STUDY OF SULFINATE AND SULFENATE COMPLEXES DERIVED FROM THE OXYGENATION OF THIOLATE SULFUR IN [1,5-BIS(2-MERCAPTO-2 METHYLPROPYL)-1,5-DIAZACYCLOOCTANATO(2-)]NICKEL(II)
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abstract
A series of nickel(II) complexes containing sulfinate and sulfenate S-donor sites has been prepared from systematic oxygenations of the dithiolate complex [1,5-bis(2-mercapto-2-methylpropyl)-1,5-diazacyclooctanato-(2)]nickel(II) ((bme*-daco)Ni, 1*) and the whole series characterized by mass spectrometry and X-ray crystallography. The dithiolate complex reacts in organic solvents with molecular oxygen to produce sulfinate (NiS-(O)2R) complexes, while reactions with hydrogen peroxide have, in addition, permitted the isolation of sulfenate (NiS(O)R) products. The X-ray crystal structures of the complexes [1-(2-mercapto-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2)]nickel(II) (2*), [1,5-bis(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato-(2)]nickel(H) (3*), [1,5-bis(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2)]nickel(II) (5*), and [1-(2-sulfeno-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (6*) were determined and metric data compared with previously characterized 1* and 4*, [1-(2-mercapto-2-methylpropyl)-5-(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II). Analysis of the NiS(aV) bond distances for homoleptic complexes reveals that the bond distances are in the order Ni-S(O)R (2.167(5)) > Ni-SR (2.159(3)) > NiS(O)2R (2.127(3)). The average nickel sulfinate SO distance at 1.459 is ca. 0.1 shorter than the average nickel sulfenate S-Odistance at 1.545 . These bond dimensions correlated well with spectroscopic and reactivity data. Electrochemical studies find the Nilm reversible couple to be stabilized by ca. 100 mV with conversion of thiolate-S to sulfenate-S donor, while conversion of a sulfenate to a sulfinate stabilized the Ni1 state by an additional 200 mV. Mass spectrometry delineated O-atom loss pathways to dominate initial fragmentation patterns from the parent ions in the profic matrix thioglycerol; however, SO2 extrusion also occurs and is prominent in a nitrobenzyl alcohol (NBA) matrix. The sulfenate complexes are unexpectedly stable and do not undergo either inter- or intramolecular disproportionation reactions to thiolate and sulfinate, nor do they transfer oxygen to triphenyl- or tributylphosphine. Sulfur dioxide removed oxygen from the sulfenates, yielding thiolates and SO3, whereas no reaction occurred with the sulfinate complexes. Complexes that represent partial oxidation of the sulfurs further reacted with hydrogen peroxide to produce higher oxygenates and also reacted with electrophiles such as alkyl halides to produce S-bound sulfoxide ligands. 1995, American Chemical Society. All rights reserved.
