Isolable Spirocyclic Silylone: π-Delocalized Spiro[3.3]heptasila-2,6-diylidone.

Strained cyclic tetrylones are important synthons due to various synthetic applications. Connecting two cyclic tetrylone rings through a single shared quaternary group 14 element atom to form a spirocyclic molecule has been unexplored both theoretically and experimentally. The formation of a spirocyclic motif has been a synthetic challenge. In contrast, the reaction of amidinato disilicon(I) 1, (Me3P)2SiCl4, and KC8 afforded π-delocalized spiro[3.3]heptasila-2,6-diylidone2 and tetrasilacyclobutadiene byproducts 3 and 4. Compound 2 is the smallest spirocyclic tetrylone derivative, which is composed of a σ-type lone pair and delocalized π bond in each all-silicon spirocyclic ring. The electronic property is supported by its coordination with a W(CO)5 moiety.

Carbon dioxide capture and functionalization by bis(N-heterocyclic carbene)-borylene complexes.

Derivatives of free monocoordinated borylenes have attracted considerable interest due to their ability to exhibit transition-metal-like reactivity, in particular small molecules capture. However, such complexes are rare as the formation is either endergonic, or the resulting adduct is a transient intermediate that is prone to reaction. Here, we present the synthesis of two bis(N-heterocyclic carbene)-borylene complexes capable of capturing and functionalizing carbon dioxide. The capture and subsequent functionalization of CO2 by the bis(NHC)-disilylamidoborylene 1 is demonstrated by the formation of the bis(NHC)-isocyanatoborylene-carbon dioxide complex 3. Reversible capture of CO2 is observed using the bis(NHC)-mesitylborylene 2, and the persistent bis(NHC)-mesitylborylene-carbon dioxide adduct 4 can be stabilized by hydrogen bonding with boric acid. The reactions of 4 with ammonia-borane and aniline demonstrate that the captured CO2 can be further functionalized.

A Digermanium(III) 1,2-Dication Stabilized by Amidinate and cAAC-Phosphinidenide Ligands.

A digermanium(III) 1,2-dication comprises two cationic centers located at two interconnected Ge atoms. The strong Coulombic repulsion between two positively charged germanium cations hinders their bond formation. Balancing these two oppositions was achieved by using amidinate and cyclic (alkyl)amino carbene (cAAC)-phosphinidenide ligands, where an amidinato cAAC-phosphinidenidogermylene complex, [LGeP(cAACMe)] (2, where L = PhC(NtBu)2, cAACMe = :C{C(Me)2CH2C(Me)2NAr}, and Ar = 2,6-iPr2C6H3), underwent one-electron oxidation with a bis(phosphinidene) radical cation, [(cAACMe)P]2•+, to form a digermanium(III) 1,2-dication, [LGeP(cAACMe)]22+, in compound 4.

NHC-Silyliumylidene Cation-Catalyzed Hydroboration of Isocyanates with Pinacolborane.

The low-oxidation-state silicon-catalyzed hydroboration of isocyanates with pinacolborane (HBpin) using the NHC-silyliumylidene cation catalyst [(IMe)2SiH]I (1, IMe = :C{N(Me)C(Me)}2) is described. In the catalysis, the Si lone pair electrons activate isocyanates, and the latter react with HBpin to form N-boryl formamides at room temperature. Catalyst 1 further activates N-boryl formamides at 70 °C, the intermediates of which react with HBpin to form N-boryl methylamines and (pinB)2O.

Tetrakis(N-heterocyclic Carbene)-Diboron(0): Double Single-Electron-Transfer Reactivity.

