Photoinduced Charge Transfer and Bimetallic Bond Dissociation of a Bi-W Complex in Solution

Organometallic complexes including metal carbonyls have been widely utilized in academic and industrial settings for purposes ranging from teaching basic catalytic reactions to developing state-of-the-art electronic circuits. Characterization of these materials can be obtained via steady-state measurements; however, the intermediate photochemical events remain unclear, hindering effective and rational molecular engineering methods for new materials. We employed femtosecond transient absorption (fs-TA) and ground-state femtosecond stimulated Raman spectroscopy (FSRS) on triphenylbismuth-tungsten pentacarbonyl complex, a solution precursor for bimetallic oxide thin films. Upon 280 nm excitation into a charge-transfer band, an ultrafast bimetallic bond dissociation occurs within ∼140 fs. The subpicosecond nondiffusive solvation events are followed by ∼10 ps (15 ps) methanol (ethanol) complexation of the nascent tungsten pentacarbonyl intermediate, which mainly undergoes vibrational relaxation after crossing into a hot ground state. The trans ligand to axial CO is revealed to play a key role in the electronic and vibrational structure and dynamics of the complex. These findings could power rational design of bimetallic and functional solution precursors for the light-driven nanopatterning of thin films.

New advances in homoleptic organotransition-metal compounds: The case of perhalophenyl ligands

Homoleptic derivatives of formula [M(C(6)X(5))(n)](z-) (X = F, Cl) have been prepared and isolated for every first-row transition metal as well as for several of the heavier ones. The stoichiometry attained in each case (n ranging between 2 and 6) can be understood considering the tendency of a given metal ion to compensate its coordinative and electronic unsaturation, while not incurring severe interligand repulsive effects. The molecular structures associated with each stoichiometry seem, in turn, to be governed by electronic rather than steric factors. Most of these [M(C(6)X(5))(n)](z-) compounds are unsaturated, open-shell organometallic species, not fulfilling the 18-electron (or Effective Atomic Number) rule. This behaviour can be attributed to the absence of pi stabilising ligands (such as CO, phosphines, alkenes, alkynes, a variety of substituted aromatic rings, and so on) which are otherwise ubiquitous in organotransition-metal chemistry. The magnetic properties of the [M(C(6)X(5))(n)](z-) species have been determined by EPR spectroscopy and/or bulk magnetisation measurements. Excellent correlation between molecular geometry and magnetic properties (whether diamagnetic or paramagnetic) has been observed. Many of these compounds undergo chemically- or electrochemically-induced electron exchange processes. These redox reactions proceed without alteration in the stoichiometry of the [M(C(6)X(5))(n)](z-) compound, but usually involve a sharp change in the molecular geometry according to the different electron configuration of the interrelated species.

Unusually accelerated silylmethyl transfer from tin in stille coupling: implication of coordination-driven transmetalation

The palladium-catalyzed cross-coupling reaction of 2-PyMe2SiCH2SnBu3 with aryl iodide (Ar-I) exclusively produced the 2-PyMe2SiCH2 transferred product 2-PyMe2SiCH2Ar. The relative transfer ability of organic group from tin was found to be 2-PyMe2SiCH2 >> Ph > Me > Bu >> PhMe2SiCH2, which implies the beneficial pyridyl-to-palladium coordination effect. Thus, the transfer of the silylmethyl group from tin to palladium was remarkably accelerated by simply appending the 2-pyridyl group on silicon. The pyridyl-to-palladium coordination was validated in the palladium(II) complex 2-PyMe2SiCH2PdClPPh3 by 1H NMR and X-ray crystal structure analysis. The cross-coupling product was used for further transformations. The C-Si oxidation of the cross-coupling product 2-PyMe2SiCH2Ar afforded ArCH2OH in high yield. The fluoride ion-catalyzed 1,2-addition of 2-PyMe2SiCH2Ar to carbonyl compound (RR'C=O) gave ArCH2C(OH)RR' in high yield.