Lyudmila G. Kuzmina

Diversity of Catalysis by an Imido-Hydrido Complex of Molybdenum. Mechanism of Carbonyl Hydrosilylation and Silane Alcoholysis

New Imido hydride complex 1 catalyzes a variety of silylation reactions that proceed via initial substrate activation but not silane addition.

Cp(Pri2MeP)FeH2SiR3 : Nonclassical Iron Silyl Dihydride

Reactions of a new borohydride complex 2 with hydrosilanes afford half-sandwich dihydride silyl complexes 3a-f. According to X-ray and DFT evidence complexes 3 have unprecedented double H...Si...H interligand interactions.

Nonhydride mechanism of metal-catalyzed hydrosilylation.

A 1:1:1 reaction between complex (Tp)(ArN═)Mo(H)(PMe(3)) (3), silane PhSiD(3), and carbonyl substrate established that hydrosilylation catalyzed by 3 is not accompanied by deuterium incorporation into the hydride position of the catalyst, thus ruling out the conventional hydride mechanism based on carbonyl insertion into the M-H bond. An analogous result was observed for the catalysis by (O═)(PhMe(2)SiO)Re(PPh(3))(2)(I)(H) and (Ph(3)PCuH)(6).

Mechanistic Aspects of Hydrosilylation Catalyzed by (ArN=)Mo(H)(Cl)(PMe3)3

The reaction of (ArN=)MoCl(2)(PMe(3))(3) (Ar = 2,6-diisopropylphenyl) with L-Selectride gives the hydrido-chloride complex (ArN=)Mo(H)(Cl)(PMe(3))(3) (2). Complex 2 was found to catalyze the hydrosilylation of carbonyls and nitriles as well as the dehydrogenative silylation of alcohols and water. Compound 2 does not show any productive reaction with PhSiH(3); however, a slow H/D exchange and formation of (ArN=)Mo(D)(Cl)(PMe(3))(3) (2(D)) was observed upon addition of PhSiD(3). Reactivity of 2 toward organic substrates was studied. Stoichiometric reactions of 2 with benzaldehyde and cyclohexanone start with dissociation of the trans-to-hydride PMe(3) ligand followed by coordination and insertion of carbonyls into the Mo-H bond to form alkoxy derivatives (ArN=)Mo(Cl)(OR)(PMe(2))L(2) (3: R = OCH(2)Ph, L(2) = 2 PMe(3); 5: R = OCH(2)Ph, L(2) = η(2)-PhC(O)H; 6: R = OCy, L(2) = 2 PMe(3)). The latter species reacts with PhSiH(3) to furnish the corresponding silyl ethers and to recover the hydride 2. An analogous mechanism was suggested for the dehydrogenative ethanolysis with PhSiH(3), with the key intermediate being the ethoxy complex (ArN=)Mo(Cl)(OEt)(PMe(3))(3) (7). In the case of hydrosilylation of acetophenone, a D-labeling experiment, i.e., a reaction of 2 with acetophenone and PhSiD(3) in the 1:1:1 ratio, suggests an alternative mechanism that does not involve the intermediacy of an alkoxy complex. In this particular case, the reaction presumably proceeds via Lewis acid catalysis. Similar to the case of benzaldehyde, treatment of 2 with styrene gives trans-(ArN=)Mo(H)(η(2)-CH(2)═CHPh)(PMe(3))(2) (8). Complex 8 slowly decomposes via the release of ethylbenzene, indicating only a slow insertion of styrene ligand into the Mo-H bond of 8.

The unexpected mechanism of carbonyl hydrosilylation catalyzed by (Cp)(ArN[double bond, length as m-dash])Mo(H)(PMe(3)).

Complex (Cp)(ArN[double bond, length as m-dash])Mo(H)(PMe(3)) (2, Ar = 2,6-diisopropylphenyl) catalyzes the hydrosilylation of carbonyls by an unexpected associative mechanism. Complex 2 also reacts with PhSiH(3) by a σ-bond metathesis mechanism to give the silyl derivative (Cp)(ArN[double bond, length as m-dash])Mo(SiH(2)Ph)(PMe(3)).

