The stereoselective coordination chemistry of the helicating ligand N,N '-bis(-2,2 '-dipyridyl-5-yl)carbonyl-(S/R,S/R)-1,2-diphenylethylenediamine

Enantiomerically pure N,N'-bis(-2,2'-dipyridyl-5-yl)carbonyl-(S/R,S/R)-1,2-diphenylethylenediamine has been synthesised by linking two 2,2'-bipyridine units by (R,R)- and (S,S)-1,2-diphenylethylenediamine. The ligands possess a hindered rotation between the bipyridine chromophores, which are held together by intramolecular hydrogen bonds. ES mass spectroscopy confirmed that reaction with Fe(II), Co(III) and Cd(II) afforded dinuclear complexes. CD spectroscopy implied that enantiopure ligands conferred helicity to the metals centre giving a dominant triple helicate diastereoisomer (with the RR isomer giving a P helicate). H-1 NMR spectroscopy of the cadmium complex confirmed the presence of a single diastereoisomer. (C) 2003 Elsevier B.V. All rights reserved.

Stereoselective coordination chemistry of the tetradentate chelating ligand (2R,3R)-bis(2,2 '-dipyridyl-5-methoxyl) butane

The enantiomerically pure ligand L-3RR (2R, 3R)-bis(2,2'-dipyridyl-5-methoxyl) butane has been synthesised by linking two 2,2'-bipyridine units with (2R, 3R)-butandiol. The reaction of L-3RR with Zn(II) afforded a mononuclear species and the H-1 NMR spectroscopy points to a C-1 symmetry, expected for a distorted trigonal bipyramidal coordination environment. These observations were confirmed by MM2 calculations and electrospray mass spectrometry. The reaction of L-3RR with iron(II) indicated the formation of a dinuclear species by mass spectrometry. Solution state CD spectroscopy indicates that both complexes adopt a Lambda-configuration, implying a single stranded dinuclear iron(II) complex is present rather than the anticipated triple helical architecture.

Platinum bis-acetylide complexes with the 4,4'-dimethyl-2,2'-bipyridyl ligand

[Pt(Me(2)bipy)Cl-2](Me(2)bipy = 4,4'-dimethyl-2,2'-bipyridine) and HC=CC6H4-4-R react in the presence of diisopropylamine and CuI as catalyst to give the platinum bis-acetylides [Pt(Me(2)bipy)(C=CC6H4-4-R)(2)] R = H, Me, NO2. Initial spectroscopic, electrochemical and reactivity studies are presented. (C) 1997 Elsevier Science S.A.

PHOTOPERTURBATION OF THE (1)A-][-(5)T SPIN EQUILIBRIUM IN AN IRON(II) COMPLEX IN SOLUTION VIA LIGAND-FIELD EXCITATION

Variable-temperature magnetic susceptibility measurements in the solid state of the bis complex of tris(1-pyrazolyl)-methane with Fe(II), [Fe(tpm)2](ClO4)2, suggest the existence of singlet-quintet spin crossover with the singlet isomer largely favored at room temperature. In acetonitrile solution, measurement of the absorption spectrum as a function of temperature reveals a spin equilibrium with the quintet population varying from ca. 6% at 233 K to ca. 30% at 295 K. When the complex in solution is irradiated with a laser pulse at wavelengths within the ligand field absorption band of the singlet isomer, ground-state depletion occurs within the pulse duration followed by fast recovery to the original absorbance level with a time constant of 25 +/- 5ns. The recovery time is virtually independent of temperature over the range +23 to -43-degrees-C, but the signal:noise ratio of the transient signals increases with decreasing temperature. The effect was observable at several monitoring wavelengths spanning the LF and MLCT absorption regions of the complex but only when the irradiation wavelength fell within the LF absorption region. Irradiation within the MLCT band produced no effect other than that of laser pulse scatter. The observations are interpreted in terms of photoperturbation of the singlet-quintet spin state equilibrium, which in this case occurs solely through excitation in the ligand field absorption region of the complex and is the first reported instance of this type for a spin-crossover complex in solution.

