Disproportionation and Ligand Lability in Low Oxidation State Boryl-Tin Chemistry

Reaction of a Potassium Aluminyl with Sn[N(SiMe3)2]2 - Isolation of a Stable, Trimetallic Sn(I) Radical Anion

The reaction of the potassium aluminyl K[Al(NON)] ([NON]2-=[O(SiMe2NDipp)2]2-, Dipp=2,6-iPr2C6H3) with the stannylene Sn[N(SiMe3)2]2 in benzene afforded K3[(Sn4){Al(NON)}2{N(SiMe3)2}], containing a distorted tetrahedral Sn4-cluster. Computational analysis indicates that four of the edges in this unit are composed of Sn-Sn bonds, with the remaining two that are spanned by aluminium involved in three centre two electron (3c2e) Sn-Al-Sn bonds. The formation of Al(II) species during this reaction is indicated by the isolation of the dialuminated cyclohexadiene 1,4-[Al(NON)]2(μ-C6H6). Repeating the reaction in methylcyclohexane generated a thermally stable, trimetallic Sn(I) radical anion in K[Sn{Al(NON)}2]. Compared to all other reported Sn(I) radicals, its EPR spectrum is unique; the main turning points of its spectrum appear at g values above 2 and the Sn hyperfine coupling is substantially smaller in magnitude. These data, together with ENDOR measurements and DFT calculations show that the SOMO is entirely localised in an unhybridised 5p orbital, such that spin-orbit contributions to the g and Sn hyperfine tensors are quenched.

Isolable zero-valent Ditin(0) and Diplumbum(0) complexes

Although complexes with monatomic zero-valent main group centers have been reported, diatomic zero-valent complexes are extremely rare and all previously reported examples were stabilized by either carbene or silylene ligands. Here, we present the isolation of diatomic E(0)-E(0) (E = Sn, Pb) species supported by two [N{CH₂CH₂NPiPr₂}₃Sn] fragments. The reaction of trilithium salt N{CH2CH2NLiPiPr2}3 with SnCl2 yields complex [N{CH2CH2NPiPr2}3]2Sn3 (1) with a Sn3 chain. The reduction of the mixture of 1 and SnCl2 with KC8 produces the catenated Sn4 chain [N{CH2CH2NPiPr2}3Sn2]2 (2), featuring a diatomic Sn(0)-Sn(0) unit. Further reduction of 2 with KC8 yields the alkali metal ion-bridged complex [N{CH2CH2NPiPr2}3SnK]2 (3). Moreover, the reaction of 3 with PbI2 and KC8 affords [N{CH2CH2NPiPr2}3SnPb]2 (4), which can also be generated by the reaction of KC8 with PbI2 and [N{CH2CH2NPiPr2}3SnLi]2 (5). Complex 4 features a diatomic Pb(0)-Pb(0) unit, representing a heavy diatomic zero-valent main group complex. The presence of diatomic E(0)-E(0) (E = Sn, Pb) units in complexes 2 and 4, respectively, is further confirmed by computational studies.

Carbene-Stabilized Phosphagermylenylidene: A Heavier Analog of Isonitrile

Phosphagermylenylidenes (R-P═Ge), as heavier analogs of isonitriles, whether in their free state or as complexes with a Lewis base, have not been previously identified as isolable entities. In this study, we report the synthesis of a stable monomeric phosphagermylenylidene within the coordination sphere of a Lewis base under ambient conditions. This species was synthesized by Lewis base-induced dedimerization of a cyclic phosphagermylenylidene dimer or via Me3SiCl elimination from a phosphinochlorogermylene framework. The deliberate integration of a bulky, electropositive N-heterocyclic boryl group at the phosphorus site, combined with coordination stabilization by a cyclic (alkyl)(amino)carbene at the low-valent germanium site, effectively mitigated its natural tendency toward oligomerization. Structural analyses and theoretical calculations have demonstrated that this unprecedented species features a P═Ge double bond, characterized by conventional electron-sharing π and σ bonds, complemented by lone pairs at both the phosphorus and germanium atoms. Preliminary reactivity studies show that this base-stabilized phosphagermylenylidene demonstrates facile release of ligands at the Ge atom, coordination to silver through the lone pair on P, and versatile reactivity including both (cyclo)addition and cleavage of the P═Ge double bond.

