Edge-bridged half-open zirconocenes: Synthesis, characterization, and reaction with diphenylacetylene

Article abstract of DOI:10.1016/j.jorganchem.2007.02.019

The synthesis and characterization of the new, 16 electron half-open zirconocenes, Zr(C₅H₅)(c-C₈H₁₁)(PR₃) (R = Me, Et) are reported, together with a structural study of the PEt₃ complex. As with other low valent half-open zirconocenes, the Zr-C distances are significantly shorter on average for the electronically open dienyl ligand than those for the C₅H₅ ligand, 2.343 vs. 2.512 ?. Reaction of either of these compounds with PhC₂Ph led to the incorporation of two equivalents of the alkyne, resulting in a formally 14 electron complex with coordination from cyclopentadienyl, allyl, σ-alkyl, and σ-vinyl units.

Full text of DOI:10.1016/j.jorganchem.2007.02.019

Journal of Organometallic Chemistry 692 (2007) 4460–4466
www.elsevier.com/locate/jorganchem
Edge-bridged half-open zirconocenes: Synthesis, characterization,
and reaction with diphenylacetylene
*
Benjamin G. Harvey, Vichien Kulsomphob, Atta M. Arif, Richard D. Ernst
Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, United States
Received 18 January 2007; received in revised form 17 February 2007; accepted 17 February 2007
Available online 24 February 2007
Abstract
The synthesis and characterization of the new, 16 electron half-open zirconocenes, Zr(C5H5)(c-C8H11)(PR3) (R = Me, Et) are
reported, together with a structural study of the PEt3 complex. As with other low valent half-open zirconocenes, the Zr–C distances
˚
are significantly shorter on average for the electronically open dienyl ligand than those for the C5H5 ligand, 2.343 vs. 2.512 A. Reaction
of either of these compounds with PhC2Ph led to the incorporation of two equivalents of the alkyne, resulting in a formally 14 electron
complex with coordination from cyclopentadienyl, allyl, r-alkyl, and r-vinyl units.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Pentadienyl; Coupling reaction; Zirconium complex
1. Introduction
electropositive nature of zirconium should serve even better
to promote coupling reactions with the heteroatom-con-
taining substrates listed above, while still retaining favor-
ability for coupling with alkynes, due to the conversion
of p C–C bonds to r bonds. Indeed, some of these expec-
tations have already been borne out for the 2,4-C7H11 [8]
and 6,6-dmch [9] ligands (C7H11 = dimethylpentadienyl;
dmch = dimethylcyclohexadienyl). Herein we report on
the extension of these studies to half-open zirconocenes
containing the c-C8H11 (cyclooctadienyl) ligand.
The chemistry of low valent half-open titanocenes has
proven to be very rich, yielding for example numerous
products of coupling reactions between the pentadienyl
ligands and ketones [1], imines [2], nitriles [3], isonitriles
[1], alkynes [4], and even combinations of these substrates
[5]. A number of these reactions are quite similar to reac-
tions observed for the earlier investigated zirconium diene
compounds [6]. The reactions for the electronically open
pentadienyl ligands are especially interesting given that it
has been demonstrated that these ligands, whether edge-
bridged or not, are more strongly bound than their ‘‘stabi-
lizing’’ cyclic counterparts [7]. Several reasons suggest that
an extension to the larger, more electropositive zirconium
would lead to even more promising opportunities. As the
large girth of the pentadienyl ligands leads to a reduced
degree of orbital overlap relative to C5H5, the larger zirco-
nium center would be ideal for minimizing this loss, result-
ing in even more effective bonding. In addition, the more
2. Experimental
All reactions were carried out under a nitrogen atmo-
sphere in Schlenk apparatus. Hydrocarbon and aromatic
solvents were dried by passage through activated alumina
columns under a nitrogen atmosphere, while THF was
dried by distillation from sodium benzophenone ketyl
under a nitrogen atmosphere. Elemental analyses were
obtained from Desert Analytics. 1,3-Cyclooctadiene was
prepared by the catalytic isomerization of 1,5-cyclooctadi-
ene [10], and thereafter converted to K(c-C8H11) by stan-
dard procedures [11]. Zr(C5H5)Cl2Br was prepared as
*
Corresponding author. Tel.: +1 801 581 8639.
