THE INFLUENCE OF THE STERIC PROPERTIES OF THE LIGANDS PR2Ph AND L ON THE FORMATION AND PROPERTIES OF THE COMPLEXES Mo(η6-PhPR2)(L)(PPh2CH2CH2PPh2), R = Et, L = PPhEt2 and R = Ph, L = PPh3, PR'3, CO, CNR, N2, H2

Article abstract of DOI:10.1016/0022-328X(85)87215-6

The reduction of MoCl4(DPPE) (DPPE = PPh2CH2CH2PPH2) with Mg or Na/Hg in the presence of 2 PPhR2 under Ar results in the formation of the new complexes Mo(η⁶-PhPR2)(PPhR2)(DPPE) when R is Ph(Ia) or Et(II).No η⁶-PhPR2 complex is obtained when R is Me because this small ligand forms strong Mo-P ?-bonds; nor is one obtained for R = Cy because of too much steric crowding.The limits for η⁶-complexation can be quantified in terms of cone angle sums.Complex Ia is very similar to Mo(η⁶-PhPMePh)(PMePh2)3 (IIIa) in that both react at similar rates with a variety of small ligands L = PMePh2, PMe2Ph, PMe3, P(OMe)3, N2, CO, CNBu^t and H2 via dissocation of a labile ?-bonded ligand.Several other less crowded η⁶-arylphosphinemolybdenum complexes including II do not have labile ligands at 25 degC.The new complexes Mo(η⁶-PhPPh2)(L)(DPPE) have been characterized by 31P and 1H NMR, IR and gas uptake measurements.Ia has a higher affinity for H2 than IIIa possibly because Mo(η⁶-PhPPh2)(H)2(DPPE) adopts a non-fluxional trans-configuration.The 31P chemical shift of the η⁶-bonded ligand in 8 derivatives of Ia and 12 of IIIa correlate with the sum of cone angles of the three ?-bonded ligands in each complex.