Ring and Cage Structures

3- diborolanes [12 R = NR2, R = C(H)Ph] have been made from [R (PhCsC)B]2CH2 and Cp2Zr(THF) via the 6,8-dibora-3-zircona-pentalene analogue (13) 

2 Boron and Heteroatoms from Group 15 Only.- Several iminoboranes RBsNR have been synthesised, by either HF elimination from R(F)BN(H)R, reaction of RBF and Li2NR, or the gas-phase thermolysis of either Cl ( Bu) B=N (R ) SiMe3 or 

Cl2BNPr 2 d l,8-Li2CioC6 combine to give the expected product containing a BC3 ring, which in turn undergoes ring expansion with BX3 to form (14) (X = Cl, Br,OEt). Al,4- 

4 Boron, Carbon, and Heteroatoms from Groups 15 and/or 16.- A spectroscopic study of transannular B-N interactions in endo-1-[(dialkylamino)methyl]-3-borabicyclo(3.3.1]nonanes has been published.The lithium salt of 1,2-azaborole can be converted to its thallium analogue at -50°C using TlCl, and the latter used as reagent for the formation of phosphorylated (26  

X = R2 )or borylated (26 X = R2B)heterocycles. Several crystal structure determinations are available for these series, for example (26 X = Ph2P, Y = Me3Si) incorporates a planar 

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AIN, GaN, and InN are attractive materials for applications such as blue lasers and field emitters single-source precursors for these of formula [R2MNR 2]2 (R = alkyl, R = alkyl or H) have been reported.236 The reaction of alkylamines with group 13 trialkyl metal compounds affords oligomeric or polymeric ring and cage structures of metal amides and imides (see section on nitrides). 

Figure 16 Examples of ring and cage structures formed by organo-silicon, -germanium and -tin phosphines...

The singly deprotonated 2,6-dimesitylphenyl trisphosphanosilane (4) is stable at room temperature in the reaction mixture, which means that the presence of a terphenyl ligand increases the thermal stability of the adjacent phosphano silyl unit. On the other hand, removal of the solvent under reduced pressure results in the evolution of PH3 and formation of Si—P rings. For the major products, an assignment to the respective ring and cage structures in solution was possible because of the characteristic shift values and P-P and P-H coupling patterns. 

Catenation is an important property of the heavier chalcogens. A variety of chains, rings, and cage structures are known for S, Se, and Te. 

Main group elements form a wide variety of neutral, cationic, and anionic compounds having chain, ring, and cage structures (e.g. Zintl anions). [366] All of these may be useful starting materials to be combined with mono- and polynuclear transition metal moieties to generate molecules with novel and exciting structural features. This alternative type of synthetic approach has been used for the synthesis of all the other derivatives included in Table 3-11. For example, as shown in Scheme 3-12, the reaction of either Se4 or Te4 with such mononuclear metal carbonyls as [Fe(CO)s] and [W(CO)6] can yield cluster compounds... 

Several books and general reviews are already available on phosphorus ring and cage systems (16). This one will focus more specifically on the coordination chemistry of molecular tetraphos-phorus-based doso-compounds, including itself and closely related analogs, and will also include structural data on both free and coordinated species. The questions of the transmission of electronic and structural effects through the molecular frame, and of the extent oftt-bonding, will be critically considered. 

The systematic treatment of such structures is beyond the scope of the present review. The majority of examples selected belongs to bonding type 12, constructed of two or more three-membered rings and other structural elements. Propellanes are of the 11 type. A monograph on cage molecules has appeared recently308. 

There are several ways to combine rings into polycychc and cage structures (e.g. spirocyclic systems and fused rings). These will not be discussed here. Theoretical speculations have been made about the possible existence of purely inorganic (carbon-free) fullerene-like polycychc cages, for example, boron-nitrogen molecules or sihcon analogs. ... 

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