Complex Cp2Ti Research Articles

Triazenido Complexes of Titanocene(III)

Triazenido metal complexes have been extensively investigated for more than a century, especially transition metal complexes. However, in each of the known examples for titanium, the oxidation state of the metal is +4. Therefore, we sought to prepare a complex containing titanium(III). To achieve this goal, triazenes RNNN(H)R′ (1R, with R = R′ = Ph; Dipp; Ter; R = Mes*, R′ = mTol) and triazenido salts Li[RNNNR′] (R = R′ = Ter; R = Ter, R′ = mTol) were prepared. These were treated with suitable titanium precursors either from reaction with the alkyne complex Cp2Ti(η2‐Me3SiC2SiMe3) or in a salt metathesis with [Cp2TiCl]2 to give chelate complexes of the type Cp2Ti[RNNNR′] (2R, with R =R′ = Ph; Dipp; R = Ter; R′ = mTol). The synthesis, reactivity, and bonding of the titanocene triazenides were studied.

Recent Synthetic and Catalytic Applications of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes

With the 30 years old first example of a stable group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complex Cp2Ti(η2‐btmsa) a series of similar complexes like Cp′2M(η2‐btmsa) (M = Ti, Zr; Cp′ = Cp, Cp* as η5‐pentamethylcyclopentadienyl and Cp′2 = rac‐(ebthi) as rac‐1,2‐ethylene‐1,1′‐bis(η5‐tetrahydroindenyl) ) represent excellent sources for the generation of the very reactive coordinatively and electronically unsaturated complex fragments [Cp'2M], which were used in many synthetic and catalytic reactions. Examples for this were oresented in several papers and summarized in some reviews. In this update new reactions of group 4 metallocene bis(trimethylsilyl)acetylene complexes towards symmetrically and unsymmetrically α‐dihetero‐substituted alkynes, reactions with other alkynes, di‐ and polyynes to metallacyclopentadienes as well as the conversions of the formed products are summarized. Additionally, novel synthetic applications of the formed metallacyclopentadienes on the basis of the zirconocene bis(trimethylsilyl)acetylene complex Cp2Zr(py)(η2‐btmsa) are highlighted. Reactions with imines, neutral N‐donor ligands, E‐H compounds (E = N, O, P), molecular hydrogen, water, phosphino‐ and aminoboranes, E‐Cl compounds (E = C, P), disilylated germylenes and aryloxy ketones were described. Different self‐assembly reactions to multinuclear complexes by using group 4 metallocene bis(trimethylsilyl)acetylene complexes in C‐C coupling reactions with or without C‐H bond activation to tri‐ or tetranuclear complexes are considered, too. These examples are discussed following the general L‐M‐S principle for stoichiometric and catalytic reactions, whereby different ligands L (L = Cp′ = Cp, Cp*, rac‐ebthi), metals M (M = Ti, Zr, Hf) and substrate substituents S influence the reactivity and the obtained products.

Di-tert-butylcatecholate derivatives of titanocene

Titanocene dichloride reacts with sodium 3,5-di-tert-butyl-catecholate to give the mixed-valence binuclear Ti(iii,iv) complex Cp2Ti(μ-Cat35)2TiCp.

Complexation of Titana‐ and Zirconadihydrofuran Metallacycles with Organoaluminium Compounds and Catalytic Activity of the Resulting Complexes in Polymerization of ϵ‐Caprolactone

