Synthesis, molecular structure, and C-C coupling reactions of carbeneruthenium(II) complexes with C₅H₅Ru(=CRR′) and C₅Me₅Ru(=CRR′) as molecular units

The ethene derivatives [(η⁵-C₅R₅)RuX(C₂ H₄)(PPh₃)] with R=H and Me, which have been prepared from the η³-allylic compounds [(η⁵-C₅R₅)Ru(η³-2- MeC₃H₄)(PPh₃)] (1, 2) and acids HX under an ethene atmosphere, are excellent starting materials for the synthesis of a series of new halfsandwich-type ruthenium(II) complexes. The olefinic ligand is replaced not only by CO and pyridine, but also by internal and terminal alkynes to give (for X = Cl) alkyne, vinylidene, and allene compounds of the general composition [(η⁵-C₅R₅)RuCl(L)(PPh₃)] with L = C₂(CO₂Me)₂, Me₃SiC₂CO₂Et, C=CHCO₂R, and C₃H₄. The allenylidene complex [(η⁵-C₅H₅)RuCl(=C=C=CPh₂) (PPh₃)] is directly accessible from 1 (R=H) in two steps with the propargylic alcohol H≡C=-CC(OH)Ph₂ as the precursor. The reactions of the ethene derivatives [(η⁵-C₅H₅)RuX(C₂ H₄)(PPh₃)] (X = Cl, CF₃CO₂) with diazo compounds RR′CN₂, yield the corresponding carbene complexes [(η⁵-C₅R₅)RuX(=CRR′) (PPh₃)], while with ethyl diazoacetate (for X = Cl) the diethyl maleate compound [(η⁵-C₅H₅)RuCl{η²-Z- C₂H₂(CO₂Et)₂}(PPh₃)] is obtained. Halfsandwich-type ruthenium(II) complexes [η⁵-C₅R₅)RuCl(=CHR′) (PPh₃)] with secondary carbenes as ligands, as well as cationic species [(η⁵-C₅H₅)Ru(=CPh₂) (L)(PPh₃)]X with L = CO and CNtBu and X = AlCl₄ and PF₆, have also been prepared. The neutral compounds [(η⁵-C₅H₅)RuCl(=CRR′) (PPh₃)] react with phenyllithium, methyllithium, and the vinyl Grignard reagent CH₂=CHMgBr by displacement of the chloride and subsequent C-C coupling to generate halfsandwich-type ruthenium(II) complexes with η³-benzyl, η³-allyl, and substituted olefins as ligands. Protolytic cleavage of the metal-allylic bond in [η⁵-C₅H₅)Ru(η³- CH₂CHCR₂)(PPh₃)] with acetic acid affords the corresponding olefins R₂C=CHCH₃. The by-product of this process is the acetato derivative [η⁵C₅H₅)Ru(κ²- O₂CCH₃)(PPh₃)], which can be reconverted to the carbene complexes [η⁵-C₅H₅)RuCl(=CR₂) (PPh₃)] in a one-pot reaction with R₂CN₂ and Et₃NHCl.