Róbert Gyepes

SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF PD(II) AND PT(II) COMPLEXES WITH P-BONDED 1'-(DIPHENYLPHOSPHINO)FERROCENECARBOXYLIC ACID

Abstract The title hybrid phosphine ligand (Hdpf) coordinates to Pt(II) and Pd(II) as a monodentate phosphine. In the absence of deprotonating agents, its carboxyl group remains uncoordinated to metal, but takes part in various types of hydrogen bonding. Using K2MCl4 as the metal ion source, trans-square planar complexes of the M(Hdpf-P)2X2 type (MPd, XCl, Br; MPt, XCl) were obtained. While Pd(Hdpf-P)2Cl2 is formed also from Pd(cycloocta-1,5-diene)Cl2, the analogous Pt(II)–cod complex provides cis-square planar Pt(Hdpf-P)2Cl2. The trans-chlorides behave inconsistently on recrystallization from carboxylic acids. While acetic acid gives single crystals of the solvates M(Hdpf-P)2Cl2·2 AcOH, propionic or formic acid does not form solvates with Pt(Hdpf-P)2Cl2 at comparable conditions. Single crystal X-ray structure determination of the last four complexes revealed remarkable differences in the conformation of the ferrocenyl moiety and in inter- and intramolecular hydrogen bonding. The two isostructural solvates have molecular arrangement with solvent molecules hydrogen-bonded to the carboxyl groups of the ligand, thus saturating their hydrogen-bond capability. As can be expected, the structure of the unsolvated trans-Pt(Hdpf-P)2Cl2 is that of a one-dimensional polymer linked by intermolecular hydrogen bonds. Finally, the cis-complex is dimeric in the crystal, being joined by pairs of the peripheral carboxyls; there is a further bonding π–π interaction between the phenyl groups of the cis-phosphines.

Nucleophilic reactivity of perhydro-3,6,9,12-tetraazacyclopenteno[1,3-f,g]acenaphthylene. A unified approach to N-monosubstituted and N,N′′-disubstituted cyclene derivatives

Abstract Perhydro-3,6,9,12-tetraazacyclopenteno[1,3- f,g ]acenaphthylene is readily mono- and dialkylated on nitrogen with alkyl bromides and iodides giving mono- and bis-quarternary ammonium salts. The title compound is a unified starting material for the preparation of cyclene based chelators.

Reduction of Bis[η5-(ω-alkenyl)tetramethylcyclopentadienyl]titanium Dichlorides: An Efficient Synthesis of Long-Chainansa-Bridged Titanocene Dichlorides by Acidolysis of Cyclopentadienyl-Ring- Tethered Titanacyclopentanes

The reduction of symmetric, fully-substituted titanocene dichlorides bearing two pendant ω-alkenyl groups, [TiCl2(η5-C5Me4R)2], RCH(Me)CH=CH2 (1 a), (CH2)2CH=CH2 (1 b) and (CH2)3CH=CH2 (1 c), by magnesium in tetrahydrofuran affords bis(cyclopentadienyl)titanacyclopentanes [TiIV{η1:η1:tlsb&endash;3%>η5:η5-C5Me4CH(Me)CH(Ti)CH2CH(CH2(Ti))CH(Me)C5Me4}] (2 a), [TiIV{η1:η1:η5:η5-C5Me4(CH2)2CH(Ti)(CH2)2CH(Ti)(CH2)2C5Me4}] (2 b) and [TiIV{η1:η1:η5:η5-C5Me4(CH2)2CH(Ti)CH(Me)CH(Me)CH(Ti)(CH2)2C5Me4}] (2 c), respectively, as the products of oxidative coupling of the double bonds across a titanocene intermediate. For the case of complex 1 c, a product of a double bond isomerisation is obtained owing to a preferred formation of five-membered titanacycles. The reaction of the titanacyclopentanes with PbCl2 recovers starting materials 1 a from 2 a and 1 b from 2 b, but complex 2 c affords, under the same conditions, an isomer of 1 c with a shifted carbon-carbon double bond, [TiCl2{η5-C5Me4(CH2CH2CH=CHMe)}2] (1 c′). The titanacycles 2 a-c can be opened by HCl to give ansa-titanocene dichlorides ansa-[{η5:η5-C5Me4CH(Me)CH2CH2CH(Me)CH(Me)C5Me4}TiCl2] (3 a), ansa-[{η5:η5-C5Me4(CH2)8C5Me4}TiCl2] (3 b), along with a minor product ansa-[{η5:η5-C5Me4CH2CH=CH(CH2)5C5Me4}TiCl2] (3 b′), and ansa-[{η5:η5-C5Me4(CH2)3CH(Me)CH(Me)CH=CHCH2C5Me4}TiCl2] (3 c), respectively, with the bridging aliphatic chain consisting of five (3 a) and eight (3 b, 3 b′ and 3 c) carbon atoms. The course of the acidolysis changes with the nature of the pendant group; while the cyclopentadienyl ring-linking carbon chains in 3 a and 3 b are fully saturated, compounds 3 c and 3 b′ contain one asymetrically placed carbon-carbon double bond, which evidently arises from the β-hydrogen elimination that follows the HCl addition.

