Chelate-enforced phosphine coordination enables α-abstraction to give zirconium alkylidenes

Article abstract of DOI:10.1021/om049670u

The rigid PNP pincer ligand (PNP = deprotonated anion of bis(ortho-diisopropylphoshinoaryl)amine) is shown to stabilize the (Zr=CHR) ²⁺ fragment. (PNP)Li(THF) (2-THF) contains P-Li bonds, as evinced by the observation of the Li-P coupling in the solution ³¹P NMR spectrum and by the X-ray structural determination in the solid state. 2-THF reacts with ZrCl₄(Et₂O)₂ to give (PNP)ZrCl₃ (3). (PNP)ZrCl₃ (3) can be alkylated with RCH₂MgCl to give (PNP)Zr(CH₂R)₃ (4a-c). (PNP)ZrMe₃ (4a) is thermally stable, and its solid-state structure is characterized by severe distortions from the octahedral geometry. The (PNP)Zr(CH₂R) ₃ (R = phenyl (4b) or p-tolyl (4c)) compounds undergo α-abstraction at ambient temperature to give isolable Zr alkyl/alkylidenes (PNP)Zr(=CHR)(CH₂R) (5b,c). The reaction follows a first-order rate law (t_1/2 at 298 K ≈ 2.3 h). The activation parameters were determined from the VT NMR studies (4b → 5b): ΔH? = 19(1) kcal/mol; ΔS? = -14(3) cal/(mol K); ΔG?₂₉₈ = 23(2) kcal/mol. The importance of the enforcement of the phosphine coordination by the rigid PNP ligand is discussed.

Full text of DOI:10.1021/om049670u

4700
Organometallics 2004, 23, 4700-4705
Ch ela te-En for ced P h osp h in e Coor d in a tion En a bles
r-Abstr a ction to Give Zir con iu m Alk ylid en es
Wei Weng, Lin Yang, Bruce M. Foxman, and Oleg V. Ozerov*
Department of Chemistry, Brandeis University, MS015, 415 South Street,
Waltham, Massachusetts 02454
Received May 10, 2004
The rigid PNP pincer ligand (PNP ) deprotonated anion of bis(ortho-diisopropylphoshino-
aryl)amine) is shown to stabilize the (ZrdCHR)2+ fragment. (PNP)Li(THF) (2-THF ) contains
P-Li bonds, as evinced by the observation of the Li-P coupling in the solution 31P NMR
spectrum and by the X-ray structural determination in the solid state. 2-THF reacts with
ZrCl4(Et2O)2 to give (PNP)ZrCl3 (3). (PNP)ZrCl3 (3) can be alkylated with RCH2MgCl to give
(PNP)Zr(CH2R)3 (4a -c). (PNP)ZrMe3 (4a ) is thermally stable, and its solid-state structure
is characterized by severe distortions from the octahedral geometry. The (PNP)Zr(CH2R)3
(R ) phenyl (4b) or p-tolyl (4c)) compounds undergo R-abstraction at ambient temperature
to give isolable Zr alkyl/alkylidenes (PNP)Zr(dCHR)(CH2R) (5b,c). The reaction follows a
first-order rate law (t1/2 at 298 K ≈ 2.3 h). The activation parameters were determined from
the VT NMR studies (4b f 5b): ∆Hq ) 19(1) kcal/mol; ∆Sq ) -14(3) cal/(mol K); ∆Gq
)
298
23(2) kcal/mol. The importance of the enforcement of the phosphine coordination by the rigid
PNP ligand is discussed.
In recent years, the interest in metal alkylidenes has
give alkylidenes is typically facile,4 it is not so for group
4 tetraalkyls.5f R-Abstraction in M(CH2R)4 would gener-
ate a three-coordinate (RCH2)2MdCHR (M ) Ti, Zr, Hf).
The available evidence indicates that three-coordinate
compounds of group 4 metals with metal-element
multiple bonds are exceptionally reactive (unstable).5f,9
Ostensibly, some combination of neutral and anionic
ligands is necessary to stabilize the MdCR2 fragment
(M ) Ti, Zr, Hf).
Utilization of a hybrid chelating ligand is arguably
the best way of introducing neutral donors into the
coordination sphere of the metal in a manner that is
controlled in terms of both stereochemistry and stoi-
chiometry.6-8 Since the early 1980s, the Fryzuk group
has been exploring the chemistry of the signature
ligands SiPNP and P2Cp (Chart 1).7,8,10 SiPNP and P2Cp
are conformationally flexible, and in the context of
been on the rise, largely owing to the advances in
catalysis of olefin metathesis.1-3 Alkylidene complexes
of the metals of groups 5 and 6 are quite numerous.4
Examples of alkylidenes of the group 4 metals are rare,
with only a single family of stable alkylidenes known
for Zr and Hf.4-8 The most common route to alkylidenes
of early transition metals involves R-hydrogen abstrac-
tion in polyalkyl compounds. This process is strongly
driven by steric pressure and is therefore favored by
bulkier ligands and higher coordination numbers. While
for the group 5 homoleptic pentaalkyls R-abstraction to
* To whom correspondence should be addressed. E-mail: ozerov@
brandeis.edu.
(1) (a) Hoveyda, A. H.; Schrock, R. R. Chem. Eur. J . 2001, 7, 945.
(b) Schrock, R. R. Tetrahedron 1999, 55, 8141. (c) Schrock, R. R.
Polyhedron 1995, 14, 3177.
(2) (a) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18. (b)
Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413. (c) Grubbs, R.
H.; Miller, S. J .; Fu, G. C. Acc. Chem. Res. 1995, 28, 446.
(3) (a) J afarpour, L.; Nolan, S. P. J . Organomet. Chem. 2001, 617-
618, 17. (b) Fuerstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012. (c)
Buchmeiser, M. R. Chem. Rev. 2000, 100, 1565. (d) Ivin, K. J . J . Mol.
Catal. A 1998, 133, 1. (e) Pariya, C.; J ayaprakash, K. N.; Sarkar, A.
Coord. Chem. Rev. 1998, 168, 1. (f) Armstrong, S. K. J . Chem. Soc.,
Perkin Trans. 1 1998, 371. (g) Schuster, M.; Blechert, S. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2037.
(4) (a) Schrock, R. R. Chem. Rev. 2002, 102, 145. (b) Schrock, R. R.
In Reactions of Coordinated Ligands; Braterman, P. R., Ed.; Plenum:
New York, 1986. (c) Feldman, J .; Schrock, R. R. Prog. Inorg. Chem.
