Pentamethylcyclopentadienyl zirconium and hafnium polyhydride complexes: Synthesis, structure, and reactivity

Article abstract of DOI:10.1021/om0010969

The half-sandwich zirconium and hafnium N,N-dimethylaminopropyl complexes Cp*M[(CH₂)₃NMe₂]Cl₂ (Cp* = η⁵-C₅Me₅, M = Zr, 1; Hf, 2) and Cp*M[(CH₂)₃NMe₂]₂Cl (M = Zr, 3; Hf, 4) were synthesized by mono- or dialkylation of Cp*MCl₃ with the corresponding alkyllithium and Grignard reagents. Hydrogenolysis of the monoalkyl species resulted in the formation of the polyhydride complexes Cp*₃M₃(μ-H)(μ-Cl)₂Cl₃ (M = Zr, 5; Hf, 6) and Cp*MCl₃. A crystal structure determination of Cp*₃Hf₃H₄Cl₅ (6) revealed a fully asymmetric trinuclear structure with three widely differing Hf?Hf distances. Reaction of Cp*₃M₃H₄Cl₅ with PMe₃ resulted in fragmentation of the cluster and ligand redistribution to give Cp*MCl₃(PMe₃) and the dimeric hydride complexes Cp*₂M₂(μ-H)₃Cl₃ (PMe₃) (M = Zr, 7; Hf, 8), structurally characterized for M = Zr. The trinuclear polyhydride Cp*₃Hf₃H₄Cl₅ reacts with 2,6-xylylisocyanide to give three distinct products, a μ-enediamide complex, [Cp*HfCl₂]₂[μ-xyNCH=CHNxy] (11, xy = 2,6-dimethylphenyl), which was structurally characterized, an imido complex, [Cp*Hf(μ-Nxy)Cl]₂ (12), and an azaallyl species, Cp*Hf(η³-CH₂CHNxy)Cl₂ (13). The reactivity of 6 can be interpreted as proceeding through initial cleavage of the trinuclear complex into the fragments Cp*₂Hf₂ (μ-H)₃Cl₃ and Cp*HfHCl₂ , followed by the separate reactivity of these fragments.

Full text of DOI:10.1021/om0010969

1620
Organometallics 2001, 20, 1620-1628
P en ta m eth ylcyclop en ta d ien yl Zir con iu m a n d Ha fn iu m
P olyh yd r id e Com p lexes: Syn th esis, Str u ctu r e, a n d
Rea ctivity†
Cindy Visser, J ohannes R. van den Hende, Auke Meetsma, Bart Hessen,* and
J an H. Teuben
Center for Catalytic Olefin Polymerization, Stratingh Institute for Chemistry and Chemical
Engineering, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
Received December 28, 2000
The half-sandwich zirconium and hafnium N,N-dimethylaminopropyl complexes Cp*M-
[(CH2)3NMe2]Cl2 (Cp* ) η5-C5Me5, M ) Zr, 1; Hf, 2) and Cp*M[(CH2)3NMe2]2Cl (M ) Zr, 3;
Hf, 4) were synthesized by mono- or dialkylation of Cp*MCl3 with the corresponding alkyl-
lithium and Grignard reagents. Hydrogenolysis of the monoalkyl species resulted in the
formation of the polyhydride complexes Cp*3M3(µ-H)4(µ-Cl)2Cl3 (M ) Zr, 5; Hf, 6) and
Cp*MCl3. A crystal structure determination of Cp*3Hf3H4Cl5 (6) revealed a fully asymmetric
trinuclear structure with three widely differing Hf‚‚‚Hf distances. Reaction of Cp*3M3H4Cl5
with PMe3 resulted in fragmentation of the cluster and ligand redistribution to give Cp*MCl3-
(PMe3) and the dimeric hydride complexes Cp*2M2(µ-H)3Cl3(PMe3) (M ) Zr, 7; Hf, 8),
structurally characterized for M ) Zr. The trinuclear polyhydride Cp*3Hf3H4Cl5 reacts with
2,6-xylylisocyanide to give three distinct products, a µ-enediamide complex, [Cp*HfCl2]2[µ-
xyNCHdCHNxy] (11, xy ) 2,6-dimethylphenyl), which was structurally characterized, an
imido complex, [Cp*Hf(µ-Nxy)Cl]2 (12), and an azaallyl species, Cp*Hf(η3-CH2CHNxy)Cl2
(13). The reactivity of 6 can be interpreted as proceeding through initial cleavage of the
trinuclear complex into the fragments “Cp*2Hf2(µ-H)3Cl3” and “Cp*HfHCl2”, followed by the
separate reactivity of these fragments.
In tr od u ction
to a number of interesting mixed group 4 metal-boron
polyhydride species,7 but it is difficult to obtain boron-
free compounds. A range of polynuclear mixed hydrido-
Group 4 metal metallocene hydride species are used
for stoichiometric1 as well as catalytic2 reductions of
organic substrates. The synthesis and organometallic
chemistry of these metallocene hydrides have been in-
vestigated quite extensively, especially for zirconium.3-6
In contrast, relatively little is known on the synthesis
and chemisty of non-metallocene group 4 metal hy-
drides.7-11 We expect interesting structural and reactive
chemistry of highly electron-deficient group 4 metal
polyhydride species and tried to devise a synthesis route
to access mono(pentamethylcyclopentadienyl) group 4
metal polyhydrides of the type Cp*MHnCl3-n (Cp* ) η5-
C5Me5).
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Shore, S. G. Inorg. Chem. 1998, 37, 496. (e) Liu, F.-C.; Liu, J .; Meyers,
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Liu, J .; Meyers, E. A.; Shore, S. G. Inorg. Chem. 1999, 38, 3228. (g)
Liu, F.-C.; Liu, J .; Meyers, E. A.; Shore, S. G. J . Am. Chem. Soc. 2000,
122, 6106.
The synthesis of group 4 metal hydrides is usually
performed either by reaction of metal halide species with
boron hydrides or trialkyl tin hydrides or by hydro-
genolysis of metal alkyl species. The first route has led
† Netherlands Institute for Catalysis Research (NIOK) publication
no. RUG 00-4-6.
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Organic Syntheses; Paquette L. A., Ed.; Wiley: Chichester, 1995; Vol.
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Chem. 1988, 53, 3752. (b) Willoughby, C. A., Buchwald, S. L. J . Am.
Chem. Soc. 1992, 114, 7562. (c) Broene R. D.; Buchwald, S. L. J . Am.
Chem. Soc. 1993, 115, 12569. (d) Yun, J .; Buchwald, S. L. J . Am. Chem.
Soc. 1999, 121, 5640.
(3) (a) Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.;
Pergamon Press: Oxford, 1982; Vol. 3, Chapters 23.2.3 and 23.2.6, and
references therein. (b) Comprehensive Organometallic Chemistry II;
Wilkinson, G., Ed.-in-Chief; Elsevier Science Ltd.: Oxford, 1995; Vol.
