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Photoreactions of Phenylborylene with Dinitrogen and Carbon Monoxide
journal contribution
posted on 2017-10-10, 16:55 authored by Klara Edel, Matthias Krieg, Dirk Grote, Holger F. BettingerFormal removal of
two bonding partners from boranes, BR3, yields borylenes,
RB, which have been inferred as reactive intermediates
in a number of reactions. Phenylborylene (R = C6H5; 1) is accessible from phenyldiazidoborane by photochemical
extrusion of dinitrogen under matrix isolation conditions. Concomitantly,
the nitrene PhNBN is formed via phenyl rearrangement. Here we used
a combination of UV/vis, IR, and ESR spectroscopy under cryogenic
matrix isolation conditions to investigate the properties and reactivity
of phenylborylene. We detected an absorption band of phenylborylene
at 375 nm (S0 → S2) and tentatively assigned
the S0 → S1 transition to a very weak
band at 518 nm. We also show for the first time that an electrophilic
borylene such as 1 can react with N2 reversibly
and with CO irreversibly under photochemical conditions. The corresponding
photoproducts PhBNN and PhBCO have triplet electronic ground states.
Their small E values are in agreement with the linear
arrangements Ph–B–N–N and Ph–B–C–O
obtained by density functional theory computations. The D values decrease in the series PhNBN > PhBNN > PhBCO and approach
the value for phenylcarbene (PhCH). Indeed, the boron center in PhBCO
is isoelectronic with the carbene center in PhCH. The compounds are
the first examples of boron analogues of diazoalkanes (R2CNN) and ketenes (R2CCO), and their formation may serve
as a demonstration of the high reactivity of phenylborylene.
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Keywords
R 2 CNNCCOC 6 H 5matrix isolation conditionsESR spectroscopyRBabsorption bandboron analoguescryogenic matrix isolation conditionsBR 3E valuesground statesphenyl rearrangementphenylborylenenitrene PhNBND values decreasereactive intermediatestheory computationselectrophilic boryleneCarbon Monoxide Formal removalPhBCOPhCHyields borylenes375 nmCOUVboron centercarbene centerN 2 reversiblyseries PhNBNreactivityIR518 nmphotoproducts PhBNNPhenylborylene
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