Wilberth J. J. Smeets

Synthesis, spectroscopic properties and X-ray crystal structures of two dinuclear alkoxo-bridged copper(II) compounds with the ligand bis(1-methyl-2-benzimidazolyl) propane. A unique alkoxo-bridged Cu(II) dinuclear compound with an additional bidentate bridging triflate anion

Abstract Based on the new ligand bis(1-methyl-2-benzimidazolyl) propane (abbreviated as mtbz) several new copper(II) coordination compounds have been prepared and characterized structurally and spectroscopically. Two representative compounds, i.e. [Cu 2 (mtbz) 2 (CH 3 ) 2 - (CF 3 SO 3 )](CF 3 SO 3 ) ( 1 ) and [Cu 2 (mtbz) 2 (CH 3 O) 2 ](ClO 4 ) 2 ( 4 ) were characterized structurally by X-ray diffraction. Crystal data for 1 : monoclinic, space group P 2 1 / c , a=13.6585(5), b=39.981(3), c=20.919(1) A , β=125.98(1)°, Z=8 . Crystal data for 4 : monoclinic, space group P 2 1 / c , a=13.115(2), b=9.523(2), c=17.908(4) A , β=111.71(1)°, Z=2 . Structures 1 and 4 each consist of a dinuclear unit with bridging methoxo groups and one ligand linked to each copper via an N atom. Structure 1 (which consists of two dinuclear, crystallographically independent, but chemically identical units) has the two copper atoms bridged by a triflate anion, providing each copper atom a square-pyramidal coordination, while the copper atoms in structure 4 have an almost a square-planar geometry. The CuCu distances (A) within the dinuclear units are: 1 , 2.9775(13), 2.9751(13); 4 , 2.9872(16); the CuOCu bridging angles (°) are: 1 , 101.7(3), 101.7(3), 100.9(3), 102.1(3); 4 , 103.2(2). The mid-IR section focused on the vibrations of the triflate anion reveals interesting results concerning the assignments of that anion related to the v as (SO) band. Characteristic CuO vibrations in the far-IR section were found at 386 and 230 cm −1 for the methoxo-bridged and 454 and 332 cm −1 for the ethoxo-bridged compounds. These dinuclear species are EPR silent, and only a weak signal of monomeric impurities is observed. They also show a diamagnetic behavior below room temperature.

X-ray structural analyses of organomagnesium compounds

Publisher Summary This chapter discusses the X–ray structural analyses of organomagnesium compounds. Organomagnesium compounds are well-established tools in organic chemistry. Compared to the long history of the synthetic applications of organomagnesium compounds, the investigation of their structure and bonding covers a much shorter period. By the use of gas-phase electron diffraction (GED), it is possible to determine the structure of molecules in the gas phase. A major drawback of GED is that only small molecules can be resolved completely; for larger molecules, the degrees of freedom must be limited during the calculations by assuming and optimizing values for many of the structural parameters. In almost all structure determinations of simple Grignard or diorganylmagnesium compounds, the magnesium atoms are surrounded by four ligands. In the absence of coordinating solvents such as ethers, most organomagnesium compounds tend to form polymeric structures. Solid and volatile organomagnesium compounds can be slowly sublimed in a static high vacuum. On the symmetrization of di-Grignard reagents to the analogous halogen-free compounds, both polymeric and cyclic species may be expected. Although the tetrahedral coordination geometry is preferred by organomagnesium compounds, many examples have been structurally characterized, which show deviating coordination numbers. Increased coordination numbers for magnesium are also found for an ethylmagnesium-chloride/magnesium-chloride adduct. Fascinating structures can be obtained on the complexation of organomagnesium compounds with polyether ligands.

Reactions of bis(iminophosphoranes) with palladium(II) dichloride: Metal-induced tautomerization orthopalladation and unexpected platinum-assisted [2 + 2] cycloaddition of an aryl-nitrile with a phosphinimine moiety

