Boron halides metal complexes

A series of Rh and Ir complexes is also basic enough to add boron halides, although the metal-boron bonds are weak, e.g., dppe and PPh3-Rh complexes serve as electron-pair bases when they react with BF3 and BCI3 . Table 1 summarizes the results. 

N.m.r. studies are reported on the triethylphosphine and trisdi-methylaminophosphine complexes with boron halides, and triethylphos-phine complexes with aluminium chloride. A correlation of Sp with the number of phosphorus ligands in metal carbonyl complexes has led to a qualitative rationalization of 8p in terms of a- and 7r-bonding. ... 

The first borinate-transition metal complex to be prepared was actually the first known derivative of borin. Bis(cyclopentadienide)cobalt (94) reacts with organic halides and was analogously found to react with boron halides in a redox reaction to give (95), followed by an insertion to yield (cyclopentadienide)(borinato)cobalt (97) (72CB3413). The product composition depends on the ratio of reactants. Compound (97) is the main product (80% yield when R = Ph, X = Br) when the molar ratio between (94) and the boron halide is 2.5 1. A second and slower insertion occurs to give (28) when (97) is treated with another equivalent of the boron halide (Scheme 13). Compounds (28), (29) and (97) have one electron more than predicted by the 187r-electron rule for transition metal complexes. They are red in colour and, of course, paramagnetic. The mixed complexes (97) are thermally labile, in contrast to (28) and (29), which can be heated to 180 °C and sublimed at 90 °C. Their ionization potentials are low and the complexes are sensitive to air. 

Boroles are readily reduced to the respective dianions owing in part to the empty p orbital on the boron atom. The reduction of 6-(4-/i< t/-butylphenyl)-3-/i t/-butyl-5-(bis-2,6-(4-/< /r-butylphenyl)phenyl)dibenzoborole 37 with excess lithium powder in diethyl ether suspension at — 10°C led to deep red crystalline dianionic bis(diethylether)dilithium salt 38. An attempt to obtain transition metal complexes by metathesis reactions of transition metal halides SnCU,... 

In reactions with metal or metalloidal halides, primary amines, because of their difunctionality, tend to yield more complex molecules, such as cyclic, cage, or polymeric structures. For example, cage-type structures of the type P4(NCH3)e and As4(NCH3)e have been prepared by methylaminolysis of phosphorus(III) or arsenic(III) chloride, respectively, and cyclic structures of formula (HNBC1)3 or (RBNC1)4 have been prepared from boron halides and ammonium chloride or mono-alkylamines. 

The Suzuki-Miyaura cross-coupling reaction is a standard method for carbon-carbon bond formation between an aryl halide or triflate and a boronic acid derivative, catalyzed by a palladium-metal complex. As with the Mizoroki-Heck reaction, this cross-coupling reaction has been developed in ionic liquids in order to recycle and reuse the catalyst. In 2000, the first cross-coupling of a halide derivative with phenylboronic acid in [bmim] [BF4] was described. As expected, the reaction proceeded much faster with bromobenzene and iodobenzene, whereas almost no biphenyl 91 was obtained using the chloride derivative (Scheme 36). The ionic liquid allowed the reactivity to be increased, with a turnover number between 72 and 78. Furthermore, the catalyst could be reused repeatedly without loss of activity, even when the reaction was performed under air. Cross-coupling with chlorobenzene was later achieved - although with only a moderate yield (42%) - using ultrasound activation. 

In general, the simple metal hydrides are less reactive toward boron halides than the complex aluminum hydrides. Thus LiH gives very little, if any, diborane on direct interaction with, for example, BF3 or BBr3 at temperatures as high as 180 C (279). [It has recently been claimed that at still higher temperatures... 

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