B–H Bond Activation by an Amidinate-Stabilized Amidosilylene: Non-Innocent Amidinate Ligand

The activation of B–H and B–Cl bonds in boranes by base-stabilized low-valent silicon compounds is described. The reaction of the amidinato amidosilylene–borane adduct [L­{Ar­(Me₃Si)­N}­SiBH₃] [<b>1</b>; L = PhC­(N<i>t</i>Bu)₂, and Ar = 2,6-<i>i</i>Pr₂C₆H₃] with MeOTf in toluene at room temperature formed [L­{Ar­(Me₃Si)­N}­SiBH₂OTf] (<b>2</b>). [LSiN­(SiMe₃)­Ar] in compound <b>2</b> then underwent a B–H bond activation with BH₂OTf in refluxing toluene to afford the B–H bond activation product [LB­(H)­Si­(H)­(OTf)­{N­(SiMe₃)­Ar}] (<b>3</b>). On the other hand, when compound <b>2</b> was reacted with 4-dimethylaminopyridine in refluxing toluene, another B–H bond activation product [(μ-κ1:κ1-L)­B­(H)­(DMAP)­Si­(H)­{N­(Ar)­SiMe₃}]­OTf (<b>4</b>) was afforded. Mechanistic studies show that “(μ-κ1:κ1-L)­B­(H)­(OTf)­Si­(H)­{N­(Ar)­SiMe₃}” (<b>2A</b>) is the key intermediate in the reactions mentioned above. The formation of <b>2A</b> is further evidenced by the activation of the B–Cl bond in PhBCl₂ by the amidinato silicon­(I) dimer [LSi:]₂ to form the B–Cl bond activation product [(μ-κ1:κ1-L)­B­(Cl)­(Ph)­Si­(Cl)]₂ (<b>6</b>). Compounds <b>2–4</b> and <b>6</b> were characterized by nuclear magnetic resonance spectroscopy and X-ray crystallography