Borane anions oxidation

Scheme 3.2-9. Synthesis of the simplest monocarba-closo-borane anion 15a starting from triborabicyclo[l. 1. OJbutane 13a, and the one-electron oxidation product of 15a.

Grimes153 have prepared 11-13 atom nido-cages by the insertion of transition metal atom moieties into carboranes. Recently, 13 and 15-vertex m rfo-carboranes have been prepared by Hosmane and Grimes1S4) by the oxidative fusion of carboranes and borane anions. 

These nucleophilic reagents react with most common electrophiles such as organohalides, tosylates, aldehydes, ketones, epoxides, and activated alkenes. It should be noted that many workers have found much higher yields if the phosphides are protected as phosphine oxide or borane anions (see Section 3). Phosphide reagents also react with activated arenes to give mixed aryl phosphines (Protocol 2). Metal phosphides therefore provide an alternative, complementary tertiary phosphine synthesis to the electrophilic routes outlined in Section 2.1. 

Other ligands have been synthesized more recently utilizing the same synthetic and theoretical philosophy.52,53 A chiral ditosylate or dimesylate is generally reacted with a metal phosphide to produce the diphosphine ligand. There have been problems with these displacement reactions with secondary ditosylates as has been discussed earlier. More recent procedures report success with phosphine oxide or borane anions. 

In the area of synthesis, the structural and theoretical framework contributed by Lipscomb provided a foundation for the monumental synthetic work of M. F. Hawthorne and his students, who transformed boron cluster chemistry first by their synthesis of the polyhedral borane anions BioHio and Bi2Hi2 (30) and later by the synthesis of metallacarboranes (31). In our own laboratory, considerations of charge distribution in borane anions (14) prompted us to explore reactions of transition metal ions with small borane and carborane anions (32). This, in turn, led to a number of advances including the first closed polyhedral metallaboranes (33), the discovery of metal-induced oxidative cage fusion (34), and the synthesis of B12H16, the only neutral Bi2 hydride, via metal-promoted fusion of BeHQ (35)... 

The oxidation of dimethylamine borane (DMAB), a reducing agent used in electroless plating baths [53], on gold is also assumed to involve the intervention of Au s as a mediator [54]. Similarly, the reduction of anionic oxidants such as the peroxide ion [55], HO2, may involve the intervention of Au as a reductant. Other electrocatalytic processes involving anionic species whose responses at gold in base commence and terminate at ca. 0.15 V [19] include polysulfide ion (S/ ) reduction and formaldehyde (which exists in base in anionic form, H2CO OH) oxidation. 

Neutral carboranes and boranes react with transition-metal complexes forming metallocarboranes or metalloboranes, respectively. However, most metallocarboranes and metalloboranes are prepared from transition-metal halides and anionic carborane and borane species ( 6.5.3.4) or by reacting metal atoms and neutral boranes and carboranes. These reactions are oxidative addition reactions ( 6.5.3.3). 

A radical initiator based on the oxidation adduct of an alkyl-9-BBN (47) has been utilized to produce poly(methylmethacrylate) (48) (Fig. 31) from methylmethacrylate monomer by a living anionic polymerization route that does not require the mediation of a metal catalyst. The relatively broad molecular weight distribution (PDI = (MJM ) 2.5) compared with those in living anionic polymerization cases was attributed to the slow initiation of the polymerization.69 A similar radical polymerization route aided by 47 was utilized in the synthesis of functionalized syndiotactic polystyrene (PS) polymers by the copolymerization of styrene.70 The borane groups in the functionalized syndiotactic polystyrenes were transformed into free-radical initiators for the in situ free-radical graft polymerization to prepare s-PS-g-PMMA graft copolymers. 

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