The Donor‐Stabilized Silylene Bis[N,N′‐diisopropylbenzamidinato(−)]silicon(II): Synthesis, Electronic Structure, and Reactivity

Abstract

A convenient and robust synthesis of bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) (1), a donor-stabilized silylene, has been developed (35 g scale). To get further information about the reactivity profile of 1, a series of oxidative addition reactions were studied. Treatment of 1 with PhSe-SePh (Se-Se bond activation), C6F6 (C-F activation), and CO2 (C=O activation/cycloaddition) yielded the neutral six-coordinate silicon(IV) complexes 10, 11, and 13, respectively. Treatment of 1 with N2O resulted in the formation of the dinuclear five-coordinate silicon(IV) complex 12 (oxidative addition/dimerization), which contains a four-membered Si2O2 ring. Compounds 10-13 were characterized by NMR spectroscopic studies in the solid state and in solution and by crystal structure analyses. Silylene 1 is three-coordinate in the solid state (from crystal structure analysis) and exists as the four-coordinate isomer 1' in benzene solution (from computational studies). Based on state-of-the-art relativistic DFT analyses, the four-coordinate species 1' was demonstrated to be the thermodynamically favored isomer in benzene solution (favored by ΔG = 6.6 kcal mol(-1) over the three-coordinate species 1). The reason for this was studied by bonding analyses of 1 and 1'. Furthermore, the (29)Si NMR chemical shifts of 1 and 1' were computed, and in the case of 1' it was analyzed how this NMR spectroscopic parameter is affected by solvation. These studies further supported the assumption that the silylene is four-coordinate in solution.

Investigations of the Nature of ZnII−SiII Bonds

“…Comparison of the effect of the C 6 H 5 and C 6 F 5 groups on the Zn−Si bond length is thus possible. Although amidinato silylenes and bis‐amidinato silylenes as well as other silylenes tend to react with different fluorobenzenes through C−F bond activation to give silicon(IV) fluorides, we isolated [ L Zn(C 6 F 5 ) 2 ] ( 5 ) in good yields. In situ 1 H NMR‐scale experiments in C 6 D 6 did not show any sign of C−F bond activation.…”

SO2 Activation by the Bis(guanidinato)silylene [iPrNC(NiPr2)NiPr]2Si: Formation of Neutral Six‐Coordinate Silicon(IV) Complexes with a Chelating Sulfito or Dithionito Ligand

“…The donor‐stabilized bis(amidinato)silylene 1 has been demonstrated to activate small molecules, such as N 2 O,[1b] CO 2 ,[1b] SO 2 , and CS 2 (for reviews dealing with stable silylenes, see the literature). The higher‐coordinate silicon(IV) complexes 2 ,[1b] 3 ,[1b] 4 , 5 , and 6 are the products formed in these oxidative addition reactions. The analogous bis(guanidinato)silylene 7 also activates N 2 O, CO 2 , and CS 2 to afford the respective higher‐coordinate silicon(IV) complexes 8 , 9 , and 10 .…”

“…Except for the CO 2 activation, which leads to the structurally analogous six‐coordinate carbonatosilicon(IV) complexes 3 and 9 , all the other small‐molecule activations by the amidinato/guanidinato analogues 1 and 7 studied so far resulted in the formation of structurally different products ( 2 vs. 8 and 6 vs. 10 ). In this context, it is interesting to note that the reactions of silylenes 1 and 7 with the transition‐metal carbonyl complexes [M(CO) 6 ] (M = Cr, Mo, W; nucleophilic substitution reactions)[1a], , and with the chalcogenes S 8 , Se, and Te (oxidative addition reactions), also resulted in the formation of structurally different products each. Furthermore, silylenes 1 and 7 themselves differ in their structural chemistry: compound 1 is three‐coordinate in the solid state and four‐coordinate in solution, whereas 7 is three‐coordinate in both phases , .…”

A Silacyclopropene with a Six‐Coordinate Silicon Atom and an SiN4C2 Skeleton: Synthesis and Structural Characterization

“…Since the first report on a stable silylene by Jutzi et al three decades ago, the chemistry of stable silylenes has developed into one of the most actively studied fields in molecular silicon chemistry . We have also contributed to this area by synthesizing the first bis(amidinato)silylene (compound 10 ) that is three‐coordinate in the solid state and four‐coordinate in solution . As part of our systematic reactivity studies with 10 ,, we already investigated a series of [4+1] cycloaddition reactions with 1,3‐dienes and 1,2‐diketones.…”

“…We have also contributed to this area by synthesizing the first bis(amidinato)silylene (compound 10 ) that is three‐coordinate in the solid state and four‐coordinate in solution . As part of our systematic reactivity studies with 10 ,, we already investigated a series of [4+1] cycloaddition reactions with 1,3‐dienes and 1,2‐diketones. [7d] Herein, we report on a [2+1] cycloaddition reaction of 10 .…”