Hydrogen electron counting

As the C B series of tetracarbaboranes is classified in the electron-counting formaUsm as nido, these molecules are expected to have open stmctures even though extra hydrogens are absent. Spectroscopic studies (130) have confirmed this expectation for 2,3,4,5-C4B2H3 [28323-17-3]. One isomer of (CH3)4C4BgHg has the open nonicosahedral stmcture shown in Figure 11 and another isomer, the 1,2,3,8-tetramethyl compound [54387-54-1], is apparently even more open (131). Other tetracarbaboranes include isomers of nido-Q]. and (132). 

The molecule has one nitrogen atom p ). Interpreting the parentheses in the formula reveals that there are four carbon atoms p ) and eleven hydrogen atoms (5 ). You should be able to verify that the valence electron count is 32 e. ... 

Compounds and complexes of the early transition metals are oxophilic because the low d-electron count invites the stabilization of metal-oxo bonds by 7T-bond formation. To a substantial extent, their reactivity is typical of complexes of metals other than rhenium. That is particularly the case insofar as activation of hydrogen peroxide is concerned. Catalysis by d° metals - not only Revn, but also CrVI, WVI, MoVI, Vv, ZrIV and HfIV - has been noted. The parent forms of these compounds have at least one oxo group. Again the issue is the coordination of the oxygen donating substrate, HOOH, to the metal, usually by condensation ... 

At first glance, electron count in these clusters gives a remarkable analogy to the carbaboranes. Each aluminum atom contributes two electrons to the cluster, three electrons are from each carbon atom, and one electron is added by the bridging hydrogen atom. A total count of 32 electrons or 16 electron pairs results, which in accordance with the Wade rules [6] gives an arachno-type 13-vertex cluster. Indeed,... 

Electron counting in these electron-deficient systems is slightly different than in electron-precise hydrides. As noted by Green,8 canonical forms can be written in which the hydrogen is treated normally vis-a-vis one metal and the M—H bond is treated as a two-electron ligand to the second... 

In drawing Lewis structures for covalently bonded molecules, the octet rule is used as a guide (remember that for hydrogen the octet is changed to a duet). Shared electrons count toward the electron total for both atoms in the bond. For example, the Lewis structure for SiH4 looks like this ... 

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