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10.1021/om0010969 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 03/22/2001

Zirconium and Hafnium Polyhydride Complexes
Organometallics, Vol. 20, No. 8, 2001 1621
Sch em e 1
halide zirconium species were obtained by reaction of
zirconium halides with trialkyl tin hydrides in the
presence of phosphines.11 Most of these are structurally
derived from an octahedral hexametallic framework,
with central or bridging hydrides. Hydrogenolysis of
simple mono(pentamethyl)cyclopentadienyl group 4 metal
alkyl species such as Cp*M(CH3)nCl3-n has not yielded
well-defined products so far, producing mostly poorly
soluble materials.10 Only when bulky phosphido ligands
are used in the starting materials were complexes such
as {Cp*Hf(R)[µ-PtBu2](µ-H)}2 (R ) Cl, Me) obtained.10b
The observation, made previously in our group, that
hydrogenolysis of the hafnium 2,3-dimethyl-1,3-buta-
diene complex Cp*Hf(C6H10)Cl yielded a soluble, well-
defined tetrameric hydride, [Cp*Hf(H)2Cl]4,12 suggested
that the nature of the hydrocarbyl precursor is of cru-
cial importance for the formation of well-defined sol-
uble polyhydride species. We therefore investigated the
synthesis and hydrogenolysis of mono(pentamethylcy-
clopentadienyl) zirconium and hafnium N,N-dimethyl-
aminopropyl complexes. It was expected that the amine
substituent on the alkyl group would ensure the mon-
omeric nature of the starting hydrocarbyls and provide
(transient) stabilization of the hydride species generated
upon hydrogenolysis. Here we describe the synthesis of
the alkyl compounds Cp*M[(CH2)3NMe2]nCl3-n (M ) Zr,
Hf; n ) 1, 2) and their use in generating well-defined
polyhydride complexes. The reactivity of these species
with trimethylphosphine and 2,6-xylylisocyanide is also
described. A part of this study has been communicated
previously.13
bipyramidal geometry of the complex with Cs symmetry
or a very rapid rotation and inversion of the NMe2 group
on the NMR time scale. The IR spectra of the dialkyls
3 and 4 show a νCH absorption around 2760 cm-1
,
indicative of a noncoordinated NMe2 group,14 which is
absent in the IR spectra of the monoalkyls 1 and 2. This
suggests that in all the alkyl complexes 1-4 only one
dimethylaminopropyl group is chelating. At 20 °C the
1H NMR spectra of the dialkyls 3 and 4 are indicative
of a symmetrically averaged structure, but at -60 °C
the fluxionality is frozen out completely for the Hf
dialkyl complex 4. All R-methylene protons are in-
equivalent at that temperature, and the NMe2 reso-
nance is split into three resonances in a 3:3:6 ratio. At
this temperature the fluxionality in the Zr complex 3 is
not yet completely frozen out. From the coalescence
temperatures for one of the MCH2 groups the energy of
activation ∆GqTc of this process was estimated to be 43.9
( 0.2 kJ mol-1 (at Tc ) -46 ( 1 °C) for 3 and 45.8 (
0.6 kJ mol-1 (at Tc ) -36 ( 1 °C) for 4.15 These NMR
data indicate that in the dialkyl species only one
dimethylaminopropyl group is chelating at a time, which
is consistent with the IR data.
Resu lts a n d Discu ssion
Syn th esis of Zir con iu m a n d Ha fn iu m N,N-Di-
m eth yla m in op r opyl Com p lexes. The monoalkyl com-
plexes Cp*M[(CH2)3NMe2]Cl2 (Cp* ) η5-C5Me5, M ) Zr,
1; Hf, 2) were obtained in 65% isolated yield from the
reaction of Cp*MCl3 with 1 equiv of Li(CH2)3NMe2 in
THF (Scheme 1). The dialkyl complexes Cp*M[(CH2)3-
NMe2]2Cl (M ) Zr, 3; Hf, 4) were most conveniently
prepared by the reaction of Cp*MCl3 with 2 equiv of
the corresponding Grignard reagent ClMg(CH2)3NMe2
(Scheme 1). Mixtures of the monoalkyl and dialkyl com-
plexes were obtained when the alkyl-lithium reagent
was used. The monoalkyl zirconium complex 1 was also
obtained in high yield from a ligand redistribution
reaction between the dialkyl complex 3 and Cp*ZrCl3.
Hyd r ogen olysis of th e Mon oa lk yl Com p lexes 1
a n d 2. Reaction of the monoalkyl complexes 1 and 2
with H2 (benzene-d6 solvent) at ambient temperature
and pressure resulted in clear, pale yellow solutions.
Monitoring the reactions by 1H NMR spectroscopy
revealed gradual formation of free (n-propyl)dimethyl-
amine, Cp*MCl3, and a polyhydride species with three
inequivalent Cp* groups and four inequivalent hydrides
(compounds 5, 6, eq 1). For Zr, the reaction takes about
1
The H NMR spectra of the monoalkyl complexes 1
and 2 each show a single resonance for the NMe2 group,
which does not show coalescence broadening even down
to -60 °C. This indicates either a pseudo trigonal-
(9) (a) Fischer, M. B.; J ames, E. J .; McNeese, T. J .; Nyburg, S. C.;
Posin, B.; Wong-Ng, W.; Wreford, S. S. J . Am. Chem. Soc. 1980, 102,
4941. (b) Wielstra, Y.; Meetsma, A.; Gambarotta, S. Organometallics
1989, 8, 258.
(10) (a) Wolczanski, P. T.; Bercaw, J . E. Organometallics 1982, 1,
793. (b) Roddick, D. M.; Santarsiero, B. D.; Bercaw, J . E. J . Am. Chem.
Soc. 1985, 107, 4670.
(11) (a) Cotton, F. A.; Lu, J .; Shang, M.; Wojtczak, W. A. J . Am.
Chem. Soc. 1994, 116, 4364. (b) Chen, L.; Cotton, F. A.; Wojtczak, W.
A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1877. (c) Chen, L.; Cotton,
F. A.; Wojtczak, W. A. Inorg. Chem. 1996, 35, 2988. (d) Chen, L.;
Cotton, F. A. Inorg. Chim. Acta 1997, 257, 105.
24 h at ambient temperature to go to completion; for
Hf about 48 h. The hydride resonances for the Zr
compound are found at δ 4.23, 3.92, 2.96, and 0.88 ppm;
(12) Booij, M.; Blenkers, J .; Sinnema, J . C. M.; Meetsma, A.; van
Bolhuis, F.; Teuben, J . H. Organometallics 1988, 7, 1029.
(13) Van den Hende, J . R.; Hessen, B.; Meetsma, A.; Teuben, J . H.
Organometallics 1990, 9, 537.
(14) Lappert, M. F.; Sanger, A. R. J . Chem. Soc. A 1971, 874.
(15) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
London, 1982; Chapter 7.

1622 Organometallics, Vol. 20, No. 8, 2001
Visser et al.
F igu r e 2. Molecular structure of Cp*2Zr2(µ-H)3Cl3(PMe3)
(7).
F igu r e 1. Molecular structure of Cp*3Hf3(µ-H)4(µ-Cl)2Cl3
(6).
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
Two sides of the cluster, Hf(1)Hf(2) and Hf(2)Hf(3), are
bridged by one chloride ligand. The three metal-metal
distances are all quite different, Hf(2)‚‚‚Hf(3) being the
longest, 3.721(7) Å (with a bridging chloride), and
Hf(1)‚‚‚Hf(3) the shortest, 3.061(6) Å (without bridging
chloride). Unfortunately, the hydrides could not be
located from the difference Fourier map, but the struc-
tural features and the spectroscopic data of 6 allow us
to make a proposal for their positions (see below for a
more detailed description of the structure).
Rea ction of 5 a n d 6 w ith P Me3. Reaction of the
trinuclear hydrides 5 and 6 with an excess of the Lewis
base PMe3 was found to induce fragmentation of the
trinuclear core and ligand redistribution to yield a
mixture of a dinuclear hydrido complex, Cp*2M2(µ-H)3-
Cl3(PMe3) (M ) Zr, 7; Hf, 8), and Cp*MCl3(PMe3) (M )
Zr, 9; Hf, 10; eq 2). The complexes 7 and 8 were obtained
analytically pure by crystallization from diethyl ether.
(d eg) for Cp *3Hf3(µ-H)4(µ-Cl)2Cl3 (6)
Hf(1)‚‚‚Hf(2)
Hf(2)‚‚‚Hf(3)
Hf(1)‚‚‚Hf(3)
Hf(1)-av C(Cp)
Hf(2)-av C(Cp)
Hf(3)-av C(Cp)
Hf(1)-Cl(1)
Hf(2)-Cl(1)
Hf(2)-Cl(2)
Hf(3)-Cl(2)
Hf(1)-Cl(3)
Hf(2)-Cl(4)
Hf(3)-Cl(5)
3.241(6)
3.721(7)
3.061(6)
2.473
Hf(1)-Cl(1)-Hf(2)
Hf(2)-Cl(2)-Hf(3)
Cl(1)-Hf(1)-Cl(3)
Cl(1)-Hf(2)-Cl(2)
Cl(1)-Hf(2)-Cl(4)
Cl(2)-Hf(2)-Cl(4)
Cl(2)-Hf(3)-Cl(5)
77.71(7)
94.93(10)
79.24(9)
143.11(9)
89.91(10)
92.18(10)
93.59(10)
2.472
2.484a
2.648(3)
2.516(3)
2.536(3)
2.514(3)
2.470(3)
2.394(3)
2.399(3)
a
The largest being 2.524 and the smallest 2.459 Å.
for the Hf congener at δ 9.17, 8.46, 7.71, and 4.63 ppm,
with each resonance integrating as a single hydride. On
the basis of the NMR data, as well as elemental analysis
and X-ray diffraction data for the compound with M )
Hf (vide infra), these products are formulated as
Cp*3M3H4Cl5 (M ) Zr, 5; Hf, 6).
