Carbon−Carbon Coupling of Two Alkenyl Fragments on a Saturated Compound

The monohydrido complex RuHCl(CO)(P i Pr 3 ) 2 ( 1 ) reacts with 2-methyl-1-buten-3-yne to give Ru{( E )-CH CHC(CH 3 ) CH 2 }Cl(CO)(P i Pr 3 ) 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 + ] CHCH C(CH 3 )CH 2 - to the structure of 2 . In agreement with this, complex 2 reacts with HBF 4 to afford the carbene derivative [Ru{ CHCH C(CH 3 ) 2 }Cl(CO)(P i Pr 3 ) 2 ]BF 4 ( 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 )-CH CHC(CH 3 ) CH 2 }Cl(CO) 2 (P i Pr 3 ) 2 ( 4 ). Complex 4 reacts with CH 3 Li to give Ru(CH 3 ){( E )-CH CHC(CH 3 ) CH 2 }(CO) 2 (P i Pr 3 ) 2 ( 5 ) and with CH 2 CHMgBr to afford Ru(CH CH 2 ){( E )-CH CHC(CH 3 ) CH 2 }(CO) 2 (P i Pr 3 ) 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 HBF 4, complex 6 evolves to a mixture of products containing the α,β-unsaturated allyl compound [Ru{η 3 -CH 2 CHCHCH C(CH 3 ) 2 }(CO) 2 (P i Pr 3 ) 2 ]BF 4 ( 7 ) in about 50% yield. Treatment of this mixture with an excess of NaCl gives Ru{η 3 -CH 2 CHCHCH C(CH 3 ) 2 }Cl(CO) 2 (P i Pr 3 ) ( 8 ). Similarly, the addition of an excess of K(CH 3 CO 2 ) to the mixture affords Ru{η 3 -CH 2 CHCHCH C(CH 3 ) 2 }{η 1 -OC(O)CH 3 }(CO) 2 (P i Pr 3 ) ( 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 DBF 4, which affords [Ru{η 3 -CH 2 CHCHCH C(CH 2 D)CH 3 }(CO) 2 (P i Pr 3 ) 2 ]BF 4 ( 7 - d 1 ).