Reactions of the Doubly Bridged Bis(cyclopentadienyl) Dinuclear Molybdenum Complex (Me 2 C)(Me 2 Si)[(η 5 ‐C 5 H 3 )Mo(CO) 3 ] 2 with a Carboxylate‐Substituted Allene

Reaction of the doubly bridged bis(cyclopentadienyl) dinuclear molybdenum complex (Me 2 C)(Me 2 Si)[(η 5 ‐C 5 H 3 )Mo(CO) 3 ] 2 ( 1 ) with equivalent molar amount of allene H 2 C=C=CHCO 2 Me in refluxing toluene gave four products: complex (Me 2 C)(Me 2 Si)[(η 5 ‐C 5 H 3 ) 2 Mo 2 (CO) 4 (μ‐η 2 ‐η 2 ‐HC≡CCH 2 CO 2 Me)] ( 3 ) (10 %) with a crosswise substituted alkyne bridge, η 2 ‐η 2 ‐HC≡CCH 2 CO 2 Me derived from a 1,3‐hydrogen shift of H 2 C=C=CHCO 2 Me, complex (Me 2 C)(Me 2 Si)[(η 5 ‐C 5 H 3 ) 2 Mo 2 (CO) 2 (O) 2 {μ‐η 1 ‐η 3 ‐C(CO 2 Me)CHCH 2 }] ( 6 ) (16 %) with a bridging η 1 ,η 3 ‐C(CO 2 Me)CHCH 2 allylic group, and allene C–C coupled complexes (Me 2 C)(Me 2 Si)[(η 5 ‐C 5 H 3 ) 2 Mo 2 (CO) 4 {μ‐η 3 ‐η 3 ‐{MeO 2 CCH(CH 2 )C}(CHCHCHCO 2 Me)}]( 4 ) (7 %) and (Me 2 C)(Me 2 Si)[(η 5 ‐C 5 H 3 ) 2 Mo 2 (CO) 4 {μ‐η 3 ‐η 3 ‐{MeO 2 CCH(CH 2 )C} 2 }] ( 5 ) (13 %), in which the two allene molecules were coupled in head‐to‐center and center‐to‐center coupling modes, respectively. When 1 was treated with an excess amount of H 2 C=C=CHCO 2 Me, only C–C coupled products 4 (10 %) and 5 (22 %) were obtained. In comparison, reaction of the singly bridged bis(cyclopentadienyl) dinuclear molybdenum complex (Me 2 C)[(η 5 ‐C 5 H 4 )Mo(CO) 3 ] 2 ( 2 ) with H 2 C=C=CHCO 2 Me only gave the η 2 ‐η 2 coordinated complex (Me 2 C)[(η 5 ‐C 5 H 4 )Mo 2 (CO) 4 (μ‐η 2 ‐η 2 ‐H 2 CCCHCO 2 Me)] ( 7 ) (21 %). These results marked the different reactivities of doubly bridged bis(cyclopentadienyl) dinuclear molybdenum complex 1 and the corresponding singly bridged analogue 2 . The formation of these complexes was discussed and the molecular structures of 3 – 7 were determined by X‐ray diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)