Stefan Mitzinger

We present the η³‐coordination of the 2‐phosphaethynthiolate anion in the complex (PN)₂La(SCP) (2) [PN=N‐(2‐(diisopropylphosphanyl)‐4‐methylphenyl)‐2,4,6‐trimethylanilide)]. Structural comparison with dinuclear thiocyanate‐bridged (PN)₂La(μ‐1,3‐SCN)₂La(PN)₂ (3) and azide‐bridged (PN)₂La(μ‐1,3‐N₃)₂La(PN)₂ (4) complexes indicates that the [SCP]⁻ coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π*‐orbital of the [SCP]⁻ ligand to the LUMO of complex 2, rendering it the ideal precursor for the first functionalization of the [SCP]⁻ anion. Complex 2 was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]⁻ ligand to form the first CAAC stabilized group 15–group 16 fulminate‐type complexes (PN)₂La{SPC(^RCAAC)} (5 a,b, R=Ad, Me). A detailed reaction mechanism for the SCP‐to‐SPC isomerization is proposed based on DFT calculations.

We present the η³‐coordination of the 2‐phosphaethynthiolate anion in the complex (PN)₂La(SCP) (2) [PN=N‐(2‐(diisopropylphosphanyl)‐4‐methylphenyl)‐2,4,6‐trimethylanilide)]. Structural comparison with dinuclear thiocyanate‐bridged (PN)₂La(μ‐1,3‐SCN)₂La(PN)₂ (3) and azide‐bridged (PN)₂La(μ‐1,3‐N₃)₂La(PN)₂ (4) complexes indicates that the [SCP]⁻ coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π*‐orbital of the [SCP]⁻ ligand to the LUMO of complex 2, rendering it the ideal precursor for the first functionalization of the [SCP]⁻ anion. Complex 2 was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]⁻ ligand to form the first CAAC stabilized group 15–group 16 fulminate‐type complexes (PN)₂La{SPC(^RCAAC)} (5 a,b, R=Ad, Me). A detailed reaction mechanism for the SCP‐to‐SPC isomerization is proposed based on DFT calculations.

This review article provides a survey of contemporary investigations on main group metal cluster formation, addressing homo‐ and heterometallic clusters (including small numbers of transition metal atoms), with or without an external ligand shell, thereby excluding clusters with non‐metal atoms as bridging ligands. Most of the studies reflected herein represent insights into the formation of intermediates from the starting material, or the final cluster formation from established intermediates. In rare cases, the entire process was suggested as a result of comprehensive, multi‐method elucidations. The article is to be understood as a state‐of‐the‐art report, as the subject matter is currently a rising field of research, which is still in its infancy, despite some early activities that date back to the 1980s. At the same time, the article intends to point toward both the importance and the feasibility of according studies, in order to encourage researchers to gain even more knowledge in this field. Only deep understanding of cluster formation will allow for design, and ultimately control, of their syntheses, with the long‐term goal of their optimization and purposeful application in catalysis or novel material synthesis.

The novel binary P₄analogue (Ge₂P₂)²⁻proved to be a suitable precursor for heteroatomic cluster synthesis. Upon reaction with CdPh₂, an unprecedented cluster anion is formed, [Cd₃(Ge₃P)₃]⁻.

The elucidation of formation mechanisms is mandatory for understanding and planning of synthetic routes. For (bio-)organic and organometallic compounds, this has long been realized even for very complicated molecules, whereas the formation of ligand-free inorganic molecules has widely remained a black box to date. This is due to poor structural relationships between reactants and products and the lack of structurally related intermediates—due to the comparably high coordination flexibility of involved atoms. Here we report on investigations of the stepwise formation of multimetallic clusters, based on a series of crystal structures and complementary quantum-chemical studies of (Ge₂As₂)²⁻, (Ge₇As₂)²⁻, [Ta@Ge₆As₄]³⁻, [Ta@Ge₈As₄]³⁻and [Ta@Ge₈As₆]³⁻. The study makes use of efficient quantum-chemical tools, enabling the first detailed screening of the energy hypersurface along the formation of ligand-free inorganic species for a semi-quantitative picture. The results can be generalized for an entire family of multimetallic clusters.

The first known M–As–Ge clusters, [V@Ge₈As₄]³⁻and [Nb@Ge₈As₆]³⁻, exhibit non-deltahedral topologies, with “V⁵⁺” being the hardest cation ever embedded in endohedral Zintl anions.

The ligation of a N-heterocyclic carbene (NHC) to group 11 metal salts (Cu, Ag) was explored as an alternative to PR₃ ligands for the formation of copper- and silver-chalcogenolate cluster complexes. AgOAc and CuCl salts ligate with the NHC 1,3-di-isopropylbenzimidazole-2-ylidene (ⁱPr₂-bimy) forming [Ag(OAc)(ⁱPr₂-bimy)] 1, [Ag(OAc)(ⁱPr₂-bimy)₂] 2, [CuCl(ⁱPr₂-bimy)]₂3 and [CuCl(ⁱPr₂-bimy)₂] 4 depending on the ratio of ligand to metal used. These have been characterized via spectroscopic and crystallographic methods. Complexes 1 and 3 were reacted with S(Ph)SiMe₃ and Se(Ph)SiMe₃ to form the polynuclear metal–chalcogenolates [Ag₄(μ-EPh)₄(ⁱPr₂-bimy)₄] (5, E = S; 6, E = Se) and [Cu₃(μ-EPh)₃(ⁱPr₂-bimy)₃] (7, E = S; 8, E = Se) in good yields. The structures of 5–8, as determined by single crystal X-ray crystallography, are described.