From Coordination to Noncoordination: Syntheses and Substitution Lability Studies of Titanium Triflato Complexes

A new concept for obtaining cationic complexes with triflate counteranions from coordinating triflato ligands was developed. Various routes are leading to titanium(IV) and titanium(III) triflato complexes efficiently. The reactions of pentafulvene titanium complexes with either triflic acid or silver triflate give the corresponding titanium(IV) triflato complexes in excellent yields. Hydrolysis of the titanium(IV) bistriflato complexes leads to cationic aqua complexes via displacement of the triflato ligand, which consequently acts as a noncoordinating anion. A functionalized titanium(IV) monotriflato complex was synthesized by insertion of a nitrile into the Ti–C bond and the triflato ligand was displaced by an NHC. While the titanium(IV) complexes are mostly inert toward substrates, the donor-free titanium(III) triflato complex is a strong Lewis acid and forms various adducts with monodentate Lewis bases. The titanium(III) complex was oxidized by reaction with TEMPO, resulting in a diamagnetic titanium(IV) complex. The reaction with bidentate ligands results in cationic titanium(III) complexes due to displacement of the triflato ligand by the bidentate ligands. Treatment with acetone leads to an aldol reaction of two acetone molecules and the formation of a cationic diacetone alcohol complex.


Synthesis of Ti2b:
OTf 2 2 Ti1b (200 mg, 0.231 mmol) was dissolved in 50 mL of dry toluene.Degassed water (0.46 mL, 1 M in THF, 0.463 mmol) was added slowly to the stirred solution.The reaction mixture was stirred for 3 h at room temperature.The resulting yellow solid was isolated by separation of the supernatant and the residue was washed with 10 mL of n-hexane.The residue was dried under vacuum to yield the product as a yellow solid.Caution: The obtained solid is only stable for a couple of hours and decomposes back to Ti1b over time.Yellow crystals suitable for single-crystal X-ray diffraction analysis precipitated from a slowly evaporating solution of Ti2b in benzene after several days.Yield: 138 mg, 0.156 mmol, 68 %.
Due to the presence of a second species in the 19 F{ 1 H} NMR spectrum (Figure S7) and the general instability of the solid, further characterization was omitted.

Synthesis of Ti5:
Ti III OTf Route A: Titanocene bis(trimethylsilyl)acetylene (1.00 g, 2.87 mmol) and silver(I) trifluoromethanesulfonate (737 mg, 2.87 mmol) were dissolved in 40 ml of dry toluene.The reaction mixture was stirred for 1 h at room temperature to give a dark green solution.Ag(0) was removed by filtration and the residue was washed with toluene (3 x 20 mL) and filtered.
The solvent was removed under reduced pressure and the residue was dried under vacuum to yield the product as a green blue solid.Crystals of Ti5 suitable for single-crystal X-ray diffraction analysis were obtained by storing the toluene solution of Ti5 at -20 °C over night, forming greenish blue crystals.
Route B: Titanocene bis(trimethylsilyl)acetylene (500 mg, 1.43 mmol) was dissolved in 20 ml of dry n-hexane.The resulting solution was cooled to -80 °C and trifluoromethanesulfonic acid (14.3 mL, 0.1 M in Et 2 O, 1.43 mmol) was added slowly to the stirred solution.The reaction mixture was stirred for 1 h at -80 °C to give an orange red suspension.After warming to room temperature and stirring for an additional hour, the reaction mixture was stored at -20 °C over night.A pale green solid precipitated which was isolated by separation of the supernatant.The residue was dried under vacuum to yield the product as a green blue solid.

