Abstract
A detailed experimental and theoretical analysis is presented of unprecedented molybdenum complexes featuring a linearly coordinated, multiply bonded silicon atom. Reaction of SiBr2 (SIdipp) (SIdipp = C[N(C6H3-2,6-iPr(2))CH2](2)) with Na[Tp'Mo(CO)(2) (PMe3)] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO)(2)Mo Si-Mo(CO)(2) (PMe3)Tp'] (Tp' = ...
Abstract
A detailed experimental and theoretical analysis is presented of unprecedented molybdenum complexes featuring a linearly coordinated, multiply bonded silicon atom. Reaction of SiBr2 (SIdipp) (SIdipp = C[N(C6H3-2,6-iPr(2))CH2](2)) with Na[Tp'Mo(CO)(2) (PMe3)] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO)(2)Mo Si-Mo(CO)(2) (PMe3)Tp'] (Tp' = kappa(3)-N,N',N"-hydridotris(3,5-dimethylpyrazolyl)borate) (2), in which an almost linearly coordinated silicon atom (angle(Mo1-Si-Mo2) = 162.93(7)degrees) is bridging the 1SVE metal fragment Tp'Mo(CO)(2) with the 17VE metal fragment Tp'Mo(CO)(2) (PMe3) via a short Mo1-Si bond (2.287(2)angstrom) and a considerably longer Mo2-Si bond (2.438(2)angstrom), respectively. The reddish-orange silylidyne complex [Tp'(CO)(2) Mo Si-Tbb] (3) was also prepared from Na-1 and the 1,2-dibromodisilene (E)-Tbb(Br)Si=Si(Br)Tbb (Tbb = C6H2 -2,6-[CH(SiMe3)(2)](2) -4-tBu) and contains as 2 a short Mo-Si bond (2.2614(9)angstrom) to an almost linearly coordinated Si atom (angle(Mo-Si-C-Tbb) = 160.8(1)degrees). Cyclic voltammetric studies of 2 in diglyme revealed an irreversible reduction of 2 at -1.907 V vs the [Fe(eta(5)-C-5 Mes)(2)](+)(/0) redox couple. Two-electron reduction of 2 with potassium graphite yielded selectively the 1,3-dimetalla-2-silaallene dianion [Tp'(CO)(2) Mo=Si=Mo(CO)(2) Tp'](2)- (4(2-)), which was isolated as the bright yellow dipotassium salt [K(diglyme)](2)-4. Single crystal X-ray diffraction analysis revealed a centrosymmetric structure of 4(2-). The Mo-Si bond length of 4(2-) (2.3494(2)angstrom) compares well with those of Mo-Si double bonds and lies in-between the Mol-Si triple bond and Mo2-Si single bond length of 2. Compounds 2, 3 and [K(diglyme)(2)]-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(2-) shed light into the electronic structures of these compounds.
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