Borylentransfer unter thermischen Bedingungen: Synthese und Struktur eines Tetrarhodium‐Bisborylenkomplexes

Braunschweig, Holger; Forster, Melanie; Radacki, Krzysztof

doi:10.1002/ange.200504093

Cited by 45 publications

(29 citation statements)

References 33 publications

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“…The BÀRh bond length is similar to analogous distances found in the bridged bisborylene complex [Rh 4 {m-BN(SiMe 3 ) 2 } 2 (m-Cl) 4 (m-CO)(CO) 4 ], which features two threecoordinate boron atoms linked to two rhodium centers (2.004(3) , 2.076(3) , 2.051 (3) ). [5] The molecular geometry also closely resembles that of the methylene-bridged…”

Section: Holger Braunschweig* Melanie Forster Thomas Kupfer and Famentioning

confidence: 81%

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Borylene Transfer under Thermal Conditions for the Synthesis of Rhodium and Iridium Borylene Complexes

et al. 2008

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The recent development of the photochemical transfer of borylene ligands from chromium and tungsten borylene complexes to inorganic, [1] and more recently, organic [2] substrates has shown the "DBX" fragment to be a useful synthon. As is the case for many reactive species, the feisty nature of the difficult-to-generate free borylenes [3] is tempered by coordination to a transition metal, so that their reactivity, which is reminiscent of the neighboring carbene species, [4] can be harnessed in conventional syntheses.In particular, the above-mentioned transfer reaction has proven a boon for the synthesis of borylenes with other metal centers, and has uncovered a surprising synthesis of borirenes from terminal or internal alkynes. However, with the exception of one example, [5] this reaction requires activation by UV light, and is thus limited to photochemically inert substrates. Herein we describe the use of a terminal molybdenum borylene complex [6] which performs this task without irradiation and at ambient temperatures. This new reactivity is borne out in the synthesis of the first terminal borylene complexes of the Group 9 elements rhodium and iridium. These two metals have been the subject of intense investigation regarding their application in catalytic borylation reactions. A variety of boryl complexes have therefore been prepared, [7] however their complexes with lower-coordinate boron have been overlooked owing to the lack of reliable synthetic routes. The complexes presented herein go some way in addressing this deficiency.When the rhodium dicarbonyl complex 2 was added to an equimolar amount of 1 in C 6 D 6 at ambient temperature, multinuclear NMR spectroscopy revealed gradual consumption of the starting materials within 16 h and formation of what appeared to be the terminal borylene species [(h 5 -C 5 H 5 )(OC)Rh = BN(SiMe 3 ) 2 ] (4) with concomitant generation of [Mo(CO) 6 ], as indicated by a resonance at d = 201.49 ppm in the 13 C NMR spectrum for the latter [Eq.(1)]. After workup, 4 was isolated as an analytically pure dark orange oil in 67 % yield.The 11 B{ 1 H} NMR spectrum of 4 features a broad signal at d = 75 ppm (w 1/2 = 309 Hz) which is shifted upfield relative to the signal for 1 (d = 91 ppm), [6] suggesting the formation of a terminal borylene species. [8] The 1 H NMR spectrum shows a singlet for the trimethylsilyl group at d = 0.21 ppm, which is deshielded with respect to that of the molybdenum borylene precursor (d = 0.15 ppm).[6] A single conspicuous band at ñ = 1955 cm À1 in the solution IR spectrum of 4 suggests that a lone CO ligand at rhodium was terminally coordinated. Unfortunately, owing to its oily consistency, it was not possible to obtain single crystals of 4 suitable for X-ray diffraction.Borylene 4 is unstable in solution, which was revealed by 11 B{ 1 H} NMR spectroscopy. The 11 B{ 1 H} NMR spectrum indicated the formation of a new boron-containing product even under mild conditions (hexane at À35 8C). Conversion into the new product was complete after about 15 days, at wh...

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Section: Holger Braunschweig* Melanie Forster Thomas Kupfer and Famentioning

confidence: 81%

“…However, with the exception of one example, [5] this reaction requires activation by UV light, and is thus limited to photochemically inert substrates. Herein we describe the use of a terminal molybdenum borylene complex [6] which performs this task without irradiation and at ambient temperatures.…”

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Borylene Transfer under Thermal Conditions for the Synthesis of Rhodium and Iridium Borylene Complexes

et al. 2008

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“…By contrast, the incorporation of two borylene or carbyne ligands into a mononuclear transition-metal complex has always proven problematic. While in the former case a suitable synthetic approach is still lacking, [12] the synthesis of bis(carbyne) species is further hampered by reductive coupling to form acetylenes, particularly with alkyl-substituted carbynes.[13] It has not yet been elucidated whether bis-(borylene) complexes are resistant towards reductive coupling. In any case, it would require the availability of experimental data before this question could be clarified.…”