E-mail address: ernst@chem.utah.edu (R.D. Ernst).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.02.019

B.G. Harvey et al. / Journal of Organometallic Chemistry 692 (2007) 4460–4466
4461
previously described [9]. NMR assignments for 2 were con-
firmed by 2D spectra.
J = 164 Hz), 76.4 (d, C-1,5, J = 135 Hz), 38.5 (t, C-6,8,
J = 122 Hz), 20.7 (t, C-7, J = 124 Hz), 17.3 (t, PEt3,
J = 129 Hz), 7.9 (q, PEt3, J = 127 Hz).
2.1. (Trimethylphosphine)(cyclopentadienyl)-
(cyclooctadienyl)zirconium, Zr(C5H5)(g5-c-C8H11)-
(PMe3) (1a)
Anal. Calc. for C19H31PZr: C, 59.71; H, 8.19. Found: C,
59.54; H, 7.97%.
2.3. Bis(diphenylacetylene)/Zr(C5H5)(c-C8H11) coupling
product, ‘‘Zr(C5H5)(c-C8H11)(PhCCPh)2’’ (2)
To a solution of Zr(C5H5)Cl2Br (0.50 g, 1.6 mmol) in
40 mL THF under a nitrogen atmosphere at ꢀ78 ꢁC was
added PMe3 (0.17 mL, 1.6 mmol) yielding a pale pink solu-
tion. To the resulting solution was added dropwise K(c-
C8H11) (0.70 g, 4.9 mmol) in 50 mL of THF. The resulting
red solution was allowed to warm to room temperature and
a color change to green-blue was observed. Then the sol-
vent was removed in vacuo and the crude product extracted
with three portions of 20 mL pentane and filtered through
a Celite pad on a coarse frit. Concentration in vacuo of
the green-blue filtrate was carried out until incipient crys-
tallization. Cooling of the mixture to ꢀ90 ꢁC for one day
afforded 0.42 g of an air-sensitive blue crystalline solid
(mp 95–96 ꢁC) in 65% yield.
0.21 g (0.056 mmol) of Zr(C5H5)(c-C8H11)(PEt3) were
partially dissolved in 40 mL of hexane in a 100 mL Schlenk
flask. 0.22 g (1.2 mmol) of diphenylacetylene was added as
a solid under nitrogen and the flask was swirled several
times. The originally bright blue-green solution rapidly
converted to a dark red color and was left to sit undis-
turbed for 18 h. Bright red needle-like crystals precipitated
from the solution and were collected by syringing off the
supernatant, washing with 3 · 10 mL pentane, and drying
in vacuo. Yields ranged from 50% to 70% depending on
the purity of the starting materials. The title compound
can also be synthesized from the PMe3 adduct with similar
results. Crystals suitable for an X-ray crystallographic
study were grown by carefully layering a dilute, filtered
solution of the phosphine adduct in hexane with a dilute
solution of the acetylene in the same solvent.
1H NMR (benzene-d6, ambient): d 6.95 (dt, 1H, H-3,
J = 10.1, 4.2 Hz), 6.28 (s, 5H, C5H5), 5.30 (dt, 2H, H-2,4,
J = 10.1, 4.2 Hz), 2.50 (m, 2H, H-1,5), 0.6–1.0 (m, 6H,
H-(6–8)), 0.33 (d, 9H, PMe3, J = 5.4 Hz).
13C NMR (benzene-d6, ambient): d 135.6 (d, C-3,
J = 150 Hz), 106.1 (d, C5H5, J = 169 Hz), 80.6 (d, C-2,4,
J = 161 Hz), 76.0 (d, C-1,5, J = 134 Hz), 38.4 (t, C-6,8,
J = 122 Hz), 21.1 (t, C-7, J = 124 Hz), 18.5 (dq, PMe3,
J = 121, 15 Hz).
