No abstract

Late-transition-metal complexes with silylene (SiR 2 ) ligands have attracted considerable attention since the proposal of platinum-silylene intermediates in the [PtCl 2 (PEt 3 ) 2 ]-catalyzed reactions that convert organodisilanes into oligosilanes and the cyclic adducts into alkynes.[1] Mononuclear silylene complexes of platinum [2] and other late transition metals [3] were not isolated until some years later, probably because of the extremely high reactivity of most M = Si double bonds. Dinuclear complexes of late transition metals with bridging silylene ligands are more common.[4] The dinuclear platinum complex [{Pt(PR 3 )} 2 (m-SiHPh 2 ) 2 ] (PR 3 = PPh 3 , PCy 3 etc.) has been reported.[5] However, in spite of the stable coordination of bridging silylene ligands, complexes containing three or more metal atoms with bridging Si ligands have few precedents, [6] and those known are stabilized by electron-withdrawing CO and CNR ligands.[7] Braddock-Wilking and coworkers [8] and our group [9,10] have reported zero-valent triangular Pt 3 complexes, stabilized by bridging silylene and phosphine ligands. Chen, Shimada, and Tanaka employed 1,2-disilabenzene as a ligand and prepared trinuclear Pd complexes supported by the Si ligands.[11]Herein, we report the synthesis and unexpected structure of a planar tetranuclear Pd 0 complex with three bridging SiPh 2 ligands as well as facile exchange of the bridging silylene ligands to yield a dumbbell-shaped octapalladium complex composed of two Pd 4 units bridged by a diphosphine ligand. These complexes, composed of Pd 0 centers and electrondonating Si and phosphine ligands, possess a unique planar {Pd 4 Si 3 } core.Heating a mixture of a dipalladium complex with bridging diphenylsilyl ligands, [{Pd(PCy 3 )} 2 (m-h 2 -SiHPh 2 ) 2 ] (1), [12] The molecular structure of 2 was determined by singlecrystal X-ray diffraction (Figure 1). [14] Complex 2 has a hexagonal {Pd 4 Si 3 } core incorporating one central Pd atom,

Eine ungewöhnliche Struktur: Die neuartigen Titelverbindungen (siehe Schema) wurden synthetisiert und vollständig charakterisiert. Der vierkernige Komplex enthält einen sechseckigen Pd4Si3‐Kern mit einem zentralen Pd‐Atom, drei äußeren Pd‐Atomen und drei verbrückenden Si‐Atomen in einer Ebene, während der hantelförmige achtkernige Pd‐Komplex aus zwei durch einen Diphosphanliganden verbrückten Pd4Si3‐Gruppen besteht.