The crystal and molecular structure of tricyclohexylphosphine-(trimethylsilyl)borane CY3P·BH2SiMe3

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.

An alkyl-substituted aluminium anion with strong basicity and nucleophilicity

Aluminium anions with an unoccupied orbital are generally considered as highly difficult synthetic targets, as aluminium is the most electropositive element in the p block. Stabilizing effects from two nitrogen substituents and/or the coordination of a Lewis base were recently used to synthesize the first examples of anionic nucleophilic aluminium species. Here we show the synthesis and properties of a potassium salt of a non-stabilized dialkylaluminium anion that exhibits very strong basicity, which reflects the electropositive character of aluminium. An X-ray diffraction analysis revealed a monomeric structure and the shortest Al-K distance hitherto reported. The ultraviolet visible spectrum in combination with density functional theory calculations suggests an electronic structure characterized by a lone pair of electrons and an unoccupied p orbital on the aluminium centre. This species readily deprotonates benzene to form the corresponding (hydrido)(phenyl)aluminate. Reactions with other electrophiles corroborate the nucleophilicity of the aluminium centre.

Boryllithium: A novel boron nucleophile and its application in the synthesis of borylmetal complexes

The first boryl anion, boryllithium, was synthesized by a reduction of bromoborane precursor using lithium naphthalenide in tetrahydrofuran (THF) solvent at -45 °C. Structural and spectroscopic study revealed an ionic character of B-Li bond. Boryllithium could be utilized as a source of boryl ligand in the transition-metal chemistry. Structural and spectroscopic features of the resulting boryl complexes confirmed the large trans influence of boryl ligand.

Boryllithium: Isolation, Characterization, and Reactivity as a Boryl Anion

Nucleophilic, anionic boryl compounds are long-sought but elusive species. We report that reductive cleavage of the boron-bromine bond in N,N'-bis(2,6-diisopropylphenyl)-2-bromo-2,3-dihydro-1H-1,3,2-diazaborole by lithium naphthalenide afforded the corresponding boryllithium, which is isoelectronic with an N-heterocyclic carbene. The structure of the boryllithium determined by x-ray crystallography was consistent with sp(2) boron hybridization and revealed a boron-lithium bond length of 2.291 +/- 0.006 angstroms. The structural similarity between this compound and the calculated free boryl anion suggests that the boron atom has an anionic charge. The (11)B nuclear magnetic resonance spectrum also supports the boryl anion character. Moreover, the compound behaves as an efficient base and nucleophile in its reactions with electrophiles such as water, methyl trifluoromethanesulfonate, 1-chlorobutane, and benzaldehyde.

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.

Preparation and Characterization of Halogen-Boron-Phosphorus Compounds. X-ray Crystal Structures of X(3)B.P(SiMe(3))(3) and [X(2)BP(SiMe(3))(2)](2) (X = Cl, Br)

The 1:1 mole ratio reactions of boron trihalides (BX(3)) with tris(trimethylsilyl)phosphine [P(SiMe(3))(3)] produced 1:1 Lewis acid/base adducts [X(3)B.P(SiMe(3))(3), X = Cl (1), Br (2), I (5)]. Analogous 1:1 mole ratio reactions of these boron trihalides with lithium bis(trimethylsilyl)phosphide [LiP(SiMe(3))(2)] produced dimeric boron-phosphorus ring compounds {[X(2)BP(SiMe(3))(2)](2), X = Br (3), Cl (4)}. X-ray crystallographic studies were successfully conducted on compounds 1-4. Compound 1 crystallized in the orthorhombic space group Pbca, with a = 13.420(3) Å, b = 17.044(5) Å, c = 21.731(7) Å, V = 4970.6(25) Å(3), and D(calc) = 1.229 g cm(-3) for Z = 8; the B-P bond length was 2.022(9) Å, Compound 2 crystallized in the orthorhombic space group Pbca, with a = 13.581(6) Å, b = 17.106(7) Å, c = 22.021(9) Å, V = 5116(4) Å(3), and D(calc) = 1.540 g cm(-3) for Z = 8; the B-P bond length was 2.00(2) Å. Compound 3 crystallized in the monoclinic space group P2(1)/n, with a = 9.063(5) Å, b = 16.391(8) Å, c = 9.331(4) Å, V = 1379.2(12) Å(3), and D(calc) = 1.676 g cm(-3) for Z = 2; the B-P bond length was 2.023(10) Å. Compound 4 crystallized in the monoclinic space group P2(1)/n, with a = 9.143(5) Å, b = 16.021(8) Å, c = 9.170(4) Å, V = 1342.2(11) Å(3), and D(calc) = 1.282 g cm(-3) for Z = 2; the B-P bond length was 2.025(3) Å. Thermal decomposition studies were performed on compounds 1-4, yielding colored powders with boron:phosphorus ratios greater than 1:1 and significant C and H contamination indicated by elemental analyses.