One ligand different metal complexes: Biological studies of titanium(IV), tin(IV) and gallium(III) derivatives with the 2,6-dimethoxypyridine-3-carboxylato ligand

The reaction of 2,6-dimethoxypyridine-3-carboxylic acid (DMPH) with different precursors [Ti(η⁵-C₅H₅)₂Cl₂], [Ti(η⁵-C₅H₄Me)₂Cl₂], [Ti(η⁵-C₅H₄SiMe₃)(η⁵-C₅H₅)Cl₂], [Ti(η⁵-C₅Me₅)Cl₃], SnMe₃Cl and Ga^tBu₃ yielded the complexes [Ti(η⁵-C₅H₅)₂(DMP-κO)₂] (1), [Ti(η⁵-C₅H₄Me)₂(DMP-κO)₂] (2), [Ti(η⁵-C₅H₄SiMe₃)(η⁵-C₅H₅)(DMP-κO)₂] (3), [Ti(η⁵-C₅Me₅)(DMP-κ²O,O′)₃] (4), [SnMe₃(μ-DMP-κO:κO′)]_∞ (5), and [Ga^tBu₂(μ-DMP-κO:κO′)]₂ (6). 1-6 have been characterized by spectroscopic methods and the molecular structure of the complexes 1, 2, 3, 5 and 6 have been determined by X-ray diffraction studies. The cytotoxic activity of 1-6 was tested against the tumour cell lines human adenocarcinoma HeLa, human myelogenous leukaemia K562, human malignant melanoma Fem-x and human breast carcinoma MDA-MB-361. The results of this study show a higher cytotoxicity of the tin(IV) and gallium(III) derivatives in comparison to their titanium(IV) counterparts. Furthermore, the different titanium compounds showed differences in their cytotoxicities with a higher activity of complex 4 (mono-(cyclopentadienyl) derivative) compared to that of 1-3 (bis-(cyclopentadienyl) complexes). A qualitative UV-vis study of the interactions of these complexes with DNA has also been carried out.     

Titanium(IV) carboxylate complexes: Synthesis,structural characterization and cytotoxic activity

Four titanium(IV) carboxylate complexes [Ti(η⁵-C₅H₅)₂(O₂CCH₂SMes)₂] (1), [Ti(η⁵-C₅H₄Me)₂(O₂CCH₂SMes)₂] (2), [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)(O₂CCH₂SMes)₂] (3) and [Ti(η⁵-C₅Me₅)(O₂CCH₂SMes)₃] (4; Mes = 2,4,6-Me₃C₆H₂) have been synthesised by the reaction of the corresponding titanium derivatives [Ti(η⁵-C₅H₅)₂Cl₂], [Ti(η⁵-C₅H₄Me)₂Cl₂], [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)Cl₂] and [Ti(η⁵-C₅Me₅)Cl₃] and two (for 1–3) or three (for 4) equivalents of mesitylthioacetic acid. Complexes 1–4 have been characterized by spectroscopic methods and the molecular structure of the complexes 1, 2 and 4 have been determined by X-ray diffraction studies. The cytotoxic activity of 1–4 was tested against tumor cell lines human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, and normal immunocompetent cells, that is peripheral blood mononuclear cells PBMC and compared with those of the reference complexes [Ti(η⁵-C₅H₅)₂Cl₂] (R1), [Ti(η⁵-C₅H₄Me)₂Cl₂] (R2), [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)Cl₂] (R3) and cisplatin. In all cases, the cytotoxic activity of the carboxylate derivatives was higher than that of their corresponding dichloride analogues, indicating a positive effect of the carboxylato ligand on the final anticancer activity. Complexes 1–4 are more active against K562 (IC₅₀ values from 72.2 to 87.9 μM) than against HeLa (IC₅₀ values from 107.2 to 142.2 μM) and Fem-x cells (IC₅₀ values from 90.2 to 191.4 μM).     

Preparation and characterization of Cp-functionalized cycloheptatrienyl–cyclopentadienyl titanium sandwich complexes (troticenes)

