Bis stannylenes

Figure 2.8.2 Molecular structure of the donor-functionalized bis-stannylene 7 (top) and arrangement of the molecules in the crystal lattice (bottom)...

Scheme 2.8.7 Preparation of the homoleptic complexes 15-18 with bis-stannylene ligands...

Bis-stannylenes with different bridging groups react with M° precursors (pSii(cod)2] or [Pt(nbe)3]) to give the homoleptic tetrakis-stannylene complexes 15-18 (Scheme 2.8.7). ... 

Figure 2.8.7 Molecular structures of the homoleptic platinum (0) complexes of bis-stannylenes 17 (left, coordinated THF molecules are not shown for clarity) and 18 (right)...

Table 2.8.1 Bond parameters and vibrational data for complexes 14, 20-22, and bis-stannylene 7...

The lutidine-bridged bis-stannylene 23 can act as a trapping agent for Sn=0 and Pb=0 generated in situ Hydrolysis of E[N(SiMe3)2]2 (E = Sn, Pb) leads to tin(ll) and lead(II) monoxides which were trapped by the bis-stannylene 23 (Scheme 2.8.9). In both cases the bis-stannylene acts as a pentadentate... 

Figure 2.8.8 Molecular structures of the molybdenum complexes with the N-alkyl-substituted bis-stannylene 20 (right) and the N-donor-substituted bis-stannylene 22 (right)...

A redox process also occurs in the reaction of selenium diimides with bis(amino)stannylenes. Eor example, the cyclic stannylene McaSi)//-N Bu)2Su reacts in a 1 1 molar ratio with BuN=Sc=N Bu to give a spirocyclic tin complex, which reacts with a second equivalent of the stannylene to generate a Sn-Sn bond [d(Sn-Sn) = 2.85 A, /( Sn- Sn) = 13,865 Hz)] (Scheme 10.6). ... 

Scheme 10.6 Reaction of a selenium diimide with a bis(amino)stannylene...

The synthesis of doubly bonded tin compounds by the coupling of stannylenes, however useful, is limited by the need for a stable stannylene and often a second divalent species (for example, a carbene or isonitrile). The simplest example of this reaction is the formation of tetrakis[bis(tri-methylsilyl)methyl]distannene from two molecules of the corresponding stannylene,83 with which it is in equilibrium in solution as evidenced by NMR spectroscopy.91... 

A stable diarylstannanethione has been synthesized by the reaction of an extremely bulky stannylene with either styrene episulfide95 or less than one equivalent of elemental sulfur.9 If the 2,4,6-tris[bis(trimethylsilyl) methyl]phenyl group (Tb) is replaced by the smaller mesityl group, no monomeric products are observed thus the stability of the stannanethione is attributed to the demand of the substituents. 

The structure of these typical stannylenes 1 and 2 are discussed in Chapter 4 as well as that of bis(pentamethylcyclopentadienyl)tin(II) (3) which does not aggregate either but contains two r 5-bonded cyclopentadieny] ligands29), the coordination number being difficult to establish. 

This outstanding behavior of bis(pentamethylcyclopendienyl)stannylene has been explained by the energetically favorable formation of the ionic compound 79 which contains the 6-membered cluster C5Sn 174>. The structure of the boron tetrafluoride compound is illustrated in Fig. 15 the tin atom in the cation is located at the apex of a pentagonal pyramide 173). 

Bis(amido)-germylene and -stannylene react with [Pt(COD)2] to give the platinum(O) complexes [Pt(M NTMS 2)3], M = Ge or Sn.78 The stannylene complex has a trigonal-planar structure with Pt—Sn bond lengths of 2.47-2.50 A.79... 

According to the data of Griitzmacher et al., the isomerization of the proposed intermediate betaine 41, which is formed in the reaction of bis[2,4,6-tris(trifluoromethyl)phenyl]stannylene 39 with phosphorus ylide 40, affords stannylene 41 (Scheme 18).76... 

