The (phosphino)tetraphenylborate ligand in ruthenium-arene chemistry

The synthesis of a series of anionic half-sandwich ruthenium-arene complexes [E][RuCl₂(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (E = Bu₄N⁺: R = Ph, 1a, ⁱPr, 1b or Cy, 1c; E = bis(triphenylphosphine)iminium or PNP⁺: R = Ph, 1a′, ⁱPr, 1b′ or Cy, 1c′) are reported. X-ray crystallographic studies of 1a′ and 1b′ confirmed the three-legged piano-stool coordination geometry. In solution, complexes 1a-c and 1a′-c′ are proposed to form monomer-dimer equilibria as a result of chloride ligand dissociation. Complexes 1a-c and 1a′-c′ also form the formally neutral zwitterionic complexes [RuCl(L)(η⁶-p-cymene){PR₂(p-Ph₃BC₆H₄)}] (L = pyridine: R = Ph, 2a, ⁱPr, 2b or Cy, 2c; L = MeCN: R = Ph, 3a, ⁱPr, 3b or Cy, 3c) via chloride ligand abstraction using AgNO₃ or MeOTf.     

Synthesis, characterization, and norbornene polymerization of η-benzylnickel(II) complexes of N-heterocyclic carbenes

Neutral η¹-benzylnickel carbene complexes, [Ni(η¹-CH₂C₆H₅)(IiPr)(PMe₃)(Cl)] (3) (IiPr = 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene) and [Ni(η¹-CH₂C₆H₅)(SIiPr)(PMe₃)(Cl)] (4) (SIiPr = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-ylidene), were prepared by the reaction between [Ni(η³-CH₂C₆H₅)(PMe₃)(Cl)] and an equivalent amount of the corresponding free N-heterocyclic carbene. The preparation of η³-benzylnickel carbene complexes, [Ni(η³-CH₂C₆H₅)(IiPr)(Cl)] (5) and [Ni(η³-CH₂C₆H₅)(SIiPr)(Cl)] (6) were carried out by the abstraction of PMe₃ from 3 and 4 by the treatment of B(C₆F₅)₃. The treatment of AgX on 5 and 6 produced the anion-exchanged complexes, [Ni(η³-CH₂C₆H₅)(NHC)(X)] (7, NHC = IiPr, X = O₂CCF₃; 8, NHC = IiPr, X = O₃SCF₃; 9, NHC = SIiPr, X = O₂CCF₃; 10, NHC = SIiPr, X = O₃SCF₃). The solid state structures of 3 and 10 were determined by X-ray crystallography. The η³-benzyl complexes of IiPr (5, 7, and 8) alone, in the absence of any activators such as borate and MAO, showed good catalytic activity towards the vinyl-type norbornene polymerization. The catalyst was thermally robust and the activity increases as the temperature rises to 130 °C.     

Palladium(II)/allylpalladium(II) complexes with xanthate ligands: Single-source precursors for the generation of palladium sulfide nanocrystals

In an effort to find simple and common single-source precursors for palladium sulfide nanostructures, palladium(II) complexes, [Pd(S₂X)₂] (X = COMe (1), COⁱPr (2)) and η³-allylpalladium complexes with xanthate ligands, [(η³-CH₂C(CH₃)CR₂)Pd(S₂X)] (R = H, X = COMe (3); R = H, X = COEt (4); R = H, X = COⁱPr (5); R = CH₃, X = COMe (6)), have been investigated. The crystal structures of [Pd(S₂X)₂] (X = COMe (1), CoⁱPr (2)) and [(η³-CH₂C(CH₃)CH₂)Pd(S₂COMe)] (3) have been established by single crystal X-ray diffraction analysis. The complexes, 1, 2 and 3 all contain a square planar palladium(II) centre. In the allyl complex 3, this is defined by the two sulfurs of the xanthate and the outer carbons of the 2-methylallyl ligand, while in the complexes, 1 and 2 it is defined by the four sulfur atoms of the xanthate ligand. Thermogravimetric studies have been carried out to evaluate the thermal stability of η³-allylpalladium(II) analogues. The complexes are useful precursors for the growth of nanocrystals of PdS either by furnace decomposition or solvothermolysis in dioctyl ether. The solvothermal decomposition of complexes in dioctyl ether gives a new metastable phase of PdS which can be transformed to the more stable tetragonal phase at 320 °C. The nanocrystals obtained have been characterized by PXRD, SEM, TEM and EDX.     

