Triamidoamine Chemistry of Zirconium

Article abstract of DOI:10.1021/om990347e

The reactions of H₃(NN′₃) (NN′₃ = N(CH₂CH₂NSiBu^tMe₂)₃) with [Zr(CH₂Ph)₄] and [Zr-(NMe₂)₄] give the azazirconatranes [Zr(NN′₃)(CH₂Ph)] and [Zr(NN′₃)(NMe₂)], respectively. The reaction of [Li₃(NN′₃)(THF)₃] with [ZrCl₄(THF)₂] fails to yield [Zr(NN′₃)Cl] cleanly, but this compound is accessible by reaction of [Zr(NN′₃)(CH₂Ph)] with BCl₃ or of [Zr(NN′₃)(NMe₂)] with SiMe₃Cl. The molecular structures of [Zr(NN′₃)X] (X = CH₂Ph, NMe₂, Cl) show that the triamidoamine ligands adopt the usual 3-fold symmetric arrangement to give approximately trigonal-bipyramidal complexes. Attempted sublimation of [Zr(NN′₃)(CH₂Ph)] or its treatment with H₂ leads to clean conversion to the metallacyclic complex [Zr{N(CH₂-CH₂NSiBu^tMe₂) ₂CH₂CH₂NSiBu^tMeCH₂}] via deprotonation of a silylmethyl group and elimination of toluene. The molecular structure of this complex contrasts with those above in that the tert-butyldimethylsilyl groups adopt an upright conformation as a consequence of the presence of the metallacyclic unit. The dihedral angles N_ax-Zr-N_eq-Si are in the range 173.8-177.2°. Exposure of the metallacycle to D₂ gas leads to deuteration of all three Me₂Si groups via sequential deuteriolysis/σ-bond metathesis. The less acidic ^tBuSi and backbone CH₂ groups are unaffected.

Full text of DOI:10.1021/om990347e

4608
Organometallics 1999, 18, 4608-4613
Tr ia m id oa m in e Ch em istr y of Zir con iu m
Colin Morton, Ian J . Munslow, Christopher J . Sanders, Nathaniel W. Alcock, and
Peter Scott*
Department of Chemistry, University of Warwick, Coventry CV4 7AL, U.K.
Received May 10, 1999
The reactions of H3(NN′3) (NN′3 ) N(CH2CH2NSiButMe2)3) with [Zr(CH2Ph)4] and [Zr-
(NMe2)4] give the azazirconatranes [Zr(NN′3)(CH2Ph)] and [Zr(NN′3)(NMe2)], respectively.
The reaction of [Li3(NN′3)(THF)3] with [ZrCl4(THF)2] fails to yield [Zr(NN′3)Cl] cleanly, but
this compound is accessible by reaction of [Zr(NN′3)(CH2Ph)] with BCl3 or of [Zr(NN′3)(NMe2)]
with SiMe3Cl. The molecular structures of [Zr(NN′3)X] (X ) CH2Ph, NMe2, Cl) show that
the triamidoamine ligands adopt the usual 3-fold symmetric arrangement to give ap-
proximately trigonal-bipyramidal complexes. Attempted sublimation of [Zr(NN′3)(CH2Ph)]
or its treatment with H2 leads to clean conversion to the metallacyclic complex [Zr{N(CH2-
CH2NSiButMe2)2CH2CH2NSiButMeCH2}] via deprotonation of a silylmethyl group and
elimination of toluene. The molecular structure of this complex contrasts with those above
in that the tert-butyldimethylsilyl groups adopt an upright conformation as a consequence
of the presence of the metallacyclic unit. The dihedral angles Nax-Zr-Neq-Si are in the
range 173.8-177.2°. Exposure of the metallacycle to D2 gas leads to deuteration of all three
t
Me2Si groups via sequential deuteriolysis/σ-bond metathesis. The less acidic BuSi and
backbone CH2 groups are unaffected.
In tr od u ction
paper we show that the SiButMe2-substituted ligand can
be successfully applied to the synthesis of triamido-
amine complexes of zirconium.
