Unsymmetrical Bidentate Ligands Research Articles

Highly Anisotropic Pd2Lab 2Lcc 2 and Pd2Lab 2Lcd 2 Type Cages by Heteromeric Completive Self-Sorting.

Pd(II)-based low-symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low-symmetry Pd2Lab 2Lcd 2-type cage. It was accomplished by high-fidelity integrative self-sorting of two different low-symmetry cages having Pd2Lab 4 and Pd4Lcd 8-type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non-statistical exclusive self-assembly of the Pd2Lab 2Lcd 2-type cage. By taking advantage of the complemental geometries between ligands, a low-symmetry Pd2Lab 2Lcc 2-type cage was also obtained. Heteromeric completive self-sorting of three homoleptic assemblies (Pd2Lab 4, Pd4Lcc 8 and Pd4Lcd 8-type cages) into an exclusive mixture of Pd2Lab 2Lcd 2 and Pd2Lab 2Lcc 2-type mixed ligated assemblies was demonstrated through cage-to-cage transformations.

Highly Anisotropic Pd2Lab2Lcc2 and Pd2Lab2Lcd2 Type Cages by Heteromeric Completive Self‐Sorting

AbstractPd(II)‐based low‐symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low‐symmetry Pd2Lab2Lcd2‐type cage. It was accomplished by high‐fidelity integrative self‐sorting of two different low‐symmetry cages having Pd2Lab4 and Pd4Lcd8‐type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non‐statistical exclusive self‐assembly of the Pd2Lab2Lcd2‐type cage. By taking advantage of the complemental geometries between ligands, a low‐symmetry Pd2Lab2Lcc2‐type cage was also obtained. Heteromeric completive self‐sorting of three homoleptic assemblies (Pd2Lab4, Pd4Lcc8 and Pd4Lcd8‐type cages) into an exclusive mixture of Pd2Lab2Lcd2 and Pd2Lab2Lcc2‐type mixed ligated assemblies was demonstrated through cage‐to‐cage transformations.

Synthesis, structure, and magnetic properties of lanthanide(III) complexes incorporating a tris-chelate cobalt(III) complex as a metalloligand

A series of CoIII–LnIII–CoIII trinuclear complexes [Ln{Co(Hmtimn)3}2](NO3)3 were prepared by following a simple one-pot synthesis method, mixing an unsymmetrical bidentate ligand 2-(2-imidazolinyl)-6-methoxypheol (H2mtimn) with Co(NO3)2·6H2O and LnX3· 6H2O (where Ln = La, Ce, Pr, Nd, Gd or Dy and X = NO3 − or Cl−) in methanolic solution in the presence of triethylamine in air. In the reaction mixture, this leads to the in situ formation of a tris-chelate CoIII metalloligand unit, which can coordinate LnIII ions through the interactions of phenolato- and methoxy-O donors. X-ray structural analysis revealed that the CoIII metalloligand functions as a rigid tripodal ligand to coordinate to a LnIII ion by six oxygen donors. The two metalloligands in the complex exhibit homochiral aggregation (ΔΔ or ΛΛ) upon coordination to the LnIII ion. The coordination of the central LnIII ion was found to be a distorted icosahedral geometry. Magnetic susceptibility measurements reveal that both cobalt and central lanthanide ions exist in trivalent states.

Slow Magnetic Relaxation in Cobalt(II) Complexes with One-Dimensional Hydrogen-Bonded Networks

Two new cobalt(II) complexes with an unsymmetrical bidentate ligand, 2-(1,4,5,6-tetrahydropyrimidin-2-yl)-6-methoxyphenol (H2mthp), were synthesized and crystallographically characterized. Tetra- and hexa-coordinate mononuclear complexes were selectively obtained by adjusting the stoichiometry of the base. The coordination geometry of hexa-coordinated complex was severely distorted from an ideal octahedron, due to the NO5 coordination environment from the mixed coordination of one Hmthp− and two H2mthp ligands. Both complexes formed one-dimensional chain networks by hydrogen-bond and N-H···π interactions. Single-molecule magnet behavior was observed for the tetrahedral complex under zero magnetic field. The relatively short Co···Co distances induced non-zero intermolecular magnetic coupling, which split the ground ±Ms levels to suppress quantum-tunneling of magnetization. In the octahedral complex, by contrast, the distance was not short enough to induce the coupling. As a consequence, single-molecule magnetic behavior was observed for the octahedral complex only in the presence of an external static field.

