Migratory insertion of isocyanide into a ketenyl–tungsten bond as key step in cyclization reactions. Issue 1 (6th December 2021)

• Record Type: Journal Article
• Authors: Timmermann, Christopher; Thiem, Paula; Wanitschke, Dominik; Hüttenschmidt, Mareike; Romischke, Johanna; Villinger, Alexander; Seidel, Wolfram W.
• Is Part Of: Chemical science. Volume 13:Issue 1(2022)
• Page Start: 123
• Page End: 132
• Publication Date: 2021-12-06
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc06149f
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The prototype ketenyl ligand is bound end-on despite a formal 16 valence electron count at the metal. This situation opens a reaction pathway for a multicomponent cyclization centred on the migration of the ketenyl ligand. Abstract : Treatment of the side-on tungsten alkyne complex of ethinylethyl ether [Tp*W(CO)2 (η 2 - C, C ′-HCCOCH2 CH3 )] + {Tp* = hydridotris(3, 4, 5-trimethylpyrazolyl)borate} (2a ) with n -Bu4 NI afforded the end-on ketenyl complex [Tp*W(CO)2 (κ 1 -HCCO)] (4a ). This formal 16 ve complex bearing the prototype of a ketenyl ligand is surprisingly stable and converts only under activation by UV light or heat to form a dinuclear complex [Tp*2 W2 (CO)4 (μ-CCH2 )] (6 ). The ketenyl ligand in complex 4a underwent a metal template controlled cyclization reaction upon addition of isocyanides. The oxametallacycles [Tp*W(CO)2 {κ 2 - C, O -C(NHXy)C(H)C(Nu)O}] {Nu = OMe (7 ), OEt (8 ), N(i-Pr)2 (9 ), OH (10 ), O1/2 (11 )} were formed by coordination of Xy-NC (Xy = 2, 6-dimethylphenyl) at 4a and subsequent migratory insertion (MI) into the W-ketenyl bond. The resulting intermediate is susceptible to addition reactions with protic nucleophiles. Compounds 2a -PF6, 4a /b, and 7–11 were fully characterized including XRD analysis. The cyclization mechanism has been confirmed both experimentally and by DFT calculations. In cyclic voltammetry, complexes 7–9 are characterized by a reversible W(ii )/W(iii ) redox process. The dinuclear complex 11 however shows two separated redox events. Based on cyclic voltammetry measurements with different conducting electrolytes and IR spectroelectrochemical (SEC) measurements the W(ii )/W(iii ) mixed valent complex 11 + is assigned to class II in terms of the Robin-Day classification.