Switchable thiophene coordination in Ru(II) bipyridyl phosphinoterthiophene complexes

Switching between P,S- and P,C coordination modes of 3'-phosphinoterthiophene to Ru(II) results in substantial differences in the electronic spectra and cyclic voltammetry of these complexes.     

Azetidines as ligands in the Pd(II) complexes series

The preparation of palladium (II) complexes having sterically congested azetidines as ligands is described. Diastereomerically pure α-alkylamino and α-alkylimino azetidines react with Na₂PdCl₄ to afford the corresponding bidendate Pd(II) complexes, whereas 2-cyano azetidines can be used to access bidendate Pd(II) complexes containing an amino-imidate moiety. Preliminary study of the catalytic activity of these new complexes in the Suzuki cross-coupling reaction is presented.     

Four- and five-coordinate copper(II) complexes containing mixed ligands

New copper(II) complexes of general formula, Cu(ONS)B (ONS = the di-negatively charged Schiff base, S-benzyl-β-N-(2-hydroxyphenyl) methylendithiocarbazate; B = pyridine, 2,2′-dipyridyl or 1,10-phenanthroline) have been synthesized and characterised by magnetic and spectroscopic measurements. The complex, Cu(ONS)py is four-coordinate and square-planar. Magnetic and spectroscopic data support a five-coordinate, presumably, a trigonal-bipyramidal structure for the [Cu(ONS)dipy] and (Cu(ONS)phen] complexes     

Achiral banana-shaped mesogenic bidentate ligands and their Cu(II) and Pd(II) complexes

The first achiral bent-core banana-shaped bidentate ligands and their Cu(II) and Pd(II) metal complexes have been synthesized and investigated for mesomorphic behaviour. The bidentate ligands exhibit only one enantiotropic mesophase. The ligand having C 6 -alkoxy chains shows a mesophase that has been assigned as a two-dimensional B 1 phase while the C 8 and C 10 homologues stabilize the fluid B 2 mesophase showing antiferroelectric switching characteristics. In constrast, their corresponding Cu(II) and Pd(II) metal complexes are non-mesomorphic.     

Achiral banana-shaped mesogenic bidentate ligands and their Cu(II) and Pd(II) complexes

The first achiral bent-core banana-shaped bidentate ligands and their Cu(II) and Pd(II) metal complexes have been synthesized and investigated for mesomorphic behaviour. The bidentate ligands exhibit only one enantiotropic mesophase. The ligand having C6 -alkoxy chains shows a mesophase that has been assigned as a two-dimensional B1 phase while the C8 and C10 homologues stabilize the fluid B2 mesophase showing antiferroelectric switching characteristics. In constrast, their corresponding Cu(II) and Pd(II) metal complexes are non-mesomorphic.     

Fluxional five-coordinate platinum(II) complexes containing chelating triphosphine ligands

Platinum(II) dimethyl complexes of the three triphosphines PhP(CH₂CH₂CH₂PPh₂)₂, PhP(CH₂CH₂PPh₂)₂, and PhP(CH₂CH₂PMe₂)₂ have been shown by ³¹P NMR to undergo exchange of the terminal phosphino groups. An exchange route involving a five-coordinate platinum(II) complex is proposed.     

Palladium(II)-allyl complexes containing chiral N-donor ferrocenyl ligands

A study of the reactivity of enantiopure ferrocenylimine (S_C)-[FcCHN-CH(Me)(Ph)] {Fc =  (η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-} (1a) with palladium(II)-allyl complexes [Pd(η³-1R¹,3R²-C₃H₃)(μ-Cl)]₂ {R¹ = H and R² = H (2), Ph (3) or R¹ = R² = Ph (4)} is reported. Treatment of 1a with 2 or 3 {in a molar ratio Pd(II):1a = 1} in CH₂Cl₂ at 298 K produced [Pd(η³-3R²-C₃H₄){FcCHN-CH(Me)(Ph)}Cl] {R² = H (5a) or Ph (6a)}. When the reaction was carried out under identical experimental conditions using complex 4 as starting material no evidence for the formation of [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (S_C)-[FcCHN-CH(R³)(CH₂OH)] {R³ = Me (1b) or CHMe₂ (1c)} with complex 4 showed the importance of the bulk of the substituents on the palladium(II) allyl-complex (2-4) or on the ferrocenylimines (1) in this type of reaction. The crystal structure of 5a showed that: (a) the ferrocenylimine adopts an anti-(E) conformation and behaves as an N-donor ligand, (b) the chloride is in acis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η³-fashion. Solution NMR studies of 5a and 6a and [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(CH₂OH)}Cl] (7b) revealed the coexistence of several isomers in solution. The stoichiometric reaction between 6a and sodium diethyl 2-methylmalonate reveals that the formation of the achiral linear trans-(E) isomer of Ph-CHCH-CH₂Nu (8) was preferred over the branched derivative (9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine (S_C)-H₂N-CH(Me)(Ph) (11) as catalysts in the allylic alkylation of (E)-3-phenyl-2-propenyl (cinnamyl) acetate with the nucleophile diethyl 2-methylmalonate (Nu⁻) is reported.     