Recyclable copper catalysts based on imidazolium-tagged bis(oxazolines): A marked enhancement in rate and enantioselectivity for Diels-Alder reactions in ionic liquid

Imidazolium-tagged bis(oxazolines) have been prepared and used as chiral ligands in the copper(II)-catalysed Diels-Alder reaction of N-acryloyl- and N-crotonoyloxazolidinones with cyclopentadiene and 1,3-cyclohexadiene in the ionic liquid 1-ethyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, [emim][NTf2]. A significant and substantial enhancement in the rate and enantioselectivity was achieved in [emim][NTf2] compared with dichloromethane. For example, complete conversion and enantioselectivities up to 95 % were obtained for the reaction between N-acryloyloxazolidinone and cyclopentadiene within 2 min in [emim][NTf2] whereas the corresponding reaction in dichloromethane required 60 min to reach completion and gave an ee of only 16 %. The enhanced rates obtained in the ionic liquid enabled a catalyst loading as low as 0.5 mol % to give complete conversion within 2 min while retaining the same level of enantioselectivity. The imidazolium-tagged catalysts can be recycled ten times without any loss in activity or enantioselectivity and showed much higher affinity for the ionic liquid phase during the recycle procedure than the analogous uncharged ligand.

Ruthenium complexes of the 1,4-bis(diphenylphosphino)-1,3-butadiene-bridged diphosphine 1,2,3,4-Me-4-NUPHOS: Solvent-dependent interconversion of four- and six-electron donor coordination and transfer hydrogenation activity

In chloroform, [RuCl2(nbd)(py)(2)] (1) (nbd = norbornadiene; py = pyridine) reacts with 1,4-bis(diphenylphosphino)-1,2,3,4-tetramethyl-1,3-butadiene (1,2,3,4-Me-4-NUPHOS) to give the dimer [Ru2Cl3(eta(4)-1,2,3,4-Me-4-NUPHOS)(2)]Cl (2a), whereas, in THF [RuCl2(1,2,3,4-Me-4-NUPHOS)(PY)(2)] (3) is isolated as the sole product of reaction. Compound 2 exists as a 4:1 mixture of two noninterconverting isomers, the major with C, symmetry and the minor with either C, or C-2 symmetry. A single-crystal X-ray analysis of [Ru2Cl3 (eta(4)-1,2,3,4-Me-4-NUPHOS)(2)] [SbF6] (2b), the hexafluoroantimonate salt of 2a, revealed that the diphosphine coordinates in an unusual manner, as a eta(4)-six-electron donor, bonded through both P atoms and one of the double bonds of the butadiene tether. Compounds 2a and 3 react with 1,2-ethylenediamine (en) in THF to afford [RuCl2(1,2,3,4-Me-4-NUPHOS)(en)] (4), which rapidly dissociates a chloride ligand in chloroform to give [RuCl(eta(4)-1,2,3,4-Me-4-NUPHOS)(en)] [Cl] (5a). Complexes 4 and 5a cleanly and quantitatively interconvert in a solvent-dependent equilibrium, and in THF 5a readily adds chloride to displace the eta(2)-interaction and re-form 4. A single-crystal X-ray structure determination of [RuCl(eta(4)-1,2,3,4-Me-4-NUPHOS)(en)][ClO4] (5b) confirmed that the diphosphine coordinates in an eta(4)-manner as a facial six-electron donor with the eta(2)-coordinated double bond occupying the site trans to chloride. The eta(4)-bonding mode can be readily identified by the unusually high-field chemical shift associated with the phosphorus atom adjacent to the eta(2)-coordinated double bond. Complexes 2a, 2b, 4, and 5a form catalysts that are active for transfer hydrogenation of a range of ketones. In all cases, catalysts formed from precursors 2a and 2b are markedly more active than those formed from 4 and 5a.

