Site selectivity in the reaction of tetracyanoethene with tetracyclo [5.3.2.02,10. 03,6] dodeca-4,8,11-triene : A borderline case of homo-diels-alder reaction

Tetracyanoethene reacted with tetracyclo [5.3.2.0^2,10.0^3.6] dodeca-4,8,11-triene (1) according to two competitive reaction modes, both involving the sole homotropilidene moiety, to give a mixture of adducts 4 and 6. Structure 6 was established by X-ray analysis. Compounds 4 and 6 result from a thermally allowed homocycloaddition and a forbidden[Π²₅ + σ²₅+ Π²_s+Π²_s] reaction, respectively. The reaction rate and the 6:4 ratio increased on passing from benzene to nitromethane as reaction medium. The homo-Dies-Alder reaction leading to 4 was shown to be reversible. In methanol compound 4 gave rise to a zwitterion which was trapped by solvent. Reaction mechanisms are discussed. A zwitterion is proposed as intermediate on the pathway to 6 whereas experimental findings do not permit a definitive choice between an ionic two step and a concerted cycloaddition in the formation of 4. The neutral and base catalyzed addition of methanol to the tetracyanoethylene moiety of 4, 6 and related derivatives was also investigated.     

Investigation into the reactivity of oxoniobocene complexes [Cp*2Nb(O)R] (Cp*=η5-C5Me5; R=H,OH, OMe) towards heterocumulenes: formation of carbamato and thiocarbamato complexes and catalytic cyclization of PhNCO

The reaction of [Cp*₂NbCl₂] (Cp*=η⁵-C₅Me₅) with KOH or Ba(OH)₂·8H₂O in THF was investigated under slightly modified conditions. In addition to the known complex [Cp*₂Nb(O)H] (1), the new compound [Cp*₂Nb(O)OH] (2) was formed. The reaction of 2 with PhNCS gave yellow [Cp*₂Nb(O){SC(O)NHPh}] (3), while PhNCO formed yellow [Cp*₂Nb(O){OC(O)NHPh}] (4). Complexes 3 and 4 were analytically and spectroscopically characterized. X-ray diffraction analyses of both compounds show that they contain either η¹-S-thiocarbamato (3) or η¹-O-carbamato ligand (4) along with a terminal NbO group. The reaction of 1 with one equivalent of PhNCO mainly gave orange [Cp*₂NbH{OC(O)NPh}] (5) along with some 4. The molecular structure of 5 contains a niobocene unit comprising η²-N,O-carbamato chelate, which formally is a [2+2] cycloaddition product of the NbO group and the heterocumulene. A hydride ligand completes the coordination sphere around Nb. Reaction of 1 with excess PhNCO gave a mixture of heterocycles (PhNCO)₂ (6) and (PhNCO)₃ (7) in the approximate ratio 3:2. By contrast, the reaction of [Cp*₂Nb(O)OMe] with PhNCO in molar ratios from 1:3 to 1:100 gave nearly pure triphenylisocyanurate 7.     

Preparation and reactivity of CpRu(OMe)PCy3 and CpRuHL2 (L = PCyPh2, PCy2H) from [CpRu(OMe)]2 and bulky phosphines

The reaction of [CpRu(OMe)]₂ (1) with PCy₃ yields the 16-electron alkoxo derivative, CpRu(OMe)(PCy₃) (2). 2 reacts with H₂ and HBF₄ to give the known CpRuH₃PCy₃ (3) and [CpRu(C₆H₉PCy₂)]BF₄ (4). The reaction of 1 with one or two equivalents of L yields CpRuHL₂ (L = PCyPh₂ (5), PCy₂H (6)) through a β-elimination process. Upon protonation, 5 and 6 are converted into [CpRuH₂L₂]BF₄ (L = PCyPh₂ (7), PCy₂H (8)).     

