Synthesis and reactivity of cationic group 4 tropocoronand complexes

Article abstract of DOI:10.1021/om971126g

The tropocoronand complexes [M(TC-3,3)(CH₂Ph)₂] (M = Zr, Hf) react with either oxidants or protic reagents to afford the five-coordinate cations [M(TC-3,3)(CH₂Ph)]⁺, in which the benzyl ligand interacts weakly i

Full text of DOI:10.1021/om971126g

Organometallics 1998, 17, 1769-1773
1769
Syn th esis a n d Rea ctivity of Ca tion ic Gr ou p 4
Tr op ocor on a n d Com p lexes
Michael J . Scott and Stephen J . Lippard*
Department of Chemistry, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139
Received December 23, 1997
The tropocoronand complexes [M(TC-3,3)(CH2Ph)2] (M ) Zr, Hf) react with either oxidants
or protic reagents to afford the five-coordinate cations [M(TC-3,3)(CH2Ph)]+, in which the
benzyl ligand interacts weakly in an η2 manner with the group 4 metal center. Isocyanides
react with the resulting cations to afford ketenimine complexes, whereas benzophenone
inserts into the M-C bond to yield [M(TC-3,3){η1-OCPh2(CH2Ph)}]+. These properties reflect
the greater electron-releasing character of the tropocoronand ligands compared to cationic
zirconium complexes of other tetraaza macrocyclic ligands and to zirconocenes.
In tr od u ction
to other macrocycles, aryloxides, and the bis(cyclopen-
tadienyl) fragment. All of these ligands systems for-
Significant attention has focused on delineating the
characteristics of cationic group 4 metal centers because
of their high reactivity and utility in catalysis.1-3 When
an alkyl substituent is removed from a LnMR2 species,
the enhanced Lewis acidity of the d0 metal center
polarizes the metal-ligand bonds and produces cations
that are considerably more reactive then their neutral
precursors. Group 4 metallocene cations {Cp2MR}+
have proved to be especially useful in this regard, being
able to polymerize olefins in a controlled manner and
induce a variety of insertion and coupling reactions.4,5
mally donate the same number (12) of electrons to the
metal.13 By decreasing the electrophilicity of the d0
metal, the tropocoronand ligand attenuates the M-R
interaction, affording novel reactions such as the inser-
tion of isocyanate into the C-O bond of [Hf(TC-3,5)(η2-
OC(CH2Ph)2)].14 In the present work, we have extended
our studies to cationic tropocoronand group 4 organo-
metallic complexes, where the reduction in the number
of strong σ-donor ligands was expected to enhance even
further the differences in Lewis acidity between tropo-
coronands and their metallocene analogues. As re-
ported here, the use of tropocoronand ligands influences
not only the insertion chemistry but also the structural
properties of the resulting complexes.
Recently, macrocyclic auxiliary ligands have been
employed to prepare group 4 metal organometallic
complexes, and although the systems are less efficient
as olefin polymerization catalysts, the resulting com-
plexes exhibit many distinctive and promising attri-
butes.6-12 Previous work in this laboratory demon-
strated the tetraazamacrocyclic tropocoronand ligand
{TC-3,3}2- to be a particularly good electron donor in
Zr(IV) and Hf(IV) complexes, especially by comparison
(1) Collmann, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
(2) Fu¨rstner, A.; Bogdanovic, B. Angew. Chem., Int. Ed. Engl. 1996,
35, 2442-2469 and references therin.
(3) Applied Homogeneous Catalysis with Organometallic Complexes;
Cornils, B., Hermann, W. A., Eds.; VCH: Weinheim, Germany, 1996.
(4) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325-387 and
references therein.
(5) Bochmann, M. J . Chem. Soc., Dalton Trans. 1996, 255-270.
(6) Uhrhammer, R.; Black, D. G.; Gardner, T. G.; Olsen, J . D.;
J ordan, R. F. J . Am. Chem. Soc. 1993, 115, 8493-8494.
(7) Tjaden, E. B.; Swenson, D. C.; J ordan, R. F.; Peterson, J . L.
Organometallics 1995, 14, 371.
(8) Lee, L.; Berg, D. J .; Bushnell, G. W. Organometallics 1997, 16,
2556-2561.
