Palladium and platinum complexes are versatile catalysts for the transformation of organosilicon compounds. However, the utility of nickel complexes has not been as well established. [2] The understanding of the structure and the reactivity of silylnickel species is indispensable for the development of new catalytic methodologies. Although a number of mononuclear silylmetal complexes are known for all Group 10 metals, structurally characterized silylene-bridged dinuclear complexes have been reported only for platinum and palladium. [5, These dinuclear species are considered to play important roles in catalytic processes. For example, silylene-bridged Pt 2 Si 2 rings are potential key intermediates in the platinum-catalyzed dehydrocoupling of hydrosilanes. [4b±d] Here we report on the reaction of 1,2disilylbenzene (1) with nickel(0) complexes, which led to the isolation of the dinuclear (m-silylene
Me or Et), which contain the first structurally characterized four-membered Ni 2 Si 2 rings. The short contact between the SiH 2 and m-SiH moieties revealed by X-ray crystallography suggests the possibility of SiÀSi bond formation, which indeed takes place in a similar reaction of 1-(dimethylsilyl)-2silylbenzene (2) with [Ni(dmpe) 2 ] (dmpe 1,2-bis(dimethylphosphanyl)ethane).
Previously, we reported that treatment of 1 with [Ni(dmpe) 2 ] results in the dimeric bis(silyl)nickel(ii) complex 3 and the first tetrakis(silyl)nickel(iv) complex 4 a. A similar reaction under somewhat different conditions led to the formation of a new dimeric Ni III complex. While studying 3 by variable-temperature NMR spectroscopy in [D 8 ]toluene, we observed, upon heating the solution to 80 8C, a color change from pale yellow to orange and the emergence of new weak signals in the 1 H and 31 P NMR spectra. Further heating at 110 8C for 30 min gave a new complex 5 a, which could be isolated as orange crystals (34 %) by crystallization from benzene. The similar complex 5 b, ligated by 1,2-bis(diethylphosphanyl)ethane (depe), was also obtained directly from 1 and [Ni(PEt 3 ) 2 (depe)] (1:Ni 1:1.05); the reaction proceeded even at room temperature and gave 5 b as the main product (49 % yield). The 29 Si NMR spectrum of the crude mixture showed the presence of the tetrakis(silyl)nickel(iv) complex 4 b as a side product [d À 2.11 (dd, 2 J(Si,P cis ) 20, 2 J(Si,P trans ) 101 Hz), 3.03 (t, 2 J(Si,P) 16 Hz)].
qualitatively identified by using 1 H NMR spectroscopy and GC-mass spectrometry.