Solvent-dependent fac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part.

Tris–chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers, facial (fac) and meridional (mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of the fac/mer isomers of the triply helical FeII complexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example of fac/mer isomerism of a labile tris(2,2′-bipyridine) FeII complex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only the fac isomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.

Low-Symmetry Self-Assembled Coordination Complexes with Exclusive Diastereoselectivity: Experimental and Computational Studies.

A pyridine/aniline appended unsymmetrical bidentate ligand N-(4-(4-aminobenzyl)phenyl)nicotinamide, investigated in this work has two well-separated coordination sites. Combination of the ligand with cis-protected palladium(II) (i.e., PdL') and palladium(II) in separate reactions produced the corresponding Pd2L'2Lun2 and extremely rare Pd2Lun4 type self-assembled binuclear complexes, respectively. Notably, both varieties of complexes are prepared from a common ligand system. Two diastereomers (i.e., (2,0) and (1,1)-forms) are possible for Pd2L'2Lun2 type complex, whereas four diastereomers (i.e., (4,0), (3,1), trans(2,2), and cis(2,2)-forms) can be imagined for the Pd2Lun4 type complex. However, exclusive diastereoselectivity was observed, and the complexes formed belong to (1,1)-Pd2L'2Lun2 and cis(2,2)-Pd2Lun4 forms. The diastereomers are predicted from NMR study in solution and DFT calculations in gas-phase and implicit-solvent media; however, single-crystal structures of both the complexes provided unambiguous support. The rare Pd2Lun4 type complex is studied in further detail. Parameters like counteranion, concentration, temperature, and stoichiometry of metal to ligand did not influence the diastereoselectivity in complex formation. DFT calculations show the cis(2,2) form to be the most stable, followed by the (3,1) isomer. The lowest conformational strain in the bound ligand strands in the cis(2,2)-arrangement along with optimal intermolecular interactions makes it the energetically most stable of all the isomers. Molecular dynamics (MD) simulations were carried out to visualize the self-assembly process toward the formation of Pd2Lun4 type complex and the free energy difference between the cis(2,2) and (3,1) isomers. Snapshots of MD simulation elucidate the step-by-step progress of complexation leading to the cis(2,2)-isomer.

Unsymmetrical bidentate ligands as a basis for construction of ambidentate ligands for functional materials: Properties of 4,4-dimethyl-1-phenylpentane-1,3-dionate

To establish a background to the possible use of its ambidentate derivatives as stimulus-responsive ligands in functional complexes, the basic coordination chemistry of the anion derived from 4,4-dimethyl-1-phenylpentane-1,3-dione (benzoylpivaloylmethane, bpmH) has been re-examined with selected main group and transition metal M(II) and M(III) species. There is evidence that the steric bulk of the 1,3-dione substituents is not sufficient to prevent oligomerisation of the Ni(II) complex and equilibrium mixtures of geometric isomers can be detected in solution for at least the Al(III), Co(III) and Pd(II) complexes. Crystal structure determinations on both [Cu(bpm)2] and [Pd(bpm)2] show, however, that a single isomer can be isolated in the solid state.

