 22, 567–575. (c) Yang, X.;
Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10015–10031.
(d) Pellecchia, C.; Grassi, A.; Zambelli, A. J. Mol. Catal. 1993, 82, 57–65.
(17) (a) Amor, F.; Butt, A.; du Plooy, K. E.; Spaniol, T. P.; Okuda, J.
Organometallics 1998, 17, 5836–5849. (b) Horton, A. D.; de With, J.; van
der Linden, A. J.; van de Weg, H. Organometallics 1996, 15, 2672–2674.
(c) Bochmann, M.; Lancaster, S. J.; Hursthouse, M. B.; Malik, K. M. A.
Organometallics 1994, 13, 2235–2243.
(18) (a) Dryden, N. H.; Legzdins, P.; Phillips, E. C.; Trotter, J.; Yee,
V. C. Organometallics 1990, 9, 882–884. (b) Lee, L.; Berg, D. J.; Bushnell,
G. W. Organometallics 1997, 16, 2556–2561. (c) Jordan, R. F.; LaPointe,
R. E.; Bajgur, C. S.; Echols, S. F.; Willett, R. J. Am. Chem. Soc. 1987, 109,
4111–4113.
(19) Scott, M. J.; Lippard, S. J. Organometallics 1998, 17, 1769–1773.

ꢀ
Munha et al.
3758 Organometallics, Vol. 29, No. 17, 2010
Scheme 3
the precipitate did not dissolve completely, the 19F NMR
spectrum reveals the formation of [B(C6F5)3(CH3)]-, sugges-
ting that a solvent-stabilized zirconium cation [(Bn2Cyclam)-
ZrMe(Tol)][B(C6F5)3(CH3)] (13) is present in solution. As
pointed out earlier, the formation of a cationic compound is
also revealed by the AB system assigned to the benzylic
group that is shifted upfield (3.32 and 3.17 ppm vs 4.53 and
4.35 ppm in 13 and 2, respectively). The proton and carbon
NMR spectra of the macrocycle are diagnostic of an average
C2 symmetry. [(Bn2Cyclam)ZrMe(Tol)][B(C6F5)3(CH3)] is
much less stable than the other solvent-stabilized cations
obtained in dichloromethane and THF; along with methane
formation, a new complex starts to form in solution. The 19F
NMR of this sample after one week at room temperature
shows the presence of 13, and a new species that was identi-
fied as (Bn2Cyclam)Zr(C6F5)(CH2B(C6F5)2) (14) formed
upon methane elimination (see DFT results below). The
identification of 14 was based on characteristic 19F and 11
B
NMR resonances. In the 19F NMR spectrum there are two
sets of resonances corresponding to two different C6F5 envi-
ronments: the one of the Zr-(C6F5) group appears at -119.0,
-150.4, and -158.9 ppm, whereas the signals assigned to the
boron-bound C6F5 groups appear at -135.6, -160.6, and
-164.7 ppm. The 11B NMR spectrum shows a resonance at
86.6 ppm; this is in accordance with the expected trigonal-
planar geometry around boron. The ZrCH2B group was
identified in the 1H NMR spectrum by a signal at 5.80 ppm,
which shows a correlation to a carbon at 100.5 ppm.21 In
summary, taking into account the existence of (i) two sets of
resonances in the 19F NMR, (ii) a trigonal-planar geometry
around boron, which is bound to a methylenic group, and
(iii) the identification of signals corresponding to a Zr-CH2B
attributed to the macrocycle did not allow a limiting spec-
trum until -80 °C.
On the other hand, the reaction of B(C6F5)3 with (Bn2-
Cyclam)ZrMe2 (2) was carried out in a sealed NMR tube by
addition of one equivalent of the borane to a frozen CD2Cl2
solution of the complex, and the reaction was followed by
19F, 1H, and 11B NMR spectroscopy. At -80 °C the 1H NMR
spectrum is best described as a set of several broad reso-
nances. Upon warming, these start to resolve, and at -20 °C
the 19F and 11B NMR spectra indicate the formation of two
species. The signals corresponding to the major product are
consistent with a cationic species having the counterion
[B(C6F5)3(CH3)]-, as described for 10. The minor product
of this reaction is characterized by a signal at -4.2 ppm in the
11B spectrum and a set of resonances in the 19F spectrum with
Δ(δFpara - δFmeta) of 3.6 ppm. The NMR data associated
with this latter species hint at the presence of a bridging Zr-
CH3-B(C6F5)3 moiety, corresponding to the zwitterionic
[(Bn2Cyclam)ZrMe(CH3B(C6F5)3) (11); over time 11 con-
verts to 10.4a,20
1
group and methane in the H NMR, all data support the
formulation of this compound as 14.
DFT Calculations. The reaction of the dimethyl complex
[(Bn2Cyclam)2ZnMe2] (2) withB(C6F5)3 was studied by means
of DFT calculations22 (see Computational Details) and the
calculated free energy profiles are presented in Figures 3 and 4.
The mechanism represented in Figure 3 starts with the pair
of reagents, 2 and B(C6F5)3, labeled A in the profile. In A,
two independent molecules are present with a B-CMe sepa-
˚
ration of 3.58 A. In the first step of the mechanism one
methyl is transferred from zirconium to boron, resulting in
an inner-sphere ion pair,23 [{(Bn2Cyclam)ZrMe}þ{(CH3)-
B(C6F5)3}-] (B). The Zr-CMe distance in B (2.76 A) is only
˚
The reaction of 2 with B(C6F5)3 was also done in d8-THF.
The formation of the solvent-stabilized cationic species
[(Bn2Cyclam)ZrMe(THF)][B(C6F5)3(CH3)] (12) was confirmed
by 11B and 19F NMR spectroscopy. The resonance assigned
to the zirconium-bound methyl group appears at 0.23 ppm as
a singlet in the 1H NMR spectrum, whereas the signal corres-
ponding to the boron-bound methyl group appears at 0.51 ppm
as a broad peak. In the 13C{1H} NMR spectrum, the latter is
observed at 10.2 ppm, while the former is characterized by a
resonance at 41.3 ppm.
The addition of one equivalent of B(C6F5)3 to 2 was
performed in d8-toluene to assess the role of a less coordinating
solvent. Upon mixing of the reagents and heating the NMR
tube to -80 °C, a yellow oil precipitates out of solution. The
NMR spectra at this temperature are inconclusive, as only
weak signals are observed. At room temperature, although
slightly longer than the corresponding distances in the
zwitterionic species taken from the Cambridge Structural
Data Base,24 which spread over a range of 2.47-2.67 A. The
˚
long Zr-CMe distance in B is associated with a weak inter-
action, as denoted by a Wiberg index (WI)25 of 0.16. It
should be noticed that B corresponds to the minor species
(21) (a) Wondimagegn, T.; Xu, Z.; Vanka, K.; Ziegler, T. Organo-
metallics 2004, 23, 3847–3852. (b) Gauvin, R. M.; Mazet, C.; Kress, J.
J. Organomet. Chem. 2002, 658, 1–8. (c) Yue, N.; Hollink, E.; Guerin, F.;
Stephan, D. W. Organometallics 2001, 20, 4424–4433. (d) Woodman, T. J.;
Thornton-Pett, M.; Hughes, D. L.; Bochmann, M. Organometallics 2001, 20,
4080–4091. (e) Woodman, T. J.; Bochmann, M.; Thornton-Pett, M. Chem.
Commun. 2001, 329–330. (f) Karl, J.; Erker, G.; Froehlich, R. J. Am. Chem.
Soc. 1997, 119, 11165–11173.
(22) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett.
1989, 157, 200–206.
(23) (a) Clot, E. Eur. J. Inorg. Chem. 2009, 2319–2328. (b) Song, F.;
Lancaster, S. J.; Cannon, R. D.; Schormann, M.; Humphrey, S. M.; Zuccac-
cia, C.; Macchioni, A.; Bochmann, M. Organometallics 2005, 24, 1315–
1328. (c) Macchioni, A. Chem. Rev. 2005, 105, 2039–2073.
(24) Allen, F. H. Acta Crystallogr. 2002, B58, 380.
