Synthesis of dimethylcobalt(III) complexes containing trimethylphosphine and 2-formyl-phenolato- or 2-formyl-enolato(O:O) ligands

Substituted salicylaldehydes [C₆HR¹R²R³(CHO)(OH)] react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-phenolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[C₆HR¹R²R³(CHO)(O)Me₂](PMe₃)₂ (1: R¹ = H; R² = Me; R³ = tert-Bu; 2: R¹, R² = C₆H₄; R³ = H). Accordingly, substituted enolated malonic dialdehydes (CHO-CR⁴CR⁵-OH) react with CoMe₃(PMe₃)₃ to afford 6-coordinate (cis-dimethyl)(2-formyl-enolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[(CHO-CR⁴CR⁵-O)(Me)₂](PMe₃)₂ (3: R⁴, R⁵ = (CH₂)₂C₆H₄; 4: R⁴ = R⁵ = C₆H₅). In the molecular structure of 4, the cobalt atom is centred in an octahedral coordination geometry brought about by a six-membered chelate ring (O:O-ligand), cis-dimethyl and trans-trimethylphosphine groups. A reaction mechanism is suggested.     

Synthesis and characterization of metallatranes with phenyl substituents in atrane cage

A new series of mono- and diphenylsubstituted silatranes and boratranes N(CH₂CH₂O)₂(CHR³CR¹R²O)MZ (M = Si, Z = CH₂Cl, CCPh, H, OMenth, R¹, R², R³ = H, Ph; M = B, Z = nothing, R¹, R², R³ = H, Ph) have been synthesized. Both transalkoxylation and stepwise modification of a preformed metallatrane skeleton were used. The chloromethyl derivatives N(CH₂CH₂O)₂(CHRCHRO)SiCH₂Cl (R = H, Ph) react with tert-BuOK under intramolecular cycle expansion to give 1-tert-butoxy-2-carba-3-oxahomosilatranes N(CH₂CH₂O)(CH₂CH₂OCH₂)(CHRCHRO)SiO^tBu (R = H, Ph). The treatment of boratranes N(CH₂CH₂O)₂(CH₂CR¹R²O)B (R¹,R² = H, Ph) with triflic acid and trimethylsilyl triflate results in the products of electrophilic attack at the nitrogen atom. The molecular structures of four silatranes and one boratrane bearing phenyl groups in the atrane skeleton were determined by the X-ray structure analysis.     

Nickel(II) complexes bearing pyrazolylimine ligands: Synthesis, characterization, and catalytic properties for ethylene oligomerization

Four phenyl-substituted pyrazolylimine ligands 2-(C₃HN₂Me₂-3,5)(C(Ph)N(4-R₂C₆H₂(R₁)₂-2,6)) (L1: R₁ = ⁱPr, R₂ = H; L2: R₁ = H, R₂ = NO₂; L3: R₁ = R₂ = H; L4: R₁ = H, R₂ = OCH₃) were synthesized. The influences of steric bulk and electronic effect of pyrazolylimine ligands on the structures of their corresponding nickel complexes were investigated. Ligands with more bulky and electron withdrawing substituents on N-phenyl ring produced four-coordinate nickel complexes (2-(C₃HN₂Me₂-3,5))(C(Ph)(4-R₂C₆H₂(R₁)₂-2,6)NiBr₂ (1, R₁ = ⁱPr, R₂ = H; 2, R₁ = H, R₂ = NO₂)), whereas the ligands with less bulky and electron donating substituents on N-phenyl ring formed bis-pyrazolylimine dinickel tetrahalides (bis-2-(C₃HN₂Me₂-3,5))(C(Ph)N(4-R₂C₆H₂ (R₁)₂-2,6)Ni₂Br₄ (3, R₁ = R₂ = H; 4, R₁ = H, R₂ = OCH₃)) and six-coordinate nickel dihalides (bis-2-(C₃HN₂Me₂-3,5))(C(Ph)N(4-R₂C₆H₂(R₁)₂-2,6) NiBr₂ (5, R₁ = R₂ = H;6, R₁ = H, R₂ = OCH₃)). The solid-state structures of complexes 1, 4 and 5 have been confirmed by X-ray single-crystal analyses. Activated by methylaluminoxane (MAO), complexes 1, 2, 5 and 6 showed moderate to high activity for ethylene oligomerization, and complex 5 revealed the highest activity up to 8.96 × 10⁵ g oligomer/(mol Ni · h). The proportions of resultant oligomers were mainly C4-C8 and a little C10-C14 determined by gas chromatography/mass spectrometry.     

