Solution and crystal structure of the dihydrogen complex [Ru(H2)(H)(PMe2Ph)4]PF6, an active alkyne hydrogenation catalyst

The complex [Ru(H₂)(H)(PMe₂Ph)₄]PF₆ (1) has been prepared by reaction of [Ru(H)(PMe₂Ph)₅] FP₆ (2) in THF with 1 atm H₂ and characterised by variable temperature ³¹P and ¹H NMR. It undergoes four distinct fluxional processes listed in order of decreasing activation energy: (i) exchange of H₂ in solution with the dihydrogen ligand above 273 K; (ii) isomerisation of cis and trans isomers of 1 above 230 K; (iii) exchange of H atoms between H₂ and hydride in trans-1 above 180 K; (iv) rapid H₂/hydride exchange in cis-1 to below 180 K. A single crystal X-ray diffraction study of 1 at 173 K shows that the complex has the cis geometry in the solid state but does not clearly reveal the positions of the hydrogen ligands. Complex 1 starts out as a catalyst of high activity for the selective hydrogenation of 1-alkynes to 1-alkenes (RC≡CH; R=¹¹Bu, Ph) but it is rapidly deactivated, possibly because of formation of the enynyl complex [Ru(η³RC₃CHR)(PMe₂Ph)₄]⁺. Complex 1 efficiently catalyzes the hydrogenation of internal alkynes (3-hexyne, 2-pentyne) to internal cis-alkenes with little deactivation, although some isomerisation of the alkene produced is observed. These observations are consistent with those of Nkosi, Coville, Albers and Singleton who reported that complex 2 must dissociate one PMe₂Ph ligand to produce the species active for alkyne hydrogenation. Complex 2 catalyses these hydrogenations with slower initial rates than complex 1 but deactivates less readily. In contrast to 1, complex 2 does not appear to cause the isomerisation of internal alkenes.     

NMR coalescence effects resulting from stereochemical non-rigidity and halide exchange in octahedral rhodium(III) and iridium(III) tertiary phosphine complexes

The PMe₂Ph ligands in the aquo-cations mer- [MCl₂(H₂O)(PMe₂Ph)₃][ClO₄] rapidly exchange on the NMR time-scale giving coalescence in the ¹H and ³¹P NMR spectra. Dissociation of the H₂O ligand which is trans to PMe₂Ph leads to a five- coordinate intermediate. This intermediate (M = Rh) is believed to be involved in the rapid reaction of [RhCl₂(H₂O)(PMe₂Ph)₃] [ClO₄] with mer- [RhCl₃(PMe₂Ph)₃] by a chloride transfer mechanism leading to total exchange of the PMe₂Ph ligands.     

Thermal and photochemical substitution reactions of CpRe(PPh3)2H2 and CpRe(PPh3)H4. Catalytic insertion of ethylene into the C-H bond of benzene

The thermal and photochemical reactions of CpRe(PPh₃)₂H₄ and CpRe(PPh₃)H₄ (Cp = η⁵-C₅H₅) with PMe₃, P(p-tolyl)₃, PMe₂Ph, DMPE, DPPE, DPPM, CO, 2,6-xylylisocyanide and ethylene have been examined. While CpRe(PPh₃)₂H₂ is thermally inert, it will undergo photochemical substitution of one or two PPh₃ ligands. With ethylene, substitution is followed by insertion of the olefin into the C-H bond of benzene, giving ethylbenzene. CpRe(PPh₃)H₄ undergoes thermal loss of PPh₃, which leads to substituted products of the type CpRe(L) H₄. Photochemically, reductive elimination of dihydrogen occurs preferentially. The complex trans-CpRe(DMPE)H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 6.249(6), b = 16.671(8), c = 13.867(7) Å, β = 92.11(6)°, V = 1443.7(2.9) Å and Z = 4. The complex trans-CpRe(PMe₂Ph)₂H₂ was structurally characterized, crystallizing in the monoclinic space group P2₁/n (No. 14) with a = 7.467(3), b = 23.874(14), c = 11.798(6) Å, β = 100.16(4)°, V = 2070.2(3.4) ų and Z = 4.     

