Sila- and Germametallacycles of Late Transition Metals

Reductive Retrocyclization of a Mangana(II)cyclopentasilane to Form Manganese(0) Bis(η2-disilene) Complexes

Ligand-exchange reactions on a mangana(II)cyclopentasilane complex that contains two THF ligands with aryl isocyanides led to the formation of manganese(0) bis(η2-disilene) complexes via a retrocyclization. In stark contrast, ligand-exchange reactions with CNtBu, an N-heterocyclic carbene, or pyridine-based ligands furnished manganese(II) complexes wherein the manganacyclopentasilane framework remained intact. The thermolysis of the obtained bis(η2-disilene) complex in the presence of mesityl isocyanide led to the formation of a cyclotetrasilane via the formal dimerization of the two η2-disilene moieties. The insertion of a mesityl isocyanide into the Mn-Siβ bond results in the formation of a manganese(II) complex supported by a [SiCSi]-type tridentate ligand scaffold.

Bulky 1,1'-bisphosphanoferrocenes and their coordination behaviour towards Cu(i)

Two bulky mesityl substituted dppf-analogues Fe(C₅H₄PMes₂)₂ (Mes = 2,4,6-Me₃C₆H₂, 1) and Fe(C₅H₄PMes₂)(C₅H₄PPh₂) (Mes = 2,4,6-Me₃C₆H₂, Ph = C₆H₅, 3) have been prepared and their properties as donor ligands have been explored using heteronuclear NMR spectroscopy and in particular via¹J_P-Se coupling, cyclic voltammetry and DFT calculations. Based on the results obtained, a series of mono- and dinuclear Cu(i) complexes have been prepared with these new diphosphane ligands using Br^-, I^-, and BF₄^- as counter anions. For the very bulky ligand 1 rare and unprecedented double bridging complexation modes have been observed containing two non-planar Cu₂Br₂ units, while for the other dinuclear complexes planar Cu₂Br₂ units have been found. The Cu(i) complexes of 1 and 3 were then used as catalysts for CO₂-fixation reaction with terminal alkynes, and complexes with ligand 3 were found to be more efficient than those with 1. DFT calculations performed on compounds 1, 3 and their Cu(i) complexes were able to verify the trend of these catalytic reactions.

A Four Coordinated Iron(II)-Digermyl Complex as an Effective Precursor for the Catalytic Dehydrogenation of Ammonia Borane

A coordinatively unsaturated iron(II)-digermyl complex, Fe[Ge(SiMe3)3]2(THF)2 (1), was synthesized in one step by the reaction of FeBr2 with 2 equiv of KGe(SiMe3)3. Complex 1 shows catalytic activity comparable to that of its silicon analogue in reduction reactions. In addition, 1 acts as an effective precursor for the catalytic dehydrogenation of ammonia borane. Catalytically active species can also be generated in situ by simple mixing of the easy-to-handle precursors FeBr2, Ge(SiMe3)4, KOtBu, and phenanthroline.

Disilametallacyclic chemistry for efficient catalysis

Disilametallacyclic species of late transition metals behave as key intermediates for efficient catalytic reactions proceeding through new mechanisms.

The chemistry of benzodisilacyclobutenes and benzobis(disilacyclobutene)s: new development of transition-metal-catalyzed reactions, stereochemistry and theoretical studies

The synthesis and reactions of 3,4-benzo-1,2-disilacyclobut-3-enes and benzo[1,2:4,5]bis(1,2-disilacyclobut-3-ene)s developed by our group are reported in this review. The palladium-, platinum- and nickel-catalyzed reactions of benzodisilacyclobutenes and benzobis(disilacyclobutene)s with unsaturated compounds afford various types of products. The structures of the products are dependent upon the nature of the transition metal used as a catalyst. The reactions of cis- and trans-benzodisilacyclobutenes with alkenes and alkynes in the presence of a transition-metal catalyst proceed with high stereospecificity to give the respective adducts. The thermal reactions of cis- and trans-benzodisilacyclobutenes with various substrates also proceed stereospecifically to give adducts. The results of theoretical calculations for the platinum-catalyzed reaction of disilacyclobutene with acetylene, the nickel-catalyzed reaction of benzodisilacyclobutene and the thermal reaction of benzobis(disilacyclobutene) are discussed in this review.

Bond formation and coupling between germyl and bridging germylene ligands in dinuclear palladium(I) complexes

The dinuclear palladium(I) complexes [L(Ar2 HGe)Pd(μ-GeAr2 )2 Pd(GeHAr2 )L] (Ar=Ph, p-Tol; L=PMe3 , tBuNC) contain terminal germyl and bridging germylene ligands with the experimentally observed Ge⋅⋅⋅Ge bond lengths of 2.8263(4) Å (L=PMe3 ) and 2.928(1) Å (L=tBuNC), which are close to the longest Ge-Ge bond reported to date [2.714(1) Å]. Significant Ge⋅⋅⋅Ge interactions between the germylene and germyl ligands (PMe3 complexes > tBuNC complexes) are supported by DFT calculations, Wiberg bond indices (WBI), and natural bond orbital (NBO) analyses. Exchanging tBuNC for PMe3 ligands increases the Ge⋅⋅⋅Ge interaction, and simultaneously activates two Pd-Ge bonds. Adding the chelating diphosphine 1,2-bis(diethylphosphino)ethane (depe) to the PMe3 complexes results in the intramolecular coupling of germyl and germylene ligands followed by extrusion of a digermane.