Cationic zirconium dialkyl and alkyl complexes supported by DAC (deprotonated 4,13-diaza-18-crown-6) ligation

Article abstract of DOI:10.1021/om961027n

The synthesis, characterization, and reactivity of a series of neutral and cationic Zr alkyls supported by DAC (deprotonated 4,13-diaza-18-crown-6) ligation are reported. Reaction of H₂DAC with Zr(CH₂Ph)₄ affords a 1:4 mixture of cis- and trans-Zr(DAC)(CH₂Ph)₂ (cis-/trans-1a). The pure isomers undergo slow cis-trans isomerization in solution to regenerate the 1:4 cis:trans equilibrium mixture. X-ray crystallographic results are reported for both cisand trans-1a. Reaction of Zr(CH₂Ph)₂Cl₂ with H₂DAC, followed by treatment with LiR (2 equiv), gives cis-Zr(DAC)R₂ (R = CH₂SiMe₃, cis-1b; R = CH₂CMe₃, cis-1c) exclusively. Alkyl abstraction from cis- or trans-1a using B(C₆F₅)₃ (1 equiv) produces the stable cation [Zr(DAC)(CH₂Ph)]⁺[B(CH₂Ph)(C₆F ₅)₃]^- (2a) as a yellow oil. NMR studies on 2a in CD₂Cl₂ show no evidence for η²-benzyl formation or anion coordination. Protonation of cis- or trans1a with [n-Bu₃NH]⁺[BPh₄]^- similarly yields [Zr(DAC)(CH₂Ph)]⁺[BPh₄]^- (2b). Cation 2a reacts with t-BuNC to form the vinyl amide complex [Zr(DAC){N(t-Bu)CH=CHPh}]+[B(CH₂Ph)(C₆F₅) ₃]^- (3). p-Tolylacetylene undergoes catalytic dimerization to (Z)-1,4-di-p-tolyl-1-buten-3-yne in the presence of 2a.

Full text of DOI:10.1021/om961027n

2556
Organometallics 1997, 16, 2556-2561
Ca tion ic Zir con iu m Dia lk yl a n d Alk yl Com p lexes
Su p p or ted by DAC (Dep r oton a ted 4,13-Dia za -18-cr ow n -6)
Liga tion
Lawrence Lee, David J . Berg,* and Gordon W. Bushnell
Department of Chemistry, University of Victoria, P.O. Box 3065,
Victoria, British Columbia, Canada V8W 3V6
Received December 5, 1996X
The synthesis, characterization, and reactivity of a series of neutral and cationic Zr alkyls
supported by DAC (deprotonated 4,13-diaza-18-crown-6) ligation are reported. Reaction of
H2DAC with Zr(CH2Ph)4 affords a 1:4 mixture of cis- and trans-Zr(DAC)(CH2Ph)2 (cis-/tr a n s-
1a ). The pure isomers undergo slow cis-trans isomerization in solution to regenerate the
1:4 cis:trans equilibrium mixture. X-ray crystallographic results are reported for both cis-
and tr a n s-1a . Reaction of Zr(CH2Ph)2Cl2 with H2DAC, followed by treatment with LiR (2
equiv), gives cis-Zr(DAC)R2 (R ) CH2SiMe3, cis-1b; R ) CH2CMe3, cis-1c) exclusively. Alkyl
abstraction from cis- or tr a n s-1a using B(C6F5)3 (1 equiv) produces the stable cation
[Zr(DAC)(CH2Ph)]+[B(CH2Ph)(C6F5)3]- (2a ) as a yellow oil. NMR studies on 2a in CD2Cl2
show no evidence for η2-benzyl formation or anion coordination. Protonation of cis- or tr a n s-
1a with [n-Bu3NH]+[BPh4]- similarly yields [Zr(DAC)(CH2Ph)]+[BPh4]- (2b). Cation 2a
reacts with t-BuNC to form the vinyl amide complex [Zr(DAC){N(t-Bu)CHdCHPh}]+[B(CH2-
Ph)(C6F5)3]- (3). p-Tolylacetylene undergoes catalytic dimerization to (Z)-1,4-di-p-tolyl-1-
buten-3-yne in the presence of 2a .
Recently we have been investigating the use of
complexes, the saturated framework avoids problems
associated with alkyl migration to an unsaturated
center on the ancillary ligand.4a,6f In any event, a
comparison of the reactivity of DAC, Schiff base mac-
rocycles, and Cp ligand systems should provide valuable
insights into ancillary ligand effects for this important
class of organometallic molecules.
deprotonated 4,13-diaza-18-crown-6 (DAC) as an ancil-
lary ligand in group 3 and f-element chemistry.1 From
our previous studies, it is apparent that DAC is the
-
approximate steric equivalent of two Cp* (C5Me5
)
ligands; however, greater flexibility and variable donor
capacity distinguish the DAC ligand system from Cp*.
The successful synthesis of Y(DAC)R (R ) CH2SiMe3,
CH(SiMe3)2)1b suggested that preparation of the isoelec-
tronic (DAC)Zr(R)+ cations should be possible.
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mann, M.; Lancaster, S. J . Organometallics 1993, 12, 633.
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Chem., Int. Ed. Engl. 1987, 26, 70. (b) Yang, C. H.; Ladd, J . A.;
Goedken, V. L. J . Coord. Chem. 1988, 18, 317. (c) Cotton, F. A.;
Czuchajowska, J . Polyhedron 1990, 21, 2553. (d) DeAngelis, S.; Solari,
E.; Gallo, E.; Chiesi-Villa, A.; Floriani, C.; Rizzoli, C. Inorg. Chem. 1992,
31, 2520. (e) Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen, J .
D.; J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 8493. (f) J acoby, D.;
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3595.
