Ytterbium(II) Complex-Catalyzed Selective Single and Double Hydrophosphination of 1,3-Enynes.

1,3-Enynes with the conjugated alkene and alkyne moieties are attractive building blocks in synthetic chemistry. However, neither 4,1-hydrophosphination nor dihydrophosphination of 1,3-enynes has been reported. In this paper, the divalent ytterbium and calcium amide complexes supported by silaimine-functionalized cyclopentadiene ligands (C5Me4-Si(L)=NR) were developed, which successfully catalyzed the efficient single and double hydrophosphination of 1,3-enynes with diarylphosphines. These two hydrophosphination reactions selectively produced homoallenyl phosphines and (E)-propenylene diphosphines, respectively. This work demonstrated the potential of hemilabile silaimine-Cp ligands in supporting the efficient and selective rare- and alkaline-earth catalysts.

Selective Access to Silacyclopentanes and Homoallylsilanes by La-Catalyzed Hydrosilylations of 1-Aryl Methylenecyclopropanes.

Methylenecyclopropanes (MCPs) have emerged as versatile building blocks in synthetic chemistry because of their unique reactivity. However, metal-catalyzed hydrosilylation of MCPs has met with very limited successes. In this paper, catalytic selective hydrosilylations of MCPs with some primary silanes using an ene-diamido lanthanum ate complex as the catalyst were described. The catalytic reactions resulted in the selective formation of silacyclopentanes and (E)-homoallylsilanes, respectively, depending on the substituents on MCPs. The formation of silacyclopentanes via a catalytic cascade inter- and intramolecular hydrosilylation mechanism is strongly supported by the control and deuteration-labeling experiments and DFT calculations. The unique reactivity and selectivity could be attributed to the large lanthanum ion and ate structure of the catalyst.

Boryl-substituted low-valent heavy group 14 compounds.

Low valent group 14 compounds exhibit diverse structures and reactivities. The employment of diazaborolyl anions (NHB anions), isoelectronic analogues to N-heterocyclic carbenes (NHCs), in group 14 chemistry leads to the exceptional structures and reactivity. The unique combination of σ-electron donation and pronounced steric hindrance impart distinct structural characteristics to the NHB-substituted low valent group 14 compounds. Notably, the modulation of the HOMO-LUMO gap in these compounds with the diazaborolyl substituents results in novel reaction patterns in the activation of small molecules and inert chemical bonds. This review mainly summarizes the recent advances in NHB-substituted low-valent heavy Group 14 compounds, emphasizing their synthesis, structural characteristics and application to small molecule activation.

Synthesis and Reactivity of Aluminum Disilacyclopropenes. Cyclic AlSi2 Delocalized 2π Systems.

The synthesis, structures, and reactivity of the first unsaturated AlSi2 three-membered ring systems were described. Reactions of dilithiodisilene [(NHB)LiSi═SiLi(NHB)] (1, NHB = diazaborolyl) with aluminum halides AlCl3, Ar(SiMe3)NAlCl2 (Ar = 2,6-iPr2C6H3), Cp*AlBr2 (Cp* = C5Me5), and TipAlBr2·Et2O (Tip = 2,4,6-iPr3C6H2) led to the formation of AlSi2 three-membered ring species, solvated (NHBSi)2AlCl(OEt2) (2) and solvent-free (NHBSi)2AlN(SiMe3) Ar (3), (NHBSi)2AlCp* (4), and (NHBSi)2AlTip (5), in good yields. X-ray diffraction studies and DFT calculations disclosed delocalized AlSi2 2π electron systems. Methanolysis of 4a resulted in cleavage of the Al-Si σ and Si-Si π bonds, giving trihydrodisilane (NHB)H(MeO)SiSiH2 (NHB) (6). Reaction of 4b with 4 equiv of N2O and H2C═CH2 resulted in the insertion of four oxygen atoms and four H2C═CH2 π bonds into all of the Al-Si and Si-Si bonds, yielding the O- and CH2CH2-bridged polycyclic species 7 and 8, demonstrating the synergistic reactivity of the Al-Si and Si-Si bonds in the AlSi2 ring system.

π-Aromaticity Dominating in a Saturated Ring: Neutral Aromatic Silicon Analogues of Cyclobutane-1,3-diyls.

