Tetramethylcyclopentadienyl Ligand Research Articles

Tetramethylcyclopentadienyl Ligands Allow Isolation of Ln(II) Ions across the Lanthanide Series in [K(2.2.2-cryptand)][(C5Me4H)3Ln] Complexes

Although previous studies of the stabilization of Ln(II) ions across the lanthanide series have relied on Me3Si-substituted cyclopentadienyl ligands, we now find surprisingly that these ions can also exist surrounded by three tetramethylcyclopentadienyl ligands. Reduction of the 4fn Ln(III) complexes, Cptet3Ln (Cptet = C5Me4H) using potassium graphite in the presence of 2.2.2-cryptand (crypt) produces the Ln(II) complexes, [K(crypt)][Cptet3Ln] for Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, and Dy, all of which were characterized by X-ray crystallography. These complexes display intense absorptions in the UV–visible–near IR region that are red-shifted compared to those of previously characterized (Cp′3Ln)1– complexes (Cp′ = C5H4SiMe3). The thermal stability of these new Ln(II) complexes decreases with the size of the metal.

Efficient aerobic oxidation of alcohols to aldehydes and ketones using a ruthenium carbonyl complex of a tert-butyl-substituted tetramethylcyclopentadienyl ligand as catalyst

Tert-butyl-substituted tetramethylcyclopentadiene [C5HMe 4 Bu] was reacted with Ru3(CO)12 to prepare [(η5-C5Me 4 Bu)Ru(CO)(μ-CO)]2. The complex was characterized by IR, 1H NMR, 13C NMR, elemental analysis, and single-crystal X-ray diffraction. The complex was investigated as a catalyst in the aerobic oxidation of alcohols to the corresponding aldehydes and ketones in the presence of 2,2’,6,6’-tetramethylpiperidine N-oxide (TEMPO) as co-oxidant. The combination of [(η5-C5Me 4 Bu)Ru(CO)(μ-CO)]2 and TEMPO afforded an efficient catalytic system for the aerobic oxidation of a variety of primary and secondary alcohols, giving the corresponding carbonyl compounds in good-to-excellent yields.

Synthesis and catalytic activity of rhenium carbonyl complexes containing alkyl-substituted tetramethylcyclopentadienyl ligands

A series of six alkyl-substituted tetramethylcyclopentadienyl mononuclear metal carbonyl complexes [(η 5-C5Me4R)Re(CO)3] [R = allyl (1), i-Pr (2), n-butyl (3), t-butyl (4), benzyl (5), CH(CH2)4 (6)] have been synthesized by treating the corresponding ligands (C5Me4R) [R = allyl, i-Pr, n-butyl, t-butyl, benzyl, CH(CH2)4] with Re2(CO)10 in refluxing xylene. The six new complexes were characterized by elemental analysis, IR, 1H NMR and 13C NMR spectroscopy. The crystal structures of all six complexes were determined by X-ray crystal diffraction analysis, showing that they have similar molecular structures, being mononuclear carbonyl complexes. In each of these complexes, the Re atom is η 5 -coordinated to the cyclopentadienyl ring. Complexes 1–5 have significant catalytic activity in Friedel–Crafts reactions of aromatic compounds with alkylation reagents. Compared with traditional catalysts, these mononuclear rhenium carbonyl complexes have obvious advantages such as lower amounts of catalyst, mild reaction conditions and environmentally friendly chemistry.

Five dinuclear iron carbonyl complexes based on substituted tetramethylcyclopentadienyl ligands: synthesis and crystal structures

Thermal treatment of the substituted tetramethylcyclopentadienes [C5Me4HR] [R = n-propyl (1), i-propyl (2), cyclopentyl (3), cyclohexyl (4), and 4-NMe2Ph (5)] with Fe(CO)5 gave five new substituted tetramethylcyclopentadienyl dinuclear iron carbonyl complexes, [η5-C5Me4CH2CH2CH3]2Fe2(CO)4 (6), [η5-C5Me4CH(CH3)2]2Fe2(CO)4 (7), [η5-C5Me4CH(CH2)4]2Fe2(CO)4 (8), [η5-C5Me4CH(CH2)5]2Fe2(CO)4 (9), and [(η5-C5Me4)(4-NMe2Ph)]2Fe2(CO)4 (10). The new complexes were characterized by elemental analysis, IR, and 1H NMR spectra. The molecular structures of 6, 8, 9, and 10 were determined by X-ray single crystal diffraction.

