Dibenzylzirconium complexes of chelating aminodiolates. Synthesis, structural studies, thermal stability, and insertion chemistry

Article abstract of DOI:10.1021/om9907324

Aminodiolate ligands, RN(CH₂CH₂C(O)R′₂)₂ (1a-e), allow the isolation of soluble, monomeric zirconium dialkyl complexes, [RN(CH₂CH₂C(O)R′2)2]ZrR″2 (2a-e, 5, 6). The fluxional behavior and th

Full text of DOI:10.1021/om9907324

Organometallics 2000, 19, 509-520
509
Diben zylzir con iu m Com p lexes of Ch ela tin g
Am in od iola tes. Syn th esis, Str u ctu r a l Stu d ies, Th er m a l
Sta bility, a n d In ser tion Ch em istr y
Pengcheng Shao,† Roland A. L. Gendron, David J . Berg,* and
Gordon W. Bushnell
Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria,
British Columbia, Canada V8W 3V6
Received September 20, 1999
Aminodiolate ligands, RN(CH2CH2C(O)R′2)2 (1a -e), allow the isolation of soluble, mono-
meric zirconium dialkyl complexes, [RN(CH2CH2C(O)R′2)2]ZrR′′2 (2a -e, 5, 6). The fluxional
behavior and thermal stability of these complexes are strongly dependent on the nature of
the substituents at the nitrogen center, with smaller substituents (R ) Me; 2a ,b, 5, 6)
increasing the rigidity and thermal stability of the complexes. Complexes bearing tert-butyl
groups (2c,d ) readily undergo thermal decomposition by elimination of isobutene. Thermal
ortho metalation of the chiral complex Zr[((S)-PhC(H)Me)N(CH2CH2C(O)Me2][CH2Ph]2 (2e)
affords the chiral metallacycle Zr[N{CH2CH2C(O)Me2}2{((S)-2-C6H4C(H)Me}][CH2Ph] (7),
which has been structurally characterized. Reaction of 7 with 1 equiv of aryl aldehyde (ArC-
(O)H; Ar ) Ph, â-naphthyl) results in regiospecific insertion of the aldehyde into the phenyl-
zirconium bond. The resulting aminotriolate complex Zr[N{CH2CH2C(O)Me2}2{((S)-2-((R)-
(â-naphthyl)CH(O))-C6H4C(H)Me}][CH2Ph] (8b) is formed in 91% de and has been characterized
by X-ray crystallography. Further insertion of ArC(O)H into the remaining Zr-benzyl bond
of 8b proceeds with poorer stereochemical control. Complex 7 also catalyzes the slow
cyclotrimerization of phenylacetylene to 1,2,4- and 1,3,5-triphenylbenzene (2.5 turnovers/
day). Complexes 2b,d and 7 function as precatalysts for ethylene polymerization when treated
with MAO activator, although the activity is very low.
In tr od u ction
to offer promising stereoselectivity in epoxide ring
opening with azidotrialkylsilanes and in oxidation of
alkyl aryl sulfides.7 Similarly, chiral binaphtholate
(BINOL) complexes have been explored.8
In this contribution, we report the synthesis and
reactivity of zirconium alkyl complexes containing a
series of chelating aminodiolate ligands, derived from
the aminodiols RN(CH2CH2C(OH)R′2)2 (1a -e). The
aminodiolate framework is of interest for several rea-
The vast majority of early-transition-metal and f-
element organometallic chemistry is supported by the
cyclopentadienyl group, or its derivatives, as ancillary
ligation.1 While this class of ligands remains extremely
productive, an ever-increasing number of researchers
are turning their attention to alternative ligands.2 Much
of the motivation for this work is the belief that the
dramatically different steric and electronic environ-
ments available with these supporting ligands will
result in new and unusual reactivity for the metal-
carbon bond not seen in cyclopentadienyl complexes.
Simple monodentate and polydentate alkoxides have
been used extensively in this role.3 Alkoxide-based group
4 organometallic compounds have been used as alkene
polymerization4 and alkyne cyclotrimerization5 cata-
lysts. Chelating alkoxide complexes, such as those
derived from triethanolamine,6 have been prepared
which display remarkable kinetic stability. Recently,
chiral analogues of these complexes have been shown
(2) See for example: (a) Floriani, C.; Ciurli, S.; Chiesi-Villa, A.;
Guastini, C. Angew. 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.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J .
Am. Chem. Soc. 1993, 115, 3595. (g) Arnold, J .; Hoffman, C. G. J . Am.
Chem. Soc. 1990, 112, 8620. (h) Schaverien, C. J . J . Chem. Soc., Chem.
Commun. 1991, 458. (i) Schaverien, C. J .; Orpen, A. G. Inorg. Chem.
1991, 30, 4968. (j) Shibata, K.; Aida, T.; Inoue, S. Tetrahedron Lett.
1992, 33, (k) Shibata, K.; Aida, T.; Inoue, S. Chem. Lett. 1992, 1173.
(l) Brand, H.; Arnold, J . J . Am. Chem. Soc. 1992, 114, 2266. (m) Brand,
H.; Arnold, J . Organometallics 1993, 12, 3655. (n) Kim, H.-J .; Whang,
D.; Kim, K.; Do, Y. Inorg. Chem. 1993, 32, 360. (o) Ryu, S.; Whang, D.;
Kim, J .; Yeo, W.; Kim, K. J . Chem. Soc., Dalton Trans. 1993, 2005. (p)
Dell’Amico, G.; Marchett, F.; Floriani, C. J . Chem. Soc., Dalton Trans.
1982, 2197. (q) Mazzanti, M.; Rosset, J . M.; Floriani, C.; Chiesi-Villa,
A.; Guastini, C. J . Chem. Soc., Dalton Trans. 1989, 953. (r) Floriani,
C. Polyhedron 1989, 8, 1717. (s) Cobrazza, F.; Solari, E.; Floriani, C.;
Chiesi-Villa, A.; Guastini, C. J . Chem. Soc., Dalton Trans. 1990, (t)
Solari, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. J . Chem. Soc., Dalton
Trans. 1992, 367. (u) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F.;
Petersen, J . L. Organometallics 1995, 14, 371.
* To whom correspondence should be addressed.
† Current address: Department of Chemistry, University of Roch-
ester, Rochester, NY 14620.
(1) (a) Marks, T. J .; Ernst, R. D. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Perga-
mon: New York, 1982; Vol. 3, p 173. (b) Sikora, D. J .; Macomber, D.
W.; Rausch, M. D. Adv. Organomet. Chem. 1986, 25, 317. (c) Schav-
erien, C. J . Adv. Organomet. Chem. 1994, 36, 283. (d) J ordan, R. Adv.
Organomet. Chem. 1991, 32, 325. (e) Bochmann, M. J . Chem. Soc.,
Dalton Trans. 1996, 255.
(3) Rothwell, I. P. Acc. Chem. Res. 1988, 21, 153.
10.1021/om9907324 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 01/20/2000