Synthesis of Ti5b:
Ti III OTf N Route A: Titanocene triflate Ti5 (100 mg, 0.306 mmol) was dissolved in 5 ml of dry toluene.0.1 mL of pyridine were added and the reaction mixture was stirred for 1 h at room temperature to give a green solution.The solvent was removed under reduced pressure and the residue was dried under vacuum to yield the product as a green solid.
Route B: Titanocene bis(trimethylsilyl)acetylene (200 mg, 0.574 mmol) and pyridinium trifluoromethanesulfonat (132 mg, 0.574 mmol) were dissolved in 10 ml of dry toluene.The reaction mixture was stirred for 2 h at room temperature to give a yellow green solution.
Green crystals precipitated from the reaction mixture.The solid was isolated by separation of the supernatant and dried under vacuum to yield the product as a green solid.Crystals of Ti5b suitable for single-crystal X-ray diffraction analysis were obtained by storing the toluene solution of Ti5b at -20 °C over night, forming green crystals.Titanocene triflate Ti5 (100 mg, 0.306 mmol) and TEMPO (47.8 mg, 0.306 mmol) were dissolved in 5 ml of dry toluene.The reaction mixture was stirred for 2 h at room temperature to give a brown yellow solution.The solvent was removed under reduced pressure.The residue was washed with n-hexane and dried under vacuum to yield the product as a yellow solid.Yellow crystals suitable for single-crystal X-ray diffraction analysis precipitated from a slowly evaporating solution of Ti5e in benzene after several days.

Crystallographic data
Single crystal X-ray data for Ti5c and Ti5oxo were measured on a Bruker AXS Apex II diffractometer (graphite monochromator, Mo-Kα radiation, λ = 0.71073 Å, Kappa 4-circle goniometer, Apex II CCD detector).All other data were measured on a Bruker AXS D8 Venture diffractometer (multilayer optics, Mo-Kα and Cu-Kα radiation with λ = 0.71073 Å and 1.54178 Å respectively, Kappa 4-circle goniometer, Photon III C14 CPAD detector).The crystal of Ti5e was measured at a temperature of 150 K; the crystals crack below 150 K.All other crystals were measured at a temperature of 100 K. Absorption corrections using equivalent reflections were performed with the program SADABS. [1]For Ti5c and Ti5oxo numerical absorption corrections were performed using the same program.The crystals of Ti5 and Ti5d were nonmerohedral twins, and the absorption corrections were performed with the program TWINABS. [2]All structures were solved with the program SHELXS [3] and refined with SHELXL [4] using the OLEX2 [5] GUI.
All non H atoms were refined using anisotropic atomic displacement parameters (ADPs).H atoms bonded to C were located in the difference Fourier maps and placed on idealized geometric positions with idealized atomic displacement parameters using the riding model.H atoms bonded to N, O and P were refined freely.
The crystals of Ti5b tested undergo a slow phase transition at low temperature, resulting in a poor diffraction pattern, which is (partially) reversible at room temperature.For this reason a quick 2 h data collection was performed on the crystal at 100 K to yield the current dataset.
The structure of Ti5 exhibits whole molecule disorder.The disordered sites were refined using restraints on the anisotropic ADPs (RIGU instruction within SHELXL).In Ti5e the Cp and TEMPO ligands are disordered with refined site occupancies of 0.887 : 0.113.The disordered sites were refined using restraints on the geometry (SAME).In Ti5g the triflate anions are disordered with refined site occupancies of 0.820 : 0.180 and 0.874 : 0.126 respectively.The disordered sites were refined using restraints on the geometry (SAME), and the isotropic ADPs were constrained to be the same (EADP).

R1Figure S22 :
Figure S22: EPR spectrum of complex Ti5 in toluene at room temperature.

Figure S23 :
Figure S23: EPR spectrum of complex Ti5a in toluene at room temperature.

Figure S24 :
Figure S24: EPR spectrum of complex Ti5b in toluene at room temperature.

Figure S25 :
Figure S25: EPR spectrum of complex Ti5c in toluene at room temperature.

Figure S26 :
Figure S26: EPR spectrum of complex Ti5d in toluene at room temperature.

Figure S27 :
Figure S27: EPR spectrum of complex Ti5f in toluene at room temperature.

