Synthesis and Structure of a Carbene-Stabilized Boraallene Coordinated to Rhodium

Reaction of the (B,C-η²)-1-aza-2-borabutatriene rhodium complex <b>1</b> with 1,3-dimethylimidazol-2-ylidene) (<i>I</i>Me, <b>2</b>) afforded the N-heterocyclic carbene-stabilized (C,C-η²)-1-boraallene rhodium complex <b>3</b>, which has been characterized in solution and by X-ray crystallography. Density functional theory calculations were carried out to elucidate the observed base-induced B–C to C–C coordination mode shift, which suggested that the latter is 25 kJ/mol lower in energy

Ring Expansion of 7‑Boranorbornadienes by Coordination with an N‑Heterocyclic Carbene

In the context of our longstanding interest in subvalent boron compounds, we targeted the liberation of a carbene-stabilized borylene from a suitable organoboron precursor. For this purpose, we tested 7-borabicyclo[2.2.1]­hepta-2,5-dienes (or 7-boranorbornadienes in short) obtained from facile [4 + 2] cycloaddition of boroles and alkynes. By formation of a Lewis adduct with an N-heterocyclic carbene (NHC), we intended to block previously reported pericyclic reactions leading to undesired ring expansion and achieve a cheletropic elimination of the borylene species instead. Our results presented herein indicate that coordination of the NHC to 7-boranorbornadienes indeed weakens the bridgehead boron–carbon bonds. However, ring expansion to form borepine-NHC Lewis adducts remains the favorable reaction pathway. This process is independent of excessive NHC in the reaction mixture, which precludes participation of a free borylene species. As an alternative, an intramolecular mechanism driven mainly by molecular strain and steric factors is most plausible. Our investigations are based on spectroscopic measurements and single-crystal X-ray diffraction analyses

Synthesis and Reactivity of Palladium- and Platinum-Bridged Heterobimetallic [3]Trochrocenophanes

Heterobimetallic [3]­trochrocenophanes with PdCl₂ and PtCl₂ bridges were prepared in reasonable yields. The PdCl₂ species possess, like their Pt analogues, poor solubility but can be made more soluble by ligand substitution. By reaction of Pd-bridged [3]­trochrocenophanes with MeLi, both Cl atoms can be substituted by a Me group. Likewise, reaction of Pt-bridged complexes with LiCCPh leads to the expected disubstituted compound. Herein we present the synthesis of MCl₂- and MR₂-bridged (M = Pd, Pt; R = Me, CCPh) [3]­trochrocenophanes, as well as some solid-state structures of these [3]­trochrocenophanes

Synthesis and Reactivity of Palladium- and Platinum-Bridged Heterobimetallic [3]Trochrocenophanes

Heterobimetallic [3]­trochrocenophanes with PdCl₂ and PtCl₂ bridges were prepared in reasonable yields. The PdCl₂ species possess, like their Pt analogues, poor solubility but can be made more soluble by ligand substitution. By reaction of Pd-bridged [3]­trochrocenophanes with MeLi, both Cl atoms can be substituted by a Me group. Likewise, reaction of Pt-bridged complexes with LiCCPh leads to the expected disubstituted compound. Herein we present the synthesis of MCl₂- and MR₂-bridged (M = Pd, Pt; R = Me, CCPh) [3]­trochrocenophanes, as well as some solid-state structures of these [3]­trochrocenophanes

Borole-Derived Spirocyclic Tetraorganoborate

Preparation of a novel conjugated tetraorganoborate is presented in a facile two-step procedure. Successful utilization as a halide abstraction reagent is demonstrated in a metathesis reaction with the platinum­(II) boryl complex [(Cy₃P)₂Pt­(Br)­(BC₄Ph₄)], which was obtained by oxidative addition of 1-bromo-2,3,4,5-tetraphenylborole to a platinum(0) species. The novel compounds were investigated by means of spectroscopic and X-ray diffraction techniques