510 Organometallics, Vol. 19, No. 4, 2000
Shao et al.
1a -e and the bis(ligand) complexes Zr[RN(CH2CH2C(O)R′2)2]2
(3a -e) is described elsewhere.12
1H (360 MHz), 13C (90.55 MHz), 19F (338.86 MHz), and all
variable-temperature NMR spectra were recorded on a Bruker
AMX 360 MHz spectrometer. Spectra were recorded in d6-
benzene, d8-toluene, or d8-THF solvent, previously distilled
from sodium under argon, using 5 mm tubes fitted with a
Teflon valve (Brunfeldt) at room temperature unless otherwise
specified. 1H and 13C NMR spectra were referenced to residual
solvent resonances. 19F NMR spectra were referenced to
external CCl3F. Proton and carbon NMR assignments were
confirmed by 1H-1H or 1H-13C COSY experiments for most
compounds. Melting points were recorded using a Reichert hot
stage and are not corrected. Elemental analyses were per-
formed by Canadian Microanalytical, Delta, BC, Canada, or
Atlantic Microanalytical, Atlanta, GA. Despite the use of co-
oxidants such as V2O5 and PbO2, the analytical data for most
complexes were consistently 2-4% low in carbon. This may
be due to metal carbide formation. Mass spectra were recorded
on a Finnegan 3300 or a Kratos Concept H spectrometer using
chemical ionization, electron impact (70 eV), or positive ion
liquid secondary ionization (+LSIMS) methods.
sons. The chelating nature of the ligand is expected to
increase the stability of the complexes with respect to
ligand redistribution. Additionally, the steric and elec-
tronic properties of the ligand can be tuned by varying
the alkoxide carbon and amine nitrogen substituents.
Incorporation of substituents at the alkoxide carbon is
particularly desirable, because this helps to prevent
formation of oligomeric species via alkoxide bridges.6,9
In the course of this work, it has become increasingly
clear that the substituent at nitrogen is far from
innocent and in fact plays a pivotal role in the thermal
and coordinative stability of these complexes.
Zir con iu m Dia lk yl Com p lexes. The zirconium dialkyl
complexes 2a -e, 5, and 6 were prepared by hydrocarbon
elimination (2a -e), ligand redistribution (2c-e), or metathesis
(2b, 5, and 6). Representative examples of each procedure are
given as follows, followed by characterization data for each
new complex.
Exp er im en ta l Section
(a ) Hyd r oca r bon Elim in a tion . A solution of 1d (0.829 g,
1.68 mmol) in 10 mL of toluene was added dropwise to a stirred
solution of tetrabenzylzirconium (0.763 g, 1.68 mmol) in 10
mL of toluene. After the mixture was stirred for 30 min, the
solvent was removed in vacuo to afford 2d as an off-white
powder. Recrystallization from a toluene-hexane mixture
afforded pale yellow crystals.
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. Tetrahydrofuran (THF), hexane,
and toluene were dried by distillation from sodium benzophe-
none ketyl under argon immediately prior to use. Tetraben-
11
zylzirconium10 and Zr[N(SiMe3)2]2Cl2 were prepared accord-
(b) Liga n d Red istr ibu tion . A solution of 3d (1.08 g, 1.00
mmol) in 20 mL of toluene was added to solid tetrabenzylzir-
conium (0.456 g, 1.00 mmol). The solution was stirred for 30
min, and the solvent was removed to yield 2d as a powder.
Recrystallization as above yielded pale yellow needles.
(c) Meta th esis. A solution of (trimethylsilyl)lithium (0.061
g, 0.66 mmol) in toluene (20 mL) was added to a suspension
of 4 (0.20 g, 0.33 mmol), prepared as described below, in 20
mL of toluene. The solution increased in cloudiness im-
mediately on addition of the lithium reagent but slowly
decreased in turbidity overnight. The solution was filtered
through a Celite plug on a glass frit, and the resulting clear
yellow filtrate was evaporated to yield a sticky yellow-brown
oil which solidified on standing. The solid was recrystallized
from hexane at -30 °C to afford yellow crystalline 5.
Zr [MeN(CH2CH2C(O)Me2)2][CH2P h ]2 (2a ). Yellow oil.
The product contained significant amounts of tetrabenzylzir-
conium (identified by the characteristic doublet in the 1H NMR
at 6.39 ppm) and 3a (ca. 20%), which could not be removed.
Yield: 56%. 1H NMR (d6-benzene): δ 7.0-7.2 (m, 9H, aryl H),
ing to literature procedures. The synthesis of aminodiol ligands
(4) (a) Fandos, R.; Meetsma, A.; Teuben, J . H. Organometallics 1991,
10, 59. (b) Fandos, R.; Teuben, J . H.; Helgesson, G.; J agner, S.
Organometallics 1991, 10, 1637. (c) Rieger, B. J . Organomet. Chem.
1991, 420, C17. (d) Masi, F.; Malguori, S.; Barazzoni, L.; Ferrero, C.;
Moalli, A.; Marconi, F.; Invernizzi, R.; Zandora, N.; Altomare, A.;
Ciardelli, F. Makromol. Chem. Suppl. 1989, 15, 147. (e) Kakugo, M.;
Miyatake, T.; Mizunuma, K. Chem. Express 1987, 2, 445. (f) Miyatake,
T.; Mizunuma, K.; Seki, Y.; Kakugo, M. Makromol. Chem., Rapid
Commun. 1989, 10, 349. (g) Miyatake, T.; Mizunuma, K.; Kakugo, M.
Makromol. Chem., Macromol. Symp. 1993, 66, 203. (h) Fokken, S.;
Spaniol, T. P.; Kang, H. C.; Massa, W.; Okuda, J . Organometallics
1996, 15, 5069. (i) Porri, L.; Ripa, A.; Colombo, P.; Moana, E.; Capelli,
S.; Meille, S. V. J . Organomet. Chem. 1996, 514, 213. (j) Fokken, S.;
Spaniol, T. P.; Okuda, J .; Sernetz, F. G.; Mu¨lhaupt, R. Organometallics
1997, 16, 4240. (k) Floriani, C.; Corazza, F.; Lesueur, W.; Chiesi-Villa,
A.; Guastini, C. Angew. Chem., Int. Ed. Engl. 1989, 28, 66. (l) Corazza,
F.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem. 1991, 30,
146. (m) Okuda, J .; Fokken, S.; Kang, H. C.; Massa, W. Chem. Ber.
1995, 128, 221.
(5) (a) van der Linden, A.; Schaverien, C. J .; Meijboom, N.; Ganter,
C.; Orpen, A. G. J . Am. Chem. Soc. 1995, 117, 3008. (b) Hill, J . E.;
Fanwick, P. E.; Rothwell, I. P. Organometallics 1990, 9, 2211. (c) Hill,
J . E.; Balaich, G.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1993,
12, 2911.
(6) (a) Naiini, A. A.; Ringrose, S. L.; Su, Y.; J acobson, R. A.; Verkade,
J . G. Inorg. Chem. 1993, 22, 1290. (b) Menge, W.; Verkade, J . G. Inorg.
Chem. 1991, 30, 4628. (c) Naiini, A.; Menge, W. M. P. B.; Verkade, J .
G. Inorg. Chem. 1991, 30, 5009.
3
4
6.72 (tt, 1H, p-benzyl H, J HH ) 7.1 Hz, J HH ) 1.4 Hz), 2.56
(s, 2H, ZrCH2), 2.49 (t, 2H, NCHaCH2, J HH ) 13.2 Hz), 1.64 (s,
2H, ZrCH2), 1.26 (m, 2H, NCH2CHb), 1.25 (s, 6H, C(O)Mea),
1.24 (s, 3H, MeN), 1.22 (s, 6H, C(O)Meb), 1.03 (m, 2H, NCHb-
CH2). 13C{1H} NMR (d6-benzene): δ 150.1, 137.9 (quat aryl
C); 130.3, 129.7, 129.3, 128.6 (o,m aryl C); 122.8, 120.3 (p aryl
(7) (a) Nugent, W. A.; Harlow, R. L. J . Am. Chem. Soc. 1994, 116,
6142. (b) Bonchio, M.; Calloni, S.; DiFuria, F.; Licini, G.; Modena, G.;
Moro, S.; Nugent, W. A. J . Am. Chem. Soc. 1997, 119, 6935. (c) DiFuria,
F.; Licini, G.; Modena, G.; Motterle, R.; Nugent, W. A. J . Org. Chem.
1996, 61, 5175.
1
C); 73.2 (ZrOC); 58.0 (NCH2); 53.4, 52.7 (ZrCH2, J CH ) 130
Hz); 38.7 (CH2C(O)); 37.7 (MeN); 32.7, 30.3 (C(O)Me).
(8) (a) Boyle, T. J .; Barnes, D. L.; Heppert, J . A.; Morales, L.;
Takusagawa, F.; Connolly, J . W. Organometallics 1992, 11, 1112. (b)
Boyle, T. J .; Eilerts, N. W.; Heppert, J . A.; Takusagawa, F. Organo-
metallics 1994, 13, 2218.
(9) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Metal Alkoxides;
Academic Press: London, 1978.
(10) Zucchini, U.; Albizatti, E.; Giannini, U. J . Organomet. Chem.
1971, 26, 357.
(11) Andersen, R. A. J . Chem. Soc., Dalton Trans. 1980, 2010.
(12) The aminodiol ligands 1a -e were prepared in two steps.
Michael addition of the appropriate amine (RNH2, 2 equiv) to methyl
acrylate afforded the aminodiesters RN(CH2CH2C(O)OMe)2. The ami-
nodiesters were then converted to the aminodiols by reaction with 4
equiv of R′Li, followed by hydrolysis and standard workup. The bis-
(ligand) complexes 3a -e were prepared from tetrabenzylzirconium10
and 2 equiv of the aminodiol 1a -e. Full experimental details for these
reactions will be reported elsewhere: Shao, P.; Gendron, R. A. L.; Berg,
D. J . Can. J . Chem., in press.

