Reactivity of an NHC-Coordinated Trisilacyclopropylidene with Transition Metal Carbonyl Compounds

Abstract

The reaction of the NHC-coordinated trisilacyclopropylidene F with freshly prepared W(CO) 6−n (thf) n (n = 1, 2) yielded in addition to the targeted tungsten pentacarbonyl complex 1 the unexpected NHC-coordinated Si 3 W-heterocycle 2 via oxidative insertion of a W(CO) 4 unit into the peripheral Si−Si single bond of F. The structurally analogous insertion product 3 is selectively accessible by reacting F with Mo(CO) 4 (nbd) in 71% yield. Moreover, F reacts selectively with Fe 2 (CO) 9 giving rise to the iron tetracarbonyl complex 4 that can either thermally or photolytically be converted under release of one equivalent of carbon monoxide into the NHCcoordinated Si 3 Fe-heterocycle 5 featuring a butterfly-type structural motif. FT-IR spectroscopy and DFT calculations of 1 and 4 reveal strong σ-donor and negligible π-acceptor properties of F. Natural bond orbital analysis (NBO) and quantum theory of atoms in molecules (QTAIM) of 2, 3, and 5 give evidence for weak transannular interactions in 2 and 3 and the presence of a transannular bond in 5.

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

“…[ 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 ] Moreover, it is in the range of Si−W single bond lengths (2.69 Å mean) measured in silanide complexes, for example [(SiMe 3 ) 3 Si−W(CO) 5 ] − . [26] …”

“…For base‐coordinated silylenes, numerous transition metal complexes have already been reported. [ 5 , 20 , 21 , 22 ] The entry into this chemistry is provided by the straightforward reaction of 2 with Fe 2 (CO) 9 , which resulted in the formation of 4 in 52 % yield (Scheme 5 ). The 29 Si NMR spectroscopic resonance for the Si2 atom is detected at δ=−71.5 ppm and, upon coordination of the Fe(CO) 4 unit, is shifted to lower field by 131.2 ppm relative to the resonance in uncoordinated 2 .…”

“…[ 5 , 14 ] However, similar Si−Fe bond lengths have been reported for silyl anion iron complexes as well as for trisilacyclopropylidene iron complexes (2.34–2.40 Å). [ 22 , 23 ]…”

“…On the basis of the low selectivity of the photolysis reactions giving pentacarbonyl molybdenum and tungsten THF complexes, [22] we also investigated the simultaneous photolysis of 2 with M(CO) 6 (M=Mo and W) in THF (Scheme 7 ). Interestingly, we found a very selective reactivity, and both compounds ( 5 a , b ) were now isolable nearly quantitatively.…”

“…[5,14] However, similar SiÀ Fe bond lengths have been reported for silyl anion iron complexes as well as for trisilacyclopropylidene iron complexes (2.34-2.40 Å). [22,23] The reaction of 2 with equimolar amounts of a freshly prepared solution of M(CO) 5 •THF (M = Mo and W, synthesized by the photolysis of the corresponding hexacarbonyl metal complexes in THF) resulted in the formation of the pentacarbonyl tungsten complex 5 a in good yields, and of the pentacarbonyl molybdenum complex 5 b in very low yields (Scheme 6).…”