DITUNGSTEN HEXAALKOXIDES - TEMPLATES FOR ORGANOMETALLIC CHEMISTRY ANDCATALYSIS

The reactions between W-2(OR)(6) compounds and carbon monoxide, ethene , acetylene, allene, 1,3-dienes, ketones, aldehydes and eneones are de scribed. The selection of R allows for control of steric access to the (W=W)(6+) centre and the relative reducing power of the W-W pi electr ons and Lewis acidity of the W atoms. With CO, W-2(OBu(t))(6) gives W- 2(OBu(t))(6)(mu-CO), <(v)over tilde (CO)> = 1575 cm(-1), while W-2[OCM e(2)(CF3)](6) yields W-2[OCMe(2)(CF3)](6)(Co)(2) with (v) over tilde(C O)=2081 and 2050 cm(-1). Similarly, whereas MeCN and W-2(OBu(t))(6) re act rapidly in hydrocarbons to yield products of metathesis (Bu(t)O)(3 )W=N and (Bu(t)O)(3)W=CMe, W-2[OCMe(2)(CF3)](6) reversibly forms the L ewis-base adduct W-2[OCMe(2)(CF3)](6)(NCMe)(2). Allene and W-2(OBu(t)) (6) react to give a 1:1 adduct having a mu-C-C-C fragment that is para llel to the W-W;axis and a 2:1 adduct wherein one allene forms a metal laallyl that is eta(1) bound to one W atom and eta(3) to the other. No vel modes of binding to the dinuclear centre lead to novel modes of su bstrate activation. Examples include the reductive cleavage of ketone and aldehyde C-O bonds which forms the basis of an olefination reactio n. Also co-ordination of 1,3-dienes as a mu-eta(1):eta(4) carbon fragm ent to the dinuclear centre facilitates the specific hydrogenation to give 3-enes.