Bonding mode

TThe x-ray stmcture of the novel bis-dicarboUide sandwich compound i (9y y (9-3,3 -Si(3,l,2-SiC2B2H22)2 contains a siUcon atom iu a highly unusual bonding mode (245). TThis compound, which is quite stable thermally, is prepared iu good yield. 

The multiplicities of signals due to Jqh coupling (splitting occurs due to CH coupling across one bond) indicates the bonding mode of the C atoms, whether quaternary (R4C, singlet S), tertiary doublet D), secondary (R2CH2, triplet T) or primary (RCHj, quartet Q). 

A number of transition-metal complexes of RNSO ligands have been structurally characterized. Three bonding modes, r(A,5), o-(5)-trigonal and o (5 )-pyramidal, have been observed (Scheme 9.1). Side-on (N,S) coordination is favoured by electron-rich (et or j °) metal centers, while the ff(S)-trigonal mode is preferred for less electron-rich metal centres (or those with competitive strong r-acid co-ligands). As expected ti (N,S)... 

Scheme 9.1 Common bonding modes for RNSO ligands...

The H3+ ion is the simplest possible example of a three-centre two-electron bond (see discussion of bonding in boranes on p. 157) and is also a model for the dihapto bonding mode of the ligand r] -H2 (pp. 44-7) ... 

Dinitrogen might coordinate to metals in at least 4 ways, but only the end-on modes, structures (1) and (2), are well established as common bonding modes by numerous well-defined examples ... 

Complexes are known which feature more than one N2 ligand, e.g. cK-[W(N2)2(PMe2Ph)4] and tran5-[W(N2)2(diphos)2] (where diphos = Ph2PCH2CH2PPh2) and some complexes feature more than one bonding mode, e.g. ... 

The coordination chemistry of SO2 has been extensively studied during the past two decades and at least 9 different bonding modes have been established.These are illustrated schematically in Fig. 15.26 and typical examples are given in Table 15.17.1 It is clear that nearly all the transition-metal complexes involve the metals in oxidation state zero or -bl. Moreover, SO2 in the pyramidal >7 -dusters tends to be reversibly bound (being eliminated when... 

Although the cyclopentadienyls dominate the aromatic chemistry of this group, bis(arene) compounds are also well established. They are able to satisfy the 18-electron rule as the dications, [M(arene)2] " or by the two rings adopting different bonding modes one tj the other tj". ... 

Interesting new sulfido complexes of tin have been prepared by the reaction of styrene sulfide with the N-alkylated tin(II) amidinate complexes Sn[RC(NCy)2]2 (Cy = cyclohexyl R = Me, Bu ). The products exhibit two very different bonding modes for the sulfido ligands in one case, S = Sn[RC(NCy)2]2/ a terminal Sn = S moiety was found while in the other case the bridging... 

Neurock and coworkers [M. Neurock, V. Pallassana and R.A. van Santen, J. Am. Chem. Soc. 122 (2000) 1150] performed density functional calculations for this reaction scheme up to the formation of the ethyl fragment, for a palladium(lll) surface. Figure 6.38(a) shows the potential energy diagram, starting from point at which H atoms are already at the surface. As the diagram shows, ethylene adsorbs in the Jt-bonded mode with a heat adsorption of 30 kj mol and conversion of the latter into the di-a bonded mode stabilizes the molecule by a further 32 kJ mol . ... 

Figure 6.38. Potential energy diagram for the hydrogenation of ethylene to the ethyl (C2H5) intermediate on a palladium(m) surface. The zero of energy has been set at that of an adsorbed H atom, (a) Situation at low coverage ethylene adsorbed in the relatively stable di-cr bonded mode, in which the two carbon atoms bind to two metal atoms. In the three-centered transition state, hydrogen and carbon bind to the same metal atom, which leads to a considerable increase in the energy...

High sensitivity of species vibrational frequency to bonding modes at surfaces. 

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