η and η olefin complexation by S, S-[Ru(Me2edda)]: a structural change to accommodate bidentate dienes

[Ru^II(Me₂edda)(H₂O)₂] (1), Me₂edda²⁻ = N,N′-dimethylethylenediaminediacetate, exhibits a sterically-controlled molecular recognition in forming η² and η⁴ olefin complexes. 1 exists with an N₂O₂ in-plane set of chelate donors and axial H₂O ligands. The two CH₃ functionalities of Me₂edda²⁻ are poised above and below the N₂O₂ plane of the glycinato rings. Studies herein of the 2,2′-bipyridine complex, [Ru^II(Me₂edda)(bpy)], with bidentate bpy chelation as established via ¹H NMR and electrochemical methods show 1 to be ligated in the S,S configuration with the glycinato rings in-plane as a cis-O form. 1 is sterically discriminating in forming η² complexes with smaller olefins (ethylene, 2-propene, cis-2-butene, methyl vinyl ketone and 3-cyclohexene-1-methanol), but rejects larger decorated ring structures and branched olefins (1,2-dimethyluracil, cyclohexene-1-one 2-methyl-2-propene). η² complexes of 1 have characteristic Ru^II/III DPP waves near 0.55 V which vary slightly with olefin structure. Potentially bidendate dienes (1,3-butadiene, 1,3-cyclohexadiene and 2,5-norbornadiene (nbd) form η⁴ complexes as shown by Ru^II/III waves between 0.94 and 1.30 V, indicate of a highly stabilized Ru^II center by π-backboning. An η²η⁴ ‘equilibrium’ with apparent K = 22 at 25 °C is observed for nbd coordinated to 1. (The η² and η⁴ distribution may be a kinetic one and not a thermodynamic one). To allow formation of the cis η⁴ complexes, 1 must undergo a shift of one or both glycinato donors from the N₂O₂ plane into the axial site away from the dimethyl functionalities. η⁴ chelation by 1,3-butadiene has been confirmed by ¹H NMR spectral assignments of two [Ru^II(Me₂edda)] isomers, one in the axial rans-O glycinato configuration, e.g. 1,3-butadiene is bidentate in the original N₂O₂ plane and a second unsymmetrical glycinato arrangement with in-plane and axial glycinato as well as in-plane and axial η⁴-1,3-butadiene coordination. [Ru^II(hedta)(H₂O)]⁻ (2), hedta³⁻ = N-hydrpxyethylenediaminetriacetate, is less discriminating for olefin structures, forming η² complexes with all eleven olefins and dienes mentioned for studies with 1. However, 2 does not undergo displacement of a carboxylate donor by the second olefin unit of a diene [Ru^II(hedta)(diene)]⁻ complexes possess a pendant non-coordinated olefin and on η²-bound olefin in the complex, indicated by a normal Ru^II(pac)(olefin)Ru^II/III wave near 0.55 V.     

The synthesis and characterization of dinuclear platinum complexes bridged by the 4,4′-dipyrazolylmethane ligand

Monobridged-dinuclear platinum(II) complexes, where the bridging ligand is 4,4′-dipyrazolylmethane, have been prepared for use as potential anticancer agents. The complexes synthesized include [{cis-PtCl₂(NH₃)}₂(μ-dpzm)], [{trans-PtCl₂(Me₂SO)}₂(μ-dpzm)] and [{cis-PtCl₂(Me₂SO)}₂(μ-dpzm)]. The characterization of these complexes is based on microanalytical, IR and ¹H NMR data.     

Molecular structure and reactions of azobenzene complexes with iron-lithium compounds

Reactions of azobenzene have been studied with heteronuclear iron-lithium compounds formed in the reaction of FeCl₃ with LiPh, one of the dinitrogen reducing systems of the Vol'pin type: Ph₄FeLi₄(OEt₂)₄ (1) and (H₂)FePh₄Li₄(OEt₂)₄ (2). The structures of the azobenzene complexes formed, (N₂Ph₂)₃FeLi₃(OEt₂)₃ (3) and (N₂Ph₂)₃FeLi₂(THF)₂ (4), as well as an ether-containing analog of the latter, (N₂Ph₂)₃FeLi₂(OEt₂)₂ (5), were determined by X-ray analysis of single crystals. Coordination of azobenzene at FeLi₃ and FeLi₂ clusters was shown to result in a sigificant elongation of the NN bond; partial cleavage of this bond on protolysis of the complexes resulted in the formation of hydrazobenzene and aniline. Magnetic susceptibility measurements and theoretic analysis of a similar model complex leads to the conclusion that the iron oxidation state in 3 may be considered between iron (I) and iron(III) (close to iron(I)), whereas in 4 and 5 it is close to iron(II).     