Warming the solutions of the polyhydrides in the
NMR spectrometer reveals that the compounds
Cp*3M3H4Cl5 5 and 6 show complicated fluxional be-
havior. Initially, the two upfield Cp* signals coalesce
into a single resonance (around 40 °C). At about 70 °C
the third Cp* signal also broadens significantly, but the
full fast exchange limit could not be reached for either
compound (100 °C). The three downfield hydride reso-
nances also collapse, and at elevated temperature the
upfield hydride signal broadens as well.
From reactions on a 1.5-2.5 mmol scale (toluene
solvent) the polyhydrides could be isolated as crystalline
material by slow diffusion of pentane or hexane into the
solution. It proved difficult to obtain the Zr derivative
5 analytically pure due to cocrystallization of Cp*ZrCl3.
A structural characterization of 5 was hampered by
facile loss of cocrystallized solvent from the crystal
lattice, rendering the material unsuitable for X-ray
analysis. In contrast, the Hf analogue 6 was isolated
analytically pure in 80% yield from this procedure, and
suitable crystals were obtained for an X-ray structure
determination.
At -30 °C the 1H NMR spectrum of 7 (toluene-d8
solvent) shows three separate hydride resonances at δ
4.73, 4.44, and 2.97 ppm. For the Hf congener 8 two of
the hydride resonances overlap at δ 9.15 ppm in
addition to a resonance at δ 7.67 ppm. Upon warming
the solution of 7 to 75 °C, the hydride resonances
coalesce into one single resonance at 4.09 ppm, but the
two Cp* resonances remain inequivalent, indicating that
Cl/PMe3 exchange between the metal centers does not
take place at a significant rate and that the observed
fluxional process corresponds to a rotation around the
metal-metal axis. For the Hf analogue 8 similar
behavior is seen, although this process appears to be
substantially slower, as even at 100 °C the fast exchange
limit for the hydride resonances had not been reached.
A crystal structure determination of the Zr complex
7 reveals that the compound is dinuclear, with one
Cp*ZrCl2 fragment and one Cp*ZrCl(PMe3) fragment
bridged by three hydrides that could be located from
the difference Fourier analysis (Figure 2, pertinent
The crystal structure of 6 (Figure 1, pertinent inter-
atomic distances and angles in Table 1) reveals a
triangular trinuclear arrangement, with each Hf atom
bearing one η5-Cp* ligand and one terminal chloride.

Zirconium and Hafnium Polyhydride Complexes
Organometallics, Vol. 20, No. 8, 2001 1623
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
Sch em e 2
(d eg) for Cp *2Zr 2(µ-H)3Cl3(P Me3) (7)
Zr(1)‚‚‚Zr(2)
Zr(1)-av C(Cp)
Zr(2)-av C(Cp)
Zr(1)-Cl(1)
Zr(2)-Cl(2)
Zr(2)-Cl(3)
Zr(1)-P(1)
Zr(1)-H(1)
Zr(1)-H(2)
Zr(1)-H(3)
Zr(2)-H(1)
Zr(2)-H(2)
Zr(2)-H(3)
3.126(1)
2.508
2.510
Zr(1)-H(1)-Zr(2)
Zr(1)-H(2)-Zr(2)
Zr(1)-H(3)-Zr(2)
P(1)-Zr(1)-Cl(1)
Cl(2)-Zr(2)-Cl(3)
104.1(19)
103.2(14)
85.9(17)
86.06(3)
101.77(3)
2.470(1)
2.456(1)
2.452(1)
2.744(1)
1.92(3)
2.00(3)
2.24(5)
2.04(4)
1.98(3)
2.35(5)
interatomic distances and angles in Table 2). As is
expected for a (µ-H)3 dimer,16 the Zr(1)‚‚‚Zr(2) distance
of 3.126(1) Å is considerably shorter than the 3.460 Å
in the (µ-H)2 complex [(η5-C5H4Me)2ZrH(µ-H)]2.4f The
Cp*, Cl, and PMe3 ligands adopt a nearly eclipsed
configuration around the Zr‚‚‚Zr axis, with relatively
small torsion angles P(1)-Zr(1)-Zr(2)-Cl(3) ) -11.34-
(3)°, CT(1)-Zr(1)-Zr(2)-Cl(2) ) 6.29(3)°, and Cl(1)-
Zr(1)-Zr(2)-CT(2) ) 28.38(3)° (with CT(x) being the
centroid of the Cp* ligand on the Zr(x) atom). The three
hydride ligands take up positions staggered relative to
the other ligands.
The proposed structure for the trinuclear species
Cp*3
M (µ-H) (µ-Cl) Cl (5, 6) can also shed light on the
3
4
2
3
formation of the dinuclear hydrides Cp*2M2(µ-H)3Cl3-
(PMe3) (7, 8) and Cp*MCl3(PMe3) (9, 10) upon reaction
of 5 or 6 with the Lewis base PMe3. The side of the
trinuclear cluster that is bridged only by a single
chloride ligand is likely to be the “weakest link” in the
cluster and most susceptible to attack by a Lewis base.
Cleavage of the cluster in this position can lead to
formation of Cp*2M2(µ-H)3Cl3(PMe3), one of the observed
products, and “Cp*MHCl2”. The latter is the same
species that was presumed to be generated in the
reaction of the monoalkyl complexes Cp*M[(CH2)3NMe2]-
Cl2 with H2 and that was found to rearrange to give the
trinuclear hydride cluster and Cp*MCl3. The latter will
bind PMe3 to generate Cp*MCl3(PMe3), the other ob-
served product in the reaction of 5 and 6 with PMe3.
Rea ction of 6 w ith 2,6-Xylylisocya n id e. Isocya-
nides are Lewis bases, but are also known to insert
readily into early transition metal hydride bonds.19 As
described above, the trinuclear polyhydrides 5 and 6
were found to fragment and redistribute readily upon
reaction with the Lewis base trimethylphosphine. To
study the relation between the Lewis base-induced
fragmentation and the reactivity of the hydride func-
tionalites, the reactivity of 6 toward 2,6-xylylisocyanide
was investigated.
The reaction of the trinuclear Hf-hydride 6 with 2,6-
xylylisocyanide was studied by 1H NMR (benzene-d6
solvent) and was found to give full conversion of 6 when
2.7-3 equiv of isocyanide per trinuclear cluster are
used. In the course of the reaction several transient
intermediates can be observed (vide infra), but eventu-
ally the reaction yields three end-products (Scheme 3),
one of which is poorly soluble and crystallizes from the
solution. This product was identified as the dimeric
µ-enediamide complex [Cp*HfCl2]2[µ-xyNCHdCHNxy]
(11, xy ) 2,6-dimethylphenyl) by an X-ray structure
determination (Figure 3, pertinent interatomic distances
and angles in Table 3). The Hf atoms have a three-
legged piano-stool configuration. The Hf-N distance is
relatively short at 2.039(3) Å (indicating substantial
π-donation from the amide nitrogen),20 and the enedia-
mide ligand is planar with an E-configuration around
the CHdCH double bond (1.343(5) Å). This product can
be considered to derive from reaction of the isocyanide
with “Cp*Hf(H)Cl2”, one of the fragments proposed to
Str u ctu r a l Rela tion sh ip betw een Cp *3M3H4Cl5
a n d Cp *2M2H3Cl3(P Me3). A comparison of the avail-
able structural data on Cp*3Hf3H4Cl5 (6) and Cp*2Zr2H3-
Cl3(PMe3) (7) allows for a proposal for the location of
the hydrides in 6. As mentioned above, in the crystal
structure determination of the trinuclear hafnium hy-
dride 6 the hydrides themselves could not be located.
