Key points: Tin and lead form tetravalent organo compounds; organotin compounds are used as fungicides and pesticides.
Many organometallic compounds of Group 14 are of great commercial importance, although the use of lead is illegal in many parts of the world, owing to its toxicity. Generally, organometallic compounds of the group are tetravalent and have low polarity bonds. Their stability decreases from silicon to lead.
Organotin Compounds and its Derivatives
Organotin compounds differ from organosilicon and organogermanium compounds in several ways. There is a greater occurrence of the +2 oxidation state, a greater range of coordination numbers, and halide bridges are often present.
Most organotin compounds are colourless liquids or solids that are stable to air and water. The structures of R4Sn compounds are all similar, with a tetrahedral tin atom.
The halide derivatives, R3SnX, often contain Sn-X-Sn bridges and form chain structures. The presence of bulky R groups may affect the shape.
For example, in (SnFMe3)n, the Sn-F-Sn backbone is in a zigzag arrangement, in Ph3SnF the chain has straightened, and (Me3SiC)Ph2SnF is a monomer.
The haloalkyls are more reactive than the tetraalkyls and are useful in the synthesis of tetraalkyl derivatives.
Alkyltin compounds may be prepared in a variety of ways, including by using a Grignard reagent and by metathesis:
SnCl4 + RMgBr ——> SnR4 + MgBrCl
3 SnCl4 + 2 Al2R6 ——-> 3 SnR4 + 2 Al2Cl6
Organotin compounds have the widest range of uses of all main group organometallic compounds. Their annual worldwide industrial production exceeds 50 kt. Their major application is in the stabilization of PVC plastics.
Without the additive, halogenated polymers are rapidly degraded by heat, light, and atmospheric oxygen to give discoloured, brittle products. The tin stabilizers scavenge labile Cl– ions that initiate the loss of HCl, the first step in the degradation process.
Organotin compounds also have a wide range of applications relating to their biocidal effects. They are used as fungicides, algaecides. They are also used to stabilize poly(vinyl chloride) (PVC) as antifouling agents on ships, as wood preservatives, and as pesticides.
However, their widespread use on boats to prevent fouling and attachment of barnacles has caused environmental concerns. High levels of organotin compounds kill some species of marine life and affect the growth and reproduction of others.