Nevenka Bresciani-Pahor

Organocobalt B12 models: axial ligand effects on the structural and coordination chemistry of cobaloximes

Article de synthese presentant les structures cristallines et moleculaires de molecules contenant la moitie Co(DH) 2 , ou DH est le monoanion de la dimethylglyoxime. Les structures RX sont comparees aux structures en solution. Discussion des implications pour la biochimie de la vitamine B 12

Enantioselective hydrogen transfer reactions from propan-2-ol to ketones catalyzed by pentacoordinate iridium(I) complexes with chiral Schiff bases

Abstract Some diastereoisomeric pentacoordinate complexes of the type [Ir(COD)-(NNR ★ )I] (COD = cis , cis -1,5-cyclooctadiene; NNR ★ = 2-pyridinal-1-phenylethylimine (PPEI) (I), 2-acetylpyridine-1-phenylethylimine (APPEI) (II)) have been synthesized. The complexes are active and selective catalysts for asymmetric hydrogen transfer from propan-2-ol to prochiral ketones. Optical yields of up to 84% have been obtained in the reduction of t-butyl phenyl ketone. The structure and absolute configuration of complexes I and II were determined by X-ray diffraction.

Organocobalt B12 models. Structures of trans-bis(glyoximato)(alkyl)(pyridine)cobalt(III), with alkyl=Me, Et, i-Pr

Abstract The crystal structures of the organocobalt complexes, pyCo(GH) 2 Me(1), pyCo(GH) 2 Et(2) and pyCo(GH) 2 Pr i (3) (py = pyridine, GH = monoanion of glyoxime) are reported. Compound (1) crystallizes in the space group P2 1 2 1 2 1 with cell parameters a = 8.508(1), b = 13.586(2) and c = 11.614(6) A; (2) crystallizes in the space group P 2 1 2 1 2 1 with cell parameters a = 8.448(4), b = 12.164(2) and c = 13.651(2) A; (3) crystallizes in the space group P 2 1 /c with cell parameters a = 8.443(7), b = 12.913(2), c = 14.341(2) A and β = 92.86(4). The three structures have been solved by Patterson and Fourier methods and refined by least squares methods to final R values of 0.045 (1) , 0.068 (2) and 0.057 (3) using 1819 (1) , 1653 (2) and 1582 (3) independent reflections. The pyCoalkyl fragment shows significant variation of CoN and CoC bond lengths. The latter increase from 2.003(4) to 2.084(9) A following the increase of the alkyl bulk. The CoN(py) distances increase from 2.064(3) to 2.101(6) A with the increasing σ-donor power of the alkyl group trans to pyridine. In comparison with cobaloximes having the same axial ligands, pyCo(DH) 2 alkyl (DH = monoanion of dimethylglyoxime) does not show significant differences on the pyCo alkyl fragment. CoN axial bond lengths and exchange rates of the axial neutral ligand are consistent for the two series, although changes in bond lengths are detected only when rate constants are from two to three orders of magnitude different.

Structural study of cobaloxime derivatives. The molecular structure of the sodium salt oftrans-dinitro(dimethylglyoximato)(ditmethylglyoxime)cobaltate(III) dihydrate and trans-nitrobis(dimethylglyoximato)(triphenylphosphine)cobalt(III)

Abstract The crystal structure analysis of two title cobaloximes: [ trans -(NO 2 ) 2 Co(dmg)(dmgH 2 )]Na·2H 2 O (I), trans (NO 2 )(PPh 3 )Co(dmgH) 2 , (II), has revealed that crystals of (I) are triclinic. space group P 1 , with a = 16.23, b = 6.621, c = 8.018 A , α = 91.59, β = 104.4, γ = 92.61°; Z = 2, while crystals of (II) are orthorhombic, space group, P 2 1 2 1 2 1 , with a = 17.357, b = 14.360, c = 10.783 A ; Z = 4. The structures have been solved by three-dimentional Patterson and Fourier methods and refined by the least-squares technique. The final R values were 0.044 for (I) and 0.049 for (II), calculated on the basis of 3157 and 1349 independent reflections respectively. The CoN and NO bond lengths. of (I) are significantly different in the two equatorial moieties and are in agreement with the above formulation [dmgH 2 : CoN 1.918(2), NO 1.369(3) A ; dmg: CoN 1.903(2), NO 1.352(3) A ]. The sodium ion is surrounded by five oxygen atoms with a co-ordination polyhedron intermediate between a distorted trigonal bipyramid and a square-planar pyramid. The lengthening of the CoNO 2 bond distance 1.980(9) A ) in (II) with respect to the mean value found in complex (I) (1.946(3) A ) could be due to the trans -influence of the phosphine ligand. On the other hand the CoP bond length (2.392(3) A ) is longer than those usually found. The structure of both compounds confirms the marked rigidity of the equatorial ligand.

