Formation and structural and dynamic features of atropisomeric η2-iminoacyl zirconium complexes

Article abstract of DOI:10.1021/om7005968

The Cp₂ZrCl(μ-1,4-diphenylbutenyne)PX₂ complexes 7a [-P(C₆H₅)₂] and 10 [-P(C₆F ₅)₂] insert tert-butylisonitrile into the Zr-C(sp ²) σ bond to yield the N-inside η²-iminoacyl zirconocene complexes 13a and 13b. X-ray crystal structure analysis of complexes 13a and 13b revealed the presence of a chiral atropisomeric structure with a torsion angle of 74.8(2)° (13a) and 72.9(6)° (13b), respectively, around the central iminoacyl/alkenyl C(sp²)-C(sp²) σ bond. In solution an analogous chiral structure is observed. The barrier of interconversion of the enantiomeric atropisomers of 13a and 13b was determined at ΔG? (327K) = 14.9 ± 0.3 kcal mol^-1 (13a) and ΔG? (325K) = 14.8 ± 0.3 kcal mol^-1 (13b) by temperature-dependent dynamic NMR spectroscopy. Reaction of 7a and 10 with methyllithium followed by treatment with B(C₆F₅) ₃ gave the corresponding cationic zirconocene complexes 12a and 12b. These complexes took up 2 mol equiv of tert-butylisonitrile to yield the cationic N-inside η²-iminoacyl zirconocene systems 14a and 14b as isonitrile adducts. The cationic complexes 14a and 14b are also axially chiral. The barriers of enantiomerization (ΔG? (288 K) = 13.1 ± 0.3 kcal mol^-1 (14a), ΔG? (293 K) = 13.4 ± 0.3 kcal mol^-1 (14b)) were also determined by dynamic NMR spectroscopy.

Full text of DOI:10.1021/om7005968

5612
Organometallics 2007, 26, 5612-5620
Formation and Structural and Dynamic Features of Atropisomeric
η2-Iminoacyl Zirconium Complexes
Patrick Spies, Gerald Kehr, Seda Kehr,† Roland Fro¨hlich,† and Gerhard Erker*
Organisch-Chemisches Institut der UniVersita¨t Mu¨nster, Corrensstrasse 40, 48149 Mu¨nster, Germany
ReceiVed June 18, 2007
The Cp2ZrCl(µ-1,4-diphenylbutenyne)PX2 complexes 7a [-P(C6H5)2] and 10 [-P(C6F5)2] insert tert-
butylisonitrile into the Zr-C(sp2) σ bond to yield the N-inside η2-iminoacyl zirconocene complexes 13a
and 13b. X-ray crystal structure analysis of complexes 13a and 13b revealed the presence of a chiral
atropisomeric structure with a torsion angle of 74.8(2)° (13a) and 72.9(6)° (13b), respectively, around
the central iminoacyl/alkenyl C(sp2)-C(sp2) σ bond. In solution an analogous chiral structure is observed.
The barrier of interconversion of the enantiomeric atropisomers of 13a and 13b was determined at ∆Gq
(327K) ) 14.9 ( 0.3 kcal mol-1 (13a) and ∆Gq (325K) ) 14.8 ( 0.3 kcal mol-1 (13b) by temperature-
dependent dynamic NMR spectroscopy. Reaction of 7a and 10 with methyllithium followed by treatment
with B(C6F5)3 gave the corresponding cationic zirconocene complexes 12a and 12b. These complexes
took up 2 mol equiv of tert-butylisonitrile to yield the cationic N-inside η2-iminoacyl zirconocene systems
14a and 14b as isonitrile adducts. The cationic complexes 14a and 14b are also axially chiral. The barriers
of enantiomerization (∆Gq (288 K) ) 13.1 ( 0.3 kcal mol-1 (14a), ∆Gq (293 K) ) 13.4 ( 0.3 kcal
mol-1 (14b)) were also determined by dynamic NMR spectroscopy.
(4) must be assumed6 that surprisingly seems to contain a planar
tetracoordinated carbon center (see Scheme 1).7-9
Introduction
We have recently shown that bis(alkynyl)zirconocenes (1)
rapidly react with a stoichiometric amount of the strong Lewis
acid B(C6F5)3 (2) to yield the zwitterionic diyne-bridged
zirconocenium/borate betaine products (3).1,2 Upon treatment
with an isonitrile the systems 3 rapidly undergo further internal
C-C coupling at room temperature or below to yield the unique
functionalized methylenecyclopropene derivatives (5). Related
chemistry is observed upon treatment of the compounds 3 with
organonitrile reagents.3-5 Thermodynamically, the endother-
micity of the methylenecyclopropene formation is more than
compensated by the energy gain associated with the newly
formed C-C and Zr-N bonds. Kinetically, the situation is more
complex. From a detailed theoretical analysis (DFT) it seems
that the three-membered ring formation, which topologically
requires insertion of the remaining -CtC triple bond into the
adjacent Zr-C(sp2) σ bond, is triggered by nitrile (or isonitrile)
addition to make a sufficiently kinetically favorable reaction
pathway available.6 From the respective DFT calculation
formation of a reasonably stabilized local minimum intermediate
This posed the question of whether such unique methyl-
enecyclopropene formation might occur specifically within the
zwitterionic Zr+/-BR3- framework of 3 or if combinations of
an electropositive group 4 metal with other types of electroni-
cally active peripheral substituents might be possible within this
unique reaction scheme. We, therefore, developed a synthetic
pathway to systems 7 which may be regarded as phosphine
analogues of 3.10 Synthesis of 7 was straightforward: Treatment
of the metallacyclocumulene 611,12 with ClPPh2 gave 7a. The
analogous reaction of 6 with PCl3 led to formation of 7b (see
Scheme 2).10
We have now prepared a series of derivatives from the readily
available precursors 7a,b and investigated whether a related
formation of stabilized methylenecyclopropene derivatives (8)
would be observable under a variety of conditions. This actually
(7) Hoffmann, R.; Alder, R. W.; Wilcox, C. F., Jr. J. Am. Chem. Soc.
1970, 92, 4992-4993. Collins, J. B.; Dill, J. D.; Jemmis, E. D.; Apeloig,
Y.; Schleyer, P. v. R.; Seeger, R.; Pople, J. A. J. Am. Chem. Soc. 1976, 98,
5419-5427. Sorger, K.; Schleyer, P. v. R.; Fleischer, R.; Stalke, D. J. Am.
Chem. Soc. 1996, 118, 6924-6933 and references cited therein.
(8) Erker, G.; Zwettler, R.; Kru¨ger, C.; Noe, R.; Werner, S. J. Am. Chem.
Soc. 1990, 112, 9620-9621. Reviews: Ro¨ttger, D.; Erker, G. Angew. Chem.
1997, 109, 840-856; Angew. Chem., Int. Ed. Engl. 1997, 36, 812-827.
Erker, G. Chem. Soc. ReV. 1999, 28, 307-314.
* To whom correspondence should be addressed. E-mail: erker@
uni-muenster.de.
† X-ray crystal structure analyses.
(1) Temme, B.; Erker, G.; Fro¨hlich, R.; Grehl, M. Angew. Chem. 1994,
106, 1570-1572; Angew. Chem., Int. Ed. Engl. 1994, 33, 1480-1482.
(2) Ahlers, W.; Temme, B.; Erker, G.; Fro¨hlich, R.; Fox, T. J. Organomet.
Chem. 1997, 527, 191-201. Ahlers, W.; Erker, G.; Fro¨hlich, R.; Peuchert,
U. J. Organomet. Chem. 1999, 578, 115-124.
(3) Temme, B.; Erker, G.; Fro¨hlich, R.; Grehl, M. J. Chem. Soc., Chem.
Commun. 1994, 1713-1714.
(4) Erker, G.; Ahlers, W.; Fro¨hlich, R. J. Am. Chem. Soc. 1995, 117,
5853-5854. Ahlers, W.; Erker, G.; Fro¨hlich, R.; Zippel, F. Chem. Ber./
Recl. 1997, 130, 1079-1084. Venne-Dunker, S.; Ahlers, W.; Erker, G.;
Fro¨hlich, R. Eur. J. Inorg. Chem. 2000, 1671-1678.
(5) For related organic systems, see, e.g.: Eicher, T.; Lo¨schner, A. Z.
Naturforsch. 1966, 21B, 295-296. Eicher, T.; Hansen, A. Tetrahedron Lett.
1967, 44, 4321-4326.
(6) Erker, G.; Venne-Dunker, S.; Kehr, G.; Kleigrewe, N.; Fro¨hlich, R.;
Mu¨ck-Lichtenfeld, C.; Grimme, S. Organometallics 2004, 23, 4391-4395.
(9) Choukroun, R.; Cassoux, P. Acc. Chem. Res. 1999, 32, 494-502.
Hora´cˇek, M.; Sˇteˇpnicˇka, P.; Kubisˇta, J.; Gyepes, R.; Mach, K. L.