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(b) Schaverien, C. J . J . Chem. Soc., Chem. Commun. 1991, 458. (c)
Schaverien, C. J .; Orpen, A. G. Inorg. Chem. 1991, 30, 4968. (d)
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Shibata, K.; Aida, T.; Inoue, S. Chem. Lett. 1992, 1173. (f) Brand, H.;
Arnold, J . J . Am. Chem. Soc. 1992, 114, 2266. (g) Brand, H.; Arnold,
J . Organometallics 1993, 12, 3655. (h) Kim, H.-J .; Whang, D.; Kim,
K.; Do, Y. Inorg.Chem. 1993, 32, 360. (i) Ryu, S.; Whang, D.; Kim, J .;
Yeo, W.; Kim, K. J . Chem.Soc., Dalton Trans. 1993, 2005.
(6) (a) Dell’Amico, G.; Marchett, F.; Floriani, C. J . Chem. Soc., Dalton
Trans. 1982, 2197. (b) Mazzanti, M.; Rosset, J . M.; Floriani, C.; Chiesi-
Villa, A.; Guastini, C. J . Chem. Soc., Dalton Trans. 1989, 953. (c)
Floriani, C. Polyhedron 1989, 8, 1717. (d) Cobrazza, F.; Solari, E.;
Floriani, C.; Chiesi-Villa, A.; Guastini, C. J . Chem. Soc., Dalton Trans.
1990, 1335. (e) Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J .
Chem. Soc., Dalton Trans. 1992, 367. (f) Tjaden, E. B.; Swenson, D.
C.; J ordan, R. F.; Petersen, J . L. Organometallics 1995, 14, 371.
Cationic d0 Cp2M(R)+ (M ) Ti, Zr, Hf) complexes
exhibit impressive stoichiometric and catalytic reactivity
due to the increased Lewis acidity at the metal center
and the presence of a vacant site cis to a highly polarized
Mδ+-Rδ- bond.2 Specifically, J ordan has demonstrated
rich insertion chemistry2 while several groups have
explored the high Ziegler-Natta olefin polymerization
activity of these systems.2,3 By comparison, the reactiv-
ity of group 4 alkyl cations with ancillary ligands other
than Cp has not been as well-studied. Recently, tet-
raaza macrocycles,4 porphyrins,5 and acyclic Schiff base
ligands ([R6-acen]Zr(R′)+; R ) H, F)6 have seen increas-
ing use. The DAC ligand system differs from these
ligands in three important ways: (i) greater flexibility,
(ii) complete saturation, and (iii) increased electron-
donating ability. While the last point may be expected
to decrease the reactivity of the DAC-derived alkyl
* Author to whom correspondence should be addressed. E-mail:
djberg@uvic.ca.
X Abstract published in Advance ACS Abstracts, April 15, 1997.
(1) (a) Lee, L.; Berg, D. J .; Bushnell, G. W. Inorg. Chem. 1994, 33,
5302. (b) Lee, L.; Berg, D. J .; Bushnell, G. W. Organometallics 1995,
14, 8. (c) Lee, L.; Berg, D. J .; Bushnell, G. W. Organometallics 1995,
14, 5021.
(2) (a) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. (b)
J ordan, R. F. J . Chem. Educ. 1988, 65, 285. (c) Guram, A. S.; J ordan,
R. F. In Comprehensive Organometallic Chemistry, 2nd ed.; Lappert,
M. F., Ed.; Pergamon Press: Oxford, U.K., 1995; Vol. 4, pp 589-625.
S0276-7333(96)01027-8 CCC: $14.00 © 1997 American Chemical Society

Cationic Zr Dialkyl and Alkyl Complexes
Organometallics, Vol. 16, No. 12, 1997 2557
Ta ble 1. 1H NMR Sp ectr oscop ic Da ta a
In this contribution, we report the synthesis and
characterization of dialkyl and cationic alkyl complexes
of zirconium which contain the DAC ligand: Zr(DAC)-
R2 (R ) CH2Ph, 1a ; R ) CH2SiMe3, 1b; R ) CH2CMe3,
1c) and [Zr(DAC)(CH2Ph)]+[BR4]- (2: (BR4 ) B(CH2-
Ph)(C6F5)3, 2a ; BR4 ) BPh4, 2b). Preliminary reactivity
studies are also reported for 2a .
compd
δ, ppm (int)
mult
J , Hz
assignt
cis-1a b
7.22-7.31 (8)
6.84 (2)
m
tt
m
m
m
s
o,m-aryl
7.0, 1.5 p-aryl
NCH2CH2OCH2
3.57 (4), 3.15c (4)
3.40 (4), 2.84c (4)
3.05d (8)
NCH2CH2OCH2
NCH2CH2OCH2
CH2Ph
2.46 (4)
tr a n s-1a b,e 7.11 (4)
6.81 (4)
t
7.3
7.8
7.3
5.2
m-aryl
o-aryl
p-aryl
br d
t
t
br s
t
s
m
m
m
s
Exp er im en ta l Section
6.72 (2)
3.52 (8)
3.37 (8)
3.11 (8)
NCH2CH2OCH2
NCH2CH2OCH2
NCH2CH2OCH2
CH2Ph
NCH2CH2OCH2
NCH2CH2OCH2
NCH2CH2OCH2
SiMe3
Gen er a l P r oced u r es. All manipulations were carried out
under an argon atmosphere, with the rigorous exclusion of
oxygen and water, using standard glovebox (Braun MB150-
GII) or Schlenk techniques, except as noted in the text.
Tetrahydrofuran (THF), diethyl ether, hexane, and toluene
were dried by distillation from sodium benzophenone ketyl
under argon immediately prior to use. 4,13-Diaza-18-crown-6
(H2DAC) was prepared according to a literature procedure7
from 1,2-bis(2-iodoethoxy)ethane8 and 1,8-diamino-3,6-dioxa-
octane7 in 30% yield after recrystallization from hexane.
