A mechanistic insight into metal-cluster π-envelopment: a dual binding mode involving bent and planar ligand-conformers

We report a stepwise mechanism of the π-envelopment of a Pd₄ chain cluster. Bent- and planar binding modes of π-conjugated unsaturated hydrocarbon ligands are involved in the π-envelopment process.

Investigations on the catalytic carboxylation of olefins with CO2 towards α,β-unsaturated carboxylic acid salts: characterization of intermediates and ligands as well as substrate effects

The carboxylation of olefins beyond ethylene towards α,β-unsaturated carboxylic acid salts and a detailed investigation on the critical steps in the catalysis are reported. The influence of two chelating phosphine ligands and several olefins on the elemental steps of the catalysis is shown. The work focusses on the formation of intermediate olefin complexes, lactone formation and base induced elimination of the lactone. The direct carboxylation of olefins is possible using nickel catalysts, which opens a new route towards the desired α,β-unsaturated carboxylic acid salts. The reaction works particularly well for 1,3-dienes and proceeds via the formation of allyl-carboxylates. The ability to form such allyl-type lactone complexes seems in this case to be the most challenging step towards satisfactory turnover numbers.

Nickelalactones with an allyl subunit – the effect of penta-coordination on structures and stability

Nickelalactone derivatives with an allyl subunit containing different mono- and bidentate ligands were synthesized and characterized. The introduced neutral ligands strongly affect the structures of these versatile molecules and can be used to modulate their stabilities.

Ni(0)-catalyzed 1,4-selective diboration of conjugated dienes

A catalytic stereoselective 1,4-diboration of conjugated dienes with B(2)(pin)(2) was accomplished with Ni(cod)(2) and PCy(3) as the catalyst. This reaction broadens the substrate scope of current methods for catalytic diene diboration by including internal and sterically hindered dienes, and it proceeds efficiently at low catalyst loadings. The intermediate allylboronate was oxidized to the stereodefined allylic 1,4-diol.

Regio- and stereoselective Ni-catalyzed 1,4-hydroboration of 1,3-dienes: access to stereodefined (Z)-allylboron reagents and derived allylic alcohols

A catalytic regio- and stereoselective 1,4-hydroboration of 1,3-dienes was accomplished with pinacolborane in the presence of Ni(cod)(2) and PCy(3). This reaction exhibits broad substrate scope operating on a range of substituted dienes and occurs with generally high levels of selectivity and efficiency. Reactivity patterns suggest that the reactive conformation of the diene is the S-cis form. The intermediate allylboronate can be oxidized to stereodefined allylic alcohols or can be used in stereoselective carbonyl addition reactions.

Pt(0) and Pd(0) olefin complexes of the metalloid N-heterocyclic carbene analogues [E(I)(ddp)] (ddp=2-{(2,6-diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-pentene; E=Al, Ga): ligand substitution, H--H and Si--H bond activation, and cluster formation

Various products of the reaction of [E(ddp)] (ddp=2-{(2,6-diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}-2-pentene; E=Al, Ga) with Pt(0) and Pd(0) olefin complexes are reported. Thus, the reaction of [Pt(cod)(2)] (cod=1,5-cyclooctadiene) with two equivalents of [Ga(ddp)] yields [Pt(1,3-cod){Ga(ddp)}(2)] (1), whereas treatment of [Pd(2)(dvds)(3)] (dvds=1,1,3,3-tetramethyl1,3-divinyldisiloxane) with [E(ddp)] leads to the monomeric compounds [(dvds)Pd{E(ddp)}] (E=Ga (2 a), Al (2 b)) by substitution of the bridging dvds ligand. Both 1 and 2 a readily react with strong pi-acceptor ligands such as CO or tBuNC to give the dimeric compounds [M{mu(2)-Ga(ddp)}(L)] (L=CO, tBuNC; M=Pt (3 a, 5 a), Pd (3 b, 5 b)), respectively. Based on (1)H NMR spectroscopic data, [Pt{Ga(ddp)}(2)(CO)] is likely to be an intermediate in the formation of 3 a. Furthermore, reactions of 1 with H(2) and HSiEt(3) yield the monomeric compounds [Pt{Ga(ddp)}(2)(H)(2)] (7) and [Pt{Ga(ddp)}(2)(H)(SiEt(3))] (8). Finally, the reaction of [Pt(cod)(2)] with one equivalent of [Ga(ddp)] in the presence of H(2) in hexane gives the new dimeric cluster [Pt{mu(2)-Ga(ddp)}(H)(2)](2) (9).