Galina L. Starova

Difference in Energy between Two Distinct Types of Chalcogen Bonds Drives Regioisomerization of Binuclear (Diaminocarbene)PdII Complexes

The reaction of cis-[PdCl2(CNXyl)2] (Xyl = 2,6-Me2C6H3) with various 1,3-thiazol- and 1,3,4-thiadiazol-2-amines in chloroform gives a mixture of two regioisomeric binuclear diaminocarbene complexes. For 1,3-thiazol-2-amines the isomeric ratio depends on the reaction conditions and kinetically (KRs) or thermodynamically (TRs) controlled regioisomers were obtained at room temperature and on heating, respectively. In CHCl3 solutions, the isomers are subject to reversible isomerization accompanied by the cleavage of Pd-N and C-N bonds in the carbene fragment XylNCN(R)Xyl. Results of DFT calculations followed by the topological analysis of the electron density distribution within the formalism of Baders theory (AIM method) reveal that in CHCl3 solution the relative stability of the regioisomers (ΔGexp = 1.2 kcal/mol; ΔGcalcd = 3.2 kcal/mol) is determined by the energy difference between two types of the intramolecular chalcogen bonds, viz. S···Cl in KRs (2.8-3.0 kcal/mol) and S···N in TRs (4.6-5.3 kcal/mol). In the case of the 1,3,4-thiadiazol-2-amines, the regioisomers are formed in approximately equal amounts and, accordingly, the energy difference between these species is only 0.1 kcal/mol in terms of ΔGexp (ΔGcalcd = 2.1 kcal/mol). The regioisomers were characterized by elemental analyses (C, H, N), HRESI+-MS and FTIR, 1D (1H, 13C{1H}) and 2D (1H,1H-COSY, 1H,1H-NOESY, 1H,13C-HSQC, 1H,13C-HMBC) NMR spectroscopies, and structures of six complexes (three KRs and three TRs) were elucidated by single-crystal X-ray diffraction.

Reactions of diacetylene ligands with trinuclear clusters. I Reactions of 2,4-hexadiyne-1,6-diol and its dicobalthexacarbonyl derivatives with H2Os3(CO)10

Abstract Reactions of H 2 Os 3 (CO) 10 with the diyne ligand HOCH 2 C 2 C 2 CH 2 OH and its dicobalthexacarbonyl derivatives {CO 2 (CO) 6 }(μ 2 ,η 2 -HOCH 2 C 2 C 2 CH 2 OH) and {Co 2 (CO) 6 } 2 (μ 2 ,η 2 : μ 2 ,η 2 -HOCH 2 C 2 C 2 CH 2 OH) have been studied. The reaction of the uncomplexed ligand yields the cluster with the completely rearranged starting ligand. The structure of this compound was determined by a single-crystal X-ray study. The rearranged ligand forms a pseudo-furan ring with the C CH 3 substituent in the α-position. The reactions of H 2 Os 3 (CO) 10 with the both dicobalthexacarbonyl derivatives yield the (μ-H)(μ-OH)Os 3 (CO) 10 cluster ar the main osmium-containing product. The structure of this compound was also established by a single-crystal X-ray study.

A family of heterotetrameric clusters of chloride species and halomethanes held by two halogen and two hydrogen bonds

Two previously reported 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT) chloride platinum(II) complexes [PtCl{HNC(R)NCN[C(Ph)C(Ph)]CNC(R)NH}] (R = tBu 1, Ph 2) form solvates with halomethanes 1·1¼CH2Cl2, 1·1⅖CH2Br2, and 2·CHCl3. All these species feature novel complex-solvent heterotetrameric clusters, where the structural units are linked simultaneously by two C–X⋯Cl–Pt (X = Cl, Br) halogen and two C–H⋯Cl–Pt hydrogen bonds. The geometric parameters of these weak interactions were determined using single-crystal XRD, and the natures of the XBs and HBs in the clusters were studied for the isolated model systems (1)2·(CH2Cl2)2, (1)2·(CH2Br2)2, and (2)2·(CHCl3)2 using DFT calculations and Baders AIM analysis. The evaluated energies of the weak interactions are in the range 0.9–3.0 kcal mol−1. The XBs and HBs in the reported clusters are cooperative. In the cases of (1)2·(CH2Cl2)2 and (1)2·(CH2Br2)2, the contribution of the HBs to the stabilization of the system is dominant, whereas for (2)2·(CHCl3)2 contributions of both types of the non-covalent interactions are almost the same. Crystal packing and other forces such as, e.g. dipole–dipole interactions, also affect the formation of the clusters.