Organometallics 2004, 23, 3388-3397. Pancharatna, P. D.; Me´ndez-Rojas,
M. A.; Merino, G.; Vela, A.; Hoffmann, R. J. Am. Chem. Soc. 2004, 126,
15309-15315. Esteves, P. M.; Ferreira, N. B. P.; Correa, R. J. J. Am. Chem.
Soc. 2005, 127, 8680-8685 and references cited therein.
(10) Spies, P.; Kehr, G.; Fro¨hlich, R.; Erker, G.; Grimme, S.; Mu¨ck-
Lichtenfeld, C. Organometallics 2005, 24, 4742-4746.
(11) Rosenthal, U.; Ohff, A.; Baumann, W.; Kempe, R.; Tillack, A.;
Burlakov, V. V. Angew. Chem. 1994, 106, 1678-1680; Angew. Chem, Int.
Ed. Engl. 1994, 33, 1605-1607. Burlakov, V. V.; Ohff, A.; Lefeber, C.;
Tillack, A.; Baumann, W.; Kempe, R.; Rosenthal, U. Chem. Ber. 1995,
128, 967-971.
(12) Rosenthal, U.; Burlakov, V. V.; Arndt, P.; Baumann, W.; Span-
nenberg, A. Organometallics 2005, 24, 456-471 and references therein.
10.1021/om7005968 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 10/03/2007

Atropisomeric η2-Iminoacyl Zirconium Complexes
Organometallics, Vol. 26, No. 23, 2007 5613
Scheme 1
Scheme 3
Scheme 2
linear (C41-C42 1.201(3) Å, angles Zr-C41-C42 173.6(2)°,
C41-C42-C43 177.8(2)°) as expected. The sterically encum-
bered tetrasubstituted σ-alkenyl ligand has the dC(alkynyl)-
PPh2 end oriented toward the lateral sector of the bent
metallocene wedge. It is only marginally rotated from the central
σ-ligand plane (dihedral angle C41-Zr-C2-C3 173.8(2)°). In
contrast, the phenyl substituent at the alkenyl R-carbon is rotated
substantially out of the plane (θ C3-C2-C1-C11 104.2(2)°,
C3-C2-C1-C15 -82.3(2)°). The C2-C3 bond is slightly
elongated (1.351(2) Å), and the angles at the olefinic sp2-carbon
center C2 are markedly distorted [Zr-C2-C1 100.6(1)°, Zr-
C2-C3 136.3(1)°, C1-C2-C3 123.0(2)° vs C2-C3-C4
122.0(2)°, C2-C3-P1 121.5(1)°, C4-C3-P1 116.5(1)°]. The
phosphorus atom features a typical near to nonhybridized
coordination sphere [bond lengths C3-P1: 1.843(2) Å, C31-
P1 1.833(2) Å, C21-P1 1.826(2) Å, bond angles C3-P1-
C21: 103.58(8)°, C3-P1-C31 99.82(8)°, C21-P1-C31 101.57-
(8)°]. Eventually, carbon atom C3 bears the linear phenylacetylide
substituent (C3-C4 1.431(2) Å, C4-C5 1.198(3) Å, angles
C3-C4-C5 174.1(2)°, C4-C5-C6 177.8(2)°).
was never the case. However, isonitrile insertion into the Zr-
C(sp2) bond of some of the obtained systems resulted in
formation of new sterically very encumbered η2-iminoacyl
zirconocene complexes that showed very remarkable structural
and dynamic features. The synthetic pathways to these unique
compounds and characterization of their remarkable properties
will be described in this paper.
Results and Discussion
Formation of the Starting Materials and Structural
Reference Systems. We prepared two series of complexes.
Synthesis of one series started from 7a (-PPh2) and the other
from 7b (-PCl2). Treatment of starting material 7a with
methyllithium in ether gave the corresponding Zr-CH3 deriva-
1
tive 11a. Its H/13C NMR spectra each exhibit a single Cp
Complex 9 behaves achiral in solution. It exhibits a single
10H intensity 1H NMR Cp resonance at δ 6.17 (in d6-benzene,
13C Cp feature at δ 110.1). Also, the phenyl groups at the
phosphorus center behave enantiotopic, i.e., they show a single
set of resonances at δ 140.5 (1JPC ) 17.2 Hz, i), δ 133.8 (2JPC
) 19.5 Hz, o), δ 128.4 (3JPC ) 5.9 Hz, m), and δ 128.3 (p-Ph).
The 13C NMR features of the Zr-alkenyl unit are typical: δ
225.2 (2JPC ) 17.4 Hz, CR), 127.0 (1JPC ) 29.3 Hz, Câ). The
31P NMR resonance of complex 9 occurs at δ -8.3, and there
resonance at δ 6.21 (10H)/δ 110.8 and Zr-CH3 resonances at
δ -0.86 (3H)/δ 31.1. The CdC 13C NMR resonances are very
diagnostic: the CR resonance occurs at δ 226.4 (2JPC ) 17.1
Hz), which is very characteristic for a sterically encumbered
[Zr]-C(sp2) situation. The adjacent Câ carbon NMR resonance
is found at δ 126.4 (1JPC ) 29.0 Hz). The 13C NMR signals of
the CtC unit were located at δ 94.4 and δ 92.7, respectively.
We observed a single set of NMR resonances of the phenyl
substituents of the -PPh2 group [13C δ 140.8 (1JPC ) 17.3, i-Ph),
δ 133.9 (2JPC ) 19.7 Hz, o-Ph), δ 128.6 (3JPC ) 5.9 Hz, m-Ph),
δ 128.4 (p-Ph)]. The 31P NMR signal of complex 11a is at δ
-9.8.
Complex 7a was reacted with propynyllithium to give the
corresponding [Zr]-(σ-propynyl) complex 9 (ca. 50% isolated,
see Scheme 3). Since this complex must be regarded as an
important structural and spectroscopic reference (see below), it
was characterized in some detail.
is a V˜(CtC) IR band at 2095 cm-1
.
Complex 11a was used for metallocene cation generation.
13
For this purpose it was treated with B(C6F5)3 in d8-THF to
effect methyl anion equivalent abstraction.14 The resulting THF-
-
stabilized metallocene cation 12a (with [CH3-B(C6F5)3
]
counteranion) was not isolated but only characterized in situ
after generation in d8-THF solution.15,16 It features a single Cp
(13) Massey, A. G.; Park, A. J.; Stone, F. G. A. Proc. Chem. Soc. 1963,
212-213. Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2, 245-
250. Massey, A. G.; Park, A. J. In Organometallic Syntheses; King, R. B.,
Eisch, J. J., Eds.; Elsevier: New York, 1986; Vol. 3, pp 461-462. Erker,
G. Dalton 2005, 1883-1890.
(14) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1994, 116,
10015-10031. Reviews: Strauss, H. S. Chem. ReV. 1993, 93, 927-942.
Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391-1434.
Single crystals suitable for the X-ray crystal structure analysis
of 9 were obtained from diethyl ether. The compound features
a bent metallocene framework that shows Zr-C(Cp) bond
lengths in a rather narrow range between 2.471(2) and 2.531-
(2) Å. The angle between Zr-C41 (2.233(2) Å) and Zr-C2
(2.301(2) Å) amounts to 110.56(7)°. The σ-propynyl ligand is

5614 Organometallics, Vol. 26, No. 23, 2007
Spies et al.
-
Scheme 4
The corresponding cation system 12b (with [CH3-B(C6F5)3
]
anion was generated by treatment of B(C6F5)3 in d8-THF
solution (see Scheme 3). Again, this salt was not isolated but
only characterized directly in solution [1H δ 6.72 (s, 10H, Cp);
13C δ 114.8 (Cp), 221.0 (Zr-Cd); 19F δ - 129.2 (o), - 150.7
(p), - 160.9 (m of P-C6F5); - 131.0 (o), - 165.0 (p), - 167.1
(m of MeBC6F5)3-]; 31P δ - 43.8 (quin, JPF ) 28 Hz).
3
Formation and Characterization of the η2-Iminoacyl
Zirconium Complexes. The neutral complexes 7a and 10 were
each treated with a slight excess of tert-butylisonitrile in toluene
at ambient temperature. A clean monoinsertion of the CN-
CMe3 reagent into the Zr-C(sp2) σ bond took place to yield
the η2-iminoacylzirconium complexes 13a [-P(C6H5)2] and 13b
[-P(C6F5)2] that were isolated as yellow solids in ca. 80% yield.
Complexes 13a and 13b were characterized by X-ray
diffraction (single crystals were obtained from diethyl ether).
