No abstract

The reaction of Pt(SiHPh 2 ) 2 (dmpe) (dmpe ) 1,2-bis(dimethylphosphino)ethane) with Pd(PCy 3 ) 2 forms (Cy 3 P)Pd(µ-η 2 -HSiPh 2 ) 2 Pt(PCy 3 ) (1), which contains two diphenylsilyl ligands bridged to Pd and Pt centers. A comparison of the crystallographic results and the NMR spectra of 1 with those of [(Cy 3 P)Pd(µ-η 2 -HSiPh 2 )] 2 ( 3) and [(Cy 3 P)Pt(µ-η 2 -HSiPh 2 )] 2 (4) indicates that the structure of 1 contains two inequivalent Si-H hydrogens, Pd-H-Si and Pt-H-Si, with three-center twoelectron bonds.

The reaction of Pt(SiHPh 2 ) 2 (PEt 3 ) 2 with Pd(PEt 3 ) 3 produced heterodinuclear complexes with bridging diphenylsilyl ligands (Et 3 P)Pt(µ-η 2 -SiHPh 2 ) 2 Pd(PEt 3 ) (1) and (Et 3 P) 2 Pt-(µ-η 2 -SiHPh 2 ) 2 Pd(PEt 3 ) (2). Each product was isolated and fully characterized. X-ray crystallography of 2 and NMR spectra of 2 and 2-d 2 at 25 °C indicated the presence of two bridging SiHPh 2 (or SiDPh 2 ) ligands, which were bonded to one metal center via a M-Si single bond and to the other via a Si-H-M three-center, two-electron bond. The 1 H NMR spectrum of 2 at -90 °C exhibited a peak at δ -8.61 due to a hydrido ligand bonded to the Pt center, indicating the structure (Et 3 P) 2 PtH(µ-SiPh 2 )(µ-η 2 -SiHPh 2 )Pd(PEt 3 ) in the solution at low temperature. Complex 2 reacted with CN-t-Bu to form a mixture of (Et 3 P)(t-BuNC)-Pt(SiPh 2 -CH 2 -N(t-Bu)-SiPh 2 ) (3) and [(Et 3 P)(t-BuNC)Pt(µ-SiPh 2 )] 2 (4). Complex 3 contained the platinacyclopentane group, whose five-membered ring was composed of Pt, Si, N, and C atoms.Supporting Information Available: Crystallographic data of 1-4. This material is available free of charge via the Internet at http://pubs.acs.org. OM049858D

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,