A Silylene Stabilized by a σ-Donating Nickel(0) Fragment.

A donor-stabilized silylene 4 featuring a Ni0 -based donating ligand was synthesized. Complex 4 exhibits a pyramidalized and nucleophilic SiII center and shows a peculiar behavior due to the cooperative reactivity of Si and Ni centers. Calculations indicate that the orientation of Ni-ligands with respect to the silylene moiety is crucial in determining the role of the Ni-fragment (Lewis acid or Lewis base) towards silylene. Indeed, a simple 90° rotation of the Si-Ni bond, reverses the role of Ni, and transforms a classical silylene→Ni0 complex into an unprecedented Ni0 →silylene complex.

Unique Approach to Copper(I) Silylene Chalcogenone Complexes.

Silylene-S-thione [PhC(NtBu)2Si(═S)N(SiMe3)2] (2) and silylene-Se-selone [PhC(NtBu)2Si(═Se)N(SiMe3)2] (3) compounds were prepared from the silylene [PhC(NtBu)2SiN(SiMe3)2] (1) with 1 equiv of 1/8 S8 and 1 equiv of Se powder, respectively, in high yields. Furthermore, compounds 2 and 3 reacted with CuCl and CuBr and yielded [{PhC(NtBu)2}Si(═S→CuX)N(SiMe3)2] (X = Cl (4), Br (5)) and [{PhC(NtBu)2}Si(═Se→CuX)N(SiMe3)2] (X = Cl (6), Br (7)), respectively. Complexes 4-7 can also be obtained from the direct reaction of sulfur and selenium with the corresponding silylene copper complexes [{PhC(NtBu)2}Si{N(SiMe3)2}]2Cu2X2 (X = Cl (8), Br (9)). The latter route avoids the preparation of the highly reactive silylene chalcogenones. For comparison purposes the silylene PhC(NtBu)2SiN(SiMe3)2 in 2 and 3 was replaced by NHC (1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) (10). The resulting products NHC═S (thione 11) and NHC═Se (selenone 12) react with CuBr and lead to the expected complexes (NHC═S→CuBr) (13) and (NHC═Se→CuBr) (14). However, unlike silylene complexes, 13 and 14 cannot be prepared by reacting NHC-CuBr (15) with chalcogens.

A hybrid silylene-Pd catalyst: efficient C-N cross-coupling of sterically bulky amines and chiral amines.

Herein, we report a catalytic system with N-heterocyclic silylene (NHSi)-phosphine-based hybrid bidentate ligands [PhC(NtBu)2SiN(PR2)(2,6-iPr2-C6H3)] and Pd(dba)2, which serves as an effective catalyst for C-N cross-coupling of a wide range of sterically bulky amines and optically active amines, which is challenging otherwise.

Diverse structural reactivity patterns of a POCOP ligand with coinage metals.

We have utilised the 4,6-di-tert-butyl resorcinol bis(diphenylphosphinite) (POCOP) ligand for exploring its coordination ability towards group 11 metal centres. The treatment of the bidentate ligand 1 with various coinage metal precursors afforded a wide range of structurally diverse complexes 2-12, depending upon the metal precursors used. This furnishes several multinuclear Cu(I) complexes with dimeric (2) and tetrameric cores (3, 4, and 5). The tetrameric stairstep complex 4 shows thermochromic behaviour, whereas the dimeric complex 2 and tetrameric complex 3 show luminescence properties at cryogenic temperatures. Interestingly, the halide substitution reaction of the dimeric complex 2 with KPPh2 produces a unique mixed phosphine-based tetrameric Cu(I) complex, 5. Treatment of the POCOP ligand with [CuBF4(CH3CN)4] in the presence of 2,2'-bipyridine afforded heteroleptic complex 6, consisting of tri- and tetra-coordinated cationic Cu(I) centres. Furthermore, we could also isolate cubane (8) and stairstep (9) complexes of Ag(I). The cationic Au(I) complex (12) was obtained from the dinuclear Au(I) complex of POCOP, 11. Complex 12 revealed the presence of a strong intramolecular aurophilic interaction with an Au⋯Au bond distance of 3.1143(9) Å. Subsequently, the photophysical properties of these complexes have been studied. All the complexes were characterised by single-crystal X-ray diffraction studies, routine NMR techniques, and mass spectroscopy.

The diverse reactivity of NOBF4 towards silylene, disilene, germylene and stannylene.