Reactions of the haloalcohols HO(CH2)nCl (n = 2, 3) with platinum(II) - alkynyl and -alkyne complexes. X-ray crystal structure of trans-[Pt(Me) {C(OCH2CH2Cl) (CH2Ph)} (PPh3)2] [BF4]

The chloro complexes trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄, react with 1-alkynes HC---C---R in the presence of NEt₃ to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh₃)₂] (R = p-tolyl (1), Ph (2), C(CH₃)₃ (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH₂)_nCl (n = 2, 3) in the presence of 1 equiv. of HBF₄ to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH₂)_nCl](CH₂R) } (PPh₃)₂][BF₄] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)₂(PMe₂Ph)₂] with 2 equiv. HBF₄ and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH₂CH₂CH₂Cl)(CH₂Ph) } (PMe₂Ph)₂][BF₄] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH₂CH₂Cl)(CH₂Ph) } (PPh₃)₂][BF₄] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh₃)₂], after treatment with AgBF₄ in HOCH₂CH₂Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe₂Ph)]₂ with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl₂{C(OCH₂CH₂CH₂Cl)(CH₂C₆H₄-p-Me}(PMe₂Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2₁, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) ų and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry.     

Reactivity of {(Ph3P)Pt[μ-η-H---SiH(Ar)]}2 (Ar=2-isopropyl-6-methylphenyl) with phosphines. X-ray crystal structure of trans-{(dppe)Pt[μ-SiH(Ar)]}2

The dinuclear Pt---Si complex {(Ph₃P)Pt{μ-η²-H---SiH(IMP)]}₂ (trans-1a–cis-1b=3:1; IMP=2-isopropyl-6-methylphenyl) reacted with basic phosphines such as 1,2-bis(diphenylphosphino)ethane (dppe) and dimethylphenylphosphine (PMe₂Ph) to afford different dinuclear Pt---Si complexes with loss of H₂, {(P)₂Pt[μ-SiH(IMP)]}₂ [P=dppe, trans-2a (major), cis-2b (trace); PMe₂Ph, 3 (trans only)]. Complexes 2 and 3 were characterized by multinuclear NMR spectroscopy and X-ray crystallography (2a). In contrast, the reaction of 1a,b with the sterically demanding tricyclohexylphosphine (PCy₃) afforded {(Cy₃P)Pt{μ-η²-H---SiH(IMP)]}₂ (trans-4a–cis-4b 2:1) analogous to 1a,b where the central Pt₂Si₂(μ-H)₂ core remains intact but the PPh₃ ligands have been replaced by PCy₃. Complexes 4a and 4b was characterized by multinuclear NMR and IR spectroscopies.     

Substitution reaction mechanisms of dihydrido-ruthenium(II) phosphine complexes: hydribe basicity and molecular hydrogen intermediates

Kinetic and activation parameter data for the reactions of cct-Ru(H)₂(CO)₂(PPh₃)₂ (1) (cct = cis, cis, trans) in THF with thiols, CO and PPh₃ to give cct-RuH(SR)(CO)₂(PPh₃)₂, Ru(CO)₃(PPh₃)₂ and Ru(CO)₂(PPh₃)₂, respectively, reveal a common, rate-determining step, the initial dissociation of H₂ from 1; the activated complex probably resembles the corresponding Ru(η²-H₂) species. Reaction of Ru(H)₂(dppm)₂ (2) (as a cis/trans mixture, DPPM = bis(diphenylphosphino)methane) with thiols initially generated cis- and trans- RuH(SR) (dppm)₂ with a rate that depends on both the type and concentration of thiol. The higher basicity of the hydride ligands in 2 (versus 1), which is demonstrated by deuterium exchange with CD₃OD, gives rise in the thiol reaction to an initial protonation step prior to loss of H₂. A species detected in the thiol reaction is possibly [RuH(η²-H₂ (dppm)₂]², the anticipated intermediate for this reaction and for the hydrogen exchange with alcohol. A longer reaction of 2 with PhCH₂SH gives solely cis-Ru(SCH₂Ph)₂(dppm)₂.     

