Boron Insertion into the N≡N Bond of a Tungsten Dinitrogen Complex

The 1,3-addition of 1,2-diaryl-1,2-dibromodiboranes (B2Br2Ar2) to trans-[W(N2)2(dppe)2] (dppe = κ2-(Ph2PCH2)2), which is accompanied by a Br–Ar substituent exchange between the two boron atoms, is followed by a spontaneous rearrangement of the resulting tungsten diboranyldiazenido complex to a 2-aza-1,3-diboraallenylimido complex displaying a linear, cumulenic B=N=B moiety. This rearrangement involves the splitting of both the B–B and N=N bonds of the N2B2 ligand, formal insertion of a BAr boranediyl moiety into the N=N bond, and coordination of the remaining BArBr boryl moiety to the terminal nitrogen atom. Density functional theory calculations show that the reaction proceeds via a cyclic NB2 intermediate, followed by dissociation into a tungsten nitrido complex and a linear boryliminoborane, which recombine by adduct formation between the nitrido ligand and the electron-deficient iminoborane boron atom. The linear B=N=B moiety also undergoes facile 1,2-addition of Brønsted acids (HY = HOPh, HSPh, and H2NPh) with concomitant Y–Br substituent exchange at the terminal boron atom, yielding cationic (borylamino)borylimido tungsten complexes

Functionalization of N2 via Formal 1,3-Haloboration of a Tungsten(0) σ-Dinitrogen Complex

Boron tribromide and aryldihaloboranes were found to undergo 1,3-haloboration across one W−N≡N moiety of a group 6 end-on dinitrogen complex (i.e. trans-[W(N2)2(dppe)2]). The N-borylated products consist of a reduced diazenido unit sandwiched between a WII center and a trivalent boron substituent (W−N=N−BXAr), and have all been fully characterized by NMR and IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction. Both the terminal N atom and boron center in the W−N=N−BXAr unit can be further derivatized using electrophiles and nucleophiles/Lewis bases, respectively. This mild reduction and functionalization of a weakly activated N2 ligand with boron halides is unprecedented, and hints at the possibility of generating value-added nitrogen compounds directly from molecular dinitrogen

Diverse ring-opening reactions of rhodium η4-azaborete complexes

Sequential treatment of [Rh(COE)2Cl]2 (COE = cyclooctene) with PiPr3, alkyne derivatives and tBuN[triple bond, length as m-dash]BMes (Mes = 2,4,6-trimethylphenyl) provided functionalized rhodium η4-1,2-azaborete complexes of the form (η4-azaborete)RhCl(PiPr3). The scope of this reaction was expanded to encompass alkynes with hydrogen, alkyl, aryl, ferrocenyl, alkynyl, azaborinyl and boronate ester substituents. Treatment of these complexes with PMe3 led to insertion of the rhodium atom into the B–C bond of the BNC2 ring, forming 1-rhoda-3,2-azaboroles. Addition of N-heterocyclic carbenes to azaborete complexes led to highly unusual rearrangements to rhodium η2,κ1-allenylborylamino complexes via deprotonation and C–N bond cleavage. Heating and photolysis of an azaborete complex also led to rupture of the C–N bond followed by subsequent rearrangements, yielding an η4-aminoborylallene complex and two isomeric η4-butadiene complexes

Optically induced charge-transfer in donor-acceptor-substituted p- and m- C2B10H12 carboranes

Icosahedral carboranes, C2B10H12, have long been considered to be aromatic but the extent of conjugation between these clusters and their substituents is still being debated. m- and p-Carboranes are compared with m- and p-phenylenes as conjugated bridges in optical functional chromophores with a donor and an acceptor as substituents here. The absorption and fluorescence data for both carboranes from experimental techniques (including femtosecond transient absorption, time-resolved fluorescence and broadband fluorescence upconversion) show that the absorption and emission processes involve strong intramolecular charge transfer between the donor and acceptor substituents via the carborane cluster. From quantum chemical calculations on these carborane systems, the charge transfer process depends on the relative torsional angles of the donor and acceptor groups where an overlap between the two frontier orbitals exists in the bridging carborane cluster

Dynamic, reversible oxidative addition of highly polar bonds to a transition metal

The combination of Pt0 complexes and indium trihalides leads to compounds that form equilibria in solution between their In-X oxidative addition (OA) products (PtII indyl complexes) and their metal-only Lewis pair (MOLP) isomers (LnPt→InX3). The position of the equilibria can be altered reversibly by changing the solvent, while the equilibria can be reversibly and irreversibly driven towards the MOLP products by addition of further donor ligands. The results mark the first observation of an equilibrium between MOLP and OA isomers, as well as the most polar bond ever observed to undergo reversible oxidative addition to a metal complex. In addition, we present the first structural characterization of MOLP and oxidative addition isomers of the same compound. The relative energies of the MOLP and OA isomers were calculated by DFT methods, and the possibility of solvent-mediated isomerization is discussed

Synthesis and Reactivity of a Dialane-Bridged Diradical

Radicals of the lightest group 13 element, boron, are well established and observed in numerous forms. In contrast to boron, radical chemistry involving the heavier group 13 elements (aluminum, gallium, indium, and thallium) remains exceedingly underexplored, primarily attributed to the formidable synthetic challenges associated with these elements. Herein, we report the synthesis and isolation of planar and twisted conformers of a doubly CAAC (cyclic alkyl(amino)carbene)-radical-substituted dialane. Extensive characterization through spectroscopic analyses and X-ray crystallography confirms their identity, while quantum chemical calculations support their open-shell nature and provide further insights into their electronic structures. The dialane-connected diradicals exhibit high susceptibility to oxidation, as evidenced by electrochemical measurements and reactions with o-chloranil and a variety of organic azides. This study opens a previously uncharted class of dialuminum systems to study, broadening the scope of diradical chemistry and its potential applications

