Diverse Reactivity of Hypersilylsilylene with Boranes and Three-Component Reactions with Aldehyde and HBpin

Abstract

The recently reported hypersilylsilylene PhC-(NtBu) 2 SiSi(SiMe 3 ) 3 (1) reacts with BH 3 , 9-BBN, and PhBCl 2 to yield the respective Lewis acid base adducts 2−4, respectively. Compound 4 undergoes isomerization to form a ring expansion product 5. The same silylene was found to initially form an adduct with HBpin (6) and subsequently isomerized to 7 via the rupture of the B−H bond of HBpin ( 7), where the hydride was bound to the carbon atom of the amidinate ligand and the Bpin unit was attached to the silicon center. Surprisingly, the reaction of 1 with HBcat results in PhC(NtBu) 2 Bcat (8). Subsequently, we have shown that HBcat forms the same product when it reacts with related silylene PhC(NtBu) 2 SiN(SiMe 3 ) 3 (1′). With all of these reactions in hand, we ponder if silylene can activate two small molecules at one time. In this work, we delineate the three-component reactions of silylenes 1 and 1′ with 4-fluorobenzaldehyde and HBpin, which afforded unusual coupling products, 9 and 10, respectively. Note that 9 and 10 were prepared from the cleavage of the B−H and CO bonds by silylene in a single reaction and are the first structurally attested Si−C−O−B coupled products.

Unsymmetrical sp2‐sp3 Disilenes

“…9 crystallizes in the triclinic space group P-1 (Figure 5). The Si atom features an approximate trigonal bipyramidal geometry with Si-P bond lengths of 2.2467 (5) , slightly shorter than the Si II -P bond length in 5.…”

“…A vinyl‐silylsilylene made of a hypersilyl group is also known for the activation of strong bonds (B−H, Si−Cl, C−O, and P 4 ) from Rivard and co‐workers [3] . Our group has introduced the hypersilyl group in the benz‐amidinato silylene moiety and synthesized a benz‐amidinato hypersilylsilylene having the composition PhC(N t Bu) 2 SiSi(SiMe 3 ) 3 ( 1 ), [4] and investigated its reactivity towards chalcogens, acetone and boranes [5] …”

“…[3] Our group has introduced the hypersilyl group in the benzamidinato silylene moiety and synthesized a benz-amidinato hypersilylsilylene having the composition PhC(NtBu) 2 SiSi-(SiMe 3 ) 3 (1), [4] and investigated its reactivity towards chalcogens, acetone and boranes. [5] The next question that arises is whether it is feasible to displace one of the SiMe 3 groups from 1, which would render a Si= Si doubly bound species. Typically, three classical synthetic strategies have been developed towards the preparation of disilenes: a) the photolysis of linear and cyclic trisilanes, [6] b) reductive dehalogenation of halosilanes, [7] and c) the coupling reaction between dilithiosilane and dihalosilane derivatives.…”

The Hypersilyl Substituent in Heavier Low‐Valent Group 14 Chemistry

“…The reactions of 26 with boranes such as BH 3 ⋅SMe 2 , 9‐BBN, and PhBCl 2 were explored, which formed the respective Lewis acid base adducts 33 , 34 , and 35 , respectively (Scheme 11). [16] The latter underwent isomerization to form a ring expansion product 36 . The reaction of 26 with HBpin afforded an addition product 37 , which was relatively unstable, and underwent cooperative B−H bond activation across Si center and amidinate backbone ( 38 ).…”

“…The 1,1 oxidative addition product 38’ (Scheme 12) was also obtained as a minor product. By contrast, the reaction with HBcat, led to amidinato borane 39 [16] …”