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.     

Anticancer drugs based on alkenyl and boryl substituted titanocene complexes

The alkenyl-substituted titanocene complex [Ti(η⁵-C₅H₅)(η⁵-C₅H₄{CMe₂(CH₂CH₂CHCH₂)})Cl₂] (1) has been synthesized and characterized using traditional methods. The reaction of 1 with 9-BBN gave the boryl substituted complex [Ti(η⁵-C₅H₅)(η⁵-C₅H₄{CMe₂(CH₂CH₂CH₂CH₂BC₈H₁₄)})Cl₂] (2). The cytotoxic activity of 1 and 2 was tested against tumour cell lines human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, human breast carcinoma MDA-MB-361 and normal immunocompetent cells peripheral blood mononuclear cells PBMC and compared with those of the reference complexes [Ti(η⁵-C₅H₅)₂Cl₂] (R1), [Ti(η⁵-C₅H₄Me)₂Cl₂] (R2) and [Ti(η⁵-C₅H₅)(η⁵-C₅H₄SiMe₃)Cl₂] (R3). Complex 1 showed higher cytotoxic activities on HeLa, Fem-x and K562 (IC₅₀ values from 96.6 ± 3.4 to 149.2 ± 2.9 μM) than the reference complexes R1, R2 and R3 which presented IC₅₀ values from 173.3 ± 6.0 to >200 μM. On the other hand, boryl substituted complex 2, present slightly lower cytotoxic activities than 1 on HeLa, Fem-x and K562 (IC₅₀ values from 155.6 ± 5.5 to 167.9 ± 4.2 μM). However, 2 was the most active of the studied complexes against MDA-MB-361 (IC₅₀ value of 161.1 ± 0.1 μM). Structural studies based on DFT calculations of 1 and 2 have also been carried out in order to gain a possible insight into the relationship between metal complex structure and cytotoxicity.     

Amidoamine-based dendrimers with end-grafted Pd-Fe units: Synthesis, characterization and their use in the Heck reaction

The synthesis and characterization of novel amidoamine-based metallodendrimers with heterobimetallic end-grafted amidoferrocenyl-palladium-allyl chloride units is described. Dendrimer (Fe((η⁵-C₅H₄PPh₂)(η⁵-C₅H₄))C(O)HNCH₂CH₂NHC(O)CH₂CH₂)N[CH₂CH₂N(CH₂CH₂C(O)NHCH₂CH₂NH-C(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂)))₂]₂ (9-Fe) and the corresponding metal species (Fe((η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))(η⁵-C₅H₄))C(O)HNCH₂CH₂NHC(O)CH₂CH₂)N[CH₂CH₂N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))))₂]₂ (9-Fe-Pd) were prepared by a consecutive divergent synthesis methodology including addition-amidation cycles, standard peptide coupling, and coordination procedures. For comparative reasons also the monomeric and dimeric molecules (Fe(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄C(O)NHⁿC₃H₇)) (5-Fe) and [Fe(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄C(O)NHCH₂)]₂ (6-Fe) as well as N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂)))₃ (7-Fe) and [CH₂N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂)))₂]₂ (8-Fe) were prepared from Fe(η⁵-C₅H₄PPh₂)(η⁵-C₅H₄CO₂H) (3). Using [Pd(η³-C₃H₅)Cl]₂ (4) as palladium source heterobimetallic metallodendrimers (Fe(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))(η⁵-C₅H₄C(O)NHⁿC₃H₇)) (5-Fe-Pd), [Fe(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))(η⁵-C₅H₄C(O)NHCH₂)]₂ (6-Fe-Pd), N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))))₃ (7-Fe-Pd) and [CH₂N(CH₂CH₂C(O)NHCH₂CH₂NHC(O)(Fe(η⁵-C₅H₄)(η⁵-C₅H₄PPh₂(Pd(η³-C₃H₅)Cl))))₂]₂ (8-Fe-Pd) were synthesized. Additionally, seleno-phosphines of 5-Fe-Se and 9-Fe-Se, respectively, were prepared by addition of elemental selenium to 5-Fe or 9-Fe to estimate their σ-donor properties.The palladium-containing amidoamine supports are catalytically active in the Heck-Mizoroki cross-coupling of iodobenzene with tert-butyl acrylate. The catalytic data are compared to those obtained for the appropriate mononuclear and dinuclear compounds 5-Fe-Pd and 6-Fe-Pd. This comparison confirms a positive cooperative effect. The mercury drop test showed that (nano)particles were formed during catalysis, following on heterogeneous carbon-carbon cross-coupling.     

