A study of the photochemical reaction between W2(OCH2tBu)6 and P4. Characterization of the phosphido cluster W4(P)2(OCH2tBu)10

Abstract

The photochemical reaction between W2(OCH2tBu)6 and P4 has been studied by NMR spectroscopy in toluene-d8 and those reactions have been complemented by studies on the bench top. A complex sequence of reactions is implicated by the formation of a variety of products, one of which has been observed previously in the thermal reaction between W2(OCH2tBu)6L2 where L = py and HNMe2 and P4, namely W3(μ3-P)(OCH2tBu)9, while others must arise from degradation of OR ligands. A new compound W4(μ3-P)2(μ-OCH2tBu)4 (OCH2tBu)6 has been isolated 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 a distorted rhombus of metal atoms having two different W--W edge distances 2.6938(8) and 2.7981(8) Å and a bonding W--W distance of 2.692(1) Å between the back-bone W atoms of the planar W4 butterfly. The outer or wing-tip tungsten atoms are in a square based pyramidal environment with respect to the PWO4 moiety with the W--P bond in the apical position. The O4 basal plane involves two terminal and two bridging OR groups. The internal or back-bone tungsten atoms are also five coordinate, P2WO3, where two bridging OR groups occupy axial and the two W--P bonds and one W--OR terminal group occupy equatorial sites of a trigonal bipyramid. The cluster geometry is compared with those seen for W3(μ3-X)(OR)9, where X = CCH3 and P, W4(OiPr)12 and W4(OEt)16. The latter contains a central centrosymmetric W16+4 cluster as does the present compound and the presence of the distorted rhomboidal geometry observed in both is proposed to arise from a second order Jahn-Teller distortion.