A highly efficient general synthesis of phosphine–borane complexes

McNulty, James; Zhou, Yuehui

doi:10.1016/j.tetlet.2003.10.145

Cited by 29 publications

(24 citation statements)

References 18 publications

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“…For the cyclohexyl (Cy) series (1,4,5,6; n = 0, 1, 2, 3 respectively; Figure 1) the equilibrium constants were also determined by 11 B{ 1 H} NMR analysis of the kinetics of the reverse reaction in which borane is transferred from the quinuclidine adduct 3 to the phosphine (Table 1). The effect of sequentially replacing the phenyl groups by cyclohexyl groups is a strong and progressive attenuation of both the rate (k) and favourability (K) of borane transfer from P-to-N.…”

Section: Effect Of Phosphine Substituentsmentioning

confidence: 99%

“…[5] However, the deprotection step can be more problematic, and a number of alternative strategies to achieve this have been reported. [6][7][8][9] Nonetheless, the most commonly applied procedure is still the use of an amine, [3,[10][11][12][13][14][15] which acts as a competing Lewis base to generate the free phosphine R 3 P, and the corresponding amine-borane (R 3 N·BH 3 ) species.…”

Section: Introductionmentioning

confidence: 99%

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Mechanism of Phosphine Borane Deprotection with Amines: The Effects of Phosphine, Solvent and Amine on Rate and Efficiency

Lloyd‐Jones

Taylor

2015

Chemistry A European J

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The kinetics of borane transfer from simple tertiary phosphine borane adducts to a wide range of amines have been determined. All data obtained, including second-order kinetics, lack of cross-over, and negative entropies of activation for reaction of triphenylphosphine borane with quinuclidine and triethylamine, are consistent with a direct (SN 2-like) transfer process, rather than a dissociative (SN 1-like) process. The identities of the amine, phosphine, and solvent all impact substantially on the rate (k) and equilibrium (K) of the transfer, which in some cases vary by many orders of magnitude. P-to-N transfer is more efficient with cyclic amines in apolar solvents due to reduced entropic costs and ground-state destabilisation. Taken as a whole, the data allow informed optimisation of the deprotection step from the stand-point of rate, or synthetic convenience. In all cases, both reactants should be present at high initial concentration to gain kinetic benefit from the bimolecularity of the process. Ultimately, the choice of amine is dictated by the identity of the phosphine borane complex. Aryl-rich phosphine boranes are sufficiently reactive to allow use of diethylamine or pyrrolidine as a volatile low polarity solvent and reactant, whereas more alkyl-rich phosphines benefit from the use of more reactive amines, such as 1,4-diaza[2.2.2]bicyclooctane (DABCO), in apolar solvents at higher temperatures.

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Section: Effect Of Phosphine Substituentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Mechanism of Phosphine Borane Deprotection with Amines: The Effects of Phosphine, Solvent and Amine on Rate and Efficiency

Lloyd‐Jones

Taylor

2015

Chemistry A European J

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“…2c,d,10 The phosphine boranes are also interesting in their 50 own right, with respect to both their metal complexation and polymer chemistry. 11,12 Herein, we report our discovery of an easy, convenient (one pot) and cheap method for the direct conversion, with or without stereocontrol, of phosphine oxide (or sulfide) to phosphine borane, by making use of readily available 55 laboratory reagents. We believe that this is the first report of direct oxide to borane conversion.…”

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confidence: 99%

Simple unprecedented conversion of phosphine oxides and sulfides to phosphine boranes using sodium borohydride

2012

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“…Two reviews of such complexes as sources for use of chiral phosphines have recently appeared [46][47]. While common commercially available complexes of borane (borane-THF; borane-dimethyl sulfide) may be used for the preparation of the phosphine complexes, sodium borohydride may also be used to generate high-purity materials in high yield [48], as shown in Scheme (4). Previously, sodium borohydride had been used in conjunction with lithium aluminum hydride and cerium trichloride for the reduction of tertiary phosphine oxides and the in situ formation of the borane complexes [49].…”

Section: Tricoordinated Phosphorusmentioning

confidence: 99%