Synthesis and Structures of Triple-Decker Complexes with a Bridging Tetramethylcyclopentadienyl Ligand

New triple-decker complexes with bridging tetramethylcyclopentadienyl ligands were synthesized by the reaction of electrophilic metal fragments with octamethylferrocene, Cp′2Fe (Cp′ = C5Me4H). The reaction of coordinatively unsaturated ruthenium cations [(C5R5)Ru]+ (R = H, CH3) with Cp′2Fe afforded purple-colored heterometallic triple-decker complexes [(C5R5)Ru(μ-Cp′)FeCp′]+ by direct electrophilic addition. Surprisingly, the analogous reaction with the coordinatively unsaturated manganese cation [Mn(CO)3]+ and Cp′2Fe produced a blue homometallic triple-decker complex, [Cp′Fe(μ-Cp′)FeCp′]+, by ring abstraction and subsequent addition of the newly generated cation [Cp′Fe]+ to an equivalent of Cp′2Fe. Three air-stable triple-decker complexes, [Cp′Fe(μ-Cp′)FeCp′]+ (2), [CpRu(μ-Cp′)FeCp′]+ (3), and [Cp*Ru(μ-Cp′)FeCp′]+ (4), have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Simple synthesis and structure characterization of a phosphoniomethylidyne tantalum(V) complex

A high-valent phosphoniomethylidyne tantalum complex [(C5Me4H)Ta(C-PPh3)(CH-PPh3)Cl] (3) was obtained via transylidation reactions of (C5Me4H)TaCl4 with 5 equivalents of the phosphorus ylide Ph3P = CH2. The addition of strong base Li(N(SiMe3)2 is beneficial to the transylidation reaction and improves the yield of complex 3. The ylide adduct complex [(C5Me4H)TaCl4(CH2PPh3)] (4) as the reaction intermediate was isolated through the reaction of (C5Me4H)TaCl4 with one equivalent of the phosphorus ylide Ph3P = CH2. Both complexes 3 and 4 were structurally characterized by X-ray single crystal diffraction. A comparison on the preparation and properties of the phosphoniomethylidyne tantalum complexes with different supporting ligands, [CpTa(C-PPh3)(CH-PPh3)Cl] (1) (Cp = cyclopentadieneyl ligand), [(C5Me4H)Ta(C-PPh3)(CH-PPh3)Cl] (3) (C5Me4H = tetramethylcyclopentadienyl ligand) (3) and [Cp⁎Ta(C-PPh3)(CH-PPh3)Cl] (2) (Cp⁎ = pentamethylcyclopentadienyl ligand) was discussed.

Mixed-Metal Cluster Chemistry. 31. Reactions of Dimolybdenum–Diiridium Clusters with Alkylidyne Complexes

Reactions of the tetrahedral clusters Mo2Ir2(μ-CO)3(CO)7(η5-L)2 (L = C5H5, C5HMe4) with the molybdenum alkylidyne complex Mo(≡CC6H4OMe-4)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} afford the pentanuclear clusters Mo3Ir2(μ4-C)(μ3-CC6H4OMe-4)(μ-O)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5H5)2 (1; 62%) and Mo3Ir2(μ3-CC6H4OMe-4)(μ3-η2-CO)(μ-CO)(CO)6{(N2C3H3)3BH-κ3N,N′,N″}(η5-C5Me4H)2 (2; 65%), respectively, while the reaction of Mo2Ir2(μ-CO)3(CO)7(η-C5H5)2 with W(≡CC≡CSiMe3)(CO)2{(N2C3H3)3BH-κ3N,N′,N″} yields the butterfly cluster Mo2Ir2(μ4-η2-SiMe3C2C≡W(CO)2{(N2C3H3)3BH-κ3N,N′,N″})(μ-CO)4(CO)4(η5-C5H5)2 (3; 60%). The identities of 1–3 have been confirmed by single-crystal X-ray diffraction studies. Cluster 1 contains μ4-carbido and μ-oxido ligands resulting from CO cleavage. Cluster 2, with sterically more encumbering tetramethylcyclopentadienyl ligands that arrest CO cleavage, possesses a μ3-η2-CO ligand with a weak CO bond (1.272(7), 1.257(7) Å). Cluster 2 could not be converted into an analogue of cluster 1. The reaction with alkyne is more facile than the reaction with alkylidyne; cluster 3 results from addition of the C≡C bond (rather than the W≡C bond) across the Mo–Mo vector.

