Balancing Adduct Formation and Ligand Coupling with the Bulky Allyl Complexes [1,3-(SiMe₃)₂C₃H₃]₂M (M = Fe, Co, Ni)

Abstract

Passage of CO at atmospheric pressure through solutions of A′ 2 M (M = Fe, Co, Ni; A′ = [1,3-(SiMe 3 ) 2 C 3 H 3 ] − ) in hexanes produces the corresponding allyl complexes A′ 2 Fe(CO) 2 , A′Co(CO) 3 , and A′ 2 Ni(CO), respectively.Although the iron and nickel species can be isolated as pure liquids, the cobalt complex is accompanied by the coupling product 1,3,4,6-tetrakis(trimethylsilyl)-1,5-hexadiene. A′Co(CO) 3 was independently prepared from the reaction of Co 2 (CO) 8 , A′Br, and PhCH 2 N(C 2 H 5 ) 3 + Cl − in aqueous base. The IR stretching frequencies of A′ 2 Fe(CO) 2 and A′Co(CO) 3 are lower than those in the unsubstituted analogues, indicating that the trimethylsilated allyl ligand is a better electron donor than the parent version. Density functional theory calculations were performed on various conformations of the complexes, which reproduced the frequency-lowering effect of the trimethylsilyl groups. They also indicate that the thermodynamics of the formation of A′ 2 Ni(CO) and the unknown (C 3 H 5 ) 2 Ni(CO) are similar, suggesting that the thermal stability of the former is of kinetic origin. Oxidative coupling of the allyl ligands in A′ 2 Fe and A′ 2 Co is induced with I 2 ; this is different from the case with A′ 2 Ni, which has previously been shown to produce the mixed allyl halide complex [A′Ni(μ-I) 2 ] 2 .(2) Article pubs.acs.org/Organometallics

Mechanochemical Influence on the Stereoselectivity of Halide Metathesis: Synthesis of Group 15 Tris(allyl) Complexes

“…14 The range of R groups that might be explored is large, but allyl ligands are attractive in this regard, as they can display conformational flexibility when bound to metals (σ, π, μ x , and various combinations of these bonding modes) 15 and on substitution can introduce stereochemical features into structures and reactions. 16 Specifically, 1,3-disubstituted allyls are known to exist in syn,syn and syn,anti conformations when they are π-bound to metals 17 1a). 18,19 In solution, the molecules are highly fluxional, appearing π-bound in 1 H NMR spectra (e.g., all SiMe 3 groups are equivalent).…”

“…The range of R groups that might be explored is large, but allyl ligands are attractive in this regard, as they can display conformational flexibility when bound to metals (σ, π, μ x , and various combinations of these bonding modes) and on substitution can introduce stereochemical features into structures and reactions . Specifically, 1,3-disubstituted allyls are known to exist in syn , syn and syn , anti conformations when they are π-bound to metals and if σ-bound, as in p-block complexes, can generate chiral centers. For example, the tris­(allyl) complexes [AlA′ 3 ] and [GaA′ 3 ] (A′= [1,3-(SiMe 3 ) 2 C 3 H 3 ] − ) possess R , S , S (or S , R , R ) configurations around the C α of the allyl ligands in the solid state (Figure a). , In solution, the molecules are highly fluxional, appearing π-bound in 1 H NMR spectra (e.g., all SiMe 3 groups are equivalent).…”