Diphenylphosphine borane

Nucleophilic Attack at Other Atoms. - The chemistry of phosphine-borane adducts continues to develop. The diphenylphosphine-borane adduct has been employed in the synthesis of linear systems having a skeleton consisting of alternating phosphorus and boron atoms, e.g., (73). Unusual salt-like systems, e.g., (74), have been isolated from the reactions of trialkylphosphines with the dimethylsulphide adduct of dibromoborane. 

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. 

In 2002, Grubbs and co-workers reported the first CM reactions of allyl phosphines.In an initial reaction, subjecting allyl diphenylphosphine to catalyst 5 (5 mol%) failed to produce any of the desired cross-product. However, by protecting the phosphine as its borane complex, CM reactions could be achieved in good yield with high E-selectivity (Equation (5)). Notably, catalyst 5 failed to dimerize borane-protected vinyl diphenylphosphine. This result was attributed to substrate trapping of the catalyst as an unreactive Fischer carbene, a situation analogous to that observed in the CM reactions of alkyl vinyl ethers. 

Diamminedihydroboron(l-I-) tetrahydroborate, synthesis 2 Trimethylamine-borane, (dimethylamino)borane, and N,N, JV"-trimethylborazine, synthesis 3 Hydrazine-mono- and -bisborane, synthesis 4 Diphenylphosphine and dimeric (diphenylphosphino)boranes, S3mthesis 6... 

The addition of diphenylphosphine oxide to the triple bond of dimethyl acetylenedicarboxylate was performed under solvent-free and microwave-assisted conditions. Carbodiimides underwent hydrophos-phination with phosphine boranes to provide phosphaguanidines. A deboronation followed by oxidation gave the corresponding phosphine oxides. A representative reaction sequence is shown in Scheme 28. ... 

---