Trapping of Acetylene by a Zirconocene Terminal Imido Complex

Treatment of the zirconocene terminal imido complex (CpR) 2 Zr N t Bu(THF) ( 1a-THF: R = H; 1b-THF: R = Me) with acetylene results in the formation of a dinuclear product, [(CpR) 2 Zr] 2 (μ-CHCHN t Bu)(μ-N t Bu) ( 3a, R = H; 3b, R = Me), in which the zirconium centers are bridged by nitrogen and carbon. Upon heating, the dinuclear complex 3 is cleaved into the azametallacyclobutene (CpR) 2 Zr(η 2 -N t BuCHCH) ( 4 ) and the terminal imido complex (CpR) 2 Zr N t Bu ( 1 ), which can be trapped with Lewis bases or alkynes. Heating 3 in the absence of traps cleanly produces the alkynyl-bridged species [(CpR) 2 ZrNH t Bu] 2 (μ-C⋮C) ( 5 ). Kinetic data indicate that the dinuclear complex 3 fragments into the mononuclear species 4 and 1 prior to C−H activation to form 5 . The X-ray structures of [Cp 2 Zr] 2 (μ-CHCHN t Bu)(μ-N t Bu) ( 3a ) and [Cp 2 ZrNH t Bu] 2 (μ-C⋮C) ( 5a ) are reported; the structure of the dinuclear species [(Cp 2 Zr)((CpMe) 2 Zr)](μ-CHCHN t Bu)(μ-N t Bu) ( 3c ) is included in the Supporting Information.