Jiří Pinkas

Preparation and solid-state characterization of nickel(II) complexes with 1'-(diphenylphosphino)ferrocenecarboxylic acid

1′-(Diphenylphosphino)ferrocenecarboxylic acid (Hdpf) reacts with nickel(II) halides and nickel(II) thiocyanate to give the paramagnetic complexes [NiX2(Hdpf-κP)2] (X = Cl, 1; Br, 2; I, 3) and the diamagnetic planar isothiocyanato complex [Ni(SCN-κN)2(Hdpf-κP)2] (4), respectively. In situ neutralization of Hdpf followed by reaction with nickel(II) sulfate affords the salt [Ni(dpf)2] (5). The halide complexes 1–3 easily undergo dissociative decomposition in polar donor solvents; compound 5 is insoluble in all common solvents. All compounds were characterized by IR and UV/vis spectroscopies and magnetic measurements in the solid state. The solid-state structure of the solvate 4·2CHCl3 was determined by single-crystal X-ray diffraction. A series of complexes, including the ligand Hdpf and its Ca salt (6) as reference compounds, were further studied by X-ray photoelectron spectroscopy. Spectral data and magnetic measurements indicate compound 5 contains the dpf − anion as a P,O-coordinated ligand.

Synthetic transformations of a pendant nitrile moiety in group 4 metallocene complexes

Functional group transformations at the group 4 metallocene framework have been demonstrated, which have provided relatively straightforward access to otherwise synthetically challenging derivatives. The pendant nitrile group in Ti and Zr metallocene complexes of the type [(η(5)-C5Me5)(η(5)-C5H4CMe2CH2CN)MCl2] was converted into an intramolecularly bound ketimido moiety by alkylation, which took place not only at the nitrile, but also at the metal centre. The choice of an alkylating reagent (alkyl/aryl lithium, Grignard reagent) was crucial: e.g., 2 equiv. of MeMgBr effected the alkylation only at the metal, yielding selectively complexes [(η(5)-C5Me5)(η(5)-C5H4CMe2CH2CN)MMe2], while the use of PhMgBr, PhLi, or MeLi instead gave selectively the ketimido complexes. Organyl lithium reagents were, however, not compatible with the titanocene derivatives. The metal-bound ketimides were subsequently cleaved off by the reaction with HCl, which afforded metallocene dichlorides with a pendant imino group. These compounds were easily protonated again at the nitrogen atom to produce a cationic iminium moiety. Aqueous hydrolysis of the imine or its respective hydrochloride proved to be viable in the case of Zr and it finally afforded a pendant ketone group attached to the zirconocene framework.

Mixed amido-cyclopentadienyl group 4 metal complexes

The reactivity of substituted half-sandwich complexes of Ti, Zr, and Hf towards 2,6-diisopropylaniline NH2C6H3-2,6-iPr2 (LNH) and 2-[(dimethylamino)methyl]aniline NH2C6H4-2-(CH2NMe2) (LNNH) was investigated. Two series of mononuclear complexes (η5-C5Me5)LNMCl2 (M = Ti (3), Zr (4), Hf (5)) and (η5-C5Me5)LNNMCl2 (M = Ti (7), Zr (8), Hf (9)) were prepared from corresponding (pentamethylcyclopentadienyl)metal trichlorides and the lithium precursors LNLi and LNNLi. Besides the desired products a dimeric hafnium compound [(η5-C5Me5){µ-NC6H4-2-(CH2NMe2)}HfCl]2 (10) was also isolated and structurally characterized. The formation of dimeric complexes of this type was also achieved by reacting a series of (η5-C5Me4R)LCNMCl2 (M = Zr, Hf; R = Me, H; LCN = C6H4-2-(CH2NMe2)-µ2C,N) complexes with lithium precursors LNLi and LNNLi generating [(η5-C5Me4H){µ-NC6H3-2,6-iPr2}MCl]2 (M = Zr (11), Hf (13)), [(η5-C5Me5){µ-NC6H3-2,6-iPr2}MCl]2 (M = Zr (12), Hf (14)), [(η5-C5Me4H){µ-NC6H4-2-(CH2NMe2)-µ2N,N}ZrCl]2 (15), and [(η5-C5Me5){µ-NC6H4-2-(CH2NMe2)}ZrCl]2 (16), respectively. The formation of 10 by this reaction procedure was not detected; instead monomeric complexes (η5-C5Me4R)LNNLCNHfCl (R = H (17), Me (18)) were observed as major products. NMR and IR spectroscopy techniques and elemental analysis were used for characterization of the prepared complexes, whereas the structures in most cases were determined by X-ray crystallography.

Substituent effects in reduction-induced synthesis of ansa-titanocenes

Bis{(diphenylvinylsilyl)tetramethylcyclopentadienyl}titanium dichloride [TiCl2{η5-C5Me4(SiPh2CH=CH2)}2] (1) is reduced with a half molar equivalent of magnesium to the monochloride ([TiCl{η5-C5Me4(SiPh2CH=CH2)}2] (2), whereas one molar equivalent of magnesium affords the titanocene [Ti{η5-C5Me4(SiPh2CH=CH2)}{η5:η2-C5Me4(SiPh2CH=CH2)}] (3) stabilized by η2-coordination of one of the two vinyl groups to titanium(II). In the presence of excess magnesium, the vinyl moieties of 3 undergo intramolecular coupling to afford the ansa-titanocene [Ti(η5:η5:η2-C5Me4SiPh2CH=CHCH2CH2SiPh2C5Me4)] (4) possessing the η2-coordinated double bond in lateral position of its ansa-chain. The symmetrical ansa-titanocene [Ti(η5:η5:η2-C5Me4SiPh2CH2CH=CHCH2SiPh2C5Me4)] (5) was not obtained although its DFT-calculated energy is only slightly higher than that of 4. It is considered that transient 5 gives rise to non-identified tar-like by-products which inherently accompany the formation of 4.

Synthesis, molecular and electronic structure of a stacked half-sandwich dititanium complex incorporating a cyclic π-faced bridging ligand

A thermally robust triple-decker complex [bis(η5-pentamethylcyclopentadienyltitanium)-μ-(η4:η4-1,2,4,5-tetrakis(trimethylsilyl)cyclohexa-1-4-diene-3,6-diyl)] (3) was obtained in 4% yield by thermolysing Cp*TiMe3 in the presence bis(trimethylsilyl)acetylene (BTMSA). The solid-state structure of centrosymmetric 3 features rather long all C–C bonds in the nearly planar bridging ligand (1.4720(14)–1.4896(15) A) and a short distance of its least-square plane to the titanium atoms (1.7381(5) A). Computational results revealed the bonding of the central ligand to be accomplished through back-bonding of its two CC bonds and through the simultaneous generation of two σ-Ti–C(H) bonds. Based on CASSCF and CASPT2 results, the molecule acquires several electronic configurations simultaneously, which hinders its representation by one single Lewis structure. Apart from being coordinated to the central ligand, the metal atoms are involved in a direct Ti–Ti bonding by the formation of one σ- and two δ-bonds between them. The bond order of this Ti–Ti overlap shows only a slight decrease upon electronic excitation. The presence of ionic contribution to the bonding of the central ligand is manifested by the charge −1.4e summed on the carbon atoms of the bridging ring. Based on computational results, the spin multiplicity of the ground state is singlet, while the first low lying excitation state is triplet. This is in agreement with the absence of EPR signal in either toluene solution and glass, and with slight downfield shifts of broadened 1H NMR signals of SiMe3 and Cp* methyl groups observed with increasing temperature.