1991, 39, 1. (d) Schrock, R. R. Pure Appl. Chem. 1994, 66, 1447. (e)
Beckhaus, R.; Santamaria, C. J . Organomet. Chem. 2001, 617-618,
81.
(5) Ti: (a) van der Heijden, H.; Hessen, B. J . Chem. Soc. Chem.
Commun. 1995, 145. (b) Sinnema, P.-J .; van der Veen, L., Spek, A. L.;
Veldman, N.; Teuben, J . H. Organometallics 1997, 16, 4245. (c)
Kahlert, S.; Goerls, H.; Scholz, J . Angew. Chem., Int. Ed. 1998, 37,
1857. (d) Kruger, C.; Mynott, R.; Siedenbiedel, C.; Stehling, L.; Wilke,
G. Angew. Chem., Int. Ed. Engl. 1991, 30, 1668. (e) See also Tebbe’s
reagent: Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J . Am. Chem.
Soc. 1978, 100, 3611. (f) For studies of the thermal decomposition of
Ti(CH2CMe3)4, see: Cheon, J .; Rogers, D. M.; Girolami, G. S. J . Am.
Chem. Soc. 1997, 119, 6804.
(6) Ti with chelating ligands: (a) van Doorn, J . A.; van der Heijden,
H.; Orpen, A. G. Organometallics 1994, 13, 4271. (b) van Doorn, J . A.,
van der Heijden, H.; Orpen, A. G. Organometallics 1995, 14, 1278. (c)
Baumann, R.; Stumpf, R.; Davis, W. M.; Liang, L.-C.; Schrock, R. R.
J . Am. Chem. Soc. 1999, 121, 7822. (d) Basuli, F.; Bailey, B. C.;
Tomaszewski, J .; Huffman, J . C.; Mindiola, D. J . J . Am. Chem. Soc.
2003, 125, 6052. (e) Coville et al. described a series of bis(iminophos-
phorano)methanediide complexes of the group 4 metals that resemble
metal alkylidenes. Babu, R. P. K.; McDonald, R.; Cavell, R. G.
Organometallics 2000, 19, 3462.
(7) Zr: (a) Fryzuk, M. D.; Mao, S. S. H.; Zaworotko, M. J .;
MacGillivray, L. R. J . Am. Chem. Soc. 1993, 115, 5336. (b) Fryzuk, M.
D.; Duval, P. B.; Mao, S. S. H.; Zaworotko, M. J .; MacGillivray, L. R.
J . Am. Chem. Soc. 1999, 121, 2478. (c) Fryzuk, M. D.; Duval, P. B.;
Mao, S. S. H.; Rettig, S. J .; Zaworotko, M. J .; MacGillivray, L. R. J .
Am. Chem. Soc. 1999, 121, 1707.
(8) Fryzuk, M. D.; Duval, P. B.; Patrick, B. O.; Rettig, S. J .
Organometallics 2001, 20, 1608.
(9) (a) Cummins, C. C.; Schaller, C. P.; Van Duyne, G. D.; Wolc-
zanski, P. T.; Chan, E. A.-W.; Hoffmann, R. J . Am. Chem. Soc. 1991,
113, 2985. (b) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J .
Am. Chem. Soc. 1996, 118, 591. (c) Schaller, C. P.; Bonanno, J . B.;
Wolczanski, P. T. J . Am. Chem. Soc. 1994, 116, 4133. (d) Bennett, J .
L.; Wolczanski, P. T. J . Am. Chem. Soc. 1997, 119, 10696.
10.1021/om049670u CCC: $27.50 © 2004 American Chemical Society
Publication on Web 09/02/2004

Chelate-Enforced Phosphine Coordination
Organometallics, Vol. 23, No. 20, 2004 4701
Ch a r t 1
Sch em e 1
F igu r e 1. ORTEP drawing (30% probability ellipsoids) of
2-THF showing selected atom labeling. Omitted for clar-
ity: H atoms, Me groups, and disorder in the â-position of
THF.
the ground state. This enforced Zr-P bonding leads to
R-abstraction in Zr polyalkyl complexes that is much
faster than in analogous complexes of P2Cp and ulti-
mately to unsaturated, isolable Zr alkylidenes.
Resu lts a n d Discu ssion
Syn th esis a n d Str u ctu r e of (P NP )Li-THF . 1 is
easily deprotonated by n-BuLi in a variety of solvents
(Scheme 1), and the Li derivative 2 can be isolated
either in a donor-free form or as a mono-THF adduct
(2-THF ). The solid-state structure determination on a
single crystal of 2-THF revealed a distorted tetrahedral
coordination geometry about Li (P-Li-P angle of
139.1(2)°) with a single THF donor (Figure 1).14a,c 2-THF
displays a well-resolved quartet in the 31P NMR spec-
trum (δ -4.1 ppm, J P-Li ) 48 Hz) and a triplet in the
7Li NMR spectrum (δ 2.4 ppm) in C6D6 at ambient
alkylidene synthesis, this means that dissociation of the
phosphine arm may be preferred to R-hydrogen abstrac-
tion as a means of alleviating steric congestion at the
metal center. In (P2Cp)Zr(CH2Ph)2Cl only one phosphine
arm is coordinated to Zr in the ground state, and
thermolysis leads to R-abstraction and formation of
(P2Cp)Zr(dCHPh)Cl.7 Fryzuk et al. proposed, on the
basis of the kinetic evidence, that coordination of the
second phosphine arms occurs in the transition state.
(P2Cp)Zr(CH2Ph)3 possesses two dangling phosphine
arms and does not undergo R-abstraction to give an
alkyl-alkylidene product. Hf analogues behave simi-
larly.8 For SiPNP, the chemistry of alkylidene formation
has not been explored, but the similarity of the 31P NMR
chemical shift of (SiPNP)Zr(CH2Ph)2Cl to that of the free
ligand indicates free phosphine arms for this com-
pound.11
We have recently reported a synthesis of a new PNP
ligand (Scheme 1, plain “PNP” from here on refers to
the deprotonated 1) that has a more rigid backbone than
SiPNP or P2Cp. Some of its Rh, Ir, and Pd chemistry
has been communicated.12 Two recent reports described
the synthesis of the related ligand ((o-Ph2PC6H4)2N)-
(PNPPh).13 The present work describes how utilization
of this rigid pincer-type PNP ligand provides for much
more favorable coordination of both phosphine arms in
temperature, while no Li-P coupling was observed for
(PNPPh)Li(THF)2
or (SiPNP)Li.15 This demonstrates
13a
that (a) the greater rigidity of the PNP backbone in
2-THF versus (SiPNP)Li enforces Li-P interaction in
2-THF ; (b) the greater basicity and steric bulk of PPri
2
compared with PPh2 leads to a stronger Li-P interac-
tion in 2-THF versus (PNPPh)Li(THF)2 and to a lower
coordination number (CN) at Li. The stronger Li-P
interaction in 2-THF is also evident from the solid-state
structure (Figure 1). The Li-P distances are 2.556(5)
and 2.531(5) Å, ca. 0.25 Å shorter than the Li-P
distances in (PNPPh)Li(THF)2. The Li-N (1.942(6) Å)
and Li-O (1.929(6) Å) distances are also slightly (by
<0.1 Å) shorter, probably as a consequence of a lower
CN at Li.
