Structural elucidation of tungsten compounds containing arylamine, piperazine and morpholine fragments of pyrrole and keto-amine ligands

Abstract

Various imido tungsten derivatives incorporating bidentate pyrrole–piperazine, pyrrole–morpholine, pyrrole–imine and keto-amine precursors were synthesized. Reacting W(NtBu)2(NHtBu)2 with one equivalent of the pyrrole–phenylpiperazine ligand {C4H3NH-[2-CH2N(CH2CH2)2NPh]} in toluene generated [W(NtBu)2(NHtBu){C4H3N-[2-CH2N(CH2CH2)2NPh]}] (1). Similarly, addition of W(NtBu)2(NHtBu)2 to one equivalent of the pyrrole–morpholine ligand {C4H3NH-[2-CH2N(CH2CH2)2O]} in toluene afforded [W(NtBu)2(NHtBu){C4H3N-[2-CH2N(CH2CH2)2O]}] (2), which was converted to [W(NtBu)2{C4H3N-[2-CH2N(CH2CH2)2O]}]2(μ2-O) (3) in moisture. Reacting the pyrrole–imine ligand {C4H3NH-[2-CHN(C6H3-2,6-iPr2)]} with one equivalent of W(NtBu)2(NHtBu)2 in toluene gave [W(NtBu)2(NHtBu){C4H3N-[2-CHN(C6H3-2,6-iPr2)]}] (4), which was transformed to [W(NtBu)(NHtBu){C4H3N-[2-CHN(C6H3-2,6-iPr2)]}(μ-O)]2 (5) upon absorbing moisture. Furthermore, when one equivalent of {C4H3NH-[2-CHNC2H4N(C2H4)2O]} reacted with W(NtBu)2(NHtBu)2 in toluene, {W(NtBu)2{C4H3N-[2-CHNC2H4N(C2H4)2O]}2} (6) was isolated. The tungsten keto-amine compounds {W(NtBu)2[OCMeCHCMeN(C6H3-2,6-iPr2)]2} (7) and {W(NtBu)2[OCMeCHCMeNCH2CH2N(CH2CH2)2O]2} (8) were obtained by the reaction between W(NtBu)2(NHtBu)2 and two equivalents of the corresponding keto-amine ligands in toluene. All the tungsten derivatives were characterized by 1H and 13C NMR spectroscopy. Single crystal X-ray diffraction analysis revealed that in compounds, 1, 3, 5, 6 and 7, the central W atom belonged to either a distorted trigonal bipyramidal or an octahedral geometrical arrangement. Overall, the influence of the substituted pyrrole and keto-amine bidentate precursors on the imido tungsten derivatives were explored and structurally constructed.