Nevertheless, it may be observed that the shortest
metal-metal distance in 6, Hf(1)‚‚‚Hf(3) (3.061(6) Å),
is not bridged by a chloride ligand and is close to the
Zr(1)‚‚‚Zr(2) distance (3.126(1) Å) in the Zr(µ-H)3Zr
dimer 7. Therefore, it seems reasonable to propose that
Hf(1) and Hf(3) are connected by three bridging hy-
drides. The two remaining Hf‚‚‚Hf sides in triangular
6 are each bridged by one chloride. The Hf(2)‚‚‚Hf(3)
distance of 3.721(7) Å is quite long and close to the
intermetallic distances observed in Hf(µ-Cl)2Hf units
(3.9-4.0 Å).17 It seems unlikely that Hf(2) and Hf(3) are
bridged by a hydride as well as a chloride ligand. The
Hf(1)‚‚‚Hf(2) distance of 3.241(6) Å is much closer to
known intermetallic distances in Hf2(µ-H)2 units, for
example, the Hf‚‚‚Hf distance of 3.397 Å in the Hf(µ-
H)2Hf dimer [Cp*Hf(iPr-DAB)(µ-H)]2 (iPr-DAB ) N,N′-
diisopropyl-1,4-diaza-1,3-butadiene).18 It thus seems
possible that Hf(1) and Hf(2) in 6 are bridged by one
chloride and one hydride. This would lead to a proposed
structure for 6 as shown in Scheme 2. The Hf(1)-Cl(3)
bond is the longest of the three Hf-Clterminal bonds, and
the Cl(1)-Hf(1)-Cl(3) and Cg-Hf(1)-Cl(3) angles are
the smallest of the Clbridging-Hf-Clterminal and Cg-Hf-
Clterminal angles. This indicates that Hf(1) has a higher
coordination number than the other two Hf centers, in
agreement with the proposed structure.
(16) Moore, D. S.; Robinson, S. D. Chem. Soc. Rev. 1983, 12, 415.
(17) (a) Calderazzo, F.; Pallavicini, P.; Pampaloni, G.; Zanazzi, P.
F. J . Chem. Soc., Dalton Trans. 1990, 2743. (b) Shaw, S. L.; Morris,
R. J .; Huffman, J . C. J . Organomet. Chem. 1995, 489, C4.
(18) Hessen, B.; Bol J . E.; de Boer, J . L.; Meetsma, A.; Teuben, J .
H. J . Chem. Soc., Chem. Commun. 1989, 1276.
(19) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059, and
references therein.
(20) Hillhouse, G. L.; Bulls, A. R.; Santarsiero, B. D.; Bercaw, J . E.
Organometallics 1988, 7, 1309.

1624 Organometallics, Vol. 20, No. 8, 2001
Visser et al.
not be crystallized, but a combination of NMR spectros-
copy and the product formation upon its reaction with
ethanol suggested its formulation as an azaallyl com-
1
plex, Cp*Hf(η3-CH2CHNxy)Cl2 (13). The H NMR spec-
trum of 13 shows (in addition to the resonances of one
Cp* group and one xylyl group) one resonance at δ 7.53
ppm (t, J 11.0 Hz, 1H, attached to one carbon with 13C
δ 137.62 ppm, d, J CH 160.4 Hz) and one at δ 3.77 ppm
(d, J 11.0 Hz, 2H, attached to one carbon with 13C δ
88.24 ppm, t, J CH 160.2 Hz). These spectroscopic char-
acteristics are compatible with the presence of a (flux-
ional) trihapto N-xylyl-1-azaallyl ligand. Cooling a
toluene-d8 solution of 13 to -90 °C results in a splitting
of the resonance at δ 3.77 ppm (the 1-azaallyl methylene
group), although the resulting resonances are still broad
at that temperature. The IR spectrum of 13 shows
strong bands at 1600 and 1592 cm-1 that may be
associated with the azaallyl moiety. The presence of a
N-xylyl-1-azaallyl group in 13 is also suggested by the
organic products formed in its reaction with an excess
of ethanol: 2,6-dimethylaniline and 1,1-diethoxyethane
(identified by GC/MS). These can be generated by
protonation of the azaallyl group in 13 to give the imine
xyNdCHMe, followed by alcoholysis of the latter.
F igu r e 3. Molecular structure of [Cp*HfCl2]2[µ-(xyNCHd
CHNxy)] (11).
Sch em e 3
From the observed product formation it thus seems
that, after an initial C,C-coupling step, a cleavage of
one of the N-C bonds occurs, resulting in one 1-azaallyl
and one imido ligand. Cleavage of the N-C bond in a
zirconium η2-imine complex to give an imido species
has been observed in the (TC-3,3)Zr[(PhCH2)2CN(2,6-
Me2C6H3)] system (TC-3,3 ) tropocoronand ligand),
leading to formation of the imido dimer [(TC-3,3)Zr(µ-
NAr)]2.22
Rea ction of 8 w ith 2,6-Xylylisocya n id e. The prod-
ucts 12 and 13 as described above could derive from a
reaction of two molecules of isocyanide with the “Cp*2-
Hf2(µ-H)3Cl3” fragment. Taken together with the ob-
served formation of 11, this seems to indicate that, like
in the reaction with PMe3, the reaction of 6 with
isocyanide initially involves a specific cleavage of the
cluster into a monohydride and a bimetallic trihydride
fragment.
To test this hypothesis, we studied the reaction of the
dimeric hafnium hydride 8 with 2,6-xylylisocyanide. In
this reaction, the same intermediates could be observed
by NMR as those that lead to the products 12 and 13
in the reaction of 6 with isocyanide, and the poorly
soluble enediamide dimer 11 did not form in this case
(Scheme 4). Of the observable intermediates (seen in
the reactions of both 6 and 8 with isocyanide), the first
one that is formed (A) is probably a (bimetallic) imino-
formyl complex with composition Cp*2Hf2(xyCHN)H2-
Cl3, derived from the reaction of 8 with one molecule of
isocyanide. The iminoformyl hydrogen resonance in A
is found at δ 10.38 ppm with the two remaining hydride
resonances at δ 3.43 and 2.15 ppm. By 1H,1H COSY
NMR it was seen that these exhibit scalar coupling with
each other, and the δ 2.15 ppm resonance also couples
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Cp *HfCl2]2[µ-(xyNCHdCHNxy)] (11)
Hf-C1
Hf-C2
Hf-C3
Hf-C4
Hf-C5
Hf-Cl1
Hf-Cl2
Hf-N
2.471(4)
2.470(3)
2.483(4)
2.485(4)
2.493(4)
2.376(12)
2.374(12)
2.039(3)
1.446(5)
1.417(5)
1.343(5)
Hf-N-C11
Hf-N-C19
C11-N-C19
Cl1-Hf-Cl2
Cl1-Hf-N
Cl2-Hf-N
108.9(2)
136.8(3)
114.3(3)
100.87(4)
109.02(10)
104.89(9)
Hf-N-C11-C16
C11-N-C19-C19a
93.3(3)
-6.2(5)
N-C11
N-C19
C19-C19a
be produced by the cleavage of 6 with a Lewis base, by
insertion of isocyanide into the Hf-H bond and subse-
quent iminoformyl C,C-coupling.
The other two end-products could be crudely sepa-
rated by pentane extraction, as one of these products is
considerably less soluble than the other. The least sol-
uble product was obtained analytically pure by recrys-
tallization from toluene. From its composition, solubil-
ity, and spectroscopic characteristics, this compound
was identified as a dimeric imido complex, [Cp*Hf-
(µ-Nxy)Cl]2 (12). Related compounds [(C5R5)M(µ-NR′)-
Cl]2 (M ) Ti, Zr, Hf) have been prepared previously via
various routes.21 The pentane-soluble end-product could
(21) (a) Vroegop, C. T.; Teuben, J . H.; van Bolhuis, F.; van der
Linden, G. M. J . Chem. Soc., Chem. Commun. 1983, 550. (b) J ekel-
Vroegop, C. T.; Teuben, J . H. J . Organomet. Chem. 1985, 286, 309. (c)
Grigsby, W. J .; Olmstead, M. M.; Power, P. P. J . Organomet. Chem.
1996, 513, 173. (d) Arney, D. J .; Bruck, M. A.; Huber, S. R.; Wigley, D.
E. Inorg. Chem. 1992, 31, 3749.
(22) Scott, M. J .; Lippard, S. J . Organometallics 1997, 16, 5857.