F NMR spectroscopy as useful tool for determining the structure in solution of coordination compounds of MF5 (M = Nb, Ta)

The salts [S(NMe₂)₃][MF₆] (M = Nb, 2a; M = Ta, 2b) and [S(NMe₂)₃][M₂F₁₁] (M = Nb, 2c; M = Ta, 2d) have been prepared by reacting MF₅ (M = Nb, 1a; M = Ta, 1b) with [S(NMe₂)₃][SiMe₃F₂] (TASF reagent) in the appropriate molar ratio. The solid state structure of 2b has been ascertained by X-ray diffraction. The 1:1 molar ratio reactions of 1a with a variety of organic compounds (L) give the neutral adducts NbF₅L [L = Me₂CO, 3a; L = MeCHO, 3b; L = Ph₂CO, 3c; L = tetrahydrofuran (thf), 3d; L = MeOH, 3e; L = EtOH, 3f; L = HOCH₂CH₂OMe, 3g; L = Ph₃PO, 3h; L = NCMe, 3i] in good yields. The complexes MF₅L [M = Nb, L = HCONMe₂, 3j; M = Nb, L = (NMe₂)₂CO, 3k; M = Ta, L = (NMe₂)₂CO, 3l; M = Nb, L = OC(Me)CHCMe₂, 3m] have been detected in solution in admixture with other unidentified products, upon 2:1 molar reaction of 1 with the appropriate reagent L. The ionic complexes [NbF₄(tht)₂][NbF₆], 4a, and [NbF₄(tht)₂][Nb₂F₁₁], 4b, have been obtained by combination of tetrahydrothiophene (tht) and 1a, in 1:1 and 2:3 molar ratios, respectively. The treatment of 1 with a two-fold excess of L leads to the species [MF₄L₄][MF₆] [M = Nb, L = HCONMe₂, 5a; M = Ta, L = HCONMe₂, 5b; M = Nb, L = thf, 5c; M = Ta, L = thf, 5d; M = Nb, L = OEt₂, 5e]. The new complexes have been fully characterised by NMR spectroscopy. Moreover, the revised ¹⁹F NMR features of the known compounds MF₅L [M = Ta, L = Me₂CO, 3n; M = Ta, L = Ph₂CO, 3o; M = Ta, L = MePhCO, 3p; M = Ta, L = thf, 3q; M = Nb, L = CH₃CO₂H, 3r; M = Nb, L = CH₂ClCO₂H, 3s; M = Ta, L = CH₂ClCO₂H, 3t], TaF₄(acac), TaF₄(Me-acac) and [TaF(Me-acac)₃][TaF₆] (Me-acac = methylacetylacetonato anion) are reported.     

Allylpalladium (II) complexes with dichalcogenoimidodiphosphinate ligands: Synthesis, structure, spectroscopy and their transformation into palladium chalcogenides

The synthesis, characterization and thermal behavior of new monomeric allylpalladium (II) complexes with dichalcogenoamidodiphosphinate anions are reported. The complexes [R = H, R′ = Prⁱ, E = S (1a); R = H, R′ = Prⁱ, E = Se (1b); R = H, R′ = Ph, E = S (1c); R = H, R′ = Ph, E = Se (1d); R = Me, R′ = Prⁱ, E = S (2a); R = Me, R′ = Prⁱ, E = Se (2b); R = Me, R′ = Ph, E = S (2c); R = Me, R′ = Ph, E = Se (2d)] have been prepared by room temperature reaction of [Pd(η³-CH₂C(R)CH₂)(acac)] (acac = acetylacetonate) with dichalcogenoimidodiphosphinic acids in acetonitrile solution. The complexes have been characterized by multinuclear NMR (¹H, ¹³C{¹H}, ³¹P{¹H}, ⁷⁷Se{¹H}), FT-IR and elemental analyses. The crystal structures of complexes 1a, 1d and 2d have been reported and they consist of a six-membered PdE₂P₂N ring (E = S for 1a and Se for 1d and 2d) and an allyl group, C₃H₄R(R = H for 1a and 1d and Me for 2d). Thermogravimetric studies have been carried out for few representative complexes. The complexes thermally decompose in argon atmosphere to leave a residue of palladium chalcogenides, which have been characterized by PXRD, SEM and EDS.     