The blue anthocyanin pigments from the blue flowers of Heliophila coronopifolia L. (Brassicaceae)

Six acylated delphinidin glycosides (pigments 1-6) and one acylated kaempferol glycoside (pigment 9) were isolated from the blue flowers of cape stock (Heliophila coronopifolia) in Brassicaceae along with two known acylated cyanidin glycosides (pigments 7 and 8). Pigments 1-8, based on 3-sambubioside-5-glucosides of delphinidin and cyanidin, were acylated with hydroxycinnamic acids at 3-glycosyl residues of anthocyanidins. Using spectroscopic and chemical methods, the structures of pigments 1, 2, 5, and 6 were determined to be: delphinidin 3-O-[2-O-(β-xylopyranosyl)-6-O-(acyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which acyl moieties were, respectively, cis-p-coumaric acid for pigment 1, trans-caffeic acid for pigment 2, trans-p-coumaric acid for pigment 5 (a main pigment) and trans-ferulic acid for pigment 6, respectively. Moreover, the structure of pigments 3 and 4 were elucidated, respectively, as a demalonyl pigment 5 and a demalonyl pigment 6. Two known anthocyanins (pigments 7 and 8) were identified to be cyanidin 3-(6-p-coumaroyl-sambubioside)-5-(6-malonyl-glucoside) for pigment 7 and cyanidin 3-(6-feruloyl-sambubioside)-5-(6-malonyl-glucoside) for pigment 8 as minor anthocyanin pigments. A flavonol pigment (pigment 9) was isolated from its flowers and determined to be kaempferol 3-O-[6-O-(trans-feruloyl)-β-glucopyranoside]-7-O-cellobioside-4′-O-glucopyranoside as the main flavonol pigment.On the visible absorption spectral curve of the fresh blue petals of this plant and its petal pressed juice in the pH 5.0 buffer solution, three characteristic absorption maxima were observed at 546, 583 and 635 nm. However, the absorption curve of pigment 5 (a main anthocyanin in its flower) exhibited only one maximum at 569 nm in the pH 5.0 buffer solution, and violet color. The color of pigment 5 was observed to be very unstable in the pH 5.0 solution and soon decayed. In the pH 5.0 solution, the violet color of pigment 5 was restored as pure blue color by addition of pigment 9 (a main flavonol in this flower) like its fresh flower, and its blue solution exhibited the same three maxima at 546, 583 and 635 nm. On the other hand, the violet color of pigment 5 in the pH 5.0 buffer solution was not restored as pure blue color by addition of deacyl pigment 9 or rutin (a typical flower copigment). It is particularly interesting that, a blue anthocyanin-flavonol complex was extracted from the blue flowers of this plant with H₂O or 5% HOAc solution as a dark blue powder. This complex exhibited the same absorption maxima at 546, 583 and 635 nm in the pH 5.0 buffer solution. Analysis of FAB mass measurement established that this blue anthocyanin-flavonol complex was composed of one molecule each of pigment 5 and pigment 9, exhibiting a molecular ion [M+1] ⁺ at 2102 m/z (C₉₃H₁₀₅O₅₅ calc. 2101.542). However, this blue complex is extremely unstable in acid solution. It really dissociates into pigment 5 and pigment 9.     

