Coordinated 2-halo-1,3,2-dioxaphosphorinane ligands. III. cis-Mo(CO)4{REP(OCH2CMe2CH2O)}2 (E O, S, NH; R alkyl, aryl or ER Cl, Br) complexes: syntheses, spectroscopic studies and the molecular structures of the cis-Mo(CO)4{iPrEP(OCH2CMe2CH2O)}2 (E O, NH) complexes

Academic Article

Abstract

  • A study of the reactions of cis-Mo(CO)4{XP(OCH2CMe2CH2O)}2 (X Cl, Br) complexes with a variety of nucleophiles of the type HER (E NH, O, S; R H, alkyl, aryl) is reported. The 13C, 31P and 95Mo NMR and IR data for the cis-Mo(CO)4{REP(OCH2CMe2CH2O)}2 complexes are presented and compared to those previously reported for some Mo(CO)5{REP(OCH2CMe2CH2O)} and cis-Mo(CO)4(Ph2PER)2 complexes. This comparison demonstrates that the effects of variations in the RE substituents in these complexes are similar to those previously observed for the Mo(CO)5{REP(OCH2CMe2CH2O)} complexes. The X-ray crystal structures of cis-Mo(CO)4{iPrOP(OCH2CMe2CH2O)}2 (triclinic space group P1; a = 8.818(3), b = 8.899(1), c = 18.847(2) A; α = 93.35(1), β = 89.46(2), λ = 115.31(1)°; V = 1334.6(4) Å3; Z = 2) and cis-Mo(CO)4{iPrNHP(OCH2CMe2CH2O)}2 (monoclinic space group C2/c; a = 18.30(1), b = 10.72(2), c = 16.87(1) Å; β = 119.82(5)°; V = 2871(4) Å3; Z = 4) have also been determined. In these complexes, the OiPr group is in an axial position, but the NHiPr group is in an equatorial position. The rates of halide substitution by N-, O- and S-nucleophiles in the cis-Mo(CO)4{XP(OCH2CMe2CH2O)}2 (X Cl, Br) complexes are significantly lower than in the Mo(CO)5{XP(OCH2CMe2CH2O)} complexes. This appears to be due to the increased steric congestion in the cis complexes and supports our hypothesis that the steric effects are the primary reason for the low rates of nucleophilic displacement of halides in 1,3,2-dioxaphosphorinane complexes. The correlations between chemical shifts of similar NMR resonances of the cis-Mo(CO)4{REP(OCH2CMe2CH2O)}2 and Mo(CO)5{REP(OCH2CMe2CH2O)} (E NH, O, S; R alkyl, aryl, silyl or ER Cl, Br) complexes as the RE groups are varied are good. In contrast, correlations between chemical shifts of similar NMR resonances of the cis-Mo(CO)4{REP(OCH2CMe2CH2O)}2 and cis-Mo(CO)4(Ph2PER)2 complexes as the RE groups are varied are poor. These results indicate that the effects of the variations in RE groups on the steric and electronic properties of REP(OCH2CMe2CH2O) and Ph2PER ligands are quite different. The isoelectronic cis-Mo(CO)4{iPrEP(OCH2CMe2CH2O)}2 (E NH (VII), O (IV)) complexes have different molecular structures. The i-propylamino group in VII is equatorial but the i-propoxy group in IV is axial. Studies of related systems provide no explanation for this behavior; however, it would seem to be electronic, rather than steric in origin because the i-propylamino and i-propoxy groups, with the exception of the sterically insignificant amine hydrogen, are the same size. © 1992.
  • Authors

    Published In

    Digital Object Identifier (doi)

    Author List

  • Gray GM; Watt W
  • Start Page

  • 181
  • End Page

  • 199
  • Volume

  • 434
  • Issue

  • 2