Synthesis and structural chemistry of oxazolinyl-carbene copper(I) complexes

Reaction of a series of directly connected oxazoline–imidazolium salts with potassium tert-butoxide and in the presence of CuBr · SMe₂ at −78 °C cleanly gave the corresponding 2-oxazolinyl-(N-mesityl)imidazolidenecopper(I) complexes which are monomeric in solution but aggregate in the solid state. X-ray diffraction studies established a dimeric structure for [{2-(4,4-dimethyl)-oxazolinyl-(N-mesityl)imidazolidene}(bromo)copper(I)]₂ (2a) whereas the chiral derivative [{2-(4-S-isopropyl)-oxazolinyl-(N-mesityl)imidazolidene}(bromo)-copper(I)]_∝ (2b) forms infinite chains of a coordination polymer.     

Synthesis and reactions of heterodinuclear organopalladium complex having an unsymmetrical PN ligand

Novel heterodinuclear organopalladium complexes having an unsymmetrical PN ligand (Et₂NC₂H₄PPh₂-κ²N,P)RPd-ML_n (ML_n = Co(CO)₄; R = Me (2a), Ph (2b), ML_n = MoCp(CO)₃; R = Ph (3b)) are synthesized by metathetical reactions of PdRX(Et₂NC₂H₄PPh₂-κ²N,P) (X = I, NO₃) with Na⁺[ML_n]⁻. Reversible dissociation of the Pd-N bond in 3b is revealed by variable temperature NMR studies. Reactions of 2a and 2b with CO yield corresponding acyl complexes (Et₂NC₂H₄PPh₂-κ²N,P)(RCO)Pd-Co(CO)₄ (R = Me (5a), Ph (5b)). Rate of CO insertion for 2a and 2b is significantly faster than those for mononuclear methylpalladium complex, PdMeI(Et₂NC₂H₄PPh₂-κ²N,P) (1a), and methylpalladium-cobalt complex with a 1,2-bis(diphenylphosphino)ethane (dppe) ligand, (dppe-κ²P,P′)MePd-Co(CO)₄ (6a). 5a smoothly reacts with nucleophiles such as diethylamine, methanol and benzenethiol to give corresponding amide, ester and thioester, respectively. These reactions of 5a are also significantly faster than those of corresponding mononuclear analogues and the similar heterodinuclear complexes with symmetrical bidentate ligands such as 1,2-bis(diphenylphosphino)ethane or N,N,N′,N′-tetramethylethylenediamine ligand.     

Author index

Electromotive-force measurements on cells without liquid junction have been used to determine the pK_a values of 7 mono-, 6 di-, and 2 tricarboxylic acids in formamide at 9 temperatures from 5 to 45°C. From the pK_a values, the thermodynamic quantities ΔG⁰, ΔH⁰, and ΔS⁰ for the acids have been calculated in formamide at 25°C.     

Synthesis of new β-trifluoromethyl containing GABA and β-fluoromethyl containing N-benzylpyrrolidinones

A whole series of 3-(mono-, di-, trifluoro)methyl-substituted N-benzylpyrrolidinones 5a-c was synthesized by deoxyfluorination of corresponding 3-functionalized N-benzylpyrrolidinones. New β-trifluoromethyl containing GABA 4a was obtained in two alternative ways: by successive hydrolysis and hydrogenolysis of 3-trifluoromethyl N-benzylpyrrolidinone 5a and from trifluoroacetone as starting compound.     

Iron complexes of N-allylbenzotriazoles

Sodium benzotriazolide reacts with π-C₃H₅Fe(CO)₃I to give 1-N-allylbenzotriazoletricarbonyliron (I). The same product and the isomeric complex, 2-N-allylbenzotriazoletricarbonyliron (II), have been prepared independently, from the corresponding N-allylbenzotriazoles and Fe₂(CO)₉. The IR, ¹H NMR, and mass spectra of the complexes are reported. The structure of isomer I has been determined by X-ray diffraction. The crystals are monoclinic, P2₁/c, a = 10.65(1), b = 9.95(1), c = 12.90(1) Å, β = 113.69(7)°, d_calc = 1.39 g cm^?3, Z = 4.     