While triamidoamine [N(CH2CH2NR)3]3- ligand chem-
istry is well-developed for most of the early transition
metals,1 complexes of the later group 4 elements Zr and
Hf are limited to those of the type [M(NR′2){N(CH2CH2-
NR)3}].2 Titanium triamidoamines have been reported
by Verkade,3 Schrock,4 and Gade;5 the last author has
also reported closely related triamide complexes (vide
infra).6 We have recently found that 3-fold symmetric
complexes of metals with large van der Waals radii such
as the lanthanides7 and actinides8 can be isolated by
using the triamidoamine ligand with the substituent R
) SiButMe2 (henceforth NN′3).9 Use of the ligand R )
SiMe3, on the other hand, is either unsuccessful or leads
to complexes with unsymmetrical structures.10 In this
Exp er im en ta l Section
All manipulations were carried out under an inert atmo-
sphere of argon either using standard Schlenk techniques or
in an MBraun drybox. Sublimation was performed by oven
heating ((1 °C) of the material under study contained in one
end of a horizontal glass tube, dynamic vacuum in the system
being maintained by a turbomolecular pumping system pro-
tected by a wide-bore liquid-nitrogen-cooled trap. NMR samples
were made up in the drybox, and the sample tubes were sealed
in vacuo or using Young type concentric stopcocks. Pentane
was predried over sodium wire and then distilled over sodium-
potassium alloy under an atmosphere of dinitrogen. Deuter-
ated solvents were dried by refluxing over molten potassium
in vacuo and were then distilled trap-to-trap, also in vacuo.
NMR spectra were recorded at ca. 295 K on Bruker AC-250,
AC-400, or DMX-300 spectrometers and the spectra referenced
internally using residual protio solvent resonances relative to
tetramethylsilane (δ 0 ppm). EI mass spectra were obtained
on a VG Autospec mass spectrometer. Elemental analyses were
performed by Warwick Analytical Services. BCl3 and SiMe3Cl
were purchased from Aldrich Chemical Co. Ltd., while H2
(grade 6.0, 99.999%) was purchased from Air Products.
[Zr(CH2Ph)4]11 and [Zr(NMe2)4]12 were synthesized by litera-
ture methods.
(1) Schrock, R. R. Acc. Chem. Res. 1997, 30, 99.
(2) Duan, Z. B.; Naiini, A. A.; Lee, J .-H.; Verkade, J . G. Inorg. Chem.
1995, 34, 5477.
(3) (a) Duan, Z. B.; Verkade, J . G. Inorg. Chem. 1996, 35, 5325. (b)
Duan, Z. B.; Verkade, J . G. Inorg. Chem. 1995, 34, 4311.
(4) (a) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Organometallics
1992, 11, 1452. (b) Schrock, R. R.; Cummins, C. C.; Wilhelm, T.; Lin,
S.; Reid, S. M.; Kol, M.; Davis, W. M. Organometallics 1996, 15, 1470.
(5) Schubart, M.; O’Dwyer, L.; Gade, L. H.; Wan-Sheung, L.;
McPartlin, M. Inorg. Chem. 1994, 33, 3893.
(6) (a) Friedrich, S.; Gade, L. H.; Li, W. S.; McPartlin, M. Chem.
Ber. 1996, 129, 1287. (b) Findeis, B.; Schubart, M.; Gade, L. H.; Mo¨ller,
F.; Scowen, I.; McPartlin, M. J . Chem. Soc., Dalton Trans. 1996, 125.
(c) Friedrich, S.; Gade, L. H.; Scowen, I. J .; McPartlin, M. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1338. (d) Memmler, H.; Walsh, K.;
Gade, L. H.; Lauher, J . W. Inorg. Chem. 1995, 34, 4062. (e) Schubart,
M.; Findeis, B.; Gade, L. H.; Li, W. S.; McPartlin, M. Chem. Ber. 1995,
128, 329.
(7) Roussel, P.; Alcock, N. W.; Scott, P. Chem. Commun. 1998, 801.
(8) Roussel, P.; Alcock, N. W.; Boaretto, R.; Kingsley, A. J .; Munslow,
I. J .; Sanders, C. J .; Scott, P. Inorg. Chem. 1999, 38, 3651. Roussel,
P.; Hitchcock, P. B.; Tinker, N. D.; Scott, P. Chem. Commun. 1996,
2053. Roussel, P.; Scott, P. J . Am. Chem. Soc. 1998, 120, 1070.
(9) (a) Roussel, P.; Alcock, N. W.; Scott, P. Inorg. Chem. 1998, 37,
3435. (b) Duan, Z.; Verkade, J . G. Inorg. Chem. 1995, 34, 1576. (c)
Cummins, C. C.; Lee, J .; Schrock, R. R.; Davis, W. M. Angew. Chem.,
Int. Ed. Engl. 1992, 31, 1501.
