Syntheses and Structures of Five-Coordinate Zirconium Alkyl Complexes Supported by Diketiminate Ligands

Article abstract of DOI:10.1021/om980950h

An alkane elimination reaction generates the diketiminate compound (TTP)Zr(CH₂Ph)₃ (1) from Zr(CH₂Ph)₄ and TTPH (TTPH = 2-p-tolylamino-4-p-tolylimino-2-pentene). The molecular structure of 1 was solved, and it shows a five-coordinate zirconium with three η¹-coordinated benzyl groups and an η²-bound TTP ligand. When 1 is heated to 45 °C in hydrocarbon solvents, toluene is eliminated and the orthometalated product 2 is formed. The molecular structure of 2 indicates η¹ and η² benzyl groups. The variable-temperature ¹H NMR (-78 to 50 °C) spectra exhibit a single benzyl resonance. The magnitude of ¹J_CH for the benzyl methylene resonance is consistent with a rapid exchange between η¹ and η² bonding modes in solution. Isotopic labeling experiments employing (PPP-d₁₀)Zr(CH₂Ph)₃-(3-d₁₀, PPP = 2-phenylamino-4-phenylimino-2-pentenato) support direct C-H activation through a four-centered transition state. Based on kinetic experiments, C-H activation is unimolecular, and the rate-limiting step exhibits a large kinetic isotope effect: k_H/k_D = 5.2-(5) at 65 °C. The thermal stability of alkyl complexes is improved by replacing the ortho protons with isopropyl groups. (DDP)ZrMe₃ (5) can be prepared from (DDP)ZrCl₃ via halide metathesis using MeLi (DDP = 2-(2,6-diisopropyl)phenylamino-4-(2,6-diisopropyl)phe-nylimino-2-pentenato). The thermal stability of 5 is greatly enhanced compared to those of 1 and 3.

Full text of DOI:10.1021/om980950h

Organometallics 1999, 18, 1693-1698
1693
Syn th eses a n d Str u ctu r es of F ive-Coor d in a te Zir con iu m
Alk yl Com p lexes Su p p or ted by Dik etim in a te Liga n d s
Baixin Qian, William J . Scanlon, IV, and Milton R. Smith, III*
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824
Douglas H. Motry
Department of Chemistry, Kent State University, Salem Campus, Salem, Ohio 44460-9412
Received November 25, 1998
An alkane elimination reaction generates the diketiminate compound (TTP)Zr(CH2Ph)3
(1) from Zr(CH2Ph)4 and TTPH (TTPH ) 2-p-tolylamino-4-p-tolylimino-2-pentene). The
molecular structure of 1 was solved, and it shows a five-coordinate zirconium with three
η1-coordinated benzyl groups and an η2-bound TTP ligand. When 1 is heated to 45 °C in
hydrocarbon solvents, toluene is eliminated and the orthometalated product 2 is formed.
The molecular structure of 2 indicates η1 and η2 benzyl groups. The variable-temperature
1H NMR (-78 to 50 °C) spectra exhibit a single benzyl resonance. The magnitude of 1J CH for
the benzyl methylene resonance is consistent with a rapid exchange between η1 and η2
bonding modes in solution. Isotopic labeling experiments employing (PPP-d10)Zr(CH2Ph)3-
(3-d10, PPP ) 2-phenylamino-4-phenylimino-2-pentenato) support direct C-H activation
through a four-centered transition state. Based on kinetic experiments, C-H activation is
unimolecular, and the rate-limiting step exhibits a large kinetic isotope effect: kH/kD ) 5.2-
(5) at 65 °C. The thermal stability of alkyl complexes is improved by replacing the ortho
protons with isopropyl groups. (DDP)ZrMe3 (5) can be prepared from (DDP)ZrCl3 via halide
metathesis using MeLi (DDP ) 2-(2,6-diisopropyl)phenylamino-4-(2,6-diisopropyl)phe-
nylimino-2-pentenato). The thermal stability of 5 is greatly enhanced compared to those of
1 and 3.
In tr od u ction
have recently appeared.12-18 In this paper we describe
synthesis, structure, and reactivity of five-coordinate Zr
alkyl complexes supported by â-diketiminate ligands.
In particular, ligand activation reactions are examined,
and an approach for their prevention is described.
The search for noncyclopentadienyl ligands in Zie-
gler-Natta catalysis has recently attracted considerable
attention. In this respect, nitrogen-based ligands have
been found to be particularly attractive in early and late
transition metal systems.1-5 Diketimines in their neu-
tral and uninegative forms are potentially useful ligands
for catalytic applications since they can be readily
prepared by condensation reactions of amines with 2,4-
Resu lts a n d Discu ssion
Alkyl migration to imine carbons of tetraazamacro-
cycles has been reported by J ordan and co-workers.19
This is a potential point of vulnerability for closely
related diketiminate compounds. Thus, our first goal in
group 4 alkyl systems was to prepare diketiminate alkyl
compounds and determine whether alkyl migrations
would pose similar problems. The diketimine 2-p-
tolylamino-4-p-tolylimino-2-pentene (TPPH) reacted
pentanedione.6-8 In addition to our own efforts in main-
9-11
group and early transition metal systems,
other
applications of â-diketimine and diketiminate ligands
* Corresponding author. E-mail: smithmil@pilot.msu.edu.
