Neue Methoden zur Fluorierung von Verbindungen früher Übergangsmetalle

Ziel der vorliegenden Arbeit war die Darstellung neuer Organometall-Fluor- Verbindungen unter Einbeziehung alternativer Fluorierungsmittel. Im ersten Teil der Arbeit wurden Alkylierungsreaktionen vorgestellt, wodurch die Synthese der neuen Komplexe BisMX4 (M = Ta (1), Nb (4) für X = Cl und M = Ta (2), Nb (5) für X = Br) gelang. Die röntgenstrukturelle Charakterisierung von 1 und 4 zeigt monomere Molekülstrukturen mit trigonal-bipyramidal koordinierten Metallatomen. Ausgehend von den Chloro-Komplexen wurden die Komplexe BisMF4 (M = Ta (9), Nb (11)) mit Hilfe von Me3SnF über einen Chlor-Fluor-Austausch dargestellt. Mit Verbindung 11 wurde ein C-Nb-F-Fragment aufgebaut, das eine Nb-C-Sigmabindung aufweist. Die entsprechende Tantalverbindung 9 stellt den ersten Vertreter eines monoalkyl-substituierten Tantalfluorids dar. Eine röntgenographische Untersuchung von Verbindung 9 ergab, daß sich die oktaedrisch koordinierten Metallzentren in Zickzackketten anordnen. Mit der Darstellung dieser beiden Verbindungen konnte das Substitutionsverhalten von Me3SnF gegenüber Alkylgruppen genauer untersucht werden. Dabei hat sich gezeigt, daß der sterische Anspruch des Liganden einen entscheidenden Einfluß hat. Als alternative und dem Me3SnF verwandte Fluorierungsmittel wurden Ph2PbF2 (13) und Ph3BiF2 (14) mit Metallocenkomplexen der vierten Gruppe zu den entsprechenden Fluorokomplexen umgesetzt. Es war das erste Mal, daß Blei- und Bismutfluoride für die metathetische Fluorierung eingesetzt wurden. Als Ausgangsverbindungen wurden neben Cp*TiCl3, Cp2ZrCl2 und Cp2HfCl2 auch die bislang unbekannten Verbindungen Cp*Cp MCl2 (M = Zr (15), Hf(16)) gewählt. Die Chloro- und Fluorokomplexe wurden röntgenstrukturell charakterisiert. Alle Verbindungen liegen monomer mit verzerrt tetraedrisch koordinierten Metallzentren vor. Fluorierungsmittel vom Typ Q+HF2- (Q+ = n-Bu4N+; Et4N+; K+) wurden bislang für die Synthese kaum erschlossen. Sie reagieren mit Metallalkoxiden unter Alkoholabspaltung zu komplex aufgebauten Metallclustern. Meist gibt erst eine Einkristallröntgenstrukturanalyse Aufschluß über die Konstitution der Produkte. Auf diesem Weg gelang die Charakterisierung eines großen Aggregats, bestehend aus 8 Ta-Metallzentren, 20 Ethoxidresten und 10 Sauerstoffatomen, das in einer Reaktion von n-Bu4NHF2 mit Ta(OEt)5 dargestellt werden konnte. Die punktsymmetrische Struktur von Verbindung 23 besitzt im Zentrum einen achtgliedrigen Ring, der von sechsgliedrigen Ringen umgeben ist. Die Reaktion von Ti(Oi-Pr)4 mit KHF2 liefert ein ganz anderes Ergebnis. Nach Substitution eines Alkoxids durch ein Fluorid und einer Etherabspaltung erhält man Verbindung 20. Eine röntgenstrukturelle Analyse zeigt, daß ein sechsgliedriger Ring aus Alkoxidmolekülen und Titan aufgebaut wurde, in dessen Zentrum je ein Sauerstoff- und Fluoratom positioniert sind. Neben den Reaktion von Alkoxiden mit Q+HF2- ist die Fluorierung von Acetaten, Hydriden, Alkylderivaten und Acetylacetonaten in dieser Arbeit untersucht worden. Bei den Reaktionen mit Acetaten entsteht als Nebenpodukt Q+OAc-, dessen Abtrennung Probleme bereitet. Hydrid- und Alkylderivate von Hauptgruppenelementen konnten erfolgreich mit TBADF fluoriert werden. Reaktionen an entsprechenden Verbindungen der Nebengruppen führten zu uneinheitlichen Produkten. Die Substitution von Acetylacetonat gegen zwei Fluoratome war erfolgreich. Die Acetylacetonate VO(acac)2 und MoO2(acac)2 konnten mit TBADF erfolgreich fluoriert werden. Die weitere Erforschung des Synthesepotentials der hydrogenbifluoridhaltigen Fluorierungsmittel wird in naher Zukunft zu einer Vielzahl von interessanten Fluorokomplexen führen