In the crystal both complexes (values for 13b in square brackets)
feature a bent metallocene backbone with Zr-C(Cp) bond
lengths in a range between 2.480(3) [2.481(5)] and 2.539(3)
[2.545(5)] Å. One important feature of the structure of 13a is
the presence of a η2-iminoacyl ligand that is located in the
σ-ligand plane. It is bonded in the N-inside fashion,19,20 i.e.,
the iminoacyl nitrogen atom resides in a central position between
the Zr-Cl (2.546(1) [2.539(1)] Å) and Zr-C1 (2.241(2) [2.248-
(4)] Å) vectors (Zr-N1 2.233(2) [2.223(3)] Å, angles Cl-Zr-
C1 117.3(1)° [117.5(1)°], C1-Zr-N1 32.9(1)° [32.9(1)°]). The
C1-N1 bond length is in the CdN range (1.265(2) [1.266(5)]
Å), and the iminoacyl nitrogen is planar tricoordinate (angles
Zr-N1-C6152.9(1)°[151.3(2)°],Zr-N1-C173.9(1)°[74.6(2)°],
C1-N1-C6 133.0(2)° [134.0(3)°]). The adjacent iminoacyl
carbon center C1 is also planar tricoordinate with the individual
bond angles in the plane deviating substantially from the ideal
sp2-C values (N1-C1-Zr 73.2(1)° [72.5(2)°], C2-C1-Zr
148.9(1)° [149.3(3)°], N1-C1-C2 137.9(2)° [138.1(4)°]).
A remarkable structural feature of complexes 13 is the
conformational orientation of the per-substituted alkenyl group
that is attached at the iminoacyl carbon atom C1 (C1-C2
1.463(2) [1.465(5)] Å): it is strongly rotated out of the central
η2-iminoacyl plane (dihedral angles N1-C1-C2-C3 74.8(3)°
[73.0(6)°], Zr-C1-C2-C3 -102.0(3)° [-102.7(6)°]) to create
a chiral atropisomeric situation. Consequently, the C2-C21(aryl)
vector is also located out of the central plane (dihedral angles
N1-C1-C2-C21 -118.9(2)° [-118.0(5)°], C1-C2-C21-
C22 -97.5(2)° [-79.8(5)°]). The alkenyl C2dC3 bond length
(1.361(2) [1.350(5)] Å) and its bonding angles are in the normal
range. The alkynyl substituent attached at C3 is close to linear
(C4-C5 1.201(3) [1.192(5)] Å, angles C3-C4-C5 175.5(2)°
[174.6(4)°], C4-C5-C51 179.2(2)° [176.3(4)]°). The geminal
-PPh2 substituent features a normal coordination geometry
[C3-P 1.849(2) [1.844(4)] Å vs C31-P 1.832(2) [1.839(5)]
resonance [1H δ 6.68 (10H), 13C δ 114.5] and typical [Zr]-
alkenyl sp2-C carbon resonances at δ 218.2 (2JPC ) 19.6 Hz,
CR) and 132.8 (1JPC ) 30.3 Hz, Câ). Again, the system features
an enantiotopic pair of phenyl groups at phosphorus [δ 139.4
(1JPC ) 15.7 Hz, i), 134.0 (2JPC ) 19.9 Hz, o), 129.0 (3JPC
)
6.4 Hz, m), and 130.3 (p-Ph)], indicating an achiral structure
in solution.
A second series of compounds was synthesized starting from
the corresponding -PCl2-containing derivative 7b. Reaction
with 2 mol equiv of the in-situ-generated (caution: explosiWe!)
reagent LiC6F5 proceeded very selectively. Only C6F5 addition
to phosphorus was observed under the applied reaction condi-
tions to give the product 10, which was isolated in ca. 40%
1
yield as a white solid (see Scheme 3). It features a single H
NMR Cp resonance at δ 6.49 (10H) in d8-THF (13C 113.8).
The Zr-alkenyl 13C NMR resonances occur at δ 227.7 (2JPC
)
20 Hz, CR) and 120.3 (1JPC ) 25.6 Hz, Câ). There is a single
set of 19F NMR signals of the pair of enantiotopic C6F5
substituents at phosphorus [δ -131.0 (o), -153.9 (p), -163.5
(m)].
Complex 10 was also characterized by X-ray diffraction. Its
structure is similar to that of 9 (see above). The P-C bonds to
the C6F5 ring system in 10 amount to 1.835(4) (P-C21) and
1.848(3) Å (P-C31), respectively (C21-P-C31 angle 105.2(2)°).
The P-C3 bond (1.855(3) Å) is slightly longer, and the C2-
C3 bond (1.346(5) Å) is marginally shorter than in the reference
compound (9).17
Subsequent methylation at zirconium was carried out by
treatment of complex 10 with a slight excess (1.3 mol equiv)
of methyllithium in THF. The corresponding [Zr]-CH3 product
(11b) was isolated in ca. 50% yield. It shows the new [Zr]-
CH3 methyl resonances at δ -0.78 (1H, 3H) and 33.0 (13C),
respectively. Complex 11b shows a single 1H NMR Cp
resonance at δ 6.25 (10H; corresponding 13C NMR signal at δ
111.2). In 11b the enantiotopic C6F5 substituents at phosphorus
show a single set of characteristic 19F NMR resonances at δ
-131.1 (o), -154.0 (p), and -163.5 (m). The complex features
(18) Adams, R. D.; Chodosh, D. F. Inorg. Chem. 1978, 17, 41-48.
Review: Durfee, L. D.; Rothwell, I. P. Chem. ReV. 1988, 88, 1059-1079.
(19) Valero, C.; Grehl, M.; Wingbermu¨hle, D.; Kloppenburg, L.;
Carpenetti, D.; Erker, G.; Petersen, J. L. Organometallics 1994, 13, 415-
417. Bendix, M.; Grehl, M.; Fro¨hlich, R.; Erker, G. Organometallics 1994,
13, 3366-3369. Temme, B.; Erker, G. J. Organomet. Chem. 1995, 488,
177-182. Ahlers, W.; Erker, G.; Fro¨hlich, R. J. Organomet. Chem. 1998,
571, 83-89. Sebastia´n, A.; Royo, P.; Go´mez-Sal, P.; Ram´ırez de Arellano,
C. Eur. J. Inorg. Chem. 2004, 3814-3821.
(20) Erker, G.; Rosenfeldt, F. Angew. Chem. 1978, 90, 640-641; Angew.
Chem., Int. Ed. Engl. 1978, 17, 605-606. Erker, G.; Rosenfeldt, F. J.
Organomet. Chem. 1980, 188, C1-C4. Erker, G. Acc. Chem. Res. 1984,
17, 103-109 and references therein. Hofmann, P.; Stauffert, P.; Tatsumi,
K.; Nakamura, A.; Hoffmann, R. Organometallics 1985, 4, 404-406.
Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hoffmann, R. J.
Am. Chem. Soc. 1985, 107, 4440-4451. Hofmann, P.; Stauffert, P.; Frede,
M.; Tatsumi, K. Chem. Ber. 1989, 122, 1559-1577. De Angelis, F.;
Sgamellotti, A.; Re, N. Organometallics 2000, 19, 4904-4911.
a
31P NMR resonance at δ -48.8.
(15) Jordan, R. F. AdV. Organomet. Chem. 1991, 32, 325-387.
(16) See, for comparision: Erker, G. Acc. Chem. Res. 2001, 34, 309-
317. Erker, G. Chem. Commun. 2003, 1469-1476.
(17) Czisch, P.; Erker, G. J. Organomet. Chem. 1983, 253, C9-C11.
Erker, G.; Fro¨mberg, W.; Angermund, K.; Schlund, R.; Kru¨ger, C. J. Chem.
Soc., Chem. Commun. 1986, 372-374. Erker, G.; Dorf, U.; Rheingold, A.
L. Organometallics 1988, 7, 138-143. Erker, G.; Schlund, R.; Kru¨ger, C.
Organometallics 1989, 8, 2349-2355. Hyla-Kryspin, I.; Gleiter, R.; Kru¨ger,
C.; Zwettler, R.; Erker, G. Organometallics 1990, 9, 517-523.

Atropisomeric η2-Iminoacyl Zirconium Complexes
Organometallics, Vol. 26, No. 23, 2007 5615
Figure 3. Molecular structure of complex 13a. Thermal ellipsoids
are drawn at the 50% probability level.
Figure 1. View of the molecular structure of complex 9. Thermal
ellipsoids are drawn at the 50% probability level.
Figure 4. Projection of the structure of complex 13b featuring
the atropisomeric situation along the C1-C2 vector. Thermal
ellipsoids are drawn at the 50% probability level.
Scheme 5
Figure 2. Projection of the molecular structure of complex 10.
Thermal ellipsoids are drawn at the 50% probability level. Selected
bond lengths (Å) and angles (deg): Zr-C2 2.317(3), Zr-Cl 2.456-
(1), Zr-C(Cp) range 2.473(4)-2.524(4), C1-C2 1.498(4), C2-
C3 1.346(5), C3-C4 1.433(4), C4-C5 1.195(4), C5-C6 1.443(4),
C2-Zr-C1 103.2(1), C3-C2-C1 118.8(3), C3-C2-Zr 133.0-
(2), C1-C2-Zr 108.2(2), C2-C3-C4 121.7(3), C2-C3-P 118.7-
(2), C4-C3-P 119.5(3), C4-C5-C6 176.4(4), C5-C4-C3
178.9(4), C21-P-C31 105.2(2), C21-P-C3 101.4(2), C31-P-
C3 102.2(1).
Å, C41-P 1.826(2) [1.844(4)] Å; bond angles at phosphorus
C3-P-C41 103.0(1)° [99.7(2)°], C3-P-C31 101.1(1)° [107.5-
(2)°], C31-P-C41 102.3(1)° [100.0(2)°]].