Anhydrous ZrCl4 was purchased from Aldrich and used
5.2
1.71 (4)
cis-1bb
cis-1cb
2a f
3.47 (4), 3.12c (4)
3.05 (4), 2.68c (4)
2.93 (4), 2.51c (4)
0.43 (18)
-1.39 (4)
s
CH2SiMe3
3.50 (4), 3.13c,d (4)
3.13d (4), 2.74c (4)
2.99 (4), 2.54c (4)
1.49 (18)
m
m
m
s
NCH2CH2OCH2
NCH2CH2OCH2
NCH2CH2OCH2
CMe3
10
without further purification. Zr(CH2Ph)49 and Zr(CH2Ph)2Cl2
0.09 (4)
s
CH2CMe3
6.78-6.98 (10)
4.29 (4), 4.02c (4)
3.88 (8)
m
m
m
m
br s
s
aryl
were prepared according to literature procedures. Tris(penta-
fluorophenyl)boron was a gift from Boulder Scientific Co.
1H and 13C spectra were recorded on a Bruker WM 250 MHz
or a Bruker AMX 360 MHz spectrometer. Spectra were
recorded in C6D6, C7D8, or C4D8O solvent, previously distilled
from sodium under argon or in CD2Cl2 dried over 4 Å molecular
sieves, using 5 mm tubes fitted with a Teflon valve (Brunfeldt).
All solvents were thoroughly degassed prior to use. 1H and
13C NMR data for all compounds are collected in Tables 1 and
2, respectively. Melting points were recorded using a Reichert
hot stage and are not corrected. Elemental analyses were
performed by Canadian Microanalytical, Delta, BC, Canada,
or Atlantic Microanalytical, Atlanta, GA. Gas chromatography
was performed using a Varian 3700 gas chromatograph.
cis- a n d tr a n s-Zr (DAC)(CH2P h )2 (cis-/tr a n s-1a ). A solu-
tion of H2DAC (0.215 g, 0.953 mmol) in 20 mL of toluene was
added rapidly to a stirred solution of Zr(CH2Ph)4 (0.434 g, 0.953
mmol) in 20 mL of toluene. After the mixture was stirred for
1 h, the stirbar was removed and the reaction solution was
cooled at -30 °C overnight. Pale yellow cis-1a and orange
tr a n s-1a slowly deposited and were collected by decanting the
mother liquor. Combined yield: 0.41 g (80%). Manual
separation afforded the pure cis and trans isomers in a 1:4
ratio. cis-1a : mp 85-86 °C. Anal. Calcd for C26H38N2O4Zr:
C, 58.50; H, 7.18; N, 5.24. Found: C, 58.05; H, 7.11; N, 4.95.
tr a n s-1a : mp 108-110 °C. Anal. Calcd for C26H38N2O4Zr:
C, 58.50; H, 7.18; N, 5.24. Found: C, 57.92; H, 7.15; N, 5.00.
Pure samples of cis- or tr a n s-1a slowly isomerized back to a
1:4 equilibrium mixture over a period of days in d6-benzene
or weeks in d8-THF.
NCH2CH2OCH2
NCH2CH2OCH2
NCH2CH2OCH2
BCH2Ph
3.58 (4), 3.13c (4)
2.86 (2)
2.20 (2)
ZrCH2Ph
2bg
7.31 (8)
6.98 (2)
6.90 (8)
br m
t
t
m-aryl B
m-aryl (benzyl)
o-aryl B
7.5
7.4
6.76 (4)
6.74 (2)
tt
d
7.3, 1.0 p-aryl B
7.0
o-aryl (benzyl)
6.63 (1)
tt
m
m
m
s
m
m
d
7.3, 1.0 p-aryl (benzyl)
NCH2CH2OCH2
NCH2CH2OCH2
NCH2CH2OCH2
ZrCH2Ph
3.90 (4), 3.77c,d (4)
3.77d (4), 3.05c (4)
3.64 (4), 3.38c (4)
1.87 (2)
3f
7.35 (2)
7.22 (3)
7.14 (1)
6.92 (2)
6.74 (3)
6.42 (1)
m-aryl Bh
o,p-aryl Bh
14.0
NCHdCH
m
m
d
m-aryl (benzyl)h
o,p-aryl (benzyl)h
NCHdCH
14.0
4.42 (2), 4.32 (2),
4.25 (2), 4.19 (2),
4.00 (2), 3.95 (2),
3.89 (2), 3.84 (2),
3.73 (2), 3.53 (2),
3.32 (4)
m
DAC CH2
2.86 (2)
1.26 (9)
br s
s
BCH2Ph
CMe3
a
Spectra were recorded at 360 MHz and 293 K unless otherwise
b
specified. d6-Benzene. c exo and endo protons have not been
d
assigned. Partially overlapping resonances. e Recorded at 343 K.
g
h
f CD2Cl2. d8-THF. Assignments tentative.
were collected by decanting the mother liquors. cis-1b: yield
0.097 g (92%); mp 165 °C dec. 29Si NMR (d6-benzene, 49.69
MHz): δ 0.24. cis-1c: yield: 0.080 g (81%); mp 190 °C dec.
Anal. Calcd for C22H46N2O4Zr: C, 53.51; H, 9.39; N, 5.67.
Found: C, 52.49; H, 9.01; N, 5.19.
cis-Zr (DAC)R2 (R ) CH2SiMe3, cis-1b; R ) CH2CMe3,
cis-1c). H2DAC (0.053 g, 0.20 mmol) and Zr(CH2Ph)2Cl2 (0.10
g, 0.20 mmol) were separately dissolved in 10 mL of toluene,
followed by dropwise addition of the H2DAC solution to that
of the zirconium complex. Immediate precipitation of a white
solid, presumed to be polymeric [Zr(DAC)Cl2]x, was observed.
