A study of the photochemical reaction between W2(OCH2 tBu)6 and P4.: Characterization of the phosphido cluster W4(P)2(OCH2 tBu)10

The photochemical reaction between W-2((OCH2Bu)-Bu-t)(6) and P-4 has been studied by NMR spectroscopy in toluene-nk 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 W-2((OCH2Bu)-Bu-t)(6)L-2 where L = py and HNMe2 and P-4, namely W-3(mu(3)-P)((OCH2Bu)-Bu-t)(9), while others must arise from degradation of OR ligands. A new compound W-4(mu(3)-P)(2)(mu-(OCH2Bu)-Bu-t)(4)((OCH2Bu)-Bu-t)(6) has been isolated and characterized. Crystal data at -165 degrees C: a = 19.955(4), b = 25.222(3), c = 12.775(2) Angstrom, 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 2.7951(8) Angstrom and a bonding W-W distance of 2.692(1) Angstrom between the back-bone W atoms of the planar W-4 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 O-4 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 W-3(mu(3)-X)(OR)(9), where X = CCH, and P, W-4((OPr)-Pr-i)(12) and W-4(OEt)(16). The latter contains a central centrosymmetric W-4(16+) 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. (C) 1998 Elsevier Science Ltd. All rights reserved.