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.     

Iridium(I) complex of chelating pyridine-2-thiolate ligand: Synthesis, reactivity, and application to the catalytic E-selective terminal alkyne dimerization via C-H activation

A novel iridium(I) complex bearing a chelate-coordinated pyridine-2-thiolate ligand [Ir(η²-SNC₅H₄)(PPh₃)₂] (2) was prepared by the reaction of iridium ethylene complex [IrCl(C₂H₄)(PPh₃)₂] (1) with lithium salt of pyridine-2-thiol (Li[SNC₅H₄]). On the treatment of iridium(I) complex 2 with chloroform, iridium(III) dichloro-complex [IrCl₂(η²-SNC₅H₄)(PPh₃)₂] (3) was formed. Reactions of complex 2 with methyldiphenylsilane, acetic acid, and p-tolylacetylene afforded iridium(III) hydride complexes [IrH(SiMePh₂)(η²-SNC₅H₄)(PPh₃)₂] (4), [IrH(O₂CCH₃)(η²-SNC₅H₄)(PPh₃)₂] (5), and [IrH(CC(p-tolyl))(η²-SNC₅H₄)(PPh₃)₂] (6), respectively. Complex 2 catalyzed dimerization of terminal alkynes leading to enynes (7) with high E-selectivity via C-H bond activation.     

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.     

Hydro- and chloro-substituted silyl- and silyl-η-amido-η-tetramethylcyclopentadienyl titanium complexes

Chlorosilyl-cyclopentadienyl titanium precursors [Ti(η⁵-C₅Me₄SiMeXCl)Cl₃] (X=H 2, Cl 3) were prepared by reaction of TiCl₄ with the trimethylsilyl derivatives of the corresponding cyclopentadienes. Methylation of these compounds with MgClMe under appropriate conditions afforded the methyl complexes [Ti(η⁵-C₅Me₄SiMe₂R)XMe₂] (R=H, X=Cl 5, Me 6; R=X=Me 7). Reactions of 2 and 3 with two equivalents of LiNH^tBu afforded the ansa-silyl-η-amido compounds [Ti{η⁵-C₅Me₄SiMeX(η¹-N^tBu)}Cl₂] (X=H 8, Cl 9). Methylation of 8 gave [Ti{η⁵-C₅Me₄SiMeH(η¹-N^tBu)}Me₂] 10. Complex 9 was also obtained by reaction of 8 with BCl₃, whereas the same reaction using alternative chlorinating agents (TiCl₄, HCl) resulted in deamidation to give 2, which was also converted into 3 by reaction with BCl₃. All of the new compounds were characterized by NMR spectroscopy and the molecular structures of 2 and 4 were determined by X-ray diffraction methods.     

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 reactivity of new mono- and dinuclear niobium and tantalum imido complexes: X-ray crystal structure of [Ta(η-C5H4SiMe3)Cl2{NC6Me4-4-(N(SiMe3)2)}]