(20) Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen, M.-C.;
Roberts, J. A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448–1464.

Article
Organometallics, Vol. 29, No. 17, 2010 3759
absence of a solvent molecule, as is the case in the model used
for the calculations. In solution, the anion is expected to be
readily displaced by the solvent, leading to a solvent-stabi-
lized cationic complex. At the transition state, TSAB, the
methyl transfer from Zr to B is only incipient. The Zr-CMe
˚
bond is only slightly longer (2.42 A) and weaker (WI = 0.42)
˚
than the corresponding one in the reagent A (dZr-C = 2.32 A,
WIB-C = 0.57), and it is still far from the values observed in
the ion pair B (see above). Simultaneously, the new B-CMe
bond is only starting to be formed, as shown by the long
˚
boron-carbon distance (2.43 A) and by the WI of 0.33,
which alludes to a weak interaction. The free energy barrier
calculated for the first step (4.6 kcal/mol) denotes an easy
process that is also favorable from the thermodynamic point
of view (ΔG = -12.5 kcal/mol).
In the second step of the mechanism there is methane
elimination from the ion pair B with formation of an
unsaturated complex, [(Bn2Cyclam)Zr{(CH2)B(C6F5)3}], as
shown in C. In the former complex the coordination of the
borate is accomplished by the methylene C atom, as revealed
by the corresponding bond distance and Wiberg index (dZr-C
=
˚
2.18 A, WI = 0.80), but it is further reinforced by a Zr-F
interaction and by a C-H agostic bond,26 in order to
compensate for a coordinatively unsaturated Zr(IV) metal
center. The Zr-F bond in this complex corresponds to a
Figure 3. Free energy profile calculated (PBE1PBE) for methane
elimination from [(Bn2Cyclam)2ZnMe2] (2) and B(C6F5)3. The
minima and the transition states were optimized, and the corres-
ponding structures are represented with the relevant parts high-
lighted, in each step. Free energy values (kcal/mol) are referred
to the pair of reactants (A), and energy barriers are presented in
italics.
˚
moderately strong interaction (dZr-F = 2.56 A, WI = 0.17),
and the C-H agostic bond is characterized by a short Zr-H
distance (2.24 A) and a Wiberg index of 0.09.
˚
At the transition state TSBC, both the Zr-CMe bond cleav-
age (dZr-C = 2.55 A, WI = 0.35) and the formation of the
˚
˚
new C-H bond (dC-H = 1.37 A, WI = 0.49) are already
evident; yet these values are still far from the ones existing in
C, where methane is displaced from the metal (dZr-C = 7.47
˚
A) and formation of the C-H bond is accomplished (dC-H
=
˚
1.09 A, WI = 0.93). More importantly, the H transfer from
B(C6F5)3(CH3)- to CH3 is a process assisted by the metal,
since in TSBC the H atom involved in the transfer is weakly
˚
bonded to Zr, as shown by a short Zr-H length of 1.98 A and
a significant interaction with WIZr-H = 0.10. The second
step of the calculated mechanism is thermodynamically
favored (ΔG = -5.8 kcal/mol) and presents a moderate
energy barrier of 26.1 kcal/mol, which, being the highest of
the entire path, indicates methane elimination as the reaction
rate-limiting step.
The final step of the mechanism corresponds to an in-
tramolecular rearrangement of complex [(Bn2Cyclam)Zr-
{(CH2)B(C6F5)3}] (D) giving the final product (Bn2Cyclam)-
Zr(C6F5)(CH2B(C6F5)2) (E). The free energy profile associated
with this process is depicted in Figure 4. It should be high-
lighted that the difference between C and D is that in the
former there is a methane molecule, while the latter only
comprises the complex [(Bn2Cyclam)Zr{(CH2)B(C6F5)3}].
In the process depicted in Figure 4, the system goes from
one unsaturated complex (D) to a six-coordinated complex
with two new anionic ligands, C6F5- and CH2B(C6F5)2-. In
other words, it corresponds to the transfer of one penta-
fluorophenyl group from boron to the metal. In this com-
Figure 4. Free energy profile calculated (PBE1PBE) for the
formationof[(Bn2Cyclam)Zr(C6F5)CH2B(C6F5)2] (E). The minima
and the transition state were optimized, and the corresponding
structures are represented with the relevant parts highlighted.
Free energy values (kcal/mol) are referenced to the reactant
[(Bn2Cyclam)Zr{B(C6F5)3(CH2)}] (D).
(11) that was detected in the 19F NMR spectrum when the
reaction was carried out in CD2Cl2 at low temperature, and it
can be seen as the precursor of complex 10, 12, or 13 in the
˚
pound, the new Zr-C bond distances are 2.34 and 2.35 A, for
Zr-CC F and Zr-CCH B(C F ) , respectively, and the corres-
ponding Wiberg indices are 0.49 and 0.48, respectively. At the
6
5
2
6 6 2
transition state, TSD-E, B-CC F bond breaking is manifested
6
5
(25) (a) Wiberg, K. B. Tetrahedron 1968, 24, 1083–1096. (b) Wiberg
indices are electronic parameters related to the electron density between
atoms. They can be obtained from a natural population analysis and provide
an indication of the bond strength.
(26) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad.
Sci. U. S. A. 2007, 104, 6908-6914.

ꢀ
Munha et al.
3760 Organometallics, Vol. 29, No. 17, 2010
˚
by a weak B-CC F interaction (dB-C = 2.00 A, WI = 0.52).
Experimental Section
6
5
Conversely, formation of the new Zr-CC F is well advanced,
with a Zr-CC F distance of 2.69 A and a Wiberg index of
0.24, indicating a significant interaction. It should be noted
6
5
˚
General Considerations. Unless otherwise stated, all manipu-
lations were performed under an atmosphere of dry oxygen-
free dinitrogen by means of standard Schlenk and glovebox
6
5
that until the formation of the new Zr-CC F bond the metal
6
5
˚
techniques. Solvents were predried using 4 A molecular sieves,
refluxed over sodium-benzophenone (diethyl ether, toluene,
THF) or CaH2 (n-hexane) under an atmosphere of N2, and
center remains unsaturated, and thus, at the transition state
TSD-E, where this bond is not yet completely formed, there is
one Zr-F interaction, similar to one present in D. This
interaction involves one F atom of a pentafluorophenyl
group that remains bonded to boron and stabilizes TSD-E
by providing extra electron density to the electron-deficient
Zr(IV) center. The reaction from D to E is favorable from the
thermodynamic point of view (ΔG = -6.0 kcal/mol) and has
an accessible energy barrier of 16.7 kcal/mol.
˚
collected by distillation. Deuterated solvents were dried with 4 A
molecular sieves and freeze-pump-thaw degassed prior to use.
Proton and carbon NMR spectra were recorded in a Bruker
AVANCE 300 or 400 MHz, at 296 K unless stated otherwise,
referenced internally to residual proton-solvent (1H) or solvent
(13C) resonances, and reported relative to tetramethylsilane
ꢀ
(0 ppm). Elemental analyses were obtained from Laboratorio
de Analises do IST, Lisbon, Portugal, and were also performed
ꢀ
The calculations indicate a plausible path for the formation
of (Bn2Cyclam)Zr(C6F5)(CH2B(C6F5)2) (E) with methane
elimination as the rate-determining step. E corresponds to
species 14 and was identified by NMR as the final product of
the reaction of the dimethyl complex (Bn2Cyclam)2ZrMe2
(2) with B(C6F5)3.
in the departmental facility of the University of British Colum-
bia. The compounds (Bn2Cyclam)ZrCl25b and B(C6F5)327 were
prepared according to described procedures. All other reagents
were commercial grade and used without further purification.
(Bn2Cyclam)Zr(Me)2 (2). To a THF suspension of (Bn2-
Cyclam)ZrCl2 (0.31 g, 0.58 mmol) at -10 °C was slowly added
0.54 mL of a MgClMe solution (2.18 M in THF). After a while
the suspension completely dissolved and the light yellow solu-
tion started to become colorless. The mixture was allowed to
come to room temperature, and it reacted for further 3 h. The
solvent was evaporated and the light beige residue was extracted
with 15 mL of toluene. To the toluene extract was added 0.2 mL
of dioxane, and the suspension was filtered and taken to dryness.