Boryl-substituted low-valent heavy group 14 compounds

Low valent group 14 compounds exhibit diverse structures and reactivities. The employment of diazaborolyl anions (NHB anions), isoelectronic analogues to N-heterocyclic carbenes (NHCs), in group 14 chemistry leads to the exceptional structures and reactivity. The unique combination of σ-electron donation and pronounced steric hindrance impart distinct structural characteristics to the NHB-substituted low valent group 14 compounds. Notably, the modulation of the HOMO-LUMO gap in these compounds with the diazaborolyl substituents results in novel reaction patterns in the activation of small molecules and inert chemical bonds. This review mainly summarizes the recent advances in NHB-substituted low-valent heavy Group 14 compounds, emphasizing their synthesis, structural characteristics and application to small molecule activation.

A planar per-borylated digermene

A tetraboryl digermene synthesized by the reaction between a dianionic digermanide nucleophile and a boron halide electrophile is dimeric both in the solid state and in hydrocarbon solution. It features both a planar 'alkene-like' geometry for the Ge2B4 core, and an exceptionally short GeGe double bond. These structural features are consistent with the known electronic properties of the boryl group, and with lowest energy (in silico) fragmentation into two triplet bis(boryl)germylene fragments.

A silylene-stabilized ditin(0) complex and its conversion to methylditin cation and distannavinylidene

Due to their intrinsic high reactivity, isolation of tin(0) complexes remains challenging. Herein, we report the synthesis of a silylene-stabilized ditin(0) complex (2) by reduction of a silylene-supported dibromostannylene (1) with 1 equivalent of magnesium (I) dimer in toluene. The structure of 2 was established by single crystal X-ray diffraction analysis. Density Functional Theory calculations revealed that complex 2 bears a Sn=Sn double bond and one lone pair of electrons on each of the Sn(0) atoms. Remarkably, complex 2 is readily methylated to give a mixed-valent methylditin cation (4), which undergoes topomerization in solution though a reversible 1,2-Me migration along a Sn=Sn bond. Computational studies showed that the three-coordinate Sn atom in 4 is the dominant electrophilic center, and allows for facile reaction with KHBBus3 furnishing an unprecedented N-heterocyclic silylenes-stabilized distannavinylidene (5). The synthesis of 2, 4 and 5 demonstrates the exceptional ability of N-heterocyclic silylenes to stabilize low valent tin complexes.

Synthesis, Structure, and Spectroscopy of the Biscarboranyl Stannylenes ()Sn·THF and K2[()Sn]2 ( = 1,1'(ortho-Biscarborane)) and Dibiscarboranyl Ethene ()CH=CH()

Two compounds containing a Sn(II) atom supported by a bidentate biscarborane ligand have been synthesized via salt metathesis. The synthetic procedures for (bc)Sn·THF (bc = 1,1' (ortho-carborane) (1) and K2[(bc)Sn]2 (2) involved the reaction of K2[bc] with SnCl2 in either a THF solution (1) or in a benzene/dichloromethane solvent mixture (2). Using the same solvent conditions as those used for 2 but using a shorter reaction time gave a dibiscarboranyl ethene (3). The products were characterized by 1H, 13C, 11B, 119Sn NMR, UV-vis, and IR spectroscopy, and by X-ray crystallography. The diffraction data for 1 and 2 show that the Sn atom has a trigonal pyramid environment and is constrained by the bc ligand in a planar five-membered C4Sn heterocycle. The 119Sn NMR spectrum of 1 displays a triplet of triplets pattern signal, which is unexpected given the absence of a Sn-H signal in the 1H NMR, IR spectrum, and X-ray crystallographic data. However, a comparison with other organotin compounds featuring a Sn atom bonded to carboranes reveal similar multiplets in their 119Sn NMR spectra, likely arising from long-range nuclear spin-spin coupling between the carboranyl 11B and 119Sn nuclei. Compound 3 displays structural and spectroscopic characteristics typical of conjugated alkenes.