(1) For leading references describing late metal olefin polymerization
catalysts see: Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am.
Chem. Soc. 1998, 120, 4049-4050.
(2) For leading references describing early metal olefin polymeri-
zation catalysts see: Scollard, J . D.; McConville, D. H.; Vittal, J . J .;
Payne, N. C. J . Mol. Catal. A: Chem. 1998, 128, 201-214.
(3) Gibson, V. C.; Kimberley, B. S.; White, A. J . P.; Williams, D. J .;
Howard, P. J . Chem. Soc., Chem. Commun. 1998, 313-314.
(4) Black, D. G.; J ordan, R. F.; Rogers, R. D. Inorg. Chem. 1997, 36,
103-108.
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J .; Calabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514-
1516.
(13) Radzewich, C. E.; Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc.
1998, 120, 9384-9385.
(14) Rahim, M.; Taylor, N. J .; Xin, S.; Collins, S. Organometallics
1998, 17, 1315-1323.
(5) Scott, M. J .; Lippard, S. J . Organometallics 1998, 17, 1769-1773.
(6) Scheibe, G. Chem. Ber. 1923, 56, 137-148.
(15) Budzelaar, P. H. M.; de Gelder, R.; Gal, A. W. Organometallics
1998, 19, 4121-4123.
(7) Parks, J . E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408-1416.
(8) For a recent review of related macrocyclic ligands prepared by
amine condensations with 2,4-pentanedione see: Mountford, P. Chem.
Soc. Rev. 1998, 27, 105-115.
(9) Qian, B.; Ward, D. L.; Smith, M. R., III. Organometallics 1998,
17, 3070-3076.
(10) Qian, B.; Baek, S. W.; Smith, M. R., III. Polyhedron, in press.
(11) Kakaliou, L.; Scanlon, W. J ., IV; Qian, B.; Baek, S. W.; Smith,
M. R., III; Motry, D. H. Submitted for publication.
(16) Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J . Am. Chem. Soc.
1998, 120, 11018-11019.
(17) Hitchcock, P. B.; Lappert, M. F.; Layh, M. J . Chem. Soc., Chem.
Commun. 1998, 2179-2180.
(18) Kim, W.-K.; Fevola, M. J .; Liable-Sands, L. M.; Rheingold, A.
L.; Theopold, K. H. Organometallics 1998, 17, 4541-4543.
(19) Martin, A.; Uhrhammer, R.; Gardner, T. G.; J ordan, R. F.;
Rogers, R. D. Organometallics 1998, 17, 382-397.
10.1021/om980950h CCC: $18.00 © 1999 American Chemical Society
Publication on Web 04/09/1999

1694 Organometallics, Vol. 18, No. 9, 1999
Qian et al.
Ta ble 1. NMR Da ta for th e Ben zyl Gr ou p s (CH2P h )
in Com p ou n d s 1-4a
1
3
2
4
1H NMR
2.61
2.54b
2.14c
2.09c
1.66c
1.57c
13C NMR
75.62
122.2
75.4b
122.0
66.62
131.4
66.97
130.9
1J C-H (Hz)
a
NMR spectra were taken at room temperature in C6D6 and
reported in ppm; 1H NMR (500 MHz), 13C NMR (75 MHz). Ref
b
14. c Doublet, | J HH| ) 9.6 Hz.
2
smoothly with Zr(CH2Ph)4 to eliminate toluene, afford-
ing the diketiminate complex (TTP)Zr(CH2Ph)3 (1) in
1
78% yield (eq 1). The H and 13C{1H} NMR spectra for
(1)
F igu r e 1. Molecular structure of (TTP)Zr(CH2Ph)3 (1) with
atom-labeling scheme. Selected bond lengths (Å) and angles
(deg): Zr-N(2), 2.189(2); Zr-N(1), 2.205(2); Zr-C(20),
2.253(3); Zr-C(27), 2.304(3); Zr-C(34), 2.313(3); N(2)-Zr-
N(1), 76.51(8); N(2)-Zr-C(20), 111.35(11); N(1)-Zr-C(20),
112.51(10); N(2)-Zr-C(27), 84.79(9); N(1)-Zr-C(27),
133.30(9); C(20)-Zr-C(27), 114.13(11); N(2)-Zr-C(34),
139.09(10); N(1)-Zr-C(34), 81.81(10); C(20)-Zr-C(34),
108.90(12); C(27)-Zr-C(34), 85.48(11); C(21)-C(20)-Zr,
99.1(2); C(28)-C(27)-Zr, 117.6(2); C(35)-C(34)-Zr, 110.7-
(2).
