Diboran(4)yl Platinum(II) Complexes

The platinum diboran(4)­yl complexes <b>1</b>–<b>3</b> have been prepared by the selective oxidative addition of one B–Hal bond in aryl-substituted diboranes(4) Hal₂B₂Ar₂ (Hal = Cl, Ar = mes, dur; Hal = I, Ar = mes). Because of the electron deficiency of the remote B2 atom, all species show a rare dative Pt–B bonding interaction, whose magnitude is strongly dependent on the nature of the halide substituent

Diboran(4)yl Platinum(II) Complexes

The platinum diboran(4)­yl complexes <b>1</b>–<b>3</b> have been prepared by the selective oxidative addition of one B–Hal bond in aryl-substituted diboranes(4) Hal₂B₂Ar₂ (Hal = Cl, Ar = mes, dur; Hal = I, Ar = mes). Because of the electron deficiency of the remote B2 atom, all species show a rare dative Pt–B bonding interaction, whose magnitude is strongly dependent on the nature of the halide substituent

Bond-strengthening p backdonation in a transition-metal p-diborene complex

Transition-metal catalysis is founded on the principle that electron donation from a metal to a ligand is accepted by an antibonding orbital of the ligand, thereby weakening one of the bonds in the ligand. Without this, the initial step of bond activation in many catalytic processes would simply not occur. This concept is enshrined in the well-accepted Dewar–Chatt–Duncanson model of transition-metal bonding. We present herein experimental and computational evidence for the first true violation of the Dewar–Chatt–Duncanson bonding model, found in a p-diborene complex in which an electron-rich group 10 metal donates electrons into an empty bonding p orbital on the ligand, and thereby strengthens the bond. The complex is also the first transition-metal complex to contain a bound diborene, a species not isolated before, either in its free form or bound to a metal

Synthesis and Structure of New [3]Silametallocenophanes of Group 8 Metals

The synthesis and characterization of new [3]­silametallocenophanes of the group 8 metals via salt elimination is presented. Thereby, new [3]­silaferrocenophanes as well as the first [3]­silametallocenophanes of the heavier metals ruthenium and osmium could be synthesized and characterized. Also, the first solid-state structure of a [3]­silaferrocenophane was determined by X-ray crystallographic analysis

Synthesis and Structure of New [3]Silametallocenophanes of Group 8 Metals

The synthesis and characterization of new [3]­silametallocenophanes of the group 8 metals via salt elimination is presented. Thereby, new [3]­silaferrocenophanes as well as the first [3]­silametallocenophanes of the heavier metals ruthenium and osmium could be synthesized and characterized. Also, the first solid-state structure of a [3]­silaferrocenophane was determined by X-ray crystallographic analysis

Synthesis and Structure of Group IV Distanna[2]metallocenophanes

1,2-Dichloro-1,1,2,2-tetra-<i>tert</i>-butyldistannane reacts with 2 equiv of sodium cyclopentadienide to give a bis­(cyclopentadienyl)­distannane. Subsequent dilithiation with lithium diisopropylamide and reactions with suitable metal halides yield [(C₅H₄Sn<i>t</i>Bu₂)₂MCl₂] (M = Ti, Zr, Hf). The group 4 <i>ansa</i>-metallocenes have all been fully characterized by means of multinuclear NMR spectroscopy, elemental analysis, and X-ray diffraction

Si–H Bond Activation at the Boron Center of Pentaphenylborole

Si–H bond activation is usually considered a domain of transition-metal complexes, and only few metal-free systems have proven suitable for this task. We have now found that Et₃SiH readily reacts with pentaphenylborole to afford 1-bora-3-cyclopentenes as the <i>syn</i> and <i>anti</i> addition products. Here, Si–H bond cleavage is accomplished at a single boron center, a reactivity that is facilitated by a combination of high electrophilicity and loss of antiaromaticity. The mechanism of this transformation most likely involves a sequence of adduct formation, σ-bond metathesis, and conrotatory ring closure, similar to that observed for H/D exchange between H₂ and silanes mediated by HB­(C₆F₅)₂ and heterolytic H₂ splitting by boroles, respectively

Si–H Bond Activation at the Boron Center of Pentaphenylborole

Si–H bond activation is usually considered a domain of transition-metal complexes, and only few metal-free systems have proven suitable for this task. We have now found that Et₃SiH readily reacts with pentaphenylborole to afford 1-bora-3-cyclopentenes as the <i>syn</i> and <i>anti</i> addition products. Here, Si–H bond cleavage is accomplished at a single boron center, a reactivity that is facilitated by a combination of high electrophilicity and loss of antiaromaticity. The mechanism of this transformation most likely involves a sequence of adduct formation, σ-bond metathesis, and conrotatory ring closure, similar to that observed for H/D exchange between H₂ and silanes mediated by HB­(C₆F₅)₂ and heterolytic H₂ splitting by boroles, respectively

Unprecedented luminescence behavior of coinage metal p-diborene complexes

A number of unprecedented photophysical phenomena are observed in the study of luminescent p-diborene complexes of Cu and Ag, including unusually high fluorescence quantum yields in solution for complexes of these metals (up to unity). This indicates that very little or no intersystem crossing between S1 and Tn occurs in the complexes, despite the strong spin-orbit coupling of the metal atoms. The substitution of carbon for boron thus yields luminescent isolobal analogues of otherwise non-emissive olefin complexes of Cu and Ag

Tin-Bridged <i>ansa</i>-Metallocenes of the Late Transition Metals Cobalt and Nickel: Preparation, Molecular and Electronic Structures, and Redox Chemistry

Using the flytrap approach, paramagnetic <i>ansa</i>-metallocenes of the late transition metals cobalt and nickel containing a tetra-<i>tert</i>-butyldistannane bridge have been prepared. The complexes were identified using a combination of analytical methods (NMR, EPR, cyclic voltammetry, and X-ray crystallography) and further converted to their corresponding cations by one-electron oxidation with ferrocenium hexafluorophosphate. Spectral and structural analyses of the ionic products are consistent with metal-based oxidations