Reactions of organic isocyanates and tert-butyl isocyanide with manganese(II) alkyls and trimesitylchromium

Abstract

The dialkylmanganese compounds [Mn(CH₂Bu^t)₂]₄ and [Mn(CH₂CMe₂Ph)₂]₂ react with organic isocyanates to give chelating amido products that can be verified by hydrolysis to the amides. For Me₃SiNCO the products of reaction with [Mn(CH₂Bu^t)₂]₄ with 2 and 4 equivalents have been shown by X-ray crystallography to be, respectively, Mn₃(CH₂Bu^t)₂[µ-OC(CH₂Bu^t)N(SiMe₃)]₂(µ-CH₂Bu^t)₂ and Mn₄(CH₂Bu^t)₂(µ₃-NCO)₂[µ-OC(CH₂Bu^t)N(SiMe₃)]₄. In the triangular, and quite unsymmetrical, trinuclear species each manganese has a distorted four-co-ordinate geometry. Two manganese atoms are chelated by the amide ligands (Mn–O 2.208, 2.276 Å; Mn–N 2.149, 2.184 Å) the oxygen of which then bridge to a neighbouring metal atom. Two of the manganese atoms carry one terminal alkyl (Mn–C 2.122 and 2.154 Å) and one edge of the Mn₃ triangle is bridged by one symmetrical (Mn–C 2.309 and 2.311 Å) and one unsymmetrical (Mn–C 2.184 and 2.646 Å) bridging alkyl. The tetranuclear species is centrosymmetric. One of the unique Mn atoms carries a terminal alkyl (Mn–C 2.092 Å) and is further co-ordinated by two bridging amide oxygens (Mn–O 2.070 and 2.073 Å) and one triply bridging cyanate nitrogen (Mn–N 2.282 Å). The other independent manganese is chelated by two amides with Mn–O 2.308 and 2.359 Å, Mn–N 2.146 and 2.176 Å, and its six-co-ordination is completed by bonds to both triply bridging cyanate groups with Mn–N 2.298 and 2.138 Å. The reaction of Cr(mes)₃(thf)(mes = 2,4,6-Me₃C₆H₂, thf = tetrahydrofuran) with BuNCO gives Cr[OC(mes)NBu^t]₃. Similar interactions using Bu^tNC lead to Mn[Bu^tCH₂CNBu^t]₂(PMe₃) and Cr[(mes)CNBu^t]₃.