Derivatives of cyclooctatetraenecyclopentadienyl-titanium containing substituents in the five-membered ring

The syntheses of some substituted cyclooctatetraenecyclopentadienyl-titanium compounds are described, viz: (h⁸-C₈H₈)(h⁵-R)Ti with R = C₅H₄CH₃, C₅H₄C(CH₃)₃, C₅H₄Si(CH₃)₃, indenyl (= Ind) and fluorenyl (= Flu). The compounds have been prepared by reaction of [(h⁸-C₈H₈)TiCl·THF]₂ with RNa in ether solution. The paramagnetic compounds are thermally stable to ca. 350°, but they are sensitive to air and water. The IR spectra and dipole moments of the compounds are given. The mass spectra of the complexes (h⁸-C₈H₈)(h⁵-C₅H₅)Ti, (h⁸-C₈H₈)(h⁵-Ind)Ti and (h⁸-C₈H₈)(h⁵-Flu)Ti indicate weakening of the Tih⁵R bond-strength in this sequence.     

Darstellung und eigenschaften von und reaktionen mit metallhaltigen heterocyclen XXII. Synthese, eigenschaften und kristallstruktur des sechsgliedrigen heterocyclus [(h-C5H5)NiSP(CH3)2]2 und dessen verhalten gegenüber alkinen

The heterocycle [(h⁵-C₅H₅)NiSP(CH₃)₂]₂ is obtained by treatment of (h⁵-C₅H₅)₂Ni with (CH₃)₂HPS in toluene and crystallizes monoclinic in the space group P2₁/c with Z = 2. The highly reactive three-membered ring (h⁵-C₅H₅)$\text{NiSP}$(CH₃)₂ which is a dissociation product of [(h⁵-C₅H₅)NiSP(CH₃)₂]₂, can be trapped with bis(methoxycarbonyl)acetylene to give the PS containing nickelacyclopentadiene (h⁵-C₅H₅)$\text{NiSP(CH}{}_3\text{)}{}_2\text{CRC}$R (R  CO₂CH₃).     

Intermediates in the intramolecular ligand transfer reactions of h5-C5H5Fe(CO)2R complexes

Dissolution of h⁵-C₅H₅Fe(CO)₂R (I) (R = cyclohexyl or cyclohexylmethyl) in DMSO leads to the formation of a solvent coordinated acyl complex, h⁵-C₅H₅Fe(CO)(COR)(DMSO) (II). Treatment of this complex with triphenylphosphine leads to its conversion to h⁵-C₅H₅Fe(COR)(PPh₃) (III). Rates for the reaction I ? and II → III have been determined. A comparison of the rates of the reaction I → III in eight solvents shows no specific rate acceleration in DMSO and no correlation with solvent donicity. The results are in accord with a two step mechanism in which the first intermediate is the coordiantively-unsaturated species h⁵-C₅H₅Fe(COR)(CO). The small spread in rates for solvents of widely different dielectric constants suggests little charge separation in the transition state for this step.     

The stereospecificity at the iron center of the decarbonylation of an ironacetyl complex

The dinuclear complex [(h⁵-1-CH₃-3-C₆H₅C₅H₃)Fe(CO)₂]₂ was synthesized by reaction of Fe₂(CO)9 with 1-methyl-3-phenylcyclopentadiene; it was converted to (h⁵-1-CH₃-3-C₆H₅C₅H₃)Fe(CO)₂CH₃ by reduction with sodium amalgam and addition of CH₃l, and thence to (h⁵-1-CH₃-3-C₆H₅C₅H₃)Fe(CO)[P(C₆H₅)₃] (COCH₃) (I) by reaction with P(C₆H₅)₃. The acetyl I was separated into two diastereomerically related pairs of enantiomers. Ia and Ib, by a combination of column chromatography on alumina and crystallization from benzene/pentane. The photochemical decarbonylation of Ia and Ib in benzene or THF solution was examined by ¹H NMR spectroscopy. This reaction proceeds with high stereospecificity (>84% retention or inversion) at the iron center to yield (h⁵-1-CH₃-3-C₆H₈C₅H₃)Fe(CO)[P(C₆H₅)₃]CH₃(II), enriched in the diastereomerically related pairs of enantiomers, IIa and IIb, respectively. Since IIa and IIb epimerize under the photolytic conditions of decarbonylation, the actual stereospecificity of the conversion of I to II is higher than 84%, and likely 100%. This is supported by the data from kinetic studies of the decarbonylation of I and the epimerization of II, carried out under identical photolytic conditions. The implications of the foregoing results to the mechanism of the decarbonylation are considered. Also described herein is the synthesis of other complexes with two asymmetric centers of the general formula (h⁵-cyclopentadienyl)Fe(CO)(L)(COR) and (h⁵-cyclopentadienyl)Fe(CO)(L)R that contain either an unsymmetrically substituted h⁵-cyclopentadienyl ring or a chiral tertiary phosphine.     