Zirconium and Hafnium Polyhydride Complexes
Organometallics, Vol. 20, No. 8, 2001 1625
Schlenk, and vacuum-line techniques. Solvents were predried
over Na wire, distilled from Na (toluene) or Na/K alloy (Et2O,
pentane, hexane, THF), and stored under nitrogen. Deuterated
solvents (C6D6, C7D8, C4D8O; Aldrich) were vacuum transferred
from Na/K alloy. Hydrogen gas (AGA 99.9%) and 2,6-xylyliso-
cyanide (Fluka) were used as purchased. Cp*MCl3 (M ) Zr,
Hf),23 Li(CH2)3NMe2,24 and PMe325 were synthesized according
to published procedures. Me2N(CH2)3MgCl was prepared in
THF from the corresponding alkyl chloride. NMR spectra were
recorded on Varian VXR 300 or Varian Unity 500 spectrom-
eters. The 1H and 13C NMR spectra were referenced internally
using the residual solvent resonances and reported in ppm
relative to TMS (δ 0 ppm); J is reported in Hz. IR spectra were
recorded from Nujol mulls between KBr disks on a Mattson-
4020 Galaxy FT-IR spectrometer. Elemental analyses were
performed at the Microanalytical Department of the University
of Groningen. Found values are the average of at least two
independent determinations.
Sch em e 4
weakly with the iminoformyl proton. In A there are two
inequivalent Cp* ligands. The second intermediate (B)
shows three proton resonances, one at δ 4.63 ppm, one
at 4.47 ppm (both dd, J 6.2 and 9 Hz, and attached to
a single carbon with 13C δ 60.35 ppm), and one at δ 4.12
ppm (t, J 9 Hz, attached to a carbon with 13C δ 56.68
ppm). This intermediate probably derives from a reac-
tion of the iminoformyl intermediate A with a second
molecule of isocyanide, involving transfer of the remain-
ing hydrides to carbon and a C,C-coupling reaction to
give a xyN-CH-CH2-Nxy moiety. The intermediate
B (Cp*2Hf2(xyCHCH2Nxy)Cl3) then apparently under-
goes cleavage of the N-CH2 bond to produce the imido
and azaallyl final products 12 and 13.
Cp *Zr [(CH2)3NMe2]Cl2 (1). A mixture of 3 (0.35 g, 0.86
mmol) and Cp*ZrCl3 (0.28 g, 0.84 mmol) was dissolved in 10
mL of toluene and stirred for 1 h at 20 °C. Concentrating and
cooling the solution to -80 °C yielded 0.52 g (1.41 mmol, 84%)
1
of colorless crystalline 1. H NMR (300 MHz, C6D6, 20 °C): δ
2.67 (m, 2H, NCH2), 2.47 (s, 6H, NMe2), 1.91 (s, 15H, C5Me5),
1.80 (m, 2H, -CH2-), 0.69 (m, 2H, ZrCH2). 13C NMR (75.4
MHz, C6D6, 20 °C): δ 122.77 (s, Cp* C), 65.23 (t, J ) 116.8,
ZrCH2), 63.06 (t, J ) 135.8, NCH2), 48.03 (q, J ) 137.0, NMe2),
26.73 (t, J ) 126.6, -CH2-), 12.18 (q, J ) 127.0, Cp* Me). IR:
2710(vw), 1481(vw), 1390(m), 1262(vw), 1248(w), 1231(mw),
1166(m), 1099(m), 1048(m), 1008(vs), 979(s), 905(m), 872(m),
810(w), 773(vs), 723(mw), 640(vw), 593(w), 488(m), 356(mw)
cm-1. Anal. Calcd for C15H27NCl2Zr: C, 46.98; H, 7.10; Cl,
18.49; Zr, 23.79. Found: C, 46.69; H, 7.08; Cl, 18.38; Zr, 23.73.
Cp *M[(CH2)3NMe2]Cl2 (M ) Hf, 2; Zr , 1). Onto a mixture
of solid Cp*HfCl3 (1.71 g, 4.07 mmol) and Li(CH2)3NMe2 (0.34
g, 3.65 mmol), which was frozen in liquid nitrogen, 10 mL of
THF was condensed. The mixture was allowed to warm to
room temperature, and after stirring for 1 h at room temper-
ature the solvent was removed in vacuo. The white mixture
was extracted twice with 20 mL of pentane. Concentrating the
extract and cooling to -80 °C yielded 1.11 g (2.36 mmol, 65%)
Con clu sion s
The hydrogenolysis of pentamethylcyclopentadienyl
Zr and Hf N,N-dimethylaminopropyl dichloride com-
plexes leads to the formation of a well-defined, crystal-
lizable trinuclear hydride species, Cp*3M3(µ-H)4(µ-
Cl)2Cl3. The use of the N,N-dimethylaminopropyl group
thus appears to aid the formation of this discrete species
(unlike the ill-defined polymeric products produced upon
hydrogenolysis of other Cp*M(alkyl)Cl2 compounds), but
the (n-propyl)dimethylamine itself is not incorporated
into the final product. This principle should be more
widely applicable in the synthesis of polynuclear poly-
hydrides of highly electron-deficient metal centers, and
we are presently investigating the scope of this ap-
proach.
The highly asymmetric trinuclear structure of Cp*3M3-
(µ-H)4(µ-Cl)2Cl3 is rather unusual, but probably repre-
sents the thermodynamically most stable structure, as
the complex readily self-assembles in solution via ligand
exchange reactions, eliminating a molecule of Cp*MCl3.
The reactivity of Cp*3M3(µ-H)4(µ-Cl)2Cl3 studied so far
(with PMe3 and 2,6-xylylisocyanide) may be interpreted
on the basis of its structure, where the cluster is initially
attacked by Lewis basic substrates on the most “open”
side of the M3 triangle. The product formation is then
dependent on the separate reaction pathways of the
“Cp*2M2(µ-H)3Cl3” and “Cp*MHCl2” fragments thus
generated. The highly electron-deficient metal hydride
species show a variety of reaction steps with 2,6-
xylylisocyanide, inducing both C,C-coupling and C,N-
cleavage processes.
1
of white crystalline 2. H NMR (500 MHz, toluene-d8, 0 °C): δ
2.52 (t, 2H, J ) 7.0, NCH2), 2.35 (s, 6H, NMe2), 1.96 (s, 15H,
C5Me5), 1.91 (m, 2H, -CH2-), 0.57 (t, 2H, J ) 8.0, HfCH2).
13C NMR (125.68 MHz, toluene-d8, 0 °C): δ 120.91 (s, Cp* C),
64.44 (t, J ) 114.4, HfCH2), 63.69 (t, J ) 135.8, NCH2), 47.69
(q, J ) 132.0, NMe2), 25.17 (t, J ) 125.9, -CH2-), 11.93 (q, J
) 126.7, Cp* Me). IR: 2726(m), 2672 (w), 1311(m), 1235(vw),
1169(s), 1155(sh), 1105(m), 1055(m), 1015(s), 974(s), 907(m),
891(w), 870(m), 808(w), 774(s), 723(vs), 593(mw), 488(m) cm-1
.
Anal. Calcd for C15H27NCl2Hf: C, 38.27; H, 5.78; N, 2.98; Cl,
15.06; Hf, 37.91. Found: C, 37.95; H, 5.77; N, 2.85; Cl, 14.92;
Hf, 37.78.
The same procedure using Cp*ZrCl3 (1.75 g, 5.26 mmol)
yielded 1.35 g (3.52 mmol, 67%) of yellow crystalline Cp*Zr-
[(CH2)3NMe2]Cl2 (1).
Cp *M[(CH2)3NMe2]2Cl (M ) Zr , 3; Hf, 4). At -30 °C, 3.5
mL of a 0.78 M solution of Me2N(CH2)3MgCl in THF was added
dropwise to a suspension of Cp*ZrCl3 (0.31 g, 0.92 mmol) in
10 mL of Et2O. The mixture was allowed to warm to room
temperature, and after 3 h the solvent was pumped off. The
pale yellow mixture was extracted twice with 30 mL of
pentane. Concentrating the extract and cooling to -80 °C
yielded 0.27 g (0.61 mmol, 67%) of pale yellow crystalline 3,
after a cold (-80 °C) washing with pentane. 1H NMR (300
(23) Blenkers, J .; Hessen, B.; van Bolhuis, F.; Wagner, A. J .; Teuben,
J . H. Organometallics 1987, 6, 459.
(24) Thiele, K.-H.; Langguth, E.; Mu¨ller, G. E. Z. Anorg. Allg. Chem.
1980, 462, 152.
(25) Prepared according to Inorg. Synth. 1989, 26, 7, using MeMgI
instead of MeMgBr.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All manipulations were carried
out under nitrogen atmosphere using standard glovebox,

1626 Organometallics, Vol. 20, No. 8, 2001
Visser et al.
