Electron ionization mass spectrometry of cobalt(III) β-diketonates and monothio-β-diketonates possessing aryl and fluorinated alkyl substituents

Abstract

. Can. J. Chem. 70, 952 (1992).Electron ionization positive ion mass spectra of 15 substituted cobalt(II1) P-diketonates and monothio-P-diketonates, CO"'L,, where L = RCXCHCOR', R = phenyl, 2-thienyl, or 2-naphthyl; X = 0 or S; and R' = CHF2, CF,, C2FS, or n-C,F,, show a marked dependence on the ligand. Molecular ions, [CO"'L,]+', are observed only for some of the more highly fluorinated complexes (R' = C2FS or n-C3F7). The [Co1"L2] '' ion, possibly generated by ionization of CO"L forme! by thermal degradation, or by electron ionization of Col''L,, typically decomposes by elimination of a radical, i.e., L or R' , to yield ions containing Co(I1); subsequent decompositions proceed preferentially by loss of even-electron neutral species, also to yield ions containing Co(l1). Cobalt-containing ions in which fluorine has rearranged to the metal decrease in variety and abundance for the ligands with higher fluorine content. When metal-bonded oxygen is replaced by sulfur, fluorine migration to Co(III), rather than to Co(II), is preferred. These trends are consistent with a combination of several different concepts including the ability of the metal to undergo valency change, the principle of Hard and Soft Acids and Bases, and the inductive capabilities of the ligand donor atoms and of the R and R' groups. Ion decomposition pathways are proposed.Key words: mass spectrometry, cobalt complexes, P-diketonates, fluorinated chelate complexes. Mots clts : spectrometric de masse, complexes du cobalt, P-dicktonates, complexes de chelates fluorCs.[Traduit par la redaction] Introduction The significant volatility and stability of metal P-diketonates and their derivatives make them suitable for gas chromatography (1). When this technique is combined with mass spectrometry, analytical methods, based upon the use of isotopic tracers, can be devised for metals. Recently, metal P-diketonates were used as precursors for chemical vapor deposition (2-4), a promising technique for the preparation of thin films of high T, superconducting oxides (5), and the application of mass spectrometry to characterize the alkaline earth complexes for this purpose has been described (6).The mass spectra of these complexes are of interest in their own right because their wide variety permits assessment of the influence exerted by bonding and structure factors, i.e., (i) the central metal atom, (ii) the ligand donor atoms, and

Electron ionization mass spectrometry of aryl- and fluoroalkyl-substituted nickel(II) β-diketonates and monothio-β-diketonates

“…Although not supported here, the latter decomposition has been confirmed for an analogous cobalt complex by a product ion scan (1). The formation of the bare Ni+ ion, which has also been reported in the mass spectrum of nickel(I1) acetylacetonate (26,27), confirms that reduction of nickel(I1) has occurred.…”

“…Thus, nickel(I1) is able to abstract a hard fluorine atom from the carbon of a CHF, substituent but is less effective at abstracting fluorine from the harder carbons of CF,, C2F5, or n-C,F7 groups. We have discussed the relative hardnesses of the carbon atoms in the perfluoroalkyl substituents in more detail in the previous publication (1).…”

The gas‐phase ligand exchange of copper and nickel acetylacetonate, hexafluoroacetylacetonate and trifluorotrimethylacetylacetonate complexes

“…The loss of what amounts to an intact (tftm) ligand is observed for both Cu at m/z 258 and Ni at m/z 253 as well as the subsequent loss of another t Bu group in both complexes at m/z 201 and 196 to yield [Cu(tftm‐ t Bu)] + and [Ni(tftm‐ t Bu)] + , respectively. Fluorine migration17, 21–24 was observed at m/z 203 for the Ni complex, but not for Cu at m/z 220. It is also interesting to note the presence of a [M(tftm)+ t Bu] + species that is observable in both the Cu and Ni spectra.…”

Electron ionization mass spectrometry of aryl- and fluoroalkyl-substituted palladium(II) β-diketonates and monothio-β-diketonates

“…-. tonates (1,2). For such complexes the decomposition would result in a formal reduction of the metal to its +I oxidation state.…”

“…Our recent efforts in characterizing the mass spectral behavior of volatile transition metal chelates under electron ionization (EI) conditions have included the examination of fluorinated P-diketonates and monothio-P-diketonates of cobalt(II1) (1) and nickel(I1) (2). The mass spectra of these complexes showed interesting differences, which could be attributed to the relative stabilities of the +3, +2, and +1 oxidation states of the metals, and also to the relative acid hardness of the metals in these oxidaion states, according to the Hard and Soft Acid and Base (HSAB) principle (3)(4)(5)(6).…”