Oxidative reactions of tetrametal Pd(0)...Mo(II)-Mo(II)...Pd(0) clusters: electrochemical communication of two Pd(0) centers through the Mo(2) moiety and oxidative formation of a Pd(I)-Mo(II)-Mo(II)-Pd(I) array.
Reaction of Mo(2)(pyphos)(4) (1) (pyphos = 6-diphenylphosphino-2-pyridonate) with Pd(dba)(2) (dba = dibenzylideneacetone) afforded the Pd(0) complex Mo(2)Pd(2)(pyphos)(4) (2) which has two Pd(0) centers at both axial positions of the Mo(2) core. The unsaturated Pd(0) centers of 2 were coordinated with donor molecules such as olefins, acetylenes, isonitriles, carbon monoxide, and triphenylphosphine to give the corresponding adducts, Mo(2)Pd(2)(pyphos)(4)(L)(2) (3a: L = acrylonitrile, 3b: L = fumaronitrile, 3c: L = tetracyanoethylene, 3d: L = diisopropyl fumarate, 3e: L = diethyl fumarate, 3f: L = dimethyl fumarate, 3g: L = dimethyl maleate, 3h: L = 2,6-xylylisocyanide, 3i: L = tert-butylisocyanide, 3j: L = dimethyl acetylenedicarboxylate, 3k: L = 1,4-benzoquinone, 3l: L = 1,4-naphthoquinone, 3m: L = carbon monooxide, and 3n: L = triphenylphosphine). Oxidative 1,4-addition of ArSSAr and benzoyl peroxide to the Pd(0) centers of 2 afforded the corresponding Pd(I) complexes Mo(2)Pd(2)(SAr)(2)(pyphos)(4) (7a: Ar = C(6)H(5), 7b: Ar = 4-Me(3)CC(6)H(4), 7c: Ar = 4-MeC(6)H(4), 7d: 4-NO(2)C(6)H(4)) and Mo(2)Pd(2)(OCOPh)(2)(pyphos)(4) (9). Chemical oxidation of 2 with [Cp(2)Fe][BF(4)] in CH(3)CN afforded a dicationic Pd(I) complex [Mo(2)Pd(2)(pyphos)(4)(CH(3)CN)(2)][BF(4)](2) (10a). Similarly, the reaction of 2 with [Cp(2)Fe][BF(4)] in the presence of excess amounts of various donor molecules in THF gave rise to corresponding dicationic Pd(I) complexes [Mo(2)Pd(2)(pyphos)(4)(L')(2)][BF(4)](2) (10b; L' = dimethylsulfoxide, 10c: L' = THF, 10d: L' = benzonitrile, 10e: L' = p-methoxyphenylnitrile, 10f: L' = p-trifluoromethylphenylnitrile, 10g: L' = pyridine, and 10h: L' = p-dimethylaminopyridine), whereas complexes [Mo(2)Pd(2)(pyphos)(4)(CNXyl)(2)][BF(4)](2) (10i) and [Mo(2)Pd(2)(pyphos)(4)(CN(t)Bu)(2)][BF(4)](2) (10j) were prepared by oxidation of the corresponding isonitrile-Pd(0) complexes 3h and 3i. Cyclic voltammetry of 10aj displayed two different oxidation profiles of Pd(0) depending on the donor molecules: complexes 10af showed two waves ascribed to electron communication through monocationic species as intermediates, whereas complexes 10gj showed one wave due to two-electron process. Furthermore, the oxidative addition of alkyl and aryl halides to 2 gave rise to two different reaction patterns: excess amounts of benzyl halides BnX (X = Cl, Br, I), PhCl, and PhBr, and 2 equiv of PhI reacted with 2 to give Pd(I) complexes Mo(2)Pd(2)(X)(2)(pyphos)(4) (4a: X = Cl, 4b: X = Br, 4c: X = I), and the reactions of 2 with excess amounts of PhI and MeI afforded Pd(II) complexes Mo(2)Pd(2)(Ph)(2)I(2)(pyphos)(4) (11) and Mo(2)Pd(2)(CH(3))(2)I(2)(pyphos)(4) (13) bearing two "Pd(Ph)I" and "Pd(CH(3))I" moieties.
Mashima
Kazushi
K
Department of Chemistry, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan. mashima@chem.es.osaka-u.ac.jp
Shima
Asuka
A
Nakao
Keisuke
K
Fukumoto
Atsushi
A
Kaneda
Yutaka
Y
Kusumi
Yoshitaka
Y