Slippage of η-allenyl/propargyl to an η structure and tautomerization of η-propargyl to η-allenyl in ligand addition and substitution reactions of platinum(II) complexes

Reactions of [(PPh₃)₂Pt(η³-CH₂CCPh)]OTf with each of PMe₃, CO and Br⁻ result in the addition of these species to the metal and a change in hapticity of the η³-CH₂CCPh to η¹-CH₂CCPh or η¹-C(Ph)=C=CH₂. Thus, PMe₃ affords [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]⁺, CO gives both [trans-(PPh₃)₂Pt(CO)(η¹-CH₂CCPh)]⁺ and [trans-(PPh₃)₂Pt(CO)(η¹-C(Ph)=C=CH₂)]⁺, and LiBr yields cis-(PPh₃)₂PtBr(η¹-CH₂CCPh), which undergoes isomerization to trans-(PPh₃)₂PtBr(η¹-CH₂CCPh). Substitution reactions of cis- and trans-(PPh₃)₂PtBr(η¹-CH₂CCPh) each lead to tautomerization of η¹-CH₂CCPh to η¹-C(Ph)=C=CH₂, with trans-(PPh₃)₂PtBr(η¹-CH₂CCPh) affording [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]⁺ at ambient temperature and the slower reacting cis isomer giving [trans-(PPh₃)(PMe₃)₂Pt(η¹-C(Ph)=C=CH₂)]⁺ at 54 °C . All new complexes were characterized by a combination of elemental analysis, FAB mas spectrometry and IR and NMR (¹H, ¹³C{¹H} and ³¹P{¹H}) spectroscopy. The structure of [(PMe₃)₃Pt(η¹-C(Ph)=C=CH₂)]BPh₄·0.5MeOH was determined by single-crystal X-ray diffraction analysis.     

The interaction of Lewis acidic boron derivatives with Re(CO)5−nH(PMe3)n complexes

Lewis acid adducts of the hydrides cis- and trans-Re(CO)(PMe₃)₄H (1) and (2), mer-Re(CO)₂(PMe₃)₃H (3), fac-Re(CO)₂(PMe₃)₃H (4) and trans-Re(CO)₃(PMe₃)₂H (5) were studied with BH₃ and 9-borabicyclo[3,3,1] norbonane (BBNH). Using BH₃·THF and (BBNH)₂ 1 and 2 afforded Re(CO)(PMe₃)₃(η²-BH₄) (6) and Re(CO)(PMe₃)₃(η²-BBNH₂) (7) as stable and isolable products. VT IR studies established for the reaction to 7 that BBNH first attaches in a pre-equilibrium to the O_CO atom of 1 or 2. At higher temperatures ReH adduct formation occurs with instantaneous transformation to 7 and elimination of PMe₃·BBNH. In a similar way, the hydrides 3 and 4 were converted with BH₃·THF and (BBNH)₂ to yield the stable complexes Re(CO)₂(PMe₃)₂(η²-BH₄) (8) and Re(CO)₂(PMe₃)₂(η²-BBNH₂) (9). The intermediacy of the η¹-BH₄ adducts mer-/fac-Re(CO)₂(PMe₃)₃(η¹-BH₄) was confirmed by VT ¹H, ³¹P NMR and VT IR experiments. The conversion of 5 with BH₃·THF led to equilibria with adducts at the O_CO terminus in trans position to H and with H_Re as revealed by VT IR studies. Temperature dependent ³¹P equilibrium studies allowed to calculate ΔH=−4.9 kcal mol⁻¹ and ΔS=+0.034 e.u. for this reaction. These adducts could not be isolated. Compound 5 does not react with (BBNH)₂ even at elevated temperatures. DFT calculations were carried out to support the structures of the BH₃ adducts of 5. In addition a vibrational analysis helped to unravel the IR band assignments of the involved compounds. DFT calculations on 8 confirmed its C_2v structure. X-ray diffraction studies were carried out on single crystals of 6 and 7.     