Resu lts a n d Discu ssion
Following the methodology previously developed for
the synthesis of cationic group 4 complexes,4,7,15,16 we
prepared [M(TC-3,3)(CH2Ph)](BPh4) (M ) Zr (1a ), Hf
(1b)) cations from [M(TC-3,3)(CH2Ph)2]13 in modest
yields (21-56%) either by oxidation with [Cp2Fe](BPh4)
or protonation with 1 equiv of (HNMe3)(BPh4). Crystal-
lographic chemical analysis (CCA) (Figure 1; Table 1)
revealed 1a and 1b to have five-coordinate, distorted
square-pyramidal geometries. These complexes repre-
(9) Giannini, L.; Solari, E.; De Angelis, S.; Ward, T. R.; Floriani, C.;
Chiesi-Villa, A.; Rizzoli, C. J . Am. Chem. Soc. 1995, 117, 5801-5811.
(10) Brand, H.; Arnold, J . Angew. Chem., Int. Ed. Engl. 1994, 33,
95-96.
(13) Scott, M. J .; Lippard, S. J . Inorg. Chim. Acta 1997, 263, 287-
299.
(14) Scott, M. J .; Lippard, S. J . Organometallics 1998, 17, 466-474.
(15) Nikonov, G. I.; Blake, A. J .; Mountford, P. Inorg. Chem. 1997,
36, 1107-1112.
(16) Bei, X.; Swenson, D. C.; J ordan, R. F. Organometallics 1997,
16, 3282-3302.
(11) Brand, H.; Capriotti, J . A.; Arnold, J . Organometallics 1994,
13, 4469-4473.
(12) Black, D. G.; J ordan, R. F.; Rogers, R. D. Inorg. Chem. 1997,
36, 103-108.
S0276-7333(97)01126-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/31/1998

1770 Organometallics, Vol. 17, No. 9, 1998
Scott and Lippard
F igu r e 1. ORTEP diagram of the cation in [Zr(TC-3,3)-
(CH2Ph)](BPh4) (1a ) showing 50% ellipsoids and the atom-
labeling scheme. Selected distances and angles for both 1a
and 1b are available in Table 1.
F igu r e 2. ORTEP diagram of the cation in [Hf(TC-3,3)N-
(t-Bu)(C{)CdN-t-Bu}{CH2Ph})](BPh4) (2b) showing 50%
ellipsoids and the atom-labeling scheme. Selected distances
and angles for both 2a and 2b are contained in Table 2.
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for [M(TC-3,3)(CH2P h )](BP h 4), M ) Zr
(1a ), Hf (1b)a
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) for
[M(TC-3,3)N(t-Bu )(C{dCdN-t-Bu }{CH2P h })](BP h 4),
Zr(1)-N(1)
Zr(1)-N(2)
Zr(1)-N(3)
Zr(1)-N(4)
Zr(1)-C(21)
Zr(1)-C(22)
2.149(3)
2.140(3)
2.149(3)
2.146(3)
2.279(4)
2.687(4)
Hf(1)-N(1)
Hf(1)-N(2)
Hf(1)-N(3)
Hf(1)-N(4)
Hf(1)-C(21)
Hf(1)-C(22)
2.126(4)
2.118(4)
2.136(4)
2.117(4)
2.266(5)
2.745(5)
M ) Zr (2a ), Hf (2b)a
Zr(1)-N(1)
Zr(1)-N(2)
Zr(1)-N(3)
Zr(1)-N(4)
Zr(1)-N(5)
Zr(1)-C(21)
C(21)-C(29)
N(6)-C(29)
2.150(4)
2.161(4)
2.145(5)
2.139(4)
2.036(4)
2.724(5)
1.314(8)
1.230(8)
Hf(1)-N(1)
Hf(1)-N(2)
Hf(1)-N(3)
Hf(1)-N(4)
Hf(1)-N(5)
Hf(1)-C(21)
C(21)-C(29)
N(6)-C(29)
2.137(5)
2.145(5)
2.121(5)
2.123(5)
2.024(5)
2.734(6)
1.328(9)