Cp-functionalized monotroticenes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄E)] (2, E = Ph₂SiCl; 3, E = tBu₂SnCl; 12, E = I) and bitroticenes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄)]₂E′ (5, E′ = PPh; 6, E′ = BN(SiMe₃)₂; 7, E′ = Cp₂Ti) were prepared by salt elimination metathesis between the monolithiated troticene [(η⁷-C₇H₇)Ti(η⁵-C₅H₄Li)]·pmdta (1b) (pmdta = N,N′,N′,N″,N″-pentamethyldiethylene-triamine) and the appropriate electrophile. The troticenyl-substituted zirconocene monochloride [(η⁷-C₇H₇)Ti(η⁵-C₅H₄ZrClCp*₂)] (Cp* = η⁵-C₅Me₅) (8) and hafnocene ethoxide [(η⁷-C₇H₇)Ti{η⁵-C₅H₄Hf(OEt)Cp₂}] (Cp = η⁵-C₅H₅) (11), and the heterobimetallic μ-oxo complexes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄MCp₂)]₂O (9, M = Zr; 10, M = Hf) were obtained instead of the expected zircona- and hafna[1]troticenophanes by reaction of the dilithiated troticene [(η⁷-C₇H₆Li)Ti(η⁵-C₅H₄Li)]·pmdta (1a) with [Cp₂MCl₂] (M = Zr, Hf) or [Cp*₂ZrCl₂] in stoichiometric amounts. These compounds were characterized by single crystal X-ray diffraction analyses and, in the case of 2, 3, 5–7, 9, 10 and 12, also by elemental analyses and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. Exposure of the troticenyl organotin chloride 3 to moisture resulted in its partial hydrolysis and formation of the organostannoxane-bridged bitroticene 4, while palladium-catalyzed Negishi C–C cross-coupling reaction between the troticenylzinc chloride [(η⁷-C₇H₇)Ti(η⁵-C₅H₄ZnCl)] (13) and the iodotroticene 12 or iodobenzene (PhI) led to the fulvalene complexes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄)]₂ (14) and [(η⁷-C₇H₇)Ti(η⁵-C₅H₄Ph)] (15). Compound 4 displays an unsymmetrical structure with the troticenyl fragments cis with respect to the Sn–O–Sn core, whereas compound 14 is centrosymmetrically trans oriented.     

Preparation and characterization of Cp-functionalized cycloheptatrienyl–cyclopentadienyl titanium sandwich complexes (troticenes)

Cp-functionalized monotroticenes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄E)] (2, E = Ph₂SiCl; 3, E = tBu₂SnCl; 12, E = I) and bitroticenes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄)]₂E′ (5, E′ = PPh; 6, E′ = BN(SiMe₃)₂; 7, E′ = Cp₂Ti) were prepared by salt elimination metathesis between the monolithiated troticene [(η⁷-C₇H₇)Ti(η⁵-C₅H₄Li)]·pmdta (1b) (pmdta = N,N′,N′,N″,N″-pentamethyldiethylene-triamine) and the appropriate electrophile. The troticenyl-substituted zirconocene monochloride [(η⁷-C₇H₇)Ti(η⁵-C₅H₄ZrClCp*₂)] (Cp* = η⁵-C₅Me₅) (8) and hafnocene ethoxide [(η⁷-C₇H₇)Ti{η⁵-C₅H₄Hf(OEt)Cp₂}] (Cp = η⁵-C₅H₅) (11), and the heterobimetallic μ-oxo complexes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄MCp₂)]₂O (9, M = Zr; 10, M = Hf) were obtained instead of the expected zircona- and hafna[1]troticenophanes by reaction of the dilithiated troticene [(η⁷-C₇H₆Li)Ti(η⁵-C₅H₄Li)]·pmdta (1a) with [Cp₂MCl₂] (M = Zr, Hf) or [Cp*₂ZrCl₂] in stoichiometric amounts. These compounds were characterized by single crystal X-ray diffraction analyses and, in the case of 2, 3, 5–7, 9, 10 and 12, also by elemental analyses and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. Exposure of the troticenyl organotin chloride 3 to moisture resulted in its partial hydrolysis and formation of the organostannoxane-bridged bitroticene 4, while palladium-catalyzed Negishi C–C cross-coupling reaction between the troticenylzinc chloride [(η⁷-C₇H₇)Ti(η⁵-C₅H₄ZnCl)] (13) and the iodotroticene 12 or iodobenzene (PhI) led to the fulvalene complexes [(η⁷-C₇H₇)Ti(η⁵-C₅H₄)]₂ (14) and [(η⁷-C₇H₇)Ti(η⁵-C₅H₄Ph)] (15). Compound 4 displays an unsymmetrical structure with the troticenyl fragments cis with respect to the Sn–O–Sn core, whereas compound 14 is centrosymmetrically trans oriented.     

Komplexe mit sterisch anspruchsvollen Liganden: IV. Gehinderte Rotation der Ringliganden in Tetrakis(trimethylsilyl)metallocenen des Eisens und des Titans

Variable-temperature ¹H NMR studies have revealed that in 1,1′,3,3′-tetrakis(trimethylsilyl)ferrocene, Fe[η⁵-C₅H₃(SiMe₃)₂-1,3]₂, as well as in 1,1′,3,3′-tetrakis(trimethylsilyl)titanocene dichloride, Ti[η⁵-C₅H₃(SiMe₃)₂-1,3]₂Cl₂, the rotation of the five-membered ring about the metal-ring vector is hindered at lower temperatures. The titanocene complex was prepared from TiCl₃ and bis(trimethylsilyl)cyclopentadienyllithium via Ti[η⁵-C₅H₃(SiMe₃)₂-1,3]₂Cl.     

