Group 3 and 4 metal alkyl and hydrido complexes containing a linked amido-cyclopentadienyl ligand: “constrained geometry” polymerization catalysts for nonpolar and polar monomers

In order to understand the nature of the putative cationic 12-electron species [M(η⁵:η¹-C₅R₄SiMe₂NR′)R″]⁺ of titanium catalysts supported by a linked amido-cyclopentadienyl ligand, several derivatives with different cyclopentadienyl C₅R₄ and amido substituents R′ were studied systematically. The use of tridentate variants (C₅R₄SiMe₂NCH₂CH₂X)²⁻ (C₅R₄=C₅Me₄, C₅H₄, C₅H₃^tBu; X=OMe, SMe, NMe₂) allowed the NMR spectroscopic observation of the titanium benzyl cations [Ti(η⁵:η¹-C₅Me₄SiMe₂NCH₂CH₂X)(CH₂Ph)]⁺. Isoelectronic neutral rare earth metal complexes [Ln(η⁵:η¹-C₅R₄SiMe₂NR′)R″] can be expected to be active for polymerization. To arrive at neutral 12-electron hydride and alkyl species of the rare earth metals, we employed a lanthanide tris(alkyl) complex [Ln(CH₂SiMe₃)₃(THF)₂] (Ln=Y, Lu, Yb, Er, Tb), which allows the facile synthesis of the linked amido-cyclopentadienyl complex [Ln(η⁵:η¹-C₅Me₄SiMe₂NCMe₃)(CH₂SiMe₃)(THF)]. Hydrogenolysis of the linked amido-cyclopentadienyl alkyl complex leads to the dimeric hydrido complex [Ln(η⁵:η¹-C₅Me₄SiMe₂NCMe₃)(THF)(μ-H)]₂. These complexes are single-site, single-component catalysts for the polymerization of ethylene and a variety of polar monomers such as acrylates and acrylonitrile. Nonpolar monomers such as -olefins and styrene, in contrast, give isolable mono-insertion products which allow detailed studies of the initiation process.     

A study of ortho- and para-siloxyanilines for the synthesis of mono-, bi-, and tetra-nuclear early transition metal–imido complexes

The siloxyanilines o-Me₃SiOC₆H₄NH₂ (1) and p-RMe₂SiOC₆H₄NH₂ (R=H (2); R=Me (3)), and their N-silylated derivatives p-Me₃SiOC₆H₄NHSiMe₃ (4) and p-Me₃SiOC₆H₄N(SiMe₃)₂ (5) have been prepared from ortho- or para-aminophenol and used in the synthesis of imido complexes. Thus, binuclear [{Ti(η⁵-C₅H₅)Cl}{μ-NC₆H₄(p-OSiMe₃)}]₂ (6) and mononuclear [TiCl₂{NC₆H₄(p-OSiMe₃)}(py)₃] (7) imido complexes have been obtained from the reaction of 3 and [Ti(η⁵-C₅H₅)Cl₃] or [TiCl₂(N^tBu)(py)₃], respectively. In contrast, the reaction of 1 with TiCl₄ and ^tBupy affords the titanocycle [TiCl₂{OC₆H₄(o-NH)---N,O}(^tBupy)₂] (8). Compound 5 has also been used to prepare the niobium imide complex [NbCl₃{NC₆H₄(p-OSiMe₃)}(MeCN)₂] (9), by its reaction with NbCl₅ in CH₃CN. These findings have been applied to the synthesis of polynuclear systems. Thus, chlorocarbosilane Si[CH₂CH₂CH₂Si(Me)₂Cl]₄ (CS–Cl) has been functionalized with the ortho- and para-aminophenoxy groups to give 10 and 11, respectively. The use of 11 has allowed the formation of the tetranuclear compound 12. Attempts to synthesize terminal imido titanium complexes from 10 and TiCl₄ in the presence of ^tBupy and Et₃N, give complex 8 and carbosilane CS–Cl.     