Synthesis and characterization of metal diselenophosphates: M[Se2P(OR)2]2 (M = Pd,Pt; R = Et,Pr, Pr)

The first Pd(II) and Pt(II) complexes incorporating diselenophosphate (dsep) ligands are presented. Treatment of M(II) (M = Pd, Pt) salts with two equivalents of the dsep ligand in CH₂Cl₂ yielded square-planar compounds of the type M[Se₂P(OR)₂]₂ (M = Pd, Pt; R = Et, ⁱPr, ⁿPr) (1a–2c). These complexes were characterized by elemental analysis, multinuclear NMR spectroscopy and X-ray diffraction (1b and 2b). The dsep ligands coordinate to the metal in an approximately isobidentate fashion and form four-membered Se–P–Se–M chelate rings. Structural elucidations indicated that minute differences exist in the M–Se bond distances and these were observed from solution ³¹P NMR studies, which exhibited two sets of satellites arising from one-bond coupling to ⁷⁷Se nuclei. A packing diagram showed a chain-like motif which was composed of square-planar M[Se₂P(OR)₂]₂ units and occurred via non-covalent Se?Se secondary interactions.     

Reactions of trimethylsiloxychlorosilanes with lithium metal - On the mechanism of the formation of trimethylsiloxysilyllithium compounds LiSiRR’(OSiMe3)

The reaction pathway for the formation of the trimethylsiloxysilyllithium compounds (Me₃SiO)RR′SiLi (2a: R = Et, 2b: R = ⁱPr, 2c: R = 2,4,6-Me₃C₆H₂ (Mes); 2a-c: R′ = Ph; 2d: R = R′ = Mes) starting from the conversion of the corresponding trimethylsiloxychlorosilanes (Me₃SiO)RR′SiCl (1a-d) in the presence of excess lithium in a mixture of THF/diethyl ether/n-pentane at −110 °C was investigated.The trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a: R = Et, 1b: R = ⁱPr, 1c: R = Mes) react with lithium to give initially the trimethylsiloxysilyllithium compounds (Me₃SiO)RPhSiLi (2a-c). These siloxysilyllithiums 2 couple partially with more trimethylsiloxychlorosilanes 1 to produce the siloxydisilanes (Me₃SiO)RPhSi-SiPhR(OSiMe₃) (Ia-c), and they undergo bimolecular self-condensation affording the trimethylsiloxydisilanyllithium compounds (Me₃SiO)RPhSi-RPhSiLi (3a-c). The siloxydisilanes I are cleaved by excess of lithium to give the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2). In the case of the two trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a: R = Et, 3b: R = ⁱPr) a reaction with more trimethylsiloxychlorosilanes (Me₃SiO)RPhSiCl (1a, 1b) takes place under formation of siloxytrisilanes (Me₃SiO)RPhSi-RPhSi-SiPhR(OSiMe₃) (IIa: R = Et, IIb: R = ⁱPr) which are cleaved by lithium to yield the trimethylsiloxysilyllithiums (Me₃SiO)RPhSiLi (2a, 2b) and the trimethylsiloxydisilanyllithiums (Me₃SiO)RPhSi-RPhSiLi (3a, 3b). The dimesityl-trimethylsiloxy-silyllithium (Me₃SiO)Mes₂SiLi (2d) was obtained directly by reaction of the trimethylsiloxychlorosilane (Me₃SiO)Mes₂SiCl (1d) and lithium without formation of the siloxydisilane intermediate. Both silyllithium compounds 2 and 3 were trapped with HMe₂SiCl giving the products (Me₃SiO)RR′Si-SiMe₂H and (Me₃SiO)RPhSi-RPhSi-SiMe₂H.     