Silicon-containing carbene complexes 16. Intramolecular agostic stabilization versus nucleophilic addition to the 16-electron carbene complex (CO)4(L)W=C(NMe2)SiPh2Me

The 16-electron complex (CO)₄W=C(NMe₂)SiPh₂Me (1) was photochemically prepared from (CO)₅W=C- (NMe2)SiPh₂Me. Reactions with selected nucleophiles, having different ligand properties, were performed to test the strength of the intramolecular agostic interaction of one of the phenyl groups, by which 1 is stabilized. The stable complexes cis-(CO)₄LW=C(NMe₂)SiPh₂Me were formed with L=P(OMe)₃, P(OEt)₃ or 2,6-Me₂C₆H₃NC. The substituted complexes had no tendency for ligand elimination. Addition of acetonitrile or pyridine to an ether solution of 1 resulted in the formation of cis-(CO)₄(MeCN)W=C(NMe₂)SiPh₂Me or cis-(CO)₄(C₅H₅N)- W=C(NMe₂)SiPh₂Me, respectively. These reactions were reversed on evaporation of the solutions. No reaction was observed with triethylamine.     

Ammonia ruthenium complexes for the access to new hydrido, carbonyl and isocyanide ruthenium-alkynyl derivatives

The potential in preparative chemistry of the precursors trans-[Ru(NH₃)(CC---R¹)(Ph₂PCH₂CH₂PPh₂)₂]PF₆ (3) has been studied. They offer a convenient access, by NH₃ displacement, to new functional alkynyl-ruthenium derivatives. Complexes 3 react with alkynes HCC---R² to give unsymmetrical trans-Ru(---CC---R¹)(---CC---R²)(dppe)₂ compounds 4a-c, and with sodium methoxide in methanol they open the route to a variety of mixed hydride complexes 5a-c, trans-Ru(H)(---CC---R¹)(dppe)₂. In contrast, with carbon monoxide or isocyanides CN---R³ (R³:CH₂Ph, C₆H₁₁, Me₃C) they allow the preparation of cationic derivatives trans-(Ru(CO)(---CC---R¹)(dppe)₂]PF₆ (6a-c) or trans-[Ru(CNR³)(---CC---R¹)(dppe)₂]PF₆ (7a-d).     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

Geometrical configuration of monomethyl–platinum(II) complexes driven by the size of entering nitrogen ligands

The reaction of the monoalkyl complex trans-[Pt(DMSO)₂Cl(CH₃)] with a large variety of heterocyclic nitrogen bases L, in chloroform solution, leads to the formation of uncharged complexes of the type [Pt(DMSO)(L)Cl(CH₃)], containing four different groups coordinated to the metal center. Only two out of the three different possible isomers were detected in solution. These two trans(C,N) and cis(C,N) species can be unambiguously identified through ¹H NMR spectroscopy. For the trans(C,N) isomers, average values of ²J_PtH=75±4 Hz and ³J_PtH=36±4 Hz have been observed for the coordinated methyl and DMSO ligands, respectively. In the case of the cis(C,N) isomers, these values increase to ²J_PtH=83±2 Hz, and decrease to ³J_PtH=26±3 Hz due to the mutual exchange of ligands in trans position to CH₃ and DMSO. In the case of bulky asymmetric ligands, such as quinoline, 2-quinolinecarboxaldehyde, 2-methylquinoline, 5-aminoquinoline, 2-phenylpyridine and 2-chloropyridine, slow rotation of the hindered group around the Pt---N bond makes the coordinated DMSO ligand prochiral. NMR experiments have shown that the first reaction product is the trans(C,N) isomer as a consequence of the very fast removal of one DMSO ligand by the nitrogen bases from the starting complex trans-[Pt(DMSO)₂Cl(CH₃)]. This trans kinetic product undergoes a geometrical conversion into the more stable cis(C,N) isomer through the intermediacy of fast exchanging aqua-species. The rate of isomerization and the relative stability of the two isomers depends essentially on the rate of aquation and on the steric congestion imposed by the new L ligand on the metal.     

