Evgeny V. Dikarev

Unligated dirhodium tetra(trifluoroacetate): preparation, crystal structure and electronic structure

Abstract The title compound, Rh2(O2CCF3)4, without any exogenous axial ligands, has been obtained in crystalline form by sublimation. Its crystal structure has been determined: space group P 1 with α = 5.2499(5), b = 8.491(2), c = 9.172(2) A , α = 88.80(2), β = 88.53(1), γ = 76.43(1)°, V = 397.3(1) A 3 , Z = 1 . The molecules are linked by axially ligating each other to form infinite chains. The Rh-Rh distance is 2.3813 (8) A. The volatility of Rh2(O2CCF3)4 should allow spectrospcopic study of the isolated molecules and therefore the electronic structure has been treated by the SCF-Xα-SW method. The level ordering and composition show significant differences from those of Rh2(O2CH)2, although in both molecules there is a strong Rh-Rh σ bond. Ionizatio potential have been estimated by the transition state method.

Studies of tetrakis(trifluoroacetate) dirhodium: Part 4. Solventless synthesis of Rh2(O2CCF3)2(CO)4 combined with Rh2(O2CCF3)4, a compound with infinite chains of rhodium atoms

Abstract By reaction of Rh2(O2CCF3)4 and Mo(CO)6 in an evacuated sealed tube placed in a thermal environment where there is a thermal gradient (125–120°C), we have obtained a compound in which one Rh2(O2CCF3)4 unit is sandwiched between two Rh2(O2CCF3)2(CO)4 units, to give an essentially linear array of six rhodium atoms, with Rh–Rh distances of 2.960(1), 2.790(1) and 2.412(1) A. These arrays of six rhodium atoms are then linked into infinite chains which lie parallel in the crystal, with Rh to Rh contacts of 3.062(1) A. The crystals are markedly dichroic and relatively air stable.

Dinuclear TiIV and TiIII complexes supported by calix[4]arene ligands. Binding alkali-metal cations inside and outside the cavity of calix[4]arenes

New dinuclear Ti I V and Ti I I I complexes with the calix[4]arene ligand C 2 8 H 2 0 O 4 H 4 (H 4 L) have been isolated from the reaction of Ti(NMe 2 ) 4 , H 4 L, and Na (or KC 8 ) in THF. X-ray analyses revealed a similar core structure for the two complexes Na 4 (THF) 8 [Ti I V 2 (μ-O) 2 L 2 ] (1) and K 4 (THF) 8 [Ti I I I 2 (μ-NMe 2 ) 2 L 2 ] (2). Two titanium atoms are bridged by two oxygen atoms in 1 and by two dimethylamido groups in 2 and are also supported by two deprotonated calix[4]arene ligands in a cone conformation. This resulted in a similar Ti...Ti separation of about 3.29 A in 1 and 3.28 A in 2 and in a distorted octahedral environment for each Ti center in both complexes. In contrast, in a novel complex 3, Na 2 (THF) 6 [Ti I I I 2 L 2 ], two Ti I I I atoms are supported only by two deprotonated ligands. This results in a five-coordinate environment for both titanium(III) centers with the separation between them being 3.133(1) A.

Studies of dirhodium(II) tetrakis(trifluoroacetate).: Part 8. One-dimensional polymers of Rh2(O2CCF3)4 with aromatic ligands: benzene, p-xylene and naphthalene

The interaction of benzene, p-xylene, and naphthalene with a strong two-ended Lewis acid, Rh2(O2CCF3)4, led to one-dimensional linear polymers of 1:1 composition, [Rh2(O2CCF3)4·L], where L C6H6 (1), p-(CH3)2C6H4 (2), and C10H8 (3). Compounds 1‐3 have been characterized by elemental analysis and IR spectroscopy and their structures have been determined by X-ray diffraction. In the crystal structures of the compounds the alternating arrangement of the dirhodium(II) tetrakis(trifluoroacetate) units with the aromatic ligands coordinated to their axial positions forms infinite chains extended along one direction of the unit cell. The rare bridging off-centered, h 2 :h 2 coordination of arene groups by the Rh(II) centers was found to be preferred in all three cases with the two closest RhCarene distances averaged to 2.662(6) A, in the benzene complex (1), to 2.684(7) A, in the p-xylene analogue (2), and to 2.588(9) A, in the naphthalene product (3).

Synthesis and crystal structure of [Re(CO)3(μ-CH3CO2)(THF)]4

Abstract A tetrameric complex [Re(CO)3(μ-CH3CO2)(THF)]4 (1) is formed in high yield when the reaction product of Re(CO)5Cl with acetic acid in refluxing 1,2-dichlorobenzene is dissolved in THF. The use of Re2(CO)10 instead of rhenium pentacarbonyl chloride also affords 1. The characterization of 1·3THF·0.5C6H14 has been accomplished by X-ray crystallography. The structure of the tetrameric molecule 1 consists of four rhenium(I) atoms bridged by four acetate ligands. The coordination of each metal center is fulfilled by three CO groups and one THF molecule in a way that all carbonyls are trans to oxygen atoms. The geometry of each acetate bridge is anti–syn providing a Re to Re separation of 5.40xa0A. This bonding mode is seen here for the first time in rhenium carboxylates. Different coordination types for Re–RCO2 interaction are also discussed in the paper.

