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In the interaction of the five-membered zirconacyclocumulene Cp2Zr(η4-tBuC4tBu) (6) with 1,4-bis(trimethylsilyl)butadiyne Me3SiC C–C CSiMe3 in toluene at 60–80 °C, two isomeric zirconacyclopentadiene complexes (7) and (8) are formed in 4.4–4.7 : 1 ratio. Complex 7 has been isolated from the solution in the individual state and its structure Cp2Zr[η2-tBuC C(C2tBu)–C(SiMe3) C(C2SiMe3)] has been determined by X-ray crystallography. Prolonged heating of a mixture of 6 and Me3SiC C–C CSiMe3 at 100 °C leads to a gradual disappearance of the resulting zirconacyclopentadienes and to the formation of the seven-membered zirconacyclocumulene complex Cp2Zr[η4-tBuC4(tBu)–C(C2SiMe3) CSiMe3] (9) as the main product and two its analogues, viz., Cp2Zr[η4-Me3SiC4(SiMe3)–C(C2SiMe3) CSiMe3] (1) and Cp2Zr[η4-tBuC4(tBu)–C(C2tBu) CtBu] (2) as the admixtures. The same products are produced from individual compound 7 at 100 °C. Heating of complex 6 with tolane and phenylacetylene in toluene at 100 °C also gives rise to the corresponding zirconacyclopentadiene metallacycles, viz. Cp2Zr[η2-tBuC C(C2tBu)–C(Ph) CPh] (10) and Cp2Zr[η2-tBuC C(C2tBu)–CH CPh] (11). However these metallacycles do not form seven-membered zirconacyclocumulene complexes in any significant amounts even under prolonged keeping of the mixture at 100 °C. The structure of complexes 9–11 has also been established by X-ray crystallography. Mechanisms of the reactions found are discussed.

The interaction of the three-mercury anticrown ( o -C 6 F 4 Hg) 3 ( 1 ) with [PPN]NO 3 and [PPh 4 ]NO 3 in an ethanol solution yields nitrate complexes, [PPN]{[( o -C 6 F 4 Hg) 3 ] 2 (NO 3 )} ( 2 ) and [PPh 4 ]{[( o -C 6 F 4 Hg) 3 ] 2 (NO 3 )} ( 3 ), respectively, having double-decker sandwich structures. In both adducts, the nitrate anion behaves as a tridentate ligand and is coordinated through the oxygen atoms with the Hg sites of each anticrown unit in an η 3 : η 1 fashion. However, whereas complex 3 constitutes a bent sandwich in the crystal, the planes of the anticrown molecules in complex 2 are parallel to each other. The reaction of 1 with [PhNMe 3 ] 2 SO 4 results in the formation of a sulfate complex, [PhNMe 3 ] 2 {[( o -C 6 F 4 Hg) 3 ] 2 (SO 4 )} ( 4 ), the subsequent recrystallization of which from the acetone/ethanol mixture yields a solvate, 4 ·Me 2 CO·3EtOH, representing also a double-decker sandwich according to X-ray crystallography. The sulfate anion in this sandwich is a tetradentate ligand and is bound to each anticrown species by two oxygen atoms in an η 3 : η 1 fashion as well. Like 3 , complex 4 ·Me 2 CO·3EtOH has a bent sandwich geometry. The complex is characterized also by the presence of H-bonds between two oxygen atoms of the coordinated sulfate anion and two ethanol molecules. The synthesized sandwich compounds 2 , 3 and 4 ·Me 2 CO·3EtOH are the novel structural type of complexes of an anticrown with nitrate and sulfate anions as well as the first examples of structurally characterized complexes of 1 with oxygen-containing anions.

The paper reports new data evidencing for a high electrophilicity of the positively charged titanium atom in the previously described zwitterionic titanocene monochloride Cp[η 5 -C 5 H 4 B(C 6 F 5 ) 3 ]TiCl ( 1 ) and titanocene monobromide Cp[η 5 -C 5 H 4 B(C 6 F 5 ) 3 ]TiBr ( 2 ), containing a B(C 6 F 5 ) 3 group in one of the C 5 rings. It has been established that on a contact of a toluene solution of these zwitterions with water vapour at 20 °C under Ar, a rapid protolytic cleavage of the otherwise inert B–C 6 F 5 bond in the tris(pentafluorophenyl)borane moiety occurs to afford pentafluorobenzene and the corresponding halogenide hydroxide complex of titanocene Cp[η 5 -C 5 H 4 B(C 6 F 5 ) 2 ]TiX(μ-OH), where X = Cl ( 3 ), Br ( 4 ). An X-ray diffraction study of the complexes has shown that the hydroxide group in 3 and 4 is bonded via the oxygen atom both to the titanium and boron atoms. Under similar conditions, the interaction of zwitterion 1 with methanol gives rise to pentafluorobenzene and the chloride methoxide complex of titanocene Cp[η 5 -C 5 H 4 B(C 6 F 5 ) 2 ]TiCl(μ-OCH 3 ). It has been suggested that the driving force of the protolysis of the B–C 6 F 5 bond in 1 and 2 is a sharp increase in the acidity of water or methanol molecule as a result of their complexation with the positively charged titanium centre in the starting zwitterion.

The interaction of cyclic trimeric perfluoro-o-phenylenemercury (o-C6F4Hg)3 (1) with azulene results in the formation of a complex, {[(o-C6F4Hg)3](azulene)} (2), containing one molecule of azulene per one macrocycle molecule. The complex represents a polydecker sandwich wherein the azulene units alternate with the molecules of the mercury anticrown. The reaction of 1 with 6-(N,N-dimethylamino)pentafulvene (DMAPF) also gives a 1:1 complex, {[(o-C6F4Hg)3](DMAPF)} (3), having a polydecker sandwich structure in the crystal. In complex 2, both the C5 and C7 rings of the azulene ligand are involved in the bonding to the Hg sites of 1. In complex 3, the C5 ring of the fulvene ligand together with its exocyclic carbon atom take part in the coordination to the mercury centres. In both adducts, the negatively charged five-membered ring of the azulene and, correspondingly, the fulvene moieties is arranged in the space between the central Hg3C6 rings of the adjacent macrocycles while the remaining portion of these moieties is disposed outside this space. The molecules of azulene and DMAPF in 2 and 3 are bonded to 1 through donation of their π-electrons on vacant orbitals of the Hg atoms. The synthesized 2 and 3 are the first examples of structurally characterized complexes of azulene and DMAPF with a non-transition metal compound.

The reaction of the titanium(III) zwitterionic complex Cp[η5-C5H4B(C6F5)3]Ti (1) with CCl4 at 20 °C under Ar results in the formation of hexachloroethane and the zwitterionic titanocene monochloride Cp[η5-C5H4B(C6F5)3]TiCl (3) containing a B(C6F5)3 moiety in the η5-cyclopentadienyl ring. Under similar conditions, the reaction of 1 with 1,2-dibromoethane affords ethylene and the corresponding zwitterionic monobromide Cp[η5-C5H4B(C6F5)3]TiBr (4). An X-ray diffraction study of 3 and 4 revealed the presence of a coordinative bond between the ortho-fluorine atom of one of the C6F5 substituents and the positively charged titanium centre. In the interaction of 1 with n-propyl iodide at 20 °C, titanocene diiodide, B(C6F5)3 and propylene are produced. The mechanism of this interesting reaction is discussed. The synthesized zwitterions 3 and 4 are able to catalyze the ring-opening polymerization of e-caprolactone in a toluene solution and in bulk. The highest activity in this process is exhibited by 3. The first X-ray diffraction study of Cp2TiI2 has been carried out.