Mixed-ligand rhenium(V) oxo monomers with triphenylphosphine oxide and lopsided and symmetrical heterocyclic ligands. Putative intermediates in rhenium(V) oxo synthetic chemistry

Normally, ReOCl₃ (Me₂S) (OPPh₃) (1) serves as a useful source of ReO³⁺ or ReOCl_x^(3−x)+ for the synthesis of Re complexes by ligand exchange. Complexes of the type ReOCl₃(OPPh₃)(L) (L = 1,5,6-trimethylbenzimidazole (Me₃Bzm) (2); 3,5-lutidine (3,5-lut) (3); pyridine (py) (4)) were prepared from 1 and one equivalent of L. Formation of these mixed-ligand complexes is unsual because the normally labile OPPh₃ in 1 was retained. Addition of non-coordinating triethylamine (NEt₃) gave [HNEt₃][ReOCl₄(OPPh₃] (5). The anion in 5 has been populated to be an intermediate in some synthetic schemes. ReOCl₃(OPPh₃)(Me₃Bzm) (2) was characterized by X-ray crystallography. Crystallographic data are: C₂₈H₂₇Cl₃N₂O₂PRe, P2₁/c, A = 18.503(3), B = 9.780(2), C = 15.735(4) Å, β = 97.56(2)°, D_calc = 1.76 g cm⁻³, Z = 4, R = 0.041, R_w = 0.066 for 3193 independent reflections. In 2, the pseudo-octahedral Re has the OPPh₃ ligand trans to the oxo ligand, and one of the OPPh₃ phenyl rings lies nearly over the five-membered ring of Me₃Bzm. Reaction of ReOCl₃(OPPh₃)(Me₃Bzm) (2) with one equivalent of 3,5-lut or py resulted in the precipitation of mixed-ligand species best formulated as Re₂O₃Cl₄(Me₃Bzm)₂(3,5-lut)₂ (6) and Re₂O₃Cl₄(Me₃Bzm)₂(py)₂ (7), respectively.     

Methylene bridged binuclear bis(imino)pyridyl iron(II) complexes and their use as catalysts together with Al(i-Bu)3 for ethylene polymerization

Three novel methylene bridged binuclear iron(II) complexes: (R,R′ = i-C₃H₇ (6); R = i-C₃H₇, R′ = CH₃ (7); R,R′ = CH₃ (8))} have been synthesized. Activated by Al(i-Bu)₃, complex 6 shows very poor activity for the polymerization of ethylene at one bar ethylene pressure, whereas, 7 and 8 exhibit much higher activity than mononuclear iron catalysts {[ArNC(Me)C₅H₃N(Me)CNAr′]FeCl₂ (Ar,Ar′ = 2,6-C₆H₃-i-Pr (9); Ar = 2,6-C₆H₃-i-Pr₂, Ar′ = 2,6-C₆H₃–Me₂ (10); Ar,Ar′ = 2,6-C₆H₃–Me₂ (11))}. The molecular weight (M_w) of PE produced by 7 and 8 are in the range 13.2–46.0 × 10⁴ and much higher than those produced by mononuclear iron catalysts 9 and 10. GPC results demonstrate that 7 and 8 yield PE with a broad/bimodal molecular weight distribution (MWD). In contrast, 9 and 10 yield PE with relatively narrow and unimodal MWD (4.26 and 3.55). Elevating the temperature and Al/Fe molar ratio will narrow the MWD of PE.     