Isatin N-protected ketimines with nitromethane catalyzed by chiral binol linked monomeric macrocyclic Cu(II)–salen complex

Chiral Cu-1B generated in situ was used as an efficient catalyst for the synthesis of β-nitroamines in high yield (88%) with excellent enantioselectivity (ee up to 99%) at RT in absence of co-catalyst via asymmetric aza-Henry reaction of various isatin derived N-Boc ketimines with nitromethane. This catalytic system did not work well with other nitroalkanes under the above optimized reaction conditions. To examine this catalytic behaviour, quantum chemical DFT calculations were performed with the nucleophiles (CH₂NO₂^? and CH₃CHNO₂^?) for the conversion of 1a to 2a using macrocyclic Cu-1B complex. The DFT calculated results have shown that the reaction with CH₂NO₂^? is more favourable than the corresponding CH₃CHNO₂^?. The calculated activation barriers suggest that the reaction with CH₂NO₂^? is ～8.0?kcal/mol energetically favoured than CH₃CHNO₂^?. This catalytic protocol was further used to obtain chiral β-diamines (a building block for pharmaceuticals) at gram scale. In order to elucidate the reaction mechanism of asymmetric aza Henry reaction kinetic experiments were performed with different concentrations of the catalyst Cu-1B, nitromethane and 1g as the representative substrate. The reaction of isatin N-Boc ketimine was first order with respect to the concentration of the catalyst and the nitromethane but did not depend on the initial concentration of the substrate. A possible mechanism for the aza Henry reaction was proposed.     

Übergangsmetall-methylen-komplexe: LVI. Organoruthenium-komplexe mit offenkettigen und carbocyclischen alkyliden-brücken: Synthese,konstitution, isomerie,protonierung und thermolytischer abbau

The eighteen new μ-alkylidene ruthenium complexes 5a–r and 5t are very easily and cleanly obtained along the diazoalkane or the hydrazone routes that involve treatment of the dinuclear, metal-metal doubly bonded precursor compound [(η⁵-C₅H₅)Ru(μ-NO)]₂ (3) either with the diazoalkanes oxidizing agent (e.g., MnO₂), with the respective hydrazones. Similarly, sulfur dioxide adds cleanly to the RuRu double bond of 3, thus giving the complex (μ-SO₂)[(η⁵-C₅H₅)Ru(NO)]₂ (5s). Regardless of the nature of the carbene bridge ligands, the dimetallacyclopropanes exhibit, in contrast to their iron analogues, exclusively terminal nitrosyl ligands. cis/trans-Isomerism with predominating amounts of the trans-isomers is observed for the derivatives that display unsymmetrically substituted carbene bridges.Treatment of the μ-methylene- and μ-ethylidene complexes (μ-CH₂)[(η⁵-C₅H₅)Ru(NO)]₂ (5a) and (μ-CHCH₃)[(η⁵-C tetrafluoroboric acid or trifluoromethanesulfonic acid in diethyl ether yields, at ambient temperature, quantitatively the ionic complexes 6a,b and 7a,b, respectively, which were shown by ¹H NMR spectroscopy to contain metal-metal bridging hydrogen functionalities. The reaction of hydrogen bromide with 5a under the same conditions gives the neutral bromo(methyl) complex 6d. This latter compound results from the isolable ionic intermediate of composition [(μ-CH₂)(μ-H){(η⁵C₅H₅)Ru(NO)}₂]⁺Br^? (6c), which reaction stems from the nucleophilicity of the halide ion present in 6c.     

η1-Alkynylplatinum(II) complexes with cycloocta-1,5-diene and tri(1-cyclohepta-2,4,6-trienyl)phosphane ligands

η¹-Alkynylplatinum(II) complexes of the type (cod)Pt(CCR)₂ (1, cod=η⁴-cycloocta-1,5-diene; R=Me (a), ^tBu (b), Ph (c), Fc (d), SiMe₃ (e)) were prepared in good yields from the reaction of (cod)PtCl₂ with either HCCR and NaOEt (R=^tBu, Ph, Fc) or di(1-alkynyl)dimethyltin, Me₂Sn(CCR)₂ (R=Me, SiMe₃). The analogous reaction of [P]PtCl₂ ([P]=tri(1-cyclohepta-2,4,6-trienyl)phosphane, {P(C₇H₇)₂(η²-C₇H₇)}) with Me₂Sn(CCR)₂ (R=Me, ^tBu, Ph, Fc, SiMe₃), afforded selectively the complexes [P]PtCl(CCR) 2a–e in high yield, in which the 1-alkynyl group is in cis position with respect to the phosphorus atom, and one of the C₇H₇ rings is η²-coordinated to platinum through the central CC bond. Complexes 3a–e of the type [P]Pt(CCR)₂ could not be prepared by the reaction of 2 with an excess of the 1-alkynyltin reagents. However, the reaction of 1 with the phosphane P(C₇H₇)₃ gave compounds 3a–e in quantitative yield by substitution of the cod ligand. The molecular structures of 2b and 3d were determined by X-ray structure analysis, and complexes 1–3 were characterised in solution by multinuclear magnetic resonance spectroscopy (¹H-, ¹³C-, ²⁹Si-, ³¹P-, ¹⁹⁵Pt-NMR). The structures of 2 and 3 in solution were found to be fluxional with respect to coordination of the C₇H₇ rings to platinum.     

