Gallaphosphene L(Cl)GaPGaL: A novel phosphinidene transfer reagent

Gallaphosphene L(Cl)GaPGaL 1 (L=HC[C(Me)N(Ar)]2 ; Ar=2,6-iPr2 C6 H3 ) reacts with N-heterocyclic carbenes R NHC (R NHC=[CMeN(R)]2 C; R=Me, iPr) to R NHC-coordinated phosphinidenes R NHC→PGa(Cl)L (R=Me 2 a, iPr 2 b) and with isonitriles RNC (R=iPr, Cy) to 1,3-phosphaazaallenes L(Cl)GaP=C=N-R (R=iPr 3 a, Cy 3 b), respectively. Quantum chemical calculations reveal that 2 a/2 b possess two localized lone pair of electrons, whereas 3 a/3 b only show one localized lone pair as was reported for gallaphosphene 1. 2 b reacts with 2.5 equivalents of a borane (THF ⋅ BH3 ) to the NHC-stabilized phosphinidene-borane complex [iPr NHC→P(BH2 )]2 (BH3 )3 4 with concomitant formation of LGa(H)Cl 5. 2-5 are characterized by heteronuclear (1 H, 13 C{1 H}, 31 P{1 H}) NMR and IR spectroscopy, elemental analysis, and single crystal X-ray diffraction (sc-XRD).

Coordination Chemistry of Bis-Cyclic Alkyl(Amino) Carbene (cAAC)-Supported Di-Phosphorus (P2 ): An Efficient Route to Donor Base-Stabilized Elusive Di-Phosphorus-Monoxide(P2 O)-Gold Complex

The stability and reactivity studies of heavier di-atomic group-15 congeners of alkynes, e. g., the di-phosphorus (P≡P) compounds have been the topic of huge interest because of their contrasting transient properties and lower stability compared to those of the stable molecular di-nitrogen (N≡N). Herein, we depict the reactivity studies of the bis-cAAC-stabilized di-phosphorus (P2 ) having an inversely polarized phosphaalkene nature featuring the C=P double bonds with Au(I)Cl. Both the mono-, and the di-aurated phosphaalkenes with the formulae [(Me2 -cAAC=P)2 (AuCl)] (2), and [(Me2 -cAAC=P)2 (AuCl)2 ] (3), respectively have been isolated in the solid state. Moreover, for the first time, we have been able to isolate the cAAC-stabilized tetra-aurated elusive di-phosphorus-monoxide (P2 O) with the formula [(Cy-cAAC=P)-O-(P=cAAC-Cy)(AuCl)4 ] (5) in presence of oxygen. Complexes 2-3, 5 have been structurally characterized by single crystal X-ray diffraction, and further studied by NMR spectroscopy. Our findings reveal significant elongation of the CcAAC -P bonds in 2-3, 5, and the presence of aurophilic interaction in 5. Quantum chemical calculations, including density functional theory (DFT), and energy decomposition analysis coupled with natural orbitals for chemical valence (EDA-NOCV) have been performed to study the electron densities distribution and nature of bonding in 2-3, 5.

Counterintuitive Chemistry: Carbene Stabilization of Zero-Oxidation State Main Group Species

Carbenes have evolved from transient laboratory curiosities to a robust, diverse, and surprisingly impactful ligand class. A variety of different carbenes have significantly contributed to the development of low-oxidation state main group chemistry. This Perspective focuses upon advances in the chemistry of carbene complexes containing main group element cores in the formal oxidation state of zero, including their diverse synthetic strategies, unusual bonding and structural motifs, and utility in transition metal coordination chemistry and activation of small molecules.

Base-stabilized formally zero-valent mono and diatomic molecular main-group compounds

Various compounds are known for transition metals in their formal zero-oxidation state, while similar compounds of main-group elements are recently realized and limited to only a few examples. Lewis-base-stabilized mono and diatomic molecular species (B₂, C, C₂, Si, Si₂, Ge, Ge₂, Sn, P₂, As₂, Sb₂) represent groundbreaking examples of main-group compounds with formally zero-oxidation state. In recent years, the isolation of low-valent main-group compounds has attracted increasing attention of both experimental and theoretical chemists. This is not only due to their fascinating electronic structures and exceptional reactivities, but also their use as valuable precursors for the synthesis of exotic yet important chemical species. This has led to a better understanding of the intricate balance of the donor-acceptor properties of the ligand(s) used to stabilize elements in a formally zero-oxidation state. Owing to the unusual oxidation state of the central element, many compounds containing formally zero-valent elements can efficiently activate otherwise inert small molecules. This review describes the synthesis, characterization, and reactivity of reported mono and diatomic formal zero-oxidation state main-group compounds. This review also emphasizes the comparative description of systems where different ligands are used to stabilize an element in its formal zero-oxidation state.

