Water- and oxygen-sensitive compounds R*EHal2•D, R*EHal2 and R*2EHal (R* = SitBu3; E = B, Al, Ga, In, TI; Hal = F, Cl, Br, I; D = OR2, NR3) have been synthesized by reaction of EHal3 with NaR* in the absence or presence of donors as well as by substitution of D, Hal or R* by other substituents, or by reaction of R*2E-ER*2 (E = Al, In) with I2, H2, AgF2 or HBr. Thermal decomposition of the compounds in solution or in the gas phase leads to elimination of D from R*EHal2•D, or of R*Hal from R*EHal2 and R*2EHal, respectively. The dihalides R*EHal2 act as Lewis acids with respect to donors OR2 or NR3 (formation of adducts R*EHal2•D), the monohalides R*2EHal as Lewis bases with respect to acceptors EHal3 (formation of R*2E+ EHal4-). Dehalogenations of R*2EHal and R*EHal2 with alkali metals or NaR* leads to compounds R*4E2 (E = AI, In, Tl), R*3E2• (E = AI, Ga), R*4E3• (E = Al, Ga), R*4E4 (E = AI, Ga), R*6Ga8, R*8In12, (R*2B- ), R*2A- , R*3Ga2-, R*4Ga3-, R*4Ga42-, R*4Tl3Cl, or R*6Tl6Cl2. The structures of R*BBr2•Py, R*AlBr2•NEtMe2, (R*AlClOBu)2, R*2BF as well as R*2ECl (E = B, Al, Ga, Tl) have been determined by X-ray structure analyses.

The most common structure for a 10-vertex polyhedral cluster with a 2n2 skeletal electron count (where n is the number of vertices) is the bicapped square antiprism (I; Scheme 1). [1] In one of the two known isomeric forms of these least one constituent of the product has a limited solubility in it. Under our reaction conditions, indium metal (m.p. 1578C) is indeed molten and dissolves less than 0.001 atomic % nitrogen. [13] The most obvious characteristics of the VLS [12] and SLS [5,6] mechanismsÐone-dimensional fiber or whisker growth morphologies and attached metal-catalyst particlesÐ were clearly evident in the InN samples produced. Consequently, all the key indicators of the SLS growth mechanism were present.The SLS growth process has been previously demonstrated for group III element phosphides and arsenides, [5,6] which are thermally stable at conventional growth temperatures. However, indium nitride is not. The SLS mechanism operates at very low temperatures in comparison to conventional materials-synthesis methods, presumably because it is catalytic and lowers energy barriers for both precursor decomposition and the interfacial steps required for nonmolecular crystal growth (crystal lattice assembly). SLS synthesis of other thermally unstable compounds and crystal structures should be possible. Experimental SectionCompounds tBu 3 In [14] and iPr 3 In [15] were prepared according to the literature. The synthesis of tBu 2 InN 3 (1 b) is described here; iPr 2 InN 3 (1 a) was prepared similarly. MeOH (225 mL, 0.178 g, 5.55 mmol) was added to a dry, O 2 -free solution of tBu 3 In (1.61 g, 5.63 mmol) in hexane (20 mL) at 258C. The mixture was stirred for 10 min and then N 3 SiMe 3 (0.800 mL, 0.660 g, 5.73 mmol) was added, instantly generating a fine white precipitate. The slurry was stirred for 2 h. Precursor 1 b was then collected by filtration and washed with 2 Â 5 mL of hexane (yield: 1.39 g, 5.12 mmol, 91 %).

Key Words: Diborane(4) dianion, 1,2-bis(dimethylamino)-1,2-di-9-fluorenyl-/ Li, Na, K, Cs salts / Ca, Ba salts / Main group metallocenes / Hetero-ansa-bridged metallocenes 1,2-Bis(dimethylamino)-1,2-di-9-fluorenyldiborane(4) (1) is res can be described as main group metallocenes. The potasdoubly metallated with group 1 and 2 metals to yield metal sium derivatives form contact ion pairs, leading to polymeric 1,2-bis(dimethylamino)-1,2-di-9-fluorenyldiborate(4) 2-Li to chain-like structures. In contrast, 2-Li . 5 THF exhibits 2-Ba. 2 THF are determined by X-ray diffraction. All four structu-also monomeric, adapts a severely distorted geometry.Organolithium compounds and Grignard reagents are among the most frequently used and intensely studied compounds in organic and organometallic chemi~try [~,~]. Much less is known about the structures and chemistry of organometallic compounds of the heavier group 1 and 2 metals. Due to their extreme reactivity a detailed investigation of their structures and coordination chemistry has started only r e~e n t l y [~,~.~] .In the course of our investigations of diborane(4) derivatives, we studied the solution and solid-state structures of alkali and alkaline earth metal salts of difluorenyldiborane(4)[6,71 in order to obtain information about possible B-C-7c interaction. However, these compounds proved to be suitable starting materials for new heterocycles [*]. In this paper, we report on the synthesis, crystal structures and NMR-spectroscopic properties of metal 1,2-bis(dimethylamino)-1,2-di-9-fluorenyldiborate(4) compounds M, (fl)2B2-(NMe)2, where M is an alkali (x = 2) or an alkaline earth metal (x = 1, fl = 9-fluorenyl). We suggest to name this new class of compounds (2) hetero-ansa-bridged, since in contrast to most previously described organometallic compounds, the ansa-bridge is not a carbon chain but a diborane(4) moiety. After presentation of the crystal structures, the NMR data will be discussed in terms of probable structures in solution as well as of boron-carbon 7c bonding. To our knowledge, this paper is the first systematic study on ansa-bridged main group organometallic compounds. Formation and Characterization of Bis(dimethylamino)difluorenyldiborane(4) Anions 2The synthesis and spectroscopic properties of 1,2-bis(dialkylamino)-l,2-di-9-fluorenyldiborane(4) derivatives with dimethylamino (1) and pyrrolidinyl (1 a) groups attached to the boron atoms as well as the X-ray single crystal structure of l a have been described beforeL91. In a dianion of 1, the negative charge is delocalized not only on the fluorenyl rings, but also in a p orbital on the boron atom. Consequently, 1 can easily be deprotonated to yield compounds 2, which are the subject of this study.Deprotonation of 1 with alkali metal (M) amides in tetrahydrofuran (THF) yields pure 2-Li, 2-Na, and 2-K after removal of the solvent and washing of the residue with hexane. 2-Cs can more easily be prepared from 1 and Cs metal in hexane/THF. All these compounds were characterized by NMR spectroscopy (IH, 7Li, "...

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0 100 200 300 T IK1 -Fig. 3. A plot of pr,, versus temperature for 1. The curvature in this graph is due to the presence of zero-field splitting terms in the spin Hamiltonian.