Organometalloidal derivatives of the transition metals : XXX. Mass spectrometry of transition metal substituted disilanes

Mass spectral fragmentation of a series of transition metal substituted disilanes, LMSiMe₂SiMe₂ML, LM = (η⁵-C₅H₅)Fe(CO)₂- (Fp), (η⁵-C₅H₅)Fe(η⁵-C₅H₄)- (Fc), RFe(CO)₂(η⁵-C₅H₄), are reported. They exhibit significant distinctions depending on the nature of LM. Direct cleavage of the Si---Si bond occurs in the order Fc å Fp å RFe(CO)₂(η⁵-C₅H₄) owing to the capacity of the LM fragment to stabilize positive charge. For complexes containing a direct Fe---Si bond, i.e. Fp-SiMe₂SiMe₂ML, disilene complexed ions are observed, and those complexes containing both an Fp group and a (η⁵-C₅H₄-SiMe₂SiMe₂) group exhibit significant formation of (C₅H₄=Si=SiMe₂) complexed ions. Little disproportionation is observed for any of the complexes studied, in contrast to organodisilanes.     

Synthese et etude des complexes [C5H4(CH2)3C5H4]Ti(C5H5)2 presentant un pont entre deux ligands cyclopentadienyles

The complex (di-η⁵-C₅H₄CH₂CH₂CH₂C₅H₄)Ti(η¹-C₅H₅)₂ (I) can be obtained unambiguously starting from the corresponding bridged titanocene dichloride. Attempts to synthesize the isomeric compounds (η⁵-C₅H₅)₂ Ti(di-η¹-C₅H₄-CH₂CH₂CH₂C₅H₄) (I′) by the action of a convenient bridged dianion on (C₅H₅)₂ TiCl₂ afford several compounds, one of them is the complex I. The possibility of interconversion of these complexes by a fluctional process is discussed.     

Synthesis and crystal structure of the complex [MoW(OEt)(μ-CH2){μ-C(C6H4Me-4)C(Me)O}(η-C7H7)(η-C2B9H10Me)]

The complex [MoW(μ-CC₆H₄Me-4)(CO)₂(η⁷-C₇H₇)(η⁵-C₂B₉H₁₀Me)] reacts with diazomethane in Et₂O containing EtOH to afford the dimetal compound [MoW(OEt)(μ-CH₂){μ-C(C₆H₄Me-4)C(Me)O}(η⁷-C₇H₇)(η⁵-C₂B₉H₁₀Me)]. The structure of this product was established by X-ray diffraction. The Mo---W bond [2.778(4) Å] is bridged by a CH₂ group [μ-C---Mo 2.14(3), μ-C---W 2.02(3) Å] and by a C(C₆H₄Me-4)C(Me)O fragment [Mo---O 2.11(3), W---O 2.18(2), Mo---C(C₆H₄Me-4) 2.41(3), W---C(C₆H₄Me-4) 2.09(3), Mo---C(Me) 2.26(3) Å]. The molybdenum atom is η⁷-coordinated by the C₇H₇ ring and the tungsten atom is η⁵-coordinated by the open pentagonal face of the nido-icosahedral C₂B₉H₁₀Me cage. The tungsten atom also carries a terminally bound OEt group [W---O 1.88(3) Å]. The ¹H and ¹³C-{¹H} NMR data for the dimetal compound are reported and discussed.     

Synthesis and structure of ansa-cyclopentadienyl pyrrolyl titanium complexes: [(η-C5H4)CH2(2-C4H3N)]Ti(NMe2)2 and [1,3-{CH2(2-C4H3N)}2(η-C5H3)]Ti(NMe2)

Reaction of ansa-cyclopentadienyl pyrrolyl ligand (C₅H₅)CH₂(2-C₄H₃NH) (2) with Ti(NMe₂)₄ affords bis(dimethylamido)titanium complex [(η⁵-C₅H₄)CH₂(2-C₄H₃N)]Ti(NMe₂)₂ (3) via amine elimination. A cyclopentadiene ligand with two pendant pyrrolyl arms, a mixture of 1,3- and 1,4-{CH₂(2-C₄H₃NH)}₂C₅H₄ (4), undergoes an analogous reaction with Ti(NMe₂)₄ to give [1,3-{CH₂(2-C₄H₃N)}₂(η⁵-C₅H₃)]Ti(NMe₂) (5). Molecular structures of 3 and 5 have been determined by single crystal X-ray diffraction studies.     

