Borane groups

The borane group of MiniPHOS was removed using the same protocol (Scheme 21). In contrast, however, reaction of free diphosphines 13 with [Rh(nbd)2]+X (X=Bp4, PFg) afforded in all cases, and independently of the reaction conditions, bischelate complexes 106. James and Mahajan demonstrated... 

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. 

The development of polypyrroles bearing supported diphosphine ligands protected from oxidation by borane groups has been reported.86 The polymer was produced by the electropolymerization of l-(7V-but-4-yl-pyrrol)-l,2-bis(diphenylphosphinoborane) (62) (Fig. 40). These preformed polymeric films lend themselves to the incorporation... 

Equation 1 illustrates a synthetic scheme which we have used in the preparation of polyolefin graft copolymers. Borane group containing polyolefin copolymers (I) were obtained by direct copolymerization [9,10] of a-olefin/borane containing a-olefin and a... 

Controlled radical polymerization (CRP) is an attractive tool, because of the resultant controllability of polymerization, and because of it being a versatile method to synthesize of well-defined polymer hybrids. The three main radical polymerization techniques, ATRP, NMP, and RAFT polymerization, have thus been employed. Other techniques, such as the oxidation of borane groups, have also been studied. In general, using CRP techniques, block copolymers can be synthesized from terminally functionalized PO as PO macroinitiator, and block copolymers can be prepared from functionalized PO produced by the copolymerization of olefins with functional monomers. 

The use of borane-containing monomers clearly presents an effective and general approach in the functionalisation of polyolefins, which has the following advantages stability of the borane moiety to coordination catalysts, solubility of borane compounds in hydrocarbon solvents (such as hexane and toluene) used as the polymerisation medium, and versatility of borane groups, which can be transformed to a remarkable variety of functionalities as well as to free radicals for graft-form polymerisations. The functionalised polymers are very effective interfacial modifiers in improving the adhesion between polyolefin and substrates and the compatibility in polyolefin blends and composites [518],... 

Attack of diborane occurs at the jS-carbon atom with the exception of enamines of acetaldehyde for which a-borane product is formed. When isomerism is possible, as in the case of a 2-methylcyclohexanone enamine, the less substituted isomer is the more reactive form, for steric reasons. Proto nolysis with propionic acid in diglyme afforded alkenes, as a consequence of a trans elimination of the base and the borane group . 

On the basis of known behavior most boron hydride reactions may be assigned to two main classes. The first class involves removal of a borane group from a boron hydride structure, while the second class involves nonsymmetrical cleavage of the hydrogen bridge bonds in a borane.2... 

Removal of a borane group often occurs when a borane is treated with a nucleophilic reagent. The initial product of this type of reaction is an adduct of the borane group, but the nature of the donor part of the adduct controls the subsequent fate of the whole. For all such compounds there is a tendency, varying from complex to complex, to dissociate reversibly into donor and acceptor parts. Thus whereas (CH3)2S BH3 (49) is appreciably dissociated in the gas phase at 50°, the compound (CH3)3P BH3 (48) may be heated to 200° without appearance of significant amounts of borane decomposition products. 

Besides removal of borane groups and unsymmetrical bridge-bond cleavage, other types of boron hydride reaction are known but at present appear to be much less common 2 for example, loss of protons, as in the ionization of BioHm in dioxane-water or ethanol-water solutions (61, 62),... 

Aminoboranes undergo an interesting reaction when heated with di-borane a borane group is absorbed and aminodiboranes are formed (35, 36). The structure of 7V,jV-dimethylaminodiborane has been determined by electron diffraction (70) it (I) is related to the structure of diborane and to the probable structure of dimeric iV,iV-dimethylaminoborane (II).3 It is likely that all aminodiboranes have similar structures. The first member of the group, H2NB2H5, may be prepared by passing diborane over its... 

The compound borane-carbonyl occupies a special position in any discussion of molecules derived from boron hydrides with boron-carbon bonds. Carbon monoxide reacts with diborane (20 atm/room temperature) to give an adduct of the borane group which does not rearrange or lose hydrogen (39) The adduct OC BH3 does, however, dissociate into carbon monoxide and diborane at ordinary temperatures. No carbonyls of other Group III acceptor molecules have been prepared so far 133), and it has been suggested 27, 58) that borane-carbonyl owes its existence to the ability of the hydrogen atoms of borane to transfer electrons to a vacant p,-orbital in carbon monoxide. 

This paper reviews the chemistry of metalloborane derivatives that contain borane or heteroatom borane groups which function as monohapto ligands. These compounds can be divided into three classes according to the number of electrons formally donated by the borane ligand to the metal. The electron pair acceptor class, represented by the compound Na[(OC)5Mn BHg], has received little attention thus far. The one-electron donor class, exemplified by the complex, l,2-(CH3)2-3- (C5H5)Fe(CO)2]-BioC2Ho, has a rich chemistry of metal-carbon and metal-boron derivatives. The third class includes two-electron donor derivatives that are represented by the compound (CHs)f,N[7,8-BoHioCHP - CrfCO),]. 

It is now apparent that there are as many diverse structural types in this area as there are in the more established field of organo-transition metal chemistry. There are now many known examples where the borane or hetroatom borane moiety functions as a mono-, di-, tri-, tetra- or penta-hapto ligand. This paper is limited to borane and heteroatom borane groups which function as monohapto ligands. 

The third group also includes unsaturated boranes, which have the advantage of (i) the stability of borane groups towards tungsten catalysts (ii) the stability of borane monomers and polymers in hydrocarbon solvents and (iii) the versatility of borane groups, which can be transformed to a variety of functionalities under mild reaction conditions (Chung 1992a). 

Aminoboranes and Other Compounds containing B—N Bonds.— H n.m.r. measurements (120—350 K) for MesNBHa have been used to elucidate molecular motions in the adduct. Minima in Tj found at 157 and 259 K could be attributed to three-fold reorientation of each of the three Me groups and the borane group, and to three-fold reorientation of the whole molecule about the B—N axis, respectively. ... 

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