AbstractThe interaction of the titanadihydrofuran metallacycles Cp2Ti[η2‐C(SiMe3)=C(Ph)‐C(Me)2O] (1) and Cp2Ti[η2‐C(SiMe3)= C(Ph)‐CH(Ph)O] (2) with iBu2AlH in n‐hexane at 20°C yields 1 : 1 complexes Cp2Ti[η2‐C(SiMe3)=C(Ph)‐C(Me)2O](iBu2AlH) (4) and Cp2Ti[η2‐C(SiMe3)=C(Ph)‐CH(Ph)O](iBu2AlH) (5) respectively. According to X‐ray diffraction data, the iBu2AlH molecule in 4 is coordinated by its aluminium centre with the oxygen atom whereas the hydride hydrogen atom of the iBu2AlH forms a bridge with the titanium. As a result of the complexation with iBu2AlH, the Ti−O and Ti‐C(SiMe3) bonds of the starting 1 are strongly elongated. An analogous 1 : 1 adduct (11) is formed in the interaction of iBu2AlH with the zirconadihydrofuran derivative Cp2Zr[η2‐C(SiMe3)=C(SiMe3)‐C(Me)2O] (3). Like the Ti−O and Ti‐C(SiMe3) bonds in 1, the Zr−O and Zr‐C(SiMe3) bonds in 3 are considerably elongated as a result of the coordination with iBu2AlH. The reaction of 1 with EtAlCl2 gives a complex, Cp2Ti[η2‐C(SiMe3)=C(Ph)‐C(Me)2O](EtAlCl2) (8), in which the organoaluminium compound is also coordinated by its aluminium centre with the oxygen atom. This leads to a strong elongation of the Ti−O bond. The C−O bond of the metallacycle in 8 is noticeably elongated as well but the Ti‐C(SiMe3) bond length even somewhat shortens. Complexes 4, 5, 8 and 11 are capable of catalysing ring‐opening polymerization of ϵ‐caprolactone. The highest activity is exhibited by complexes 4 and 5.

Complexes with Tunable Intramolecular Ferrocene to Ti(IV) Electronic Transitions: Models for Solid State Fe(II) to Ti(IV) Charge Transfer.

Iron(II)-to-titanium(IV) metal-to-metal-charge transfer (MMCT) is important in the photosensitization of TiO2 by ferrocyanide, charge transfer in solid-state metal-oxide photocatalysts, and has been invoked to explain the blue color of sapphire, blue kyanite, and some lunar material. Herein, a series of complexes with alkynyl linkages between ferrocene (Fc) and Ti(IV) has been prepared and characterized by UV-vis spectroscopy and electrochemistry. Complexes with two ferrocene substituents include Cp2Ti(C2Fc)2, Cp*2Ti(C2Fc)2, and Cp2Ti(C4Fc)2. Complexes with a single ferrocene utilize a titanocene with a trimethylsilyl derivatized Cp ring, (TMS)Cp, and comprise the complexes (TMS)Cp2Ti(C2Fc)(C2R), where R = C6H5, p-C6H4CF3, and CF3. The complexes are compared to Cp2Ti(C2Ph)2, which lacks the second metal. Cyclic voltammetry for all complexes reveals a reversible Ti(IV/III) reduction wave and an Fe(II/III) oxidation that is irreversible for all complexes except (TMS)Cp2Ti(C2Fc)(C2CF3). All of the complexes with both Fc and Ti show an intense absorption (4000 M(-1)cm(-1) < ε < 8000 M(-1)cm(-1)) between 540 and 630 nm that is absent in complexes lacking a ferrocene donor. The energy of the absorption tracks with the difference between the Ti(IV/III) and Fe(III/II) reduction potentials, shifting to lower energy as the difference in potentials decreases. Reorganization energies, λ, have been determined using band shape analysis (2600 cm(-1) < λ < 5300 cm(-1)) and are in the range observed for other donor-acceptor complexes that have a ferrocene donor. Marcus-Hush-type analysis of the electrochemical and spectroscopic data are consistent with the assignment of the low-energy absorption as a MMCT band. TD-DFT analysis also supports this assignment. Solvatochromism is apparent for the MMCT band of all complexes, there being a bathochromic shift upon increasing polarizability of the solvent. The magnitude of the shift is dependent on both the electron density at Ti(IV) and the identity of the linker between the titanocene and the Fc. Complexes with a MMCT are photochemically stable, whereas Cp2Ti(C2Ph)2 rapidly decomposes upon photolysis.