Charge-transfer luminescence from ruthenium(II) complexes containing tridentate ligands

Four complexes of the general formula Ru(NNN)²⁺₂ (N NN = tridentate N-heterocyclic ligand) were synthesized and studied spectroscopically. All exhibit visible absorption spectra that are charge-transfer-to-ligand in origin, are luminescent in glasses at 77 K, and display emission spectra that possess energies, structures, and decay tines that label them as charge transfer.     

Ni(II), Pd(II) and Pt(II) complexes of PNP and PSP tridentate amino-phosphine ligands

The ligands D((CH(2))(2)NHPiPr(2))(2) (D = NH 1, S 2) react with (dme)NiCl(2) or (PhCN)(2)MCl(2) (M = Pd, Pt) to give complexes of the form [D((CH(2))(2)NHPiPr(2))(2)MX]X (X = Cl, I; M = Ni, Pd, Pt) which were converted to corresponding iodide derivatives by reaction with Me(3)SiI. Reaction of 1 or 2 with (COD)PdMeCl affords facile routes to [κ(3)P,N,P-NH((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (8a) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)PdMe]Cl (9a) in high yields. An alternative synthetic approach involves oxidative addition of MeI to a M(0) precursor yielding [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)NiMe]I (10), [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 8b Pt 11) and [κ(3)P,S,P-S(CH(2)CH(2)NHPiPr(2))(2)MMe]I (M = Pd 9b, Pt 12). Alternatively, use of NEt(3)HCl in place of MeI produces the species [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MH]X (X = Cl, M = Ni 13a, Pd 14a, Pt 16a). The analogs containing 2; [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)MH]X (M = Pd, X = PF(6)15: M = Pt, X = Br, 17a, PF(6)17b) were also prepared in yields ranging from 74-93%. In addition, aryl halide oxidative addition was also employed to prepare [κ(3)P,N,P-HN(CH(2)CH(2)NHPiPr(2))(2)MC(6)H(4)F]Cl (M = Ni 18, Pd 19) and [κ(3)P,S,P-S((CH(2))(2)NHPiPr(2))(2)Pd(C(6)H(4)F)]Cl (20). Crystal structures of 3a, 4a, 5a, 6a, 8a, 9a, 14b and 16b are reported.     

Novel chiral dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal complexes

The synthesis and characterization of cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens are reported in detail. To understand structure-property relationships in these materials the terminal alkoxy chains and the central metal atom have been varied. Our studies reveal that chiral dimesogenic bidentate ligands with n-butyloxy chains exhibit smectic A (SmA), twist grain boundary and chiral nematic (N*) mesophases while substitution with either n -decyloxy or 3,7-dimethyloctyloxy chains also show a ferroelectrically switchable chiral smectic C (SmC*) mesophase. The metal complexes with n-butyloxy chains show only the SmA phase whereas higher chain length derivatives exhibit N* phase irrespective of the metal atom present. The ligands are thermally stable whereas their metal complexes, especially Pd(II) systems, seem to be heat sensitive. Spontaneous polarization, response time and tilt angle measurements have been carried out in the smectic C* phase of the two ligands.     

Novel chiral dimesogenic bidentate ligands and their Cu(II) and Pd(II) metal complexes

The synthesis and characterization of cholesterol-based dimesogenic bidentate ligands and their Cu(II) and Pd(II) metallomesogens are reported in detail. To understand structure-property relationships in these materials the terminal alkoxy chains and the central metal atom have been varied. Our studies reveal that chiral dimesogenic bidentate ligands with n -butyloxy chains exhibit smectic A (SmA), twist grain boundary and chiral nematic (N * ) mesophases while substitution with either n -decyloxy or 3,7-dimethyloctyloxy chains also show a ferroelectrically switchable chiral smectic C (SmC * ) mesophase. The metal complexes with n -butyloxy chains show only the SmA phase whereas higher chain length derivatives exhibit N * phase irrespective of the metal atom present. The ligands are thermally stable whereas their metal complexes, especially Pd(II) systems, seem to be heat sensitive. Spontaneous polarization, response time and tilt angle measurements have been carried out in the smectic C * phase of the two ligands.     

