A Silyl Cation with a Three-Center Si-H-Si Bond

Abstract

Three-center, two-electron bonds involving hydrogen as a bridging atom are a common feature in the chemistry of early main group metals. Several hydrido-bridged carbocations were identified by low-temperature NMR spectroscopy. [1] It was predicted that the isoelectronic silylium ions will even interact with methane, [2] and it was suggested that such interactions between a positively charged silicon atom and appropriately arranged alkyl groups on its substituents can be 60 kOe, which is very close to the expected value of 7.0 Nm B for a parallel alignment of the magnetic moments of two Ru III and one Mn II ion. Furthermore, a characteristic hysteresis loop is observed at 1.85 K but with negligible remanent magnetization (0.06 Nm B ) and coercive field (6 Oe). Although ferromagnetic Ru III ± Mn II interaction was also observed in two-dimensional (NBu 4 )[Mn II Ru III (ox) 3 ] via the oxalato bridges, no long-range ordering occurs down to 2 K. [4] We are currently investigating related 3d ± 4d and 4d ± 5d systems in order to understand the origin of the ferromagnetic behavior in 2. Experimental Section1: trans-Ph 4 P[Ru III (acac) 2 Cl 2 ] [12] (355 mg, 0.5 mmol) and KCN (325 mg, 5.0 mmol) were heated in refluxing methanol (30 mL) for 24 h. The solution was evaporated to dryness, and the residue was dissolved in CH 2 Cl 2 (10 mL). After filtration, the product was precipitated as a dark purple solid by adding diethyl ether. Yield: 225 mg (65 %). Crystals suitable for X-ray crystallography were obtained by slow diffusion of diethyl ether into a solution of 1 in CH 2 Cl 2 . IR (KBr): n Ä CN 2099 cm À1 ; UV/Vis (CH 3 CN): l max (lge) 349 (3.76), 407 sh (3.16), 540 (3.22); elemental analysis (%) calcd for C 36 H 34 N 2 O 4 RuP: C 62.60, H 4.96, N 4.06; found: C 62.96, H 5.05, N 4.21. 2: A mixture of MnClO 4´6 H 2 O (36 mg, 0.1 mmol) and 1 (69 mg, 0.1 mmol) was stirred in methanol (30 mL) at room temperature. The solution was filtered after 3 h, and slow evaporation of the filtrate afforded dark purple crystals. Yield: 34 mg (45 %). IR (KBr): n Ä CN 2125 cm À1 ; elemental analysis (%) calcd for Ru 2 MnN 4 C 24 O [7] a) Crystal data for 1 (C 36 H 34 N 2 O 4 RuP): M r 690.72, dark purple prisms, monoclinic, space group P2 1 /c (no. 14), a 7.727(8), b 27.541(8), c 15.645(9) , b 103.13(8)8, V 3242(3) 3 , F(000) 1420.00, Z 4, 1 calcd 1.415 g cm À3 , m(Mo Ka ) 5.74 cm À1 . Data were measured on a Rigaku AFC7R diffractometer with graphite-monochromatized Mo Ka radiation and a 12-kW rotating anode generator at 28.0 8C. Of the 3670 reflections measured, 3298 were unique (R int 0.053), and 1403 with I b 2 s(I) were observed. Data were corrected for Lorentzian and polarization effects. The structure was solved by direct methods (SHELXS86), and the full-matrix least-squares refinement converged to R 0.094 and R w 0.077 with a GOF of 3.91. b) Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication...

Quantum Chemical Study of Solvent and Substituent Effects on the 1,5-Hydride Shift in 2,6-Dimethyl-2-heptyl Cations

“…Consequently, solvation in a polar solvent has a substantial effect on the relative energies of both isomers . Similar effects were reported for a sila analogue of cation 1 with a symmetrical Si−H−Si bridge . While many experimental solution-phase structures of carbocations appear to be well described by gas-phase calculations, , recent studies have reported differential solvation in some isomeric carbocation systems 25 solvation effects on closely balanced equilibria of carbocations 26 and on the rate of reorientation of carbocations in solution .…”

The Family of Ferrocene‐Stabilized Silylium Ions: Synthesis, 29Si NMR Characterization, Lewis Acidity, Substituent Scrambling, and Quantum‐Chemical Analyses

“…Table 5 shows that the by far lowest Lewis acidity is found for compound 6 ,10 which possesses a rigid structure and a cationic silicon center stabilized by two additional interactions with hydrogen atoms from the neighboring silyl groups. In contrast, the highest FIAs in this series are predicted for the hydrogen‐bridged disilyl cation, 4 ,9a and [FcSiMe 2 ] + .…”

Structure and Solution Reactivity of (Triethylsilylium)triethylsilane Cations

“…In free triethylsilane, 1 J SiH = 177 Hz. It is anticipated that the coupling constant in 1 is on the order of 40 Hz, on the basis of similar species characterized by Müller and Nikonov, but any coupling is predicted be unobservable when the exchange rate is ≥200 s –1 . If the exchange process is sufficiently rapid, complete coalescence of the bridging hydrogen atom in 1 and Et 3 Si H will result…”