The reaction of [1,4-{SiMe₃(H)N}₂C₆Me₄] (1) with 2 equivalents of LiBuⁿ followed by the addition of SiMe₃Cl gave the diamine compound [1,4-{(SiMe₃)₂N}₂C₆Me₄] (2). [Ta(η⁵-C₅H₄SiMe₃)Cl₄] reacts with 2, in a 2:1 stoichiometric ratio, to initially yield a mixture of the dinuclear, [{Ta(η⁵-C₅H₄SiMe₃)Cl₂}₂(μ-1,4-NC₆Me₄N)] (3), and mononuclear, [Ta(η⁵-C₅H₄SiMe₃)Cl₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (4), imido complexes. 3 can be obtained exclusively by submitting the reaction mixture to repeated cycles of evacuation, to remove volatiles, followed by addition of solvent and subsequent heating. The mononuclear imido complex 4 was isolated from the reaction of [Ta(η⁵-C₅H₄SiMe₃)Cl₄] with 2 in a 1:1 stoichiometric ratio. The molecular structure of 4 was determined by X-ray diffraction studies. [TaCl₃(CH₃CN)₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (5) has been prepared by the reaction of one molar equivalent of TaCl₅ with 2 in a CH₃CN/CH₂Cl₂ solvent mixture. The synthesis of the niobium complexes, [{Nb(η⁵-C₅H₄SiMe₃)Cl₂}₂(μ-1,4-NC₆Me₄N)] (6) and [Nb(η⁵-C₅H₄SiMe₃)Cl₂{NC₆Me₄-4-(N(SiMe₃)₂)}] (7), was achieved in a similar manner to their tantalum analogues. The reactivity of 7 towards nucleophilic reagents, namely lithium benzamidinate, lithium (trimethylsilyl)cyclopentadienyl or lithium dimethylamide, has been studied and the following compounds prepared:[Nb(η⁵-C₅H₄SiMe₃)RCl{NC₆Me₄-4-(N(SiMe₃)₂)}] (R = η⁵-C₅H₄SiMe₃ (8), PhC(NSiMe₃)₂ (9), NMe₂ (10)). In an attempt to form the hetero bimetallic complex, [{Nb(η⁵-C₅H₄SiMe₃)Cl₂}(μ-1,4-NC₆Me₄N){Ta(η⁵-C₅H₄SiMe₃)Cl₂}] (11), the reaction of 7 with [Ta(η⁵-C₅H₄SiMe₃)Cl₄] has been studied. Analysis of the reaction products showed that 11 may exist in equilibrium with the homo bimetallic complexes 3 and 6.     

The effect that 6-tert-butoxyhexyl functionalization has on ethylene polymerization in ansa-zirconocene dichlorides

Ethylene polymerization studies have been carried out with novel precatalysts of the type: [(η⁵-C₁₃H₈)-X(t-BuOC₆H₁₂)Me-(η⁵-C₅H₄)]ZrCl₂ [X=C [1a], Si [2a]], [(η⁵-C₁₃H₈)-XMe₂-(η⁵-(t-BuOC₆H₁₂C₅H₃))] ZrCl₂ [X=C [3a], Si [4a]] in the presence of excess methylalumoxane (MAO) to compare their catalytic activity and to delineate the effect of the 6-t-butoxyhexyl functionality on ethylene polymerization. The precatalysts [1a] and [2a] with the bridge functionality showed higher activity in ethylene polymerization than the corresponding complexes [3a] and [4a] which have it on the Cp ring moiety. On the other hand the silyl bridged complexes [2a] and [4a] produced a higher molecular weight polyethylene than the carbon-bridged one, regardless of the location of functional group.     

New alkenyl-substituted group 4 C-ansa-metallocene complexes. Reactivity of the substituent at the carbon ansa bridge