compound 1 indicated one benzyl and symmetric ligand
environments, proving that alkyl migration to the TTP
1
imine carbon did not occur. The value of J C-H for the
benzyl methylene resonance is sensitive to the hapticity
1
of the benzyl group,20-22 and the J C-H value of 122.0
Hz (Table 1) is consistent with η1-coordination for the
benzyl ligands in compound 1. The spectroscopic data
provided little information regarding the coordination
geometry at Zr for compound 1 since the benzyl and TTP
ligand resonances did not decoalesce at low tempera-
ture.
close to that in (η5-C5H5)Zr(η1-CH2Ph)3 (2.299(8) Å).26
The Zr-C(20)-C(21) angle of 99.1(2)° is significantly
more acute than the corresponding angles for the basal
ligands (Zr-C(27)-C(28), 117.6(2)°; Zr-C(34)-C(35),
110.7(2)°). A similar ligation for benzyl groups in (η5-
C5H5)Zr(η1-CH2Ph)3 was described as intermediate be-
tween η1- and η2-coordination.26 In a related tribenzyl
Zr complex supported by a hindered aryloxide ligand,
The molecular structure of 1 was determined, and its
ORTEP diagram is shown in Figure 1 with selected bond
lengths and angles. The geometry at zirconium is best
described as square pyramidal with C(20) in apical and
C(27), C(34), N(1), and N(2) in basal positions. Although
the ligand set of compound 1 contains potential π-do-
nors, theoretical treatments predict square pyramidal
structures for five-coordinate d0 hydride and alkyl deriv-
atives, and a C4v structure is observed for TaMe5 in the
gas phase.23,24 The diketiminate ligand is η2-bound to
Zr, which contrasts structures of Zr{N(SiMe3)C(tBu)-
CHC(Ph)N(SiMe3)}Cl3 and (Cp)(PPP)ZrCl2 (PPP ) 2-phe-
nylamino-4-phenylimino-2-pentenato), where the diketim-
inate ligands bind η5 to the Zr centers.14,25 Substitution
of benzyl for chloride ligands should render the Zr center
in compound 1 less electrophilic. Thus, the stabilization
afforded by η5-coordination may be reduced relative to
the chloride complexes; however, the stabilization pro-
vided by η5-coordination has not been quantified, and
we have not determined whether steric factors could
also be responsible for the change in hapticity. The
benzyl ligands in compound 1 are η1-coordinated, and
the average Zr-C bond distance in 1 (2.290(5) Å) is very
one of the benzyl groups is η2-bound (Zr-C-Cipso
)
88.0(3)°).22 The increased benzyl hapticity for this
compound parallels the decreased hapticity of the sup-
porting ligand. The structure of compound 1 confirms
the predominant η1-coordination inferred from the
spectroscopic data for the benzyl groups.
Attempted preparation of (TTP)2Zr(CH2Ph)2 from
compound 1 and TTPH resulted in toluene elimination;
however, TTPH was not consumed. Independent ther-
molysis of 1 (45 °C, 48 h) confirmed that 1 eliminated
toluene, and the orthometalated compound (η3-MeC-
(NC7H6)CHC(N-p-Tol)Me)Zr(η2-CH2Ph)(η1-CH2Ph) (2)
was isolated in 68% yield (eq 2). Toluene loss was
(2)
(20) J ordan, R. F.; Lapointe, R. E.; Bajgur, C. S.; Echols, S. F.;
Willett, R. J . Am. Chem. Soc. 1987, 109, 4111-4113.
(21) J ordan, R. F.; Lapointe, R. E.; Baenziger, N.; Hinch, G. D.
Organometallics 1990, 9, 1539-1545.
(22) Latesky, S. L.; McMullen, A. K.; Niccolai, G. P.; Rothwell, I.
P.; Huffman, J . C. Organometallics 1985, 4, 902-908.
(23) Landis, C. R.; Kirman, T. K.; Root, D. M.; Cleveland, T. J . Am.
Chem. Soc. 1998, 120, 1842-1854.
1
confirmed by H NMR and GC-MS data. This reaction
is similar to an intramolecular alkane elimination
reported by Schrock and co-workers.27 Upon extended
(24) Pulham, C.; Haaland, A.; Hammel, A.; Rypdal, K.; Verne, H.
P.; Volden, H. V. Angew. Chem., Int. Ed. Engl. 1992, 31, 1464-1467.
(25) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J . Chem. Soc., Chem.
Commun. 1994, 2637-2638.
(26) Scholz, J .; Rehbaum, F.; Thiele, K.-H.; Goddard, R.; Betz, P.;
Kru¨ger, C. J . Organomet. Chem. 1993, 443, 93-99.
