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Methacrylated lignin was reacted with PH3(g) to prepare a phosphorus rich bio-based polymer containing PH/PH2 functional groups, which were converted to tertiary phosphine units via the phosphane-ene reaction. This represents a straightforward method for the upconversion of low-value biomass waste to useful inorganic polymer with potential utility in metal scavenging applications.

A bidentate nitrogen-donor ligand with an appended phenol group, C5H4NCHN-2-C6H4OH, H(L1) was treated with a palladium cycloneophyl complex [Pd(CH2CMe2C6H4)(COD)], with both Pd-aryl and Pd-alkyl bonds, to give a Pd-alkyl complex, [Pd(CH2CMe2C6H5)(κ3-N,N′,O-OC6H4NCH(2-C5H4N))], 1. The cleavage of the Pd-aryl bond and the deprotonation of the ligand phenol to afford a bound aryloxide, indicates facile Pd-aryl bond protonolysis. Deuterium labelling experiments confirmed that the ligand phenol promotes protonolysis and that the reverse, aryl C-H activation, occurs under very mild reaction conditions (within 10 min at room temperature). An unusual isomerization of the Pd-alkyl complex 1 to a Pd-aryl complex, [Pd(C6H4(2-t-Bu))(κ3-N,N′,O-OC6H4NCH(2-C5H4N))], 2, was observed to give an equilibrium with [2]/[1] = 9 after 5 days in methanol. The isomerization requires that both aryl C-H activation and Pd-alkyl protonolysis steps occur. The very large KIE value (kH/kD = ca. 40) for isomerization of 1 to 2, suggests a concerted SE2-type mechanism for the Pd-alkyl protonolysis step.

The ligand N(CH2-2-C5H4N)2(CH2CH2CH2OH), L1, reacted with [Pd(CH2CMe2C6H4)(COD)] to give a new fluxional "cycloneophyl" organopalladium complex [Pd(CH2CMe2C6H4)(κ2-L1)], 1, which on attempted recrystallization from THF gave the monodentate carbonate complex [Pd(CO3)(κ3-L1)], 2. Complex 2 was prepared in designed syntheses by reaction of [PdCl(κ3-L1)]+ with silver carbonate or by reaction of [Pd(OH)(κ3-L1)]+ with CO2. Complex 1 reacted with aqueous CO2 to give the cationic neophylpalladium complex [Pd(CH2CMe2C6H5)(κ3-L1)]+(HCO3)-, 6. Complex 6 reacts with hydrogen peroxide to give complex 2 with release of a mixture of organic products, the major one being 2-phenyl-2-butanol, PB. The formation of PB involves a neophyl rearrangement with the unprecedented preference for methyl over phenyl migration. A mechanistic basis for this unexpected reaction is proposed, involving β-carbon elimination at a palladium(IV) center.

A dimer with two PdII–Me fragments is stabilized by the bridging coordination of the supporting 1-azaallyl/phosphine ligand. Heating the complex results in C(sp3)–C(sp3) bond formation and the release of ethane. Two different palladium products are generated, each with distinct coordination modes of the 1-azaallyl/phosphine ligand.

Two phosphine-imine ligands were synthesized in which the heteroatoms were connected by an ethyl (1a) or a propyl (1b) linker. Both ligands were reacted with PdCl(Me)(COD), which gave the square planar complexes PdCl(Me)(κ2-P,N-1a) (2a) and PdCl(Me)(κ2-P,N-1b) (2b). Both complexes were treated with base in pyridine in an effort to prepare phosphine 1-azaallyl complexes of the type Pd(Me)(κ2-P,N-L)(py). Deprotonation of 2a gave an intractable mixture of products. In contrast, deprotonation of 2b afforded a new product 4b. However, the site of deprotonation was the methylene adjacent to the phosphine rather than Cα to the imine carbon, deprotonation of which would have afforded a 1-azaallyl moiety.

The first successful use of the PR2NR′2 (1,5-R′-3,7-R-1,5-diaza-3,7-diphosphacyclooctane) ligand family toward an organic synthesis is described. The precatalysts [Ru(Cp)(PR2NBn2)(MeCN)]PF6 are active toward cyclization of 2-ethynylbenzyl alcohol at low catalyst loading and mild temperatures. Catalyst performance however is limited by both low conscription and by competitive deactivation.