[Zr (NN′3)(CH2P h )] (1). Pentane (30 cm3) was added to a
mixture of [H3(NN′3)]13,14 (0.27 g, 0.55 mmol) and [Zr(CH2Ph)4]
(10) (a) Scott, P.; Hitchcock, P. B. J . Chem. Soc., Dalton Trans. 1995,
603. (b) Scott, P.; Hitchcock, P. B. J . Chem. Soc., Chem. Commun. 1995,
579. (c) Roussel, P.; Hitchcock, P. B.; Tinker, N. D.; Scott, P. Inorg.
Chem. 1997, 36, 5716.
(11) Zucchini, U.; Albizatti, E.; Gianni, U. J . Organomet. Chem.
1971, 26, 357.
(12) Bradley, D. C.; Thomas, I. M. J . Chem. Soc. 1960, 3857.
(13) Roussel, P.; Alcock, N. W.; Scott, P. Inorg. Chem. 1998, 37, 3435.
(14) Cummins, C. C.; Lee, J .; Schrock, R. R.; Davis, W. M. Angew.
Chem., Int. Ed. Engl. 1992, 31, 1501.
10.1021/om990347e CCC: $18.00 © 1999 American Chemical Society
Publication on Web 10/01/1999

Triamidoamine Chemistry of Zirconium
Organometallics, Vol. 18, No. 22, 1999 4609
Sch em e 1. Syn th esis of th e Com p lexes 1-4
(0.25 g, 0.55 mmol) at room temperature. The Schlenk vessel
was wrapped in aluminum foil, and the solution was stirred
at ambient temperature for 3 days. After filtration, the pale
orange solution was concentrated by evaporation in vacuo and
cooled to -30 °C to afford colorless crystals (0.33 g, 90%).
Anal. Calcd for C31H64N4Si3Zr: C, 55.83; H, 9.68; N, 8.41.
Found: C, 54.18; H, 9.47; N, 8.14. 1H NMR (293 K, d6-
benzene): δ 7.36 (m, 2H, Ph), 7.28 (m, 2H, Ph), 6.92 (m, 1H,
Ph), 3.32 (t, 6H, CH2), 2.63 (s, 2H, CH2Ph), 2.21 (t, 6H, CH2),
1.04 (s, 27H, But), 0.33 (s, 18H, Me2Si). 13C{1H} NMR (293 K,
d6-benzene): δ 150.99 (s, Ph), 125.94 (s, Ph), 120.11 (s, Ph),
63.95 (s, CH2Ph), 63.35 (s, CH2), 48.15 (s, CH2), 27.12 (s, Me3C),
20.72 (s, Me3C), -3.59 (s, Me2Si). MS (EI): m/z 575 (28%, M+-
CH2Ph), 536 (57%, M+- SiMe2But - Me), 517 (55%, M+ - CH2-
Ph - But).
[Zr (NN′3)(NMe2)] (2). Pentane (30 cm3) was added to a
mixture of [H3(NN′3)] (0.91 g, 1.87 mmol) and [Zr(NMe2)4] (0.5
g, 1.87 mmol) at room temperature. The solution was stirred
at ambient temperature for 3 days with periodic evacuation
of the vessel. After filtration, the pale orange solution was
concentrated and cooled to -30 °C, which on standing over-
night afforded colorless crystals (1.01 g, 87%). NMR spectro-
scopic data were in accord with those of the original report.2
[Zr (NN′3)Cl] (3). Meth od A. Boron trichloride (0.45 cm3,
1 M solution in hexanes, 1 equiv) was added to a solution of 1
(0.30 g, 0.45 mmol) in pentane (10 cm3) at -78 °C. The mixture
was stirred and warmed to room temperature to give a cloudy
white solution. After evaporation of volatiles, the residue was
extracted with warm pentane (2 × 20 cm3), filtered, and
evaporated under reduced pressure to give a white solid (0.14
g, 51%).
Meth od B. Chlorotrimethylsilane (1.07 g, 9.90 mmol) was
added to a solution of 2 (1.15 g, 1.80 mmol) in toluene (10 cm3).
After the mixture was refluxed for 3 days, all volatiles were
removed under reduced pressure. The residue was sublimated
at 180 °C and 10-6 mbar to give a colorless crystalline solid
(0.93 g, 85%).