Palladiumdichloride (ferrocenylethynyl)phosphanes and their use in Pd-catalyzed Heck-Mizoroki- and Suzuki-Miyaura carbon-carbon cross-coupling reactions

In this work the synthesis of phosphane selenides (FcCC)_nPh_3−nPSe (2a, n = 1; 2b, n = 2; 2c, n = 3; Fc = ferrocenyl, (η⁵-C₅H₄)(η⁵-C₅H₅)Fe) from (FcCC)_nPh_3−nP (1a, n = 1; 1b, n = 2; 1c, n = 3) and selenium is described to estimate the σ-donor properties of these systems by ³¹P{¹H} NMR spectroscopy. Progressive replacement of phenyl by ferrocenylethynyl causes a shielding of the phosphorus atom with increasing of the ¹J(³¹P-⁷⁷Se) coupling constants.The palladiumdichloride metal-organic complexes [((FcCC)_nPh_3−nP)₂PdCl₂] (3a, n = 1; 3b, n = 2; 3c, n = 3) have been used as (pre)catalysts in the Suzuki-Miyaura (reaction of 2-bromo-toluene (4a) and 4-bromo-acetophenone (4b), respectively, with phenyl boronic acid (5) to give 2-methyl biphenyl (6a) and 4-acetyl biphenyl (6b)) and in the Heck-Mizoroki reaction (treatment of iodobenzene (7) with tert-butyl acrylate (8) to give E-tert-butyl cinnamate (9)).The structures of molecules 1a, 1c, 2c, and 3c in the solid state were determined by single X-ray structure analysis showing that the structural parameters of these systems are unexceptional and correspond to those of related phosphanes, seleno phosphanes, and palladium dichloride complexes.     

Diiron-aminocarbyne complexes with amine or imine ligands: C-N coupling between imine and aminocarbyne ligands promoted by tolylacetylide addition to [Fe2{μ-CN(Me)R}(μ-CO)(CO)(NHCPh2)(Cp)2][SO3CF3]

A terminally coordinated CO ligand in the complexes [Fe₂{μ-CN(Me)R}(μ-CO)(CO)₂(Cp)₂][SO₃CF₃] (R = Me, 1a; R = Xyl, 1b; Xyl = 2,6-Me₂C₆H₃), is readily displaced by primary and secondary amines (L), in the presence of Me₃NO, affording the complexes [Fe₂{μ-CN(Me)R}(μ-CO)(CO)(L)(Cp)₂][SO₃CF₃] (R = Me, L = NH₂Et, 4a; R = Xyl, L = NH₂Et, 4b; R = Me, L = NH₂Prⁱ, 5a; R = Xyl, L = NH₂Prⁱ, 5b; R = Xyl, L = NH₂C₆H₁₁, 6; R = Xyl, L = NH₂Ph, 7; R = Xyl, L = NH₃, 8; R = Me, L = NHMe₂, 9a; R = Xyl, L = NHMe₂, 9b; R = Xyl, = NH(CH₂)₅, 10). In the absence of Me₃NO, NH₂Et gives addition at the CO ligand of 1b, yielding [Fe₂{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(O)NHEt}(Cp)₂] (11). Carbonyl replacement is also observed in the reaction of 1a-b with pyridine and benzophenone imine, affording [Fe₂{μ-CN(Me)R}(μ-CO)(CO)(L)(Cp)₂][SO₃CF₃] (R = Me, L = Py, 12a; R = Xyl, L = Py, 12b; R = Me, L = HNCPh₂, 13a; R = Xyl, L = HNCPh₂, 13b). The imino complex 13b reacts with p-tolylacetylide leading to the formation of the μ-vinylidene-diaminocarbene compound [Fe₂{μ-η¹:η²- CC(Tol)C(Ph)₂N(H)CN(Me)(Xyl){(μ-CO)(CO)(Cp₂)] (15) which has been studied by X-ray diffraction.     

The influence of alkane spacer of bis(diphenylphosphino)alkanes on the nuclearity of silver(I): Syntheses and structures of P,P′-bridged clusters and coordination polymers involving dithiophosphates

