Abstract
A di(o-tolyl)borylgold complex was synthesized via the metathesis reaction of a gold alkoxide with tetra(o-tolyl)diborane(4). The resulting diarylborylgold complex exhibited a Lewis acidic boron center and a characteristic visible absorption that arises from its HOMO–LUMO excitation, which is narrower than that of a previously reported dioxyborylgold complex. The diarylborylgold complex reacted with isocyanide in a stepwise fashion to afford single- and double-insertion products and a C–C coupled product. Reactions of this diarylborylgold complex with C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O/N double bond species furnished addition products under concomitant formation of Au–C and B–O/N bonds, which suggests nucleophilic reactivity of the gold metal center. DFT calculations provided details of the underlying reaction mechanism, which involves an initial coordination of the CO/N bond to the boron vacant p-orbital of the diarylboryl ligand followed by a migration of the gold atom from the tetracoordinate sp3-hybridized boron center, which is analogous to the reactivity of the conventional sp3-hybridized borate species. The DFT calculations also suggested a stepwise mechanism for the reaction of this diarylborylgold complex with isocyanide, which afforded three different reaction products depending on the applied reaction conditions.
Highlights
Property of transition-metal–boryl complexes: (a) synthetic equivalent to boron nucleophileTransition metal (TM)–boryl complexes with a three-coordinate boron atom as an X-type ligand on the to boron nucleophileTransition metal (TM) center have been identi ed as key intermediates in TM-catalyzed borylation reactions of organic molecules.[1]
The diarylborylgold(I) complex 2 was obtained in the form of orange crystals in 68% yield from the reaction of 1 with (IPr)Au– OtBu under concomitant elimination of (o-tol)2BOtBu via a metathesis reaction (Scheme 4)
Compared to the frontier orbitals of (IPr)Au–Bpin which were independently calculated at the same level of theory in this study, the HOMO and LUMO of 2 are higher and lower respectively, which indicates stronger s-donor and p-acceptor properties for the diarylboryl ligand in 2 relative to those of the Bpin ligand in (IPr) Au–Bpin
Summary
Property of transition-metal–boryl complexes: (a) synthetic equivalent to boron nucleophileTransition metal (TM)–boryl complexes with a three-coordinate boron atom as an X-type ligand on the TM center have been identi ed as key intermediates in TM-catalyzed borylation reactions of organic molecules.[1]. Lewis-acidic diboranes(4) undergo similar C–C-bond-forming reactions to generate isocyanide dimers.24a,26 The 11B NMR signal of 6 (dB 43) was down eld shi ed relative to that of 5, re ecting the regeneration of the sp2-hybridized B center.
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