Preparation and characterization of dinuclear Pd(II) complexes of binucleating tetraaza-thiophenolate ligands

The thioethers 4-tert-butyl-2,6-bis((2-(dimethylamino)ethylimino)methyl)phenyl(tert-butyl)sulfane (tBu-L3) and 4-tert-butyl-2,6-bis((2-(dimethylamino)ethylimino)methyl)phenyl(tert-butyl)sulfane (tBu-L4) react with PdCl2(NCMe)2 to give the dinuclear palladium thiophenolate complexes [(L3)Pd2Cl2]+ (2) and [(L4Pd2(mu-Cl)]2+ (3) (HL3= 2,6-bis((2-(dimethylamino)ethylimino)methyl)-4-tert-butylbenzenethiol, HL4 = 2,6-bis((2-(dimethylamino)ethylamino)methyl)-4-tert-butylbenzenethiol). The chloride ligands in could be replaced by neutral (NCMe) and anionic ligands (NCS-, N3-, CN-, OAc-) to give the diamagnetic Pd(II) complexes [(L3)Pd2(NCMe)2]3+ (4), [(L3)Pd2(NCS)2]+ (5), [(L3)Pd2(N3)2]+ (6), [{(L3)Pd2(mu-CN)}2]4+ (7) and [(L3)Pd2(OAc)]2+ (9). The nitrile ligands in and in [(L3)Pd2(NCCH2Cl)2]3+ are readily hydrated to give the corresponding amidato complexes [(L3)Pd2(CH3CONH)]2+ (8) and [(L3)Pd2(CH2ClCONH)]2+ (10). The reaction of [(L3)Pd2(NCMe)2]3+ with NaBPh4 gave the diphenyl complex [(L3)Pd2(Ph)2]+ (11). All complexes were either isolated as perchlorate or tetraphenylborate salts and studied by IR, 1H and 13C NMR spectroscopy. In addition, complexes 2[ClO4], 3[ClO4]2, 5[BPh4], 6[BPh4], 7[ClO4]4, 9[ClO4]2, 10[ClO4]2 and 11[BPh4] have been characterized by X-ray crystallography.     

Neutral and cationic alkylmanganese(II) complexes containing 2,6-bisiminopyridine ligands

Manganese alkyl complexes stabilised by 2,6-bis(N,N'-2,6-diisopropyl-phenyl)acetaldiminopyridine ((iPr)BIP) have been selectively prepared by reacting suitable alkylmanganese(II) precursors, such as homoleptic dialkyls [(MnR(2))(n)] or the corresponding THF adducts [{MnR(2)(thf)}(2)] with the mentioned ligand. For R=CH(2)CMe(2)Ph or CH(2)Ph, formally Mn(I) derivatives are produced, in which one of the two R groups migrates to the 4-position of the central pyridine ring in the (iPr)BIP ligand. In contrast, a true dialkyl complex [MnR(2)((iPr)BIP)] can be isolated for R=CH(2)SiMe(3). In solution, this compound slowly evolves to the corresponding Mn(I) monoalkyl derivative. A detailed study of this reaction provides insights on its mechanism, showing that it proceeds through successive alkyl migrations, followed by spontaneous dehydrogenation. Protonation of [Mn(CH(2)SiMe(3))(2)((iPr)BIP)] with the pyridinium salt [H(Py)(2)][BAr'(4)] (Ar'=3,5-C(6)H(3)(CF(3))(2)) leads to the cationic species [Mn(CH(2)SiMe(3))(Py)((iPr)BIP)](+). Alternatively, the same complex can be produced by reaction of the pyridine complex [{Mn(CH(2)SiMe(3))(2)(Py)}(2)] with the protonated ligand salt [H(iPr)BIP](+)[BAr'(4)](-). This last reaction allows the synthesis of analogous cationic alkylmanganese(II) derivatives, when precursors of type [MnR(2)((iPr)BIP)] are not available. Treatment of these neutral and cationic (iPr)BIP alkylmanganese derivatives with a range of typical co-catalysts (modified methylaluminoxane (MMAO), B(C(6)F(5))(3), trimethyl or triisobutylaluminum) does not lead to active ethylene polymerisation catalysts.     

Novel dinuclear platinum(II) complexes containing mixed nitrogen-sulfur donor ligands

