Taming Neutral Silylidenebismuthanes (Si═Bi) with a Low-Coordinate Bismuth Atom

High Resolution Image Download MS PowerPoint Slide Unsaturated main-group compounds containing heteroleptic double bonds of bismuth remain exceedingly rare due to inherent p π –p π bond weakness. Here we report the synthesis and characterization of the first isolable silylidenebismuthane complexes, L(Me 3 Si)Si═Bi(SiMe 3 ) and L(Me 3 Si)Si═Bi(Si i Pr 3 ) (( E )- 1a, b ) (L = PhC(N t Bu) 2 ), containing a neutral but strongly polarized silicon–bismuth double bond. The complexes were obtained as the E isomers in 55% and 60% yield through the salt metathesis reaction of LSi II Cl with the corresponding potassium bis(silyl)bismuthanide complexes. Remarkably, LSi II –Bi(SiMe 3 ) 2 and LSi II –Bi(SiMe 3 )(Si i Pr 3 ) could not be observed but undergo a trimethylsilyl group migration from the Bi III atom to the Si II atom to form a Si═Bi moiety containing σ 3 λ 4 -coordinate Si II and σ 2 λ 2 -coordinate Bi I atoms. The reactions of ( E )- 1a, b with [W(CO) 5 (thf)] cause the ( E ) → ( Z ) isomerization with respect to the silyl groups attached to furnish the corresponding terminal Bi→W(CO) 5 complexes ( Z )- 2a,b, in which the Si═Bi π bonding interaction is significantly weakened. This and the nature of the Si═Bi bonds are corroborated by DFT calculations.