Ligand design for metal-ligand cooperative (MLC) catalysis is inherently more complex than that for traditional non-cooperative ligands. The basicity, sterics and structure of the acid/base group in MLC proton-transfer (PT) complexes, for instance, undoubtedly influence catalyst performance. Herein, we evaluate the highly tunable PR2NR′2 (1,5-R′-3,7-R-1,5-diaza-3,7-diphosphacyclooctane) ligand family for the first time in an organic transformation. With [Ru(Cp)(PtBu2NBn2)(MeCN)][PF6] as the catalyst, no turnover was observed in the anti-Markovnikov hydration of alkynes, a known PT MLC reaction. Treatment of the cooperative complex with phenylacetylene affords a vinylammonium product in which the pendant nitrogen atom of the PtBu2NBn2 ligand forms a Lewis acid-base adduct with the alpha-carbon atom of the vinylidene intermediate. Characterization by X-ray crystallography and NMR spectroscopy conclusively assign this structure in both the solid and the solution state. The adduct formation is irreversible, and the adduct is characterized as a catalyst deactivation product. Snapping Shut: The PR2NR′2 ligand family (R and R′ are removed for clarity in the graphic) open the door for easily tuned catalysts for cooperative organic transformations. However, the ligand swings toward the vinylidene, forming a stable (and catalytically inactive) Lewis acid-base adduct. (□ = open coordination site)

The synthesis of three new NiCl(allyl/cinnamyl)(NHC) complexes, containing a bifunctional NHC (N-heterocyclic carbene) ligand is described. Two different NHCs were utilized that contain a secondary amine (HNR; R=t-Bu or Mes) moiety on one of the N-imidazolylidene arms. Complexes with allyl (2 a) and cinnamyl (3 a and 3 b) were each crystallographically characterized and η3-allyl and κ1-C NHC ligand coordination modes were found in the solid-state. In the solution-state, each of the ligands shows highly fluxional behaviour. Halide substitution of the chloro ligand for iodo effectively slows the ligand dynamics and permits solution-state characterization that is in agreement with the solid-state structures. The complexes react with oxygen to ultimately oxidize the allyl or cinnamyl ligands to acrolein (AC) or cinnamaldehyde (CA) and phenyl vinyl ketone (PVK), respectively. The bifunctional nature of the NHC has limited influence on oxidation reactivity, but preliminary evidence suggests it plays a role in the stability of the nickel oxidation products.

[Ru(Cp)(PPh2NBn2)(MeCN)]PF6 (1; PPh2NBn2 = 1,5-benzyl-3,7-phenyl-1,5-diaza-3,7-diphosphacyclooctane) and [Ru(Cp)(dppp)(MeCN)]PF6 (2; dppp = 1,3-bis(diphenylphosphino)propane) are both active toward the acceptorless dehydrogenation of benzylamine (BnNH2) and N-heterocycles. The two catalysts have similar activities but different selectivities for dehydrogenation products. Independent synthesis of a [Ru(Cp)(PPh2NBn2)(NH2Bn)]PF6 adduct (3) reveals the presence of a hydrogen bond between the bound amine and the pendent base of the PPh2NBn2 ligand. Preliminary mechanistic studies reveal that the benzylamine adduct is not an on-cycle catalyst intermediate.

The synthesis of a new tripodal ligand family that contains tertiary amine groups in the second-coordination sphere is reported. The ligands are tris(amido)amine derivatives, with the pendant amines attached via a peptide coupling strategy. They were designed to function as new molecular catalysts for the oxygen reduction reaction (ORR), in which the pendant acid/base group could improve the catalyst performance. Two members of the ligand family were each metalated with cobalt(II) and zinc(II) to afford trigonal-monopyramidal complexes. The reaction of the cobalt complexes [Co(L)](-) with dioxygen reversibly generates a small amount of a cobalt(III) superoxo species, which was characterized by electron paramagnetic resonance (EPR) spectroscopy. Protonation of the zinc complex Zn[N{CH2CH2NC(O)CH2N(CH2Ph)2}3)](-) ([Zn(TN(Bn))](-)) with 1 equiv of acid occurs at a primary-coordination-sphere amide moiety rather than at a pendant basic site. The addition of excess acid to any of the complexes [M(L)](-) results in complete proteolysis and formation of the ligands H3L. These undesired reactions limit the use of these complexes as catalysts for the ORR. An alternative ligand with two pyridyl arms was also prepared but could not be metalated. These studies highlight the importance of the stability of the primary-coordination sphere of ORR electrocatalysts to both oxidative and acidic conditions.

