While tetrahedranes as a family are scarce, neutral heteroatomic species are all but unknown, with the only reported example being AsP3. Herein, we describe the isolation of a neutral heteroatomic X2Y2 molecular tetrahedron (X, Y=p‐block elements), which also is the long‐sought‐after free phosphaalkyne dimer. Di‐tert‐butyldiphosphatetrahedrane, (tBuCP)2, is formed from the monomer tBuCP in a nickel‐catalyzed dimerization reaction using [(NHC)Ni(CO)3] (NHC=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (IMes) and 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene (IPr)). Single‐crystal X‐ray structure determination of a silver(I) complex confirms the structure of (tBuCP)2. The influence of the N‐heterocyclic carbene ligand on the catalytic reaction was investigated, and a mechanism was elucidated using a combination of synthetic and kinetic studies and quantum chemical calculations.

The synthesis of rare anionic heteroleptic and homoleptic α-diimine iron complexes is described. Heteroleptic BIAN (bis(aryl)iminoacenaphthene) complexes 1-[K([18]c-6)-(thf) 0.5 ] and 2-[K([18]c-6)(thf) 2 ] were synthesized by reduction of the [(BIAN)FeBr 2 ] precursor complex using stoichiometric amounts of potassium graphite in the presence of the corresponding olefin. The electronic structure of these paramagnetic species was investigated by numerous spectroscopic analyses (NMR, EPR, 57 Fe Mossbauer, UV−vis), magnetic measurements (Evans NMR method, SQUID), and theoretical techniques (DFT, CASSCF). Whereas anion 1 is a low-spin complex, anion 2 consists of an intermediate-spin Fe(III) center. Both complexes are efficient precatalysts for the hydroboration of carbonyl compounds under mild reaction conditions. The reaction of bis(anthracene) ferrate(1−) gave the homoleptic BIAN complex 3-[K([18]c-6)(thf)], which is less catalytically active. The electronic structure was elucidated with the same techniques as described for complexes 1-[K([18]c-6)(thf) 0.5 ] and 2-[K([18]c-6)(thf) 2 ] and revealed an Fe(II) species in a quartet ground state.

Reaction of the imidazolium‐substituted iphosphate‐diide, (Ipr)2C2P2 (IDP), with GeCl2 ⋅ dioxane and KBArF24 [(BarF24)−=tetrakis[(3,5‐trifluoromethyl)phenyl]borate)] afforded the dicationic spherical‐aromatic nido‐cluster [Ge(η4‐IDP)]2+ ([1]2+) (Ipr=1,3‐bis(2,6‐diisopropylphenyl)imidazolium‐2‐ylidene). This complex is a rare heavy analogue of the elusive pyramidane [C(η4‐C4H4)]. [1]2+ undergoes two reversible one‐electron reductions, which yield the radical cation [2]⋅+ and the neutral GeII species 3. Both [2]⋅+ and 3 rearrange in solution forming the 2D aromatic and planar imidazolium‐substituted digermolide [4]2+ and germole‐diide 5, respectively. Both planar species can be oxidized back to [1]2+ using AgSbF6. These redox‐isomerizations correspond to the fundamental transformation of a 3D aromatic cluster into a 2D aromatic ring compound upon reduction and vice versa. The mechanism of these reactions was elucidated using DFT calculations and cyclic voltammetry experiments.

The first homoleptic cobalt phosphanido complex [K(thf) ][Co{1,2-(PtBu ) C B H } ] (1) was prepared by an unprecedented oxidative P-P bond addition of an ortho-carborane-substituted 1,2-diphosphetane to cobalt(-I) in [K(thf) ][Co(η -cod) )] (cod=1,5-cycloctadiene). Compound 1 is a rare distorted tetrahedral 3d complex with a low-spin ground state configuration. Magnetic measurements revealed that the complex is diamagnetic between 2 to 270 K in the solid state and at 298 K in [D ]THF solution. Based on DFT calculations, the unusual singlet ground state is caused by the strong σ-donor and moderate π-donor properties of the bis(phosphanido) ligand.

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