1.229(8)
N(1)-Zr(1)-N(2)
N(1)-Zr(1)-N(3)
N(1)-Zr(1)-N(4)
N(2)-Zr(1)-N(3)
N(2)-Zr(1)-N(4)
N(3)-Zr(1)-N(4)
72.42(10) N(1)-Hf(1)-N(2)
132.38(10) N(1)-Hf(1)-N(3)
86.74(10) N(1)-Hf(1)-N(4)
85.16(10) N(2)-Hf(1)-N(3)
124.02(10) N(2)-Hf(1)-N(4)
71.67(11) N(3)-Hf(1)-N(4)
73.27(14)
133.87(14)
87.19(14)
85.85(14)
126.50(14)
72.77(14)
N(1)-Zr(1)-N(2)
N(1)-Zr(1)-N(3)
N(1)-Zr(1)-N(4)
N(1)-Zr(1)-N(5)
N(2)-Zr(1)-N(3)
N(2)-Zr(1)-N(4)
N(2)-Zr(1)-N(5)
N(3)-Zr(1)-N(4)
N(3)-Zr(1)-N(5)
N(4)-Zr(1)-N(5)
71.9(2)
128.9(2)
86.9(2)
118.1(2)
88.1(2)
131.2(2)
117.0(2)
71.8(2)
112.9(2)
111.7(2)
N(1)-Hf(1)-N(2)
N(1)-Hf(1)-N(3)
N(1)-Hf(1)-N(4)
N(1)-Hf(1)-N(5)
N(2)-Hf(1)-N(3)
N(2)-Hf(1)-N(4)
N(2)-Hf(1)-N(5)
N(3)-Hf(1)-N(4)
N(3)-Hf(1)-N(5)
N(4)-Hf(1)-N(5)
73.1(2)
132.9(2)
87.8(2)
115.4(2)
87.0(2)
130.7(2)
118.4(2)
73.5(2)
111.6(2)
110.9(2)
N(1)-Zr(1)-C(21) 121.07(13) N(1)-Hf(1)-C(21) 118.2(2)
N(2)-Zr(1)-C(21) 117.84(13) N(2)-Hf(1)-C(21) 115.7(2)
N(3)-Zr(1)-C(21) 106.53(13) N(3)-Hf(1)-C(21) 107.9(2)
N(4)-Zr(1)-C(21) 117.45(13) N(4)-Hf(1)-C(21) 117.5(2)
Zr(1)-C(21)-C(22) 88.6(2)
Hf(1)-C(21)-C(22) 91.6(3)
a
Numbers in parentheses are estimated standard deviations
in the last digit(s) listed. See Figure 1 for atom-labeling scheme.
C(21)-C(29)-N(6) 170.2(6)
C(21)-C(29)-N(6) 171.8(8)
a
Numbers in parentheses are estimated standard deviations
in the last digit(s) listed. See Figure 2 for atom-labeling scheme.
sent some of the few examples6,7,16 of group 4 cations
which can be isolated without a stabilizing interaction
with either the counterion or extrinsic bases such as
aniline, THF, or acetonitrile.4 The acute M-CH2-Ph
angles of 88.6(2)° (1a ) and 91.6(3)° (1b) and the short
M-C(22) distances of 2.687(4) (1a ) and 2.745(5) Å (1b)
reflect η2-binding of the benzyl group. This interaction
stabilizes the complexes in the absence of a sixth ligand,
but the M-R bond is weak compared with other
formally pentacoordinate, cationic complexes. The analo-
gous distance and angle in one of the few examples of a
structurally characterized pentacoordinate cationic Zr-
(IV) complex, [Zr(MeBr2Ox)2(η2-CH2Ph)]+, where MeBr2-
Ox ) 2-Me-5,7-Br2-8-quinolinolato, are 2.448(5) Å and
80.0(3)°, respectively.16
center following removal of one of the alkyl substituents.
As was the case for the neutral [M(TC-n,m)Y2] and
related metallocene complexes,13 the spectral and struc-
tural (longer M-Y bonds) results demonstrate that 1a
and 1b are significantly less electrophilic compared to
cationic zirconocene analogues, and the difference is
especially apparent in the absence of a stabilizing ligand
such as THF.