A highly tunable phosphine-imine ligand family is introduced. Following metallation with ruthenium, deprotonation of the ligand affords a phosphine-enamido species. Complexes with the ligand in both the imine and enamido forms are active toward acceptorless dehydrogenation reactions.

The chemistry of a palladium(II) complex containing both an alkyl– and an aryl–palladium bond is reported. The reaction of [Pd(CH2CMe2C6H4)(MesN═CHCH═NMes)] with bromine or iodine leads to reductive elimination of 1,1-dimethylcyclobutabenzene with formation of [PdX2(MesN═CHCH═NMes)] (X = Br, I). However, the reaction with hydrogen peroxide gives [Pd(CH2CMe2C6H4O)(MesN═CHCH═NMes)] by overall oxygen atom insertion into the aryl–palladium rather than the alkyl–palladium bond. This complex [Pd(CH2CMe2C6H4O)(MesN═CHCH═NMes)] reacts with bromine, iodine, or hydrogen peroxide to give 3,3-dimethyl-2,3-dihydrobenzofuran and the corresponding complex [PdX2(MesN═CHCH═NMes)]. The mechanisms of reaction and basis for selectivity are discussed. The results support the view that oxygen atom insertion is a mechanistically viable pathway for selective catalytic oxidation of hydrocarbons by the green oxidant hydrogen peroxide.

A versatile Ru-BINO building block is reported, which offers a straightforward entry point into the chemistry of atropisomeric binaphtholate complexes of ruthenium. Reaction of RuCl(2)(PPh(3))(3)6a with Tl(2)((S)-BINO) affords Ru((S)-BINO)(PPh(3))(2)7 as a mixture of isomers: in 7', the BINO ligand is bound via η(3)-CCO,η(1)-O' donors, and in symmetrical 7″, via η(3)-CCO,η(3)-O'C'C' interactions. The bis(enolate) BINO bonding mode in the latter, not previously observed for any metal, underscores the remarkable geometric and electronic flexibility of the binaphtholate moiety. The BINO ligand proves able to stabilize complexes containing as few as two, and as many as four, additional ligands in 7 and its derivatives, enabling a synthetic versatility that contrasts with that of the superficially similar o-catecholate complex Ru(o-cat)(PPh(3))(3). As with the important achiral Ru precursor 6a, complex 7 undergoes facile transformation into a range of products under mild conditions, including acetonitrile, pyridine, and vinylidene derivatives. Single-crystal X-ray structures are reported for three of these complexes: Ru(η(3),η(3)-(S)-BINO)(PPh(3))(2)7″, Ru(η(3),η(1)-(S)-BINO)(PPh(3))(2)(MeCN) 9, and Ru(η(3),η(1)-(S)-BINO)(PPh(3))(py)(2)11. (13)C{(1)H} NMR signatures are proposed for new and known BINO coordination modes (η(1)-O,η(1)-O'; η(1)-C1,η(1)-O'; η(3)-CCO,η(3)-O'C'C'; η(3)-CCO,η(1)-O'; η(6)-C(6),η(1)-O'), as a potential aid to further developments in late-metal BINO chemistry.

High-throughput experimentation has enormous potential to accelerate the discovery and implementation of new methodologies based on organometallic catalysis. A perspective is presented of technical challenges and opportunities for advance. We highlight what we believe to be essential inventions, and key areas for exploration, for progress that will facilitate enlistment of organometallic chemistry in meeting the needs of the future.

