Organometallic Lewis Acid Research Articles

ChemInform Abstract: Stereoselective Synthesis with Zirconium Complexes

Two types of electrophilic zirconium based catalyst systems are described in several variants. The organometallic Lewis acid CpZrCl is easily available. It catalyzes a variety of organic reactions quite selectively. Starting from &e camphor enantiomers the chiral Lewis acid (diborna-Cp)ZrClg was prepared. It catalyzes the enantioselective ortho-hydroxylation of a- naphthol. In separate experiments the enantiomeric a-naphthoVethylpyruvate addition products were obtained on a preparative scale with 285% ee using 1 to 5 mol% of the optically pure (+) or (-)(diborna-Cp)zirconium mchloride catalyst, respectively. Bis(cyclopentadieny1)zirconium dihalides (R*Cp)2ZrCl bearing chiral substituents at the Cp-rings were used for generating homogeneous group 3 metallocene/alumoxane Ziegler catalysts for the stereoselective polymerization of propene. Systematic variation of substituents at the chiral Cp-side chains revealed a substituent additivity effect of the stereoselective CC-coupling process. Non-bridged bis( 1-alkylindeny1)zirconium complexes exhibiting planar chirality can very easily be prepared optically pure in an asymmemc organometallic synthesis using terpene- or steroid-derived indenyl substituents. Some of these complexes produce homogeneous Ziegler catalysts that are nearly as stereoselective propene polymerization catalysts as the commonly used ansa- metallocene complexes. Bis(isopropylcyclopentadieny1)titanium dichloride/alumoxane is an achiral organometallic catalyst system that produces isotactic block polypropylene at -50°C by means of chain end control. At +lO°C this is changed to slightly syndiotactic polymer formation. A reaction scheme is proposed that may account for the observed linear lg o/(l-o) vs l/r relationship observed for this specific catalyst system.

ChemInform Abstract: Approaches to Hexane-Soluble Cationic Organometallic Lewis Acids. Synthesis, Structure, and Reactivity of Titanocene Derivatives Containing Polysilylated Cyclopentadienyl Ligands.

A series of titanocene dichloride derivatives was synthesized where the total trimethylsilyl substitution on the two cyclopentadienyl rings was 0, 2, 3, 4, and 5. Treatment of these complexes with methyllithium afforded 88-93% yields of the dimethyl derivatives, while reaction of the dichlorides with silver tetrafluoroborate afforded 45-57% yields of the difluoro derivatives

Inside Cover: Perfluoropentaphenylborole (Angew. Chem. Int. Ed. 16/2009)

Perfluoroaryl boranes are an important class of organometallic Lewis acids. The synthesis of perfluorinated compounds brings special challenges to tried-and-true synthetic methodologies. In their Communication on page 2955 ff., W. E. Piers and co-workers present the synthesis of a new, fully fluorinated heterocyclic borane that is also a member of the rare antiaromatic borole class of compounds. The route relies on normally facile transmetallation reactions made more difficult by the electron-withdrawing C6F5 groups of the target product.

Evolution of Organo‐Cyanometallate Cages: Supramolecular Architectures and New Cs+‐Specific Receptors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Proton-Induced Lewis Acidity of Unsaturated Iridium Amides

Oxidation of Cp*Ir((rac-TsDPEN)H (DPEN = H2NCHPhCHPhNTs) with Cp2FePF6 or Ph3CPF6 in MeCN solution generates [Cp*Ir(TsDPEN)(NCMe)]PF6 ([1H(NCMe)]PF6) together with H2 and Ph3CH, respectively. Labeling studies revealed that the Ir-H was abstracted. The formation of a transient electrophilic species is implicated by the formation of a cyclometalated derivative. The labile species [1H(NCMe)]+ was also obtained by protonation of the diamido derivative Cp*Ir(TsDPEN-H) (1) in MeCN solution (BArF4- = B(C6H3-3,5-(CF3)2)4-). The unsaturated, "naked" cation [1H]BArF4 can be prepared by protonation of 1 with H(OEt2)2BArF4 in CH2Cl2 solution or by thermal elimination of MeCN from [1H(NCMe)]+. Crystallographic analysis confirms the structure of this 16e cation in [1H]BArF4. The formally unsaturated species 1 and [1H]BArF4 have strongly contrasting Lewis acidities, with the cation binding PPh3, CO, and NH3. 1 does not measurably bind these same ligands. [1H]BArF4 is reactive toward H2, at least in the absence of inhibiting donor ligands such as MeCN. [1H]BArF4 (CH2Cl2 solutions) catalyzes the addition of H2 to 1 by proton transfer from an apparent dihydrogen complex. This work demonstrates that the protonation activates the Lewis acidity of unsaturated Ir(III) amides, giving rise to novel organometallic Lewis acids.