Reactivity of silyl-substituted allyl compounds with group 4, 5, 9, and 10 metals: Routes to eta(3)-allyls, alkylidenes, and sec-alkyl carbocations

Whereas the reaction of alkali-metal salts of silyl-allyls E+[C3H3(SiMe3)(2)-1,3](-) (E = Li, K) with group 4 and group 5 metal halides gave intractable reduction products, Co(acac)(3) and Ni(acac)(2) reacted with K[C3H3(SiMe3)(2)-1,3] to give Co{eta(3)-C3H3(SiMe3)(2)-1,3}(2) (1) and Ni-{eta(3)-C3H3(SiMe3)(2)-1,3}(2) (2), respectively. The reaction of K[C3H3(SiMe3)(2)-1,3] with Me3SnCl afforded Me3SiCH=CHCH(SiMe3)(SnMe3) (3), which reacted cleanly with TaCl5 to give {eta(3)-C3H3(SiMe3)(2)-1,3}TaCl4 (4). Treatment of this complex with tetramethylethylenediamine led to HCl abstraction, and the allyl complex was transformed into the vinyl-alkylidene compound Me3SiCH=CHC(SiMe3)=TaCl3(TMEDA) (5). Whereas in the case of TaCl5 dehalostannylation was facile, the reaction of 3 with ZrCl4 and HFCl4 took a different course, leading instead to the addition of Me3Sn+ to 3 to give [HC{CH(SiMe3)(SnMe3)}(2)](+)[M2Cl9](-) (6, M = Zr; 7, M = Hf), the first examples of isolable sec-alkyl carbocations. These salts are surprisingly thermally stable and melt > 100 degrees C; this stability is largely due to delocalization of the positive charge over the two tin atoms. The crystal structures of 1, 2, and 5-7 are reported

Synthesis, structure and catalytic activity of new iminophenolato complexes of scandium and yttrium

The reaction of equimolar amounts of 2-(2,4,6-Me3C6H2N=CH)(6-But)C6H3OH (HL1) with M(CH2SiMe3)3(THF)3 (M=Sc or Y) under mild conditions gives M(CH2SiMe3)2(THF)(L1). The trigonal-bipyramidal structure of these dialkyls was confirmed crystallographically for M=Sc. Whereas the scandium complex is stable in solution at room temperature, the yttrium derivative slowly disproportionates to give Y(L1)3 which is also accessible from Y(CH2SiMe3)3(THF)3 and three HL1. The X-ray structure of Y(L1)3 indicates a chiral tris-chelate complex. While the reaction of the related ligand (2-CyN=CH)(6-But)C6H3OH (HL2, Cy=cyclohexyl) with Sc(CH2SiMe3)3(THF)3 gives the expected dialkyl Sc(CH2SiMe3)2(THF)(L2), the reaction with the yttrium analogue affords the six-coordinate monoalkyl product Y(CH2SiMe3)(THF)(L2)2. This product is stable in solution towards disproportionation. The reaction of Y[N(SiMe3)2]3 with (2-C6F5N=CH)(6-But)C6H3OH (HL3) affords Y{N(SiMe3)2}(L3)2 and Y(L3)3. Both complexes are seven-coordinate in the solid state due to Y•••F co-ordination to the C6F5 substituents. The scandium alkyl complexes are efficient catalysts for the ring-opening polymerisation of e-caprolactone

Synthesis, Structure, and Luminescent Behavior of Anionic Oligomeric and Polymeric Ag₂Au₂ Clusters