SYNTHESIS, CRYSTAL STRUCTURES AND SOME PROPERTIES OF DIMETHYLSILYLENE-BRIDGED ANSA-PERMETHYLTITANOCENE TI(IV), (III) AND (II) COMPLEXES

Dimethylsilylene-bridged complexes Me2Si(C5Me4)2TiCl (2), Me2Si(C5Me4)2Ti[η2-C2(SiMe3)2] (3) and Me2Si(C5H4)2Ti[η2-C2(SiMe3)2] (4) have been prepared by the general methods which are known for obtaining of analogous non-bridged titanocene complexes. X-ray crystal structures of Me2Si(C5Me4)2TiCl2 (1), 2, and 3 reveal that the dihedral angle between the least-squares planes of cyclopentadienyl rings increases in the order 2 < 3 < 1. Comparison with the structures of analogous (C5HMe4)2Ti and (C5Me5)2Ti compounds shows that the value of increases in the series (C5Me5)2Ti < (C5HMe4)2Ti < Me2Si(C5Me4)2Ti, e.g. in the bis(trimethylsilyl)acetylene complexes from 41.1° for (C5Me5)2Ti[η2-C2(SiMe3)2] (9) to 50.0° for (C5HMe4)2Ti[η2-C2(SiMe3)2] (8) and to 53.5° for 3. Compounds 3, 8 and 9 induce the head-to-tail dimerization of 1-hexyne with the selectivity of 72%, 21% and ca. 100% respectively. The discrepancy between the selectivities and the values of for 3 and 8 is accounted for by a larger flexibility of the titanocene skeleton in 8, affording a larger space for a non-specific coordination of 1-hexyne. The effects of the μ-Me2Si group in 2 and 3 on some of their properties are compared with the effects of Me and H substituents in the non-ansa compounds with controversial results. For instance, the affinity of 2 to 2-methyltetrahydrofuran approaches that of (C5H2Me3)2TiCl whereas the shift of the v(C≡C) vibration in 3 indicates a stronger metal-acetylene bond than in 9.

Syntheses and structures of doubly tucked-in titanocene complexes with tetramethyl(aryl)cyclopentadienyl ligands