Formation of Isomeric BAr3 Adducts of 2-Lithio-N-methylimidazole

N-Methylimidazole added to the strong organometallic Lewis acid B(C6F5)3 at the donor nitrogen atom to form the adduct 3 (characterized by X-ray diffraction). Deprotonation at the imidazole carbon atom C-2 was achieved by treatment with methyllithium to generate the reactive “Arduengo carbene anion” intermediate 4, which underwent a rapid subsequent intramolecular nucleophilic aromatic substitution reaction at one of the adjacent C6F5 groups to form the tricyclic betaine-type product 5. Rearrangement of 4 by 1,2-boron migration was not observed. The respective isomer 7 was prepared independently by deprotonation of N-methylimidazole, followed by C-2 addition of B(C6F5)3. The corresponding N-methylimidazolide-2−B(C6H5)3 adduct 8 was characterized by X-ray diffraction and shown to have a cyclodimeric structure made up of intermolecular bis(π-arene)(imidazole)lithium units. A DFT study revealed that the N-borated Arduengo carbene anions are in general very effectively kinetically protected from undergoing intramolecular rearrangement to their thermodynamically favored 2-boratoimidazole anion isomers by 1,2-BR3 migration. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Cationic scandium methyl complexes supported by a beta-diketiminato ("Nacnac") ligand framework.

The base-free dimethyl scandium complex supported by the bulky beta-diketiminato ligand ArNC((t)Bu)CHC((t)Bu)NAr (Ar = 2,6-(i)Pr(2)C(6)H(3), 1) reacts with various equivalencies of the strong organometallic Lewis acid B(C(6)F(5))(3) to give scandium alkyl cations. With 0.5 equiv, a monocationic mu-methyl dimer (2) was observed spectroscopically. Reaction with a further 0.5 equiv of borane gives the monomeric methyl cation 3, which was fully characterized, including via X-ray crystallography. This compound is fluxional on the NMR time scale via a "ligand flip" mechanism. Reaction with another equivalent of borane gives the unique dication 4, which exhibits a static structure on the NMR time scale. Dimethyl compound 1 is a highly active catalyst precursor for ethylene polymerization under borane or MAO-type activation. Activities for this group 3 metal based catalyst approach those observed for group 4 based metallocene systems.

Structural Dichotomy in Single-Component Ziegler Catalyst Systems: Characterization of Zr···F and Zr···C-Bonded Structural Types of Group 4 Metallocene [C4H6−B(C6F5)3] Betaines