The use of 1,3,4,5-tetramethylimidazol-2-ylidene (IMe) to coordinate with diatomic B2 species afforded a tetrakis(N-heterocyclic carbene)-diboron(0) [(IMe)2B-B(IMe)2] (2). The singly bonded B2 moiety therein possesses a valence electronic configuration 1σg21πu21πg*2 with four vacant molecular orbitals (1σu*, 2σg, 1πu', 1πg'*) coordinated with IMe. Its unprecedented electronic structure is analogous to the energetically unfavorable planar hydrazine with a D2h symmetry. The two highly reactive πg* antibonding electrons enable double single-electron-transfer (SET) reactivity in small-molecule activation. Compound 2 underwent a double SET reduction with CO2 to form two carbon dioxide radical anions CO2•-, which then reduced pyridine to yield a carboxylated pyridine reductive coupling dianion [O2CNC5(H)5-C5(H)5NCO2]2- and converted compound 2 to the tetrakis(N-heterocyclic carbene)-diborene dication [(IMe)2B═B(IMe)2]2+ (32+). This is a remarkable transition-metal-free SET reduction of CO2 without ultraviolet/visible (UV/vis) light conditions.

Stability studies of ALD-52 and its homologue 1P-LSD.

With the emergence of new psychoactive substances (NPSs) over the years, the substances detected on stamps (also known as blotter papers) have also evolved from the traditional drug-lysergic acid diethylamide (LSD) to the multiple variants of lysergamides such as ALD-52 and 1P-LSD. The analysis of such blotter papers is usually done by solvent extraction followed by identification using gas chromatography-mass spectrometry (GC-MS). This study has shown that hydrolysis to form LSD was observed in GC-MS analysis when ALD-52 was extracted with methanol. The extraction of ALD-52 using other solvents such as acetonitrile, ethanol, isopropyl alcohol, ethyl acetate, and acetone, followed by GC-MS analysis, was investigated. It is shown that alcoholic solvents such as methanol and ethanol will result in the conversion of ALD-52 to LSD during GC-MS analysis, whereas the sterically hindered isopropyl alcohol will prevent this conversion. Investigation also shows that the hydrolysis of ALD-52 to LSD occurs at the GC injector port. It was also observed that the degree of hydrolysis was more pronounced at a lower concentration (0.1 mg/mL). The study was extended to a close analog-1P-LSD, and the results showed that 1P-LSD similarly hydrolyzes to LSD. However, 1P-LSD was observed to be more stable than ALD-52 due to steric hindrance because of the propanoyl group.

N-Phosphinoamidinato Silylene- and Phosphine-Borylborylene Complexes.

This work describes a straightforward method to synthesize a borylborylene without proceeding via the rearrangement of a diborene. An amidinato amidosilylene [LSiNMe2] (L = PhC(NtBu)2) and PMe3 were reacted with an N-phosphinoamidinato diborane 1 and KC8 to form a stable silylene-borylborylene 2 and a persistent phosphine-borylborylene 3, respectively. Compound 2 is stable as the borylene center is well stabilized by the silylene donor and boryl substituent, whereas compound 3 is unstable in solution due to labile PMe3. The latter was illustrated by reacting compound 3 with Ar'NC (Ar' = 2,6-Me2C6H3), where Ar'NC displaced PMe3 and inserted into the N-phosphinoamidinate ligand and B-B bond to form compound 4.

A Pyridine-Stabilized N-Phosphinoamidinato N-Heterocyclic Carbene-Diboravinyl Cation: Boron Analogue of Vinyl Cation.

A boron analogue of vinyl cation, pyridine-stabilized N-phosphinoamidinato N-heterocyclic carbene (NHC)-diboravinyl cation 2+ , was synthesized by displacement of bromide in diborene 1 with excess pyridine. Experimental and computational studies showed that the positive charge is mainly at the B-B skeleton with delocalization to the pyridine ligand. One of the main modes of reactivity is through the B=B double bond alongside activation of the pyridine substituent, where the Bpyridine center is the predominant nucleophilic center and the predominant electrophilic center is either the activated pyridine para position or the BNHC center, illustrating the presence of diborene cation A, borylene-borenium cation B and diborene-pyridinium cation C resonance structures in cation 2+ .

Reversible CO2 activation by a N-phosphinoamidinato digermyne.

The N-phosphinoamidinato digermynes [LG̈e-G̈eL] (L = tBu2PNC(Ph)NAr, 4: Ar = 2,6-iPr2C6H3, 5: Ar = Ph) underwent reversible CO2 activation to form [LG̈eOC(O)G̈eL] (6: Ar = 2,6-iPr2C6H3, 7: Ar = Ph). Compound 7 was further reacted with diphenylacetylene and hexafluorobenzene, which proceeded through compound 5 in the first step, to form CO2, [LG̈eC(Ph) = C(Ph) G̈eL] (8), [LG̈eF] (9) and [LG̈eC6F5] (10), respectively.

