A Monomeric Dilithio Methandiide with a Distorted trans‐Planar Four‐Coordinate Carbon

Abstract

It's plain to see: A monomeric dilithio methandiide features a distorted trans‐planar four‐coordinate carbon atom. The nature of this compound as established by an X‐ray diffraction study (see picture: C black, N blue, P magenta, Li red) and supported by calculations.

Four Decades of the Chemistry of Planar Hypercoordinate Compounds

“…[173] Cblack, Pblue, Ni ght blue, Li red, (Reprinted with permission from Ref. [173] [179] and Al 4 Oin1991. [180] ptO in ab ulk solid structure was predicted in 2008.…”

A Cerium(IV)–Carbon Multiple Bond

“…[12] The 1 H NMR spectrum of 5 spans the range d =+ 0.4 to + 7.5 ppm and exhibits eight sharp resonances consistent with C s symmetry on the NMR timescale. The carbene center, located definitively by a 13 C-31 P 2D NMR correlation experiment, appears in the 13 C NMR spectrum as a triplet at d = 324.6 ppm (J PC = 148.7 Hz). The carbene nature is thus confirmed by this downfield chemical shift, which is well within the 200-400 ppm range of covalent transition-metal carbenes [14] and at much higher frequency than ionic yttrium-(III) analogues (d = 10-40 ppm).…”

“…We began [12] [12,13] With 4 in hand, we reasoned that the electron-rich "ate" formulation would promote straightforward removal of the 4f-electron, thereby avoiding the unpredictable sidereactions of neutral cerium(III)-compound oxidations. [8] Treatment of 4 with one equivalent of AgBPh 4 resulted in elimination of Ag 0 and KBPh 4 to give, after work-up and recrystallization, dark purple crystals of the cerium(IV) carbene bis(aryloxide) [Ce(BIPM TMS )(ODipp) 2 ] (5, 28% yield).…”

Geminal dianions stabilized by phosphonium substituents

“…This contrasts with the reactivity of the anion Sm[C(Ph 2 P S) 2 ] 2 − which already at room temperature gave full metathesis to Ph 2 C C(Ph 2 P S) 2 and samarium oxide [59]. Reaction of 29 with adamantylcyanide (which possesses a more accessible two-coordinate C center) only led to isolation of an adduct (37). Due to the much smaller spatial demand of the needle-like cyanide, two substrate molecules can coordinate to the dimer.…”

“…Very recently, however, the first monomeric structure has been reported [37]. This unusual complex was obtained by use of a bulky imino-substituent (DIPP) and a chelating co-solvent (TMEDA = N,N,N ,Ntetramethylethylenediamine), both factors which disfavour the dimerization reaction.…”