The activity of RuHCl(H2)(PCy3)(L) 2a/b and RuHCl(CO)(PCy3)(L) 3a/b (a: L = PCy3; b: L = IMes; IMes = 1,3-dimesitylimidazol-2-ylidene) was assessed in hydrogenation of a range of molecular and polymeric olefins and in hydrogenation and isomerization of allylbenzene. Elevated temperatures and/or high H2 pressures are required for efficient hydrogenation. Under these conditions, 3a/b outperform their dihydrogen analogues in both total productivity and turnover frequencies, despite theoretical and experimental evidence that the π-acid CO ligand should be deactivating. A thermolysis study reveals that the CO complexes are much less susceptible to deactivation under conditions relevant to catalysis (also, the IMes derivative 2b is shorter-lived than 2a). We attribute the superior performance of 3a/b to their greater stability, which maintains higher concentrations of active catalyst than that possible for their H2 analogues over the time scale of hydrogenation.

The addition of formylphenylboronic acid derivatives to thiourea and ethyl acetoacetate proceeds in the presence of an additional Lewis acid catalyst to give the corresponding 3,4-dihydropyrimidin-2(1H)-(thio)ones (Biginelli products) in moderate yield. Compounds were tested for antifungal activity against pure cultures of Aspergillus niger, Aspergillus flavus, Candida albicans and Saccharomyces cerevisiae but, unfortunately, none showed any appreciable activity.

The hydroboration of phenyl vinyl sulfide with catecholborane (HBcat) and pinacolborane (HBpin) has been examined with a number of rhodium complexes, all of which proceed with excellent regiocontrol in favour of the branched product PhSCH(B(OR)2)CH3. The corresponding linear product can be obtained exclusively in reactions employing [Cp*IrCl2]2 and HBcat. Catalysed hydroborations of (E)-2-(p-toluenethio)styrene with HBcat using Rh(acac)(dppp) gave predominant formation of one product while reactions using HBpin afforded several products arising from a competing C–S bond cleavage (acac = acetylacetonato, dppp = 1,3-bis(diphenylphosphino)propane). Although reactions of phenyl vinyl sulfoxide were complicated by a competing deoxygenation reaction, hydroborations of phenyl vinyl sulfone using HBcat once again gave regioselective formation of either the branched or linear products, depending on the choice of catalyst used to effect this transformation. Catalysed hydroborations of phenyl vinyl sulfonate were less chemo- and regioselective, yielding hydrogenation and diboration products in addition to the two hydroboration product isomers. © 2007 Elsevier B.V. All rights reserved.

The addition of formylphenylboronic acid derivatives to urea and ethyl acetoacetate proceeds in the absence of an additional Lewis acid catalyst to give the corresponding dihydropyrimidinones (Biginelli products) in good yields. Novel boron-containing dihydropyrimidinones have been investigated for their ability to act as anticancer agents against the breast cancer cell line MCF7.Key words: anticancer, Biginelli compounds, boronic acids, breast cancer, dihydropyrimidinones.

Schiff bases (HL) derived from sulfanilamides or aminobenzothiazoles add to Pd(OAc)2 to give complexes of the type PdL2 (1–7) in moderate to excellent yields. Reactions of Schiff bases containing pyrimidine groups, however, gave several products arising from competing coordination of the pyrimidine nitrogen. Palladium complexes and Schiff bases have been investigated as antifungal agents against Aspergillus niger and Aspergillus flavus.

We report here the first example of a homogeneous first row transition-metal-based catalyst which is active for dehydrogenation of ammonia−borane, H3NBH3, a promising chemical hydrogen storage material. Addition of ammonia−borane to an active catalyst formed in situ from the reaction of Ni(cod)2 and 2 equiv of an appropriate N-heterocyclic carbene (NHC) rapidly evolves hydrogen at 60 °C. Using a gas burette to quantify the gas evolved, 29 of a possible 31 mL of H2 for 3 equiv of H2 was produced, equating to >2.5 equiv of H2 from ammonia−borane. Kinetic isotope effects of deuterated derivatives of ammonia−borane suggest that both N−H and B−H bonds are being broken in the rate-determining step(s).

The title compound, C34H35BN2O4, was readily synthesized via an Ugi four-component reaction (U-4CR) by condensation of benzoic acid, benzaldehyde, benzyl isocyanide and an aniline derivative containing a boronate ester group. No significant intra- or inter­molecular inter­actions are observed between the amide groups and the Lewis acidic B atom.