Amidinatoamidosilylene-Dibromodiborene.

The amidinatoamidosilylene [LSiNMe2] [1; L = PhC(NtBu)2] was reacted with B2Br4(SMe2)2 in toluene at room temperature to form the bis(silylene)tetrabromodiborane [L{Me2N}Si]2B2Br4 (2). It was then reacted with excess KC8 in tetrahydrofuran at room temperature to afford the bis(silylene)dibromodiborene [L{Me2N}Si]2B2Br2 (3).

Si(II) Cation-Promoted Formation of an Abnormal NHC-Bound Silylene and a cAAC-Silanyl Radical Ion.

The reaction of amidinatosilylene LSi(:)Cl [L = PhC(NtBu)2] with N-heterocyclic carbene IAr [:C{N(Ar)CH}2, where Ar = 2,6-iPr2C6H3] and NaOTf in tetrahydrofuran (THF) facilely afforded a silicon(II) cation [LSi(:)-aIAr]+OTf- (1+OTf-), where IAr isomerizes to abnormal N-heterocyclic carbene aIAr, coordinating to the silicon(II) center. Its Ge homologue, [LGe(:)-aIAr]+OTf- (2+OTf-), was also accessed via the same protocol. For the formation of 1+, we propose that an in situ-generated Si(II) cation [LSi(:)]+ under the treatment of LSi(:)Cl with NaOTf may isomerize IAr in THF. In contrast, the replacement of IAr with cyclic alkyl(amino) carbene (cAAC) furnished a cAAC-silanyl radical ion [LSi(H)-cAAC]•+(LiOTf2)- [3•+(LiOTf2)-], which may undergo an abstraction of the H radical from THF. All of the products were characterized by nuclear magnetic resonance spectroscopy, electron paramagnetic resonance, and X-ray crystallography, and their bonding scenarios were investigated by density functional theory calculations. These studies provide new perspective on carbene-silicon chemistry.

Aluminum-Hydride-Catalyzed Hydroboration of Carbon Dioxide.

This study describes the first use of a bis(phosphoranyl)methanido aluminum hydride, [ClC(PPh2NMes)2AlH2] (2, Mes = Me3C6H2), for the catalytic hydroboration of CO2. Complex 2 was synthesized by the reaction of a lithium carbenoid [Li(Cl)C(PPh2NMes)2] with 2 equiv of AlH3·NEtMe2 in toluene at -78 °C. 2 (10 mol %) was able to catalyze the reduction of CO2 with HBpin in C6D6 at 110 °C for 2 days to afford a mixture of methoxyborane [MeOBpin] (3a; yield: 78%, TOF: 0.16 h-1) and bis(boryl)oxide [pinBOBpin] (3b). When more potent [BH3·SMe2] was used instead of HBpin, the catalytic reaction was extremely pure, resulting in the formation of trimethyl borate [B(OMe)3] (3e) [catalytic loading: 1 mol % (10 mol %); reaction time: 60 min (5 min); yield: 97.6% (>99%); TOF: 292.8 h-1 (356.4 h-1)] and B2O3 (3f). Mechanistic studies show that the Al-H bond in complex 2 activated CO2 to form [ClC(PPh2NMes)2Al(H){OC(O)H}] (4), which was subsequently reacted with BH3·SMe2 to form 3e and 3f, along with the regeneration of complex 2. Complex 2 also shows good catalytic activity toward the hydroboration of carbonyl, nitrile, and alkyne derivatives.

A N-Phosphinoamidinato NHC-Diborene Catalyst for Hydroboration.