The solid was washed with cold hexanes and stored at -20 °C
Concluding Remarks
In summary, a series of zirconium alkyl complexes that
incorporate a saturated tetraazamacrocycle ancillary ligand
were prepared. Variation on the alkyl ligands induces differ-
ent geometry around the metal center; such changes are
dictated by the steric bulk of the ligands that occupy the
remaining coordination positions and are intimately related
to the flexibility of the dianionic cyclam ligand. This beha-
vior has already been observed in analogous complexes
supported by this ligand set.
1
(0.16 g, 63%). H NMR (C6D6, 300.1 MHz, 296 K): δ (ppm)
7.20-7.10 (br, 10H, H-Ph), 4.54 (d, 2H, 2JHH = 14 Hz, PhCH2N),
4.35 (d, 2H, 2JHH = 14 Hz, PhCH2N), 4.00 (m, 2H, [C3]NCH2),
3.62 (m, 2H, [C2]NCH2), 2.91 (m, 2H, [C3]NCH2), 2.75-2.54
(overlapping, 6H total, 2H, [C3]NCH2, 4H, [C2]NCH2), 2.26
(m, 2H, [C3]NCH2), 2.15 (m, 2H, [C2]NCH2), 1.49 (m, 2H, CH2-
CH2CH2), 1.02 (m, 2H, CH2CH2CH2), 0.58 (s, 6H, ZrCH3).
13C{1H} NMR (C6D6, 75.5 MHz, 296 K): δ (ppm) 133.0 (i-Ph),
132.7 (o-Ph), 128.1, 127.9 (m-Ph and p-Ph), 56.5 (PhCH2N), 55.9
([C3]NCH2),52.3([C2]NCH2),50.9([C3]NCH2),49.9([C2]NCH2),
36.5 (ZrCH3), 24.8 (CH2CH2CH2). 1H NMR (CD2Cl2, 400.1
MHz, 296 K): δ (ppm) 7.38-7.34 (overlapping, 10H, H-Ph),
4.55(d, 2H, 2JHH =14Hz, PhCH2N), 4.26 (d, 2H, 2JHH = 14Hz,
PhCH2N), 3.84-3.72 (overlapping, 4H total, 2H, [C3]NCH2,
2H, [C2]NCH2), 3.05-2.96 (overlapping, 6H total, 2H, [C3]NCH2,
4H, [C2]NCH2), 2.77 (m, 2H, [C3]NCH2), 2.49-2.39 (overlapp-
ing, 4H total, 2H, [C3]NCH2, 2H, [C2]NCH2), 1.82 (m, 2H,
CH2CH2CH2), 1.34 (m, 2H, CH2CH2CH2), -0.14(s, 6H, ZrCH3).
13C{1H} NMR (CD2Cl2, 100.6 MHz, 296 K): δ (ppm) 133.3
(i-Ph), 132.9 (o-Ph), 128.6 (p-Ph), 128.5 (m-Ph), 56.9 (PhCH2N),
55.9 ([C3]NCH2), 52.3 ([C2]NCH2), 50.7 ([C3]NCH2), 50.3
([C2]NCH2), 34.5 (ZrCH3), 24.8 (CH2CH2CH2). Satisfactory
elemental analysis was not possible due to thermal instability of
the product.
The stability of the alkyl complexes was assessed, and it
was found that C-H activation of the benzyl groups of the
macrocycle occurs with concomitant alkane elimination; this
process occurs both in solution and in the solid state. The
bis(ortho-metalated) complex reacts with HCCPh to regen-
erate the ancillary ligand and two phenylacetylide ligands.
These results indicate that the ortho-metalation reaction and
the Zr-C bond formation may be reversible and raise the
expectation of exploring both the reactivity of the ortho-
metalated species and its potential in catalytic processes.
Reactions of the bis(alkyl) complexes with B(C6F5)3 gene-
rate cationic derivatives upon abstraction of one alkyl ligand.
The structure and coordination around the zirconium metal
center are solvent and alkyl-ligand dependent. This is well
illustrated in two examples. In the zirconium-benzyl cation,
the benzyl ligand is η2-ligated in noncoordinating solvents,
whereas in the presence of a coordinating solvent such as
THF it displays the η1-coordination mode. In the zirconium-
methyl cation case, whereas it is stable in dichloromethane or
THF solutions, it shows a different behavior in toluene. In
the latter case, the transfer of a pentafluoro group to zirco-
nium is observed. This rearrangement involves the cleavage
of one B-C6F5 bond and the C-H activation of a bridging
methyl group of an intermediate zwitterionic complex. DFT
studies provided a plausible mechanism for this reaction,
indicating methane elimination as the rate-determining step.
Preliminary studies with dichloro complexes supported by
this ligand set, in the presence of MAO in toluene, have
shown them to be moderately active as precatalysts for the
polymerization of ethylene. Motivated by the stability of the
cationic complexes in solution, we are now interested in
evaluating their competence in the polymerization of olefins.
(Bn2Cyclam)Zr(CH2Ph)2 (3). To a THF suspension of (Bn2-
Cyclam)ZrCl2 (0.39 g, 0.70 mmol) at -10 °C was slowly added
0.88 mL of a MgClCH2Ph solution (1.64 M in diethyl ether). The
suspension completely dissolved after 1 h. The mixture was
allowed to come to room temperature, and it reacted for a
further 3 h. The solution was taken to dryness, and the yellow
residue was extracted with 10 mL of toluene. The toluene extract
was concentrated, and 0.2 mL of dioxane was added. The sus-
pension was filtered and evaporated to dryness. The yellow solid
obtained in 80% yield (0.36 g) was stored at -20 °C. Crystals
suitable for X-ray diffraction were obtained from a concen-
trated toluene solution. 1H NMR (C6D6, 400.1 MHz, 296 K): δ
(ppm) 7.44 (m, 4H, o-PhCH2Zr), 7.29 (m, 4H, m-PhCH2Zr),
7.18-7.11 (overlapping, 6H total, 4H, m-PhCH2N, 2H, p-PhCH2N),
(27) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2, 245–250.

Article
Organometallics, Vol. 29, No. 17, 2010 3761
7.01-6.92 (overlapping, 6H total, 2H, p-PhCH2Zr, 4H,
o-PhCH2N), 4.37 (d, 2H, 2JHH = 14 Hz, PhCH2N), 3.51 (d, 2H,
2JHH = 14 Hz, PhCH2N), 3.05 (m, 2H, [C3]NCH2), 2.87 (over-
lapping, 6H total, 2H, [C3]NCH2, 4H, [C2]NCH2), 2.72 (d, 2H,
2JHH = 9 Hz, PhCH2Zr), 2.63 (d, 2H, 2JHH = 9 Hz, PhCH2Zr),
2.38 (m, 4H, [C3]NCH2), 2.19 (m, 2H, CH2CH2CH2), 2.08 (m,
2H, [C2]NCH2), 2.00 (m, 2H, [C2]NCH2), 1.48-1.37 (br, 2H,
CH2CH2CH2). 13C{1H} NMR (C6D6, 100.6 MHz, 296 K): δ
(ppm) 150.6 (i-PhCH2Zr), 132.9 (i-PhCH2N), 132.7 (o-PhCH2N),
130.1 (o-PhCH2Zr), overlapping with C6D6 (m-PhCH2N,
p-PhCH2N, m-PhCH2Zr), 119.7 (p-PhCH2Zr), 66.1 (PhCH2Zr),
60.3 (PhCH2N), 59.1 ([C3]NCH2), 55.6 ([C2]NCH2), 55.2
4.40 (d, 2H, 2JHH = 14 Hz, PhCH2N), 3.69 (m, 2H, [C3]CH2N),
3.60 (m, 2H, [C2]CH2N), 2.84 (m, 2H, [C2]CH2N), 2.74-2.68
(overlapping, 4H total, 2H [C3]CH2N, 2H [C2]CH2N), 2.43 (m,
2H, [C3]CH2N), 2.17 (m, 2H, [C2]CH2N), 1.61-1.51 (br, 2H,
CH2CH2CH2), 1.17 (m, 2H, CH2CH2CH2). 13C{1H} NMR
(C6D6, 100.6 MHz, 296 K): δ (ppm) 150.7 (PhCCZr), 133.4 (i-
PhCH2N), 133.2 (PhCH2N), 132.3 (o-PhCCZr), 128.9, 128.5,
128.3 (PhCH2N and PhCCZr), 127.7 (i-PhCCZr), 126.8 (PhCH2N
or PhCCZr), 106.3 (PhCCZr), 57.6 (PhCH2N), 57.1 ([C3]CH2N),
53.4 ([C2]CH2N), 52.8 ([C3]CH2N), 49.8 ([C2]CH2N), 25.6
(CH2CH2CH2). IR: 2069 cm-1 (CtC stretching). Anal. Calcd
for C40H44N4Zr: C 71.49, H 6.60, N 8.34. Found: C 69.91, H
6.74, N 7.47.
