Synthesis and solid state structures of tri-t-butyl-cyclopropenyl derivatives of main group elements: Cyp*MPh3 (M = Si, Ge, Sn)

The reaction of Ph3MLi (M = Si, Ge, and Sn) with tri-t -butylcyclopropenium tetrafluoroborate View the MathML source(Cyp∗BF4-) gives the cyclopropenyl compounds Cyp*MPh3 as air and moisture stable solids in 11%, 74%, and 77% yields, respectively. Attempts to prepare Cyp*PbPh3 by this method were unsuccessful. The X-ray crystal structures of all three of these compounds were obtained. The M–C(Cyp*) bond distances increase with the order: Sn–C (2.19 Å) > Ge–C (2.00 Å) > Si–C (1.91 Å). A high degree of steric strain is evidenced for the silicon derivative which forms an exocyclic bond angle (Si–C(Cyp*)–C(tBu)) of 121.6°. The high degree of steric strain for the silicon analog is believed to be responsible for the low yields for its synthesis.