Structural study of steric effects in cobalt dimethylglyoximates containing phosphine ligands. The structure of trans-Bis(dimethylglyoximato)methyltriphenylphosphinecobalt(III) and of trans-Bis(dimethylglyoximato)chlorotricyclohexyl phosphinecobalt(III) toluene solvate

Abstract The crystal and molecular structure of the title compounds has revealed that crystals of trans -bis(dimethylglyoxinate)methyltriphenylphosphinecobalt(Ill) (I) are monoclinic space group P2 1 with a = 10.4061(8), b = 15.54(1), c = 8.963(5) A β = 108. 75(7)°, Z = 2 and crystals of trans-bis (dimethylglyoximate)chlorotricyclohexylphotphinecobalt(1II) (II) are monoclinic, space group P2 1 / c with a = 9.501(7), b = 29.33(1), c = 12.98(1) A β = 99.0(1)°, Z = 4. The structures have been solved by three-dimensional Patterson and Fourier methods and refined by the least-squares technique. The final R values were 0.032 for (I) and 0.072 for (II), calculated on the basis of 1850 and 1651 independent reflections respectively. In (I) the Co-P bond length of 2.418(1) A is the largest value so far reported and confirms the strong trans -influence of the methyl group (Co--CH 3 , 2.026(6) A ). The coordinated N atoms are coplanar within ±0.015 A ; the cobalt is displaced of O. 112 A above their mean plane towards the phosphine. The two dmgH units are bent away from the photphine ligand and their mean planes make an angle of 13. 6°. The axial bond lengths in (II) are: Co-P 2.369(5) A , Co-CI 2.294(5) A. The coordinated N atoms are coplanar within 0.007 A with Co displaced of O. 10 A towards phosphine ligand, whereas the two dmgH mean planes make an angle of 15.7° These results are discussed in terms of steric factors. Correlation with experimental cone angles and n.m.r. results is discussed.

Properties and structural characterization of copper(II) mixed complexes with 2,2′:6′,2″-terpyridyl and iminodiacetate or pyridine-2,6-dicarboxylate

X-Ray analysis of the mixed complexes [Cu(bipy)(ida)]·6H2O (1) and [Cu2(bipy)2(pydca)2]·4H2O (2b)(bipy = 2,2′-bipyridyl, ida = iminodiacetate, and pydca = pyridine-2,6-dicarboxylate) shows that different stereochemistries are involved in the solid state in spite of the similarity of the two chromophores around the copper(II) ion. In the crystals of (1) the copper is five-co-ordinate and the co-ordination polyhedron may be described as a distorted square pyramid. The crystal structure of (2b) consists of binuclear units in which Cu(bipy)2 and Cu(pydca)2 moieties are bound through an oxygen bridge, the former having a distorted square-pyramidal geometry, the latter a trigonal-bipyramidal arrangement. Cell parameters: (1)a= 11.200(7), b= 13.252(8), c= 7.975(7)A, α= 66.8(1)β= 115.3(1), γ= 102.0(1)°, triclinic, space group P1; (2b)a= 13.103(6), b= 17.815(7), c= 15.302(7), β= 90.8(2)°, monoclinic, space group P21/c. Both structures have been solved by conventional Patterson and Fourier methods and refined to R factors of 0.043 and 0.041 respectively.

Synthesis and molecular structure of cis-1-[(C6H5CH2)3PHC6H5)(CH2C6H5)2]-2-CH3-1,2-(σB10C2H10)

Abstract The title complex has been prepared from the reaction of cis-[(C6H5CH2)3P]2PtCl2 with 1-Li-2-Ch3-1,2-B10C2H10 and the crystal structure determined by X-ray single-crystal analysis. Crystals are triclinic, space group P 1 , with a 13.826(5), b 15.269(5), c 13.234(4) » and α 104.74(8), β 60.78(8), γ 107.46(8)°. The structure was solved by the heavy-atom method and refined to R 0.060 for 3855 independent reflections. The carboranyl group is σ-bonded to Pt through it C(1) atom. One phosphine is coordinated to the metal atom through its P atom, the other through its P atom and the C atom bonded to phosphorus of one benzyl side group, leading to a three-membrane P tPC chelate ring.