Facile synthesis of new polyolefinic ruthenium(0) complexes from ruthenium(II) precursors

The new ruthenium(II) complex [(C₈H₁₀)RuCl₂]_n (1) (C₈H₁₀ = 1,3,5-cyclooctatriene; n ⩾ 2) has been obtained from the reaction of RuCl₃·xH₂O with 1,3,5,7-cyclooctatetraene in refluxing ethanol. Reduction of [(C₈H₁₀)RuCl₂]_n and [(C₇H₈)RuCl₂]₂ (2) (C₇H₈ = 1,3,5-cyclooctatriene) by Na/Hg amalgam in the presence of isoprene (C₅H₈) gives the novel ruthenium(O) complexes [(η⁶-C₈H₁₀)Ru(η⁴-C₅H₈)] (3) and [(η⁶-C₇H₈)Ru(η⁴-C₅H₈)] (4). [(η⁶-C₇H₈Ru(η⁴-C₅H₈)] reacts with CO and HBF₄ to give [(η⁶-C₇H₈)Ru(η³-C₅H₉)(CO)][BF₄] (C₅H₉ = trans-1,2-dimethylallyl (5a); 1,1-dimethylallyl (5b)).     

Homo- and hetero-binuclear ansa-metallocenes of the group 4 transition metals as homogeneous co-catalysts for the polymerisation of ethene and propene

The compounds [M{(CH₂)₄C(η-C₅H₄)₂}(η-C₅H₅)Cl] (M=Zr^*, Hf), [M{(CH₂)₄C(η-C₅H₄)₂}(η-C₅H₅)Me] (M=Zr, Hf), [(η-C₅H₅)MCl₂{(CH₂)₄C(η-C₅H₄)₂}MCl₂(η-C₅H₅)] (M=Zr, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)(η-C₉H₆)}ZrCl₂(η-C₅H₅)], [(η-C₅H₅)MMe₂{(CH₂)₄C(η-C₅H₄)₂}MMe₂(η-C₅H₅)] (M=Zr, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)₂}HfCl₂(η-C₅H₅)], [(η-C₅H₅)MCl₂{(CH₂)₄C(η-C₅H₄)₂}Rh(η-C₈H₁₂)] (M=Zr^*, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)₂}TiCl₃], [(η-C₅H₅)ZrMe₂{(CH₂)₄C(η-C₅H₄)₂}HfMe₂(η-C₅H₅)], [(η-C₅H₅)MMe₂{(CH₂)₄C(η-C₅H₄)₂}Rh(η-C₈H₁₂)] (M=Zr^*, Hf) have been prepared and characterised. ^* indicates the crystal structure has been determined. Their catalytic properties for ethene and propene polymerisation have been explored.     

Formation of ferraboranes from pentaborane(9) or BH3 · thf and an electron-rich cyclopentadienyl iron phosphine hydride

