Coordination chemistry and FLP reactivity of 1,1- and 1,2-bis-boranes

Coordination chemistry and frustrated Lewis pair (FLP) chemistry have been most commonly studied using monodentate Lewis acids. In this paper, we examine the corresponding reactions employing the 1,1- and 1,2-bis-boranes, PhCH2CH(B(C6F5)2)21 and Me3SiCH(B(C6F5)2)CH2B(C6F5)22, respectively. Coordination of isocyanide to these species results in the formation of the products RCH(B(C6F5)2CNtBu)CH2(B(C6F5)2CNtBu) (R = Ph 3, Me3Si 4). The rearrangement of 1 to give the 1,2-bis-borane adduct 3 was probed and attributed to a donor-induced retrohydroboration and subsequent hydroboration. The analogous reaction of 1 is evident in efforts to use the Gutman-Beckett method to assess its Lewis acidity. However, in combination with tBu3P, bis-boranes 1 and 2 form FLPs and react with H2 to give [tBu3PH][PhCH2CH(B(C6F5)2)2(μ-H)] 5a and [tBu3PH][Me3SiCH(B(C6F5)2)CH2(B(C6F5)2)(μ-H)] 6, respectively. Reactions of 1 and 2 with various donors and PhCCH were shown to give deprotonation and addition products, depending on the nature of the base. However, in the case of 1, products resulting from retrohydroboration, and subsequent hydroboration are evident. Several of these alkyne products are crystallographically characterized.

Boron and Silicon-Substituted 1,3-Dienes and Dienophiles and Their Use in Diels-Alder Reactions

Boron and silicon-substituted 1,3-dienes and boron and silicon-substituted alkenes and alkynes have been known for years and the last 10 years have seen a number of new reports of their preparation and use in Diels-Alder reactions. This review first covers boron-substituted dienes and dienophiles and then moves on to discuss silicon-substituted dienes and dienophiles.

Metallomimetic Chemistry of Boron

The study of main-group molecules that behave and react similarly to transition-metal (TM) complexes has attracted significant interest in recent decades. Most notably, the attractive idea of replacing the all-too-often rare and costly metals from catalysis has motivated efforts to develop main-group-element-mediated reactions. Main-group elements, however, lack the electronic flexibility of TM complexes that arises from combinations of empty and filled d orbitals and that seem ideally suited to bind and activate many substrates. In this review, we look at boron, an element that despite its nonmetal nature, low atomic weight, and relative redox staticity has achieved great milestones in terms of TM-like reactivity. We show how in interelement cooperative systems, diboron molecules, and hypovalent complexes the fifth element can acquire a truly metallomimetic character. As we discuss, this character is powerfully demonstrated by the reactivity of boron-based molecules with H₂, CO, alkynes, alkenes and even with N₂.

Geminal bis-borane formation by borane Lewis acid induced cyclopropyl rearrangement and its frustrated Lewis pair reaction with carbon dioxide

The borylated tetrahydroborole obtained by the reaction of cyclopropylacetylene with Piers' borane adds carbon dioxide under frustrated Lewis pair conditions.

Cyclopropylacetylene reacts with two molar equivalents of Piers' borane [HB(C₆F₅)₂] under mild conditions by an addition/rearrangement sequence with cyclopropyl ring opening to give a mixture of two α-B(C₆F₅)₂ substituted tetrahydroboroles. This compound forms an active frustrated Lewis pair with P^tBu₃ that heterolytically splits dihydrogen and adds carbon dioxide as a geminal chelate bis-boryl component. The respective reactions of the two-fold HB(C₆F₅)₂ addition to Ph-CH₂CH₂C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH were studied as a geminal Lewis acid reference. Most of the products were characterized by X-ray diffraction.