The reaction of the chlorosilyl-substituted cyclopentadienyltitanium compound [Ti(η 5 -C 5 H 4 -SiMe 2 Cl)Cl 3 ] with N,N′-dimethylethylenediamine in the presence of 2 equiv of NEt 3 gave a mixture of two complexes, [Ti{η 5 -C 5 H 4 SiMe 2 NMe(CH 2 ) 2 -η-NMe}Cl 2 ] (1) and [Ti{η 5 -C 5 H 4 SiMe 2η-N(CH 2 ) 2 -η-NHMe}Cl 2 ] (2), in a molar ratio of 3:1. However, a similar reaction with N-methylethylenediamine afforded complex 2 regiospecifically. The dialkyl derivatives [Ti- 3), CH 2 Ph (4)) were prepared by reacting the dichloride complex 1 with 2 equiv of MgClMe or 1 equiv of Mg(CH 2 Ph) 2 •2THF, respectively. The analogous reaction with LiNMe 2 afforded the diamido derivative [Ti{η 5 -C 5 H 4 SiMe 2 NMe(CH 2 ) 2 -η-NMe}(NMe 2 ) 2 ] (5) in high yield. Complex 1 reacts with dry CO 2 via insertion of a molecule of CO 2 into each of the Ti-N and Si-N bonds to yield the dicarbamate compound [Ti{(η 5 -C 5 H 4 SiMe 2 OC(O)NMe(CH 2 ) 2 NMe(η 2 -CO 2 )}Cl 2 ] (6), in which the carbamate groups are bound in η 2 -and η 1 -fashion. Thermal decomposition of complex 6 afforded the known oxo derivatives [Ti{µ-(η 5 -C 5 H 4 SiMe 2 -η-O)}Cl 2 ] 2 and [(TiCl 2 ) 2 (µ-O)-[µ-{(η 5 -C 5 H 4 SiMe 2 ) 2 -(µ-O)}] with elimination of CO 2 and 1,3-dimethyl-2-imidazolidinone. The conformational interconversion of 1 and 6 and the reversible coordination of the terminal "NHMe" group to the metal center in 2 were studied in solution by DNMR spectroscopy. The crystal structure of 1 was determined by X-ray diffraction methods.

The reaction of [Ti(η 5 -C 5 H 4 SiMe 2 -κO)(CH 2 -Ph) 2 ] 2 with the Lewis acid B(C 6 F 5 ) 3 in toluene at room temperature affords the new dinuclear monocationic species [{Ti(η 5 5)). Different isomers of 1 are observed, depending on the temperature, as deduced by variable-temperature NMR spectroscopic studies. 1). This compound is thermally unstable and decomposes in aromatic solvents to give the paramagnetic mixed-valence species [{Ti(η

New imido and oxo dimetallic complexes of Mo and W with the monobridged or dibridged bis(cyclopentadienyl) ligands Cp1Cp or Cp2Cp [Cp1Cp = (η5-C5H4)2SiMe2, Cp2Cp = (η5-C5H3)2(SiMe2)2] have been synthesized. The Cp2Cp complexes have been obtained as both cis and trans isomers which differ in the stereodisposition of the two metal fragments with respect to the Cp2Cp system, the stereochemistry being unchanged in all the reactions described. Addition of H2N t Bu to [(MCl4)2(μ-Cp n Cp)] (M = Mo, n = 1, 2a; n = 2, 2b; M = W, n = 2, 2c) affords the imido M(V) complexes [{M(N t Bu)Cl2}2(μ-Cp n Cp)] (4a−c). Complexes 4a,c are oxidized by PCl5 to give [{M(N t Bu)Cl3}2(μ-Cp n Cp)] (5a,c). Both 4a and 5a afford [{MoCl(μ-N t Bu)}2(μ-Cp1Cp)] (6) by reduction with sodium amalgam. The differences found between this reaction and the related reductions of the mononuclear Cp analogues are discussed. Reaction of 6 with HgO affords the oxo complex [{MoO(μ-N t Bu)}2(μ-Cp1Cp)] (7). [(MoOCl)2(μ-O)(μ-Cp2Cp)] (3) is obtained by reaction of [{Mo(CO)3Cl}2(μ-Cp2Cp)] with CH3NO2 or bubbling air through a THF solution of cis-[(MoCl4)2(μ-Cp2Cp)]. The molecular structure of 7 has been determined by a single-crystal X-ray analysis.

