Osmium complex boryl

Roper, however, succeeded in converting the osmium boryl complex [Cl2BOsCl(CO)(PPh3)2] (E) into the terminal borylene complex [Os (=BNHC9H6N)Cl2(CO)(PPh3)2]147 (26) upon reaction with 8-aminoquino-line according to Fig. 7. Compound 26 is noteworthy as it represents the first example of a base stabilized terminal borylene complex of the type [LXM = B(L)-R] (IVa, Fig. 1). 

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... 

Organoboron compound, geminal, 219 Organodiboron derivatives, 193 Organodielement halides, 79-83 Organoelement halides, 99 Os-Cl exchange, 186 Osmium boryl complexes, 179 Oxidation, ionic liquids, 278-279... 

B2(cal)2 adds readily to the ruthenium zero oxidation state compounds, Ru(CO)L(PPh3)3 (L = CO, CN-p-tolyl), to give six coordinate bis(boryl)-complexes in which both the two phosphine ligands, and the two boryl ligands, arc mutually cix (see Scheme 2).6 This reaction is not general since the corresponding osmium complexes do not react directly with B2(cat)2, however, bis(boryl)-osmium... 

Part of the intense interest in M-B compounds derives from the participation of these species in various catalytic processes.1,2 Scheme 6 depicts proposed catalytic cycles for metal-catalysed alkene hydroboration and alkyne diborylation. Key steps involve the insertion of unsaturated organic substrates into M-B bonds and a key intermediate involved in the formation of product is molecule A in which there are ad jacent M-C and M-B bonds. The ruthenium and osmium boryl complexes described in this section provide models for these steps and intermediates. 

A range of five- and six-coordinate osmium boryl complexes has been synthesized making use of similar approaches to those reported above for ruthenium. In particular, the reaction of phenylosmium(II) precursors with boranes, which proceed via elimination of benzene, has been shown to be a useful entry point into octahedral and square pyramidal osmium boryl complexes. Significant further chemistry has been reported on these systems, including substitution at both boron and metal centres, which has shed light on fundamental issues of structure/bonding and reactivity [12]. 

Scheme 11 The synthesis of five-coordinate osmium(II) boryl complexes 8.104-8.108...

Table 7 Selected spectroscopic and structural parameters for osmium boryl complexes... 

Scheme 12 Osmium boryl complexes generated from catecholboryl system 8.104...

Scheme 13 Generation of osmium boryl complexes from oxidative addition of B2cat2 and HBcat...

Scheme 15 Generation of bidentate osmium boryl complexes from reaction of 8.127 with diols...

A number of tethered osmium boryl complexes have been developed recently in which one of the boryl substituents features an additional pendant donor which coordinates to the metal centre as a tether . For systems resulting from reactions with bifunctional donors such as 2-aminopyridine two possibilities exist, depending on which donor atom interacts with the boron centre and which with the metal. Thus, tethered boryl complexes result from coordination of the anionic donor at boron, with the neutral donor tether coordinated at osmium the reverse coordination possibility leads to the formation of intramolecular base-stabilized borylene complexes. 

Scheme 16 Substitution at either osmium or boron centres in tethered boryl complex 8.134...

Iron, Ruthenium, and Osmium - In this section of work Fp = Fe(CO)2Cp - and Rp = Ru(CO)2Cp is used throughout. The inclusion compounds of aromatic ruthenium complexes, e.g. (Bn)Ru(Cp) PF in a-cyclodextrin has been investigated and die mentioned example has been crystallographically characterised. Two transition m boryl complexes, FpB(OCeH40) and FpBPh2 have been reported the reaction of the former complex with Et2NH results in the formation of FpH and die aminoborane. Gas phase and solution studies have been carried out on the first pentafluorocyclopentadienyl complex ICp Rufn-CsFs)]. The redox chemistry of this complex is not unusual in any way. ... 

Esteruelas MA, Fernandez I, L6pez AM, Mora M, Onate E. Preparation, structure, bonding, and preliminary reactivity of a six-coordinate d osmium-boryl complex. Organometallics. 2012 31 4646-4649. 

Scheme 8 Tethered osmium boryl and base-stabilized borylene complexes...

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