A study of the photochemical reaction between W 2(OCH 2 tBu) 6P 4. Characterization of the phosphidocluster W 4 (P) 2 (OCH 2 tBu) 10

Abstract

The photochemical reaction between W 2 (OCH 2 tBu) 6 and P 4 has been studied by NMRspectroscopy in toluene- d 8 and those reactions have been complemented by studies on the benchtop. A complex sequence of reactions is implicated by the formation of a variety of products, oneof which has been observed previously in the thermal reaction between W 2 (OCH 2 tBu) 6L 2 whereL = py and HNMe 2 and P 4, namely W 3 ( μ 3-P) (OCH 2 tBu) 9, while others must arise fromdegradation of OR ligands. A new compound W 4 ( μ 3-P) 2 ( μ-OCH 2 tBu) 4 (OCH 2 tBu) 6 has beenisolated and characterized. Crystal data at −165°C : a = 19.955 (4) , b = 25.222 (3) , c = 12.775 (2) Å, Z = 4 and space group Pcab. The centrosymmetric structure consists of adistorted rhombus of metal atoms having two different W — W edge distances 2.6938 (8) and2.7981 (8) Å and a bonding W — W distance of 2.692 (1) Å between the back-bone W atomsof the planar W 4 butterfly. The outer or wing-tip tungsten atoms are in a square based pyramidalenvironment with respect to the PWO 4 moiety with the W — P bond in the apical position. The O 4 basal plane involves two terminal and two bridging OR groups. The internal or back-bonetungsten atoms are also five coordinate, P 2WO 3, where two bridging OR groups occupy axial andthe two W — P bonds and one W — OR terminal group occupy equatorial sites of a trigonalbipyramid. The cluster geometry is compared with those seen for W 3 ( μ 3-X) (OR) 9, where X = CCH 3 and P, W 4 (O iPr) 12 and W 4 (OEt) 16. The latter contains a central centrosymmetric W 16+ 4cluster as does the present compound and the presence of the distorted rhomboidal geometryobserved in both is proposed to arise from a second order Jahn-Teller distortion.