Photochemical and thermal rearrangements of a benzoylnaphthobarrelene-like system

8-Benzoyl-9-deuterionaphtho[de-2.3.4]bicyclo[3.2.2]nona-2,6,8-triene (12a)rearranges in a photochemical di-π-methane-type process to the l-benzoylatho[de-[2.3.4]tricyclo[4.3.0.0^2,9]nona-3,7-dienes 14a-c.The dihydro derivate 13a and the hydroxypheoylmethyl analogs 21a and 22a undergo similarly regioselective rearrangements to 15a+c, 23a-c, and 24a, respectively. At 298 K the primary photoreaction directly occus from the S₁(n,π^*) and T₂(n,π^*) states, and it proceeds from T₁(π,π^*) and from S₂(π,π^*) either directly or via T₂. At lower temperature on direct irradiation. S₁→T intersystem crossing and triplet reaction compete with reaction from the singlet. The rearrangement 12a→14a-c proceeds along three reaction paths evolving from the two primary photochemical processes of naphthyl-vinyl and vinyl-vinyl bonding in β-position to the CO (12→25+29). Two ground-state triplet diradical intermediates such as 25 and 27 have been shown to intervene consecutively—for the first time in di-π-methane photochemistry. Each has been characterized by ESR and IR, and the second one additionally by fluorescence and fluorescence excitation, and by laser flash photolysis.The failure of products 14a-c to interconvert photochemically is ascribed to efficient energy dissipation through thermally reversible pbotocleavage of the 3-membered ring.Compounds 12 and 14 thermally interconvert in the dark which constitutes the first example of a ground-state counterpart of a di-π-methane photorearrangement. The thermal reaction includes a path with highly regioselective (and possibly concerted) product formation competing with a stepwise process causing positional scrambling. The sequence 12→14 (photochemically; Φ = 1.0 at 366 nm and 298 K) and an electrophile-catalyzed reversal 14→12 in the dark is a model of a chemical light energy storage cycle which can be conducted without loss of reactants.     

Synthesis of RuHCl(CO)(Hdmpz)(L)2 (L=PPh3, AsPh3, and Hdmpz=3,5-dimethylpyrazole) and crystal structure of RuHCl(CO)(Hdmpz)(AsPh3)2

Treatment of RuHCl(CO)(L)₃ with a slight excess amount of K[HB(3,5-Me₂pz)₃] in boiling MeOH solution yielded unusual 3,5-dimethylpyrzaole (Hdmpz) complexes, RuHCl(CO)(Hdmpz)(L)₂ (L=PPh₃, 1 or AsPh₃, 2). Unexpectedly the dissociation of the bonds between the boron atom and the nitrogen atoms of the potentially tridentate [HB(3,5-Me₂pz)₃]⁻ ligand during the coordination of the ligand to the Ru^II metal has been observed. In a separate preparation, the RuHCl(CO)(Hdmpz)(PPh₃)₂ complex has also been synthesized from the reaction between RuHCl(CO)(PPh₃)₃ and the monodentate Hdmpz ligand. Complexes 1 and 2 have been characterized by elemental analysis, IR and ¹H NMR spectroscopies. Compound 1 has also been prepared by the reaction between RuHCl(CO)(PPh₃)₃ and K[H₂B(3,5-Me₂pz)₂] in boiling toluene solution. The crystal structure of 2 has been studied by X-ray crystallography. The geometrical structure around Ru^II of 2 is a distorted octahedral structure. The crystal structure of 2 consists of a discrete monomeric compound. It is interesting to find that the sterically-demanding [HB(3,5-Me₂pz)₃]⁻ or [H₂B(3,5-Me₂pz)₂]⁻ ligands break up during the reaction with the Ru^II complexes to form the neutral 3,5-dimethylpyrazole complexes. In contrast to these observations, [H₂Bpz₂]⁻ and [H₂B(4-Brpz)₂]⁻ ligands form very stable Ru^II complexes.     