The crystal structures of AuTe2Cl and AuTe2I

The structures of AuTe₂Cl and AuTe₂I have been determined. Both compounds are orthorhombic: for AuTe₂Cl, a = 4.020 Å, b = 11.867 Å, c = 8.773Å, Z = 4, space group Cmcm; for AuTe₂I, a = 4.056 Å, b = 12.579 Å, c = 4.741 Å, Z = 2, Pmmb. Intensities were measured on an automatic diffractometer, and the structures were refined, with anisotropic temperature factors, to R = 2.1% and R = 3.5%, respectively. The structures consist essentially of corrugated two-dimensional nets of gold and tellurium atoms, with interleaving halogen atoms. The tellurium atoms form pairs coordinated to four gold atoms, and each gold atom is coordinated to four tellurium atoms.     

He(I) and He(II) photoelectron spectra of some mixed sandwich compounds of titanium,zirconium and hafnium

The He(I) and He(II) photoelectron spectra are reported for two series of transition metal mixed sandwich complexes of general formula L_aML_b (M = Ti, L_a = η⁵-C₅H₅, η⁵-CH₃C₅H₄, η⁵-C₅(CH₃)₅; M = Zr, Hf, L_a = η⁵-C₅(CH₃)₅; L_b = η⁷-C₇H₇ (series I); M = Ti, L_a = η⁵-CH₃C₅H₄, η⁵-C₅(CH₃)₅; M = Zr, L_a = η⁵-C₅(CH₃)₅; L_b = η⁸-C₈H₈ (series II)). Assignments were made of the metal d, cyclopentadienyl and carbocyclic π orbitals on the basis of He(I)/He(II) intensity ratios and shift effects and by comparison with UP data for related compounds. For series I no influence of the central metal upon the IEs of the highest occupied molecular orbital e₂ was observed. The IE of the non-bonding metal d_z2 orbital of Ti or Zr (5.28 and 4.70 eV, respectively) in the complexes of series II (L_a = η⁵-C₅(CH₃)₅) is very low.     

Synthesis of enantiomerically pure Sb-chirogenic organoantimony compounds and their crystal structures

Sb-chirogenic organoantimony compounds (±)-5a-c bearing heteroatom moieties such as 4,4-dimethyl-2-oxazolinyl, methoxymethyl, and diphenylphosphanyl substituents on the o-position of an aryl group have been prepared by nucleophilic displacement of the ethynyl moiety on (1-naphthyl)(phenylethynyl)(p-tolyl)stibane (3) with aryllithium reagents (2a-c). The optical resolution of the racemic (±)-5a,b was attained via separation of a diastereomeric mixture of their palladium complexes (S)-7 formed from the reactions of (±)-5a,b with di-μ-chlorobis[(S)-dimethyl(1-ethyl-α-naphthyl)aminato-C²,N]dipalladium(II) (6). The enantiomerically pure Sb-chirogenic stibanes isolated here were optically stable, and no racemization on the chiral antimony center was observed even when they were allowed to stand at room temperature for over 72 h in chloroform. The structure of 5a,b including the absolute configuration was determined by single crystal X-ray analyses of (+)-5aB and antimony-palladium complex (7bB), respectively. The analyses also revealed the presence of intramolecular interaction between the antimony and sp²-nitrogen atoms in the molecule Sb(S)-(+)-5aB.     

Nucleophilic substitution reactions at the Si-Cl bonds of the dichloro(methyl)silyl ligand in five- and six-coordinate complexes of ruthenium(II) and osmium(II)