Syntheses and structural characterization of rhenium-bis-hydrazinopyrimidine core complexes with thiolate and Schiff base coligands

The reaction of perrhenate with 2-hydrazinopyrimidine in MeOH–HCl yields [ReCl₃(η¹-NNC₄H₃N₂H)(η²-HNNC₄H₃N₂)] (1). The analogous reaction with Na₂MoO₄ yields [MoCl₃(η¹-NNC₄H₃N₂H)(η²-HNNHC₄H₃N₂)] (1a). The reaction of 1 with pyrimidine-2-thiol and triethylamine produces [Re(η¹-C₄H₃N₂S)(η²-C₄H₃N₂S)(η¹-NNC₄H₃N₂)(η²-HNNC₄H₃N₂)] (2), while reaction of 1 with the Schiff base HSC₆H₄N=C(H)C₆H₄OH provides [Re(η³-SC₆H₄N=C(H)C₆H₄O)(η¹-NNC₄H₃N₂)(η²-HNNC₄H₃N₂)]·0.6CH₂Cl₂ (3·0.6CH₂Cl₂). The analogous hydrazinopyridine complex of the Schiff base, [Re(η³-SC₆H₄N=C(H)C₆H₄O)(η¹-NNC₅H₄N)(η²-HNNC₅H₄N)] (4), was also synthesized by reacting [ReCl₃(η¹-NNC₅H₄NH)(η²-HNNC₅H₄N)] with HSC₆H₄N=C(H)C₆H₄OH. The crystal structures of 1–4 have been determined.     

Steric control in the formation of Co2(CO)6-alkyne complexes from Group 14 tetraalkynes and their reactions with acid

A series of tetrakis(trimethylsilylethyne) derivatives of Group 14 metals (2–4) was prepared. Co₂(CO)₆ complexes 5–10 were synthesised by the reaction of 2–4 with Co₂(CO)₈. From the silyl and germyl based compounds 2 and 3, either one or two alkynes could be complexed with Co₂(CO)₆. In contrast, the tin derived compound 4 could accommodate up to four Co₂(CO)₆ complexes. The longest wavelength UV-Vis absorbances of the silicon and germanium-based complexes were consistent with multiple, non-conjugated Co₂(CO)₆ chromophores. The tetrakis Co₂(CO)₆ complex 10, however, absorbs at a much longer wavelength suggesting conjugation of Co₂(CO)₆ complexes through the tin. The reactivity towards protonolysis of the uncomplexed alkynes 2–4 is a consequence of the hyperconjugative stabilisation of the intermediate β-vinyl cation (the β-effect): Sn(CCSiMe₃)₃>SnOTf(CCSiMe₃)₂>SiMe₃>Ge(CCSiMe₃)₃. The reactivity of the Co₂(CO)₆ complexes, however, was quite different from the reactions of 2–4 and from analogous all-carbon systems. Treatment of 5–10 with strong acid led neither to protiodemetallation of the complexed or non-complexed alkynes but to decomplexation of the cobalt. Similarly, ligand metathesis reactions between 10 and Ph₂SiCl₂ were not observed. The normal reactivity of silylalkynes towards electrophiles, which was expected to be enhanced by the presence of the cobalt complex, was diminished by the particular steric environment of the molecules under examination (5–10). As a result, the favoured reaction under these conditions was decomplexation of the cobalt.     

Preparation of trimethylsilyl alkyne complexes of bis(pentamethylcyclopentadienyl)zirconium, (η-C5Me5)2Zr(RC≡CSiMe3), and their regioselective reactions with nitrous oxide

