Further Chemistry of Ruthenium Alkenyl Acetylide Complexes: Routes to Allenylidene Complexes via a Series of Electrophilic Addition Reactions

Abstract

The methyl substituents in the cationic allenylidene complexes trans-[Ru{C═C═C(Me)R}Cl(dppe)2]OTf ([1a–f]OTf) are readily deprotonated to give the corresponding alkenyl acetylide complexes trans-[Ru{C≡CC(═CH2)R}Cl(dppe)2] (3; R = Me (a), Ph (b), cC5H10 (c), 4-MeS-C6H4 (d), cC4H3S (e), cC5H4N (f)). Similar chemistry is also observed from [Ru{C═C═C(Me)Ph}(dppe)Cp*]PF6 ([2b]PF6) and [Ru{C═C═C(Me)(4-MeS-C6H4)}(dppe)Cp*]PF6([2b]PF6), chosen to broaden the reaction scope, giving [Ru{C≡CC(═CH2)Ph}(dppe)Cp*] (4b) and [Ru{C≡CC(═CH2)(4-MeS-C6H4)}(dppe)Cp*] (4d). In turn, reactions of 3b,d and 4b,d with the [BF4]− salt of the electrophilic tritylium [CPh3]+ cation give the functionalized allenylidene complexes trans-[Ru{C═C═C(CH2CPh3)R}Cl(dppe)2]BF4 ([5b,d]BF4) and [Ru{C═C═C(CH2CPh3)R}(dppe)Cp*]BF4 ([6b,d]BF4) formed by addition of the electrophile to the remote vinylic carbon (C(δ)). Although trans-[Ru{C═C═C(CH2CPh3)Me}Cl(dppe)2]BF4 ([5a]BF4) could not be successfully purified from reactions of 3a with [CPh3]BF4, deprotonation of the crude product gave the Zaitsev vinyl product trans-[Ru{C≡CC(═CHCPh3)Me}Cl(dppe)2] (7a) in good yield. The initial cycloheptatrienyl adducts formed from reactions of 3b,d and 4b,d with the tropylium salt [C7H7]BF4 undergo a ring-contraction process in chloroform solutions upon exposure to air, to give the styrene-like products trans-[Ru{C═C═C(R)C(H)═CHPh}Cl(dppe)2]BF4 ([10b,d]BF4) and [Ru{C═C═C(R)C(H)═CHPh}(dppe)Cp*]BF4 ([11b,d]BF4), through what is believed to be a radical mechanism mediated by triplet oxygen.