Synthesis, crystal structure and nuclear magnetic resonance spectral study of the (+)-(R,R,R*,S*)- and (–)-(S,S,R*,S*)-enantiomers of the chiral diphosphine [C6H4(PPhCH2CHO)2CMe2]-1,2

Abstract

Treatment of the dilithiodiphosphide [Li(tmen)]₂[C₆H₄(PPh)₂-1,2](tmen =N,N,N′,N′-tetramethylethylenediamine) with (–)-(R,R)- or (+)-(S,S)-Me₂C(OCHCH₂OSO₂C₆H₄Me-p)₂ afforded the enantiomeric chiral diphosphine (+)-(R,R,R*,S*)- or (–)-(S,S,R*,S*)-[C₆H₄(PPhCH₂CHO)₂CMe₂]-1,2, respectively. Their crystal structures have been determined which show them to be isostructural; hence they are enantiomers rather than diastereoisomers. Thus the original chirality of Me₂C(OCHCH₂OSO₂C₆H₄Me-p)₂ induces a preferred chirality at the P atoms of the product diphosphines. A ¹H and ³¹P NMR spectral study of (+)-(R,R,R*,S*)-[C₆H₄(PPhCH₂CHO)₂CMe₂]-1,2 has been carried out, involving selective decoupling and nuclear Overhauser experiments, Karplus curves for both ³J_HH and ²J_PH couplings and ring current shielding effects. This allows assignments to be made of the ³¹P and non-aromatic ¹H signals, and demonstrates that the structure determined by X-ray crystallography in the solid state is not significantly changed in solution.