Gino Paolucci

Polynuclear transition metal complexes. The reactivity of the new potentially binucleating ligand 2,6-diacetylpyridine-bis(1'-phthalazinylhydrazone) towards NiII, CuII and ZnII salts, and crystal and molecular structure of {bis[2,6-diacetylpyridine-bis(1-phthalazinylhydrazonato)nickel(II)]} dimethylformamide and water solvate

Abstract The interaction of the new, potentially binucleating, ligand 2,6-diacetylpyridine-bis(1′-phthalazinylhydrazone) (H 2 dapz), containing only nitrogen donor atoms, towards nickel(II), copper(II) and zinc(II) salts is reported. Depending on the nature of the counteranions, Ni II and Cu II ions selectively enter in one of the two ‘compartments’ present in the ligand. Analytical and spectroscopic characterizations of five series of mononuclear complexes [dapzM], [H 2 dapzMCl 2 ], [HdapzMCl], [(H 2 dapz) 2 M][ClO 4 ] 2 , [HdapzM][ClO 4 ], coming from reactions of metal acetates, metal chlorides and metal perchlorates, respectively, and the ligand in the bisdeprotonated, monodeprotonated and undeprotonated forms, are reported together with some interconversion reactions. Some tentative stereochemical assignments of these compounds are reported on the basis of their physicochemical properties. Different behaviour has been observed in the case of zinc(II) chloride and perchlorate. Crystal structure analysis on the bisdeprotonated complex [dapzNi] 2 , shows that the compound is dimeric, with the metal ions octahedrally coordinated into the upper compartment, and the pyridine nitrogens bridging the two nickel atoms.

New dinuclear bis(cyclopentadienyl)lanthanoid chlorides containing η5-C5H4 ligands linked by a metal-coordinated 2,6-dimethylenepyridyl unit

The salts M2[2,6-(CH2C5H4)2C5H3N] (i.e. Na2L, Li2L) react under mild conditions with anhydrous LnCl3 in the molar ratio 1:1 to afford complexes of the type [(LLnCl)2] (Ln = Y, Pr, Nd, Sm, Dy, Er, Yb, or Lu; 1–8). The dinuclear nature of the products 1–8 has been confirmed by mass spectrometry. Extended B/E-linked scans of metastable transitions suggest that L is chelating and not metal-bridging. Direct coordination of the pyridine-N atom to the Ln ion has been deduced from XPS measurements. Reaction of PrCl·(THF)x, and Na2L in the molar ratio 2:3 leads to the compound [L3Pr2] (9) which has been characterized by elemental analysis, 1H NMR and mass spectrometry. Some preliminary results on the catalytic activity of 1–8 during hydrogenation of 1-hexene by LiAlH4 suggest the formation of catalytically active, intermediate hydrides.

Lanthanocene (Ln=PrIII, YbIII) chlorides involving tetramethyldisiloxane-interlinked cyclopentadienyl ligands

Two new lanthanocenophanes [{O(Me2SiC5H4)2}PrIIICl · THF]x(2; x = 1 or 2) and [{O(Me2SiC5H4) 2}YbIII Cl]23, were made from LnCl3 (Ln = Pr or Yb) and K2[O(Me2SiC5H4)2] in THF. The 1H NMR spectra of THF-d8 solutions of paramagnetic 2 (at + 35 to −25°C) and 3 (at 10°C), respectively, display somewhat less complex 1H NMR spectra consistent with a virtually symmetrical position of the Me2SiOSiMe2 unit with respect to the cent-Ln- cent′ plane (cent = C5H4Si centroid). A low-temperature (−100°C) single-crystal X-ray study of 3 has confirmed the presence of centrosymmetric, Cl-bridged dimers in which the molecular configuration of the mononuclear {O(Me2SiC5H4)2}YbIII Cl2 units correspond to that of the previously described complex [{O(Me2SiC5H4)2TiIVCl2] 1. The high-resolution mass spectrum of 3 displays several signals from dinuclear fragments, the B/E-linked scans of which suggest, inter alia, intramolecular reorientation of at least one O(Me2SiC5H4)2 ligand from the chelating into a metal-bridging position.