After the mixture was stirred for 1 h, a solution of the
appropriate alkyllithium reagent (2 equiv) was added and the
resulting suspension was stirred for a further 30 min. This
suspension was then filtered through Celite, and the clear, pale
yellow filtrate was concentrated to ca. 2 mL and cooled to -30
°C. Crystals of pure cis-1b (colorless) and cis-1c (pale yellow)
[Zr (DAC)(CH2P h )]+[B(CH2P h )(C6F 5)3]- (2a ). Reaction of
a mixture of cis- and tr a n s-1a (1.00 g, 1.88 mmol) with 1 equiv
of B(C6F5)3 (0.960 g, 1.88 mmol) in benzene resulted in
quantitative formation of 2a as a sparingly soluble, bright
yellow oil. This oil was freely soluble in d8-THF and CD2Cl2,
but we were unsuccessful in crystallizing 2a from these
solvents, either as a neat compound or as mixtures with
toluene or hexane. Satisfactory elemental data could not be
obtained, probably due to difficulties in removing trace solvent.
(7) Gatto, V. J .; Arnold, K. A.; Viscariello, A. M.; Miller, S. R.;
Morgan, C. R.; Gokel, G. W. J . Org. Chem. 1986, 51, 5373.
(8) Kulstad, S.; Malmsten, L. A. Acta Chem. Scand., Ser. B 1979,
33B, 469.
(9) Zucchini, U.; Albizatti, E.; Giannini, U. J . Organomet. Chem.
1971, 26, 357.
19F NMR (CD2Cl2, 338.86 MHz): δ -129.6 (o-arylF, d, J FF
)
22 Hz), -162.9 (m-arylF, t, J FF ) 22 Hz), -165.8 (p-arylF, t,
J FF ) 21 Hz).
[Zr (DAC)(CH2P h )]+[BP h 4]- (2b). Reaction of a mixture
of cis- and tr a n s-1a (0.060 g, 0.11 mmol) with 1 equiv of
[n-Bu3NH]+[BPh4]- (0.057 g, 0.11 mmol) in benzene resulted
(10) Wengrovius, J . H.; Schrock, R. R. J . Organomet. Chem. 1981,
205, 319.

2558 Organometallics, Vol. 16, No. 12, 1997
Ta ble 2. 13C{1H} NMR Sp ectr oscop ic Da ta a
δ, ppm (assignt)
Lee et al.
compound
cis-1a b
154.7 (ipso-aryl), 127.6 (o-aryl), 126.8 (m-aryl), 118.7 (p-aryl), 73.9 (OCH2), 72.0 (OCH2), 56.3 (NCH2), 60.0 (CH2Ph,
1J CH ) 119 Hz)
tr a n s-1a b,c 155.3 (ipso-aryl), 127.5 (o-aryl), 125.9 (m-aryl), 117.7 (p-aryl), 74.5 (OCH2), 71.6 (br s, OCH2), 56.1 (NCH2), 54.2(CH2Ph,
1J CH ) 120 Hz)
cis-1bb
cis-1cb
2a d
71.5 (OCH2), 67.6(OCH2), 52.7 (NCH2), 4.9 (SiMe3), -9.9 (CH2Si, J CH ) 103 Hz)
1
1
71.4 (OCH2), 67.5 (OCH2), 53.0 (NCH2), 37.6 (CMe3), 33.0 (CMe3), 29.2 (CH2CMe3, J CH ) 100 Hz)
1
1
148.9 (ipso-aryl), 148.0 (o-aryl CF, J CF ) 228 Hz), 144.4 (ipso-aryl), 137.9 (p-aryl CF, J CF ) 243 Hz), 136.9 (m-arylCF,
1J CF ) 258 Hz), 129.2 (aryl), 129.1 (aryl), 128.7 (aryl), 127.20 (aryl), 123.2 (aryl), 122.9 (aryl), 75.8 (OCH2), 72.3 (OCH2),
1
53.8 (NCH2), 59.8 (ZrCH2Ph, J CH ) 127 Hz), 32.4 (BCH2Ph)
2be
3d,f
152.5 (benzyl ipso-aryl), 137.2 (o-BPh4), 128.1 (benzyl o-aryl), 127.4 (benzyl m-aryl), 125.9 (m-BPh4), 122.1 (p-BPh4),
120.4 (benzyl p-aryl), 76.1 (OCH2), 73.5 (OCH2), 59.1 (ZrCH2Ph), 56.8 (NCH2)
1
1
148.9 (ipso-aryl), 148.6 (aryl CF, J CF ) 241 Hz), 139.1 (ipso-aryl), 137.9 (arylCF, J CF ) 244 Hz), 135.4 (arylCF,
1J CF ) 246 Hz), 135.0 (NCH)CH), 129.0 (aryl), 129.0 (aryl), 127.2 (aryl), 125.8 (aryl), 125.4 (aryl), 122.8 (aryl),
111.2 (CH)CHPh), 77.1 (OCH2), 73.6 (OCH2), 73.2 (OCH2), 69.2 (OCH2), 58.5 (NCMe3), 55.1 (NCH2), 54.8 (NCH2),
32.3 (BCH2Ph), 30.2 (NCMe3)
a
b
d
Spectra were recorded at 90.55 MHz and 293 K unless otherwise specified. d6-Benzene. c Recorded at 343 K. CD2Cl2. e d8-THF.
f ipso-C6F5B resonance not observed.
Ta ble 3. Su m m a r y of Cr ysta llogr a p h ic Da ta for
crystal was transferred to a Nonius CAD4F diffractometer
equipped with Ni-filtered Cu KR radiation. The unit cell was
refined using 25 reflections in the 2θ range 48-76°. Experi-
mental density was not determined because of the air and
moisture sensitivity of the compound. Three standard reflec-
tions, measured periodically during data collection (10,0,0, 040,
and 802), showed no significant decline in combined intensity.
