Reaction SMILES: [CH2:1]([Mg]Cl)[CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8].[CH2:11]([Si:19]([CH2:34][CH2:35][CH2:36][Si:37](Cl)(Cl)Cl)([CH2:27][CH2:28][CH2:29][Si:30](Cl)(Cl)Cl)[CH2:20][CH2:21][CH2:22][Si:23](Cl)(Cl)Cl)[CH2:12][CH2:13][CH2:14][CH2:15][CH2:16][CH2:17][CH3:18].Cl>O1CCCC1>[CH2:11]([Si:19]([CH2:34][CH2:35][CH2:36][Si:37]([CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])([CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])[CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])([CH2:27][CH2:28][CH2:29][Si:30]([CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])([CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])[CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])[CH2:20][CH2:21][CH2:22][Si:23]([CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])([CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])[CH2:1][CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH3:8])[CH2:12][CH2:13][CH2:14][CH2:15][CH2:16][CH2:17][CH3:18]
Reactant: CCCCCCCC[Mg]Cl
Reactant: CCCCCCCC[Si](CCC[Si](Cl)(Cl)Cl)(CCC[Si](Cl)(Cl)Cl)CCC[Si](Cl)(Cl)Cl
Agent: Cl
Solvent: C1CCOC1
Product: CCCCCCCC[Si](CCCCCCCC)(CCCCCCCC)CCC[Si](CCCCCCCC)(CCC[Si](CCCCCCCC)(CCCCCCCC)CCCCCCCC)CCC[Si](CCCCCCCC)(CCCCCCCC)CCCCCCCC
Temperature: 25 °C
Yield: 78.1 %

Procedure:
Under strong nitrogen flow, into a 1 L three-neck round bottom flask equipped with rubber septum, reflux condenser, nitrogen bypass inlet, and magnetic stirring bar were added, via a flex-needle, n-octylmagnesium chloride (310 Ml, 2.0M in tetrahydrofuran, 620 mmol) and tetrahydrofuran (350 Ml). In an inert atmosphere enclosure, to a 50 Ml addition funnel was added n-octyl-tris-[3-(trichlorosilyl)propyl]silane (23.0 g, 34.3 mmol, prepared as in Example 1, Step (b)). The addition funnel was attached to the flask containing n-octylmagnesium chloride, and n-octyl-tris-[3-(trichlorosilyl)propyl]silane was subsequently added to the tetrahydrofuran solution of n-octylmagnesium chloride over a period of 25 minutes. The reaction was exothermic. After completion of addition, the reaction mixture was heated at reflux temperature for 10 days and then allowed to cool to room temperature. At this time it was cooled in an ice-water bath and hydrochloric acid (500 Ml, 1.2N) was cautiously added. The reaction mixture separated into two layers on standing. The aqueous layer was washed with diethyl ether (2×200 Ml). The organic layers were combined, washed with water (200 Ml), and dried over magnesium sulfate, and the solvent removed under reduced pressure. Purification by silica gel column chromatography yielded 36.7 g (78.1%) of n-octyl-tris-[3-(trioctylsilyl)propyl]silane. This tetrasilahydrocarbon had a kinematic viscosity of 66.2 centistokes at 40° C., a kinematic viscosity of 12.5 centistokes at 100° C., and a viscosity index of 191. Onset of volatilization under 0.44 mm Hg pressure, based on the thermogravimetric analysis, was at 275° C. Thus, it is shown that by the use of a higher alkyl organometallic compound in Step (c), a far more viscous tetrasilahydrocarbon product with lower volatility can be prepared from the same intermediate as was used to prepare the relatively low viscosity base stock of Example 1.