Synthesis, spectroscopy, and crystal structure of a new stable biscyclopentadienyl uranium(IV) dichloride containing two C5H4-rings interlinked by a metal-coordinated 2,6-bis(methylene)pyridyl unit

Reaction of the new disodium salt: Na2[2,6-C5H3N(CH2C5H4)2 (2; 2,6-C5H3N = 2,6-pyridyl) with UCl4 in THF affords the reddish-green, mononuclear Cp2UIVCl2-derivative (Cp  η5-C5H5): μ-{2,6-CH2C5H3NCH2}(η5-C5H4)2UIVCl2 (1. According to a single-crystal X-ray study, 1 involves a notably strong UN bond (UNav: 2.62(1) A) along with two nonequivalent Cl ligands (UCl: 2.615(3) and 2.636(3) A). The low-temperature 1H NMR spectrum of the paramagnetic complex is in full accord with the solid state structure 1. Up to room temperature, the dissolved molecules of 1 show no fluxionality on the NMR time scale, although the two CH2 proton resonances appear to undergo coalescence.

Cyclopentadienyluranium(IV) complexes containing phosphido and/or amido ligands: Access to the new complex (C5H5)3UP(C6H5)2☆

Abstract The first organoactinide complex involving a phosphido ligand, Cp3UPPh2 (Cp = η5-C5H5, Ph = C6H5), has been prepared by several routes, the best of which involves the reaction of equimolar quantities of Cp2U(NEt2)2 and HPPh2. The complex Cp3UPPh2 is also formed on treatment of the new compounds (NEt2)3UPPh2 and CpU(NEt2)3 with HCp and PPh2 respectively. The by-products containing both amido and phosphido ligands, e.g. (NEt2)2U(PPh2)2, CpU(NEt2)2PPh2 and Cp2U(NEt2)(PPh2), are very unstable. The direct UP bond in Cp3UPPh2 is very reactive towards all types of chemically unsaturated or (proton) acidic molecules. The MS-, NIR/VIS- and 1H NMR-spectroscopic data show that the virtually free electron pair of the P atom is notably less involved in the UP bonding than, e.g., the corresponding electron pair of the related amido complexes Cp3UNEt2 and Cp3UNPh2.

Reactivity of uranyl ion with quinquedentate chelating hydrazine derivatives. Part 1. 2,6-Diacetylpyridine bis(2′-pyridylhydrazone)

Uranyl nitrate reacts with 2,6-diacetylpyridine bis(2′-pyridylhydrazone)(H2dapp) to give [UO2(H2dapp)(NO3)]2–[UO2(NO3)4](1) or a mixture (2) of ionic mononuclear species, in each of which H2dapp acts as a quinquedentate chelating ligand, depending on the experimental conditions. The complexes have been characterized by a number of physicochemical measurements including the X-ray analysis of (1). Crystals of (1) are triclinic with a= 14.071(9), b= 10.801(7), c= 10.122(6)A, α= 63.86(7), β= 75.65(9), γ= 78.86(9)°, space group P[graphic ommitted], and Z= 1. The structure has been solved by conventional techniques, and refined to a final R of 0.07. The unit cell contains two very highly distorted eight-co-ordinated cations [UO2(H2dapp)(NO3)]+, related by a centre of symmetry and with the N5O donor set in a symmetrically twisted ‘equatorial plane’[U–N (mean) 2.62 A, N–U–N (mean) 59.5°, and U–O 2.48 A for the unidentate nitrate group], and an uranyl tetranitrate counter anion [UO2(NO3)4]2–[two bidentate nitrates (U–O 2.53 A) and two unidentate (U–O 2.45 A)], at the centre of symmetry, in a hexagonal bipyramidal arrangement. The nature of the solvent(s), the high stabilizing effect of the 5,5,5,5 chelation mode, and reactivity tests, which allow the isolation of [UO2(H2dapp)(NO3)][BPh4](3) and [UO2(H2dapp)][ClO4]2(4), are discussed. Owing to the deprotonation of the diazapropenic sequences CN–NH–, the neutral complex [UO2(dapp)](6), containing U–N covalent bonds, can be obtained by the action of non-hydroxylated bases on (1)–(4). Like uranyl amides, compound (6) reacts with alcohols to give alkoxy-derivatives. Polymeric [{(UO2)2(H2dapp)(OCH3)4·xCH3OH}n](7) has been isolated.

Metal-bridging vs. chelating Me2Si(C5H4)2 ligands in dinuclear complexes: III. Mass spectrometry of organo-rare earth (M Y, Yb) hydrides containing the Me2Si(C5H4)2 ligand, and crystal structure of the new complex [{Me2Si(η5-C5H4)2YbIII(THF)}2(μ-H)(μ-Cl]