(27) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics
1996, 15, 562-569.

Five-Coordinate Zirconium Alkyl Complexes
Organometallics, Vol. 18, No. 9, 1999 1695
Sch em e 1
average of typical η1 (119 Hz) and η2 (145 Hz) values
(Table 1).21 This spectroscopic feature confirms that η2-
coordination is maintained in solution and supports
rapid exchange between η1- and η2-coordinated benzyl
groups in solution.
Two paths can be envisioned to account for the
conversion of 1 to 2 (Scheme 1). Path a involves
R-abstraction to form the zirconium benzylidene inter-
mediate A, followed by arene C-H activation to give 2.
Path b involves a direct σ-bond metathesis via the four-
centered transition state, B.
Paths a and b can be distinguished by isotopic labeling
experiments. Specifically, deuterium labeling at the
arene positions will give toluene-d0 and toluene-d1 for
paths a and b, respectively. Collins and co-workers
reported the synthesis of the related diketiminate
compound, (PPP)Zr(CH2Ph)3 (3, PPP ) 2-phenylamino-
4-phenylimino-2-pentenato).14 Since the desired isotopic
label is more conveniently introduced by preparing
PPPH-d10 from aniline-d5 and 2,4-pentanedione, we
have examined the thermolysis of 3. Compound 3 reacts
in analogous fashion to 1, affording the orthometalated
F igu r e 2. Molecular structure of (η3-MeC(NC7H6)CHC-
(N-p-Tol)Me)Zr(η2-CH2Ph)(η1-CH2Ph) (2) with atom-label-
ing scheme. Selected bond lengths (Å) and angles (deg):
Zr-N(1), 2.175(2); Zr-N(2), 2.253(2); Zr-C(13), 2.781(2);
Zr-C(14), 2.260(2); Zr-C(27), 2.288(2); Zr-C(20), 2.302-
(2); Zr-C(21), 2.584(2); N(1)-Zr-N(2), 77.91(6); N(1)-Zr-
C(14), 138.48(6); N(2)-Zr-C(14), 60.63(7); N(1)-Zr-C(27),
100.45(7); N(2)-Zr-C(27), 114.65(6); C(14)-Zr-C(27), 98.65-
(7); N(1)-Zr-C(20), 98.92(7); N(2)-Zr-C(20), 116.16(6);
C(27)-Zr-C(20), 128.25(7); N(1)-Zr-C(21), 113.00(6); N(2)-
Zr-C(21), 147.23(6); C(14)-Zr-C(21), 101.84(7); C(27)-
Zr-C(21), 94.32(6); C(20)-Zr-C(21), 34.13(6); C(28)-
C(27)-Zr, 99.64(11); C(21)-C(20)-Zr, 83.58(11); C(22)-
C(21)-Zr, 91.32(11).
1
analogue of 2, compound 4. H and 2H NMR indicate
that orthometalation of 3-d10 gives toluene-d1, predomi-
nantly (>95%).28 This observation excludes path a in
Scheme 1. Plots of ln{[3t]/[30]} vs time are linear, and
the slopes of these plots are concentration independent.
The rate constants for arene activation in 3-d0 and 3-d10
give kH/kD ) 5.2(5) at 65 °C. The kinetic data are
consistent with unimolecular, rate-limiting C-H activa-
tion via transition state B. The magnitude of the
primary kinetic isotope effect is slightly smaller than
that reported by Wolczanski and co-workers for toluene
loss from Zr(NHR)3(CH2Ph) and Zr(NDR)3(CH2Ph) (R
) SitBu3, kH/kD ) 7.1(6)).29,30
thermolysis at 90 °C, solutions of compound 2 darkened
1
and intensities of H NMR resonances for compound 2
diminished.
The 1H and 13C NMR data are consistent with
orthometalation in compound 2. The nonequivalence of
tolyl and pentene methyl groups indicates that the
symmetry of the TTP ligand has been broken, and
diastereotopic benzylic proton resonances are observed
2
at δ 2.14 and 1.58 ppm (| J HH| ) 9.6 Hz). The inferred
To prevent orthometalation, we attempted the syn-
thesis of the ortho-substituted compound (DDP)Zr(CH2-
Ph)3 from DPPH (DPPH ) 2-(2,6-diisopropyl)pheny-
lamino-4-(2,6-diisopropyl)phenylimino-2-pentene) and
orthometalation was crystallographically confirmed, and
the molecular structure of compound 2 with selected
bond distances and angles is shown in Figure 2. The
X-ray study establishes that the diketiminate ligand is
η3-bonded to Zr. One of the benzyl groups is η2-
coordinated (Zr-C(20), 2.302(2) Å; Zr-C(21), 2.584(2)
Å; Zr-C(20)-C(21), 83.58(11)°), while the other ap-
proaches η1-coordination (Zr-C(27), 2.288(2) Å; Zr‚‚‚
C(28), 2.928(2) Å; Zr-C(27)-C(28), 99.64(11)°).
