A Stable N-Heterocyclic Silylene with a 1,1'-Ferrocenediyl Backbone.

Nadine Weyer,Julia I. Schweizer,Clemens Bruhn,Max C. Holthausen,Myron Heinz,Ulrich Siemeling

doi:10.1002/anie.202011691

Nadine Weyer, Julia I. Schweizer + Show 4 more

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https://doi.org/10.1002/anie.202011691

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Abstract

The N‐heterocyclic silylene [{Fe(η5‐C5H4‐NDipp)2}Si] (1DippSi, Dipp=2,6‐diisopropylphenyl) shows an excellent combination of pronounced thermal stability and high reactivity towards small molecules. It reacts readily with CO2 and N2O, respectively affording (1DippSiO2)2C and (1DippSiO)2 as follow‐up products of the silanone 1DippSiO. Its reactions with H2O, NH3, and FcPH2 (Fc=ferrocenyl) furnish the respective oxidative addition products 1DippSi(H)X (X=OH, NH2, PHFc). Its reaction with H3BNH3 unexpectedly results in B−H, instead of N−H, bond activation, affording 1DippSi(H)(BH2NH3). DFT results suggest that dramatically different mechanisms are operative for these H−X insertions.

Highlights

The N-heterocyclic silylene [{Fe(h5-C5H4-NDipp)2}Si] (1DippSi, Dipp = 2,6-diisopropylphenyl) shows an excellent combination of pronounced thermal stability and high reactivity towards small molecules
The rapid development of carbene chemistry has led to acyclic diaminocarbenes (ADACs),[8] ring-expanded NHCs with ring sizes > 5[9] and cyclic(amino)carbenes (CAACs),[10] which are all closely related to standard NHCs, but exhibit a more pronounced ambiphilicity, and higher reactivity.[11]
We here report on the reNHSi [{Fe(h5-C5H4-NDipp)2}Si] (1DippSi), which contains a six-membered FeC2N2Si ring. 1DippSi is an analogue of our stable ferrocene-based NHCs, whose ambiphilicity allowed for small-molecule activation reactions unprecedented for diaminocarbenes.[16,17]

Summary

Introduction

Its reaction with 1MesLi2 in C6D6 afforded the silylene 1MesSi together with IPr (Scheme 1). When generated by reaction of 1DippSi with N2O in benzene at room temperature, this silanone forms the expected dimer (1DippSiO)2 (Scheme 2; see the SI).[21] An analogous stepwise reaction with CO2 was first reported for decamethylsilicocene (Cp*2Si).[22] Dialkylsilylene C[23] as well as IPr = N-Si-OSitBu3 and IPr = N-SiSi(SiMe3)3, an acyclic (imino)(siloxy)- and (imino)(silyl)silylene,[24] are the only examples containing dicoordinate SiII in this context to date.[25] We found that IPr is removed by complexation with ZnCl2, which is inert towards 1DippSi. In contrast to 1DippSi, [ZnCl2(IPr)][26] is insoluble in hexane.

Results

Conclusion