Anal. Calcd for C24H57ClN4Si3Zr: C, 47.05; H, 9.38; N, 9.14.
Found: C, 46.01; H, 9.32; N, 9.15. 1H NMR (293 K, d6-
benzene): δ 3.32 (t, 6H, CH2), 2.26 (t, 6H, CH2), 1.13 (s, 27H,
But), 0.37 (s, 18H, Me2Si). 13C{1H} NMR (293 K, d6-benzene):
δ 63.67 (s, CH2) 47.88 (s, CH2), 27.00 (s, Me3C), 20.93 (s, Me3C).
MS (EI): m/z 611 (12%, M+), 596 (63%, M+ - Me), 576 (28%,
M+ - Cl), 554 (95%, M+ - But).
[Zr (bitNN′3)] (4). Meth od A. Sublimation of 1 (0.50 g, 0.87
mmol) at 200 °C and 10-6 mbar gave a colorless crystalline
solid (0.45 g, 96%) which was recrystallized from pentane at
-30 °C.
Meth od B. Hydrogen was added to an NMR tube containing
a solution of 1 in d6-benzene. The tube was shaken at room
temperature for 24 h. 1H NMR spectroscopy indicated es-
sentially quantitative conversion.
SHELXS15 with additional light atoms found by Fourier
methods. Hydrogen atoms were added at calculated positions
and refined using a riding model with freely rotating methyl
groups. Anisotropic displacement parameters were used for
all non-H atoms; H atoms were given isotropic displacement
parameters Uiso(H) ) 1.2Ueq(C) or 1.5Ueq(C) for methyl groups.
The structures were refined using SHELXL 96.16 In the
structure of 3 the tert-butyl group at Si(3) shows resolved
disorder with two positions of half-occupancy. Correspondingly,
Si(3) itself, the methyl groups at C(19) and C(20), and the
backbone methylene groups at C(5) and C(6) have relatively
large thermal ellipsoids but these were not modeled with
alternative positions. For 4 the C atoms of a pentane molecule
in the lattice was modeled at half-occupancy and the absolute
structure of the individual crystal chosen was checked by
refinement of the ∆F′′ multiplier.
Resu lts a n d Discu ssion
Anal. Calcd for C24H56N4Si3Zr: C, 50.03; H, 9.80; N, 9.72.
Found: C, 49.98; H, 9.79; N, 9.78. 1H NMR (293 K, d6-
benzene): δ 3.68 (m, 2H, CH2), 3.23 (m, 4H, CH2), 2.31 (m,
6H, CH2), 1.23 (s, 9H, But), 1.04 (s, 18H, But), 0.49 (s, 3H,
MeSi), 0.43 (s, 3H, MeSi), 0.42 (s, 3H, MeSi), 0.30 (s, 3H, MeSi),
0.29 (d, 1H, CH2Si), 0.16 (d, 1H, CH2Si), 0.15 (s, 3H, MeSi).
13C{1H} NMR (293 K, d6-benzene): δ 57.49 (s, CH2), 57.14 (s,
CH2), 56.39 (s, CH2), 50.59 (s, CH2), 47.29 (s, CH2), 47.21 (s,
CH2), 28.67 (s, CH2Si), 27.22 (s, Me3C), 27.15 (s, Me3C), 27.01
(s, Me3C), 20.18 (s, Me3C), 20.04 (s, Me3C), 19.77 (s, Me3C),
-3.13 (s, Me2Si), -3.83 (s, Me2Si), -4.59 (s, Me2Si), -4.81 (s,
Me2Si), -4.97 (s, Me2Si). MS (EI): m/z 575 (96%, M+), 518
(93%, M+ - But).
Cr ysta llogr a p h y. Crystals were coated with inert oil and
transferred to the cold N2 gas stream on the diffractometer
(Siemens SMART three-circle with CCD area detector). Graph-
ite-monochromated Mo KR radiation (λ ) 0.710 73 Å) was
used. Absorption correction was performed by multiscan
(SADAB). The structures were solved by direct methods using
Syn th eses a n d Sp ectr oscop ic Ch a r a cter iza tion .
The pure triamine H3(NN′3) reacts smoothly with
[Zr(CH2Ph)4] in pentane to give the benzyl complex
[Zr(NN′3)(CH2Ph)] (1) in 90% isolated yield. (Scheme 1).