MHz, toluene-d8, -75 °C): δ 3.01 (s, 3H, NMe), 2.4 (br m, 6H,
3 CH2), 2.22 (s, 6H, NMe2), 2.0 (br m, 2H, CH2), 1.88 (s, 15H,
C5Me5), 1.83 (s, 3H, NMe), 0.54 (br m, 2H, ZrCH2), -0.03 (br
m, 1H, Zr-CHH), -0.35 (br d, 1H, J ) 11.4, Zr-CHH). 13C
NMR (75.4 MHz, toluene-d8, -65 °C): δ 119.74 (s, Cp* C),
67.57 (t, J ) 136.4, NCH2), 63.29 (t, J ) 128.9, NCH2), 59.95
(t, J ) 128.9, ZrCH2), 51.94 (t, J ) 120.3, ZrCH2), 50.70 (q, J
) 132.9, NMe), 49.38 (q, J ) 131.1, NMe), 46.14 (q, J ) 131.2,
NMe2), 28.32 (t, J ) 126.6, -CH2-), 26.49 (t, J ) 124.3, -CH2-
), 12.28 (q, J ) 126.2, Cp* Me). IR: 2805(w), 2760(mw), 2705-
(w), 1390(mw), 1309(m), 1275(mw), 1251(s), 1223(w), 1198(s),
1167(mw), 1148(m), 1093(m), 1043(s), 1028(s), 1002(sh), 960-
(s), 896(s), 880(s), 843(s), 802(w), 774(s), 718(mw), 591(w), 568-
C5Me5); hydride couplings: J AB ) 8.3, J AC ) 8.9, J BD ) 4.3,
J AD ) 2.1, J BC ) J CD ) 0 (determined by selective decoupling
experiments). Anal. Calcd for C30H49Cl5Hf3: C, 32.10; H, 4.40;
Cl, 15.79; Hf, 47.71. Found: C, 32.11; H, 4.28; Cl, 15.91; Hf,
47.42.
Cp *2M2(µ-H)3Cl3(P Me3) (M ) Zr , 7; Hf, 8). To a solution
of 5 (0.249 g, 0.83 mmol Zr) in 10 mL of toluene was added
0.25 mL of PMe3 (excess). After stirring for 20 h at 20 °C the
solvent was evaporated and the residue was extracted with
diethyl ether. After concentrating the extract, the solution was
gradually (3 °C h-1) cooled to -25 °C to produce analytically
pure pale yellow crystalline 7 (0.101 g, 0.316 mmol Zr, 41%).
Formation of Cp*ZrCl3(PMe3) (9) was observed by NMR
(identified by comparison with an authentic sample, see below).
The corresponding deuteride 7-d3 was obtained from a similar
(m), 515(mw), 496(m), 467(w), 455(w), 420(m), 347(w) cm-1
.
Anal. Calcd for C20H39N2ClZr: C, 55.32; H, 9.05; Cl, 8.16; Zr,
21.01. Found: C, 55.21; H, 9.22; Cl, 7.62; Zr, 20.51.
1
procedure using D2. H NMR (300 MHz, toluene-d8, -30 °C):
2
2
2
δ 4.73 (d, J PH ) 12.1, t, J HH ) 8, 1H, µ-H), 4.44 (d, J PH
)
The same procedure using Cp*HfCl3 (0.31 g, 0.74 mmol)
yielded 0.20 g (0.38 mmol, 51%) of white crystalline Cp*Hf-
2
2
2
18.3, t, J HH ) 8, 1H, µ-H), 2.97 (ps q, J PH ≈ J HH ) 8, 1H,
2
1
µ-H), 2.17 (s, 15H, C5Me5), 2.03 (s, 15H, C5Me5), 1.03 (d, J PH
[(CH2)3NMe2]2Cl (4). H NMR (500 MHz, toluene-d8, -60 °C):
) 8.4, 9H, PMe3). At 75 °C only one µ-H resonance is observed
δ 2.50 (br, 1H, -CHH′), 2.37 (s, 3H, NMe), 2.33 (br, 1H,
N-CHH′), 2.32 (br, 1H, N-CHH′), 2.23 (s, 6H, NMe2′), 2.15
(br, 1H, -CHH′), 1.97 (br, 1H, -CHH), 1.88 (br, 1H, -CHH),
1.84 (br, 1H, N-CHH), 1.83 (s, 15H, C5Me5), 1.80 (s, 3H, NMe),
1.59 (br, 1H, N-CHH), 0.65 (br, 1H, Hf-CHH), 0.48 (br, 1H,
Hf-CHH′), 0.35 (br, 1H, Hf-CHH), 0.11 (br, 1H, Hf-CHH′).
13C NMR (125.68 MHz, toluene-d8, -60 °C): δ 118.97 (s, Cp*
C), 70.09 (t, J ) 117.2, HfCH2′), 67.44 (t, J ) 130.0, NCH2′),
64.92 (t, J ) 134.0, NCH2), 54.98 (t, J ) 114.7, HfCH2), 47.95
(q, J ) 136.8, NMe), 46.06 (q, J ) 135, NMe2+NMe), 29.36 (t,
J ) 123.3, CH2′), 24.77 (t, J ) 132.3, CH2), 11.89 (q, J ) 126.2,
Cp* Me). With 2D NMR experiments (DQCOSY, HSQC, and
NOESY) the different signals could be assigned to the various
CH2 groups. Resonances belonging to the nonchelating alkyl
group are indicated by a prime (′). IR: 2817(w), 2765(m), 2705-
(vw), 1400(w), 1317(mw), 1302(w), 1277(vw), 1254(s), 1231-
(w), 1217(s), 1165(s), 1115(w), 1098(m), 1042(s), 1031(vw),
1007(s), 972(sh), 901(m), 851(s), 802(w), 762(s), 723(mw), 594-
(s), 552(m), 530(m), 482(m), 467(vw) cm-1. Anal. Calcd for
at 4.09 ppm (br, 3H). 31P NMR (121.4 MHz, toluene-d8, -30
2
°C, PMe3-protons selectively decoupled): δ -18.1 (ddd, J PH
) 18.3, 12.1, 8.3). At 75 °C a quartet is observed (2J PH ) 12.9).
IR: 2710(vw), 1465*(vs sh), 1445*(vs), 1327*(m), 1285(m),
1148*(m), 1116*(mw), 1087(w), 1023(mw), 960 (s), 848(w),
780*(m), 765*(mw), 734(vw), 723(w), 413(vw), 366(m) cm-1
.
The starred wavenumbers are shifted by a factor 1/(1.38-1.42)
in the spectrum of 7-d3. Anal. Calcd for C23H42Zr2Cl3P: C, 43.28;
H, 6.63; Cl, 16.66; Zr, 28.58. Found: C, 43.16; H, 6.66; Cl, 16.63;
Zr, 28.46.
A similar procedure using 6 (0.22 g, 0.20 mmol) yielded 0.10
1
g (46%) of the Hf analogue 8. H NMR (300 MHz, toluene-d8,
2
25 °C): δ 9.15 (m, 2H, µ-H), 7.67 (ps. q, 2J PH ≈ J HH ) 7.6, 1H,
2
µ-H), 2.23 (s, 15H, C5Me5), 2.11 (s, 15H, C5Me5), 1.08 (d, J PH
) 8.3, 9H, PMe3). IR: 2726(mw), 2679(vw), 1306(vw), 1289-
(w), 1204(m), 1173(m), 1094(mw), 1026(s), 964(vs), 856(w), 822-
(m), 812(m), 774(vw), 731(w), 723(w), 592(mw) cm-1. Anal.
Calcd for C23H42Hf2Cl3P: C, 33.98; H, 5.21; Hf, 43.91. Found:
C, 34.06; H, 5.12; Hf, 43.71.
C
20H39N2ClHf: C, 46.06; H, 7.54; N, 5.37; Cl, 6.80; Hf, 34.23.
Found: C, 45.90; H, 7.47; N, 5.29; Cl, 6.75; Hf, 34.05.