(28) The 1H NMR spectrum of PhCH2D (500 MHz, C6D6) contained
2
a 1:1:1 triplet at δ 2.09 (| J H-D|) ) 2.0 Hz). This chemical shift matches
that of the compound independently prepared from PhCH2MgCl and
D2O. Also, when the reaction was monitored by 2H NMR (46 MHz) in
C6H6, a peak corresponding to PhCH2D at δ 2.06 was observed.
(29) Schaller, C. P.; Cummins, C. C.; Wolczanski, P. T. J . Am. Chem.
Soc. 1996, 118, 591-611.
Even at -80 °C, one benzyl environment is observed
(30) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schafer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203-219.
1
in compound 2 by H NMR. However, the value of 131
1
Hz for J CH in compound 2 is very near the weighted

1696 Organometallics, Vol. 18, No. 9, 1999
Qian et al.
F igu r e 4. Another view of (TTP)Zr(CH2Ph)3 (1) with three
phenyl groups removed from the benzyl groups for clarity.
The angle between the N(1), C(2), C(3), C(4), N(2) plane
and the square base C(27), C(34), N(1), N(2) is 67.7(3)°.
F igu r e 3. Molecular structure of (DDP)ZrMe3 (5) with
atom-labeling scheme. Selected bond lengths (Å) and angles
(deg): Zr-N(1), 2.2712(14); Zr-N(1A), 2.2712(14); Zr-C(4),
2.274(2); Zr-C(4A), 2.274(2); Zr-C(5), 2.237(3); C(5)-Zr-
N(1), 107.37(7); C(5)-Zr-N(1A), 107.37(7); N(1)-Zr-
N(1A), 81.72(7); C(5)-Zr-C(4), 107.75(9); N(1)-Zr-C(4),
87.71(6); N(1A)-Zr-C(4), 144.88(8); C(5)-Zr-C(4A), 107.75-
(9); N(1)-Zr-C(4A), 144.88(8); N(1A)-Zr-C(4A), 87.71(7);
C(4)-Zr-C(4A), 81.95(12).
pound 1. Furthermore, the diketiminate ligand back-
bones in compounds 1 and 5 have significantly different
orientations. In Figure 4, the phenyl rings of the benzyl
ligands in compound 1 have been removed, and the
molecule has the same orientation as compound 5 in
Figure 3. The least-squares plane defined by the TTP
ligand atoms N(1), N(2), C(2), C(3), and C(4) in com-
pound 1 forms an angle of 67.7(3)° with that of the least-
squares plane defined by the basal atoms N(1), N(2),
C(27), and C(34) (Figure 4). For compound 5, the
analogous least-squares plane defined by the DDP
ligand atoms N(1), N(1A), C(2), C(2A), and C(3) is nearly
parallel (7.0(3)°) to the least-squares plane defined by
the basal atoms C(4), C(4A), N(1), and N(1A). A closer
examination of the structure for compound 5 reveals
several contacts between Zr methyl and iPr methyl
groups that approach the van der Waals limit. When
the DDP backbone in compound 5 is constrained to the
TTP geometry in compound 1, severe steric interactions
are apparent. These are relieved only by distortion of
the DDP backbone. Thus, the differences in diketimi-
nate ligand orientations almost certainly have steric
origins.
Zr(CH2Ph)4. Zr(CH2Ph)4 did not react with DDPH at
room temperature, and at elevated temperatures Zr-
(CH2Ph)4 decomposed, leaving unreacted DDPH. Pre-
i
sumably, increased steric requirements of Pr groups
impose a substantial kinetic barrier on alkane elimina-
tion. Nonetheless, trialkyl compounds can be prepared
by halide substitution routes, and we have synthesized
(DDP)ZrMe3 (5) from Zr(DDP)Cl3 and MeLi (54% yield,
eq 3). The identity of 5 was established by 1H, 13C NMR,
(3)
and X-ray diffraction methods. 1H and 13C NMR spectra
indicate fluxional behavior, as a single Zr methyl
resonance is observed from -70 to 25 °C.
The molecular structure of 5 is shown in Figure 3.
