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Silicon is the closest element to carbon in the PeriodicTable, both belonging to group 14, but, the structural rules, chemical behavior and physical properties of their compounds are very different. These differences
 

Summary: 22
Silicon is the closest element to carbon in the PeriodicTable, both belonging to group 14, but, the structural
rules, chemical behavior and physical properties of their compounds are very different. These differences
are most pronounced for low-coordination compounds. Doubly- and triply-bonded carbon compounds
e.g., alkenes, benzenes, butadienes, allenes, acetylenes etc. are among the most important building blocks
of organic chemistry. In contrast, until the 1970s only transient compounds with double bonds to silicon
wereknown,1 leadingtotheconsensusthat "compoundscontainingdoublebondstosiliconorotherheavier
main group elements must be unstable".2 This statement was refuted in 1981 by the landmark syntheses
and X-ray crystallography characterization of the first stable disilene, Mes2Si=SiMes2 (Mes=mesityl),3
and silene, Me3SiSi=C(OSiMe3)Ad (Ad=1­adamantyl).4 This important breakthrough was followed by
the syntheses and isolation of other stable silenes and disilenes and of compounds with heteroatom-
silicon double bonds (as well as double bonds to other group 14 elements).5 Yet, only recently have other
important low-coordination silicon building blocks been synthesized. Thus, the first tetrasilabutadiene
and trisilaallene were synthesized only in 19976 and in 2003,7 respectively, and the first silicon analogue
of acetylene, i.e., disilyne (RSiSiR), was synthesized only in 2004.8 On the other hand, a stable silyne
(RSiCR') is still unknown and its synthesis remains a major challenge. Thus, low-coordination silicon
chemistry is still a field in its infancy and presents many challenges for the future.
While the field of low-coordination silicon chemistry was evolving, computational chemistry reached
maturity mainly due to the pioneering work of J. A. Pople and his group9 and to the fast development
of computers. Consequently, theory played a major role in the development of low-valent silicon

  

Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology

 

Collections: Chemistry