Aurophilicity in Action: Fine-Tuning the Gold(I)-Gold(I) Distance in the Excited State To Modulate the Emission in a Series of Dinuclear Homoleptic Gold(I)-NHC Complexes.

The solution-state emission profiles of a series of dinuclear Au(I) complexes 4-6 of the general formula Au2(NHC-(CH2)n-NHC)2Br2, where NHC = N-benzylbenzimidazol-2-ylidene and n = 1-3, were found to be markedly different from each other and dependent on the presence of excess bromide. The addition of excess bromide to the solutions of 4 and 6 leads to red shifts of ca. 60 nm, and in the case of 5, which is nonemissive when neat, green luminescence emerges. A detailed computational study undertaken to rationalize the observed behavior revealed the determining role aurophilicity plays in the photophysics of these compounds, and the formation of exciplexes between the complex cations and solvent molecules or counterions was demonstrated to significantly decrease the Au-Au distance in the triplet excited state. A direct dependence of the emission wavelength on the strength of the intracationic aurophilic contact allows for a controlled manipulation of the emission energy by varying the linker length of a diNHC ligand and by judicial choice of counterions or solvent. Such unique stimuli-responsive solution-state behavior is of interest to prospective applications in medical diagnostics, bioimaging, and sensing. In the solid, the investigated complexes are intensely phosphorescent and, notably, 5 and 6 exhibit reversible luminescent mechanochromism arising from amorphization accompanied by the loss of co-crystallized methanol molecules. The mechano-responsive properties are also likely to be related to changes in bromide coordination and the ensuing alterations of intramolecular aurophilic interactions. Somewhat surprisingly, the photophysics of NHC ligand precursors 2 and 3 is related to the formation of ground-state associates with bromide counterions through hydrogen bonding, whereas 1 does not appear to bind its counterions.

Synthesis and characterization of bis-(diphenylphosphinoethane) -substituted hexarhodium clusters: Rh6(CO)14(μ2,η2 -Ph2P(CH2)2PPh2), Rh6(CO)152 (μ2,η1 : η1-Ph2P(CH2)2 PPh2) and Rh6(CO)15(η1-Ph2 P(CH2)2P(O)Ph2). X-Ray crystal structures of Rh6(CO)15PPh3 and Rh6(CO)14 (μ2,η2-Ph2P(CH2)2PPh2) clusters

Abstract Two major products of the photoreaction between Rh6(CO)16 and bis-(diphenylphosphinoethane) (dppe) were isolated and characterized as Rh6(CO)14(μ2, η2 -Ph2P(CH2)2 PPh2) with μ2-bridging bidentate dppe and Rh6(CO)15(η1-Ph2P(CH2)2P (O)Ph2) where one P atom of dppe is terminally coordinated, the other being oxidized and thus non-coordinated. Substitution of the labile acetonitrile ligand in Rh6(CO)15,NCMe by dppe yields Rh6(CO)15 2(μ2,η1:η1-Ph2P(CH2)2PPh2) with dppe bridging two Rh6 cores. The structures of Rh6(CO)14(μ2,η2 -Ph2P(CH2)2PPh2) and Rh6(CO)15PPh 3 have been determined by single-crystal X-ray diffraction studies. Solution structures of Rh6(CO)14(μ2,η2-Ph2P(CH2)2PPh 2), Rh6(CO)15PPh3, Rh6(CO)15(η1- Ph2P(CH2)2 P(O)Ph2) and Rh6(CO)152(μ2,η1:η1-Ph2P(CH2) 2PPh2) have been established by IR, and 13C and 31P NMR spectroscopy.

Cu(I)–NHC-Catalyzed (2 + 3)-Annulation of Tetramic Acids with 2H-Azirines: Stereoselective Synthesis of Functionalized Hexahydropyrrolo[3,4-b]pyrroles

A stereoselective and high-yield synthesis of hexahydropyrrolo[3,4-b]pyrroles from tetramic acids and 2H-azirines under Cu(I)-NHC catalysis is developed. An unusual N-C2 azirine bond cleavage, initiated by a copper enolate, was rationalized in terms of a free radical reaction mechanism.

