Methane vs benzene activation via transient [sup t]Bu[sub 3]SiNHTa([double bond]NSi[sup t]Bu[sub 3])[sub 2]: Structure of (py)[sub 2]MeTa([double bond]NSi[sup t]Bu[sub 3])[sub 2]

Addition of Me[sub 3]TaCl[sub 2] to 2.0 equiv of LiNHSi[sup t]Bu[sub 3] in hexanes resulted in CH[sub 4] and ([sup t]Bu[sub 3]SiNH)Me[sub 2]Ta[double bond]NSi[sup t]Bu[sub 3] (1, 63%). Thermolysis of 1 in benzene resulted in disproportionation, but in pyridine and THF, L[sub 2]MeTa([double bond]NSi[sup t]Bu[sub 3])[sub 2] (L = py, 2(py)[sub 2], 68%; THF, 2(THF)[sub 2], 13%) and MeH were produced. Addition of TaCl[sub 5] to 4.0 equiv of LiNHSi[sup t]Bu[sub 3] in Et[sub 2]O at [minus]78[degrees]C afforded ([sup t]Bu[sub 3]SiNH)[sub 2]ClTa[double bond]NSi[sup t]Bu[sub 3] (3-Cl) [sup t]Bu[sub 3]SiNH[sub 2]. Alkylation of 3-Cl with AlMe[sub 3] (hexanes), PhLi (Et[sub 2]O/hexanes), PhCH[sub 2]K (toluene), and [sup t]BuCH[sub 2]Li(Et[sub 2]O) provided ([sup t]Bu[sub 3]SiNH)[sub 2]RTa[double bond]NSi[sup t]Bu[sub 3] (R = Me, 3-Me, 78%; Ph, 3-Ph, 64%; CH[sub 2]Ph, 3-CH[sub 2]Ph, 51%; CH[sub 2][sup t]Bu, 3-CH[sub 2][sup t]Bu, 39%). Addition of [sup t]Bu[sub 3]SiNH[sub 2] or [sup t]Bu[sub 3]SiOH to 1 yielded 3-Me or ([sup t]Bu[sub 3]SiNH)([sup t]Bu[sub 3]SiO)MeTa[double bond]NSi[sup t]Bu[sub 3] (5-Me, 52%) and CH[sub 4]. Thermolysis of 3-R effected 1,2-RH-elimination to form transient ([sup t]Bu[sub 3]SiNH)Ta([double bond]NSi[sup t]Bu[sub 3])[sub 2] (4), a species capable of adding C-H bonds across one imido linkage. Moderate rates of elimination from 3-R could be obtained only at 182.8 (4) [degrees]C.