Preparation and structure of the first ansa-molybdenocene and tungstenocene derivatives. Reaction of [O(SiMe 2C 5H 4) 2]MoH 2 with methyl methacrylate to probe the olefin attacking site

Abstract

Bridged-bis(cyclopentadienyl) molybdenum and tungsten dihydrides and their derivatives have been synthesized for the first time. [(1,1,3,3-Tetramethyldisiloxane-1,3-diyl)bis(η 5-cyclopentadienyl)lmolybdenum dihydride ( 1a) and tungsten dihydride ( 1b) were prepared by sodium borohydride reduction of [O(SiMe 2C 5H 4) 2]MCl 2 ( 2a: M  Mo, 2b: M  W) which was obtained by the reaction of disodium 1,1,3,3-tetramethyl-1,3-bis(cyclopentadienyl)disiloxane with MCl 4(thf) 2 (M  Mo, W). The dichlorides 2 reacted with ZnMe 2 and NaSEt to afford [O(SiMe 2C 5H 4) 2]MMe 2 ( 3a: M  Mo, 3b: M  W) and [O(SiMe 2C 5H 4) 2]M(SEt) 2 ( 4a: M  Mo, 4b: M  W), respectively. Photolysis of 1b in benzene gave [O(SiMe 2C 5H 4) 2]WH(C 6H 5) ( 5b). An X-ray crystal analysis of 3a has proved that the bridging chain blocks one of the side positions 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 1a with methyl methacrylate was found to be nearly one half that of the parent Cp 2MoH 2 ( 6a).