Dinuclear Palladium Complex with a Bridging Dialkylsilylene Ligand

Abstract

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...

Synthesis and structures of (dialkylsilylene)bis(phosphine)-nickel, palladium, and platinum complexes and (η6-arene)(dialkylsilylene)nickel complexes

“…11 The Si(1)-Pd(1) distance in 6 (2.2395(8) Å) is also remarkably shorter than those of the typical Si-Pd single bond (2.259-2.520 Å) 12 and even shorter than those of bis(dialkylsilylene)palladium 2 (2.263(1) and 2.260(1) Å). 7 The Si(1)-Pt(1) bond length of 7 (2.2123(11) Å) is also significantly shorter than those of the typical Si-Pt single bond (2.224-2.451 Å) 12 and almost comparable to that of 13a (2.210(2) Å). 8…”

“…Formation of (dialkylsilylene)(Cy 3 P)Pd (3) from silylene and 1 equivalent of (Cy 3 P) 2 Pd was confirmed as follows. 7 In a J. Young NMR tube, (Cy 3 P) 2 Pd (16.3 mg, 0.0244 mmol) and silylene 1 (10.0 mg, 0.0268 mmol) were placed.…”

“…5c Recently, silylene 1 was found to be applicable to the synthesis of dialkylsilylene-transition metal complexes. Silylene 1 reacted with 0.5, 1 and 2 equivalents of (Cy 3 P) 2 Pd (Cy = cyclohexyl) to give bissilylene-palladium complex (R H 2 Si) 2 Pd (2), 6 monosilylene-palladium (R H 2 Si)(Cy 3 P)Pd (3) 7 and monocyclic mono(m-silylene)dipalladium complex (m-R H 2 Si)(Cy 3 P) 2 Pd 2 complex (4). 7 During the course of our study on the synthesis of novel transition metal complexes having silylene 1, we synthesized and characterized a series of dialkylsilylene-group 10 metal complexes 5-7 and novel (h 6 -arene)(silylene)nickel complexes 8 and 9 (Chart 1).…”

An isolable dialkylsilylene and its derivatives. A step toward comprehension of heavy unsaturated bonds

“…When the molar ratio is 1/1, monosilylene complex 32 is formed in a high yield as an air-sensitive purple oil but the isolation was unsuccessful due to the contamination of free tricyclohexylphosphine (eqn (11)). 20,47 The reaction of 6 with (Cy 3 P) 2 Pd at the ratio o1/2 gives an interesting dinuclear palladium complex 33 with a bridging dialkylsilylene ligand (eqn ( 12)). 47 ð10Þ ð11Þ ð12Þ Interestingly, bis(silylene)complex 31 reacts with molecular hydrogen in benzene-d 6 at room temperature to give an unprecedented 12-electron dicoordinate palladium complex 34, as orange crystals (eqn ( 13)).…”

A Helmeted Dialkylsilylene

“…80 While the reaction of silylene 1 with 1 equiv of bis(tricyclohexylphosphine)palladium in benzene at room temperature gave mono(silylene)palladium complex 62 as an oil, a similar reaction of 1 with 0.5 equiv of bis(tricyclohexylphosphine)palladium gave bis(silylene)palladium complex 63 as air-and moisture-sensitive dark red crystals (mp 124 C decomp.) in 40% yield.…”