Synthesis of homo- and heterodinuclear metal complexes with dimethylsilylene bridged unsymmetrical bis(cyclopentadienyl) ligand

The reaction of the dilithium salt Li₂[Me₂Si(C₅H₄)(C₅Me₄)] (2) of Me₂Si(C₅H₅)(C₅HMe₄) (1) with [MCl(C₈H₁₂)]₂ (M=Rh, Ir) and [RhCl(CO)₂]₂ afforded homodinuclear metal complexes [{Me₂Si(η⁵-C₅H₄)(η⁵-C₅Me₄)}{M(C₈H₁₂)}₂] (M=Rh: 3; M=Ir: 4) and [{Me₂Si(η⁵-C₅H₄)(η⁵-C₅Me₄)}Rh₂(CO)₂(μ-CO)] (5), respectively. The reaction of 2 with RhCl(CO)(PPh₃)₂ afforded a mononuclear metal complex [{Me₂Si(C₅HMe₄)(η⁵-C₅H₄)}Rh(CO)PPh₃] (6) leaving the C₅HMe₄ moiety intact. Taking advantage of the difference in reactivity of the two cyclopentadienyl moieties of 2, heterodinuclear complexes were prepared in one pot. Thus, the reaction of 2 with RhCl(CO)(PPh₃)₂, followed by the treatment with [MCl(C₈H₁₂)]₂ (M=Rh, Ir) afforded a homodinuclear metal complex [Rh(CO)PPh₃{(η⁵-C₅H₄)SiMe₂(η⁵-C₅Me₄)}Rh(C₈H₁₂)] (7) consisting of two rhodium centers with different ligands and a heterodinuclear metal complex [Rh(CO)(PPh₃){(η⁵-C₅H₄)SiMe₂(η⁵-C₅Me₄)}Ir(C₈H₁₂)] (8). The successive treatment of 2 with [IrCl(C₈H₁₂)]₂ and [RhCl(C₈H₁₂)]₂ provided heterodinuclear metal complex [Ir(C₈H₁₂){(η⁵-C₅H₄)SiMe₂(η⁵-C₅Me₄)}Rh(C₈H₁₂)] (9). The reaction of 2 with CoCl(PPh₃)₃ and then with PhCCPh gave a mononuclear cobaltacyclopentadiene complex [{Me₂Si(C₅Me₄H)(η⁵-C₅H₄)}Co(CPhCPhCPhCPh)(PPh₃)] (10). However, successive treatment of 2 with CoCl(PPh₃)₃, PhCCPh and [MCl(C₈H₁₂)]₂ in this order afforded heterodinuclear metal complexes [M(C₈H₁₂){(η⁵-C₅H₄)SiMe₂(η⁵-C₅Me₄)}Co(η⁴-C₄Ph₄)] (M=Rh: 11; M=Ir: 12) in which the cobalt center was connected to the C₅Me₄ moiety. Although the heating of 10 afforded a tetraphenylcyclobutadiene complex [{Me₂Si(C₅Me₄H)(η⁵-C₅H₄)}Co(η⁴-C₄Ph₄)] (13), in which the cobalt center was connected to the C₅H₄ moiety, simple heating of the reaction mixture of 2, CoCl(PPh₃)₃ and PhCCPh resulted in the formation of a tetraphenylcyclobutadiene complex [{Me₂Si(C₅H₅)(η⁵-C₅Me₄)}Co(η⁴-C₄Ph₄)] (14), in which the cobalt center was connected to the C₅Me₄ moiety. The mechanism of the cobalt transfer was suggested based on the electrophilicity of the formal trivalent cobaltacyclopentadiene moiety. In the presence of 1,5-cyclooctadiene, the reaction of 2 with CoCl(PPh₃)₃ provided a mononuclear cobalt cyclooctadiene complex [{Me₂Si(C₅Me₄H)(η⁵-C₅H₄)}Co(C₈H₁₂)] (15). The reaction of 15 with n-BuLi followed by the treatment with [MCl(C₈H₁₂)]₂ (M=Rh, Ir) afforded the heterodinuclear metal complexes of [Co(C₈H₁₂){(η⁵-C₅H₄)SiMe₂(η⁵-C₅Me₄)}M(C₈H₁₂)] (M=Rh: 16; M=Ir: 17). Treatment of 6 with Fe₂(CO)₉ at room temperature afforded a heterodinuclear metal complex [{Me₂Si(C₅HMe₄)(η⁵-C₅H₄)}{Rh(PPh₃)(μ-CO)₂Fe(CO)₃}] (18) in which the C₅HMe₄ moiety was kept intact. Treatment of dinuclear metal complex 5 with Fe₂(CO)₉ afforded a heterotrinuclear metal complex [{(η⁵-C₅H₄)SiMe₂(η⁵-C₅Me₄)}{Rh(CO)Rh(μ-CO)₂Fe(CO)₃}] (19) having a triangular metal framework. The crystal and molecular structures of 3, 11, 12, 18 and 19 have been determined by single-crystal X-ray diffraction analysis.     