The reactivity of NOBF4 towards silylene, disilene, germylene, stannylenes has been described. Smooth syntheses of compounds of composition [PhC(NtBu)2E(= O → BF3)N(SiMe3)2, E = Si (3) and Ge (4)] were accomplished from the corresponding tetrylenes. An unusual heterocycle (10) featuring B, Sn, N, P, and O atoms was obtained from the reaction with a stannylene, while a 1,2-vicinal anti addition of fluoride was observed with a disilene (12).

N-Heterocyclic silylene/germylene ligands in Au(i) catalysis.

Cationic Au(i) complexes (2, 5 and 8) supported by N-heterocyclic carbene, silylene and germylene ligands were prepared and their potential as catalysts in glycosidation chemistry has been evaluated. Insights into the mechanism are provided using DFT studies. Practical application of them as catalysts was achieved by the synthesis of the branched pentamannan core of the HIV-gp120 envelope under mild conditions.

N-heterocyclic silylene stabilized monocordinated copper(i)-arene cationic complexes and their application in click chemistry.

Herein for the first time we report monocoordinated cationic Cu(i) complexes with unsymmetrical arenes (toluene and m-xylene) [LCu(η3-C7H8)]+[SbF6]- and [{LCu(η2-Me2C6H4)}]+[SbF6]- [L = {PhC(NtBu)2SiN(SiMe3)2}], [IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)], their reactivity and catalytic applications in CuAAC reactions (12 examples). The bonding analysis was performed in both silylene and carbene complexes using the EDA-NOCV method at the BP86/TZ2P level of theory.

Facile Buchwald-Hartwig coupling of sterically encumbered substrates effected by PNP ligands.

The diphosphinoamine ligands [(Ph2P)2N(Ar); 1 (Ar = C6H5), 2 (Ar = 2,6-iPr2C6H3)] were effectively utilized in Buchwald-Hartwig coupling of a range of sterically demanding substrates. The reaction was carried out using conventional and microwave routes and the latter reduces the reaction time from 3 d to 15-30 min. A broad substrate scope was achieved in this protocol and most of the coupling products are isolated on a mutligram scale. DFT calculations were carried out to elucidate the reaction mechanism.

Taming a monomeric [Cu(η6-C6H6)]+ complex with silylene.

Previous theoretical and experimental endeavors suggested that [Cu(C6H6)]+ prefers the η1/η2 mode over the η6 mode due to the augmented repulsion between the benzene ring and metal d-electrons. Nevertheless, the use of silylene as a neutral ligand has led to the isolation of the first monomeric copper cation, [{PhC(NtBu)2SiN(SiMe3)2}Cu(η6-C6H6)]+[SbF6]- (3), where a copper atom is bound to the benzene ring in an unsupported η6 fashion. However, the use of IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) in place of silylene results in the formation of [IPr·Cu(η2-C6H6)]+[SbF6]- (6), where the copper atom is bound to the benzene ring in the η2 mode. The discrepancy in hapticities is also reflected when hexamethylbenzene is employed as the arene ring. The silylene supported copper cation continues to bind in the η6 mode in 2 while the NHC copper cation displays an η3 bonding mode in 5. DFT calculations are carried out to understand how the use of silylene led to the η6 binding mode and why IPr afforded the η2 binding mode.

Strikingly diverse reactivity of structurally identical silylene and stannylene.

The reactivity of structurally identical silylene and stannylene [PhC(NtBu)2EN(SiMe3)2] (E = Si (1) and Sn (2)) towards coinage metals has been explored. While 1 has the propensity to form an adduct with coinage metals (4 and 5), 2 undergoes a ligand exchange reaction with copper halides and silver triflate leading to PhC(NtBu)2SnX (X = Br (6), Cl (7), and OSO2CF3 (8)) with concomitant formation of [M{N(SiMe3)2}] (M = Cu, Ag). However, with AgSbF6 both 1 and 2 led to ion pairs, 9+·SbF6-and 10+·SbF6- displaying weaker Ag·F interactions in the latter.

C(sp3)-F, C(sp2)-F and C(sp3)-H bond activation at silicon(ii) centers.

Silylene [PhC(NtBu)2SiN(SiMe3)2] (1) cleaves the C(sp3)-H and C-F bonds of acetophenone and 1,1,1-trifluoroacetophenone, respectively, under mild conditions. The reaction is initiated via a nucleophilic attack from the oxygen to the silicon atom followed by C-F/H bond cleavage. The scope of C-F bond activation has further been extended with C6F6 and C6F5CF3.