Titanocene(III) complexes with 2-phosphinoaryloxide ligands for the catalytic dehydrogenation of dimethylamine borane.

A study of the dehydrogenation of dimethylamine borane using different titanocene(III) complexes with 2-phosphinoaryloxide ligands is presented. Complexes Cp2Ti(κ(2)-O, P-O-C6H4-PR2) (3a: R = i-Pr, 3b: R = Ph) (Cp = η(5)-cyclopentadienyl) and Cp*2Ti(κ(1)-O-O-C6H4-PR2) (5a: R = i-Pr, 5b: R = Ph) (Cp* = η(5)-pentamethylcyclopentadienyl) were prepared by reactions of the 2-phosphinophenol ligand with different titanocene sources and fully characterised. Their catalytic activity depends on the steric influence of the cyclopentadienyl ligand, the coordination mode of the 2-phosphinoaryloxide ligand and on the used solvent. Complex 3a showed a turnover number of 43.2 in the neat substrate after 24 hours. EPR investigations were used to elucidate the fate of the Ti(III) catalyst.

Metallocene-made mad metallacycles in synthesis and catalysis

Metallacycles of transition metals are generally of great interest because of their multifaceted structural chemistry and they are often discussed as key intermediates in multiple catalytic processes, whereupon recent studies are dealing with the participation of metallacycles in polymerization as well as oligomerization reactions. Synthesis and characterization of the titanocene bis(trimethylsilyl)acetylene complex Cp2Ti(η2-Me3SiC2SiMe3) paved the way towards the discovery of three-membered metallacyclopropenes of Group 4 metals (titanium, zirconium, and, later, hafnium) having their own history which is strongly connected with the names of M. E. Vol´pin and his co-workers. Starting from these compounds the very unusual ring-strained “all-C”-five-membered metallacyclocumulenes, metallacyclopentynes, and metalla-cycloallenes of Group 4 metals were obtained and characterized having all their roots in Vol´pin´s chemistry. This mini review gives an overview of these unusual molecules as well as some more common molecules like metallacyclopentanes, metallacyclopentenes, and metalla-cyclopentadienes. Very recently instead of these “all-C”-metallacycles the analogous heteroring systems (with N, S, O atoms instead of C) as well as the smaller four-membered metallacycles became the focus of our interest.

Reactions of Titanocene with Triazines and Dicyandiamide: Formation of Novel Di‐ and Trinuclear Metallacyclic Complexes

AbstractThe titanocene bis(trimethylsilyl)acetylene complex Cp2Ti(η2‐Me3SiC2SiMe3) (1) reacts with different triazines to give trinuclear titanocene compounds. Cleavage of the heterocyclic unit takes place in the reaction with cyanuric chloride, which furnishes a trinuclear cyanide bridged titanocene complex [Cp2Ti(CN)]3 (2). Reaction with cyanuric acid yields the paramagnetic ate complex (Cp2Ti)3(C3N3O3) (3). With melamine the structurally similar amide species (Cp2Ti)3[C3N3(NH)3] (4) is formed. A dinuclear, paramagnetic complex 5 is obtained in the reaction of 1 with dicyandiamide. Complexes 2, 4, and 5 were characterized by X‐ray analyses.

Titanium(IV) Trifluoromethyl Complexes: New Perspectives on Bonding from Organometallic Fluorocarbon Chemistry

