Complexation and disproportionation of group 4 metal (alkoxy) halides with phosphine oxides

Group 4 Lewis acids are well-known catalysts and precursors for (non-aqueous) sol–gel chemistry. Titanium, zirconium and hafnium halides, and alkoxy halides are precursors for the controlled synthesis of nanocrystals, often in the presence of Lewis base. Here, we investigate the interaction of Lewis bases with the tetrahalides (MX4, X = Cl, Br) and metal alkoxy halides (MXx(OR)4−x, x = 1–3, R = OiPr, OtBu). The tetrahalides yield the expected Lewis acid–base adducts MX4L2 (L = tetrahydrofuran or phosphine oxide). The mixed alkoxy halides react with Lewis bases in a more complex way. 31P NMR spectroscopy reveals that excess of phosphine oxide yields predominantly the complexation product, while a (sub)stoichiometric amount of phosphine oxide causes disproportionation of the MXx(OR)4−x species into MXx+1(OR)3−x and MXx−1(OR)5−x. The combination of complexation and disproportionation yields an atypical Job plot. In the case of zirconium isopropoxy chlorides, we fitted the concentration of all observed species and extracted thermodynamic descriptors from the Job plot. The complexation equilibrium constant decreases in the series: ZrCl3(OiPr) > ZrCl2(OiPr)2 ≫ ZrCl(OiPr)3, while the disproportionation equilibrium constant follows the opposite trend. Using calculations at the DFT level of theory, we show that disproportionation is driven by the more energetically favorable Lewis acid–base complex formed with the more acidic species. We also gain more insight into the isomerism of the complexes. The disproportionation reaction turns out to be a general phenomenon, for titanium, zirconium and hafnium, for chlorides and bromides, and for isopropoxides and tert-butoxides.


Crystallographic data
Table S1: Comparison of bond lengths in the adducts of metal halides with Lewis bases (THF or TPPO).Thermogravimetric Analysis (TGA) Table S3: TGA Analysis of the newly synthesized compounds.The larger deviation from the ideal weight loss is likely due to the formation of zirconium phosphate.The complete weight loss for the titanium complex is attributed to the volatile nature of TiCl 4 .

S-4
Infrared Spectroscopy  The concentration of all species was determined as described below.Firstly, all the resonances in the 31 P NMR spectra are integrated to determine the equilibrium concentrations.The sum of integrals is normalized for the total concentration of TOPO in the solution (see Table 5 in the main text).The majority of the resonances were assigned as shown in Figures S8B, S9B and S10B.However a few small peaks remain unassigned (indicated by a star symbol).For the assigned complexes with two TOPO ligands per zirconium, the concentration of the complex is half of the integral.For the free TOPO resonance and the ZrCl 4 (TOPO) complex, the concentration is equal to the integral.
In the input file, we also tell the COPASI program the initial concentration of the reagents (here: TOPO and ZrCl x (O i Pr) 4-x ), before equilibration.In principle, these columns would correspond to the values in Table 5 in the main text.However, a minority of resonances in the 31 P NMR spectra remained unassigned and thus we slightly corrected the initial concentrations.The corrected initial concentration of TOPO is the sum of the integrals of the assigned peaks in the spectrum.The other peaks represented also species with bound S-9 TOPO, which is therefore unavailable for the equilibria that we are modeling.Also the initial ZrCl x (O i Pr) 4-x concentration is corrected, by assuming that there is one TOPO molecule bound per Zr atom in the unassigned species.Therefore, the corrected initial concentration of ZrCl x (O i Pr) 4-x is equal to the theoretical concentration (Table 5) minus the sum of all unassigned species in the 31 P NMR spectrum.These corrections lead typically to 5-10% difference with the theoretical value.

Figure S1 :
Figure S1: Crystal structures of the synthesized metal halide complexes captured with Single Crystal XRD.The hydrogen atoms are omitted for clarity.

Figure S2 :
Figure S2: Room temperature A) 1 H NMR B) 31 P NMR spectra of the newly reported compounds.Note that all compounds are very poorly soluble.

Figure S7 :
Figure S7: 31 P NMR spectrum at room temperature of HfCl 4 (TPPO) 2 with 1 equivalent of TOPO with respect to the metal.

Figure
Figure S8: A) 1 H NMR and B) 31 P NMR spectra of ZrCl 3 (O i Pr) with different amounts of TOPO.From the 31 P NMR spectra the Job Plot has been calculated.

Figure
Figure S9: A) 1 H NMR and B) 31 P NMR spectra of ZrCl 2 (O i Pr) 2 with different amounts of TOPO.From the 31 P NMR spectra the Job Plot has been calculated.

Figure
Figure S10: A) 1 H NMR and B) 31 P NMR spectra of ZrCl(O i Pr) 3 with different amounts of TOPO.From the 31 P NMR spectra the Job Plot has been calculated.

Figure S11 :
Figure S11: 31 P NMR spectra at room temperature of ZrCl 2 (O i Pr) 2 titrated with TEPO.The ratio of Zr to TEPO is indicated in the figures.

Figure S12 :
Figure S12: The different possible isomers for the ZrCl x (O i Pr) 4-x (x=1-3) complexes with THF.The relative energy compared to the most stable isomer is indicated.

Figure S13 :
Figure S13: 31 P NMR spectra at room temperature of ZrCl 3 (O i Pr) with 1 equivalents of TOPO once synthesized from Zr(O i Pr) 4 and acetyl chloride, once mixing ZrCl 4 (THF) 2 and Zr(O i Pr) 4 .

Figure S15 :
Figure S15: 31 P NMR spectra at room temperature of zirconium tertbutoxy chloride complexes with 4 equivalents of TOPO.

Figure S16 :
Figure S16: 31 P NMR spectra at room temperature of hafnium isopropoxy chloride complexes with 4 equivalents of TOPO.

Table S2 :
Crystallographic parameters for the reported crystal structures.Cl 4 O 2 P 2 Zr C 36 H 30 Cl 4 O 2 P 2 Ti C 36 H 30 Cl 4 HfO 2 P 2 C 36 H 30 Br 4 O 2 P 2 Zr C 8 H 16 Br 4 O 2 Zr D calc./ g cm −3 S-3Characterization of Single Crystals1 H NMR and 31 P NMR

Table S4 :
Input file used to fit the Job Plots of ZrCl 3 (O i Pr) in Figure3.The concentrations of the species considered in the fittings are reported in mol/L.TOPO is abbreviated with T. ZrCl 4 T 2 ZrCl 3 (O i Pr)T 2 free T ZrCl 3 (O i Pr)

Table S5 :
Input file used to fit the Job Plots of ZrCl 2 (O i Pr) 2 in Figure3.The concentrations of the species considered in the fittings are reported in mol/L.TOPO is abbreviated with T. ZrCl 3 (O i Pr)T 2 ZrCl 2 (O i Pr) 2 T 2 free T ZrCl 2 (O i Pr) 2

Table S6 :
Input file used to fit the Job Plots of ZrCl(O i Pr) 3 in Figure3.The concentrations of the species considered in the fittings are reported in mol/L.TOPO is abbreviated with T. Pr)T 2 ZrCl 2 (O i Pr) 2 T 2 ZrCl(O i Pr) 3 T 2 free T ZrCl(O i Pr) 3