New Chromium(III) Complexes with Imine−Cyclopentadienyl Ligands: Synthesis, Characterization, and Catalytic Properties for Ethylene Polymerization

A series of new half-sandwich chromium(III) complexes chelated with (2-((arylimino)methyl)phenyl)tetramethylcyclopentadienyl ligands, 2-(ArN═CH)C6H4Me4CpCrCl2 (Ar = 2,6-Me2C6H3 (1), 2,6-Et2C6H3 (2), 2,6-iPr2C6H3 (3), 4-MeC6H4 (4)), have been synthesized from the reaction of CrCl3 with the lithium salt of the corresponding ligand 2-(ArN═CH)C6H4Me4CpLi (Ar = 2,6-Me2C6H3 (LiL1), 2,6-Et2C6H3 (LiL2), 2,6-iPr2C6H3 (LiL3), 4-MeC6H4 (LiL4)). Free ligands HL1−HL4 were prepared by the condensation reaction of 2-(tetramethylcyclopentadienyl)benzaldehyde with 2,6-dialkylaniline. The free ligands were characterized by 1H NMR spectroscopy, while the chromium(III) complexes were characterized by elemental analyses and single-crystal X-ray crystallography. The X-ray crystallographic analysis indicates that the imine N atom in these complexes coordinates to the central chromium atom. Upon activation with AlR3 and Ph3CB(C6F5)4, these complexes exhibit high catalytic activity for ethylene polymerization and produce polyethylene with moderate to high molecular weights. These chromium(III) complexes can also be activated with AlR3 alone. In the latter case, they show slightly lower catalytic activity for ethylene polymerization in comparison to the AlR3/Ph3CB(C6F5)4 activated catalyst systems. The effects of ligand structure, polymerization temperature, AlR3, and Al/Cr molar ratio on the catalytic behavior of these complexes were examined.

Reactions of cationic complex [(η 5-C 5Me 5)Re(CO) 3I] + with primary amines leading to cyclic carbamoyl complexes

The reaction of cationic complex [( 5-C 5Me 5)Re(CO) 3I] + with aliphatic and aromatic primary amines unexpectedly produced the chelated carbamoyl species trans-( 5: 1-C 5Me 4CH 2NRC( O))Re(CO) 2(I) ( 1, R = Me; 2, R = Pr; 3, R = Ph; 4, R = p-tolyl). The 1-coordination of carbamoyl moiety linkages to a methylene group of tetramethylcyclopentadienyl ligand was confirmed by X-ray crystallography of complex 3. All the complexes were isolated as pure samples and fully characterized by IR, 1H and 13C NMR spectroscopies, mass spectrometry and elemental analysis.