The allyl-substituted group 4 metal complexes [M{(R)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti, R = CH₂CHCH₂, (2); R = CH₂C(CH₃)CH₂ (3); M = Zr, R = CH₂CHCH₂ (4), R = CH₂C(CH₃)CH₂ (5)] have been synthesized by the reaction of allyl ansa-magnesocene derivatives and the tetrachloride salts of the corresponding transition metal. The dialkyl complexes ] [M = Ti, R = CH₂=CHCH₂, R′ = Me (6), R′ = CH₂Ph (7); R = CH₂C(CH₃)CH₂, R′ = Me (8), R′ = CH₂Ph (9); M = Zr, R = CH₂CHCH₂, R′ = Me (10), R′ = CH₂Ph (11); R = CH₂C(CH₃)CH₂, R′ = Me (12), R′ = CH₂Ph (13)] have been synthesized by the reaction of the corresponding ansa-metallocene dichloride complexes 2-5 and two molar equivalents of the alkyl Grignard reagent. Compounds 2-5 reacted with H₂ under catalytic conditions (Wilkinson’s catalyst or Pd/C) to give the hydrogenation products [M{(R)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti and R = CH₂CH₂CH₃ (14) or R = CH₂CH(CH₃)₂ (15); M = Zr and R = CH₂CH₂CH₃ (16) or R = CH₂CH(CH₃)₂ (17)]. The reactivity of 2-5 has also been tested in hydroboration and hydrosilylation reactions. The hydroboration reactions of 3, 4 and 5 with 9-borabicyclo[3.3.1]nonane (9-BBN) yielded the complexes [M{(9-BBN)CH₂CH(R)CH₂CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti and R = H (18); M = Zr and R = H (19) or R = CH₃ (20)]. The reaction with the silane reagents HSiMe₂Cl gave the corresponding [M{ClMe₂SiCH₂CHRCH₂CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] [M = Ti and R = H (21); M = Zr and R = H (22) or R = CH₃ (23)]. The reaction of 22 with t-BuMe₂SiOH produced a new complex [Zr{t-BuMe₂SiOSi(Me₂)CH₂CH₂CH₂CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}Cl₂] (24) through the formation of Si-O-Si bonds. On the other hand, reactivity studies of some zirconocene complexes were carried out, with the insertion reaction of phenyl isocyanate (PhNCO) into the zirconium-carbon σ-bond of [Zr{(n-Bu)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)}₂Me₂] (25) giving [{(n-Bu)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)]}Zr{Me{κ²-O,N-OC(Me)NPh}] as a mixture of two isomers 26a-b. The reaction of [Zr{(n-Bu)(H)C(η⁵-C₅Me₄)(η⁵-C₅H₄)}(CH₂Ph)₂] (27) with CO also provided a mixture of two isomers [{(n-Bu)CH(η⁵-C₅Me₄)(η⁵-C₅H₄)]}Zr(CH₂Ph){κ²-O,C-COCH₂Ph}] 28a-b. The molecular structures of 4, 11, 16 and 17 have been determined by single-crystal X-ray diffraction studies.     

Synthesis and characterization of cyclopentadienyl/alkoxo titanium dichlorides: structural analysis of monocyclopentadienyl titanium dichlorides with ligands derived from menthol and borneol

A variety of monocyclopentadienyl alkoxo titanium dichloride and bisalkoxo titanium dichloride complexes have been prepared and characterized by spectroscopic techniques. The titanium derivatives containing both cyclopentadienyl and various alkoxo ligands [Ti(η⁵-C₅H₅)(OR)Cl₂] (1-5) have been synthesized from the reaction of [Ti(η⁵-C₅H₅)Cl₃] with 1 equivalent of the corresponding alcohol in THF in the presence of triethylamine (ROH = Adamantanol, 1R,2S,5R-(−)-menthol, 1S-endo-(−)-borneol, cis-1,3-(−)-benzylideneglycerol, 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose). The bisalkoxo titanium dichloride derivatives [TiCl₂(OR)₂] (6-10) have been prepared by a redistribution reaction between Ti(OR)₄ and TiCl₄ compounds 6-8 (OR = Adamantanoxy, (1R,2S,5R)-(−)menthoxy, (1S-endo)-(−)-borneoxy) and by reaction of [Ti(OR)₂(OPrⁱ)₂]₂ with CH₃COCl compounds 9 and 10 (OR = 1,2:3,4-di-O-isopropylidene-α-d-galactopyranoxy, and 1,2:5,6-di-O-isopropylidene-α-d-glucofuranoxy). The molecular structures of 2 and 3 have been determined by single crystal X-ray diffraction studies.     

