Protonolysis of [((PrO)-Pr-i)TiMo5O18](3-): access to a family of TiMo5 Lindqvist type polyoxometalates

作者：Coyle Laura; Middleton Paul S; Murphy Christopher J; Clegg William; Harrington Ross W; Errington R John^*

来源：Dalton Transactions, 2012, 41(3): 971-981.

DOI：10.1039/c1dt11256b

The tetra-n-butylammonium (TBA) salts of [((PrO)-Pr-i)TiMo5O18](3-) 1 and [((BuO)-Bu-i)TiMo5O18](3-) 2 were prepared by hydrolysis of mixtures of (TBA)(2)[Mo2O7], (TBA)(4)alpha-[Mo8O26] and Ti(OR)(4) (R = Pr-i or Bu-i) in acetonitrile. Treatment of (TBA)(3)1 with alcohols ROH afforded primary and tertiary alkoxide derivatives [(RO)TiMo5O18](3-) (R = Me 3, Bu-t 4), whilst aryloxides [(ArO)TiMo5O18](3-) were prepared by reacting 1 with phenols ArOH (Ar = C6H4Me-4 5, and C6H4CHO-2 6). Oxo-bridged [(mu-O)(TiMo5O18)(2)](6-) 7 rather than the hydroxo derivative [(HO)TiMo5O18](3-) was obtained upon hydrolysis of 1. X-Ray crystal structures of TBA salts of anions 3-7 show that titanium is six-coordinate in all cases, although titanium sites are disordered over two trans positions in 3. Mo-O bond length alternation is observed in the Mo4O4 planes of 4 and 7 and in one of the two independent anions in the structure of 3. In solution, O-17 NMR spectra are consistent with the higher anionic charge compared to [Mo6O19](2-) and reveal an order of basicity for the anions [LM%26apos;Mo5O18](3-) associated with the ability of {LM%26apos;}(3+) to donate/withdraw electron density from {Mo5O18}(6-). Protonolysis reactions of 1 and 3 were slower than for tungstate analogues and the possibility of initial protonation at TiOM (M = Mo) rather than TiOR (M = W) in a proton-assisted S(N)1 mechanism for ligand exchange in [(RO)TiM5O18](3-) is discussed.

• 出版日期2012