Rea ction of 1a a n d 1b w ith Isocya n id es. Nucleo-
philes usually bind to cationic group 4 metals before
inserting into a metal-carbon bond. Compounds 1a
and 1b react similarly, even though they have reduced
electrophilicity.4 Addition of several equivalents of tert-
butyl isocyanide to dichloromethane solutions of 1a and
1b induced a rapid color change from orange to orange-
red and formation of the ketenimine complexes [M(TC-
3,3)N(t-Bu)(C{dCdN-t-Bu}{CH2Ph})](BPh4), M ) Zr
(2a ), Hf (2b) (Figure 2; Table 2). As in the precursor
complexes, the metal centers adopt a square-pyramidal
stereochemistry with the four nitrogen atoms of the
macrocycle bonding in the equatorial plane. Although
the M-N distances are essentially indistinguishable,
The lack of a strong interaction between the ipso
carbon and the metal is also evident in the 1H NMR
spectra of 1a and 1b, which do not display the signifi-
cant upfield shift of the ortho proton resonance char-
acteristic of η2-coordination of benzyl ligands.4,8 Al-
though the interaction with the ipso carbon atom is not
strong, the acute angle at C(21) and the downfield shift
of the C(21) resonance in the 13C NMR spectrum, from
δ 72.18 in [M(TC-3,3)(CH2Ph)2] to 76.31 in 1b, are
consistent with increased in Lewis acidity at the metal

Group 4 Tropocoronand Complexes
Organometallics, Vol. 17, No. 9, 1998 1771
Sch em e 1
the distance to the apical ligand decreases dramatically
from 2.279(4) Å in 1a to 2.036(4) Å in 2a , reflecting the
enhanced orbital overlap with the amide functionality.
The M-C(21) distances of 2.724(5) Å in 2a and 2.734-
(6) Å in 2b suggest that the metal center may still
maintain some degree of orbital communication with the
carbon atom of the apical ligand. The linear CdCdN
angle of 170.2(6)° in 2a and short CdC and CdN
distances of 1.314(8) and 1.230(8) Å, respectively, are
consistent with those observed in other group 4 keten-
imine species, as is the intense stretch at 1988 cm-1 in
the infrared spectrum of 2b.17,18
of η2-iminoacyl groups in a few zirconocene systems
having constrained metallacycles are also susceptible
to such direct nucleophilic attack by external isocyan-
ides, but unlike the reactions of 2a and 2b, pressures
of up to 12 kbar are required to induce this reversible
conversion.18 The decreased electrophilicity of the metal
in the tropocoronands may disfavor binding of a second
equivalent of isocyanide and could facilitate direct
nucleophilic attack on the intermediate, although there
is no direct evidence for this pathway. The result is
irreversible conversion to the ketenimine moiety at room
temperature and pressure.
R ea ct ion of 1a a n d 1b w it h Ben zop h en on e.
Cationic group 4 complexes readily bind carbonyl groups
owing to their high Lewis acidity. Except in rare
instances,23 the carbonyl-containing substrate inserts
into the metal-carbon bond producing an alkoxide
ligand. Ordinarily, the metal center then rapidly binds
a second equivalent of substrate in order to stabilize the
metal-alkoxy species.7 Both 1a and 1b also insert
benzophenone into the metal-carbon bond forming the
alkoxides [M(TC-3,3){η1-OCPh2(CH2Ph)}], M ) Zr (3a ),
Hf (3b) (Figure 3). In contrast to most group 4 com-
plexes, however, the metal center does not bind a second
equivalent of ketone, even in the presence of a large
excess of substrate. As indicated above, the donating
character of the tropocoronand ligand system tempers
the Lewis acidity of the metal center and stabilizes the
resulting pentacoordinate species. Although the electron-
withdrawing phenyl substituents may exert some influ-
ence, the Zr-O distance of 1.927(4) Å in 3a is only
marginally longer than the analogous distance of 1.899-
(3) Å in [Cp2Zr(O-t-Bu)(THF)], despite the presence of
an additional THF ligand.24 When compared to other
tropocoronand complexes, for example, the bis(iminoa-
The products isolated can be rationalized by double
insertion of tert-butyl isocyanide into the metal-carbon
bond of 1a and 1b, as outlined in Scheme 1. Several
observations support this proposal. After binding to the
metal center, isocyanides typically insert into the M-R
bonds in organometallic group 4 complexes containing
ligands such as cyclopentadienyl, aryloxide, and tet-
raazamacrocycles including tropocoronands.14,19 The
nitrogen atom of the isocyanide then rapidly coordi-
nates, forming an η2-iminoacyl complex. Normally, in
these systems, additional extrinsic substrates either
bind directly to the metal center20 or insert, in a 1,1- or
1,2-fashion, into the M-C bond of the η2-iminoacyl
moiety.21,22 With 1a and 1b, however, the electrophilic
nature of the bound carbon atom promotes nucleophilic
attack by an additional equivalent of isocyanide, forming
the ketenimine complexes 2a and 2b. The carbon atoms
(17) Scott, M. J .; Lippard, S. J . J . Am. Chem. Soc. 1997, 119, 3411-
3412.