The synthesis, structures, and reactivity of the first neutral 2π-aromatic Si4 rings [LSiSiAr(X)]2 (3: X = Br; 4: X = Cl; L = PhC(NtBu)2, Ar = 2,4,6-Me3C6H2) were described. Compounds 3 and 4 were obtained by 1,3-halogenation of tetrasilacyclobutadiene (LSiSiAr)2 (2), which was prepared by the reductive cross-coupling of trisilane (ArSiCl2)2SiHAr with two equiv of chlorosilylene LSiCl. The reaction of 3 with two equiv of PhLi yielded the corresponding substitution Si4 ring [LSiSiAr(Ph)]2 (5). Single-crystal X-ray diffraction analysis of 3 disclosed that it adopts both puckered (3a) and planar (3b) structures in the solid state, whereas 4 and 5 exhibit only a puckered structure. DFT calculations suggested that the puckered 3a features almost the same electronic structure with fully delocalized 2π planar 3b. The dominant 2π-aromaticity of 3 in a σ-frame has been demonstrated by DFT calculations, providing the first example of aromatics featuring both planar and puckered structures.

Synthesis of Phosphine-Functionalized Silicon Cubane and Its Oxidative Addition, Giving a Bis(silyl)copper Complex.

A new strategy for the introduction of a second type of Si atom to silicon cubanes has been developed starting from the tricyclic hexasilane dianion [Ar6Si6]2- (Ar = 2,4,6-Me3C6H2). Treatment of the dianion with Ar'SiCl3, followed by KC8, gave new types of octasilacubanes Ar6Ar'2Si8 [Ar' = 2,4,6-iPr2C6H2 (3a), 2-Ph2PC6H4 (3b)] in high yields. Remarkably, treatment of cubane 3b bearing with two phosphine groups with 2 equiv of CuCl in CH2Cl2 yielded the bis(silyl)copper complex via the selective oxidative addition of the newly formed Si-Si bond to Cu ion. Single-crystal X-ray analysis indicated the unique square-planar, four-coordinate Cu cation paired with the [CuCl2]- counteranion.

Synthesis and reactivity of a µ-1,2-dinitrogen dinickel(II) complex with a C-H activated silaamidinate pincer ligand.

Reaction of the silaamidinate nickel bromide LSi(NAr)2NiBr2Li(thf)(OEt2) (L = PhC(NtBu)2, Ar = 2,6-iPr2C6H3, 1) with NaHBEt3 led to intramolecular C-H activation with the formation of the µ-1,2-dinitrogen dinickel pincer complex [LSi(NAr)(NAr)Ni]2(µ-1,2-N2) (Ar = 2-C(CH3)2-6-iPrC6H3, 2). Single-crystal X-ray diffraction analysis of 2 disclosed a square planar Ni(II) atom bridged by N2. Reaction of 2 with carbon monoxide and 2,6-dimethylphenyl isocyanide yielded square planar carbonyl and isocyanide complexes 3 and 4 with release of N2. These results provide new approaches for the coordination of N2 with nickel(II) species.

Disilicon Dicarbonyl Complex: Synthesis and Protonation of CO with O-H Bond.

Reaction of solid NHB-stabilized disilyne (NHB)Si≡Si(NHB) (1, NHB = [ArN(CMe)2NAr]B, Ar = 2,6-iPr2C6H3) with 1 atm of carbon monoxide yielded the first 1,2-disilicon dicarbonyl complex (NHB)(OC)SiSi(CO)(NHB) (2). Hydrolysis and methanolysis of 2 led to the C-C coupling and protonation of two CO oxygen atoms giving disilacyclobutene derivatives 3 and 4. In contrast, reaction of 2 with iodomethane resulted in the oxidative addition to the silicon atoms with the formation of 1,2-diiodo-disilane 5 with the liberation of CO molecules. Single-crystal X-ray diffraction analysis of 2 disclosed the coordination of CO to the two silicon atoms with a unique 1,2-dicarbonyl-disilane skeleton, in which the pronounced backbonding from the lone pairs of silicon p orbitals to CO π* orbitals was elucidated by DFT calculations.

Synthesis of an N-Heterocylic Boryl-Stabilized Disilyne and Its Application to the Activation of Dihydrogen and C-H Bonds.