[(η⁵-C₅R₅)Fe(PMe₃)₂H] (R = H, Me) can be made in good yields in a simple one-pot reaction between FeCl₂, PMe₃, C₅R₅H (R = H, Me) and Na/Hg in thf. Reaction of [(η⁵-C₅H₅)Fe(PMe₃)₂H] with pentaborane(9) gives the known metallaborane [(η⁵-C₅H₅)-nido-2-FeB₅H₁₀] (1) in improved yield as well as the new metallaboranes [(η-C₅H₅)-nido-2-FeB₅H₈{μ-5,6-Fe(η⁵-C₅H₅)(PMe₃)(μ-6,7-H)}] (2), [(η-C₅H₅)(PMe₃)-arachno-2-FeB₃H₈] (3), [(η⁵-C₅H₅)₂-capped-nido-2,3-Fe₂B₄H₈] (4), [(η⁵-C₅H₅)-nido-2-FeB₄H₇(PMe₃)] (5) and [(η⁵-C₅H₅)-nido-2-FeB₅H₈(PMe₃)] (6). Reaction of [(η⁵-C₅Me₅)Fe(PMe₃)₂H] with pentaborane(9) gives predominantly [(η⁵-C₅Me₅)-nido-2-FeB₅H₁₀] (7) and [(η⁵-C₅Me₅)(PMe₃)-arachno-2-FeB₃H₈] (8). Reaction of [(η⁵-C₅H₅)Fe(PMe₃)₂H] with 2 equiv. of BH₃ · thf gives low yields of ferrocene and compound 3. Compound 7 thermally isomerises to the apical isomer [(η⁵-C₅H₅)-nido-2-FeB₅H₁₀] (9) in low yield. Compounds 1 and 7 deprotonate cleanly in the presence of KH at the unique B-H-B bridge to give [(η⁵-C₅H₅)-nido-2-FeB₅H₉⁻][K⁺] (10) and [(η⁵-C₅Me₅)-nido-2-FeB₅H₉⁻][K⁺] (11) respectively, whilst 6 deprotonates more slowly at one of two equivalent B-H-B bridges to give the fluxional anion [(η⁵-C₅H₅)-nido-2-FeB₅H₇(PMe₃)⁻] (12).     

The hapticity of cyclooctatetraene in its first row mononuclear transition metal carbonyl complexes: Several examples of octahapto coordination

The two cyclooctatetraene metal carbonyls that have been synthesized are the tetrahapto derivative (η⁴-C₈H₈)Fe(CO)₃ and the hexahapto derivative (η⁶-C₈H₈)Cr(CO)₃ using the reactions of cyclooctatetraene with Fe(CO)₅ and with fac-(CH₃CN)₃Cr(CO)₃, respectively. Related C₈H₈M(CO)_n (M = Ti, V, Cr, Mn, Fe, Co, Ni; n = 4, 3, 2, 1) species have now been investigated by density functional theory in order to explore the scope of cyclooctatetraene metal carbonyl chemistry. In this connection, the existence of octahapto (η⁸-C₈H₈)M(CO)_n species is predicted as long as the central metal M does not exceed the 18-electron configuration by receiving eight electrons from the η⁸-C₈H₈ ring. Thus the lowest energy structures (η⁸-C₈H₈)Ti(CO)_n (n = 3, 2, 1), (η⁸-C₈H₈)M(CO)_n (M = V, Cr; n = 2, 1), and (η⁸-C₈H₈)Mn(CO) all have octahapto η⁸-C₈H₈ rings. An exception is (η⁶-C₈H₈)Fe(CO), with a hexahapto η⁶-C₈H₈ ring and thus only a 16-electron configuration for the iron atom. Hexahapto (η⁶-C₈H₈)M(CO)_n structures are predicted for the known (η⁶-C₈H₈)Cr(CO)₃ as well as the unknown (η⁶-C₈H₈)Ti(CO)₄, (η⁶-C₈H₈)V(CO)₃, (η⁶-C₈H₈)Mn(CO)₂, and (η⁶-C₈H₈)Fe(CO)₂ with 18, 18, 17, 17, and 18 electron configurations, respectively, for the central metal atoms. There are two types of tetrahapto C₈H₈M(CO)_n complexes. In the 1,2,3,4-tetrahapto (η⁴-C₈H₈)M(CO)_n complexes two adjacent CC double bonds, forming a 1,3-diene unit similar to butadiene, are bonded to the metal atom. In the 1,2,5,6-tetrahapto (η^2,2-C₈H₈)M(CO)₃ derivatives two non-adjacent CC double bonds of the C₈H₈ ring are bonded to the metal atom. The known (η⁴-C₈H₈)Fe(CO)₃ is a 1,2,3,4-tetrahapto complex. The unknown isomeric 1,2,5,6-tetrahapto complex (η^2,2-C₈H₈)Fe(CO)₃ is predicted to lie ∼15 kcal/mol above (η⁴-C₈H₈)Fe(CO)₃. The related 1,2,5,6-tetrahapto complexes (η^2,2-C₈H₈)Cr(CO)₄, (η^2,2-C₈H₈)Mn(CO)₄, [(η^2,2-C₈H₈)Mn(CO)₃]⁻, (η^2,2-C₈H₈)Co(CO)₂, and (η^2,2-C₈H₈)Ni(CO)₂ are all predicted to be low-energy structures.     

