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.

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