(18) Valero, C.; Grehl, M.; Wingbermu¨hle, D.; Kloppenburg, L.;
Carpenetti, D.; Erker, G.; Petersen, J . L. Organometallics 1994, 13,
415-417.
(19) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059-1079.
(20) Bochman, M.; Wilson, L. M.; Hursthouse, M. B.; Short, R. L.
Organometallics 1987, 6, 2556-2563.
(21) Bocarsly, J . R.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
Organometallics 1986, 5, 2380-2383.
(23) Sun, Y.; Piers, W. E.; Yap, G. P. A. Organometallics 1997, 16,
2509-2513.
(24) Collins, S.; Koene, B. E.; Ramachandran, R.; Taylor, N. J .
Organometallics 1991, 10, 2092-2094.
(22) Scott, M. J .; Lippard, S. J . Organometallics 1997, 16, 5857-
5868.

1772 Organometallics, Vol. 17, No. 9, 1998
Scott and Lippard
135 FTIR spectrometer. All compounds were characterized
by CCA, and elemental analyses were obtained on representa-
tive species.
P r ep a r a tion of [M(TC-3,3)(CH2P h )](BP h 4), M ) Zr (1a ),
Hf (1b). In a typical reaction, a rapidly stirred dark red
solution of 279 mg (0.411 mmol) of [Hf(TC-3,3)(CH2Ph)2] in 2
mL of dichloromethane was treated with a 156 mg (0.411
mmol) portion of (HNMe3)(BPh4) at -30 °C. The mixture was
allowed to warm to room temperature, and after several
minutes, the solution became bright orange and homogeneous.
With a further 15 min of stirring, a precipitate formed in the
mixture. Following the addition of 0.5 mL of ether, the
mixture was cooled to -30 °C. The resulting bright orange
solid was collected, washed with ether and pentane, and dried
to yield 190 mg (51%) of 1b. The crude material was
recrystallized from dichloromethane/ether or chlorobenzene/
ether to afford large orange rhombohedral crystals. An
analogous procedure was used to obtain 1a , typical yields being
43-56%. Alternatively, substitution of the amine in the
synthetic scheme with [Cp2Fe](BPh4) also generated 1a and
1b, although the yields were lower (21-36%). 1a : 1H NMR
(CD2Cl2) δ 7.49 (t, J ) 10.7 Hz, 4H), 7.32 (m, 11H), 7.00 (m,
12H), 6.84 (m, 8H), 3.75 (m, 4H), 3.44 (d of t, J ) 2.0, 7.2 Hz,
4H), 2.70 (s, 2H, CH2), 2.44 (m, 2H), 1.96 (m, 2H); IR (KBr,
cm-1) 3051m, 3029w, 2996w, 2981m, 2901w, 1589s, 1512vs,
1478m, 1454w, 1433m, 1423w, 1416m, 1378s, 1363m, 1354w,
1341m, 1281m, 1228s, 1180w, 1137w, 1107w, 1080w, 1035w,
996m, 941w, 886m, 848w, 790w, 730vs, 705vs, 614w, 603m,
490m, 437w. 1b: 1H NMR (CD2Cl2) δ 7.54 (t, J ) 10.6 Hz,
4H), 7.30 (m, 8H), 7.17 (t, J ) 7.6 Hz, 2H), 7.06 (t, J ) 9.4 Hz,
2H), 6.99 (m, 8H), 6.86 (m, 11H), 3.78 (m, 4H), 3.51 (m, 4H)
2.46 (s, 2H, CH2), 2.43 (m, 2H), 2.30 (m, 2H); 13C{1H} NMR
(CD2Cl2) δ 163.44, 138.94, 136.56, 130.40, 128.49, 128.40,
126.24 (m), 124.91, 122.34, 119.02, 76.31 (Hf-C), 50.44, 24.01;
IR (KBr, cm-1) 3051m, 2991w, 2981m, 2901w, 1591s, 1580w,
1513vs, 1476m, 1454w, 1434w, 1424m, 1376s, 1362m, 1342m,
1283m, 1229s, 1139w, 1112w, 1083w, 1038w, 1031w, 1001m,
942w, 886w, 821w, 786w, 731vs, 705s, 614w, 604w, 486m.
Anal. Calcd for C51H49BN4Hf: C, 67.50; H, 5.44; N, 6.18.