Tetra-acylated cyanidin 3-sophoroside-5-glucosides from the flowers of Iberis umbellata L. (Cruciferae)

The structures of 11 acylated cyanidin 3-sophoroside-5-glucosides (pigments 1-11), isolated from the flowers of Iberis umbellata cultivars (Cruciferae), were elucidated by chemical and spectroscopic methods. Pigments 1-11 were acylated with malonic acid, p-coumaric acid, ferulic acid, sinapic acid and/or glucosylhydroxycinnamic acids.Pigments 1-11 were classified into four groups by the substitution patterns of the linear acylated residues at the 3-position of the cyanidin. In the first group, pigments 1-3 were determined to be cyanidin 3-O-[2-O-(2-O-(acyl)-β-glucopyranosyl)-6-O-(trans-p-coumaroyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which the acyl moiety varied with none for pigment 1, ferulic acid for pigment 2 and sinapic acid for pigment 3. In the second one, pigments 4-6 were cyanidin 3-O-[2-O-(2-O-(acyl)-β-glucopyranosyl)-6-O-(4-O-(β-glucopyranosyl)-trans-p-coumaroyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which the acyl moiety varied with none for pigment 4, ferulic acid for pigment 5 and sinapic acid for pigment 6. In the third one, pigments 7-9 were cyanidin 3-O-[2-O-(2-O-(acyl)-β-glucopyranosyl)-6-O-(4-O-(6-O-(trans-feruloyl)-β-glucopyranosyl)-trans-p-coumaroyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which the acyl moiety varied with none for pigment 7, ferulic acid for pigment 8, and sinapic acid for pigment 9. In the last one, pigments 10 and 11 were cyanidin 3-O-[2-O-(2-O-(acyl)-β-glucopyranosyl)-6-O-(4-O-(6-O-(4-O-(β-glucopyranosyl)-trans-feruloyl)-β-glucopyranosyl)-trans-p-coumaroyl)-β-glucopyranoside]-5-O-[6-O-(malonyl)-β-glucopyranoside], in which acyl moieties were none for pigment 10 and ferulic acid for pigment 11.The distribution of these pigments was examined in the flowers of four cultivars of I. umbellata by HPLC analysis. Pigment 1 acylated with one molecule of p-coumaric acid was dominantly observed in purple-violet cultivars. On the other hand, pigments (9 and 11) acylated with three molecules of hydroxycinnamic acids were observed in lilac (purple-violet) cultivars as major anthocyanins. The bluing effect and stability on these anthocyanin colors were discussed in relation to the molecular number of hydroxycinnamic acids in these anthocyanin molecules.     

Synthesis, characterisation and solution behaviour of fluoroalkyl phosphoryl complexes of tin tetrachloride

The synthesis, characterisation and solution behaviour of a series of octahedral complexes SnCl₄·2L (L = R₂NP(O)(OCH₂CF₃)₂; R = Me (1); Et (2) or L = P(O)(OCH₂R_f)₃; R_f = CF₃ (3); C₂F₅ (4)) are described. Complexes 1-4 were prepared from SnCl₄ and 2 equiv. of the ligand, L, in anhydrous CH₂Cl₂ solution. The adducts have been characterised by multinuclear (¹H, ³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analysis. In dichloromethane solution, the NMR data showed the presence of a mixture of cis and trans isomers for 1 and 2 and only the cis isomer for 3 and 4. The difference could be interpreted in terms of the electronic effects of the substituents on the phosphorus atom of the ligand. In addition, the solution structure of the complexes studied by variable temperature ³¹P-{¹H} and ¹H NMR in the presence of excess ligand indicated that the ligand exchange on the cis isomer dominates the chemistry. The metal-ligand exchange barriers were estimated to be 13.38 and 11.39 kcal/mol for 1 and 3, respectively. The results are discussed and compared with those previously reported for the related hexamethylphosphoramide adduct, SnCl₄·2HMPA.     

