Multiple Bonding Between Heavier Group 13 Elements
Experimental and theoretical data for stable compounds that have the potential for multiple bonding between heavier group 13 metals have been surveyed. In spite of the fact that only about a dozen such compounds have been isolated under ambient conditions
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Experimental and theoretical data for stable compounds that have the potential for multiple bonding between heavier group 13 metals have been surveyed. In spite of the fact that only about a dozen such compounds have been isolated under ambient conditions, the area has generated widespread debate owing to widely differing opinions on the multiplicity of the bonding in some compounds, especially the `gallyne' Na2Ga2(C6H3-2,6-Trip2)2 (Trip = C6H2-2,4,6-i-Pr3). The experimental and theoretical data show that group 13A13 heavier element multiple bonding is weak. Only two neutral multiply bonded compounds, i.e., the radical species (t-Bu)3SiMM{Si(t-Bu)3}2 (M = Al or Ga), are known to be stable at room temperature. The other compounds, the majority of which are gallium derivatives, are either mono- or dianionic. All the currently known dianionic species depend on the presence of bridging alkali metal counter cations for stability. Recent computational data also indicate the presence of some alkali metal-group 13 metal bonding in the dianion complexes. Possible future directions and experimental routes to resolving bonding arguments are outlined. Keywords: Multiple bonding, Clusters, Group 13 elements, Radicals, Terphenyls, Silyl ligands, Bulky groups
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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2 Bonding in the Neutral Dimers RMMR (M = Al, Ga, In, Tl, R = H, alkyl or aryl) and the Neutral Radicals RMMR2´ [M = Al or Ga, R = Si(t-Bu)3] . . . . . . . . . . . . . . . . . . . . . .
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3 Multiple MAM Bonds via Reduction of R2MMR2 Species [M = Al, Ga; R = C6H2-2,4,6-i-Pr3 (Trip) or ±CH(SiMe3)2] and R2MMR´ [M = Al, Ga; R = Si(t-Bu)3] to Monoanions . . . . . . . .
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4 Heavier Group 13 MAM Multiple Bonding in Reduced Metal Cluster Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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5 Bonding in the Compound Na2Ga2(C6H3-2,6-Trip2)2 . . . . . . . . . . . .
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6 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Structure and Bonding, Vol. 103 Ó Springer-Verlag Berlin Heidelberg 2002
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P. P. Power
List of Abbreviations Mes THF TMEDA Trip
C6H2-2,4,6-Me3 (mesityl) tetrahydrofuran 1,1,2,2-tetramethylethylenediamine C6H2-2,4,6-i-Pr3
1 Introduction The investigation of multiple bonding between heavier main group elements of periods 13 through 16 has been a major focus of inorganic and organometallic research since the mid 1970s [1, 2]. However, this work has been concentrated mainly on the multiple bonding of elements of groups 14, 15, or 16, and the ®rst authentic reports of multiple bonding between heavier group 13 elements were not published until 1993 [3±5]. There were several reasons for this belated development. The major one was the undoubted weakness of bonding between these elements. Although there are no thermochemical data currently available for heavier group 13 elemen
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