While cobalt complexes have already shown their potential for CÀ H and CÀ F bond activation of fluoroarenes, their reactivity as metalating agents via CoÀ H exchange towards these substrates has not been explored. Herein, we report a Co(HMDS) 2 [HMDS = N(SiMe 3 ) 2 ] system which, when synergistically enhanced via sodium amide Na(HMDS) mediation, can render chemo-and regioselective cobaltation of a series of fluoroarenes to produce a new class of homoleptic square planar [Na 2 CoAr 4 ] complexes. Density functional theory calculations elucidate the key roles of the Na/Co counterparts in a stepwise sodiation/cobalt transmetalation process, leading to this novel CÀ H metalation. Depending on the reaction stoichiometry, this process can occur inter-or intramolecularly, furnishing transient [NaCo(HMDS) 2 Ar] intermediates which can undergo ligand rearrangement to afford [Na 2 CoAr 4 ] with concomitant formation of Co(HMDS) 2 and [NaCo-(HMDS) 3 ].

Recent advances in cooperative chemistry have shown the enormous potential of main group heterobimetallic complexes for the functionalisation of aromatic molecules. Going beyond main group metal chemistry, here we provide an overview on the synthesis, structure and reactivity of bimetallic complexes which combine an alkali-metal (AM= Li, Na) with a divalent earth-abundant transition metal (M= Mn, Fe, Co, Ni), containing the utility silyl amide HMDS (HMDS = N(SiMe3)2). Advancing the understanding on how cooperative effects operate in these bimetallic (ate) systems, selected examples of their applications in deprotonative metalation are also discussed with special emphasis on the constitution of the metalated intermediates.

Heterobimetallic base NaCo(HMDS)3 [HMDS = N(SiMe3)2] enables regioselective di-cobaltation of activated polyfluoroarenes under mild reaction conditions. For 1,3,5-C6H2X3 (X= Cl, F), NaCo(HMDS)3 in excess at 80oC impressively induces the collective...

While cobalt complexes have already shown their potential for C−H and C−F bond activation of fluoroarenes, their reactivity as metalating agents via Co−H exchange towards these substrates has not been explored. Herein, we report a Co(HMDS)2 [HMDS=N(SiMe3)2] system which, when synergistically enhanced via sodium amide Na(HMDS) mediation, can render chemo‐ and regioselective cobaltation of a series of fluoroarenes to produce a new class of homoleptic square planar [Na2CoAr4] complexes. Density functional theory calculations elucidate the key roles of the Na/Co counterparts in a stepwise sodiation/cobalt transmetalation process, leading to this novel C−H metalation. Depending on the reaction stoichiometry, this process can occur inter‐ or intramolecularly, furnishing transient [NaCo(HMDS)2Ar] intermediates which can undergo ligand rearrangement to afford [Na2CoAr4] with concomitant formation of Co(HMDS)2 and [NaCo(HMDS)3].

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The sodium‐mediated cobaltation of pentafluorobenzene using the bimetallic base [NaCo(HMDS)3] (HMDS= N(SiMe3)2) has been reported to afford a novel tetraaryl Co(II) square planar complex. Yet, the preparation of analogue structures with 1,2,3,4‐tetrafluorobenzene, 1,3,5‐trichlorobenzene, and 1,4‐dibromo‐2,5‐difluorobenzene remains elusive. While the metalation step proceeds leading to stable [NaCo(HMDS)2Ar] species, the ligand redistribution process to afford the tetraaryl Co(II) square planar complexes does not take place. Herein we report a density functional theory study in combination with electronic structure and energy decomposition analyses to shed light on the electronic and steric requirements to afford such complexes. Our findings show that the formation of the Co(II) square planar complexes depends on the right balance between intramolecular X···X and Na···X (X=H, F, Cl, Br) interactions. The latter further induce a ‘seesaw effect’, whereby the aryl ligand acts as a ‘seesaw’ allowing two X atoms in ortho positions to interdependently interact with Na. Only by considering both attractive and repulsive Na(X)···X interactions, the correct stability of the square planar complexes observed in experiments can be predicted computationally. We envision these insights to guide the rational design of novel square planar metal complexes for C–C coupling, a field that is dominated by scarce and expensive precious metals.