Study of reactions between alkyl(pyridine)cobaloximes and trifluoroacetic acid; formation and crystal structure of cis-bis(butane-2,3 dione dioxime)bis(trifluoroacetoxy)cobalt(II)

Abstract

The reactions between several alkyl(pyridine)cobaloximes [CoR(Hdmg)₂(py)][R = Me, CH₂Cl, CHCl₂, Et, Prⁱ, Buⁿ, CH₂CH₂CHCH₂, or CH₂CHMeCHCH₂, (1a)–(1h) respectively; py = pyridine; Hdmg = monoanion of dimethylglyoxime] and trifluoroacetic acid in deuteriochloroform have been monitored by ¹H n.m.r. spectroscopy. This technique indicates that addition of trifluoroacetic acid to an alkyl(pyridine)cobaloxime initially causes reversible protonation without loss of pyridine, then a second protonation occurs leading to the loss of pyridine as pyridinium trifluoroacetate. With excess of trifluoroacetic acid, the alkylcobaloximes lose their alkyl group as RH [e.g. propane from (1e)] and slowly deposit a red crystalline solid, identified as the title complex (4) by analysis of its crystal structure. Crystals of (4) are triclinic, space group P, with a= 10.068(3), b= 10.716(5), c= 13.030(3)Å, α= 100.15(3), β= 116.76(3), γ= 88.97(3)°, and Z= 2. 1 873 Reflections collected at –80 °C by a four-circle diffractometer were refined to R= 0.053. The Co–O distances are 2.069(2) and 2.057(2)Å; and Co–N are 2.126(3), 2.138(2), 2.139(3), and 2.149(3)Å.