Crystal structure of bis(η5-cyclopentadienyl)(2,3-diethylbutane-1,4-diyl)hafnium(IV)

The title compound, [Hf(C5H5)2(C8H16)], proves a structural motif of hafnacyclopentane besides the coordination of two cyclopentadienyl ligands in an η5-fashion. The hafnacyclopentane ring has a twist conformation and is substituted by two ethyl groups in the β,β′-positions, which are trans orientated to each other. One cyclopentadienyl ring and one ethyl group are each disordered over two positions with site-occupancy ratios of 0.679 (15):0.321 (15) and 0.702 (18):0.298 (18), respectively.


S1. Synthesis and crystallization
A suspension of Cp 2 HfCl 2 (2.243 g, 5.91 mmol) in 20 ml of toluene was treated with 7.5 ml (12.0 mmol) of a 1.6 M solution of n-BuLi in n-hexane. The mixture was stirred for 30 minutes at room temperature. After filtration bis(trimethylsilyl)acetylene (1.5 ml, 6.67 mmol) and pyridine (0.60 ml, 7.45 mmol) were added to the resulting yellow solution.
The reaction mixture was stirred 3.5 hours at 100 °C. All volatiles were evaporated from the dark purple solution and the residue was extracted with 40-50 ml of n-hexane at 55 °C. The solution was filtered, concentrated in vacuum to 10-15 ml and stored at -78°C. After one day dark purple crystals had formed which were isolated by decanting of the mother liquor, washed with cold n-hexane and dried in vacuum to give a mixture of the alkyne complex Cp 2 Hf(η 2 -Me 3 SiC 2 SiMe 3 )(py) and the title compound in a ratio of 2:1 (checked by NMR). After recrystallization from n-hexane brown crystals of the title complex were isolated: 0,120 g, yield: 5 %. Anal. Calcd. for C 18 H 26 Hf (420.89 g·mol -1 ): C 51.37, H 6.23%. Found: C 50.99, H 6.03%.
Single Crystals were obtained from a saturated solution (n-hexane) at ambient temperature.

S2. Refinement
H atoms were placed in idealized positions with d(C-H) = 0.95-1.00 Å (CH), 0.99 Å (CH 2 ) and 0.98 Å (CH 3 ), and refined using a riding model with U iso (H) fixed at 1.2 U eq (C) for CH and CH 2 and 1.5 U eq (C) for CH 3 . SADI and SAME instructions were used to improve the geometry of the cyclopentadienyl rings. Additionally, the anisotropic displacement parameters of C6A-C10A were restrained to be equal (SIMU). SADI was used for the disordered ethyl group. For the ethyl group C15, C16 the use of DFIX was necessary due to unresolved disorder. Atoms of the disordered ethyl group and the minor occupied atoms of the disordered cyclopentadienyl ring are refined isotropically. The highest peak in the final difference Fourier map is located 1.36 Å from C13 and the deepest hole 0.83 Å from C3.

Figure 1
Molecular structure of the title compound with atom labelling and displacement ellipsoids drawn at 30% probability level. H atoms have been omitted for clarity.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (