A silyliumylidene ion 2 stabilized by two σ-donating Ni(0)and Pd(0)-fragments was successfully synthesized. Due to the donation of MSi interactions, 2 presents a pyramidalized cationic silicon center with a localized lone pair. The additional coordination of basic Pd(0) fragment to the mono-Ni(0)-stabilized silyliumylidene 1 results in a higher HOMO level and an unchanged HOMO-LUMO gap and thus, 2 remains highly reactive. Interestingly, the coordination mode at the Si center is closely related to the nature of M-ligands. Indeed, the donor/donor-stabilized silyliumylidene ion 2 has been transformed into a donor/acceptor-stabilized ion 13, featuring a trigonal planar Si center with a vacant orbital, just via a ligand exchange reaction from PCy3/NHC toward PMe3.

Compound 2 from 5: In an NMR tube, to a mixture of 5 (74 mg, 0.062 mmol) and NaBArF4 (55 mg, 0.062 mmol, 1.0 equiv.), C6H5F (0.5 mL) was added at room temperature. After 5 min, full conversion of 5 to 2 was confirmed by 31 P{ 1 H} NMR spectroscopy. The reaction mixture was filtered and the filtrate was concentrated (ca. 0.1 mL) under reduced pressure. Compound 2 was crystallized from a C6H5F/pentane solution (0.1 : 0.5 mL) at -30 °C and was obtained as black crystals (121 mg, 96%). 1 H NMR (400 MHz, 25 °C, C6H5F/C6D6): δ = 0.30 (s, 3H, SiMe2), 0.37 (s, 3H, SiMe2), 0.67 (m, 3H, CH2cyclohexyl), 0.89 (m, 3H, CH2cyclohexyl), 0.94 (m, 3H, CH2cyclohexyl), 1.04 (m, 3H, CH2cyclohexyl), 1.04 (overlapped, 1H, CH2Norb), 1.09 (overlapped, 1H, CH2Norb), 1.10 (s, 9H, CH3tBu), 1.14 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.14 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.20 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.20 (overlapped, 1H, CH2Norb),1.21 (s, 9H, CH3tBu), 1.27 (d, JHH = 7.0 Hz, 3H, CH3iPr-NHC), 1.28 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.31 (d, JHH = 7.0 Hz, 3H, CH3iPr-NHC), 1.34 (m, 3H, CH2cyclohexyl), 1.36 (overlapped, 1H, CH2Norb), 1.45 (m, 3H, CH2cyclohexyl), 1.47 (d, JHH = 7.0 Hz, 3H, CH3iPr-NHC), 1.47 (m, 3H, CHcyclohexyl), 1.50 (d, JHH = 7.0 Hz, 3H, CH3iPr-NHC), 1.53 (overlapped, 1H, CH2Norb), 1.54 (m, 3H, CH2cyclohexyl),1.64 (m, 1H, CH2Norb), 1.81 (s, 3H, C=C-CH3NHC), 1.83 (s, 3H, C=C-CH3NHC), 2.34 (s, 1H, CHbridgehead), 3.11 (sept, JHH = 6.9 Hz, 1H, CHiPr-Dip), 3.18 (sept, JHH = 6.8 Hz, 1H, CHiPr-Dip), 3.34 (s, 1H, CHbridgehead), 4.19 (sept, JHH = 7.0Hz, 1H, CHiPr-NHC), 5.56 (sept, JHH = 7.0 Hz, 1H, CHiPr-NHC), 7.05-7.15 (m, 3H, CHAr), 7.62 (s, 4H, CHB-Ar), 8.29 (s, 8H, CHB-Ar). 13 C{ 1 H} NMR (100 MHz, 25 °C, C6H5F/C6D6): δ = 4.4 (SiMe2), 5.8 (d, JCP = 2.7 Hz, SiMe2), 9.9 (C=C-CH3NHC), 10.2 (C=C-CH3NHC), 21.9 (CH3iPr-NHC), 22.9 (CH3iPr-Dip), 23.6 (CH3iPr-Dip), 23.8 (CH3iPr-NHC), 24.4 (CH3iPr-NHC), 25.4 (CH2Norb), 25.6 (CH3iPr-NHC), 26.1 (CH2cyclohexyl), 26.7 (CH3iPr-Dip), 26.9 (CH3iPr-Dip), 27.6 (d, JCP = 9.2 Hz, CH2cyclohexyl), 27.6 (d, JCP = 12.9 Hz, CH2cyclohexyl), 27.8 (CH2Norb), 28.7 (CHiPr-Dip), 28.7 (CHiPr-Dip), 30.3 (CH2cyclohexyl), 32.0 (d, JCP = 3.9 Hz, CH3tBu), 32.4 (d, JCP = 7.4 Hz, CH2cyclohexyl), 32.4 (d, JCP = 5.7 Hz, CH3tBu), 34.0 (JCP = 13.2 Hz, CHcyclohecyl), 44.4 (CHbridgehead), 45.4 (d, JCP = 10.9 Hz, CHbridgehead), 47.6 (d, JCP = 3.9 Hz, CH2Norb), 51.0 (d, JCP = 3.2 Hz, CtBu), 51.9 (d, JCP = 4.2 Hz, CtBu), 55.1 (CHiPr-NHC), 55.5 (CHiPr-NHC), 119.7 (d, JCP = 40.4 Hz, PC=CN), 118.0 (br sept, JCF = 3.7 Hz, p-CHB-Ar), 124.5 (CHAr), 124.8 (CHAr), 124.9 (q, JCF = 272.4 Hz, CF3), 128.7 (CHAr), 129.9 (qq, JCF = 31.6 Hz, JCB = 2.7 Hz, m-CB-Ar), 130.0 (C=CNHC), 135.4 (o-CHB-Ar), 135.8 (N-CAr), 146.1 (iPr-CAr), 146.5 (iPr-CAr), 160.8 (d, JCP = 22.9 Hz, PC=CN), 162.8 (q, JCB = 49.6 Hz, ipso-CB-Ar), 167.8 (dd, JCP = 26.3 and 6.0 Hz, Ccarbene). 11 B{ 1 H} (160 MHz, 25 °C, C6H5F/C6D6): δ = -6.0 (BAr F 4). 19 F NMR (470 MHz, 25 °C, C6H5F/C6D6): δ = -62.4 (s, BAr F 4). 31 P{ 1 H} NMR (121 MHz, 25 °C, C6H5F/C6D6): δ = 93.8 (d, JPP = 57.3 Hz, PN2), 37.0 (d, JPP = 57.3 Hz, Si-satellite: JPSi = 62.3 Hz, PCy3). 29 Si{ 1 H} NMR (79 MHz, 25 °C, C6H5F/C6D6): δ = 333.5 (dd, JSiP = 62.0 and 18.2 Hz, N-Si-Ni), 10.5 (d, JSiP = 1.7 Hz, SiMe2).