Trifluoromethyltrimethylsilane, (CH3)3SiCF3, in the presence of CsF serves as an excellent CF3 group-transfer reagent, and reaction with Cp2TiF2 in THF gives the titanocene trifluoromethyl fluoride complex Cp2Ti(CF3)(F) (1; Cp = C5H5) in 60% isolated yield. Reaction of complex 1 with the trimethylsilyl reagents, (CH3)3SiX (X = OTf = OSO2CF3, Cl, Br, I, N3, and OSO2Ph), in a tetrahydrofuran or toluene solution affords the corresponding Ti–CF3 derivatives Cp2Ti(CF3)(X) (X = OTf (2), Cl (12), Br (13), I (14), N3 (15), and OSO2Ph (16)) in good isolated yields of 67–84%. These compounds have been characterized by a combination of reactivity studies, IR and 1H/13C{1H}/19F NMR spectroscopies, and single-crystal X-ray diffraction. The Ti–CF3 linkage in these complexes is remarkably robust, and although the α-C–F bonds are elongated, there is no evidence of an α-fluoride (Ti···F–CF2) between the electrophilic Ti(IV) metal center and any of the C–F bonds in the trifluoromethyl group in the solid-state or in solution. In the solid-state, these complexes are shock-sensitive; energetic decomposition of Cp2Ti(CF3)(F) (1) produces uniform spherical nanoparticles ranging from ∼70 to 120 nm in size and porous fluorinated oligomers and polymers containing both −(CF2–CF2)– and −(CF2–CFH)– units, as determined by a combination of SEM, XRD, XRF, XPS, and 19F MAS NMR. Density functional theory results show good agreement with experimental structural data obtained for Cp2Ti(CF3)(X) (X = F (1), OTf (2), Cl (12), N3 (15)) and accurately predicts longer Ti–CF3 distances than for each specific CH3 analogue, and the trend extends to structurally related Zr and Hf analogues. Simpler model compounds from groups 4 and 8 (M(CH3)4, M(CH3)3(CF3), M(CH3)3(CCl3), and M(CH3)3(CF2CF2CF2CF3); M = Ti, Zr, Hf, Fe, Ru, Os)) were also examined and show that, for group 4 complexes, π-bonding is a significant factor in shortening the strongly ionic M–CH3 relative to M–CF3, whereas for the predominantly covalent group 8 analogues, π-back-bonding helps to shorten the predominantly covalent M–CF3 relative to M–CH3. The bonding analysis suggests that the significant elongation of C–F bonds α to metals is mainly a consequence of the electropositivity of the group 4 metal centers, with minor, if any, contributions from π-effects; the bond-lengthening effect is most pronounced at the α-position and decays rapidly on moving away from the metal.

Peculiarities of Vibrational Spectra and Electronic Structure of the Five‐Membered Metallacyclocumulenes of the Group 4 Metals

AbstractThe vibrational (Raman and IR) spectra of metallacyclic cumulenes of the type Cp2M(η4‐tBuC4tBu) [M = Ti (1), Zr (2), Hf (3)] were obtained and analyzed in terms of normal coordinate calculations. The system of three cumulated C=C bonds in the five‐membered metallacycle was shown to exhibit a peculiar spectral pattern with three normal modes with frequencies at ca. 1900 (νs1), 1650 (νas2), and 1280 cm–1 (νs3). The νs1 mode is a symmetric stretch of the two equivalent C1–C2 and C3–C4 bonds (with simultaneous contraction of the central C2–C3 bond), the νas2 mode is their antisymmetric combination, while the νs3 mode has a complex eigenvector and involves a “breathing” motion of the metallacycle as a whole along with C–CtBu bond stretches. Reconstruction of the electron‐density distribution in the molecules studied by using Bader's AIM theory resulted in a specific molecular graph of the metallacycle, that with the so‐called “T‐shaped” configuration, pointing to topological instability of the system. This is in contrast to analogously calculated “normal” bonding patterns for related cyclopropene complexes Cp2Ti(η2‐RC2R).

Reaction of the titanocene alkyne complex Cp2Ti(η2-Me3SiC2SiMe3) with selenium dioxide: Preparation and characterization of a novel tetranuclear titanium complex with selenium and oxo bridges

Abstract The low valent titanocene(II) source Cp2Ti(η2-Me3SiC2SiMe3) 1 reacts with selenium dioxide ( 2 ) to obtain a tetranuclear selenium and oxygen bridged titanocene(IV) [{Cp2Ti(µ2-O; µ2-Se)CpTi}2(µ2-O)] 6 . The molecular structure was confirmed by X-ray analysis.

