Syntheses and Structures of Molecular Diphenolatonickel Compounds Containing Trimethylphosphane Ligands

✍ Scribed by Hans-Friedrich Klein; Attila Dal; Thomas Jung; Siegmar Braun; Caroline Röhr; Ulrich Flörke; Hans-Jürgen Haupt

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 649 KB
• Volume: 1998
• Category: Article
• ISSN: 1434-1948
• DOI: 10.1002/(sici)1099-0682(199805)1998:5<621::aid-ejic621>3.0.co;2-p

✦ Synopsis

The reaction of substituted phenols and dioxygen with Ni(PMe 3 ) 4 yields the low-spin tetracoordinate diphenolatonickel compounds Ni(OAr) 2 (PMe 3 ) 2 [ArOH = 2-tert-butylphenol (1), 2-tert-butyl-4-methylphenol (2), 2-tert-butyl-6methylphenol (3), 2,4-di(tert-butyl)phenol (4), 2-tert-butyl-4methoxophenol (5), 2-chloro-4-tert-butylphenol (6), 2-isopropylphenol (7), 3-tert-butylphenol (8)]. As is revealed by variable temperature 1 H-and 13 C-NMR spectroscopy the complexes constitute a mixture of two isomers, each of which can be observed separately at lower temperatures when inter-Many low-valent metal compounds, if combined with a proton source and dioxygen, form an oxidizing system. Examples are Fentons reagent, Bartons Gif systems and the Wacker process. Peroxometal complexes are believed to be key intermediates in these reactions. [1] Strongly reducing phosphane complexes of zerovalent nickel are known to form peroxo species according to Eq. 1. In exceptional cases these may be isolated, e.g. with space-filling tricyclohexylphosphane ligands. [2] Ni(PR

With the small trimethylphosphane the peroxo intermediate is explosive, and for this reason even small crystals of Ni(PMe 3 ) 4 crackle upon contact with air. Using mol-equivalent amounts of oxygen in solution the system becomes a mild oxidant. On this basis we have developed a new synthesis of molecular diphenolatonickel complexes containing trimethylphosphane ligands.

Conventionally, but not conveniently, unsolvated diphenolatonickel compounds may be prepared in an anhydrous medium as insoluble coordination polymers. Methods using NiCl 2 and sodium or lithium phenolates usually afford products which pertinaciously occlude halide impurities.

Some ortho-substituted phenols form diphenolatonickel dihydrates that can be converted into anhydrous com-