The first metal complexes bearing ligated 3-iminoisoindolin-1-ones

The reaction between Zn(OAc)₂ · 2H₂O (1) and the 3-iminoisoindolin-1-ones H₂NCNC(O)C₆R¹R²R³R⁴ (R¹-R⁴ = H 2; R¹, R⁴ = H, R², R³ = Cl 3; R¹, R³, R⁴ = H, R² = Me 4) in EtCN at 70 °C for ca. 12 h affords the novel family of complexes [Zn{H₂NCNC(O)C₆R¹R²R³R⁴}₂(OAc)₂] (R¹-R⁴ = H 5; R¹, R⁴ = H, R², R³ = Cl 6; R¹, R³, R⁴ = H, R² = Me 7) in excellent (90% and 93% for 5 and 6, correspondingly) to good (64% for 7) yields. The isolated compounds were characterized by elemental analyses (C, H, N), IR, NMR and ESI⁺-MS. X-ray diffraction data for 2 and 5 indicate that both free (2) and ligated (5) 3-iminoisoindolin-1-ones exist in the zwitterionic form.     

Synthesis of new mer,trans-rhodium(III) hydrido-bis(acetylide) complexes: Structure of mer,trans-[(PMe3)3Rh(CC–C6H4-4-NMe2)2H]

Terminal alkynes (R–CC–H, R = 1-naphthyl, 9-anthryl, 4-Me₂N–C₆H₄–, or the longer analogue, 4-(4-Me₂N–C₆H₄–CC–)–C₆H₄–) react with [Rh(PMe₃)₄Me] at ambient temperature, with loss of methane and one PMe₃ ligand, to form the corresponding mer,trans-[(PMe₃)₃Rh(CCR)₂H] compounds in excellent yield. In this preliminary study, the synthesis and spectroscopic characterization of the four new compounds are reported, along with the single-crystal structure of the R = 4-Me₂N–C₆H₄ derivative.     

Bimetallic copper(II) and zinc(II) complexes of acyclic Schiff base ligands derived from amino acids

The acyclic Schiff-base ligands (2-(OH)-5-(R³)C₆H₂-1,3-(HCNC(R¹)(R²)CO₂H), derived from the dialdehyde 2-hydroxy-5-R-1,3-benzenedicarboxaldehyde (R = Me or t-Bu) and two equivalents of the amino acids glycine, 2,2-diphenylglycine or phenylalanine, have been reacted with the metal acetates M(OAc)₂ (M = Cu, Zn) in the presence of triethylamine, affording the complexes [HNEt₃][M₂(CH₃CO₂)₂(2-(O)-5-(t-Bu)C₆H₂-1,3-(HCNC(R¹)(R²)CO₂)₂] (M = Cu, R¹ = R² = C₆H₅, R³ = Me (1); M = Zn, R¹ = R² = H, R³ = t-Bu (2); M = Zn, R¹ = R² = C₆H₅, R³ = t-Bu (3); M = Zn, R¹ = H, R² = CH₂C₆H₅, R³ = t-Bu (4)) in good yields. The crystal structures of 1·MeCN, 2·, 3·2MeOH, and 4·3MeOH have been determined.     

Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki-Heck catalysis mediated by complexes of N,S-donor ligands

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-position of the pyridyl ring, R⁴,R⁶-pyCH₂ER¹ [R⁴ = R⁶ = H, ER¹ = SMe (1), SeMe (2), SPh (6), SePh (7); R⁴ = Me, R⁶ = H, ER¹ = SMe (3), SPh (8), SePh (9); R⁴ = H, R⁶ = Me, ER¹ = SMe (4), SPh (10), SePh (11); R⁴ = H, R⁶ = Ph, ER¹ = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R⁴,R⁶-pyMe with LiBuⁿ followed by R¹EER¹. On reaction with PdCl₂(NCMe)₂, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C₆H₄)pyCH₂ER¹-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER¹ = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl₂(R⁴,R⁶-pyCH₂ER¹). Complexes with R⁶ = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R⁴ = Me, ER¹ = SMe), 7a (R⁴ = H, ER¹ = SePh) and 9a (R⁴ = Me, ER¹ = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl₂(N,E) motifs and bridging ligands, trimeric [PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃ (10a) and dimeric [PdCl₂(μ-6-MepyCH₂SePh-N,Se)]₂ (11a). This behaviour is attributed to avoidance of the Me···Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)-16.8(2)°]. When examined as precatalysts for the Mizoroki-Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 °C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC₆H₄Br and 4-RC₆H₄Cl). The most active precatalysts are PdCl₂(R⁴-pyCH₂SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl₂(pyCH₂SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Buⁿ₄NCl at 120 °C as a solvent under non-aqueous ionic liquid (NAIL) conditions.     

