Infrared study of some specificities of the dπpπ interaction in organogermanium compounds

The analysis is presented for the frequencies of stretching modes ν(GeH) in the IR spectra of organogermanium compounds R₂XGeH, RX₂GeH, RXYGeH, X₂YGeH and XYGeH₂ (where R is a substituent which does not make a d_πp_π bond with germanium, and X and Y are groups capable of d_πp_π interaction with germanium). It is shown that ν(GeH) in these compounds is dependent on both the I effect of R, X and Y, and the d_πp_π interaction in GeX and GeY bonds. If only one substituent capable of d_πp_π interaction with germanium is present, the value of such an effect is determined by itsσo_Rconstant. However, when germanium is bound to several substituents capable of d_πp_π interaction its magnitude depends on the effective charge at germanium which is determined by the inductive and mesomeric effects of X and Y. The data obtained are compared to the dependences observed in the IR spectra of similar organosilicon compounds.     

High resolution NMR studies of allylic derivatives of group IVB elements

The high resolution NMR spectra of certain Group IVB allyl compounds, FC₃M(CH₂)_nCHCH₂R′ (where R = Me, Et, Ph; R′ = H, Ph; M = Sn, Si, Ge; n = 1 or 2), have been studied in an attempt to detect manifestations of ground state p_πd_π overlap. Analyses, using sub-spectral techniques for ABMX₂ and ABX₂ systems, were confirmed using computer iteration methods. The emphasis has been placed here on the sensitivity of the coupling constants of the allyl group towards anticipated steric and electronic perturbation or towards the interaction between the Group IVB atom d orbitals and the olefinic p_π orbitals. Some ¹¹⁹Sn chemical shifts have also been recorded. The conclusions reached do not support the existence of ground state d_πp_π overlap in these compounds.     

Electron diffraction investigation of the molecular structure of cyclopropyl silane

The molecular structure of cyclopropyl silane (CPS) has been determined by gas phase electron diffraction. Among other parameters the bond distances (r_a) are: C₁C₂ = 1.528(2) Å, C₂C₃ = 1.490(4) Å, SiC = 1.840(2) Å, CH = 1.095(3) Å. The angle between the ring plane and the bond SiC is 55.9(3)°. The introduction of a tilt of the silyl group is in agreement with the secondary effect of substituents. The role of the silicon 3d orbitals in the interpretation of the structural data of CPS is discussed. Our results support the interpretation of the SiC bond to silicon in terms of dπ conjugation. This causes an asymmetry in the structure of the ring. The (pd)_π bonding concept is considered to be the sum of three different contributions: ionic, steric and dπ conjugation.     

Application des spectrographies RMN 13C et 1H a l'etude de derives cycliques du silicium et germanium,interactions pπdπ

The properties of 1-sila- and 1-gemma-cyclopent-2-(or -3-)enes with various substituents have been investigated by ¹³C and ¹H NMR spectroscopies. Values of chemical shifts and coupling constants in olefinic cyclic systems and in aromatic or ethylenic substituents attached to the hereto atom suggest the presence of a mesomeric p_πd_π interaction, particularly for the silicon atom. Studies at low temperatures given conformational data, which have been compared with data from the literature.     

Tetra-tert-butyl-pentafulvalen als Ligand in zweikernigen Molybdänkomplexen: cis-Anordnung ohne Metall-Metall-bindung

Reaction of 1,1′,3,3′-tetra-tert-butyl-5-′-pentafulvalenedipotassium (1) with hexacarbonylmolybdenum leads to hexacarbonyl-dipotassium(1,1′,3,′-tetra-tert-butyl-5,5′-pemtafulvalene)dimolybdate (2), which on further treatment with stoichiometric amounts of iodomethane yields the hexacarbonyldimethyl(1,1′-3,3′-tetra-tert-butyl-5,5′-pentafulvalene)dimolybdenum, (η⁵ : η⁵-^tBu₄C₁₀H₄)Mo₂(CO)₆-(CH)₃)₂ (3). Compound 3 is obtained as yellow needles and brownish cube-like crystals, and it is characterized by ¹H-NMR, ¹³C-NMR, IR, and MS data. The cubes crystallize in the space group C2/c with four molecules in the unit cell. Each molecule consists of two tricarbonylmethyl(cyclopentadienyl) molybdenum units which are connected by a central CC-bond, twisted against each other by 64.8° and bent by 25.8°. Due to the steric requirements of the tertbutyl substituents in the fulvalene ligand, 3 should be formed only from cis-configurated 2.     

