Direct Hydroboration of BB Bonds: A Mild Strategy for the Proliferation of BB Bonds

Braunschweig, Holger; Dewhurst, Rian D.; Hörl, Christian; Phukan, Ashwini K.; Pinzner, Florian; Ullrich, Stefan

doi:10.1002/anie.201309325

Cited by 125 publications

(127 citation statements)

References 35 publications

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“…This can be attributed to the decrease in the length of the boron-boron bond (3: 1.602(2) Å) which falls in the normal range of B=B double bonds in base-stabilized diborenes. [15][16][17][18][19][20][21] As a result of the increase in bond order in the ansa bridge, the Ct− To elucidate the effect of both the cis-configuration and the molecular strain on the physical properties of diborene 3, we carried out a series of analytical and computational studies. The unstrained trans-diborenes of the general formula [(L)RB=BR(L)] (L = Lewis base) were used as a reference to which the properties and reactivity of the cyclic diborene 3 were compared.…”

Section: Abstract: Unsaturated Bridges That Link the Two Cyclopentadimentioning

confidence: 99%

Dibora[2]ferrocenophane: A Carbene‐Stabilized Diborene in a Strained cis‐Configuration

et al. 2016

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Metallocenes with bridged cyclopentadienyl ligands, commonly named ansa metallocenes or metallocenophanes, have emerged as a class of organometallic compounds with an exceptionally wide and diverse range of applications.[1] Among other applications, ansa metallocenes are employed as catalyst precursors in the industrial production of polyolefins [2] and as monomers for ring-opening polymerization to form functional metallopolymers.[3] Their versatility and usefulness stems largely from the fact that their physical properties, and hence reactivity, can be tuned through structural modifications of the ligand framework. For instance, unsaturated two-atom bridges have been developed to increase the configurational rigidity [4] as well as the molecular strain of metallocenophanes, but also to add additional functionality to the metallocene fragment. In part due to difficulties encountered in their synthesis, these types of bridges are relatively rare and only a handful of these have been successfully incorporated into the ferrocene structure, as shown in Figure 1 (I-V). The first examples involved bridging aromatic rings, such as an ortho-phenylene (I), [5,6] a cyclobutadiene cobalt (II) [6] and a ruthenacyclopentadiene fragment (III). [7] Whereas the focus of the initial studies was on synthesis and structural features, the vinylene-bridged dicarba[2]ferrocenophanes IV and V have been developed as candidates for ring-opening metathesis polymerization (ROMP) to produce conjugated metal-containing polymers. [8][9][10] As shown by the groups of Tilley and Manners, such strained ferrocenophanes can indeed undergo ROMP with Schrock-and Grubbs-type catalysts to form conjugated metallopolymers. [9,10] Although homo-and heteronuclear multiple bonding is common for other p-block elements, especially the second-period elements, [11] unsaturated ansa bridges in metallocenophanes are to date restricted to carbon. By capitalizing on the isoelectronic relationship between Lewis base-stabilized diborenes, [(L)RB=BR(L)] (L = Lewis base), [12,13] and olefins, R2C=CR2, we sought to prepare the first ansa metallocene with a heteroatomcontaining multiple bond in the bridge. Herein, we describe the successful synthesis of a strained dibora[2]ferrocenophane (VI), in which the bridging diborene moiety is forced to adopt a cis rather than the prevailing trans configuration. The effects of changing the regiochemistry, as well as the interrelationship between the strain and properties of the diborene are addressed.[a]Prof.

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Section: Abstract: Unsaturated Bridges That Link the Two Cyclopentadimentioning

confidence: 99%

Dibora[2]ferrocenophane: A Carbene‐Stabilized Diborene in a Strained cis‐Configuration

et al. 2016

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“…TheSe 2À bridge in 3 is significantly upfield-shifted in comparison to the singleselenide bridge in the triselenadiborolane (d = 417 ppm). [39] If the NHC-stabilized triple bond is capable of delivering six reducing equivalents,i ts tands to reason that an NHCstabilized diborene (compound containing aB =Bb ond), should be capable carrying out four-electron reductions.T o test this logic we treated aN HC-stabilized diborene with elemental sulfur.W hen at hienyl-substituted, IMe-stabilized diborene (4) [40] was treated with elemental sulfur by sonication, the clean formation of the IMe-stabilized 1,2,4-trithia-3,5-diborolane 5 (Figure 3) was observed, resulting from the reductive transfer of four equivalents of electrons to three sulfur atoms [Eq. [34] Thed ifferences are perhaps ac onsequence of the coordination between two tetrahedral boron atoms in 3, though quarternization of the boron atoms of at riselenadiborolane with pyridine gave ac ompound showing only one 77 Se NMR resonance at d = 211 ppm.…”