(14) (a) Crystal data for 2-THF , C30H48Li1N1O1P2, Mr ) 507.61,
crystal dimensions 0.22 × 0.58 × 0.72 mm3, monoclinic, space group
C2/ c, a ) 39.230(5) Å, b ) 9.6657(13) Å, c ) 17.041(3) Å, â )
103.126(13)°, V ) 6292.8(16) Å3, Z ) 8, Fcalcd ) 1.072 Mg m-3, µ(Mo
KR) ) 0.159 cm-1, T ) 294 K, F(000) ) 2208, 2θmax ) 47.4°. 4947
reflections measured, of which 4755 were unique (Rint ) 0.01). Final
R1 ) 0.0451 with wR2 ) 0.0516 for 2755 observed reflections with I >
1.96σ(I). (b) Crystal data for 4a , C29H49N1P2Zr1, Mr ) 564.88, crystal
dimensions 0.22 × 0.58 × 0.58 mm3, orthorhombic, space group Pbcn,
a ) 23.8250(19) Å, b ) 14.1571(9) Å, c ) 18.2978 (13) Å, V ) 6171.7(8)
Å3, Z ) 8, Fcalcd ) 1.216 Mg m-3, µ(Mo KR) ) 0.476 cm-1, T ) 294 K,
F(000) ) 2400, 2θmax ) 47.6°. 4702 reflections measured, of which 4693
were unique. Final R1 ) 0.0453 with wR2 ) 0.0491 for 2313 observed
reflections with I > 1.96σ(I). (c) ORTEP plots were generated using
Ortep-3 for Windows. Farugia, L. J . J . Appl. Crystallogr. 1997, 30,
565.
(10) (a) Fryzuk, M. D. Can. J . Chem. 1992, 70, 2839. (b) Fryzuk, M.
D.; Berg, D. J .; Haddad, T. S. Coord. Chem. Rev. 1990, 99, 137. (c)
Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95, 1.
(11) Fryzuk, M. D.; Mylvaganam, M.; Zaworotko, M. J.; MacGillivray,
L. R. Polyhedron 1996, 15, 689.
(12) (a) Fan, L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2004,
23, 326. (b) Ozerov, O. V.; Guo, C.; Papkov, V. A.; Foxman, B. F. J .
Am. Chem. Soc. 2004, 126, 4792.
(13) (a) Liang, L.-C.; Lin, J .-M.; Hung, C.-H. Organometallics 2003,
22, 3007. (b) Winter, A. M.; Eichele, K.; Mack, H.-G.; Potuznik, S.;
Mayer, H. A.; Kaska, W. C. J . Organomet. Chem. 2003, 682, 149.
(15) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. G. Organometallics
1997, 16, 725.

4702 Organometallics, Vol. 23, No. 20, 2004
Weng et al.
4a stem from the difference in the rigidity of the PNP
ligand, the difference in the bulk of the phosphine
substituents, or both. A regular, mer-(PNP)ZrMe3 struc-
ture seems sterically sound, but is probably avoided to
maximize Zr-Me σ-bonding and, in particular, to escape
placement of two Me groups trans to each other.
Polyalkyl compounds with d0 metal centers often display
related electronic structural distortions.19
It is telling that the phosphine arms were found to
coordinate strongly to Li (2-THF ) and Zr (4a ) in the
solid state. Both LiI and ZrIV are hard acids and
generally would have little affinity for the bulky, soft
phosphine donors. We view the observed phosphine
coordination as evidence that the relative rigidity of the
PNP ligand enforces phosphine coordination. The rota-
tion about the N-C bond may move the phosphine away
from the metal in a PNP complex, but even a dihedral
angle between the aromatic rings of ca. 59° (4a ) is
compatible with metal-phosphorus bonding.
F igu r e 2. ORTEP drawing (50% probability ellipsoids) of
4a showing selected atom labeling. Omitted for clarity: H
atoms, Me groups except for Zr-Me. Selected distances
(Å): Zr1-C40, 2.255(7); Zr1-C41, 2.285(7); Zr1-C42,
2.253(7); Zr1-P1, 2.7549(17); Zr1-P2, 2.7984(18); Zr1-N1,
2.223(4).
Syn th esis a n d Str u ctu r e of th e P NP Com p lexes
of Zr . 2-THF reacts with ZrCl4(OEt2)2 to give (PNP)-
ZrCl3 (3) in good yield as a sparingly soluble red solid.
The 31P NMR chemical shift of 3 (27.1 ppm), which lies
considerably downfield from 1 or 2, is indicative of the
coordination of the phosphine arms to Zr. The overall
Solution NMR studies indicate average C2 or Cs
symmetry for the PNP ligand in 4a -c and show that
all three Zr-CH2R groups are equivalent. In contrast to
1
i
3, the H resonances of the methyls of the Pr groups
are doublets of doublets and not doublets of virtual
triplets. The observed equivalence of the alkyl groups
cannot be reconciled with the static structure found in
the solid state or any other static structure. Fryzuk et
al. outlined several possible fluxional processes for
(SiPNP)MMe3 (M ) Zr, Hf); the same are possible for
4.18 Consistent with a non-trans disposition of phosphine
arms, virtual triplet fine structures are not observed for
1
symmetry displayed by 3 in its 31P, H, and 13C NMR
spectra is C2 or Cs. An idealized facial-PNP coordination
can be ruled out on the basis of the observation of
doublets of virtual triplets for the Me groups of the PPri
2
moieties.16 In addition, the frame of this PNP ligand is
clearly more adapted to a meridional configuration.