Hydrogen-Bonded Supramolecular Structures of Cobalt(III) Complexes with Unsymmetrical Bidentate Ligands: mer/fac Interconversion Induced by Hydrogen-Bonding Interactions

Cobalt(III) complexes with three unsymmetrical bidentate ligands containing a noncoordinating N–H bond and a phenolate-O donor as hydrogen-bond donor and acceptor, respectively, were prepared and characterized. 1H NMR spectroscopy indicated that all the tris-chelate Co(III) complexes prepared favor the mer configuration in solution. [Co(Hthp)3] and [Co(Himn)3] also possess the mer configuration in the crystals (Hthp– = 2-(1,4,5,6-tetrahydropyrimidin-2-yl)phenolate, Himn– = 2-(2-imidazolinyl)phenolate). On the other hand, [Co(Himl)3] takes the fac configuration in the crystal (Himl– = 2-(2-imidazolyl)phenolate). These Co(III) complexes showed three types of characteristic supramolecular structures: ladder, distorted hexagonal sheet, and honeycomb sheet structure, constructed by intermolecular hydrogen bonds. Heating [Co(Himn)3] and [Co(Himl)3] in methanol selectively afforded precipitates of the fac isomer due to the low solubility of the hydrogen-bonded supramolecular structures. This mer to fac isomeriza...

Reversible Intramolecular Cyclization in Ruthenium Complexes Induced by Ligand-centered One-electron Transfer on Bidentate Naphthyridine: An Important Intermediate for Both Metal– and Organo–Hydride Species

Abstract Two types of dicarbonylruthenium(II) complexes bearing the unsymmetrical bidentate ligand 2-(2-pyridyl)-1,8-naphthyridine were prepared. The complexes undergo irreversible ligand-localized one-electron reduction to form redox-induced metallacyclization between the bidentate naphthyridyl ligand and the terminal CO ligand located nearby. Chemical reductions using NaBH4 were also performed to isolate the reaction products; the formation of both a metal–hydride (Ru–H) and an organo–hydride (C–H) species was confirmed.

Synthesis, structures and electrochemical and photophysical properties of anilido-benzoxazole boron difluoride (ABB) complexes.

A new series of four-ring-fused π-conjugated anilido-benzoxazole boron difluoride (ABB) dyes were synthesized by employing an unsymmetrical bidentate ligand under a mild reaction condition. X-ray structural analysis demonstrated that the four-ring-fused π-conjugated skeleton is nearly coplanar, and almost orthogonal to the side anilido phenyl group with dihedral angles of 74-86°. The synthesized complexes exhibit very bright luminescence in solution (Φf = 0.45-0.96 in CH2Cl2) and in the solid-state (Φf = 0.07-0.37). These complexes show a larger Stokes shift (56-128 nm) than the well-known boron dipyrromethene dyes (8-12 nm, in most cases). The role of molecular packing patterns elucidated by the assistance of their X-ray crystal structures rationalizes the solid-state fluorescence. One of the tested compounds displayed aggregation induced emission (AIE). First-principle-based quantum-chemical studies were carried out on complexes . Time-dependent DFT (TD-DFT) calculations support the experimental results. The participation of the anilido phenyl moiety and the fluorine atoms was found to be negligible in the LUMO orbitals.

Kinetic and Mechanistic Studies of Geometrical Isomerism in Neutral Square-Planar Methylpalladium Complexes Bearing Unsymmetrical Bidentate Ligands of α-Aminoaldimines