Alkynyl Ti-M complexes based on M(CO)4 and MO2 building blocks (M = Mo, W)

The synthesis and properties of heterobimetallic Ti-M complexes of type {[[Ti](μ-η¹:η²-CCSiMe₃)][M(μ-η¹:η²-CCSiMe₃)(CO)₄]} (M = Mo: 5, [Ti] = (η⁵-C₅H₅)₂Ti; 6, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti; M = W: 7, [Ti] = (η⁵-C₅H₅)₂Ti; 8, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) and {[Ti](μ-η¹:η²-CCSiMe₃)₂}MO₂ (M = Mo: 13, [Ti] = (η⁵-C₅H₅)₂Ti; 14, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti). M = W: 15, [Ti] = (η⁵-C₅H₅)₂Ti; 16, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) are reported. Compounds 5-8 were accessible by treatment of [Ti](CCSiMe₃)₂ (1, [Ti] = (η⁵-C₅H₅)₂Ti; 2, [Ti] = (η⁵-C₅H₄SiMe₃)₂Ti) with [M(CO)₅(thf)] (3, M = Mo; 4, M = W) or [M(CO)₄(nbd)] (9, M = Mo; 10, M = W; nbd = bicyclo[2.2.1]hepta-2,5-diene), while 13-16 could be obtained either by the subsequent reaction of 1 and 2 with [M(CO)₃(MeCN)₃] (11, M = Mo; 12, M = W) and oxygen, or directly by oxidation of 5-8 with air. A mechanism for the formation of 5-8 is postulated based on the in-situ generation of [Ti](CCSiMe₃)((η²-CCSiMe₃)M(CO)₅), {[Ti](μ-η¹:η²-CCSiMe₃)₂}-M(CO)₄, and [Ti](μ-η¹:η²-CCSiMe₃)((μ-CCSiMe₃)M(CO)₄) as a result of the chelating effect exerted by the bis(alkynyl) titanocene fragment and the steric constraints imposed by the M(CO)₄ entity.The molecular structure of 5 in the solid state were determined by single crystal X-ray diffraction analysis. In doubly alkynyl-bridged 5 the alkynides are bridging the metals Ti and Mo as a σ-donor to one metal and as a π-donor to the other with the [Ti](CCSiMe₃)₂Mo core being planar.     

Synthesis and structures of binuclear half-sandwich cobalt (III) ortho-carboranedithiolato complexes with silyl-bridged bis(cyclopentadienyl) ligands

Five binuclear half-sandwich cobalt complexes, [(η⁵-C₅H₄)Co(CO)I₂]₂SiMe₂ (3), [(η⁵-C₅H₄)Co(S₂C₂B₁₀H₁₀)]₂SiMe₂ (4), [(η⁵-C₅H₄)]₂Co₂(μ₂-S₂C₂B₁₀H₁₀)SiMe₂ (5), [(η⁵-C₅H₃)CoI₂](μ-I)[(η⁵-C₅H₃)Co(CO)I](SiMe₂)₂ (8), [(η⁵-C₅H₃)Co(S₂C₂B₁₀H₁₀)]₂(SiMe₂)₂ (9), were successfully synthesized in moderate yield by the reactions of corresponding ligands, (C₅H₅)₂SiMe₂ (1) and (C₅H₄)₂(SiMe₂)₂ (6), respectively. The molecular structures of 3, 5, 6, 8 and 9 was determined by X-ray crystallographic analysis, which distinctly depict various molecular structures containing the Cp rings and the metal centers with halide or 1,2-dicarba-closo-dodecaborane-1,2-dithiolato ligands. For the (η⁵-C₅H₄)₂SiMe₂ complexes, coordination of the fragments CpCo favors a exo conformation. With the rigid structure of the di-bridged ligand (C₅H₄)₂(SiMe₂)₂, only cis isomers of the corresponding (η⁵-C₅H₃)₂(Si₂Me₂)₂ complexes are formed. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Synthesis and structure of isopropyldimethylsilyl-substituted octamethyltitanocene