Ring-Opening of a Furyl Group Appended to the Cyclopentadienyl Ligand in Rare-Earth Metal Half-Sandwich Complexes

A series of scandium, lutetium, and yttrium complexes containing a tetramethylcyclopentadienyl ligand with a pendant furyl group, [Ln{η5-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)2(THF)] (Ln = Sc, Lu, Y; R = H, Me), have been synthesized and structurally characterized. Single-crystal X-ray diffraction studies of the scandium complexes [Sc{η5-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)2(THF)] (R = H, Me) revealed a pseudo-four-coordinate metal center without additional coordination of the furyl group. The previously elusive lutetium complex [Lu{η5-C5Me4SiMe2(C4H2MeO-2)}(CH2SiMe3)2(THF)] could be isolated and exhibited structural features analogous to those of the scandium compound. Variable-temperature 1H NMR spectroscopic studies of the entire series confirmed the labile nature of both the THF ligands and furyl donor in solution. Rates for the ring-opening reaction, triggered by intramolecular C−H bond activation, were shown to depend primarily on the metal size. The ring-opening reaction resulted in the formation of the corresponding dinuclear yne−enolate complexes [Ln{η5:η1-C5Me4SiMe2(C⋮CCHCRO)}(CH2SiMe3)]2 (Ln = Sc, Lu, Y; R = H, Me). Substitution at the 5-furyl position did not markedly influence the rate of the ring-opening reaction but shifted the position of the monomer−dimer equilibrium toward the monomer. Only a large excess of THF allowed the observation of monomeric yne−enolate complexes such as [Y{η5:η1-C5Me4SiMe2(C⋮CCHCHO)}(CH2SiMe3)(THF)2], which was characterized by X-ray crystallography. Addition of THF increased the stability of the lutetium bis(alkyl) complexes and allowed the formation of the corresponding cationic compounds by treatment with [NEt3H][BPh4] to yield [Lu{η5:η1-C5Me4SiMe2(C4H2RO-2)}(CH2SiMe3)(THF)n][BPh4] (Ln = Lu; R = H, Me), which resisted ring- opening of the furyl group.

Divalent Lanthanide Metal Complexes of a Triazacyclononane-Functionalized Tetramethylcyclopentadienyl Ligand: X-ray Crystal Structures of [C5Me4SiMe2(iPr2-tacn)]LnI (Ln = Sm, Yb; tacn = 1,4-Diisopropyl-1,4,7-triazacyclononane)

The synthesis and characterization of divalent lanthanide complexes of a triazacyclononane-functionalized tetramethylcyclopentadienyl ligand are described. Addition of LnI2(THF)2 (Ln = Sm, Yb; THF = tetrahydrofuran) to [C5Me4SiMe2(iPr2-tacn)]K (tacn = 1,4-diisopropyl-1,4,7-triazacyclononane) in THF yields the monomeric organolanthanides [C5Me4SiMe2(iPr2-tacn)]SmI (1) and [C5Me4SiMe2(iPr2-tacn)]YbI (2). The crystal structures of 1 and 2 have been determined.

Syntheses and structures of doubly tucked-in titanocene complexes with tetramethyl(aryl)cyclopentadienyl ligands

Titanocene–bis(trimethylsilyl)ethyne complexes [Ti(η 5-C 5Me 4R) 2(η 2-Me 3SiCCSiMe 3)], where R=benzyl (Bz, 1a), phenyl (Ph, 1b) and p-fluorophenyl (FPh, 1c), thermolyse at 150–160°C to give products of double CH activation [Ti(η 5-C 5Me 4Bz){η 3:η 4-C 5Me 3(CH 2)(CHPh)}] ( 2a), [Ti(η 5-C 5Me 4Bz){η 3:η 4-C 5Me 2Bz(CH 2) 2}] ( 2a′), [Ti(η 5-C 5Me 4Ph){η 3:η 4-C 5Me 2Ph(CH 2) 2}] ( 2b), and [Ti(η 5-C 5Me 4FPh){η 3:η 4-C 5Me 2FPh(CH 2) 2}] ( 2c). In the presence of 2,2,7,7-tetramethylocta-3,5-diyne (TMOD) the thermolysis affords analogous doubly tucked-in compounds bearing one η 3:η 4-allyldiene and one η 5-C 5Me 4R ligand having TMOD attached by its C-3 and C-6 carbon atoms to the vicinal methylene groups adjacent to the substituent R (R=Bz ( 3a), Ph ( 3b), and FPh ( 3c)). Compound 3a is smoothly converted into air-stable titanocene dichloride [TiCl 2{η 5-C 5Me 2Bz(CH 2CH( t-Bu)CHCHCH( t-Bu)CH 2)}(η 5-C 5Me 4Bz)] ( 4a) by a reaction with hydrogen chloride. Yields in both series of doubly tucked-in complexes decrease in the order of substituents: Bz≫Ph>FPh. Crystal structures of 1c, 2a, 2b, and 3b have been determined.

