Ditungsten hexaalkoxides: Templates for organometallic chemistry and catalysis

The reactions between W-2(OR)(6) compounds and carbon monoxide, ethene, acetylene, allene, 1,3-dienes, ketones, aldehydes and eneones are described. 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 electrons 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[OCMe(2)(CF3)](6) yields W-2[OCMe(2)(CF3)](6)(Co)(2) with (v) over tilde(CO)=2081 and 2050 cm(-1). Similarly, whereas MeCN and W-2(OBu(t))(6) react 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 Lewis-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 parallel to the W-W;axis and a 2:1 adduct wherein one allene forms a metallaallyl that is eta(1) bound to one W atom and eta(3) to the other. Novel modes of binding to the dinuclear centre lead to novel modes of substrate activation. Examples include the reductive cleavage of ketone and aldehyde C-O bonds which forms the basis of an olefination reaction. Also co-ordination of 1,3-dienes as a mu-eta(1):eta(4) carbon fragment to the dinuclear centre facilitates the specific hydrogenation to give 3-enes.