Partial incorporation of a cyclopentadienyl ligand into a molybdaborane to form a molybdacarbaborane

Reaction of the molybdaborane arachno-2-[Mo(η-C₅H₅)(η⁵:η¹-C₅H₄)B₄H₇] (I) with NEt₃ in toluene at 120 °C for 7 days gives a 90% yield of the molybdacarbaborane nido-1-[Mo(η-C₅H₅)(η³:η²-C₃H₃)C₂B₃H₅] (II). Two of the carbon atoms in the substituted cyclopentadienyl ring in I are incorporated into the metallacarbaborane cluster II. The carbaborane {C₂B₃H₅} fragment in II is attached to an allylic {C₃H₃} group and can be thought of as a new non-planar {C₅B₃H₈} ligand providing seven electrons to the molybdenum atom. Reaction of I with KH in thf at 20 °C gives the anion via deprotonation of a B-H-B bridging proton.     

Complexes of titanium and zirconium based on [C5Me4CH2-(2-C5H4N)] ligand

Half-sandwich [η⁵:η¹-κN-C₅Me₄CH₂-(2-C₅H₄N)]MCl₃ (M = Ti (4), Zr (5)) and sandwich [η⁵-C₅Me₄CH₂-(2-C₅H₄N)][η⁵-C₅Me₅]ZrCl₂ (6) ring-peralkylated complexes have been prepared and characterized. Evidence of the intramolecular coordination of the side-chain pyridyl group both in 4 and 5 in solutions is provided by NMR spectroscopy data. Crystal structure of an adduct 5-py with one molecule of pyridine has been established by X-ray diffraction analysis.     

Study of novel η-cyclopentadienyl and η-arene platinum group metal complexes containing a N4-type ligand and their structural characterization

The mononuclear η⁵-cyclopentadienyl complexes [(η⁵-C₅H₅)Ru(PPh₃)₂Cl], [(η⁵-C₅H₅)Os(PPh₃)₂Br] and pentamethylcyclopentadienyl complex [(η⁵-C₅Me₅)Ru(PPh₃)₂Cl] react in the presence of 1 eq. of the tetradentate N,N′-chelating ligand 3,5-bis(2-pyridyl)pyrazole (bpp-H) and 1 eq. of NH₄PF₆ in methanol to afford the mononuclear complexes [(η⁵-C₅H₅)Ru(PPh₃)(bpp-H)]PF₆ ([1]PF₆), [(η⁵-C₅H₅)Os(PPh₃)(bpp-H)]PF₆ ([2]PF₆) and [(η⁵-C₅Me₅)Ru(PPh₃)(bpp-H)]PF₆ ([3]PF₆), respectively. The dinuclear η⁵-pentamethylcyclopentadienyl complexes [(η⁵-C₅Me₅)Rh(μ-Cl)Cl]₂ and [(η⁵-C₅Me₅)Ir(μ-Cl)Cl]₂ as well as the dinuclear η⁶-arene ruthenium complexes [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂ and [(η⁶-p-ⁱPrC₆H₄Me)Ru(μ-Cl)Cl]₂ react with 2 eq. of bpp-H in the presence of NH₄PF₆ or NH₄BF₄ to afford the corresponding mononuclear complexes [(η⁵-C₅Me₅)Rh(bpp-H)Cl]PF₆ ([4]PF₆), [(η⁵-C₅Me₅)Ir(bpp-H)Cl]PF₆ ([5]PF₆), [(η⁶-C₆H₆)Ru(bpp-H)Cl]BF₄ ([6]BF₄) and [(η⁶-p-ⁱPrC₆H₄Me)Ru(bpp-H)Cl]BF₄ ([7]BF₄). However, in the presence of 1 eq. of bpp-H and NH₄BF₄ the reaction with the same η⁶-arene ruthenium complexes affords the dinuclear salts [(η⁶-C₆H₆)₂Ru₂(bpp)Cl₂]BF₄ ([8]BF₄) and [(η⁶-p-ⁱPrC₆H₄Me)₂Ru₂(bpp)Cl₂]BF₄ ([9]BF₄), respectively. These compounds have been characterized by IR, NMR and mass spectrometry, as well as by elemental analysis. The molecular structures of [1]PF₆, [5]PF₆ and [8]BF₄ have been established by single crystal X-ray diffraction studies and some representative complexes have been studied by UV–vis spectroscopy.     

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.     

