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

The monohydrido complex RuHCl(CO)(PiPr3)2 (1) reacts with 2-methyl-1-buten-3-yne to give Ru{(E)-CHCHC(CH3)CH2}Cl(CO)(PiPr3)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 α,β-unsaturated alkenyl ligand located in the apex. The ruthenium alkenyl separation is short (1.989(3) Å), suggesting a significant contribution of the zwitterionic resonance form [Ru+]CHCHC(CH3)CH2- to the structure of 2. In agreement with this, complex 2 reacts with HBF4 to afford the carbene derivative [Ru{CHCHC(CH3)2}Cl(CO)(PiPr3)2]BF4 (3). The coordination number 6 for 2 can be achieved by addition of carbon monoxide. Thus, bubbling carbon monoxide through a hexane solution of 2 results in the formation of Ru{(E)-CHCHC(CH3)CH2}Cl(CO)2(PiPr3)2 (4). Complex 4 reacts with CH3Li to give Ru(CH3){(E)-CHCHC(CH3)CH2}(CO)2(PiPr3)2 (5) and with CH2CHMgBr to afford Ru(CHCH2){(E)-CHCHC(CH3)CH2}(CO)2(PiPr3)2 (6). Complex 6 is stable, and the carbon−carbon coupling between the vinyl and the α,β-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 α,β-unsaturated allyl compound [Ru{η3-CH2CHCHCHC(CH3)2}(CO)2(PiPr3)2]BF4 (7) in about 50% yield. Treatment of this mixture with an excess of NaCl gives Ru{η3-CH2CHCHCHC(CH3)2}Cl(CO)2(PiPr3) (8). Similarly, the addition of an excess of K(CH3CO2) to the mixture affords Ru{η3-CH2CHCHCHC(CH3)2}{η1-OC(O)CH3}(CO)2(PiPr3) (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 α,β-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{η3-CH2CHCHCHC(CH2D)CH3}(CO)2(PiPr3)2]BF4 (7-d1).We thank the DGICYT (Project PB 95-0806, Programa de Promoción General del Conocimiento) for financial support.Peer reviewe