Intensity measurements were collected for one-fourth of the
sphere. After the usual data reduction procedures, the
structure was solved using SHELX76 and the Patterson
function. The refinements minimized Σw((|Fo| - |Fc|)2) and
proceeded normally using SHELX76.12 The criterion for
inclusion of reflections was I > 2.5σ(I). The weighting scheme
was determined by counting statistics using w ) 1/σ2(F) +
0.001(F2). Convergence was satisfactory: max shift/esd )
0.004. A total of 298 parameters (33 × 9 parameters per atom
+ scale) were refined. No intermolecular contacts shorter than
3.4 Å were observed. The structural plots were drawn with
ORTEP13 or the ZORTEP14 modification.
cis-1a
formula
fw
cryst syst
C26H38N2O4Zr
533.81
monoclinic
Z
4
F(calcd) (g cm-3
)
1.391
38.34
Cu KR, 1.542
ambient
100
µ (cm-1
)
space group P21/c (No. 14) radiation, λ (Å)
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
20.178(3)
7.805(2)
16.711(2)
90
104.350(9)
90
T
2θmax (deg)
no. of obsd rflns
2663
no. of unique rflns 2447
Ra
Rw
0.0634
0.0754
b
2549.5
a
b
2
R ) Σ(|Fo| - |Fc|)/Σ|Fo|. Rw ) [Σw(|Fo| - |Fc| )/Σw(|Fo|)2]1/2
.
in precipitation of 2b as a pale yellow solid: yield 0.080 g
(95%); mp 180 °C dec. Anal. Calcd for C43H51BN2O4Zr: C,
67.79; H, 6.75; N, 3.67. Found: C, 66.80; H, 6.44; N, 3.44.
[Zr (DAC)(N(t-Bu )CHdCHP h )]+[B(CH2P h )(C6F 5)3]- (3).
A toluene solution of tert-butyl isocyanide (0.413 mL of a 0.136
M solution; 0.056 mmol) was added to a stirred solution of 2a
(generated in situ from 0.030 g of cis-/tr a n s-1a and 0.029 g
of B(C6F5)3 in 10 mL of toluene). After the mixture was stirred
for 1 h, the volatiles were removed under reduced pressure to
yield 3 as a yellow oil. 19F NMR (CD2Cl2, 338.86 MHz): δ
-129.6 (o-arylF, d, J FF ) 24 Hz), -162.8 (m-arylF, m), -165.8
(p-arylF, t, J FF ) 21 Hz).
Rea ction of 2a w ith Excess p-Tolyla cetylen e. An
excess of p-tolylacetylene (20-fold excess, 2.0 mmol) was added
to a Schlenk tube containing a solution of 2a in toluene (0.10
mmol in 20 mL). The solution was stirred vigorously, and
samples were withdrawn periodically and examined by GC to
determine the extent of conversion. Catalytic dimerization of
p-tolylacetylene to an isomeric mixture of 1,4-di-p-tolyl-1-
buten-3-ynes (Z:E ratio ) 85:15) was observed. An initial
turnover rate of 2 mol of enyne/(mol of 2a h) was observed.
The product was identified by comparison of the 1H and 13C
NMR spectra with literature values for the phenyl analog11
and by comparison of the GC-MS traces of the hydrolyzed
product with an authentic sample.
Resu lts a n d Discu ssion
Syn th esis of cis- a n d tr a n s-Zr (DAC)R2 (R )
CH2P h , 1a ; R ) CH2SiMe3, 1b; R ) CH2CMe3, 1c).
Direct protonation of Zr(CH2Ph)4 with H2DAC proceeds
smoothly in toluene to produce a 1:4 mixture of cis- and
tr a n s-1a (Scheme 1). The isomers are difficult to
separate by fractional crystallization, but small quanti-
ties of the pure isomers can be separated manually (cis-
1a , pale yellow; tr a n s-1a , orange). The cis isomer is
identifiable by the presence of six DAC multiplets in
the 1H NMR spectrum due to inequivalent exo and endo
protons on each of the three unique DAC carbons
(Tables 1 and 2). The trans isomer is expected to show
only three CH2 multiplets, since the protons on each
unique DAC carbon are equivalent in this geometry. At
room temperature, however, tr a n s-1a shows six proton
and six carbon resonances for the DAC ligand. When
the temperature is raised, the resonances in both the
X-r a y Str u ctu r a l Stu d ies of 1a . Both cis- and tr a n s-1a
were characterized by X-ray crystallography; however, disorder
in the DAC backbone of tr a n s-1a prevented satisfactory
refinement of this structure. Further crystallographic details
for tr a n s-1a are included in the supporting material. Crystal-
lographic data for cis-1a is given in Table 3. A crystal of cis-
1a (0.9 × 0.4 × 0.4 mm) was loaded into a glass capillary in
the glovebox and subsequently examined by photographic
methods using Weissenberg and precession cameras. The
space group was determined by the systematic absences. The
1
13C and H NMR spectra coalesce between ca. 30 and
50 °C and re-emerge as three new resonances at 70 °C.
The variable-temperature behavior of tr a n s-1a is most
clearly illustrated by 13C NMR (Figure 1). The lower
molecular symmetry apparent in the room-temperature
(12) Sheldrick, G. M. SHELX76, Programs for Crystal Structure
Determination; University of Cambridge, Cambridge, U.K., 1976.
(13) J ohnson, C. K. ORTEPII; Oak Ridge National Laboratory, Oak
Ridge, TN, 1976.
(11) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.; Zanobini,
F. Organometallics 1994, 13, 4616.
(14) Zsolnai, L. ZORTEP; University of Heidelberg, Heidelberg,
Germany, 1995.

Cationic Zr Dialkyl and Alkyl Complexes
Organometallics, Vol. 16, No. 12, 1997 2559
F igu r e 2. ZORTEP14 drawing illustrating the general
coordination geometry in one molecule of tr a n s-1a .
structural evidence for oxygen dissociation noted above
for tr a n s-1a and the large DAC ring size. The slower
rate of isomerization in THF could be due to strong
solvent coordination which enforces a high coordination
number at Zr and prevents rearrangement on steric
grounds.