Alkyl Complexes of Group 4 Metals Containing a Tridentate-Linked Amido−Cyclopentadienyl Ligand: Synthesis, Structure, and Reactivity Including Ethylene Polymerization Catalysis

A series of group 4 metal complexes M(η5:η1:η1-C5Me4SiMe2NCH2CH2X)R2 (M = Ti; R = Me, CH2Ph; M = Zr, Hf; R = Me, Et, nPr, nBu, CH2Ph, CH2SiMe3, Ph) containing the tridentate-linked amido−tetramethylcyclopentadienyl ligand C5Me4SiMe2NCH2CH2X (X = OMe, NMe2) were synthesized by alkylation of the dichloro complexes M(η5:η1:η1-C5Me4SiMe2NCH2CH2X)Cl2. The complexes were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Nuclear Overhauser effect measurements of the dimethyl complexes show that, in solution, the side chains of the zirconium derivatives coordinate intramolecularly, in contrast to the titanium complexes. The crystal structures of the zirconium alkyls Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2OMe)R2 (R = Me, Ph) were determined by X-ray diffraction studies. Both complexes adopt a trigonal-bipyramidal structure, with the five-membered ring and the methoxy group in the apical positions. Insertion of carbon monoxide into the hafnium dimethyl and di(n-butyl) complexes led to the η2-acyl derivatives Hf(η5:η1:η1-C5Me4SiMe2NCH2CH2OMe)(η2-COR)R (R = Me, nBu). Chloro mono(ethyl) complexes underwent insertion of tert-butyl isonitrile to give η2-iminoacyl derivatives M(η5:η1-C5Me4SiMe2NCH2CH2X){η2-C(NtBu)Et}Cl. The X-ray diffraction structure of the titanium complex Ti(η5:η1-C5Me4SiMe2NCH2CH2OMe){η2-C(NtBu)Et}Cl showed a square-pyramidal configuration with the imino nitrogen trans to the amido nitrogen. The zirconium dimethyl complexes Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2X)Me2 reacted with B(C6F5)3 to form the contact ion pairs [Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2X)Me]+[MeB(C6F5)3]-. Reaction between the titanium dibenzyl Ti(η5:η1-C5Me4SiMe2NCH2CH2X)(CH2Ph)2 and B(C6F5)3 resulted in the clean formation of the solvent-separated ion pair [Ti(η5:η1:η1-C5Me4SiMe2NCH2CH2X)(CH2Ph)]+[(PhCH2)B(C6F5)3]-. When activated with methylaluminoxane, the complexes Ti(η5:η1-C5Me4SiMe2NCH2CH2OMe)Cl2 and M(η5:η1:η1-C5Me4SiMe2NCH2CH2OMe)R2 (M = Zr, Hf; R = Me, nBu) are active in the polymerization of ethylene.

Zirconium and hafnium mono(alkyl) complexes containing a tridentate linked amido-tetramethylcyclopentadienyl ligand. Molecular structure of Hf( η5: η1: η1-C 5Me 4SiMe 2NCH 2CH 2OCH 3)Cl 2