Construction of Linear and Branched Tetraboranes via 1,1- and 1,2-Diboration of Diborenes

Sterically unencumbered diborenes based on a benzylphosphine chelate undergo diboration reactions with bis(catecholato)diboron in the absence of a catalyst to yield tetraboranes. The symmetrical diborenes studied undergo 1,2- diborations, whereas an unsymmetrical derivative was found to yield a triborylborane-phosphine adduct as the result of a formal 1,1-diboration. A related borylborylene compound also underwent a 1,2-diboration to produce a borylene-borane adduct

N‐Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Germanium(IV) and Tin(IV) Chlorides and Organyl Chlorides

A study on the reactivity of N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAAC$^{Me}$ with selected germanium(IV) and tin(IV) chlorides and organyl chlorides is presented. The reactions of the NHCs Me$_{2}$Im$^{Me}$, iPr$_{2}$Im$^{Me}$ and Dipp2Im with the methyl chlorides ECl$_{2}$Me$_{2}$ afforded the adducts NHC ⋅ ECl$_{2}$Me$_{2}$ (E=Ge (1), Sn (2)), NHC=Me$_{2}$Im$^{Me}$ (a), iPr$_{2}$Im$^{Me}$ (b), Dipp$_{2}$Im (c)). The reaction of Me2Im$^{Me}$ with GeCl$_{4}$ led to isolation of Me$_{2}$Im$^{Me}$ ⋅ GeCl$_{4}$ (3), the reaction of iPr$_{2}$Im$^{Me}$ with SnCl$_{4}$ in THF afforded the THF adduct iPr$_{2}$Im$^{Me}$ ⋅ SnCl$_{4}$ ⋅ THF (4). Dipp$_{2}$Im ⋅ GeCl$_{2}$Me$_{2}$ (1 c) isomerized into the backbone coordinated imidazolium salt [aDipp$_{2}$Im ⋅ GeClMe$_{2}$][Cl] (5) upon thermal treatment. The reactions of cAAC$^{Me}$ with (i) ECl$_{2}$R$_{2}$ (E=Ge, Sn) gave the adducts cAAC$^{Me}$ ⋅ ECl$_{2}$R$_{2}$ (R=Me: E=Ge (6); Sn (7); Ph: E=Ge (8)), with (ii) GeClMe$_{3}$ and GeCl$_{4}$ the salts [cAAC$^{Me}$ ⋅ GeMe$_{3}$][Cl] (9) and [cAACMeCl][GeCl$_{3}$] (10), and (iii) with SnCl$_{4}$ the salt [cAACMeCl][SnCl$_{3}$] (11) and the adduct cAAC$^{Me}$ ⋅ SnCl$_{4}$ (12). Reduction of 2 a with KC$_{8}$ afforded the NHC‐stabilized stannylene Me$_{2}$Im$^{Me}$ ⋅ SnMe$_{2}$ 13, reduction of 7 with either KC8 or 1,4‐bis‐(trimethylsilyl)‐1,4‐dihydropyrazin in the presence of SnCl$_{2}$Me$_{2}$ yielded cAAC$^{Me}$ ⋅ SnMe$_{2}$ ⋅ SnMe$_{2}$Cl$_{2}$ (14)

Activation of Ge−H and Sn−H Bonds with N‐Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene

A study of the reactivity of several N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene (cAAC$^{Me}$) with the group 14 hydrides GeH2Mes2 and SnH2Me2 (Me=CH$_{3}$, Mes=1,3,5‐(CH$_{3}$)$_{3}$C$_{6}$H$_{2}$) is presented. The reaction of GeH$_{2}$Mes$_{2}$ with cAAC$^{Me}$ led to the insertion of cAAC$^{Me}$ into one Ge−H bond to give cAAC$^{Me}$H−GeHMes$_{2}$ (1). If 1,3,4,5‐tetramethyl‐imidazolin‐2‐ylidene (Me$_{2}$Im$^{Me}$) was used as the carbene, NHC‐mediated dehydrogenative coupling occurred, which led to the NHC‐stabilized germylene Me$_{2}$Im$^{Me}$⋅GeMes$_{2}$ (2). The reaction of SnH$_{2}$Me$_{2}$ with cAAC$^{Me}$ also afforded the insertion product cAAC$^{Me}$H−SnHMe$_{2}$ (3), and reaction of two equivalents Me$_{2}$Im$^{Me}$ with SnH$_{2}$Me$_{2}$ gave the NHC‐stabilized stannylene Me$_{2}$Im$^{Me}$⋅SnMe$_{2}$ (4). If the sterically more demanding NHCs Me$_{2}$Im$^{Me}$, 1,3‐di‐isopropyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene (iPr$_{2}$Im$^{Me}$) and 1,3‐bis‐(2,6‐di‐isopropylphenyl)‐imidazolin‐2‐ylidene (Dipp$_{2}$Im) were employed, selective formation of cyclic oligomers (SnMe$_{2}$)$_{n}$ (5; n=5–8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAAC$^{Me}$H−SnHMe$_{2}$ (3)