Ethoxycarbonyl-, cyano- and methoxy-methyl complexes of nickel(II) and their carbonylation reactions

Abstract

The oxidative addition of ClCH₂CO₂Et, ClCH₂CN and BrCH₂OMe to [Ni(cod)₂](cod = cycloocta-1,5-diene), in the presence of 2 equivalents of PMe₃, affords the β-functionalized nickel(II) methyl derivatives trans-[Ni(CH₂R)X(PMe₃)₂](R = CO₂Et, X = Cl 1; R = CN, X = Cl 2; R = OMe, X = Br 3). The interaction of these complexes with carbon monoxide has been studied. The methoxymethyl derivative 3 forms a stable acyl of composition trans-[Ni{C(O)CH₂OMe}Br(PMe₃)₂]7, but for the ethoxycarbonylmethyl complex 1 the corresponding acyl 8 forms reversibly and, although stable as a solid, only exists in solution under an atmosphere of carbon monoxide. No stable acyl has been observed from the reaction of 2 with CO; only decomposition occurs. Stable 18-electron alkyl and acyl cyclopentadienyl derivatives of composition [Ni(CH₂R)(η-C₅H₅)(PMe₃)](R = CO₂Et 4; CN 5, or OMe 6) and [Ni{C(O)CH₂R}(η-C₅H₅)(PMe₃)](R = OMe 9 or CO₂Et 10) are easily obtained upon reaction of the above 16-electron complexes with Na(C₅H₅). The new compounds have been fully characterized by analytical and spectroscopic (IR and ¹H, ¹³C and ³¹P NMR) methods.