The structure of [Co(H-tptz)Cl-3] center dot H2O (tptz=2,4,6-tri(2-pyridyl)-1,3,5-triazine) prepared by crystallization from the ionic liquid, N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide

The structure of tris-chloro[2,6-bis(2'-pyridyl)-4-(2'-pyridinium)-1,3,5-triazine]cobalt(II) monohydrate, [Co(C18H13N6)Cl-3]center dot H2O (C2/c (No. 15), a = 7.783(11), b = 22.42(3), c = 11.001(15) angstrom, beta = 90.05(2)degrees), crystallized from the open air reaction of CoCl2 and 2,4,6-tri(2-pyridyl)-1,3,5-triazine in the ionic liquid, N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide is reported. The structure consists of six coordinate cobalt in an octahedral geometry bonded to the tridentate tptz ligand and three chlorines. The non-coordinating pyridyl group in the tptz ligand is protonated (with the protonated nitrogen crystallographically disordered over two possible sites), providing overall charge neutrality for the complex.

Bis(trifluoromethyl)mercury(II) complexes with purine and 3,5-dimethyl-4 '-amino-triazole as ligands, [Hg(CF3)(2)(Pur)](4) and [Hg(CF3)(2)(Dat)](2)

Colourless single crystals of [Hg(CF3)(2)(Pur)](4) and [Hg(CF3)(2)(Dat)](2) were obtained from aqueous and etheric solutions of the respective components Purine, (imidazo[4,5-d]pyrimidine, Pur), 3,5-dimethyl-4 '-amino-triazole (Dat) and bis(trifluoromethyl)mercury(II), Hg(CF3)(2). [Hg(CF3)(2)(Pur)](4) crystallizes with the tetragonal system (P-4, Z = 8, a = 1486.8(2), c = 1026.2(l) pm, R-all = 0.0657) with tetrameric molecules consisting of four purine molecules bridged by slightly bent Hg(CF3)2 molecules forming a cage with the CF3 ligands surrounding this cage. The two modifications of [Hg(Dat)(CF3)2]2 (1: 170 K, triclinic, P-1, Z = 2, a 814.9(2), b = 845.4(2), c = 968.4(3) pm, alpha = 106.55(2)degrees, beta= 103.41(2)degrees, gamma = 110.79(2)degrees, R-all = 0.1189; II: monoclinic, P2(1)/c, Z = 8, a = 879.8(2), b = 1731.0(3), c = 1593.9(3) pm, beta = 106.89(2)degrees, R-all = 0.1199) both contain dimeric molecules that are stacked parallel to one crystal axis to strands which are arranged in a parallel fashion in I and rotated against each other in 11 by 110 degrees. In both, the tetrameric [Hg(CF3)(2)(Pur)](4) and the dimeric [Hg(CF3)(2)(Dat)](2) the Hg(CF3)(2) molecules are slightly bent (around 167 and 170 degrees) and rather weakly attached to the N-donor ligands Pur and Dat with Hg-N distances around 272 pm, although in both cases the Hg atoms bridge between two ligand molecules.

Sequential C-H and C-Ru bond formation and cleavage during the thermally induced rearrangement of aryl ruthenium(II) complexes with [C6H3(CH2NMe2)(2)-2,6](-) as a bidentate eta(2)-C,N coordinated ligand. The crystal structures of the isomeric pairs [RuCl{eta(6)-C10H14}{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,n}] (n = 4 or 6) and [Ru(eta(5)-C5H5){(eta(2)-C,N-C6H3(CH2NMe2)(2)-2,n} (PPH3)] (n = 4 or 6)

