No abstract

Main group analogues of cyclobutane‐1,3‐diyls are fascinating due to their unique reactivity and electronic properties. So far only heteronuclear examples have been isolated. Here we report the isolation and characterization of all‐silicon 1,3‐cyclobutanediyls as stable closed‐shell singlet species from the reversible reactions of cyclotrisilene c‐Si3Tip4 (Tip=2,4,6‐triisopropylphenyl) with the N‐heterocyclic silylenes c‐[(CR2CH2)(NtBu)2]Si: (R=H or methyl) with saturated backbones. At elevated temperatures, tetrasilacyclobutenes are obtained from these equilibrium mixtures. The corresponding reaction with the unsaturated N‐heterocyclic silylene c‐(CH)2(NtBu)2Si: proceeds directly to the corresponding tetrasilacyclobutene without detection of the assumed 1,3‐cyclobutanediyl intermediate.

Suppressed aggregation: The unprecedented alumoxane hydrogensulfide [{LAl(SH)}2(μ‐O)] and the unique sulfide‐bridged compound [{LAl(SH)}2(μ‐S)] can be prepared from the easily accessible aluminum dihydride [LAlH2] (L=HC[(CMe)N(2,4,6‐Me3C6H2)]2−). Owing to the cis conformation of the terminal SH groups, these compounds represent ideal precursors for the synthesis of heterometallic compounds.

A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon-based metalloligand [κ(3)N-Si(3,5-Me2pz)3Mo(CO)3](-) is presented (pz = pyrazolyl). This metalloligand is straightforwardly accessible by reacting the ambidentate ligand tris(3,5-dimethylpyrazolyl)silanide ({Si(3,5-Me2pz)3}(-)) with [Mo(CO)3(η(6)-toluene)]. The compound features a fac-coordinated tripodal chelating ligand and an outward pointing, "free" pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers. Several bimetallic silyl halido cuprates of the general formula [CuX{μ-κ(1)Si:κ(3)N-Si(3,5-Me2pz)3Mo(CO)3}](-) (X = Cl, Br, I) have been synthesized. The electronic and structural properties of these complexes were probed in detail by X-ray diffraction analysis, electrospray mass spectrometry, infrared-induced multiphoton dissociation studies, cyclic voltammetry, spectroelectrochemistry, gas-phase photoelectron spectroscopy, as well as UV/Vis and fluorescence spectroscopy. The heterobimetallic complexes contain linear two-coordinate copper(I) entities with the shortest silicon-copper distances reported so far. Oxidation of the anionic complexes in methylene chloride and acetonitrile solutions at E(1/2)(0( = -0.60 and -0.44 V (vs. ferrocene/ferrocenium (Fc/Fc(+))), respectively, shows substantial reversibility. Based on various results obtained from different characterization methods, as well as density functional theory calculations, these oxidation events were attributed to the Mo(0)/Mo(I) redox couple.

The synthesis and characterization of several rhodium(I) complexes of amidinate and linker-bridged bis(amidinate) ligands are presented. The amidinate ligands for the mononuclear complexes CH 3 {C(NMes) 2 Rh(cod)} (1), CH 3 -{C(NDipp) 2 Rh(cod)} (2), and HCC{C(NDipp) 2 Rh(cod)} (3) (cod = 1,5-cyclooctadiene) were synthesized by reacting the corresponding organometallic precursor [Rh(cod)Cl] 2 with the alkali metal amidinates CH 3 {C(NR) 2 Li} L1Li (R = Mes = 2,4,6-Me 3 C 6 H 2 ) and L2Li (R = Dipp = 2,6-iPr 2 C 6 H 3 ). Analogously, the alkynylfunctionalized sodium amidinate (HCC{C(NDipp) 2 Na}·2DME, L3Na) could be further deprotonated and reacted with carbodiimine to form the alkyne-bridged bis(amidinate) CC{C(NDipp) 2 -Na(thf )} 2 (L4Na), which serves as suitable starting material for the synthesis of CC{C(NDipp) 2 Rh(cod)} 2 (4). The bis(amidinate) ligands for the corresponding para-(5) and meta-(6) phenyl- [a] 3024 Scheme 4. Synthesis of L5Na and L6Na via their protonated analogues L5H and L6 H, respectively PPSE (polyphosphoric acid trimethylsilyl ester).