Carbene complexes. Part 14. The synthesis and steric and electronic effects in electron-rich olefin-derived bis-, tris-, and tetrakis-(carbene)-ruthenium(II) and a tetrakis(carbene)osmium(II) complex; the crystal and molecular structure of trans-dichiorotetrakis(1,3-diethylimidazo-lidin-2-ylidene)ruthenium(II)

Abstract

The reaction of [RuCl₂(PPh₃)₃] with [[graphics omitted]R]₂(L^R₂; R Me, Et, or CH₂Ph) affords tans-[RuCl₂(L^R)₄][R = Me (1), Et (Z), or CH₂Ph (3)]. The instability and reactivity of these complexes increases in the order (3) < (1) < (2). Thus in CH₂Cl, complex (2) readily loses L^Et to give [RuCl₂(L^Et)₃](13), but (1) requires pro-longed heating for similar L^Me loss, affording [RuCl₂(L^Me)₃](12), and (3) does not react. Complex (1)(i) loses L^Me on reaction with NaI to form [Rul₂(L^Me)₃](4), (ii) reacts with excess of P(OMe)₃ to give [RuCl(L^Me)_2^–{P(OMe)₃}₃]Cl (14). and (iii) reacts with C₅H₅N in the presence of CO to give trans-[Ru(CO)Cl(L^Me),(NC₅H₅)₂]Cl (16). Carbon monoxide displaces Cl^– from complex (1) to give trans-[Ru(CO)Cl(L^Me)₄]Cl (9), but (2) preferentially eliminates L^Et forming trans-[Ru(CO)Cl₂(L^Et)₃](7) which isomerises in CHCl₃ or CH₂Cl₂, to the, cis isomer (8), and the benzyl derivative (3) does not react. With PF₃ complex (1) forms trans-[RuCl(L^Me)_4^–(PF₃)] Cl (10) which exhibits severe steric crowding and restricted rotation of the carbene ligands, as is also shown for the tris- or tetrakis-(carbene) ruthenium(II) complexes derived from L^Et or L^CH₂Ph ligands, by analysis of their ¹H and ¹³C n.m.r. spectra. The complex mer-[OsCl₃(PBuⁿ₁Ph)₃] and the olefin L^Me₂ give trans-[OsCl₂(LMe)₄]. An X-ray crystal structure determination of the title complex (as its 0.50Buⁿ₂ solvate) has been refined to R 0.055 (R′ 0.087) for 2 641 independent reflections measured with MO-Kα radiation: the molecule has nearly D₄ sym-metry, with regular octahedral co-ordination about the metal, trans-chlorine atoms, and the four carbene ligands in a propeller arrangement in the equatorial plane; each almost planar imidazolidine ring is arranged at an angle of ca. 45 ° to the RuC₄ equatorial plane. The Ru–C_carb. distance is 2.105(5)Å and Ru-Cl is 2.459(4)Å. Crystals are monoclinic with a= 19.076(2), b= 13.409(l), c= 14.952(2)Å, β= 102.85(6)°, Z= 4, and space group P2₁/c(No. 14).