1
([C2]NCH2), 49.6 ([C3]NCH2), 26.1 (CH2CH2CH2). H NMR
((C6H4CH2)2Cyclam)Zr (6). A C6D6 solution of 2 or 4 in a
NMR tube was heated at 70 °C over a period of 2 h. On the basis
of the 1H NMR spectrum, the conversion was complete. Alter-
natively, a Schlenk was charged with 4 (0.80 g, 1.36 mmol) and
heated at 70 °C for 2 days, obtaining 6 quantitatively. Starting
from complex 3, the reaction was monitored by NMR, and
complete conversion was achieved over a period of 72 h under
mild reflux of the C6D6 solution. 1H NMR (C6D6, 400.1 MHz,
296 K): δ (ppm) 8.20 (m, 2H, H(6)-Ph) 7.30-7.10 (overlapping,
6H total, 2H, H(3)-Ph, 2H, H(4)-Ph, 2H, H(5)-Ph), 4.81 (d, 2H,
2JHH = 14 Hz, PhCH2N), 3.60 (m, 2H, [C2]CH2N), 3.23 (m, 2H,
[C3]CH2N), 3.02 (m, 2H, [C2]CH2N), 2.84 (d, 2H, 2JHH = 14 Hz,
PhCH2N), 2.82 (m, 2H, [C3]CH2N), 2.62 (m, 2H, [C2]CH2N),
2.28 (m, 2H, [C3]CH2N), 2.07 (overlapping, 4H total, 2H,
[C2]CH2N, 2H, [C3]CH2N), 1.39 (m, 2H, CH2CH2CH2), 0.89
(m, 2H, CH2CH2CH2). 13C{1H} NMR (C6D6, 100.6 MHz, 296 K):
δ (ppm) 188.5 (C(1)-Ph), 151.1 (C(2)-Ph), 140.8 (C(6)-Ph), 126.8,
125.4, 124.1 (C(3)-Ph, (C(4)-Ph, (C(5)-Ph), 63.3 (PhCH2N), 59.7
([C3]CH2N),55.4([C2]CH2N),52.9([C2]CH2N),50.0([C3]CH2N),
26.4 (CH2CH2CH2). MS (ESI): m/z 466. A m/z of 466 is also ob-
served when 2 is analyzed, indicative of how thermally sensitive
and prone to decomposition complex 2 is. Anal. Calcd for C24-
H32N4Zr: C 61.62, H 6.90, N 11.98. Found: C 61.83, H 7.16, N 11.63.
((C6H4CH2)BnCyclam))Zr(CCPh) (7). One equivalent of
HCCPh (5 mg, 0.05 mmol) was added to a solution of 6,
obtained in situ by heating a C6D6 solution of 2 (0.03 g, 0.05
mmol). After 18 h at room temperature, the 1H NMR spectrum
showed a set of resonances corresponding to compound 7 (about
38%) and to compound 5. Full assignment of the aromatic reso-
(CD2Cl2, 300.1 MHz, 296 K): δ (ppm) 7.33-7.31 (overlapping,
6H total, 4H, m-PhCH2N, 2H, p-PhCH2N), 7.25-7.15 (over-
lapping, 8H total, 4H, o-PhCH2Zr, 4H, m-PhCH2Zr), 7.07 (m,
4H, o-PhCH2N), 6.86 (m, 2H, p-PhCH2Zr), 4.40 (d, 2H, 2JHH
=
2
14 Hz, PhCH2N), 3.39 (d, 2H, JHH = 14 Hz, PhCH2N),
3.13-2.89 (overlapping, 6H total, 4H, [C3]NCH2, 2H,
[C2]NCH2), 2.76 (m, 2H, [C2]NCH2), 2.67-2.33 (overlapping,
6H total, 4H, [C3]NCH2, 2H, CH2CH2CH2), 2.41 (d, 2H, 2JHH
=
8 Hz, PhCH2Zr), 2.35 (d, 2H, 2JHH = 8 Hz, PhCH2Zr), 2.02-
1.82 (overlapping, 6H total, 4H, [C2]NCH2, 2H, CH2CH2CH2).
13C{1H} NMR (CD2Cl2, 75.5 MHz, 296 K): δ (ppm) 150.8
(i-PhCH2Zr), 133.1 (i-PhCH2N), 132.9 (o-PhCH2N), 129.8
(o-PhCH2Zr), 128.7 (p-PhCH2N), 128.4 (m-PhCH2N), 128.0
(m-PhCH2Zr), 119.6 (p-PhCH2Zr), 64.9 (1JCH = 124 Hz,
PhCH2Zr), 60.4 (PhCH2N), 59.3 ([C3]NCH2), 55.7 ([C2]NCH2),
55.1 ([C2]NCH2), 49.9 ([C3]NCH2), 26.4 (CH2CH2CH2). Anal.
Calcd for C38H48N4Zr(C7H8): C 72.63, H 7.58, N 7.53. Found:
C 73.02, H 7.43, N 7.49.
(Bn2Cyclam)Zr(nBu)2 (4). To a THF suspension of (Bn2-
Cyclam)ZrCl2 (1.08 g, 2.0 mmol) at -30 °C was slowly added
2.5 mL of a LiBun solution (1.6 M in hexanes). After a while the
suspension started to dissolve and the light yellow solution
turned yellowish-brown. The mixture reacted for a further 2 h,
and the solvent was evaporated. The residue was extracted with
15 mL of toluene. The solvent was evaporated to yield 1.0 g of 4
(86%). The solid was redissolved in diethyl ether and stored at
-20 °C. Crystalline material suitable for X-ray diffraction was
obtained from this diethyl ether solution. 1H NMR (C6D6, 400.1
MHz, 296 K): δ (ppm) 7.15-7.05 (br, 10H, H-Ph), 4.65 (d, 2H,
2JHH = 14 Hz, PhCH2N), 4.39 (d, 2H, 2JHH = 14 Hz, PhCH2N),
3.85 (m, 2H, [C3]CH2N), 3.69 (m, 2H, [C2]CH2N), 2.98 (m, 2H,
[C3]CH2N), 2.75 (m, 2H, [C3]CH2N), 2.72-2.57 (overlapping,
4H total, 2H, [C2]CH2N and 2H, [C2]CH2N), 2.27-2.13
(overlapping, 8H total, 4H, ZrCH2CH2CH2, 2H, [C3]CH2N
and 2H, [C2]CH2N), 1.81 (m, 4H, ZrCH2CH2CH2), 1.48 (m,
2H, CH2CH2CH2), 1.25 (m, 6H, Zr(CH2)3CH3), 1.10-0.99
(overlapping, 4H total, 2H, ZrCH2CH2 and 2H, CH2CH2CH2),
0.60 (m, 2H, ZrCH2CH2). 13C{1H} NMR (C6D6, 100.6 MHz,
296 K): δ (ppm) 132.7 (o-Ph), 132.0 (i-Ph), 128.2 and 128.0
(overlapping with C6D6, m-Ph and p-Ph), 58.2 (ZrCH2CH2), 56.1
(PhCH2N), 55.9 ([C3]CH2N), 53.0 ([C2]CH2N), 51.8 ([C3]CH2N),
50.9 ([C2]CH2N), 32.9 (ZrCH2CH2CH2), 31.4 (ZrCH2CH2CH2),
25.4 (CH2CH2CH2), 14.7 (Zr(CH2)3CH3). Anal. Calcd for C32H52-
N4Zr: C 65.81, H 8.97, N 9.59. Found: C 65.66, H 8.67, N 9.60.
