Denis Vidovic

Molecular zinc phosphonates: synthesis and X-ray crystal structures of [{(ZnMe)4(THF)2}{tBuPO3}2] and [{(ZnEt)3(Zn(THF))3}{tBuPO3}4{μ3-OEt}]

The reactions of zinc alkyls with tert-butylphosphonic acid in 2 : 1 and 1 : 1 molar ratios afforded [[(ZnMe)(4-)(THF)2][tBuPO3]2] (2) and [[(ZnEt)3(Zn(THF))3][tBuPO3]4[mu3-OEt]] (3), respectively. Compounds 2 and 3 have been fully characterised by means of spectroscopic and analytical methods. Single-crystal X-ray diffraction studies revealed that zinc phosphonates 2 and 3 are tetra- and hexa-nuclear, respectively. This is in contrast to the dodecanuclear zinc phosphonate [[Zn2(THF)2(ZnEt)6Zn4(mu4-O)][(tBuPO3)8]] (1) obtained in a 1.5 : 1 reaction between zinc alkyls and tBuP(O)(OH)2.

Azirinium ylides from alkoxycarbonylcarbenoids and 2H-azirines: Generation and transformations

Dirhodium tetraacetate-catalyzed decomposition of diazo esters in the presence of 3-aryl-2H-azirines having no substituent in the 2-position gives rise to azirinium ylides which then undergo isomerization into 2-azabuta-1,3-diene derivatives or (in the presence of excess diazo ester) react with the corresponding rhodium carbenoid to form substituted 3,4-dihydro-2H-pyrroles. 2-Mono-and 2,2-disubstituted 3-phenyl-2H-azirines react with rhodium carbenoids generated from diazo esters to give azirinium ylides which are converted into the corresponding 2-azabuta-1,3-dienes.

Synthesis and investigation of the stability of Ti(III) β-diketiminato complexes. Structure of the tetrameric non-metallocene titanium fluoride complex (L2)4Ti4F6O2·2toluene supported by the β-diketiminato ligand

Abstract The titanium β-diketiminato complexes (L1)TiCl2 (1), (L1)TiCl(N2,6-iPr2C6H3) (2), and (L2)2TiCl (3) [L1=(2,6-iPr2C6H3)NC(Me)CHC(Me)N(2,6-iPr2C6H3), L2=iPrNC(Me)CHC(Me)NiPr] have been prepared by the reaction of the lithium salt of the ligand, L, with titanium trichloride. Complex 2 was isolated from supernatant solutions of 1 containing excess of the (L1)Li salt. The monochloride complex [(L2)TiCl(NiPr)]2 (4) was prepared by reduction of (L2)2TiCl2 with the excess of Na/K alloy. Fluorination of the monochloride complex 3 with Me3SnF affords polymeric [(L2)TiF2]n (5). Oxidation of 5 gives the tetrameric complex, (L2)4Ti4F6O2·2toluene (6). Compounds 1–6 were characterized by single crystal X-ray structural analyses, elemental analyses, NMR and mass spectra. The bulky ligand (L1) stabilizes the Ti(III) complex 1 with an unusual distorted square-planar pyramidal geometry around the titanium atom, by sigma bonding to the metal. The less bulky ligand (L2) in complexes 3, 4 and 6 has mixed σ and π coordination to the titanium center. Investigation of the CC, NC distances in the NCCCN unit of the coordinated β-diketiminato ligands (L1) and (L2) demonstrated the localization of the double bonds in the ligand in complexes 1–3 and 6. The stability of the complexes in solution was studied by means of NMR spectroscopy. Complexes 2 and 4 are stable in solution, the polymeric and the tetrameric nature of complexes 5 and 6 is not evident in C6D6 solution. The (L2)2TiCl stoichiometry of the complex is unstable.