The effect of the length of alkane spacer in diphosphines on the nuclearity of Ag(I) complexes containing dialkyl dithiophosphates (dtp) ligands has been investigated. 1,1-Bis(diphenylphosphino)methane (dppm) yielded tetranuclear [Ag₄(dppm)₂{S₂P(OEt)₂}₄] (1), [Ag₄(dppm)₂{S₂P(OⁱPr)₂}₄] (3), trinuclear [Ag₃(dppm)₃{S₂P(OEt)₂}₂](PF₆) (2), and a dinuclear [Ag₂(dppm)₂{S₂P(OⁱPr)}](PF₆) (4). The increase in spacer length from one methylene in dppm to two in 1,2-bis(diphenylphosphino)ethane (dppe) resulted in the formation of polymeric, [Ag(dppe){S₂P(OR)₂}]_∞ (R = Et, 5a and 5a′; ⁱPr, 5b), and [Ag₄(μ₃-Cl)(dppe)_1.5{S₂P(OR)₂}₃]_∞ (R = Et, 6a; ⁱPr, 6b). Compounds 5a, 5b, 6a and 6b were reported earlier [C.W. Liu, B.-J. Liaw, L.-S. Liou, J.-C. Wang, Chem. Commun. (2005) 1983]. Further increase in the chain length to four methylene units in 1,4-bis(diphenylphosphino)butane (dppb) yielded dppb-bridged polymers, [Ag(dppb){S₂P(OEt)₂}]_∞ (7) and [Ag₂(dppb){S₂P(OEt)₂}₂]_∞ (8). In all the polynuclear compounds, diphosphines acted as P,P′-bridging ligands, while the dtp ligands (S,S′-donors) adopted varieties of coordination patterns: S,S′-chelating (5, 7), S,S′-bridging (4), bimetallic-triconnective, μ₂:η²,η¹ (1, 3, 8), bimetallic-diconnective, μ₂:η² (2, 3) and trimetallic-triconnective, μ₃:η²,η¹ (6). Some of the complexes exhibit argentophilicity with Ag?Ag distances in the range, 2.918-3.360 Å. Concomitant bridging of two silver atoms either by dppm and dtp ligands (1, 3 and 4) or two dtp ligands (8) lead to close silver-silver contacts. The diphosphines (dppe and dppb) with longer spacer appeared to favor 1D or 2D polymers due to the flexibility of the spacer within the diphosphine unit by adopting anti conformation as opposed to syn conformation of the dppm linker is revealed in complexes.     

On the reactivity of [IrCl(N2)(PPh3)2] with alkynylsilanes - A new route to vinylidene iridium(I) complexes

The iridium dinitrogen complex [IrCl(N₂)(PPh₃)₂] (1) was found to react with alkynylsilanes to form the vinylidene iridium(I) complexes trans- (R/R′ = Ph/Me, 2; Me/Me, 3; Bn/Me, 4; SiMe₃/Me, 5; SiEt₃/Et, 6; ⁱPr/Me, 7) and with Me₃SiCCC(O)R to yield the iridium η²-alkyne complexes trans-[IrCl{η²-Me₃SiCCC(O)R}(PPh₃)₂] (R = OEt, 9; Me, 11). Complex 9 was found to isomerize upon heating or upon UV irradiation yielding the vinylidene complex trans-[IrCl{CC(SiMe₃)CO₂Et}(PPh₃)₂] (10). The reaction of 1 with Me₃SiCCCCSiMe₃ yielded the complex trans-[IrCl{CC(SiMe₃)CCSiMe₃}(PPh₃)₂] (8), whereas with MeO₂CCCCO₂Me the iridacyclopentadiene complex [Ir{C₄(CO₂Me)₄}Cl(PPh₃)₂] (13) was formed. The complexes were characterized by means of ¹H, ¹³C and ³¹P NMR spectroscopy as well as by IR spectroscopy and microanalysis.     

Iron(0) and ruthenium(0) complexes with tridentate phosphonite ligands and their potential for ketene formation from methyl iodide, CO and a base

