Interaction between Spirosilanes and Lewis Bases: from Coordination to Frustration

Abstract

In this work, the interaction between Lewis bases, especially N-heterocyclic carbenes (NHCs), and hindered neutral silicon derivatives featuring high Lewis acidity is described.T he formation of normal and abnormal Lewis adducts could be controlled by varying the acidity of the corresponding tetravalent spiro organosilane. Some DFT calculations permitted to gain insight into the thermodynamics of the NHC-spirosilane interaction featuring various NHCs differing in sizea nd s-donor capacity.S pirosilanes are introduceda sn ew Lewis partners in frustrated Lewis pair (FLP) chemistry and some FLP-typer eactivities are presented, in particular the activation of formaldehyde that could occur with both hindered NHCs andp hosphines.

A Parisian Vision of the Chemistry of Hypercoordinated Silicon Derivatives

“…As previously mentioned, the Martin's spirosilane 4 exhibits a FLP character when confronted to encumbered NHCs. The same trend was also observed with other hindered bases such as tert ‐butylphosphine and 2,2,6,6‐tetramethylpiperidine since in both cases, no adducts are formed when they are in presence of silane 4 [18] . This behavior is similar to that of B(C 6 F 5 ) 3 , the most employed Lewis acid in FLP chemistry [19] .…”

Synthesis and Optical Resolution of Configurationally Stable Zwitterionic Pentacoordinate Silicon Derivatives

“…The same barrier was obtained for the abnormal adduct 3 b bearing tert ‐butyl groups on the imidazolium ring as for 3 a , but with additional trifluoromethyl groups on the substituted benzene rings attached to the silicon [14b] . The higher barrier can be attributed either to an increased steric hindrance slowing down the Berry pseudorotations or to an electronic effect of the withdrawing groups on the silicon atom.…”

Identification of Bond‐Weakening Spirosilane Catalyst for Photoredox α‐C−H Alkylation of Alcohols

“…When other HAT catalysts ( 5 d and 5 e ) and quinuclidine derivatives ( 5 b and 5 c ) were used instead of 5 a , the C−H alkylation product was obtained in only low yield (Entries 14–17). 5 a might function as not only a HAT catalyst but also a base to form a silicate . When we applied previously reported reaction conditions of α‐C−H alkylation of alcohols to 1 a and 2 a , products 3 aa + 3 aa′ were not obtained .…”

“…When using a PC with either a lower oxidation potential (4 b) or a much higher oxidation potential (4 d), the desired products 3 aa and 3 aa' were not obtained (Entries 11 and 13). [21] When we applied previously reported reaction conditions of α-CÀ H alkylation of alcohols [9a,b,10] to 1 a and 2 a, products 3 aa + 3 aa' were not obtained. The oxidation potential of PC 4 c was almost identical to that of 4 a (E(Ir III* /Ir II ) = + 1.68 V for 4 c and + 1.65 V for 4 a vs SCE in CH 3 CN), but the slightly weaker reduction potential (E 1/2 (Ir II /Ir III ) = À 0.69 V for 4 c and À 0.79 V for 4 a vs SCE in CH 3 CN) perhaps rendered the catalyst regeneration step more difficult.…”