Titanocene–bis(trimethylsilyl)ethyne complexes [Ti(η5-C5Me4R)2(η2-Me3SiCCSiMe3)], where R=benzyl (Bz, 1a), phenyl (Ph, 1b) and p-fluorophenyl (FPh, 1c), thermolyse at 150–160°C to give products of double CH activation [Ti(η5-C5Me4Bz){η3:η4-C5Me3(CH2)(CHPh)}] (2a), [Ti(η5-C5Me4Bz){η3:η4-C5Me2Bz(CH2)2}] (2a′), [Ti(η5-C5Me4Ph){η3:η4-C5Me2Ph(CH2)2}] (2b), and [Ti(η5-C5Me4FPh){η3:η4-C5Me2FPh(CH2)2}] (2c). In the presence of 2,2,7,7-tetramethylocta-3,5-diyne (TMOD) the thermolysis affords analogous doubly tucked-in compounds bearing one η3:η4-allyldiene and one η5-C5Me4R ligand having TMOD attached by its C-3 and C-6 carbon atoms to the vicinal methylene groups adjacent to the substituent R (R=Bz (3a), Ph (3b), and FPh (3c)). Compound 3a is smoothly converted into air-stable titanocene dichloride [TiCl2{η5-C5Me2Bz(CH2CH(t-Bu)CHCHCH(t-Bu)CH2)}(η5-C5Me4Bz)] (4a) by a reaction with hydrogen chloride. Yields in both series of doubly tucked-in complexes decrease in the order of substituents: Bz≫Ph>FPh. Crystal structures of 1c, 2a, 2b, and 3b have been determined.

Reactions of titanocene-bis(trimethylsilyl)ethyne complexes with diethynylsilane derivatives

Titanocene complexes [Ti(η 5 -C 5 H 5− n Me n ) 2 (η 2 -Me 3 SiCCSiMe 3 )] ( n =0, 4 and 5) react uniformly with siladiynes R 2 2 Si(CCR 1 ) 2 , where R 1 =Ph, and R 2 =Ph or Me, at elevated temperature in hydrocarbon solvents to give the corresponding silacyclobutene-annelated titanacyclobutene complexes, 3-bis(η 5 -cyclopentadienyl)titana-6-diorganylsilabicyclo[2.2.0]hexa-1(2),4(5)-dienes, [(η 5 -C 5 H 5− n Me n ) 2 Ti{R 1 2 C 4 (SiR 2 2 )}]. Products arising from [Ti(η 5 -C 5 H 5− n Me n ) 2 (η 2 -Me 3 SiCCSiMe 3 )] ( n =0, 2 (1,3-isomer), 4 and 5) and Me 2 Si(CCCMe 3 ) 2 vary with n : the non-methylated titanocene complex affords a mixture of an analogous silacyclobutene-annelated titanacyclobutene and [{Ti(η 5 -C 5 H 5 ) 2 } 2 {μ-η(3–5):η(4–6)-Me 3 CCCCCCMe 3 }], the permethylated titanocene precursor gives mainly the allyldiene complex [Ti(η 5 -C 5 Me 5 )(η 3 :η 4 -C 5 Me 3 (CH 2 ) 2 )] while no titanium-containing product could be isolated for n= 4. The reaction of [Ti(η 5 -1,3-C 5 H 3 Me 2 ) 2 (η 2 -Me 3 SiCCSiMe 3 )] with Me 2 Si(CCCMe 3 ) 2 , however, cleanly affords the expected silacyclobutene–titanacyclobutene complex. All complexes were studied by spectral methods and solid-state structure of two representatives, [(η 5 -C 5 Me 5 ) 2 Ti{Ph 2 C 4 (SiMe 2 )}] and [(η 5 -1,3-C 5 H 3 Me 2 ) 2 Ti{(Me 3 C) 2 C 4 (SiMe 2 )}] was determined by single-crystal X-ray diffraction.

Synthesis, structural characterisation and bonding in an anionic hexavanadate bearing redox-active ferrocenyl groups at the periphery

Amide FcCONHC(CH2OH)3 (1; Fc = ferrocenyl), prepared from fluorocarbonylferrocene and tris(hydroxymethyl)methylamine, reacts with (Bu4N)3[H3V10O28] in N,N-dimethylacetamide to afford a salt containing a bis(triolato) capped hexavanadate anion bearing two ferrocenyl groups at its periphery, (Bu4N)2[{FcC(O)NHC(CH2O)3}2V6O13] (2). Compounds 1 and 2 were characterised by elemental analysis, spectroscopic methods (IR, NMR, and MS) and by cyclic voltammetry; the crystal structures of 1·1/2CH3CO2Et and (Bu4N)2[{FcC(O)NHC(CH2O)3}2V6O13]·2Me2NCHO were determined by X-ray diffraction analysis. Single-point DFT calculations performed for the isolated hexavanadate anion revealed the presence of 3-centre 4-electron (3c4e) O–V–O bonds on the hexavanadate cage, which are responsible for the high energy of the occupied frontier orbitals. The upper eleven occupied molecular orbitals including the HOMO are all delocalized over the hexavanadate cage and, therefore, any electrochemical oxidation can be expected to occur preferentially at the hexavanadate anion without affecting the pendant ferrocene moieties.