Stabile Bis(η-alkin)MCl2-komplexe; Darstellung und reaktivität

The synthesis and reactivity of {(η⁵-C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂} MCl₂ (M = Fe: 3a; M = Co: 3b; M = Ni: 3c) is described. The complexes 3 are accessible by the reaction of (η⁵-C₅H₄SiMe₃) ₂Ti(CSiMe₃)₂ (1) with equimolar amounts of MCl₂ (2) (M = Fe, Co, Ni). 3a reacts with the organic chelat ligands 2,2′-dipyridyl (dipy) (4a) or 1,10-phenanthroline (phen) (4b) in THF at 25°C to afford in quantitative yields (η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂ (1) and [Fe(dipy)₂]Cl₂ (5a) or [Fe(phen)₂]Cl₂ (5b). 1/n[Cu^IHal]_n (6) or 1/n[Ag^IHal]_n (7) (Hal = Cl, Br) react with {(η⁵ -C₅H₄SiMe₃)₂Ti(CCSiMe₃)₂}FeCl₂ (3a), by replacement of the FeCl₂ building block in 3a, to yield the compounds {(η⁵-C₅H₄SiMe₃)₂Ti(C CSiMe₃)₂}Cu^IHal (8) or {(η⁵-C₅H₄SiMe₃)₂Ti(CSiMe₃)₂}Ag^IHal (9) (Hal = Cl, Br), respectively. In 8 and 9 each of the two Me₃SiCC-units is η²-coordinated to monomeric Cu^I Hal or Ag^IHal moieties. Compounds 8 and 9 can also be synthesized by the reaction of (η⁵-C₅H₄SiMe₃)₂ Ti(CSiMe₃)₂ (1) with 1/n[Cu^IHal]_n (6) or 1/n [Ag^IHal]_n (7) in excellent yields. All new compounds have been characterized by analytical and spectroscopic data (IR, ¹H-NMR, MS). The magnetic moments of compounds 3 were measured.     

Reactivity of niobocene dihalogenides toward nitroso derivatives. EPR and IR characterization of the first niobium(IV) complexes containing an ArNO-N,O ligand

The reaction of [Nb(η⁵-C₅H₄R)₂X₂] [1: R = SiMe₃, X = Cl; 2: R = SiMe₃, X = Br; 3: R = H, X = Cl; 4: R =^t, X = Cl] with nitroso derivatives ArNO [a: Ar = Ph; b: Ar = o-CH₃-C₃H₄; c: Ar = p-(CH₃)₂NC₆H₄] yields paramagnetic complexes formulated as [Nb(η⁵-C₅H₄R)(η³-C₅H₄R)X₂(ArNO-N,O) 1a, 1b, 1c, 2a, 3a, 4a and 4c, which have been characterized by ESR and IR spectroscopy.     

Highly stereoselective reduction of methyl ketone complexes of the chiral Lewis acid [(η-C5H5)Re(NO)(PPh3)] by K(s-C4H9)3BH; synthesis of optically active secondary alcohols and derivatives

Reaction of optically active ketone complexes (+)-(R)-[(η⁵-C₅H₅)Re(NO)-(PPh₃)(η¹-O=C(R)(CH₃)]⁺ BF₄⁻ (R = CH₂CH₃, CH(CH₃)₂m C(CH₃)₃, C₆H₅) with K(s-C₄H₉)₃BH gives alkoxide complexes (+)-(RS)-(η⁵-C₅H₅)Re(NO)(PPh₃)-(OCH(R)CH₃) (73–90%) in 80–98% de. The alkoxide ligand is then converted to Mosher esters (93–99%) of 79–98% de.     