An efficient route to the novel tridentate phosphine ligands RP[CH₂CH₂CH₂P(OR′)₂]₂ (I: R = Ph; R′ = i-Pr; II: R = Cy; R′ = i-Pr; III: R = Ph; R′ = Me and IV: R = Cy; R′ = Me) has been developed. The corresponding ruthenium and iron dicarbonyl complexes M(triphos)(CO)₂ (1: M = Ru; triphos = I; 2: M = Ru; triphos = II; 3: M = Ru; triphos = III; 4: M = Ru; triphos = IV; 5: M = Fe; triphos = I; 6: M = Fe; triphos = II; 7: M = Fe; triphos = III and 8: M = Fe; triphos = IV) have been prepared and fully characterized. The structures of 1, 3 and 5 have been established by X-ray diffraction studies. The oxidative addition of MeI to 1-8 produces a mixture of the corresponding isomeric octahedral cationic complexes mer,trans-(13a-20a) and mer,cis-[M(Me)(triphos)(CO)₂]I (13b-20b) (M = Ru, Fe; triphos = I-IV). The structures of 13a and 20a (as the tetraphenylborate salt (21)) have been verified by X-ray diffraction studies. The oxidative addition of other alkyl iodides (EtI, i-PrI and n-PrI) to 1-8 did not afford the corresponding alkyl metal complexes and rather the cationic octahedral iodo complexes mer,cis-[M(I)(triphos)(CO)₂]I (22-29) (M = Ru, Fe; triphos = I-IV) were produced. Complexes 22-29 could also be obtained by the addition of a stoichiometric amount of I₂ to 1-8. The structure of 22 has been verified by an X-ray diffraction study. Reaction of 13a/b-20a/b with CO afforded the acetyl complexes mer,trans-[M(COMe)(triphos)(CO)₂]I, 30-37, respectively (M = Ru, Fe; triphos = I-IV). The ruthenium acetyl complexes 30-33 reacted slowly with 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) even in boiling acetonitrile. Under the same conditions, the deprotonation reactions of the iron acetyl complexes 34-37 were completed within 24-40 h to afford the corresponding zero valent complexes 5-8. It was not possible to observe the intermediate ketene complexes. Tracing of the released ketene was attempted by deprotonation studies on the labelled species mer,trans-[Fe(COCD₃)(triphos)(CO)₂]I (38) and mer,trans-[Fe(¹³COMe)(triphos)(CO)₂]I (39).     

Bimetallic nickel complexes of macrocyclic tetraiminodiphenols and their ethylene polymerization

Schiff’s base condensation of 2,6-diformyl-4-R-phenol and affords 34-membered macrocyclic tetraiminodiphenol compounds, (R = H and R′ = iPr, 1; R = Me and R′ = iPr, 2; R = F and R′ = iPr, 3; R = Me and R′ = Et, 4; R = F and R′ = Et, 5) in good yields (47-62%), from which dinuclear nickel complexes, (R = H and R′ =  iPr, 6; R = Me and R′ = iPr, 7; R = F and R′ = iPr, 8) are prepared. Molecular structures of 2, dipotassium salt of 1, and 7 were confirmed by X-ray crystallography. Addition of B(C₆F₅)₃ to a toluene solution of 6-8 gives insoluble precipitates which show good activity for ethylene polymerization.     

Synthesis, characterization and bromination of bis(phosphinoferrocenyl) gold(I) compounds

Reaction of [(dppf)Au₂Br₂] (3) {dppf = 1,1′-bis(diphenylphosphino)ferrocene} and [(dippf)Au₂Br₂] (4) {dippf = 1,1′-bis(diisopropylphosphino)ferrocene} with excess bromine yields two new complexes [(C₅H₄Br₃)(PR₂)AuBr] (R = Ph, 5; R = i-Pr, 6). Bromination of the free diphosphinoferrocene ligands produces the expected brominated cyclopentenes (C₅H₄Br₃)(PR₂) (R = Ph, 7; R = i-Pr, 8) in good yields; however, these compounds could not be complexed to gold due to reduced basicity of 7 and 8. When the bromination is performed under wet aerobic conditions the oxidized pseudo-centrosymmetric product, [doppf][FeBr₄] (9) {doppf = 1,1′-bis(oxodiphenylphosphino)ferrocene, is formed as the major product. Solid-state structures of 1, 2, 4, 6, and 9 have been established by means of single-crystal X-ray crystallography.     