Benzene solutions of Cp^*₂ZrCl₂ (1) (Cp^* = η⁵-C₅Me₅) react with the alkynes Me₃SiC≡CPh, Me₃SiC≡C(c-C₅H₉) and Me₃SiC≡CCMe₃ in the presence of Na/Hg amalgam to afford high yields of the respective alkyne complexes Cp^*₂Zr(Me₃SiC≡CPh) (2), Cp^*₂Zr{Me₃SiC≡C(c-C₅H₉)} (3) and Cp^*₂Zr(Me₃SiC≡CCMe₃) (4) as crystalline compounds. Complex 2 crystallizes in the triclinic space group with a = 9.791(6), b = 10.466(6), c = 15.756(12) Å, = 86.09 (5), β = 72.09(5), γ = 72.06(4)° and Z = 2. The least-squares refinement converged to R(F) = 0.0604 and R(wF) = 0.0628 for the 3655 unique data with F_o > 4σ (F_o). Salient metrical parameters of the bound alkyne include the following: C(30)-C(31) = 1.340(9) Å; Zr-C(30) = 2.178(6) Å; Zr-C(31) = 2.219(5) Å; C(30)-C(31)-Si = 141.0(5)°; C(31)-C(30)-C(26) = 135.5(5)°. Nitrous oxide reacts with 2 or 3 to afford ((5) R = Ph; (6) R = c-C₅H₉) and 1 equiv. of N₂ via an intermediate, , which is unstable with respect to loss of dinitrogen to give the oxametallacyclobutene derivatives 5 and 6. The oxygen-atom insertion is regiospecific for the Zr-C bond that is attached to the carbyl (Ph or c-C₅H₉) substituent. Under similar conditions, complex 4, in which the alkyne is particularly labile, gives a myriad of products in its reaction with N₂O.     

Beta(3)-adrenoceptor agonists for the treatment of frequent urination and urinary incontinence: 2-[4-(2-[[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino]ethyl)phenoxy]-2-methylpropionic acid.

In a search for novel analogues of β₃-adrenoceptor (AR) agonists relaxing the bladder for treatment of urinary dysfunction, 2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)phenoxy]-2-methylpropionic acids (1a–e), into which a fibrate-like structure had been incorporated, were synthesised. Compound 1a was found to be a selective β₃-AR agonist in functional assays using the ferret detrusor (β₃-AR), rat uterus (β₂-AR), and rat atrium (β₁-AR); β₃: EC₅₀=7.8 nM, β₂: IC₅₀=7,300 nM, β₁: EC₂₀=23,000 nM. The introduction of a chlorine atom or methyl substituent at the ortho-position on the phenyl ring of 1a further improved β₃-AR selectivity. In an in vivo study, 1a lowered intrabladder pressure (ED₅₀=31 μg/kg) in rats, without increasing heart rate, in keeping with the in vitro results. Consequently, it is proposed that 1a and its analogues (1b–e), possess β₃-AR agonistic activity in the absence of undesirable β₁- or β₂-AR mediated actions, and may be useful for clinical treatment and pharmacological studies.     

On the reduction behaviour of 2-methoxyethyl and 2-methylthioethyl substituted zirconocene dichlorides: crystal structure of (η,σ-C5Me4CH2CH2S)2Zr

A reduction of previously reported 2-methoxyethyl and 2-methylthioethyl functionalized zirconocenedichlorides (η⁵-C₅Me₄CH₂CH₂EMe)(η⁵-C₅Me₅)(ZrCl₂ (E = O, S) and (η⁵-C₅Me₄CH₂CH₂EMe)(η⁵-C₅Me₄CH₂CH₂E′Me)ZrCl₂ (E = O, S; E′ = O, S) with Mg/Hg in THF leads unexpectedly to the products of O---Me and S---Me bond cleavage (η⁵,σ-C₅Me₄CH₂CH₂E)(η⁵-C₅Me₅)ZrMe (E = O, S), (η⁵,σ-C₅Me₄CH₂CH₂E)(η⁵-C₅Me₄CH₂CH₂E′Me)ZrMe (E = O, S; E′ = O), and (η⁵,σ-C₅Me₄CH₂CH₂S)₂Zr respectively. The crystal structure of (η⁵,σ-C₅Me₄CH₂CH₂S)₂Zr was established by X-ray analysis. At that same time the reduction of (ηsu5-C_{5Me4CH2CH2EMe)(η⁵-C5Me5)ZrCl2 (E> = O, S)} under 1 atm of CO gives either only the dicarbonyl derivative (η⁵-C₅Me₄CH₂CH₂EMe) (η⁵-C₆Me₅)Zr(CO)₂ (E = O) or a complex mixture of products (E = S).     

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.     