Found: C, 67.30; H, 5.33; N, 5.92
F igu r e 3. ORTEP diagram of the cation in [Zr(TC-3,3)-
{η1-OCPh2(CH2Ph)}](BPh4) (3a ) showing 50% ellipsoids
and atom-labeling scheme. Selected bond distances (Å) and
angles (deg): Zr(1)-O(1), 1.927(4); Zr(1)-N(1), 2.139(4); Zr-
(1)-N(2), 2.153(4); Zr(1)-N(3), 2.147(5); Zr(1)-N(4), 2.134-
(5); O(1)-C(21), 1.418(6); Zr(1)-O(1)-C(21), 170.6(3).
cyl) species [Hf(TC-3,3){η2-CyNdC(CH2Ph)}2],22 the
coordination sphere of the metal center in 3a appears
to be relatively unencumbered. Electronic factors,
rather than the stereochemical requirements of the
bulky phenoxide ligand, therefore, appear to be respon-
sible for the long Zr-O bond.
In summary, we have isolated and characterized
stable cationic organometallic zirconium(IV) and haf-
nium(IV) complexes of the tropocoronand ligand system
which react to afford ketenimine and alkoxide products.
A comparison of the structural data for both 1a and 3a
with those of zirconocene-based systems suggests that
the donor properties of the tropocoronand ligand are
similar to that of the bis(cyclopentadienyl)zirconium
fragment when coordinated by an auxiliary ligand such
as THF. Furthermore, by comparison to other ligands,
the decreased Lewis acidity of the tropocoronand com-
plex attenuates the electrophilicity of the ancillary
carbon-based ligands and influences their reactivity
with substrates such as isonitriles. Similar results with
the complexes [M(TC-n,m)R2] have recently been re-
ported14 which, together the present work, highlight
some of the unique coupling reactions which can be
promoted by organometallic group 4 tropocoronand
complexes.
P r ep a r a tion of [M(TC-3,3)N(t-Bu )(C{dCdN-t-Bu }{CH2-
P h })](BP h 4), M ) Zr (2a ), Hf (2b). In a typical procedure,
a slurry of 31.2 mg (0.034 mmol) of 1b in dichloromethane was
treated with 14.4 µL (0.138 mmol) of tert-butyl isocyanide at
-30 °C. The mixture was allowed to warm to room temper-
ature and filtered through Celite, and the filtrate was cooled
to -30 °C. Over the course of several days, ether was slowly
diffused into the solution, resulting in the formation of large
red-orange crystals. The solid was collected, washed with
ether, and dried to afford 19 mg (52%) of 1b. Following the
procedure outlined above, compound 2a was obtained in
moderate yield (32-47%). Although 2b is stable in solution,
complex 2a decomposes in a matter of hours in dichloro-
methane at room temperature. For X-ray crystallographic
studies, crystals of 2a were grown in a mixture of dichloro-
methane/pentane at -30 °C. Single crystals of 2b were
obtained from chlorobenzene/ether solutions. 2a : 1H NMR
(CD2Cl2) δ 7.49 (m, 4H), 7.31 (m, 11H), 7.00 (m, 12H), 6.82
(m, 8H), 4.05 (m, br, 4H), 3.40 (m, vbr, 6H), 2.50 (m, vbr, 4H),
1.24 (s, 9H), 0.89 (s, 9H). 2b: 1H NMR (CD2Cl2) δ 7.51 (t, J )
10.8 Hz, 4H), 7.32 (m, 11H), 7.00 (m, 12H), 6.83 (m, 8H), 4.00
(m, br, 4H), 3.44 (m, vbr, 4H), 2.66 (m, vbr, 4H), 2.00 (m, vbr,
2H), 1.23 (s, 9H), 0.88 (s, 9H); 13C{1H} NMR (CD2Cl2) δ 183.93,
165.63, 165.00, 164.36, 163.32, 138.30, 137.42, 136.52, 130.00,
128.93, 127.49, 126.66, 126.23 (m), 122.32, 118.16, 72.00, 60.53,
59.78, 50.10, 42.335, 32.70, 29.96, 25.73; IR (KBr, cm-1) 3054m,
2998w, 2980m, 1988m, 1592s, 1513vs, 1473m, 1432m, 1420m,
1379m, 1363s, 1347m, 1281m, 1231s, 1184w, 1140w, 1112w,
1085w, 1031w, 1003m, 970w, 942w, 886w, 848w, 731s, 704vs,
612m, 487w, 472w. Anal. Calcd for C61H67BN6Hf‚0.5CH2Cl2
Exp er im en ta l Section
P r ep a r a tion of Com p ou n d s. The complexes [M(TC-3,3)-
(CH2Ph)2] (M ) Zr(IV), Hf(IV)) were synthesized as described.13
All operations, excluding ligand preparations, were conducted
under
a pure dinitrogen or argon atmosphere by using
standard Schlenk and glovebox techniques. Solvents were
dried according to established protocols and degassed prior to
use. Unless otherwise specified, reagents were obtained from
commercial suppliers and thoroughly degassed and dried
before use. 1H NMR spectra were recorded on a Bruker AM-
250 and 13C{1H} NMR spectra on a Varian Unity 300 spec-
trometer. Due to the limited solubility of the complexes in
the solvents used, data were collected at room temperature.