π-Olefin-Iridium-Komplexe : XXI. Synthese und Kristallstrukturen heterobinuclearer Komplexe mit wannenförmiger, synfacial gebundener η: η-Benzolbrücke

CpIr(η⁴-C₆H₆) (2) has been obtained in high yield by a four-step synthesis. Thermal reaction of 2 with CpCO(C₂H₄)₂ and photochemical reaction of 2 with CpRh(C₂H₄)₂ or CpRh(C₂H₄)₂ give the compounds μ-(η³: η³-C₆H₆)CoIrCp₂ (3), μ-(η³: η³-C₆H₆)RhIrCp₂ (4), and μ-(η³: η³-C₆H₆)(RhCp)(IrCp) (5), respectively. The X-ray crystallography data of 3 and 4 reveal a boat-shaped conformation of the synfacially bridging benzene ligand with a rather long Co---Ir bond distance in 3 and a relatively short Rh---Ir bond length in 4 which are caused by almost constant folding angles of the benzene unit. The dynamic behaviour of the benzene bridge was investigated by NMR spectrometry.     

Interaction of half-sandwich alkylmolybdenum(III) complexes with B(C6F5)3. The X-ray structure of [CpMo(η-C4H6)(μ-Cl)(μ-CH2)(O)MoCp][CH3B(C6F5)3]

The reactions of the half-sandwich molybdenum(III) complexes CpMo(η⁴-C₄H₄R₂)(CH₃)₂, where Cp=η⁵-C₅H₅ and R=H or CH₃, with equimolar amounts of B(C₆F₅)₃ have been investigated in toluene. EPR monitoring shows the formation of an addition product which does not readily react with Lewis bases such as ethylene, pyridine, or PMe₃. The analysis of the EPR properties and the X-ray structure of a decomposition product obtained from dichloromethane, [CpMo(η⁴-C₄H₆)(μ-Cl)(μ-CH₂)(O)MoCp][CH₃B(C₆F₅)₃], indicate that the borane attack has occurred at the methyl position.     

Synthesis and characterization of new oligosilane derivatives of iron and molybdenum

By use of salt elimination, the transition metal substituted oligosilanes (η⁵-C₅Me₄Et)Fe(CO)₂SiMe₂SiMe₂Cl 1, (η⁵-C₅Me₄Et)Mo(CO)₃SiMe₂SiMe₂Br 2, (η⁵-C₅Me₄Et)Fe(CO)₂(SiMe₂)₆(CO)₂Fe(η⁵-C₅Me₄Et) 3 and (η⁵-C₅Me₄Et)Fe(CO)₂(SiMe₂)₆Br 4 were prepared and characterized. Compound 1 is well crystallized from pentane and its structure has been determined by X-ray diffraction analysis.     

Synthesis and X-ray crystal structures of [Ph2PMe2][(η-C5H4Bu)2Li] and [(η-C5H4Bu)2Yb(Cl)CH2P(Me)Ph2]

The interaction of [(η⁵-C₅H₄Bu^t)₂YbCl · LiCl] with one equivalent of Li[(CH₂) (CH₂)PPh₂] in tetrahydrofuran gave [Ph₂PMe₂][(η⁵-C₅H₄Bu^t)₂Li] (1) and [(η⁵-C₅H₄Bu^t)₂Yb(Cl)CH₂P(Me)Ph₂] (2) in 10% and 30% yields, respectively. 1 could also be prepared in 70% yield from the reaction of [Ph₂PMe₂][CF₃SO₃] with two equivalents of (C₅H₄Bu^t)Li. Both compounds have been fully characterized by analytical, spectroscopic and X-ray diffraction methods. The solid state structure of 1 reveals a sandwich structure for the [(η⁵-C₅H₄Bu^t)₂Li]⁻ anion.     