The synthesis of low-valent silicon compounds that enable the activation of small molecules has been of great current interest. Reduction of N-heterocyclic boryltribromosilane (NHB)SiBr3 (2, NHB=[ArN(CMe)2 NAr]B, Ar=2,6-iPr2 C6 H3 ) with three equiv. of lithium in diethyl ether yielded the NHB-stabilized disilyne (NHB)Si≡Si(NHB) (3). Disilyne 3 slowly reacted with toluene, leading to the activation of one benzylic C-H bond and one C=C double bond with the formation of 4. Treatment of 3 with dihydrogen under 1 atm at room temperature resulted in the exclusive formation of the first boryl-stabilized 1,2-dihydrodisilene. Compounds 3-5 have been characterized by single-crystal X-ray diffraction studies, which indicated the co-planarity of the B-Si-Si-B plane with the NHB rings in compounds 3 and 5. DFT calculations indicated the significant π electron delocalization of the Si-Si multiple bonds to the B-N bonds in NHB rings.

Synthesis and Reactivity of N-Heterocyclic Silylene Stabilized Disilicon(0) Complexes.

Synthesis and reactivity of disilicon(0) complexes are of fundamental and application importance. Herein, we report the development of an N-heterocyclic imino-substituted silylene (1), which has strong σ-donating ability and is significantly sterically hindered. The one-pot reaction of this silylene with [IPr→SiCl2 ] (IPr=1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene) and KC8 (2 equiv) in THF at -30 °C leads to a silylene-ligated disilicon(0) complex (2), isolated as red crystals in 60 % yield. Characterization data and DFT calculations show that the trans-bent Si4 skeleton in 2 features a Si0 =Si0 double bond with significant π-π bonding and one lone pair of electrons on each of these two Si0 atoms. Complex 2 reacts readily with phenylacetylene, producing a structurally intriguing silatricyclic complex 6,8-diaza-1,2,5-trisilatricyclo-[3.2.1.02,7 ]-oct-3-ene (3), and revealing new aspects of low-valent silicon chemistry.

Isolation of a planar 1,2-dilithio-disilene and its conversion to a Si-B hybrid 2π-electron system and a planar tetraboryldisilene.

Lithium reagents have long played important roles in synthetic chemistry. However, unsaturated organosilicon lithium reagents are few in number. Herein, we describe the first isolation of a 1,2-dilithiodisilene: [(boryl)SiLi]2 (2) was prepared in 73% yield by the reduction of (boryl)tribromosilane (1, boryl = (HCArN)2B, Ar = 2,6-iPr2C6H3) with lithium in Et2O. The salt elimination reaction of 2 with dihaloboranes RBX2 afforded disilaborirenes [(boryl)Si]2BR (3a-c), whereas the reaction with two equivalents of B-bromocatecholborane ((cat)BBr) yielded the first tetraboryldisilene [(boryl)(cat)BSi]2 (4). X-ray diffraction analysis and density functional theory calculations indicated that the disilene 2 and tetraboryldisilene 4 feature an almost planar geometry and disilaborirenes 3a-c are aromatic with a silicon-boron hybrid 2π-electron delocalized structure. The results indicate that 1,2-dilithiodisilene 2 is a powerful synthetic reagent for the construction of novel silicon multiply bonded species with unique electronic structures and that the boryl substituents have significant electronic effects on the structure of silicon multiple bonding.

Synthesis of Cationic Silaamidinate Germylenes and Stannylenes and the Catalytic Application for Hydroboration of Pyridines.

The N-heterocyclic germylenes and stannylenes LSi(NAr)2EX (L = PhC(NtBu)2, Ar = 2,6-iPr2C6H3; E = Ge, Sn; X = Cl, CF3SO3, BPh4) supported by the bulky silaamidinate ligand [LSi(NAr)2]- have been synthesized and fully characterized. The germylene triflate LSi(NAr)2GeOTf (3b) and dimeric borate [LSi(NAr)2Ge]2ClBPh4 (3a) enabled highly regio- and chemoselective catalytic hydroboration of pyridines and may represent the most active catalytic system for the transformation. DFT calculations disclosed that the cationic germylene [LSi(NAr)2Ge]+ with a low-lying LUMO energy initiated the catalytic process. In contrast, the analogous amidinate germylene triflates are almost inactive, indicating the silaamidinate ligand is essential for the stabilization of cationic species.