Chemical shifts are referenced with respect to the residual
solvent peak. FTIR spectra were recorded on a BioRad FTS-

Group 4 Tropocoronand Complexes
Organometallics, Vol. 17, No. 9, 1998 1773
(C61.5H68BClN6Hf): C, 66.19; H, 6.14; N, 7.53. Found: C,
66.37; H, 6.06; N, 7.13.
were refined anisotropically. Hydrogen atoms were normally
assigned idealized locations and given a thermal parameter
equal to 1.2 times that of the carbon atom to which it was
attached, unless otherwise noted.
P r ep a r a tion of [M(TC-3,3){η1-OCP h 2(CH2P h )}](BP h 4),
M ) Zr (3a ), Hf (3b). A slurry of 28 mg (0.031 mmol) of 1b
in 1.5 mL of dichloromethane was treated with a 6.2 mg (0.034
mmol) portion of solid benzophenone at -30 °C. The solution
rapidly changed color from orange to bright yellow-orange and
became homogeneous upon warming to room temperature. The
reaction mixture was filtered, and several volume equivalents
of ether were diffused into the filtrate at -30 °C over the
course of several days. The solid material was collected,
washed with ether, and dried to afford 15 mg (45%) of feathery
yellow-orange crystals. An identical procedure was used to
prepare 3a , but after the addition of ether, solutions of the
complex tended to form oily residues, hindering characteriza-
tion of the material. Single yellow crystals of 3a were selected
manually and characterized by CCA. 3b: 1H NMR (CD2Cl2)
δ 7.54 (t, J ) 10.4 Hz, 4H), 7.32 (m, 18H), 6.99(m, 11H), 6.83
(m, 10H), 6.60 (d, J ) 7.4 Hz, 2H), 3.80 (s, 2H, CH2), 3.61 (m,
4H), 3.38 (m, 4H), 2.16 (m, 2H) 1.84 (m, 2H); 13C{1H} NMR
(CD2Cl2) δ 163.73, 148.19, 138.79, 137.35, 136.56, 130.85,
129.05, 128.42, 127.95, 127.70, 127.26, 126.26 (m), 122.33,
118.82, 89.74, 50.00, 48.74, 24.46; IR (KBr, cm-1) 3053m,
3028w, 2981m, 2940w, 1592s, 1579w, 1514vs, 1477m, 1434m,
1422s, 1385w, 1370vs, 1345m, 1288m, 1233s, 1185w, 1142w,
1094w, 1081w, 1060m, 1039w, 1031w, 1004m, 941w, 885m,
848w, 791w, 732s, 703vs, 654w, 610m, 568w, 490m. Anal.
Calcd for C64H59BN4HfO: C, 70.56; H, 5.46; N, 5.14. Found:
C, 69.72; H, 5.35; N, 5.10.