Abstract Reactions of [Me 2 Si(C 5 H 4 ) 2 MCl] 2 (Me  CH 3 ; M  Y, Yb) with NaH in THF have given several new hydride species which have been investigated mainly by high-resolution mass spectrometry (MS). For M  Y, the MS results suggest, as expected, that the reaction gives the dimeric hydride with the ligands Me 2 Si(C 5 H 4 ) 2 in a chelating mode, while for M  Yb the dimeric species isolated ( 4 ) contains only one chlorine and one hydrogen bridging the two Yb atoms. An X-ray crystallographic study of the extremely labile Yb-chloro-hydride crystallized from THF-solution has confirmed the formulation [{Me 2 Si(C 5 H 4 ) 2 Yb(THF)} 2 (μ-H) (μ-Cl)] ( 4 *) with metal-bridging Me 2 Si(C 5 H 4 ) 2 ligands and one THF ligand on each Yb atom. The unit cell contains two different dimers each of which is accompanied by one additional THF molecule. The starting complex with M  Yb undergoes reversible addition of MeCN, and all its Cl − ligands may readily be replaced by NCS − or [Me 2 Si(C 5 H 4 ) 2 ] 2− .

Organometallic amides of uranium(IV) and thorium(IV) involving one, two, or three cyclopentadienyl ligands

Abstract Both U(NEt2)4 and Th(NEt2)4 can be treated stoichiometrically and kinetically controlled with cyclopentadiene so that the various products CpnfM(NEt2)4−n (n = 2, 3, fM = U; n = 1, 2, 3, fM = Th) may be separately obtained in high yields. Cp3UNEt2 also reacts with an excess of HCp to give UCp4. For the preparation of the complexes Cp2U(NR2)2 (R = Et or Ph) and Cp3UNEt2, an alternative route, starting from UCl4, TlCp and LiNEt2 (KNPh2) and from Cp3UCl and LiNEt2, respectively, has also been developed. The new complex CpU(NEt2)3 does not readily undergo ligand redistribution to give Cp2U(NEt2)2 and U(NEt2)4, but it appears to react with another HCp molecule appreciably faster than does U(NEt2)4.

Bis(cyclopentadienyl)lanthanoid(III) alkoxides derived from chiral alcohols with a nitrogen donor functionality: Solution NMR studies of paramagnetic complexes

Abstract The first crystallographically elucidated example of a chiral organolanthanoid alkoxide complex [LnCp′ 2 ( μ -OCHRCHR 1 NR 2 R 3 )] 2 with Ln=Sm, R=Ph, R 1 =H, R 2 =Me and R 3 =CH 2 Ph ( 11 ; prepared from the pure (1R)-(+)-aminoalcohol) is presented. While crystalline 11 involves distinct N–Sm bonds (283.3 pm) in enantiomorphic {(-CHPhCH 2 )(CH 2 Ph)MeN–Sm} fragments, its solution NMR spectra ( 1 H, 13 C) suggest a complete or partial rupture of the N–Sm bonds. More systematic solution 1 H-NMR studies of likewise chiral representatives of the series with R=H, R 1 =Et, R 2 , R 3 =Me and Ln=Pr, Nd, Sm, Yb and Lu, respectively, indicate that at room temperature (r.t.) only the dissolved complexes with Ln=Pr, Nd and Sm involve N–Ln bonds that are stable on the NMR time scale. The homologues with Ln=Yb and Lu are fluxional. The paramagnetic nature of the complexes with Ln=Pr, Nd and Yb turns out to be particularly helpful for the structural deductions in magnifying significantly e.g. the diastereotopic splitting of the ring proton resonances of various CH 3 C 5 H 4 ligands.

Zirconocenophane dichlorides with di- and trisiloxane-bridged ring ligands: crystal structure of rac-[1,1,3,3-tetramethyldisiloxane-diyl-bis(3-tert-butyl-η5-cyclopentadienyl)zirconium(IV) dichloride]

Abstract The three novel zirconocenophane dichlorides [(O(Me2SiC5H4)2)ZrC12] (3), [O(Me2SiC5H3-tC4H9)2)ZrC12] (4) and [{Me2Si(OMe2SiC5H4)2)ZrCl2]n (5) have been prepared and characterized by 1H NMR spectroscopy. According to a successful single-crystal X-ray study, 4 crystallizes from n-hexane as a racemic mixture with exclusively 1,3-disubstituted cyclopentadienyl ligands and Cl2 centres oriented transoid to the O atoms. 4: monoclinic; space group P2 1 c , a = 1167.7(2), b = 1590.2(2), c = 1491.3(3) pm; β = 104.64(2)°; R = 0.061 (Rw = 0.058). In solution (room temperature), all three complexes are fluxional; moreover the NMR spectrum of 4 displays the resonances of two isomers (25:1). According to a mass spectrometry study of 5, the B 2 E -coupled scan of the molecular ion M+ ( m z = 494 ) indicates at least four “parent” fragments with 509 ⪕ m z ⩽ 1275 , suggesting here trinuclear or even trinuclear precursors.