The ZrCH2 group in 1 gives rise to a singlet at δ 2.63
1
ppm in the H NMR spectrum and at 63.95 ppm in the
13C spectrum, as assigned by 13C-1H correlation spec-
troscopy.
Verkade has reported a range of group 4 amido
complexes, including [Zr(NN′3)(NMe2)] (2), which was
synthesized by refluxing H3(NN′3) with [Zr(NMe2)4] in
THF in the presence of catalytic (NH4)2SO4.2 We found
that the reaction in pentane is complete within 3 days
(15) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(16) Sheldrick, G. M. SHELX-96 (beta-test) (including SHELXS and
SHELXL), 1996.

4610 Organometallics, Vol. 18, No. 22, 1999
Morton et al.
Sch em e 2. Selective H/D Exch a n ge P r ocess for 4
F igu r e 1. Part of the 1H NMR spectrum of 4 in d8-toluene
measured (a) before and (b) after admission of D2 (1 atm).
The metallacyclic methylene group AB doublets are indi-
cated by arrows, and the peak marked “x” is due to an
impurity.
nearing complete deuteration. The remaining low-
intensity overlapping multiplets in (b) are due to
mixtures of isotopomers containing, for example, SiCHD2
groups. The deuteration process presumably occurs via
sequential deuteriolysis/metalation reactions as de-
picted in Scheme 2. The less acidic t-Bu and backbone
CH2 groups are not affected, as evidenced by integration
at room temperature with no added catalyst. Concen-
tration of the solvent gives large crystals of 2 directly.
Reaction of the trilithium compound [Li3(THF)3-
(NN′3)]9 with [ZrCl4(THF)2] gives a low yield of [Zr-
(NN′3)Cl] (3) that is inseparable from oily coproducts.
The complex is more efficiently synthesized by the
reaction of 1 with BCl3 or the reaction of 2 with SiMe3-
Cl in pentane. Colorless, crystalline 3 is best purified
by sublimation.
The reaction of 1 at ambient temperature with pure
hydrogen (1 atm) leads to clean metalation of one of the
relatively acidic SiMe groups, presumably via elimina-
tion of hydrogen from the unobserved hydrido species
[Zr(NN′3)H] (Scheme 2), to give the colorless zircona-
cycle [Zr(bitNN′3)] (4). By comparison, the equilibrium
conversion of II (X ) H) to its metallacycle by a similar
process occurs only slowly, at elevated temperatures.13
Also, while sublimation of 1 also leads to pure 4 with
elimination of toluene, no metallacycle is formed when
II (X ) Me) decomposes. The 13C NMR spectrum of 4
recorded in d6-benzene contains a total of 18 resonances,
indicating that the product is chiral; the metallacyclic
Si atom is stereogenic.17 Of these, 17 resonances are
assigned to methyl and tert-butyl groups or methylene
groups in the ligand backbone. A resonance at 28.67
ppm, assigned to the Si-CH2-Zr group, correlates in
the 1H NMR spectrum with a pair of AB doublets at
apparent chemical shifts 0.29 and 0.16 ppm.
1
of the H NMR spectrum.
Molecu la r Str u ctu r es. Single crystals of the com-
pounds 1, 2, and 4 were readily grown by slow cooling
of saturated solutions of the pure compounds in pentane.
Crystals of 3 were grown by heating an evacuated and
sealed tube of the presublimed material to 120 °C for a
few days. The molecular structures were determined by
X-ray crystallography (Table 1).
The molecular structure of 1 is shown in Figure 2
along with selected bond lengths and angles. It is
instructional to compare the structure of this compound
with that of Verkade’s trimethylsilyl-substituted aza-
hafnatrane I,2 Schrock’s range of molybdenum com-
plexes II19 and Gade’s tri(amidosilyl)silane of zirconium
III.6b The triamidoamine ligand in 1 is disposed with
All CH groups in Andersen’s uranacycle [U{N-
(SiMe3)2}2{N(SiMe3)(CH2SiMe2)}] are deuterated on
exposure of the complex to D2.18 Under similar condi-
tions (d8-toluene at ambient temperature) addition of
dry D2 to 4 leads to deuteration of all SiMe2 groups and
the metallacyclic CH2 group. Figure 1 shows the 1H
NMR spectrum due to (a) the five inequivalent silyl
methyl groups and the metallacyclic CH2 group of 4 and
(b) the same region after exposure to D2 for 2 h, i.e.,
(17) If 3 had dimerized in solution via Zr-C σ-bond metathesis (in
order perhaps to relieve metallacycle ring strain), we would expect to
see evidence in the NMR spectra for the presence of diastereomeric
pairs (i.e. 36 13C resonances).