In order to establish a more general route to com-
pounds of this type, we also explored the preparation
of Zr(DAC)Cl2. Attempts to prepare the dichloride from
ZrCl4 and M2DAC (M ) Li, Na, K) failed to yield clean
products. However, reaction of Zr(CH2Ph)2Cl2 with H2-
DAC produced an insoluble powder, presumed to be
polymeric [Zr(DAC)Cl2]x. Alkylation of this dichloride,
prepared in situ in toluene, with LiR (2 equiv) produced
cis-Zr(DAC)R2 (R ) CH2SiMe3, 1b; CH2CMe3, 1c) ex-
clusively (eq 1). Isomerization was not observed for
F igu r e 1. Variable-temperature 13C{1H} NMR spectra of
the DAC region of tr a n s-1a in d6-benzene: (A) NCH2; (B)
OCH2; (C) OCH2; (D) CH2Ph (cis-1a impurity resonances
are denoted by an asterisk).
Sch em e 1
either cis-1b or cis-1c over a period of weeks in
d6-benzene. The increased size of CH2CMe3 and CH2-
SiMe3 relative to CH2Ph may make isomerization
impossible for steric reasons, or the cis isomers may
simply represent the thermodynamically more stable
forms.
X-r a y Str u ctu r es of Zr (DAC)(CH2P h )2. cis- and
tr a n s-1a were investigated by X-ray crystallography.
Refinement was not satisfactory for the trans isomer
due to unreasonable thermal parameters for the mac-
rocyclic ring atoms, especially the dangling oxygen (O3).
As a result, the bond distances and angles are of low
precision and do not warrant further discussion. A plot
of the structure (Figure 2) reveals a distorted pentagonal
NMR spectrum of tr a n s-1a is most easily explained by
asymmetric coordination of the DAC ligand. The solid-
state structure of tr a n s-1a (vide infra) shows a seven-
coordinate, distorted-pentagonal-bipyramidal structure
with one dangling oxygen donor (Figure 2). While this
structure cannot represent the room-temperature solu-
tion structure since it would have 12 inequivalent
carbons, a similar structure with two dangling oxygens
is reasonable. The dynamic process therefore likely
involves rapid dissociation and reassociation of the DAC
oxygens (∆G* ) 62 ( 2 kJ /mol).15
Pure cis- and tr a n s-1a slowly undergo isomerization
to a 1:4 cis:trans equilibrium mixture when redissolved.
Isomerization proceeds more rapidly in d6-benzene
(days) than in d8-THF (weeks). cis-trans isomerization
requires one benzyl group to pass through the DAC
ring.16 This appears to be possible, given the NMR and
(15) The free energy of activation for this process was calculated
from the coalescence temperature (Tc) using the equal-population, two-
site exchange equation: ∆G* ) (1.912 × 10-2)Tc[9.972 + log(Tc/δν)] in
kJ /mol, where δν is the separation of the resonances in Hz and Tc is
in K (Sandstrom, J . Dynamic NMR Spectroscopy; Pergamon: London,
1982; pp 77-91). The value of ∆G* was estimated for the δ 73.6 and
69.6 (δν ) 366 Hz, Tc ) 323 K) and for the δ 56.5 and 55.35 ppm (δν
) 100 Hz, Tc ) 308 K) sets of resonances. The error in ∆G* of (2
kJ /mol was estimated by assuming liberal errors of (5 K in Tc and
(5 Hz in δν.
(16) This is based on the assumption that the process is unimolecu-
lar in nature. A bimolecular process involving alkyl transfer between
two Zr centers cannot be ruled out.

2560 Organometallics, Vol. 16, No. 12, 1997
Lee et al.
the Zr-C bond lengths are long by the same comparison
(cis-1a , 2.417(7) and 2.389(6) Å; Y(DAC)(CH2SiMe3),
2.45(2) Å). Unlike the Y-O distances in Y(DAC)(CH2-
SiMe3), which were found to span a wide range
(2.431(13)-2.622(11) Å), the four Zr-O distances
(2.466(6)-2.477(5) Å) in cis-1a are very nearly identical
with one another. Despite the fact that the basket
geometry found in cis-1a appears to provide a better
fit to Zr than the distorted-belt arrangement in tr a n s-
1a , NMR evidence (vide supra) points to the latter
complex as the most stable in benzene solution.
Syn t h esis of Ca t ion ic Zir con iu m Com p lexes.
