31P shielding in phosphine derivatives of tricarbonyl-?5-cyclopentadienyl-manganese(I), [Mn(?5-C5H5)(CO)3]

The 31P NMR parameters ?(31P), nJ(31P31P), coordination shifts ?? and chelate-ring contributions ? are reported and discussed for various [Mn(Cp)(CO)3-n(PR3)n] complexes (Cp = ?5-C5H5; n = 1, 2), [Mn(Cp)(CO)2PP], [{Mn(Cp)(CO)2}2µ-PP] and [Mn(Cp)(CO)PP]. PR3 and PP are mono- and bidentate phosphines, respectively. ?? decreases, mainly as a consequence of decreasing MnP ? interaction, as the steric requirement of the phosphine increases; the shielding trends in the chelate structures reflect steric and torsional strains: ?? and ? decrease in the series Ph2P(CH2)nPPh2 (n = 2>3 ? 4 > 1), and in five-membered rings the ordering is cis-Ph2PCHCHPPh2 > Ph2P(CH2)2ER2 (ER2 = AsPh2, PEt2PPh2 ? o-C6H4PPh2(EPh2) (E = As, P) > Cy2P(CH2)2PCy2> (p0Tol)2P(CH2)2P(p-Tol)2. © 1985