1H NMR (benzene-d6, ambient): d 7.35–6.65 (m, 20H,
Ph), 6.03 (t, 1H, J = 8 Hz, H3), 5.75 (s, 5H, Cp), 4.91 (t,
1H, J = 9 Hz, H5), 4.69 (dd, 1H, J = 11.5, 9.5 Hz, H4),
4.60 (dd, 1H, J = 7.2, 2.1 Hz, H6), 3.82 (d, 1H, J = 8 Hz,
H2), 3.53 (s, 1H, H10), 3.05 (t, 1H, J = 7 Hz, H6), 2.50–
2.34 (1H, H7endo), 1.98–1.84 (m, 1H, H7exo), 1.54–1.34
(m, 2H, H8a,b).
Anal. Calc. for C16H25PZr: C, 56.59; H, 7.42. Found: C,
56.71; H, 7.39%.
13C NMR (benzene-d6, ambient): d 154.4 (s, 1C), 152.0
(s, 1C), 149.0 (s, 1C), 145.7 (s, 1C), 139.4 (s, 1C), 127.7
(d, 1C, J = 162 Hz, C4), 111.4 (d, 5C, J = 171 Hz, Cp),
107.8 (d, 1C, J = 164 Hz, C3), 96.1 (d, 1C, J = 157 Hz,
C5), 90.6 (d, 1C, J = 125 Hz, C10), 69.0 (s, 1C, C9), 60.0
(d, 1C, J = 136 Hz, C6), 59.8 (d, 1C, J = 136 Hz, C1),
46.4 (d, 1C, J = 131 Hz, C2), 37.8 (t, 1C, J = 130 Hz,
C7), 30.2 (t, 1C, J = 129 Hz, C8).
2.2. (Triethylphosphine)(cyclopentadienyl)
(cyclooctadienyl)zirconium, Zr(C5H5)(g5-c-C8H11)
(PEt3) (1b)
To a solution of Zr(C5H5)Cl2Br (0.50 g, 1.6 mmol) in
40 mL THF under a nitrogen atmosphere at ꢀ78 ꢁC was
added PEt3 (0.25 mL, 1.6 mmol), yielding a pale pink solu-
tion. To the resulting solution was added dropwise K(c-
C8H11) (0.70 g, 4.9 mmol) in 50 mL of THF. The resulting
red solution was allowed to warm to room temperature and
a color change to green-blue was observed. Then the sol-
vent was removed in vacuo and the crude product extracted
with several portions of pentane and filtered through a Cel-
ite pad on a coarse frit. Concentration in vacuo of the blue
filtrate was carried out until incipient crystallization. Cool-
ing of the mixture to ꢀ90 ꢁC for one day afforded 0.40 g of
an air-sensitive blue crystalline solid (mp 127–128 ꢁC) in
62% yield.
Anal. Calc. for C41H36Zr: C, 79.43; H, 5.85. Found: C,
79.23; H, 6.07%.
2.4. Crystallographic studies
Crystal, data collection, and refinement parameters are
presented in Table 1. Single crystals of each compound
were examined under Paratone oil. Suitable crystals were
then transferred to a Nonius Kappa diffractometer for
study, which in the case of 2 was equipped with a CCD
detector. Initial structural solutions came from direct
methods using SIR-97 [12], while SHELXL-97 [13] was used
for the location of additional atoms and structural refine-
ments. All nonhydrogen atoms were refined anisotropi-
cally. The hydrogen atoms in 1b were placed in
idealized positions while those in 2 were successfully
refined isotropically.
1H NMR (benzene-d6, ambient): d 6.95 (br, 1H, H-3),
6.28 (s, 5H, C5H5), 5.32 (m, 2H, H-2,4), 2.51 (m, 2H, H-
1,5), 0.8–1.2 (m, 6H, H-(6–8)), 0.75 (m, 6H, PEt3), 0.30
(m, 9H, PEt3).
