Isomers in fac-[ReBr(CO)3( Lc)2](Lc=cis-3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole) arising from chirality of phosphorus ligands: separation and X-ray structural studies

Abstract

Reaction of cis-[ReBr(CO)₄( L_c)] with chiral L_c(cis-3,4-dihydro-2,3,4,5-tetraphenyl-2H-1,2,3-diazaphosphole) afforded fac-[ReBr(CO)₃(L_c)₂] which, owing to the racemic nature of L_c(R,S-L), should be a mixture of three predictable diastereoisomers: fac-[ReBr(CO)₃(R-L)(S-L)][meso-(A) or meso-(B)] and the enantiomeric pair fac-[ ReBr(CO)₃(R,S-L)₂]. Two of these forms, meso-(A) and the enantiomeric pair, have been separated by column chromatography and their nature unambiguously attributed by X-ray studies. fac-[ReBr(CO)₃(R-L)(S-L)] crystallizes in the monoclinic space group P2₁/n, with a= 19.481(4), b= 13.204(3), c= 20.083(8)Å, β= 110.56(3)°, and Z= 4; R′= 0.046. fac-[ReBr(CO)₃(R,S-L)₂]·C₆H₁₄·C₇H₁₆ crystallizes in the monoclinic space group P2₁/n, with a= 12.191(3), b= 20.939(4), c= 21.713(5)Å, β= 93.93(3)°, and Z= 4; R′= 0.048. Attempts to separate or detect spectroscopically isomers of fac-[ReBr( CO)₃( L)₂](L = racemic PMeEtPh) failed, indicating that interligand interactions are the determining factors in achieving the separation.