Mono- and dinuclear zirconocene(iv) amide complexes for the catalytic dehydropolymerisation of phenylsilane

The dehydropolymerisation of phenylsilane is investigated using group 4 metallocene amide complexes as catalysts. The dinuclear zirconocene amide complex Cp2Zr(NMe2)(μ-Me3SiC3SiMe3)Zr(NMe2)Cp2 (2) (Cp = η5-cyclopentadienyl) shows high activity in dehydrocoupling reactions, producing polyphenylsilanes with molecular weights ranging from 200 to 3000 g mol−1 and linear-to-cyclic product ratios of up to 80 : 20. Likewise, different ratios of oligomers and polymers with different tacticities could be described. Ansa-zirconocene amide complexes possessing the ebthi (ebthi = 1,2-ethylene-1,1′-bis(η5-tetrahydroindenyl)) ligand systems were prepared and evaluated for catalytic dehydropolymerisation in comparison to the dinuclear catalyst system.

CHN analysis was done using a Leco TruSpec elemental analyser. At this point it should be pointed out that in the case of the bimetallic zirconocene complexes we could not obtain satisfactory elemental analysis in most cases. Despite repeated recrystallisation, repeated measurements with and without oxidiser V 2 O 5 and modified furnace temperature, we observed up to 20% less carbon content than calculated/expected. This behaviour might be explained by formation of mixed zircon-silicon-carbides (ceramics) in the furnace and therefore the carbon content dramatically decreases. 4 Melting points are uncorrected and were determined in sealed capillaries under Ar atmosphere using a Mettler-Toledo MP 70.
Chloride analysis was done using a Radiometer Analytical SAS TitraLab 870 TIM 870. Titration was performed with a turning point titration using a MC6091Ag combination electrode in a range of ± 2000 mV and a resolution of 0.1 mV. The exploration were carried out by oxygen oxidation of Schöniger followed by Mohr titration. 56 X-Ray diffraction data were collected on a Bruker Kappa APEX II Duo diffractometer. The structures were solved by direct methods (SHELXS-97) 7 and refined by full-matrix least-squares procedures on F 2 (SHELXL-2018). 8 Diamond 9 was used for graphical representations.
All DFT calculations were carried out with the Gaussian 16 package of molecular orbital programs. S3

General procedure of dehydropolymerisation experiments
A mixture of the catalyst (0.01 mmol, 0.2 mol%) and PhSiH 3 (0.23 mL, 6.47 mmol) in a Schlenk tube was stirred (magnetic stirring bar) at the reported temperatures in an open system with pressure compensation. The reaction mixture was stirred for one or more days at room temperature. To obtain an NMR sample, an aliquot of the reaction mixture was added to a dried, argon-filled NMR tube containing C 6 D 6 . For the GPC sample an aliquot was removed, added to THF and measured immediately.

Synthesis of 2
Compound 1b (400 mg, 0.57 mmol) and LiNMe 2 (58.6 mg, 1.15 mmol) were dissolved in 15 mL of Et 2 O and the mixture was stirred overnight. The colour of the reaction mixture changed from red to orange and Et 2 O was removed in vacuo. The orange solid residue was dissolved in benzene, followed by filtration. After washing with benzene (3x2 mL) the solution was concentrated to obtain orange crystals of 4 (326 mg, 82%). Crystals suitable for X-ray analysis were obtained from a pentane solution.

Synthesis of rac-3
[rac-(ebthi)ZrCl 2 ] (527 mg 1.24 mmol) and LiNMe 2 (126 mg, 2.47 mmol) were dissolved in 20 mL of Et 2 O and the mixture was stirred overnight at room temperature. Et 2 O was removed in vacuo. The orange solid residue was dissolved in 20 mL of toluene, followed by filtration.

Synthesis of meso-3
[meso-(ebthi)ZrCl 2 ] (436 mg, 1.02 mmol) and LiNMe 2 (105 mg, 2.04 mmol) were dissolved in 15 mL of Et 2 O and the mixture was stirred overnight at 60 °C. The colour of the reaction mixture changed from colourless to yellow and Et 2 O was removed in vacuo. The yellow residue was dissolved in 15 mL of toluene and filtered off. After addition of 4 eq of LiNMe 2 the yellow solution was stirred over four days at 60 °C to obtain [meso-(ebthi)Zr(NMe 2 ) 2 ].

Synthesis of rac-4
[rac-(ebthi)ZrCl 2 ] (300 mg, 0.70 mmol) and LiNMe 2 (36 mg, 0.70 mmol) were dissolved in 10 mL of Et 2 O and the mixture was stirred overnight at room temperature. Subsequently Et 2 O was removed in vacuo and dried for 3 h. The orange foam was dissolved in 5 mL of benzene and stirred for 15 minutes. Benzene was filtered off and the orange oil was washed with benzene (3x 1 mL). The orange solution was removed in vacuo and the orange oil was dissolved in 3 mL Et 2 O. The Et 2 O was removed in vacuo to obtain [rac-(ebthi)Zr(Cl)(NMe 2 )] as an orange solid (226 mg, 75 %).

Synthesis of meso-4
[meso-(ebthi)ZrCl 2 ] (328 mg 0.77 mmol) and LiNMe 2 (80 mg, 1.58 mmol) were dissolved in 15 mL of Et 2 O and the mixture was stirred overnight at room temperature. Et 2 O was removed in vacuo. The yellow solid residue was dissolved in 15 mL of benzene, followed by filtration. After washing with benzene (3x3 mL) the solution was removed to obtain [meso-(ebthi)Zr(Cl)(NMe 2 )] as a yellow solid (294 mg, 89%). Crystals suitable for X-ray diffraction analysis were obtained from benzene solution.

NMR spectra of the catalytic reaction of PhSiH3 with LiNMe2
Figure S 43. 1

Vibrational spectroscopy
In the following chapter the experimental infrared and Raman spectra are reported. Furthermore, selected significant bands were assigned to molecule-specific vibrations. The assignment of the vibrations was done with the help of the uncorrected calculated vibration spectra at the B3LYP/GD3BJ/def2svpp level of the theory (further details see in Chapter 7).

Computational details
In this chapter, we give the summary of a detailed analysis of the steric demand of the ebthi amide and halide complexes. For this analysis, we used the Web Tool SambVca 2.0. 10 Since not all complexes could be analysed by SC-XRD, all structures were optimised using Gaussian 16. 11 We optimised the real-size molecules using the hybrid density functional method B3LYP, 12,13 in combination with the basis set def2svpp, 14 and the empirical dispersion correction GD3BJ 15 (notation: B3LYP/GD3BJ/def2svpp). Vibrational frequencies were computed, to include zero-point vibrational energies in thermodynamic parameters and to characterise all structures as minima on the potential energy surface. To be able to generate a coordinate system/axis system that is as uniform as possible during the subsequent buried volume analysis, a "dummy" hydrogen atom was inserted into the optimised structures with the aid of GaussView. This dummy atom was placed exactly in the middle between the hetero atoms N and Cl in each of the seven complexes studied and was deleted again during the analysis. Generation of the respective coordinate system with the help of this dummy atom is documented for each molecule. For the calculation of thermodynamic relative energies of the different isomers we furthermore performed single point calculations on triple-ζ basis (def2tzvp) to obtain more accurate values.
In addition to the electronic supporting information, we provide a multi-structure xyz-file including all calculated molecules.
Please note that all computations were carried out for single, isolated molecules in the gas phase (ideal gas approximation). There may well be significant differences between gas phase and condensed phase.

Thermodynamic considerations of the isomerism between rac-3 and meso-3
as well as two different isomers of meso-4