Treatment of either RuHCl(CO)(PPh₃)₃ or MPhCl(CO)(PPh₃)₂ with HSiMeCl₂ produces the five-coordinate dichloro(methyl)silyl complexes, M(SiMeCl₂)Cl(CO)(PPh₃)₂ (1a, M = Ru; 1b, M = Os). 1a and 1b react readily with hydroxide ions and with ethanol to give M(SiMe[OH]₂)Cl(CO)(PPh₃)₂ (2a, M = Ru; 2b, M = Os) and M(SiMe[OEt]₂)Cl(CO)(PPh₃)₂ (3a, M = Ru; 3b, M = Os), respectively. 3b adds CO to form the six-coordinate complex, Os(SiMe[OEt]₂)Cl(CO)₂(PPh₃)₂ (4b) and crystal structure determinations of 3b and 4b reveal very different Os-Si distances in the five-coordinate complex (2.3196(11) Å) and in the six-coordinate complex (2.4901(8) Å). Reaction between 1a and 1b and 8-aminoquinoline results in displacement of a triphenylphosphine ligand and formation of the six-coordinate chelate complexes M(SiMeCl₂)Cl(CO)(PPh₃)(κ²(N,N)-NC₉H₆NH₂-8) (5a, M = Ru; 5b, M = Os), respectively. Crystal structure determination of 5a reveals that the amino function of the chelating 8-aminoquinoline ligand is located adjacent to the reactive Si-Cl bonds of the dichloro(methyl)silyl ligand but no reaction between these functions is observed. However, 5a and 5b react readily with ethanol to give ultimately M(SiMe[OEt]₂)Cl(CO)(PPh₃)(κ²(N,N-NC₉H₆NH₂-8) (6a, M = Ru; 6b, M = Os). In the case of ruthenium only, the intermediate ethanolysis product Ru(SiMeCl[OEt])Cl(CO)(PPh₃)(κ²(N,N-NC₉H₆NH₂-8) (6c) was also isolated. The crystal structure of 6c was determined. Reaction between 1b and excess 2-aminopyridine results in condensation between the Si-Cl bonds and the N-H bonds with formation of a novel tridentate “NSiN” ligand in the complex Os(κ³(Si,N,N)-SiMe[NH(2-C₅H₄N)]₂)Cl(CO)(PPh₃) (7b). Crystal structure determination of 7b shows that the “NSiN” ligand coordinates to osmium with a “facial” arrangement and with chloride trans to the silyl ligand.     

Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines

The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac₂O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac₂O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography.     

Symmetry analysis of periodicity and internal torsional conformers around a single bond

A simple formula to predict the number of equivalent conformations upon internal rotation around a single bond is derived. If the separate parts A and B, of a single bonded molecule A-B, possess N_a and N_b symmetry planes that contain the single bond, the number of symmetrical conformations is found to be Z = N_aN_b/J, where J is the number of these planes which are common. The energy potential for internal rotation then has a period of 2π/Z. Unsymmetrical conformations are infinite in number, but are shown to occur in infinite sets, each set with 2N_aN_b/J equivalent conformations. Extension to three-center molecules is also made.     

Structure of di-μ-N-Phenylanthranilato-di-1, 5-cyclooctadiene dirhodium(I)

The reaction of [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene) with sodium N-phenylanthranilate leads to the formation of the new crystalline rhodium(I) complex [RhFA(COD)]₂ (FA = N-phenylanthranilate anion). The compound is a dimer with two N-phenylanthranilate ions bridging and COD ligands terminally bonded to rhodium with an Rh … Rh distance equal to 3.424(3) Å. Strong intramolecular hydrogen bonding occurs between the hydrogen of the NH group and the closest carbonyl oxygen in the FA ligands. The crystals are monoclinic, space group P2₁/c, with a = 11.246(8), b = 14.999(9), c = 21.82(2) Å, β = 105.11(6)°. The structure was solved by the heavy-atom method and refined by least squares to R = 0.035 for 4260 diffractometer data.     

High-Pressure Synthesis and Crystal Structures of β-MNX (M=Zr, Hf; X=Br, I)

The single crystals of four kinds of metal nitride halides, β-MNX (M=Zr, Hf; X=Br, I), were prepared in Pt (or Au) capsules by the reaction of MN or α-MNX powders with NH₄X as fluxes under a high pressure of 3-5 GPa at 1000-1100°C. Their crystal structures were determined by single-crystal X-ray diffraction techniques. All four compounds crystallize in a rhombohedral space group R-3m, Z=6 with a=3.6403(6) Å, c=29.270(5) Å for β-ZrNBr, a=3.718(2) Å, c=31.381(9) Å for β-ZrNI, a=3.610(1) Å, c=29.294(6) Å for β-HfNBr, and a=3.689(1) Å, c=31.329(6) Å for β-HfNI. β-ZrNBr is isotypic with SmSI and the others are isotypic with YOF. Both structure variants are composed of structural slabs [X-M-N-N-M-X] (M=Zr, Hf; X=Br, I) stacked together by X…X van der Waals forces, but the ways of the layer stacking sequence are different: X_AM_cN_BN_CM_bX_A∣X_CM_bN_AN_BM_aX_C∣X_BM_aN_CN_AM_cX_B∣ in the SmSI-type and X_AM_bN_CN_BM_cX_A∣X_CM_aN_BN_AM_bX_C∣X_BM_cN_AN_CM_aX_B∣ in the YOF-type polymorphs.     

