23.5C: Tin

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Learning Objectives

In this lecture you will learn the following

Organotin and organolead compounds and their preparation.
Bonding in tin compounds with Sn=Sn double bonds.
Uses and environmental issues with tin compounds.
Reactivity of tetraethyl lead.
Structural features of organolead compounds.

Preparation of Sn(IV) derivatives

Tin(II) organometallics of the type R₂Sn, containing Sn-C σ-bonds, are stabilized only if R is sterically demanding.

(monomeric in solution and dimeric in solid state). But the dimer does not possess a planar Sn₂R₄framework unlike an analogous alkene, and Sn—Sn bond distance (267 pm) is shorter than a normal Sn—Sn single bond (276 pm).

Sn₂R₄ has a trans bent structure with a weak Sn=Sn double bond

Look into the reactions of R₃SnCl with various reagents to form useful tin containing starting materials
The first organotin(II) hydride was reported only in 2000.

Shows dimeric structure in the solid state containing hydride bridges (Sn-Sn = 312 pm).

Commercial uses and environmental problems

Organotin(II) compounds find wide range of applications due to their catalytic and biocidal properties.

ⁿBu₃SnOAc is an effective fungicide and bactericide and also a polymerization catalyst.

ⁿBu₂Sn(OAc)₂is used as a polymerization catalyst and a stabilizer for PVC.

ⁿBu₃SnOSnⁿBu₃ is algicide, fungicide and wood-preserving agent.

ⁿBu₃SnCl is a bactericide and fungicide.

Ph₃SnOH used as an agricultural fungicide for crops such as potato, sugar beet and peanuts.

The cylic compound (ⁿBu₂SnS)₃is used as a stabilizer for PVC.

Tributyltin derivatives have been used as antifouling agents, applied to the underside of ships’ hulls to prevent the build-up of, for example, barnacles.

Global legislation now bans or greatly restricts the use of organotin-based anti-fouling agents on environmental grounds. Environmental risks associated with the uses of organotin compounds as pesticides, fungicides and PVC stabilizers are also a cause for concern.

*A barnacle is a type of arthropod belonging to infraclass Cirripedia in the sub-phylum Crustacea, and is hence related to crabs and lobsters.

Contributors and Attributions

http://nptel.ac.in/courses/104101006/12