Carbene complexes. Part 16. Synthesis and properties of NN′N″N‴-tetra-aryl-substituted electron-rich olefin-derived carbeneruthenium(II) complexes containing a spontaneously formed ortho-metallated-N-arylcarbene ligand; the crystal and molecular structures of [RuCl{CN(C6H4Me-4)CH2CH2NC6H3Me-4}(PEt3)2](6) and [Ru(CO)Cl{CN(C6H4Me-4)CH2CH2NC6H3Me-4}(PEt3)2](16)

Abstract

The complex [RuCl₂(PPh₃)₃] reacts thermally with the electron-rich olefin [[graphic omitted]R′]₂(R′= Ph, C₆H₄Me-4, C₆H₄OMe-4, or C₆H₄OMe-2), L^R′_2′ with elimination of PPh₃ and HCl, forming the five-co-ordinate carbeneruthenium(II) complex containing an ortho-metallated N-arylcarbene ligand [[graphic omitted]″}(PPh₃)₂], abbreviated as [[graphic omitted]^R′)(PPh₃)₂]. One of these complexes (R′= C₆H₄Me-4) is also formed from [RuCl(NO)(PPh₃)₂] and L^R′₂. The five-co-ordinate ruthenium(II) complexes readily undergo PR₃ exchange [R₃= Et₃, Buⁿ₃, Buⁿ₂Ph, Et₂Ph, Me₂Ph, but not (C₆H₁₁)₃]; with [[graphic omitted]Et]₂(L^Et₂), the unusual bis-(carbene) complex [[graphic omitted]^R′)(L^Et)(PPh₃)](R′= C₆H₄Me-4) is formed. Small ligands [e.g. CO, PF₃, P(OMe)₃, or NCMe] generally add to form six-co-ordinate complexes of variable thermal stability. The complex [RuCl₃(NO)(PPh₃)₂] with L^R′₂, also affords an ortho-metallated complex [[graphic omitted]^R′)(NO)(PPh₃)]; this, like the other six-co-ordinate ruthenium(II) derivatives, does not undergo PR₃ exchange, but with L^Et₂ NOCl is lost and [[graphic omitted]^R′)(L^Et)(PPh₃)](R′= C₈H₄Me-4) is formed. Spectroscopic data provide information on the nature and stereochemistry of the complexes, the magnitude of ²J(¹³C–³¹P) being especially useful, with ²J_trans²J_cis. The five- and six-co-ordinate complexes are stereochemically rigid in solution. X-Ray analyses of the two title compounds have been refined to R and R′ of 0.054 and 0.093 for [[graphic omitted]^R′)(PEt₃)₂](R′= C₆H₄Me-4)(6), and 0.045 and 0.053 for [[graphic omitted]^R′)(PEt₃)₂](R′= C₆H₄Me-4)(16), respectively. In overall pseudo-octahedral geometry about ruthenium, complexes (6) and (16) differ only in the replacement of a weak Ru ⋯ HC contact (2.23 Å) in the former for a CO ligand in the latter. The bond lengths within the co-ordination sphere of (6) are slightly greater in (16), the smallest increase (0.011 Å) being for the Ru–P bonds and the largest (0.119 Å) for the Ru–C(6) bond [C(6) is the C of the metallated phenyl ring]. In complex (6) the two Ru–C(sp²) distances are 2.006(8)[Ru–C(6)] and 1.911(6)Å(Ru–C_carb.).