Treatment of either cis- or tr a n s-1a with B(C6F5)3 in
toluene yielded [Zr(DAC)(CH2Ph)]+[B(CH2Ph)(C6F5)3]-
(2a ) as a bright yellow oil which dissolved readily in
THF or CH2Cl2 (Scheme 1). The 1H NMR spectrum,
recorded in CD2Cl2 (Table 1), shows the presence of
inequivalent exo and endo protons on each of the three
unique DAC carbons. In comparison to cis-1a , the DAC
protons are shifted downfield by 0.3-0.6 ppm, in keep-
ing with coordination of the DAC ring to a positively
charged center. However, little difference in 13C chemi-
cal shift is observed for the ring carbons. The ZrCH2
proton resonance shifts upfield by 0.26 ppm in cationic
2a ; a similar upfield shift has been observed previously
for Schiff base supported zirconium alkyl cations.6f The
presence of a benzyl group bound to boron is clearly
evident from the broad singlet at δ 2.86 and the
presence of two sets of aryl proton and carbon reso-
nances. A number of NMR parameters which have been
cited as evidence for an η2-CH2Ph interaction are
notably absent. Specifically, upfield shifts of the benzyl
ipso carbon and ortho proton resonances to ca. 137.5 and
less than 6.40 ppm,19 respectively, and an unusually
F igu r e 3. ZORTEP14 drawings of cis-1a showing the side
(A) and top (B) views.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for cis-1a a
Distances
Zr(1)-O(1)
Zr(1)-O(3)
Zr(1)-N(1)
Zr(1)-C(13)
2.471(5)
2.477(5)
2.119(7)
2.417(7)
Zr(1)-O(2)
Zr(1)-O(4)
Zr(1)-N(2)
Zr(1)-C(14)
2.466(6)
2.470(5)
2.2124(6)
2.389(8)
Angles
O(1)-Zr(1)-O(2)
O(1)-Zr(1)-O(4)
O(1)-Zr(1)-N(2)
O(1)-Zr(1)-C(14)
O(2)-Zr(1)-O(4)
O(2)-Zr(1)-N(2)
O(2)-Zr(1)-C(14)
O(3)-Zr(1)-N(1)
O(3)-Zr(1)-C(13)
O(4)-Zr(1)-N(1)
O(4)-Zr(1)-C(13)
N(1)-Zr(1)-N(2)
N(1)-Zr(1)-C(14)
N(2)-Zr(1)-C(14)
65.3(2) O(1)-Zr(1)-O(3)
131.4(2) O(1)-Zr(1)-N(1)
81.8(2) O(1)-Zr(1)-C(13)
81.4(2) O(2)-Zr(1)-O(3)
148.8(2) O(2)-Zr(1)-N(1)
68.9(2) O(2)-Zr(1)-C(13)
75.5(2) O(3)-Zr(1)-O(4)
81.1(2) O(3)-Zr(1)-N(2)
82.0(2) O(3)-Zr(1)-C(14)
68.8(2) O(4)-Zr(1)-N(2)
76.8(2) O(4)-Zr(1)-C(14)
106.5(2) N(1)-Zr(1)-C(13)
96.3(3) N(2)-Zr(1)-C(13)
144.2(3) C(13)-Zr(1)-C(14)
128.4(2)
68.4(2)
143.2(2)
130.8(2)
133.7(2)
79.1(2)
64.6(2)
67.9(2)
144.5(2)
132.4(2)
81.3(2)
145.5(3)
94.4(2)
80.8(3)
1
large J CH value of greater than 140 Hz for the benzyl
CH2 group20 are not observed here (for 2a : benzyl ipso
carbon, δ 148.93 ppm; ortho benzyl proton, δ 6.78-
1
6.85 ppm; benzyl CH2, J CH ) 127 Hz). The small
∆δ(m,p-F) value of 2.9 ppm and the upfield ipso carbon
resonance (δ 144.4 ppm; free anion, δ 148.6 ppm) for
-
the B(CH2Ph)(C6F5)3 anion in the 19F and 13C NMR
spectra indicate that no significant anion-cation inter-
actions are present.20
Reaction of 1a with [n-Bu3NH]+[BPh4]- afforded a
pale yellow precipitate of [Zr(DAC)(CH2Ph)]+[BPh4]-
(2b) in high yield. Complex 2b, unlike 2a , does not
dissolve in CD2Cl2, presumably reflecting stronger
anion-cation interactions in 2b. However, 2b dissolves
readily in d8-THF and shows no evidence for strong
anion-cation pairing in this solvent.
Zr(1)-C(13)-C(15) 123.7(5) Zr(1)-C(14)-C(21) 128.3(6)
a
Estimated standard deviation in parentheses.
bipyramid with one dangling oxygen donor. It appears
that Zr is too small to coordinate all six donors in a
planar array without introducing strain into the
macrocyclic ring.
R ea ct ion Ch em ist r y of [Zr (DAC)(CH2P h )]+-
[B(CH2P h )(C6F 5)3]- (2a ). Reaction of 2a with p-
The structure of cis-1a is shown in Figure 3. Frac-
tional atomic coordinates are given in the Supporting
Information, and selected bond distances and angles are
collected in Table 4. The zirconium center is eight-
coordinate, with all four ether oxygens of the DAC
ligand being coordinated. The coordination geometry
may be described as a highly distorted square antiprism
(Figure 3B). The most significant features of the
structure are the open Zr-CH2-Cipso angles (123.7(5)
and 128.3(6)° for Zr-C13-C15 and Zr-C14-C20, re-
spectively), indicating strictly η1-benzyl coordination.17
The Zr-N distances (2.124(6) and 2.119(7) Å) are very
similar to those found in seven-coordinate Y(DAC)(CH2-
SiMe3) (2.27(2) and 2.26(2) Å) after correcting for the
0.12 Å larger ionic radius of the Y3+ ion.18 However,
(17) Many examples of η2-benzyl ligands are known in early-
transition-metal and lanthanide chemistry, typically with M-C-Cipso
angles of less than 100°. See for example: (a) Mintz, E. A.; Moloy, K.
G.; Marks, T. J .; Day, V. W. J . Am. Chem. Soc. 1982, 104, 4692. (b)
Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B.
J . Chem. Soc., Dalton Trans. 1984, 2789. (c) Edwards, P. G.; Andersen,
R. A.; Zalkin, A. Organometallics 1984, 3, 293. (d) Latesky, S. L.;
McMullen, A. K.; Niccolai, G. P.; Rothwell, I. P.; Huffman, J . C.
Organometallics 1985, 4, 902. (e) J ordan, R. F.; LaPointe, R. E.; Bajgur,
C. S.; Echols, S. F. J . Am. Chem. Soc. 1987, 109, 4111. (f) J ordan, R.
F.; LaPointe, R. E.; Baenziger, N.; Hinch, G. D. Organometallics 1990,
9, 1539.
(18) Shannon, R. D. Acta Crystallogr. Sect. A 1976, A32, 751.
(19) Pellecchia, C.; Immirzi, A.; Grassi, A.; Zambelli, A. Organome-
tallics 1993, 12, 4473.
(20) Horton, A. D.; de With, J .; van der Linden, A.; van de Weg, H.
Organometallics 1996, 15, 2672.