13C NMR (benzene-d6, ambient): d 136.0 (d, C-3,
J = 157 Hz), 106.2 (d, C5H5, J = 169 Hz), 80.6 (d, C-2,4,

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B.G. Harvey et al. / Journal of Organometallic Chemistry 692 (2007) 4460–4466
Table 1
ences between the separations between the dienyl termini
Crystallographic parameters for Zr(C5H5)(c-C8H11)(PEt3) (1b) and the
bis(diphenylacetylene) coupling product, 2
(C1, C5). For Ti(C5H5)(c-C8H11)(PMe3), the C1–C5 sepa-
˚
ration is 3.08 A [15], whereas for Ti(C5H5)(6,6-
Formula
C
381.65
173(1)
19H31PZr
C41H36Zr
619.92
200(1)
˚
dmch)(PMe3) [1d], the separation is 2.43 A. Not only does
Formula weight
Temperature (K)
this increase in girth make c-C8H11 more sterically
demanding, but that extra girth also geometrically requires
a closer approach of the dienyl ligand plane to the metal,
just to maintain similar M–C distances. For these two com-
plexes, the respective deviations of the titanium center from
˚
k (A)
Crystal system
Space group
Triclinic
Monoclinic
P21/n
ꢀ
P1
Unit cell dimensions
˚
a (A)
8.289(2)
9.770(5)
12.656(7)
95.68(6)
105.27(5)
108.72(3)
917.4(8)
2
13.0909(4)
15.8198(5)
14.2531(3)
90
91.4619(16)
90
2950.79(14)
4
1.395
˚
the open dienyl planes are 1.50 and 1.72 A, vs. 2.07 and
˚
b (A)
˚
2.06 A for the C5H5 ligands.
˚
c (A)
The structure of Zr(C5H5)(c-C8H11)(PEt3) (1b, Fig. 1
and Table 2, c-C8H11 = cyclooctadienyl) is observed to be
similar to that of Ti(C5H5)(6,6-dmch)(PMe3) (dmch = dim-
ethylcyclohexadienyl) in that the phosphine ligand resides
near the central carbon atom (C3) of the electronically
open dienyl ligand, whereas for related species without
edge-bridges, the phosphine would be positioned by the
open edge. Similar to related early metal complexes [16],
a (ꢁ)
b (ꢁ)
c (ꢁ)
Volume (A )
Z
Dcalc
3
˚
1.382
6.68
Absorption coefficient
(cmꢀ1
h Range (ꢁ)
Limiting indices
4.02
)
2.0–24.0
0 6 h 6 9,
ꢀ11 6 k 6 10,
ꢀ14 6 l 6 13
3081
3.3–25.3
ꢀ15 6 h 6 15,
ꢀ19 6 k 6 17,
ꢀ17 6 l 6 17
9924
Reflections collected
Independent reflections
n: I > nr(I)
2455
3
5374
2
R(F)
Rw(F2)
0.0632
0.0830
0.0407
0.0824
Zr
Et3 P
Maximum differenceꢀ3
1.79
0.40
˚
Fourier peak (e A
)
1b
3. Results and discussion
the Zr–C bonds for the electronically open dienyl ligand
˚
˚
The reaction of Zr(C5H5)Cl2Br with three equivalents of
K(c-C8H11) in the presence of PMe3 or PEt3 yields the
respective 16 electron Zr(C5H5)(c-C8H11)(PR3) complexes
(Eq. (1); R = Me, Et)
(2.260(7)–2.428(7) A, avg. 2.343 A) are significantly shorter
than those for the aromatic C5H5 ligand (2.491(10)–
˚
˚
2.534(10) A, avg. 2.512 A). This translates into a substan-
tial difference in the deviations of the zirconium center
from the dienyl planes (vide infra). For the c-C8H11 ligand,
the Zr–C distances differ significantly, with average values
for the three types of carbon atom positions being
Zr(C5H5)Cl2Br + 3K(c-C8H11) + PR3