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Towards Homoleptic Borylene Complexes: Incorporation of Two Borylene Ligands into a Mononuclear Iridium Species

et al. 2010

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The incorporation of subvalent Group 13 ligands into the coordination sphere of transition metals has always been a challenging task, particularly in the formation of homoleptic complexes. Although metastable or sterically protected subvalent E I (E = Al, Ga, In) precursors have become accessible during the last few decades, [1] for example, E I halides, [1, 2] [{Cp*E} n ] (Cp* = h 5 -C 5 Me 5 ), [1, 3] and [{EC(SiMe 3 ) 3 } n ], [1, 4] stable and isolable boron congeners have still not been prepared. For this reason, only homoleptic transition-metal complexes with Al-, Ga-, and In-based ligands have so far been realized, for example, mononuclear [Ni(ECp*) 4 ] (A; E = Al, Ga) [5,6] and [Ni{EC(SiMe 3 ) 3 } 4 ] (B; E = Ga, In), [7,8] as well as numerous heteroleptic examples with two or more E I ligands. [9] The corresponding subvalent boron ligands, that is, borylenes, have only been generated directly in the coordination sphere of transition metals [10] to form species such as [(OC) 5 M=BN(SiMe 3 ) 2 ] (C; M = Cr, Mo, W).[11] To date, both mononuclear borylene complexes containing more than one borylene substituent as well as homoleptic borylene species have continuously resisted isolation. Nonetheless, borylene complexes have sparked increasing interest in fundamental organometallic research because of their close relationship with important organometallic compounds such as carbene, carbyne, and vinylidene complexes, and the similarity of the bonding properties of borylene and carbonyl ligands. Numerous experimental and computational studies have previously examined these bonding properties in detail.[10] It was thus shown that BR has stronger s-donor and p-acceptor properties than CO, which makes the M À BR bond even more stable with respect to homolytic dissociation than the M À CO bond, but in turn it is kinetically labile due to the high polarity. Getting back to the series of related ligands mentioned above, the predominance of the CO and carbene ligands in organometallic chemistry is also manifested by the fact that homoleptic complexes have only been accessible with these two ligands. By contrast, the incorporation of two borylene or carbyne ligands into a mononuclear transition-metal complex has always proven problematic. While in the former case a suitable synthetic approach is still lacking, [12] the synthesis of bis(carbyne) species is further hampered by reductive coupling to form acetylenes, particularly with alkyl-substituted carbynes.[13] It has not yet been elucidated whether bis-(borylene) complexes are resistant towards reductive coupling. In any case, it would require the availability of experimental data before this question could be clarified. We have been studying borylene complexes for more than a decade now, but all our efforts to synthesize a complex with more than one terminal borylene have so far failed.Herein, we describe the successful generation and isolation of a long-sought after mononuclear, terminal bis-(borylene) complex derived from the [Cp*Ir] half-sandwich fragment,...

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“…[19] Nachfolgende Versuche zur B-B-Kupplung von Borylenliganden waren jedoch zunächst erfolglos; die Einführung von zwei Borylenliganden in einen Komplex erwies sich als überaus schwierig und blieb auf ein zufälliges Einzelbeispiel beschränkt. [20] Der Tabelle 1). [22] Wir gingen jedoch davon aus, dass die starke p-Donierung der Bor-gebundenen Aminogruppen das grçßte Hindernis für eine B-B-Kupplung darstellt und somit der Einsatz von Borylenliganden ohne p-basische Substituenten grçßeren Erfolg versprechen sollte.…”

Section: B-b-einfachbindungen üBer Borylenkupplungunclassified

Einfach‐, Doppel‐, Dreifachbindungen und Ketten: Knüpfung elektronenpräziser B‐B‐Bindungen

2013

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Trotz des großen präparativen Interesses an Diboranen und der hohen B‐B‐Bindungsenthalpie ist die Knüpfung von Bor‐Bor‐Bindungen immer noch schwierig, kaum zu kontrollieren und schlecht vorhersagbar. Methoden zur Herstellung von B‐B‐Mehrfachbindungen sind sogar noch seltener. In den letzten Jahren gab es nun einige Fortschritte zur Lösung dieser Probleme, und dieser Kurzaufsatz unternimmt den Versuch, einen Überblick über die Geschichte der B‐B‐Bindungsbildung zu geben und neue Ergebnisse auf diesem Gebiet zusammenzufassen.

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Borylentransfer unter thermischen Bedingungen: Synthese und Struktur eines Tetrarhodium‐Bisborylenkomplexes

Cited by 45 publications

References 33 publications

Borylene Transfer under Thermal Conditions for the Synthesis of Rhodium and Iridium Borylene Complexes

Borylene Transfer under Thermal Conditions for the Synthesis of Rhodium and Iridium Borylene Complexes

Towards Homoleptic Borylene Complexes: Incorporation of Two Borylene Ligands into a Mononuclear Iridium Species

Einfach‐, Doppel‐, Dreifachbindungen und Ketten: Knüpfung elektronenpräziser B‐B‐Bindungen

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