Heavier Tetrylenes as Single Site Catalysts

Abstract

An overview of the development of compounds with heavier low-valent group 14 elements (known as tetrylenes) as single component catalyst for organic transformation has been provided. Compounds with heavier group 14 elements possess stereochemically active lone pairs and energetically accessible π-antibonding orbitals, thereby resembling the electronic configuration of transition-metal compounds. Such compounds with low-valent group 14 elements has been known for small molecule activation since Power's report of dihydrogen activation by a digermyne, but their utilization in catalysis remained as a "Holy Grail" in main group chemistry. In recent years, numerous methodologies have been discovered epitomizing the use of Si(II), Ge(II) and Sn(II) compounds as single site catalysts for hydroboration of aldehydes, ketones, pyridines, cyanosilylation of aldehydes and ketones, N-formylations aromatic amines, dehydrocoupling reactions. This mini-review highlights these significant developments with an emphasis on the mechanistic investigation.

Amidinato Isopropylmethylamidosilylene‐Catalyzed Hydroboration of Carbonyl Compounds

“…[4][5] However, heavier congeners, germylenes and stannylenes, were shown to be competent in catalysis through a diversity of mechanisms. [6][7][8][9][10][11][12][13][14][15][16] The first example is the hydridogermylene [Ar*(iPr 3 Si)NGeH] (Ar* = 2,4,6-iPr{C(H)Ph 2 } 2 C 6 H 2 ) that catalyzes the hydroboration of carbonyl compounds via the GeÀ H and BÀ H σ-bond metathesis reactions. [17] The second example is the phosphine-tetrylene complexes [Ar iPr EC(H)(Ph)PPh 2 ] (E = Ge, Sn; Ar iPr = 2,6-(2,4,6-iPr 3 C 6 H 2 ) 2 C 6 H 3 ), which mediates the catalytic hydroboration of aldehyde via two mechanisms: the activation of aldehyde by forming adduct with the phosphine donor and tetrylene acceptor, as well as the activation of pinacolborane (HBpin) at the tetrylene center.…”

“…However, heavier congeners, germylenes and stannylenes, were shown to be competent in catalysis through a diversity of mechanisms [6–16] . The first example is the hydridogermylene [Ar*( i Pr 3 Si)NGeH] (Ar*=2,4,6‐ i Pr{C(H)Ph 2 } 2 C 6 H 2 ) that catalyzes the hydroboration of carbonyl compounds via the Ge−H and B−H σ‐bond metathesis reactions [17] .…”

NHC-Stabilized 1,2-Dihalodiborenes: Synthesis, Characterization, and Reactivity Toward Elemental Chalcogens

“…The last 2 decades have seen an increasing interest in the synthesis and reactivity of low oxidation state main group compounds, which are formally isolobal and/or isoelectronic to classical organic molecules, but most often significantly more reactive than the latter. − Doubly Lewis-base-stabilized diborenes of the form B 2 Y 2 L 2 (Y = anionic substituent, L = neutral Lewis base) display a BB double bond and are thereby isoelectronic to alkenes. In 2007, Robinson and co-workers reported the first examples of isolable diborenes, B 2 H 2 (IDip) 2 and B 2 H 2 (IMes) 2 (Figure , IDip = 1,3-bis­(di iso propylphenyl)­imidazol-2-ylidene; IMes = 1,3-bis­(trimethylphenyl)­imidazol-2-ylidene), stabilized by highly sterically demanding and strongly σ-donating N-heterocyclic carbenes (NHCs). , Since then the range of synthetically accessible B 2 Y 2 L 2 diborenes has greatly expanded. − NHC-stabilized diborenes (B 2 Y 2 (NHC) 2 ) are best accessed through the reductive coupling of the corresponding (NHC)­BYX 2 precursors (X = halide) and can be isolated for a wide range of Y substituents, including various aryl (e.g., B 2 Dur 2 (IMe) 2 , Dur = 2,3,5,6-tetramethylphenyl; IMe = 1,3-dimethylimidazol-2-ylidene, Figure ), , furyl and thienyl derivatives, , i Pr, vinyl, and organometallic fragments such as ferrocenediyl and cymantrenyl .…”

Tetrylenes: Electronic Structure, Stability, Reactivity, and Ligand Properties—A Comparative DFT Study

“…Scheme shows a number of tetrylenes that are not considered in this article, but worth noting: sterically shielded diorgano tetrylenes XI , , XII (Tip = 2,4,6-triisopropylphenyl, Tb = 2,4,6-tris­[bis­(trimethylsilyl)­methyl]­phenyl), , and XIII (Dipp = 2,6-diisopropylphenyl); tetrylenes stabilized by a combination of heteroatom and extensive steric bulk XIV ; Lappert’s diamido compounds XV ; , Veith’s cyclic diamido compounds XVI ; various amidinates XVII ; and diiminates XVIII . Chemistry and various applications of heavier tetrylenes as bond activators, ligands, and building blocks for the construction of new chemical entities was extensively reviewed recently. − …”