Fluxional behavior of {eta}{sup 1},{eta}{sup 2}-cyclooctenylpalladium acetylacetonate and related complexes
- Univ. of Missouri, St. Louis, MO (United States). Dept. of Chemistry
The cyclooctenylpalladium complexes [Pd({eta}{sup 1},{eta}{sup 2}-C{sub 8}H{sub 12}{center_dot}R)(acac)] exhibit fluxional behavior in solution that equilibrates the acac methyl environments. Free energies of activation for the process have been determined by variable-temperature NMR spectroscopy. These appear to show no dependence on the nature of exo substituents, and they are higher for bulky endo groups. Lower {Delta}G{sup {double_dagger}} values are obtained in more polar solvents or with added phosphines, suggesting the operation of an associative mechanism. In contrast, the platinum complex [Pt({eta}{sup 1},{eta}{sup 2}-C{sub 8}H{sub 12}{center_dot}OMe)(acac)] is static up to 380 K, as is the C,N-bonded palladium species [Pd(C{sub 6}H{sub 4}N{double_bond}NC{sub 6}H{sub 5}-2)(acac)]. These are fluxional, however, in the presence of a tertiary phosphine. The hexafluoroacetylacetonate (hfac) complex [Pd({eta}{sup 1},{eta}{sup 2}-C{sub 8}H{sub 12}{center_dot}OMe)-(hfac)] exhibits a lower value of {Delta}G{sup {double_dagger}} than its acad analogue, with or without added PEt{sub 3}. When a phosphine is added to one of the metal complexes, low-temperature {sup 31}P NMR studies reveal equilibria involving a phosphine-ligated species, the starting acac complex, and free phosphine. The position of equilibrium depends on the nature of the R group and on the phosphine. The rearrangement is proposed to take place from a five-coordinate species, either by a series of pseudorotations or by way of a turnstile mechanism. Although it is not possible to distinguish between these two, the simplicity of the latter in this case is particularly attractive.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-92CH10499
- OSTI ID:
- 315971
- Journal Information:
- Organometallics, Vol. 17, Issue 21; Other Information: PBD: 12 Oct 1998
- Country of Publication:
- United States
- Language:
- English
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