Experimental and computational evidence of solid-state anion–π and π–π interactions in [VO(O2)(L)(pa)]·xH2O complexes (L = picolinate, pyrazinate or quinolinate; pa = picolinamide)

Two new neutral monoperoxidovanadium(V) complexes [VO(O2)(L)(pa)]·xH2O have been synthesized: [VO(O2)(pic)(pa)]·H2O (1) and [VO(O2)(Hquin)(pa)]·2H2O (2) [pic: pyridine-2-carboxylato(1–) or picolinato(1–), Hquin: pyridine-2,3-dicarboxylato(1–) or quinolinato(1–), and pa: picolinamide]. The solid state structures of 1 and 2 feature a typical distorted pentagonal bipyramid coordination polyhedron around the central vanadium atoms. The bidentate anionic ligands are coordinated in two equatorial positions, while the bidentate picolinamide molecule is bound via the aromatic nitrogen and the carboxamide oxygen in one equatorial and one apical position. The experimental geometric parameters were used for a detailed study of intermolecular interactions between the pic–pic and pa–pa aromatic rings in 1. Interestingly, no π–π interactions were observed between the pyridine rings of Hquin or pa in 2, however, the less common anion–π solid-state interactions were found between the pic ligands in 1 and pca [pca = pyrazinecarboxylato(1–)] ligands in the already published structure of the related complex [VO(O2)(pca)(pa)]·H2O (3). The presence of anion–π and π–π interactions in 1 and 3 was confirmed by DFT computations performed on their solid-state structures. Computational results suggested a direct analogy between anion–π and π–π interactions, both being of predominantly electrostatic character.

Solid-state structures of persubstituted titanocene chlorides bridged with long aliphatic ansa-chains

Abstract A series of three ansa-titanocene monochlorides containing η5-tetramethylcyclopentadienyl ligands bridged by five- or eight-membered aliphatic chains were prepared via reduction of the corresponding dichlorides with half molar equivalent of magnesium and characterized by spectral methods. The solid-state structures of the monochloride complexes ansa-[TiCl{η5:η5-C5Me4CH(Me)CH2CH2CH(Me)CH(Me)C5Me4}] (1a) and ansa-[TiCl{η5:η5-C5Me4(CH2)3CH(Me)CH(Me)CHCHCH2C5Me4}] (4a), and of the bridge-unsaturated titanocene dichloride complex ansa-[TiCl2{η5:η5-C5Me4CH2CHCH(CH2)5C5Me4}] (3) were determined by single-crystal X-ray diffraction. All the compounds show bent metallocene structures with the ansa-chain situated in a side position with respect to Cg, Ti, Cg (Cg=centroid of the cyclopentadienyl ligand) plane. Angles subtended by the least-squares planes of the cyclopentadienyl rings and conformation of the ansa-chains indicates the absence of steric strain in the metallocene framework.

Vanadium‐Controlled Crystallization of Stereoisomers of NBu4[VO2(N‐Salicylidene‐isoleucinato)] through Epimerization

Reported herein is a simple synthetic and crystallization procedure for sequential isolation of two stereoisomers of isoleucine-derived vanadium(V) complexes from a racemic mixture with three stereogenic centers and therefore eight hypothetical species. The products of this crystallization were characterized by electronic and vibrational circular dichroism, NMR spectroscopy, and polarimetry to compare the chiroptic properties of the enantiomerically pure analogues prepared from L-isoleucine and D-allo-isoleucine. NMR studies pointed to the yet unobserved phenomenon of vanadium-catalyzed epimerization of isoleucine.