Cationic d 3-d 3 dinuclear compounds of tungsten: [W 2(O 2CBu t) 5] +X −, where X −=BF 4− and CF 3SO 3−

Abstract

Ditungsten hexapivalate, W 2(O 2CBu t) 6, and triethyloxonium tetrafluoroborate, Et 3O +BF 4 −, react in CH 2Cl 2 at room temperature to yield the 1:1 complex [W 2(O 2CBu t) 5][BF 4] ( 1), as a yellow crystalline solid. A similar reaction involving trimethylsilyltrifluoromethane-sulfonate, TMS-OTf, yields [W 2(O 2CBu t) 5][OTf] ( 2). Compounds 1 and 2 are 1:1 electrolytes in CH 3CN but show ion pairing in THF and CH 2Cl 2 solutions with the degree of ion pairing being greater for 2 than for 1. Only 1 is soluble in toluene. 1H NMR spectroscopy shows there are 3 types of O 2CBu t ligands in the integral ratio 1:2:2 which is consistent with the structure found in the solid state for 1 which has a (WW) 6+ unit, WW=2.28(1) Å supported by three bridging pivalates and two chelating η 2-O 2CBu t ligands. The local geometry about each tungsten is a distorted pentagonal pyramid, WWO 5, with relatively weak axial interactions ( trans to the WW bond) to the BF 4 − counter anions, WF=2.50(1) Å (av.). This leads to an infinite polymeric structure in the solid state. Crystal data for (W 2(O 2CBu t) 5][BF 4] at −171 °C: a=29.44(1), b=36.05(1), c=20.80(1) Å, β=133.30(1)°, Z=16, D calc=1.82 g cm −3 and space group C2/ c.