Crystal structure of catena-(2-thiobarbiturato) dithallium(I)

By powder X-ray diffraction the crystal structure of catena-(2-thiobarbiturato)dithallium(I) C₄H₂N₂O₂STl₂ (C₄H₄N₂O₂S is 2-thiobarbituric acid, H₂TBA), Tl₂TBA, is determined. Crystallographic data for Tl₂TBA are as follows: a = 15.1039(3) Å, b = 12.0818(2) Å, c = 3.86455(6) Å, β = 97.203(1)°, V = 741.34(2) ų, space group P2₁/n, Z = 4. There are two non-equivalent thallium atoms in the structure. The Tl1 polyhedron is a distorted trigonal prism due to the shortened Tl-S contact (3.634 Å), and the Tl2 polyhedron is a distorted square antiprism.     

Click reactions of 2H-azaphosphirene chromium and molybdenum complexes and a surprisingly facile access to a 2H-1,4,2-diazaphosphole derivative

Ring expansion reactions of 2H-azaphosphirene chromium and molybdenum complexes 1a,b with dimethyl cyanamide, triflic acid, and, subsequently at ambient temperature, with triethylamine gave a mixture of the respective 2H-1,4,2-diazaphosphole complex 2a,b and the non-ligated heterocycle 3. If the deprotonation with NEt₃ was carried out at low temperature, the selective formation of complexes 2a,b was observed, which were isolated in excellent yields and fully characterized (including single-crystal X-ray crystallography). Experimental and computational results revealed that the P, Cr and P, Mo bonds of 2H-1,4,2-diazaphosphole complexes are significantly weakened upon N-protonation of the heterocyclic ligand. When mixtures of 1a,b, TfOH, and Me₂NCN were warmed to ambient temperature, the primarily formed N-protonated of 2H-1,4,2-diazaphosphole complexes 4a,b could be observed by ³¹P NMR spectroscopy. The latter underwent decomplexation to give the N-protonated free ligand 5, which could be isolated and characterized by multinuclear NMR experiments. The neutral non-ligated heterocycle 3 was isolated from a one-pot reaction of 1b with TfOH and Me₂NCN by adding NEt₃ to a solution of intermediately formed 5.     

Crystal structures of allyltriphenyl-phosphonium halogenocuprates(I)

Alternating-current electrochemical synthesis is used to obtain for the first time halogenocuprates of an allyl derivative of phosphonium of the composition (CH₂=CHCH₂(C₆H₅)₃P)CuX₂ (X = Br (I), Cl (II)). Compound I crystallizes in the space group P2₁, a = 9.6341(3) Å, b = 12.4167(4) Å, c = 9.9618(4) Å, β = 117.484(5)°, Z = 2. Compound II crystallizes in the space group P2₁/n, a = 9.9725(5) Å, b = 15.4586(8) Å, c = 13.7557(5) Å, β = 90.429(4)°, Z = 4. In the structures of I and II quasilinear CuX ₂ ^? anions are held by C-H…X hydrogen bonds inside a framework formed by the stacking of phenyl groups from CH₂=CHCH₂(C₆P₅)₃P⁺ cations. Allyl groups are not involved in coordination with copper(I) atoms.     