(Bn2Cyclam)Zr(CCPh)2 (5). To a THF suspension of (Bn2-
Cyclam)ZrCl2 (0.38 g, 0.71 mmol) was slowly added 1.6 mL of a
LiCCPh solution (1.0 M in THF). After a while the suspension
started to dissolve and the light yellow solution turned orange.
The mixture reacted for a further 12 h, and the solvent was
evaporated. The oily residue was extracted with 15 mL of
toluene. After taking the extract to dryness, diethyl ether was
added to remove a brown impurity. The solution was again
taken to dryness and washed with minimal hexanes to give a
yellow solid in 52% yield (0.25 g). 1H NMR (C6D6, 400.1 MHz,
296 K):δ (ppm) 7.71(d, 4H, o-PhCCZr), 7.21-7.11 (overlapping,
10H total, H-PhCH2N), 7.06-7.00 (overlapping, 6H, H-PhCCZr),
5.42 (d, 2H, 2JHH = 14 Hz, PhCH2N), 4.73 (m, 2H, [C3]CH2N),
nances was not possible due to the complexity of the 1H and 13
C
spectra. 1H NMR (C6D6, 400.1 MHz, 296 K): δ (ppm) 8.97 (d,
1H, H(6)-Ph), 5.31 (d, 1H, 2JHH = 14 Hz, PhCH2N), 4.77-4.67
(overlapping with 5, 1H, PhCH2N), 4.51 (d, 1H, 2JHH = 14 Hz,
PhCH2N), 4.18 (m, 1H, CH2N), 3.37 (overlapping, 2H total,
1H, CH2N and, 1H, CH2N), 3.11-2.96 (overlapping with 2, 2H
total, 1H, CH2N and, 1H, PhCH2N), 2.88-2.67 (overlapping
with 6 and 5, 5H, CH2N), 2.53-2.41 (overlapping with 5, 5H,
CH2N), 2.32-2.19 (overlapping with 6 and 5, 1H, CH2N),
2.11-2.05 (overlapping with 6 and 5, 1H, CH2N), 1.63-1.37
(overlapping with 6 and 5, 2H, CH2CH2CH2), 1.19-1.15 (over-
lapping with 6, 1H, CH2CH2CH2), 0.86-0.82 (overlapping with
6, 1H, CH2CH2CH2). 13C{1H} NMR (C6D6, 100.6 MHz, 296
K): δ (ppm) 188.3 (C(1)-Ph), 150.4 (PhCCZr), 150.1 (C(2)-Ph),
142.2 (C(6)-Ph), 134.3, 133.1, 133.0, 132.3, 132.2, 129.7, 128.9,
127.8, 127.3, 126.7, 125.7, 125.6, 124.2 (PhCH2N, PhCCZr,
C(3)-Ph, C(4)-Ph, C(5)-Ph), 63.9 (PhCH2N), 58.7 (PhCH2N),
58.7 (CH2N), 57.1 (CH2N), 56.0 (CH2N), 54.7 (CH2N), 52.1
(CH2N), 51.1 (CH2N), 49.5 (CH2N), 48.5 (CH2N), 24.9 (CH2-
CH2CH2), 24.5 (CH2CH2CH2).
[(Bn2Cyclam)Zr(η2-CH2Ph)][PhCH2B(C6F5)3] (8). Method
A1: At room temperature, a J-Young NMR tube was charged
with complex 3 (0.03 g, 0.05 mmol) and B(C6F5)3 (0.02 mg, 0.05
mmol), and approximately 0.5 mL of CD2Cl2 was added to the
mixture, leading to the formation of a light yellow solution.
NMR shows the conversion was complete after 15 min. Method
A2: To a solution of complex 3 (0.31 g, 0.47 mmol) in dichloro-
methane was added a solution of B(C6F5)3 (0.24 g, 0.47 mmol) in

ꢀ
Munha et al.
3762 Organometallics, Vol. 29, No. 17, 2010
the same solvent. The mixture was stirred overnight at room
temperature. Evaporation of the solvent afforded 8 as a yellow
solid in quantitative yield. 1H NMR (CD2Cl2, 300.1 MHz, 296 K):
δ (ppm) 7.65 (m, 2H, m-PhCH2Zr), 7.51-7.43 (overlapping, 7H
total, 1H, p-PhCH2Zr, 4H, m-PhCH2N, 2H, p-PhCH2N), 7.25
(m, 4H, o-PhCH2N), 6.96 (m, 2H, o-PhCH2Zr), 6.89 (m, 2H,
m-PhCH2B), 6.82-6.76 (overlapping, 3H total, 2H, o-PhCH2B,
1H, p-PhCH2B), 4.19 (d, 2H, 2JHH = 14 Hz, PhCH2N), 3.88-3.67
(overlapping, 4H total, 2H, [C3]NCH2, 2H, [C2]NCH2), 3.21-
2.82 (overlapping, 8H total, 4H, [C3]NCH2, 4H, [C2]NCH2),
3.08 (d, 2H, 2JHH = 14 Hz, PhCH2N), 3.00 (d, 1H, 2JHH = 9 Hz,
PhCH2Zr), 2.86 (s, 2H, PhCH2B), 2.74-2.60 (overlapping, 4H
NMR (d8-THF, 100.6 MHz, 296 K): δ (ppm) 150.3 (br, C6F5),
149.5 (i-PhCH2B), 148.0 (br, C6F5), 147.1 (i-PhCH2Zr), 139.4
(br, C6F5), 138.3 (br, C6F5), 137.1 (br, C6F5), 136.0 (br, C6F5),
133.3 (PhCH2N), 130.9 (i-PhCH2N), 130.5 (PhCH2N), 129.7
(PhCH2N), 129.4, 128.9, 127.2, 123.7 (Ph), 122.9 (PhCH2Zr),
68.2 (1JCH = 124 Hz, PhCH2Zr),57.5(PhCH2N), 57.3 ([C3]NCH2),
54.7 ([C3]NCH2), 53.6 ([C2]NCH2), 51.0 ([C2]NCH2), 32.2 (br,
BCH2Ph), 25.3 (CH2CH2CH2). 19F NMR (d8-THF, MHz, 296
K): δ (ppm) -133.1 (d, 3JFF = 23 Hz, Fo), -168.8 (t, 3JFF = 21
Hz, Fp), -171.0 (t, 3JFF = 20 Hz, Fm). 11B NMR (d8-THF, 128.8
MHz, 296 K): δ (ppm) -14.6 (br).