! Zr(C5H5)(c-C8H11)(PR3) R = Me, Et
ð1Þ
˚
˚
˚
2.268(5) A for C(1,5), 2.374(5) A for C(2,4), and
These complexes are of interest for several reasons. Their
deep blue colors are quite unique among related open
and half-open metallocenes. Further, half-open zirconoc-
enes with other pentadienyl ligands thus far have incorpo-
rated two phosphorus donor centers, as in Zr(C5H5)(6,6-
dmch)(PMe3)2 [9] and Zr(C5H5)(2,4-C7H11)(dmpe) [8]. In
this respect, the Zr(C5H5)(c-C8H11)(PR3) complexes resem-
ble analogous 16 electron titanium complexes [1], in which
only one donor center has thus far been observed, whether
the accompanying pentadienyl ligand is 2,4-C7H11, 6,6-
dmch, or c-C8H11. The formation of 16 electron half-open
zirconocenes with the c-C8H11 ligand must be due to the c-
C8H11 ligand being more sterically demanding than either
2,4-C7H11 or 6,6-dmch. It has been recognized for some
time that the edge-bridged ligands such as 6,6-dmch and
c-C8H11 are more sterically demanding than 2,4-C7H11
[1d,7,14]. That c-C8H11 is more sterically demanding than
6,6-dmch can readily be explained on the basis of differ-
2.428(7) A for C3. This trend may be attributed to the loca-
˚
tion of the phosphine ligand (Zr–P = 2.755(2) A) near the
C3 atom. One observes significant tilts of the hydrogen
atom substituents below the c-C8H11 plane, averaging
22.4ꢁ for H(1,5), 11.3ꢁ for H(2,4), and 3.0ꢁ for H3. The re-
lated Ti(C5H5)(c-C8H11)(PMe3) complex displays respec-
tive tilts of 23.0ꢁ, 15.0ꢁ, and 4.6ꢁ [15]. For purposes of
comparison with the Ti(C5H5)(c-C8H11)(PMe3) and
Ti(C5H5)(6,6-dmch)(PMe3) complexes discussed above,
Zr(C5H5)(c-C8H11)(PEt3) displays a C1–C5 separation of
˚
3.16 A, and respective deviations of the zirconium center
˚
by 2.233 and 1.609 A from the C5H5 and c-C8H11 planes.
For the 18 electron Zr(C5H5)(2,6,6-tmch)(PMe3)2 complex,
the corresponding distances were found to be 2.37, 2.220,
˚
and 2.024 A [9].
While several coupling products have been readily iso-
lated from the reactions of Ti(C5H5)(c-C8H11)(PR3)

B.G. Harvey et al. / Journal of Organometallic Chemistry 692 (2007) 4460–4466
4463
Table 2
C12
˚
C13
Selected bond distances (A) and angles (ꢁ) for Zr(C5H5)(c-C8H11)(PEt3) (1)
˚
Bond distances (A)
C9
C15
C14
C19
C11
Zr–P
2.755(2)
2.276(7)
2.367(7)
2.428(7)
2.382(8)
2.260(7)
2.510(9)
2.520(10)
2.491(10)
2.505(11)
2.534(10)
1.437(11)
C1–C8
C2–C3
C3–C4
C4–C5
C5–C6
C6–C7
C7–C8
C9–C10
C9–C13
C10–C11
C11–C12
C12–C13
1.530(10)
1.417(11)
1.409(10)
1.438(10)
1.531(10)
1.514(11)
1.509(11)
1.429(20)
1.413(19)
1.337(21)
1.267(20)
1.309(20)
C10
Zr–C1
Zr–C2
Zr–C3
Zr–C4
Zr–C5
Zr–C9
Zr–C10
Zr–C11
Zr–C12
Zr–C13
C1–C2
P
Zr
C18
C5
C6
C4
C16
C17
C8
C3
C1
C7
C2
Bond angles (ꢁ)
Zr–P–C14
117.7(3)
115.2(2)
115.8(2)
C1–C2–C3
C2–C3–C4
C3–C4–C5
126.7(7)
130.6(7)
126.3(7)
Fig. 1. Solid state structure of Zr(C5H5)(c-C8H11)(PEt3) (1b).
