-metallocenes have attracted considerable interest as precursors for olefin polymerization catalysts. Anderson & Lin (1987
) reported the synthesis of the title ansa
. We are interested in novel donor-functionalized cycloheptatrienyl–cyclopentadienyl zirconium sandwich compounds, using zirconocenes as starting materials (Büschel et al.
; Tamm, 2008
; Tamm et al.
). During these studies, we accidentally obtained single crystals of (I)
that were suitable for X-ray diffraction studies. The molecular structure of (I)
in the solid state is shown in Fig. 1.
Figure 1 The molecule of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
The two Cl ligands and the centroids of the two cyclopentadienyl (Cp) ligands in (I)
adopt a distorted tetrahedral arrangement about the Zr atom due to the presence of a PhP moiety as the bridging unit between the two carbocyclic fragments. The angle α subtended by the Cp centroids at the metal atom is 122.63 (3)°. The angle β between the Cp ring normals is 116.3 (1)°, resulting in a value of 3.2° for the tilt angle γ [γ = (α − β)/2; the angles α, β and γ, which describe the bending of the ansa
-zirconocene compound in more detail, are defined graphically in the second scheme
, taken from Shin et al.
)]. As the tilt angle increases, the metal atom is displaced further towards the ansa
bridge. The Cl1—Zr—Cl2 angle is 101.490 (16)°, and the Zr—Cl bond lengths are 2.4224 (4) and 2.4316 (4) Å. The deviation from a symmetric η5
-coordination towards a η3
-coordination mode, associated with the tilting, is indicated by a range of 0.111 Å for the individual Zr—CCp
bond lengths [2.454 (1)–2.565 (1) Å]. Distortion involving the P atom is also observed; it lies 0.474 (3) Å out of the plane of the ring C1–C5 and 0.496 (3) Å out of the plane of the ring C6–C10. The C6—P1—C1 angle, at 91.42 (7)°, is considerably narrowed by the pincer effect of the two Cp rings [cf.
C11—P1—C6 = 106.40 (8)° and C11—P1—C1 = 100.40 (8)°].
Table 2 collates related data for the compounds [PhP(C5
, (II) (Shin et al.
), and [MeP(C5
, (III) (Häp et al.
). The closely related compound [MeP(C5
(Shin et al.
) must be omitted from a detailed comparison because it suffers from disorder. Inspection of the supplementary material reveals that the reported space group is C
, with the Zr and P atoms lying on a twofold axis, and the methyl C atom is therefore disordered over two sites; the CCp
angle seems improbably large at 107.8°. For comparison with systems lacking the bridging atom, the compound Cp2
, (IV), may be used, but the structure suffers somewhat from high U
values (Corey et al.
) of the Cp rings. Some more recent redeterminations at lower temperature can be found in the Cambridge Structural Database (Version 1.11; Allen, 2002
), but suffer from various imperfections such as a lack of s.u. values. The complex Cp*2
, (V) (Böhme & Rittmeister, 1998
), is also adduced.
Table 2 Selected dimensions (Å, °) of (I) and related structures
Table 2 indicates that the β angles are almost identical for all three compounds (I)–(III), so that the relative disposition of the Cp rings is also closely similar. Indeed, all three bending angles are very similar in (I)
and (III). However, the α angle is significantly smaller in (I)
than in (II), necessarily leading to a more pronounced tilting. The γ angle is largest for (II), also reflected in a larger deviation of (II) from a symmetric η5
-coordination towards a η3
-coordination mode [the range of Zr—CCp
distances for (II) is 0.173 Å]. The Cl1—Zr—Cl2 angle in (I)
[101.490 (19)°] is appreciably larger than that in (III), perhaps reflecting the differing spatial demands of methyl and phenyl groups at P, but the Zr—Cl bond lengths of both compounds are similar.
The unbridged complexes (IV) and (V), as expected, display larger values of α and (especially) β, somewhat lower Cl—Zr—Cl bond angles and a smaller range of Zr—CCp bond lengths, corresponding to more symmetric coordination of the Cp rings.
As would be expected, there are no unusually short intermolecular contacts in (I)
. Four weak hydrogen bonds are given in Table 1, of which we regard the H3
P1 interaction as borderline. There is also a C—H
π contact to the centroid of the phenyl ring, and finally a short Cl1
contact of 3.5064 (7) Å (symmetry code as in Table 1). The molecules are connected by all these interactions to form thick layers parallel to the bc
plane at x
. However, the general view of such a layer is too complex to be useful. We therefore present two separate packing diagrams. Fig. 2(a
) shows that the three H
Cl contacts link the molecules to form double chains parallel to the b
axis, whereas the other three contacts (Fig. 2
) form chains parallel to the c
Hydrogen-bond geometry (Å, °)
Figure 2 Packing diagrams for (I). (a) The three C—HCl contacts (thin dashed lines) connect the molecules to form double chains parallel to the b axis. The origin is at the bottom right, the c axis out of the paper, the a axis vertical (more ...)