Amino boryl complexes

As already indicated, the chemistry of terminal borylene complexes is as yet almost unexplored. In addition to the photochemically induced borylene transfer, which was already discussed in Chapter 3.2, studies of the reactivity of terminal borylene complexes are restricted to two recent reports by Roper.147,148 The base-stabilized borylene complex [Os (=BNHC9H6N)Cl2(CO)(PPh3)2] (26) undergoes a reaction with ethanol to yield the ethoxy(amino)boryl complex [Os B(OEt)NHCgH6N Cl(CO) (PPh3)2] (35) according to Eq. (13) with a 1,2-shift of the quinoline nitrogen atom from the boron to the osmium center. The alcoholysis of 26 indicates that even the boron atom in base-stabilized borylene complexes displays some electrophilic character—a fact already predicted by a theoretical study.117... 

The reaction of 15 with 2-aminopyridine yields a mixture of the amino-(chloro)boryl complex 19a and the base-stabilized borylene complex 20a [40]. 20a reacts readily with ethanol, leading to the corresponding ethoxyborylene complex 20b, which was crystallographically characterized. 19a is stable in boiling ethanol but reacts, in the presence of Ag[SbF6] in undried thf, to the hydroxyboryl complex 19b (Scheme 8). The key structural parameters of 19b and 20b are very similar, which leads to the very important conclusion that there is only little difference in the nature of the Os-B bond in these types of base-stabilized borylene and boryl complexes. 

The stabilization derived from n interaction between the nitrogen and boron atoms in amino(halo)boryl complexes has made them amenable to the generation of cationic borylene systems via halide abstraction methodology [81,82,268]. The first such use of amino-containing compounds for this purpose was documented in 2004, the reaction of 8.26 with Na[BAr ] being shown to generate [Cp Fe(CO)2B(NMe2)] + [BAr ] . Because of the... 

Given the structural and reaction studies carried out on iron amino- and aryl(halo)boryl complexes, research effort has also been directed at analogous aryloxy(halo)boryl systems. The complexes ( 5-C5R5)Fe(CO)2B(OMes)X (R = H, X = Cl, 8.55 R = H, X = Br, 8.56 R = Me, X = Cl, 8.57) have been synthesized from the reaction of the corresponding haloborane with one equivalent of Na[( 5-C5R5)Fe(CO)2] (Fig. 22) [75]. Boryl complexes 8.55 and 8.57 both feature relatively short Fe-B distances [1.977(4) A for each] with the torsion angle (0) for 8.57 [87.6°] being consistent with the possibility for tc overlap between the boron-centred p orbital and the metal-based HOMO-2. 

Fig. 26 Ruthenium boryl and related complexes bearing amino substituents...

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