Dibenzyl Zr Complexes of Chelating Aminodiolates
Organometallics, Vol. 19, No. 4, 2000 511
Zr [MeN(CH2CH2C(O)P h 2)2][CH2P h ]2 (2b). White crys-
tals. Yield: 85%. Mp: 166-168 °C. H NMR (d6-benzene): δ
Calcd for C31H31NO2ZrCl2: C, 60.86; H, 5.11; N, 2.29. Found:
C, 59.02; H, 5.15; N, 2.13.
1
7.62 (d, 4H, o aryl H, J HH ) 7.4 Hz), 7.52 (d, 4H, o aryl H, J HH
) 7.6 Hz), 7.31 (t, 4H, aryl H, J HH ) 6.5 Hz), 6.9-7.2 (m, 17H,
aryl H), 6.77 (t, 1H, aryl H, J HH ) 5.8 Hz), 2.58 (t, 2H, NCHa-
CH2, J HH ) 11.4 Hz), 2.34 (dd, 2H, NCH2CHa), 2.27 (s, 2H,
ZrCH2), 2.20 (t, 2H, NCH2CHb), 1.95 (s, 2H, ZrCH2), 1.48 (dd,
2H, NCHbCH2, J HH ) 11.1, 5.7 Hz), 1.32 (s, 3H, MeN). 13C-
{1H} NMR (d6-benzene): δ 151.5, 148.4, 148.6, 139.2 (quat aryl
C); 130.1, 130.0, 129.3, 128.6, 128.5, 128.4, 127.0, 126.8, 126.6,
125.3, 123.7, 121.3 (aryl C); 82.2 (ZrOC); 58.0 (NCH2); 57.5,
55.4 (ZrCH2, 1J CH ) 130 Hz); 39.5 (MeN); 36.9 (CH2C(O)). Anal.
Calcd for C45H45NO2Zr: C, 74.75; H, 6.27; N, 1.94. Found: C,
70.62; H, 6.11; N, 1.93.
Zr [MeN(CH2CH2C(O)P h 2)2][CH2SiMe3]2 (5). Yellow crys-
tals. Yield: 74%. Mp: 157-159 °C. H NMR (d6-benzene): δ
1
7.73 (d, 4H, o aryl Ha, J HH ) 7.2 Hz), 7.48 (d, 4H, o aryl Hb,
J HH ) 7.2 Hz), 7.25 (t, 4H, m aryl Ha, J HH ) 7.8 Hz), 7.15 (t,
4H, m aryl Hb, J HH ) 7.8 Hz), 7.06 (t, 2H, p aryl Ha, J HH ) 7.3
Hz), 7.00 (t, 2H, p aryl Hb, J HH ) 7.4 Hz), 2.20 (m, 6H, NCH2a,b
and CH2aC(O) overlapping), 1.62 (s, 3H, MeN), 1.58 (m, 2H,
CH2bC(O)), 0.84 (s, 2H, ZrCH2a), 0.69 (s, 2H, ZrCH2b), 0.33 (s,
9H, SiMe3a), 0.23 (s, 9H, SiMe3b). 13C{1H} NMR (d6-benzene):
δ 149.7, 148.1 (quat aryl C); 128.4, 126.8, 126.5, 126.0 (aryl
C); 83.6 (ZrOC); 57.6 (NCH2); 52.4 (ZrCaH2); 51.8 (ZrCbH2); 42.2
(MeN); 37.9 (CH2C(O)); 3.4 (SiMe3a); 3.2 (SiMe3b). Anal. Calcd
for C39H53NO2Si2Zr: C, 65.49; H, 7.47; N, 1.96. Found: C,
63.04; H, 6.01; N, 2.27. MS (EI): m/z 698 (M+ - Me, 3%), 626
Zr [ter t-Bu N(CH2CH2C(O)Me2)2][CH2P h ]2 (2c). Pale yel-
low oil. Yield: 95%. 1H NMR (d6-benzene): δ 7.09 (t, 4H, m
benzyl H, J HH ) 5.8 Hz), 6.89 (t, 2H, p benzyl H, J HH ) 7.3
Hz), 6.79 (d, 4H, o benzyl H, J HH ) 8.2 Hz), 2.77 (m, 4H,
NCH2), 1.83 (s, 4H, ZrCH2), 1.62 (m, 4H, CH2C(O)), 1.06 (s,
12H, C(O)Me), 1.05 (s, 9H, tert-BuN). 1H NMR (d8-toluene, -60
°C): δ 7.03 (t, 4H, m benzyl H), 6.93 (t, 2H, p benzyl H), 6.80
(d, 4H, o benzyl H), 2.90 (br s, 2H, NCHa), 2.72 (br s, 2H,
NCHb), 1.82 (s, 4H, ZrCH2), 1.75 (br s, 2H, CHaC(O)), 1.56 (br
s, 2H, CHbC(O)), 1.19 (s, 6H, C(O)Mea), 1.08 (s, 9H, tert-BuN),
0.99 (s, 6H, C(O)Meb). 13C{1H} NMR (d6-benzene): δ 144.0
(quat aryl C), 130.8 (o aryl C), 126.7 (m aryl C), 122.6 (p aryl
C), 80.5 (ZrOC), 54.0 (Me3CN), 52.9 (NCH2), 43.2 (ZrCH2, 1J CH
) 128 Hz), 41.6 (CH2C(O)), 30.3 (C(O)Me2), 28.9 (Me3CN).
(M+ - CH2SiMe3, 50%), 180 (100%). Simulation of the M+
-
CH2SiMe3 envelope: m/z, obsd intensity (calcd intensity) 626,
100% (100); 627, 62% (60); 628, 57% (53); 629, 20% (19); 630,
36% (37); 631, 14% (13); 632, 10% (5); 633, 4% (2).
Zr [MeN(CH 2CH 2C(O)P h 2)2]Me2 (6). Dark brown oil.
Yield: ca. 40%. 1H NMR (d6-benzene): δ 7.85 (d, 4H, o aryl H,
J HH ) 7.3 Hz), 7.69 (d, o aryl H, J HH ) 7.3 Hz), 7.27 (t, 4H, m
aryl H, J HH ) 7.8 Hz), 7.05-7.20 (m, 6H, m,p aryl H), 6.99 (t,
2H, p aryl H, J HH ) 7.3 Hz), 2.25 (m, 6H, NCH2a,b and CH2aC-
(O) overlapping), 1.48 (m, 2H, CH2bC(O)), 1.43 (s, 3H, MeN),
0.84 (s, 3H, ZrMea), 0.75 (s, 3H, ZrMeb); 13C{1H} NMR
(d6-benzene): δ 150.8, 148.4 (quat aryl C); 128.4, 128.3, 126.7,
126.6, 126.5, 125.4 (aryl C); 82.3 (ZrOC); 57.4 (NCH2); 38.5
(MeN); 37.9 (CH2C(O)); 37.6 (ZrMea); 34.8 (ZrMeb).
Zr [ter t-Bu N(CH2CH2C(O)P h 2)2][CH2P h ]2 (2d ). White mi-
1
crocrystalline powder. Yield: 90%. Mp: 180 °C dec. H NMR
Th er m a l Decom p osition Stu d ies. The decomposition of
2a -e was followed by NMR spectroscopy. In each experiment,
30 mg of complex was dissolved in 0.8 mL of d8-toluene and
the sample placed in a hot oil bath. The 1H spectrum of the
complex was monitored periodically. Kinetic studies were
carried out in a similar fashion, except that the sample was
heated in the NMR probe and the amount of starting complex
remaining and product formed (in the case of 7) were estab-
lished by integration. Preparative scale experiments were
carried out by heating 0.5-1.0 g of the appropriate dialkyl in
an oil bath for a period of time previously established as
sufficient to complete the conversion.
(d6-benzene): δ 7.35 (d, 8H, o phenyl H, J HH ) 7.4 Hz), 7.15
(t, 8H, m phenyl H, J HH ) 7.4 Hz), 7.04 (t, 4H, m benzyl H,
J HH ) 8.5 Hz), 7.03 (d, 4H, p phenyl H, J HH ) 7.5 Hz), 6.90 (t,
2H, p benzyl H, J HH ) 7.3 Hz), 6.55 (d, 4H, o benzyl H, J HH
7.6 Hz), 2.69 (br t, 4H, NCH2), 2.55 (t, 4H, CH2C(O), J HH
)
)
6.4 Hz), 1.85 (s, 4H, ZrCH2), 0.86 (s, 9H, tert-BuN); 13C{1H}
NMR (d6-benzene): δ 148.2 (quat phenyl C); 143.6 (quat benzyl
C); 128.5, 128.3, 127.9, 127.3, 126.9, 123.1 (aryl C); 87.3
(ZrOC); 59.0 (Me3CN); 55.8 (br, NCH2); 45.0 (br, CH2C(O)); 41.1
(ZrCH2, 1J CH ) 129 Hz); 28.6 (Me3CN). Anal. Calcd for C48H51
-
NO2Zr: C, 75.35; H, 6.72; N, 1.83. Found: C, 73.02; H, 6.76;
N, 1.85. The ortho benzyl proton signal shifts to 6.70 ppm on
addition of 0.1 mL of d8-THF.
Zr [N{CH2CH2C(O)Me2}2{(S)-2-C6H4C(H)Me}][CH2P h ] (7).
Pale yellow crystals. Yield: 60%. Mp: 175 °C. 1H NMR (d6-
benzene): δ 8.16 (m, 1H, R phenyl H), 7.35 (m, 1H, o benzyl
H), 7.30 (m, 2H, â,γ phenyl H), 7.25 (m, 1H, m benzyl H), 7.03
(m, 1H, δ phenyl H), 6.90 (tt, p benzyl H, J HH ) 7.3, 1.2 Hz),
Zr [N{CH2CH2C(O)Me2)2}{S-P h C(H)Me}][CH2P h ]2 (2e).
Colorless oil. Yield: 85%. 1H NMR (d6-benzene): δ 6.7-7.3 (m,
3
15H, aryl H), 3.96 (q, 1H, MeC(H)N, J HH ) 7.0 Hz), 2.75 (m,
2
2H, NCHa), 2.29 (d, 2H, ZrCHa, J HH ) 9.6 Hz), 2.13 (d, 2H,
3
4.61 (q, 1H, MeC(H)N, J HH ) 6.9 Hz), 3.10 (d, 1H, ZrCHa,
ZrCHb, 2J HH ) 9.6 Hz), 1.95 (m, 2H, NCHb), 1.65 (m, 2H, CHaC-
(O)), 1.30 (m, 2H, CHbC(O)), 1.26 (s, 6H, C(O)Mea), 1.25 (d,
2
2J HH ) 9.1 Hz), 3.00 (d, 1H, ZrCHb, J HH ) 9.1 Hz), 2.81 (m,
1H, NCHa), 2.71 (m, 1H, NCHb), 1.80 (m, 2H, NCHc,d), 1.78
(m, 1H, CHaC(O)), 1.58 (m, 1H, CHbC(O)), 1.04 (s, 3H, C(O)-
Mea), 1.03 (s, 3H, C(O)Meb), 1.02 (m, 1H, CHcC(O)), 0.96 (s,
3H, C(O)Mec), 0.92 (m, 1H, CHdC(O)), 0.89 (d, 3H, MeC(H)N,
3J HH ) 6.9 Hz), 0.83 (s, 3H, C(O)Med). The designators R-γ
refer to the position with respect to the metalated phenyl ring
carbon, with R being adjacent to this site. 13C{1H} NMR (d6-
benzene): δ 182.9 (phenyl C-Zr); 152.2 (quat phenyl C); 144.1
(quat benzyl C); 139.4, 129.8, 128.9, 127.6, 125.8, 123.5, 121.5
3
3H, MeC(H)N, J HH ) 7.0 Hz), 1.19 (s, 6H, C(O)Meb). 13C{1H}
NMR (d6-benzene): δ 146.2 (quat phenyl C); 141.1 (quat benzyl
C); 129.3, 129.0, 128.8, 128.6, 128.2, 127.6 (aryl C); 75.5
1
(ZrOC); 58.7 (MeC(H)N); 58.6 (ZrCH2, J CH ) 126 Hz); 50.1
(NCH2); 40.1 (CH2C(O)); 31.7, 30.3 (C(O)Me); 21.7 (MeC(H)N).
The complex slowly decomposes at room temperature by ortho
metalation.
{Zr [MeN(CH2CH2C(O)P h 2)2]Cl2}x (4). A solution of 1b
(2.00 g, 4.42 mmol) in 10 mL of toluene was added to a solution
of Zr[N(SiMe3)2]2Cl2 (2.13 g, 4.42 mmol) in 30 mL of toluene.
The reaction mixture was heated at 70 °C for 1 h, resulting in
the precipitation of a large amount of white solid. The solid
was isolated by flitration on a glass frit and washed repeatedly
with toluene (100 mL total volume). The solid was dried under
vacuum for several hours to yield a free-flowing white powder.
1
(aryl C); 76.2 (ZrOCa); 74.8 (ZrOCb); 60.5 (ZrCH2, J CH ) 131
Hz); 59.5 (MeC(H)N); 46.9 (NCaH2); 46.7 (NCbH2); 37.9 (CaH2C-
(O)); 37.6 (CbH2C(O)); 32.5, 31.6, 30.3, 30.2 (C(O)Me); 7.6 (MeC-
(H)N). MS (EI): m/z 471 (M+, 5%), 380 (M+ - CH2Ph, 15%),
91 (C7H7+, 100%). Anal. Calcd for C25H35NO2Zr: C, 63.51; H,
7.46; N, 2.96. Found: C, 61.49; H, 7.26; N, 2.97.
In ser tion Rea ction s. (i) P h en yl-Zr In ser tion . A solu-
tion of benzaldehyde or â-naphthaldehyde in toluene (0.25
mmol in 10 mL) was rapidly added to a cooled (-30 °C) toluene
solution of 7 (0.25 mmol in 20 mL). The reaction mixture was
stirred for 1 h while still cold and then warmed to room
temperature. Removal of solvent in vacuo afforded the inser-
tion product as a white or yellow powder. In some experiments
1
Yield: 57%. Mp: 255-257 °C. H NMR (d5-pyridine; 107 °C):
δ 7.9 (br s, 8H, aryl H), 7.25 (br s, 12H, aryl H), 2.6-3.3 (br
unresolved singlet, 11H, backbone CH2 and NMe). 13C{1H}
NMR (d5-pyridine; 93 °C): δ 128.2, 129.0, 129.2 (aryl C), 56.8
(s, NCH2), 37.7 (very broad singlet, CH2C(O)). The methyl, ipso
aryl, and alkoxide carbon resonances were not observed. Anal.