Complex 13a exhibits an analogous structure in solution. The
presence of the η2-iminoacyl group is indicated by a typical
13C NMR CdN resonance at δ 223.4 (3JPC ) 2.0 Hz) [13b δ
222.8 (3JPC ) 2.9 Hz)]. The carbon NMR signals of the adjacent
CdC double bond occur at δ 163.9 (2JPC ) 37.7 Hz, C2) and
110.2 (1JPC ) 24.1 Hz, C3) (tentative relative assignments) [13b
δ 166.0 (2JPC ) 45.7 Hz) and 103.4 (1JPC ) 18 Hz)]. The carbon
NMR resonances of the conjugated alkynyl substituent were
located at δ 89.7 (2JPC ) 4.0 Hz) and 100.0, respectively [13b
δ 86.9 (2JPC ) 4.5 Hz) and 99.1]. The 31P NMR signal of
complex 13a is at δ -7.5 [13b δ -41.9].
δ 6.06, 5.43 (each 5H Cp)/δ 110.2, 109.7]. The chirality of the
complexes 13 is due to an element of axial chirality,21 which
most likely originates from the strong conformational distortion
of the RNdC and CdC groups along their connecting C1-C2
σ-bond vector (see Figures 3 and 4 and Scheme 5). This results
in formation of a pair of atropisomeric enantiomers whose
interconversion is slow on the NMR time scale under the applied
conditions at 300 K.
This interpretation is strongly supported by the observed
1
dynamic H NMR spectra of the complexes 13 in d8-toluene.
Complexes 13 are chiral in solution. This becomes evident
from the observation of the signals of a pair of diastereotopic
Cp ligands of, e.g., 13a in d2-dichloromethane solution at 258
K: δ 6.02, 5.41 (each 5H)/δ 110.1, 109.5 (13C) [13b (258 K)
Upon increasing the temperature from 300 to 355 K (at 200
(21) Stereochemistry of Organic Compounds; Eliel, E. L., Wilen, S. H.,
Mander, L. N., Eds.; Wiley: New York, 1994; Chapter 14.

5616 Organometallics, Vol. 26, No. 23, 2007
Spies et al.
Zr-C(sp2) bond of 12 to form the “N-inside” η2-iminoacyl
moiety [13C NMR 14a δ 216.5 (3JPC ) 1.6 Hz); 14b δ 216.2
(3JPC ) 3.3 Hz)], the other is used to replace the coordinating
THF ligand [κC-CNCMe3 14a δ 145.9 (13C); 14b δ 145.4
(13C), V˜ 2203 cm-1 (IR)]. The 13C NMR resonances of the enyne
substituent of 14a were found at δ 161.2 (2JPC ) 38.2 Hz, CR),
113.0 (1JPC ) 26.1 Hz, Câ), 88.3 (2JPC ) 3.8 Hz, Cγ), and 100.9
(Cδ) [14b δ 163.3 (2JPC ) 46.3 Hz, CR), 106.5 (1JPC ) 22.3
Hz, Câ), 85.5 (2JPC ) 3.9 Hz, Cγ), and 100.0 (Cδ)].
The cationic η2-iminoacyl complexes 14a and 14b are also
chiral, again probably due to an element of axial chirality in
this atropisomeric system. At low temperature in d2-dichlo-
romethane solution at 600 MHz complex 14b features an equal
1
intensity pair of H NMR Cp signals at δ 5.98 and 5.33 (13C
NMR signals at δ106.9/106.4) that rapidly coalesce upon
warming the sample. From the temperature-dependent 1H NMR
spectra a Gibbs activation energy of ∆Gq (293 K) ) 13.4 (
0.3 kcal mol-1 was calculated for the internal enantiomerization
process of the cation 14b [14a ∆Gq (288 K) ) 13.1 ( 0.3 kcal
mol-1].
1
Figure 5. Temperature-dependent H NMR spectra (200 MHz,
d8-toluene) featuring the thermally induced enantiomerization
process of complex 13a.
MHz see Figure 5), coalescence of the 1:1 intensity pair of 1H
NMR resonances at δ 5.98 and 5.32 to an averaged singlet of
double intensity was observed. We also noticed a concurrent
coalescence of a pair of phenyl resonances from the -PPh2
substituentsthe phenyl groups at phosphorus are also diaste-
reotopic due to the presence of the element of axial chirality in
complex 13a. A similar 1H NMR Cp coalescence behavior was
observed for 13b.
Chirality at the central moiety of the cation of 14b implies
that the -C6F5 substituents at the adjacent phosphorus center
are prochiral and, consequently, diastereotopic. This is actually
monitored in the 19F NMR spectrum of 14b at low temperature
(see Figure 6). The 19F NMR spectrum of 14b (d2-dichlo-
romethane, 218 K) shows three prominent features of the
[CH3B(C6F5)3-] anion [δ -133.9 (o), -164.7 (p), -167.4 (m)].
The -P(C6F5)2 moiety exhibits a double set of signals of the
pairwise diastereotopic C6F5 substituents [δ -130.1 (o), -148.9
(p), -161.0 (m)/δ -131.9 (o), -151.3 (p), -160.7 (m)].
Increasing the monitoring temperature rapidly resulted in a
pairwise coalescence of the ortho, para, and meta 19F NMR
signals of the -P(C6F5)2 groups (see Figure 6), leaving the
corresponding [CH3B(C6F5)3-] anion 19F NMR resonances
unchanged.
1
From the coalescence of the H NMR Cp resonances we
calculated an activation energy of the enantiomerization
process (i.e., 13a/ent-13a) of ∆Gq(327 K) ) 14.9 ( 0.3 kcal
mol-1 and for 13b/ent-13b of ∆Gq(325 K) ) 14.8 ( 0.3 kcal
mol-1
.
Reaction of tert-butylisonitrile with salts 12a and 12b takes
a similar course (see Scheme 4). The cations react with 2 mol
equiv of the CN-R reagent to form 14a and 14b, respectively.
In each case, 1 equiv of isonitrile has been inserted into the
Figure 6. Temperature-dependent 19F NMR spectra of the salt 14b in d2-dichloromethane (564 MHz) (asterisks (*) indicate largely temperature
invariant signals belonging to the [CH3B(C6F5)3-] anion).

Atropisomeric η2-Iminoacyl Zirconium Complexes
Organometallics, Vol. 26, No. 23, 2007 5617
SHELXS-97 (Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-
473), structure refinement SHELXL-97 (Sheldrick, G. M. Univer-
sita¨t Go¨ttingen: Go¨ttingen, 1997), graphics XP (BrukerAXS, 2000).
Dynamic NMR Spectroscopy. For vt-low-temperature NMR a
Varian UNITY plus NMR spectrometer (1H, 600 MHz; 13C, 151
MHz; 31P, 243 MHz; 19F, 564 MHz) and for vt-high-temperature
NMR a Bruker AC 200 P spectrometer (11B, 64 MHz; 31P, 81 MHz)
were used. Activation energies were calculated from the coalescence
temperature (Tc) and δν of the respective resonances [∆Gq(Tc) )
RTc(22.96 + ln(Tc/δν)].23 Estimated errors (ca. 0.3 kcal mol-1) were
achieved from the accuracy range (ca. (3 K) of the coalescence
temperature determined from the spectra.
General Procedure for the Preparation of 9 and 11a. Complex
7a was suspended in 100 mL of toluene and cooled to -78 °C. A
solution of the respective organolithium reagent (1.1 equiv) in ether
(for 11a) or thf (for 9) was added. The reaction mixture was stirred
overnight while being allowed to warm to room temperature. Then
the mixture was filtered over Celite, and the solvent was removed
in vacuo until the product started to precipitate. To complete
precipitation the reaction mixture was put in the freezer at -30 °C
overnight. The product was isolated on a Schlenk frit, washed 3
times with 15 mL of pentane, and dried in vacuum.
Conclusions
None of the conjugated enyne Zr/P systems studied here
showed any indication of a favorable ring-closure reaction to
its methylenecyclopropene isomers neither upon electrophilic
activation nor treatment with an organoisonitrile. This behavior
of the Zr/enyne/P systems is in this respect quite contrary to
that of their formally related Zr/enyne/B analogues which
undergo this remarkable rearrangement readily when treated with
a nitrile or an isonitrile.4,5 It seems that the specific combination
of the electrophilic group 4 metal center with the strongly Lewis
acidic -B(C6F5)3 substituent is very advantageous for this
unusual intramolecular carbon-carbon coupling reaction (see
Scheme 1).
The Zr/enyne/P systems investigated in this experimental
study instead undergo the normal isonitrile insertion reaction
into the reactive Zr-C(sp2) σ bond to yield linearly conjugated
η2-iminoacyl zirconium complexes that bear a conjugated highly
substituted enyne substituent at the electrophilic iminoacyl
carbon atom. The η2-iminoacyl moiety is found in the N-inside
form at the front side of the bent metallocene wedge.
