113587-85-2Relevant academic research and scientific papers
Stereoselective syntheses of coordinated secondary and tertiary phosphines. Crystal and molecular structure of [(R*,R*),(R*)]-(±)-[(η5-C 5H5){1,2-C6H4(PMePh) 2}Fe-(PHMePh)]PF6·0.5CH2Cl2
Crisp, Geoffrey T.,Salem, Geoffrey,Wild, S. Bruce,Stephens, Frederick S.
, p. 2360 - 2367 (2008/10/08)
Reaction of (R*,R*)-(±)-[(η5-C5H 5){1,2-C6H4(PMePh)2}Fe(PH 2Ph)]PF6 with methyl or ethyl iodide in the presence of triethylamine at 20°C produces separable mixtures of the corresponding alkyl derivatives [(R*,R*),(R*)]-(±)- and [(R*,R*),(S*)]-(±)-[(η5-C 5H5){1,2-C6H4(PMePh) 2}Fe(PHRPh)]PF6 (R = Me or Et) with ca. 3.5:1 diastereoselectivity in favor of the [(R*,R*),(R*)] diastereomer in each case. Major diastereomer [(R*,R*),(R*)]-(±)-[(η5-C 5H5){1,2-C6H4(PMePh) 2}Fe(PHMePh)]PF6·0.5CH2Cl2 crystallizes in the monoclinic space group P21/n (nonstandard No. 14) with a = 11.013 (9) A?, b = 26.143 (14) A?, c = 11.551 (4) A?, β = 90.65 (5)°, V = 3325.5 A?3, dcalcd = 1.51 g cm-3, Z = 4, and R = 0.051 (Rw = 0.046) for 2768 data having [I > 3σ(I)]. The secondary phosphido-iron complex (R*,R*)-(±)-[(η5-C5H 5){1,2-C6H4(PMePh) 2}FePHPh]·thf was isolated by deprotonation of the primary phosphine compound with KOBu-t in tetrahydrofuran; variable-temperature 1H NMR spectra of this complex in [2H8]tetrahydrofuran gave ΔG? (253 K) = 60 ± 4 kJ mol-1 for the inversion barrier of the pyramidal phenylphosphido-iron phosphorus stereocenter in the molecule with the diastereomer ratio [(R*,R*),(R*)]:[(R*,R*),(S*)] = 4.5:1 at the slow-exchange limit (-65°C). Alkylations of the secondary phenylphosphido-iron intermediate at -65°C give secondary phosphine complexes with diastereoselectivities corresponding to the concentrations of secondary phosphido-iron diastereomers at equilibrium (4,5:1). At -95°C, however, deprotonation of the secondary phosphine complex [(R*,R*),(R*)]-(±)-[(η5-C 5H5){1,2-C6H4(PMePh) 2}Fe(PHMePh)]PF6·0.5CH2Cl2 is stereospecific giving the tertiary phosphido-iron complex [(R*,R*),(R*)]-(±)-[(η5-C 5H5){1,2-C6H4-(PMePh) 2}FePMePh] with complete stereoselectivity, as demonstrated by the quantitative recovery of the diastereomerically pure starting material following acidification of the reaction mixture at this temperature. Alkylations of the tertiary phosphido-iron complex, generated and maintained at -95°C, also proceed with retention of configuration and complete stereoselectivity; reactions above this temperature give mixtures of thermodynamic products because of the relatively low barrier to inversion of the pyramidal phosphorus stereocenter in the intermediate tertiary phosphido-iron complex (ΔG? (278 K) = 59 ± 2 kJ mol-1). The corresponding optically active complexes of (±)-methylphenylphosphine have also been prepared, the first examples of complexes containing resolved secondary phosphines.
