Stabilizing Monoatomic Two-Coordinate Bismuth(I) and Bismuth(II) Using a Redox Noninnocent Bis(germylene) Ligand.

The formation of isolable monatomic BiI complexes and BiII radical species is challenging due to the pronounced reducing nature of metallic bismuth. Here, we report a convenient strategy to tame BiI and BiII atoms by taking advantage of the redox noninnocent character of a new chelating bis(germylene) ligand. The remarkably stable novel BiI cation complex 4, supported by the new bis(iminophosphonamido-germylene)xanthene ligand [(P)GeII(Xant)GeII(P)] 1, [(P)GeII(Xant)GeII(P) = Ph2P(NtBu)2GeII(Xant)GeII(NtBu)2PPh2, Xant = 9,9-dimethyl-xanthene-4,5-diyl], was synthesized by a two-electron reduction of the cationic BiIIII2 precursor complex 3 with cobaltocene (Cp2Co) in a molar ratio of 1:2. Notably, owing to the redox noninnocent character of the germylene moieties, the positive charge of BiI cation 4 migrates to one of the Ge atoms in the bis(germylene) ligand, giving rise to a germylium(germylene) BiI complex as suggested by DFT calculations and X-ray photoelectron spectroscopy (XPS). Likewise, migration of the positive charge of the BiIIII2 cation of 3 results in a bis(germylium)BiIIII2 complex. The delocalization of the positive charge in the ligand engenders a much higher stability of the BiI cation 4 in comparison to an isoelectronic two-coordinate Pb0 analogue (plumbylone; decomposition below -30 °C). Interestingly, 4[BArF] undergoes a reversible single-electron transfer (SET) reaction (oxidation) to afford the isolable BiII radical complex 5 in 5[BArF]2. According to electron paramagnetic resonance (EPR) spectroscopy, the unpaired electron predominantly resides at the BiII atom. Extending the redox reactivity of 4[OTf] employing AgOTf and MeOTf affords BiIII(OTf)2 complex 7 and BiIIIMe complex 8, respectively, demonstrating the high nucleophilic character of BiI cation 4.

Isolation and Reactivity of Homoleptic Diphosphene Lead Complexes.

Due to their limited capacity for π-backdonation, isolation of π-complexes of main-group elements remains a great challenge. We report herein the synthesis of a homoleptic diphosphene lead complex (2) from the degradation of P4 with a bis(germylene)-stabilized Pb(0) complex. Structural and computational studies showed that 2 possesses significant π bonding interactions between Pb atom and diphosphene ligands, which is reminiscent of transition-metal diphosphene complexes. Consistent with its unique electronic structure, complex 2 can deliver Pb(0) atoms to perform redox reaction with an iminoquinone to produce a cyclic plumbylene (4) and perform 2,5-dimethyl-3,4-dimethylimidazol-1-ylidene (IMe2 Me2 ) induced phosphorus cation abstraction to give an anionic PbP3 complex (6).

Genuine quadruple bonds between two main-group atoms. Chemical bonding in AeF- (Ae = Be-Ba) and isoelectronic EF (E = B-Tl) and the particular role of d orbitals in covalent interactions of heavier alkaline-earth atoms.

Quantum chemical calculations of anions AeF- (Ae = Be-Ba) and isoelectronic group-13 molecules EF (E = B-Tl) have been carried out using ab initio methods at the CCSD(T)/def2-TZVPP level and density functional theory employing BP86 various basis sets. The equilibrium distances, bond dissociation energies and vibrational frequencies are reported. The alkali earth fluoride anions AeF- exhibit strong bonds between the closed-shell species Ae and F- with bond dissociation energies between 68.8 kcal mol-1 for MgF- and 87.5 kcal mol-1 for BeF- and they show an unusual increasing trend MgF- < CaF- < SrF- < BaF-. This is in contrast to the isoelectronic group-13 fluorides EF where the BDE continuously decreases from BF to TlF. The calculated dipole moments of AeF- are very large between 5.97 D for BeF- and 1.78 D for BaF- with the negative end always at the Ae atom (Ae→F-). This is explained by the location of the electronic charge of the lone pair at Ae, which is rather distant from the nucleus. The analysis of the electronic structure of AeF- suggests significant charge donation Ae←F- into the vacant valence orbitals of Ae. A bonding analysis with the EDA-NOCV method suggests that the molecules are mainly covalently bonded. The strongest orbital interaction in the anions comes from the inductive polarization of the 2pσ electrons of F-, which leads to a hybridization of the (n)s and (n)pσ AOs at Ae. There are two degenerate π donor interactions Ae←F- in all anions AeF-, which provide 25-30% to the covalent bonding. There is another σ orbital interaction in the anions, which is very weak in BeF- and MgF-. In contrast, the second stabilizing σ orbital interaction in CaF-, SrF- and BaF- yields a strongly stabilizing σ orbital, because the Ae atoms use their (n - 1)dσ AOs for bonding. The energy lowering of the second σ interaction in the latter anions is even stronger than the π bonding. The EDA-NOCV results suggest that BeF- and MgF- have three strongly polarized bonds, whereas CaF-, SrF- and BaF- have four bonding orbitals. The quadruple bonds in the heavier alkaline earth species are made possible because they use s/d valence orbitals like transition metals for covalent bonding. The EDA-NOCV analysis of the group-13 fluorides EF gives a conventional picture with one very strong σ bond and two rather weak π interactions.

Isolation and characterization of bis(silylene)-stabilized antimony(I) and bismuth(I) cations.

Monovalent group 15 cations L2Pn + (L = σ-donor ligands, Pn = N, P, As, Sb, Bi) have attracted significant experimental and theoretical interest because of their unusual electronic structures and growing synthetic potential. Herein, we describe the synthesis of a family of antimony(I) and bismuth(I) cations supported by a bis(silylene) ligand [(TBDSi2)Pn][BArF4] (TBD = 1, 8, 10, 9-triazaboradecalin; ArF = 3,5-CF3-C6H3; Pn = Sb, (2); Bi, (3)). The structures of 2 and 3 have been unambiguously characterized spectroscopically and by X-ray diffraction analysis and DFT calculations. They feature bis-coordinated Sb and Bi atoms which exhibit two lone pairs of electrons. The reactions of 2 and 3 with methyl trifluoromethane sulfonate provide a approach for the preparation of dicationic antimony(III) and bismuth(III) methyl complexes. Compounds 2 and 3 serve as 2e donors to group 6 metals (Cr, Mo), giving rise to ionic antimony and bismuth metal carbonyl complexes 6-9.

An Isolable Bis(Germylene)-Stabilized Plumbylone.

We report herein the synthesis of a stable plumbylone (3) by reduction of a bromodigermylplumbylene (2) with 2.2 equiv of potassium graphite (KC8 ). The molecular structure of 3 was established by a single-crystal X-ray diffraction study and features a two-coordinated Pb center with an acute Ge-Pb-Ge bond angle. Computational studies showed that this complex (3) possesses a singlet electronic ground state with a Pb0 center. Its high thermal stability can be most likely ascribed to the delocalization of π electrons over the Ge-Pb-Ge moiety. A preliminary reactivity study demonstrates that complex 3 can deliver Pb0 atoms to an organic azide producing a tetrameric imido complex [(PbNDipp)4 ] (Dipp=2,6-i Pr-C6 H3 , 4) and perform a metathesis reaction with GeCl2 ⋅dioxane to produce a bis(germylene)-stabilized germylone (5), highlighting the synthetic utility of 3.