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Chalcogen Extrusion from Heteroallenes and Carbon Monoxide by a Three-Coordinate Rh(I) Disilylamide

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posted on 2015-12-17, 07:50 authored by Matthew T. Whited, Lisa Qiu, Alex J. Kosanovich, Daron E. Janzen
We report the reactions of several heteroallenes (carbon disulfide, carbonyl sulfide, and phenyl isocyanate) and carbon monoxide with a three-coordinate, bis­(phosphine)-supported Rh­(I) disilylamide (1). Carbon disulfide reacts with 1 to afford a silyltrithiocarbonate complex similar to an intermediate previously invoked in the deoxygenation of CO2 by 1, and prolonged heating affords a structurally unusual μ-κ2(S,S′):κ2(S,S′)-trithiocarbonate dimer. Carbonyl sulfide reacts with 1 to afford a structurally unique Rh­(SCNCS) metallacycle derived from two insertions of OCS and N-to-O silyl-group migrations. Phenyl isocyanate reacts with 1 to afford a dimeric bis­(phenylcyanamido)-bridged complex resulting from multiple silyl-group migrations and nitrogen-for-oxygen metathesis, akin to reactivity previously observed with carbon dioxide. The ability of 1 to activate carbon–chalcogen multiple bonds via silyl-group migration is further supported by its reactivity with carbon monoxide, where a nitrogen-for-oxygen metathesis is also observed with expulsion of hexamethyldisiloxane. For all reported reactions, intermediates are observable under appropriate conditions, allowing the formulation of mechanisms where insertion of the unsaturated substrate is followed by one or more silyl-group migrations to afford the observed products. This rich variety of reactivity confirms the ability of metal silylamides to activate exceptionally strong carbon–element multiple bonds and suggests that silylamides may be useful intermediates in nitrogen-atom and nitrene-group-transfer schemes.