Methylphenylphosphine borane

Phosphorylation of At2PH-BH3 with aryl halides proceeds under mild conditions using Pd-Cu catalyst and P-chiral phosphine-boranes of high enantiopurity are prepared by this method. As an effective ligand, MePPh2 is used with Pd(OAc)2. The phosphine-borane 50 was prepared in 68 % yield by phosphorylation of optically active (Sp)-methylphenylphosphine-borane (47) via 48 with the iodide 49 in the presence of the Pd(OAc)2-MePPh2 catalyst and Cul as a cocatalyst at 0°C for 3 days. The reaction proceeded with retention of stereochemistry and the asymmetrically substituted phosphine 51 with 99% ee was obtained [15]. 

Scheme 2.22 Preparation of optically pure methylphenylphosphine boranes and a diphosphine borane.

Compounds 32-35 reaet smoothly with MeLi to furnish the expected aryl-methylphenylphosphine boranes. In contrast, they are unreaetive towards t-BuLi. With i-PrLi, 32 and 33 give the expected substitution product whereas no reaction is observed for 35. For the 9-phenanthryl substituted derivative 34 an unexpeeted produet was formed (37 in Scheme 4.19). ... 

The same reaction was performed in the presence of a source of Pd and a bidentate phosphine in toluene at 50 °C. Methylphenylphosphine borane (41a) was reacted with 1-octyne in the presence of palladium acetate (5%) and dppp (10%) for 35 minutes. Interestingly, the Markovnikov product 43a is obtained in 85% yield, with no trace of 42, meaning that in this case the phosphorus attacks the internal carbon of 1-octyne. The same reaction using bdpp (2,4-dw(diphenylphosphino)pentane) and phenylacetylene (39, R = Ph) also yields regioisomer of 43 with 53% yield. Several experiments with diphenylphosphine borane under different reaction conditions (palladium source, temperature, alkyne) showed that the reaction does not occur in the absence of palladium (0) and that hydrophosphination of 1-ethynylcyclohexene (42) undergoes selective hydrophosphination at the triple bond, with the alkeneic bond untouched. 

A route to non-racemic P-stereogenic vinylphosphine-boranes, e.g., (100), is afforded by the addition of methylphenylphosphine-borane with alkynes in the presence of a chiral diphosphine-palladium catalyst. The ehiral diphosphine-platinum complex-catalysed addition of diethylphosphine to the diene cis,cis-muco-nitrile has given the new diphosphine (101) as a 3 2 mixture of diastereoisomers. Further work has been reported on the use of cyclopentadienyliron complexes that act as metal templates for the intramolecular hydrophosphination of coordinated vinylphosphines with 1,2-diphosphino-alkanes and -benzenes, leading to 1,4,7-triphosphacyclononanes, e.g., (102), capable of further elaboration to form new cyclic phosphines. 

The initially discovered ruthenium catalyst, [((i )-i-Pr-PHOX)2Ru(H)][BPh4], was found to be effective in the reaction of methylphenylphosphine with benzylic chlorides, providing the corresponding tertiary phosphine-borane products with high yields and moderate to high enantioselectivities, as shown in Scheme 2.44. 

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