Preparation and Reactions of Compounds with Heavier Group 14 Elements in Low Oxidation States

Abstract

Facile synthesis of chlorosilylene (PhC(NtBu)2SiCl) in 90% yield was reported using LiN(TMS)2 as a dehydrochlorinating agent and its versatile reactivity with various organic substrates was examined. Furthermore, the bis(silylene) [PhC(NtBu)2]2Si2 was isolated in low yield (5.2%) from the reduction of amidinato trichlorosilane with 3 equiv of potassium graphite. Theoretical calculation shows that the compound has two Si(I) centers which are connected by means of a σ-bond. Reactivities of this compound towards ketone, diketone, N2O were probed and several siloxane derivatives were obtained. Also, the addition of 2 equiv of diphenylacetylene to [PhC(NtBu)2]2Si2 has been reported. Both diphenylacetylene equivalents add across the Si-Si, with concomitant Si-Si bond rupture, to give the 1,4-disilabenzene derivative. This disilabenzene species is nearly planar in the solid state despite the tetrahedral silicon centers, and calculations show that there is some aromatic character to the system [NICS(1) = -3.6]. We also studied the reactions of elemental phosphorus with [PhC(NtBu)2]2Si2, which afforded a of the first complex with a Si-P-Si-P core through activation of the P4 molecule. X-ray structural analysis revealed most apparent feature of the compound is the planar Si-P-Si-P four membered ring, which consists of four equivalent Si P bonds. The preparation of bis-silylene was followed by the synthesis of its germanium version [PhC(NtBu)2]2Ge2. A theoretical study indicates clearly that it can be best viewed as digermylenes although they can formally be drawn as donor-stabilized digermynes. The reactivity reflects the digermylene nature of the species. For example, reaction of [PhC(NtBu)2]2Ge2 with 2 equiv of Fe2(CO)9 gives the diiron complex where each germanium center is coordinated by one Fe(CO)4 moiety to give the complex [LGe(Fe(CO)4-Ge(Fe(CO)4L, L= PhC(NtBu)2]. The only other reactivity of this species is the addition of azobenzene across the Ge-Ge bond with concomitant bond rupture to give the new 1,2-digermylene hydrazine species [LGeN(Ph)N(Ph)GeL]. All the compounds were characterized by multinuclear NMR spectroscopy, EI-MS spectrometry, elemental analysis, and single crystal X-ray diffraction studies.