A series of hemilabile ligands of alpha-aminoaldimines and their methylpalladium complexes have been prepared and characterized. Neutral square-planar methylpalladium complexes in the form of [R(1)R(2)NCMe(2)CH horizontal lineNR]Pd(Me)Cl (R = Me, R(1) = R(2) = Me (3a); R = Me, R(1) = R(2) = Et (3b); R = Et, R(1) = R(2) = Me (4a); R = (n)Pr, R(1) = R(2) = Me (5a); R = (i)Pr, R(1) = R(2) = Me (6a); R = (i)Pr, R(1) = R(2) = Et (6b); R = (i)Pr, (R(1), R(2)) = c-C(4)H(8) (6c); R = (i)Pr, R(1) = (i)Pr, R(2) = H (6d); R = (i)Pr, R(1) = (t)Bu, R(2) = H (6e); R = (t)Bu, R(1) = R(2) = Me (7a); R = (t)Bu, R(1) = R(2) = Et (7b); R = (t)Bu, (R(1), R(2)) = c-C(4)H(8) (7c); R = (t)Bu, R(1) = (i)Pr, R(2) = H (7d); R = (t)Bu, R(1) = (t)Bu, R(2) = H (7e); R = Ph, R(1) = R(2) = Me (8a); R = Ph, R(1) = R(2) = Et (8b)) show geometrical isomerism. The relative ratios of trans/cis isomers appear to be predominated by the steric hindrance between the Pd-bound methyl group and imino or amino substituents (R and R(1) and R(2)). The NMR studies for the substitution reaction of (COD)Pd(Me)Cl with Et(2)NCMe(2)CH horizontal lineN(i)Pr at -20 degrees C indicate that cis-6b is the major kinetic product, which isomerizes to the thermodynamic product in trans form quantitatively above -5 degrees C. Kinetic results show that the ligand substitution reaction likely undergoes an associative pathway, and the isomerization reaction proceeds via an intramolecular process that comprises imine dissociation and recoordination.

Unsymmetrical bidentate ligands of α-aminoaldimines leading to sterically controlled selectivity of geometrical isomerism in square planar coordination

New alpha-aminoaldimines with the formula of Et(2)NCMe(2)CH[double bond, length as m-dash]NR (R = (i)Pr, (t)Bu, Ph) and their dichloro or diacetato complexes of Ni, Pd, Pt are prepared and structurally characterized. A nickel complex is in a distorted tetrahedral configuration, and the Pd and Pt complexes () are of square planar form. The alpha-aminoaldimines can chelate to the metal in a C(2)-unsymmetric bidentate motif through the hetero functionalities of amine and imine, which show comparable trans influence. Square planar organometallic palladium derivatives bearing alpha-aminoaldimines, including Pd-methyl, Pd-acetyl, and Pd-(eta(2)-acetylnorboryl) (), are also synthesized. The latter two species are a result of CO-insertion into Pd-methyl complexes and ensuing norbornene-insertion, respectively. The geometrical isomerism is found in the trans configuration in most studied cases. Such a stereoselectivity results from the thermodynamic stability governed predominantly by steric control. The stereoselectivity is also supported by DFT calculations.

Accelerated Arene Ligand Exchange in the (Arene)Cr(CO)2L Series

Arene ligand exchange in the (eta(6)-arene)Cr(CO)(2)L series can be accelerated if the ligand L is an electronically unsymmetrical bidentate ligand. The system evaluated here employs derivatives of tris(pyrrolyl)phosphine as L. A series of 2-L'-substituted pyrroles was prepared, where the substituents include: L' = -SMe, -CH(2)SMe, -SPh, -CH(2)SPh, -SCF(3), -S-tBu, -CO(2)Me, -CONMe(2), -2-pyridinyl, and -PPh(2). Reaction with ClP(pyrrolyl)(2) gave a new series of phosphines, (2-L'-pyrrolyl)(pyrrolyl)(2)P. Each of these phosphines was converted to (arene)Cr(CO)(2)[P(2-L'-pyrrolyl)(pyrrolyl)(2)P) complexes. The substituents L'are proposed to provide temporary coordination to the Cr and to lower the barrier to arene exchange. The series was evaluated where the arene in the complex (departing) is benzene, fluorobenzene, toluene, o-xylene, m-xylene, or p-xylene and the incoming arene is C(6)D(6), chlorobenzene-d(5), anisole-d(8), fluorobenzene-d(5), toluene-d(8), o-xylene-d(10), m-xylene-d(10), p-xylene-d(10), or mesitylene-d(12). Most of the new complexes showed a significant increase in the rate of arene exchange due to the side chain unit L'. The strongest effects were seen with the examples where X = -CO(2)Me, -CONMe(2), and -(2-pyridinyl), allowing exchange with a half lifetime as low as 8 h/22 degrees C.