Catalytic reduction of acetylene in the presence of molybdenum and iron clusters, including FeMo cofactor of nitrogenase

Acetylene was reduced by zinc amalgam in the presence of three synthetic polynuclear complexes: {[Mg₂Mo₈O₂₂(OMe)₆(MeOH)₄]⁻²·[Mg(MeOH)₆]²⁺}6MeOH (I), (Bu₄N)₂[Fe₄S₄(SPh)₄] (II), [Me₄N][VFe₃S₄Cl₃(DMF)₃]·2DMF (III) and the iron-molybdenum cofactor of nitrogenase Azotobacter vinelandii MoFe₇(S²⁻)₉·homocitrate, FeMo-co (IV). Thiophenol was found to greatly facilitate the reaction in the presence of complexes I, II, IV. The reaction is catalytic and for I and IV proceeds at the amalgam surface. Thiophenol seems to increase the adsorption of the complexes, serving as an electron bridge to transfer electrons to the catalyst. In the case of II a homogeneous reduction of the substrate occurs presumably after the cluster reduction at the surface and with III the catalytic reduction proceeds only under the action of sodium amalgam; no thiophenol cocatalytic action is observed. Relevance to N₂ enzymatic reduction is discussed.     

Reactivity study of cyclopentadienyl osmium(II) bisphosphine azido complexes with activated alkynes and nitriles: Isolation of osmium triazolato and tetrazolato complexes by 1,3-dipolar addition

The cyclopentadienyl osmium(II) complexes [(η⁵-C₅H₅)Os(PPh₃)₂X] [X = Br (1), CH₃CN (2)] reacts with sodium azide (NaN₃) to yield the corresponding azido complex [(η⁵-C₅H₅)Os(PPh₃)₂N₃] (3). This undergoes [3+2] dipolar cycloaddition reaction with activated alkynes like dimethyl and diethyl acetylenedicarboxylate to yield triazolato complexes [(η⁵-C₅H₅)Os(PPh₃)₂{N₃C₂(CO₂R)₂}] [R = –CH₂CH₃ (4) and –CH₃ (5)]. The complex 3 also reacts with nitriles such as tetracyanoethylene (TCE), fumaronitrile and p-nitrobenzonitrile to yield complexes of the type [(η⁵-C₅H₅)Os(PPh₃)₂{N₄C₂(CN)C(CN)₂}] (6), [(η⁵-C₅H₅)Os(PPh₃)₂{N₃C₂HCN}] (7) and [(η⁵-C₅H₅)Os(PPh₃)₂{N₄C(C₆H₄–p-NO₂)}] (8). These complexes were fully characterized on the basis of microanalyses, FT-IR and NMR spectroscopic data. The molecular structure of the representative complex [(η⁵-C₅H₅)Os(PPh₃)₂{N₃C₂(CO₂CH₂CH₃)₂}] (4) was determined by single crystal X-ray analysis.     

Heterobimetallic chloro bridgedcomplexes of (η:η−C10H16)-ruthenium(IV) with palladium(II), platinum(II), rhodium(III), iridium(III), copper(I) and rhodium(I)

Metathesis of [(η³:η³−C₁₀H₁₆)Ru(Cl) (μ−Cl)]₂ (1) with [R₃P) (Cl)M(μ-Cl)]₂ (M = Pd, Pt), [Me₂NCH₂C₆H₄Pd(μ-Cl)]₂ and [(OC)₂Rh(μ-Cl)]₂ affords the heterobimetallic chloro bridged complexes (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂M(PR₃)(Cl) (M = Pd, Pt), (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂PdC₆H₄CH₂NMe₂ and (η³:η³-C₁₀H₁₆) (Cl)Ru(μ-Cl)₂Rh(CO)₂, respectively. Complex 1 reacts with [Cp^*M(Cl) (μ-Cl)]₂ (M = Rh, Ir), [p-cymene Ru(Cl) (μ-Cl]₂ and [(Cy₃P)Cu(μ-Cl)]₂ to give an equilibrium of the heterobimetallic complexes and of educts. The structures of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂Pd(PR₃) (Cl) (R = Et, Bu) and of one diastereoisomer of (η³:η³-C₁₀H₁₆)Ru(μ-Cl)₂IrCp^*(Cl) were determined by X-ray diffraction.     