It is probably the large steric bulk of the substituents at the
η2-iminoacyl core that strongly forces the R,â-unsaturated
iminoacyl system out of its usually favored planar conjugated
situation into a bisected chiral atropisomeric conformation. Close
inspection of the structural features of a pair of typical examples
(13) of this class of compounds reveals that the rotational barrier
is probably influenced to some degree by the combined steric
bulk of all the substituents at the central CdC double bond as
well as the proximal groups and substituents at the η2-iminoacyl
zirconocene core. Therefore, it is not unexpected that subtle
changes of these groups have caused measurable differences in
the activation barrier of the thermally induced automerization
process of the respective organometallic atropisomers. Our study
shows that sterically originated atropisomerism can be a major
structural factor not only in purely organic systems, where it is
important, e.g., in chiral ligand chemistry for asymmetric
catalysis,22 but also in the structural chemistry of organometallic
systems in a more general sense.
Preparation of Complex 11a. A sample of 500 mg (0.78 mmol)
of 7a was treated with 0.53 mL (0.85 mmol) of a 1.6 M
methyllithium solution in diethyl ether to yield 360 mg (74%) of a
white solid, mp 194 °C (DSC, dec). Anal. Calcd for C39H33PZr
1
(623.88): C, 75.08; H, 5.33. Found: C, 74.61; H, 5.33. H NMR
(d8-thf, 600 MHz, 298 K): δ ) 7.44 (m, 4H, o-PhP); 7.31 (m, 4 H,
m-PhP); 7.27 (m, 2H, p-PhP); 7.22 (m, 3H, p/m-PhCt); 7.08 (m,
2H, o-PhCt); 7.06 (m, 2H, m-PhCd); 7.01 (m, 1H, p-PhCd); 6.74
(m, 2H, o-PhCd); 6.21(s, 10H, Cp); -0.86 (s, 3H, CH3). 13C{1H}
2
NMR (d8-thf, 151 MHz, 298 K): δ ) 226.4 (d, JPC ) 17.1 Hz,
1
3
Zr-Cd); 140.84 (d, JPC ) 17.3, i-PhP); 140.78 (d, JPC ) 18.9
Hz, i-PhCd); 133.9 (d, 2JPC ) 19.7 Hz, o-PhP); 131.7 (o-PhCt); 129.0
(m-PhCt); 128.6 (d, 3JPC ) 5.9 Hz, m-PhP); 128.41 (m-PhCd); 128.37
(p-PhP); 128.1 (p-PhCt); 128.0 (d, JPC ) 1.7 Hz, o-PhCd); 126.4
4
(d, 1JPC ) 29.0 Hz, dC-P); 126.1 (p-PhCd); 125.2 (i-PhCt); 110.8
(Cp); 94.4 (-Ct); 92.7 (tC-Ph); 31.1 (CH3). 31P{1H} NMR (d8-
thf, 81 MHz, 300 K): δ ) -9.8 (ν1/2 ) 2.5 Hz).
Preparation of Complex 9. A sample of 1.00 g (1.55 mmol)
7a was treated with a solution of 78 mg (1.71 mmol) of
propynyllithium in 10 mL of thf to give 560 mg (56%) of a white
solid, mp 161 °C (DSC, dec). Anal. Calcd for C41H33PZr (647.91):
C, 76.01; H, 5.13. Found: C, 75.63; H, 4.89. 1H NMR (d6-benzene,
600 MHz, 298 K): δ ) 7.72 (m, 4H, o-PhP); 7.21 (m, 2H, o-PhCt
); 7.14 (m, 6H, m-PhP, m-PhCd); 7.07 (m, 2H, p-PhP); 7.03 (m, 1H,
p-PhCd); 7.02 (m, 2H, m-PhCt); 6.95 (m, 1H, p-PhCt); 6.87 (m,
2H, o-PhCd); 6.17 (s, 10H, Cp); 1.57 (s, 3H, CH3). 13C{1H} NMR
Experimental Section
General Procedures. Reactions with organometallic compounds
were carried out under argon using Schlenk-type glassware or in a
glovebox. Solvents were dried and distilled under argon prior to
use. Compounds 7a and 7b were prepared analogously as described
in the literature.10
2
(d6-benzene, 151 MHz, 298 K): δ ) 225.2 (d, JPC ) 17.4 Hz,
The following instruments were used for physical characterization
of the compounds. Melting points: DSC 2010 TA-instruments.
Elemental analyses: Foss-Heraeus CHNO-Rapid. NMR: Bruker
AC 200 P (1H, 200 MHz; 11B, 64 MHz; 31P, 81 MHz), ARX 300
(1H, 300 MHz; 13C, 75 MHz, 31P, 121 MHz; 19F, 282 MHz), Varian
UNITY plus NMR spectrometer (1H, 600 MHz; 13C, 151 MHz;
31P, 243 MHz; 19F, 564 MHz). Assignments of the resonances are
supported by 2D experiments and chemical shift calculations.
X-ray Crystal Structure Analyses. Data sets were collected
with a Nonius KappaCCD diffractometer, equipped with a rotating
anode generator. Programs used: data collection COLLECT
(Nonius B.V., 1998), data reduction Denzo-SMN (Otwinowski, Z.;
Minor, W. Methods Enzymol. 1997, 276, 307-326), absorption
correction Denzo (Otwinowski, Z.; Borek, D.; Majewski, W.;
Minor, W. Acta Crystallogr. 2003, A59, 228-234), and SORTAV
(Blessing, R. H. Acta Crystallogr. 1995, A51, 33-37. Blessing, R.
H. J. Appl. Crystallogr. 1997, 30, 421-426), structure solution
1
3
Zr-Cd); 140.5 (d, JPC ) 17.2 Hz, i-PhP); 137.5 (d, JPC ) 18.5
Hz, i-PhCd); 133.8 (d, 2JPC ) 19.5 Hz, o-PhP); 131.3 (o-PhCt); 128.9
(d, JPC ) 1.3 Hz, o-PhCd); 128.7 (m-PhCt); 128.4 (d, JPC ) 5.9
4
3
Hz, m-PhP); 128.3 (p-PhP); 128.2 (m-PhCd); 128.0, 118.8 (Zr-Ct
C); 127.8 (p-PhCt); 127.1 (p-PhCd); 127.0 (d, JPC ) 29.3 Hz, d
1
C-P); 124.8 (i-PhCt); 110.1 (Cp); 94.4 (-Ct); 92.9 (tC-Ph);
6.3 (CH3). 31P{1H} NMR (d6-benzene, 81 MHz, 300K): δ ) -8.3
(ν1/2 ) 2.0 Hz). IR (KBr): V˜ ) 2095 (m,νCtC).
X-ray Crystal Structure Analysis of 9. Formula C41H33PZr,
Mw ) 647.86, light yellow crystal 0.45 × 0.30 × 0.15 mm, a )
8.291(1) Å, b ) 25.129(1) Å, c ) 15.434(1) Å, â ) 92.97(1)°, V
) 3211.3(5) Å3, Fcalcd ) 1.340 g cm-3, µ ) 0.420 mm-1, empirical
absorption correction (0.834 e T e 0.940), Z ) 4, monoclinic,
space group P21/n (No. 14), λ ) 0.71073 Å, T ) 198 K, ω and æ
scans, 22 545 reflections collected ((h, (k, (l), [(sinθ)/λ] ) 0.67
Å-1, 7862 independent (Rint ) 0.035) and 6509 observed reflections
[I g 2σ(I)], 389 refined parameters, R ) 0.036, wR2 ) 0.092, max
(22) Catalytic Asymmetric Synthesis; Ojima, E., Ed.; Wiley, VCH: New
York, 1993.
(23) NMR Spektroskopie; Gu¨nther, H., Ed.; Thieme: Stuttgart, 1992.

5618 Organometallics, Vol. 26, No. 23, 2007
Spies et al.
residual electron density 0.32 (-0.65) e Å-3, hydrogens calculated
and refined as riding atoms.
General Procedure for Generation of Cations 12a and 12b.
The respective neutral methylzirconium complexes (11a/11b) and
tris(pentafluorophenyl)borane (1 equiv) were dissolved in 0.8 mL
of d8-thf, and the resulting cationic products were characterized by
NMR spectroscopy.
