Ditungsten hexaalkoxides: templates for organometallic chemistry and catalysis

Abstract

The reactions between W₂(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 (WW)⁶⁺ centre and the relative reducing power of the W–W π electrons and Lewis acidity of the W atoms. With CO, W₂(OBu^t)₆ gives W₂(OBu^t)₆(µ-CO), (CO)= 1575 cm^–1, while W₂[OCMe₂(CF₃)]₆ yields W₂[OCMe₂(CF₃)]₆(CO)₂ with (CO)= 2081 and 2050 cm^–1. Similarly, whereas MeCN and W₂(OBu^t)₆ react rapidly in hydrocarbons to yield products of metathesis (Bu^tO)₃ WN and (Bu^tO)₃ WCMe, W₂[OCMe₂(CF₃)]₆ reversibly forms the Lewis-base adduct W₂[OCMe₂(CF₃)]₆(NCMe)₂. Allene and W₂(OBu^t)₆ react to give a 1:1 adduct having a µ-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 η¹ bound to one W atom and η³ 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 µ-η¹:η⁴ carbon fragment to the dinuclear centre facilitates the specific hydrogenation to give 3-enes.