Reactions of bis(iminophosphoranyl)methane, CH 2 (PPh 2  N-aryl) 2 , (BIPM; 1a,b ) or 1,1-bis(iminophosphoranyl)ethane (1,1-BIPE; 1e ) with Pd- and Pt-dichlorides containing weakly coordinating ligands (L) such as nitriles or cyclo-octadiene, afforded several products depending on the reaction time, type of ligand ( 1a-c ) or nature of the metal. The first reaction observed is a metal-assisted tautomerization of BIPM to aryl-NPPh 2 CHPPh 2 NH-aryl. When BIPM reacts with PdCl 2 (L) 2 , exclusive formation of the C , N -chelate PdCl 2 {CH(PPh 2  N-aryl)(PPh 2 NHaryl)} ( 2a,b ) is observed, whereas with 1,1-BIPE ( 1c ) a product mixture consisting of C , N -chelate ( 2c ) and an N , N ′-chelate ( 3 ) is found. Orthometallation of the four-membered palladacycle ( 2 ) took place upon heating. giving the five-membered palladacycle [PdCl 2 {2-C 6 H 4 -PPh(NH[-pTol)-C′H-PPh 2 (NH-pTol)})- C , C ′] ( 4 ). The molecular structure of 4 has been determined by X-ray crystallography. Reactions of BIPM ( 1a,b ) with PtCl 2 (RCN) 2 (Rphenyl, p -tolyl) affored entirely different products: the six-membered platinacycles [PtCl(RCN)(arylN(R)NPPl 2 CHPPb 2 NHaryl)- C , N ]Cl ( 5 ) and [PtCl 2 (arylNC(R)NPPh 2 NHaryl]- C , N ] ( 6 ), due to an unexpected 2 + 2 cycloaddition of a nitrile with a PN group.

Synthesis, characterization, crystal structures and magnetic properties of di- and polynuclear bis(μ-3-pyridin-2-yl-1,2,4- triazolato)copper(II) compounds containing N-methylimidazole, pyrazole or 4,4′-bipyridine as co-ligands

A group of new compounds 1–5 of general formula [Cu2(pt)2L2(NO3)2(H2O)2](H2O)n, with n=1, 2, 3 or 4 and L=N-methylimidazole, pyrazole, 4,4′-bipyridine, H2O and N-butylimidazole, has been prepared and characterized spectroscopically and structurally. The synthesis, characterization, spectral and magnetic properties as well as crystal and molecular structures of [bis(μ-3-pyridin-2-yl-1,2,4-triazolato-N′,N1,N2)]-bis[(1-methylimidazole-N3)(nitrato)(aqua)copper(II)] tetrahydrate, ([Cu2(pt)2(Meim)2(NO3)2(H2O)2](H2O4)4 (1), in which pt=3-pyridin-2-yl-1,2,4-triazolato and Meim=N-methylimidazole, [bis(μ-3-pyridin-2-yl-1,2,4-triazolato-N′,N1,N2)]-bis[(pyrazole-N1)(nitrato)(aqua)copper(II)], [Cu2(pt)2(Hpz)2(NO3)2(H2O)2] (2) in which Hpz=pyrazole, and an unusual chain of dimers, catena-(μ-4,4′-bipyridine)[bis(μ-3-pyridin-2-yl-1,2,4-triazolato-N′N1N2)(nitrato)(aqua)copper(II))], [Cu2(pt)2(4,4′-bpy)(NO3)(H2O)2](NO3)(H2O)4 (3) in which 4,4′-bpy=4,4′-bipyridine, have been studied Crystal structure data are as follows. 1: Cu2N14C22H34O12, T=293 K, triclinic, space group P, with a=9.2685(6), b=9.6897(6), c=10.2313(4) A, α=108.700(4), β=97.884(4), γ=95.396(5)°, Z=1 and V=852.75(8) A3. The least-squares refinement based on 2111 significant reflections (I>2σ(I) converged to R=0.0411 and Rw=0.0446. 2: Cu2N14C20H22O8, T=298 K, monoclinic, space group P21/c, with a=10.812(1), b=13.750(1), c=10.003(1) A, β=113.94(1)°, Z=2 and V=1359.1(2) A3. The least-squares refinement based on 1863 significant reflections (I>2.5σ(I)) converged to R=0.0522 and Rw=0.0485. 3: Cu2N12C24H30O12, T=295 K, monoclinic, space group P21/c, with a=8.8802(11), b=12.9975(8), c=28.7208(19) A, β=92.970(7)°, Z=4 and V=3310.5(5) A3. The least-squares refinement based on 5100 significant reflections (I>2σ(I)) converged to R=0.056 and Rw=0.051. The structures of 1, 2 and 3 consist of dinuclear units, in which the copper(II) ions are linked by two via N(1), N(2) bridging dehydronated Hpt ligands in the equatorial plane. CuN distances vary from 1.970(3) to 1.988(3) A. All copper(II) ions are in a distorted octahedral environment, of which the equatorial plane around the copper atoms is formed by three donor atoms of the pt ligand and one donor atom of another ligand (Meim, Hpz or 4,4′-bpy). A water molecule and a monodentate nitrate anion occupy the axial positions. The CuCu distances within the dinuclear unit are: 1, 4.022(1); 2, 3.9741(12); 3, 4.0198(7) A. The 4,4′-bpy ligand bridges the dinuclear units to form a ladder type chain, with a CuCu distance measured over the 4,4′-bpy ligand of 11.1220(5) A. The magnetic susceptibility data are interpreted on the basis of the spin Hamiltonian Ĥ=−2J[ŜCu1·Ŝcu2] and yielded 1: J=−47 cm−1, g=2.14; 2: J=−49 cm−1, g=2.04; 3: J=−51 cm−1, g=2.14; 4: J=−51 cm−1, g=2.00; 5: J=−51 cm−1, g=2.07. No interdimer interaction was found for 3. The X-band powder EPR spectra recorded at various temperatures for all compounds are typical of a triplet state, with D values in the range 0.08–0.10 cm−1.