Cp *Zr Cl3(P Me3) (9). At 20 °C, 0.5 mL of PMe3 (excess) was
added to a suspension of Cp*ZrCl3 (0.502 g, 1.51 mmol) in 20
mL of benzene. After stirring for 2 days a clear pale yellow
solution had formed. After filtration and concentraation,
pentane was condensed into the mixture, yielding 0.477 g (1.17
mmol, 77%) of crystalline 9. 1H NMR (300 MHz, C6D6, 20 °C):
Cp *3Zr 3(µ-H)4(µ-Cl)2Cl3 (5). A solution of 1 (0.95 g, 2.47
mmol) in 25 mL of benzene was stirred at room temperature
in the dark under H2 (1 atm) for several days. The clear yellow
solution was concentrated, and slow diffusion of pentane into
the solution produced large yellow crystals. The solvent was
decanted, and the solid was dried in vacuo, yielding 0.515 g of
material (approximately 1.8 mmol of Zr). The product thus
obtained can contain varying amounts of Cp*ZrCl3 and is
somewhat photosensitive, solutions turning green in daylight
within an hour. The corresponding deuteride 5-d4 was obtained
from a similar procedure using D2. 1H NMR (300 MHz, toluene-
d8, -50 °C): δ 4.23 (m, 1H, HA), 3.92 (m, 1H, HB), 2.96 (m,
1H, HC), 2.21 (s, 15H, C5Me5), 2.10 (s, 15H, C5Me5), 1.86 (s,
15H, C5Me5), 0.88 (1H, HD); hydride couplings: J AB ) 9.9, J AC
) 10.6, J BD ) 6.2, J AD ) 3.3, J CD ) 1.5, J BC ) 0 (determined
by selective decoupling experiments). IR: 2710(vw), 1575*(br,
vs), 1480(m), 1417(m), 1310*(br, mw), 1150*(w), 1105*(w),
1063(w), 1016(s), 926*(mw), 901*(mw), 855*(w), 806(vw), 592-
(w), 418(w), 369(s) cm-1. The starred wavenumbers are shifted
by a factor 1/(1.38-1.42) in the spectrum of 5-d4. No consistent
elemental analyses could be obtained, due to the presence of
varying amounts of cocrystallized Cp*ZrCl3 and interstitial
benzene. Zr:Cl ratios between 1:1.7 and 1:2.0 were found.
Cp *3Hf3(µ-H)4(µ-Cl)2Cl3 (6). A solution of 2 (0.77 g, 1.64
mmol) in 10 mL of toluene was stirred at room temperature
in the dark under H2 (1 atm) for 2 days. The pale yellow
solution was concentrated, and slow diffusion of 15 mL hexane
into the solution gave 0.37 g (0.33 mmol, 80%) of white
2
δ 1.97 (s, 15H, Cp*), 0.98 (d, J PH ) 6.6, 9H, PMe3). 31P{1H}
NMR (121.4 MHz, C6D6, 20 °C): δ -23.13 (s, PMe3). Anal.
Calcd for C13H24ZrCl3P: C, 38.19; H, 5.92; Cl, 26.01; Zr, 22.31.
Found: C, 38.48; H, 5.98; Cl, 25.68; Zr, 22.29.
Rea ction of 6 w ith 2,6-Dim eth ylxylylisocya n id e on a
P r ep a r a tive Sca le. To a solution of 2,6-xylylisocyanide (69.1
mg, 0.53 mmol) in 4.0 mL of toluene was added 6 (0.23 g, 0.20
mmol). The solution turned red immediately. After a few hours,
crystals started to form. After 5 days at ambient temperature
the solution was decanted and the crystals were washed with
pentane. This gave 60 mg (0.058 mmol, 57%) of yellow
crystalline [Cp*HfCl2]2[µ-(xyNCHdCHNxy)] (11). Anal. Calcd
for C38H50N2Cl4Hf2: C, 44.16; H, 4.88; N, 2.71. Found: C, 44.08;
H, 4.92; N, 2.53. IR: 2725(mw), 2671(w), 2353(mw), 1307(mw),
1252(w), 1196(s), 1163(w), 1128(s), 1081(m), 1023(m), 982(w),
924(m), 897(vw), 859(s), 802(vw), 777(s), 722(s), 702(mw), 669-
(vw), 601(w), 573(vw), 517(m), 498(sh), 464(w), 450(w), 430-
(m) cm-1. The compound is very poorly soluble in most
solvents, precluding NMR spectroscopic characterization.
The volatiles of the mother liquor were evaporated, leaving
a yellow-brown powder. This is a mixture of two compounds
that could be crudely separated by extraction with pentane,
one compound, [Cp*Hf(µ-Nxy)Cl]2 (12), being less soluble in
pentane than the other, Cp*Hf(η3-CH2CHNxy)Cl2 (13). Re-
crystallizing a portion of crude 12 from toluene yielded
1
crystalline 6. H NMR (500 MHz, toluene-d8, -60 °C): δ 9.17
(m, 1H, HA), 8.46 (m, 1H, HB), 7.71 (m, 1H, HC), 4.63 (m, 1H,
HD), 2.26 (s, 15H, C5Me5), 2.14 (s, 15H, C5Me5), 1.90 (s, 15H,
1
analytically pure material. H NMR (500 MHz, C6D6, 25 °C):

Zirconium and Hafnium Polyhydride Complexes
Organometallics, Vol. 20, No. 8, 2001 1627
Ta ble 4. Cr ysta llogr a p h ic Da ta for Cp *3Hf3(µ-H)4(µ-Cl)2Cl3 (6), Cp *2Zr 2(µ-H)3Cl3(P Me3) (7), a n d
[Cp *HfCl2]2[µ-(xyNCHdCHNxy)] (11)
6
7
11
chem formula
Mr
C
30H49Cl5Hf3
C23H42Cl3PZr2
638.36
monoclinic
pale yellow, plate
0.18 × 0.25 × 0.30
P21/c
15.599(3)
11.203(3)
16.862(4)
(C19H25Cl2HfN)2
1033.62
triclinic
orange, plate
0.06 × 0.24 × 0.56
P1h
9.451(1)
10.885(1)
11.774(1)
116.363(6)
92.371(8)
113.232(8)
962.17(19)
1
1122.45
triclinic
white, plate
0.12 × 0.38 × 0.48
P1h
9.029(1)
11.214(1)
17.449(2)
88.912(9)
83.370(8)
88.690(8)
1754.2(3)
2
cryst syst
color, habit
size (mm)
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
103.27(2)
2868(1)
4
1.478
10.6
Z
D
calc (g cm-3
)
2.125
92.5
1060
1.784
57.0
504
µ(Mo KR) (cm-1
F(000)
)
1304
data collection
temp (K)
130
130
130
θ range (deg)
1.17-27.5
0.90 + 0.34 tan θ
-11:11, -14:0, -22:22
0.0579, 0.4111
8737
8065
7308 (Fog 4σ(Fo))
5.89
1.24-28.0
2.00-27.0
0.90 + 0.34 tan θ
0:12, -13:12, -15:15
0.264, 0.717
4442
4183
3865 (Fo g 4σ(Fo))
2.18
ω scan width (deg)
data collected (h,k,l)
min and max transm
no. of rflns collected
no. of indpndt rflns
observed rflns
1.05 + 0.35 tan θ
-20:20, -1:14, 0:22
8206
6899
5557 (I g 2.5σ(I))
3.4
R(F) (%)
wR(F2) (%)
15.6
5.61
GOF
weighting a,b
no. of params refined
1.013
0.0924,49.26
358
2.045
432
1.046
0.0409,0.585
308
δ 7.22 (d, 4H, J ) 7.3, m-Ar), 6.74 (t, 2H, J ) 7.3, p-Ar), 2.78
(s, 12H, xy-Me), 1.71 (s, 30H, Cp*). 13C NMR (125.68 MHz,
C6D6, 25 °C): δ 148.05 (s, Ar C), 130.93 (s, Ar CMe), 128.59 (d,
J ) 157.9, Ar CH), 122.91 (d, J ) 158.4, Ar CH), 121.16 (s,
Cp* C), 24.06 (q, J ) 124.2, xy-Me), 10.76 (q, J ) 127.5, Cp*
Me). IR: 2728(mw), 2670(w), 1588(m), 1253(m), 1186(s), 1165-
(sh), 1134(vw), 1104(s), 1027(m), 978(m), 957(sh), 916(m), 878-
(s), 803(w), 764(s), 739(s), 720(m), 612(m), 580(s), 542(m),
512(m), 488(m). Anal. Calcd for C36H48N2Cl2Hf2: C, 46.16; H,
5.17; N, 2.99. Found: C, 46.23; H, 5.24; N, 2.97.
