Linearly Two-Coordinated Silicon: Transition Metal Complexes with the Functional Groups M≡Si—M and M═Si═M

Abstract

A detailed experimental and theoretical analysis is presented of unprecedented molybdenum complexes featuring a linearly coordinated, multiply bonded silicon atom. Reaction of SiBr(SIdipp) (SIdipp = C[N(CH-2,6- iPr)CH]) with Na[Tp'Mo(CO)(PMe)] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO)Mo≡Si-Mo(CO)(PMe)Tp'] (Tp' = κ- N, N', N″-hydridotris(3,5-dimethylpyrazolyl)borate) (2), in which an almost linearly coordinated silicon atom (∠(Mo1-Si-Mo2) = 162.93(7)°) is bridging the 15VE metal fragment Tp'Mo(CO) with the 17VE metal fragment Tp'Mo(CO)(PMe) via a short Mo1-Si bond (2.287(2) Å) and a considerably longer Mo2-Si bond (2.438(2) Å), respectively. The reddish-orange silylidyne complex [Tp'(CO)Mo≡Si-Tbb] (3) was also prepared from Na-1 and the 1,2-dibromodisilene ( E)-Tbb(Br)Si═Si(Br)Tbb (Tbb = CH-2,6-[CH(SiMe)]-4- tBu) and contains as 2 a short Mo-Si bond (2.2614(9) Å) to an almost linearly coordinated Si atom (∠(Mo-Si-C) = 160.8(1)°). Cyclic voltammetric studies of 2 in diglyme revealed an irreversible reduction of 2 at -1.907 V vs the [Fe(η-CMe)] redox couple. Two-electron reduction of 2 with potassium graphite yielded selectively the 1,3-dimetalla-2-silaallene dianion [Tp'(CO)Mo═Si═Mo(CO)Tp'] (4), which was isolated as the bright yellow dipotassium salt [K(diglyme)]-4. Single crystal X-ray diffraction analysis revealed a centrosymmetric structure of 4. The Mo-Si bond length of 4 (2.3494(2) Å) compares well with those of Mo-Si double bonds and lies in-between the Mo1-Si triple bond and Mo2-Si single bond length of 2. Compounds 2, 3 and [K(diglyme)]-4 were characterized by elemental analyses, IR and multinuclear NMR spectroscopy. Comparative ELF (electron localization function), NBO (natural bond orbital) and NRT (natural resonance theory) analyses of 2, 3 and 4 shed light into the electronic structures of these compounds.

An NHC‐Mediated Metal‐Free Approach towards an NHC‐Coordinated Endocyclic Disilene

“…Single crystal X‐ray analysis for both compounds revealed that the transition metals adopt a close‐to‐octahedral coordination sphere with five terminal carbonyl ligands (Figures 7 and 8). The Si2−Mo bond length of 2.6629(7) Å is at the upper end of the reported range for Si−Mo bond lengths (2.41–2.71 Å) [21,24] . In close analogy, the Si2−W bond of 2.6594(4) Å is also long in comparison to previously published examples (2.34–2.67 Å) [21,22,25] .…”

Transition-metal Complexes with Triple Bonds to Si, Ge, Sn, and Pb and Relevant Complexes

“…In Complexes 35 (Mo) 49 and 36 (Co) 50 have been studied in detail by computational methods. Importantly, both complexes have two •-bonding orbitals (1• and 2•) and two orthogonal πbonding orbitals (1³ and 2³) described in Figure 6, which can explain the formation of the M=Si=M bonding.…”

σ or π? Bonding interactions in a series of rhenium metallotetrylenes

“…[54][55][56][57][58][59][60] More recently, however, the first bridging silicon centers have also been reported within different transition metal systems. 61,62 We also investigated the electronic structures of germylene 2 and germanium-bridged complex 3 computationally. Natural bond orbital analysis of rhenium-germylene 2 revealed a nearly identical bonding scheme to rhenium-silylene 1a.…”