The basic strengths of some dinitrogen complexes of molybdenum(0), tungsten(0), rhenium(I), and osmium(II)

Abstract

The formation of adducts containing the grouping M–XY–AIR₃ by the reaction, in benzene solution, of the Lewis acids AlR₃(R = Me, Ph, or Cl) with the XY (XY = CO or N₂) ligand in a variety of molybdenum(0), tungsten(0), rhenium(I), and osmium(II) complexes, has been examined by i.r. and ¹H n.m.r. spectroscopy, and in some cases by the isolation of crystalline 1 : 1 adducts. The order of relative basic strengths thf >trans-[ReCl(N₂)(PMe₂Ph)₄] > trans-[Mo(N₂)₂(dpe)₂] > trans-[W(N₂)₂(dpe)₂] > trans-[ReCl(N₂)(PMe₂Ph)₂{P(OMe)₃}₂] > trans-[ReCl(CO)-(PMe₂Ph)₄] > Et₂O > mer-[OsCl₂(N₂)(PEt₂Ph)₃](thf = tetrahydrofuran, dpe = Ph₂PCH₂CH₂PPh₂) towards trimethylaluminium in benzene has been deduced from ¹H n.m.r. studies of the equilibrium between trimethylaluminium, the above compounds and diethyl ether. Comparison of the dipole moments of the pair of compounds trans-[ReCl(XY)(PMe₂Ph)₄](XY = N₂ or CO) shows that the dinitrogen ligand is only slightly more negatively charged than carbonyl.