For a long time d(10)-ML2 fragments have been known for their potential to activate unreactive bonds by oxidative addition. In the development of more active species, two approaches have proven successful: the use of strong σ-donating ligands leading to electron-rich metal centers and the employment of chelating ligands resulting in a bent coordination geometry. Combining these two strategies, we synthesized bis-NHC chelate complexes of nickel(0) and platinum(0). Bis(1,5-cyclooctadiene)nickel(0) and -platinum(0) react with bisimidazolium salts, deprotonated in situ at room temperature, to yield tetrahedral or trigonal-planar bis-NHC chelate olefin complexes. The synthesis and characterization of these complexes as well as a first example of C-C bond activation with these systems are reported. Due to the enforced cis arrangement of two NHCs, these compounds should open interesting perspectives for bond-activation chemistry and catalysis.

Platinum(II) cis-dimethyl and cis-dineopentyl complexes bearing the alkyl-substituted bis-NHC ligands L t-Bu , L Me , and L i-Pr (L t-Bu = 1,1′-di-tert-butyl-3,3′-methylenediimidazolin-2,2′-diylidene, L Me = 1,1′-dimethyl-3,3′-methylenediimidazolin-2,2′-diylidene, L i-Pr = 1,1′-diisopropyl-3,3′methylenediimidazolin-2,2′-diylidene) as well as novel cisalkyl chloro and cis-alkyl hydrido compounds were synthesized. The reactivity of the dimethyl complexes toward dichloromethane and methanol was investigated. Reductive elimination of alkanes from cis-alkyl hydrido complexes requires much higher temperatures than in related bisphosphine systems, which limits their applicability for the generation of reactive, bent platinum(0) d 10 -ML 2 fragments for bond-activation chemistry. The platinum(II) complexes were characterized by NMR and IR spectroscopy, mass spectrometry, elemental analysis, and X-ray diffraction in most cases.

The employment of lithium hexamethyldisilazide for the deprotonation of methylene-bridged bis­(imidazolium) salts led to the formation of lithium carbene adducts. Depending on the crystallization method and the substituents of the ligands, monomeric, dimeric, or polymeric solid-state structures were obtained. These lithium carbene complexes represent the first examples of lithium complexes bearing neutral bis­(N-heterocyclic carbene) ligands.

A direct one-pot copper-catalyzed oxidative C–C bond cleavage route to the synthesis of pyridoquinazolinones is described. This one-pot strategy involves a copper-catalyzed C–N coupling followed by concomitant C­(sp3)–H oxidation and amidation via oxidative C–C bond cleavage under an O2 atmosphere to deliver the target molecules in high yields.

d 10 -ML 2 -Fragmente sind seit langem für ihr Potenzial bekannt, unreaktive Bindungen durch oxidative Addition zu aktivieren. Bei der Entwicklung aktiverer Spezies haben sich zwei Ansätze bewährt: Der Einsatz von starken s-Donorliganden, die zu elektronenreichen Metallzentren führen, sowie von Chelatliganden, die eine gewinkelte Koordinationsgeometrie erzeugen. Wir haben beide Strategien kombiniert und Nickel(0)-sowie erstmals Platin(0)-Bis-NHC-Chelatkomplexe synthetisiert. Bis(1,5-Cyclooctadien)nickel(0) und -platin(0) reagieren mit in situ deprotonierten Bisimidazoliumsalzen bei Raumtemperatur zu tetraedrischen oder trigonal-planaren Bis-NHC-Chelat-Olefinkomplexen. Die Synthese und Charakterisierung dieser Komplexe sowie ein erstes Beispiel einer C-C-Bindungsaktivierung mit diesen Systemen werden beschrieben. Wegen der erzwungenen cis-Anordnung zweier NHCs erçffnen diese Verbindungen interessante Perspektiven für Bindungsaktivierungen und Katalyse. Schema 1. Bisphosphanplatin(0)-Systeme, die Bindungsaktivierungen ermçglichen (R = Me, Et; Cy = Cyclohexyl).

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