Lewis Bases Trigger Intramolecular CH–Bond Activation: (tBu3SiO)2W=NtBu [rlhar2] (tBu3SiO)(κO,κC‐tBu2SiOCMe2CH2)HW=NtBu

摘要: The symmetry-forbidden cyclometalation of (silox)2W=NtBu (1, silox = OSitBu3) to (silox)(tBuN)W(H)(κO,κC-OSitBu2CMe2CH2) (2) was investigated by kinetics [ΔH‡ 19.2(9) kcal/mol; ΔS‡ –23(3) eu; ΔG‡(25 °C) 26.1(10) kcal/mol], isotopic labeling {[D54]1 [D54]2; kH/kD 2.7(4)}, and equilibrium studies [ΔH° –6.7(3) ΔS° –12.1(8) ΔG°(25 –3.1(4) kcal/mol]. crystal structure 2 reveals a pseudo-square-pyramidal that can be viewed as distorted tetrahedron with the W–H W–C bonds occupying one site. addition H2 (or D2) 1 proceeds similarly afford (silox)2(tBuN=)WH2 (3), also affords 3, but experiments show it via 1. Phosphane bases cone angles < 160° trigger in 5 min, PMe3 catalyzed dihydrogen Quantum mechanics/molecular mechanics (QM/MM) calculations support experimental findings Lewis promote σ/π mixing. experimentally observed intermediate (silox)2(tBuN=)WPMe3 (1-PMe3) has (dyz)2 (i.e., π2) ground state contrast (d)2 σ2) configuration mixing circumvents constraints orbital symmetry for both addition.