Mixed halide/phosphine complexes of the dirhenium core. Part 7. Reactions of [Re2I8]2− with monodentate phosphines ☆

Abstract Reactions of the octaiododirhenate anion [Re2I8]2− with monodentate phosphines (PR3=PMe3 (1), PMe2Ph (2), PEt3 (3), and PEt2Ph (4)) have been studied in two different solvents, ethanol and benzene, at room temperature. The reactions in ethanol resulted in two-electron reduction products having the Re2xa04+ core, Re2I4(PR3)4 (R3=Me3 (1a) and Me2Ph (2a)), for which X-ray diffraction study revealed a 1,3,6,8 isomer type. The reaction of [Re2I8]2− with PMe3 in benzene led to an intermediate edge-sharing bioctahedral dirhenium(III) complex, Re2(μ-I)2I4(PMe3)4 (1b), with no metal–metal bond. The interaction of PEt3 with [Re2I8]2− in benzene again yielded a kinetic product with a different stoichiometry and a Re2xa05+ core, [Bun4N][Re2I6(PEt3)2] (3c). The analogous reactions of [Re2I8]2− with PMe2Ph and PEt2Ph in benzene involved two-electron reductions and gave complex 2a and Re2I4(PEt2Ph)4 (4a), as products. Reduction of 1b with KC8 gave 1a as the main product along with a few crystals of 1,3,6-Re2I5(PMe3)3 (1d). Mixed iodide/phosphine complexes of the dirhenium core Re2xa0n+, where n=4 (1a, 2a, 4a), 5 (1d, 3c), and 6 (1b) have for the first time been characterized by X-ray crystallography. In addition, these products have been further identified by a combination of mass spectrometry and cyclic voltammetric measurements.

New family of quadruply-bonded ditungsten(II,II) species with chloride and amine ligands

Abstract The first ditungsten(II,II) complexes with amine ligands of the formula W2Cl4(NH2R)4 (R=Prn (1), But (2), Cy (3)) have been prepared by reduction of a tungsten(IV) compound with potassium graphite in the presence of the appropriate amine. The X-ray crystal structure determination of 3 revealed a quadruply-bonded ditungsten molecule having D2d geometry and a trans arrangement of the amine ligands on each metal atom.

W2Cl4(NR2)2(PR′3)2 molecules: 6. New triply-bonded ditungsten complexes with bis(diphenylphosphino)methane or bis(diphenylphosphino)amine as a bridging ligand. Crystal structures of cis,cis-W2Cl4(NR2)2(dppm) (R=Et, Bun) and W2Cl3(NHCMe3)2(NH2CMe3)(PPh2NPOPh2)

Abstract The reactions of W 2 Cl 4 (NR 2 ) 2 (NHR 2 ) 2 (R=Et, Bu n ) with a stoichiometric amount of bis(diphenylphosphino)methane (dppm) readily resulted in the isolation of two new triply-bonded ditungsten(III) compounds cis,cis -W 2 Cl 4 (NR 2 ) 2 (dppm) (R=Et ( 1 ), R=Bu n ( 2 )) in moderate yields. The molecular structures of both compounds have been determined by X-ray crystallography and their crystallographic data are as follows: 1 ·CH 2 Cl 2 , monoclinic, space group C 2/ c , a =38.729(5), b =11.662(1), c =19.045(2) A, β =113.57(1)°, V =7884(2) A 3 , Z =8, R =0.026, wR 2=0.055; 2 , monoclinic, space group P 2 1 / n , a =14.4962(5), b =18.6305(8), c =17.1667(6) A, β =97.974(4)°, V =4591.4(3) A 3 , Z =4, R =0.043, wR 2=0.102. Both molecules are characterized by a W 2 6+ core with a σ 2 π 4 bond of order three and the W–W distances are 2.3350(3) and 2.3463(4) A, respectively, for 1 and 2 . They entail an essentially staggered rotational geometry and exhibit significant torsion angles in the solid state. Similar procedure has also been used to prepare similar W 2 6+ complexes containing bis(diphenylphosphino)amine (dppa) ligands and complexes of the type W 2 Cl 4 (NR 2 ) 2 (dppa) (R=Et ( 3 ), R=Bu n ( 4 )) have been characterized by 31 P{ 1 H} NMR spectroscopy at room temperature. In leading to the reaction pathway of complexes of this kind, the time sequences for the formation of 1 and 2 have been followed by variable temperature 31 P{ 1 H} NMR spectroscopic method. In all cases, the trans,trans -isomers of W 2 Cl 4 (NR 2 ) 2 (L–L) (R=Et, Bu n ; L–L=dppm, dppa) are the kinetically favored products while the cis,cis -isomers are the thermodynamic products. The corresponding cis,trans compounds are believed to be the likely intermediate complexes. In the course of a synthetic program directed towards the preparation of a dppa substitution complex of W 2 Cl 4 (NHCMe 3 ) 2 (NH 2 CMe 3 ) 2 , an unexpected ditungsten compound W 2 Cl 3 (NHCMe 3 ) 2 (NH 2 CMe 3 )(PPh 2 NPOPh 2 ) ( 5 ) has been prepared and structurally characterized. Compound 5 crystallizes in the triclinic space group P 1 , a =11.269(2), b =12.020(5), c =18.182(2) A, α =93.27(1), β =89.72(1), γ =93.275(2)°, V =2455(1) A 3 , Z =2, R =0.068, wR 2=0.153. The W–W distance in 5 is 2.3030(8) A and the molecule consists of an anionic bridging ligand [N(OPPh 2 )PPh 2 ] − , forming a six-membered metallacycle with the ditungsten unit.

A new rectangular Re4 cluster compound of the metallocyclodiyne Type

AbstractThe compound (n-Bu4N)2[Re4Cl8(μ-Cl)2(μ-O)2 · 2THF] has been prepared from (n-Bu4N)2 Re2Cl8 by refluxing it in wet trifluoroacetic acid. It forms brown, block-shaped crystals in space group Pn