Disproportionation and Ligand Lability in Low Oxidation State Boryl-Tin Chemistry.

Boryltin compounds featuring the metal in the+1 or 0 oxidation states can be synthesized from the carbene-stabilized tin(II) bromide (boryl)Sn(NHC)Br (boryl={B(NDippCH) ₂ }; NHC=C{(N ⁱ PrCMe) ₂ }) by the use of strong reducing agents. The formation of the mono-carbene stabilized distannyne and donor-free distannide systems (boryl)SnSn(IPrMe)(boryl) (2) and K ₂ [Sn ₂ (boryl) ₂ ] (3), using Mg(I) and K reducing agents mirrors related germanium chemistry. In contrast to their lighter congeners, however, systems of the type [Sn(boryl)] _n are unstable with respect to disproportionation. Carbene abstraction from 2 using BPh ₃ , and two-electron oxidation of 3 both result in the formation of a 2 : 1 mixture of the Sn(II) compound Sn(boryl) ₂ , and the hexatin cluster, Sn ₆ (boryl) ₄ (4). A viable mechanism for this rearrangement is shown by quantum chemical studies to involve a vinylidene intermediate (analogous to the isolable germanium compound, (boryl) ₂ Ge=Ge), which undergoes facile atom transfer to generate Sn(boryl) ₂ and trinuclear [Sn ₃ (boryl) ₂ ]. The latter then dimerizes to give the observed hexametallic product 4, with independent studies showing that similar trigermanium species aggregate in analogous fashion.
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