Zr–P–C16
Zr–P–C18
(R = Me, Et) complexes with PhC2SiMe3, the correspond-
ing reactions for the analogous zirconium complexes have
been more complicated, thereby leading to an attempt with
another alkyne, Ph2C2. Notably, with either Zr(C5H5)(c-
C8H11)(PR3) complex (R = Me, Et), a single, identical di(a-
lkyne) coupling product resulted, 2, whose complexity
required a single crystal X-ray-diffraction study for its elu-
cidation. In contrast, Ti(C5H5)(c-C8H11)(PMe3) and
C38
C39
C32
C40
C37
C41
C3
C31
C4
C5
C12
C25
Zr1
C2
C11
C26
C6
C1
Ph
Zr
C7
C10
C8
C9
C19
Ph
Ph
C20
C13
C14
Ph
2
Ti(C5H5)(c-C8H11)(PEt3) each gave rise to its own coupling
product(s) with PhC2SiMe3 at least, incorporating two [4b]
and three (and/or four) [15] equivalents of alkyne,
respectively.
Fig. 2. Structure of the Zr(C5H5)(c-C8H11)/bis(Ph2C2) coupling product,
2.
The structure of compound 2 is presented in Fig. 2,
while pertinent bonding parameters are given in Table 3.
The zirconium center is coordinated by a cyclopentadienyl
ligand, an allyl fragment (C3–C5), a r-alkyl ligand (C10),
and a formally r-vinyl ligand (C12). The Zr–C r-bond dis-
˚
1.393(5) A) nonetheless suggests little if any contribution
from a r-allyl resonance form. As a result of the above-
mentioned ligand coordinations, the complex has a formal
14 electron count, an extremely low value for a zirconium
center. Based on the results obtained for related electron
deficient coupling products [15a,17], the possibility of the
presence of (C–H) ! Zr agostic interactions needs to be
considered. There is, in fact, one C–H bond in a position
to engage in an agostic interaction, although structural
parameters do not suggest it to be very strong (e.g., Zr–
˚
˚
tances are shortest at 2.249(3) A for C12 and 2.264(3) A for
C10. The shorter r-vinyl coordination is in accord with the
greater s character on the bound carbon atom, sp2 vs. sp3.
The Zr–C distances for the cyclopentadienyl ligand are
˚
fairly regular, averaging 2.524 A, while the allyl coordina-
tion is decidedly asymmetric, with the respective Zr–C(3–
˚
5) distances being 2.385(3), 2.439(3), and 2.505(3) A. The
˚
˚
H10, 2.60 A; Zr–C10–H10, 100(2)ꢁ; C10–H10, 0.94(3) A).
similarity of the C3–C4 and C4–C5 distances (1.385(5),

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B.G. Harvey et al. / Journal of Organometallic Chemistry 692 (2007) 4460–4466
Table 3
˚
Selected bond distances (A) and angles (ꢁ) for the bis(diphenylacetylene)
coupling product
˚
Bond distances (A)
Zr–C3
Zr–C4
Zr–C5
Zr–C10
Zr–C12
Zr–C37
Zr–C38
Zr–C39
Zr–C40
Zr–C41
2.385(3)
2.439(3)
2.505(3)
2.264(3)
2.249(3)
2.500(3)
2.532(3)
2.556(4)
2.530(3)
2.500(3)
C1–C2
C1–C9
C2–C3
C2–C11
C3–C4
C4–C5
C5–C6
C6–C9
C9–C10
C11–C12
1.566(4)
1.570(4)
1.525(4)
1.536(4)
1.385(5)
1.393(5)
1.523(5)
1.550(4)
1.562(4)
1.347(4)
Ph
Zr
10
2
6
9
1
Ph
8
4
Bond angles (ꢁ)
C10–Zr–C12
Zr–C10–C9
Zr–C12–C11
C10–C9–C6
C10–C9–C1
C12–C11–C2
C11–C2–C1
97.36(11)
106.8(2)
105.7(2)
106.8(2)
119.3(2)
116.4(3)
115.8(2)
C2–C1–C9
C11–C2–C3
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C5–C6–C9
120.6(2)
The larger size of zirconium, and/or its ability to form stron-
ger bonds, appear(s) to lead its complexes through a differ-
ent course. One possibility is that activation of a C–H bond
on C6, formerly a CH2 group adjacent to dienyl terminus
C5, regenerates a dienyl fragment, together with formation
