Challenging an old paradigm by demonstrating transition metal-like chemistry at a neutral nonmetal center

We describe nonmetal adducts of the phosphorus center of terminal phosphinidene complexes using classical C- and N-ligands from metal coordination chemistry. The nature of the L-P bond has been analyzed by various theoretical methods including a refined method on the variation of the Laplacian of electron density ∇2ρ along the L-P bond path. Studies on thermal stability reveal stark differences between N-ligands such as N-methyl imidazole and C-ligands such as tert-butyl isocyanide, including ligand exchange reactions and a surprising formation of white phosphorus. A milestone is the transformation of a nonmetal-bound isocyanide into phosphaguanidine or an acyclic bisaminocarbene bound to phosphorus; the latter is analogous to the chemistry of transition metal-bound isocyanides, and the former reveals the differences. This example has been studied via cutting-edge DFT calculations leading to two pathways differently favored depending on variations in steric demand. This study reveals the emergence of organometallic from coordination chemistry of a neutral nonmetal center.

Stereospecific synthesis of silicon-stereogenic optically active silylboranes and general synthesis of chiral silyl Anions

Silicon-stereogenic optically active silylboranes could potentially allow the formation of chiral silyl nucleophiles as well as the synthesis of various chiral silicon compounds. However, the synthesis of such silicon-stereogenic silylboranes has not been achieved so far. Here, we report the synthesis of silicon-stereogenic optically active silylboranes via a stereospecific Pt(PPh3)4-catalyzed Si-H borylation of chiral hydrosilanes, which are synthesized by stoichiometric and catalytic asymmetric synthesis, in high yield and very high or perfect enantiospecificity (99% es in one case, and >99% es in the others) with retention of the configuration. Furthermore, we report a practical approach to generate silicon-stereogenic silyl nucleophiles with high enantiopurity and configurational stability using MeLi activation. This protocol is suitable for the stereospecific and general synthesis of silicon-stereogenic trialkyl-, dialkylbenzyl-, dialkylaryl-, diarylalkyl-, and alkylary benzyloxy-substituted silylboranes and their corresponding silyl nucleophiles with excellent enantiospecificity (>99% es except one case of 99% es). Transition-metal-catalyzed C-Si bond-forming cross-coupling reactions and conjugate-addition reactions are also demonstrated. The mechanisms underlying the stability and reactivity of such chiral silyl anion were investigated by combining NMR spectroscopy and DFT calculations.

Unprecedented insertion reaction of a silylene into a B–B bond and generation of a novel borylsilyl anion by boron–metal exchange reaction of the resultant diborylsilane

A kinetically stabilized diarylsilylene, Tbt(Mes)Si: (1, Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes = mesityl), thermally generated from overcrowded disilene Tbt(Mes)Si=Si(Mes)Tbt (2) or stable silylene-isocyanide complex (3a), was found to insert into a B-B bond of bis(pinacolato)diboron, B2(pin)2 (4), and the boron-lithium exchange reaction of the resulting diborylsilane gave the first borylsilyl anion.