Reactions of alkali metal and yttrium alkyls with a sterically demanding bis(aryloxysilyl)methane: Formation of aryloxide complexes by Si-O bond cleavage

Reaction of bis(bromodimethylsilyl)methane (BrSiMe₂)₂CH₂ (1) with two equivalents of 2,6-diisopropylphenol (Ar′OH) in the presence of the auxiliary base NEt₃ affords the bis(aryloxysilyl)methane (Ar′OSiMe₂)₂CH₂ (2) as a colourless oil following work-up. The reaction of 2 with [Li(Buⁿ)] in the presence of [K(OBu^t)] promoted Si-O bond cleavage and the sole isolable product from this reaction was found to be the colourless, crystalline heterobimetallic complex [{Li(OAr′)}₂{K(OAr′)}₂(THF)₄] (3). The in situ reaction of 2 with one equivalent of [Li(Buⁿ)] in the presence of one equivalent of [K(OBu^t)] and subsequent addition to one equivalent of [Y(I)₃(THF)_3.5] afforded colourless, crystalline [Y(OAr′)(I)₂(THF)₃] (4) as the only isolable product. No reaction was observed between [Y(Bn)₃(THF)₃] (Bn = CH₂C₆H₅) and one equivalent of 2 in toluene at room temperature; heating solutions led to decomposition and recovery of 2. In THF, the reaction between 2 and one equivalent of [Y(Bn)₃(THF)₃] resulted in Si-O bond cleavage with concomitant Si-C bond formation to give (BnSiMe₂)₂CH₂ (5) as a colourless oil and the colourless, crystalline compounds [Y(OAr′)₂(Bn)(THF)] (7), and [Y(OAr′)₃(THF)₂] (8) which were separated by fractional crystallisation. In an attempt to prepare 7 by a rational route, [Y(OAr′)₂(I)(THF)₂] (6) was prepared from the reaction of [Y(I)₃(THF)_3.5] with two equivalents of [K(OAr′)]. However, although 6 could be prepared by a rational salt elimination route, attempts to convert it to 7 resulted instead in 8 being recovered as the only isolable product. This is proposed to be the result of Schlenk-type equilibria, which is supported by the observation that dissolution of pure 6 in benzene results in the additional presence of 8 in the ¹H NMR spectrum over 12 h. Compound 7 was prepared rationally from the reaction between [Y(Bn)₃(THF)₃] and two equivalents of HOAr′. However, although crystalline 7 could be isolated in sufficient quantities for analysis, NMR spectra were consistent with the formation of 8 in solution from Schlenk-type equilibria. Compounds 2–8 have been variously characterised by X-ray diffraction, NMR and FTIR spectroscopy, and CHN microanalyses.     

Carbonylmetall-verbindungen des bis(di-t-butylphosphino)schwefeldiimids: Bildung von zweikernkomplexen S{NPtBu2[MLn]}2 (MLn = Cr(CO)5), Mo(CO)5, W(CO)5, Fe(CO)4) und chelatkomplexen S(NPtBu2)2M(CO)4 (M = Cr,Mo, W). Kristall- und molekülstruktur von S(NPtBu2)2Cr(CO)4

The reaction of bis(di-t-butylphosphino) sulphur diimide, S(NP^tBu₂)₂ (1) ¹, with coordinatively unsaturated 16-electron complex fragments [M(CO)₅] leads to both binuclear 1 : 2 adducts S{NP^tBu₂[M(CO)₅]}₂ (M = Cr (2B), Mo (3B) and W (4B)) and mononuclear chelate complexes S(NP^tBu₂)₂M(CO)₄ (M = Cr (2C), Mo (3C) and W (4C)). A binuclear compound S{NP^tBu₂[Fe(CO)₄]}₂ (5B) is obtained from the reaction of 1 with Fe₂(CO)₉. The new complexes which all contain the intact sulphyr diimide 1 are characterized on the basis of their infrared, ¹H, ¹³C and ³¹P NMR spectra. An X-ray structure analysis of S(NP^tBu₂)₂Cr(CO)₄ (2C) reveals a distorted octahedral coordination sphere around the central chromium atom and an almost planar but twisted six-membered Cr(PN)₂S heterocycle with angles of 91.98(2)° at chromium (P(1)CrP(2)) and 124.6(1)° at sulphur (N(1)SN(2)).     