Improved preparation of h5-C5H5 Fe(CO)2(h1-alkyl) complexes from [h5-C5H5Fe(CO)2(h2-alkene)]+BF4−

Sodium cyanoborohydride has been found to be very effective for the conversion of [(h⁵-C₅H₅)Fe(CO)₂(h²-alkene)]⁺BF₄^? complexes to the corresponding h¹-alkyl derivatives.     

The preparation and structure of μ-iodobis(h5-cyclopentadienyldicarbonyliron) fluoroborate

The identity and structure of a compound which arises frequently in the generation of (h⁵-C₅H₅)Fe(CO)₂⁺ ion from (h⁵-C₅H₅)Fe(CO)₂I and AgBF₄ have been determined. The substance was shown to be {[h⁵-C₅H₅)Fe(CO)₂]₂I}BF_4s a compound already known from the work of Fischer and Moser. It consists of a BF₄^? anion and a cation formed by two (h⁵-C₅H₅)Fe(CO)₂, groups having the expected shape and dimensions, united by a bridging iodine atom. The FeI bonds have an average lenght of 2.588 » and the FeIFe angle is 110.8(1)°. The FeFe distance of 4.26 » is consistent with the expectation that there should be no metalmetal bond. Presumably the large FeIFe angle results from a compromise between the tendency of I to maximize p character in its bonding orbitals and the necessity of niminizing non-bonded contact between the (h⁵-C₅H₅)Fe(CO)₂ groups. Crystallographic data are: space group, P2/a; unit cell dimensions, a=15.605(2)», b=9.607(2)», c=12.373(2)», β=104.86(1)°, V=1792.9(6)»³; d_ealc=2.10 g/cm³ for Z=4; d_obs=2.08±0.02 g/cm³. Refinement using 1595 independent reflections with F_o²>3σ(F_o² was terminated at residuals of R₁=0.076 and R₂=0.114.     

Tricyanmethanido-tris(pentahapto-cyclopentadienyl) Uran(IV): Polymere Uran-Organyle mit ungewöhnlicher Koordination am Uran(IV)

Tricyanmethanide-tris(h⁵-cyclopentadienyl)uranium (IV): Polymeric Organouranium Systems with an Unusual Coordination of the Uranium (IV)Ion (h⁵-C₅H₅)₃UCl viz. (h⁵-C₅H₄CH₃)₃UCl react in H₂O or THF with K[C(CN)₃] to give in good yields the new complexes (h⁵-C₅H₅)₃U[C(CN)₃] and (h⁵-C₅H₄CH₃)₃U[C(CN)₃] which turn out surprisingly stable relative to the organometallic starting material. The chemical and spectroscopic properties (IR, NIR/VIS and ¹H-NMR spectra) indicate the formation of extended oligomeric structures linked via C(CN)₃-bridges involving most probably linear sections: along with a trigonal planar arrangement of the three cyclopentadienyl ring normals.     

Heteroleptic rhodium complexes containing both the dipyrrin/cyclooctadiene ligands and application of [(η-C8H12)Rh(4-pyrdpm)] in the construction of homo-/hetero-bimetallic complexes

Heteroleptic rhodium(I) complexes with the general formulations [(η⁴-C₈H₁₂)Rh(L)] [η⁴-C₈H₁₂ = 1,5-cyclooctadiene; L = 5-(4-cyanophenyl)dipyrromethene, cydpm; 5-(4-nitrophenyl)dipyrromethene, ndpm; and 5-(4-benzyloxyphenyl)dipyrromethene, bdpm; 5-(4-pyridyl)dipyrromethene, 4-pyrdpm; 5-(3-pyridyl)dipyrromethene, 3-pyrdpm] have been synthesized. The complex [(η⁴-C₈H₁₂)Rh(4-pyrdpm)] have been used as a synthon in the construction of homo-bimetallic complex [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Rh(η⁵-C₅Me₅)Cl₂] and hetero-bimetallic complexes [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ir(η⁵-C₅Me₅)Cl₂], [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ru(η⁶-C₁₀H₁₄)Cl₂] and [(η⁴-C₈H₁₂)Rh(μ-4-pyrdpm)Ru(η⁶-C₆H₆)Cl₂]. Resulting complexes have been characterized by elemental analyses and spectral studies. Molecular structures of the representative mononuclear complexes [(η⁴-C₈H₁₂)Rh(ndpm)] and [(η⁴-C₈H₁₂)Rh(4-pyrdpm)] have been authenticated crystallographically.     