Synthesis and structural studies of phenyl(iodo)- and methyl(phenyl)palladium(II) complexes of bidentate nitrogen donor ligands

Phenylpalladium(I1) complexes of the type PdIPh(N-N), with N-N = N,N,N’,N’-tetramethylethylenediamine (tmeda) or 2,2’-bipyridyl (bpy), can be conveniently prepared in 70-95% yield by oxidative addition of iodobenxene to bis(dibenzylideneacetone)palladium(0) in the presence of the appropriate nitrogen donor ligand. The bromo analogues were obtained in only S-12% yield in this way. The complex PdIPh(tmeda) (la) reacts readily with MeLi to give PdMePh(tmeda) (3) in 88% yield, whereas PdIPh(bpy) (la) gives PdMePh(bpy) (4) and PdMe,(bpy) in varying ratios. The formation of PdMe,(bpy) was found to result from the synergistic action of lithium iodide and methyllithium. Pure PdMePh(bpy) (4) was obtained in 82% yield via ligand-exchange from PdMePh(tmeda) (3). The crystal structures of PdIPh(N-N) (la, 2a) and PdMePh(N-N) (3, 4) complexes were determined by X-ray diffraction studies. The results show that the phenyl group is always oriented perpendicular to the coordination plane aroutd palladium, with the largest deviation found for 3 (14.3(2)“). The Pd-N bond distances in the tmeda complexes (2.127(6)-2.210(3) A) are larger than those in the bpy-coordinated complexes (2.870(8)-2.144f8) A). Similarly, the Pd-CfMe) bond distances (2.5703(8) and 2.575(l) & are larger than the Pd-C(Ph) bond distances (1.985(3)-1.996tlO) A)>.

Synthesis, magnetism and X-ray structures of [Cu(2-aminopyrimidine)2(μ-OH)(CF3SO3)]2(2-aminopyrimidine)2, a new hydroxo-bridged dinuclear Cu(II) compound generating extremely small antiferromagnetism

The synthesis, optical and magnetic properties and X-ray crystal structure of [Cu(2-aminopyrimidine)2(OH)(CF3SO3)]2(2aminopyrimidine)2, a new dinuclear hydroxo-bridged copper(II) compound with a CuOCu angle of 97.96° and a very small antiferromagnetic interaction for which the singlet–triplet exchange parameter J, is described. The magnetic exchange coupling is almost negligible and, depending on the actual sample, varies from − 1.8 to − 7.2 cm − 1 .

Synthesis of Pt compounds containing chiral (2S,4S)-pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole) as ligand and their use in asymmetric hydroformylation of styrene derivatives

Unlike bis(diphenyl)phosphine derivatives in general, (2S,4S)-pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole), S,S-BDBPP, gives a trans oligomeric compound [PtCl2(S,S-BDBPP)]n, 1, in reaction with dichloro-Pt precursors such as PtCl2(PhCN)2, PtCl2(CH3CN)2 and PtCl2(COD) at room temperature. Compound 1, which could be readily isolated, slowly rearranges in solutions at room temperature to the expected cis-monomer PtCl2(S,S-BDBPP), 3. Heating or the presence of PtCl2(COD) accelerates the transformation of compound 1 to 3. SnCl2 adducts of both compounds, trans-[PtCl(SnCl3)(S,S-BDBPP)]n, 2, and cis-PtCl(SnCl3)(S,S-BDBPP), 4, as well as the known cis-PtCl(SnCl3)(S,S-BDPP), 5, (S,S-BDPP = (2S,4S)-2,4-bis(dipbenylphosphino)pentane) have been tested as catalysts in the asymmetric hydroformylation of p-isobutylstyrene. The phenyl analog 5 provides up to 75% e.e. but moderate yields to chiral 2-(4-isobutylphenyl)-2-propanal. Compared to this, the regioselectivity to the branched aldehyde is remarkably increased; however, the enantioselectivity is drastically decreased by the use of both dibenzophosphole derivatives 2 and 4. The similarities in the selectivities provided by 2 and 4 indicate that the trans oligomer 2 transforms to the cis-monomer 4 during the catalytic process. X-ray crystal structure determination of compound 3 shows a half-chair conformation for the chelate ring with a symmetric arrangement of dibenzophosphole groups. Besides a preference for the latter achiral conformation, the planar structure of the dibenzophosphole groups can also be considered as reason for the moderate enantioselectivities provided by 4.