[(Bn2Cyclam)Zr(Me)][MeB(C6F5)3] (10). Method A: At room
temperature, a J-Young NMR tube was charged with complex 2
(20 mg, 0.04 mmol) and B(C6F5)3 (21 mg, 0.04 mmol), and
approximately 0.5 mL of CD2Cl2 was added to the mixture. The
2
total, 2H, [C2]NCH2, 2H, [C3]NCH2), 2.70 (d, 1H, JHH = 9
Hz, PhCH2Zr), 1.88-1.76 (br, 2H, CH2CH2CH2), 1.65 (m, 2H,
CH2CH2CH2). 13C{1H} NMR (CD2Cl2, 75.5 MHz, 296 K): δ
(ppm) 150.0 (BC6F5), 149.2 (i-PhCH2B), 147.2 (BC6F5), 140.0
(BC6F5), 139.4 (i-PhCH2Zr), 138.5 (BC6F5), 136.4 (BC6F5),
135.3 (BC6F5), 134.9 (m-PhCH2Zr), 132.6 (o-PhCH2N), 130.0
(i-PhCH2N), 129.7 (p-PhCH2N), 129.2 (m-PhCH2N), 129.2
(o-PhCH2B), 128.7 (o-PhCH2Zr), 127.9 (p-PhCH2Zr), 127.3
(m-PhCH2B), 122.9 (p-PhCH2B), 69.2 (1JCH = 139 Hz, PhCH2Zr),
57.3 ([C3]NCH2), 56.6 (PhCH2N), 51.5 ([C2]NCH2), 51.1
([C3]NCH2), 49.5 ([C2]NCH2), 32.0 (br, PhCH2B), 24.6 (CH2-
CH2CH2). 19F NMR (CD2Cl2, 282.4 MHz, 296 K): δ (ppm)
1
formation of a yellow solution was immediately observed. H
NMR (CD2Cl2, 300.1 MHz, 296 K): δ (ppm) 7.43-7.26 (over-
lapping, 10H, H-Ph), 4.00-3.93 (overlapping, 6H total, 2H,
=
PhCH2N, 2H, [C3]CH2Nand2H, [C2]CH2N), 3.77 (d, 2H, 2JHH
12 Hz, PhCH2N), 3.51-3.36 (overlapping, 6H total, 2H, [C3]CH2N
and 4H, [C2]CH2N), 3.12-3.00 (overlapping, 4H total, 2H,
[C3]CH2N and 2H, [C2]CH2N), 2.88 (m, 2H, [C3]CH2N), 2.17
(m, 2H, CH2CH2CH2), 2.00 (m, 2H, CH2CH2CH2), 0.49 (s, 3H,
BCH3). 13C{1H} NMR (CD2Cl2, 75.5 MHz, 296 K): δ (ppm)
150.4 (br, C6F5), 147.2 (br, C6F5), 139.6 (br, C6F5), 138.6 (br,
C6F5), 136.4 (br, C6F5), 135.3 (br, C6F5), 132.1 (o-Ph or m-Ph),
131.1 (p-Ph), 130.5 (o-Ph or m-Ph), 127.7 (i-Ph), 58.5 ([C3]CH2N),
56.2 (PhCH2N), 52.8 (overlapping, 2C, [C3]CH2N and [C2]CH2N),
52.2 ([C2]CH2N), 24.8 (CH2CH2CH2), 11.0 (br, BCH3). 19F{1H}
3
3
-131.2 (d, JFF = 23 Hz, Fo), -164.7 (t, JFF = 21 Hz, Fp),
3
-167.5 (t, JFF = 19 Hz, Fm). 11B NMR (CD2Cl2, 96.3 MHz,
296 K): δ (ppm) -12.9. MS (ESI): m/z 603.1 [PhCH2B(C6F5)3]-.
Anal. Calcd for C56H48BF15N4Zr: C 57.78, H 4.16, N 4.81. Found:
C 57.88, H 4.58, N 4.39.
Method B: The reaction conditions were analogous to method
A, but it was carried out in d8-toluene. H NMR (d8-toluene,
NMR (CD2Cl2, 282.4 MHz, 296 K): δ (ppm) -133.1 (d, 3JFF
=
1
20 Hz, Fo), -165.0 (t, 3JFF =20Hz, Fp), -167.7 (dt, 3JFF = 20Hz,
4JFF = 7 Hz, Fm). 11B{1H} NMR (CD2Cl2, 96.3 MHz, 296 K):
δ (ppm) -14.9 (s). MS (ESI): m/z 526.9 [MeB(C6F5)3]-.
500.1 MHz, 296 K): δ (ppm) 7.22-6.77 (overlapping, 20H total,
H-Ph), 3.63 (d, 2H, JHH = 14 Hz, PhCH2N), 3.39 (s, 2H,
2
PhCH2B), 3.27 (m, 2H, [C2]NCH2), 3.13 (m, 2H, [C3]NCH2),
2.60 (m, 2H, [C2]NCH2), 2.53-2.41 (overlapping, 7H total, 2H,
PhCH2N, 1H, PhCH2Zr, 2H, [C3]NCH2, 2H, [C2]NCH2),
2.21-2.16 (overlapping, 5H total, 1H, PhCH2Zr, 2H,
[C3]NCH2, 2H, [C2]NCH2), 2.11-2.05 (overlapping with d8-
toluene, 2H, [C3]NCH2), 1.31-1.23 (br, 2H, CH2CH2CH2),
1.05 (m, 2H, CH2CH2CH2). 13C{1H} NMR (CD2Cl2, 125.8 MHz,
296 K): δ (ppm) 151.0 (i-PhCH2B), 139.9 (i-PhCH2Zr), 134.9
(m-PhCH2Zr), 133.0 (o-PhCH2N), 130.2 (i-PhCH2N), 130.1-
128.5 (overlapping with d8-toluene, p-PhCH2N, m-PhCH2N,
o-PhCH2B, o-PhCH2Zr), 128.3 (p-PhCH2Zr), 126.5 (m-PhCH2B),
124.0 (p-PhCH2B), 69.3 (1JCH = 138 Hz, PhCH2Zr), 57.4 ([C3]-
NCH2), 56.9 (PhCH2N), 51.5 ([C2]NCH2), 51.2 ([C3]NCH2),
49.4 ([C2]NCH2), 32.0 (br, PhCH2B), 24.7 (CH2CH2CH2). The
low solubility of this compound in d8-toluene does not allow the
clear identification of the carbon resonances for the pentafluoro-
phenyl groups, as they are weak, and due to the coupling with
19F, they show as broad multiplets ranging from 151 to 137 ppm.
19F NMR (d8-toluene, 282.4 MHz, 296 K): δ (ppm) -130.2 (d,
Method B: A solution of 2 (21 mg, 0.04 mmol) in CD2Cl2 was
transferred to a J-Young NMR tube and frozen in a liquid
nitrogen bath. A solution of B(C6F5)3 (22 mg, 0.04 mmol) was
added, and the NMR tube was sealed. The tube was then placed
in an ethanol/liquid nitrogen bath at -80 °C and yielded a
yellow solution. The tube was rapidly transferred into the NMR
spectrometer (precooled to -80 °C), and NMR data were recor-
ded from -80 to 25 °C. The spectra show a mixture of species 10
and 11. NMR data for 11: 19F{1H} NMR (CD2Cl2, 282.4 MHz,
296 K): δ (ppm) -136.3 (d, 3JFF = 23 Hz, Fo), -162.0 (t, 3JFF
=
20 Hz, Fp), -165.7 (t, 3JFF = 19 Hz, Fm). 11B NMR (CD2Cl2,
96.3 MHz, 296 K): δ (ppm) -4.2 (br).
[(Bn2Cyclam)Zr(Me)(THF)][MeB(C6F5)3] (12). A vial was
charged with 2 (0.03 g, 0.06 mmol) and dissolved in 0.5 mL of
d8-THF. A solution of B(C6F5)3 (0.3 g, 0.06 mmol) was added
dropwise, and the NMR spectra were recorded after 1 h, show-
1
ing only signals attributed to complex 12. H NMR (d8-THF,
400.1 MHz, 296 K): δ (ppm) 7.40 (br, 10H total, H-Ph), 4.52 (d,
2H, JHH = 14 Hz, PhCH2N), 4.27 (br, 2H, PhCH2N), 3.80
2
3JFF = 23 Hz, Fo), -164.0 (t, 3JFF = 21 Hz, Fp), -166.7 (t, 3JFF
=
(overlapping, 4H total, [C2]NCH2), 3.24 (m, 2H, [C3]NCH2),
3.19 (m, 2H, [C2]NCH2), 3.09 (m, 2H, [C3]NCH2), 2.90 (m, 2H,
[C2]NCH2), 2.75 (m, 2H, [C3]NCH2), 2.60 (m, 2H, [C3]NCH2),
1.96 (m, 2H, CH2CH2CH2), 1.59 (m, 2H, CH2CH2CH2), 0.51
(br, 3H, CH3B), 0.23 (s, 3H, ZrCH3). 13C{1H} NMR (d8-THF,
100.6 MHz, 296 K): δ (ppm) 149.6 (br, C6F5), 147.2 (br, C6F5),
138.7 (br, C6F5), 137.6 (br, C6F5), 136.3 (br, C6F5), 135.2 (br,
C6F5), 132.9 (PhCH2N), 128.8 (PhCH2N), 128.1 (i-PhCH2N),
56.8 (PhCH2N), 56.1 ([C3]NCH2), 52.8 (overlapping, [C2]NCH2),
50.5 ([C3]NCH2), 41.3 (ZrCH3), 24.9 (CH2CH2CH2), 10.2 (br,
BCH3). 19F NMR (d8-THF, MHz, 296 K): δ (ppm) -135.0 (d,
20 Hz, Fm). 11B NMR (d8-toluene, 96.3 MHz, 296 K): δ (ppm)
-12.2.