Reduction of isopropyldimethylsilyl-substituted titanocene dichloride [TiCl₂(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (1) by excess magnesium in the presence of excess bis(trimethylsilyl)ethyne (btmse) in tetrahydrofuran at 60 °C yielded a mixture of products amongst them only the trinuclear Ti-Mg-Ti hydrido-bridged complex Mg[Ti(μ-H)₂(η⁵-C₅Me₄SiMe₂Prⁱ)]₂ (3) was isolated and characterized. The precursor of titanocene, [Ti(η⁵-C₅Me₄SiMe₂Prⁱ)₂(η²-btmse)] (6), was obtained from the identical system which, after initial formation of [TiCl(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (2), reacted at −18 °C overnight and then the solution was rapidly separated from the remaining magnesium. Titanocene [Ti(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (7) was obtained by thermolysis of 6 at 75 °C in vacuum. Crystal structures of 1, 2, 3, 6, and 7 were determined.     

Transition-metal complexes of two valence tautomers of a bulky phenoxide, 2,6-Bu-t2-4-MeC6H2O− (ArO−); preparation and crystal and molecular structure of a phenoxytitanium(III) and a cyclohexadienonylrhodium(I) complex, [Ti(η-C5H5)2 OAr] and [Rh(ArO-η5)(PPh3)2]

The 2,6-di-t-butyl-4-methylphenoxo ligand (ArO^?) is ambidentate, giving rise to the O-bonded 15-electron d¹ [Ti(η-C₅H₅)₂OAr] and the η⁵ -[C(2)-C(6)]-bonded 18-electron d⁸ complex [Rh(ArO-η⁵)(PPh₃)₂], obtained from [{Ti(η-C₅H₅)₂Cl}₂]-LiO Ar and [Rh{N(SiMe₃)₂}(PPh₃)₂]-ArOH, respectively; the average TiC(η) distance is 2.362(10) Å, TiO 1.892(2) Å, and O:C(of Ar) 1.352(3) Å, and TiOC 142.3(2)°; in the Rh^I complex, C(2)C(6) are coplanar (with CC(av.) 1.38(2) Å). C(1)O 1.28 Å, and Rh to C(2) C(6) bond lengthsare in the range 2.19–2.65 Å.     

Derivatisation of boryl substituted titanium half-sandwich complexes - Molecular structures of [Ti{(η-C5H4)B(NiPr2)N(H)tBu}Cl2(NMe2)] and [{TiCl2(μ-{OB(NHMe2)-η-C5H4})}2-μ-O]

The half-sandwich complex [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}(NMe₂)₃] (6) was prepared from (η¹-C₅H₅)B(NiPr₂)N(H)iPr (5) and [Ti(NMe₂)₄] with cleavage of one equivalent of HNMe₂ and further converted into the corresponding constrained geometry complex [Ti{(η⁵-C₅H₄)B(NiPr₂)NiPr}(NMe₂)₂] (7) by elimination of a second equivalent of HNMe₂. Reaction of the half-sandwich complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}(NMe₂)₃] (R = iPr, tBu) with excess Me₃SiCl yielded the corresponding dichloro complexes [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)R}Cl₂(NMe₂)] (R = tBu (10), iPr (11)). The intermediate species [Ti{(η⁵-C₅H₄)B(NiPr₂)N(H)iPr}Cl(NMe₂)₂] (9) could also be spectroscopically characterised. Partial hydrolysis of 10 and 11, respectively, resulted in formation of [{TiCl₂(μ-{OB(NHMe₂)-η⁵-C₅H₄})}₂-μ-O] (12). The molecular structures of 10 and 12 have been determined by X-ray crystallographic analyses. Complex 10, when activated with MAO, was found to be a highly active styrene polymerisation catalyst while being inactive towards the polymerisation of ethylene.     

Novel heterotetrametallic compounds derived from 1-(ferrocenylethynyl)(η6-arene)tricarbonylchromium

The synthesis and characterization of two new heterotetrametallic complexes are described. Reaction of [Cr(CO)₃(η⁶-C₆H₅)CC-{(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}](1) with Co₂(CO)₈ or Cp₂Mo₂(CO)₄ afford the heterotetrametallic complexes [Cr(CO)₃(η⁶-C₆H₅){Co₂(CO)₆-μ²-η²-CC–}(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}](2), and [Cr(CO)₃(η⁶-C₆H₅){Mo₂Cp₂(CO)₄-μ²-η²-CC–}(η⁵-C₅H₄)Fe(η⁵-C₅H₅)](3) in 80% and 41% yield, respectively. All complexes have been characterized by elemental analysis, multinuclear (¹H, ¹³C) NMR, and by single-crystal X-ray diffraction studies for 1 and 3. Structural data reveal that the coordination of dimolybdenum moiety to the alkyne unit influence the orientation of the carbonyl groups coordinated to the chromium as well as the Cp rings bound to the iron metal centre.     

