Tetrahedranes—

Tetrahedranes belong to the most strained molecules. The molecular structure of tetra- r butyltetrahedrane (209) has been determined in its low-temperature modification at 213 K. The molecule lies on a mirror plane in the hexagonal P /m crystal, and is close to symmetry. The C—C bonds in the tetrahedron, 1.485 (4) A, are shorter than in 

If209 is crystallized at 213 K from ethyl acetate saturated with argon, inclusion crystals are formed which contain Ar atoms in one of the two types of octahedral holes in the close- 

FIGURE 25. Stereo view of thermal ellipsoids (50 percent probability) for the carbon atoms in tetra-/ r -butyltetrahedrane (209) at 213 K. Reproduced by permission of VCH Verlagsgesellschaft mbH from Reference 321 

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THE cvcLOBUTADENE-TETRAHEDRANE SYSTEM. A related reaction is the photoisomerization of cyclobutadiene (CBD). It was found that unsubstituted CBD does not react in an argon matrix upon irradiation, while the tri-butyl substituted derivative forms the corresponding tetrahedrane [86,87]. These results may be understood on the basis of a conical intersection enclosed by the loop shown in Figure 37. The analogy with the butadiene loop (Fig. 13) is obvious. The two CBDs and the biradical shown in the figure are the three anchors in this system. With small substituents, the two lobes containing the lone electrons can be far... 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

Taxus baccata 656 Taxus brevifolia 655 Tebbe reagent 703 telomerization 354 ff. a-terpineol 5 tertiary radicals 409, 413 tether, disposable 664 tetrahedrane 12... 

Molecules such as P4 and the polyanionic clusters such as Si4- or As2- that are discussed in Section 13.2 are representatives of electron precise closo clusters. Organic cage molecules like tetrahedrane (C4R4), prismane (C6H6), cubane (C8H8), and dodecahedrane (C20H20) also belong to this kind of cluster. 

During all these studies on cyclobutadienes and tetrahedranes formed via carbenes as transient species we wondered whether matrix isolation IR spectroscopy might be a good tool for the direct observation of cyclopropenylidene (2) and trimethylenemethane (3). This is indeed the case. 

FIGURE 5.7 Momentum density isosurfaces (in a.u.) of cyclopropane and (a) momentum density of tetrahedrane along the p. axis. Parts b, c, and d show the variation of the density for the same axis for a single, two, and three CH2 insertions, respectively. 

Figure 25 Synthesis and structures of supersilyl-substituted gallanyls 396 and 400, gallanide 398 and tetrahedrane 401.

Tetrahedron. Sn2Bi22- and Pb2Sb22 have (2)(2) + (2)(3) + 2 = 12 skeletal electrons for tetrahedra analogous to P4 and organic C4R4 tetrahedrane derivatives (see Section 1.1.3.4). 

In addition, R 4Si4 (R = Dis2MeSi with Dis = CH(SiMe3)2 has been synthesized by reaction of R Br2Si-SiBr2R and NaR in THF [17]. The tetrahedrane (Si-Si,.rldo/... 

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