Synthetic and structural studies on some 1,3-diselena- and 1,3-dithia-[3]ferrocenophanes of germanium and tin. crystal and molecular structure of 1,3-diselena-2,2- dichlorogermyl-[3]ferrocenophane

A series of [3]ferrocenophanes of general formula Fe(C₅H₄X)₂YCl₂ and the spiro compounds [Fe(C₅H₄X)₂]₂Ge (X = S, Se; Y = Ge, Sn) have been prepared by the reaction of ferrocene 1,1′-dithiol and ferrocene 1,1′-diselenol with tetrahalides of germanium and tin. Spectroscopic properties of the compounds are reported. In solution, the compounds are fluxional by a bridge reversal process. The crystal structure of 1,3-diselena-2,2-dichlorogermyl-[3]ferrocenophane at 163 K. has been determined by X-ray diffraction methods. At that temperature, crystals have space group P2₁/n with a 6.222(3), b 16.156(13), c 12.968(4) Å, β 97.53(1)° and Z = 4. Least-squares refinement gave R = 0.033 for 2834 unique significant reflections whose intensities were measured by counter diffractometry. The two SeGe bond lengths are 2.323 and 2.325(1) Å, with GeCl 2.148 and 2.161(1) Å. The SeGeSe bond angle is 118.2(1)°, ClGeCl 104.7(1)°, and SeGeCl angles range from 106.2 to 109.8(1)°. The SeC bond lengths are 1.901 and 1.904(5) Å, with CSeGe angles of 95.8 and 96.5(2)°. The cyclopentadienyl rings are in an eclipsed conformation with a mean twist angle of 2.7°, and are inclined to one another at 6.1°. The Se atoms are displaced from the ring planes by 0.17 and 0.20 Å yielding a non-bonded intramolecular Se…Se contact of 3.99 Å.     

Fourier transform NMR investigations of 13C labeled silyl and stannyl acetylenes

The ¹³C NMR spectra of ¹³C labeled mono- and di-substituted silyl- and stannyl-acetylenes have been studied. It was found that the values of ¹J(CC) coupling constants between acetylenic carbons decrease very sharply in the series Alk₃SiCCH, Alk₃SnCCH, Alk₃SiCCSiAlk₃ and Alk₃SnCCSnAlk₃. These results and the observed changes in the geminal hetero-atom β-acetylenic carbon couplings suggest a very strong p_πd_π interaction between the π-electrons of the triple bond and the vacant d orbitals of silicon and tin.     

Mass spectrometry of π-complexes of transition metals XI. Manganese and rhenium vinylidene complexes

The mass spectra of (π-C₅H₅)_nM_n(CO)(L)₁(L′) (M = Mn, Re; L = CO, P(C₆H₅)₃, P(OC₆H₅)₃; L′ is a vinylidene ligand) are reported and characterised by strong dehydrogenation of the rhenium complexes. In bimetallic analogues, the ReRe bond is stronger than the MnMn.     

Etude comparative en luminescence UV-visible du 1,1′-binaphtyle et du 2,2′-binaphtyle

The modifications of emission spectra obtained in fluid and rigid media as a function of temperature show a conformation change for 1,1′-binaphthyl in the excited state. This change is facilitated in fluid medium by the rotation of the two naphthyl groups around the C₁C_1′ bond. The molecular twisting in this excited state explains the original results for 1,1′-binaphthyl where the intensity ratio of phosphorescence to fluorescence (I_ph/I_fluo) varies with excitation wavelength. This result agrees with the charge transfer (CT) character obtained by the excited state S*₂ due to the twist of this molecule.The emission spectra of 2,2′-binaphthyl, a molecule which is practically identical in its electronic structure to 1,1′-binaphthyl, do not undergo significant modification with effects of temperature variation, and as a function of the excitation wavelength. These different effects for 1,1′-binaphthyl and 2,2′-binaphthyl agree with the difference of twist for the naphthyl rings around the single bond between these rings.     

Distorted tetrahedral copper(I)′complexes of 2,2′bi-4,5-dihydrothiazine and 2,2′-bi-2-thiazoline

