Gold( i )-catalyzed addition of aldehydes to cyclopropylidene bearing 6-aryl-1,5-enynes

A diastereoselective, gold-catalyzed cascading cycloisomerization of alkylidene cyclopropane bearing 1,5-enynes that terminates in a cyclo-addition of aldehydes has been developed

{Bis[2-(diphenyl­phosphan­yl)eth­yl]phenyl­phosphane-κ3 P,P′,P′′}[(Z)-8-mesityl­cyclo­oct-4-en-1-yl]platinum(II) tetra­fluorido­borate dichloro­methane disolvate

In the title ionic compound, [Pt(C17H23)(C34H33P3)](BF4)·2CH2Cl2, the PtII atom adopts a square-planar coordination geometry with the large (Z)-8-mesityl­cyclo­oct-4-en-1-yl group occupying the fourth coordination site. The (triphos)Pt moiety and the mesityl group are attached to the cyclo­oct-4-ene motif at the 1- and 8-position in a syn configuration. The (BF4)− anion and one of the dichloromethane solvate molecules each are disordered over two sets of sites

Pd(0)/Au(i) redox incompatibilities as revealed by Pd-catalyzed homo-coupling of arylgold(i)-complexes

A Pd(ii)-catalyzed homo-coupling of Au(i)-aryls is reported. The reaction is driven by a Pd(0)/Au(i) redox reaction that generates a gold mirror and Pd(ii), and illustrates one of the challenges for developing dual catalytic Au–Pd systems

Dinuclear Gold−Silver Resting States May Explain Silver Effects in Gold(I)-Catalysis

The resting state of the gold(I)-catalyzed hydroarylation of 1 changes in the presence of Ag+, with silver free catalysts resting at the dinuclear gold structure 5 and Ag+ containing solutions resting at a heteronuclear species like 6. Adventitious Ag+ (typically from LAuCl activation) can therefore intercept key organogold intermediates and effect the catalysis even when it does not effect the reaction in Au free control experiments

Enantioselective Cascade Cyclization/Protodemetalation of Polyenes with N 3 Pt 2+ Catalysts

The combination of the N-based pincer ligand PyBOX with Pt2+ leads to new catalysts for the enantioselective cycloisomerization of dienyl- and trienyl-ols. The mechanistic combination of electrophilic cyclization followed by rapid protodemetalation is surprising and leads to a powerful construct for developing new reactions

σ–π-Diauration as an alternative binding mode for digold intermediates in gold( i ) catalysis

While investigating the gold(i)-catalyzed intramolecular hydroarylation of allenes, the structure of a digoldvinyl intermediate was verified. Instead of the previously proposed geminally diaurated binding mode for the digold when L = PPh3, an alternative σ–π-diauration mode was observed with the bulkier ligand L = P(o-Tol)3. Reactivity studies indicate the σ–π-mode has a disproportionate effect on protonolysis reactivity

Cyclization/Oxygenation Scheme for the Conversion of Polyenes into C3-Oxygenated Polycycles

Oxidatively induced halogenation and oxygenation reactions of complex Pt(II) organometallic complexes provide a route to a catalytic cation–olefin cyclization/oxygenation sequence. The evidence suggests the involvement of a Pt(III) intermediate, which reacts homolytically to generate an organic free radical that can be intercepted by O2 followed by the Russell breakdown of the resulting alkyl peroxy radicals or by CuX2 (X = Br, Cl) to yield the X–R product

Diastereoselective Pt Catalyzed Cycloisomerization of Polyenes to Polycycles

Application of a tridentate NHC containing pincer ligand to Pt catalyzed cascade cyclization reactions has allowed for the catalytic, diastereoselective cycloisomerization of biogenic alkene terminated substrates to the their polycyclic counterparts

Platinum(II) Enyne Cycloisomerization Catalysis: Intermediates and Resting States

In situ generated [(PPP)Pt][BF4]2 (PPP = triphos) catalyzes the cycloisomerization of 1,6-enyne-ols by initiative π-activation of the alkyne. This generates an isolable cationic Pt-alkenyl species which subsequently participates in turnover limiting protonolysis with in situ generated acid. This latter reactivity contrasts cationic Pt-alkyls which are more difficult to protonolyze. Mechanistic studies on isolated Pt-alkenyls, and deuterium labeling helped to elucidate the mechanistic details

Reversibility Effects on the Stereoselectivity of Pt(II)-Mediated Cascade Poly-ene Cyclizations

Cyclization of 1,5-dienes bearing nucleophilic traps with electrophilic trisphosphine pincer ligated Pt(II) complexes results in the formation of a polycyclic Pt-alkyl via an Pt(η2-alkene) intermediate. With electron rich triphosphine ligands an equilibrium between the Pt(η2-alkene) and Pt-alkyl was observed. The position of the equilibrium was sensitive to ligand basicity, conjugate acid strength, solvent polarity, and ring size. In cases where the ligand was electron poor and did not promote retro-cyclization, then kinetic products adhering to the Stork-Eschenmoser postulate were observed (E-alkenes give trans-ring junctions). When retrocyclization was rapid, then alternative thermodynamic products resulting from multi-step rearrangements were observed (cis [6,5]-bicycles). Under both kinetic and thermodynamic conditions remote methyl substituents led to highly diastereoselective reactions. In the case of trienol substrates, long-range asymmetric induction from a C-ring substituent was considerably attenuated and only modest diastereoselectivity was observed (~2:1). The data suggests that for a tricyclization, the long-range stereocontrol results from diastereo-selecting interactions that develop during the organization of the nascent rings. In contrast, the bicyclization diastereoselectivities result from reversible cascade cyclization