Β-hydride Abstraction Research Articles

Emergence of a New [NNN] Pincer Ligand via Si-H Bond Activation and β-Hydride Abstraction at Tetravalent Cerium.

The cerium(IV) pyrazolate complexes [Ce(Me2pz)4]2 and [Ce(Me2pz)4(thf)] initiate β‐hydride abstraction of the bis(dimethylsilyl)amido moiety, to afford a heteroleptic cerium(IV) species containing a dimethylpyrazolyl‐substituted silylamido ligand, namely [Ce(Me2pz)3(bpsa)] (bpsa=bis((3,5‐dimethylpyrazol‐1‐yl)dimethylsilyl)amido; Me2pz =3,5‐dimethylpyrazolato), along with some cerium(III) species. Remarkably, the nucleophilic attack of the pyrazolyl at the silicon atom and concomitant Si−H‐bond cleavage is restricted to the tetravalent cerium oxidation state and appears to proceed via the formation of a transient cerium(IV) hydride, which engages in immediate redox chemistry. When [Ce(Me2pz)4]2 is treated with [Li{N(SiMe3)2}], that is, in the absence of the SiH functionality, any redox chemistry did not occur. Instead, the ceric ate complex [LiCe2(Me2pz)9] and the stable mixed‐ligand ceric species [Ce(Me2pz)2{N(SiMe3)2}2] were obtained.

A study of β-hydride abstraction from alkanediyl homobimetallic complexes [{Cp(CO) 2Fe} 2{μ-(C nH 2 n)}] ( n = 4–10, Cp = η 5-C 5H 5)

The alkyl-bridged iron(II) complexes [{Cp(CO) 2Fe} 2{μ-(C n H 2 n )}] ( n = 6–10, Cp = η 5-C 5H 5) undergo both single and double hydride abstraction when reacted with one equivalent of Ph 3CPF 6 to give both the monocationic complexes, [{Cp(CO) 2Fe} 2{μ-(C n H 2 n−1 )}]PF 6, and the dicationic complexes, [{Cp(CO) 2Fe} 2{μ-(C n H 2 n−2 )}](PF 6) 2. The ratios of monocationic to dicationic complexes decrease with the increase in the value of n. The complexes where n = 4 and 5 undergo only single hydride abstraction under similar conditions. When reacted with two equivalents of Ph 3CPF 6, the complexes where n = 6–10 undergo double hydride abstraction to give dicationic complexes only. In contrast, the complex where n = 5 gives equal amounts of the monocationic and the dicationic complexes, while the complex where n = 4 only gives the monocationic complex. 1H and 13C NMR data show that in the monocationic complexes one metal is σ-bonded to the carbenium ion moiety while the other is bonded in a η 2-fashion forming a chiral metallacylopropane type structure. In the dicationic complexes both metals are bonded in the η 2-fashion. The monocationic complexes where n = 4–6, react with methanol to give η 1-alkenyl complexes[Cp(CO) 2Fe(CH 2) n CH CH 2] ( n = 2–4) as the major products and σ-bonded ether products [{Cp(CO) 2Fe} 2{μ-(CH 2) n CH(OCH 3)CH 2}] as the minor products. The complex where n = 8 reacted with iso-propanol to give the η 1-alkenyl complex [Cp(CO) 2Fe(CH 2) 6CH CH 2]. The dicationic complexes where n = 5, 8 and 9 were reacted with NaI to give the respective α, ω-dienes and [Cp(CO) 2FeI].