The azaallyl complex 13 could not be crystallized, but was
characterized by NMR spectroscopy. 1H NMR (500 MHz, C6D6,
25 °C): δ 7.53 (t, 1H, J ) 11.0, N-CH)CH2), 7.0-6.9 (m, 3H,
Ar), 3.77 (d, 2H, J ) 11.0, N-CHdCH2), 2.18 (s, 6H, xy-Me),
1.81 (s, 15H, Cp*). 13C NMR (125.68 MHz, C6D6, 25 °C): δ
141.14 (s, Ar C), 137.65 (d, J ) 160.4, N-CHdCH2), 136.73 (s,
Ar CMe), 129.59 (s, Ar CMe), 127.02 (d, J ) 158.8, Ar CH),
119.97 (s, Cp* C), 88.24 (t, J ) 160.2, N-CH)CH2), 12.68 (q,
J ) 127.5, xy-Me), 11.43 (q, J ) 128.1, Cp* Me). The remaining
Ar CH signal is obscured by the solvent resonances. IR: 2731-
(s), 1600(s), 1592(s), 1555(m), 1339(vw), 1310(m), 1263(s),
1223(m), 1189(w), 1125(s), 1090(s), 1068(w), 1027(s), 975(s),
942(sh), 892(s), 871(w), 820(s), 768(s), 740(w), 720(w), 710(w),
651(s), 608(m), 594(w), 536(m), 495(s).
1H NMR (300 MHz, C6D6, 20 °C): δ 7.0-6.8 (m, Ar), 4.63 (dd,
J 6.2 and 9, 1H, NCHH), 4.48 (dd, J 6.2 and 9, 1H, NCHH),
4.12 (t, J 9, 1H, NCH), 2.16 (s, 6H, xy-Me), 2.10 (s, 6H, xy-
Me), 1.81 (s, 15H, Cp*), 1.79 (s, 15H, Cp*). 13C(APT) NMR
(125.68 MHz, C6D6, 25 °C): δ 129.56 (Ar CH), 128.27 (Ar CH),
60.35 (NCH2), 56.68 (NCH), 20.13 (xy Me), 18.99 (xy Me), 11.81
(Cp* Me), 11.50 (Cp* Me). The remaining Ar CH signals are
obscured by the solvent resonances. The assignment for B was
aided by 1H,13C HETCOR, and 13C APT spectra. After 1 week,
only the resonances of the end-products 12 and 13 were
observed.
Rea ction of 8 w ith 2,6-Dim eth ylxylylisocya n id e on
NMR Sca le. To 8 (10.4 mg, 12.8 µmol) was added a solution
of 2,6-dimethylxylylisocyanide (3.8 mg, 29.0 µmol) in 0.4 mL
of C6D6. The yellow solution was transferred to an NMR tube
(equipped with Teflon stopcock) and was monitored after 30
min, 6 h, 24 h, and 1 week. No crystallization occurred. In the
spectra the formation of free PMe3 was observed. The reso-
nances of the intermediates A and B and the final products
12 and 13 are the same as for the reaction of 6 with
2,6-dimethylxylylisocyanide.
X-r a y Str u ctu r es. Suitable crystals of 6, 7, and 11 were
glued on top of a glass fiber by using inert-atmosphere hand-
ling techniques and transferred into the cold nitrogen stream
on an Enraf-Nonius CAD-4F diffractometer (graphite-mono-
chromated Mo KRj radiation, λ ) 0.71073, ∆ω ) 0.90 + 0.34
tan θ). Accurate cell parameters and an orientation matrix
were determined from the setting angles (SET426) of 22
reflections in the ranges of 18.19° < θ < 20.62° (6), 16.85° <
θ < 19.27° (7), and 16.65° < θ < 21.69° (11). Reduced cell
calculations did not indicate any higher lattice symmetry.27
Crystal data and details on data collection and refinement are
presented in Table 4. Intensity data were corrected for Lorentz
and polarization effects, and for absorption in the case of 6
and 11. The structures were solved by Patterson methods and
An aliquot of 13 was reacted with an excess of ethanol, and
the products were analyzed by GC/MS (EI): m/z 117 (M-H)
(1,1-diethoxyethane), m/z 121 (2,6-dimethylaniline), m/z 136
(1,2,3,4,5-pentamethylcyclopentadiene).
Rea ction of 6 w ith 2,6-Dim eth ylxylylisocya n id e on
NMR Sca le. To 6 (22 mg, 19.7 µmol) was added a solution of
2,6-dimethylxylylisocyanide (6.4 mg, 48.8 µmol) in 0.4 mL of
C6D6. The red solution was transferred to an NMR tube
(equipped with Teflon stopcock) and was monitored after 30
min, 6 h, 24 h, and 1 week. After a few hours crystals (of 11)
started to form in the tube. After 30 min intermediate A was
observed. 1H NMR (300 MHz, C6D6, 20 °C): δ 10.38 (d, J )
1.8, 1H, CHdN), 3.44 (d, J ) 4.4, 1H, H), 2.48 (s, 3H, xy-Me),
2.34 (s, 3H, xy-Me), 2.15 (m, 1H, H), 1.90 (s, 15H, Cp*), 1.86
(s, 15H, Cp*). After 24 h intermediate B was predominant.
(26) Boer, J . L. de; Duisenberg, A. J . M. Acta Crystallogr. 1984, A40,
C410.
(27) Spek, A. L. J . Appl. Crystallogr. 1988, 21, 578.

1628 Organometallics, Vol. 20, No. 8, 2001
Visser et al.
subsequent difference Fourier techniques (DIRDIF28 in the
case of 6 and 11). All calculations for 6 and 11 were performed
eters. The hydrogen atoms were included in the final refinement
riding on their carrier atoms with their positions calculated
by using hybridization at the C atom as appropriate with Uiso
) 1.5Uequiv of their parent atom, where values Uequiv are related
to the atoms to which the H atoms are bonded. The methyl
groups were refined as rigid groups, which were allowed to
rotate free. The missing four hydride positions could not be
located in the difference Fourier map. For 7 and 11, refinement
of the positions and anisotropic thermal parameters for the
non-hydrogen atoms followed by difference Fourier synthesis
resulted in the location of all hydrogen atoms of which the
coordinates and isotropic thermal parameters were refined.
on
a HP9000/735 computer with the program packages
SHELXL29 (least-squares refinements) and PLATON30 (cal-
culation of geometric data and the ORTEP illustrations). All
calculations for 7 were performed on a CDC-Cyber 170/760
computer with the program packages XTAL31 (least-squares
refinements) and EUCLID32 (calculation of geometric data and
the ORTEP illustrations). For 6, refinement was frustrated
by a disorder problem: one of the three Cp* ligands is
rotationally disordered; the electron density of the outer carbon
atoms (C26-C30) appeared to be spread out. Attempts to
refine a disorder model with discrete C-positions with frac-
tional occupation in this region failed; so in the final refine-
ment these atoms showed unrealistic displacement param-
Ack n ow led gm en t. This work was supported by The
Netherlands Foundation for Chemical Sciences (C.W.)
with financial aid from The Netherlands Organization
for Scientific Research (N.W.O.).
(28) Beurskens, P. T.; Beurskens, G.; Bosman, W. P.; Gelder, R. de;
Garc´ıa-Granda, S.; Gould, R. O.; Israe¨l, R.; Smits, J . M. M.; Smykalla,
C. The DIRDIF-97 program system; Crystallography Laboratory;
University of Nijmegen, The Netherlands, 1997.
Su p p or tin g In for m a tion Ava ila ble: Tables showing
details of crystal structure determinations, atom coordinates,
equivalent isotropic displacement parameters, anisotropic
thermal displacement parameters, bond lengths, angles, and
hydrogen parameters for 6, 7, and 11. This material is
available free of charge via the Internet at http://pubs.acs.org.
(29) Sheldrick, G. M. SHELXL-97, Program for the refinement of
crystal structures; University of Go¨ttingen: Germany, 1997.
(30) Spek, A. L. PLATON, Program for the automated analysis of
molecular geometry; University of Utrecht: The Netherlands, Version
of March 1998.
(31) Hall, S. R.; Stewart, J . M., Eds.; XTAL2.2. User’s manual;
Universities of Western Australia and Maryland, 1987.
(32) Spek, A. L. The EUCLID package. In Computational Crystal-
lography; Sayre, D. Ed.; Clarendon Press: Oxford, 1982; p 528.
OM0010969