The organometallic Lewis acid B(C6F5)3 adds to the terminal CH2 group of the (butadiene)metallocene complexes 5a and 5b to give the ansa-metallocene betaine systems [Me2Si(C5H4)2]Zr[C4H6−B(C6F5)3] (6a) and [Me2Si(3-MeC5H3)2]Zr[C4H6−B(C6F5)3] (6b), respectively, in high yield. Both complexes were characterized by X-ray diffraction. They both contain a substituted η3-allyl ligand F of E configuration, and they show a characteristic (ortho aryl)C−F···Zr interaction that stabilizes the electron-deficient metal center inside the dipolar structure. B(C6F5)3 also adds to one butadiene terminus of (s-cis-η4-C4H6)[Me2C(C5H4)(indenyl)]Zr to give a high yield of a single isomer of the respective ansa-metallocene [C4H6−B(C6F5)3] betaine complex 9. The X-ray crystal structure analysis of 9 has revealed that in this case a (Z)-η3-allyl-CH2B(C6F5)3 ligand is formed. This precluded the (aryl)C−F···Zr coordination. Instead, the zirconium center in 9 forms a stabilizing internal ion pair interaction between the negatively polarized [B]−C(4)H2 methylene group and the positive zirconium center. The analogously structured ansa-metallocene [(Z)-C4H6−B(C6F5)3] betaine complex 12 is obtained in high yield from B(C6F5)3 addition to (s-cis-η4-butadiene)[Me2C(C5H4)(fluorenyl)]Zr. In solution the complexes 6, 9, and 12 exhibit structures that are analogous to those found in the solid state. However, treatment of (butadiene)[Me2Si(C5H4)2]Zr (5a) with B(C6F5)3 under kinetic control (233 K in toluene-d8) quantitatively yields the [Me2Si(C5H4)2]Zr[(Z)-C4H6−B(C6F5)3] betaine isomer 13, which contains the stabilizing [B]−C(4)H2···Zr internal ion pair interaction. Subsequent thermally induced rearrangement of the kinetic product 13 (ΔG⧧rearr(298 K) = 21.5 ± 0.5 kcal mol-1) then results in the formation of the eventually observed thermodynamic ansa-metallocene betaine product 6a, that contains the (E)-C4H6−B(C6F5)3 ligand and exhibits internal (aryl)C−F···Zr coordination. A similar reaction sequence was observed during the addition of B(C6F5)3 to the parent (butadiene)zirconocene system 1: at 213 K the kinetic Cp2Zr[(Z)-(1−3η),κC4-C4H6−B(C6F5)3] betaine product 14 is formed, which rapidly rearranges at temperatures above 253 K to yield the previously observed stable Cp2Zr[(E)-C4H6−B(C6F5)3] betaine system 2, which is characterized by an internal C−F···Zr bond. The ansa-metallocene betaines 6, 9, and 12 are all active homogeneous single-component Ziegler catalysts for ethene and propene polymerization. They are similarly effective as the usually employed ansa-metallocene dichloride/methylalumoxane catalyst systems.

(N-pyrrolyl)B(C6F5)2--a new organometallic Lewis acid for the generation of group 4 metallocene cation complexes.

Treatment of the (C6F5)2BF x OEt2 (3) complex with N-pyrrolyl lithium gives bis(pentafluorophenyl)(N-pyrrolyl)borane (2), a strong organometallic Lewis acid, which was characterized by X-ray diffraction (B-N bond length: 1.401(5) A). It exhibits a columnar superstructure in the crystal and contains pi-stacks of pyrrolyl units. Compound 2 readily abstracts alkyl anions from a variety of alkyl Group 4 metallocene-type complexes and leads to the clean formation of the respective metallocene ions or ion pairs. For example, the treatment of Cp3ZrCH3 (9) with 2 transfers a methyl anion to yield the ion pair [Cp3Zr]+[(C4H4N)B(CH3)(C6F5)2]- (12). The X-ray crystal structure analysis of 12 shows a close contact between zirconium and the pyrrolyl-beta-carbon (2.641(2) A). The borane 2 adds to (butadiene)zirconocene (13) to yield the betaine system [Cp2Zr]+[(C4H6)B- (NC4H4)(C6F)2]- (15). Complex 15 contains a distorted eta3-allyl moiety inside the metallacyclic framework and it features an internal Zr+...(pyrrolyl)B- ion pair interaction with a Zr...pyrrolyl-alphacarbon separation of 2.723(3) A (determined by X-ray diffraction). From the dynamic NMR spectra of 15 the bond strength of the internal ion pair interaction was estimated to be deltaGdiss (223 K) approximately = to15 kcalmol(-1). Treatment of dimethylzirconocene (16) with 2 yields the metallocene borate salt [Cp2ZrCH3]+[(C4H4N)B(CH3)(C6F5)2]- (17), which is an active catalyst for the polymerization of ethene.