The copper(I) complexes [Cu(btz)₂](BPh]₄(I) and [Cu₂(bt)₄][ClO₄]₂ (II) have been prepared (btz = 2,2′-bi-4,5-dihydrothiazine and bt = 2,2′-bi-2-thiazoline). Crystals of (I) are orthorhombic with a = 10.927(8), b = 11.743(8), c = 15.000(6) A, Z = 2, spacegroup P2₁2₁2. Crystals of (II) are monoclinic with a = 21.928(11), b = 11.925(8), c = 14.716(11) A, β = 103.6(1), Z = 8, spacegroup C2/c. 2121 and 2204 independent reflections have been measured on a diffractometer and the structures refined R 0.061 to R 0.063 respectively. In the cation of (I) the two btz ligands are coordinated via the α-di-imine groups (Cu-N 2.010(6), 2.024(6)Å). The resulting CuN₄ coordination geometry is a flattened tetrahedron with a dihedral angle of 68.9° between the two “CuN₂” planes. It is suggested that this distortion is an intrinsic property of the molecule associated with metal-to-ligand d_π-p_π* charge transfer rather than a consequence of lattice packing effects. In the dimeric cation (II), each copper(I) ion is bonded to the α-di-imine group of one bt molecule (A) but with appreciably different CuN bond lengths (2.277(6), 1.999(5)Å), to one nitrogen atom of a second ligand molecule (B) in the trans configuration (CuN 1.961(5)Å) and to one sulphur atom (CuS 2.428(2)Å) of a third ligand molecule (C). The coordination geometry is a very distorted tetrahedron if a very weak interaction (Cu…S 3.039(2)Å) with a sulphur atom of ligand B is discounted. It is suggested that the different structure arise from the different “bites” of the two ligands.     

A proton and carbon-13 nuclear magnetic resonance study of neopentylmercury compounds

Substituent effects on ¹⁹⁹Hg¹H and ¹⁹⁹Hg¹³C spinspin coupling constants have been studied for neopentylmercury derivatives, (CH₃)₃CCH₂HgR(or X), where R is covalently bonded Me, Et, t-Bu, neopentyl, and vinyl, and X is easily ionizable CN, Br, Cl, OCOCH₃, and ONO₂. Linear relationships exist between the methylene J(¹³CH) and ²J(HgH), ⁴J(HgC) and ²J(HgC) and ³J(HgC); but deviations from linearity occur for the chloride, bromide, acetate, and nitrate in the relationships between ²J(HgH) and ⁴J(HgH), ²J(HGH) and ²J(HGC). These deviations are discussed in terms of hyperconjugative p_πd_π bonding between the methylene CH bonds and mercury.     

The synthesis of a novel non-C2 symmetric H4-BINOL ligand and its application to titanium-catalyzed enantioselective addition of diethylzinc to aldehydes

The synthesis of the novel non-C₂ symmetric ligand (R)-5,6,7,8-tetrahydro-1,1′-binaphthol has been achieved via partial reduction of 2,2′-bis(methoxymethoxy)-1,1′-binaphthyl with Raney NiAl alloy in dilute aqueous NaOH solution followed by hydrolysis with HCl. Its titanium complex was found to be an effective catalyst in the asymmetric addition of diethylzinc to a variety of aldehydes, leading to the formation of secondary alcohols in high yields with good to excellent enantioselectivities.     

Indenyl and fluorenyl transition metal complexes: XV.Reactions of 1,1-dimethylindene,spirocyclopropane-1,1-indene,and spirocyclopropane-9,9-fluorene with L3M(CO)3 (L = NH3, Py; M = Cr,Mo, W)

Reaction of indene, 1,1-dimethylindene, spirocyclopropane-1,1-indene, and spirocyclopropane-9,9-fluorene with Py₃M(CO)₃/BF₃ · OEt₂ (M = Cr, Mo, W) involves two competing processes: (i) the formation of the ₆-arene complexes (A) and (ii) the oxidative addition at the C(1)R and C(9)R bonds (R = alkyl) with the formation of chelated σ,π-complex (B). The reaction pathway (A or B) is determined both by the metal and the ligand.     

Synthese und Reaktivität von Silicium-übergangsmetall-Komplexen: XXI. Ferrio-azidosilane and Ferriosilyl-iminophosphorane

Reaction of the ferriochlorosilanes R₅C₅(CO)₂FeSiR′_3-nCl_n (1a–1f) with sodium azide in tetrahydrofuran yields the ferrio- (mono-, bis-, and tris-azido)silanes R₅C₅(CO)₂FeSiR′_3-n(N₃)_n (R = H, Me; R′ = Me, H; n = 1–3) (2a–2f). CCl₄ converts Cp(CO)₂FeSiMe(H)N₃ (2a) into the ferrioazido(chloro)silane Cp(CO)₂-FeSiMe(Cl)N₃ (3). Treatment of 2d, 2f with Me₃P results in the formation of the ferriosilyl-iminophosphoranes Cp(CO)₂FeSi(N₃)(R)NPMe₃ (R = Me, N₃), (4a, 4b) by N₂ elimination.     