1,3-Dipolar Cycloaddition of Difluoro-Substituted Azomethine Ylides. Synthesis and Transformations of 2-Fluoro-4,5-dihydropyrroles

Abstract2-Fluoro-4,5-dihydropyrrole-3,4-dicarboxylic acid derivatives were obtained by reaction of difluorocarbene with N-substituted ketone imines in the presence of fumaronitrile, maleonitrile, or dimethyl maleate. The reaction involves intermediate formation of azomethine ylides and their subsequent cycloaddition at the double bond. 11H-Dibenz[b,e]azepine and 3,4-dihydroisoquinolines react with difluorocarbene in the presence of fumaronitrile to give fluoro-substituted dibenzo[c,f]pyrrolo[1,2-a]azepine and pyrrolo[2,1-a]-isoquinoline derivatives. Treatment of 2-fluoro-4,5-dihydropyrrole-3,4-dicarbonitrile with amines and alkoxides affords the corresponding 2-amino- and 2-alkoxy derivatives, while its reactions with hydrazine hydrate and benzimidamide lead to formation of substituted pyrrolo[2,3-c]pyrazole and pyrrolo[2,3-d]-pyrimidine derivatives.

Selective transannular ring transformations in azirino-fused eight-membered O,N- or S,N-heterocycles.

The first examples of transannular ring transformations in azirino-fused eight-membered O,N- or S,N-heterocycles involving selective aziridine ring opening and medium-sized ring contraction are described, which provide an access to functionalized 1,4-benzox(thi)azines or 1,3-benzox(thi)azoles.

Regioselectivity of the 1,3-dipolar cycloaddition of fluorinated fluoren-9-iminium ylides to heteroelement-containing dipolarophiles: Experimental and quantum-chemical study

N-Substituted 9H-fluoren-9-imines react with difluorocarbene to give the corresponding iminium ylides whose further transformations in the absence of active dipolarophiles depend on the substituent at the nitrogen atom and reaction conditions. N-Ethyl-, N-benzyl-, and N-(2-phenylethyl)-9H-fluoren-9-imines are thus converted in low yield into the formal cyclodimerization products and/or 9H-fluorene-9-carboxamides. N-Methyl-substituted fluoreniminium ylide readily adds at the C=N bond of initial N-(9H-fluoren-9-ylidene)-methanamine with formation of spiro-fused imidazolidine derivative; in the presence of fluorenone, acetaldehyde, or benzaldehyde, addition at the C=O group of the dipolarophile occurs to give the corresponding oxazolidine derivatives. The regioselectivity of the cycloaddition of iminium ylides having a fluorene fragment at a double carbon-heteroelement bond can be described by quantum-chemical calculations in terms of the density functional theory (DFT; local hard and soft acids and bases concept): the cycloaddition leads preferentially to the 2,2-difluoro-substituted adduct.

Synthesis and structure of the heterobimetallic Yb(II) complex of composition L2Yb2LiI3 supported with the β-diketiminato ligand [L=Et2NCH2CH2NC(Me)CHC(Me)NCH2CH2NEt2]

Abstract The heterobimetallic Yb(II) mixed ligand complex L 2 Yb 2 LiI 3 1 has been prepared by the reaction of the lithium salt of the ligand L with the ytterbium diiodide. Compound 1 is characterized by single crystal X-ray structural analysis, multinuclear NMR and mass spectrometry. Complex 1 consists of LYbI and LLi units connected with the central Yb(1) atom. The latter is surrounded by the LYbI and LLi moieties in a sandwich like structure including two bridging iodine atoms. The NCCCN unsaturated system of the ligand in each of the units is almost planar and π coordinated to the Yb(1) atom. These two planar units are tilted to each other and the pendant arms of the β-diketiminato ligand in each moiety are bent. The metal atoms are located out of the NCCCN plane of the ligands and the three metal atoms in complex 1 form almost a straight line.

New synthetic route for organic polyoxometallic clusters: synthetic and structural investigations on the first dumb-bell shaped polyoxozirconium hydroxide with the [Zr9(μ5-O)2(μ3-O)4(μ-O)4(μ-OH)8] core structure

A new route for organic polyoxometallic clusters describes the first dumb-bell-like organic polyoxozirconium hydroxide [[(Cp*Zr)4(mu5-O)(mu3-O)2(mu-OH)4]2Zr(mu-O)4] x 2C7H8 (2; Cp* = C5Me5) involving the treatment of the Brønsted acidic organozirconium hydroxide [(Cp*Zr)6(mu4-O)(mu-O)4(mu-OH)8] x 2C7H8 (1) with organozirconium compounds.