Derivatives containing bridging hydride

Co-condensation of Re atoms, benzene, and alkane (RH) results in alkane activation. The products are dirhenium systems containing bridging hydride ligands and bridging CR R whose nature depends upon the alkane. The ) -ray crystal structure of the y-CHBu derivative confirms the structural assignments. 

The geometry of triosmium derivatives containing a single unsupported (equatorial) bridging hydride ligand thus appears to be self consistent and pre-... 

R CN (Table 2) [86]. The molecular structure of the 2,2-dimethylpropanonitrile derivative contains unsymmetrically bridging alkylidene amide ligands. Reaction of the yttrium and erbium hydride species with isonitrile results in the formation of a formidoyl moiety (Table 2) [87], Surprisingly the Ln-N interaction is in the range of the nitrile product A similar molecular structure was found in the oximato complex [Cp2Gd(/i-t/2-ONCMe2)]2 (Gd-Nav 2.42(1) A) [88]. 

Recently, we have shown that iminium ions can induce a hydride shift to form a new carbocation which then reads with a nucleophile. By this way the novel unusual bridged steroid alkaloids 25 were prepared from the secoestron derivative 19 (scheme 5) M Treatment of 20 obtained from 19 by hydrogenation with aniline or an aniline derivative 21 containing an dedron-withdrawing group in the presence of the Lewis add BF3-OEt2 leads to the iminium... 

Apart from the binary hydrides of Groups 16 and 17, Lowry/ Brpnsted acids in aqueous solution are nearly all oxoacids, i.e. substances containing O-H bonds which ionise in aqueous solution to give oxo-anions and H+(aq) (or H30+). Most oxoacids are molecular hydroxides E(OH) , such as B(OH)3, Ge(OH)4 and Te(OH)6, or oxohydroxides EOm(OH) . In addition, we have more complex species containing E-E bonds or E-O-E bridges. In EOm(OH) - for example, N02(0H), PO(OH)3, S02(0H)2,103(0H) - the m O atoms are held to E by bonds having at least some double bond character, via p -p or d -p overlap. Oxohydroxides may be seen as being derived from hydroxides by elimination of H20, and are favoured by elements E whose atoms form double bonds to O atoms. 

As a side product in these reactions a novel bridged steroid alkaloid 230 is formed, presumable by an intermediate hydride shift in 227 from the benzylic position to the iminium ion to give a secondary amine, which then attacks the formed cationic benzylic position. This reaction becomes the main reaction with aniline, p-bromoaniline or nitroaniline in the presence of BF3 -OEt2 if a derivative of 224 is used containing a propyl instead of a propenyl side chain [61]. 

Complex hydrides give a variety of interesting structures. For LiBH4 derivatives, a monomeric example crystallized from THF " shows three p B-H Li bridges and a very short B-Li distance of 2.19 A (cf. C-Li, 2.36 A in the analogous (/u-H)3C environment of solid (MeLi)co). However, when TMEDA is used as the donor in the parent borohydride, a dimeric complex (16) results, containing four p and two p B-H Li contacts. A tetrameric complex with p ... 

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