New air-stable ruthenium(II) complexes that contain the aryldiamine ligand [C6H3(CH2-NMe2)(2)-2,6](-) (NCN) are described. These complexes are [RuCl{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,6}(eta(6)-C10H14)] (2; C10H14 = p-cymene = C6H4Me-Pr-i-4), [Ru{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,6}(eta(5)-C5H5)(PPh3)] (5), and their isomeric forms [RuCl{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,4}(eta(6)-C10H14)] (3) and [Ru{eta(2)-C,N-C6H3(CH2NMe2)(2)-2,4}(eta(5)-C5H5)(PPh3)] (6), respectively. Complex 2 has been prepared from the reaction of [Li(NCN)](2) with [RuCl2(eta(6)-C10H14)](2), whereas complex 5 has been prepared by the treatment of [RuCl{eta(3)-N,C,N-C6H3(CH2NMe2)(2)-2,6}(PPh3)] (4) with [Na(C5H5)](n). Both 2 and 5 are formally 18-electron ruthenium(II) complexes in which the monoanionic potentially tridentate coordinating ligand NCN is eta(2)-C,N-bonded, In solution (halocarbon solvent at room temperature or in aromatic solvents at elevated temperature), the intramolecular rearrangements of 2 and 5 afford complexes 3 and 6, respectively. This is a result of a shift of the metal-C-aryl bond from position-1 to position-3 on the aromatic ring of the NCN ligand. The mechanism of the isomerization is proposed to involve a sequence of intramolecular oxidative addition and reductive elimination reactions of both aromatic and aliphatic C-H bonds. This is based on results from deuterium labeling, spectroscopic studies, and some kinetic experiments. The mechanism is proposed to contain fully reversible steps in the case of 5, but a nonreversible step involving oxidative addition of a methyl NCH2-H bond in the case of 2. The solid-state structures of complexes 2, 3, 5, and 6 have been determined by single-crystal X-ray diffraction. A new dinuclear 1,4-phenylene-bridged bisruthenium(II) complex, [1,4-{RuCl(eta(6)-C10H14)}(2){C-6(CH2NMe2)(4)-2,3,5,6-C,N,C',N'}] (9) has also been prepared from the dianionic ligand [C-6(CH2NMe2)(4)-2,3,5,6](2-) (C2N4). The C2N4 ligand is in an eta(2)-C,N-eta(2)-C',N'-bis(bidentate) bonding mode. Compound 9 does not isomerize in solution (halocarbon solvent), presumably because of the absence of an accessible C-aryl-H bond. Complex 9 could not be isolated in an analytically pure form, probably because of its high sensitivity to air and very low solubility, which precludes recrystallization.

Diphosphine analogues of proton sponge: X-ray crystal structure of [Pd(eta(3)-allyl)(dppn)]BF4 center dot CH2Cl2 (dppn equals 1,8-bis(diphenylphosphino)naphthalene)

The X-ray crystal structure of [Pd(eta(3)-allyl)(dppn)]BF4 . CH2Cl2 (1) where dppn = 1,8-bis(diphenylphosphino)naphthalene is reported. Comparison of the conformation of the ligand in 1 with that in the free state shows that there is a relief of strain on complexation analogous to the relief of strain observed upon protonation of proton sponge.

Long-range electronic coupling in bis(cyclometalated) ruthenium complexes

Symmetrical and unsymmetrical ligands containing terpyridyl coordinating units (N, N, N) or a cyclometalating equivalent (N, C, N), connected back-to-back either directly or via a p-terphenylene or 1,3-phenylene spacer, have been used to construct new diruthenium complexes. These compounds incorporate various terdentate chelates as capping ligands, to allow a double control of the electronic properties of each subcomplex and of the ensemble: via the terminal ligand or through the bridging fragment. Electronic coupling was studied from the intervalence transitions observed in several bimetallic ruthenium complexes of the bis-(cyclometalated) type differing by the substitution of a nitrogen atom by carbon in the terminal terpyridyl unit. The largest metal-metal interaction was found in complexes for which the terminal complexing unit is of the 1,3-di-2-pyridylbenzene type, i.e., with the carbon atom located on the metal-metal C-2 axis of the molecule. Investigations of the mechanism of interaction by extended Huckel calculations showed that the replacement of nitrogen by carbon raises the filled ligand levels, increasing the mixing with ligand orbitals and thus the metal-metal coupling. Finally, the intervalence transition was still observed for a bridging ligand containing three phenylene units as spacers, corresponding to a 24-Angstrom metal-metal distance.