Quadridentate Schiff-base metal complexes as chelating ligands of alkali metals. Synthesis and structure of ammonium and sodium tetra-phenylborate addition complexes with [NN′-ethylenebis(salicylideneiminato)]nickel(II)

Transition-metal complexes of the Schiff-base NN′-erhylenebis(salicylaidimine)(H2salen) co-ordinate ammonium and alkali-metal cations to give addition complexes of different stoicheiometry. The complex [Ni(salen)] with ammonium or potassium tetraphenylborate, M′[BPh4], gives addition compounds of formula [{Ni(salen)3-,M′(BPh4)]·nL [L = solvent, e.g. tetrahydrofuran (thf), acetonitrile, or acetone]. For n= 2 and L = thf the complexes are isomorphous. Reaction with Na [BPh4] in acetonitrile yields again a compound with Ni : Na 3 : 1, from which [{Ni(salen)}2Na(NCMe)2(BPh4)]·2MeCN is obtained by very slow crystallization. The crystal structures of [{Ni(salen){3(NH4)(BPh4)]·2thf, (I), and [{Ni(salen)}2Na(NCMe)2]·2MeCN, (II), have been determined from three-dimensional X-ray data. Crystals of both compounds are triclinic, space group P, Z= 2, with cell parameters: (I), a= 18.93(1), b= 16.94(1), c= 14.84(1)A, α= 91.6(2), β= 111.4(2), γ= 116.8(2)°; (II), a= 14.64(1), b= 15.56(1), c= 14.91 A, α= 85.2(1), β= 114.2(1), γ= 98.7(1)°. The structures have been solved by Patterson and Fourier methods and refined by block-diagonal matrix least squares to R 0.11 for (I) and 0.080 for (II). The structure of (I) consists of discrete [BPh4]– anions and [{Ni(salen)}3(NH4)]+ macrocations in which the ammonium ion is surrounded by the six oxygen atoms (mean N H4+⋯ O 2.92 A) of the three Ni(salen) moieties. The co-ordination polyhedron is intermediate between a trigonal prism and an octahedron. as determined by a balance of steric and electrostatic factors. Similarly the structure of (II) has discrete [BPh4]– anions and [{Ni(salen)}2Na(NCMe)2]+ macrocations with the sodium ion on an approximately two-fold axis, co-ordinated by the four oxygen atoms of the two Ni(salen) molecules and by the nitrogen atoms of the two acetonitrile molecules occupying cis positions. The co-ordination polyhedron approximates to an octahedron with mean Na+⋯ O 2.41 and Na+⋯ N 2.49 A.

Reaction of PtOH complexes with CO2: synthesis and X-ray structure of (PBz3)4Pt2(Ph)2(η1,η1,μ-CO3)·(toluene)

Abstract The reaction of (diphoe)Pt(CH2CN)(OH) and trans-(PBz3)2Pt(Ph)(OH) with CO2 is reported as producing dimeric, bridged carbonato complexes of the type: P4Pt2(R)2(CO3). The crystal and molecular structure of (PBz3)4Pt2(Ph)2(μ-CO3)·(toluene) is also reported, showing η1, η1 bonding. The reaction is recognized to proceed in a stepwise fashion through bicarbonato intermediates.

Properties and X-ray crystal structures of copper(II) mixed complexes with thiodiacetate and 2,2′-bipyridyl or 2,2′:6′2″-terpyridyl

Spectroscopic and structural investigations have been performed for two ternary complexes of copper(II), [Cu(bipy)(tda)(H2O)]·4H2O (1) and [Cu(terpy)(tda)](2)(bipy = 2,2′-bipyridyl, terpy = 2,2′:6′,2″-terpyridyl, and tda = thiodiacetate). Crystals of (1) are monoclinic, space group P21/c, with a = 11.136(7), b= 21.13(1), c= 8.999(6)A, β= 113.2(2)°, and R= 0.057. Crystals of (2) are also monoclinic. space group C2/c, with a= 10.551(6), b= 21.23(1), c= 8.633(5)A, β= 112.0(2)°, and R= 0.035. Complex (1) consists of [Cu-(bipy)(tda)(H2O)] units connected by water molecules. The co-ordination polyhedron around the copper may be described as a distorted octahedron with the solphur atom and the water molecule in axial positions. Complex (2) consists of polymeric chains of Cu(terpy) units bridged by the tda ligand via the oxygens of the carboxylate groups. Consequently, the co-ordination polyhedron around the copper atom may be described as a distorted trigonal-bipyramidal arrangement. E.s.r. spectra confirm the crystallographic results for (1) both in the solid state and in solution. For (2). however, different e.s.r. spectra are obtained of the microcrystalline powder and of the solution. Only the powder spectrum agrees with a distorted trigonal-bipyramidal structure.