The synthesis of a novel framework cyanide with composition LiBC4N4 (1) is described. X-ray powder diffraction as well as 7Li, 11B, and 13C NMR of 1 reveal an ordered structure which consists of two interpenetrating diamond-like networks of BC4 and LiN4 tetrahedra linked by C−N bonds. The structure is simple cubic, symmetry P43̄m, a = 5476(3) Å. In solution the presence of the B(CN)4 anion has been established for the first time by spectroscopic methods. Molecular B(CN)3 is isolated for the first time as a Lewis acid−base complex with bases such as NMe3 and SiMe3CN, and a single-crystal X-ray structure of B(CN)3NMe3 (3) has been obtained. The novel solid-state cyanide BC3N3 (2) is prepared from the thermal elimination of NCSiMe3 from B(CN)3NCSiMe3 (4). In route to 4, compounds B(CN)2(SMe)NCSiMe3 (5) and B(CN)2(SMe)NMe3 (6) have also been isolated. A single-crystal X-ray structure of 6 reveals that the compound crystallizes in the monoclinic space group P21/n. The new crystalline solids 2 and 1 (isoelectronic to C) are promising precursors for high-pressure and high-temperature syntheses of novel phases with structures related to Si3N4, diamond, and graphite.

The compounds Cp*MH 3 (dppe) (M ) Mo, 1;W,2) are accessible in good yields from reacting the corresponding compound Cp*MCl 4 and LiAlH 4 in toluene/Et 2 O followed by methanolysis. The X-ray structure of 1 shows a pseudo-trigonal-prismatic geometry which is unprecedented for half-sandwich CpML 5 -type compounds. Protonation with HBF 4 ‚Et 2 OinEt 2 Oatlow temperature affords [Cp*MH 4 (dppe)] + BF 4 -salts (M ) Mo, 3;W,4). While 3 spontaneously decomposes, even at low temperatures, in coordinating solvents and CH 2 Cl 2 , 4 is stable at room temperature in MeCN. An X-ray structure of 4 is consistent with a classical tetrahydrido species with a distorted pseudo-pentagonal-bipyramidal structure. The low-temperature NMR properties, J HD e 1Hzfor 4-d 3 , and the T 1(min) value for the hydride resonance are also consistent with this structural assignment. Decomposition of 3 in MeCN at room temperature selectively affords [Cp*MoH 2 (MeCN)(dppe)] + BF 4 -, 5. The NMR properties of this complex indicate a fluxional structure with inequivalent H and P nuclei and are consistent with a pseudo-trigonal-prismatic structure analogous to that of the precursor 1. Further protonation of 5 in MeCN or direct protonation of 1 with excess acid in MeCN affords two isomers of complex [Cp*MoH(MeCN) 2 (dppe)](BF 4 ) 2 , 6 and 7. Thermal treatment in MeCN slowly converts 7 into 6 initially, but both isomers further transform into a third isomer, 8, upon prolonged heating. The structure of 6 has been elucidated by X-ray crystallography and consists of a highly distorted pseudo-octahedral geometry with relative trans MeCN ligands. The structures of 7 and 8 and mechanisms of the intercon-versions between the various isomeric structures are proposed on the basis of the solution NMR studies.

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