PREPARATION AND STRUCTURE OF THE 1ST ANSA-MOLYBDENOCENE AND TUNGSTENOCENE DERIVATIVES - REACTION OF [O(SIME2C5H4)2]MOH2 WITH METHYL-METHACRYLATE TO PROBE THE OLEFIN ATTACKING SITE

Bridged-bis(cyclopentadienyl) molybdenum and tungsten dihydrides and t heir derivatives have been synthesized for the first time. ane-1,3-diy l)bis(eta5-cyclopentadienyl)]molybdenum dihydride (1a) and tungsten di hydride (1b) were prepared by sodium borohydride reduction of [O(SiMe2 C5H4)2]MCl2 (2a: M = Mo, 2b: M = W) which was obtained by the reaction of disodium ,3-tetramethyl-1,3-bis(cyclopentadienyl)disiloxane with M Cl4(thf)2 (M = Mo, W). The dichlorides 2 reacted with ZnMe2 and NaSEt to afford [O(SiMe2C5H4)2]MMe2 (3a: M = Mo, 3b: M = W) and [O(SiMe2C5H4 )2]M(SEt)2 (4a: M = Mo, 4b: M = W), respectively. Photolysis of lb in benzene gave [O(SiMe2C5H4)2]WH(C6H5) (5b). An X-ray crystal analysis o f 3a has proved that the bridging chain blocks one of the side positio ns of the complex, the siloxy unit being present at one side of the Me -Mo-Me bisector. Consistent with side position attack by olefins, the reaction rate of la with methyl methacrylate was found to be nearly on e half that of the parent CP2MoH2 (6a).