Stereoselective synthesis of cationic heterobidentate C(NHC)/SR rhodium(I) complexes using stereodirecting N,N-dialkylamino groups

The synthesis of two different types of chiral C/S ligands based upon N-(N,N-dialkylamino)-substituted N-heterocyclic carbenes and thioether functionalities, along with their neutral [RhCl(CNH)(COD)] and cationic [Rh(I)(NHC/S)(COD)]⁺ complexes, has been accomplished. (S)-2-[(Phenylthio)methyl]pyrrolidine, carrying the thioether moiety, and (2S,5S)-2,5-diphenylpyrrolidine, combined with a thioether functionalized side chain, were studied as potential stereodirecting groups. Only the latter provided high selectivity in the formation of the neutral complex, leading to a single atropoisomer (de >98%) of the newly formed, configurationally stable C(NHC)–Rh bond. The synthesis of the corresponding cationic [Rh(I)(NHC/S)(COD)]⁺ complexes, however, resulted in the formation of single (R_a,S_S) and (S_a,S_S) diastereomers, respectively, of the four possible complexes in each case [combinations of the (R_a/S_a) C(NHC)–Rh axis and the (S_s/R_s) stereogenic S center formed upon coordination]. For the proline derivative, the resolution of the mixture of (R_a/S_a)-[RhCl(CNH)(COD)] neutral complexes proceeds via dynamic kinetic resolution through coordinatively unsaturated Rh(I) intermediates formed after halide abstraction. The absolute configurations of both types of cationic complexes were unequivocally assigned on the basis of X-ray diffraction analysis.     

Preparation and structures of 6- and 7-coordinate salen-type zirconium complexes and their catalytic properties for oligomerization of ethylene

A series of salen-type zirconium complexes of the general formula LZrCl₂ (L = N,N′-ethylenebis(salicylideneiminate), 3a; N,N′-ethylenebis(3,5-di-tert-butylsalicylideneiminate), 3b; N,N′-ethylenebis(5-methoxysalicylideneiminate), 3c; N,N′-ethylenebis(5-chlorosalicylideneiminate), 3d; N,N′-ethylenebis(5-nitrosalicylideneiminate), 3e; N,N′-o-phenylenebis(salicylideneiminate), 4a; N,N′-o-phenylenebis(3,5-di-tert-butylsalicylideneiminate), 4b; N,N′-o-phenylenebis(5-methoxysalicylideneiminate), 4c; N,N′-o-phenylenebis(5-chloro-salicylideneiminate), 4d) were prepared. The crystal structures of 6- and 7-coordinate zirconium complexes 4b and [4b · OCMe₂] were determined by X-ray crystallography, which reveals that a salen-type zirconium complex possesses a labile coordination site on the Zr center with a relatively stable framework and that the coordination and the dissociation of O-donor molecules occur readily at this site. The catalytic properties of 3(a-e) and 4(a-d) were studied for ethylene oligomerization in combination with Et₂AlCl as co-catalyst. Complex 3c featuring a methoxy-substituted salen ligand displayed higher activity than its analogous precursors having chloro and nitro groups as substituents. The catalytic reactions by 3(a-e) and 4(a-d) gave C₄-C₁₀ olefins and low-carbon linear α-olefins in good selectivity.     

An expedient approach to tetrahydrofuro[3,2-b]pyridine-2(3H)-ones via activation of pyridine N-oxide by triflic anhydride

The double addition of bis(trimethylsilyl) ketene acetals [R₁, R₂ = CH₃, -(CH₂)₅-] to pyridine N-oxide promoted by triflic anhydride under mild conditions generates N-[(trifluoromethane)sulfonyl-1,2-dihydropyridine-2,4-dicarboxylic acids 2a-b. Subsequent reaction of these acids upon iodolactonization conditions affords tetrahydrofuro[3,2-b]pyridine-2(3H)-ones 3a-b containing an exo-insaturation on the products as a result of an unexpected decarboxylation.     

Thermal decomposition of N2H6GeF6 · H2O,isolation and characterization of intermediates

The thermal behaviour of N₂H₆GeF₆ · H₂O was investigated by TG, DTG and DTA measurements. The decomposition proceeded in three steps, in which anhydrous N₂H₆GeF₆ and N₂H₅GeF₅; were isolated and characterized by chemical analysis and vibrational spectroscopy. The X-ray powder photographs of the intermediates were indexed, namely, for N₂H₆GeF₆ on the basis of a monoclinic cell with a = 8.86(9), b = 9.29(2), c =7.40(0) Å, β = 85° and for N₂H₅GeF₅ on the basis of an ortrhorhombic cell with a = 8.43(5),b = 9.19(9), c = 7.43(6) Å.