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Reductive Insertion of Elemental Chalcogens into Boron–Boron Multiple Bonds

et al. 2015

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The syntheses of sulfur- and selenium-bridged cyclic compounds containing boron stabilized by N-heterocyclic carbenes (NHCs) have been achieved by the reductive insertion of elemental chalcogens into boron-boron multiple bonds. The three pairs of bonding electrons between the boron atoms in the triply bonded diboryne enabled six-electron reduction reactions, resulting in the formation of [2.2.1]-bicyclic systems wherein bridgehead boron atoms are spanned by three chalcogen bridges. A similar reaction using a diborene (boron-boron double bond) resulted in the reductive transfer of both pairs of bonding electrons to three sulfur atoms, yielding a NHC-stabilized trisulfidodiborolane. The demonstration of these six- and four-electron reductions lends support to the presence of three and two pairs of bonding electrons between the boron atoms of the diboryne and diborene, respectively, a fact that may be useful in future discussions on bond order.

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“…[15] Eine interessante Besonderheit dieser Heteroaryl-substituierten Dibore-ne gegenüber der Mehrheit ihrer Aryl-Analoga liegt darin, dass der Thiophen-bzw.F uran-Ring hinsichtlich der B = B-Bindungen eine koplanare Orientierung aufweist und damit ein konjugiertes p-System bildet. [15] Eine interessante Besonderheit dieser Heteroaryl-substituierten Dibore-ne gegenüber der Mehrheit ihrer Aryl-Analoga liegt darin, dass der Thiophen-bzw.F uran-Ring hinsichtlich der B = B-Bindungen eine koplanare Orientierung aufweist und damit ein konjugiertes p-System bildet.…”

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Dreifach koordiniertes Bor als Superdonor und ‐akzeptor für quadrupolare Nahinfrarot‐Chromophore

et al. 2019

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Zwei neue quadrupolare A-p-D-p-A-Chromophore wurden dargestellt, die sowohl einen stark elektronendonierenden Kern als auchs tark elektronenakzeptierende Dimesitylboryl-(BMes 2 )b zw.B is(2,4,6-tris(trifluormethyl)phenyl)boryl-Endgruppen (B F Mes 2 )b esitzen.D ie Analyse der Verbindungen mittels NMR-Spektroskopie,R çntgenstrukturanalyse,C yclovoltammetrie und UV/Vis-NIR-Absorptionsbzw.E missionsspektroskopie zeigte,d ass sie ausgedehnte, konjugierte p-Systeme besitzen,d ie das gesamte B 4 C 8 -Rückgrat umfassen. Die Kombination aus außergewçhnlich starken p-Donor-(Diboren) und p-Akzeptorgruppen (Diarylboryl), die beide auf dreifach koordinierten Boratomen basieren, führt zu sehr kleinen HOMO-LUMO-Abständen, was in einer starken Absorption im nahen Infrarotbereichm it Absorptionsmaxima in THF bei 840 bzw.1 092 nm und sehr hohen Extinktionskoeffizienten von ca. 120 000 m À1 cm À1 resultiert. Zudem zeigen beide Moleküle eine schwache Fluoreszenz im nahen IR-Bereichmit kleinen Stokes-Verschiebungen.

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Direct Hydroboration of BB Bonds: A Mild Strategy for the Proliferation of BB Bonds

Cited by 125 publications

References 35 publications

Dibora[2]ferrocenophane: A Carbene‐Stabilized Diborene in a Strained cis‐Configuration

Dibora[2]ferrocenophane: A Carbene‐Stabilized Diborene in a Strained cis‐Configuration

Reductive Insertion of Elemental Chalcogens into Boron–Boron Multiple Bonds

Dreifach koordiniertes Bor als Superdonor und ‐akzeptor für quadrupolare Nahinfrarot‐Chromophore

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