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Herein, a nitrogen-embedded quintuple [7]helicene (

Noncentrosymmetry (NCS) is a prerequisite for second-order nonlinear optical (NLO) materials. In this work, a new polycation-substitution-induced centrosymmetry (CS)-to-NCS transformation strategy was applied in CS RbGaS2, affording two novel NCS salt-inclusion chalcogenides: [ABa2Cl][Ga4S8] (A = Rb, 1; Cs, 2). Remarkably, they exhibit the key merits of both Vis and IR NLO candidates, including strong phase-matchable second harmonic generation intensities (10.4-15.3 × KH2PO4 at 1064 nm; 0.9-1.0 × AgGaS2 at 1910 nm), high laser-induced damage thresholds (11-12 × AgGaS2), and a wide transparent window. Their prominent NLO performances originate from the orderly packing of T2-supertetrahedral Ga4S10 motifs resulting from the template effect of acentric polycation [ClA2Ba3]7+. The CS-to-NCS transformation first realized by polycation-substitution-induced NLO-functional motif ordering provides an effective approach for designing new NLO materials.

Noncentrosymmetry (NCS) is a prerequisite for second-order nonlinear optical (NLO) materials. In this work, a new polycation-substitution-induced centrosymmetry (CS)-to-NCS transformation strategy was applied in CS RbGaS

The activation of C(sp3)–H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)–silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp3)–H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)–Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp3 C–H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C–H bonds in −CH3 rather than the N–H bonds in −NH2 ...

The activation of C(sp(3))-H bonds is challenging, due to their high bond dissociation energy, low proton acidity, and highly nonpolar character. Herein we report a unique gold(I)-silver(I) oxo cluster protected by hemilabile phosphine ligands [OAu3Ag3(PPhpy2)3](BF4)4 (1), which can activate C(sp(3))-H bonds under mild conditions for a broad scope of methyl ketones (RCOCH3, R = methyl, phenyl, 2-methylphenyl, 2-aminophenyl, 2-hydroxylphenyl, 2-pyridyl, 2-thiazolyl, tert-butyl, ethyl, isopropyl). Activation happens via triple deprotonation of the methyl group, leading to formation of heterometallic Au(I)-Ag(I) clusters with formula RCOCAu4Ag4(PPhpy2)4(BF4)5 (PPhpy2 = bis(2-pyridyl)phenylphosphine). Cluster 1 can be generated in situ via the reaction of [OAu3Ag(PPhpy2)3](BF4)2 with 2 equiv of AgBF4. The oxo ion and the metal centers are found to be essential in the cleavage of sp(3) C-H bonds of methyl ketones. Interestingly, cluster 1 selectively activates the C-H bonds in -CH3 rather than the N-H bonds in -NH2 or the O-H bond in -OH which is traditionally thought to be more reactive than C-H bonds. Control experiments with butanone, 3-methylbutanone, and cyclopentanone as substrates show that the auration of the C-H bond of the terminal methyl group is preferred over secondary or tertiary sp(3) C-H bonds; in other words, the C-H bond activation is influenced by steric effect. This work highlights the powerful reactivity of metal clusters toward C-H activation and sheds new light on gold(I)-mediated catalysis.

Treatment of the osmabenzyne Os([triple bond]CC(SiMe(3))=C(Me)C(SiMe(3))=CH)Cl(2)(PPh(3))(2) (1) with 2,2'-bipyridine (bipy) and thallium triflate (TlOTf) produces the thermally stable dicationic osmabenzyne [Os([triple bond]CC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)](OTf)(2) (2). The dicationic osmabenzyne 2 reacts with ROH (R = H, Me) to give osmabenzene complexes [Os(=C(OR)CH=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf, in which the metallabenzene ring deviates significantly from planarity. In contrast, reaction of the dicationic complex 2 with NaBH(4) produces a cyclopentadienyl complex, presumably through the osmabenzene intermediate [Os(=CHC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf. The higher thermal stability of [Os(=C(OR)CH=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf relative to [Os(=CHC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf can be related to the stabilization effect of the OR groups on the metallacycle. A theoretical study shows that conversion of the dicationic osmabenzyne complex [Os([triple bond]CC(SiMe(3))=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)](OTf)(2) to a carbene complex by reductive elimination is thermodynamically unfavorable. The theoretical study also suggests that the nonplanarity of the osmabenzenes [Os(=C(OR)CH=C(Me)C(SiMe(3))=CH)(bipy)(PPh(3))(2)]OTf is mainly due to electronic reasons.

Treatment of OsX2(PPh3)3 (X = Cl, Br) with HCCCH(OH)CCH in THF produces OsX2(CH=C(PPh3)CH(OH)CCH)(PPh3)2, which reacts with PPh3 to give osmabenzenes [Os(CHC(PPh3)CHC(PPh3)CH)X2(PPh3)2]+.

The reactivities of benzynes and metal-carbyne complexes are normally associated with the triple bond units. However, we have now found that electrophiles do not attack the formal osmium-carbon triple bond of osmabenzyne complex 1. Instead, 1 undergoes electrophilic substitution reactions-the typical reactions of aromatic systems.

Treatment of OsX2(PPh3)3 (X = Cl, Br) with HC⋮CCH(OH)C⋮CH in THF produces OsX2(CHC(PPh3)CH(OH)C⋮CH)(PPh3)2, which reacts with PPh3 to give osmabenzenes [Os(CHC(PPh3)CHC(PPh3)CH)X2(PPh3)2]+.