Even for the more flexible Fryzuk’s ligands, the meridi-
onal coordination was found for the bulkier (SiPNP)MCl3
(M ) Zr, Hf) in the solid state.17 The solid-state struc-
ture of (PNP)PdCl is C2-symmetric owing to the twist
in the backbone of the chelate.12a While (PNP)PdCl is
C2v-symmetric in solution, implying facile intercon-
version between degenerate C2 conformers, such inter-
conversion in (PNP)ZrCl3 (3) may be slowed by the extra
chlorides attached to the metal. An alternative ex-
planation is that 3 has a structure similar to that of
(PNP)ZrMe3 (4a , vide infra) but with stronger P-Zr
1
the H and 13C NMR signals of 4a -c in solution.16 The
chemical shifts of the 31P resonances of 4a -c are similar
to each other (δ ca. 13 ppm) and different from those of
1 or 2, indicating that the phosphines in 4b,c are bound
to Zr. Presumably, 4a -c are structurally similar.
While 4a is thermally stable (no NMR-detectable
change after 5 h at 80 °C in C6D6), 4b,c slowly evolve
in solution at ambient temperature into the alkyl-
alkylidene compounds 5b,c with concomitant production
of toluene or p-xylene. Compounds 5b,c are stable at
ambient temperature in solution and in the solid state.
The definitive spectroscopic feature of 5 is the presence
of a downfield alkylidene signal in the 13C NMR
spectrum (δ 231.0 (5b), 230.6 (5c)).4 The low value (92
2
bonds (and hence larger J P-P coupling) because of the
higher Lewis acidity of Zr in 3.
Alkylation of 3 with 3-3.5 equiv of RCH2MgCl
(R ) H, Ph, p-MeC6H4) or a corresponding amount of
(RCH2)2Mg leads to the formation of (PNP)Zr(CH2R)3
(4a -c) in >85% yield (in situ by 31P NMR). An X-ray
structure determination revealed a highly distorted
geometry about Zr in 4a (Figure 2).14b,c The overall
geometry is reminiscent of the structure of (SiPNP)-
HfMe3.18 For the latter, the description of a twice
phosphine-capped N-HfMe3 tetrahedron was deemed
appropriate. In the case of the N-ZrMe3 substructure
in 4a , this description fails: the angles deviate from
tetrahedral values to a much greater extent (82°-142°)
and the P-Zr-P angle (134.33(5)°) is larger than the
P-Hf-P angle (ca. 115°) in (SiPNP)HfMe3 (here SiPNP
has PMe2 arms, see Chart 1). Both the PNP and the
Me3 sets of donors in 4a are halfway between a facial
and a meridional arrangement. It is not clear whether
the structural differences between (SiPNP)HfMe3 and
1
Hz) of the alkylidene J CH coupling constant in an
undecoupled 13C NMR spectrum is indicative of an
R-agostic alkylidene.4 The signals for the Zr-CH2-R
carbons in the undecoupled 13C NMR spectra experi-
ments are each a triplet (δ 60.3, J CH ) 131 Hz for 5b; δ
59.0, J CH ) 132 Hz for 5c). The alkylidene H resonates
at δ 7.32 (7.11) in 5b (5c). These data for 5 are similar
to those reported for (P2Cp)ZrdCHPh(Cl).7 An AB
pattern is observed for 5b,c in the 31P NMR spectrum.
The J PP value of ca. 60 Hz in 5b,c is smaller than the
typical trans-J PP values (100-300 Hz) and is indicative
of a P-M-P angle substantially smaller than 180°.16
(19) See for example: (a) Kaupp, M. Chem. Eur. J . 1998, 4, 1678.
(b) Kaupp, M. Angew. Chem., Int. Ed. 2001, 40, 3534. (c) Perrin, L.;
Maron, L.; Eisenstein, O. Faraday Discuss. 2003, 124, 25. (d)
[(tBu3SiCC)6Ta]- is trigonal prismatic, but [(tBu3SiCC)6Zr]2- is octa-
hedral: Vaid, T. P.; Veige, A. S.; Lobkovsky, E. B.; Glassey, W. V.;
Wolczanski, P. T.; Liable-Sands, L. M.; Rheingold, A. L.; Cundari, T.
R. J . Am. Chem. Soc. 1998, 120, 10067. (e) [Li(tmeda)]2[ZrMe6] was
shown to have a trigonal prismatic environment about Zr in the solid
state: Morse, P. M.; Girolami, G. S. J . Am. Chem. Soc. 1989, 111, 4114.
(16) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 3rd ed.; Wiley-Interscience: New York, 2001; pp 260-262.
(17) Fryzuk, M. D.; Carter, A.; Westerhaus, A. Inorg. Chem. 1985,
24, 642.
(18) Fryzuk, M. D., Carter, A.; Rettig, S. J . Organometallics 1992,
11, 469.

Chelate-Enforced Phosphine Coordination
Organometallics, Vol. 23, No. 20, 2004 4703
toluene, diethyl ether, tetrahydrofuran, and C6D6 were dried
over sodium-benzophenone ketyl, distilled or vacuum trans-
ferred, and stored over molecular sieves. Dichloromethane was
dried over calcium hydride prior to a final distillation under
an Ar atmosphere. CD2Cl2 was dried over calcium hydride,
then vacuum transferred and stored over molecular sieves
prior to use. Acetone-d6 was dried over molecular sieves and
then vacuum transferred. (PNP)H (1),12a Mg(CH2Ph)2‚2THF,21
and MgMe222 were prepared according to published procedures.
ZrCl4‚2Et2O was prepared by adding 4 equiv of ether to a
CH2Cl2 slurry of ZrCl4, filtering, and pumping the filtrate to
dryness to give the product as a white powder. All other
chemicals were used as received from commercial vendors.
NMR spectra were recorded on a Varian iNova 400 spectrom-
eter (1H NMR, 399.755 MHz; 13C NMR, 100.518 MHz; 31P
NMR, 161.822 MHz) or a Varian iNova 500 spectrometer (7Li
NMR, 194.205 MHz). Chemical shifts are reported in δ (ppm).
For 1H and 13C NMR spectra, the residual solvent peak was
used as an internal reference. 31P NMR spectra were refer-
enced externally using 85% H3PO4 at δ 0 ppm. 7Li NMR
spectra were referenced to the peak of 1 M LiCl in D2O at δ 0
ppm.
Unfortunately, our multiple attempts at growing X-ray
quality single crystals of 5b or 5c have been unsuccess-
ful. However, the spectroscopic data in solution clearly
establish the proposed alkylidene formulation with a
dissymmetric, five-coordinate environment about Zr,
and the empirical formula is supported by elemental
analysis. In a reaction expected for an early metal alkyl/
alkylidene, 5b,c react with (CX3)2CO to give as organic
products (CX3)2CdCH-R and RCH2X (X ) H, D) (see
Supporting Information). The fate of Zr has not been
determined, although excess acetone liberates ligand 1.