[(Bn2Cyclam)Zr(CH2Ph)(THF)][PhCH2B(C6F5)3] (9). A vial
was charged with 3 (0.03 g, 0.05 mmol) and dissolved in THF. A
solution of B(C6F5)3 (0.02 g, 0.05 mmol) was added dropwise,
and the mixture was stirred overnight. It was then transferred to
a J-Young tube, whose NMR indicated complete conversion.
1H NMR (d8-THF, 400.1 MHz, 296 K): δ (ppm) 7.40 (br, 10H
total, H-Ph), 7.22 (m, 2H, BCH2Ph), 7.11 (overlapping, 4H total,
ZrCH2Ph), 6.92 (m, 1H, ZrCH2Ph), 6.75 (m, 2H, BCH2Ph), 6.65
(m, 1H, BCH2Ph), 4.66 (d, 2H, 2JHH = 14 Hz, PhCH2N), 4.04
(d, 2H, 2JHH = 14 Hz, PhCH2N), 3.97 (m, 2H, [C2]NCH2), 3.66
(m, 2H, [C3]NCH2), 3.19 (m, 2H, [C2]NCH2), 3.05 (m, 2H,
[C2]NCH2), 2.95 (m, 2H, [C3]NCH2), 2.85 (br, 2H, BCH2Ph),
2.72 (m, 2H, [C3]NCH2), 2.57 (m, 2H, [C3]NCH2), 2.55 (d, 1H,
2JHH = 12 Hz, ZrCH2Ph), 2.21 (d, 1H, 2JHH = 12 Hz, ZrCH2Ph),
2.01 (m, 2H, CH2CH2CH2), 1.57 (m, 2H, CH2CH2CH2). 13C{1H}
3JFF = 23 Hz, Fo), -169.1 (t, 3JFF = 21 Hz, Fp), -171.2 (t, 3JFF
=
20 Hz, Fm). 11B NMR (d8-THF, 128.8 MHz, 296 K): δ (ppm)
-16.8 (br).
Reaction of [(Bn2Cyclam)Zr(Me)2] (2) with B(C6F5)3 in To-
luene-d8. A solution of 2 (19 mg, 0.04 mmol) in toluene-d8 was
transferred to a J-Young NMR tube and frozen in a liquid
nitrogen bath. A solution of B(C6F5)3 (19 mg, 0.04 mmol) was

Article
Organometallics, Vol. 29, No. 17, 2010 3763
added, and the NMR tube was sealed. The tube was then placed
in an ethanol/liquid nitrogen bath at -80 °C and yielded a pale
yellow solution, and an orange oil settled on the bottom of the
tube. The tube was rapidly transferred into the NMR spectro-
meter (precooled to -80 °C), and NMR data were recorded
from -80 to 25 °C.
In compound 3, one molecule of cocrystallized toluene was
found in the asymmetric unit. As for 4, one molecule of
cocrystallized diethyl ether per two molecules of the compound
was found in the asymmetric unit. The diethyl ether fragment
was modeled satisfactorily but is highly disordered, resulting in
large ellipsoids.
1
[(Bn2Cyclam)Zr(Me)(Tol)][MeB(C6F5)3] (13). H NMR (d8-
Computational Details. The calculations were performed using
the Gaussian 03 software package33 and the B3LYP functional,
without symmetry constraints. That functional includes a mixture
of Hartree-Fock34 exchange with DFT35 exchange-correlation,
given by Becke’s three-parameter functional36 with the Lee, Yang,
and Parr correlation functional, which includes both local and
nonlocal terms.22,37 The optimized geometries were obtained with
a VDZP basis set (basis b1) consisting of the LanL2DZ basis set38
augmented with a f-polarization function,39 for Zr, and a standard
6-31G(d,p)40 for the remaining elements. Transition-state optimi-
zations were performed with the synchronous transit-guided quasi-
Newton method developed by Schlegel et al.41 Frequency calcula-
tions were performed to confirm the nature of the stationary
points, yielding one imaginary frequency for the transition states
and none for the minima. Each transition state was further
confirmed by following its vibrational mode downhill on both
sides and obtaining the minima presented on the profiles. Free
energy values in vacuo were obtained at 298.15 K and 1 atm by
conversion of the zero-point-corrected electronic energies with the
thermal energy corrections based on the calculated structural and
vibrational frequency data. A natural population analysis (NPA)42
and the resulting Wiberg indices25 were used to study the electronic
structure and bonding of the optimized species. The free energy
values presented in the profiles and discussed in the text result from
single-point energy calculations using a VTZP basis set (basis b2)
toluene, 500.1 MHz, 296 K): δ (ppm) 6.88 (m, 4H, m-PhCH2N),
6.71 (m, 4H, o-PhCH2N), overlapping with C7D8 (p-PhCH2N),
3.51-3.45 (overlapping with 14, 2H, [C3]CH2N), 3.32 (d, 2H,
2JHH = 14 Hz, PhCH2N), 3.24 (m, 2H, [C2]CH2N), 3.17 (d, 2H,
2JHH = 14 Hz, PhCH2N), 2.86-2.76 (overlapping with 14, 4H,
[C2]CH2N), 2.54 (m, 2H, [C3]CH2N), 2.41-2.34 (overlapping
with 14, 2H, [C3]CH2N), 2.31 (m, 2H, [C2]CH2N), 2.21 (m, 2H,
[C3]CH2N), 1.50-1.39 (overlapping with 14, 2H, CH2CH2CH2),
1.22-1.16 (overlapping, 5H total, 3H, BCH3 and 2H, CH2CH2CH2).
13C{1H} NMR (d8-toluene, 125.8 MHz, 296 K): δ (ppm) 131.3
(o-Ph), 130.0 (m-Ph), 58.6 ([C3]CH2N), 57.3 (PhCH2N), 51.5
([C2]CH2N), 51.1 ([C2]CH2N), 50.2 ([C3]CH2N), 23.9 (CH2-
CH2CH2), 11.0 (br, BCH3).19F{1H} NMR (d8-toluene, 282.4 MHz,
296 K): δ (ppm) -131.8 (dd, br, 3JFF = 18 Hz, Fo), -164.2 (t,
3JFF = 21 Hz, Fp), -166.8 (dt, 3JFF = 24 Hz; 4JFF = 6 Hz, Fm).
11B{1H} NMR (d8-toluene, 32.2 MHz, 296 K): δ(ppm) -14.4 (br).
1
(Bn2Cyclam)Zr(C6F5)(CH2B(C6F5)2) (14). H NMR (d8-to-
luene, 500.1 MHz, 296 K): δ (ppm) 7.06 (m, 4H, m-PhCH2N),
6.92 (m, 4H, o-PhCH2N), overlapping with C7D8 (p-PhCH2N),
5.80 (vb, 2H, BCH2), 4.14 (d, 2H, 2JHH = 14 Hz, PhCH2N), 3.89
(d, 2H, 2JHH = 14 Hz, PhCH2N), 3.51-3.45 (overlapping with
13, 2H, [C3]CH2N), 3.39 (m, 2H, [C2]CH2N), 2.86-2.76 (over-
lapping with 13, 2H, [C3]CH2N), 2.61 (m, 2H, [C2]CH2N), 2.49
(m, 2H, [C2]CH2N), 2.41-2.34 (overlapping with 13, 4H total,
2H, [C3]CH2N and 2H, [C2]CH2N), 1.85 (m, 2H, [C3]CH2N),
1.50-1.39 (overlapping with 13, 2H, CH2CH2CH2), 1.33 (m,
2H, CH2CH2CH2). 13C{1H} NMR (d8-toluene, 125.8 MHz, 296
K): δ (ppm) 132.3 (o-Ph), overlapping with C7D8 (m-Ph), 100.5
(BCH2), 55.7 ([C3]CH2N), 53.7 ([C3]CH2N), 53.3 (PhCH2N),
52.1 ([C2]CH2N), 52.0 ([C2]CH2N), 25.1 (CH2CH2CH2). 19F{1H}
NMR (d8-toluene, 282.4 MHz, 296 K): δ (ppm) -119.0 (m, Fo-
Zr(C6F5)), -135.6 (m, Fo-B(C6F5)2), -150.4 (m, Fp-Zr(C6F5)),
-158.9 (m, Fm-Zr(C6F5)), -160.6 (t, 3JFF = 21 Hz, Fp-B(C6F5)2),
-164.7 (dt, 3JFF = 20 Hz, 4JFF = 7 Hz, Fm-B(C6F5)2). 11B{1H}
NMR (d8-toluene, 32.2 MHz, 296 K): δ (ppm) 86.6 (br).
