Organotins divalent

The reaction is of practical importance in the vulcanization of siUcone mbbers (see Rubber compounding). Linear hydroxy-terrninated polydimethyl siloxanes are conveniently cross-linked by reaction with methyldiethoxysilane or triethoxysilane [998-30-1]. Catalysts are amines, carboxyflc acid salts of divalent metals such as Zn, Sn, Pb, Fe, Ba, and Ca, and organotin compounds. Hydroxy-terrninated polysiloxanes react with Si—H-containing polysiloxanes to... 

Sn NMR chemical shifts in organotin compounds cover a range of about 5200 ppm, the current extremes being +2966 ppm in the divalent stannylene... 

Soon after the isolation of 136, Tokitoh et described the synthesis of the first kinetically stabilized diarylstannylene stable in solution, that is, Tbt(Tip)Sn (169), by treatment of TbtLi with stannous chloride followed by addition of TipLi (Scheme 14.74). Under an inert atmosphere, stannylene 169 was found to be quite stable even at 60 °C in solution, and it showed a deep purple color (A,max =561 nm) in hexane. The Sn NMR spectrum of 169 showed only one signal at 2208 ppm, the chemical shift of which is characteristic of a divalent organotin compound as in the case of a monomeric dialkylstannylene (136). The bandwidth and the chemical shift of 169 were almost unchanged between —30 and 60 °C, indicating the absence of a monomer-dimer equilibrium. 

Catalysts Catalysts are widely used for PU manufacture. Sometimes a combination of two or three catalysts is required to obtain the desired balance of reaction rates between compounds of differing active hydrogen activity. Metal compounds, especially organotin compounds, are much more efficient catalysts than tertiary amines for the -OH/NCO reaction. In addition to more commonly used dibutyltin(IV) dilaurate, dibutyltin(IV) diacetate, dialkyltin(IV) oxide or salts of divalent fin with a variety of carboxylic acids such as stannous octoate, hexoate and naphthenate etc. are available for this purpose. Combination of tin catalysts with tertiary amines has been reported to lead to a synergistic increase in catalytic activity. 

Another type of divalent organotin n complex has been reported by Noltes et al. (228,229). The cyclopentadienyltin halides LXIXa,b precipitate upon mixing concentrated THF solutions of stannocene with the tin dihalides [Eq. (38)]. The complex LXIXa can also be obtained by the reaction of LXVIIIa with hydrogen chloride in THF [Eq. (39)] (228). Similarly, the pentamethylcyclopentadienyltin compounds LXIXc,d have been prepared from decamethylstannocene LXVIIIc and the appropriate carboxylic acid [Eq. (40)] (230). 

V. I. Shiryaev, V. F. Mironov and V. P. Kochergin, Compounds of Divalent Tin and Synthesis of Organotin Compounds, NIITEKhIM, Moscow, 1977 (Russian). 

While the inorganic chemistry of divalent tin and lead is well established, there are few well-characterized divalent organotin and organo-lead compounds. The R2Sn formulation seen in the older literature has proved to be an empirical formula, the formally divalent stannylene actually being an oligomeric linear or cyclic organostannane. Neumann has commented on this point several times (1-3). 

Divalent organotin and organolead compounds can be divided into two classes, viz, those in which the organic groups are organic groups are 7r-bonded to the metal. We will deal with these two classes separately beginning with the 7r-bonded species. A third section will cover transition metal stannylene and plumbylene complexes from both classes. 

The synthesis of stable diorganylstannylenes, the true divalent organotin derivatives, was carried out only in the second half of the 20th... 

The general reaction takes place with formation of the desired metal diketonate and loss of the hydrocarbon corresponding to the organic fragment of the starting alkyl or aryl metal compound (Equation (21)). This happens, for example, with divalent organotin and organozinc. 

II. Divalent Organotin Compounds Containing a C,Y-Chelating Ligand. . 247... 

Although divalent inorganic tin compounds have been known for a long time,2 it was in 1956 that the first example of a divalent organotin compound, i.e., bis(cyclopentadienyl)tin(II), was reported (29). 

The coordination chemistry of divalent organotin compounds is a special case, since the tin atom can act both as an acceptor and as a donor, e.g., as in (CO)3CrSn(f-Bu)2 pyridine (52). 

Fig. 4. Divalent organotin - transition metal compounds containing a C,Y-chelating ligand.

C. Divalent Organotin Compounds Stabilized by Intramolecular Coordination... 

Recently the first examples of divalent organotin compounds in which intramolecular coordination as such is sufficient for stabilization were reported. These compounds are bis(2-[(dimethylamino)methyl]phenyl tin(II), 6 (74) bis(2-[l-(dimethylamino)ethyl]phenyl tin(II), 7 (78) bis[8-(dimethylamino)-l-naphthyl]tin(II), 8 (75) bis([2-(dimethylamino) phenyl (trimethylsilyl)methyl tin(II), 9 (78) and bis[(2-pyridyl)bis(tri-methylsilyl)methyl]tin(II), 10 (79) and are schematically shown in Fig. 5. 

Fig. S. Divalent organotin compounds stabilized by two C,N-chelating ligands.

Fig. 8. The first examples of heteroleptic divalent organotin compounds.

Remarkable is the acute C—Sn—Cl angle of 95.0(3)° in 14, most probably for the same reason as found for the C—Sn—C angle in homoleptic divalent organotin compounds in which the tin center has a -trigonal bipyramidal coordination geometry (vide supra). 

It has been recognized that divalent organotin compounds easily undergo oxidative addition reactions (89). Similarly, 8 reacts with alkyl halides and dihalogen to give the corresponding oxidative addition products (75). 

Addition of dibromine or diiodine to the divalent organotin compound bis[8-(dimethylamino)-l-naphthyl]tin(II) affords in a quantitative oxidative-addition reaction bis[8-(dimethylamino)-l-naphthyl]tin dibromide 108 and diiodide 109, respectively (152)... 

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