The crystal structure of averievite, Cu 5 O 2 (VO 4 ) 2 .nMX; comparison with related compounds

Abstract The crystal structure of averievite, Cu5O2(VO4)2‧nMX has been determined. Trigonal system, space group P3, a = 6.375(1), c = 8.399(1) Å, V = 295.6(1) Å3, Z = 1, Dx = 4.01(1) g/cm3. The atomic arrangement is characterized by infinite nets parallel to (001) composed of [OCu4]6+ tetrahedra linked via corners in hexagonal rings. The bases of neigbouring tetrahedra are in one plane and their non-shared corners are turned to the oppoosite sides. The [VO4]3- tetrahedra are attached to the bases of [OCu4] tetrahedra. There are large (R >3.2 Å) channels in the structure where large molecular particles can enter. The comparison of the averievite structure with related compounds (in particular, copper oxovanadates) is given from the point of view of [OT4] polyion crystal chemistry.

Reactions of diacetylene ligands with trinuclear clusters II. Reactions of hexa-2,4-diyne-1,6-diol and 1,4-diphenyl-1,3-butadiyne with Ru3(CO)12

Abstract Thermal reactions of Ru3(CO)12 with hexa-2,4-diyne-1,6-diol and 1,4-diphenyl-1,3-butadiyne were studied. Reaction of the triruthenium cluster with HOCH2C2C2CH2OH results in substitution of two CO groups and coordination of the diyne ligand to a ruthenium triangle in parallel μ3,η2-mode via one of the conjugated triple bonds. The structure of the final product Ru3(CO)10(μ3,η2-HOCH2C2C2CH2OH) was determined by a single-crystal X-ray study. The analogous reaction with PhC2C2Ph affords the binuclear ruthenium complex Ru2(CO)6, (μ3,η4-C(Ph)C(C2Ph)C(C2Ph)C(Ph)). The starting diyne ligand in this complex is dimerized forming a ruthenacyclopentadiene ring Ru-C(Ph)=C(R)C(R)=C(Ph). As a whole, the structural unit obtained can be rationalized as a cluster skeleton containing two d- and four p-elements arranged into nido pentagonal bipyramid with eight skeletal electron pairs; this cluster pattern is very typical for the iron subgroup alkyne polynuclear complexes.

Synthesis and structural characterization of the isomers of Rh6(CO)14L2 clusters (L = NCME, Py, P(OPh)3), X-ray crystal structure of trans-Rh6(CO)14{P(OPh3)}2

Abstract The reaction of Rh6(CO)16 with two equivalents of Me3 NO in the presence of a substituting ligand (L = NCME, Py, P(OPh)3) affords a mixture of isomers of the general formula Rh6(CO)14L2. The substituting ligands occupy two terminal sites in the structure of the parent cluster. For L = P(OPh)3 three isomers (I-III) were separated from the reaction mixture. The structure of the first isomer (I) has been established by X-ray analysis. This compound crystallizes in two polymorphic modifications, monoclinic and triclinic; both of which consist of identical molecules and differ only in the packing of the molecules in the crystals. It should be noted that both polymorphic forms contain in the unit cells the racemic mixture (RR and SS) of the Rh6(CO)14{P(OPh)3} 2 molecules. This octahedral cluster may be considered as a derivative of the parent Rh6(CO)16 cluster with two terminal CO groups in trans positions at Rh(1) and Rh(2) atoms substituted by phosphite ligands. The structures of two other disubstituted clusters, (II) and (III) were established by 31P NMR spectroscopy. Phosphite ligands in these compounds occupy the terminal sites at the adjacent rhodium atoms of the Rh6 octahedron but differ in their mutual orientation. Other disubstituted derivatives (L = NCME, Py) are labile compounds and exist in solution as inseparable mixtures of the isomers characterized by 1H and 13C NMR spectroscopy. A mechanism of interconversion of the isomers is proposed.

Reaction of vinylidenecyclopropanes with aromatic imines in the presence of Lewis acids

Abstract1-Methyl-2-(2-methylpropenylidene)-1-phenylcyclopropane, 7-(2-methylpropenylidene)bicyclo[4.1.0]heptane, and (Z)-9-(2-methylpropenylidene)bicyclo[6.1.0]non-4-ene react with N-benzylideneanilines in the presence of boron trifluoride-ether complex to give pyrrolidine derivatives. Reactions of 1-methyl-1-phenyl-2-diphenylvinylidenecyclopropane with N-benzylideneanilines in the presence of BF3·Et2O, Yb(OTf)3, or Sc(OTf)3 lead to the formation of substituted 1,2,3,4-tetrahydroquinolines. 7-Diphenylvinylidenebicyclo[4.1.0]heptane in the presence of BF3·Et2O undergoes isomerization into 5-phenyl-8,9,10,11-tetrahydro-7H-cyclohepta[a]naphthalene.