Stereoisomerism of bis(σ‐Zincane) Complexes: Evidence for an Intramolecular Pathway

Abstract

The first bis(σ-zincane) complexes, heterotri- metallic species [M(CO) (η -HZnBDI) ], have been prepared (BDI=κ -{2,6-(iPr) C H NCMe} CH). For M=Cr, a single stereoisomer is observed in solution and the solid-state. For M=Mo and W, cis and trans isomers were found to reversibly interconvert at 297 K. Despite the huge steric demands of the ligand on zinc, the cis isomer was found to be the most thermodynamically stable in all cases. The activation parameters for the isomerisation when M=Mo are ΔH =20.8 kcal mol and ΔS =-12.8 cal K mol . In combination with DFT calculations, the negative activation entropy suggests an intramolecular rotation mechanism for isomerisation.

Metathesis by Partner Interchange in σ‐Bond Ligands: Expanding Applications of the σ‐CAM Mechanism

“…TheMoand W analogues exhibit two isomers that interconvert by an intramolecular mechanism. [89] In as imilar way to that found with boron, the h 2 -Zn,H geometry of these neutral ligands is different from that of formally anionic dihydrozincate ligands that show a h 1 ,h 1 -H,H geometry as in the ruthenium complex in Scheme 7. This complex exhibits exchange between the dihydrogen ligand and the dihydrozincate hydrogens that proceeds via an h 2 -ZnHEt ligand (Scheme 7).…”

Palladium‐Catalysed C−H Bond Zincation of Arenes: Scope, Mechanism, and the Role of Heterometallic Intermediates

“…The bonding in 3 b was more complex. We have characterised in detail a number of compounds involving Zn−H bonds coordinated to transition metals; [35, 37] and the Zn−H distances typically range from ≈1.7 to 2.2 Å. The Zn−H distance in 3 b was calculated to be 1.9 Å.…”

“…Thebonding in 3b was more complex. We have characterised in detail an umber of compounds involving ZnÀHb onds coordinated to transition metals; [35,37] and the Zn À Hd istances typically range from % 1.7 to 2.2 .T he Zn À Hd istance in 3b was calculated to be 1.9 .T hese data, in combination with Wiberg Bond Indices,indicate that 3b contains stretched ZnÀ Hbonds (see Supporting Information). In combination, these experiments demonstrate the reversible binding of the ZnÀH bond of 1 to Pd.…”

Synthesis and reactivity of heterometallic complexes containing Mg- or Zn-metalloligands

“…Subsequently, Crimmin et al investigated the photochemical reaction of ( Dipp nacnac)Zn–H with Cr(CO) 6 in a 2 : 1 molar ratio to yield a single product 36a (Scheme 10). 33 X-ray diffraction studies allowed the assignment of 36a as a bis(σ-zincane) complex with a cis -geometry and a Zn–H⋯H–Zn arrangement. In contrast, after treatment of ( Dipp nacnac)Zn–H with heavier group 6 carbonyls, M = Mo or W, a mixture of cis -isomers ( 36b and 36c ) and trans-isomers ( 37b and 37c ) was obtained.…”