Hypervalent interaction

An intermediate allyltin trichloride, possibly stabilized by an oxygen-tin hypervalent interaction, which then reacts with the aldehyde via a chair-like six-membered ring transition state with the substituent a to tin in an axial position, may be involved94. On heating with aldehydes, the 4-benzyloxypentenylstannane shows only modest diastereofacial selectivity22. 

Whereas 3c/4e hypervalent interactions (4.77) tend to be relatively uncommon and fragile in main-group compounds (often leading to transition states for nucleophilic displacement reactions, rather than stable equilibrium species), the corresponding interactions in transition-metal coordination compounds are ubiquitous and robust. The far higher prevalence of hypervalent co-bonding in transition-metal chemistry may be attributed to three major factors. 

III. Silylhydride Complexes with Interligand Hypervalent Interactions M-H "SiX. 270... 

SILYLHYDRIDE COMPLEXES WITH INTERLIGAND HYPERVALENT INTERACTIONS M-H SIX... 

While the last elass of eomplexes considered in this section, the compounds 145, closely resemble the usual silane a-complexes, other multicenter H Si interactions discussed above have spectroscopic and structural features common to both the IHI and a-complexes. This enigmatic situation can be explained well by the structure 132 in terms of a a-coordination of the Si-H bonds of the hypervalent ligand (H +iSiX3)" 1) to metal, which thus includes both the hypervalent interaction of the silicon with the hydride atoms and the a-complexation of the Si-H bonds to metals. The key features of complexes with multicenter H Si interactions are summarized in Table VIII, where a comparison with the IHI and the residual H-Si interactions in silane a-complexes is given. 

In contrast to the reaction of y-stannyl alcohol 50, the y-stannyl benzyl ether 53 results in selective cleavage of the butyl-tin bond by reaction with (PhIO)n 18/DCC/BF3 and, after quenching of the reaction mixture with aqueous NH4C1, afforded the chlorostannane in high yield. Interestingly, the chlorostannane both in solution and in the solid state adopts a 1,3-diaxial conformation through Sn-O hypervalent interaction [82]. 

Vapor pressure osmometric and spectroscopic studies on the molecular association and dissociation of (Z)-vinyl(bromo)-A3-iodane 130 in chloroform solution indicate the equilibrium formation of the dimer 131 as well as the iodonium ion 129, which is stabilized by the coordination of the solvent chloroform via the hypervalent interaction between the positively charged iodine and a chlorine atom [212]. 

Polymeric structure of o-sulfonyl iodosylbenzene 135 with tetracoordinated iodine of pseudo square planar geometry was obtained by the single crystal X-ray analysis (Fig. 5) [217]. The bright yellow A3-iodane 135 is soluble in chloroform because of the weaker intermolecular hypervalent interaction (I-OT, 2.665 A) compared to that of iodosylbenzene 18 [218]. 

The important point to appreciate is that the formal valency of zinc is satisfied by two bonds to sulfur so that the additional interactions are indeed hypervalent interactions. Thus, the nature of the adopted structures arises from the ability of the central element to form hypervalent, or secondary, interactions and it is proposed that this ability is moderated by steric considerations associated with the alkyl substituents. As noted from the structural studies for the uncoordinated xanthate anions summarized earlier in Section II, there are no electronic differences among the xanthate ligands that can be correlated with the nature of the oxygen-bound substituent. This conclusion is vindicated by the homogeneity of the molecular structures of the binary nickel xanthates as... 

In the condensed phase Me3SiF molecules show no intermolecular interactions, while the same germanium derivatives are associated as a dimer due to intermolecular F Ge coordination. According to the tendency for tetrahedral main-group 14 elements to expand the coordination sphere, organotin fluorides show a strong tendency to associate in the solid state and even in triorganotin fluorides the tin atom is five-coordinate A common feature of this class of compounds in the solid state is coordination expansion of the tin atom due to hypervalent interaction, which in turn often results in formation of polymeric materials. 

Examples of association resnlting from intermolecular sulfur organolead hypervalent interactions are rare and componnds snch as MeyPbSMe and Ph3PbSPh are monomeric in the solid state. The cyclic diorgano dithiolate 2,2-diphenyl-l,3,2-dithiaplnmbolan ° self-assembles in the solid state via intermolecular sulfur tin interactions into a onedimensional polymeric array. The intramolecular S Pb bond lengths amonnt to 2.52 and 2.49 A, and the intermolecnlar S Pb distances are 3.55 A. 

In the case of the analogous Si-H... M systems, the only two bona fide cases of known agostic interactions are neutron structure determinations carried out by Schubert et al. in 1982, " and by Mork et al. in 2004. However, in recent years Nikonov etal. have been introducing an alternative concept, that of interhgand hypervalent interactions (IHIs), to describe related systems. ... 

CCD = charge-coupled device IHIs = interligand hypervalent interactions ILL = Institut Lane-Langevin INS = inelastic neutron scattering IPNS = intense pulsed neutron source LINAC = linear accelerator MaNDi=macro-molecular neutron diffractometer NiMH=nickel-metal OPAL = open pool Australian light-water reactor hydride SANS = small-angle neutron scattering SNS = spallation neutron source. 

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