Mixed chloride–phosphine complexes of the dirhenium core: 9. The first mixed monodentate phosphine complex, 1,2,7,8-Re2Cl4(PMe2Ph)3(PEt2H)

The reduction of the Re₂ ⁵⁺ core in 1,2,7-Re₂Cl₅(PR₃)₃ molecules, followed by addition of 1 equiv. of a different phosphine ligand, PR₃ ′, allows the preparation of the mixed monodentate phosphine compounds of the Re₂ ⁴⁺ type, namely 1,2,7,8-Re₂Cl₄(PR₃)₃(PR₃ ′). The stereochemistry of the starting materials dictates the stereochemistry of the final products. The one-electron reduction of the 1,2,7-isomer of Re₂Cl₅(PMe₂Ph)₃ with KC₈ to the corresponding anion, [1,2,7-Re₂Cl₅(PMe₂Ph)₃]⁻ (1), followed by non-redox substitution of one chloride ion by one diethylphosphine, PEt₂H, afforded the first mixed monodentate phosphine compound of the dirhenium(II) core, Re₂Cl₄(PMe₂Ph)₃(PEt₂H) (2), in good yield. Crystal structure determination as well as other physical methods and elemental analysis unambiguously confirmed the formation of 2. The related system 1,2,7-Re₂Cl₅(PMe₃)₃---Co(C₅H₅)₂---PEt₂H leads to several products, one of which is 1,2,7,8-Re₂Cl₄(PMe₃)₃(PEt₂H) (3).     

Elimination of benzene from a benzyloxy ligand to form a carbonyl group on a tungsten-phosphine center

WH₃(OCH₂C₆H₅) (PMe₃)₄ (1) is formed upon reaction of WH₂(PMe₃)₅ with benzyl alcohol for 12 days at ambient temperatures. Thermolysis of 1 at 80°C in toluene solution gives the carbonyl complex, WH₂(CO)(PMe₃)₄ (2) and benzene. The conversion is slower in the presence of H₂. Reaction of 1 with D₂ leads to H/D exchange in the hydride ligands and in the benzylic and ortho-phenyl positions of the benzyloxide. A mechanism for the thermolysis of 1, based on an H₂ elimination, sequential C-H activations, and CO deinsertion from an acyl ligand, is proposed. Thermolysis of 1 is much faster in the presence of free benzyl alcohol and 2 is not formed. The products under these conditions are toluene, bibenzyl, WH₄(PMe₃)₄, PMe₃ and unidentified material, consistent with the intermediacy of benzyl radicals.     

The propensity of alkoxide and aryloxide derivatives of tungsten carbonyls to aggregate in solution. Synthesis and X-ray structures of dinuclear, trinuclear and tetranuclear complexes derived from the MeOW(CO)5 anion

The complex [Et₄N][W(CO)₅OMe] (1) has been prepared from the reaction of the photochemically generated W(CO)₅THF adduct and [Et₄N][OH] in methanol. Complex 1 was shown to undergo rapid CO dissociation in THF to quantitatively provide the dimeric dianion, [W(CO)₄OMe]₂²⁻. The resulting THF insoluble salt [Et₄N]₂[W(CO)₄OMe]₂ (2) has been structurally characterized by X-ray crystallography, with the doubly bridging methoxide ligands being in an anti configuration. Complex 2 was found to subsequently react with excess methoxide ligand in a THF slurry to afford the face-sharing octahedron complex [Et₄N]₃[W₂(CO)₆(OMe)₃] (3) which contains three doubly bridging methoxide groups. In the absence of excess methoxide ligand complex 2 cleanly yields the tetrameric complex [Et₄N]₄[W(CO)₃OMe]₄ (4) which has been structurally characterized as a cubane-like arrangement with triply bridging μ³-methoxide groups and W(CO)₃ units. Although complex 3 was not characterized in the solid state, the closely related glycolate derivative [Et₄N]₃[W₂(CO)₆(OCH₂CH₂OH)₃] (5) was synthesized and its structure determined by X-ray crystallography. The trianions of complex 5 are linked in the crystal lattice by strong intermolecular hydrogen bonds. Crystal data for 2: space group P2₁/n, a = 7.696(2), b = 22.019(4), c = 9.714(2) Å, β = 92.22(3)°, Z = 4, R = 6.43%. Crystal data for 4: space group Fddd, a = 12.433(9), b = 24.01(2), c = 39.29(3) Å, Z = 8, R = 8.13%. Crystal data for 5: space group P2₁2₁2₁, a = 11.43(2), b = 12.91(1), c = 29.85(6) Å, Z = 8, R = 8.29%. Finally, the rate of CO ligand dissociation in the closely related aryloxide derivatives [Et₄N][W(CO)₅OR] (R = C₆H₅ and 3,5-F₂C₆H₃) were measured to be 2.15 × 10⁻² and 1.31 × 10⁻³ s⁻¹, respectively, in THF solution at 5°C. Hence, the value of the rate constant of 2.15 × 10⁻² s⁻¹ establishes a lower limit for the first-order rate constant for CO loss in the W(CO)₅OMe⁻ anion, since the methoxide ligand is a better π-donating group than phenoxide.     