512 Organometallics, Vol. 19, No. 4, 2000
Shao et al.
the solid product was hydrolyzed at this stage to release the
organic ligand and the diastereomeric excess was determined
by 1H NMR integration of unique resonances (detailed below).
In other experiments, the solid complex was recrystallized from
a toluene-hexane mixture and the NMR recorded.
(ii) Ben zyl-Zr In ser tion . A solution of benzaldehyde or
â-naphthaldehyde in toluene (0.5 mmol in 10 mL) was added
to a cooled (-30 °C) toluene solution of 7 (0.25 mmol in 20
mL), and the reaction mixture was warmed to room temper-
ature with stirring. After 6 h, the solution was quenched with
2 mL of H2O and the organic product was extracted in Et2O.
The Et2O phase was dried over MgSO4, and the product was
isolated as a pale yellow oil after removal of the solvent. The
enantiomeric excess of the benzyl insertion product was
determined by GC on a â-Dex column and by NMR using
europium tris[3-(trifluoromethylhydroxymethylene)-(+)-cam-
phorate] as a chiral shift reagent.
benzyllithium and benzaldehyde. High-resolution MS (EI): m/z
found (calcd) M+ 198.1046 (198.1045).
1
(â-n a p h th yl)C(OH)(H)(CH2P h ) (10b). H NMR (CDCl3):
δ 8.52 (s, 1H, R naphthyl H), 7.2-8.1 (m, 11H, aryl H), 5.08
(m, 1H, C(OH)H), 3.09 (m, 2H, C(OH)CH2a,b). MS (EI): m/z
248 (M+, 20%), 247 (M+ - H, 100%), 231 (M+ - OH, 25%).
High-resolution MS (EI): m/z found (calcd) M+ 248.1199
(248.1201).
Zir con iu m Alk yl Ca tion s. Treatment of a toluene (5 mL)
solution of 2b or 2e (0.1 mmol) with 1 equiv of B(C6F5)3
resulted in immediate formation of a yellow-orange oil which
separated from solution. The toluene supernatant was de-
canted, and the oil was washed with 3 × 100 mL of hexane.
Vacuum drying afforded the cations as semisolids which
generated viscous orange oils on exposure to traces of toluene.
Zr [MeN(CH2CH2C(O)P h 2)2][CH2P h ]+[B(C6F5)3(CH2P h )]-
1
(11a ). H NMR (d6-benzene): δ 6.7-7.3 (br m, 30H, aryl H),
Zr [N{CH 2CH 2C(O)Me2}2{(S)-2-((R)-P h CH (O))-C6H 4C-
(H)Me}][CH2P h ] (8a ). Pale yellow crystals. Yield: 55%. Mp:
6.05 (br d, 2H, o benzyl H), 3.42 (br s, 2H, BCH2), 1.3-3.2 (br
m, 13H, ligand backbone and ZrCH2). 19F{1H} NMR (d6-
benzene): δ 166.9, 166.5, 165.3, 165.2, 164.7, 164.6, 163.4,
162.8, 161.3, 161.2, 160.6, 160.5, 160.4 (m,p aryl F); 130.9,
130.8, 130.4, 130.3 (o aryl F). 19F{1H} NMR (5:1 d6-benzene-
1
179-183 °C. The H and 13C NMR spectra of this complex are
extremely broad and are poorly resolved at all temperatures.
Anal. Calcd for C32H41NO3Zr: C, 66.39; H, 7.14; N, 2.42.
Found: C, 61.59; H, 6.78; N, 2.37. The poor analytical data
and inability to obtain meaningful NMR data render the
identification of this compound tentative.
3
d8-THF): δ -166.9 (t, 6F, m aryl F, J FF ) 20 Hz), -164.1 (t,
3
3
3F, p aryl F, J FF ) 20 Hz), -130.6 (d, 6F, o aryl F, J FF ) 20
Hz). 13C{1H} NMR (d5-bromobenzene): δ 148.9, 148.0, 147.6,
1
Zr [N{CH2CH2C(O)Me2}2{(S)-2-((R)-(â-n a p h th yl)CH(O))-
C6H4C(H)Me}][CH2P h ] (8b). Pale yellow crystals. Yield:
145.1, 142.6 (ipso aryl C); 148.9 (d, J CF ) 224 Hz, aryl CF),
148.0 (m, ipso aryl CF), 137.8 (d, 1J CF ) 243 Hz, aryl CF), 136.8
1
1
71%. Mp: 155-156 °C. H NMR (d6-benzene, 50 °C): δ 6.9-
(d, J CF ) 242 Hz, aryl CF); 129.3, 129.3, 128.8, 128.6, 128.5,
7.8 (m, 16H, aryl H), 6.10 (s, 1H, C(H)OZr), 4.51 (q, 1H, MeC-
127.9, 127.8, 127.4, 127.0, 126.9, 126.4, 126.3, 125.9, 125.6,
123.1, 122.8, 122.1 (aryl CH); 87.5, 85.1 (C(O)Me2); 56.5
(ZrCH2); 38.3, 37.3, 37.0, 36.3, 30.2 (CH2 and NMe); 32.0 (br
s, BCH2). 19F{1H} NMR (d5-bromobenzene): δ -165.9 (t),
-163.0 (t), -129.9 (d).
3
(H)N, J HH ) 7.0 Hz), 3.02 (br m, 1H, CH2), 2.84 (br m, 1H,
CH2), 2.69 (d, 1H, ZrCHa, 2J HH ) 10.2 Hz), 2.66 (d, 1H, ZrCHb,
2J HH ) 10.2 Hz), 1.90 (m, 1H, CH2), 1.80 (m, 1H, CH2), 1.60
(m, 1H, CH2), 1.45 (m, 1H, CH2), 1.38 (s, 3H, C(O)Mea), 1.09
(s, 6H, C(O)Meb,c), 1.00 (m, 2H, CH2), 0.65 (s, 3H, C(O)Med),
Zr [N{CH2CH2C(O)Me2}2{(S)-2-C6H4C(H)Me}]+[B(C6F5)3-
(CH2P h )]- (11b). 1H NMR (5:1 d6-benzene-d8-THF): δ 6.95-
7.15 (m, 8H, aryl H), 6.83 (t, 1H, p benzyl H, J HH ) 6.7 Hz),
4.54 (br m, 1H, MeC(H)N), 3.37 (br s, 2H, BCH2), 2.84 (br t,
1H, NCHa, J HH ) 9.7 Hz), 2.57 (t, 1H, NCHb, J HH ) 13.4 Hz),
2.14 (br m, 1H, NCHc), 1.94 (br m, 1H, NCHd), 1.88 (t, 1H,
CHaC(O), J HH ) 13.4 Hz), 1.68 (t, 1H, CHbC(O), J HH ) 14.2
Hz), 1.33 (m, 1H, CHc(O)), 1.10 (CHdC(O)), 1.04 (d, 3H, MeC-
(H)N, 3J HH ) 6.8 Hz), 1.00 (s, 3H, C(O)Mea), 0.97 (s, 3H, C(O)-
Meb), 0.94 (s, 3H, C(O)Mec), 0.70 (s, 3H, C(O)Med). 13C{1H}
NMR (5:1 d6-benzene-d8-THF): δ 150.8, 150.4 (br), 149.2,
147.8 (br), 138.4 (br), 135.8 (br), 133.7, 129.2, 128.4, 127.3,
125.8, 124.4, 122.9 (aryl C); 78.0, 77.1 (ZrOCa,b); 61.0 (MeC(H)N);
48.6, 47.4 (NCa,bH2); 37.6, 37.2 (C(O)Ca,bH2); 31.7, 31.6, 30.2,
29.0 (C(O)Me); 31.5 (br, BCH2); 7.5 (MeC(H)N); the fluorinated
3
0.60 (d, 3H, MeC(H)N, J HH ) 7.0 Hz). 13C{1H} NMR (d6-
benzene, 50 °C): δ 150.4, 145.9, 143.9, 139.3, 133.7, 132.9,
132.5, 130.6, 128.3, 127.3, 127.2, 126.2, 125.8, 124.3, 123.7,
119.7 (aryl C); 83.8 (ZrOC(H)); 76.1, 75.5 (ZrOCMe); 54.4
(ZrCH2); 54.3 (MeC(H)N); 47.1, 46.9 (NCH2); 40.6, 38.2 (CH2C-
(O)); 32.7, 28.5 (br, C(O)Me); 11.4 (MeC(H)N). Anal. Calcd for
C
36H43NO3Zr: C, 68.75; H, 6.89; N, 2.23. Found: C, 66.39; H,
6.79; N, 1.81.
N{CH2CH2C(OH)Me2}2{(S)-2-((R)- a n d (S)-P h CH(OH))-
C6H4C(H)Me} (9a ). SS:SR ratio: 1:13 (93% de). 1H NMR
(CDCl3): SR (major) δ 7.1-7.3 (m, 9H, aryl H), 5.77 (s, 1H,
3
PhCH(OH)), 3.89 (q, 1H, MeC(H)N, J HH ) 7.0 Hz), 2.68 (m,
2H, NCH2a), 2.40 (m, 2H, NCH2b), 1.60 (m, 2H, CH2aC(O)), 1.40
(m, 2H, CH2bC(O)), 1.16 (d, 3H, MeC(H)N, 3J HH ) 7.0 Hz), 1.07
(s, 6H, C(O)Mea), 1.06 (s, 6H, C(O)Meb); SS (minor) δ 6.15 (s,
1H, PhCH(OH)), 4.57 (q, 1H, MeC(H)N). The remaining
protons overlap with those of the major diastereomer. High-
resolution MS (+LSIMS, m-nitrobenzoic acid): m/z found
(calcd) M+ + H 400.2859 (400.2851).
aryl carbons are not well-resolved in this solvent. 19F{1H} NMR
3
(5:1 d6-benzene-d8-THF): δ -167.5 (t, 6F, m aryl F, J FF
)
3
20 Hz), -164.8 (t, 3F, p aryl F, J FF ) 20 Hz), -130.6 (d, 6F,
o aryl F, J FF ) 20 Hz). The 19F{1H} NMR recorded in
3
d6-benzene shows resonances at δ -166.9, -164.0, and -130.7
ppm. 13C{1H} NMR (d5-bromobenzene): δ 148.8 (d, 1J CF ) 233
N{CH2CH2C(OH)Me2}2{(S)-2-((R)- a n d (S)-â-n a p h th yl)-
CH(OH))-C6H4C(H)Me} (9b). SS:SR ratio: 1:10 (91% de). 1H
NMR (CDCl3): SR (major) δ 7.1-7.9 (m, 11H, aryl H), 5.92
(s, 1H, ArC(OH)H), 3.94 (q, 1H, MeC(H)N, 3J HH ) 6.8 Hz), 2.70
1
Hz, aryl CF); 138.6 (br m, ipso aryl CF); 137.8 (d, J CF ) 244
1
Hz, aryl CF); 136.8 (d, J CF ) 256 Hz, aryl CF); 148.9, 137.7,
128.5, 127.4, 123.1, 122.8, 122.3 (aryl CH; others may be
obscured by the solvent peaks); 81.1, 80.0 (C(O)Me2); 59.1
(NCHMe); 50.3, 50.8 (NCH2); 32.4 (br s, BCH2); 31.6 (CH2C-
(O); only one peak is discernible); 14.6 (NCHMe).
(m, 2H, NCH2a), 2.40 (m, 2H, NCH2b), 1.62 (m, 2H, CH2aC-
3
(O)), 1.42 (m, 2H, CH2bC(O)), 1.10 (d, 3H, MeC(H)N, J HH
)
7.0 Hz), 1.08 (s, 12H, C(O)Meab); SS (minor) δ 6.33 (s, 1H,
ArCH(OH)), 4.68 (q, 1H, MeC(H)N). The remaining protons
overlap with those of the major diastereomer. High-resolution
P h en yla cetylen e Cyclotr im er iza tion . In a typical NMR
tube experiment, 7 (0.025 g, 0.053 mmol) and excess phenyl-
acetylene (30 equiv) were dissolved in 0.8 mL of d6-benzene
and the sample was heated at 70 °C overnight. At this point
the sample had darkened to brown and resonances due to
phenylacetylene were no longer observable. The sample was
quenched with H2O, and the organic phase was extracted with
Et2O and washed with 1 M HCl. GC-MS showed that the major
products in the organic fraction were 1,2,4- and 1,3,5-triphen-
ylbenzene in a 3:1 ratio.
MS (+LSIMS, m-nitrobenzoic acid): m/z found (calcd) M+
H 450.3002 (450.3007).
+
P h C(OH)(H)(CH2P h ) (10a ). 1H NMR (CDCl3): δ 7.15-
3
7.35 (m, 10H, aryl H), 4.90 (dd, 1H, PhC(OH)H, J HH ) 12.4,
4.9 Hz), 3.02 (m, 2H, C(OH)CH2ab). 13C{1H} NMR (CDCl3): δ
143.8, 138.0 (quat aryl C); 138.0, 129.5, 128.5, 128.4, 127.6,
127.6, 125.9 (o,m,p aryl C); 75.3 (C(OH)); 46.1 (CH2). This
product was identical with an authentic sample prepared from