Calculated energy barriers for the identity SN2 reaction H2O + CH3OH2+ → +H2OCH3 + OH2 in the gas phase,in water clusters,and in aqueous solution

The bimolecular nucleophilic substitution reaction H₂O + CH₃OH₂⁺ → ⁺H₂OCH₃ + OH₂ has been studied using various quantum chemical methods. Accurate barriers for the reaction in the gas phase are presented and discussed. The effect of microsolvation by water molecules in small clusters has been investigated. Extrapolation of the barrier obtained in the small clusters, using a linear relationship between the activation energy and the proton affinity of water clusters, gives a barrier for the reaction in aqueous solution which is in good agreement with that obtained in separate model calculations (polarized continuum model of a super molecule with the first solvation shell included).     

Anionic and neutral bis(diimine)lanthanide complexes

Oxidation of ytterbium(II) complex (dpp-BIAN)Yb(DME)₂ (1) with dpp-BIAN affords an ionic compound [(dpp-BIAN)₂Yb]^?[(dpp-BIAN)Yb(DME)₂]⁺ (2) (dpp-BIAN = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene), in which the oxidation states of the metals in anionic and cationic counterparts are different. Structurally related lanthanum(III) complex [(dpp-BIAN)₂La]^?[(dpp-BIAN)La(DME)₂]⁺ (3) has been prepared reacting excess of metallic lanthanum with dpp-BIAN. Compound [(dpp-BIAN)₂La]^?[K(Et₂O)₄]⁺ (4) has been isolated from the reaction of LaI₃ with three molar equivalents of potassium and one molar equivalent of dpp-BIAN in diethyl ether. The reaction of SmI₂ with dpp-BIAN and potassium affords complex [(dpp-BIAN)₂Sm]^?[K(C₆H₆)]⁺ (5). Treatment of compound 5 with 0.5 molar equivalent of iodine produces neutral complex (dpp-BIAN)₂Sm (6). Molecular structures of complexes 2–6 have been determined by X-ray crystallography.     

Synthesis and structural characterization of the first trialkylguanidinate and hexahydropyramidopyramidinate complexes of tin

The first guanidinate complexes of tin have been prepared using N,N′,N′′-trialkylguanidinates ([(RN)₂C(NRH)]⁻; R=cyclohexyl; isopropyl) and 1,3,4,6,7,8-hexahydro-2H-pyramido[1,2-a]pyramidinate (hpp⁻) as ligands. The direct reaction between triisopropylguanidine and SnCl₄ provided the complex {[ⁱPrN]₂C[NHⁱPr]}SnCl₃ (1) along with concomitant formation of the guanidinium salt {C[NHⁱPr]₃}⁺[SnCl₅(THF)]⁻ (2). The Sn(II) guanidinate complexes {(C₆H₁₁N)₂C[NH(C₆H₁₁)]}₂Sn (3) and {CN[N(CH₂)₃]₂}₂Sn (4) were prepared through metathesis reactions between 0.5 equiv. SnCl₂ and (C₆H₁₁N)₂C[NH(C₆H₁₁)]Li or hppLi, respectively. Complex 4 is the first reported mononuclear complex of this ligand. In contrast, the reaction of hppLi with 1 equiv. SnCl₂ afforded a bridging dinuclear species, {CN[N(CH₂)₃]₂SnCl}₂ (5). A second mononuclear complex of the hpp⁻ ligand, {CN[N(CH₂)₃]₂}₂SnCl₂ (6), was the product obtained from the reaction of 2 equiv. of hppLi with SnCl₄. The full structural details of compounds 1 and 3–6 are reported. In the case of compounds 1 and 3 these results revealed a distinctly unsymmetrical bonding mode for the bidentate guanidinate ligand and suggest variable degrees of π delocalization with the ligand. The geometries of the Sn centers in 3, 4 are derived from distorted trigonal bipyramidal coordination with a stereochemically active lone pair occupying one coordination site. In contrast, complex 5 displayed a geometry derived from a tetrahedral ligand array with one vertex occupied by a lone pair of electrons. Complex 6 is six coordinate and possesses 2 equiv. chelating bidentate hpp⁻ ligands and two cis-chloro groups.     