Versatile reactions of a para-bromophenylacetylide iron(II) derivative and X-ray structure of the fluoro analogue. Synthesis of new redox-active organoiron(II) synthons

The synthesis of the new (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,3-(C₆H₄X) (m-2a/2b; X=F/Br) and (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄I) (2c) complexes, as well as the solid-state structure of the known (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄F) (2a) complex are described. The catalytic coupling reactions of the bromo complexes with various alkynes were next investigated. Starting from the known (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄Br) complex (2b), the synthesis of the (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄)---CC---H complex (6d) and of the corresponding silyl-protected precursors (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄)CC---SiR₃ (6b/6c; R=ⁱPr/Me) are reported. By use of lithium---bromine exchange reactions on 2b, the silyl- (7a; E=Si; R=Me) and tin- (7b–7d; E=Sn; R=Me, Bu, Ph) substituted analogues (η²-dppe)(η⁵-C₅Me₅)Fe---CC---1,4-(C₆H₄)ER₃ are also isolated. The spectroscopic and electrochemical characterisations of all these new Fe(II)/Fe(III) redox-active building blocks are presented and the electronic substituent parameters for the “(η²-dppe)(η⁵-C₅Me₅)Fe---CC” group are determined by means of ¹⁹F-NMR.     

Organopolysilane oligomers bearing transition-metal moieties: Synthesis, reactivities and molecular structure of [η-Me3SiMe2SiC5H4(CO)Fe(CO)2Fe(CO)-η-C5H4SiMe2SiME3]

Reaction of Me₃SiMe₂SiC₅H₅ (4), prepared from Me₃SiMe₂SiCl and C₅H₅Na, with Fe(CO)₅ in refluxing xylene afforded the title compound (3). The silicon-silicon bond in 3 is exceptionally stable in refluxing xylene and also in succeeding reactions to prepare a series of its derivatives. Thus, 3 reacted with I₂ in either chloroform or benzene, giving [η⁵-Me₃SiMe₂SiC₅H₄Fe(CO)₂I] (6). Compound 3 was reduced by sodium amalgam and reacted subsequently with CH₃I, PhCH₂Cl, CH₃COCl, PhCOCl, Cy₃SnCl (Cy = cyclohexyl) and Ph₃SnCl, producing [η⁵-Me₃SiMe₂SiC₅H₄Fe(CO)₂R][7 : R = CH₃ (a), PhCH₂ (b), CH₃CO (c), PhCO (d), Cy₃Sn (e) and Ph₃Sn (f), respectively]. The molecular structure of 3 has been determined by X-ray diffraction crystallography. It was found that 3 has a trans-configuration with a symmetrical centre located at the middle of the Fe---Fe bond. It is abnormal that the conformation of the disilane part around the Si---Si bond is almost eclipsed rather than staggered.     

Substituted cyclopentadienyl ligands—10. Intramolecular steric interactions in [(η-C5H3(SiMe3)2)Mo(CO)2(L)I]

Reaction of C₅H₄(SiMe₃)₂ with Mo(CO)₆ yielded [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₃]₂, which on addition of iodine gave [(η⁵-C₅H₃(SiMe₃)₂Mo(CO)₃I]. Carbonyl displacement by a range of ligands: [L = P(OMe)₃, P(OPrⁱ)₃,P(O-o-tol)₃, PMe₃, PMe₂Ph, PMePh₂, PPh₃, P(m-tol)₃] gave the new complexes [(η⁵-C₅H₃(SiMe₃)₂ MO(CO)₂(L)I]. For all the trans isomer was the dominant, if not exclusive, isomer formed in the reaction. An NOE spectral analysis of [(η⁵-C₅H₃(SiMe₃)₂)Mo(CO)₂(L)I] L = PMe₂Ph, P(OMe)₃] revealed that the L group resided on the sterically uncongested side of the cyclopentadienyl ligand and that the ligand did not access the congested side of the molecule. Quantification of this phenomenon [L = P(OMe)₃] was achieved by means of the vertex angle of overlap methodology. This methodology revealed a steric preference with the trans isomer (less congestion of CO than I with an SiMe₃ group) being the more stable isomer for L = P(OMe)₃.     