Cis- and trans-titanium complexes with doubly silyl-bridged dicyclopentadienyl ligands: molecular structure of [(TiCl)2(μ-O){(SiMe2)2(η-C5H3)2}]2(μ-O)2

The reaction of TiCl₄ with Li₂[(SiMe₂)₂(η⁵-C₅H₃)₂] in toluene at room temperature afforded a mixture of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] in a molar ratio of 1/2 after recrystallization. The complex trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] was hydrolyzed immediately by the addition of water to THF solutions to give trans-[(TiCl₂)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] as a solid insoluble in all organic solvents, whereas hydrolysis of cis-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] under different conditions led to the dinuclear μ-oxo complex cis-[(TiCl₂)₂)(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}] and two oxo complexes of the same stoichiometry [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ as crystalline solids. Alkylation of cis- and trans-[(TiCl₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] with MgCIMe led respectively to the partially alkylated cis-[(TiMe₂Cl)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] and the totally alkylated trans-[(TiMe₃)₂{(SiMe₂)₂(η⁵-C₅H₃)₂}] compounds. The crystal and molecular structure of the tetranuclear oxo complex [(TiCl)₂(μ-O){(SiMe₂)₂(η⁵-C₅H₃)₂}]₂(μ-O)₂ was determined by X-ray diffraction.     

Reactivity of cationic carbonyl/phosphine ruthenium(II) compounds

Cis(or trans)-[RuCl₂(CO)₂(PPh₃)₂] react with two and one equivalents of AgBF₄ to give the recently reported [Ru(CO)₂(PPh₃)₂][BF₄]₂·CH₂Cl₂ (1) and novel [RuCl(CO)₂(PPh₃)₂][BF₄] · 1/2 CH₂Cl₂ (2), respectively. Cis-[RuCl₂(CO)₂(PPh₃)₂] also reacts with two equivalents of AgBF₄ in the presence of CO to give [Ru(CO)₃(PPh₃)₂][BF₄]₂ (3). Reactions of 1 and 2 with NaOMe and CO at 1 atm produce the carbomethoxy species [Ru(COOMe)₂(CO)₂(PPh₃)₂] (4) and [RuCl(COOMe)(CO)₂(PPh₃)₂] (5), respectively. Complex 4 can also be formed from the reaction of 3 with NaOMe and CO. Alternatively, 4 is formed from cis-[RuCl₂(CO)₂(PPh₃)₂] with NaOMe and CO at elevated pressure (10 atm); if these reactants are refluxed under 1 atm of CO, [Ru(CO)₃(PPh₃)₂] is the product. The reaction of [RuCl(CO)₃(PPh₃)₂][AlCl₄] with NaOMe provides an alternative route to the preparation of 5, but the product is contaminated with [RuCl₂(CO)₂(PPh₃)₂]. Compounds 1. 2, 4 and 5 have been characterised by IR, ¹H NMR and analysis, whilst the formulation of 3 is proposed from spectroscopic data only. This account also examines the reactivity of [Ru(CO)₂(PPh₃)₂][BF₄]₂ · CH₂Cl₂ with NaBH₄, conc. HCl, KI and, finally, MeCOONa in the presence of CO. The products of these reactions, namely cis-[RuH₂(CO)₂(PPh₃)₂], cis-[RuCl₂(CO)₂(PPh₃)₂], cis-[RuI₂(CO)₂(PPh₃)₂] and [Ru(OOCMe)₂(CO)₂(PPh₃)₂], have been identified by comparison of their spectra with previous literature.     