Trihydridoruthenium(IV) complexes: preparation and photo-induced H/D exchange reaction

The trihydrides (η⁵-C₅Me₅RuH₃(PR₃ = PMe₃, FEt₃, Pipr₃, PCy₃, PPh₂Me, and PPh₃) (2) are formed in the reaction of paramagnetic (η⁵C₅Me₅)RuCl₂(PR₃) (1) with NaBH₄ in ethanol. The reaction of 1 with NaBH₄, in THF yields intermediary tetrahydroborate complexes (η⁵-C₅Me₅)Ru(PR₃)(BH₄) (3), which are converted to the trihydrides 2 by treatment with ethanol. Irradiation of 2c and 2f in C₆D₆ solution with UV light causes H/D exchange reaction among the solvent, hydride ligands, and the coordinated phosphine.     

Substituirte η4-Cyclooctadien-1,5-η5-cyclopentadienyl-Cobalt-Komplexe durch Comproportionierung von Cobaltocenen und Alken-cobaltaten(1—)

Substituted η-cyclooctadiene-1,5-η⁵-cyclopentadienyl-cobaltcomplexes cp^RCo(COD), (2a-e), are prepared from the corresponding cobaltocenes, cp^R₂Co, (1a-e), by reaction with K(THF)_1.5[Co(COD)].     

Mechanistic studies on the oxidation of pyruvic acid by an oxo-bridged diiron(III,III) complex in aqueous acidic media

In aqueous solution [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1, phen = 1,10-phenanthroline) equilibrates with its conjugate bases [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) and [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3). In the presence of excess phen and in the pH range 2.5–5.5, the dimer quantitatively oxidizes pyruvic acid to acetic acid and carbon dioxide, the end iron species being ferroin, [Fe(phen)₃]²⁺. The observed reaction rate shows a bell-shaped curve as pH increases, but is independent of added phen. Kinetic analysis shows that (3) is non-reactive and (1) has much higher reactivity than (2) in oxidizing pyruvic acid. The basicity of the bridging oxygen increases with deprotonation of the aqua ligands. The reaction rate decreases significantly in media enriched with D₂O in comparison to that in H₂O, with a greater retardation at higher pH, suggesting the occurrence of proton coupled electron transfer (PCET; 1e, 1H⁺), which possibly drags the energetically unfavorable reaction to completion in presence of excess phen.     

Structural diversity and versatility for organoaluminum complexes supported by mono- and di-anionic aminophenolate bidentate ligands

The present contribution describes the synthesis and structural characterization of structurally diverse organoaluminum species supported by variously substituted aminophenolate-type ligands: these Al complexes are all derived from the reaction of AlMe₃ with aminophenols 2-CH₂NH(R)-C₆H₃OH (1a, R = mesityl (Mes); 1b, R = 2,6-di-isopropylphenyl (Diip)) and 2-CH₂NH(R)-4,6-^tBu₂-C₆H₂OH (1c, R = Mes; 1d, R = Diip). The low temperature reaction of AlMe₃ with 1a–b readily affords the corresponding Al dimeric species [μ-η¹,η¹-N,O-{2-CH₂NH(R)-C₆H₄O}]₂Al₂Me₄ (2a–b), consisting of twelve-membered ring aluminacycles with two μ-η¹,η¹-N,O-aminophenolate units, as determined by X-ray crystallographic studies. Heating a toluene solution of 2a (80 °C, 3 h) affords the quantitative and direct formation of the dinuclear aluminium complex Al[η²-N; μ,η²-O-{2-CH₂N(Mes)-C₆H₄O}](AlMe₂) (4a) while species 2b, under the aforementioned conditions, affords the formation of the Al dimeric species [η²-N,O-{2-CH₂N(Dipp)-C₆H₄O}AlMe]₂ (3b), as deduced from X-ray crystallography for both 3b and 4a. In contrast, the reaction of bulky aminophenol pro-ligands 1c–d with AlMe₃ afford the corresponding monomeric Al aminophenolate chelate complexes η²-N,O-{2-CH₂NH(R)-4,6-^tBu₂-C₆H₂O}AlMe₂ (5c–d; R = Mes, Diip; Scheme 3) as confirmed by X-ray crystallographic analysis in the case of 5d. Subsequent heating of species 5c–d yields, via a methane elimination route, the corresponding Al-THF amido species η²-N,O-{2-CH₂N(R)-4,6-^tBu₂-C₆H₂O}Al(Me)(THF) (6c–d; R = Mes, Diip). Compounds 6c–6d, which are of the type {X₂}Al(R)(L) (L labile), may well be useful as novel well-defined Lewis acid species of potential use for various chemical transformations. Overall, the sterics of the aminophenol backbone and, to a lesser extent, the reaction conditions that are used for a given ligand/AlMe₃ set essentially govern the rather diverse “structural” outcome in these reactions, with a preference toward the formation of mononuclear Al species (i.e. species 5c–d and 6c–d) as the steric demand of the chelating N,O-ligand increases.     