(π-Cyclopentenyl)(π-cyclopentadienyl)nickel: A novel catalyst for the conversion of ethylene to 1-butene and n-hexenes

(π-Cyclopentenyl)(π-cyclopentadienyl)nickel, (h⁵-C₅H₅)Ni(h³-C₅H₇), is a novel, highly active, unicomponent catalyst for the conversion of ethylene to n-butenes and n-hexenes at 145–150° C. At high conversions of ethylene (70–90%), the dimeric product (80–86% yield) contains a high percentage (90–82%) of 1-butene. Experimental evidence is presented which strongly indicates that the cyclopentadienyl group remains bonded to the nickel during catalysis while the cyclopentenyl group is labile. A possible mode of activation is the reversible elimination of cyclopentadiene from (h⁵-C₅H₅)N₁(h³-C₅H₇) to generate π-cyclo pentadienylnickel hydride as a catalytically active intermediate. An improved synthesis of the title compound (70% yield) by direct hydrogenation of nickelocene is also reported.     

Structure cristalline et configuration relative d'un complexe du titanocene presentant une chiralite plane et une chiralite centree sur l'atome de titane

The crystalline structure of the racemic form m.p. 164° C of the compound (h⁵ -3-MeC₅H₃C(Me₂)C₆H₅)(h⁵-C₅H₅)Ti (2,6-Me₂C₆H₃O)Cl has been determined by X-ray diffraction to establish the relative configuration of the two chiral moieties. This compound may be used further as a reference for studies on dynamic stereochemistry around the titanium atom. A systematic absolute nomenclature is proposed for this type of structure.     

The preparation,characterization and reactivity of the cyclometallosilane,cyclo-1,1-di-h5-cyclopentadienyltitana-2,2,3,3,4,4,5,5,-octaphenylpentasilane, (h5-C5H5)2TiSi(C6H5)2[Si(C6H5)2]2Si(C6H5)2

Titanium has been incorporated into a catenated silicon ring by means of the salt elimination reaction of dichlorodi-h⁵-cyclopentadienyltitanium(IV), (I), with 1,4-dilithiooctaphenyltetrasilane, Li₂Si₄(C₆H₅)₈, to yield the title compound (II). II was characterized as a cyclometallopolysilane by means of elemental analyses, base catalyzed hydrolyses, molecular weight determination, infrared and ¹H NMR spectroscopy. Electronic spectral data and electrochemical data are also discussed and support the formulation of II as a disubstituted (h⁵-C₅H₅)₂Ti^IV derivative. The reactivity of II, with CHCl₃, is described in terms of a radical decomposition pathway.     

C2-Bridged sandwich and half-sandwich entities with Ti(IV) and Cr(0) centers

The intense purple colored bi- and trimetallic complexes {Ti}(CH₂SiMe₃)[CC(η⁶-C₆H₅)Cr(CO)₃] (3) ({Ti}=(η⁵-C₅H₅)₂Ti) and [Ti][CC(η⁶-C₆H₅)Cr(CO)₃]₂ (5) {[Ti]=(η⁵-C₅H₄SiMe₃)₂Ti}, in which next to a Ti(IV) center a Cr(0) atom is present, are accessible by the reaction of Li[CC(η⁶-C₆H₅)Cr(CO)₃] (2) with {Ti}(CH₂SiMe₃)Cl (1) or [Ti]Cl₂ (4) in a 1:1 or 2:1 molar ratio. The chemical and electrochemical properties of 3, 5, {Ti}(CH₂SiMe₃)(CCFc) [Fc=(η⁵-C₅H₅)Fe(η⁵-C₅H₄)] and [Ti][(CC)_nMc][(CC)_mM′c] [n, m=1, 2; n=m; n≠m; Mc=(η⁵-C₅H₅)Fe(η⁵-C₅H₄); M′c=(η⁵-C₅H₅)Ru(η⁵-C₅H₄); Mc=M′c; Mc≠M′c] will be comparatively discussed.     

