Preparation of mer-[Mo(N2)3(PPrn2Ph)3] from trans-[Mo(N2)2(PPrn2Ph)4]; its X-ray crystal structure, spectroscopic properties, and protonation to give ammonia

Abstract

The compound trans-[Mo(N₂)₂(PPrⁿ₂Ph)₄](1), prepared by magnesium reduction of [MoCl₃(thf)₃](thf = tetrahydrofuran) or MoCl₅ in thf together with PPrⁿ₂Ph under N₂, reacts with N₂ in benzene or thf to give mer-[Mo(N₂)₃(PPrⁿ₂Ph)₃](2) in high yield. The mer configuration is confirmed by an X-ray crystal structure determination which shows the compound to have d(Mo–N)= 2.050(9), 1.984(9), and 2.01 5(8), d(N–N)= 1.092(10), 1.124(9), and 1.103(9)Å. The longest N–N and shortest Mo–N distances are for the unique N₂ ligand. Spectroscopic (i.r.; ³¹P, ¹⁵N, and ⁹⁵Mo n.m.r.) properties of the complexes are reported. Protonation of compounds (1) and (2) in methanol with H₂SO₄ gave ammonia [0.3 and 1.3 mol NH₃ per Mo atom for (1) and (2) respectively]. The occurrence of analogues of compound (2) with PEt₂Ph and PBu₃ is discussed.