A cationic imido complex of permethyltantalocene:: H2 and carbon-hydrogen bond activation, [2+2] cycloaddition reactions, and an unusual reaction with carbon dioxide that affords coordinated isocyanate

Treatment of the imido hydride complex Cp*Ta-2(=NCMe3)H(Cp*=(eta(5)-C5Me5)) with [Ph3C][B(C6F5)(4)] in tetrahydrofuran solution yields the cationic imido complex [Cp*Ta-2(=NCMe3)(THF)][B(C6F5)(4)] (1). Cation 1 reacts cleanly with H-2 to yield [Cp*Ta-2(NHCMe3)H][B(C6F5)(4)]. Carbon-hydrogen bond-activation reactions are observed with propyne or phenylacetylene to afford [Cp*Ta-2(NHCMe3)(C=CR)][B(C6F5)(4)] (R = CH3, C6H5). In the reaction with propyne, an initial mixture of the [2 + 2] cycloaddition 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 Cp* methyl group to ultimately yield [Cp*Ta(eta(5)-C5Me4CH2NCMe3)H][B(C6F5)(4)] precludes C-K activation of the carbon-hydrogen bonds of methane. An unusual reaction occurs with carbon dioxide: dealkylation of the imido group is observed, liberating isobutylene and yielding the isocyanate complex [Cp*Ta-2(OH)(NCO)][B(C6F5)(4)]. Complex 1 reacts with HCl to afford [Cp*Ta-2(NHCMe3)Cl][B(C6F5)(4)] and decomposes cleanly in methylene chloride solution to give [Cp*Ta-2(NHCMe3)Cl][B(C6F5)(4)] by formal HCl abstraction. X-ray crystal structure determinations for [Cp*Ta-2(eta(5)-C5Me4CH2NCMe3)H][B(C6F5)(4)], [Cp*Ta-2(NHCMe3)Cl][B(C6F5)(4)] , [Cp*Ta-2(NHCMe3)H][B(C6F5)(4)], [Cp*Ta-2(NHCMe3)(C=CC6H5)][B(C6F5)(4)]and [Cp*Ta-2(OH)(NCO)][B(C6F5)(4)] are reported.