Bis(2-chloro-5-methylpyridine-kappaN)bis(nitrato-kappa(2)O,O')copper(II).

In the molecule of the title compound, [Cu(NO(3))(2)(C(6)H(6)ClN)(2)], the Cu atom lies on an inversion centre and is six-coordinated by two pyridine N atoms and four nitrate O atoms in trans positions. The nitrate acts as an unsymmetrical bidentate ligand. The coordination geometry is octahedral, with the Cu-N and the two Cu-O distances being 1.9939 (16), 2.0246 (16) and 2.4866 (19) A, respectively. There are five types of C-H.O hydrogen bonds. Two of these generate two-dimensional molecular networks in the direction of the a axis, and the others connect adjacent molecular networks.

New mixed-donor unsymmetrical P–N–P ligands and their palladium(II) complexes

Unsymmetrical bidentate ligands R2P(E)-N(H)-P(E')R'(2) [R, R' = Ph, OPh, Pr-i; E, E' = O, S, Se] have been synthesised using the condensation reaction of an amino compound, R2P(E)NH2 [R = PhO, Ph; E = O, S, Se], with a phosphorus electrophile, R'P-2(E')CI [R' = Pr-i, Ph, OPh; E' = O, S, Se]. Deprotonated ligands (with (KOBu)-Bu-t) can be treated with Pd(OAC)(2) to give [Ph2P(S)-N-P(OXOPh)(2)](2)Pd, [(Pr2P)-Pr-i(S)-N-P(O)(OPh)(2)](2)Pd and [Ph2P(S)-N-P(S)(OPh)(2)](2)Pd, which show either four-membered or six-membered chelate rings. The new compounds were studied spectroscopically (NMR, IR and Raman) and by X-ray crystallography.

Mononuclear Ruthenium and Hetero-Tetranuclear Ruthenium-Silver Complexes Containing the Unsymmetrical Bidentate Ligands R2P(CH2)nER′2 (n = 1, 2; E = P, As) as Chelating or Bridging Units

The chelate complexes [(p-cym)RuCl(κ2-Ph2PCH2CH2-stBu2)]PF6 (3), [(arene)RuCl(κ2-Ph2PCH2CH2PR2)]PF6 (4, 7, 8) and [(p-cym)RuCl(κ2-iPr2PCH2AstBu2)]PF6 (11) were prepared either from [(arene)RuCl(NCMe)2]PF6 (1, 5) or from [(arene)RuCl2]2 (2, 6), in the presence of NH4PF6 or AgPF6. The stepwise reaction of [(p-cym)RuCl2]2 (2) with Ph2P-CH2CH2PtBu2 and AgPF6 gave the hetero-tetranuclear compound [{(p-cym)RuAg(μ-Cl)2(μ-P1Ru,P2Ag-Ph2P1CH2CH2P2-tBu2)}2](PF6)2 (9), the structure of which was determined by an X-ray crystal structure analysis. The bidentate As,O donor Ph2P(O)CH2CH2AstBu2 also reacted with 2, in the presence of AgPF6, to afford the chelate complex [(p-cym)RuCl{κ2(As,O)-Ph2P(O)CH2CH2AstBu2}]PF6 (10), which was also characterized crystallographically.

Mercury(II) and gold(III) derivatives of 2-phenyl pyridines and 2-phenyl-4-(methylcarboxylato)quinoline

ortho-Mercurated derivatives of several substituted 2-phenylpyridines and of 2-phenyl-4-(methylcarboxylato)quinoline have been prepared and characterised. C,N-chelated gold(III) derivatives, [AuCl 2(C 6H 4C 5H 3RN)] (R=H, 3-Me, 3,5-Me 2, 4-Pr n , 4-Bu t ) are prepared more efficiently by trans-metallation reactions than by direct reaction of AuCl 4 − with the phenylpyridines. The new gold complexes were characterised spectroscopically and a variety of substitution reactions have been effected. As is usual with unsymmetrical bidentate ligands, the softer donor atom is found trans to the N-donor of the pyridine unit. Crystal-structure determinations are reported for [Au(OAc)(pmpy)(py)]ClO 4, [Au(ppy)(dpbt)]BPh 4, [Au(ppy)(S 2CNMe 2)]BPh 4 and AuCl(pqcm) 2 [Hppy=2-phenylpyridine, Hpmpy=2-phenyl-3-methylpyridine, Hpqcm=2-phenyl-4-(methylcarboxylato)quinoline].

