A Planar Tetracoordinate Carbon and Unusual Bonding in an Organodimetallic Propynylidene Complex Arising from Double C−H Activation of an Allene Ligand

Abstract

Reduction of the organoditantalum allene complex (eta-C5Me4R)2Ta2(mu-X)X3(mu-eta1,eta3-C3H4) (R = Me (Cp*), Et; X = Cl, Br) with sodium amalgam leads to the propynylidene complex (eta-C5Me4R)2Ta2(mu-H)2X2(mu-HCCCH) by a formal double 1,3-C-H activation of the allene ligand. The solid-state molecular structure contains a planar HCCCH ligand bridging, in parallel coordination mode, the two tantalum atoms, with the HCCCH and Ta atoms coplanar. Key structural features are a Ta-Ta distance of 2.8817(7) A, propynylidene C-C-C angle of 153.7(13) degrees , C-C distance of 1.370(8) A, Ta-C(central) distance of 2.194(9) A, and Ta-C(terminal) distance of 1.970(9) A. Molecular orbital calculations on the complex at the RHF/SBK(d) and B3LYP/LanL2dz levels of theory demonstrate that the propynylidene ligand is best viewed formally as an allenediylidene(4-) ligand bonded to two d0 tantalum atoms via two Ta=C(terminal) double bonds and an unusual three-center, two-electron bridge bond involving both tantalum atoms and a lone pair on the planar, tetracoordinate central carbon. There is no net Ta-Ta bonding based on the orbital analysis.

Visiting the Limits between a Highly Strained 1‐Zirconacyclobuta‐2,3‐diene and Chemically Robust Dizirconacyclooctatetraene

“…It should be noted that similar compounds with bent C 3 units were reported, for example, Messerle et al. described the formation of a dinuclear tantalum allenediyl complex through double C−H activation of an allene ligand …”

Four Decades of the Chemistry of Planar Hypercoordinate Compounds

“…Organometallic propynylidene complex containing the ptC configuration. [171] (Reprinted with permission from Ref. [171],C opyright 2003 AmericanC hemical Society.)…”

“…[171] (Reprinted with permission from Ref. [171],C opyright 2003 AmericanC hemical Society.) Theoretical Chemistry Angewandte Chemie Some planar motifs with metal centers have been synthesized.…”

“…[12b,e] Gas-phase experimental observations were already covered in earlier Sections of this Review.T hus we will only mention that many small gas-phase clusters with planar motifs were observed by the Wang and Boldyrev groups between 2001 and 2014. [24g, 87a,b, 145] In 2003, Messerle and co-workers [171] synthesized ad inuclear propynylidene complex 65 a arising from double CÀH activation of an allene ligand. This complex featured ap tC motif and unusual bonding (Figure 65 b).…”

Vier Jahrzehnte Chemie der planar hyperkoordinierten Verbindungen

“…2003 synthetisierten Messerle und Mitarbeiter171 den zweikernigen Propinylidenkomplex 65 a , der durch doppelte C‐H‐Aktivierung eines Allenliganden entstand. Dieser Komplex enthält ein ptC‐Motiv und ungewöhnliche Bindungen (Abbildung 65 b).…”