Boron-noble gas covalent bonds in borenium and boronium compounds

The capability of the BH₂⁺ parent cation to bind noble gases (Ng) has been evaluated. The results show its potential to form borenium (BH₂Ng⁺) and boronium (BH₂Ng₂⁺) cations. Conformational search using the recently developed AUTOMATON program and Coalescence Kick method, in addition to thermochemical and Born-Oppenheimer molecular dynamics (BOMD) calculations, were performed. Results show that compounds containing Ng = Ar-Rn are thermodynamically and kinetically stable. Furthermore, it was found that the B-Ng bond has high dissociation energy values at both DFT and CCSD(T) levels suggesting a strong interaction. The nature of the chemical bond has been assessed according to the Quantum Theory of Atoms in Molecules (QTAIM), Natural Bond Orbital Theory (NBO) and Energy decomposition Analysis (EDA). Negative values of local energy density H(r_c) and high values of the Wiberg bond Index (WBI) reveal its covalent nature that is confirmed by localized natural bond orbitals with 2.0 |e| occupations. Additionally, it could be observed that the orbital term (ΔE^orb) is the most important component (84.6-90.1%) of the interaction energy between the parent BH₂⁺ and Ng atoms, supporting the polar covalent nature of the B-Ng bond.

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry

N-Heterocyclic carbenes (NHC) are nowadays ubiquitous and indispensable in many research fields, and it is not possible to imagine modern transition metal and main group element chemistry without the plethora of available NHCs with tailor-made electronic and steric properties. While their suitability to act as strong ligands toward transition metals has led to numerous applications of NHC complexes in homogeneous catalysis, their strong σ-donating and adaptable π-accepting abilities have also contributed to an impressive vitalization of main group chemistry with the isolation and characterization of NHC adducts of almost any element. Formally, NHC coordination to Lewis acids affords a transfer of nucleophilicity from the carbene carbon atom to the attached exocyclic moiety, and low-valent and low-coordinate adducts of the p-block elements with available lone pairs and/or polarized carbon-element π-bonds are able to act themselves as Lewis basic donor ligands toward transition metals. Accordingly, the availability of a large number of novel NHC adducts has not only produced new varieties of already existing ligand classes but has also allowed establishment of numerous complexes with unusual and often unprecedented element-metal bonds. This review aims at summarizing this development comprehensively and covers the usage of N-heterocyclic carbene adducts of the p-block elements as ligands in transition metal chemistry.

NHCs in Main Group Chemistry

Since the discovery of the first stable N-heterocyclic carbene (NHC) in the beginning of the 1990s, these divalent carbon species have become a common and available class of compounds, which have found numerous applications in academic and industrial research. Their important role as two-electron donor ligands, especially in transition metal chemistry and catalysis, is difficult to overestimate. In the past decade, there has been tremendous research attention given to the chemistry of low-coordinate main group element compounds. Significant progress has been achieved in stabilization and isolation of such species as Lewis acid/base adducts with highly tunable NHC ligands. This has allowed investigation of numerous novel types of compounds with unique electronic structures and opened new opportunities in the rational design of novel organic catalysts and materials. This Review gives a general overview of this research, basic synthetic approaches, key features of NHC-main group element adducts, and might be useful for the broad research community.

Recent Advances in Imidazoliumyl-Substituted Phosphorus Compounds

This review aims to highlight the recent developments in the chemistry of selected imidazoliumyl-substituted phosphorus compounds. The synthetic approaches for their preparation with phosphorus in various oxidation states and coordination environments are discussed. Their intriguing properties and versatile chemistry strongly depends on the bonding motif at the P atoms, which is given special focus.

Assembly of NHC-stabilized 2-hydrophosphasilenes from Si(iv) precursors: a Lewis acid-base complex

NHC-stabilized 2-hydrophosphasilenes are obtained from 1,2-dihydro-2-chlorophosphasilanes as Si(iv) precursors by a NHC-assisted 1,2-elimination of HCl. The NHC-exchange of these compounds is demonstrated as a proof of donor acceptor bonding between NHC and the silicon centre of the "Si[double bond, length as m-dash]P" moiety. We have also explored the possibility of similar exchanges in NHC-stabilized Si₂ and P₂ compounds. Theoretical DFT calculations were performed to address the nature of Si-P bonding in the NHC-stabilized 2-hydrophosphasilenes.

[(ClImDipp)PP(Dipp)][GaCl4]: a polarized, cationic diphosphene

The reaction of neutral diphosphanide [(^ClIm^Dipp)P–P(Cl)(Dipp)] with the Lewis acid GaCl₃ yields cationic diphosphene [(^ClIm^Dipp)PP(Dipp)]⁺, which is explained by a low P–Cl bond dissociation energy. The polarized PP double bond in [(^ClIm^Dipp)PP(Dipp)]⁺, allows for its utilization as acceptor for nucleophiles, such as Cl⁻ or PMe₃.

Protonation of carbene-stabilized diphosphorus: complexation of HP2+

The highly reactive HP₂⁺cation has been stabilized by carbene coordination.

Carbene-stabilized beryllium borohydride

The reaction of N-heterocyclic carbene, L:, with BeCl(2) quantitatively yields L:BeCl(2)1 (L: = :C{N(2,6-Pr(i)(2)C(6)H(3))CH}(2)). The carbene-stabilized beryllium borohydride monomer L:Be(BH(4))(2)2 is prepared by the reaction of 1 with LiBH(4). Compound 3, prepared by the reaction of 2 with Na(2)[Fe(CO)(4)]·dioxane, represents an unusual "dual reduction" of the imidazole ring (i.e., hydroboration of the C═C backbone and hydrogenation of the C2 carbene center).