Synthesis, spectroscopic characterization and structural studies of chloro dioxotriphenylphosphine oxide (O,O-dialkyl/diphenyl(alkylene)dithiophosphate) molybdenum(VI) complexes: crystal structure of MoO2Cl2(OSMe2)2

Reactions of dichlorodioxobis(triphenylphosphine oxide)molybdenum(VI) complexes with ammonium/sodium salts of O,O-dialkyl(alkylene) and diphenyl dithiophosphoric acids in 1:1 molar ratio in dichloromethane solution yield dioxomolybdenum complexes of the types, MoO₂Cl[S₂P(OR)₂] · OPPh₃ (R=Me, Et, i-Pr, Ph) and MoO₂Cl[S₂] · OPPh₃. (G=-CH₂CMe₂CH₂O-, -OCMe₂CMe₂O-). These newly synthesized compounds were characterized by IR, UV-visible and ¹H NMR spectroscopy and elemental analysis. The molecular structure of MoO₂Cl₂(OSMe₂)₂ was determined by single-crystal X-ray diffraction. MoO₂Cl₂(OSMe₂)₂ crystallizes as orthorhombic in the space group Pbca with cell parameters a=13.7235(3) Å, b=12.2429(2) Å, c=14.3356(3) Å, V=2408.60(8) Å⁻³, Z=8, R=0.0221, R_w=0.0519. There are two cis oxo ligands, two cis dimethylsulphoxide moieties and two trans chlorine atoms in a distorted octahedral environment around molybdenum.     

Formation and molecular structure of novel Ru(III) dimers of a symmetric antitumor drug analogue

The symmetrical anionic and neutral dimers [H(TMSO)₂]₂trans-[{RuCl₄(TMSO)}₂](μ-pyz) (1), and mer-[{RuCl₃(TMSO)₂}₂](μ-pyz) (2) were isolated by the reaction of [H(TMSO)] trans-[RuCl₄(TMSO)₂] and mer-[RuCl₃(TMSO)₃] with heterocyclic nitrogen donor ligand pyrazine (pyz) at room temperature. These complexes can be regarded as unprecedented examples in the general Creutz-Taube family of ruthenium dimers. Each ruthenium center in 1 and 2 has a coordination environment akin to that of known anionic and neutral monomeric Ru(III) complexes. Crystals of 1 · acetone are orange, needle like, space group , a=10.419(3) Å, b=10.539(3) Å, c=12.595(5) Å, α=69.837(16)°, β=69.968(15)°, γ=74.330(15)° and crystals of 2 · 4TMSO are orange prisms, trigonal, space group , a=33.971(5) Å, b=33.971(5) Å, c=12.210(2) Å, α=90°, β=90° and γ=120°.     

Synthesis and characterization of new AMTTO-imine-ligands and their silver(I) complexes: crystal structures of TAMTTO, [Ag2(TAMMTO)4](NO3)2 · 4MeOH, [Ag(TAMTTO)(PPh3)2]NO3 · 1.5THF, [Ag(FAMTTO)(PPh3)2]NO3