Formation and molecular structure of permethylyttrocene methyl tetrahydrofuranate

Abstract The reaction of Cp * 2 YCl·THF with MeLi in THF at −80°C gives the monomeric Cp * 2 YMe·THF ( 1 ), which has been characterized by spectroscopy, elemental analyses and a single crystal X-ray diffraction study. Complex 1 crystallizes in the orthorhombic space group Pnam with lattice parameters a 17.881(4), b 8.621(2), c 15.095(3) A, Z = 4, and D calc 1.274 g cm −3 . Least-squares refinement using 1056 independent observed reflections and 117 parameters gave a final R value of 0.071. The YC(σ) bond distance is 2.44(2) A. IR and NMR spectra indicate an agostic interaction between the metal center and one of the CH bonds of the methyl ligand, but this could not be confirmed by the X-ray structure determination owing to disorder.

Synthesis, characterization, spectroscopy, magnetism and X-ray structures of red and green Cu(II) chloride adducts with bis(2-benzimidazolyl)propane

Two different Cu(II) compounds, having the same stoichiometry, were obtained with the ligand bis(2-benzimidazolyl)propane (abbreviated as tbz) with the formula [Cu(tbz)Cl 2 ]. The copper atom in the red isomer ( 1 ) has a tetrahedral geometry, while in the polymeric green isomer ( 2 ) two different copper sites are present, one perfectly square planar and a second tetragonally distorted square planar. Compound 1 crystallises in the orthorhombic space group Pbca with a =13.5373(11), b =15.3002(9), c =15.9117(7) A, Z =8. Compound 2 crystallises in the monoclinic space group P2 / c with a =12.4964(13), b =10.3750(15), c =13.568(2) A, β =91.643(10)°, Z =4. Further characterization was done by ligand field, IR spectroscopy and EPR. Solid-state spectra agree with tetrahedral geometry, and square-planar based geometry. Frozen-solution EPR in DMSO shows a trigonal–bipyrimidal geometry with dz 2 ground state.

Reactions of Rh- and Ir-bis(iminophosphoranyl)methanide compounds with electrophiles; a trapped cation-anion complex in the oxidative addition of iodine to a d8 metal centre and X-ray crystal structure of IrI{CH(PPh2NC6H4CH3-4)2}(COD)]I, containing two fused four-membered metallacycles☆

Reaction of square planar M{CH(PPh2NC6H4CH3-4)2(COD)] (1a: MRh; 1b: MIr), in which the bis-iminophosphoranylmethanide ligand is bidentate N,C-coordinated, with I2, MeI and MeOSO2CF3 yields products resulting from metal or ligand (N atom) centered reactivity. Complexes 1a and 1b react with MeI and MeOSO2CF3 to yield mainly cationic N-methyl or N,N′-dimethyl derivatives. The reaction of b1 with I2 results in the selective formation of the hexacoordinate Ir(III) complex (OC-6-43)-[Ir(I)σ-N,σ-N′,σ-C-{CH(PPh2NC6H4CH4-4)2(η2,η2-COD]+I− (4). The molecular structure of 4 has beend determined by an X-ray crystal structure study; it crystallizes in space group P21/c with a=21.040(2), b=18.399(2), c=26.075(3) A and β =102.33(2)°. A total 5243 reflections (I>2.5σ(I)) has been used in the refinement which converged, after including a model for observed disorder, to R=0.061 (Rw=0.084). In the cationic part of 4 the N,N′,C ligand is facilly trridentate coordinated to Ir, thus forming a [2.2.0]-bicyclohexane structure containing an Ir, a C, two P and two N atoms. Iodine is in trans position to the methadine carbon atom. Compound 4 represents a trapped cation-anion complex and may be regarded as a model of an intermediate in the polar oxidative addition of I2 to d8 transition metal compounds. Instead of coordinating the second iodine atom, stabilization of 4 is achieved by virtue of the adaptation of the bis(iminophosphoranyl)methanide ligand by coordination of the pendant N atom.