Pyrolysis of metallocene complexes (ηC5H4R)2MR: An organometallic route to metal carbide (MC) materials (M = Ti,Zr, Hf)

The following compounds were prepared and their pyrolysis in a stream of argon was studied: (η⁵-C₅H₅)₂Ti(C?CC₆H₅)₂, (η⁵-C₅H₄SiMe₃)₂-Ti(SH)₂, [(η⁵-C₅H₅)Ti(μ-CH₂)]₂, (η⁵-C₅H₅)₂ZrR₂-(R?CH₂, CH₂C₆H₅, N(CH₃)₂), (η⁵-C₅H₄CH₃)₂-Zr(C?CC₆H₅)₂, [(η⁵-C₅H₄SiMe₃)₂Zr(μ-S)]₂, [(η⁵-C₅H₄SiMe₃)₂Hf(μ-S)]₂ and (η⁵-C₅H₄SiMe₃)₂Hf-(C?CC₆H₅)₂. The products of bulk pyrolysis of these materials were formed in 20–40% yield, based on the charged sample weight, and consisted mainly of titanium carbide together with small amounts of amorphous carbon.     

Irregular cyclization reactions in titanocenes bearing pendant double bonds

Reduction of methyl-substituted titanocene dichlorides bearing pendant double bonds [TiCl₂{η⁵-C₅Me₄(CH₂CMeCH₂)}₂] (1) and [TiCl₂{η⁵-C₅Me₄(SiMe₂(CH₂)₂CHCH₂)}₂] (2) with magnesium yielded diamagnetic Ti(IV) compound [Ti{η¹:η¹:η⁵-C₅Me₃(CH₂)(CH₂CH(Me)CH₂)}{η⁵-C₅Me₄(CH₂C(Me)CH₂)}] (4) and paramagnetic Ti(III) compound [Ti{η⁵-C₅Me₄(SiMe₂CH₂CHCHMe)}(μ-η³,η¹:η⁵,η¹(Ti:Mg){C₅Me₃(CH₂)(SiMe₂CHCHCMe)})Mg(OC₄H₈)₂] (6), respectively. The reluctance of titanocene intermediates to undergo intramolecular cyclization to cyclopentadienyl-ring-tethered titanacycles (as typically observed) can be explained by a shortness of the 2-methylallyl group and steric hindrance of its double bond in the former case and, in the latter case, by an attack of magnesium on the titanocene intermediate, faster than cyclization reactions. The crystal structures of 4 and 6 were determined by single-crystal X-ray diffraction.     

Stabile Bis(alkinyl)-Titanocen-Komplexverbindungen von FeCl2 und CuCl

The application of (η⁵-C₅H₄SiMe₃)₂Ti(CC-SiMe₃)₂ as an organometallic bidentate chelate ligand for MCl₂ building blocks (M = Fe, Co, Ni) is discussed. Reaction of the organometallic substituted alkyne Me₃Si-CC-(η⁵-C₅H₄SiMe₃)₂Ti-CC-SiMe₃, I, with FeCl₂ affords in high yields the dinuclear complex {(η⁵-C₅H₄SiMe₃)₂Ti(CC-SiMe₃)₂}FeCl₂, II. The identy of compound II is confirmed by analytical and spectroscopic data as well as by an X-ray diffraction study. Structural data for L₂Ti(CC-SiMe₃)₂, I, {L₂Ti(CC-SiMe₃)₂}FeCl₂, II, and {L₂Ti(CC-SiMe₃)₂}CuCl, III, (L = η⁵-C₅H₄SiMe₃) are discussed.     

Nucleophilic substitution reactions of acetylides on substituted tricarbonyl(η6-fluoroarene)chromium and reactions of tricarbonyl[η6-(2-trimethylsilylethynyl)toluene]chromium and tricarbonyl[η6-(p-ethynyl-phenylethynyl)benzene]chromium with dicobalt octacarbonyl