Titanocene complexes with nonlinear pseudohalide ligands: Synthesis, spectroscopic characterization and crystal structure

Binuclear titanocene complexes [Cp 2Ti(tcm)] 2O ( 4), [Cp 2Ti(dca)] 2O ( 5) and [Cp 2Ti(dcnm)] 2O ( 6) (tcm − = tricyanomethanide, dca − = dicyanamide and dcnm − = dicyanonitrosomethanide) were synthesized in moderate yields by the reaction of Cp 2TiCl 2 ( 1) with respective alkali metal pseudohalide salts in the aqueous solution. When the reaction was carried out in dry organic solvents, mononuclear compounds Cp 2Ti(tcm) 2 ( 2) and Cp 2Ti(dca) 2 ( 3) were isolated. Preparation of dipseudohalide complex Cp 2Ti(dcnm) 2 by this manner was unsuccessful due to decomposition of dcnm ligand resulting in formation of oxygen-bridged compound 6. All prepared compounds were characterized by elemental analysis, NMR, Raman, infrared and UV–Vis spectroscopy. Molecular structures of 2, 4 and 6 (two polymorphs) have been determined by single-crystal X-ray diffraction analysis.

Reaction of the titanocene alkyne complex Cp2Ti(η2-Me3SiC2SiMe3) with methanol: Preparation and characterization of a novel trinuclear titanium complex [{Cp2Ti(OMe)}2{Ti(OMe)4}

The titanocene alkyne complex Cp2Ti(η2-Me3SiC2SiMe3) (1) reacts with methanol to yield depending on the reaction conditions (solvent, temperature) different titanium methoxides [Cp2Ti(OMe)]2 (2a) and [{Cp2Ti(OMe)}2{Ti(OMe)4}] (3). The structure of the trinuclear complex 3, consisting of titanium III and IV, was confirmed by X-ray studies.

Dehydroaromatization of Quinoxalines: One-Step Syntheses of Trinuclear 1,6,7,12,13,18-Hexaazatrinaphthylene Titanium Complexes

We report the spontaneous coupling of N-heterocycles, initiated by C-H bond activation reactions. The reaction of quinoxalines and the titanocene acetylene complex Cp2Ti{eta2-C2(SiMe3)2}, as an excellent titanocene source, results in the formation of trinuclear 1,6,7,12,13,18-hexaazatrinaphthylene (HATN) titanium complexes. These HATN titanium complexes are thermally stable but sensitive to air and moisture. A three-fold dehydrogenative C-C coupling is proposed as the main step in the presented synthetic procedure. Particularly using commercial starting materials, an efficient route for the dehydrogenative coupling of N-heterocycles, leading to multidentate ligands, has been established.

From Vetiver to Patchouli: Discovery of a NewHigh‐Impact Spirocyclic Patchouli Odorant

AbstractIn the course of synthetic work on new vetiver odorants, a new, potent patchouli odorant was discovered. Its structure was elucidated as 1‐hydroxy‐1,4,7,7,9‐pentamethylspiro[4.5]decan‐2‐one (15/16), and both diastereoisomers were synthesized from the previously reported 4,7,7,9‐tetramethyl‐1‐methylenespiro[4.5]decan‐2‐one by epoxidation with m‐chloroperoxybenzoic acid, reduction with lithium aluminum hydride, and subsequent oxidation with pyridinium chlorochromate or Dess–Martin periodinane. The 1,4‐unlike‐isomer 15 was found to be the diastereoisomer with the most powerful odor, and its excellent odor threshold of 0.067 ng/L air triggered the synthesis of the derivatives 19, 22, 23, and 26 possessing a different methyl substitution pattern or ring size. Glycol cleavage in the oxidation step was circumvented by Swern oxidation. Three further 4‐demethylated derivatives, 32, 33, and 34, were prepared by a short sequence consisting of Diels–Alder reaction with 4‐methylene‐5‐oxohexanenitrile (28), reductive radical cyclization mediated by the titanocene(III) complex Cp2Ti(Ph)(iPr), and standard hydrogenation. Finally, the enantiomers of 15 were separated by forming their SAMP hydrazones, which were subsequently cleaved by ozonolysis. The odor of the racemate 15 was shown to be exclusively due to the (+)‐(1S,4R,5R,9S)‐configured enantiomer 38, the stereocenters of which superimpose well with those of (–)‐patchoulol (3), the odorous principle of patchouli oil. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

