Antimony(v) cations for the selective catalytic transformation of aldehydes into symmetric ethers, α,β-unsaturated aldehydes, and 1,3,5-trioxanes

Abstract

1-Diphenylphosphinonaphthyl-8-triphenylstibonium triflate ([][OTf]) was prepared in excellent yield by treating 1-lithio-8-diphenylphosphinonaphthalene with dibromotriphenylstiborane followed by halide abstraction with AgOTf. This antimony(v) cation was found to be stable toward oxygen and water, and exhibited exceptional Lewis acidity. The Lewis acidity of [][OTf] was exploited in the catalytic reductive coupling of a variety of aldehydes into symmetric ethers of type in good to excellent yields under mild conditions using Et3SiH as the reductant. Additionally, [][OTf] was found to selectively catalyze the Aldol condensation reaction to afford α-β unsaturated aldehydes () when aldehydes with 2 α-hydrogen atoms were used. Finally, [][OTf] catalyzed the cyclotrimerization of aliphatic and aromatic aldehydes to afford the industrially-useful 1,3,5 trioxanes () in good yields, and with great selectivity. This phosphine-stibonium motif represents one of the first catalytic systems of its kind that is able to catalyze these reactions with aldehydes in a controlled, efficient manner. The mechanism of these processes has been explored both experimentally and theoretically. In all cases the Lewis acidic nature of the antimony(v) cation was found to promote these reactions.

Noncovalent Intra‐ and Intermolecular Interactions in Peri‐Substituted Pnicta Naphthalene and Acenaphthalene Complexes

“…(R 1 ) 2 Naph [16] (R 2 ) 2 Naph (1) (R 2 ) 2 Acenaph (2) (R 3 ) 2 Naph (3) (R 4 ) 2 Naph [26] (R 5 R 2 )Acenaph [27] (R 6 ) 2 Naph [42] (R 6 ) 2 Acenaph [14] E [25] 3 agreement with the DLPNO-CCSD(T) results, overestimated dispersion interactions. Computed interaction energies are collected in Table 2.…”

“…[12][13][14] On the other hand, heteroatomic substitution may also enforce both attractive interactions or even bond formation as was reported by Gabbaï and co-workers for Au•••Sb and Hg•••Sb interactions. [15] In contrast to phosphanaphthalene (Naph) and -acenaphthene (Acenaph) complexes of type I, II and IV, [16][17][18][19][20] analogous compounds with easily polarizable heavy group 15 elements, Sb and Bi, which are promising candidates for noncovalent interactions, have been studied to a far lesser extent and structurally characterized complexes are limited to a handful of naphthyl-substituted dipnictanes including (ClAs) 2 Naph 2 (type III) and E 2 Naph 2 (E = As, Sb; type IV). Quantum chemical calculations with E 2 Naph 2 showed that the formation of Sb 2 Naph 2 dimers in the solid-state results from dispersiondominated metal•••π interactions, whereas such interactions were absent in the corresponding diarsane As 2 Naph 2 , most likely caused by the poorer polarizability of As compared to Sb.…”

Catalytic Reductive Alcohol Etherifications with Carbonyl‐Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

“…Interestingly, in 2016 Hudnall and co‐workers presented the synthesis of a novel stibonium triflate salt and its successful application as a Lewis acid catalyst for the reductive coupling of a broad range of aromatic/aliphatic aldehydes with Et 3 SiH as reductor (Scheme 6 M). [77] Spectroscopic and computational studies revealed that the interaction between a highly Lewis acidic antimony(V) center and the Lewis basic oxygen from the aldehyde is key to polarize the C=O bond.…”

Novel Si(II)+ and Ge(II)+ Compounds as Efficient Catalysts in Organosilicon Chemistry: Siloxane Coupling Reaction

“…This reaction, however, was developed for the synthesis of symmetrical ethers but not for the synthesis of siloxanes from hydrosilanes. Large amounts of Lewis acids 9 are necessary as catalysts for this transformation, for example, 5−10 mol % tritylium perchlorate, 10 11% BiCl 3 , 11 1−3 mol % BiBr 3 , 12 5 mol % trimethylsilyl triflate, 13 ∼5 mol % trimethylsilyl trifluoromethanesulfonate, 14 triflate, 15 4% w/w heterogeneous molybdenium-dioxo catalyst, 16 and stoichiometric amounts of SbI 3 . 17 Herein, we report a very efficient procedure to make siloxanes by oxidative coupling of hydrosil(ox)anes using aldehydes as oxidants and cationic Si(II) and Ge(II) compounds as catalysts.…”