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.