Mono and dinuclear complexes of half-sandwich platinum group metals (Ru, Rh and Ir) bearing a flexible pyridyl-thiazole multidentate donor ligand

The mononuclear cationic complexes [(η⁶-C₆H₆)RuCl(L)]⁺ (1), [(η⁶-p-ⁱPrC₆H₄Me)RuCl(L)]⁺ (2), [(η⁵-C₅H₅)Ru(PPh₃)(L)]⁺ (3), [(η⁵-C₅Me₅)Ru(PPh₃)(L)]⁺ (4), [(η⁵-C₅Me₅)RhCl(L)]⁺ (5), [(η⁵-C₅Me₅)IrCl(L)]⁺ (6) as well as the dinuclear dicationic complexes [{(η⁶-C₆H₆)RuCl}₂(L)]²⁺ (7), [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(L)]²⁺ (8), [{(η⁵-C₅H₅)Ru(PPh₃)}2(L)]²⁺ (9), [{(η⁵-C₅Me₅)Ru(PPh₃)}₂(L)]²⁺ (10), [{(η⁵-C₅Me₅)RhCl}₂(L)]²⁺ (11) and [{(η⁵-C₅Me₅)IrCl}₂(L)]²⁺ (12) have been synthesized from 4,4′-bis(2-pyridyl-4-thiazole) (L) and the corresponding complexes [(η⁶-C₆H₆)Ru(μ-Cl)Cl]₂, [(η⁶-p-ⁱPrC₆H₄Me)Ru(μ-Cl)Cl]₂, [(η⁵-C₅H₅)Ru(PPh₃)₂Cl)], [(η⁵-C₅Me₅)Ru(PPh₃)₂Cl], [(η⁵-C₅Me₅)Rh(μ-Cl)Cl]₂ and [(η⁵-C₅Me₅)Ir(μ-Cl)Cl]₂, respectively. All complexes were isolated as hexafluorophosphate salts and characterized by IR, NMR, mass spectrometry and UV-vis spectroscopy. The X-ray crystal structure analyses of [3]PF₆, [5]PF₆, [8](PF₆)₂ and [12](PF₆)₂ reveal a typical piano-stool geometry around the metal centers with a five-membered metallo-cycle in which 4,4′-bis(2-pyridyl-4-thiazole) acts as a N,N′-chelating ligand.     

A synthetic, structural and reactivity study of [(η-C4R4)Co(η-C5H4X)] complexes, R = Me or Et; X = CHO, CHCHFc, CHCH(η-C5H4)Co(η-C4Ph4), CHC(CN)2: Unexpected formation of [(η-cyclopentadienyl)(η-3,4,5,6-tetraethyl-α-pyrone)cobalt]

The tetraethyl- and tetramethyl-cyclobutadiene complexes [(η⁴-C₄R₄)Co(η⁵-C₅H₄CHO)] R = Et, 5, R = Me, 7, and [(η⁴-C₄R₄)Co(η⁵-C₅H₄CO₂Me)] R = Et, 6, R = Me, 8, are conveniently prepared by photolysis of the corresponding isocobaltocenium cations [(η⁴-C₄R₄)Co(η⁶-C₆H₅Me)]⁺ in acetonitrile, and subsequent treatment with Na[C₅H₄CHO] or Na[C₅H₄CO₂Me]. The aldehydes 5 and 7 undergo Wittig and Knoevenagel reactions with [FcCH₂PPh₃]I and CH₂(CN)₂, to form [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH=CHFc)] and [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH=C(CN)₂], 11 and 15, respectively. The Horner-Wittig reaction of [(η⁴-C₄R₄)Co(η⁵-C₅H₄CH₂P(O)(OEt)₂] with [(η⁴-C₄Ph₄)Co(η⁵-C₅H₄CHO)] yields [(η⁴-C₄R₄)Co(η⁵:η⁵-C₅H₄CHCH-C₅H₄)Co(η⁴-C₄Ph₄)], 12 and 13. [(η⁴-C₄Me₄)Co(η⁵-C₅H₄CHO)] also reacts with t-BuLi and FcLi to furnish the corresponding secondary alcohols, 16 and 17, respectively. Surprisingly, the attempted direct synthesis of 5 by reaction of Na[C₅H₅] and ethyl formate with [(η⁴-C₄Et₄)Co(CO)₂I], 1, instead yielded [(η⁵-C₅H₅)Co(η⁴-3,4,5,6-tetraethyl-α-pyrone)], 18, and a mechanistic proposal is advanced. The X-ray crystal structures of 1, 7, 8, 11(Z), 15 and 18, and also the isocobaltocenium salts [(η⁴-C₄Et₄)Co(η⁶-C₆H₅Me)][PF₆], 2, and [(η⁴-C₄Et₄)Co(η⁶-1,3,5-C₆H₃Me₃)][PF₆], 4, are reported.     