Actually, 64 is known to be dimeric in the solid state but monomeric in dilute solution or in the gas phase. The first monomeric dialkyl- and diarylstannylenes are 2-pyridylbis[(tri-methylsilyl)methyl]-substituted stannylenes and bis[2,4,6-tris(tiifluoromethyl)phenyl]stan-nylene it should be stressed, however, that the coordination number around Sn in the solid state is not 2 in these compounds. The first actual monomer with coordination number 2 in the solid state was found to be 2,2,5,5-tetrakis(trimethylsilyl)cyclopentane-l-stannylene, 65, prepared by the following reaction141 ... 

Cyclic stannanes can be generated by reaction of stannylenes with alkynes112. For example, bis[bis(trimethylsilyl)methyl]tin reacts with cyclooctyne to provide A1,18-9,10-(distanna-9,9,10,10-tetrakis[bis(trimethylsilyl)methyl])bicyclo[6,2,0]-decene, 69. This reaction is a typical oxidative addition on stannylenes. 

The compounds that are two coordinate in solution usually form SnSn-bonded dimers in the solid state, but the three- and four-coordinate stannylenes do not change their structures, and remain as monomers when they crystallize. Bis(2,4,6-tri-/-butylphenyl)stannylene is exceptional in that it is stable in the crystal, but in solution it rearranges to... 

Treatment of the stannylene Sn[ N(CH2Bu ) 2CioH6-l,8] with Si(NN) (3) gave the crystalline bis(silyl)stannylene 30 which underwent fluxional processes in thf-dg or PhMe-dg and in the latter or CgDg it finally fragmented yielding 31, 3 and Sn metal The crystalline complexes 32 and 33 were obtained as shown in Scheme 9.13. °... 

The crystal structures of three bis(organyl)stannylenes reveal weak coordinative intramolecular interactions between Sn and electron-donating groups and one of them shows additional weak intermolecular interaction to adjacent stannylene species in the crystal. 

The remaining stannylene with weak intramolecular stabilization by a Lewis base is the bis[2,6-(A(At-dimethylamino)phenyl]stannylene A-lN/ NbCgFLjjSn (Ar Sn) (29)33. Two Me3N groups show close Sn - N contacts of 259.9 and 266.3 pm, the proposed lone-pair being directed to the space above and below the C—Sn—C plane where the empty p-orbital of Sn is assumed (Figure 4). Similar interactions are found in the related heteroleptic aryl(silyl)stannylene 42 mentioned in Section II. A.2.b37. 

One further unique diarylstannylene which is worth discussing in more detail is the polycyclic derivative (22)34. This particular molecule possesses three divalent Sn atoms, two of them being coordinated by two amido ligands and the remaining one by two aryl substituents. The Sn atom (SnA) of the bis(aryl)stannylene fragment shows no unusual tight contacts to any other atom — there are close intramolecular contacts to the other Sn atoms, but they are most probably superimposed by the geometric needs of a bicyclic... 

Hetero-atom-substituted stannylenes, which are electron-deficient compounds, are known in a larger number91. This deficiency is compared with the interaction between the 5ptr orbital of the tin atom and the free electron pairs at the hetero atom. In contrast, alkyl- and aryl-substituted compounds are not very well investigated92-95. The first-mentioned donor-free diarylstannylene is bis[(2,4,6-tris(iert-butyl)phenyl]tin96. In solution, this compound isomerized to a less bulky alkylarylstannylene (Scheme 15). 

A similar pyramidal structure was reported two years later when a stable carbene was reacted with bis(2,4,6-triisopropylphenyl)stannylene (Scheme 14).32 The C2 carbon of the complex 23 is shifted upfield in the 13C NMR spectrum compared to the uncoordinated carbene, though only by 28 ppm which is significantly less than in the germanium adduct 22. The solid state structure has a tin-NHC bond length of 2.379(5) A. 

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