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Palladium Phosphino-Iminolate Complexes as Metalloligands for Coinage Metals:  A Versatile, Ambivalent Behavior

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posted on 20.06.2005, 00:00 by Nicola Oberbeckmann-Winter, Pierre Braunstein, Richard Welter
Reactivity studies with the bis-chelated Pd(II) phosphino-iminolate complex [Pd(dmba)(κ2-P,O-PPh2NC(O)Me)] (2) (dmba = orthometalated dimethylbenzylamine) have shown that it readily reacts as a metalloligand with electrophilic complexes of the coinage metals, selectively via the nitrogen atom of the P,O chelate. After examining its reaction with AgOTf (OTf = SO3CF3), which afforded the first 1-D coordination polymer containing Ag−Pd bonds, [{Ag(2)}OTf]n (3·OTf), we have examined and compared its reactions with H+, Au(PPh3)+, [AuCl(THT)], [Au(THT)]BF4, and [Cu(NCMe)4]BF4. Depending on the nature of the electrophilic metal reagent used, the interaction between the iminolate N atom of 2 and the electrophile can be formally described as a dative bond involving its lone pair, which would formally place the positive charge of the complex more on the coinage metal, or as a more covalent interaction resulting in an increased carbon−oxygen bond order and thus in the pos/baitive charge being more localized on the Pd(II) center. In the former case, the metalloligand formally behaves as a two-electron, L-type donor, whereas in the latter, as a one-electron, X-type donor ligand. This ambivalent behavior explains the formation of the heterobimetallic complexes (6) and ([Au(PPh3)(2)]OTf) or (7·BF4), respectively. Double substitution of the d10 metal center by 2 afforded the Pd/Au/Pd and Pd/Cu/Pd heterotrinuclear complexes (8·BF4) and (9·BF4), respectively. The complexes 2, 5·OTf, 6, 7·BF4, 8·BF4·2CH2Cl2, and 9·BF4 have been structurally characterized by X-ray diffraction.