Kin etic Stu d ies. We used VT NMR to interrogate
the kinetics of the transformation of 4b into 5b. The
reaction was found to follow the first-order rate law
d(ln[4b]) ) -k × dt over the studied 20-53 °C range
(k298 ) 8.4(4) × 10-5 s-1; t1/2(298 K) ≈ 2.3 h). Activation
parameters were determined from the Eyring plot: ∆Hq
) 19(1) kcal/mol; ∆Sq ) -14(3) cal/(mol K); ∆Gq
)
298
23(2) kcal/mol. The comparison with the kinetic data
for the R-abstraction in (P2Cp)Zr(CH2Ph)2Cl is insight-
ful.7b The conversion of 4b to 5b is much faster; the 298
K rate for 4b corresponds to the rate at 343 K for
(P2Cp)Zr(CH2Ph)2Cl. The ∆Sq for the reaction of 4b is
less negative than the -22 eu value for the Fryzuk’s
(P2Cp)Zr(CH2Ph)2Cl. (P2Cp)Zr(CH2Ph)2Cl has only one
Zr-P bond in the ground state. Fryzuk et al. concluded
that in the R-abstraction in (P2Cp)Zr(CH2Ph)2Cl part
of the entropic contribution to the activation barrier
corresponds to the need to coordinate both phosphine
arms in the transition state.7b Notably, (P2Cp)Zr-
(CH2Ph)3 has neither of the phosphine arms coordinated
to Zr in the ground state, and it is thermally stable.7
From this perspective, our results, particularly the less
negative ∆Sq, are consistent with the enforcement of
phosphine coordination by the rigid PNP ligand in the
ground state and throughout the reaction coordi-
nate. The activation barrier for R-abstraction is thus
lowered ostensibly by decreasing the unfavorable ∆Sq
contribution.
(P NP )Li (2). (PNP)H (1) (119 mg, 0.275 mmol) was sus-
pended in 20 mL of pentane and cooled to -35 °C. n-BuLi (111
µL, 0.275 mmol, 2.5 M in hexane) was slowly added via
syringe. The reaction mixture was allowed to warm to ambient
temperature and stirred for 2 h. The volatiles were removed
under reduced pressure, and the residue was dissolved in cold
pentane. The clear, yellow solution was placed into a -35 °C
freezer, and after 12 h, the yellow microcrystalline solid formed
was collected by filtration and then dried in vacuo. Yield: 77
1
mg, 64%. H NMR (C6D6): δ 7.45 (br, 2H, Ar-H), 6.99 (s, 2H,
3
Ar-H), 6.94 (d, 2H, J HH ) 8 Hz, Ar-H), 2.26 (s, 6H, Ar-Me),
3
3
1.93 (m, 4H, CHMe2), 1.06 (dd, 12H, J PH ) 14 Hz, J HH ) 7
Hz, CHMe2), 0.94 (dd, 12H, 3J PH ) 12 Hz, 3J HH ) 7 Hz, CHMe2).
13C{1H} NMR (C6D6): δ 163.9 (m), 133.0 (s), 131.9 (s), 123.0
(s), 120.3 (m), 119.7 (m), 22.6 (s, CHMe2), 20.9 (s, Ar-CH3),
2
2
20.1 (d, J PC ) 12 Hz, CHMe2), 19.7 (d, J PC ) 8 Hz, CHMe2).
31P{1H} NMR (C6D6): δ -4.4 (s). Li NMR (C6D6): δ 3.2 (br).
7
Anal. Calcd (Found) for C26H40NP2Li: C, 71.71 (71.62); H, 9.26
(9.30).
(P NP )Li‚THF (2-THF ). n-Butyllithium (3.13 mL, 7.80
mmol, 2.5 M in hexane) was slowly added to a cooled (-35 °C)
solution of 1 (2.11 g, 4.87 mmol) in 30 mL of THF. The mixture
was stirred at ambient temperature for 2 h, and then all
volatiles were removed in vacuo. The residue was triturated
with 20 mL of pentane and then placed into a -35 °C freezer.
After 8 h, the resulting yellow solid was filtered off and dried
Con clu sion
It is well known that chelating ligands often encour-
age reactivity at the metal centers that is different from
analogous complexes with monodentate ligands. How-
ever, the rigidity of otherwise similar chelating ligands
may lead to drastic differences in reactivity as well.20
In the present report the favored coordination of the
phosphine arms of the PNP chelate leads to the facilita-
tion of R-abstraction and isolation of rare zirconium
alkylidenes under ambient conditions. Kinetic studies
indicate the importance of entropic considerations.
Future studies will be aimed at the exploration of the
generality of this approach to group 4 alkylidenes and
their reactivity.
1
under vacuum. Total yield: 2.07 g (83%). H NMR (C6D6): δ
3
3
7.62 (dd, 2H, J HH ) 8 Hz, J PH ) 6 Hz, Ar-H), 7.05 (s, 2H,
3
3
Ar-H), 6.99 (d, 2H, J HH ) 8 Hz, Ar-H), 3.37 (t, 4H, J HH ) 6
Hz, OCH2CH2), 2.31 (s, 6H, Ar-Me), 2.00 (m, 4H, CHMe2), 1.16
3
3
(t, 4H, J HH ) 6 Hz, OCH2CH2), 1.12 (dd, 12H, J PH ) 15 Hz,
3J HH ) 8 Hz, CHMe2), 1.06 (dd, 12H, J PH ) 13 Hz, J HH ) 7
Hz, CHMe2). 13C{1H} NMR (C6D6): δ 161.2 (d, J PC ) 19 Hz),
132.8 (d, J PC ) 2 Hz), 131.6 (s), 121.4 (d, J PC ) 2 Hz), 119.4
(d, J PC ) 10 Hz), 116.5 (d, J PC ) 4 Hz), 68.3 (s, OCH2CH2),
25.2 (s, OCH2CH2), 22.7 (d, CHMe2, J CP ) 2 Hz), 21.1 (s, Ar-
CH3), 20.2 (d, J CP ) 14 Hz, CHMe2), 19.7 (d, J CP ) 9 Hz,
3
3
CHMe2). 31P{1H} NMR (C6D6): δ -4.1 (q, J LiP ) 48 Hz). Li
1
7
1
NMR (C6D6): δ 2.4 (t, J LiP ) 48 Hz).
