Generation of pyridyl coordinated organosilicon cation pool by oxidative Si-Si bond dissociation

Abstract

An organosilicon cation stabilized by intramolecular pyridyl coordination was effectively generated and accumulated by oxidative Si-Si bond dissociation of the corresponding disilane using low temperature electrolysis, and was characterized by NMR and CSI-MS.Page 1 of (page number not for citation purposes) FindingsWe have recently developed the "cation pool" method, which involves the irreversible oxidative generation and accumulation of highly reactive cations in the absence of nucleophiles [1][2][3][4][5]. Heteroatom-stabilized carbocations, such as N-acyliminium ion pools and alkoxycarbenium ion pools have been generated based on oxidative C-H, C-Si, and C-S bond dissociation. Very recently, the oxidative C-C bond dissociation has been found to be effective for generation of a pool of a carbocation having a stabilizing group as shown in Scheme 1 [6].We have been interested in generation and accumulation of cations of other elements such as silicon using the "cation pool" method. Organosilicon cations are known to be extremely unstable and difficult to accumulate in solution [7][8][9][10][11]. Organo- Symmetrical disilanes having coordinating groups on both silicon atoms were used as starting materials for electrochemical generation and accumulation of organosilicon cations, because oxidative dissociation of the Si-Si bond leads to the formation of two equivalents of organosilicon cations and no other product is formed.In our earlier study, it was found that the introduction of a coordinating group such as a pyridyl group decreased the oxidation potential of tetraalkylstannanes, although there is no indication of the coordination in the neutral molecule. Dynamic intramolecular coordination to tin seems to facilitate electron transfer [22]. The coordination also stabilizes the thus-generated radical cation and weakens the C-Sn bond. A similar effect of intramolecular coordination was observed in the case of silicon [23]. Another important point is that pyridyl group is rather inactive toward the anodic oxidation. Thus, we chose to use a pyridyl group as a donor ligand.First, we prepared disilanes having pyridyl groups in appropriate positions and measured their oxidation potentials [24,25]. The oxidation potential of 2-pyridylethyl substituted disilane 1b was slightly less positive than hexamethyldisilane 1a. On the other hand, the oxidation potential of 2-pyridylphenyl substituted disilane 1d was much less positive than the corresponding disilane 1c having phenyl groups (Figure 1). 29 Si NMR chemical shifts of 1b and 1d were similar to those of 1a and 1c, indicating that no coordination of the pyridyl groups on silicon existed in the neutral molecules (Supporting Information File 1). Therefore, the significant effect of the 2-pyridyl group on the oxidation potential may be ascribed to effective intramolecular coordination to stabilize the radical cation intermediate. The conformationally less flexible 2-pyridylphenyl group seems to be more effective than the 2-pyridylethyl group.The intramolecular co...

Modern Electrochemical Aspects for the Synthesis of Value‐Added Organic Products

“…An ucleophile is subsequently added to afford the product. [30] With this method, Yoshida and co-workers were able to generate abroad scope of cations such as N-acyliminium, [29,31] alkoxycarbenium, [32] diarylcarbenium, [33] glycosyl, [34] silyl, [35] iodine, [36] alkoxysulfonium, [37,38] benzylaminosulfonium, [39] arene, [40] and thioarenium cations, [41] as well as thionium cations. [42] Depending on the cation and the added nucleophile,v arious products were accessible with ah igh selectivity.…”

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

“…550 The reaction of this cation pool with a Grignard reagent was found to deliver a substituted silane.…”

Direct and indirect electrochemical generation of alkoxycarbenium ion pools from thioacetals

“…5 The cation pool method serves as a powerful tool not only for mechanistic studies on highly reactive organic cations but also for rapid parallel synthesis. The method has been successfully applied to alkoxycarbenium ions, 6 in addition to N-acyliminium ions, 7 diarylcarbenium ions, 8 organosilicon cations, 9 and iodine cations. 10 a-Silyl ethers serve as effective precursors of alkoxycarbenium ion pools (Scheme 2).…”

“…The NMR measurement was carried out at À80 C. Chemical shifts are reported using methylene signals of CH 2 Cl 2 at d 5.32 ( 1 H NMR) and d 53.80 ( 13 C NMR) as standards. The huge signal coming from CH 2 Cl 2 is reduced by usual pulse techniques 27 : 1 H NMR (600 MHz, CH 2 Cl 2 /CD 2 Cl 2 (10:1), selected) d 3.26 (t, J¼6.3 Hz, 2H), 4.92 (s, 3H),9.53 (s, 1H); 13 C NMR (150 MHz, CH 2 Cl 2 /CD 2 Cl 2 (10:1), selected) d 40.3 (CH 3 OCHCH 2 ), 75.6 (CH 3 OCH), 230.6 (CH 3 OCH). Other signals could not be assigned because of overlap with the signals of Bu 4 NBF 4 used as the electrolyte.…”