Cationic Zr Dialkyl and Alkyl Complexes
Organometallics, Vol. 16, No. 12, 1997 2561
Sch em e 2a
previously been reported in the reaction of Cp2Zr[CH2-
(2-Me-py)]2 with xylyl isocyanide.24 Surprisingly, how-
ever, a very stable iminoacyl derivative was obtained
upon xylyl isocyanide insertion into the corresponding
Zr-benzyl bond of Cp2Zr(CH2Ph)2.24 In fact, to the best
of our knowledge this is the first example of isonitrile
insertion into the Zr-alkyl bond of a cationic complex
which does not yield a stable iminoacyl.25,26 It is
possible that steric crowding drives the η2-iminoacyl to
η1-vinylamido rearrangement in the present case.
a
DAC ligands omitted.
tolylacetylene leads to slow catalytic production of 1,4-
di-p-tolyl-1-buten-3-yne (Z:E ratio ) 85:15) at an initial
rate of 2 turnovers/h. Catalytic dimerization of p-
tolylacetylene by Cp2ZrCH2Ph+ has previously been
reported to yield 2,4-di-p-tolyl-1-buten-3-yne by a simple
insertion/protonolysis cycle.21 It is likely that an equiva-
lent cycle (Scheme 2) is operative here, although it is
not obvious why a 1,4-substituted enyne is obtained in
this case while a 2,4-substituted product (“head-to-tail”
insertion) was obtained in the Cp system. This result
appears quite surprising, because 2a is more sterically
congested than [Cp2Zr(CH2Ph)]+ and would therefore
be expected to favor formation of the 2,4-substituted
enyne since the insertion leading to this isomer is clearly
less sterically crowded.22 It is possible that the DAC
backbone is flexible enough to allow electronic factors
to dictate “tail-to-tail” insertion.23
Con clu d in g Rem a r k s
The results presented here extend the use of the
deprotonated aza crown ether, DAC, to organozirconium
chemistry. It is evident from the successful preparation
of Zr(DAC)R2 and Zr(DAC)R+ derivatives that DAC
behaves similarly to the bis(cyclopentadienyl) ancillary
ligand set. The greater flexibility of the DAC framework
can, however, lead to geometries such as that found in
trans-Zr(DAC)(CH2Ph)2 (tr a n s-1a ), which are not pos-
sible in the bis-Cp system. Although some variation in
reactivity, such as the regiochemistry of alkyne insertion
(Scheme 2), has been noted here, further studies are
necessary to determine whether differences in geometry
and ligand flexibility will translate into major differ-
ences in reactivity.
Cation 2a reacts rapidly with 1 equiv of t-BuNC to
produce the vinylamide complex 3. The H NMR of 3
1
shows two alkenyl proton resonances at 7.14 and 6.42
Ack n ow led gm en t. We thank Mrs. C. Greenwood
for assistance with the NMR experiments and Ms.
Becky Chak for help with the X-ray structural studies.
A gift of tris(pentafluorophenyl)boron from the Boulder
Scientific Co. is gratefully acknowledged. This research
was supported by the NSERC (Canada) and a Univer-
sity of Victoria Internal Research Grant (to D.J .B.).
(3J HH ) 14 Hz) ppm with corresponding 13C NMR
1
resonances at 135.04 and 111.16 ppm (1H-1H and H-
13C COSY). The 3J HH coupling constant suggests a trans
stereochemistry about the double bond. 19F NMR data
again indicate that the anion is not coordinated in CD2-
Cl2 (∆δ(m,p-F) ) 3.0 ppm).20
Formation of a vinylamide is likely to arise by a 1,2-
proton rearrangement of the iminoacyl group formed by
initial insertion of the isonitrile into the zirconium-
carbon bond (eq 2). A similar rearrangement has
Su p p or tin g In for m a tion Ava ila ble: Text giving X-ray
experimental details for tr a n s-1a and tables giving complete
bond distances and angles, anisotropic thermal parameters,
and positional parameters for cis-1a (7 pages). Ordering
information is given on any current masthead page.
(21) Horton, A. D. J . Chem. Soc., Chem. Commun. 1992, 185.
(22) This conclusion is based on a comparison of the neutral dibenzyl
complexes. The substituted Cp derivatives Zr(EBTHI)2(CH2Ph)2 (EBT-
HI ) rac-(ethylenebis(tetrahydroindenyl))17f (2.314(4) Å) and Zr(Me3-
SiC5H4)2(CH2Ph)2 (see reference below, 2.291(5)-2.323(5) Å), which
may be expected to be more crowded than the simple Cp complex Cp2-
Zr(CH2Ph)2, show Zr-C bond lengths which are much shorter than
those found in cis-1a (2.417(7) and 2.389(6) Å): (a) Thiele, K. H.;
Bo¨hme, U.; Sieler, A. Z. Anorg. Allg. Chem. 1993, 619, 1951.
(23) One possible explanation for the observed insertion regiochem-
istry might involve an interaction between the alkenyl phenyl ring and
the Zr center, either through the arene π-system or, more likely,
through an ortho-aryl C-H agostic interaction (see Scheme 2). In our
opinion, this remains a possibility even though 2a is more crowded
than Cp2Zr(CH2Ph)+ because of the flexibility of the DAC ligand.
OM961027N
(24) (a) Beshouri, S. M.; Fanwick, P. E.; Rothwell, I. P.; Huffman,
J . C. Organometallics 1987, 6, 891. (b) Beshouri, S. M.; Chebi, D. E.;
Fanwick, P. E.; Rothwell, I. P.; Huffman, J . C. Organometallics 1990,
9, 2375. For a closely related rearrangement see: (c) Fandos, R.;
Meetsma, A.; Teuben, J . H. Organometallics 1991, 10, 2665.
(25) Most neutral Zr dialkyls insert isonitriles to form stable η2-
iminoacyls. For a brief review see: J ubb, J .; Song, J .; Richeson, D.;
Gambarotta, S. In Comprehensive Organometallic Chemistry, 2nd ed.;
Lappert, M. F., Ed.; Pergamon Press: Oxford, U.K., 1995; Vol. 4, pp
582-585.
(26) Guram, A. S.; J ordan, R. F. J . Org. Chem. 1993, 58, 5595.