Interactions between thiamine and large anions. Crystal structures of (H-thiamine)[Pt(SCN)4] · 3H2O and (H-thiamine)[Pt(SCN)6] · H2O

The reaction of thiamine with K₂Pt^IICl₄ and with Pt^IVCl₄ in the presence of excess NaSCN in aqueous solution gave thiamine salts, (H-thiamine)[Pt(SCN)₄] · 3H₂O (1) and (H-thiamine)[Pt(SCN)₆] · H₂O (2), respectively, structures of which have been determined by X-ray diffraction. The thiamine molecule adopts the usual F conformation in each salt. In 1, [Pt(SCN)₄]²⁻ ions act as large planar spacers in the crystal lattice and interact scarcely with thiamine, except for a hydrogen bonding with the terminal hydroxy O(5γ). Instead, water molecules form two types of host–guest-like interactions with the pyrimidine and the thiazolium moieties of a thiamine molecule, one being a C(2)–Hwaterpyrimidine bridge and the other being an N(4′)–Hwaterthiazolium bridge. In 2, despite the much larger ion size, octahedral [Pt(SCN)₆]²⁻ ions form a C(2)–Hanionpyrimidine bridge and an N(4′)–Hanionthiazolium bridge. An additional hydrogen bonding between the anion and the terminal O(5γ) of thiamine creates a hydrogen-bonded macrocyclic ring {thiaminium–[Pt(SCN)₆]²⁻}₂, a supramolecule.     

The synthesis and structures of tantalum complexes that contain a triamido or a diamidoamine ligand

Addition of (Me₃SiNHCH₂CH₂)₂NH (H₃[N₃(TMS)]) or (Me₃SiNH-o-C₆H₄)₂NH (H₃[ArN₃(TMS)]) to a solution of TaMe₅ yields [N₃(TMS)]TaMe₂ or [ArN₃(TMS)]TaMe₂, respectively. An X-ray study of [ArN₃(TMS)]TaMe₂ showed it to have an approximate trigonal bipyramidal structure in which the two methyl groups are in equatorial positions and the triamido ligand is approximately planar. Addition of (C₆F₅NHCH₂CH₂)₂NH (H₃[N₃(C₆F₅)]) to TaMe₅ yields first [(C₆F₅NCH₂CH₂)₂NH]TaMe₃, which then decomposes to [(C₆F₅NCH₂CH₂)₂N]TaMe₂. An X-ray study of [(C₆F₅NCH₂CH₂)₂N]TaMe₂ shows it to be approximately a trigonal bipyramid, but the C₆F₅ rings are oriented so that they lie approximately in the TaN₃ plane and two ortho fluorines interact weakly with the metal. Trimethylaluminum attacks the central nitrogen atom in [N₃(TMS)]TaMe₂ to give [(Me₃SiNCH₂CH₂)₂NAlMe₃]TaMe₂, an X-ray study of which shows it to be a trigonal bipyramidal species similar to the first two structures, except that the C-Ta-C bond angle is approximately 30° smaller (106.6(12)°). Addition of B(C₆F₅)₃ to [(C₆F₅NCH₂CH₂)₂NH]TaMe₃ yields {[(C₆F₅NCH₂CH₂)₂NH]TaMe₂}⁺ {B(C₆F₅)₃Me}⁻, the structure of which most closely resembles that of [(Me₃SiNCH₂CH₂)₂NAlMe₃]TaMe₂ in that the C-Ta-C angle is 102.0(6)°. The C₆F₅ rings in {[(C₆F₅NCH₂CH₂)₂NH]TaMe₂}⁺ are turned roughly perpendicular to the TaN₃ plane, i.e. ortho fluorines do not interact with the metal in this molecule.     

The influence of the catalyst preparation protocol and silane structure on the rate and enantioselectivity of ansa-titanocene catalysed hydrosilation of prochiral ketones