(18) Simpson, S. J .; Turner, H. W.; Andersen, R. A. Inorg. Chem.
1981, 20, 2991.
approximate 3-fold symmetry about the metal atom, as
(19) Schrock, R. R.; Seidel, S. W.; Mo¨sch-Zanetti, N. C.; Shih, K.-Y.;
O’Donoghue, M. B.; Davis, W. M.; Reiff, W. M. J . Am. Chem. Soc. 1997,
119, 11876.

Triamidoamine Chemistry of Zirconium
Organometallics, Vol. 18, No. 22, 1999 4611
Ta ble 1. Exp er im en ta l Da ta for th e X-r a y Diffr a ction Stu d ies of 1-4
1
2
3
4
mol formula
fwt
C
31H64N4Si3Zr
C26H63N5Si3Zr
621.30
C24H57ClN4Si3Zr
612.68
C26.5H56N4Si3Zr
606.24
668.35
cryst syst
space group
a/Å
b/Å
c/Å
monoclinic
P21/n
12.0082(15)
18.663(3)
18.131(3)
triclinic
P1h
9.69980(10)
13.1685(3)
15.2304(4)
106.48
103.5540(10)
95.8210(10)
1783.89(6)
2
monoclinic
P21/n
12.4097(2)
15.66210(10)
18.2802(2)
triclinic
P1h
12.8111(2)
13.2448(2)
13.2748(2)
60.3260(10)
67.9120(10)
86.0950(10)
1793.84(5)
2
R/deg
â/deg
108.883(5)
92.74
γ/deg
cell vol/Å3
Z
3844.7(9)
4
1.155
3548.91(7)
4
1.147
D
calcd/(Mg/m3)
1.157
1.122
F(000)
1440
0.403
160(2)
672
0.430
180(2)
1312
0.504
180(2)
650
0.426
180(2)
µ/mm-1
temp/K
cryst size/mm
0.4 × 0.4 × 0.4
0.4 × 0.1 × 0.07
0.5 × 0.2 × 0.1
0.4 × 0.3 × 0.2
θmax/deg
28.54
28.34
28.47
22.50
total no. of rflns
22792
10552
20875
7279
no. of indep rflns
no. of significant rflns, I > 2σ(I)
no. of params
8927 (R(int) ) 0.0268)
7706 (R(int) ) 0.0275)
8332 (R(int) ) 0.0493)
4650 (R(int) ) 0.0201)
6868
5321
3918
367
333
353
328
T
max, Tmin
0.93, 0.78
1.021
0.382, -0.611
0.0316, 0.0784
0.93, 0.77
0.907
0.537, -0.852
0.0450, 0.0929
0.928, 0.769
1.153
0.567, -7.30
0.0595, 0.0935
0.928, 0.707
1.049
0.737, -0.749
0.0527, 0.1215
GOF on F2
∆Fmax,min/(e Å-3) (near U)
R1, wR2 (I > 2σ(I))
F igu r e 3. Thermal ellipsoid plot of the molecular structure
of [Zr(NN′3)(NMe2)] (2) (non-hydrogen atoms) oriented
along the apical N(2)-Zr axis. Selected distances (Å) and
angles (deg): Zr(1)-N(5) ) 2.063(2), Zr(1)-N(1) ) 2.096-
(2), Zr(1)-N(4) ) 2.124(3), Zr(1)-N(3) ) 2.130(2), Zr(1)-
N(2) ) 2.509(2); N(5)-Zr(1)-N(1) ) 109.75(9), N(5)-Zr(1)-
N(4) ) 99.96(10), N(1)-Zr(1)-N(4) ) 114.44(10), N(5)-
Zr(1)-N(3) ) 107.11(10), N(1)-Zr(1)-N(3) ) 108.30(9),
N(4)-Zr(1)-N(3) ) 116.62(10), N(5)-Zr(1)-N(2) ) 173.21-
(10), N(1)-Zr(1)-N(2) ) 74.75(8), N(4)-Zr(1)-N(2) )
73.36(9), N(3)-Zr(1)-N(2) ) 75.53(9).