Electrochemical behaviour of some polyoxo clusters

We describe the redox behaviour in non-aqueous solvents of some cyclopentadienyl(oxo)titanium derivatives. The derivative [Ti₄{η⁵-C₅H₄(SiMe₃)}₄(μ-O)₆] shows an electrochemically and chemically reversible le reduction process, followed by a multi-electron, chemically complicated reduction at a fairly cathodic potential. On the basis of the overall electrochemical features and the comparison with the redox behaviour of the quasi-planar compound [[Ti{η⁵-C₅H₄(SiMe₃)}Cl(μ-O)]₄] we propose an EECCEE mechanism for the first derivative, where the second electron-transfer induces a cascade of chemical reactions giving rise to irreversible cluster breakdown. The electrochemically induced fragmentation can be viewed as a retrosynthetic pathway. The heterometallic derivative [{Ti(η⁵-C₅H₄Me)₂(μ₂-MoO₄)₂}₂] shows two consecutive reduction processes; the first is chemically reversible, and the second quasi-reversible. The molybdate bridges apparently increase the stability of the electrogenerated anions. However none of these poly-oxo clusters can be considered as good models of electron ‘sinks’.     

Acetylen-Komplexe von Di(η-cyclopentadienyl)molybdän: Synthesen und Protonierung. Struktur von [Cp2MoH{η-C2(SiMe3)2}]PF6

Cp₂MoH₂ reacts with methyl acrylate in the presence of acetylenes (L = C₂H₂, C₂Me₂, HCC^tBu, HCCSiMe₃, C₂(SiMe₃)₂, HCCCH₂OMe, HCCCH₂NMe₂) to form acetylene complexes Cp₂Mo(L) 5. Protonation takes place with CF₃CO₂H at −80°C to give short-lived cations [Cp₂MoH(L)⁺ (8) (L = C₂Me₂, HCCSiMe₃, C₂(SiMe₃)₂). The structure of [Cp₂MoH{η²-C₂(SiMe₃)₂}]PF₆(9) was determined by an X-ray diffraction study.     

Half-sandwich and mixed-ring uranium complexes

The monocyclooctatetraene uranium complex [U(COT)(I)₂(THF)₂] (COT=η-C₈H₈; THF=tetrahydrofuran), isolated from the reaction of bis(cyclooctatetraene)uranium with iodine, is a precursor for the synthesis of the alkyl derivatives [U(COT)(CH₂Ph)₂i (HMPA) ₂], [U(COT)(CH₂SiMe₃)₂(HMPA)] (HMPA=hexamethyl phosphorous triamide) and [U(COT)CH₂SiMe₃)₃] [Li(THF)₃] and of the mixed-ring compounds [U(COT)(η-C₅R₅)(I)] (R=H or Me). The last were used to prepare the amide and alkyl complexes [U(COT)(η-C₅H₅)(N{SiMe₃}₂)] and [U(COT)(η-C₅Me₅)(CH₂SiMe₃)].     

Synthese und konformationsstudien von selen-analoga der metallocen-dithiolen-chelate früher übergangsmetalle

The reaction of the metallocene dichlorides Cp₂MCl₂ (Cp = η⁵-C₅H₅; M = Ti, Zr, Hf, Mo, W) and Cp₂′TiCl₂ (Cp′ = η⁵-C₅H₄CH₃) with equimolar amounts of dilithium-benzene-o-diselenolate, 1,2-(LiSe)₂C₆H₄, gives the chelate complexes Cp₂M(Se₂C₆H₄) (M = Ti (I), Zr (II), Hf (III), Mo (IV), W (V)) and Cp₂′Ti(Se₂C₆H₄) (VI). CpTiCl₃ reacts with 1,2-(LiSe)₂C₆H₄ to give CpTiCl(Se₂C₆H₄) (VII). The ring inversion activation parameters for I–VI can be determined by means of temperature-dependent ¹H NMR spectroscopy in solution. The fragmentation behaviour of I–VII in the mass spectrometer has been investigated by pursuing metastable transitions, using linked-scan techniques.