Dibenzyl Zr Complexes of Chelating Aminodiolates
Organometallics, Vol. 19, No. 4, 2000 513
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta
Resu lts a n d Discu ssion
7
8b
Syn t h esis of (Am in od iola t e)zir con iu m Dia lk yl
Com p lexes. The zirconium dialkyl complexes 2 were
prepared by three different routes: hydrocarbon elimi-
nation (protonolysis), ligand redistribution, or meta-
thesis (eqs 1-3).
formula
fw
cryst syst
space group
a (C)
C
25H35NO2Zr
C36H43NO3Zr
628.95
472.78
orthorhombic
P212121 (No. 19)
9.795(2)
11.246(2)
22.910(3)
90
orthorhombic
P212121 (No. 19)
9.535(2)
17.675(3)
19.786(2)
90
b (C)
c (C)
1c-e + Zr(CH2Ph)4 f 2c-e
3c-e + Zr(CH2Ph)4 f 2c-e
4 + 2LiCH2SiMe3 f 5
(1)
(2)
(3)
R ) â ) γ (deg)
V (Å3)
2523.5(9)
4
3334.4(9)
4
Z
F(calcd) (g cm-3
)
1.244
37.4
1.253
29.8
µ (cm-1
)
radiation, λ (Å)
T
Cu KR, 1.542
ambient
100
1271
1525
Cu KR, 1.542
ambient
110
1647
2389
Direct reaction of aminodiols 1c-e with tetraben-
zylzirconium afforded dibenzyl complexes 2c-e in ex-
cellent yield and high purity. This method works well
for the bulkier aminodiols, but the formation of bis-
(ligand) complexes is difficult to avoid with 1a ,b.
Complex 2b can be prepared cleanly by slow addition
of a dilute solution of 1b to tetrabenzylzirconium at -78
°C. Using the same strategy for the preparation of 2a
produced a product that inevitably contained significant
amounts of the bis(ligand) complex Zr{MeN(CH2CH2C-
(O)Me2)2}2 (3a ).12 Attempts to purify 2a by recrystalli-
zation were unsuccessful because of the similarity in
solubilities of 2a and the bis(ligand) complex.
2θmax (deg)
no. of obsd rflns
no. of unique rflns
Ra
0.062
0.061
0.050
0.054
b
Rw
a
b
2
R ) ∑(|Fo| - |Fc|)/∑|Fo|. Rw ) [∑w(|Fo| - |Fc| )/∑w(|Fo|)2]1/2
.
Eth ylen e P olym er iza tion . Polymerization experiments
were carried out by saturating 450 mL of toluene with ethylene
(75 psi). Separate samples of MAO cocatalyst (10.0 mmol) and
complex (0.010 mmol) dissolved in 25 mL of toluene were
added, and the reaction was monitored by observing the
ethylene uptake. The product was isolated by removal of
solvent, washed with hexane, and vacuum-dried. The amount
of polyethylene was weighed, and the molecular weight and
polydispersity were determined by GPC using a polyethylene
standard. No significant polymerization was observed using
an equimolar amount of B(C6F5)3 as cocatalyst.
Ligand redistribution between tetrabenzylzirconium
and the previously prepared bis(ligand) complexes 3c-e
also affords 2c-e in excellent yield and purity. Com-
plexes 3c,d , containing tert-butyl-substituted ligands,
undergo very rapid (<1 min) redistribution, and neither
starting material nor intermediate are observable by
NMR immediately after mixing. Redistribution with 3e
is slower, and an intermediate is observable by 1H NMR.
The region characteristic of the R-methylbenzyl CH
X-r a y Cr ysta llogr a p h ic Stu d ies. Crystallographic data
for 7 and 8b are given in Table 1. Crystals of each compound
(7, 0.24 × 0.36 × 0.20 mm; 8b, 0.20 × 0.22 × 0.20 mm) were
loaded into glass capillaries in the glovebox and subsequently
examined by photographic methods using Weissenberg and
precession cameras. The space group (P212121 in both cases)
was uniquely determined by the systematic absences. The
crystals were transferred to a Nonius CAD4F diffractometer
equipped with Ni-filtered Cu KR radiation. The unit cells were
refined using 25 reflections in the 2θ ranges 50-75° (7) and
48-85° (8b). Experimental densities were not determined
because of the air and moisture sensitivity of the compounds.
Three standard reflections, measured periodically during data
collection (7, 400, 040, and 004; 8b, 104, 400, and 140), showed
less than a 2% decline in combined intensity for both com-
pounds. Intensity measurements were collected for one-fourth
of the sphere. After the usual data reduction procedures,14a
the structures were solved using Patterson methods. The
refinements minimized ∑w((|Fo| - |Fc|)2) and proceeded nor-
mally using SHELX86.14b The criterion for inclusion of reflec-
tions was I > 2.5σ(I) for 7 and I > 3.0σ(I) for 8b. The weighting
scheme was determined by counting statistics using w ) 1/σ2-
(F) + 0.001(F2). Convergence was satisfactory: max shift/esd
) 0.005. A total of 262 parameters (29 × 9 parameters per
atom + scale) were refined for 7 and 370 parameters (41 atoms
× 9 parameters per atom + scale) for 8b. No intermolecular
contacts shorter than 3.4 Å were observed in either case. The
benzene ring of the benzyl group in 7 was refined with bond
length constraints and is drawn isotropically in the ORTEP
plot for clarity.15 Structural plots were drawn with ORTEP or
the ZORTEP modification.16
1
proton resonance (3.9-4.4 ppm) was monitored by H
NMR over a period of 3 h (Figure 1). Shortly after
mixing, resonances due to 3e, 2e, and the intermediate
A were observed. After 30 min, the broad resonance due
to 3e had vanished while that of the intermediate was
just discernible. Over the following 2 h, the resonance
due to A disappeared, leaving only that due to 2e.
Although the identity of A is not known with certainty,
a symmetrically bridged structure such as that shown
is reasonable.13
In contrast to 3c-e, the N-methyl-substituted com-
plexes 3a and Zr{MeN(CH2CH2C(O)Ph2)2}2 (3b) do not
undergo ligand redistribution with tertrabenzylzirco-
nium, even when heated to 70 °C in benzene for
prolonged periods of time. In other work12 we showed
(13) For a similar structure see: Stephan, D. W. Organometallics
1990, 9, 2718.
(14) (a) Larson, A.; Lee, F.; Page, Y.; Webster, M.; Charland, J .;
Gabe, E. J . NRC Solver: A Program for Crystal Structure Determi-
nation; National Research Council of Canada, Chemistry Division,
Ottawa, ON, Canada, 1985. (b) Sheldrick, G. M. SHELX86, Programs
for Crystal Structure Determination; University of Cambridge, Cam-
bridge, U.K., 1986.
(15) J ohnson, C. K. ORTEPII; Oak Ridge National Laboratory, Oak
Ridge, TN, 1976.
(16) Zsolnai, L. ZORTEP; University of Heidelberg, Heidelberg,
Germany, 1995.

514 Organometallics, Vol. 19, No. 4, 2000
Shao et al.
very similar to that observed by Horton et al.17c for
zirconium dialkyl complexes of the chelating aminodi-
amide Me3SiN(CH2CH2N(SiMe3))2.17 There is no evi-
dence from 1H NMR to suggest that any of these
complexes involve η2-benzyl coordination.17c,18
In contrast to the dialkyls discussed above, 2c-e are
fluxional at room temperature, showing a single type
of benzyl group and only one set of resonances for each
chemically distinct CH2 group of the ligand backbone.
This fluxional behavior can again be accounted for by
amine dissociation and inversion at nitrogen followed
by amine recoordination as discussed previously.12
Indeed, cooling 2d to -60 °C results in splitting of the
CH2 and C(O)R2 resonances into two groups consistent
with Cs symmetry. However, the benzyl groups remain
equivalent to -80 °C, suggesting that pseudorotation
remains rapid even at low temperatures.
Th er m a l Sta bility. The thermal stabilities of 2a -e
show a marked dependence on the substituent at
nitrogen. The methyl complex 2b survives unchanged
after heating for 5 days at 100 °C in d8-toluene. In
contrast, the tert-butyl derivatives 2c,d decompose by
elimination of isobutene and toluene (Scheme 1). Con-
clusive NMR evidence for the formation of Zr[N(CH2-
CH2C(O)R′2]2[CH2Ph] could not be obtained, possibly
because of secondary decomposition processes. The
decomposition reaction of 2d , monitored by NMR, was
found to be first order in the starting dibenzyl complex.
An Eyring plot (Figure 2) gave ∆Hq and ∆Sq values of
26 ( 2 kcal mol-1 and -11 ( 1 cal mol-1 K-1 for this
decomposition reaction. The negative value of ∆Sq is
consistent with the highly ordered transition state
depicted in Scheme 1. Decomposition of the less crowded
F igu r e 1. 1H NMR spectra (360 MHz) of the R-methyl-
benzyl CH proton region as a function of time for the ligand
redistribution reaction between Zr[N{CH2CH2C(O)Me2)2}-
{((S)-PhC(H)Me}]2 (3e) and Zr(CH2Ph)4 in d6-benzene.
Resonances due to Zr[N{CH2CH2C(O)Me2)2}{((S)-PhC(H)-
Me}][CH2Ph]2 (2e) and the unknown intermediate A are
observed shortly after mixing.
that these same complexes undergo arm exchange via
amine dissociation, inversion at nitrogen, and recoor-
dination much more slowly that 3c-e. This was at-
tributed to stronger amine binding for 3a ,b, and since
amine dissociation is likely to be a prerequisite for
formation of a bridged complex such as A, it is not
surprising that these two effects are related.
The first two preparative routes are not general
because they are limited to available zirconium tet-
raalkyls. Since a more general route is desirable, the
preparation of the dichlorides was also briefly investi-
gated. Addition of aminodiol 1b to ZrCl2[N(SiMe3)2]2 in
toluene resulted in formation of a white insoluble
precipitate, presumed to be the dihalide 4. Reaction of
4 with 2 equiv of benzylpotassium or ((trimethylsilyl)-
methyl)lithium resulted in clean formation of 2b and
Zr{MeN(CH2CH2C(O)Ph2)2}{CH2SiMe3}2 (5), respec-
tively, although the former was obtained in lower yield
than by hydrocarbon elimination. A similar reaction
between 4 and methyllithium produced Zr{MeN(CH2-
CH2C(O)Ph2)2}Me2 (6), but the thermal sensitivity of
this product precluded isolation of the pure complex.
(17) (a) Cloke, F. G. N.; Hitchcock, P. B.; Love, J . B. J . Chem. Soc.,
Dalton Trans. 1995, 25. (b) Clark, H. C. S.; Cloke, F. G. N.; Hitchcock,
P. B.; Love, J . B.; Wainwright, A. P. J . Organomet. Chem. 1995, 501,
333. (c) Horton, A. D.; de With, J .; van der Linden, A. J .; van de Weg,
H. Organometallics 1996, 15, 2672.
1
Solu tion Str u ctu r es. The H NMR spectra of 2a ,b,
5, and 6 show that these complexes are conformationally
rigid in d6-benzene at room temperature. For each,
resonances due to two inequivalent sets of alkyl ligands
and one alkoxide arm are observed; however, the
geminal protons of the alkoxide arms are inequivalent,
indicating mirror plane (Cs) symmetry. These observa-
tions are consistent with the pseudo-fac trigonal bipy-
ramidal structures shown. This structure is consistent
with our earlier observation that the aminodiolate
ligands prefer to adopt fac coordination sites in the six-
coordinate bis(ligand) complexes.12 This structure is also
(18) Typically η2-benzyl groups display characteristic NMR features
including an upfield shift of the ortho benzyl protons (ca. 6.0-6.7 ppm)
and ipso benzyl carbon (ca. 10 ppm upfield), an increased benzylic CH
coupling constant (1J CH > 125 Hz), and a decreased benzylic HH
coupling constant (2J HH < 10 Hz):18e (a) Latesky, S. L.; McMullen, A.
K.; Niccolai, G. P.; Rothwell, I. P.; Huffman, J . C. Organometallics
1985, 4, 902. (b) Bochmann, M.; Lancaster, S. J . Organometallics 1993,
12, 633. (c) Bochmann, M.; Lancaster, S. J .; Hursthouse, M. B.; Malik,
K. M. A. Organometallics 1994, 13, 2235. (d) J ordan, R. F.; LaPointe,
R. E.; Bajgur, C. S.; Echolls, S. F.; Willet, R. J . Am. Chem. Soc. 1987,
109, 4111. (e) We thank one reviewer for pointing out the significance
2
of the J HH values.