Group 5 Metal Complexes with Cyclooctatetraene: Formation and Characterization of (Butadiene)(cyclooctatetraene)(cyclopentadienyl)tantalum Systems

The [(η4-diene)(η5-RCp)TaCl2] complexes 6a-e (diene = butadiene, isoprene or 2,3-dimethylbutadiene; RCp = pentamethylcyclopentadienyl, methylcyclopentadienyl or cyclopentadienyl) react with cyclooctatetraene dianion (employed as [(cot)Li2]) to yield the (η4-diene)(η3-cyclooctatetraene)(η5-RCp)tantalum complexes 7. The η3-cot coordination was confirmed by an X-ray crystal structure analysis of the compound [(supine-s-cis-η4-C4H6)(η3-cot)(η5-Cp*)Ta] 7a. In solution, the cot ligand of all the complexes 7 is fluxional. Two isomers [supine and proneorientation of the (diene)CpTa subunit] were found for the (η4-butadiene)(η3-cot)CpTa system (7e/7e′ = 95:5). Complex 7e cleanly adds the organometallic Lewis acid B(C6F5)3 to yield the betaine system [(η4-C4H6){C8H8B(C6F5)3}Cp*Ta] 8, which contains a substituted bicyclo[5.1.0]octadienyl ligand.

Group 5 Metal Complexes with Cyclooctatetraene: Formation and Characterization of (Butadiene)(cyclooctatetraene)(cyclopentadienyl)tantalum Systems

The [(η4-diene)(η5-RCp)TaCl2] complexes 6a-e (diene = butadiene, isoprene or 2,3-dimethylbutadiene; RCp = pentamethylcyclopentadienyl, methylcyclopentadienyl or cyclopentadienyl) react with cyclooctatetraene dianion (employed as [(cot)Li2]) to yield the (η4-diene)(η3-cyclooctatetraene)(η5-RCp)tantalum complexes 7. The η3-cot coordination was confirmed by an X-ray crystal structure analysis of the compound [(supine-s-cis-η4-C4H6)(η3-cot)(η5-Cp*)Ta] 7a. In solution, the cot ligand of all the complexes 7 is fluxional. Two isomers [supine and proneorientation of the (diene)CpTa subunit] were found for the (η4-butadiene)(η3-cot)CpTa system (7e/7e′ = 95:5). Complex 7e cleanly adds the organometallic Lewis acid B(C6F5)3 to yield the betaine system [(η4-C4H6){C8H8B(C6F5)3}Cp*Ta] 8, which contains a substituted bicyclo[5.1.0]octadienyl ligand.

Direct Experimental Observation of the Stereochemistry of the First Propene Insertion Step at an Active Homogeneous Single-Component Metallocene Ziegler Catalyst

rac-[Me2Si(1-indenyl)2]ZrCl2 was treated with (butadiene)magnesium to yield the respective ansa-metallocene (s-cis-η4-butadiene) complex, 6. It reacts with the organometallic Lewis acid B(C6F5)3 to give the ansa-metallocene-(μ-C4H6)-B(C6F5)3 betaine 7 that was characterized by X-ray diffraction. Complex 7 contains a distorted (σ,π-type) allyl ligand, bonded to zirconium, that bears a syn-oriented −CH2B(C6F5)3 substituent. An ortho C−F substituent of one of the C6F5 groups at boron coordinates to the electron-deficient zirconium center. Complex 7 is an active single-component Ziegler catalyst that stereoselectively polymerizes propene to give isotactic polypropylene by enantiomorphic site control (up to ca. 90% mmmm). Treatment of 7 with propene at −15 °C in toluene-d8 leads to a regioselective but stereounselective stoichiometric monoinsertion of the prochiral 1-alkene into the Zr−CH2 bond of the betaine 7 to give a 60:40 mixture of the metallacyclic products 9A and 9B. Cleavage of both the intramolecular C4−C5 olefin coordination to zirconium and the internal C6···Zr ion pair interaction in the 9A/9B pair of diastereoisomers by the addition of THF yields a 60:40 mixture of the respective open-chain THF adducts 10A and 10B. This result shows that the first propene insertion reaction at the rac-[Me2Si(1-indenyl)2]Zr derived single-component Ziegler catalyst system is not stereoselective, whereas all subsequent propene insertion steps show a high degree of stereoselectivity. A stereochemical “relay mechanism” is proposed to account for this behavior, where an intermediately generated stereogenic center at the α-carbon atom of the growing σ-ligand hydrocarbon chain effectively serves to transfer the stereochemical information from the chiral metallocene backbone onto the growing carbon chain. The ansa-metallocene backbone alone seems to have no intrinsic ability for direct stereochemical control. The essential role of the α-carbon stereochemistry is supported by the stereoselective propene insertion into the betaine (16) derived from the regioselective B(C6F5)3 addition to (1,3-pentadiene)ZrCp2.