F igu r e 2. Thermal ellipsoid plot of the molecular structure
of [Zr(NN′3)(CH2Ph)] (1) (non-hydrogen atoms). Selected
distances (Å) and angles (deg): Zr(1)-N(3) ) 2.0727(15),
Zr(1)-N(2) ) 2.0796(15), Zr(1)-N(1) ) 2.0885(16), Zr(1)-
C(25) ) 2.3243(18), Zr(1)-N(4) ) 2.5484(15); N(3)-Zr(1)-
N(2) ) 112.75(6), N(3)-Zr(1)-N(1) ) 112.55(6), N(2)-
Zr(1)-N(1) ) 111.12(6), N(3)-Zr(1)-C(25) ) 112.99(6),
N(2)-Zr(1)-C(25) ) 104.12(6), N(1)-Zr(1)-C(25) ) 102.57-
(6), N(3)-Zr(1)-N(4) ) 73.40(6), N(2)-Zr(1)-N(4) ) 73.59-
(6), N(1)-Zr(1)-N(4) ) 73.07(6), C(25)-Zr(1)-N(4) )
173.50(6).
atom rather than surround the apical coordination site
as in, for example, II (X ) Cl). The equatorial amido
N-Zr distances of 2.073(2)-2.089(2) Å are, as expected,
similar to those in I (ca. 2.08 Å) and III (2.03-2.12 Å)
but slightly longer than those in II (1.98-2.01 Å). The
amino Mo-Nax distances in II are strongly influenced
by steric compression in the apical coordination site and
range from 2.171(9) Å (X ) OTf) to 2.422(10) (X )
cyclohexyl). Hence, the Zr-N(4) distance of 2.5484(15)
Å in 1 is not unduly long compared to that of 2.488(6)
in I and II. The maximum deviation of any atom from
the least-squares planes of the amidozirconium frag-
ments, e.g. Si(1),N(1),C(2),Zr(1), is ca. 0.08 Å. The
dihedral angles Nax-Zr-Neq-Si of 128.8-133.1° are
similar to those observed in uranium complexes of NN′3
(125-140°)8 but are smaller than those in I (131-154°)
and are at the lower end of the range observed for II,
where the angle approaches 180° for small ligands X.
The effect of this on the structure of 1 is that the SiMe2-
But groups encircle the equatorial plane of the zirconium

4612 Organometallics, Vol. 18, No. 22, 1999
Morton et al.
F igu r e 5. Thermal ellipsoid plot of the molecular structure
of the metallacycle [Zr(bitNN′3)] (4) (non-hydrogen atoms).
Selected distances (Å) and angles (deg): Zr(1)-N(3) )
2.054(5), Zr(1)-N(2) ) 2.062(5), Zr(1)-N(1) ) 2.077(4), Zr-
(1)-N(4) ) 2.399(4), Zr(1)-C(14) ) 2.613(11); N(3)-Zr(1)-
N(2) ) 113.37(19), N(3)-Zr(1)-N(1) ) 112.7(2), N(2)-
Zr(1)-N(1) ) 113.7(2), N(3)-Zr(1)-N(4) ) 75.17(17), N(2)-
Zr(1)-N(4) ) 72.64(17), N(1)-Zr(1)-N(4) ) 76.13(15),
N(3)-Zr(1)-C(14) ) 123.8(2), N(2)-Zr(1)-C(14) ) 67.8-
(2), N(1)-Zr(1)-C(14) ) 117.1(2), N(4)-Zr(1)-C(14) )
140.34(18).
F igu r e 4. Thermal ellipsoid plot of the molecular structure
of [Zr(NN′3)Cl] (3) (non-hydrogen atoms). Selected distances
(Å) and angles (deg): Zr(1)-N(1) ) 2.064(3), Zr(1)-N(2)
) 2.066(3), Zr(1)-N(3) ) 2.066(3), Zr(1)-Cl(1) ) 2.4231-
(11), Zr(1)-N(4) ) 2.444(3); N(1)-Zr(1)-N(2) ) 112.84(11),
N(1)-Zr(1)-N(3) ) 112.59(12), N(2)-Zr(1)-N(3) ) 114.94-
(12), N(1)-Zr(1)-Cl(1) ) 106.50(9), N(2)-Zr(1)-Cl(1) )
104.42(9), N(3)-Zr(1)-Cl(1) ) 104.42(12), N(1)-Zr(1)-N(4)
) 75.17(11), N(2)-Zr(1)-N(4) ) 75.30(11), N(3)-Zr(1)-
N(4) ) 74.22(14), Cl(1)-Zr(1)-N(4) ) 178.22(8).
