Can low-valent silicon compounds be better transition metal ligands than phosphines and NHCs?

We investigated the potential application of low-valent silicon compounds as transition metal ligands by computing the most important ligand properties and compared them to the generally used carbene and phosphine ligands.

Branched tetrasilane substituted phosphines – synthesis and characterisation of PhSi(SiiPr2)3P and {PhSi(SiMe2)3}2P14

Reactions of branched trichlorotetrasilane with P₇(SiMe₃)₃ and Li₃P are described, yielding the new compounds PhSi(SiiPr₂)₃P and {PhSi(SiMe₂)₃}₂P₁₄.

Five-coordinate silicon(II) compounds with Si-M bonds (M = Cr, Mo, W, Fe): Bis[N,N'-diisopropylbenzamidinato(-)]silicon(II) as a ligand in transition-metal complexes

Reaction of the donor-stabilized silylene 1 with [Cr(CO)6], [Mo(CO)6], [W(CO)6], or [Fe(CO)5] leads to the formation of the transition-metal silylene complexes 2-5, which contain five-coordinate silicon(II) moieties with Si-M bonds (M = Cr, Mo, W, Fe). These compounds were characterized by NMR spectroscopic studies in the solid state and in solution and by crystal structure analyses. These experimental investigations were complemented by computational studies to gain insight into the bonding situation of 2-5. The nature of the Si-M bonds is best described as a single bond.