The Zr center adopts a square pyramidal geometry with
a crystallographic mirror plane passing through Zr,
C(3), and C(5). As is commonly found in d0 square
pyramidal compounds, the apical Zr-C(5) distance in
compound 5 (2.237(3) Å) is shorter than the basal Zr-
C(4) distance (2.274(2) Å). The average Zr-C bond
distance in compound 5 (2.262(4) Å) is significantly
shorter than Zr-C distances in six- and eight-coordinate
methyl compounds.31-33 The Zr-N bonds in compound
5 (Zr-N(1), 2.2712(14) Å; Zr-N(1A), 2.2712(14) Å) are
comparable with those of compound 1 (Zr-N(1), 2.205-
(2) Å; 1 (Zr-N(2), 2.189(2) Å). However, the bite angle
for the diketiminate ligand in compound 5 is more
obtuse than in compound 1. This is reflected by compar-
ing N(1)-Zr-N(1A) ) 81.72(7)° and C(2)-C(3)-
C(2A) ) 129.5(2)° in compound 5 to N(1)-Zr-N(2) )
76.51(8)° and C(2)-C(3)-C(4) ) 124.2(3)° in com-
The thermal stability for 5 is greatly enhanced
relative to compounds 1 and 3. When solutions of
compound 5 are heated (70 °C, 12 h, C6D6), decomposi-
1
tion is not evident by H NMR. Significantly, we could
not prepare the TTP derivative, (TTP)ZrMe3, from
(TTP)ZrCl3 and MeLi.
Con clu sion s
Diketiminate ligands are compatible with zirconium
alkyl functionality. In contrast to tetraazamacrocyclic
systems, alkyl migration to imine carbons of diketimi-
nate ligands does not occur. Orthometalation of (TTP)-
Zr(CH2Ph)3 (1) proceeds through a four-centered tran-
sition state to give a bisbenzyl compound (2) and
toluene. When the ortho hydrogens of the imine aryl
groups are removed, stability of trialkyl derivatives is
enhanced. We are actively investigating reactivity of the
alkyl compounds reported in this paper.
(31) For the six-coordinate compound [Li(tmed)]2[ZrMe6], Zrav
)
2.38(2) Å (tmed ) N,N,N′N′-tetramethylethylenediamine).32 In the
eight-coordinate compound (dmpe)2ZrMe4, Zrav
) 2.440(11) Å
(dmpe ) 1,2-bis(dimethylphosphino)ethane).33
Exp er im en ta l Section
(32) Girolami, G. S.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse,
M. B. J . Chem. Soc., Dalton Trans. 1984, 2789-2794.
(33) Morse, P. M.; Girolami, G. S. J . Am. Chem. Soc. 1989, 111,
4114-4116.
Gen er a l Con sid er a tion s. All manipulations were carried
out using standard Schlenk techniques. Solvents were freshly

Five-Coordinate Zirconium Alkyl Complexes
Organometallics, Vol. 18, No. 9, 1999 1697
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t P a r a m eter s for Com p ou n d s 1, 2, a n d 5
1
2
5
formula
fw
C
40H42N2Zr
C33H34N2Zr
C32H50N2Zr
553.96
173(2)
0.710 73
orthorhombic
Pnma
641.98
173(2)
0.710 73
monoclinic
C2/c
549.84
173(2)
0.710 73
triclinic
P1h
temp/K
wavelength/Å
cryst syst
space group
Unit cell
a/Å
40.287(8)
9.191(2)
20.566(4)
10.167(2)
11.547(2)
13.192(3)
87.81(3)
72.59(3)
69.06(3)
14.4931(1)
21.8225(1)
9.9150(1)
b/Å
c/Å
R/deg
â/deg
117.27(3)
γ/deg
V/Å3
6769(2)
8
1.270
0.354
1376.0(5)
2
1.327
0.423
3135.87(3)
4
1.173
0.371
1184
Z
d
calc/Mg/m3
abs coeff/mm-1
F(000)
2728
572
cryst size
θ range/deg
index ranges
0.20 × 0.21 × 0.21
1.98-28.40
-53 e h e 39
-11 e k e 12
-25 e l e 26
19 559
7797 [R(int) ) 0.0504]
7796/0/556
1.000
0.2 × 0.2 × 0.25
1.62-28.32
-13 e h e 13
-15 e k e 14
-17 e l e 17
16 390
6494 [R(int) ) 0.0300]
6494/459/409
1.009
0.15× 0.15 × 0. 20
1.87-28.14
-19 e h e 19
-27 e k e 28
-12 e l e 13
34 464
3884 [R(int) ) 0.0340]
3884/0/163
1.025
no. of reflns collected
no. of ind reflections
no. of data/restraints/param
GOF on F2
final R [I > 2σ(I)]
R1 ) 0.0446
wR2 ) 0.0822
R1 ) 0.0811
wR2 ) 0.0939
0.345 and -0.635
R1 ) 0.0305
wR2 ) 0.0708
R1 ) 0.0416
wR2 ) 0.0741
0.265 and -0.444
R1 ) 0.0332
wR2 ) 0.1221
R1 ) 0.0455
wR2 ) 0.1315
0.497 and -0.680
R (all data)
largest diff peak and hole/e Å-3
distilled over sodium/benzophenone ketyl and were saturated
with nitrogen before use. Elemental analyses (C, H, N) were
performed on a Perkin-Elmer CHN 2400 Series II CHNS/O
analyzer at MSU. A Varian VXR-300 NMR spectrometer was
used to record 1H (299.96 MHz) and 13C (75.43 MHz) NMR
spectra unless noted otherwise, and chemical shifts were
referenced to the residual solvent resonances. C6D6 was dried
over activated 4-Å molecular sieves and vacuum-transferred
to a sodium-mirrored air-free flask. Uncorrected melting points
of crystalline samples in sealed capillaries (under an argon
atmosphere) are reported as ranges. The synthesis and
structural characterization of (DDP)ZrCl3 have been submitted
for publication.11
106.46, 66.62, 24.62, 24.23, 21.60, 20.90. Anal. Calcd for
C33H34N2Zr: C, 72.08; H, 6.23; N, 5.09. Found: C, 71.90; H,
6.46; N, 4.70.