midoamine framework in 4. In the analogous trimeth-
ylsilyl-substituted complex of molybdenum the metal-
lacyclic Mo-C distance is at most 0.1 Å longer than that
found in the acyclic alkyls.19 In 4 the orientations of the
maximum amplitudes of the thermal ellipsoid plots of
C(14) and C(20) along the C-Zr vectors are consistent
with the presence of some sort of disorder. Given that
the overall geometry of the molecule is little distorted
from 3-fold symmetry, it seems likely that there is a
significant occupancy in the crystal where the metal-
lacyclic carbon is C(20). This may be related also to the
twist disorder in the backbone carbon atoms indicated
by their large thermal ellipsoids. To bring the metalla-
cyclic carbon atom within the above-mentioned bonding
distance of the zirconium center, the silyl groups in 4
must assume a more “upright” position than in the
structures of 1-3 with dihedral angles Nax-Zr-Neq-
Si in the range 173.8-177.2°.
Å in I. The Zr atom sits ca. 0.60 Å out of the plane
formed by the three amido nitrogen atoms compared
with that of 0.55 Å in I and 0.94 Å in III, which has no
axial donor atom. The η1-benzyl ligand in 1 has no
unusual features.
The molecular structures of 2 and 3 are shown in
Figures 3 and 4. The triamidoamine unit in 2 is oriented
with 3-fold symmetry as usual, but while the silyl
groups at Si(1) and Si(3) are oriented “anticlockwise”
in the figure, the group at Si(2) is “clockwise”. All other
structures recorded which incorporate this ligand have
these groups circulating in one direction only. We can
offer no explanation for this unusual behavior but note
that the dihedral angle N(2)-Zr(1)-N(3)-Si(2) is un-
usually large at 165.3° compared to 131.0 and 123.8°
for the other two silyl groups. The equatorial amido
N-Zr distances of 2.096(2)-2.124(3) Å in 2 are slightly
larger than those in 1, perhaps as a consequence of the
greater steric demand of the ligand in the fifth coordi-
nation site. Those in the chloride complex 3 are cor-
respondingly shorter at 2.064(3)-2.066(3) Å.
The molecular structure of 4 is shown in Figure 5.
The metallacyclic Zr-C(14) distance is 2.613(11) Å, and
although there is a relatively large error associated with
this measurement, the bond length is nevertheless
considerably greater than those of 2.324(3) and 2.309-
(3) Å in the related metallacycle [Zr{CH2SiMe2N-
(SiMe3)}2(dmpe)].20 This is presumably a consequence
of the conformational constraints imposed by the tria-
Con clu sion
The steric demand of the substituent groups in
triamidoamine ligands has a profound effect on their
ability to coordinate effectively to early transition metals
and f elements. In the latter case the geometries of the
complexes formed are also strongly influenced. It is
becoming increasingly clear that while triamidoamines
with smaller substituents (up to, for example, SiMe3)
have great synthetic utility for the first-row metals and
most of the transition metals of groups 5 onward, the
larger metals (group 3, heavier group 4 and f elements)
are better served by more sterically demanding substit-
uents. The SiMe2But-substituted triamidoamine NN′3
(20) Planalp, R. P.; Andersen, R. A. Organometallics 1983, 2, 1675.

Triamidoamine Chemistry of Zirconium
Organometallics, Vol. 18, No. 22, 1999 4613
forms volatile crystalline monomeric complexes with
these elements, but the SiMe groups are unstable with
respect to deprotonation by early-transition-metal alkyls
and hydrides. Schrock’s more recently introduced aryl-
substituted triamidoamine ligands21 may be more re-
sistant to this type of reaction.
Kline Beecham for a CASE award (to C.J .S.), and Pfizer
(U.K.) Ltd. for a CASE award (to I.J .M.). We thank the
EPSRC and Siemens Analytical Instruments for grants
in support of the diffractometer.
Su p p or tin g In for m a tion Ava ila ble: Four X-ray crystal-
lographic files (for 1-4) in CIF format. This information is
available free of charge via the Internet at http://pubs.acs.org.
Ack n ow led gm en t. P.S. wishes to thank the EPSRC
for Project Studentships (to C.M. and C.J .S.), Smith-
(21) Greco, G. E.; Popa, A. I.; Schrock, R. R. Organometallics 1998,
17, 5591.
OM990347E