Preparation of Complex 10. Brompentafluorbenzene (0.45 mL,
889 mg, 3.6 mmol) was dissolved in 80 mL of toluene and cooled
to -78 °C. A 2.25 mL (3.6 mmol) amount of 1.6 M n-butyllithium
solution in hexane was added, and the reaction mixture was stirred
for 5 min at -78 °C (Caution: LiC6F5 is a potentially explosive
reagent). A solution of 1.01 g (1.8 mmol) of 7b in 40 mL of toluene
was added at -78 °C, and the mixture was stirred for 1 h at ambient
temperature. The mixture was filtered over Celite, and the filtrate
was evaporated to dryness in the oil-pump vacuum. The residue
was suspended in 15 mL of pentane, isolated on a Schlenk frit,
and dried in vacuo to yield 632 mg (43%) of a white solid, mp
229.1 °C (DSC). Anal. Calcd for C38H20ClF10PZr (824.2): C, 55.38;
Generation of Salt 12a. Reaction of 50 mg (0.08 mmol) of 11a
with 41 mg (0.08 mmol) of tris(pentafluorophenyl)borane gave a
1
yellow solution. H NMR (d8-thf, 600 MHz, 298 K): δ ) 7.49-
7.39 (m, 7H, p-PhCd, p,o-PhP); 7.37-7.32 (m, 6H, m-PhCd, m-PhP);
7.28-7.22 (m, 5H, p,m-PhCt, o-PhCd); 7.08 (m, 2H, o-PhCt); 6.68
(s, 10H, Cp); 0.54 (br s, 3H, Me-B). 13C{1H} NMR (d8-thf, 151
MHz, 298 K): δ ) 218.2 (d, 2JPC ) 19.6 Hz, Zr-Cd); 149.2 (dm,
1
1JFC ) 239 Hz, BC6F5); 139.4 (d, JPC ) 15.7 Hz, i-PhP); 138.2
1
1
(dm, JFC ) 244 Hz, BC6F5); 137.1 (dm, JFC ) 248 Hz, BC6F5);
3
1
1
134.0 (d, JPC ) 19.9 Hz, o-PhP); 133.6 (d, JPC ) 18.2 Hz,
i-PhCd); 132.8 (d, 1JPC ) 30.3 Hz, dC-P); 131.8 (o-PhCt); 131.6
(d, 4JPC ) 1.6 Hz, o-PhCd); 130.32 (p-PhP); 130.31(p-PhCd); 129.18,
H, 2.45. Found: C, 55.42; H, 2.24. H NMR (d8-thf, 600 MHz,
253 K): δ ) 7.37 (m, 3H, m,p-PhCt); 7.32 (m, 2H, o-PhCt); 7.14
(m, 2H, m-PhCd); 7.10 (m, 1H, p-PhCd); 6.93 (m, 2H, o-PhCd);
6.49 (s, 10H, Cp). 13C NMR (d8-thf, 151 MHz, 253 K): δ ) 227.7
129.15 (m-PhCt, m-PhCd); 129.11 (p-PhCt), 129.0 (d, JPC ) 6.4
3
Hz, m-PhP); 123.9 (i-PhCt); 114.5 (Cp); 96.6 (tC-Ph); 92.9
(-Ct); 10.7 (br, Me-B). 19F NMR (d8-thf, 564 MHz, 300 K): δ
) -132.8 (2F, o-BC6F5); -166.8 (1F, p-BC6F5); -168.9 (2F,
m-BC6F5). 31P{1H} NMR (d8-thf, 81 MHz, 300 K): δ ) -3.3 (ν1/2
) 2.9 Hz) 11B{1H} NMR (d8-thf, 96 MHz, 300 K): δ ) -14.8
(ν1/2 ) 43 Hz).
2
1
(d, JPC ) 20 Hz, Zr-Cd); 148.1 (d, JFC ) 243 Hz, m-C6F5);
144.2 (d, JPC ) 22.2 Hz, i-PhCd); 142.6 (d, JFC ) 253, p-C6F5);
138.1 (d, 1JFC ) 247 Hz, o-C6F5); 131.5 (o-PhCt); 129.5 (m-PhCt
); 129.3 (p-PhCt); 128.9 (m-PhCd); 127.4 (o-PhCd); 127.2 (p-PhCd
3
1
); 123.7 (i-PhCt); 120.3 (d, JPC ) 25.6 Hz, dC-P); 113.8 (Cp);
1
93.3 (tC-Ph); 91.3 (-Ct); n.o. (i-C6F5). 19F NMR (d8-thf, 470
MHz, 298 K): δ ) -131.0 (o-C6F5); -153.9 (p-C6F5); -163.5
(m-C6F5). 31P{1H} NMR (d8-thf, 202 MHz, 298 K): δ ) -48.5
(quin, 3JPF ) 28 Hz). 31P{1H,19F} NMR (d8-thf, 202 MHz, 298K):
δ ) -48.5 (s, ν1/2 ) 1.5 Hz).
Generation of Salt 12b. Treatment of 50 mg (0.06 mmol) of
11b with 31.8 mg (0.06 mmol) of tris(pentafluorophenyl)borane
1
gave a yellow solution. H NMR (d8-thf, 600 MHz, 298 K): δ )
7.53 (m, 2H, m-PhCd); 7.47 (m, 1H, p-PhCd); 7.38 (m, 3H, m,p-
PhCt); 7.32 (m, 2H, o-PhCt); 7.30 (m, 2H, o-PhCd); 6.72 (s, 10H,
Cp); 0.51 (br s, 3H, Me-B). 13C{1H} NMR (d8-thf, 151 MHz, 298
K): δ ) 221.0 (Zr-Cd); 149.1 (dm, 1JFC ) 238 Hz, BC6F5); 148.2
(dm, 1JFC ) 247 Hz, PC6F5); 142.9 (dm, 1JFC ) 258 Hz, p-PC6F5);
X-ray Crystal Structure Analysis of 10. Formula C38H20ClF10-
PZr‚1/2C4H8O, Mw ) 860.23, light yellow crystal 0.30 × 0.20 ×
0.05 mm, a ) 21.386(1) Å, b ) 10.982(1) Å, c ) 30.684(1) Å, â
) 95.67(1)°, V ) 7171.2(8) Å,3 Fcalcd ) 1.594 g cm-3, µ) 0.508
mm-1, empirical absorption correction (0.862 e T e 0.975), Z )
8, monoclinic, space group C2/c (No. 15), λ ) 0.71073 Å, T )
198 K, ω and æ scans, 30 924 reflections collected ((h, (k, (l),
[(sinθ)/λ] ) 0.62 Å-1, 7053 independent (Rint ) 0.061) and 4938
observed reflections [I g 2σ (I)], 483 refined parameters, R ) 0.049,
1
138.2 (dm, PC6F5, p-BC6F5); 136.9 (dm, JFC ) 248 Hz, BC6F5);
134.7 (i-PhCd); 131.5 (o-PhCt); 130.8 (br, p,m-PhCd); 130.1 (o-
PhCd); 129.6 (m-PhCt); 129.5 (p-PhCt); 122.6 (i-PhCt); 114.8 (Cp);
109.6 (br, i-C6F5-P); 95.6 (tC-Ph); 89.9 (-Ct); 10.9 (Me-B);
n.o. (dC-P, i-C6F5); [each broad; assignment by 2D NMR
experiments]. 19F NMR (d8-thf, 564 MHz, 398 K): δ ) -129.2
(4F, o-PC6F5); -131.0 (6F, o-BC6F5); -150.7 (2F, p-PC6F5);
-160.9 (4F, m-PC6F5); -165.0 (3F, p-BC6F5); -167.1 (6F,
m-BC6F5). 31P{1H} NMR (d8-thf, 122 MHz, 300K): δ ) -43.8
wR2 ) 0.102, max residual electron density 0.44 (-0.36) e Å-3
,
hydrogens calculated and refined as riding atoms.
Preparation of Complex 11b. A sample of 600 mg (0.7 mmol)
of 10 was dissolved in 20 mL of thf and cooled to -78 °C. A 2.5
mL (1.3 equiv, 21 mg) amount of a methyllithium solution in thf
(c ) 84 mg/10 mg) [solution was prepared from solid methyllithium
stored in a glove box; solid methyllithium was obtained from
commercially available 1.6 M methyllithium solution by removing
the solvent in the oil-pump vacuum] was added at -78 °C. The
mixture was stirred for 2 h at ambient temperature, the solvent was
removed in vacuo, and the residue was dissolved in 30 mL of
toluene. After filtration over Celite the filtrate was brought to
dryness; the residue was suspended in 15 mL of pentane and isolated
on a Schlenk frit. After drying in the oil-pump vacuum 337 mg
(57%) of a white solid could be obtained, mp 150 °C (DSC). Anal.
Calcd for C39H23F10PZr (803.79): C, 58.28; H, 2.88. Found: C,
57.75; H, 2.85. 1H NMR (d8-thf, 600 MHz, 298 K): δ ) 7.34 (m,
3H, m,p-PhCt); 7.30 (m, 2H, o-PhCt); 7.12 (m, 2H, m-PhCd); 7.05
(m, 1H, p-PhCd); 6.77 (m, 2H, o-PhCd); 6.25 (s, 10H, Cp); -0.78
(s, 3H, CH3). 13C{1H} NMR (d8-thf, 151 MHz, 298 K): δ ) 230.6
3
(quin, JPF ) 28 Hz). 11B{1H} NMR (d8-thf, 96 MHz, 300 K): δ
) -14.8 (ν1/2 ) 250 Hz).
General Procedure for Preparation of Complexes 13a and
13b. The respective chlorozirconocene (7a/10) complex was
dissolved/suspended in 100 mL of toluene. At ambient temperature
a solution of tert-butylisonitrile (ca. 1.1 equiv) in 1 mL of toluene
was added. The solution was stirred for 2 h at room temperature.
The solvent was removed in vacuo, and the residue was suspended
in 15 mL of pentane, isolated on a Schlenk frit, and dried in the
oil-pump vacuum.