Nucleophilic substitution reactions of various acetylides on substituted tricarbonyl(η⁶-fluoroarene)chromiums were pursued. The reaction presumably underwent a more complicated mechanism rather than the direct substitution on the fluorine-bearing carbon. The organometallic compounds (η⁶-C₆H₃R¹R²R³)Cr(CO)₃ (R¹: CC–C₆H₄CH₃, R²: o-Me, R³: H (5a), R¹: CC–C₆H₄CH₃, R²: o-OMe, R³: H (6a), R¹: CC–C₆H₄CH₃, R²: m-OMe, R³: H (6b), R¹: CCPh, R²: o-Me, R³: o-OMe (8b), R¹: CCPh, R²: m-Me, R³: m-OMe (8c), R¹: CCSiMe₃, R²: o-Me, R³: H (9a), R¹: CC–C₆H₄CCH, R²: H, R³: H (12), R¹: CC–C₆H₄CCH, R²: o-Me, R³: H (13)) as well as the organometallic dimmer [{(η⁶-o-Me-C₆H₄)Cr(CO)₃(di-ethynyl)] (di-ethynyl: CC–C₆H₄CC (14)) have been synthesized from nucleophilic substitution reactions of tricarbonyl(η⁶-fluoroarene)(chromium) compounds with suitable acetylides. The products have been characterized by spectroscopic means. In addition, (8b) and (8c) were characterized by X-ray diffraction studies. Further reactions of (9a) and (12) with appropriate amount of Co₂(CO)₈ yielded μ-alkyne bridged bimetallic complexes, Co₂(CO)₆{μ-Me₃SiCC–(o-tolueneCr(CO)₃} (10) and (Co₂(CO)₆)₂{μ-HCC–C₆H₄–CC–(benzene)Cr(CO)₃)}(15), respectively. Both (10) and (15) were characterized by spectroscopic means as well as single crystal X-ray crystallography. The core of these molecules is quasi-tetrahedron containing a Co₂C₂ unit. A two-dicobalt-fragments coordinated di-enyls complex, (Co₂(CO)₆)₂{μ-HCC–C₆H₄–CC–H} (17), was synthesized from the reaction of 1,3-diethynylbenzene with Co₂(CO)₈. Crystallographic studies of (17) also show that it exhibits a distorted Co₂C₂ quasi-tetrahedral geometry.     

Diphenylcarbene rhodium complexes: of the halfsandwich type with (η5-C5H4SiMe3)Rh as a molecular unit

The square-planar rhodium(I) complexes trans-[RhCl(=CPh₂)(L)₂] (L = SbiPr₃, PiPr₃, PPh₃) react with LiC₅H₄SiMe₃ to give the halfsandwich type compounds [(η⁵-C₅H₄SiMe₃)Rh(=CPh₂)(L)] 7–9 in good to excellent yields. While the phosphine complexes 8 and 9 are rather inert toward Lewis bases, the stibine derivative 7 reacts with CO, CNtBu and PMe₃ to afford the corresponding substitution products [(η⁵-C₅H₄SiMe₃)Rh(=CPh₂)(L′] 10–12. In contrast, the reaction of 7 with C₂H₄ leads to the displacement of the carbene ligand and to the formation of the ethene complex [(η⁵-C₅H₄SiMe₃)Rh(C₂H₄)(SbiPr₃)] 14 together with the C−C coupling product Ph₂C=CHCH₃13. Upon treatment of 9 (L = PPh₃) with an equimolar amount of HCl, the chloro(hydrido)rhodium(III) compound [{η⁵-C₅H₃)(CHPH₂)(SiMe₃)}RhHCl(PPh₃)] 15 is formed. With an excess of HCl, a mixture of two products is obtained, one of which, with the composition [η⁵-C₅H₄)CHPh₂)RhCl₂(PPH₃)] 17 has been independently prepared from η⁵-C₅H₅)Rh(=CPh₂)(PPh₃] 18 and 2 equiv of HCl.     

Trimethylsilyl-functionalised bis(indenyl)iron(II) complexes: solid-state structure of [η-1,3-(SiMe3)2C9H5]2Fe

The synthesis of the bis(η⁵-indenyl)iron sandwich complexes (η⁵-1-SiMe₃-C₉H₆)₂Fe (3a), (η⁵-2-SiMe₃-C₉H₆)₂Fe (3b), [η⁵-1,2-(SiMe₃)₂C₉H₅]₂Fe (4a) and [η⁵-1,3-(SiMe₃)₂C₉H₅]₂Fe (4b), by the reaction of the appropriate lithium indenide salts [prepared from 1-SiMe₃-C₉H₇ (2a), 2-SiMe₃-C₉H₇ (2b), 1,2-(SiMe₃)₂C₉H₆ (2c) or 1,3-(SiMe₃)₂C₉H₆ (2d)] with ferrous chloride (1) in a 2:1 molar ratio is discussed. The solid-state structure of 4b was determined by single-crystal X-ray diffractometry. Complex 4b exists in a gauche conformation, showing that the indenyl ligands are sterically imposed by the bulk of the Me₃Si substituents. The average Fe-C distance is 2.091(3) Å. Cyclovoltammetric studies indicate that 3 and 4 are redox-active with one-electron oxidations [E^1/2=−270 to −360 mV versus Fc/Fc⁺, Fc=(η⁵-C₅H₅)₂Fe].     

