Molybdenum (VI) Bis(imidoaryl) Complexes Containing the Bis (amonimethyl)aryl 'Pincer' Ligand

Abstract

The synthesis and characterization of new, five-coordinate molybdenum bis(imido) chloride complexes [MoCl(NCN)(N-t-Bu)2] (2) and [MoCl(2-C,N-NCN)(NAr)2] (3) and the methylated derivative [Mo(2-C,N-NCN)(Me)(NAr)2] (5) (NCN = [C6H3(CH2NMe2)2-2,6]-, Ar = C6H3-i-Pr2-2,6) are reported. Compounds 3 and 5 react with HCl to yield the corresponding air-stable salts [MoCl2{C6H3(CH2NMe2)-2-(CH2NHMe2)-6}(NAr)2] (4) and [MoCl{C6H3(CH2NMe2)-2-(CH2NHMe2)-6}(Me)(NAr)2] (6), respectively, of which 3-5 have been characterized by X-ray analysis. X-ray structure determination of 4 shows an additional chloride anion bonded to the molybdenum metal center while one of the ortho-(dimethylamino)methyl substituents of the NCN ligand has been selectively protonated. This proton is hydrogen bonded to one of the chloride ligands (N-H···Cl 166.2; H···Cl 1.94 Å). Because the spectroscopic data (NMR, IR) of 6 are very similar to those found for 4, complex 6 is believed to have structural characteristics (both in solution and in the solid state) similar to 4. The proton on the ortho-(dimethylamino)methyl group of the NCN ligand in 4 and 6 reacts immediately with an alkyl-Grignard or lithium reagents with formation of the corresponding alkane, the magnesium or lithium salt, and 3 and 5, respectively. Further reactions of 2, 4, and 6 with an excess of HCl, aimed at cleaving one of the imido groups, yielded unidentifiable reaction mixtures instead.