Dibenzyl Zr Complexes of Chelating Aminodiolates
Organometallics, Vol. 19, No. 4, 2000 515
Sch em e 1
F igu r e 2. Eyring plot for the thermal decomposition of
Zr[t-BuN(CH2CH2C(O)Ph2)2][CH2Ph]2 (2d ).
complex 2c proceeded at roughly one-fifth the rate for
2d , suggesting that relief of steric pressure is an
important driving force in the decomposition reaction.
Thermal dealkylation, similar to that shown in Scheme
1, has been used as a method for the preparation of
primary amines from the corresponding metal amides
(eq 4).19 The negative entropies of activation observed
F igu r e 3. ZORTEP16 plot (30% probability) of Zr[N{CH2-
CH2C(O)Me2}2{((S)-2-C6H4C(H)Me}][CH2Ph] (7).
during alkene elimination according to eq 4 were taken
as evidence for a concerted cyclic transition state.19
Isobutene elimination from tert-butylamine has been
reported in the literature by both radical20 and ionic21
mechanisms.
Chiral complex 2e undergoes clean ortho metalation
during mild heating (70 °C, 4 h) in d6-benzene to afford
metallacycle 7 in 75% yield (eq 5). The structure of 7
a single-crystal X-ray investigation. The structure,
depicted in Figure 3, consists of a pseudo-trigonal-
bipyramidal geometry with the coordinated amine and
remaining benzyl CH2 group occupying the axial posi-
tions (N(1)-Zr(1)-C(8) angle 159.1(6)°). The two alkox-
ide oxygens and the ortho-metalated phenyl carbon
occupy the equatorial sites with the O-Zr-C(aryl)
angles (110.7(5) and 112.8(5)°) compressed substantially
relative to the O-Zr-O angle (125.4(4)°). Selected bond
distances and angles are collected in Table 2.
The η2-benzyl group of 7 is clearly evident from the
Zr(1)-C(8)-C(81) angle of 93.4(11)° and the short Zr-
(1)-C(81) contact of 2.817(19) Å. While η2-benzyl groups
are commonly observed for electron-deficient early-
transition-metal complexes,17c,18,22 this result stands in
contrast to the η1-benzyl bonding observed for 2b. Since
the electronic environments at zirconium in 2b and 7
was suggested by NMR spectroscopy and confirmed by
(20) Patai, S., Ed. Chemistry of the Amino Group; Wiley-Inter-
science: London, 1968; p 437.
(19) Ashby, E. C.; Willard, G. F. J . Org. Chem. 1978, 43, 4750.
(21) Ainsworth, C.; Easton, N. R. J . Org. Chem. 1962, 27, 4118.

516 Organometallics, Vol. 19, No. 4, 2000
Shao et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 7a
Distances
Zr(1)-N(1)
Zr(1)-O(1)
Zr(1)-O(2)
Zr(1)-C(8)
Zr(1)-C(12)
Zr(1)-C(81)
2.149(12)
1.938(9)
1.927(10)
2.313(16)
2.275(14)
2.82(2)
N(1)-C(1)
O(1)-C(4)
O(2)-C(7)
C(1)-C(11)
C(8)-C(81)
C(11)-C(12)
1.43(2)
1.40(2)
1.39(2)
1.54(2)
1.48(2)
1.39(2)
Angles
N(1)-Zr(1)-O(1)
N(1)-Zr(1)-O(2)
N(1)-Zr(1)-C(8)
N(1)-Zr(1)-C(12)
O(1)-Zr(1)-O(2)
O(1)-Zr(1)-C(8)
81.0(5) O(2)-Zr(1)-C(8)
82.8(5) O(2)-Zr(1)-C(12)
159.1(6) C(8)-Zr(1)-C(12)
71.7(5) Zr(1)-C(8)-C(81)
125.4(4) Zr(1)-O(1)-C(4)
107.5(8) Zr(1)-O(2)-C)7)
105.9(8)
110.7(5)
87.4(6)
93.4(11)
140.4(10)
145.2(10)
O(1)-Zr(1)-C(12) 112.8(5) Zr(1)-C(12)-C(11) 115.8(12)
a
Estimated standard deviations in parentheses.
must be very similar, the observation of η1-benzyl
coordination in 2b is probably steric in origin. Interest-
ingly, while 7 does display some of the NMR features
normally associated with η2-benzyl coordination in
solution (benzyl ipso aryl 13C resonance, 144.1 ppm;
benzyl CH2 J CH ) 131 Hz and J HH ) 9.1 Hz), the ortho
aryl 1H resonances appear in the region normally
associated with η1 coordination (δ 7.35 ppm).18 This
suggests to us that if an η2-benzyl interaction is present
in solution, it is quite weak. Certainly, stronger η2-
benzyl bonding has been observed for related com-
pounds; for example, one benzyl group in Zr(OAr′)(CH2-
Ph)3 (OAr′ ) 2,6-di-tert-butylphenoxide) shows a more
acute Zr-CH2-C(ipso) angle (84°) and a shorter Zr-
C(ipso) bond distance (2.64 Å).18a
F igu r e 4. Eyring plot for the formation of 7 by ortho
metalation.
1
2
Sch em e 2
The Zr-O bond distances in 7 are unexceptional, but
the alkoxide Zr-O-C angles (140.4(10) and 145.2(10)°)
are considerably more bent than that found in Zr(OAr′)-
(CH2Ph)3 (165.7(9)°)18a or those for the terminal alkox-
ides of [(i-PrO)3(i-PrOH)Zr(µ-i-PrO)]2 (mean 172°).23
This is not surprising, because bending at the alkoxide
oxygens is necessary if the chelating ligand is to bind
to a single metal center. The Zr-N distance of 2.419-
(12) Å is short in comparison to that found for the
structurally similar Zr[(Me3Si)N(CH2CH2NSiMe3)2][CH-
(SiMe3)2][Cl] (2.770(5) Å).17a The short Zr-N distance
in 7 is due to formation of the five-membered ring
involving the ortho-metalated phenyl group. Similarly,
exceptionally short Ti-N distances have been observed
in titanium complexes bearing deprotonated triethanol-
amine as a tripodal ligand (the titanatranes).6
In an elegant study, Bercaw26 showed conclusively that
the closely related conversion of Cp*2Hf(CH2C6H5)2 to
Cp*2Hf(CH2-o-C6H4) proceeded through a benzylidene
intermediate and an isolable “tuck” complex, Cp*Hf(η5:
η1-C5Me4CH2)(CH2C6H5). Significantly, the entropy of
activation of 1 ( 3 cal mol-1 K-1 for this reaction is
similar to that observed for the formation of 7. In
contrast, most examples of direct σ-bond metathesis
exhibit substantially more negative entropies of activa-
tion (∆Sq ) -10 to -24 cal mol-1 K-1),27 which has been
The formation of 7 was found to follow first-order
kinetics, consistent with an intramolecular process, and
an Eyring plot (Figure 4) yielded ∆Hq and ∆Sq values
of 24 ( 2 kcal mol-1 and -5 ( 1 cal mol-1 K-1
,
respectively. The two most likely pathways for metal-
lacycle formation are via direct σ-bond metathesis (A)
or via a benzylidene intermediate (B) (Scheme 2).24,25
(22) (a) J ordan, R. F.; LaPointe, R. E.; Baenziger, N. C.; Hinch, G.
D. Organometallics 1990, 9, 1539. (b) Dais, G. R.; J arvis, J . A.; Kilburn,
B. T.; Piols, A. J . P. J . Chem. Soc., Chem. Commun. 1971, 677. (c)
Davis, G. R.; J arvis, J . A.; Kilburn, B. T. J . Chem. Soc., Chem.
Commun. 1971, 1511. (d) Mintz, E. A.; Moloy, K. G.; Marks, T. J . J .
Am. Chem. Soc. 1982, 104, 4692.
(25) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J .; MacGillivray,
L. R. J . Am. Chem. Soc. 1993, 115, 5336.
(26) Bulls, A. R.; Schaefer, W. P.; Serfas, M.; Bercaw, J . E. Orga-
nometallics 1987, 6, 1219.
(23) Vaarstra, B. A.; Huffman, J . C.; Gradeff, P. S.; Hubert-Pfalzgraf,
L. G.; Daran, J .; Parraud, S.; Yunlu, K.; Caulton, K. G. Inorg. Chem.
1990, 29, 3126.
(24) Initial metalation at sites other than the ortho phenyl position
followed by subsequent metalation at this site is also possible. These
alternatives can be ruled out by labeling studies (vide infra).
(27) (a) Rothwell, I. P. Polyhedron 1985, 4, 177. (b) Smith, G. M.;
Carpenter, J . D.; Marks, T. J . J . Am. Chem. Soc. 1986, 108, 6805. (c)
Bruno, J . W.; Smith, G. M.; Marks, T. J .; Fair, C. K.; Schultz, A. J .;
Williams, J . M. J . Am. Chem. Soc. 1986, 108, 40. (d) Schock, L. E.;
Brock, C. P.; Marks, T. J . Organometallics 1987, 6, 232. (e) Luinstra,
G. A.; Teuben, J . H. Organometallics 1992, 11, 1793.