The X-ray crystal structures of ( O, O-2,3-dimethylbutylene and O, O-2-dimethylpropylene dithiophosphato)diphenyltellurium(IV) derivatives, Ph 2Te[S 2POCMe 2CMe 2O] 2 and 2Ph 2Te[S 2POCH 2CMe 2CH 2O] 2·2Ph 2TeCl 2·CS 2 and those of ( O, O-2,3-dimethylbutylene and O, O-2-dimethylpropylene dithiophosphoric acids, HS 2POCMe 2CMe 2O and HS 2POCH 2CMe 2CH 2O

The immediate environment about tellurium in Ph 2Te[S 2POCMe 2CMe 2O] 2 ( 1) and 2Ph 2Te[S 2POCH 2CMe 2CH 2O] 2·2Ph 2TeCl 2·CS 2 ( 2) is essentially that of a saw-horse structure in which the lone-pair is apparently stereochemically active and occupying an equatorial position in a distorted trigonal bipyramid. However, when the second sulfur atom of the unsymmetrical bidentate ligand is included in the coordination sphere, the arrangement about tellurium in compound 1 is better described as distorted octahedral and that in Ph 2Te[S 2POCH 2CMe 2CH 2O] 2 as distorted pentagonal pyramidal. An intermolecular association involving a chlorine atom of Ph 2TeCl 2 results in a pentagonal bipyramidal arrangement. Sulfur and chlorine bridges between the Te atoms of Ph 2Te[S 2POCH 2CMe 2CH 2O] 2 and Ph 2TeCl 2 indicate pseudo dimers or Te 2S 2Cl cages. The isolation of this mixed species rather than Ph 2TeCl[S 2POCH 2CMe 2CH 2O] was most unexpected. There is no indication of hydrogen bonding in HS 2POCMe 2CMe 2O ( 3) and HS 2POCH 2CMe 2CH 2O ( 4); even the shortest S–S internuclear distance, which is in compound 3, is 3.556(2) Å. In both acids, the P–SH bond is significantly longer than the PS terminal bond.

Synthetic and single-crystal X-ray diffraction studies of CH2I2 and aryl iodide complexes of silver carboxylates and β-diketonates

