Two Exceptional Homoleptic Iron(IV) Tetraalkyl Complexes

Abstract

The formation of the high-valent iron complex [Fe(cyclohexyl) ] from Fe under reducing conditions is best explained by disproportionation of a transient organoiron intermediate which is driven by dispersive forces between the cyclohexyl ligands and the formation of short and strong Fe-C bonds. The (meta)stability of this diamagnetic complex (S=0) is striking if one considers that it has empty d-orbitals at its disposal and contains, at the same time, no less than twenty H-atoms available for either α- or β-hydride elimination.

Iron‐ or Palladium‐Catalyzed Reaction Cascades Merging Cycloisomerization and Cross‐Coupling Chemistry

“…Our group has recently shown that the reaction of FeX n ( n =2, 3) with cyclohexylmagnesium chloride is a highly involved process, in which disproportionation of the transient organoiron species and/or allylic C−H activation processes will eventually interfere . It was for this reason that this particular nucleophile had been chosen for reaction optimization.…”

“…Our group has recently shown that the reactiono fF eX n (n = 2, 3) with cyclohexylmagnesium chloride is ah ighly involved process,i nw hichd isproportionation of the transiento rganoiron species and/or allylic CÀHa ctivation processes will eventually interfere. [31,34] It was for this reasont hat this particularn ucleophile had been chosen for reaction optimization. The fact that the cyclohexyl group was transferred almost quantitatively augured well for the scope of the reactionw ith regard to the nucleophilic partner.I ndeed, ar ange of (functionalized) alkyl-Grignardr eagents performed nicely ( Table 2);e ven the isopropyl group was successfully transferred, although cross-coupling reactions of secondary alkyl donors in general are often plaguedb yi somerization to the linear isomersv ia rapid MÀH elimination/re-addition (entry 4); [35] of the primary Grignard reagents investigated, only TMSCH 2 MgCl failed to participate in the cascade, most likely for the b-silicon effect that is thought to stabilize the transiento rganoiron species.…”

Oxidative P‐P‐Bindungsaddition an Cobalt(−I): Bildung eines Low‐spin‐Cobalt(III)‐Phosphanidokomplexes

“…[Fe(1‐norbornyl) 4 ], und [Co(1‐norbornyl) 4 ], wurden von Theopold und Tennent in den 1970er und 1980er Jahren beschrieben. Das Interesse an dieser Verbindungsklasse wurde kürzlich durch die Publikation des ersten Nickel(IV)‐Tetraalkylkomplexes [2d] und weiterer Eisen(IV)‐Komplexe [FeR 4 ] (R=Cyclohexyl, 2‐Adamantyl) wiederbelebt. Eine theoretische Studie von Power und Nagase legt nahe, dass diese Verbindungen maßgeblich durch London‐Dispersionskräfte stabilisiert werden …”

2‐Adamantyl Complexes of Platinum

“…The reason for this is twofold; first, the synthesis of adamantyl anions, specifically lithium and Grignard compounds, is fraught with highly erratic yields and side reactions, and reliable zinc chemistry has only recently been developed. [7b], [7c] Second, homoleptic metal adamantyl complexes have proven to be extremely insoluble, leading to difficulty in characterization. As such, metal complexes of the (unsupported) adamantyl group are very rare, and structurally characterized examples of 2‐adamantyl transition metal complexes have been, until very recently, non‐existent.…”

“…In 1980, Bochmann, Wilkinson, and Young attempted the synthesis of the first platinum adamantyl complex. [8c] This attempt was unsuccessful, yielding only biadamantyl as the final product. Here we present the first platinum 2‐adamantyl complexes to be isolated and characterized, namely [(COD)Pt(2‐Ad)Cl] ( 1 ), [(dppe)Pt(2‐Ad)Cl] ( 2 ), [(COD)Pt(2‐Ad)Me] ( 3 ), and [(dppe)Pt(2‐Ad)Me] ( 4 ) {COD = 1,5‐cyclooctadiene, dppe = 1,2‐bis(diphenylphosphino)ethane, Ad = adamantyl}.…”