Zirconocene-(μ-Organyl)borate Betaines Derived by Treatment of a (σ-Alkenyl)(σ-alkynyl)zirconocene Complex with Tris(pentafluorophenyl)borane⋆

Hydrozirconation of propyne followed by treatment with propynyllithium yields the (σ-propenyl)(σ-propynyl)zir-conocene complex 11. Its treatment with the organometallic Lewis acid B(C6F5)3 results in transfer of the σ-propynyl group from zirconium to boron followed by insertion of the alkynylborate triple bond into the zirconium carbon bond of the remaining metallaallyl cation to furnish the zirconocene–(μ-hydrocarbyl)borate betaine complex 14. This reacts with three molar equivalents of tert-butyl isocyanide to give 16. Complex 16 contains a five-membered carbocyclic ring, formed by carbon-carbon coupling of the former propenyl and propynyl groups with the C≡N–R reagent, to which a (η2-iminoacyl)(ĸ-tert-butyl isocyanide)zirconocene moiety is attached. Complex 16 was characterized by an X-ray crystal structure analysis.

Arriving at an Experimental Estimate of the Intrinsic Activation Barrier of Olefin Insertion into the Zr−C Bond of an Active Metallocene Ziegler Catalyst

Bis(η-methylcyclopentadienyl)(η4-butadiene)zirconium adds 1 equiv of the organometallic Lewis acid B(C6F5)3 to yield the metallocene−(μ-C4H6)−borate betaine 5, which is an active, homogeneous, one-component Ziegler catalyst for the polymerization of 1-alkenes. The metallacyclic metallocene betaine 5 undergoes a degenerate π ⇌ σ ⇌ π-allyl interconversion on the NMR time scale in toluene solution (ΔG⧧m(obs)(toluene) = 19.8 kcal mol-1) which becomes markedly faster in the presence of added reactive 1-alkenes (ΔG⧧m(obs) = 18.9 (1-hexene), 17.7 (1-pentene), 17.5 (1-butene), 17.2 kcal mol-1 (propene)). This lowering of the activation barrier is probably due to an increased stabilization of the (σ-alkyl)(π-alkene)metallocene betaine intermediate 7, which at the same time is passed as the essential intermediate stage of the insertion of these alkenes into the reactive zirconium carbon bond of 5 to yield the mono olefin insertion products 9. The Gibbs activation energies of this chemical insertion reaction (ΔG⧧chem = 20.1 (1-hexene), 18.8 (1-pentene), 18.5 (1-butene), 17.3 kcal mol-1 (propene)) are similar in magnitude to the activation energies of magnetical exchange (ΔG⧧m(obs)). This creates the interesting situation that in the presence of these reactive 1-alkenes, the (reversible) magnetical exchange rate (km(obs)), as determined by the dynamic NMR experiment, is dependent on the rate of the competing (irreversible) overall chemical addition reaction (kchem). The rate constants km(obs) and kchem were measured in the presence of these 1-alkenes, which allowed for a determination of the height of the first, i.e., the complexation barrier (ΔG⧧1 = 18.5 (1-hexene), 17.3 (1-pentene), 17.1 (1-butene), 16.4 kcal mol-1 (propene); standard state c⊖ = 1 mol L-1) and its difference (ΔΔG⧧2) to the top of the actual insertion barrier (ΔΔG⧧2 = 1.6 (1-hexene), 1.5 (1-pentene), 1.3 (1-butene), 0.7 kcal mol-1 (propene)). These values, together with the activation energy of the degenerate allyl ligand interconversion of the model system (σ-allyl)(π-allyl)zirconocene (10) (ΔG⧧3 = 7 ± 0.5 kcal mol-1), allowed for a good experimentally based estimate of the intrinsic activation energy (reaction 7 → 9) of the insertion of these 1-alkenes into the zirconium carbon bond at this group 4 bent metallocene unit. The thus obtained insertion barrier is ΔG⧧ins ≈ 10−11 kcal mol-1 for the 1-alkenes used in this study. The alkene decomplexation barrier (reaction 7 → 5) is lower by ca. 1−2 kcal mol-1.