Steric Promotion of Aromatic C–H Bond Activation in Primary Benzylamines

ortho-Palladation of a sterically crowded primary benzylamine, α-phenylneopentylamine, was accomplished in a moderate yield of 50% in the reaction with the weakest of palladation agents (Li2PdCl4) under very mild conditions, due to a steric promotion of an aromatic C–H bond activation. The structure of dimer 1a thus formed and the palladacycle conformation were established on the basis of 1H-NMR spectroscopy of its mononuclear derivatives with [D5]pyridine (3a) and triphenylphosphane (4a), and an X-ray investi-gation of the latter.

First enantiopure phosphapalladacycle with planar chirality. X-Ray study of the racemic dimer and (Spl,SCSN)-diastereomer of its prolinate derivative

Abstract The first P , C -cyclopalladated complex with planar chirality was prepared by direct cyclopalladation of prochiral di- tert -butyl(ferrocenylmethyl)phosphine. Resolution of the racemic dimer was achieved through separation of its diastereomeric ( S )-prolinate derivatives. The palladacycle structure was confirmed by the 1 H NMR spectra of the dimer and its triphenylphosphine adduct and an X-ray diffraction study of the racemic dimeric complex. The absolute configuration of the planar chirality was determined by an X-ray diffraction investigation of one of two diastereomers of the ( S )-prolinate derivative.

Supramolecular assemblies of photochromic benzodithia-18-crown-6 ethers in crystals, solutions, and monolayersElectronic supplementary information (ESI) available: crystal data, data collection, and structure solution and refinement parameters. See http://www.rsc.org/suppdata/nj/b1/b110630a/

We studied the assembly of dithiacrown ether styryl dye (CSD) molecules in crystals, solutions, and films in the presence of metal cations. X-Ray diffraction data allowed us to conclude that the anion affects the supramolecular architecture of CSDs in the crystal, specifically, the type of stacking of the dye molecules. In solution, in the presence of Pb2+, CSD molecules with the betaine structure spontaneously form dimeric complexes consisting of two dye molecules and two metal cations, with a fixed mutual arrangement of the double bonds. The dimer complex is stable due to coordination between the anion substituent of one molecule and the metal cation located in the crown ether cavity of the other molecule. Irradiation of the dimer complexes leads to regio- and stereoselective [2 + 2]-cycloaddition, giving only one cyclobutane derivative of the eleven theoretically possible products. The other photoreaction studied for CSDs is reversible Z–E isomerization. Due to its specific structure, the betaine-type CSD is able to form the ‘anion-capped’ Z-isomer. Intramolecular coordination in the ‘anion-capped’ isomer enhances its stability and causes a sharp deceleration of its dark Z–E isomerization. The amphiphilic CSD forms relatively stable monolayers on distilled water and various aqueous salt subphases. The results obtained indicate that it is possible to distinguish between two types of the dye monolayer structures based on the presence of alkali or heavy metal cations in the aqueous subphase.

An unexpected mechanism of hydrosilylation by a silyl hydride complex of molybdenum.

Carbonyl hydrosilylation catalyzed by (ArN)Mo(H)(SiH(2)Ph)(PMe(3))(3) (3) is unusual in that it does not involve the expected Si-O elimination from intermediate (ArN)Mo(SiH(2)Ph)(O(i)Pr)(PMe(3))(2) (7). Instead, 7 reversibly transfers β-CH hydrogen from the alkoxide ligand to metal.

Agostic NSiH⋅⋅⋅Mo Complexes: From Curiosity to Catalysis

2a,b with a d configuration (Scheme 1). Bonding in these species can be represented by two canonical forms (B and C ; Scheme 1), one of which has a silanimine character (C). This fact suggests that 1 and 2a,b could serve as intermediates for silanimine complexes, which, although very scarce, are known to exhibit a wealth of reactivity. Herein, we describe the preparation, structure, and reactivity of a new agostic silylamido complex, 3. For the first time, we report the catalytic and stoichiometric reactions of such a complex and provide evidence for the intermediacy of a silanimine complex. The reaction of bis(imido) compound (ArN)2Mo(PMe3)3 (Ar= 2,6-diisopropylphenyl) with two equivalents of PhSiH3 leads to a product of double silane addition, the b-agostic NSi H···Mo complex 3 [Eq. (1)]. The structure of 3 is fluxional at room temperature, but at 223 K the H NMR spectrum shows an up-field signal characteristic of the proton of an agostic Si Ha moiety at d = 4.35 ppm (brm), which is coupled to a signal assigned to the terminal Si H proton at d = 6.03 ppm (d, JH,H = 5.4 Hz). The diastereotopic protons