Organotin compounds are generally classified according to their oxidation states. Tin(IV) compounds are much more common and more useful.
Organic derivatives of tin(IV) The tetraorgano derivatives are invariably tetrahedral. Compounds of the type SnRR'R
R' have been resolved into individual enantiomers.
Organotin halides Organotin chlorides have the formula {{chem2|R_{4−
n}SnCl_{
n}|}} for values of
n up to 3. Bromides, iodides, and fluorides are also known, but are less important. These compounds are known for many R groups. They are always tetrahedral. The tri- and dihalides form adducts with good Lewis bases such as
pyridine. The fluorides tend to associate such that dimethyltin difluoride forms sheet-like polymers. Di- and especially tri-organotin halides, e.g.
tributyltin chloride, exhibit toxicities approaching that of
hydrogen cyanide.
Organotin hydrides Organotin hydrides have the formula {{chem2|R_{4−
n}SnH_{
n}|}} for values of
n up to 3. The parent member of this series,
stannane (), is an unstable colourless gas. Stability is correlated with the number of organic substituents.
Tributyltin hydride is used as a source of hydride radical in some organic reactions.
Organotin oxides and hydroxides Organotin oxides and hydroxides are common products from the hydrolysis of organotin halides. Unlike the corresponding derivatives of silicon and germanium, tin oxides and hydroxides often adopt structures with penta- and even hexacoordinated tin centres, especially for the diorgano- and monoorgano derivatives. The group {{chem2|Sn^{IV}\sO\sSn^{IV}|}} is called a
stannoxane (which is a tin analogue of
ethers), and the group {{chem2|Sn^{IV}\sO\sH}} is also called a stannanol (which is a tin analogue of
alcohols). Structurally simplest of the oxides and hydroxides are the triorganotin derivatives. A commercially important triorganotin hydroxide is the
acaricide cyhexatin (also called Plictran, tricyclohexyltin hydroxide and tricyclohexylstannanol), (. Such triorganotin hydroxides exist in equilibrium with the distannoxanes: : With only two organic substituents on each Sn centre, the diorganotin oxides and hydroxides are structurally more complex than the triorgano derivatives. The simple tin geminal diols (, the tin analogues of
geminal diols ) and monomeric stannanones (, the tin analogues of
ketones ) are unknown. Diorganotin oxides () are polymers except when the organic substituents are very bulky, in which case cyclic
trimers or, in the case where R is
dimers, with and rings. The distannoxanes exist as dimers with the formula wherein the X groups (e.g.,
chloride –Cl,
hydroxide –OH,
carboxylate ) can be terminal or bridging (see Table). The hydrolysis of the monoorganotin trihalides has the potential to generate stannanoic acids, . As for the diorganotin oxides/hydroxides, the monoorganotin species form structurally complex because of the occurrence of dehydration/hydration, aggregation. Illustrative is the hydrolysis of butyltin trichloride to give . File:R2SnO-cyclic-trimer-2D.png|Idealized structure of trimeric diorganotin oxide. File:TBu2SnO-cyclic-trimer-from-xtal-1984-Mercury-3D-balls.png|Ball-and-stick model for (. File:R2SnO-cross-linked-network-Harris-and-Sebald-1987-2D.png|Structure of diorganotin oxide, highlighting the extensive intermolecular bonding.
Hypercoordinated stannanes Unlike carbon(IV) analogues but somewhat like silicon compounds, tin(IV) can also be
coordinated to five and even six atoms instead of the regular four. These hypercoordinated compounds usually have
electronegative substituents. Numerous examples of hypercoordinated compounds are provided by the organotin oxides and associated carboxylates and related pseudohalide derivatives. while in the subsequent year a six-coordinated tetraorganotin compound was reported. A crystal structure of room-temperature stable (in
argon) all-carbon pentaorganostannate(IV) was reported as the
lithium salt with this structure: : In this distorted
trigonal bipyramidal structure the carbon to tin
bond lengths (2.26
Å apical, 2.17 Å equatorial) are longer than regular C-Sn bonds (2.14 Å) reflecting its hypercoordinated nature.
Triorganotin cations Some reactions of triorganotin halides implicate a role for intermediates. Such cations are analogous to
carbocations. They have been characterized crystallographically when the organic substituents are large, such as 2,4,6-triisopropylphenyl.
Tin radicals (organic derivatives of tin(III)) Tin radicals, with the formula , are called
stannyl radicals. They are a type of
tetrel radical, and are invoked as intermediates in certain atom-transfer reactions. For example,
tributyltin hydride (tris(
n-butyl)stannane) serves as a useful source of "hydrogen atoms" because of the stability of the tributytin radical.
Organic derivatives of tin(II) Organotin(II) compounds are somewhat rare. Compounds with the empirical formula are somewhat fragile and exist as rings or polymers when R is not bulky. The polymers, called
polystannanes, have the formula {{chem2|(SnR2)_{
n}|}}. : In principle, compounds of tin(II) might be expected to form a tin analogues of
alkenes with a formal
double bond between two tin atoms () or between a tin atom and a
carbon group atom (e.g. and ). Indeed, compounds with the formula , called
distannenes or
distannylenes, which are tin analogues of
ethylenes , are known for certain organic substituents. The Sn centres in stannenes are trigonal. But, contrary to the
C centres in alkenes which are
trigonal planar, the Sn centres in stannenes tend to be highly
pyramidal.
Monomeric compounds with the formula , tin analogues of
carbenes are also known in a few cases. One example is , where R is the very bulky . Such species reversibly
dimerize to the distannylene upon crystallization: :
Stannenes, compounds with tin-carbon double bonds, are exemplified by derivatives of
stannabenzene.
Stannoles,
structural analogs of
cyclopentadiene, exhibit little C-Sn double bond character.
Organic derivatives of tin(I) Compounds of Sn(I) are rare and only observed with very bulky ligands. One prominent family of cages is accessed by pyrolysis of the 2,6-diethylphenyl-substituted tristannylene [Sn(C6H3-2,6-Et2)2]3, which affords the
cubane-type cluster and a
prismane. These cages contain Sn(I) and have the formula [Sn(C6H3-2,6-Et2)]
n where
n = 8, 10 and Et stands for
ethyl group. A
stannyne contains a tin atom to carbon group atom
triple bond (e.g. and ), and a
distannyne a triple bond between two tin atoms (). Distannynes only exist for extremely bulky substituents. Unlike
alkynes, the core of these distannynes are nonlinear, although they are planar. The Sn-Sn distance is 3.066(1) Å, and the Sn-Sn-C angles are 99.25(14)°. Such compounds are prepared by reduction of bulky aryltin(II) halides. Grey balls:
CMagenta (largest) balls:
SnStructure of an "prismane", a compound containing Sn(I) (Ar = 2,6-diethylphenyl). == Preparation ==