of a Zr–H bond. The new dienyl terminus, C6, then could
couple to C9, the alkyne carbon atom involved in the origi-
nal coupling to C1, yielding after transfer of the hydride to
C10, 5 having (as in 4) a diene ligand formed between carbon
atoms C2–C5. The second alkyne could then simply
108.8(3)
119.8(3)
126.5(3)
126.9(3)
126.9(3)
113.7(3)
The mechanism responsible for the unique alkyne cou-
plings leading to 2 is of some interest. Although more than
one possible pathway could lead to this species, the obser-
vation of a somewhat related cage geometry in one of the
Ph
10
1
Zr
3
Ph
Zr(C5H5)(c-C8H11)/PhC2SiMe3 coupling products,
3
2
[15a], suggests a common pathway, thereby helping to nar-
row the range of possibilities. Notably, while titanium com-
plexes with
6
4
5
coordinate to the metal center, and couple to a diene termi-
nus, C2, to yield the observed product, 2. Alternatively, it is
also possible that the second alkyne is incorporated just
after the coupling of the first alkyne to C1, and that the sec-
ond alkyne then couples to the other end of the first alkyne
(C10 in 4) and to C2, yielding 6. Subsequent C6–H activa-
tion, hydride transfer to C10, C9–C6 coupling, and C10–
C12 bond activation would then yield 2.
Zr
X
X
Ph
Ph
X = SiMe3
Ph
Ph
12
10
Ph
3
11
2
1
Zr
9
6
Ph
2,4-C7H11 and c-C8H11 ligands have thus far all undergone
1,5 couplings with alkynes [1c,4,15], the Zr(C5H5)(c-
C8H11)(PR3) complexes appear to favor instead a 1,2 pro-
cess. In either case, the initial coupling occurs between a
phenyl-substituted alkyne carbon atom and a dienyl termi-
nus (1 position), presumably yielding a species such as 4,
which may incorporate a PR3 ligand. For the titanium
reactions, the other alkyne carbon atom thereafter couples
to the other dienyl terminus.
6
Interestingly, dissolution of 2 in THF for ca. 12 hours
leads to its clean conversion to another species, which
can also be prepared by carrying out the coupling reaction
of 1 with two equivalents of Ph2C2 in THF [15a]. The same

B.G. Harvey et al. / Journal of Organometallic Chemistry 692 (2007) 4460–4466
4465
(e) R. Basta, A.M. Arif, R.D. Ernst, Organometallics 24 (2005) 3982;
(f) R. Tomaszewski, A.M. Wilson, L. Liable-Sands, A.L. Rheingold,
R.D. Ernst, J. Organomet. Chem. 583 (1999) 42.
species is also formed in benzene solutions, but at a much
slower rate. It also appears possible to isolate a 1:1 cou-
pling product from 1b and PhC2SiMe3. Neither of these
species has as yet been obtained in pure crystalline form,
but spectroscopic data suggest they can be formed and iso-
lated as predominant products. It is possible that the nat-
ure of the mono(alkyne) coupling product would provide
some further indication of the likely mechanism by which
2 is formed.
[2] R. Basta, R.D. Ernst, A.M. Arif, J. Organomet. Chem. 683 (2003) 64.
´
[3] I. Hyla-Kryspin, T.E. Waldman, E. Melendez, W. Trakarnpruk,
A.M. Arif, M.L. Ziegler, R.D. Ernst, R. Gleiter, Organometallics 14
(1995) 5030.
[4] (a) A.M. Wilson, T.E. Waldman, A.L. Rheingold, R.D. Ernst, J.
Am. Chem. Soc. 114 (1992) 6252;
(b) B.G. Harvey, C.L. Mayne, A.M. Arif, R. Tomaszewski, R.D.
Ernst, J. Am. Chem. Soc. 127 (2005) 16426, corn.: 128 (2006) 1770.
[5] (a) R. Tomaszewski, A.M. Arif, R.D. Ernst, J. Chem. Soc., Dalton
Trans. (1999) 1883;
4. Conclusions
(b) R. Tomaszewski, K.-C. Lam, A.L. Rheingold, R.D. Ernst,
Organometallics 18 (1999) 4174.