Cr ysta llogr a p h ic Stu d ies. Crystals were obtained by
vapor diffusion of ether or pentane into a saturated solution
of the complexes at -30 °C, as described above. Single crystals
were coated with Paratone-N oil, selected under a microscope,
attached to a glass fiber, and transferred rapidly to the -85
°C cold stream of a Siemens CCD X-ray diffraction system
controlled by a pentium-based PC running the SMART soft-
ware package.25 The program SADABS was used to correct
the data for absorption and decay.26 Data were collected by
following standard procedures reported in detail elsewhere.27
The structures were solved by direct methods or Patterson
analysis and refined by full-matrix least-squares and Fourier
techniques with the SHELXTL-PLUS program package.28
Space groups were determined from an examination of the
systematic absences in the data and confirmed by the suc-
cessful solution and refinement of the structures. Except in
cases where disorder was apparent, all non-hydrogen atoms
Cr ysta llogr a p h ic Da ta for [M(TC-3,3)(CH 2P h )](BP h 4),
M ) Zr (1a ), Hf (1b). Complex 1a : C51H49BN4Zr, fw ) 819.97,
monoclinic, space group P21/n, a ) 15.1054(4) Å, b ) 17.0209-
(3) Å, c ) 17.6343(5) Å, â ) 114.683(1)°, V ) 4119.7(2) Å3, Z
) 4, 15 812 reflections collected, 5849 unique reflections (Rmerge
,
4.57%), 4307 reflections > 2σ, R ) 4.21%, wR2 ) 7.92%, GOF
) 1.006. Complex 1b: C51H49BHfN4, fw ) 907.24, monoclinic,
space group P21/n, a ) 15.1125(4) Å, b ) 17.0404(3) Å, c )
17.6455(5) Å, â ) 114.664(1)°, V ) 4129.6(2) Å3, Z ) 4, 16 002
reflections collected, 5898 unique reflections (Rmerge, 4.58%),
4855 reflections > 2σ, R ) 3.35%, wR2 ) 6.07%, GOF ) 1.065.
Cr ystallogr aph ic Data for [M(TC-3,3)N(t-Bu )(C{dCdN-
t-Bu }{CH 2P h })](BP h 4), M ) Zr (2a ), Hf (2b). Complex
2a ‚C5H12: C66H79BN6Zr, fw ) 1058.38, monoclinic, space group
P21/n, a ) 13.1636(3) Å, b ) 27.7436(2) Å, c ) 17.2289(2) Å, â
) 106.698(1)°, V ) 6026.8(2) Å3, Z ) 4, 23 052 reflections
collected, 8518 unique reflections (Rmerge, 6.70%), 6123 reflec-
tions > 2σ, R ) 7.00%, wR2 ) 17.51%, GOF ) 1.126. Six
carbon atom positions were isotropically refined for the pen-
tane solvate molecule, and hydrogen atoms were not included
in the refinement of this molecule. The four central carbon
atoms were refined at full occupancy, while the two outer
positions were refined with site occupancy factors of 0.5.
Complex 2b‚1.5C6H5Cl: C70H74.5BCl1.5HfN6, fw ) 1242.33,
monoclinic, space group P21/n, a ) 13.3377(2) Å, b ) 27.7601-
(1) Å, c ) 17.2046(3) Å, â ) 106.612(1)°, V ) 6104.23(14) Å3,
Z ) 4, 35 157 reflections collected, 13 817 unique reflections
(Rmerge, 10.32%), 7563 reflections > 2σ, R ) 7.34%, wR2
)
9.49%, GOF ) 1.134. In the structure of 2b, a chlorobenzene
solvate molecule is disordered across an inversion center. The
site occupancy of the chlorine atom was fixed at 0.5, and the
molecule was refined isotropically without hydrogen atoms.
Cr ysta llogr a p h ic Da ta for [Zr (TC-3,3){η1-OCP h 2(CH2-
P h )}](BP h 4) (3a ). C64H59BN4OZr, fw ) 1002.18, triclinic,
space group P1h, a ) 12.9462(3) Å, b ) 14.1065(5) Å, c )
15.9917(5) Å, R ) 109.207(1)°, â ) 96.004(1)°, γ ) 106.110-
(1)°, V ) 2587.11(14) Å3, Z ) 2, 10 078 reflections collected,
6910 unique reflections (Rmerge, 5.56%), 4592 reflections > 2σ,
R ) 6.88%, wR2 ) 11.62%, GOF ) 1.088.
Ack n ow led gm en t. This work was supported by a
grant from the National Science Foundation. M.J .S. is
grateful to the National Institute of General Medical
Science for a postdoctoral fellowship.
(25) SMART: Version 4.0; Siemens Industrial Automation, Inc.:
Madison, WI, 1994.
(26) Program written by Prof. George Sheldrick at the University
of Go¨ttingen which corrects data collected on Siemens CCD and
multiwire detectors for absorption and decay.
(27) Feig, A. L.; Bautista, M. T.; Lippard, S. J . Inorg. Chem. 1996,
35, 6892-6898.
(28) SHELXTL: Structure Analysis Program; Siemens Industrial
Automation, Inc.: Madison, WI, 1995.
Su p p or tin g In for m a tion Ava ila ble: Tables of anisotro-
pic thermal parameters, hydrogen atom parameters, and
complete bond distances and angles for all compounds (59
pages). Ordering information is given on any current mast-
head page.
OM971126G