The hydrosilation of prochiral ketones using catalysts prepared by alkylation of [1,2-bis(tetrahydroindenyl)ethane]titanium^IV(1,1′-binaphth-2,2′-diolate) with MeLi and n-BuLi, and (EtO)₃SiH, Me(EtO)₂SiH, [MeSi(H)O]₄, Me₃SiO[MeSi(H)O]_nSiMe₃ and MeSiH₃ as the hydrosilane is described. The rates obtained with the MeLi based catalyst are one to two orders of magnitude faster than previously observed with MeLi based catalysts in the presence of MePhSiH₂ and Ph₂SiH₂ and about the same as those observed with n-BuLi based catalysts. Me(EtO)₂SiH, [MeSi(H)O]₄ and Me₃SiO[MeSi(H)O]_nSiMe₃ all undergo rapid redistribution in the presence of the catalyst to give MeSiH₃, the actual hydrosilating agent in all three cases. Likewise, (EtO)₃SiH redistributes to SiH₄. The ee's for the hydrosilation product of acetophenone are consistently much higher (99%) for the n-BuLi based catalyst than for the MeLi based catalyst (40–50%). The hydride complex [(BTHIE)TiH]₂ gives essentially the same enantioselectivity as the MeLi based catalyst. The ee's for a test set of dialkylketones are relatively insensitive to either the catalyst or the hydrosilane. Some possible mechansims that are consistent with the experimental results are discussed.     

π-Arene complexes.: Part 12. Synthesis of chromiumtricarbonyl complexes of quinoline and N-methylindoles and selected metallation reactions

The lithiation of indole, using a slight excess of n-butyl lithium in THF, followed by methylation and reaction with [Cr(CO)₆] in refluxing dibutyl ether, resulted in the formation of [Cr(η⁶-N-methylindole)(CO)₃] (1a) and [Cr(η⁶-N-methyl-2-methylindole)(CO)₃] (1b). In contrast, lithiation of quinoline in THF, silylation and the subsequent reaction with [Cr(CO)₆] under similar reaction conditions, afforded [Cr(η⁶-N-trimethylsilyl-2-butyl-1,2-dihydroquinoline)(CO)₃] (2) and [Cr(η⁶-{2-butyl-1,2,3,4-tetrahydroquinoline})(CO)₃] (3). The formation of [Cr(η⁶-2,2′-bis{N-methylindolyl})(CO)₃] (4) implied lithiation at the 2-position of 1a. However, metallation at the 7-position was also indicated during the same reaction. In the presence of [Mn(CO)₅Br], product 4 and the transmetallation product [Cr(η⁶-{7-(N-methylindolyl)Mn(CO)₅})(CO)₃] (5) were isolated. Reaction with titanocene dichloride gave [Cr(η⁶-{2-(N-methylindolyl)TiCp₂Cl})(CO)₃] (6), which slowly converted into [TiCp₂{Cr(η⁶-2-(N-methylindolyl)(CO)₃}₂] (7).     

Synthesis, crystal and molecular structure, spectroscopic and electrochemical studies of trichloro-oxo(4,6-dimethylpyrimidine-2(1H)-thione)(triphenylphosphine oxide)rhenium(V) complex

Reaction of 4,6-dimethylpyrimidine-2(1H)-thione (Me₂pymSH) with mer-[ReOCl₃(Me₂S)(OPPh₃)] synthon in 1:1 molar ratio in refluxing acetone, results in the replacement of the Me₂S ligand to form the mer-[ReOCl₃(Me₂pymSH)(OPPh₃)] species. X-ray diffraction shows that the structure of the title compound consists of monomeric units with a distorted octahedral coordination around the rhenium(V) centre which includes the axial ReO and Re---OPPh₃ bonds, and in which three Cl⁻ ions and a S-monodentate neutral Me₂pymSH ligand act as equatorial ligands. The compound was also characterised using electrochemical measurements and UV–Vis–NIR and IR spectroscopy.     

Synthesis, immobilization and catalytic activity of some silylated cyclopentadienyl rhodium(I) complexes

The mixture of isomers of silylated cyclopentadiene derivative C₅H₅CH₂CH₂Si(OMe)₃ (1) has been used for the syntheses of the mononuclear Rh(I) complexes [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(CO)₂ (3). [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(COD) (4) and [η⁵-C₅H₄(CH₂)₂Si(OMe)₃]Rh(CO)(PPh₃) (5). Upon entrapment of 3–5 in silica sol-gel matrices, air stable, leach-proof and recyclable catalysts 6–8 resulted. Their catalytic activities in some hydrogenation processes were compared with those of the non-immobilized complexes 3–5, as well as with those of homogeneous and heterogenized non-silylated analogs, 9–14.