One-pot two-step mechanochemical synthesis: ligand and complex preparation without isolating intermediates

Although the use of ball milling to induce reactions between solids (mechanochemical synthesis) can provide lower-waste routes to chemical products by avoiding solvent during the reaction, there are further potential advantages in using one-pot multistep syntheses to avoid the use of bulk solvents for the purification of intermediates. We report here two-step syntheses involving formation of salen-type ligands from diamines and hydroxyaldehydes followed directly by reactions with metal salts to provide the corresponding metal complexes. Five salen-type ligands 2,2'-[1,2-ethanediylbis[(E)-nitrilomethylidyne]] bisphenol, ` salenH2', 1; 2,2'-[(+/-)-1,2-cyclohexanediylbis-[(E)-nitrilomethylidyne]] bis-phenol, 2; 2,2'-[1,2-phenylenebis( nitrilomethylidyne)]-bis-phenol, ` salphenH2' 3; 2-[[(2-aminophenyl) imino] methyl]-phenol, 4; 2,2'-[(+/-)-1,2-cyclohexanediylbis[(E)-nitrilomethylidyne]]-bis[4,6-bis(1,1-dimethylethyl)]-phenol, ` Jacobsen ligand', 5) were found to form readily in a shaker-type ball mill at 0.5 to 3 g scale from their corresponding diamine and aldehyde precursors. Although in some cases both starting materials were liquids, ball milling was still necessary to drive those reactions to completion because precipitation of the product and or intermediates rapidly gave in thick pastes which could not be stirred conventionally. The only ligand which required the addition of solvent was the Jacobsen ligand 5 which required 1.75 mol equivalents of methanol to go to completion. Ligands 1-5 were thus obtained directly in 30-60 minutes in their hydrated forms, due to the presence of water by-product, as free-flowing yellow powders which could be dried by heating to give analytically pure products. The one-armed salphen ligand 4 could also be obtained selectively by changing the reaction stoichiometry to 1 : 1. SalenH(2) 1 was explored for the onepot two-step synthesis of metal complexes. In particular, after in situ formation of the ligand by ball milling, metal salts (ZnO, Ni(OAc)2 center dot 4H(2)O or Cu(OAc)(2)center dot H2O) were added directly to the jar and milling continued for a further 30 minutes. Small amounts of methanol (0.4-1.1 mol equivalents) were needed for these reactions to run to completion. The corresponding metal complexes [M(salen)] (M = Zn, 6; Ni, 7; or Cu, 8) were thus obtained quantitatively after 30 minutes in hydrated form, and could be heated briefly to give analytically pure dehydrated products. The all-at-once ` tandem' synthesis of [Zn(salen)] 6 was also explored by milling ZnO, ethylene diamine and salicylaldehyde together in the appropriate mole ratio for 60 minutes. This approach also gave the target complex selectively with no solvent needing to be added. Overall, these syntheses were found to be highly efficient in terms of time and the in avoidance of bulk solvent both during the reaction and for the isolation of intermediates. The work demonstrates the applicability of mechanochemical synthesis to one-pot multi-step strategies.

Bis(1,4,7-trithiacyclononane-S,S ',S '')nickel(II) dibromide tetrahydrate

The Ni-II centre in the cation of the title compound, [Ni(C6H12S3)(2)]Br-2. 4H(2)O, occupies a crystallographic inversion centre and is octahedrally coordinated by six S-donors from two [9]aneS(3) ligands. Ni-S distances range from 2.3749 (16) to 2.4077 (15) Angstrom and S-Ni-S angles where both thia donors belong to the same ligand lie in a narrow range between 88.09 (5) and 88.67 (6)degrees. The water molecules participate in extensive hydrogen bonding with each other and with the Br- anions to form double chains with eight- and 12-membered hydrogen-bonded rings running along the crystallographic a direction.