Preparation of Complex 13a. Reaction of 500 mg (0.78 mmol)
of 7a and 77 mg (0.92 mmol) of tert-butylisonitrile gave 490 mg
(86%) of a yellow solid, mp 187.3 °C (DSC). Anal. Calcd for
C43H39ClNPZr (727.43): C, 71.00; H, 5.40; N, 1.93. Found: C,
70.54; H, 5.06; N, 1.87. 1H NMR (d2-dichloromethane, 600 MHz,
258 K): δ ) 7.66 (m, 2H, o-PhP); 7.50 (m, 3H, p,m-PhCd); 7.44
(m, 2H, m-PhP), 7.43 (m, 1H, p-PhP); 7.33 (m, 1H, p-PhP′); 7.32
(m, 4H, o-PhCd, m-PhP′); 7.28 (m, 2H, o-PhP′); 7.23 (m, 1H,
p-PhCt); 7.19 (m, 2H, m-PhCt); 6.90 (m, 2H, o-PhCt); 6.02 (s,
5H, Cp); 5.41 (s, 5H, Cp′); 1.49 (s, 9H, t-Bu). 13C NMR
2
1
(d, JPC ) 18.6 Hz, Zr-Cd); 148.3 (d, JFC ) 248 Hz, m-C6F5);
1
3
142.6 (d, JFC ) 254, p-C6F5); 141.2 (d, JPC ) 22.9 Hz,
i-PhCd); 138.2 (d, JFC ) 251 Hz, o-C6F5); 131.5 (o-PhCt); 129.4
1
(m-PhCt); 129.0 (p-PhCt); 128.9 (m-PhCd); 127.0 (d, JPC ) 1.9
3
(d2-dichloromethane, 151 MHz, 258 K): δ ) 223.4 (d, 3JPC ) 2.0
Hz, o-PhCd); 126.8 (p-PhCd); 124.2 (i-PhCt); 118.1 (d, 1JPC ) 27.5
Hz, dC-P); 111.2 (Cp); 92.1 (tC-Ph); 91.6 (-Ct); 33.0 (CH3);
n.o. (i-C6F5). 19F NMR (d8-thf, 564 MHz, 298 K): δ ) -131.1
(o-C6F5); -154.0 (p-C6F5); -163.5 (m-C6F5). 31P{1H}NMR (d6-
2
Hz, Zr-Cd); 163.9 (d, JPC ) 37.7 Hz, dC-); 137.6 (d, JPC
11.6 Hz, i-PhP′); 136.9 (d, JPC ) 12.7 Hz, i-PhP); 136.0 (d, JPC
)
)
9.0 Hz, i-PhCd); 133.3 (d, JPC ) 20.8 Hz, o-PhP′); 133.2 (d, JPC
2
2
) 18.8 Hz, o-PhP); 131.1 (o-PhCt); 129.4 (br, o-PhCd), 129.2 (p-
3
3
benzene, 81 MHz, 300 K): δ ) -48.8 (quin, JPF ) 27 Hz).
PhCd); 128.9 (p-PhP); 128.8 (d, JPC ) 6.3 Hz, m-PhP); 128.7 (m-

Atropisomeric η2-Iminoacyl Zirconium Complexes
Organometallics, Vol. 26, No. 23, 2007 5619
PhCd); 128.71 (p-PhP′); 128.5 (p-PhCt); 128.4 (m-PhCt); 128.3 (d,
vacuum to yield 162 mg (44%) of a pale brown/yellow solid, mp
1
3JPC ) 6.3 Hz, m-PhP′); 122.7 (i-PhCt); 110.2 (d, JPC ) 24.1 Hz,
64 °C (DSC). Anal. Calcd for C67H51BF15N2PZr (1302.14): C,
dC-P); 110.1 (Cp); 109.5 (Cp′); 100.0 (tC-Ph); 89.7 (d, 2JPC
)
1
61.80; H, 3.95; N, 2.15. Found: C, 61.46; H, 3.84; N, 2.26. H
4.0 Hz, -Ct); 64.4, 28.2 (tBu) (tentative relative assignments for
dC-, dC-P). 31P NMR (d6-benzene, 243 MHz, 300 K): δ )
-7.5 (ν1/2 ) 3.5 Hz). High-temperature NMR: 1H NMR (d8-
toluene, 200 MHz) coalescence of the Cp resonances, Tc ) 327 K,
δν(300 Κ) ) 134 Hz, ∆Gq ) 14.9 ( 0.3 kcal/mol.
NMR (d2-dichloromethane, 600 MHz, 218 K): δ ) 7.66 (m, 2H,
o-PhP); 7.54, 7.52 (m, 3H, p,m-PhCd); n.o. (o-PhCd); 7.49 (m, 2H,
m-PhP); 7.47 (m, 1H, p-PhP); 7.35 (m, 1H, p-PhP′); 7.30 (m, 2H,
m-PhP′); 7.24 (m, 1H, p-PhCt); 7.20 (m, 2H, o-PhP′); 7.18 (m, 2H,
m-PhCt); 6.82 (m, 2H, o-PhCt); 5.93 (s, 5H, Cp); 5.32 (s, 5H, Cp′);
1.63 (s, 9H, tBuNtC); 1.33 (s, 9H, (tBuNdC); 0.41 (br, 3H, Me-B).
13C{1H} NMR (d2-dichloromethane, 151 MHz, 218 K): δ ) 216.5
(d, 3JPC ) 1.6 Hz, Zr-Cd); 161.2 (d, 2JPC ) 38.2 Hz, dC); 147.7
X-ray Crystal Structure Analysis of 13a. Formula C43H39-
ClNPZr‚0.5C7H8, Mw ) 773.46, yellow crystal 0.45 × 0.30 × 0.15
mm, a ) 8.412(1) Å, b ) 11.119(1) Å, c ) 22.698(1) Å, R )
81.52(1)°, â ) 79.70(1)°, γ ) 71.34(1)°, V ) 1969.7(3) Å3, Fcalcd
) 1.304 g cm-3, µ ) 0.420 mm-1, empirical absorption correction
(0.833 e T e 0.940), Z ) 2, triclinic, space group Ph1 (No. 2), λ
) 0.71073 Å, T ) 198 K, ω and æ scans, 20 218 reflections
collected ((h, (k, (l), [(sinθ)/λ] ) 0.66 Å-1, 9348 independent
(Rint ) 0.044) and 8218 observed reflections [I g 2σ (I)], 463
refined parameters, R ) 0.038, wR2 ) 0.103, max residual electron
density 0.77 (-0.71) e Å-3, hydrogens calculated and refined as
riding atoms.
1
1
(dm, JFC ) 235 Hz, C6F5); 145.9 (CtN); 137.0 (dm, JFC ) 239
Hz, p-C6F5); 136.6 (d, JPC ) 10.9 Hz, i-PhP′); 135.9 (dm, JFC
)
)
1
1
242 Hz, C6F5); 135.5 (d, JPC ) 11.8 Hz, i-PhP); 133.9 (d, JPC
1
9.0 Hz, i-PhCd); 133.1 (d, JPC ) 20.2 Hz, o-PhP′); 132.7 (d, JPC
2
2
) 19.2 Hz, o-PhP); 130.7 (o-PhCt); 129.8 (p-PhCd); 129.0 (p-PhP);
128.9 (m-PhCd); 128.7 (p-PhP′); 128.7 (d, JPC ) 7.0 Hz, m-PhP);
3
128.7 (p-PhCt); 128.3 (m-PhCt); 128.2 (br, i-C6F5); 128.1 (d, 3JPC
) 6.6 Hz, m-PhP′); 121.5 (i-PhCt); 113.0 (d, JPC ) 26.1 Hz, d
1
2
C-P); 106.7 (Cp); 106.1 (Cp′); 100.9 (tC-Ph); 88.3 (d, JPC
)
3.8 Hz, -Ct); 60.2, 29.0 (tBuCtN); 63.0, 27.2 (tBuCdN); 9.6 (br,
Me-B); n.o. (o-PhCd) (tentative relative assignments for dC-,
dC-P). 31P{1H} NMR (d2-dichloromethane, 122 MHz, 300 K):
δ ) -6.6 (ν1/2 ) 11 Hz). 19F NMR (d2-dichloromethane, 564 MHz,
218 K): δ ) -133.5 (o-C6F5); -164.2 (p-C6F5); 166.9 (m-C6F5).
11B{1H} NMR (d2-dichloromethane, 96 MHz, 300 K): δ ) -15.0
(ν1/2 ) 31 Hz). IR (KBr): V˜ ) 2202 (νCN). Low-temperature
NMR: 1H NMR (d2- dichloromethane, 600 MHz) coalescence of
the Cp resonances, Tc ) 288 K, δν(218 Κ) ) 361 Hz, ∆Gq ) 13.1
( 0.3 kcal/mol.