(P NP )Zr Cl3 (3). To ZrCl4‚2Et2O (0.991 g, 2.60 mmol)
suspended in cold toluene (30 mL, -35 °C) was added a cold
toluene solution (20 mL, -35 °C) of 2-THF (1.33 g, 2.60 mmol).
The resulting mixture was stirred at ambient temperature for
12 h. All volatiles were then removed in vacuo. The residue
was extracted with 65 mL of CH2Cl2 and then passed through
Exp er im en ta l Section
Gen er a l Con sid er a tion s. Unless specified otherwise, all
manipulations were performed under an argon atmosphere
using standard Schlenk or glovebox techniques. Pentane,
(20) For an example of the influence of the rigidity of the bidentate
phosphine on the reactivity of (P-P)PtMe4 complexes (P-P ) Ph2PCH2-
CH2PPh2 or o-C6H4(PPh2)2) see: Crumpton-Bregel, D. M.; Goldberg,
K. I. J . Am. Chem. Soc. 1997, 119, 10696.
(21) Schrock, R. R. J . Organomet. Chem. 1976, 122, 209.
(22) Bailey, P. J .; Dick, C. M. E.; Fabre, S.; Parsons, S. J . Chem.
Soc., Dalton Trans. 2000, 1655.

4704 Organometallics, Vol. 23, No. 20, 2004
Weng et al.
a glass frit lined with Celite to remove LiCl. The solvent was
removed in vacuo from the filtrate to yield a red solid (1.38 g,
85% yield). 1H NMR (CD2Cl2): δ 7.09 (s, 2H, Ar-H), 7.03 (d,
showed that 4c constituted ca. 80% of the resulting mixture.
3
1H NMR (C6D6): 2.80 (d, 3H, J HH ) 10 Hz, ZrCH2Ph), 2.66
3
(d, 3H, J HH ) 10 Hz, ZrCH2Ph). 31P{1H} NMR (C6D6): δ 12.2
3
3
2H, J HH ) 8 Hz, Ar-H), 6.65 (d, 2H, J HH ) 8 Hz), 2.77 (br,
2H, CHMe2), 2.39 (br, 2H, CHMe2), 2.29 (s, 6H, Ar-Me), 1.49
(s). 13C{1H} NMR (C6D6): δ 77.2 (s). Identification and assign-
ment of the full set of the 1H and 13C NMR resonances of 4c
was not possible because of the presence of the (PNP)MgCl
and other, unidentified minor impurities.
3
(app. q, dvt, J PH ) 8 Hz, J HH ) 7 Hz, CHMe2), 1.40 (app. q,
dvt, J PH ) 8 Hz, 3J HH ) 7 Hz, CHMe2), 1.22 (m, 12H, CHMe2).
13C NMR (CD2Cl2): δ 159.8 (br), 133.3 (s), 132.1 (s), 122.1 (br),
120.1 (s), 26.9 (br, CHMe2), 22.2 (br, CHMe2), 21.0 (s, Ar-Me),
20.4 (s, CHMe2), 18.9 (s, two peaks overlapped, CHMe2), 17.8
(s, CHMe2). 31P{1H} NMR (CD2Cl2): δ 27.1 (s). Anal. Calcd
(Found) for C26H40NP2Cl3Zr: C, 50.08 (49.47); H, 6.42 (6.65);
Cl, 16.85 (16.19).
(P NP )Zr (dCHP h )(CH2P h ) (5b). Mg(CH2Ph)2‚2THF (187
mg, 0.556 mmol) was added to 3 (219 mg, 0.348 mmol)
suspended in toluene (30 mL) with 180 µL of dioxane. The
mixture was stirred for 16 h, and then all volatiles were
removed under vacuum. The residue was extracted with
pentane and filtered. The pentane solution was pumped to
dryness to afford the crude 5b (90% pure by NMR). The
analytically pure 5b can be obtained by recrystallization from
cold pentane. Yield: 131 mg (53%). 1H NMR (C6D6): δ 7.32 (s,
1H, ZrCHPh), 7.10-6.89 (m, 10H, Ar-H), 6.85 (br s, 2H, Ar-
H), 6.76-6.70 (m, 3H, Ar-H), 6.60 (t, 1H, J ) 7 Hz), 3.06 (d,
(P NP )Zr Me3 (4a ). Compound 3 (420 mg, 0.670 mmol) was
suspended in 30 mL of ether and cooled to -35 °C. To this
suspension were added 114 µL of dioxane and MgMe2 (72 mg,
1.30 mmol) to result in gradual dissolution of 3. The color of
the solution slowly changed to bright yellow. The mixture was
stirred at room temperature for 4 h. After that, volatiles were
removed in vacuo. The residue was extracted with pentane
and passed through a pad of Celite. The filtrate was stored in
a freezer (-35 °C) for 2 h. The supernatant was decanted, and
the pale yellow crystalline solid was dried under vacuum to
2
2
1H, J HH ) 9 Hz, ZrCH2Ph), 2.60 (dd, 1H, J HH ) 9 Hz, J ) 4