Reaction of 4-amino-6-methyl-1,2,4-triazin-thione-5-one (AMTTO, 1) with 2-thiophenecarboxaldehyde and 2-furaldehyde led to the corresponding iminic compounds 6-methyl-4-[thiophene-2-yl-methylene-amino]-3-thioxo-[1,2,4]-triazin-3,4-dihydro(2H)-5-one (TAMTTO, 2) and 4-[furan-2-yl-methylene-amino]-6-methyl-3-thioxo-[1,2,4]-triazin-3,4-dihydro(2H)-5-one (FAMTTO, 3). Treatment of 2 with AgNO₃ gave the complex [Ag₂(TAMMTO)₄](NO₃)₂ · 4MeOH (4) and of 2 and 3 with [Ag(PPh₃)₂]NO₃ gave the complexes [Ag(TAMTTO)(PPh₃)₂]NO₃ · 1.5THF (5) and [Ag(FAMTTO)(PPh₃)₂]NO₃ (6), respectively. All the compounds have been characterized by elemental analyses, IR spectroscopy and mass spectrometry. Compound 2 and all the complexes have been characterized by X-ray diffraction studies, respectively. In addition, 5 and 6 have been characterized by ³¹P NMR spectroscopy. Crystal data for 2 at −80 °C: monoclinic, space group C2/c, a=2319.6(2), b=609.8(1), c=1673.6(2) pm, β=106.14(1)°, Z=8, R₁=0.0523; for 4 at −80 °C: triclinic, space group , a=877.6(1), b=1085.2(1), c=1557.7(2) pm, α=77.14(1)°, β=80.87(1)°, γ=78.18(1)°, Z=1, R₁=0.0407; for 5 at 20 °C: triclinic, space group , a=1151.1(2), b=1225.1(2), c=1887.4(3) pm, α=78.04(1)°, β=86.20(1)°, γ=76.03(1)°, Z=2, R₁=0.0662; for 6 at −80 °C: triclinic, space group , a=1189.7(2), b=1387.8(2), c=1410.9(2) pm, α=94.74(2)°, β=95.12(2)°, γ=112.41(2)°, Z=2, R₁=0.0511.     

Mononuclear and tetranuclear palladacycles with terdentate [C,N,N] and [C,N,O] Schiff base ligands. C-H versus C-Br activation reactions

Reaction of the Schiff base ligands 2-Br-4,5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂ (a) and 4,5-(OCH₂CH₂)C₆H₃C(H)NCH₂CH₂NMe₂ (b) with Pd(OAc)₂ or K₂[PdCl₄] leads to the mononuclear cyclometallated compounds [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N,N}(OCOMe)] (1a) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H)NCH₂CH₂NMe₂-C6,N,N}(Cl)] (1b), derived from C-H activation at the C6 carbon. Treatment of a with Pd₂(dba)₃ gave [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂-C2,N,N}(Br)] (2a), via C-Br activation.The metathesis reaction of 1a with aqueous sodium chloride gave [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N,N}(Cl)] (3a), with exchange of the acetate group by a chloride ligand. Treatment of the cyclometallated monomers 1a-3a with PPh₃ in a 1:1 molar ratio yielded the mononuclear complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N}(L)(PPh₃)] (L: OAc, 4a; Cl, 5a) and [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂-C2,N}(Br)(PPh₃)] (6a), with Pd-NMe₂ bond cleavage. However, treatment of a solution of 3a or 2a with silver trifluoromethanesulfonate, followed by reaction with PPh₃ in acetone yielded the cyclometallated complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)NCH₂CH₂NMe₂-C6,N,N}(PPh₃)][CF₃SO₃] (7a) and [Pd{4-5-(OCH₂O)C₆H₂C(H)NCH₂CH₂NMe₂-C2,N,N}(PPh₃)][CF₃SO₃] (8a), respectively, where the Pd-NMe₂ bond was retained.The reaction of the ligands 2-Br-4,5-(OCH₂O)C₆H₂C(H)N(2′-OH-5′-^tBuC₆H₃) (c) and 4,5-(OCH₂CH₂)C₆H₃C(H)N(2′-OH-5′-^tBuC₆H₃) (d) with Pd(OAc)₂ gave the tetranuclear complexes [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)N(2′-O-5′-^tBuC₆H₃)-C6,N,O}]₄ (1c) and [Pd{4,5-(OCH₂CH₂)C₆H₂C(H)N(2′-O-5′-^tBuC₆H₃)-C6,N,O}]₄ (1d), respectively. Treatment of 1c with PPh₃ in 1:4 molar ratio, gave the mononuclear species [Pd{2-Br-4,5-(OCH₂O)C₆HC(H)N(2′-(O)-5′-^tBuC₆H₃)-C6,N,O}(PPh₃)] (2c) with opening of the polynuclear structure after P-O_bridging bond cleavage.The structure of compounds 2a, 1c and 1d has been determined by X-ray diffraction analysis.     