η1-Alkynylplatinum(II) complexes with cycloocta-1,5-diene and tri(1-cyclohepta-2,4,6-trienyl)phosphane ligands

η¹-Alkynylplatinum(II) complexes of the type (cod)Pt(CCR)₂ (1, cod=η⁴-cycloocta-1,5-diene; R=Me (a), ^tBu (b), Ph (c), Fc (d), SiMe₃ (e)) were prepared in good yields from the reaction of (cod)PtCl₂ with either HCCR and NaOEt (R=^tBu, Ph, Fc) or di(1-alkynyl)dimethyltin, Me₂Sn(CCR)₂ (R=Me, SiMe₃). The analogous reaction of [P]PtCl₂ ([P]=tri(1-cyclohepta-2,4,6-trienyl)phosphane, {P(C₇H₇)₂(η²-C₇H₇)}) with Me₂Sn(CCR)₂ (R=Me, ^tBu, Ph, Fc, SiMe₃), afforded selectively the complexes [P]PtCl(CCR) 2a–e in high yield, in which the 1-alkynyl group is in cis position with respect to the phosphorus atom, and one of the C₇H₇ rings is η²-coordinated to platinum through the central CC bond. Complexes 3a–e of the type [P]Pt(CCR)₂ could not be prepared by the reaction of 2 with an excess of the 1-alkynyltin reagents. However, the reaction of 1 with the phosphane P(C₇H₇)₃ gave compounds 3a–e in quantitative yield by substitution of the cod ligand. The molecular structures of 2b and 3d were determined by X-ray structure analysis, and complexes 1–3 were characterised in solution by multinuclear magnetic resonance spectroscopy (¹H-, ¹³C-, ²⁹Si-, ³¹P-, ¹⁹⁵Pt-NMR). The structures of 2 and 3 in solution were found to be fluxional with respect to coordination of the C₇H₇ rings to platinum.     

Synthesis of new chloro methyl niobium and tantalum complexes with silyl-cyclopentadienyl ligands: X-ray crystal structure of [Ta{η-C5H3(SiMe3)2}Cl2Me2]

Trichloro methyl [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₃Me] (X = Cl, 2; Me, 3), dichloro dimethyl [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₂Me₂] (X = Cl, 4; Me, 5) and tetramethyl [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Me₄] (X = Me, 6; Cl, 7) niobium complexes were synthesized by treatment of starting tetrachloro derivatives [Nb{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₄] (X = Cl, 1a; Me, 1b) with dimethyl zinc or chloro methyl magnesium in different proportions and conditions. A mixture of trichloro methyl and dichloro dimethyl tantalum complexes [Ta{η⁵-C₅H₃(SiClMe₂)(SiMe₃)}Cl_4−xMe_x] (x = 1, 8; 2, 9) in a 2:1 molar ratio was obtained in the reaction of [Ta{η⁵-C₅H₃(SiClMe₂)(SiMe₃)}Cl₄] (1c) with 0.5 equivalents of ZnMe₂ in toluene at low temperature. 8 could be isolated as single compound when 1 equivalent of 1c was added to the mixtures of 8 and 9, while the reaction of 1c with 1.5 equivalents of dimethyl zinc gave 9 as unitary product. However, [Ta{η⁵-C₅H₃(SiMe₃)₂}Cl₄] (1d) reacts with 0.5 equivalents of alkylating reagent giving the trichloro methyl compound [Ta{η⁵-C₅H₃(SiMe₃)₂}Cl₃Me] (10) in good yield. On the other hand, [Ta{η⁵-C₅H₃(SiMe₃)₂}Cl₄] (1d) reacts with 2 equivalents of MgClMe in hexane at room temperature giving a mixture of dichloro dimethyl and chloro trimethyl complexes[Ta{η⁵-C₅H₃(SiMe₃)₂}Cl_4−xMe_x] (x = 2, 11; 3, 12), while the use of 4 equivalents of MgClMe converts 1c into the tetramethyl derivative [Ta{η⁵-C₅H₃(SiClMe₂)(SiMe₃)}Me₄] (13). Finally, a tetramethyl tantalum complex [Ta{η⁵-C₅H₃(SiMe₃)₂}Me₄] (14) was prepared by reaction of [Ta{η⁵-C₅H₃(SiXMe₂)(SiMe₃)}Cl₄] (X = Cl, 1c; Me, 1d) with 5 (X = Cl) or 4 (X = Me) equivalents of MgClMe in diethyl ether (X = Cl) or hexane (X = Me), respectively, as solvent. All the complexes were studied by IR and NMR spectroscopy and the molecular structure of the complex 11 was determined by X-ray diffraction methods.