Synthesis and Structure of Group IV Distanna[2]metallocenophanes

1,2-Dichloro-1,1,2,2-tetra-<i>tert</i>-butyldistannane reacts with 2 equiv of sodium cyclopentadienide to give a bis­(cyclopentadienyl)­distannane. Subsequent dilithiation with lithium diisopropylamide and reactions with suitable metal halides yield [(C₅H₄Sn<i>t</i>Bu₂)₂MCl₂] (M = Ti, Zr, Hf). The group 4 <i>ansa</i>-metallocenes have all been fully characterized by means of multinuclear NMR spectroscopy, elemental analysis, and X-ray diffraction

Borole-Derived Spirocyclic Tetraorganoborate

Preparation of a novel conjugated tetraorganoborate is presented in a facile two-step procedure. Successful utilization as a halide abstraction reagent is demonstrated in a metathesis reaction with the platinum­(II) boryl complex [(Cy₃P)₂Pt­(Br)­(BC₄Ph₄)], which was obtained by oxidative addition of 1-bromo-2,3,4,5-tetraphenylborole to a platinum(0) species. The novel compounds were investigated by means of spectroscopic and X-ray diffraction techniques

Investigation of Steric Factors Involved in the Formation of Terminal Cationic Platinum Arylborylene Complexes

The abstraction of halido ligands from Pt^II diphosphine boryl complexes has previously been shown to yield one of two isomeric products: either T-shaped cationic boryl complexes or square-planar cationic borylene complexes. However, the latter product has only been observed in one case, that of a mesitylboryl ligand, which converts to a mesitylborylene ligand upon halido abstraction. In an effort to test the efficacy of this reaction in the presence of different steric and electronic influences, Pt^II diphosphine boryl complexes were prepared with both 4-<i>tert</i>-butylphenyl and duryl (2,3,5,6-tetramethylphenyl) groups. Halide abstraction from the 4-<i>tert</i>-butylphenyl complex resulted in a T-shaped cationic boryl complex. However, subjecting the duryl-substituted complexes to the same conditions exclusively results in terminal cationic borylene complexes, a difference we attribute to the greater steric hindrance between the boron-bound bromide and the methyl groups at the 2- and 6-positions of the duryl group. This outcome indicates that the electronic effect of alkylation at the <i>para</i> position is not a factor for this borylene formation reaction

Main-Group Metallomimetics: Transition Metal-like Photolytic CO Substitution at Boron

The carbon monoxide adduct of an unhindered and highly reactive CAAC-bound arylborylene, [(CAAC)­B­(CO)­Ar] (CAAC = cyclic (alkyl) (amino)­carbene), has been prepared using a transfer reaction from the linear iron borylene complex [(PMe₃) (CO)₃Fe=BAr]. [(CAAC)­B­(CO)­Ar] is a source of the dicoordinate [(CAAC)­ArB:] borylene that can be liberated by selective photolytic CO extrusion and that, although highly reactive, is sufficiently long-lived to react intermolecularly. Through trapping of the borylene generated in this manner, we present, among others, the first metal-free borylene­(I) species containing a nitrogen-based donor, as well as a new boron-containing radical

Ditopic Ambiphilicity of an Anionic Dimetalloborylene Complex

In early reports, the boron atom of the anionic borido complexes [{(η⁵-C₅H₄R)­(OC)₂Mn}₂B]⁻ (R = H, Me) showed nucleophilic behavior in the presence of electrophiles such as methyl iodide and group 11 metal chlorides, akin to the ground-breaking boryl lithium of Yamashita and Nozaki. Later, a reaction with the well-known transition metal Lewis base [Pt­(PCy₃)₂] suggested the possibility of boron-centered electrophilicity. In this paper we elucidate a third reactivity profile of the anion, nucleophilic substitution on heavier halides of group 14 metals by a manganese center. Meanwhile, other group 11 halides were found to interact with the boron center, but form structures different from those seen with gold. The basis of the discrimination of the anion between main group and transition metal halides is explored computationally, and the ditopic, ambiphilic reactivity of the anions is discussed