Mixtures of silver salts AgX (X = NO₃, CF₃CO₂, CF₃SO₃) with M­[Au­(C₆F₅)₂] (M = NBu₄, PPh₄) gave respectively the ionic mixed-metal clusters [M₂{(C₆F₅)₄Au₂Ag₂X₂}]_<i>n</i> (<b>1</b>, X = NO₃; <b>a</b>, M = NBu₄; <b>b</b>, M = PPh₄) and [M­{(C₆F₅)₄Au₂Ag₂X}]_<i>n</i>, (<b>2a</b>,<b>b</b>, X = CF₃CO₂; <b>3a</b>,<b>b</b>, X = CF₃SO₃). The degree of aggregation <i>n</i> of these cluster compounds depends strongly on the method of isolation (solvent evaporation or precipitation); for example, recrystallization of <b>1a</b> gave a crystalline salt of the tetraanion [(C₆F₅)₄Au₂Ag₂X₂]₂^4– as well as the polymer [(NBu₄)₂{(C₆F₅)₄Au₂Ag₂(NO₃)₂}]_<i>n</i>. The aurophilic Au···Au interactions strongly influence the photoemission wavelength. The anion X has remarkably little effect on the luminescence color but strongly influences the conformation of the polyanionic chains, leading to a variety of solid-state structures, from well-defined dimers (<b>1a</b>^<b>1</b>) to linear (<b>1b</b>) and curved (<b>1a</b>^<b>2</b>, <b>2a</b>) polymeric chain aggregates

Synthesis, ion aggregation, alkyl bonding modes, and dynamics of 14-electron metallocenium ion pairs (SBI)MCH2SiMe3+ ---X- (M = Zr, Hf): Inner-sphere (X = MeB(C6F5)3) versus outer-sphere (X = B(C6F5)4) structures and the implications for "continuous" or "intermittent" alkene polymerization mechanisms

The new mixed-alkyl metallocene complexes (SBI)M(Me)CH2SiMe3 (M = Zr, Hf) are accessible by the successive treatment of (SBI)MCl2 with Me3SiCH2MgCl and MeMgCl in toluene (SBI = rac-Me2Si(1-Ind)(2)). Reaction with B(C6F5)(3) or CPh3+[B(C6F5)(4)](-) in toluene or toluene/difluorobenzene affords (SBI)M delta+(CH2SiMe3)(mu-Me)B-delta-(C6F5)(3) and the ion pairs [(SBI)MCH2SiMe3+center dot center dot center dot B(C6F5)(4)(-)], respectively. Both types of compounds are thermally stable in aromatic solvents at ambient temperature. Whereas in the MeB(C6F5)(3)(-) complexes the alkyl ligand points away from the metal and tight anion coordination forms the familiar inner-sphere ion pair, in the B(C6F5)(4)(-) salts the alkyl ligand adopts a conformation that enables agostic bonding to a gamma-CH3 group. Here, and by implication in M-polymeryl species of similar steric requirements, agostic interactions are preferred over anion coordination, leading to an outer-sphere ion pair structure. This alkyl bonding mode retards the -SiMe3 rotation, which for M = Hf is slow on the NMR time scale at -20 degrees C (at 300 MHz), while in the zirconium analogue cooling to below -60 degrees C is required. It was shown that chain swinging involves a 180 degrees rotation of the alkyl ligand about the Zr-C bond. Measurements of diffusion coefficients by pulsed field gradient spin-echo (PGSE) techniques suggest that while (SBI)Zr(CH2SiMe3)(mu-Me)B(C6F5)(3) exists in solution as mononuclear zwitterions as expected, [(SBI)ZrCH2SiMe3+center dot center dot center dot B(C6F5)(4)(-)] forms ion quadruples ([Zr] approximate to 2 mM), rising to hextuples at higher concentration. The relative positions of cations and anions depend on the ion pair concentration; higher aggregates make it difficult to assign specific anion positions. The rate of ion pair symmetrization ("anion exchange" k(ex)), as determined by variable-temperature NMR spectroscopy, decreases with decreasing metallocene concentration. For [(SBI)ZrCH2SiMe3+center dot center dot center dot B(C6F5)(4)(-)] at 25 degrees C and [Zr] = 2 mM, k(ex) = 500 +/- 170 s(-1); this value represents the upper limit of anion mobility expected under catalytic conditions where concentrations are typically 100 times lower. Ion pair symmetrization rates are therefore at least 1 order of magnitude slower than the growth of the number-average molecular weight of polypropene chains (k(p)[M] approximate to 10(4) s(-1) at [M] = 0.59 mol L-1) generated with tetraarylborate-based (SBI)Zr and other high-activity catalysts at identical temperatures. It is suggested that while for slower, inner-sphere ion pair catalysts the rate of 1-alkene consumption is commensurate with k(ex) ("continuous" chain propagation mechanism), high-activity catalysts may operate by a mechanism where the anion does not bind to the metal center and so does not limit the rate of monomer enchainment. In such a situation, agostic metal-alkyl interactions form the caalyst resting states in preference to anion coordination