Dibenzyl Zr Complexes of Chelating Aminodiolates
Organometallics, Vol. 19, No. 4, 2000 517
Sch em e 3
attributed to the formation of a highly ordered four-
center transition state. However, while entropies of
activation values are sometimes suggestive of a mecha-
nistic pathway, they are not infallible guides. With
regard to the present reaction there are, for example,
reactions proceeding via an alkylidene which exhibit
large negative entropies of activation28 and others for
which an alkylidene is highly unlikely which show very
small activation entropy.29 Fryzuk’s study of the ther-
mal decomposition of Y[N(SiMe2CH2PMe2)2]2(CH2C6H5)
is a particularly relevant example of the latter case.29
In this reaction, intramolecular metalation occurs ex-
clusively at the CH2 site adjacent to P with elimination
of toluene (∆Sq ) -3 ( 3 cal mol-1 K-1). To accom-
modate the exceptionally small ∆Sq value, the authors
postulated that phosphine dissociation occurs in the
transition state to provide a positive contribution to ∆Sq.
Since amine dissociation could similarly occur in the
transition state leading to 7, it would be premature to
rule out a σ-bond metathesis pathway.
To establish the decomposition mechanism unequivo-
cally, two separate isotopic labeling experiments were
carried out. The labeled compounds 2e(d7-benzyl)2 and
2e(o-d2-PhC(Me)H) were prepared by reaction of 1e with
Zr(CD2C6D5)4 and of 1e(o-d2-PhC(Me)H)30 with Zr(CH2-
Ph)4, respectively. Thermolysis of the labeled compounds
for the alkylation of benzaldehyde with diethylzinc (96%
ee).31 Since 7 is enantiomerically pure, albeit with a
chiral center remote to the zirconium-carbon bond, an
investigation of the regio- and stereoselectivity of CdO
insertion was warranted.
Reaction of 1 equiv of benzaldehyde or â-naphthal-
dehyde with 7 at -30 °C resulted in exclusive insertion
of the carbonyl group into the phenyl-zirconium bond
(Scheme 3). The insertion products 9a ,b were isolated
as pure oils after hydrolysis and were identified by NMR
spectroscopy. In all three cases, the major diastereomer
(>85% de) was identified as the RS isomer by a
combination of NOE difference experiments and molec-
ular modeling;32 this absolute configuration was con-
firmed for the zirconium complex 8b by X-ray crystal-
lography (vide infra).
1
in d6-benzene (4 h, 70 °C) was monitored by H NMR.
In both cases, the NMR spectra showed no evidence for
H-D scrambling and the toluene produced was identi-
fied as exclusively d7-(CD2H)C6D5 in the first experi-
ment and d-(CDH2)C6H5 in the second. These results
conclusively rule out involvement of a benzylidene
pathway, because in both cases this would necessarily
lead to H-D scrambling (Scheme 2). A metathesis
pathway involving any sites other than the ortho aryl
protons of the phenyl ligand may also be ruled out,
because this would not result in the exclusive formation
of the d-(CDH2)C6H5 in the second experiment. The
direct σ-bond metathesis pathway is the only possibility
that explains these results.
The regioselectivity of this first insertion is interesting
since, in the case of lithium reagents at least, benzyl-
metal bonds are generally more reactive33 in addition
reactions with carbon-carbon and carbon-oxygen double
bonds. In the present system, we have found that the
benzyl-carbon bond in 7 is a better base in reactions
Rea ctivity Stu d ies. (a ) In ser tion Ch em istr y of
Ald eh yd es a n d Keton es w ith 7. Chiral group 4
alkoxides have been successfully used for enantioselec-
tive alkylations of aldehydes and ketones with lithium
reagents. In one example, closely related to the types
of complexes described here, Nugent reported that 5 mol
% of I functions as an excellent enantioselective catalyst
(31) Nugent, W. A. J . Am. Chem. Soc. 1992, 114, 2768.
(32) Molecular modeling (CAShe) of the free ligand 9b was used to
establish the distance between the PhC(H)N and CH(OH) protons for
each diastereomer. The PhC(H)N resonance showing the greatest
relative NOE effect upon irradiation of the related CH(OH) proton was
assigned as the SR diastereomer, because this isomer was calculated
to have the shortest proton-proton distance (2.1 versus 2.3 Å for the
SS diastereomer). The major isomer of 9a was also assigned as the
SR diastereomers on the basis of the strong similarity of the NMR
spectrum to that of the major isomer of 9b.
(33) In most cases, the relative rate of addition by lithium reagents
is opposite that predicted on the basis of anion basicity; that is, the
least basic carbanion reacts fastest with the substrate. For example,
the relative addition rates of benzyllithium and phenyllithium to 1,1-
diphenylethene in THF were reported to be more than 3000:1.33a,b The
relative rate of addition of phenyllithium and ethyllithium to Michler’s
ketone (4,4′-dimethylaminobenzophenone) was reported as 3:1 in THF;
the rate of addition of benzyllithium was not reported.33c Interestingly,
the relative rate of deprotonation of triphenylmethane by RLi in THF
follows the order benzyl (250) > phenyl (5.5) > Me (1.0).33d Solvation
effects and the degree of aggregation in solution no doubt play a role
in this order, but it is clear that it is not straightforward to predict
the relative reactivity of benzylic and phenyl carbanions on the basis
of simple anion stability arguments: (a) Waack, R.; Doran, M. A. J .
Am. Chem. Soc. 1969, 91, 2456. (b) Waack, R.; Doran, M. A. J . Org.
Chem. 1967, 32, 3395. (c) Swain, C. G.; Kent, L. J . Am. Chem. Soc.
1950, 72, 518. (d) Waack, R.; West, P. J . Am. Chem. Soc. 1964, 86,
4494.
(28) (a) Cheon, J .; Rogers, D. W.; Girolami, G. J . Am. Chem. Soc.
1997, 119, 6804. (b) Li, L.; Hung, M.; Xue, Z. J . Am. Chem. Soc. 1995,
117, 12746. (c) van der Heijden, H.; Hessen, B. J . Chem. Soc., Chem.
Commun. 1995, 145.
(29) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J . Organometallics
1991, 10, 2026.
(30) Ortho deuteration of 1e was achieved by repetitive quenching
of 8 with D2O. Three cycles were sufficient to give >90% o-d2-1e.

518 Organometallics, Vol. 19, No. 4, 2000
Shao et al.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 8ba
Distances
Zr(1)-N(1)
Zr(1)-O(1)
Zr(1)-O(2)
Zr(1)-O(3)
Zr(1)-C(30)
O(1)-C(1)
2.619(9)
1.928(9)
1.917(9)
1.945(10)
2.284(15)
1.429(19)
O(2)-C(8)
1.387(18)
1.370(19)
1.49(2)
1.52(2)
1.45(3)
O(3)-C(19)
C(18)-C(19)
C(19)-C(20)
C(30)-C(31)
F igu r e 5. Possible transition state geometries for alde-
hyde insertion into the Zr-phenyl bond of 7.
Angles
N(1)-Zr(1)-O(1)
N(1)-Zr(1)-O(2)
N(1)-Zr(1)-O(3)
81.0(4) Zr(1)-N(1)-C(11)
80.3(4) Zr(1)-O(1)-C(1)
84.5(3) Zr(1)-O(2)-C(8)
111.3(8)
147.4(10)
151.4(10)
161.1(9)
N(1)-Zr(1)-C(30) 179.2(4) Zr(1)-O(3)-C(19)
O(1)-Zr(1)-O(2)
O(1)-Zr(1)-O(3)
O(1)-Zr(1)-C(30)
O(2)-Zr(1)-O(3)
O(2)-Zr(1)-C(30)
O(3)-Zr(1)-C(30)
119.8(4) Zr(1)-C(30)-C(31)
119.8(4) N(1)-C(11)-C(13)
99.4(6) O(3)-C(19)-C(18)
114.5(4) O(3)-C(19)-C(20)
110.2(11)
112.8(14)
110.6(13)
112.7(13)
98.9(5) C(11)-C(13)-C(18) 122.7(15)
95.8(5) C(13)-C(18)-C(19) 120.4(14)
a
Estimated standard deviations in parentheses.
F igu r e 6. Possible transition state geometries for the
insertion of a second equivalent of aldehyde into the
benzyl-Zr bond of 8b.
with primary amines.34 The stereochemistry of the
insertion can be understood if it is assumed that the
substrate binds preferentially at the site opposite the
R-methyl substituent of the metalated R-methylbenzyl
group (Figure 5). In this site, there will be a strong steric
preference favoring nucleophilic attack at the enan-
tiotopic face of the substrate shown in Figure 5a (leading
to an R configuration at the newly formed chiral center).
Presentation of the opposite enantiotopic face of the
substrate (Figure 5b) would place the substrate aryl
group in close proximity with the ligand backbone. In
view of this interaction, it seems more likely that the
minor (SS) isomer is formed by coordination of the
substrate in the same orientation as shown in Figure
5a but at the site on the same side as the R-methyl
substituent, thus exposing the opposite enantiotopic face
to nucleophilic attack.
F igu r e 7. ZORTEP16 plot (30% probability) of Zr[N{CH2-
CH2C(O)Me2}2{((S)-2-(R-(â-naphthyl)CH(O))-C6H4C(H)Me}]-
[CH2Ph] (8b).
Addition of a second equivalent of benzaldehyde or
â-naphthaldehyde to 7 resulted in insertion into the Zr-
benzyl bond after warming to room temperature. The
The structure of 8b was confirmed by X-ray crystal-
lography. Selected bond lengths and angles are collected
in Table 3, while the structure is shown in Figure 7.
Complex 8b is distorted trigonal bipyramidal in geom-
etry with the three alkoxide groups occupying the
equatorial sites. The Zr-O bond lengths are quite
similar to one another and to those observed for 7.
However, in contrast to 7, the benzyl group of 8b is
clearly η1 bound (Zr(1)-C(30)-C(31) ) 110.2(11)°). This
is most likely the result of increased steric crowding in
8b, although decreased metal Lewis acidity due to an
increase in the number of alkoxide donors may also play
a role. The compressed O(1)-Zr(1)-O(2) angle (119.8-
(4)°) relative to the more open alkoxide angle in 7 (125.4-
(4)°) provides additional evidence for steric crowding in
8b.
(b) Alk yn e Cyclotr im er iza tion w ith 7. Catalytic
cyclotrimerization of alkynes is well-known for late-
transition-metal complexes,35 but fewer examples are
known with early-metal catalysts.5,36 This appears to
stem in part from the fact that metallocene derivatives,
by far the most heavily investigated class of complexes,
do not appear to catalyze this reaction.5c Rothwell has
shown that titanium(IV) aryloxides of the type Ti-
1
products 10a ,b were identified after hydrolysis by H
NMR. Chiral shift reagents showed that both products
were formed in approximately 45% ee; the absolute
configuration of the major and minor enantiomers was
not determined. The lower stereoselectivity for the
second insertion can probably be traced to the orienta-
tion of the aldehyde plane in Figure 6. Even assuming
that an orientation with the substrate aryl group lying
near the ligand alkoxide groups is strongly preferred
(Figure 6a), coordination on the same side as the
R-methyl group will again expose the opposite enan-
tiotopic face (Figure 6b). However, since the orientation
of the aldehyde plane is now perpendicular to that
during Zr-phenyl insertion (Figure 5), steric interac-
tions with the R-methyl group are expected to be much
less significant. Therefore, the transition states shown
in Figure 6 are likely to be closer in energy than those
in Figure 5 and less differentiation is expected to occur.
(34) Aniline or tert-butylamine (1 equiv) reacts with 7 to yield the
metallacyclic amides Zr[N{CH2CH2C(O)Me2}2{((S)-2-C6H4C(H)Me}]-
[NHR] (R ) Ph, t-Bu). Shao, P.; Berg, D. J . Unpublished results.