Cp2*Zr(μ-C4H6)B(C6F5)3, a first example of a stable unbridged homogeneous metallocene—betaine Ziegler catalyst system

Addition of the strong organometallic Lewis acid B(C6F5)3 to (η4-butadiene)ZrCp2*(Cp* = η5-pentamethylcyclopentadienyl) yields the open-chain metallocene—hydrocarbylborate—betaine complex 2. The novel betaine complex 2 is an active homogeneous single component metallocene Ziegler catalyst for α-olefin polymerization.

Mo(CO)2(PPh3)2(O3SCF3)2: Ein neuer Vorläufer einer dikationischen, metallorganischen Lewis‐Säure mit drei freien Koordinationsstellen

AbstractOrganometallic Lewis Acids, LIV. — Mo(CO)2(PPh3)2(O3SCF3)2: A New Precursor for an Organometallic Dicationic Lewis Acid with Three Accessible Coordination SitesThe reaction of Mo(CO)2(PPh3)2Br2 (1) with AgO3SCF3 gives the bis(triflate) complex Mo(CO)2(PPh3)2(O3SCF3)2 (3) which can be considered as a precursor for the 12‐e− system “Mo‐(CO)2(PPh3)2+2”. According to the spectroscopic data one of the two coordinated CF3SO−3 anions is acting as a chelate ligand. Treatment of 3 and of the in situ generated W(CO)2(PPh3)2(O3SCF3)2 (4) with H2O affords the dinuclear hydroxo‐bridged complexes [M2(μ‐OH)3(CO)4(PPh3)4][CF3SO3] (5: M = Mo; 6: M = W). Acetonitrile replaces the CF3SO−3 ligands in 3 and 4 to afford the cationic complexes [M(CO)2(PPh3)2(NCMe)3][CF3SO3]2 (7: M = Mo; 8: M = W). The reaction of 3 with an excess of 2‐butyne and 1‐phenyl‐1‐propyne leads to the monoalkyne complexes Mo(CO)(MeCCR)(PPh3)2(O3SCF3)2 (9: R = Me; 10: R = Ph) in moderate yield. In contrast, the bisalkyne complexes [M(CO)(MeCCMe)2(PPh3)2(O3SCF3)][CF3SO3] (11: M = Mo; 12: M = W) are formed in high yield when a CH2Cl2 solution of 2‐butyne is added to 1 and 2 in the presence of AgO3SCF3. At room temperature, 11 and 12 are highly fluxional in solution, while 9 and 10 are stereochemically rigid. Treatment of 11 with acetonitrile yields [Mo(CO)(MeCCMe)2(PPh3)2(NCMe)][CF3SO3]2 (13). Compounds 3–13 (except 4) are characterized by IR, 1H‐, 13C‐, 19F‐, and 31P‐NMR spectrescopy.

Controlled polymerization reaction with new catalyst: Design of metalloporphyrin-acid systems for monomer activation

Metalloporphyrin initiator coupled with an appropriate organometallic Lewis acid catalyst could make possible the first example of living anionic polymerization of oxetane. Lewis acid built-in metalloporphyrins were designed as a new highly active catalyst/initiator system. The concept of monomer activation by Lewis acid was extended to the use of appropriate protonic acid.