Figure S28 :
Figure S28: EPR spectrum of complex Ti5g in toluene at room temperature.
The reaction mixture was stirred for 2 h at room temperature to give a green suspension.Green crystals precipitated from the reaction mixture.The solid was isolated by separation of the supernatant and dried under vacuum to yield the product as a green solid.Crystals of Ti5c suitable for single-crystal X-ray diffraction analysis were obtained by storing the toluene solution of Ti5c at -20 °C over night, forming green crystals.Titanocene triflate Ti5 (100 mg, 0.306 mmol) and 4-flourobenzonitrile (37 mg, 0.306 mmol) were dissolved in 5 ml of dry toluene.The reaction mixture was stirred for 2 h at room temperature to give a yellow solution.Green crystals precipitated from the reaction mixture.The solid was isolated by separation of the supernatant and dried under vacuum to yield the product as a green solid.Crystals of Ti5d suitable for single-crystal X-ray diffraction analysis were obtained by storing the toluene solution of Ti5d at -20 °C over night, forming green crystals.
Yield: 0.151 g, 0.249 mmol, 82%.IR (ATR): ṽ = 1590, 1485, 1439, 1306, 1237, 1225, 1174, 1118, 1096, 1072, 1032, 808, 759, 722, 692, 632, 582 cm -1 .Melting point: 238 °C (dec.).EA: calcd.for C 29 H 25 F 3 SO 4 PTi: C 57.53, H 4.16.Found: C 58.10, H 3.93.EPR: g = 1.957Synthesis of Ti5d: Yield: 92 mg, 0.205 mmol, 67%.IR (ATR): ṽ = 3110, 2257, 1601, 1506, 1439, 1410, 1307, 1222, 1156, 1065, 1026, 1011, 818, 760, 706, 629, 585 cm -1 .Melting point: 149 °C (dec.).HR/MS: calculated: m/z = 448.0110[M+], measured (LIFDI): m/z = 448.0105.EA: calcd.for C 18 H 14 F 4 NSO 3 Ti: C 48.23, H 3.15.Found: C 48.05, H 3.17.EPR: g = 1.961Synthesis of Ti5e: ml of dry toluene.The reaction mixture was stirred for 2 h at room temperature to give a green solution.The solvent was removed under reduced pressure.The residue was washed with n-hexane and dried under vacuum to yield the product as a pale green solid.Crystals of Ti5f suitable for single-crystal X-ray diffraction analysis were obtained by a saturated toluene solution of Ti5f at -20 °C, forming green crystals.Titanocene triflate Ti5 (100 mg, 0.306 mmol) and acetyl ferrocene (69.7 mg, 0.306 mmol) were dissolved in 10 ml of dry toluene.The reaction mixture was stirred for 16 h at room temperature to give a dark red solution.The solvent was removed under reduced pressure.The residue was washed with n-hexane and dried under vacuum to yield the product as a red solid.Red crystals suitable for single-crystal X-ray diffraction analysis precipitated from a slowly evaporating solution of Ti5g in benzene after several days.) were dissolved in 10 ml of dry toluene.The reaction mixture was stirred for 16 h at room temperature to give a blue suspension.The solid was isolated by separation of the supernatant and dried under vacuum to yield the product as a blue solid.Crystals of Ti5h suitable for single-crystal X-ray diffraction analysis were obtained by a saturated toluene solution of Ti5h at room temperature, forming blue crystals.calcd.for C 25 H 26 F 3 N 2 SO 3 Ti: C 55.67, H 4.86.Found: C 54.92, H 4.79 .153mmol) were dissolved in 5 ml of dry toluene.The reaction mixture was stirred for 16 h at room temperature to give a yellow suspension.The solid was isolated by separation of the supernatant and dried under vacuum to yield the product as a yellow solid.Crystals of Ti5i suitable for single-crystal X-ray diffraction analysis were obtained by a saturated toluene solution of Ti5i at room temperature, forming yellow crystals.