Trivalent Phosphine-Catalyzed [4+1] Spiro-annulation Reaction Using Allenyl Imide and Methylene Cyclocompounds.

The trivalent phosphine-catalyzed [4+1] spiro-annulation reaction of allenyl imide and activated methylene cyclocompounds has been developed for the construction of various spiro-2-cyclopenten-1-ones. Oxindoles, 3-isochromanones, and 2-indanones are selected as 1C synthons to capture the in situ-generated bis-electrophilic α,ß-unsaturated ketenyl phosphonium intermediate, affording the corresponding monospiro- and bispiro-cyclopentenones in good to excellent yields (≤91%) under mild conditions. The primary attempt at asymmetric catalysis using monophosphine (R)-SITCP provides promising enantioselectivity (45% ee). A plausible reaction mechanism is also proposed.

The Narrow Synthetic Window for Highly Homogenous InP Quantum Dots toward Narrow Red Emission.

Low-toxicity InP-based quantum dots (QDs) exhibit potential for replacing Cd/Pb-containing QDs in the visible and near-infrared regions. Despite advancements, further improvement relies on synthesizing homogeneous InP QDs to achieve a high color purity. In a commonly employed two-step "seed-mediated" synthetic approach, we demonstrate the high sensitivity of InP seed sizes and size distribution to the quantities of trioctylphosphine (TOP) and tris(trimethylsilyl)phosphine [(TMS)3P], attributed to the process of "self-focusing of size distribution" and enhanced reactivity of In-oleate through coordination with TOP. During growth, the processes of size focusing and defocusing are modulated by the accumulation of oleic acid and TOP molecules, as well as the amount of (TMS)3P in the growth precursor, which may relate to the dissolution process of InP magic size clusters. Through precise control, the best valley/depth ratio of InP QDs was 0.52 at the first absorption peak at 571 nm, resulting in luminescence with a full width at half-maximum of 35 at 620 nm with an absolute photoluminescence quantum yield around 90% after heteroepitaxial growth with ZnSe and ZnS shells.

Experimental and Theoretical Study of NiII - and PdII -Promoted Double Geminal C(sp3 )-H Bond Activation Providing Facile Access to NHC Pincer Complexes: Isolated Intermediates and Mechanism.

We report the first examples of metal-promoted double geminal activation of C(sp3 )-H bonds of the N-CH2 -N moiety in an imidazole-type heterocycle, leading to nickel and palladium N-heterocyclic carbene complexes under mild conditions. Reaction of the new electron-rich diphosphine 1,3-bis((di-tert-butylphosphaneyl)methyl)-2,3-dihydro-1H-benzo[d]imidazole (1) with [PdCl2 (cod)] occurred in a stepwise fashion, first by single C-H bond activation yielding the alkyl pincer complex [PdCl(PC sp 3 H P)] (3) with two trans phosphane donors and a covalent Pd-C sp 3 bond. Activation of the C-H bond of the resulting α-methine C sp 3 H-M group occurred subsequently when 3 was treated with HCl to yield the NHC pincer complex [PdCl(PCNHC P)]Cl (2). Treatment of 1 with [NiBr2 (dme)] also afforded a NHC pincer complex, [NiBr(PCNHC P)]Br (6), but the reactions leading to the double geminal C-H bond activation of the N-CH2 -N group were too fast to allow identification or isolation of an intermediate analogous to 3. The determination of six crystal structures, the isolation of reaction intermediates and DFT calculations provided the basis for suggesting the mechanism of the stepwise transformation of a N-CH2 -N moiety in the N-CNHC -N unit of NHC pincer complexes and explain the key differences observed between the Pd and Ni chemistries.

Influence of the Flexibility of Nickel PCP-Pincer Complexes on C-H and P-C Bond Activation and Ethylene Reactivity: A Combined Experimental and Theoretical Investigation.

Using a pincer platform based on a bridgehead NHC donor with functional side arms, the combined effect of increased flexibility in six-membered pyrimidine-type heterocycles compared to the more often studied five-membered imidazole, and rigidity of phosphane side arms was examined. The unique features observed include: 1) the reaction of the azolium Csp2 -H bond with [Ni(cod)2 ] affording a carbanionic ligand in [NiCl(PCsp3 H P)] (8) rather than a carbene; 2) its transformation into the NHC, hydrido complex [NiH(PCNHC P)]PF6 (9) upon halide abstraction; 3) ethylene insertion into the Ni-H bond of the latter and ethyl migration to the N-C-N carbon atom of the heterocycle in [Ni(PCEt P)]PF6 (10); and 4) an unprecedented C-P bond activation transforming the P-CNHC -P pincer ligand of 8 in a C-CNHC -P pincer and a terminal phosphanido ligand in [Ni(PPh2 )(CCNHC P)] (15). The data are supported by nine crystal structure determinations and theoretical calculations provided insights into the mechanisms of these transformations, which are relevant to stoichiometric and catalytic steps of general interest.

Imidazolium salts and [Pt(cod)2]: from NHC hydrido complexes to the unprecedented olefinic tetrahedral cluster [Pt4(µ-H)(cod)4]BF4.

Whereas the bis(imine)imidazolium salt 1·Cl is a potential precursor to a NimineCNHCNimine pincer-type ligand, it reacted with [Pt(cod)2] to give the PtII NHC hydrido complex 3, in which chloride coordination and CNHCNimine chelation is preferred over pincer formation. Unexpectedly, reaction of 1·BF4 with [Pt(cod)2] afforded the unprecedented, 56 CVE tetrahedral cluster [Pt4(µ-H)(cod)4]BF4 (7), which was fully characterized. Imidazolium salts are ubiquitous sources of the much studied NHC ligands and not expected to lead to the formation of metal clusters.

Postpolymerization of a fluorinated and reactive poly(aryl ether): an efficient way to balance the solubility and solvent resistance of the polymer.

A new fluorinated poly(aryl ether) with reactive benzocyclobutene groups as the side chain was successfully synthesized. This polymer showed a number-average molecular weight (Mn) of 200,000 and had good solubility and film-forming ability. After being postpolymerized at high temperature (>200 °C), the polymer film converted to a cross-linked network structure, which was insoluble in the common organic solvents. Such results suggest that the postpolymerization is an efficient way to achive the balance between the solubility and the solvent resistance of the polymer. TGA data showed that the postpolymerized polymer had a 5 wt % loss temperature at 495 °C and a residual of 61% at 1000 °C under N2. The cross-linked film also exhibited good dielectric properties with an average dielectric constant of about 2.62 in a range of frequencies from 1 to 30 MHz. With regard to the mechanical properties, the cross-linked film had hardness, Young's modulus, and bonding strength to a silicon wafer of 1.22, 8.8, and 0.89 GPa, respectively. These data imply that this new polymer may have potential applications in the electrical and microelectronics industry.