X-ray Diffraction Experimental Determination. Crystallo-
graphic and experimental details of data collection and crystal
structure determinations for the two compounds are available in
the Supporting Information. Suitable crystals of compounds 3 and
4 were selected and coated in Fomblin oil or an acceptable
substitute under an inert atmosphere. Crystals were then mounted
on a glass fiber or on a loop external to the glovebox environment.
Compounds 3 and 4 were measured on Bruker X8 APEX and
Bruker AXS-KAPPA APEX II diffractometers, respectively, both
using graphite-monochromated Mo KR radiation. Data for com-
pounds 3 and 4 were collected at 173(2) and 150(2) K, respectively.
Cell parameters were retrieved using Bruker SMART software and
refined using Bruker SAINT on all observed reflections.28
Absorption corrections were applied using SADABS.29 The
structures were solved by direct methods using SIR92, SIR97, or
SIR2004. Structure refinement was done using SHELXL-97.
These programs are part of the WinGX software package
version 1.70.01.30
(30) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
(31) Sheldrick, G. M. Acta Crystallogr., Sect. A Found. Crystallogr.
2008, A64, 112–122.
(32) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(33) Frisch, M. J. T.; G., W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene,
M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;
Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz,
J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.:
Wallingford, CT, 2004.
(34) Hehre, W. J.; Radom, L.; Schleyer, P. v. R.; Pople, J. A. Ab Initio
Molecular Orbital Theory; John Wiley & Sons: New York, 1986.
(35) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989.
(36) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(37) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B: Condens. Matter
1988, 37, 785–789.
(38) (a) Dunning, T. H., Jr.; Hay, P. J. Modern Theoretical Chemistry;
Schaefer, H. F., III, Ed.; Plenum: New York, 1976; Vol. 3, p 1. (b) Hay, P. J.;
Wadt, W. R. J. Chem. Phys. 1985, 82, 270–283. (c) Wadt, W. R.; Hay, P. J.
J. Chem. Phys. 1985, 82, 284–298. (d) Hay, P. J.; Wadt, W. R. J. Chem.
Phys. 1985, 82, 299–310.
(39) Ehlers, A. W.; Boehme, M.; Dapprich, S.; Gobbi, A.; Hoell-
warth, A.; Jonas, V.; Koehler, K. F.; Stegmann, R.; Veldkamp, A.; et al.
Chem. Phys. Lett. 1993, 208, 111–114.
(40) (a) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257–2261. (b) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973,
28, 213–222. (c) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27, 209–214.
(d) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163–168.
(41) (a) Peng, C.; Schlegel, H. B. Isr. J. Chem. 1994, 33, 449–454.
(b) Peng, C.; Ayala, P.; Schlegel, H. B.; Frisch, M. J. J. Comput. Chem. 1996,
17, 49–56.
All non-hydrogen atoms were refined anisotropically. All
hydrogen atoms were included in fixed positions. Torsion
angles, mean square planes, and other geometrical parameters
were calculated using SHELX,31 just like other experimental
details that are given in the Supporting Information. Illustra-
tions of the molecular structures were made with ORTEP3.32
(28) SAINT, Version 7.03A; Bruker AXS Inc.: Madison, WI, 1997-
2003.
(29) SADABS, Bruker Nonius area detector scaling and absorption
correction, V2.10; Bruker AXS Inc.: Madison, WI, 2003.

ꢀ
Munha et al.
3764 Organometallics, Vol. 29, No. 17, 2010
~
Acknowledgment. We are grateful to Fundac-ao para a
with the geometries optimized at the B3LYP/b1 level. Basis b2
consisted of a standard 3-21G43 with an added f-polarization
function39 for Zr and standard 6-311þG(d,p)44 for the remaining
elements. Solvent (toluene) effects were considered in the PBE1PBE/
b2//PBE1PBE/b1 energy calculations using the polarizable
continuum model initially devised by Tomasi and co-workers45
as implemented in Gaussian 03.46 The molecular cavity was
based on the united atom topological model applied on UAHF
radii, optimized for the HF/6-31G(d) level.
^
Ciencia e Tecnologia, Portugal, and NSERC for funding.
We would like to thank Dr. Brian O. Patrick from
University of British Columbia for collecting the data of
compound 3. We would also like to thank the Portuguese
NMR Network (IST-UTL Centre) for providing access
to the NMR.
Supporting Information Available: Table of crystallographic
data for 3 and 4, X-ray crystallographic data for 3 and 4 in CIF
format, and coordinates of all computationally optimized struc-
tures in PDF format. This material is available free of charge via
the Internet at http://pubs.acs.org.
(42) (a) Carpenter, J. E.; Weinhold, F. J. Mol. Struct.
(THEOCHEM) 1988, 169, 41–62. (b) Carpenter, J. E. Ph.D. Thesis,
University of Wisconsin, Madison, WI, 1987. (c) Foster, J. P.; Weinhold, F.
J. Am. Chem. Soc. 1980, 102, 7211–7218. (d) Reed, A. E.; Weinhold, F.
J. Chem. Phys. 1983, 78, 4066–4073. (e) Reed, A. E.; Weinhold, F. J. Chem.
Phys. 1985, 83, 1736–1740. (f) Reed, A. E.; Weinstock, R. B.; Weinhold, F.
J. Chem. Phys. 1985, 83, 735–746. (g) Reed, A. E.; Curtiss, L. A.; Weinhold,
F. Chem. Rev. 1988, 88, 899–926. (h) Weinhold, F.; Carpenter, J. E. The
Structure of Small Molecules and Ions; Plenum: New York, 1988; p 227.
(43) (a) Binkley, J. S.; Pople, J. A.; Hehre, W. J. J. Am. Chem. Soc.
1980, 102, 939–947. (b) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1986,
7, 359–378. (c) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1987, 8, 880–
893. (d) Dobbs, K. D.; Hehre, W. J. J. Comput. Chem. 1987, 8, 861–879.
(e) Gordon, M. S.; Binkley, J. S.; Pople, J. A.; Pietro, W. J.; Hehre, W. J.
J. Am. Chem. Soc. 1982, 104, 2797–2803. (f) Pietro, W. J.; Francl, M. M.;
Hehre, W. J.; DeFrees, D. J.; Pople, J. A.; Binkley, J. S. J. Am. Chem. Soc.
1982, 104, 5039–5048.
(44) (a) Hay, P. J. J. Chem. Phys. 1977, 66, 4377–4384. (b) Krishnan,
R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650–654.
(c) McGrath, M. P.; Radom, L. J. Chem. Phys. 1991, 94, 511–516.
(d) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639–5648.
(e) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033–1036.
(45) (a) Cances, E.; Mennucci, B.; Tomasi, J. J. Chem. Phys. 1997,
107, 3032–3041. (b) Cossi, M.; Barone, V.; Mennucci, B.; Tomasi, J. Chem.
Phys. Lett. 1998, 286, 253–260. (c) Mennucci, B.; Tomasi, J. J. Chem.
Phys. 1997, 106, 5151–5158.
(46) (a) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,
2999–3093. (b) Cossi, M.; Scalmani, G.; Rega, N.; Barone, V. J. Chem.
Phys. 2002, 117, 43–54.