Synthesis of aluminium complexes bearing a piperazine-based ligand system

Aluminium complexes bearing the N,N-chelating ligand 1,4-bis(2-hydroxy-3,5-di-tert-butyl)piperazine (1) have been synthesised. Both monometallic and bimetallic aluminium methyl complexes (2 and 3, respectively) were prepared by treatment of 1 with the appropriate amount of AlMe₃. Complex 2 can be converted to 3 by addition of excess AlMe₃. Bimetallic aluminium-ethyl complex 4 was also prepared. Treatment of 1 with AlEt₂Cl afforded the monometallic chloride complex 5. Treatment of this latter complex with potassium alkoxides (KOR, R = Me, Et, ⁱPr, ^tBu) or AgOTf afforded the corresponding aluminium alkoxide complexes (6, R = Et; 7, R = Me; 8, R = ⁱPr; 9, R = ^tBu; 10, R = OTf) in good yields. Aluminium ethoxide complex 6 was also synthesised by treatment of 1 with AlEt₂OEt. All of these complexes were tested as potential catalysts in the ring-opening polymerisation of rac-lactide and caprolactone with limited success.     

Syntheses, structures and electrochemistry of some 1-(η-allylamino)-1-ferrocenylcarbene complexes of chromium(0), molybdenum(0) and tungsten(0) : Part 13: The chemistry of metallacyclic alkenylcarbene complexes

The metallacyclic complexes (OC)₄MC(η²-NHCH₂CHCHX)Fc (4; X = H) and (5; X = CH₂OH) [M = Cr: a; Mo: b; W: c; Fc = ferrocenyl = CpFe(C₅H₄)] were obtained in good yields upon photo-decarbonylation of the bimetallic allylaminocarbene complexes (OC)₅MC(NHCH₂CHCHX)Fc (2; X = H)/(3; X = CH₂OH). At room temperature complexes 2/3 exist as mixtures of E- and predominantly Z-isomers with regard to the C-N bond. The molecular structures of 4b and 4c were determined by X-ray diffraction analyses. The intermetallic communicative effects and the interplay of Fc and η²-alkene moieties of 4a and 4b were assessed by cyclovoltammetry. All complexes were also characterized in solution by one- and two-dimensional NMR spectroscopy (¹H, ¹³C, ¹H NOE, ¹H/¹H COSY, ¹³C/¹H HETCOR).     

Synthesis, characterization, reactivity and computational studies of new rhenium(I) complexes with thiosemicarbazone ligands derived from 4-(methylthio)benzaldehyde

N-thioamide thiosemicarbazone derived from 4-(methylthio)benzaldehyde (R = H, HL¹; R = Me, HL² and R = Ph, HL³) have been prepared and their reaction with fac-[ReX(CO)₃(CH₃CN)₂] (X = Br, Cl) in methanol gave the adducts [ReX(CO)₃(HLⁿ)] (1a X = Cl, n = 1; 1a′ X = Br, n = 1; 1b X = Cl, n = 2; 1b′ X = Br, n = 2; 1c X = Cl, n = 3; 1c′ X = Br, n = 3) in good yield.All the compounds have been characterized by elemental analysis, mass spectrometry (ESI), IR and ¹H NMR spectroscopic methods. Moreover, the structures of HL², HL³, HL³·(CH₃)₂SO and 1b′·H₂O were also elucidated by X-ray diffraction. In 1b′, the rhenium atom is coordinated by the sulphur and the azomethine nitrogen atoms (κS,N³) forming a five-membered chelate ring, as well as three carbonyl and bromide ligands. The resulting coordination polyhedron can be described as a distorted octahedron.The structure of the dimers is based on rhenium(I) thiosemicarbazonates [Re₂(L¹)₂(CO)₆] (2a), [Re₂(L²)₂(CO)₆] (2b) and [Re₂(L³)₂(CO)₆] (2c) as determined by X-ray studies. Methods of synthesis were optimized to obtain amounts of these thiosemicarbazonate complexes. In these compounds the dimer structures are achieved by Re-S-Re bridges, where S is the thiolate sulphur from a κS,N³-bidentate thiosemicarbazonate ligand.Some single crystals isolated in the synthesis of 2b contain [Re(L⁴)(L²)(CO)₃] (3b) where L⁴ (=2-methylamine-5-(para-methylsulfanephenyl)-1,3,4-thiadiazole) is originated in a cyclization process of the thiosemicarbazone. Furthermore, the rhenium atom is coordinate by the sulphur and the thioamidic nitrogen of the thiosemicarbazonate (κS,N²) affording a four-membered chelate ring.     

