Carbon-carbon coupling of two alkenyl fragments on a saturated compound

The monohydrido complex RuHCl(CO)((PPr3)-Pr-i)(2) (1) reacts with 2-methyl-1-buten-3-yne to give Ru{(E)-CH=CHC(CH3)=CH2}Cl(CO)((PPr3)-Pr-i)(2) (2), which has been characterized by X-ray diffraction analysis. The coordination geometry around the ruthenium atom can be rationalized as a square pyramid with the alpha,beta-unsaturated alkenyl ligand located in the apex. The ruthenium alkenyl separation is short(1.989(3) Angstrom), suggesting a significant contribution of the zwitterionic resonance form [Ru+]=CHCH=C(CH3)CH2- to the structure of 2. In agreement with this, complex 2 reacts with HBF4 to afford the carbene derivative [Ru{=CHCH=C(CH3)(2)}Cl(CO)((PPr3)-Pr-i)(2)]BF4 (3). The coordination number 6 for 2 can be achieved by addition of carbon monoxide. Thus, bubbling carbonmonoxide through a hexane solution of 2 results in the formation of Ru{(E)-CH=CHC(CH3)=CH2}Cl(CO)(2)((PPr3)-Pr-i)(2) (4). Complex 4 reacts with CH3Li to give Ru(CH3){(E)-CH=CHC(CH3)=CH2}(CO)(2)((PPr3)-Pr-i)(2) (5) and with CH2=CHMgBr to afford Ru(CH=CH2){(E)-CH=CHC(CH3)=CH2}(CO)(2)((PPr3)-Pr-i)(2) (6). Complex 6 is stable, and the carbon-carbon coupling between the vinyl and the alpha,beta-unsaturated alkenyl fragment is not observed, even at high temperature (refluxing toluene). However, in the presence of 1 equiv of HBF4, complex 6 evolves to a mixture of products containing the alpha,beta-unsaturated allyl compound [Ru{eta(3)-CH2CHCHCH=C(CH3)(2)}(CO)(2)((PPr3)-Pr-i)(2)]-BF4 (7) in about 50% yield. Treatment of this mixture with-an excess of NaCl gives Ru{eta(3)-CH2CHCHCH=C(CH3)(2)}Cl(CO2((PPr3)-Pr-i) (8). Similarly, the addition of an excess of K(CH3CO2) to the mixture affords Ru{eta(3)-CH2CHCHCH=C(CH3)(2)}{eta(1)-OC(O)CH3}(CO)(2)((PPr3)-Pr-i) Pr3) (9). The molecular structure of 8 has been determined by X-ray diffraction analysis. The complex is pseudooctahedral with the two carbonyl groups, the chlorine atom, the phosphine ligand, and both terminal carbon atoms of the allyl unit of the alpha,beta-unsaturated allyl ligand occupying the six coordination sites. The organic ligand has a w-shaped syn geometry. The mechanism for the carbon-carbon coupling is discussed on the basis of the reaction of 6 with DBF4, which affords [Ru{eta(3)-CH2CHCHCH=C(CH2D)CH3}(CO)(2)((PPr3)-Pr-i)(2)]BF4 (7-d(1)).