The influence of the steric properties of the ligands PR 2Ph and L on the formation and properties of the complexes Mo(η 6-PhPR 2)(L)(PPh 2CH 2CH 2PPh 2), R = Et, L = PPhEt 2 and R = Ph, L = PPh 3, PR′ 3, CO, CNR, N 2, H 2

Abstract

The reduction of MoCl 4(DPPE) (DPPE = PPh 2CH 2CH 2PPh 2) with Mg or Na/Hg in the presence of 2 PPhR 2 under Ar results in the formation of the new complexes Mo(η 6-PhPR 2)(PPhR 2)(DPPE) when R is Ph (Ia) or Et(II). No η 6-PhPR 2 complex is obtained when R is Me because this small ligand forms strong MoP σ-bonds; nor is one obtained for R = Cy because of too much steric crowding. The limits for η 6-complexation can be quantified in terms of cone angle sums. Complex Ia is very similar to Mo(η 6-PhPMePh)(PMePh 2) 3 (IIIa) in that both react at similar rates with a variety of small ligands L = PMePh 2, PMe 2Ph, PMe 3, P(OMe) 3, N 2, CO, CNBu t and H 2 via dissociation of a labile σ-bonded ligand. Several other less crowded η 6-arylphosphinemolybdenum complexes including II do not have labile ligands at 25°C. The new complexes Mo(η 6-PhPPh 2)(L)(DPPE) have been characterized by 31P and 1H NMR, IR and gas uptake measurements, Ia has a higher affinity for H 2 than IIIa possibly because Mo(η 6-PhPPh 2)(H) 2(DPPE) adopts a non-fluxional trans-configuration. The 31P chemical shift of the σ-bonded ligand in 8 derivatives of Ia and 12 of IIIa correlate with the sum of the cone angles of the three σ-bonded ligands in each complex.