Preparation of Complex 13b. Reaction of 500 mg (0.61 mmol)
of 10 and 120 mg (1.4 mmol) of tert-butylisonitrile gave 431 mg
(78%) of a yellow solid, mp 199 °C (DSC). Anal. Calcd for C43H29-
ClF10NPZr (907.34): C, 56.92; H, 3.22; N, 1.54. Found: C, 57.02;
1
H, 3.23; N, 1.59. H NMR (d2-dichloromethane, 600 MHz, 258
K): δ ) 7.56 (m, 3H, m,p-PhCd); 7.36 (br, 2H, o-PhCd); 7.30 (m,
3H, m,p-PhCt); 7.18 (m, 2H, o-PhCt); 6.06 (s, 5H, Cp); 5.43 (s,
5H, Cp′); 1.44 (s, 9H, t-Bu). 13C NMR (d2-dichloromethane, 150.8
3
MHz, 258 K): δ ) 222.8 (d, JPC ) 2.9 Hz, Zr-Cd); 166.0 (d,
1
2JPC ) 45.7 Hz, dC-); 147.7 (dm, JFC ) 254.0 Hz), 146.8 (dm,
1
1JFC ) 248 Hz) (C6F5); 142.4 (dm, JFC ) 257 Hz), 141.8 (dm,
Preparation of Salt 14b. A 150 mg (0.19 mmol) amount of
11b and 95.5 mg (0.19 mmol) of tris(pentafluorophenyl)borane were
dissolved in 2 mL of toluene. The resulting deep red solution was
stirred for 1 min at room temperature; then a solution of 33 mg
(0.40 mmol) of tert-butylisonitrile in 1 mL of toluene was added,
and the resulting yellow solution was stirred for 30 min at room
temperature. Pentane (1 mL) was added, and the product was
deposited as a red oil. The overlaying solution was removed with
a syringe. The product was again dissolved in 1.5 mL of diethyl
ether and precipitated by adding 1 mL of pentane. The overlaying
solution was removed via syringe, and the product was dried in
vacuum to yield 96 mg (0.06 mmol, 34%) of a pale brown/yellow
solid, mp 154 °C (DSC, decom.). Anal. Calcd for C67H41BF25N2-
PZr (1482.04): C, 54.30; H, 2.79; N, 1.89. Found: C, 54.19; H,
1
1JFC ) 260 Hz) (p-C6F5); 137.4 (dm, JFC ) 258 Hz, 2 × C6F5);
135.2 (d, 3JPC ) 11.9 Hz, i-PhCd); 131.0 (o-PhCt); 130.1 (p-PhCd
)
129.4 (m-PhCd); 129.2 (p-PhCt); 128.9 (br, o-PhCd); 128.8
(m-PhCt); 121.9 (i-PhCt); 110.2 (Cp); 109.7 (Cp′); 108.2 (br,
1
i-C6F5); 103.4 (d, JPC )18 Hz, dC-P); 99.1 (tC-Ph); 86.9 (d,
2JPC ) 4.5 Hz, -Ct); 64.7, 27.9 (tBu) (tentative relative assign-
ments for dC-, dC-P). 19F NMR (d2-dichloromethane, 564 MHz,
258 K): δ ) -129.4 (o-C6F5); -131.2 (o′-C6F5); -149.6 (p-C6F5);
-151.5 (p′-C6F5); -160.8 (m-C6F5); -161.1 (m′-C6F5). 31P{1H}
NMR (d2-dichloromethane, 122 MHz, 300 K): δ ) -41.9 (tt, each
3JPF ) 20 Hz). High-temperature NMR: 1H NMR (d8-toluene, 200
MHz) coalescence of the Cp resonances, Tc ) 325 K, δν(300 Κ)
) 131 Hz, ∆Gq ) 14.8 ( 0.3 kcal/mol.
1
X-ray Crystal Structure Analysis of 13b. Formula C43H29ClF10-
NPZr, Mw ) 907.31, yellow crystal 0.25 × 0.15 × 0.06 mm, a )
12.5348(2) Å, b ) 17.3494(3) Å, c ) 18.2500(3) Å, â ) 103.452-
2.65; N, 1.67. H NMR (d2-dichloromethane, 600 MHz, 218 K):
δ ) 7.59, 7.06 (br m, 5H, o,m,p-PhCd); 7.32 (m, 1H, p-PhCt); 7.28
(m, 2H, m-PhCt); 7.15 (m, 2H, o-PhCt); 5.98 (s, 5H, Cp); 5.33 (s,
5H, Cp′); 1.63 (s, 9H, tBuNtC); 1.31 (s, 9H, tBuNdC); 0.45 (s, 3H,
Me-B). 13C{1H} NMR (d2-dichloromethane, 151 MHz, 218 K):
(1)°, V ) 3859.96(11) Å3, Fcalcd ) 1.561 g cm-3, µ ) 0.477 mm-1
,
empirical absorption correction (0.890 e T e 0.972), Z ) 4,
monoclinic, space group P21/n (No. 14), λ ) 0.71073 Å, T ) 198
K, ω and æ scans, 26 540 reflections collected ((h, (k, (l), [(sinθ)/
λ] ) 0.66 Å-1, 9094 independent (Rint ) 0.086) and 4445 observed
reflections [I g 2σ (I)], 517 refined parameters, R ) 0.066, wR2 )
0.135, max residual electron density 0.74 (-0.95) e Å-3, hydrogens
calculated and refined as riding atoms.
3
2
δ ) 216.2 (d, JPC ) 3.3 Hz, Zr-Cd); 163.3 (d, JPC ) 46.3 Hz,
1
1
dC-); 147.8 (dm, JFC ) 240 Hz), 136.1 (dm, JFC ) 246 Hz)
(o,m-B-C6F5); 147.4 (dm, 1JFC ) 248 Hz), 146.3 (dm, 1JFC ) 248
1
1
Hz), 142.4 (dm, JFC ) 255 Hz, p), 141.6 (dm, JFC ) 255 Hz, p)
1
(P-C6F5); 145.4 (CtN); 137.4 (dm, JFC ) 252 Hz), 2 × 137.1
(dm, JFC ) 245 Hz) (C6F5); 133.3 (d, JPC ) 11.4 Hz, i-PhCd);
130.7 (o-PhCt); 130.6, 129.5 (each br, PhCd); 129.4 (p-PhCt); 128.6
(m-PhCt); 128.2 (br, i-B-C6F5); 120.8 (i-PhCt); 107.4 (br, i-C6F5-
1
3
Preparation of Salt 14a. A mixture of 173 mg (0.28 mmol) of
11a and 142 mg (0.28 mmol) of tris(pentafluorophenyl)borane was
dissolved in 5 mL of thf. The yellow solution was stirred for 1
min at room temperature; then a solution of 60 mg (0.72 mmol) of
tert-butylisonitrile in 1 mL of thf was added, and the resulting
yellow solution was stirred for 30 min at room temperature. The
solvent was removed in vacuo, and the residue was dissolved in 2
mL of toluene. Pentane (1-2 mL) was added, and the product was
deposited as a red oil. The supernatant liquid was removed via
syringe; then the product was again dissolved in 1.5 mL of diethyl
ether and precipitated by adding 1 mL of pentane. The overlaying
solution was removed via syringe, and the product was dried in
1
P); 106.9 (Cp); 106.5 (d, JPC ) 22.3 Hz, dC-P); 106.4 (Cp′);
2
100.0 (tC-Ph); 85.5 (d, JPC ) 3.9 Hz, -Ct); 63.3, 27.0
(tBuNtC); 60.3, 29.0 (tBuNtC); 9.6 (br, Me-B); (tentative relative
assignments for dC-, dC-P). 31P{1H} NMR (d2-dichloromethane,
243 MHz, 300 K): δ ) -42.7 (quin, JPF ) 28 Hz). 19F NMR
3
(d2-dichloromethane, 564 MHz, 218 K): δ ) -130.1 (2F, o),
-148.9 (1F, p), -161.0 (2F, m) (each m, P-C6F5); -131.9 (2F,
o), -151.4 (1F, p), -160.7 (2F, m) (each m, P-C6F5); -133.9
(6F, o), -164.7 (3F, p), -167.4 (6F, m) (each m, B-C6F5). 11B-
{1H} NMR (d2-dichloromethane, 96 MHz, 300 K): δ ) -15.0

5620 Organometallics, Vol. 26, No. 23, 2007
Spies et al.
(ν1/2 ) 30 Hz). IR (KBr): V˜ ) 2204 (νCN). Low-temperature
NMR: 1H NMR (d2- dichloromethane, 600 MHz) coalescence of
the Cp resonances, Tc ) 293 K, δν(218 Κ) ) 386 Hz, ∆Gq ) 13.4
( 0.3 kcal/mol; 19F NMR (d2- dichloromethane, 564 MHz)
coalescence of the p-C6F5P resonances, Tc ) 298 K, δν(238 Κ) )
1263 Hz, ∆Gq ) 13.6 kcal/mol.
Deutsche Forschungsgemeinschaft and the Fonds der Chemis-
chen Industrie is gratefully acknowledged. We thank BASF for
a generous gift of solvents.
Supporting Information Available: CIF files giving X-ray
crystal data for the compounds reported in this paper. This material
is available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. Dedicated to Professor Herbert Mayr on
the occasion of his 60th birthday. Financial support from the
OM7005968