The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes

The silyl ethers 3- Bu-t - 2- ( OSiMe3) C6H3CH = NR ( 2a- e) have been prepared by deprotonation of the known iminophenols ( 1a - e) and treatment with SiClMe3 ( a, R = C6H5; b, R = 2,6- Pr-i 2C6H3; c, R = 2,4,6- Me3C6H2; d, R = 2- C6H5C6H4; e, R = C6F5). 2a - c react with TiCl4 in hydrocarbon solvents to give the binuclear complexes [ Ti {3- Bu-t - 2-( O) C6H3CH = N( R)} Cl( mu - Cl-3) TiCl3] ( 3a - c). The pentafluorophenyl species 2e reacts with TiCl4 to give the known complex Ti {3- Bu-t - 2- ( O) C6H3CH = N( R)} Cl-2(2). The mononuclear five- coordinate complex, Ti {3- Bu-t - 2- ( O) C6H3CH = N( 2,4,6- Me3C6H2)} Cl-3 ( 4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti {3- Bu-t - 2- ( O) C6H3CH = N( R)} Cl-3( THF) ( 5a - e). The reaction with ZrCl4( THF) (2) proceeds similarly to give complexes Zr {3- Bu-t - 2- ( O) C6H3CH = N( R)} Cl-3( THF) ( 6b - e). The crystal structures of 3b, 4c, 5a, 5c, 5e, 6b, 6d, 6e and the salicylaldehyde titanium complex Ti {3- Bu-t - 2- ( O) C6H3CH = O} Cl-3( THF) ( 7) have been determined. Activation of complexes 5a e and 6b e with MAO in an ethene saturated toluene solution gives polyethylene with at best high activity depending on the imine substituent

Conversion of alkyltantalum chlorides to fluorides using trimethyltin fluoride as a fluorinating agent. Crystal structures of (p-MeC<SUB>6</SUB>H<SUB>4</SUB>CH<SUB>2</SUB>)<SUB>3</SUB>TaF<SUB>2</SUB>, (Me<SUB>3</SUB>SnCl&#183;Me<SUB>3</SUB>SnF&#183;TaF<SUB>5</SUB>)<SUB>n</SUB>, (Me<SUB>3</SUB>Si)<SUB>2</SUB>CHTaCl<SUB>4</SUB>, {(Me<SUB>3</SUB>Si)<SUB>2</SUB>CHTaCl<SUB>4</SUB>&#183;[(Me<SUB>3</SUB>Si)<SUB>2</SUB>CH]<SUB>2</SUB>Ta<SUB>2</SUB>Cl<SUB>6</SUB>(&#956;<SUB>2</SUB>-O)}, and (Me<SUB>3</SUB>Si)<SUB>2</SUB>CHTaF<SUB>4</SUB>

The reactions of alkyltantalum chlorides with trimethyltin fluoride were found to be highly dependent on the number of organic ligands on tantalum as well as on the electronic and the steric nature of the substituents. The synthesis of trialkyltantalum difluorides of general formula (RCH2)3TaF2 (R = Ph, 1; R = p-Tol, 2; R = Me3Si, 3) and the first example of the alkyltantalum tetrafluoride (Me3Si)2CHTaF4 (8) are reported. The compounds (p-MeC6H4CH2)3TaF2, (Me3SnCl&#183;Me3SnF&#183;TaF5)n, (Me3Si)2CHTaCl4, {(Me3Si)2CHTaCl4&#183;[(Me3Si)2CH]2Ta2Cl6(&#956;2-O)}, and (Me3Si)2CHTaF4 respectively have been characterized by single-crystal X-ray structural analysis