Synthesis, characterization, and reactivity of new types of constrained geometry group 4 metal complexes derived from picolyl-substituted dicarbollide ligand systems

The syntheses of group 4 metal complexes containing the picolyldicarbollyl ligand Dcab^PyH [nido-7-HNC₅H₄(CH₂)-8-R-7,8-C₂B₉H₁₀] (2) are reported. New types of constrained geometry group 4 metal complexes (Dcab^Py)MCl₂, [{(η⁵-RC₂B₉H₉)(CH₂)(η¹-NC₅H₄)}MCl₂] (M = Ti, 3; Zr, 4; R = H, a; Me, b), were prepared by the reaction of 2 with M(NMe₂)₂Cl₂ (M = Ti, Zr). The reaction of 2 with M(NMe₂)₄ in toluene afforded (Dcab^Py)M(NMe₂)₂, [{(η⁵-RC₂B₉H₉)(CH₂)(η¹-NC₅H₄)}M(NMe₂)₂] (M = Ti, 5; Zr, 6; R = H, a; Me, b), which readily reacted with Me₃SiCl to yield the corresponding chloride complexes (Dcab^Py)MCl₂ (M = Ti, 3; Zr, 4; R = H, a; Me, b). The structures of the diamido complexes (Dcab^Py)M(NMe₂)₂ (M = Ti, 5; Zr, 6) were established by X-ray diffraction studies of 5a, 5b, and 6a, which verified an η⁵:η¹-bonding mode derived from the dicarbollylamino ligand. Related constrained geometry catalyst CGC-type alkoxy titanium complexes, (Dcab^Py)Ti(OⁱPr)₂ (7), were synthesized by the reaction of 2 with Ti(OⁱPr)₄. Sterically less demanding phenols such as 2-Me-C₆H₄OH replaced the coordinated amido ligands on (Dcab^Py)Ti(NMe₂)₂ (5a) to yield aryloxy stabilized CGC complexes (Dcab^Py)Ti(OPh^Me)₂(Ph^Me  =  2- Me-C₆H₄, 8). NMR spectral data suggested that an intramolecular Ti-N coordination was intact in solution, resulting in a stable piano-stool structure with two aryloxy ligands residing in two of the leg positions. The aryloxy coordinations were further confirmed by single crystal X-ray diffraction studies on complexes (Dcab^Py)Ti(OPh^Me)₂ (8).     

Titanium and zirconium complexes containing the new 2,3-dimethyl-1,4-diphenylcyclopentadienyl ligand. Synthesis, characterization and polymerization behavior

An easy and inexpensive three-step synthesis of new 2,3-dimethyl-1,4-diphenylcyclopentadiene (3) ligand and the titanium and zirconium homometallocene dichlorides [TiCl₂(η⁵-C₅H-2,3-Me₂-1,4-Ph₂)₂] (4), [ZrCl₂(η⁵-C₅H-2,3-Me₂-1,4-Ph₂)₂] (5), and the mixed ligand zirconium complex [ZrCl₂(η⁵-C₅H-2,3-Me₂-1,4-Ph₂)(η⁵-C₅H₅)] (6) prepared thereof are described. The polymerization of ethene using 4-6/MAO catalysts revealed that zirconocene complexes 5 and 6 displayed moderate and high activity, respectively, whereas the titanium catalyst 4/MAO was inactive. The crystal structures of 4 and 5 were determined by X-ray crystallography.