(η3 -M e C (N C 6 H 4 )C H C (N P h )M e )Zr (η2 -C H 2 P h )(η1 -
CH2P h ) (4). In analogous fashion to the synthesis of compound
2, compound 4 was prepared from (PPP)ZrBz3 (3) in 51% yield
as an orange yellow: mp 135-137 °C (dec); 1H NMR (300 MHz,
C6D6) δ 7.82 (m, 1H), 7.14-6.76 (m, 17H), 6.40 (m, 1H), 5.21
(s, 1H), 2.09 (d, J ) 9.6 Hz, 2H), 2.08 (s, 3H), 1.57 (d, J ) 9.6
Hz, 2H), 1.52 (s, 3H); 13C{1H} NMR (75 MHz, C6H6) δ 186.64,
160.59, 159.44, 157.88, 142.19, 141.44, 137.84, 130.42, 130.02,
129.61, 129.17, 128.96, 127.34, 123.08, 121.77, 118.83, 106.50,
66.97, 24.66, 24.37. Anal. Calcd for C31H30N2Zr: C, 71.36; H,
5.80; N, 5.37. Found: C, 71.01; H, 5.53; N, 5.07.
(TTP )Zr (CH2P h )3 (1). A 20 mL toluene solution of TTPH
(1.97 g, 7.08 mmol) was added dropwise to a stirred solution
of Zr(CH2Ph)4 (3.21 g, 7.05 mmol) in 5 mL of toluene. The
reaction mixture was stirred for 8 h at room temperature in
the dark. The solvent volume was reduced under vacuum, and
the solution was placed in a -80 °C freezer to precipitate
(TTP)Zr(CH2Ph)3 as a yellow solid (3.55 g, 78%): mp 98-100
°C; 1H NMR (C6D6) δ 7.09 (m, 6H), 6.90 (m, 7H), 6.73 (m, 10H),
5.06 (s, 1H), 2.61 (s, 6H), 2.08 (s, 6H), 1.62 (s, 6H); 13C{1H}
NMR (C6D6) δ 160.58, 146.68, 143.52, 135.63, 130.02, 128.77,
127.65, 126.03, 121.84, 102.14, 75.62, 22.76, 20.84. Anal. Calcd
for C40H42N2Zr: C, 74.83; H, 6.59; N, 4.36. Found: C, 74.44;
H, 6.56; N, 4.60.
(η3-Me C(NC 7H 6)CH C(N-p -Tol)Me )Zr (η2-CH 2P h )(η1-
CH2P h ) (2). A 5 mL toluene solution of compound 1 (1.1 g,
1.7 mmol) was heated at 45 °C for 48 h. All volatile materials
were removed under vacuum. Orange-yellow crystals were
obtained by cooling a toluene/pentane (1:1) solution to -30 °C
(0.64 g, 68%): mp 140-142 °C (dec); 1H NMR (300 MHz, C6D6)
δ (7.80, m, 1H), 7.18-6.75 (m, 15H), 6.48 (m, 1H), 5.31 (s, 1H),
2.33 (s, 3H), 2.14 (d, J ) 9.6 Hz, 2H), 2.13 (s, 3H), 2.07 (s,
3H), 1.66 (d, J ) 9.6 Hz, 2H), 1.58 (s, 3H); 13C{1H} NMR (75
MHz, C6H6) δ 186.86, 159.11, 158.52, 141.80, 138.85, 137.45,
132.63, 130.44, 129.96, 129.84, 129.26, 128.17, 122.90, 118.71,
(DDP )Zr Me3 (5). At 0 °C, a 40 mL toluene solution of
(DDP)ZrCl3 (1.04 g, 1.7 mmol) was treated with ethereal LiMe
(4.0 mL, 1.3 M, 5.2 mmol). The solution was warmed to room
temperature and stirred for 5 h. The supernatant was sepa-
rated by filtration, and the solvent was removed under vacuum
to afford the crude compound. Pure compound 5 was isolated
as a colorless solid by recrystallization from a toluene/hexane
1
solution (0.51 g, 54%): mp 191-192 °C (dec); H NMR (300
MHz, C6D6) δ 7.12 (m, 6H), 4.96 (s, 1H), 3.24 (sept, J ) 6.9
Hz, 4H), 1.57 (s, 6H), 1.38 (d, J ) 6.9 Hz, 12H), 1.15 (d, J )
6.9 Hz, 12H), 0.73 (s, 9H); 13C{1H} NMR (75 MHz, C6H6) δ
166.51, 147.70, 141.75, 126.54, 124.42, 98.68, 56.74, 28.98,
28.89, 25.60, 24.73. Anal. Calcd for C32H50N2Zr: C, 69.38; H,
9.10; N, 5.05. Found: C, 69.25; H, 9.11; N, 5.25.