Diamidato-bis(diphenylphosphino) platinum(II) complexes: Synthesis, characterization, and reactivity in the presence of acid

The reaction of Pt(COD)Cl₂, where COD is 1,5-cyclooctadiene, with one equivalent of a diamidato-bis(phosphino) Trost ligand ((R,R)-2 = N,N′-bis(2-diphenylphosphino-1-benzoyl)-(1R,2R)-1,2-diaminocyclohexane, (R,R)-3 = N,N′-bis(2-diphenylphosphino-1-naphthoyl)-(1R,2R)-1,2-diaminocyclohexane, or (±)-4 = N,N′-bis(2-diphenylphosphino-1-benzoyl)-1,2-bis(aminobenzene)) in the presence of base afforded square planar diamidato-bis(phosphino) platinum(II) complexes (R,R)-2-Pt, (R,R)-3-Pt, (±)-4-Pt. Characterization of all complexes included the solution and solid state structure determination of each complex based on multinuclear NMR and X-ray analyses, respectively. Stability of the complexes in acid was examined on addition of HCl to (R,R)-2-Pt in chloroform and compared to the unreactive nature of the similar diamidato-bis(phosphino) complex 1-Pt (1 = 1,2-bis-N-[2′-(diphenylphosphino)benzoyl]diamino-benzene) in the presence of acid. Protonation of the bound amidato nitrogen atoms of (R,R)-2-Pt was observed along with decoordination of the nitrogen atoms from the platinum(II) center producing (R,R)-2-PtCl₂ in quantitative yield by NMR analysis. Confirmation of the product was made on comparison of the NMR spectra to that of authentic (R,R)-2-PtCl₂ prepared on reaction of Pt(COD)Cl₂ with (R,R)-2 in CH₂Cl₂ and characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy. Results add to the knowledge of rich coordination chemistry of bis(phosphino) ligands with late transition metals, metal-amidato chemistry, and has implications in catalysis.     

A family of titanium (IV) alkoxo complexes with N,O and O,O chelating ligands. Crystal structure of [Ti(O-i-Pr)2{2-(−)-menthoxo-pyridine}2]

In view of the wide applicability and versatility of titanium based Lewis acids in selective organic synthesis including asymmetric synthesis, we have synthesized a family of mono and polyatomic titanium derivatives. The polymetallic complexes prepared are bridged by pyridimine, quinone and triazine based ligands. The synthesis of [{Ti(O-i-Pr)₃(Oddbf)}₂] (1), [Ti(O-i-Pr)₂(Oddbf)₂] (2), [{Ti(O-i-Pr)₂(Oddbf)(OMent)}₂] (3) (ddbfO = 2,3-dihydro-2,2-dimethyl-benzofuranoxo; MentO = (1R,2S,5R)-(−)-menthoxo), [{Ti(O-i-Pr)₃(OMenpy)}₂] (4), [Ti(O-i-Pr)₂(OMenpy)₂] (5) (MenpyO = (1S,2S,5R)-(−)-menthoxo-pyridine); [{(Ti(OR)₃)₂L}_n] (RO = isopropoxo, (1R,2S,5R)-(−)-menthoxo) (6-11) and [{(Ti(O-i-Pr)₃)₃L}_n] (12) was accomplished from a Lewis acid such as Ti(O-i-Pr)₄, [{Ti(O-i-Pr)₃(OMent)}₂] or [Ti(OMent)₄] and chelating ligands (ddbfOH = 2,3-dihydro-2,2-dimethyl-benzofuranol; MenpyOH = (1R,2S,5R)-(−)-5-methyl-2-isopropyl-1-(2′-pyridinyl)cyclohexan-1-ol; LH₂ = 4,6-dihydroxy-2,5-diphenyl-pyrimidine, 2,4-dihydroxy-5,6-dimethyl-pyrimidine, 5,8-dihydroxy-1,4-napthoquinone, 2,5-dihydroxy-1,4-benzoquinone and LH₃ = cyanuric acid) that provide a rigid framework for the metal centre. The molecular structure of 5 has been determined by single crystal X-ray diffraction studies.