Reactions of Zirconocene Bis(trimethylsilyl)acetylene Complexes with Fluorinated Pyridines: C–H vs. C–F Bond Activation

AbstractThe zirconocene complexes Cp2Zr(L)(η2‐Me3SiC2SiMe3) (1a: L = THF; 1b: L = pyridine) and the ethylene bis(tetrahydroindenyl) complex rac‐(ebthi)Zr(η2‐Me3SiC2SiMe3) (2) react with 2,3,5,6‐tetrafluoropyridine with C–H bond activation to produce the 4‐substituted pyridyl complexes with agostic alkenyl groups Cp'2Zr(4‐C5NF4)[–C(SiMe3)=CH(SiMe3)] (Cp'2 = Cp2) (3) and (Cp'2 = ebthi) (4). With 2,3,4,6‐tetrafluoropyridine, after C–H bond activation, complex 2 yields two isomers of the 5‐substituted pyridyl complex rac‐(ebthi)Zr(3‐C5NF4)[–C(SiMe3)=CH(SiMe3)] with agostic alkenyl groups, 5a and 5b. With pentafluoropyridine complex 1b gives, after dissociation of the bis(trimethylsilyl)acetylene (btmsa), C–F bond activation at the 4‐position and formation of Cp2Zr(4‐C5NF4)F (6). Complex 1b reacts with 3‐chloro‐2,4,5,6‐tetrafluoropyridine by means of a preferred C–Cl activation to give Cp2Zr(3‐C5NF4)Cl (7). These results are in contrast to the reactions of the titanium complex Cp2Ti(η2‐Me3SiC2SiMe3) which, with 2,3,5,6‐tetrafluoropyridine, gaveC–F activation in preference to C–H activation. With pentafluoropyridine, C–F bond activation at the 2‐position was found rather than at the 4‐position. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis of heterobimetallic zinc complexes and their catalytic properties in reactions of CO2 with cyclohexene oxide

The reaction of Et2Zn with NaOCH2CH2OH yielded a bimetallic zinc complex NaOCH2CH2⋅OZnEt. Its reactions with Ph3SnCl, Cp2TiCl2, and Cp2LuCl(THF) afforded the corresponding complexes Ph3SnOCH2CH2OZnEt, Cp2Ti(OCH2CH2OZnEt)2, and Cp2LuOCH2CH2OZnEt. Cp2Ti(OCH2CH2OZnEt)2 catalyzes copolymerization of CO2 with cyclohexene oxide at room temperature and atmospheric pressure; the yield of the polycarbonate is 4 g g−1 catalyst. Ph3SnOCH2CH2OZnEt is catalytically inert under these conditions, and with Cp2LuOCH2CH2OZnEt only the polyether is formed.

Early transition-metal perfluoroalkyl complexes.

Elusive early transition-metal perfluoroalkyl complexes have been isolated and structurally characterized for the first time. Trifluoromethyltrimethylsilane, CF3SiMe3, serves as an excellent trifluoromethyl group-transfer reagent and reacts with the known Ti(IV) fluoride complex Cp2TiF2 to yield the novel Ti(IV) trifluoromethyl fluoride compound, Cp2Ti(CF3)(F) (1). Reaction of complex 1 with trimethylsilyltriflate (Me3SiOTf) affords the Ti(IV) trifluoromethyl triflate complex Cp2Ti(CF3)(OTf) (2). Both titanium perfluoroalkyl compounds have been characterized spectroscopically and by single-crystal X-ray analysis. The Ti-CF3 linkage in these complexes is remarkably robust and shows no evidence of an alpha-fluoride interaction (Ti...F-CF2) between the electrophilic Ti(IV) metal center and any of the C-F bonds in the trifluoromethyl group in the solid state or in solution.

