Introduced here is a new type of strongly donating N‐heterocyclic boryloxy (NHBO) ligand, [(HCDippN)2BO]− (Dipp=2,6‐diisopropylphenyl), which is isoelectronic with the well‐known N‐heterocyclic iminato (NHI) donor class. This 1,3,2‐diazaborole functionalized oxy ligand has been used to stabilize the first acyclic two‐coordinate dioxysilylene and its Ge, Sn, and Pb congeners, thereby presenting the first complete series of heavier group 14 dioxycarbene analogues. All four compounds have been characterized by X‐ray crystallography and density‐functional theory, enabling analysis of periodic trends: the potential for the [(HCDippN)2BO]− ligand to subtly vary its electronic‐donor capabilities is revealed by snapshots showing the gradual evolution of arene π coordination on going from Si to Pb.

We disclose the synthesis and structural characterization of the first acid-free anionic oxoborane, [K(2.2.2-crypt)][(HCDippN) 2 BO] (1), which is isoelectronic with classical carbonyl compounds. 1 can readily be accessed from its borinic acid by a simple deprotonation/sequestration sequence. Crystallographic and DFT analyses support the presence of a polarized terminal B=O double bond. Subsequent π bond metathesis converts the B=O bond to a heavier B=S containing system, affording the first anionic thioxoborane [K(2.2.2-crypt)] [(HCDippN) 2 BS] (2), isoelectronic with thiocarbonyls. Facile B=O bond cleavage can also be achieved to access B−H and B−Cl bonds, and via a remarkable oxide (O 2− ) ion abstraction to generate a borenium cation [(HCDippN) 2 B(NC 5 H 5 )][OTf] (4). By extension, 1 can act as an oxide transfer agent to organic substrates, a synthetic role traditionally associated with transition metal compounds. Hence we show that B−O linkages, which are often considered to be thermodynamic sinks, can be activated under mild conditions towards bond cleavage and transfer, by exploiting the higher reactivity inherent in the B=O double bond.

Scheme 1. Main group carbonyl analogues of types I and II.

The first example of 1,2,4,3-triazaborole-based oxoborane has been synthesized via hydrogen migration upon the coordination of AlCl3 to the corresponding borinic acid. X-ray diffraction analysis and computational study disclosed the partial B[double bond, length as m-dash]O double-bond property.

Thiele’s hydrocarbon occupies a central role as an open-shell platform for new organic materials, however little is known about its redox behaviour. While recent synthetic approaches involving symmetrical carbene substitution of the CPh2 termini yield isolable neutral/dicationic analogues, the intervening radical cations are much more difficult to isolate, due to narrow compatible redox ranges (typically < 0.25 V). Here we show that a hybrid BN/carbene approach allows access to an unsymmetrical analogue of Thiele’s hydrocarbon 1, and that this strategy confers markedly enhanced stability on the radical cation. 1•+ is stable across an exceptionally wide redox range (> 1 V), permitting its isolation in crystalline form. Further single-electron oxidation affords borenium dication 12+, thereby establishing an organoboron redox system fully characterized in all three redox states. We perceive that this strategy can be extended to other transient organic radicals to widen their redox stability window and facilitate their isolation.