A CATIONIC IMIDO COMPLEX OF PERMETHYLTANTALOCENE - H-2 AND CARBON-HYDROGEN BOND ACTIVATION, [2-CYCLOADDITION REACTIONS, AND AN UNUSUAL REACTION WITH CARBON-DIOXIDE THAT AFFORDS COORDINATED ISOCYANATE(2])

Treatment of the imido hydride complex CpTa-2(=NCMe3)H(Cp*=(eta(5)-C5 Me5)) with [Ph3C][B(C6F5)(4)] in tetrahydrofuran solution yields the c ationic imido complex [CpTa-2(=NCMe3)(THF)][B(C6F5)(4)] (1). Cation 1 reacts cleanly with H-2 to yield [CpTa-2(NHCMe3)H][B(C6F5)(4)] Carbo n-hydrogen bond-activation reactions are observed with propyne or phen ylacetylene to afford [CpTa-2(NHCMe3)(C=CR)][B(C6F5)(4)] (R = CH3, C6 H5). In the reaction with propyne, an initial mixture of the [2 + 2] c ycloaddition product and C-H activation product is thermally driven to the C-H activation product. The heterolytic cleavage reactions for 1 may be rationalized in terms of the presence of both electrophilic and nucleophilic sites of reactivity in the same molecule. Intramolecular activation of a carbon-hydrogen bond of a I I Cp methyl group to ult imately yield [CpTa(eta(5)-C5Me4CH2NCMe3)H][B(C6F5)(4)] precludes C-K activation of the carbon-hydrogen bonds of methane. An unusual reacti on occurs with carbon dioxide: dealkylation of the imido group is obse rved, liberating isobutylene and yielding the isocyanate complex [CpT a-2(OH)(NCO)][B(C6F5)(4)]. Complex 1 reacts with HCl to afford [CpTa- 2(NHCMe3)Cl][B(C6F5)(4)] and decomposes cleanly in methylene chloride solution to give [CpTa-2(NHCMe3)Cl][B(C6F5)(4)] by formal HCl abstrac tion. X-ray crystal structure determinations for [CpTa-2(eta(5)-C5Me4 CH2NCMe3)H][B(C6F5)(4)], [CpTa-2(NHCMe3)Cl][B(C6F5)(4)] , [Cp*Ta-2(NH CMe3)H][B(C6F5)(4)], [CpTa-2(NHCMe3)(C=CC6H5)][B(C6F5)(4)]and [Cp*Ta- 2(OH)(NCO)][B(C6F5)(4)] are reported.