The dinuclear cationic zirconium species [{Zr(η 5 -C 5 H 5 )} 2 (µ-CH 2 )(µ-Cl)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )]-[BMe(C 6 F 5 ) 3 ] (1) reacts in dichloromethane at -78 °C with terminal alkynes, via insertion into the Zr-µ-methylene bond, to give various dinuclear cationic derivatives. Reaction of 1 with Me 3 SiCtCH gives the hydrido complex [{Zr(η 5 -C[BMe(C 6 F 5 ) 3 ] (4). Compounds 3 and 4 show dynamic behavior in solution involving an interchange between two enantiomeric structures through a suprafacial migration of the "-RCdCH 2 " moiety. When compound 1 was treated with a molar equivalent of internal alkynes RCtCR (R ) Et, n Pr), formation of [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C(Et)dC(Et)}(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (5) and [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C( n Pr)dC( n Pr)}(µ-η 5 -C 5 H 4η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (6) was observed, which were isomerized to the [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C(Et)CHdCHMe}(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )] [BMe(C 6 F 5 ) 3 ] (7) and [{Zr(η 5 -C 5 H 5 )} 2 (µ-Cl){µ-CH 2 C( n Pr)CHdCHEt}(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (8) derivatives at room temperature, through a β-R hydrogen migration. The new complexes reported were characterized by elemental analysis and IR and NMR spectroscopy.

Methylation of the previously described isocyanide-bridged complex [{Zr(η 5 -C 5 H 5 )Cl} 2 (µ-CN t Bu)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )] with 2 equiv of MgClMe in toluene at 80 °C afforded the dinuclear dimethyl complex [{Zr(η 5 -C 5 H 5 )(CH 3 )} 2 (µ-CN t Bu)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )], 1. The same reaction with 1 or 2 equiv of MgClMe at room temperature gave a mixture of compounds containing the dimethyl derivative 1 and two isomers of the monomethyl derivative [{Zr(η3, isolated by reaction of the zirconium(III) derivative [{Zr(η 5 -1,3-t Bu 2 C 5 H 3 )(µ-Cl)} 2 (µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )] with 1 equiv of CN t Bu in toluene, gave a mixture of unidentified compounds. Treatment of the dimethyl complex [{Zr(η 5 -C 5 H 5 )(CH 3 )} 2 (µ-CN t Bu)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )], 1, with 1 equiv of the Lewis acid B(C 6 F 5 ) 3 in dichloromethane at -78 °C affords the new yellow crystalline zirconium cationic derivative [{Zr(η 5 -C 5 H 5 )} 2 (µ-CH 3 )(µ-CN t Bu)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )]-[BMe(C 6 F 5 ) 3 ], 4. Hydrolysis of the µ-methyl compound 4 led to the µ-hydroxo cationic derivative [{Zr(η 5 -C 5 H 5 )} 2 (µ-OH)(µ-CN t Bu)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ], 5. Compound 4 reacts with an excess of isocyanides CNR in dichloromethane at -78 °C to give the cationic species [{Zr(η 5 -C 5 H 5 )} 2 (CH 3 )(CNR)(µ-CNR)(µ-η 5 -C 5 H 4 -η 5 -C 5 H 4 )][BMe(C 6 F 5 ) 3 ] (R ) t Bu, 6; 2,6-Me 2 C 6 H 3 , 7). All of the reported compounds were characterized by the usual analytical and NMR spectroscopic methods, which are discussed.