The use of the N-phosphinoamidinato NHC-diborene catalyst 2 for hydroboration is described. The N-phosphinoamidine tBu2PN(H)C(Ph)═N(2,6-iPr2C6H3) was reacted with nBuLi in Et2O to afford the lithium derivative, which was then treated with B2Br4(SMe2)2 in toluene to form the N-phosphinoamidinate-bridged diborane 1. It was reacted with the N-heterocyclic carbene IMe (:C{N(CH3)C(CH3)}2) and excess potassium graphite at room temperature in toluene to give the N-phosphinoamidinato NHC-diborene compound 2. It can stoichiometrically activate ammonia-borane and carbon dioxide. It also showed catalytic capability. A 2 mol % portion of 2 catalyzed the hydroboration of carbon dioxide (CO2) with pinacolborane (HBpin) in deuterated benzene (C6D6) at 110 °C (conversion >99%), which afforded the methoxyborane [pinBOMe] (yield 97.8%, TOF 33.3 h-1) and the bis(boryl) oxide [(pinB)2O]. In addition, 5 mol % of 2 catalyzed the N-formylation of secondary and primary amines by carbon dioxide and pinacolborane to yield the N-formamides (average yield 91.6%, TOF 25.9 h-1). Moreover, 2 showed chemoselectivity toward catalytic hydroboration of carbonyl compounds. In mechanistic studies, the B═B double bond in compound 2 activated the substrates, the intermediates of which then underwent hydroboration with pinacolborane to yield the products and regenerate catalyst 2.

A Base-Stabilized Silylene-Promoted C(sp3)-H Borylation and H2 Activation.

Treatment of the amidinato amidosilylene [L{(Me3Si)2N}Si:] [1, L = PhC(NtBu)2] with a slight excess of borane-tetrahydrofuran complex [BH3·THF] in toluene at room temperature afforded the silylene-borane adduct [L{(Me3Si)2N}Si:→BH3] (2). A triflate substituent was introduced on the boron center by reacting 2 with methyl triflate [MeOTf] (OTf = OSO2CF3) in toluene at room temperature to form [L{(Me3Si)2N}Si:→BH2OTf] (3), with the elimination of CH4 gas. The intramolecular C(sp3)-H borylation and H2 elimination occurred by reacting complex 3 with 1 in refluxing toluene to form a C-B bond in the resulting silylene-boronium ion 5. Complex 5 activated H2 gas or NH3BH3 at room temperature to form silylene-borane adduct 2 and [L{(Me3Si)2N}Si-H]OTf. Additionally, the reaction of 5 with H2 was studied through density functional theory calculations.

A Versatile NHC-Parent Silyliumylidene Cation for Catalytic Chemo- and Regioselective Hydroboration.

This study describes the first use of a silicon(II) complex, NHC-parent silyliumylidene cation complex [(IMe)2SiH]I (1, IMe = :C{N(Me)C(Me)}2) as a versatile catalyst in organic synthesis. Complex 1 (loading: 10 mol %) was shown to act as an efficient catalyst (reaction time: 0.08 h, yield: 94%, TOF = 113.2 h-1; reaction time: 0.17 h, yield: 98%, TOF = 58.7 h-1) for the selective reduction of CO2 with pinacolborane (HBpin) to form the primarily reduced formoxyborane [pinBOC(═O)H]. The activity is better than the currently available base-metal catalysts used for this reaction. It also catalyzed the chemo- and regioselective hydroboration of carbonyl compounds and pyridine derivatives to form borate esters and N-boryl-1,4-dihydropyridine derivatives with quantitative conversions, respectively. Mechanistic studies show that the silicon(II) center in complex 1 activated the substrates and then mediated the catalytic hydroboration. In addition, complex 1 was slightly converted into the NHC-borylsilyliumylidene complex [(IMe)2SiBpin]I (3) in the catalysis, which was also able to mediate the catalytic hydroboration.

Correction: Synthesis of a dimeric phosphine-stabilized phosphidogermanium(i)-amidogermanium(ii) derivative.

Correction for 'Synthesis of a dimeric phosphine-stabilized phosphidogermanium(i)-amidogermanium(ii) derivative' by Muhammad Luthfi Bin Ismail et al., Chem. Commun., 2019, DOI: 10.1039/c8cc09454c.

Synthesis of a dimeric phosphine-stabilized phosphidogermanium(i)-amidogermanium(ii) derivative.