CpFe(CO)2 anion-catalyzed highly efficient hydrosilylation of ketones and aldehydes.

K[CpFe(CO)2] and [NEt4][CpFe(CO)2] enabled highly efficient hydrosilylation of ketones and aldehydes with PhSiH3 to synthesize tris- and bis(alkoxy)silanes in excellent yields depending on the substituents on the carbonyl compounds. The catalyst represents one of the most efficient and practical iron catalysts for hydrosilylation of carbonyl compounds with a TOF up to 24 540 h-1.

Rare-Earth-Catalyzed Selective 1,4-Hydrosilylation of Branched 1,3-Enynes Giving Tetrasubstituted Silylallenes.

Allenes are versatile synthons in organic synthesis and medicinal chemistry because of their diverse reactivities. Catalytic 1,4-hydrosilylation of 1,3-enynes may present the straightforward strategy for synthesis of silylallenes. However, the transition-metal-catalyzed reaction has not been successful due to poor selectivity and very limited substrate scopes. We report here the efficient and selective 1,4-hydrosilylation of branched 1,3-enynes enabled by the ene-diamido rare-earth ate catalysts using both alkyl and aryl hydrosilanes, leading to the exclusive formation of tetrasubstituted silylallenes. Deuteration reaction, kinetic study, and DFT calculations were conducted to investigate the possible mechanism, revealing crucial roles of high Lewis acidity, large ionic radius, and ate structure of the rare-earth catalysts.

Cyclic (Alkyl)(amino)carbene Lanthanide Amides: Synthesis, Structure, and Catalytic Selective Hydrosilylation of Alkenes.

The first examples of cyclic (alkyl)(amino)carbene (CAAC) lanthanide (Ln) complexes were synthesized from the reaction of CAAC with Yb[N(SiMe3)2]2 and Eu[N(SiMe3)2]2(THF)2 (THF = tetrahydrofuran). The structures of (CAAC)Yb[N(SiMe3)2]2 (2) and (CAAC)Eu[N(SiMe3)2]2(THF) (3) were determined by X-ray diffraction analysis. Density functional theory calculations of 2 revealed the predominantly ionic bond between the Ln ion and CAAC. Complex 3 enabled catalytic hydrosilylation of aryl- and silylalkenes with primary and secondary silanes in high yields and Markovnikov selectivity.

Modular Synthesis of Pentagonal and Hexagonal Ring-Fused NBN-Phenalenes Leading to an Excited-State Aromatization-Induced Structural Planarization Molecular Library.

Although polycyclic aromatic hydrocarbons (PAHs) with a nitrogen-boron-nitrogen (NBN) moiety have recently attracted tremendous interest due to their intriguing electronic and optoelectronic properties, all of the NBN-fused π-systems reported to date are called NBN-dibenzophenalenes and were synthesized by electrophilic aromatic substitution. The synthesis of NBN-phenalenes remains challenging, and transition-metal catalysis has never been utilized to construct NBN-embedded π-scaffolds. Herein, a palladium-catalyzed cyclization/bicyclization strategy was developed for the synthesis of diverse pentagonal and hexagonal ring-fused NBN-phenalenes and half-NBN-phenalenes. All of the NBN-embedded π-scaffolds presented in our paper are fluorescent in both solution and the solid state. Further investigations showed that the five-membered NBN rings exhibit the properties of traditional luminogens, while those with a six-membered NBN ring generally undergo photoinduced structural planarization (PISP) and exhibit different colors and quantum yields of fluorescence with different concentrations in solution. Time-resolved spectroscopy and TD-DFT calculations revealed that excited-state aromatization is the driving force for PISP in hexagonal ring-fused NBN-π systems, leading to the formation of excimers. Notably, the scope of PISP compounds is still quite limited, and PISP has never been observed in NBN-π systems before. These hexagonal ring-fused NBN-π systems constitute a novel PISP molecular library and appear to be a new class of aggregation-induced excimer emission (AIEE) materials. Finally, the AIEE behavior of these six-membered NBN rings was applied to the detection of nitro explosives, achieving excellent sensitivity. In general, this work provides a new viewpoint for synthesizing NBN-fused π-systems and understanding the excited-state motion of luminogens.

From BN-Naphthalenes to Benzoborole Dianions.

