A series of dialkylsilylene-group 10 metal complexes (R(H)(2)Si)(Me(3)P)(2)M (M = Ni, Pd, Pt, R(H)(2) = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) and novel (η(6)-arene)(dialkylsilylene)nickel complexes (η(6)-arene)(R(H)(2)Si)Ni were synthesized and characterized by NMR spectroscopy and X-ray analysis. The perpendicular geometry around the Si-M bond and the short Si-M distances of (R(H)(2)Si)(Me(3)P)(2)M complexes indicate the significant back donation from the metal to the silylene ligand.

Hydrogens make a difference: The first 14‐electron bis(silylene)palladium (A) and 12‐electron bis(silyl)palladium complexes (B) are synthesized from a stable dialkylsilylene (see picture; gold: Pd; dark blue: Si; light blue: C; magenta: H). The remarkable difference between the L‐M‐L angles of these two complexes is rationalized by applying the Walsh diagram.

H‐Liganden machen den Unterschied: Die ersten Bis(silylen)‐ (A) und Bis(silyl)palladiumkomplexe (B) mit 14‐ bzw. 12‐Elektronen‐Konfiguration wurden ausgehend von einem stabilen Dialkylsilylen synthetisiert (Pd gelb, Si dunkelblau, C hellblau, H magenta). Der bemerkenswerte Unterschied zwischen den L‐M‐L‐Winkeln beider Komplexe wird mithilfe des Walsh‐Diagramms erklärt.

A novel dinuclear palladium complex with one bridging dialkylsilylene ligand 6 was synthesized by the reaction of isolable dialkylsilylene 7 (R 2 Si:) with two equiv of bis(tricyclohexyl)-phosphinepalladium (8). Complex 6 as a prototypical dipalladasilacyclopropane reacts with molecular hydrogen to give dihydrosilane 10 (R 2 SiH 2 ) together with 8 and metallic palladium.Multinuclear transition-metal complexes with bridging silyl and/or silylene groups have received much attention because they show unique structural and bonding properties and would be key intermediates of transformation of silane mediated by transition-metal complexes.1 Although various multinuclear group-10 metal complexes with bridging silyl and/or silylene units have been extensively studied, there have been few reports on the corresponding dipalladium complexes. Osakada et al. have synthesized [L n Pd(-SiH(R)Ph)] 2 (1) as the first silylbridged dimeric palladium complexes with three-center-twoelectron Si-H-Pd bond.2 Fürstner et al. and Herrmann et al. have reported dipalladium complexes with two bridging N-heterocyclic silylenes (2-4) that were prepared by the reactions of stable N-heterocyclic silylenes with palladium(0) complexes. 3,4 Suginome, Ito, et al. have synthesized dipalladium complex 5, in which -silylene and -isocyanide ligands coordinate to the two palladium atoms. 5 In the present paper, we report the synthesis, structure, and an interesting reaction of novel dinuclear palladium complex having one bridging silylene unit (6) using isolable dialkylsilylene 7, which we have recently synthesized as a silylene stabilized kinetically by a bulky 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl ligand.6 To the best of our knowledge, complex 6 is the first mono(-silylene) dipalladium complex without Pd-H-Si bonding or other bridging ligands and, hence, will be useful as a prototypical dipalladasilacyclopropane to investigate the electronic structure and reactions of the ring system (Chart 1).Complex 6 was synthesized by the treatment of dialkylsilylene 7 with bis(tricyclohexylphosphine)palladium (8, 2.1 equiv) in toluene at room temperature (eq 1).7 Recrystallization from toluene gave analytically pure 6 in 24% yield as air-and moisture-sensitive dark blue-purple crystals with the decomposition temperature of 203 C. The structure of 6 was determined by NMR spectroscopy, elemental analysis, and X-ray crystallography. 8,9(1) 2.1 equiv (Cy 3 P) 2 Pd (8) toluene, rt 7 6 (24% yield) Figure 1 shows the molecular structure of 6 determined by X-ray analysis. The Pd 2 unit is disordered over two positions with almost the same site occupancy factors [0.486(3) for Pd1(Pd2) and 0.514(3) for Pd1 0 (Pd2 0 )]. The geometry around the Si1-Pd1-Pd2 ring and Si1-Pd1 0 -Pd2 0 ring are similar to each other. The dialkylsilylene unit bridges over the two palladium atoms and the silacyclopentane ring is nearly perpendicular to the SiPd 2 three-membered ring; the dihedral angle between C1-Si1-C4 and Pd1-Si1-Pd2 (Pd1 0 -Si1-Pd2 0 ) planes is 91.62 (92.28 ). Ea...

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