Trapping of acetylene by a zirconocene terminal imido complex

Treatment of the zirconocene terminal imido complex (CpR)(2)Zr=(NBu)-Bu-t(T HF) (1a-THF: R H; 1b-THF: R = Me) with acetylene results in the formation o f a dinuclear product, [(CpR)(2)Zr](2)(mu-(CHCHNBu)-Bu-t)(mu-(NBu)-Bu-t) (3 a, R = H; 3b, R = Me), in which the zirconium centers are bridged by nitrog en and carbon. Upon heating, the dinuclear complex 3 is cleaved into the az ametallacyclobutene (CpR)(2)Zr(eta(2)-(NBuCHCH)-Bu-t) (4) and the terminal imido complex (CpR)(2)Zr=(NBu)-Bu-t (1), which can be trapped with Lewis ba ses or alkynes. Heating 3 in the absence of traps cleanly produces the alky nyl-bridged species [(CpR)(2)(ZrNHBu)-Bu-t](2)(mu-C drop C) (5). Kinetic da ta indicate that the dinuclear complex 3 fragments into the mononuclear spe cies 4 and 1 prior to C-H activation to form 5. The X-ray structures of [Cp 2Zr](2)((CHCHCHNBu)-Bu-t)-(mu-(NBu)-Bu-t) (3a) and [(Cp2ZrNHBu)-Bu-t](2)(mu -C drop C) (5a) are reported; the structure of the dinuclear species [( Cp2 Zr)((CpMe)(2)Zr)] (mu-(CHCHNBu)-Bu-t)(mu-(NBu)-Bu-t) (3c) is included in th e Supporting Information.