1,1-Dimethyl-1-silaethylene : Heat of formation,ionization potential and the energy of the siliconcarbon π-bond

The thermodynamic cycle consisting of thermal decomposition and dissociative ionization processes for 1,1-dimethyl-1-silacyclobutane is calculated. The heat of formation and the ionization potential (IP) for 1,1-dimethyl-1-sila-ethylene (DMSE) have been obtained: ΔH^o_f(DMSE) = 15.5 ± 5 kcal/mol; IP(DMSE) = 7.5 ± 0.3 eV. The siliconcarbon π-bond energy in DMSE is estimated: D_π(SiC)  28 ± 8 kcal/mol.     

Photoelectron spectra of molecules : VI. Hyperconjugation versus pπdπ bonding in group IVb compounds

Helium(I) photoelectron spectra have been obtained for the compounds (CH₃)₃MPh and (CH₃)₃MCH₂Ph (M = Group IV metal). The results have been partitioned by first order perturbation theory into hyperconjugation, induction and in the phenyl derivatives p_πd_π bonding.     

Pd(BF4)2 complexes of 1,1′-bis(alkyl- or aryl-)thio]- and 1,1′-bis(diphenylphosphino)-ferrocenes. Bond formation between the Fe and Pd atoms

1,1′-Bis[(alkyl- or phenyl-)thio]- and 1,1′-bis(diphenylphosphino)-ferrocenes react with (CH₃CN)₄Pd(BF₄)₂ in the presence of triphenylphosphine to give 1/1 complexes in good yields. Spectral data have confirmed the presence of an FePd dative bond in these complexes.     

The syntheses and coordination properties of M(CO)3X(DAB) (M = Mn,Re; X = Cl,Br, I; DAB = 1,4-diazabutadiene)

M(CO)₅X (M = Mn, Re; X = Cl, Br, I) reacts with DAB (1,4-diazabutadiene = R₁N=C(R₂)C(R₂)′=NR′₁) to give M(CO)₃X(DAB). The ¹H, ¹³C NMR and IR spectra indicate that the facial isomer is formed exclusively. A comparison of the ¹³C NMR spectra of M(CO)₃X(DAB) (M = Mn, Re; X = Cl, Br, I; DAB = glyoxalbis-t-butylimine, glyoxyalbisisopropylimine) and the related M(CO)₄DAB complexes (M = Cr, Mo, W) with Fe(CO)₃DAB complexes shows that the charge density on the ligands is comparable in both types of d⁶ metal complexes but is slightly different in the Fe-d⁸ complexes. The effect of the DAB substituents on the carbonyl stretching frequencies is in agreement with the A′(cis) > A″ (cis) > A′(trans) band ordering.Mn(CO)₃Cl(t-BuNCHCHNt-Bu) reacts with AgBF₄ under a CO atmosphere yielding [Mn(CO)₄(t-BuNCHCHN-t-Bu)]BF₄. The cationic complex is isoelectronic with M(CO)₄(t-BuNCHCHNt-Bu) (M = Cr, Mo, W).     

Preparation and structural characterization of [(η5-C5H5)2Zr(SC6H5)]2O. A qualitative description of the bonding in oxo-bridged dicyclopentadienyl-transition metal dimers

The hydrolysis of (η⁵-C₅H₅)₂Zr(SC₆H₅)₂ was shown previously by IR spectroscopy to produce an oxo-bridged complex. The molecular structure of this material has been determined by X-ray diffraction methods and consists of two (η²-C₅H₅)₂Zr(SC₆H₅) units linked by an oxo bridge. The ZrOZr bond is nonlinear at 165.8(2)° with a Zr?Zr interatomic separation of 3.902(1)Å. The two independent SZrO bond angles of 98.7(1) and 103.3(1)° are consistent with a d° electronic structure for each zirconium atom. The relatively short ZrO distances of 1.968(3) and 1.964(3) Å support the presence of partial double-bond character arising from the donation of electron density from filled p_π-orbitals on the oxygen atom to unfilled d-orbitals on the electron deficient d⁰ metal atoms. This bonding feature requires based upon orbital symmetry arguments that the (ML)₂O molecular core in [(η⁵-C₅H₅)₂ML]₂O complexes must be nonplanar with a dihedral angle between the two LMO planes less than 90°. For [(η⁵-C₅H₅)₂Zr(SC₆H₅)]₂O, dihedral angle of 61.7° was observed. The compound crystallizes in an orthorhombic space group, Pbca, with refined lattices parameters a 16.458(4), b 20.281(5), and c 17.016(4) Å. Full-matrix least-squares refinement of 2613 diffractometry data I > σ(I) led to a final discrepancy index R(F₀²) = 0.044.