Exo-polyhedral Interactions

Let us begin by discussing the different kinds of exo-polyhedral interactions observed in borane clusters (Figure 5.19). All the structures shown are experimentally known, except D, which is known only with bridging CO or CHj instead of... 

Figure 5.19 (a-f) Exo-polyhedral interactions in polyhedral borane clusters. 

Exo-polyhedral interactions (Figure 5.19) do not affect the skeletal bonding in individual monomeric units and hence Wade s rales can stiU be applied. These macro-polyhedral boranes where Wade s rule is apphcable can be called connected polyhedral boranes, in contrast to condensed polyhedral boranes in which the monomeric units share one or more boron vertices and do not obey Wade s rale. In order to be applicable to condensed polyhedral boranes as well, Wade s rule can be extended by incorporating a new variable, m, corresponding to the number of polyhedra. In Wade s n-i-l-i-p rale, 1 is added to include the core BMO. If m closo clusters condense to form a condensed polyhedral borane, there will be m core BMOs. Thus, the n-El-Ep rale can be modified to where m is the... 

Figure 5.20 (a) Unfavorable exo-polyhedral interactions and (b) ways to make them favorable. 

Although stable and neutral bimetallic complexes were obtained from the dicat-ionic fragments and 129 or 130 there was the possibility that reactions with two molar equivalents of a metal-ligand monocation should give rise to trimetallic species. However, reactions of 130 with sources of the cations M (CO)3 (M = Mn, Re), namely [Mn(NCMe)3(CO)3][PF6] and [ReBr(THF)2(CO)3], yielded as products [N(PPh3)2][l,3,6- M (CO)3 -3,6-(p-H)2-l,l,l-(CO)3-2-Ph-c/ow-l,2-ReCBgHT] [M = Mn (156), Re (157)], respectively (Chart 27). ° In these molecules, the exo-polyhedral M (CO)3 moiety is almost certainly bonded to the cluster via two non-equivalent B-H M interactions with an Re-M bond completing... 

Figure 5.27 Exo-polyhedral destabilizing interactions (indicated by dotted lines) in condensed icosahedral structures.

Compounds (17) with exo-polyhedral B-H-M interactions were formed from the reaction of [w(CR)(CO)2(1.2-Me2-1.2-CgBgHg)]" (R - p-tol) with [M(C0)2(NCMe)2(n-CgH7)] salts (M = Mo,W), Scheme 3 68 Further reaction of the B-H-M unit and the bridging... 

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