Dimeric and trimeric diorganosilicon chalcogenides (PhRSiE)2,3 (E = S, Se, Te; R = Ph, Me)

Ph₂SiCl₂ and PhMeSiCl₂ react with Li₂E (E = S, Se, Te) under formation of trimeric diorganosilicon chalcogenides (PhRSiE)₃ (R = Ph: 1a-3a, R = Me: cis/trans-4a (E = S), cis/trans-5a (E = Se)). In case of E = S, Se dimeric four-membered ring compounds (PhRSiE)₂ (R = Ph: 1b-2b, R = Me: cis/trans-4b (E = S), cis/trans-5b (E = Se)) have been observed as by-products. 1a-5b have been characterized by multinuclear NMR spectroscopy (¹H, ¹³C, ²⁹Si, ⁷⁷Se, ¹²⁵Te). Four- and six-membered ring compounds differ significantly in ²⁹Si and ⁷⁷Se chemical shifts as well as in the value of ¹J_SiSe.The molecular structures of 2a, 3a and trans-5a reported in this paper are the first examples of compounds with unfused six-membered rings Si₃E₃ (E = Se, Te). The Si₃E₃ rings adopt twisted boat conformations. The crystal structure of 3a reveals an intermolecular Te-Te contact of 3.858 Å which yields a dimerization in the solid state.     

Organoplatinum(II) complexes with phosphite ligands

The phosphite complexes cis-[PtMe₂L(SMe₂)] in which L = P(OⁱPr)₃, 1a, or L = P(OPh)₃, 1b, were synthesized by the reaction of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equiv. of L. If 4 equiv. of L was used the bis-phosphite complexes cis-[PtMe₂L₂] in which L = P(OⁱPr)₃, 2a, or L = P(OPh)₃, 2b, were obtained. The reaction of cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with 2 equiv. of L gave the aryl bis-phosphite complexes cis-[Pt(p-MeC₆H₄)₂L₂] in which L = P(OⁱPr)₃, 2a′, or L = P(OPh)₃, 2b′. Use of 1 equiv. of L in the latter reaction gave the bis-phosphite complex along with the starting complex in a 1:1 ratio.The complexes failed to react with MeI. The reaction of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equiv. of the phosphine PPh₃ gave cis-[PtMe₂(PPh₃)₂] and cis-[PtMe₂(PPh₃)(SMe₂)] along with unreacted starting material. Reaction of cis-[PtMe₂L(SMe₂)], 1a and 1b with the bidentate phosphine ligand bis(diphenylphosphino)methane, dppm = Ph₂PCH₂PPh₂, gave [PtMe₂(dppm)], 8, along with cis-[PtMe₂L₂], 2. The reaction of cis-[PtMe₂L(SMe₂)] with 1/2 equiv. of the bidentate N-donor ligand NN = 4,4′-bipyridine yielded the binuclear complexes [PtMe₂L(μ-NN)PtMe₂L] in which L = P(OⁱPr)₃, 3a, or L = P(OPh)₃, 3b.The complexes were fully characterized using multinuclear NMR (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) spectroscopy.     

Synthesis and X-ray diffraction analysis/crystal structure of new germatranes containing methyl substituents in three five-membered chelating rings

Three monomeric germatranes, 1-isopropoxy-3,3,7,7,10,10-hexamethyl-2,8,9-trioxa-5-aza-1-germatricyclo[3.3.3.0^1,5]undecane (1), 1-isopropoxy-3,3,7,7-tetramethyl-2,8,9-trioxa-5-aza-1-germatricyclo[3.3.3.0^1,5]undecane (2), and 1-isopropoxy-3,3-dimethyl-2,8,9-trioxa-5-aza-1-germatricyclo[3.3.3.0^1,5]undecane (3) have been synthesized by the reaction of Ge(O-i-Pr)₄ in refluxing toluene with corresponding triethanolamines, (HOCH₂CH₂)_nN(CH₂CMe₂OH)_3−n (n = 0, L1H₃; n = 1, L2H₃; n = 2, L3H₃), where the number of CMe₂ groups adjacent to a OH functionality varied from 3 (L1H₃) to 2 (L2H₃), and to 1 (L3H₃). These germatranes 1-3 have been characterized by solution ¹H and ¹³C{¹H} NMR and the solid state structure of 2 has been determined by single crystal X-ray diffraction.