Water-soluble arene ruthenium complexes containing pyridinethiolato ligands: Synthesis,molecular structure,redox properties and anticancer activity of the cations [(η6-arene)Ru(p-SC5H4NH)3]2+

The cationic complexes [(η⁶-arene)Ru(SC₅H₄NH)₃]²⁺, arene being C₆H₆ (1), MeC₆H₅ (2), p-ⁱPrC₆H₄Me (3) or C₆Me₆ (4), have been synthesised from the reaction of 4-pyridinethiol with the corresponding precursor (η⁶-arene)₂Ru₂(μ₂-Cl)₂Cl₂ and isolated as the chloride salts. The single-crystal X-ray structure of [4](PF₆)₂ reveals three 4-pyridinethiol moieties coordinated to the ruthenium centre through the sulphur atom, with the hydrogen atom transferred from the sulphur to the nitrogen atom. The electrochemical study of 1–4 shows a clear correlation between the Ru(II)/Ru(III) redox potentials and the number of alkyl substituents at the arene ligand (E°′ (Ru^II/III): 1 > 2 > 3 > 4), whereas the cytotoxicity towards A2780 ovarian cancer cells follows the series 4 > 1 > 3 > 2, the hexamethylbenzene derivative 4 being the most cytotoxic one. The corresponding reaction of the ortho-isomer, 2-pyridinethiol, with (η⁶-C₆Me₆)₂Ru₂(μ₂-Cl)₂Cl₂ does not lead to the expected 2-pyridinethiolato analogue, but yields the neutral complex (η⁶-C₆Me₆)Ru(η²-SC₅H₄N)(η¹-SC₅H₄N) (5). The analogous complex (η⁶-C₆Me₆)Ru(η²-SC₉H₆N)-(η¹-SC₉H₆N) (6) is obtained from the similar reaction with 2-quinolinethiol.     

Reversible alkin-addition an rp-verbrückte carbonyleisen-cluster

The clusters (μ₃-RP)₂Fe₃(CO0₉ (1) photochemically add alkines R′CCR′ across their bridging phosphorus centers to yield (μ₃-η⁴-RPCR′CR′PR)Fe₃(CO)₉ (2). Thermal activation of 2 opens two different reaction channels: Complezes 2 may split into R′CCR′ and 1 in a thermally induced reversion of their photoinitiated formation reaction: in another pathway they may lose Fe(CO)₃ to yield (μ₂-η²-(PFe)RPCR′CR′PR)Fe₂(CO)₆ (3). Complex 3 is an Fe₂(CO)₆ derivative of the butterfly type with the μ₂-bridging phosphorus centers linked by an R′CCR′ moeity. The reverse transformation 3 → 2 is induced by Fe₂(CO)₉ as an “Fe(CO)₃” source.Compounds 2 undergo a CO substitution reaction with R′CCR′ to give (μ₃-η²- RPCR′CR′PR)(μ₃-η²-R′CCR′)Fe₃(CO)₇ (4) which, upon heating, also transforms into 3. The above reactions 1 ⇋ 2 ⇋ 3 and 2 → 4 → 3 ⇋ 2 present a rare example of a complete closed set of cluster transformations. An analogous subset of reactions is also verified for the arsenic homologues 1, 2 and 4.     

Synthesis of the novel bifunctional ligand,dicyclopentadienylsulfide (C5H5)2S,and its dilithium salt

The dicyclopentadienylsulfide ligand (C₅H₅)₂S (1) was synthesized via reaction of CpTl with SCl₂. The dilithium salt Li₂[(C₅H₄S] (2) was obtained by the reaction of 1 with ⁿBuLi and was characterized spectroscopically.