Bis(hydroxyphenyloxazolinato)-titanium(IV) and -zirconium(IV) triflates as novel transition metal-based Lewis acids

The preparation of novel titanium, 3, and zirconium, 4, organometallic Lewis acids by treatment of the readily available [M(L)2(C1)2] complexes (M = Ti, Zr; L = hydroxyphenyl-4,5-dihydrooxazole) with AgOSO2CF3 are described. The new homogeneous organometallic Lewis acids, prepared in situ, are active in promoting aldol reactions, additions to imines and catalytic allylations. In addition, some examples of the use of 3 and 4 in other reactions (i.e. Mukaiyama–Michael reaction, addition of Me3SiCN, Diels–Alder, and hetero Diels–Alder reaction) are presented. Some mechanistic studies on the aldol reaction and on the catalytic allylation have been performed in order to show some of the characteristics of the present Lewis acid system.

Kohlenwasserstoffverbrückte Metallkomplexe: XXVIII. Fischer-Metallcarben-dithiolat-Anionen als Nucleophile zum Aufbau Kohlenwasserstoff-verbrückter Metallkomplexe

The addition of the in situ generated anion (OC) 5WC(NEt 2)CH 2CS − 2 to the organometallic Lewis acid, (OC) 5 Re + and Ph 3PAu + gives the ligand-bridged complexes (OC) 5WC(NEt 2)CH 2C(S)SRe(CO) 5 ( 1) and (OC) 5 WC(NEt 2)CH 2C(S)-SAuPPh 3 ( 2), respectively. The dianion (OC) 5WC(NEt 2)CHCS 2 2− affords with MeI, Cl 2M(PPh 3) 2 (M  Pd, Pt) and (OC) 5Re + the complexes (OC) 4 WC(NEt 2)CH C(S Me)SMe ( 3), (OC) 5WC(NEt 2)CHCS 2M(PR 3) 2 ( 4, 5) and (OC) 5WC(NEt 2)CHCS 2 [Re(CO) 5] 2 ( 6). The anion (OC) 5WC(NEt 2)CH 2CS 2 2− is added to coordinated ethene and allyl ligands of cationic complexes with formation of the hydrocarbon-bridged compounds (OC) 5WC(NEt 2)CH 2C(S)SCH 2CH 2−W(CO) 3Cp ( 7), (OC) 5WC(NEt 2)-CH 2C(S)SCH 2CH 2−Re(CO) 5 ( 8) and (OC) 5WC(NEt 2)CH 2C(S)SCH 2CHCH 2-η 2-Mo(NO)(CO)Cp ( 9), respectively. The structure of 6 has been determined by X-ray diffraction.

Metallorganische Lewis‐Säuren, XLVIII. Neue Vorläufer metallorganischer, kationischer Lewis‐Säuren mit zwei freien Koordinationsstellen: (OC)4Re(OEt2)FBF3 und (OC)2(PPh3)2Ru(FBF3)2

Organometallic Lewis Acids, XLVIII[1]. – New Precursors to Organometallic Cationic Lewis Acids with two Accessible Coordination Sites: (OC)4Re(OEt2)FBF3 and (OC)2 (PPh3)2Ru(FBF3)2The allyl transfer reaction between Re(CO)5− and [(η31‐allyl)PdCl]2 complexes leads to (allyl)rhenium complexes (η31‐H2CCR1CR2R3) Re(CO)4 (1: R1, R2, R3H; 2; R2, R3H, R1Me; 3: R1, R2H, R3Me; 4: R1H, R2, R3Me). The 2‐methylallyl complex 2 has been characterized by low‐temperature X‐ray diffraction. Protonation of 1 with HBF4 · OEt2 in CH2Cl2 gives the complex (OC)4Re(OEt2)FBF3 (5), which is a precursor for the 14 e− System “(OC)4Re+”. THF and H2O replace the diethyl ether in 5 to give [(OC)4Re(solvent)2]BF4 (6, 7). The reaction of (OC)2(PPh3)2RuCl2 with AgBF4 yields the complex (OC)2 (PPh3)2Ru(FBF3)2 (8), which can be considered as a precursor for the 14 e− cation “(OC)2 (PPh3)2Ru2+” and reacts with H2O to give [(OC)2 (PPh3)2Ru(F)(H2O)]BF4 (9). Complexes 5–9 are characterized by IR, 1H‐, 13C‐, 31P‐and 19F‐NMR spectroscopy.