The silver(I) iodocarbon complexes [{Ag2(O2CCF3)2(CH2I2)2}n] 1, [{Ag2(O2CCF3)2(1,2-I2C6H4)2}n] 2, [{Ag2(O2CCF3)2(1,4-I2C6H4)2}n] 3, [{Ag2(O2CCF3)2(IC6H5)}n] 4, [{Ag4(O2CCF3)4(H2O)2(p-IC6H4Me)2}n] 5, [{Ag2(O2CCF3)2(1,2-I2C6H4)}n] 6, [{Ag2(O2CCCl3)2(HO2CCCl3)(1,2-I2C6H4)}n] 7, [{Ag2(O2CCCl3)2(HO2CCCl3)(IC6H5)}n] 8, [{Ag4(hfacac)4(p-IC6H4Me)2] 10 (hfacac = 1,1,1,5,5,5-hexafluoroaceylacetonate) and [Ag4(hfacac)4(1,2-I2C6H4)3] 11 have been prepared and structurally characterized by single-crystal X-ray diffraction. The silver carboxylate complexes all contain carboxylate-bridged Ag2(carboxylate-O,O′)2 dimers (Ag–O 2.22–2.40 A) with the intradimer Ag· · ·Ag distance varying in the range 2.9106(12) to 3.1527(14) A which are the values observed for the alternating dimer units Ag2(O2CCF3)2(H2O)2 and Ag2(O2CCF3)2 observed in 5. In the complexes 1–3 the silver trifluoroacetate dimers are linked by I,I′-bridging I2R ligands with one ‘short’ Ag–I bond (2.94–3.05 A) and one ‘long’ Ag–I bond (3.13–3.14 A) per silver. In 4, 7 and 8 the Ag2(carboxylate-O,O′)2 dimers are extended into a chain polymer via Ag2O2 rings formed by co-ordination of each silver to an oxygen atom (Ag–O 2.33–2.51 A) from an adjacent dimer. The 1,2-I2C6H4 forms an I,I′ bridge across the two silver atoms of the dimer unit in 7 [Ag–I 2.918(1) and 3.024(1) A]. Complex 8 contains an acute angle bridging IC6H5 [Ag–I 2.927(2) and 2.970(2) A, Ag–I–Ag 61.4(1)°], whilst in 4 the IC6H5 is semibridging [Ag–I 2.853(1) and 3.309(1) A]. In complex 5 the two structurally different dimer units are bridged in a wide-angle fashion by p-IC6H4Me [Ag–I 2.9200(9) and 2.9333(8) A, Ag–I–Ag 144.53(3)°]. Complex 6 contains eight-atom Ag2(O2CCF3-O,O′)2 rings linked to six-atom Ag2(O2CCF3-O,O′)(O2CCF3-O,O) rings which are interlinked to give an alternating 8646 ring chain polymer with I,I′-bridging 1,2-I2C6H4 across the two silvers of the six-atom rings [Ag–I 2.722(2) and 2.980(2) A]. The hfacac complex 10 contains a tetranuclear unit in which the hfacac ligands both chelate and bridge whilst the p-iodotoluenes each bridge two silvers via η1-iodocarbon and η2-aryl co-ordination. Complex 11 is a tetranuclear unit in which three hfacac ligands both chelate and bridge whilst the fourth hfacac ligand bridges two silvers and forms a monodentate interaction with a third silver in a µ-O, η1-O′ mode. One 1,2-I2C6H4 ligand forms a monodentate interaction with a silver atom [Ag–I 3.064(3) A] whilst the other two 1,2-I2C6H4 molecules function as highly unsymmetrical bidentate ligands [Ag–I 2.691(2), 3.350(2) and 2.719(2) and 3.228(2) A]. The Ag–I–C bond angles vary from 85.9(4)° in 11 to 108.70(12)° in 3.

Optically active transition metal compounds 112. Synthesis of chiral carbonylnitrosylcobalt complexes with bidentate PP ∗, PN ∗ and NN ∗ ligands

The substitution of two carbonyl groups in Co(CO) 3(NO) by optically active unsymmetrical bidentate ligands LL ∗ yields pairs of diastereomers Co(CO)(NO)(LL ∗), which differ only in the configuration at the Co atom. LL ∗ can be a bisphosphane, trisphosphane, phosphaneimine or pyridineimine. For the complexes 2 ( LL ∗ = ( S,S)-norphos), 3 ( LL ∗ = ( R)-1,2,4- triphos) and 4 ( LL ∗ = ( R)-1,2,5- triphos) the diastereomer ratios of 45:55 ( 2a:2b), 83:17 ( 3a:3b) and 63:37 ( 4a:4b) respectively indicate an optical induction from the ligand to the metal configuration during the synthesis. By crystallization it is possible to separate the diastereomers of 1 ( LL ∗ = ( R)- prophos ), 2 and 3, 1a and 3a are obtained as pure diastereomers, 2a as an enriched sample ( 2a:2b 73:27). The crystal structures and absolute configurations of ( S Co , R C )- 1a and ( S Co , R C )- 3a were determined by X-ray analysis. In 3a the cobalt center is configurationally stable at room temperature, whereas 1a epimerizes in benzene- d 6 at 35°C with a half-life of τ 1 2 = 141 min and 2a in CDCl 3 at 24°C with τ 1 2 = 160 min .