Kin etic Stu d ies. A typical procedure is described as
follows: In a glovebox, a 0.055 M solution of (PPP)ZrBz3 was
prepared by dissolving 20 mg of compound 3 in 0.60 mL of
C6D6. The solution was transferred to a J -Young NMR tube,
which was sealed. The tube was heated at 65 ( 0.5 °C in an
oil bath, and the reaction was quenched by plunging the tube
into an ice-bath at regular intervals. 1H NMR spectra (500
MHz) were recorded at room temperature. Since the aromatic
and alkyl resonances of 3 and 4 overlapped, the methine
resonances at δ 5.01 and δ 5.21 for the ligand backbone in 3

1698 Organometallics, Vol. 18, No. 9, 1999
Qian et al.
and 4, respectively, were monitored by NMR spectroscopy. The
reaction was monitored through three half-lives (t1/2 ) 52 min).
The plot of ln[3t] vs time was linear and gave kH ) 1.82 ×
10-4 s-1. When the concentration of 3 was halved ([30] ) 0.027
M), kH ) 1.74 × 10-4 s-1. For (PPP-d10)ZrBz3 ([ 3-d10] ) 0.027
M), kD ) 3.43 × 10-5 s-1. Thus the kinetic isotopic effect (kH/
kD) for loss of toluene in orthometalation was determined to
be 5.2(5) at 65 ( 0.5 °C.
X-ray quality crystals of (η3-MeC(NC7H6)CHC(N-p-Tol)Me)-
Zr(η2-CH2Ph)(η1-CH2Ph) (2) were grown from a toluene/
hexane solution at -30 °C. P1h was chosen as the space group
based on intensity statistics and successful refinement of the
structure. Cell parameters and refinement parameters are
listed in Table 2.
X-ray quality crystals of (DDP)ZrMe3 (5) were grown from
a toluene/hexane solution at -30 °C. A procedure similar to 1
was followed in collecting the data set. The Pnma was chosen
as the space group on the basis of systematic absences in
reflection data and successful refinement of the structure. Cell
parameters and refinement parameters are listed in Table 2.
X-r a y Str u ctu r e Deter m in a tion . All diffraction data were
collected using a Siemens SMART CCD diffractometer using
Mo KR radiation (λ ) 0.710 73 Å). Crystals were cooled to 173
K, and data were collected at 30 s per frame. Initial cell
parameters were calculated from three sets of 15 frames. All
data sets were collected over a hemisphere of reciprocal space.
Following integration using the SAINT program, final unit cell
parameters were obtained by least-squares refinement of
strong reflections. Absorption and decay corrections were
applied to the data by SADABS.34 The structures were solved
by direct methods and refined using the SHELXTL programs.35
Calculations were based on F2 data. All non-hydrogen atoms
were refined using anisotropic displacement parameters. All
hydrogen atoms were placed in calculated positions and refined
as riding models.
Ack n ow led gm en t. We are grateful for financial
support from an All University Research Initiation
Grant, the Center for the Fundamental Material Re-
search at MSU, and the National Science Foundation
(CHE-9817230). D.H.M. thanks the Research Council
of Kent State University for a research grant, and B.Q.
is grateful for a Carl H. Brubaker Endowed Fellowship.
The single-crystal X-ray equipment at MSU was sup-
ported by the National Science Foundation (CHE-
9634638), and the NMR equipment was provided by the
National Science Foundation (CHE-8800770) and the
National Institutes of Health (1-S10-RR04750-01).
X-ray quality crystals of (TTP)Zr(CH2Ph)3 (1) were grown
from a toluene solution at -30 °C. The choice of space group
C2/c over Cc was based on intensity statistics and successful
refinement of the structure in the C2/c space group. Cell
parameters and refinement parameters are listed in Table 2.
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
diffraction data. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM980950H
(34) SAINT and SADABS algorithms are contained in the software
package provided by Siemens Analytical X-ray Systems, Inc., Madison,
WI 53719, 1994-1996.
(35) Sheldrick, G. M. Crystallographic Computing 6; Oxford Uni-
versity Press: Oxford, U.K., 1993.