Pentacoordinate Silicon Complexes with N‐(2‐pyridylmethyl)­salicylamide as a Dianionic (ONN′) Tridentate Chelator

Abstract

The title compound, N-(2-pyridylmethyl)salicylamide (1), was synthesized by ester aminolysis of methyl salicylate and 2-picolylamine. In the presence of triethylamine as a supporting base, the salicylamide moiety reacts with the organodichlorosilanes RRЈSiCl 2 to form the desired six-membered heterocycles of the type RRЈSi-O-(o-C 6 H 4 )-C(=O)N(pic), with pic being the 2-pyridylmethyl (i.e., 2-picolyl) moiety and RRЈ = Me,Me (2a); Me,Ph (2b); Ph,Ph (2c); Bn,Bn (2d); All,Ph (2e) and Ph,H (2f). Despite the absence of notable ring strain release Lewis acidity (i.e., only a six-membered chelate is 1768 formed by the dianion, and smaller rings are not present in the compound), the poor electron withdrawal from silicon by its C-or Hsubstituents and the flexible methylene bridge between the salicylamide and the pyridine moiety, the pyridine N donor atom furnishes pentacoordinate silicon coordination spheres in all of these compounds 2a-2f. The coordination number of the silicon atom was confirmed by single-crystal X-ray diffraction analysis for the solid state and by 29 Si NMR spectroscopy for the solution state. Scheme 1. Examples of neutral and cationic halosilane pyridine adducts with hexa-or pentacoordinate silicon atom.

Disilicon Complexes with Two Hexacoordinate Si Atoms: Paddlewheel‐Shaped Isomers with (ClN4)SiSi(S4Cl) and (ClN2S2)SiSi(S2N2Cl) Skeletons

“…The same holds true for the (3,1) isomer (also DE = + 3.4 kJ mol À1 ). Only the trans- (2,2) isomer is predicted to be distinctly less stable (by DE = + + 9.9 kJ mol À1 ). The predicted Si À Si bond length is 2.42 for all of these isomers, which may be due to the stabilizing cage structure.…”

“…(The NCs of the Cl, S, and N donor atoms are less affected by this isomerism.) The contri- (2,2) isomer. [10] butions of the Si atoms to the electronic population of the relevant natural-bond orbital (NBO) of the Si À Si bond become balanced in the same order.…”

“…Si NMR observed shift [d, ppm] A C H T U N G T R E N N U N G (4,0) À104.1, À159.8 À115.5, À163.7 [a] 11.4, 3.9 [a] À121.4, À169.0 [b] A C H T U N G T R E N N U N G (3,1) À123.5, À149.7 À133.2, À155.9 [a] 9.7, 6.2 [a] À136.7, À159.8 [b] cis- (2,2) À135.8 À144.0 [a] 8.2 [a] À147.3 [b] trans-(2,2) À143.1 À150.7 [a] 7.6 [a] [a] Calculated for gas-phase-optimized structure.…”

“…The field of hypercoordinate silicon chemistry, [1] which has attracted considerable interest during the past decades, has produced a notable number of penta-and hexacoordinate Si compounds with atoms such as X = H, C, N, O, F, and Cl in the silicon coordination sphere. [2] Both hypercoordinate oligosilicon complexes (which comprise two adjacent hypercoordinate Si atoms) [3] and complexes bearing heavier elements of Groups 14-17 in the Si coordination shell [3a, 4] have scarcely been explored yet and have attracted notable attention in recent years. Oligosilicon complexes with two SiÀSibonded hexacoordinate Si atoms have been reported in 2008 by Tacke and co-workers (tetrasilanes of the general pattern R 3 Si À SiA C H T U N G T R E N N U N G (OTf) 2 SiA C H T U N G T R E N N U N G (OTf) 2 SiR 3 ; R= alkyl, OTf À = trif-A C H T U N G T R E N N U N G late).…”

“…[2] Both hypercoordinate oligosilicon complexes (which comprise two adjacent hypercoordinate Si atoms) [3] and complexes bearing heavier elements of Groups 14-17 in the Si coordination shell [3a, 4] have scarcely been explored yet and have attracted notable attention in recent years. Oligosilicon complexes with two SiÀSibonded hexacoordinate Si atoms have been reported in 2008 by Tacke and co-workers (tetrasilanes of the general pattern R 3 Si À SiA C H T U N G T R E N N U N G (OTf) 2 SiA C H T U N G T R E N N U N G (OTf) 2 SiR 3 ; R= alkyl, OTf À = trif-A C H T U N G T R E N N U N G late). [3i] The coordination spheres of the hypercoordinate Si atoms can be described as [4 + 2] coordinated (bicapped tetrahedral) because two donor atoms interact with the Si cen-ters from a far distance (Si···O separations range between 2.72 and 2.85 ) and the widest Si-Si-X angle (X = Si) amounts to 1368, which is therefore closer to the tetrahedral angle than to an angle of 90 or 1808 within an octahedral coordination sphere.…”