Hz, ZrCH2Ph), 2.33 (m, 1H, CHMe2), 2.15 (s, 3H, Ar-Me), 2.13
(s, 3H, Ar-Me), 2.20-2.00 (m, 2H, CHMe2), 1.43 (m, 1H,
CHMe2), 1.25 (dd, 3H, J ) 7 Hz, J ) 15 Hz, CHMe2), 1.19 (dd,
3H, J ) 7 Hz, J ) 15 Hz, CHMe2), 1.14 (dd, 3H, J ) 7 Hz, J
) 14 Hz, CHMe2), 1.08 (dd, 3H, J ) 7 Hz, J ) 16 Hz, CHMe2),
0.94 (dd, 3H, J ) 7 Hz, J ) 15 Hz, CHMe2), 0.86 (dd, 3H, J )
7 Hz, J ) 15 Hz, CHMe2), 0.77 (dd, 3H, J ) 7 Hz, J ) 9 Hz,
CHMe2), 0.67 (dd, 3H, J ) 7 Hz, J ) 16 Hz, CHMe2). 13C{1H}
NMR (C6D6): δ 230.7 (s, ZrCHPh), 160.0 (dd, J ) 2 Hz, J )
24 Hz), 158.2 (dd, J ) 2 Hz, J ) 20 Hz), 148.9 (s), 139.3 (s),
133.1 (d, J ) 1 Hz), 132.6 (s), 132.5 (dd, J ) 2 Hz, J ) 8 Hz),
130.2 (s), 129.3 (s), 128.7 (d, J ) 4 Hz), 128.5 (s), 128.4 (d, J
) 4 Hz), 127.7(s), 126.0 (s), 123.2 (d, J ) 22 Hz), 122.2 (s),
120.5 (d, J ) 7 Hz) 120.0 (s), 119.3 (d, J ) 7 Hz), 116.1 (d, J
) 21 Hz), 60.3 (s, ZrCH2Ph), 27.0 (d, J ) 10 Hz, CHMe2), 22.9
(d, J ) 6 Hz, CHMe2), 21.2 (d, J ) 18 Hz, CHMe2), 20.9 (d, J
) 6 Hz, CHMe2), 20.8(s, Ar-CH3), 20.7 (s, Ar-CH3), 20.6 (d, J
) 7 Hz, CHMe2), 19.6 (d, J ) 7 Hz, CHMe2), 19.5 (d, J ) 10
Hz, CHMe2), 19.4 (d, J ) 4 Hz, CHMe2), 19.1 (d, J ) 10 Hz,
CHMe2), 18.5 (d, J ) 11 Hz, CHMe2), 17.5 (s, CHMe2), 15.2 (d,
J ) 7 Hz, CHMe2). 31P{1H} NMR (C6D6): δ 28.6 (d, J ) 59
Hz), 26.6 (d, J ) 59 Hz). The selected undecoupled 13C NMR
1
afford 120 mg of product (31% yield). H NMR (C6D6): δ 7.00
3
4
3
(dd, 2H, J HH ) 8 Hz, J PH ) 4 Hz, Ar-H), 6.92 (d, 2H, J PH
)
3
4 Hz, Ar-H), 6.85 (d, 2H, J HH ) 8 Hz, Ar-H), 2.29 (m, 2H,
CHMe2), 2.23 (m, 2H, CHMe2), 2.11 (s, 6H, Ar-Me), 1.23 (dd,
6H, J PH ) 14 Hz, J HH ) 7 Hz, CHMe2), 1.14 (dd, 6H, J PH
3
3
3
)
16 Hz, 3J HH ) 7 Hz, CHMe2), 1.10 (dd, 6H, J PH ) 16 Hz, 3J HH
) 7 Hz, CHMe2), 1.00 (t, J PH ) 4 Hz, 9H, ZrMe3), 0.94 (dd,
6H, 3J PH ) 10 Hz, 3J HH ) 7 Hz, CHMe2). 13C{1H} NMR (C6D6):
δ 160.7 (m), 132.9 (s), 132.3 (s), 127.9 (s), 121.0 (m), 120.7 (m),
51.7 (t, J PC ) 2 Hz, ZrMe3), 24.5 (br, CHMe2), 21.7 (dd, J ) 4
Hz, J ) 6 Hz, CHMe2), 21.1 (s, ArCH3), 20.1 (m, CHMe2), 19.9
(m, CHMe2), 18.8 (m, CHMe2), 17.3 (s, CHMe2). 31P{1H} NMR
3
(C6D6): δ 13.0 (s). 1H{31P} NMR (C6D6): δ 7.01 (d, 2H, 3J HH
)
3
8 Hz, Ar-H), 6.92 (br, 2H, Ar-H), 6.85 (dd, 2H, J HH ) 8 Hz,
4J HH ) 2 Hz, Ar-H), 2.28 (m, 2H, CHMe2), 2.21 (m, 2H,
3
CHMe2), 2.11 (s, 6H, Ar-CH3), 1.23 (d, 6H, J HH ) 7 Hz,
3
3
CHMe2), 1.14 (d, 6H, J HH ) 7 Hz, CHMe2), 1.10 (d, 6H, J HH
) 7 Hz, CHMe2), 0.98 (s, 9H, ZrMe3), 0.95 (d, 6H, 3J HH ) 7 Hz,
CHMe2). Anal. Calcd (Found) for C29H49NP2Zr: C, 61.81
(61.60); H, 8.70 (8.87).
1
1
data follow: δ 230.7 (d, J CH ) 92 Hz, ZrCHPh), 60.3 (t, J CH
) 131 Hz, ZrCH2Ph). The selected 1H NMR data collected
while decoupling the 31P signal at 28.5 ppm follow: 2.62 (d,
1H, J ) 9 Hz, ZrCH2Ph), 1.25 (d, 3H, J ) 7 Hz, CHMe2), 1.19
(d, 3H, J ) 7 Hz, CHMe2), 1.14 (d, 3H, J ) 7 Hz, CHMe2),
1.08 (d, 3H, J ) 6 Hz, CHMe2), 0.94 (d, 3H, J ) 7 Hz, CHMe2),
0.86 (d, 3H, J ) 7 Hz, CHMe2), 0.77 (d, 3H, J ) 7 Hz, CHMe2),
0.67 (d, 3H, J ) 7 Hz, CHMe2). Anal. Calcd (Found) for
(P NP )Zr (CH2P h )3 (4b). To a cooled (-35 °C) ether slurry
of 3 (27.3 mg, 0.043 mmol) was added 22.6 µL of dioxane,
followed by Mg(CH2Ph)2‚2THF (21.9 mg, 0.064 mmol). The red
color of the slurry became orange in 2 min. The volatiles were
then removed in vacuo. The NMR sample was prepared by
dissolving the residue in C6D6 and then filtering. The 31P NMR
analysis showed that 4b, (PNP)MgCl, and 5b were present in
C
40H53NP2Zr: C, 68.53 (68.49); H, 7.62 (7.76).