The synthesis of benzoborole dianions by alkali metal reduction of BN-naphthalene derivatives via a ring-contraction strategy has been developed. Reduction of 1-alkynyl 2,1-benzazaborine 1 a in Et2 O led to the elimination of alkynyllithium with the formation of 1-amino-1-benzoborole trilithium salt 2 a, whereas reduction of 1-phenyl 2,1-benzazaborine 1 c in THF yielded 1-phenyl-1-benzoborole dilithium salt 2 c with the elimination of ArNHLi. The trilithium and dilithium salts 2 a and 2 c have been fully characterized. Treatment of trilithium salt 2 a with Et3 NHCl led to the selective protonation of the amino lithium to afford the dilithium salt 2 aH, which could be cleanly oxidized to 1-amino-1-benzoborole 3 in an excellent yield. Reaction of 1-phenyl-1-benzoborole dilithium salt 2 c with MeI yielded the lithium borate 4 c, which is luminescent both in solution and in the solid state.

Molecular diagnosis of non-syndromic hearing loss patients using a stepwise approach.

Hearing loss is one of the most common birth disorders in humans, with an estimated prevalence of 1-3 in every 1000 newborns. This study investigates the molecular etiology of a hearing loss cohort using a stepwise strategy to effectively diagnose patients and address the challenges posed by the genetic heterogeneity and variable mutation spectrum of hearing loss. In order to target known pathogenic variants, multiplex PCR plus next-generation sequencing was applied in the first step; patients which did not receive a diagnosis from this were further referred for exome sequencing. A total of 92 unrelated patients with nonsyndromic hearing loss were enrolled in the study. In total, 64% (59/92) of the patients were molecularly diagnosed, 44 of them in the first step by multiplex PCR plus sequencing. Exome sequencing resulted in eleven diagnoses (23%, 11/48) and four probable diagnoses (8%, 4/48) among the 48 patients who were not diagnosed in the first step. The rate of secondary findings from exome sequencing in our cohort was 3% (2/58). This research presents a molecular diagnosis spectrum of 92 non-syndromic hearing loss patients and demonstrates the benefits of using a stepwise diagnostic approach in the genetic testing of nonsyndromic hearing loss.

New Approaches to N-Heterocyclic-Carbene-Coordinated Iminoborane and Borenium Species.

The synthesis, characterization, and reactivity of an iminoborane-N-heterocyclic carbene (NHC) adduct were described. The reaction of DmpNHB(OEt)Br [1; Dmp = 2,6-bis(2,4,6-trimethylphenyl)phenyl] with 2 equiv of 1,3-diimethyl-4,5-dimethylimidazol-2-ylidene (IMe4) resulted in the formation of an iminoborane-NHC complex 2. Both X-ray analysis and density functional theory calculations revealed the double-bond character of the B═N bond in 2. Interestingly, compared with the corresponding Lewis-base-free iminoborane, 2 features a nitrogen atom with increased electron density, which could be attributed to coordination of the NHC. Similar to the isoelectronic species imine, this nitrogen center in 2 can be easily attacked by electrophiles. Indeed, the reaction of 2 with trimethylsilyl triflate (Me3SiOTf) afforded an NHC-stabilized borenium cation 3, representing a facile strategy to prepare cationic tricoordinate boron species.

Isolation of a 1-Magnesium-2,3-disilacyclopropene and a Related Bis(disilenide).

Herein we report the first synthesis of a 1-magnesium-2,3-disilacyclopropene and a related bis(disilenide). Reduction of (boryl)tribromosilane (1, boryl = (HCArN)2B, Ar = 2,6-iPr2C6H3) with magnesium in THF afforded boryl-substituted magnesium complex [(boryl)Si]2Mg(THF)3 (2) in good yield, whereas reduction of (boryl)trichlorosilane (3) with KC8 in THF led to the isolation of bridged alkoxy alkyl bis(disilenide) (THF)K(boryl)Si═Si(boryl)O(CH2)4(boryl)Si═Si(boryl)K(THF) (4) via ring opening of a THF molecule. X-ray diffraction analysis of 2 confirmed the presence of the novel Si2Mg three-membered ring as well as the Si═Si double bond, which existed in a noticeably twisted B-Si-Si-B array. Complex 2 also represents the first reported example of a stable disilyne dianion.