Borohydride complexes

An attempt to convert the organocalcium iodide [Cs(l,2,4-(SiMe3)3)H2]CaI(THF) to a hydride complex by reaction with NaBEt3H lead instead to the triethyl borohydride complex 167.392 Spectroscopic data indicate that the... 

Figure 86 The structure of the calcium triethyl borohydride complex 167. 

Studies on borohydride complexes of post-transition metals are as follows. Theoretical calculations on M(BH4) (M = Cu, Ag, Au) at the ab initio level indicate that Cu(i) and Ag(i) congeners have tetrahydridoborate structures, while the gold complex adopts a hydridoborane structure HAu(BH3).37 MeZn 2 /-BH4) 30 is prepared by addition of B2H6 to ZnMe2 or MeZnCl and Li[BH4]. The X-ray structure shows a polymeric helical arrangement of ZnMe + and [BH4]- fragments—similar to Be(BH4) or H2Ga(BH4) 50.38... 

Some examples of borohydride complexes of lanthanide and actinide metals are given in Table 2. 

Table 3 Borohydride complexes of main group elements...

Lippard, S.J., Ucko, D.A. 1968. Transition metal borohydride complexes. II. Th reaction of copper(I) compounds with boron hydride anions. Inorg Chem 7 1051-1058. 

Palard I, Soum A, Guillaume SM (2005) Rare earth metal tris(borohydride) complexes as initiators for e-caprolactone polymerization general features and IR investigations of the process. Macromolecules 36 54—60... 

Where X in M—H—X is a main group element, different behavior is observed. The case of carbon is particularly important,29 and here a weak or medium weak asymmetric stretch is observed at a frequency slightly lower than v(C—H) for the uncomplexed ligand. For example, v(MHC) as appears at 2510cm-1 for TaCp(C7/Me3)Cl.95 In metal borohydride complexes (X = B), the v(BHM)as vibrations are ca. 200 cm1 to lower wavenumber than the v(B—H) terminal vibrations.96... 

There are apparently no discrete TpxNi hydrides in the literature, nor any dihydrogen complexes. A single borohydride complex, Tp Ni(BH4) (92), has been obtained recently via ligand metathesis from Tp NiX (X = NO3, Cl).41 This complex was comprehensively characterized, and shown (crystallographically) to possess an octahedral nickel center, with facially tridentate Tp and BH4 ligands. In contrast to most nickel(II)... 

Divergent synthesis of POPAM dendrimers is based on the concept developed by Vogtle et al. in 1978 (see Section 1.1) [4]. Acrylonitrile is added to a primary mono- or oligo-diamine in a Michael reaction (Fig. 4.2). Suitable reducing agents are Co(II)-borohydride complexes or diisobutylaluminium hydride [5]. Subsequent iterative reaction cycles permit repeated addition of acrylonitrile followed by reduction until the limiting generation is reached. 

The boron atom dominates the reactivity of the boracyclic compounds because of its inherent Lewis acidity. Consequently, there have been very few reports on the reactivity of substituents attached to the ring carbon atoms in the five-membered boronated cyclic systems. Singaram and co-workers developed a novel catalyst 31 based on dicarboxylic acid derivative of 1,3,2-dioxaborolane for the asymmetric reduction of prochiral ketones 32. This catalyst reduces a wide variety of ketones enantioselectively in the presence of a co-reductant such as LiBH4. The mechanism involves the coordination of ketone 32 with the chiral boronate 31 and the conjugation of borohydride with carboxylic acid to furnish the chiral borohydride complex 34. Subsequent transfer of hydride from the least hindered face of the ketone yields the corresponding alcohol 35 in high ee (Scheme 3) <20060PD949>. 

Some examples of hydride and borohydride complexes of actinides are presented in Table 5.14. 

Hydrogenation of (Ej- and (Z)-Methyl-p-methylcinnamate with Rhodium (IIIj-Borohydride Complexes of Chiral Amides... 

Metathesis of the borohydride ligand for cyclopentadienyl in a reaction with KCp or diorganomagnesium compounds gives half sandwich borohydride complexes [Mg(THF)6][Cp Ln(BH4)3] (Cp =Cp, Cp C5H2Ph3, Ln — La, Nd) that are stable to redistribution. Combined with dia-lkylmagnesium, the Nd complexes provide useful catalysts for stereospecific isoprene polymerization.62... 

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