1
3
a 85:10:5 ratio. H NMR (C6D6): δ 7.12 (d, 4H, J HH ) 8 Hz,
(P NP )Zr (dCHC6H4Me)(CH2C6H4Me) (5c). A solution of
3
Ar-H), 7.01-6.90 (m, 17H, Ar-H), 2.82 (d, 3H, J HH ) 10 Hz,
ZrCH2Ph), 2.71 (d, 3H, J HH ) 10 Hz, ZrCH2Ph), 2.12 (s, 6H,
4-methylbenzylmagnesium chloride in THF (0.5 M, 4.77 mL,
2.40 mmol) was added dropwise to 3 (498 mg, 0.800 mmol)
suspended in 40 mL of ether with 0.42 mL of dioxane. The
workup procedure was similar to that for 5b. Yield: 286 mg
(50%). 1H NMR (C6D6): δ 7.11 (s, 1H, ZrCHC6H4Me), 7.10 (dd,
1H, J ) 7 Hz, J ) 4 Hz, Ar-H), 7.02 (dd, 1H, J ) 8 Hz, J ) 4
Hz, Ar-H), 6.98-6.91 (m, 2H, Ar-H), 6.90-6.80 (m, 8H, Ar-
3
Ar-Me), 2.13-2.00 (m, 2H, CHMe2), 1.04 (dd, 6H, J PH) 15 Hz,
3J HH ) 7 Hz, CHMe2), 0.96 (m, 12H, CHMe2), 0.87 (m, 6H,
CHMe2). 13C{1H} NMR (C6D6): δ 149 (s), 132.5 (d, J ) 1 Hz),
129.0 (s), 128.7 (s), 128.5 (s), 127.8 (s), 121.6 (s), 78.0 (s,
ZrCH2Ph), 25.6 (s, CHMe2), 25.1 (s, CHMe2), 22.3 (s, CHMe2),
20.8 (s, Ar-Me), 18.9 (s, CHMe2), 18.8 (s, CHMe2), 18.4 (s,
CHMe2). 31P{1H} NMR (C6D6): δ 12.9 (s).
1
H), 6.68 (d, 2H, J ) 8 Hz, Ar-H), 3.07(d, 1H, J HH ) 9 Hz,
1
ZrCH2C6H4Me), 2.60 (dd, 1H, J ) 4 Hz, J HH ) 9 Hz,
After 12 h, compound 4b was fully transferred into 5b. The
resulting mixture contains (by 31P NMR) compound 5b (85%),
(PNP)MgCl (10%), and traces of unidentified compounds.
Obser va tion of 4c by NMR. To a cooled (-35 °C) ether
slurry of 3 (53.6 mg, 0.084 mmol) was added 20 µL of dioxane,
followed by 4-methylbenzylmagnesium chloride (0.52 mL, 0.26
mmol, 0.5 M in THF). The red color of the slurry became
orange in 2 min. The volatiles were then removed in vacuo.
The NMR sample was prepared by dissolving the residue in
cold pentane (-35 °C), then pumping pentane solution to
dryness and redissolving in C6D6. The 31P NMR analysis
ZrCH2C6H4Me), 2.32 (m, 1H, CHMe2), 2.17 (s, 3H, Ar-Me), 2.15
(s, 3H, Ar-Me), 2.14(s, 3H, Ar-Me), 2.15-2.10 (m, 2H, CHMe2),
2.07(s, 3H, Ar-Me), 1.44(m, 1H, CHMe2), 1.28 (dd, 3H, J ) 7
Hz, J ) 15 Hz, CHMe2), 1.21 (dd, 3H, J ) 6 Hz, J ) 12 Hz,
CHMe2) 1.16 (dd, 3H, J ) 7 Hz, J ) 11 Hz, CHMe2), 1.13 (dd,
3H, J ) 7 Hz, J ) 14 Hz, CHMe2), 0.97 (dd, 3H, J ) 7 Hz, J
) 11 Hz, CHMe2), 0.89 (dd, 3H, J ) 7 Hz, J ) 16 Hz, CHMe2),
0.80 (dd, 3H, J ) 7 Hz, J ) 8 Hz, CHMe2), 0.68 (dd, 3H, J )
6 Hz, J ) 16 Hz, CHMe2). 13C{1H} NMR (C6D6): δ 230.1 (s,
ZrCHC6H4Me), 160.1 (dd, J ) 2 Hz, J ) 24 Hz), 158.7 (dd, J
) 3 Hz, J ) 20 Hz), 147.0 (s), 134.9(s), 133.0 (s), 132.5, 132.3

Chelate-Enforced Phosphine Coordination
Organometallics, Vol. 23, No. 20, 2004 4705
(s), 131.4 (s), 131.1 (s), 128.5 (d, J ) 4 Hz), 128.4 (s), 127.9 (s),
126.0 (s), 123.7 (d, J ) 22 Hz), 120.7 (d, J ) 7 Hz), 119.1 (d,
J ) 7 Hz), 116.3 (d, J ) 12 Hz), 59.1 (s, ZrCH2C6H4Me), 27.1
(d, J ) 9 Hz, CHMe2), 23.0 (d, J ) 6 Hz, CHMe2), 21.2 (d, J )
17 Hz, CHMe2), 21.0 (s, Ar-Me), 20.9 (d, J ) 10 Hz, CHMe2),
20.9 (s, Ar-Me), 20.8 (s, Ar-Me), 20.7 (s, Ar-Me), 20.6 (d, J ) 7
Hz, CHMe2), 19.7 (d, J ) 5 Hz, CHMe2), 19.4 (d, J ) 4 Hz,
CHMe2), 19.1 (d, J ) 10 Hz, CHMe2), 18.2 (d, J ) 11 Hz,
CHMe2), 17.7 (s, CHMe2), 15.3 (d, J ) 7 Hz, CHMe2). The
remaining CHMe2 signal is obscured by the Ar-Me resonances.
31P{1H} NMR (C6D6): δ 28.4 (d, J ) 58 Hz), 27.3 (d, J ) 58
Hz). The selected undecoupled 13C NMR data follow: δ 230.1
(d, J ) 92 Hz, ZrCHC6H4Me), 59.0 (t, J ) 132 Hz, ZrCH2C6-
J ) 7 Hz, CHMe2) 1.16 (d, 3H, J ) 7 Hz, CHMe2), 1.13 (d, 3H,
J ) 7 Hz, CHMe2), 0.97 (d, 3H, J ) 7 Hz, CHMe2), 0.89 (d,
3H, J ) 7 Hz, CHMe2), 0.80 (d, 3H, J ) 7 Hz, CHMe2), 0.68
(d, 3H, J ) 7 Hz, CHMe2). Anal. Calcd (Found) for C42H57
-
NP2Zr: C, 69.19 (68.98); H, 7.88 (7.95).
Ack n ow led gm en t. We are grateful to Brandeis
University for support of this research. We thank Sara
7
Kunz for assistance with Li NMR experiments.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails, characterization data, and crystallographic information.
This material is available via the Internet free of charge at
http://pubs.acs.org.
1
H4Me). The selected H NMR data collected while decoupling
the 31P signal at 28.3 ppm follow: 7.10 (d, 1H, J ) 7 Hz, Ar-
H), 7.02 (d, 1H, J ) 8 Hz, Ar-H), 2.60 (d, 1H, J ) 9 Hz,
ZrCH2Ph-p-Me), 1.28 (d, 3H, J ) 7 Hz, CHMe2), 1.23 (d, 3H,
OM049670U