Synthesis of new organotitanium (IV) complexes Cp 2Ti(SeR) 2 and Cp 2TiCl(SeR) via tandem reactions involving `Cp 2Ti' intermediate. Crystal structures of Cp 2TiCl(SeR) (R= p-ClC 6H 4, p-BrC 6H 4)

A simple and convenient route for synthesizing organotitanium (IV) complexes with a general formula Cp 2Ti(SeR) 2 or Cp 2TiCl(SeR) has been developed. This synthetic route includes reduction of Cp 2TiCl 2 with Mg and an in situ treatment of the intermediate `Cp 2Ti' with diselenides RSeSeR. Interestingly, while the route involving reaction of Cp 2TiCl 2, Mg and RSeSeR in a molar ratio of 1:1:1 produced Cp 2Ti(SeR) 2, ( 1– 5, R=α-C 10H 7, o-MeC 6H 4, m-MeC 6H 4, p-ClC 6H 4, p-BrC 6H 4) in 91–97% yields, the route involving reaction of Cp 2TiCl 2, Mg and RSeSeR in a molar ratio of 1: 0.5: 0.5 afforded Cp 2TiCl(SeR) ( 6– 7, R= p-ClC 6H 4, p-BrC 6H 4) in 70% and 92% yields, respectively. 1– 7 are new and have been characterized by elemental analysis and spectroscopy, as well as by X-ray diffraction analysis for 6 and 7. A possible pathway for production of these two types of organotitanium (IV) complexes, mainly depending upon the molar ratio of the starting materials, are briefly discussed.

The preparation, characterisation and in vitro cytotoxicity of potentially chemotherapeutic heterobimetallic complexes containing early and late transition metals

The reactions of phosphine Ph 2P(CH 2) 2SO 3Na with Cp 2M′Cl 2 (M′=Ti, Zr) in aqueous solution give the metallophosphines, Cp 2Ti(OSO 2(CH 2) 2PPh 2) 2 (Cp=cyclopentadienyl) and CpZr(OH)(OSO 2(CH 2) 2PPh 2) 2. These react with CODM″Cl 2 (M″=Pd, Pt) (COD=1,5-cyclooctadiene) in dichloromethane to give heterobimetallic complexes Cp 2Ti(OSO 2(CH 2) 2PPh 2) 2M″Cl 2 and CpZr(OH)(OSO 2(CH 2) 2 PPh 2) 2M″Cl 2 respectively. The compounds are characterised by infrared and NMR spectroscopies and elemental analysis. Electrospray mass spectra of the complexes are reported and compared to those of Cp 2M′Cl 2 in water and dimethylsulfoxide (DMSO). For zirconocene dichloride and its product heterobimetallic complexes, the addition of ethylenediamine tetraacetic acid disodium salt (Na 2H 2EDTA) was found to be an effective ionisation enhancement agent for the electrospray mass spectral studies. Cytotoxicity studies for the previously reported Cl 2Pt(PPh 2(CH 2) 2SO 3H) 2·3.5H 2O (Wedgwood et al., Inorg. Chim. Acta 290 (1999) 189), and the compounds Cp 2Ti(OSO 2(CH 2) 2 PPh 2) 2·1.5H 2O and Cp 2Ti(OSO 2(CH 2) 2PPh 2) 2PtCl 2·4H 2O reported here, have been evaluated by colony formation assay against cisplatin-sensitive and -resistant cell lines L929 and L929/R to highlight potential chemotherapeutic activity. The compound Cl 2Pt(PPh 2(CH 2) 2SO 3H) 2·3.5H 2O overcomes cisplatin resistance.