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

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), 'C5H10 (c), 4-MeS-C6H4 (a), 'C4H3S (e), 'C5H4N (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(delta)). 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.