[6] (a) G. Erker, C. Kruger, G. Muller, Adv. Organomet. Chem. 24
¨
The Zr–C bond distances in Zr(C5H5)(c-C8H11)(PEt3)
reveal clearly that the nonaromatic c-C8H11 ligand is
bound more strongly than the C5H5 ligand. Although
cyclopentadienyl ligands have been observed to undergo
coupling reactions [18], coupling reactions of unsaturated
organic molecules with half-open titanocenes or zirconoc-
enes nonetheless involve preferentially the more strongly
bound, but nonaromatic, pentadienyl ligands [7]. The reac-
tions of titanium and zirconium pentadienyl complexes
with alkynes have led both to compounds having (C–
C) ! M agostic interactions, and to actual C–C and C–Si
bond activations. Given the fact that the bond activations
are more common for zirconium, which typically forms
stronger bonds than titanium, it can be expected that
related hafnium chemistry will also commonly lead to C–
C bond activations, and further efforts in that direction
should therefore prove fruitful.
(1985) 1;
(b) H. Yasuda, K. Tatsumi, A. Nakamura, Acc. Chem. Res. 18
(1985) 120;
(c) M. Akita, K. Matsuoka, K. Asami, H. Yasuda, A. Nakamura, J.
Organomet. Chem. 327 (1987) 193;
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[7] R.D. Ernst, Comments Inorg. Chem. 21 (1999) 285.
[8] V. Kulsomphob, A.M. Arif, R.D. Ernst, Organometallics 21 (2002)
3182.
[9] V. Kulsomphob, B.G. Harvey, A.M. Arif, R.D. Ernst, Inorg. Chim.
Acta 334 (2002) 17.
[10] (a) J.E. Arnet, R. Pettit, J. Am. Chem. Soc. 83 (1961) 2954;
(b) D. Wittenberg, H. Seibt, German Patent DE 1136329-1962-09-
13.
[11] (a) D.R. Wilson, L. Stahl, R.D. Ernst, Organomet. Synth. 3 (1986)
136;
(b) H. Yasuda, T. Nishi, K. Lee, A. Nakamura, Organometallics 2
(1983) 21.
[12] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
vazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J.
Appl. Crystallogr. 32 (1999) 115.
5. Supplementary material
[13] G.M. Sheldrick, SHELXS-97: A Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[14] (a) P.T. DiMauro, P.T. Wolczanski, Organometallics 6 (1987) 1947;
(b) R. LeSuer, R. Basta, A.M. Arif, W.E. Geiger, R.D. Ernst,
Organometallics 22 (2003) 1487.
[15] (a) B. Harvey, Ph.D. Thesis, University of Utah, 2005;
(b) B.G. Harvey, A.M. Arif, R.D. Ernst, J. Organomet. Chem. 691
(2006) 5211.
CCDC 231988 and 632119 contain the supplementary
crystallographic data for this paper. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
´
[16] (a) E. Melendez, A.M. Arif, M.L. Zeigler, R.D. Ernst, Angew.
Chem. Int., Ed. Engl. 27 (1988) 1099;
(b) J.W. Freeman, N.C. Hallinan, A.M. Arif, R.W. Gedridge, R.D.
Ernst, F. Basolo, J. Am. Chem. Soc. 113 (1991) 6509;
(c) R.W. Gedridge, J.P. Hutchinson, A.L. Rheingold, R.D. Ernst,
Organometallics 12 (1993) 1553;
Acknowledgements
(d) R. Basta, B.G. Harvey, A.M. Arif, R.D. Ernst, Inorg. Chim.
Acta 357 (2004) 3883.
[17] S. Pillet, G. Wu, V. Kulsomphob, B.G. Harvey, R.D. Ernst, P.
Coppens, J. Am. Chem. Soc. 125 (2003) 1937.
Acknowledgement is made to the Donors of the Amer-
ican Chemical Society Petroleum Research Fund and the
University of Utah for partial support of this work.
[18] (a) G.K. Anderson, Organometallics 5 (1986) 1903;
(b) D.M. Giolando, T.B. Rauchfuss, J. Am. Chem. Soc. 106 (1984)
6455;
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