Abstract:The reactions of the group 4 metallocene alkyne complexes Cp* 2 M(η 2 -Me 3 SiC 2 SiMe 3 ) (M = Ti, Zr) with different cyanopyridines were investigated. For the zirconium compound, the unstable products Cp* 2 Zr(η 2 -Me 3 SiC 2 SiMe 3 )(N≡C-py) were first formed by the end-on coordination of the substrate. Subsequent reaction with a second equivalent resulted in the elimination of the alkyne and in the formation of 1-zircona-2,5-diazacyclopenta-2,4-dienes. By applying (2-bromo)-5-cyanopyr-

Reactions of the group 4 metallocene alkyne complexes [Cp 2 M(L)(btmsa)] (Cp = η 5 -cyclopentadienyl = η 5 -C 5 H 5 , btmsa = η 2 -Me 3 SiC 2 SiMe 3 ; 1: M = Ti, L = none; 2: M = Zr, L = pyridine) and of the [(triphos)Co I ] moiety [triphos = 1,1,1tris(diphenylphosphanylmethyl)ethane] with the benzylsulfanyl-substituted acetylenes PhCH 2 S-C 2 -SCH 2 Ph (3) and PhCH 2 S-C 2 -SFmoc (4) (Fmoc = fluorenylmethoxycarbonyl) have been investigated. Complex 1 reacted with 3 to give a mixture of a violet solid and [Cp 2 Ti(SCH 2 Ph) 2 ] (5). Subsequently, the violet solid transformed in toluene at 70°C into the dinuclear complex [(Cp 2 Ti) 2 (μ-κ 2 -κ 2 -BnSC 4 SBn)] (6) displaying two [Cp 2 Ti] moieties bridged by a 1,4-bis(benzylsulfanyl)-1,3-butadiyne in the trans configuration. Complex 6 was further degraded in toluene at 100°C to the tetranuclear cluster [CpTiS] 4 (7). Similar reactivity was deduced indirectly for the reaction partners 1/4 and 2/3. For Co I , the side-on[a] Leibniz-

The reaction of dipiperidinoacetylene (pipC Cpip, pip = NC 5 H 10 , 1a) with [Cp 2 Ti(η 2 -btmsa)] (2) or with [Cp 2 Zr(η 2 -btmsa)(py)] (4) (btmsa = bis(trimethylsilyl)acetylene, py = pyridine) afforded the metallacyclopentadienes [Cp 2 M(C 4 pip 4 )] (3, M = Ti; 5, M = Zr), which in the solid state exhibit twisted five-membered metallacycles with an unusual half-chair conformation. In contrast, the sterically more demanding decamethyltitanocene (Cp* 2 Ti) and -zirconocene (Cp* 2 Zr) complex fragments can only accommodate one alkyne ligand. Thus, the titanacyclopropene [Cp* 2 Ti(C 2 pip 2 )] ( 7) was isolated from the reaction of 1a with [Cp* 2 Ti(η 2 -btmsa)] ( 6) or with [Cp* 2 TiCl] in the presence of magnesium, whereas the zirconacyclopropenes [Cp* 2 Zr(C 2 X 2 )] (8a, X = pip; 8b, X = NC 5 H 9 -4-Me; 8c, X = NEt 2 ) were prepared by the reduction of [Cp* 2 ZrCl 2 ] with magnesium in the presence of 1a, bis(4-methylpiperidino)acetylene (1b), and bis(diethylamino)acetylene (1c), respectively. NMR studies showed that complexes 8 are in equilibrium with their tucked-in tetramethylpentafulvene−diaminovinyl isomers [Cp*(η 6 -C 5 Me 4 CH 2 )Zr(CX=CHX)] (9) in solution, which are formed by intramolecular C−H-bond activation and hydrogen transfer from one Cp* methyl group to the alkyne ligand. Thermodynamic and kinetic parameters were derived by variabletemperature NMR spectroscopy and DFT experiments. The molecular structures of 3, 5, 7, 8a, [8a•MgCl 2 ] 2 , 8b, and 8c were established by X-ray diffraction analyses.

In this work the reactivity of 1-metalla-2,5-diaza-cyclopenta-2,4-dienes of group 4 metallocenes, especially of the pyridyl-substituted examples, towards small molecules is investigated. The addition of H2 , CO2 , Ph-C≡N, 2-py-C≡N, 1,3-dicyanobenzene or 2,6-dicyanopyridine results in exchange reactions, which are accompanied by the elimination of a nitrile. For CO2 , a coordination to the five-membered cycle occurs in case of Cp*2 Zr(N=C(2-py)-C(2-py)=N). A 1,4-diaza-buta-1,3-diene complex is formed by H-transfer in the conversion of the analogous titanocene compound with CH3 -C≡N, PhCH2 -C≡N or acetone. For CH3 -C≡N a coupling product of three acetonitrile molecules is established additionally. In order to split off the metallocene from the coupled nitriles, we examined reactions with HCl, PhPCl2 , PhPSCl2 and SOCl2 . In the last case, the respective thiadiazole oxides and the metallocene dichlorides were obtained. A subsequent reaction produced thiadiazoles.

Reactions of the group 4 metallocene alkyne complexes [Cp'2 M(η(2) -Me3 SiC2 SiMe3 )] [Cp'2 =rac-(ebthi)=rac-1,2-ethylene-1,1'-bis(η(5) -tetrahydroindenyl): M=Ti, Zr, Hf; Cp'2 =Cp*2 (Cp*=η(5) -pentamethylcyclopentadienyl): M=Zr] with 2,6-dimethylphenyl isocyanide (2-xylyl isonitrile, XyNC) were investigated. Depending on the metal, the Cp' ligand, and/or the stoichiometry, as well as the reaction temperature and time, different products were obtained. The products included simple end-on coordination compounds of XyNC in addition to those of the coupling of Me3 SiC2 SiMe3 with two, three, or four isonitriles to form enimine complexes, aza-metallacycloallenes, and fused heterocyclic systems, respectively. One example of the latter tricyclic compounds was subject to demetalation by using HCl. Molecular structures of the heterometallacycles were determined by X-ray crystallography. The interconversion of the products was investigated by (1) H NMR spectroscopy.