The synthesis of a dimeric phosphine-stabilized phosphidogermanium(i)-amidogermanium(ii) derivative is described. The reaction of amidinato phosphinoamidosilylene [L{(Ar)(Ph2P)N}Si:] (1, L = PhC(NtBu)2, Ar = 2,6-iPr2C6H3) with GeCl2·dioxane afforded a phosphine-stabilized phosphidogermanium(i) dimer moiety in a mixed-valent germanium(i,ii) compound [:Ge(Cl){N(Ar)PPh2}(Ph2P)Ge:]2 (3). The mechanism for the formation of 3 is also studied and reported.

Synthesis of a Base-Stabilized Silicon(I)-Iron(II) Complex for Hydroboration of Carbonyl Compounds.

The reaction of the amidinatosilicon(I) dimer [LSi:]2 (1; L = PhC(N tBu)2) with FeBr2 in tetrahydrofuran (THF) at ambient temperature afforded the silicon(I)-iron(II) dimer [LSi(FeBr2·THF)]2 (2) after 40 h. Compound 2 can catalyze hydroboration of aliphatic and aromatic ketone compounds with HBpin in the absence of any strong reducing agent. Mechanistic studies show that complex 2 reacts with ketone compounds to form a zwitterionic intermediate in the first step of catalysis. Subsequent reaction with HBpin affords the corresponding boron esters and then regenerates complex 2.

Synthesis of a Dimeric Base-Stabilized Cobaltosilylene Complex for Catalytic C-H Bond Functionalization and C-C Bond Formation.

The synthesis of a dimeric base-stabilized cobaltosilylene complex and its catalytic reactions are described. Treatment of the amidinato silicon(I) dimer [LSi:]2 (1; L=PhC(NtBu)2 ) with CoBr2 in toluene for 10 days afforded the dimeric amidinato cobaltosilylene [(LSi)µ-{CoBr(LSiBr)}]2 (2), which is speculated to proceed via "LSiCoBr" and "LSiBr" intermediates in the reaction. Compound 2 is paramagnetic, with an effective magnetic moment of 2.8 µB. Its electronic structure was elucidated by single-crystal X-ray crystallography and DFT studies. It was capable of catalyzing C-H bond functionalization, in which a combination of 2, phosphine and MeMgI can regio- and stereoselectively promoted the addition of the C≡C triple bonds in alkynes to the ortho-C-H position in arylpyridines. In addition, compound 2 catalyzed Kumada-type coupling reactions between aryl chlorides and the Grignard reagent 2-mesitylmagnesium bromide.

B-H Bond Activation by an Amidinate-Stabilized Amidosilylene: Non-Innocent Amidinate Ligand.

The activation of B-H and B-Cl bonds in boranes by base-stabilized low-valent silicon compounds is described. The reaction of the amidinato amidosilylene-borane adduct [L{Ar(Me3Si)N}SiBH3] [1; L = PhC(N tBu)2, and Ar = 2,6- iPr2C6H3] with MeOTf in toluene at room temperature formed [L{Ar(Me3Si)N}SiBH2OTf] (2). [LSiN(SiMe3)Ar] in compound 2 then underwent a B-H bond activation with BH2OTf in refluxing toluene to afford the B-H bond activation product [LB(H)Si(H)(OTf){N(SiMe3)Ar}] (3). On the other hand, when compound 2 was reacted with 4-dimethylaminopyridine in refluxing toluene, another B-H bond activation product [(µ-κ1:κ1-L)B(H)(DMAP)Si(H){N(Ar)SiMe3}]OTf (4) was afforded. Mechanistic studies show that "(µ-κ1:κ1-L)B(H)(OTf)Si(H){N(Ar)SiMe3}" (2A) is the key intermediate in the reactions mentioned above. The formation of 2A is further evidenced by the activation of the B-Cl bond in PhBCl2 by the amidinato silicon(I) dimer [LSi:]2 to form the B-Cl bond activation product [(µ-κ1:κ1-L)B(Cl)(Ph)Si(Cl)]2 (6). Compounds 2-4 and 6 were characterized by nuclear magnetic resonance spectroscopy and X-ray crystallography.