New Tertiary Phosphines from Cinnamaldehydes and Diphenylphosphine

A 1:1 hydrophosphination of the olefinic bond of cinnamaldehyde (and substituted ones) with Ph2PH, under argon
using neat reagents, gives quantitative formation of the new tertiary phosphines Ph2PCH(Ar)CH2CHO (2) as racemic
mixtures (Ar = Ph, p-tol, and p-OMe−C6H4). α-Methylcinnamaldehyde similarly affords Ph2PCH(Ph)CH(Me)CHO,
but as a mixture of diastereomers with predominantly S,S- and R,R-chirality [diastereomeric ratio (dr) ∼20]. In a
2:1 reaction of Ph2PH with cinnamaldehyde, hydrophosphination of both the CC and CO bonds takes place to
give the diphosphine derivative Ph2PCH(Ph)CH2CH(OH)PPh2 (3) as a diastereomeric mixture with dr ∼2.3. In
most organic solvents, the hydrophosphination of the CO group is reversible, leading to a dynamic equilibrium
between 3 and 2, but 3 is stable in coordinating solvents such as DMSO, DMF, and pyridine. X-ray analysis of a
P,P-chelated PdCl2(3) complex, formed from trans-PdCl2(PhCN)2 and 3 in MeOH, reveals that the S,S/R,R-enantiomers
are favored.