Vibrational spectroscopy and EXAFS study of Ti(OC2H5)4 and alcohol exchange in Ti(iso-OC3H7)4

Abstract

The vibrational spectrum of tetraethylorthotitanate (TET) has been assigned by using vibrational and structural data from the series Ti(OEt)yCl4 − y (y = 1 to 4), to distinguish between bands due to bridging and terminally coordinated ethoxide. EXAFS studies of the series showed an increase in association with increasing y, in agreement with previous cryoscopic measurements. IR bands in the spectrum of TET in the region 1300 to 800 cm−1 have been assigned as follows: 850 and 885 cm−1 , C–C stretch of bridging ethoxide; 910 and 919 cm−1 , C–C stretch of terminal ethoxide; 1044 cm−1, C–O stretch of bridging ethoxide; 995 and 1067 cm−1, C–O stretch of terminal ethoxide; 1013 cm−1, C–O stretch of both bridging and terminal ethoxide. Unresolved bands in the region 1100 to 1200 cm−1 are assigned to in- and out-of-plane rocking modes of both bridging and terminal ethoxide. The assignment of the 885 and 1044 cm−1 bands to bridging ethoxide has been confirmed by comparison of the Ti(OEt)3(acac) and Ti(OEt)2(acac)2 spectra. The vibrational assignments of TET were used to investigate the alcohol exchange reaction between tetraisopropyltitanate (TPT) and EtOH by IR and Raman spectroscopy. Ligand exchange occurred quantitatively on reaction of TPT with one mol equivalent of EtOH, the resulting Ti(OPri)3(OEt) being five-fold coordinated with bridging predominantly occurring through the ethoxide ligand. The second isopropoxide was also exchanged quantitatively with addition of EtOH but further exchange was slower, with the final isopropoxide remaining coordinated to the Ti(IV) site, even in an excess of EtOH.