Sm(ii) reduction chemistry of heteroalkynes: stable adducts, reductive coupling, reductive C–C/C–N bond cleavage and trapping of the tert-butyl fragment with bulky nitriles, phosphaalkynes and isonitriles

Abstract

Reactions of a dimetallated N,N'-dimethyl substituted porphyrinogen Sm(II) complex with a series of t-butyl substituted heteroalkynes affords a diverse range of reactivity. The phosphaalkyne t-BuC[triple bond]P gives a dinuclear Sm(III) P-P reductively coupled complex of (t-BuC=PP=C-t-Bu)(2-) featuring a new mu-eta(2)(1,2-C,P) binding mode. In contrast, the nitrile aza analogue t-BuC[triple bond]N forms Sm(II) adducts that undergo reductive C-C bond cleavage at elevated temperatures to afford a trimeric Sm(III) cyanide (mu-C[triple bond]N(-)) complex. The isomeric isonitrile t-BuN[triple bond]C undergoes the related reductive C-N bond cleavage reactivity at milder temperatures, allowing the trapping of the tert-butyl fragment as a Sm(III) eta(2)-iminoacyl (t-BuC=N-t-Bu)(-) complex.

Magnesium(I) Dimers as Reagents for the Reductive Coupling of Isonitriles and Nitriles

“…The reduction of two equivalents of tBuN CD with 1 led to a very different result, namely reductive C À N bond cleavage and the moderate yield formation of the trimeric mag- www.chemeurj.org nesium cyanide complex, 5. It could not be determined what the fate of the cleaved tert-butyl group was in this reaction, but similar reductive N À C cleavages of tBuN C: initiated by Sm II complexes are thought to occur through one-electron processes, yielding the tert-butyl radical and trimeric samarium cyanide complexes, for example, [{L n Sm(CN)} 3 ] (L n = Cp* 2 A C H T U N G T R E N N U N G (tBuNC) [13] or the dianionic porphyrinogen ligand, [14] ). The formation of cyanides through the reduction of isonitriles has been previously achieved using a variety of other reagents, [13] though these reactions generally require harsh conditions to proceed.…”

Carbon–Nitrogen Bond Cleavage by a Thorium‐NHC‐bpy Complex

“…[7] To probe the effect of the unique electronic structure of 1 in single-and multi-electron transformations,weturned our attention to organic isocyanides.Ithas been shown that highly reducing metals (e.g.,S m II and alkali metals) promote CÀN bond cleavage in isocyanides,p resumably through oneelectron processes. [8][9][10] However, the very negative reduction potentials of the Th IV/III and Th III /Th II couples [11][12][13] often prohibit this type of reductive behavior by thorium compounds.T herefore,a ll previous reports discussing the interaction of isocyanides and thorium complexes have described conventional redox-innocent (2 e À donor or insertion) reac-tivity. [14,15] In this work, we utilize the redox non-innocence of 1 to expose an additional facet of thorium-bpy mediated reactivity and report the first examples of reductive R À NC bond cleavage by athorium complex.…”

“…[15,20] Although this work is the first example of thorium-mediated reductive cleavage of an R À NC bond, the bond activation by 1 advances that seen previously in transition metals and lanthanides. [8,9,21,22] Evans [9] and Schulten [10] introduced Sm II -mediated RÀNC bond cleavage and concluded that single-electron chemistry was probable in the formation of Sm À (CN) derivatives.O ur system goes beyond that, demonstrating that the open-shell singlet (f 1 p* 1 )e lectronic structure of 1 promotes clean RÀNC bond scission chemistry and furnishes av ery well-defined product in which both fragments of the cleaved isocyanide are retained.…”

Recent Advances in Rare‐Earth Polypnictides

“…The solid‐state structure of this complex, as determined by single crystal X‐ray diffraction study, features Sm—C/P short contacts in a μ‐ŋ 2 (1,3‐C, P) fashion and trans ‐geometry (for C=P bonds) of the dianionic bridging ligand. Conversely, when a substituted porphyrinogen was used instead of Cp* as the supporting ligand, a drastically different structural outcome was achieved: the dimerized ( t ‐BuC=P–P=C–t‐Bu) 2– bridging ligand was coordinated in a μ‐ŋ 2 (1,2‐C, P) fashion and in a cis ‐geometry (for C=P bonds) to the Sm(III) cations (Figure B) . This divergent reaction outcome is postulated to be in response to the relief of steric interactions from the porphyrinogen ligand, which has larger steric factors compared to Cp*.…”

“…Although rare earth polyphosphide/polyarsenide complexes were usually obtained using reductive methods by reacting t ‐BuC≡P or P 4 /As 4 or Cp*Fe(ŋ 5 ‐P 5 )/Cp*Fe(ŋ 5 ‐As 5 ) with divalent rare earth precursors, analogous precursors with heavier pentel elements, namely antimony and bismuth, have been found unreactive under the same reaction conditions. Hence, a number of alternative synthetic methods have been developed toward molecular polystibides/polybismuthides of the rare earth elements.…”