Dibenzyl Zr Complexes of Chelating Aminodiolates
Organometallics, Vol. 19, No. 4, 2000 519
Sch em e 4
greater substrate access to the metal center, although
electronic effects due to the presence of an amine donor
in 7 cannot be ruled out.
(c) Ca tion ic Zir con iu m Alk yl Com p lexes. Treat-
ment of 2b or 7 with 1 equiv of the strong Lewis acid
B(C6F5)3 in toluene results in an immediate color change
from pale yellow to bright yellow-orange with separation
of the cations 11a ,b as orange oils (eqs 7 and 8). The
(OAr′)2Cl2 (OAr′ ) 2,6-di-tert-butylphenoxide) must be
reduced to Ti(II) in order to function as active catalysts.5c
More recently, Schaverien has demonstrated that zir-
conium dialkyl complexes supported by binaphtholate
(BINOL) ligands function as highly active catalysts
without preactivation.5a Similarly, treatment of 7 with
phenylacetylene at 70 °C leads to slow catalytic produc-
tion of 1,2,4- and 1,3,5-triphenylbenzene (eq 6, 3:1 ratio
oils are insoluble in hexane but dissolve enough in
aromatic hydrocarbons to allow NMR spectra to be
recorded. In d6-benzene 11a has a very complex 1H and
19F NMR spectrum, suggesting strong association of the
B(C6F5)3(CH2Ph)- anion with the zirconium cation.37 In
contrast, the 19F NMR of 11b shows three well-resolved
resonances with a chemical shift difference (∆δm,p) of
2.9 ppm between the meta and para F signals, suggest-
ing that the anion is not strongly coordinated in this
case.17c,38 The cations 11a ,b are freely soluble in THF,
and addition of a few drops of d8-THF to a d6-benzene
solution of these complexes results in greatly simplified
1H and 19F NMR spectra. Most significantly, three sharp
19F resonances are now observed with a ∆δm,p value of
2.7 ppm (free B(C6F5)3, ∆δm,p ) 2.6 ppm) for both
by GC). Internal alkynes fail to react directly with 7
even at elevated temperatures. One possible catalytic
cycle, based on that proposed earlier by Rothwell, could
account for the observed cyclotrimerization activity
(Scheme 4).5c However, despite repeated attempts, we
have been unable to establish the presence of even trace
diphenylbutadiyne (or diphenylbutadiene) in the hy-
drolyzed reaction mixtures. Alternative mechanisms
involving single site insertions are also possible, al-
though linear alkyne oligomers might be expected if
such a mechanism was operative, and we have no
evidence for their formation either. It is also not clear
why the cyclotrimerization catalyst derived from 7 is
so much less active (ca. 2.5 turnovers/day at 70 °C) than
1
compounds. A broad resonance in the H NMR spectra
is observed at 3.4 ppm due to the 11B broadened CH2 of
the anion benzyl group. Taken together, these observa-
tions suggest that benzyl abstraction by B(C6F5)3 occurs
to generate an associated cation-anion pair in benzene
and that THF displaces the anion to form a solvated
cationic alkyl.
The ethylene polymerization activity of cations de-
rived from 2b,d and 7 was investigated. In all three
cases, no significant polyethylene formation was ob-
served using 1 equiv of B(C6F5)3 as cocatalyst at 50 °C.
However, using a large excess of methylaluminoxane
(MAO, 1000 equiv) resulted in moderate polymerization
activity (Table 4). This difference in reactivity may be
5a
that obtained from Zr(BINOL)(CH2Ph)2 (40 equiv in
hours at 25 °C). It is possible that the four-coordinate
zirconium center in the BINOL complex simply allows
(35) (a) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984, 23,
539. (b) Vollhardt, K. P. C. Acc. Chem. Res. 1977, 10, 1. (c) McAllister,
D. R.; Bercaw, J . E.; Bergman, R. G. J . Am. Chem. Soc. 1977, 99, 1666.
(d) Bianchini, C.; Caulton, K. G.; Chardon, C.; Eisenstein, O.; Folting,
K.; J ohnson, T. J .; Meli, A.; Peruzzini, M.; Rauscher, D. J .; Streib, W.
E.; Vizza, F. J . Am. Chem. Soc. 1991, 113, 5127. (e) Shore, N. Chem.
Rev. 1988, 88, 1081. (f) Winter, M. J . In The Chemistry of the Metal-
Carbon Bond. Carbon-Carbon Bond Formation Using Organometallic
Compounds; Hartley, F. R., Patai, S., Eds.; Wiley: Chichester, U.K.,
1985; Vol. 3, Chapter 5.
(36) (a) Wielstra, Y.; Gambarotta, S.; Meetsma, A.; de Boer, J . L.
Organometallics 1989, 8, 2696. (b) Calderazzo, F.; Marchetti, F.;
Pampaloni, G.; Hiller, W.; Antropiusova´, H.; Mach, K. Chem. Ber. 1989,
122, 2229. (c) Calderazzo, F.; Pampaloni, G.; Pallavicini, P.; Stra¨hle,
J .; Wurst, K. Organometallics 1991, 10, 896.
(37) The nature of the anion-cation interaction in 11a ,b is not
known, but examples of both arylF‚‚‚Zr and η6-benzyl‚‚‚Zr binding are
known. The structure depicted in eq 8 is shown with an η6-benzyl‚‚‚Zr
interaction for simplicity. Aryl F‚‚‚Zr interactions: (a) Temme, B.; Karl,
J .; Erker, G. Chem. Eur. J . 1996, 2, 919. (b) Horton, A. D.; Orpen, A.
G. Organometallics 1991, 10, 3910. η6-Benzyl‚‚‚Zr interactions: (c)
Horton, A. D.; Frijns, J . H. G. Angew. Chem., Int. Ed. Engl. 1991, 30,
1152. (d) Bochmann, M.; Karger, G.; J agger, A. J . J . Chem. Soc., Chem
Commun. 1990, 1038. (e) Pellecchia, C.; Immirzi, A.; Grassi, A.;
Zambelli, A. Organometallics 1993, 12, 4473. (f) Horton, A. D.; de With,
J . J . Chem. Soc., Chem. Commun. 1996, 1375. (g) Chen, Y.; Marks, T.
J . Organometallics 1997, 16, 3649.
(38) It has been suggested that a ∆δm,p value of greater than 3.0
ppm is indicative of strong anion binding.17c

520 Organometallics, Vol. 19, No. 4, 2000
Shao et al.
Ta ble 4. Eth ylen e P olym er iza tion Resu lts for Selected Gr ou p 4 Alk oxid es a n d Rela ted Com p lexes
entry
precatalyst
activity (kg mol-1 h-1
)
103Mw
Mw/Mn
ref
1
2
3
4
2b
2d
7
136
384
68
this work
this work
this work
5a
452
143
5.7
3.4
a
Zr[3,3′-R-1,1′-Bi-2-naph-O2]X2
R ) SiMe3, X ) Cl
152
203
275
inactive
8320
4400
1240
9700
3350
66
73
15
96
10
280
120
200
360
24
15
R ) SiMePh2, X ) Cl
R ) SiPh3, X ) Cl
R ) SiPh3, X ) CH2Ph
b
5
Zr[3-t-Bu-5-Me-2-O-C6H2(CHO)]2Cl2
633
906
138
225
77
17.1
16.7
4.7
2.7
2.5
39a
Zr[3-t-Bu-5-Me-2-O-C6H2(CHO)]Cl3(THF)b
c
6
7
8
9
Ti(n-BuCp)(2,6-t-Bu2-C6H3O)Cl2
39b
39c
39f
39g
ZrCp2[2,6-t-Bu2-C6H3O]Cld
Zr(salen)Cl2(THF)e
Zr(MeBr2Ox)2(CH2Ph)f
Zr(MeBr2Ox)2(CH2Ph)g
21
460
16
375
88
16.3
h
Zr(MeBr2Ox)2Cl2
Zr[PyC(CF3)2O]2[CH2Ph]2
Zr[PyC(CF3)2O]2[CH2Ph]2
Zr[pyC(4-t-Bu-C6H4)2O]2[NMe2]2
i
10
11
2.6
28
8.3
39h
39i
j
k
k
Zr[pyC(4-NEt2-C6H4)2O]2[NMe2]2
a
b
Conditions: toluene, 20 °C, 3 atm of ethylene, 500 equiv of MAO cocatalyst. Conditions: toluene, 80 °C, 10 atm, 1000 equiv of MAO.
c Conditions: toluene, 60 °C, 4 atm, 2000 equiv of MAO. Conditions: toluene, 80 °C, 10 atm, 6000 equiv of MAO. e Conditions: toluene
d
(suspension), 80 °C, 5 atm, 3200 equiv of MAO. f Conditions: 1:1 toluene/chlorobenzene, 60 °C, 3 atm, HNMePh2+[B(C6F5)4]- cocatalyst.
Conditions: 1:1 toluene/chlorobenzene, 30 °C, 8 atm, HNMePh2+[B(C6F5)4]- cocatalyst. Conditions: 1:1 toluene/chlorobenzene, 30 °C,
g
h
i
8 atm, 680 equiv of MAO. Me2Br2Ox ) 2-Me-5,7-Br2-8-quinolinolato. Conditions: benzene, 40 °C, 3 atm, 1 equiv of B(C6F5)3 cocatalyst.
Conditions: toluene, 30 °C, 8 atm, 1000 equiv of MAO. Conditions: toluene, 43 °C, 1 atm, 4:7 AlPri3/MAO cocatalysts with an overall
j
k
Al/Zr ratio of 2000:1.
attributable to strong anion coordination with B(C6F5)3
as cocatalyst. The activity of catalysts derived from all
three complexes is at least 1 order of magnitude lower
than that of traditional zirconocene-based catalysts,19b,39c
the zirconocene alkoxide chloride complex studied by
Repo et al. (entry 7, Table 4),39c or the related salicalde-
hyde39a and salen39f complexes (entries 5 and 8, respec-
tively, Table 4). However, the molecular weights were
relatively high and the polydispersity of the polymer
was among the narrowest obtained using alkoxide-based
catalysts (Table 4).5a,39 Interestingly, the catalyst de-
rived from 2d showed a distinct induction period of
approximately 30 min but the highest activity once
polymerization began. Since 2d is also the only one of
the three complexes which is known to be fluxional at
room temperature and to participate in ligand redistri-
bution reactions, it is tempting to attribute these
observations to a slow reorganization of the metal
coordination sphere to generate a more active species,
possibly involving methyl-benzyl exchange with MAO.40
The reason for the lower activity of the catalyst derived
from metallacycle 7 is not clear, because the identity of
the active catalyst is not immediately obvious.
Con clu sion
The aminodiolate ligands discussed here allow the
successful isolation of monomeric zirconium dialkyl
complexes. Notably, the fluxional behavior and thermal
stability depend critically on the nature of the substitu-
ent at nitrogen. In particular, large substituents at
nitrogen destabilize the compound thermally and lead
to fluxional behavior in solution. While this can lead to
interesting complexes such as the chiral metallacycle
7, it is generally undesirable. In addition, the presence
of an additional amine donor probably decreases po-
lymerization activity of the alkyl cations formed with
MAO by decreasing the metal Lewis acidity. Current
ligand design focuses on decreasing the strength and
number of donors available to the metal center with the
hope of increasing the metal Lewis acidity and reactiv-
ity.
Ack n ow led gm en t. The support of the Natural
Sciences and Engineering Research Council of Canada
is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond distances and angles, and anisotropic ther-
mal parameters for 7 and 8b. This material is available free
of charge via the Internet at http://pubs.acs.org.
(39) (a) Matilainen, L.; Klinga, M.; Leskela¨, M. J . Chem. Soc., Dalton
Trans. 1996, 219. (b) Nomura, K.; Naga, N.; Miki, M.; Yanagi, K.; Imai,
A. Organometallics 1998, 17, 2152. (c) Repo, T.; J any, G.; Salo, M.;
Polamo, M.; Leskela¨, M. J . Organomet. Chem. 1997, 541, 363. (d)
Sernetz, F. G.; Mu¨lhaupt, R.; Fokken, S.; Okuda, J . Macromolecules
1997, 30, 1562. (e) Froese, R. D. J .; Musaev, D. G.; Matsubara, T.;
Morokuma, K. J . Am. Chem. Soc. 1997, 119, 7190. (f) Repo, T.; Klinga,
M.; Pietika¨inen, P.; Leskela¨, M.; Uusitalo, A.; Pakkanen, T.; Hakala,
K.; Aaltonen, P.; Lo¨fgren, B. Macromolecules 1997, 30, 171. (g) Bei,
X.; Swenson, D. C.; J ordan, R. F. Organometallics 1997, 16, 3282. (h)
Tsukahara, T.; Swenson, D. C.; J ordan, R. F. Organometallics 1997,
16, 3303. (i) Kim, I.; Nishihara, Y.; J ordan, R. F.; Rogers, R. D.;
Rheingold, A. L.; Yap, G. P. A. Organometallics 1997, 16, 3314.
OM9907324
(40) No evidence for loss of the aminodiolate ligand from zirconium
in the presence of MAO (1 equiv) was observed by 1H NMR. It would
obviously be difficult to determine whether ligand loss is occurring in
the presence of a very large excess of MAO; therefore, we cannot state
unequivocally that this is not occurring under the polymerization
conditions.