The synthesis and characterization of a cationic technetium(V) phenylimido complex. The X-ray crystal structure of [TcCl2(NPh)(PMe2Ph)3](BPh4)

The reaction of the neutral Tc(V) phenylimido complex [TcCl₃(NPh)(PPh₃)₂] with excess PMe₂Ph in refluxing MeOH gives the cationic, tris-dimethylphenylphosphine complex [TcCl₂(NPh)(PMe₂Ph)₃]⁺, which is isolated as the tetraphenylborate salt. The IR spectrum of the crystalline product shows a medium intensity band at 1102 cm⁻¹ which is assigned to ν(TcN) from the phenylimido core. The ¹H NMR spectrum of the diamagnetic complex shows a series of multiplets in the aryl region and three distinct signals near 2 ppm from the phosphine methyl groups. The X-ray crystal structure, which is the first for a cationic technetium organoimido complex, shows a meridional arrangement of phosphine ligands with a chloride ligand coordinated trans to the phenylimido unit. The TcN bond length of 1.711(2) Å is consistent with the dianionic nature of the organonitrogen core. The Tc---N---C bond angle of 178.8(2)° reflects the sp hybridization of the phenylimido nitrogen atom. The coordination geometry is best described as a distorted octahedron. Crystal data for C₅₄H₅₈BCl₂NP₃Tc: triclinic space group

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. Structure solution based on 9986 observed reflections converged at R = 3.65%, R_w = 5.43%, GOF = 1.82.     

Preparation and crystal structure of trans-dihydroxo-[tetrakis(2,6-dichlorophenyl)porphinato]ruthenium(IV)·2toluene

Trans-dihydroxo-[tetrakis(2,6-dichlorophenyl)porphinato]ruthenium(IV) ([Ru(OH)₂(TDCPP)]) was prepared by meta-chloroperbenzoic acid oxidation of [Ru(CO)(TDCPP)] in dichloromethane-toluene, and its crystal structure is reported. Crystal data for [Ru(OH)₂(TDCPP)]·2toluene:C₄₄H₂₂N₄O₂Cl₈Ru·2C₇H₈, orthorhombic, space group Pbca a = 13.149(1), B = 19.893(2), C = 21.093(2)Å, U = 55.17.3(2) ų, Z = 4. The short axial Ru---O bond distance, 1.790(7) Å, is in the range expected for a double Ru(IV)-oxygen bond. Both hydroxo ligands are approximately located in the mean plane of two opposite dichlorophenyl groups. Full-matrix least-squares refinement of positional and thermal parameters, using 2368 unique reflections with F > 2.5 σ (F) led to R(F) = 0.063; R_w = 0.066.     

Stopped-flow mechanistic study of bromide substitution by an organonitrile at an iron(II) phosphinic centre; a π-electron driven process

The kinetics of the displacement reactions of the bromide ligands of trans-[FeBr₂(depe)₂] (depe = Et₂PCH₂CH₂PEt₂) by the organonitrile NCCH₂C₆H₄OMe-4, in tetrahydrofuran (either in the absence or in the presence of added Br⁻), to give the corresponding mono- and dinitrile complexes trans-[FeBr(NCCH₂C₆H₄OMe-4)(depe)₂]⁺ and trans-[Fe(NCCH₂C₆H₄OMe-4)₂(depe)₂]²⁺, have been investigated by stopped-flow spectrophotometry. The substitution reaction occurs by a mechanism involving rate-limiting dissociation of bromo ligands to form the unsaturated intermediates [FeBr(depe)₂]⁺ (k₁ = 1.52 ± 0.02 s⁻¹) and [Fe(NCR)(depe)₂]²⁺ (k₃ = 0.063 ± 0.008 s⁻¹) which add the nitrile ligand to form those nitrile complexes. The competition between the nitrile and Br⁻ for such metal centres has also been investigated and a stronger inhibiting effect of added Br⁻ is observed for the substitution of the second bromo ligand relative to the first one. The kinetic data are rationalized in terms of π-electronic effects of these unsaturated metal centres and of the bromide and nitrile ligands.