A series of novel dinuclear platinum(II) complexes were synthesized containing a mixed nitrogen-sulfur donor bidentate chelate system in which the two platinum centers are connected by an aliphatic chain of variable length. The bidentate chelating ligands were selected to stabilize the complex toward decomposition. The pK(a) values and reactivity of the four synthesized complexes, namely, [Pt(2)(S(1),S(4)-bis(2-pyridylmethyl)-1,4-butanedithioether)(OH(2))(4)](4+) (4NSpy), [Pt(2)(S(1),S(6)-bis(2-pyridylmethyl)-1,6-hexanedithioether)(OH(2))(4)](4+) (6NSpy), [Pt(2)(S(1),S(8)-bis(2-pyridylmethyl)-1,8-octanedithioether)(OH(2))(4)](4+) (8NSpy), and [Pt(2)(S(1),S(10)-bis(2-pyridylmethyl)-1,10-decanedithioether)(OH(2))(4)](4+) (10NSpy), were investigated. This system is of special interest because only little is known about the substitution behavior of dinuclear platinum complexes that contain a bidentate chelate that forms part of the aliphatic bridging ligand. Moreover, the ligands as well as the dinuclear complexes were examined in terms of their cytotoxic activity, and the 10NSpy complex was found to be active. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of all the coordinated water molecules. The substitution of coordinated water by thiourea was studied under pseudo-first-order conditions as a function of nucleophile concentration, temperature, and pressure, using stopped-flow techniques and UV-vis spectroscopy. The results for the dinuclear complexes were compared to those for the corresponding mononuclear reference complex [Pt(methylthiomethylpyridine)(OH(2))(2)](2+) (Pt(mtp)), by which the effect of the increasing aliphatic chain length of the bridged complexes could be investigated. The results indicate that there is a clear interaction between the two platinum centers, which becomes weaker as the chain length between the metal centers increases. Furthermore, differences and similarities of the N,S-system were compared to the corresponding dinuclear N,N-system studied previously in our group. In addition, quantum chemical calculations were performed to support the interpretation and discussion of the experimental data.     

Dirhodium(II) dicarboxylato complexes containing carbonyl and C-bonded methoxycarbonyl ligands

Oxidation of rhodium(I) carbonyl chloride, [Rh(CO)₂Cl]₂, with copper(II) acetate or isobutyrate in methanol solutions yields binuclear double carboxylato bridged rhodium(II) complexes with RhRh bonds, [Rh(μ-OOCRκO)(COOMeκC)(CO)(MeOH)]₂, where R=CH₃ or i-C₃H₇. According to X-ray data, surrounding of each rhodium atom in these complexes is close to octahedral and consists of another rhodium atom, two oxygens of carboxylato ligands, terminal carbonyl group, C-bonded methoxycarbonyl ligand, and axial CH₃OH. Methoxycarbonyl ligand is shown to originate from CO group of the parent [Rh(CO)₂Cl]₂ and OCH₃ group of solvent. N- and P-donor ligands L (p-CH₃C₆H₄NH₂, P(OPh)₃, PPh₃, PCy₃) readily replace the axial MeOH yielding [Rh(μ-OOCRκO)(COOMeκC)(CO)(L)]₂. The X-ray data for the complex with R=i-C₃H₇, L=PPh₃ showed the same molecular outline as with L=MeOH. Electronic effects of axial ligands L on the spectral parameters of terminal carbonyl group are essentially the same as in the known series of rhodium(I) complexes (an increase of δ¹³C and a decrease of ν(CO) with strengthening of σ-donor and weakening of π-acceptor ability of L).     

New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties

The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear Pd^II-complex [(PPh₃)Pd(HL1)Cl]Cl·2CH₃CN (1). The complex [(PPh₃)Pd(HL1)I]Cl·1/2H₂O (2) was prepared via halogen exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) complex containing singly deprotonated HL1, [(PPh₃)₂ClPd(L1)Pd(PPh₃)Cl]Cl·1/3H₂O·CH₃OH (3), was prepared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of sodium acetate in methanol.     

Preparation and crystallographic characterization of Pd(II) complexes containing imidobis(diphenylthiophosphinato) ligand

The reactions of PdCI₂(L-L) [L-L = Ph₂PCH₂PPh₂(dppm), Ph₂PCH₂CH₂PPh₂(dppe) and Ph₂PCH₂CH₂CH₂PPh₂(dppp)] with equivalent amount of (Ph₂P(S)NHP(S)Ph₂)(dppaS₂) gave the complexes [Pd(L-L)(dppaS₂-H)]ClO₄ [L-L = dppm (1), dppe (2), dppp (3)]. The different synthetic route was used for complex 2 by using of Pd(dppe)Cl₂ and K[N(PSPh₂)₂] as starting materials (2a). All of these complexes have been characterized ³¹P{¹H} NMR, IR and elemental analyses. The complexes 2, 2a and 3 were crystallographically characterized. The coordination geometry around the Pd atoms in these complexes distorted square planar. Six membered dppaS₂-H rings are twist boat conformations in three complexes.     

Synthesis and reactivity of water-soluble platinum(II) complexes containing nitrogen ligands

A series of water-soluble platinum(II) complexes containing bidentate imino pyridine ligands L of the general formula LPtX₂ (X=Cl or Me) have been prepared. The dichloro complexes are very stable in water or dimethyl sulfoxide (DMSO), even at elevated temperatures, whereas the dimethyl complexes are less stable in these strongly polar solvents. In DMSO, an equilibrium between the complex LPtMe₂ and (DMSO)₂PtMe₂ is observed, whereas in water decomposition is observed within 1 day at room temperature.