Cyclic Silylated Onium Ions of Group 15 Elements

Abstract

Five- and six-membered cyclic silylated onium ions of group 15 elements I were synthesized by intramolecular cyclization of transient silylium ions II. Silylium ions II were prepared by the hydride transfer reaction from silanes III using trityl cation as hydride acceptor. It was found that smaller ring systems could not be obtained by this approach. In these cases tritylphosphonium ions IV were isolated instead. Cations I and IV were isolated in the form of their tetrakispentafluorphenyl borates and characterized by multinuclear NMR spectroscopy and, in two cases, by X-ray diffraction analysis. Cyclic onium ions I showed no reactivity similar to that of isoelectronic intramolecular borane/phosphane frustrated Lewis pairs (FLPs). The results of DFT computations at the M05-2X level suggest that the strength of the newly formed Si-E linkage is the major reason for inertness of I[B(C6F5)4] versus molecular hydrogen.

Mapping the Trajectory of Nucleophilic Substitution at Silicon Using a peri‐Substituted Acenaphthyl Scaffold

“…The 31 PNMR chemical shift of 1 (d = À18.6 ppm) is at higherf ield relative to the 31 PNMR chemicals hift of 1-Ph 2 P-C 6 H 4 -2-SiMe 2 F( d = À9.3 ppm). The 29 Si NMR chemical shift of 2 (d = 15.8) is very similart ot hat of the phosphonium cations[ Me 3 SiPPh 3 ] + (d = 16.6 ppm) [38] and [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (d = 8.6 ppm), [34] whichs upports the assumption that 2 is better described as as ilyl-substituted phosphonium ion, rather than ap hosphine-supported silyl cation. The J( 31 P, 29 Si)c ouplingc onstant of 2 (J = 54.8 Hz) is significantly larger than the 1 J coupling in [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (J = 11.3 Hz) [34] and larger than those in relatedn eutral silylphosphines, such as Ph 2 MeSiPPh 2 (J = 25 Hz) and PhMe 2 SiPPh 2 (J = 23 Hz).…”

“…The 29 Si NMR chemical shift of 2 (d = 15.8) is very similart ot hat of the phosphonium cations[ Me 3 SiPPh 3 ] + (d = 16.6 ppm) [38] and [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (d = 8.6 ppm), [34] whichs upports the assumption that 2 is better described as as ilyl-substituted phosphonium ion, rather than ap hosphine-supported silyl cation. The J( 31 P, 29 Si)c ouplingc onstant of 2 (J = 54.8 Hz) is significantly larger than the 1 J coupling in [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (J = 11.3 Hz) [34] and larger than those in relatedn eutral silylphosphines, such as Ph 2 MeSiPPh 2 (J = 25 Hz) and PhMe 2 SiPPh 2 (J = 23 Hz). [39] The 31 PNMR chemical shifto f2 (d = À10.5 ppm) is at higher field relative to that of [Me 3 SiPPh 3 ] + (d = À2.8 ppm) [38] and at significantly lower field than those of [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (d = À51.3 ppm) [34] and silylphosphines Ph 2 MeSiPPh 2 (d = À59.2 ppm) and PhMe 2 SiPPh 2 (d = À58.2 ppm).…”

“…The J( 31 P, 29 Si)c ouplingc onstant of 2 (J = 54.8 Hz) is significantly larger than the 1 J coupling in [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (J = 11.3 Hz) [34] and larger than those in relatedn eutral silylphosphines, such as Ph 2 MeSiPPh 2 (J = 25 Hz) and PhMe 2 SiPPh 2 (J = 23 Hz). [39] The 31 PNMR chemical shifto f2 (d = À10.5 ppm) is at higher field relative to that of [Me 3 SiPPh 3 ] + (d = À2.8 ppm) [38] and at significantly lower field than those of [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (d = À51.3 ppm) [34] and silylphosphines Ph 2 MeSiPPh 2 (d = À59.2 ppm) and PhMe 2 SiPPh 2 (d = À58.2 ppm). [39] Analysis of the pseudoreaction coordinate…”

“…[33] In combination with the almost linear P-Si-F bond angles in 1 and 1' (175.53(6)8 and 175.96(6)8), the elongated SiÀFb onds and short transannular SiÀPc ontacts mark the beginning of three-center-four-electron bonding( 3c-4 e) expected for the trigonal bipyramidal transition/intermediate stage of nucleophilic substitution. The SiÀP bond length of 2 (2.3208 (9) )i sr eminiscent of those of the disilylphosphonium cation [Ph 2 P-1,3-(SiMe 2 ) 2 C 3 H 6 ] + (2.308(2)/ 2.312(2) ) [34] and shorter than the SiÀPd istance in cationic [tBu 3 PSi(iPr) 3 ] + (2.4843 (5) ). [35] The average SiÀCd istances in 1/1' (SiÀC Me :1 .859(4)/1.859(4) ,S i ÀC Ace :1 .887(2)/1.888(2) ) are longert han those in 2 (SiÀC Me :1 .847 (6) ,S i ÀC Ace : 1.866 (3) ).…”

Enantioselective Diels–Alder Reactions of Cyclohexa-1,3-diene and Chalcones Catalyzed by Intramolecular Silicon–Sulfur Lewis Pairs as Chiral Lewis Acids

“…This trend is in agreement with an analysis disclosed by Muller. 18 Diels−Alder Reactions Catalyzed by the Chiral Sulfur-Stabilized Silicon Cations. To test both the catalytic activity and ability to induce enantioselectivity, we used the novel sulfur-stabilized silicon cations (S,S)-5 and (S,R)-5 as catalysts in the Diels−Alder reaction of cyclohexa-1,3-diene (1) and chalcone (2).…”