Errata

The molecular structure of cyclopentadienyliron nitrosyl consists of dimeric [(h⁵-C₅ H₅)Fe(μ-NO)]₂ molecules; the bonding parameters indicate the presence of symmetrically-bridged nitrosyl groups, as well as a novel FeFe double bond.     

Photochemistry of methyl- and n1-benzyl-n5-cyclopentadienyltricarbonyltungstein(II)

Irradiation of solutions of n⁵-C₅H₅W(CO)₃R (R  CH₃n1-CH₂C₆H₅) in cyclohexane at ca. 310490 nm leads to the formation of [n⁵-C₅H₅W(CO)₃]₂ and methane and of n⁵-C₅H₅W₅(CO)₂(n³-CH₂C₆H₅) and some [n⁵-C₅H₅W(CO)₃]₂, respectively. When the irradiation is carried out in the presence of excess P(C₆H₅)₃, the photoproducts are n⁵-C₅H₅W(CO)₂[P(C₆H₅)₃]CH₃ (R  CH₃) and n⁵-C₅H₅W(CO)₂(n₃-CH₂C₆H₅) and trace [n⁵-C₅H₅W(CO)₃]₂ (R  n¹-CH₂C₆H₅). Photolysis of the n⁵-C₅H₅W(CO)₃R in the presence of benzyl chloride affords n⁵-C₅H₅W(CO)₃Cl (R  CH₃) and both n⁵-C₅H₅W(CO)₂(n³-CH₂C₂H₅) and n⁵-C₅H₅W(CO)₃Cl (R  n¹-CH₂C₆H₅), the relative amounts of the latter products depending on the quantity of added C₆H₅CH₂Cl. Irradiation of n⁵-C₅H₅W(CO)₃-CH₃ in the presence of both P(C₆h₅)₃ and C₆H₅CH₂Cl affords n⁵-C₅H₅W(CO)₂-[P(C₆H₅)₃]CH₃, but no n⁵-C₅H₅W(CO)₃Cl. It is proposed that the primary photo-reaction in these transformations is dissociation of a CO group from n⁵-C₅H₅W-(CO)₃R to generate n⁵-C₅H₅W(CO)₂R, which can either combine with L to form a stable 18 electron complex, n⁵-C₅H₅W(CO)₂(L)R (L  CO, P(C₅H₅)₃; LR  n³-CH₂C₆H₅), or lose the group R in a competing, apparently slower step. This proposal receives support from the observation that, light intensifies being equal, n⁵-C₅H₅W(CO)₃CH₃ undergoes a considerably faster photoconversion to [n⁵-C₅H₅W(CO)₃]₂ under argon than under carbon monoxide.     

Chloro(η-dihydropentalenyl)bis(triphenylphosphine)ruthenium(II): synthesis, structural characterization and catalytic activity in the dimerization of phenylacetylene

Reactions between HRuCl(PPh₃)₃ and 1,3- or 1,5-cyclooctadiene yield the 1,2-dihydropentalenyl complex (η⁵-C₈H₉)Ru(PPh₃)₂Cl through a series of steps including olefin insertion and electrocyclization. The reaction is accompanied by the loss of two equivalents of hydrogen. The product crystallizes in the monoclinic space group (No. 2). (η⁵-C₈H₉)Ru(PPh₃)₂Cl catalyzes the dimerization of phenylacetylene to a ≈2:1 mixture of Z:E 1,4-diphenyl-1-buten-3-yne. Comparison of the catalytic activity of (η⁵-C₈H₉)Ru(PPh₃)₂Cl with (η⁵-C₅H₅)Ru(PPh₃)₂Cl, (η⁵-C₅Me₅)Ru(PPh₃)H₃ and {η⁵-HB(pz)₃}Ru(PPh₃)₂Cl suggests that the more electron-rich η⁵ ligands favor formation of the Z isomer.