Compound 5: In an NMR tube, to a solution of 2 (80 mg, 0.40 mmol) in THF (0.4 mL), Bu4NCl (11 mg, 0.04 mmol, 1.0 equiv.) was added at room temperature. After overnight, all volatiles were removed under reduced pressure. Compound 5 was crystallized from a saturated C6H5F solution (ca. 0.1 mL) at -30 °C and was obtained as black crystals (32 mg, 67%). Crystals suitable for X-ray diffraction analysis were obtaind from saturated C6H5F/ solution at room temperature. Mp. 173-176 °C (decomp.). 1 H NMR (300 MHz, 25 °C, THF-d8): δ = 0.40 (s, 3H, SiMe2), 0.43 (s, 3H, SiMe2), 0.96 (m, 1H, CH2Norb), 1.02 (m, 3H, CH2cyclohexyl), 1.08 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.12 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.12 (m, 9H, CH2cyclohexyl), 1.30 (s, 9H, CH3tBu), 1.32 (overlapped, 3H, CH3iPr-Dip), 1.39 (m, 3H, CH2cyclohexyl), 1.42 (overlapped, 1H, CH2Norb), 1.43 (s, 9H, CH3tBu), 1.47 (d, JHH = 6.8 Hz, 3H, CH3iPr-NHC), 1.50 (m, 3H, CHcyclohexyl), 1.56 (m, 1H, CH2Norb), 1.57 (d, JHH = 6.8 Hz, 6H, CH3iPr-NHC), 1.61 (m, 12H, CH2cyclohexyl), 1.68 (d, JHH = 6.8 Hz, 3H, CH3iPr-NHC), 1.71 (d, JHH = 6.8 Hz, 3H, CH3iPr-Dip), 1.71 (overlapped, 1H, CH2Norb), 1.80 (m, 4H, CH2Norb and CH2cyclohexyl), 2.18 (s, 6H, C=C-CH3NHC), 2.34 (m, 1H, CHbridgehead), 3.41 (m, 1H, CHbridgehead), 3.85 (sept, JHH = 6.8 Hz, 1H, CHiPr-Dip), 4.02 (sept, JHH = 6.8 Hz, 1H, CHiPr-Dip), 4.96 (sept, JHH = 6.8 Hz, 1H, CHiPr-NHC), 5.93 (sept, JHH = 6.8 Hz, 1H, CHiPr-NHC), 7.08-7.13 (m, 3H, CHAr). 13 C{ 1 H} NMR (75 MHz, 25 °C, THF-d8): δ = 6.5 (SiMe2), 7.1 (d, JCP = 4.9 Hz, SiMe2), 10.5 (C=C-CH3NHC), 10.7 (C=C-CH3NHC), 22.3 (CH3iPr-NHC), 22.8 (CH3iPr-NHC), 22.3 (CH3iPr-Dip), 23.2 (CH3iPr-NHC), 25.5 (CH3iPriDip), 25.7 (CH3iPr-Dip), 26.2 (CH3iPr-Dip), 27.1 (d, JCP = 11.4 Hz, CH2cyclohexyl), 27.1 (CH2Norb), 28.4 (d, JCP = 10.4 Hz, CH2cyclohexyl), 28.5 (CHiPr-Dip), 28.6 (CH2cyclohexyl), 28.6 (CHiPr-Dip), 29.2 (CH3iPr-NHC), 29.5 (CH2Norb), 30.8 (d, JCP = 5.2 Hz, CH2cyclohexyl), 31.5 (d, JCP = 6.6 Hz, CH2cyclohexyl), 32.4 (d, JCP = 5.2 Hz, CH3tBu), 33.7 (d, JCP = 4.2 Hz, CH3tBu), 35.2 (d, JCP = 8.0 Hz, CHcyclohexyl), 44.5 (d, JCP = 2.4 Hz, CHbridgehead), 46.3 (d, JCP = 4.2 Hz, CH2Norb), 46.6 (d, JCP = 11.4 Hz, CHbridgehead), 51.3 (d, JCP = 4.5 Hz, CtBu), 51.5 (d, JCP = 5.9 Hz, CtBu), 54.2 (CHiPr-NHC), 54.4 (CHiPr-NHC), 117.4 (d, JCP = 29.3 and 1.9 Hz, Hz, PC=CN), 124.1 (CHAr), 124.5 (CHAr), 124.5 (C=CNHC), 125.7 (C=CNHC), 126.6 (CHAr), 139.6 (N-CAr), 149.1 (iPr-CAr), 149.6 (iPr-CAr), 164.2 (d, JCP = 22.5 Hz, PC=CN), 193.4 (d, JCP = 8.0 Hz, Ccarbene). 31 P{ 1 H}