Zirconium and hafnium complexes M( η 5: η 1: η 1-C 5Me 4SiMe 2NCH 2CH 2OMe)Cl 2 (M=Zr, Hf) containing the tridentate 2-methoxyethylamido-functionalized tetramethylcyclopentadienyl ligand C 5Me 4SiMe 2NCH 2CH 2OMe have been synthesized by the reaction of the dilithium derivative Li 2[C 5Me 4SiMe 2NCH 2CH 2OMe] with MCl 4(THF) 2. Selective monoalkylation of the dichloro complexes gave complexes of the type M( η 5: η 1: η 1-C 5Me 4SiMe 2NCH 2CH 2OMe)(R)Cl (R=CH 2Ph, o-C 6H 4CH 2NMe 2). The crystal structure of the hafnium dichloro complex Hf( η 5: η 1: η 1-C 5Me 4SiMe 2NCH 2CH 2OMe)Cl 2 has been determined by X-ray crystal diffraction and shows a trigonal bipyramidal structure in which the five-membered ring and the methoxy function adopt the apical positions. Crystal data: monoclininc P2 1/ c, a=12.069(2) Å, b=15.362(3) Å, c=9.949(2) Å, β=92.04(1)°, V=1843.4(6) Å 3, Z=4, R=0.0471, R w=0.0952.

Vinyltitanium Complexes Containing the [2-(N,N-Dimethylamino)ethyl]tetramethylcyclopentadienyl Ligand Cp*N. Generation and Reactivity of the Vinylidene Intermediate [(Cp*N)(Cp*)TiCCH2] (Cp*N= η5-C5Me4(CH2)2NMe2, Cp* = η5-C5Me5)

The reaction of [CpTiCl2]n and Cp*TiCl2(thf) with Cp*NLi (Cp*N, C5Me4CH2CH2NMe2; Cp*, C5Me5) leads to Cp*NCpTiCl (7) and Cp*NCp*TiCl (8), respectively. The monochlorides are oxidized by PbCl2 to give Cp*NCpTiCl2 (9) and Cp*NCp*TiCl2 (10). The molecular structures of 7 and 10 have been determined by X-ray diffraction analysis, which reveals a chelating bonding mode of the Cp*N−ligand in 7 (Ti−N, 2.437(3) Å) and noncoordination of the NMe2 group in 10. The fulvene complex Cp*N(C5Me4CH2)TiCHCH2 (18) and the titanacyclobutane respectively, are formed under mild conditions via the titanocenevinylidene intermediate [Cp*NCp*TiCCH2] (17), generated by α-H transformation from the vinyl complexes Cp*NCp*Ti(CHCH2)(CH3) (15) and Cp*NCp*Ti(CHCH2)2 (12). The formation of 14 is suggested to be influenced by the nitrogen-containing side chain in the Cp*N−ligand. A stabilization of 17 by intramolecular Ti−N coordination is not observed under the reaction conditions. Intermolecular trapping of 17 with transition metal carbonyls M(CO)6 leads to the (21, M = Cr (a), W (b)).

Bis(tetramethylcyclopentadienyl)titanium Chemistry. Molecular Structures of [(C5HMe4)(μ-η1:η5-C5Me4)Ti]2and [(C5HMe4)2Ti]2N2

Thermolysis of bis(tetramethylcyclopentadienyl)-stabilized titanium(III) compounds (C(5)HMe(4))(2)TiR (R = Me (2), Ph (3)) yields, in marked contrast with the bis(pentamethylcyclopentadienyl) analog, the dimeric product [(C(5)HMe(4))(mu-eta(1):eta(5)-C(5)Me(4))Ti](2) (4), With a bridging metalated tetramethylcyclopentadienyl ligand. The hydride (C(5)HMe(4))(2)TiH (5), synthesized by hydrogenolysis of 2 or 3, reacts with N-2 to form the dinuclear Ti(II) dinitrogen compound [(C(5)HMe(4))(2)Ti]N-2(2) (8) Under a dynamic vacuum, the dinitrogen complex 8 loses the N-2 ligand to give the titanocene (C(5)HMe(4))(2)Ti (10). The molecular structures of both 4 and 8 were determined by X-ray diffraction methods.

Construction of several functionally-substituted tetramethylcyclopentadienyl ligands, their use in the syntheses of several organometallic compounds, and incorporation of the organometallic compounds into polymers

Construction of several functionally-substituted tetramethylcyclopentadienyl ligands, their use in the syntheses of several organometallic compounds, and incorporation of the organometallic compounds into polymers