Isolation of Bis- and Mono-Cyclometallated Ru-IMes Complexes Upon Reaction of [Ru(PPh3)3HCl], IMes and ZnMe2

Addition of an excess of ZnMe2 to a mixture of [Ru(PPh3)3HCl] and IMes (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) yields the bis-cyclometallated complex, [Ru(IMes)“(PPh3)2] 2, together with the mono-cyclometallated, Ru−Zn heterobimetallic complex [Ru(IMes)′(PPh3)2(ZnMe)] 3. Treatment of 2 with H2, PhSiH3 or pinacolborane yields the previously reported complex, [Ru(IMes)′(PPh3)2H] 1, the synthesis of which has been reinvestigated. Further studies of small molecule reactivity show that 1 adds H2 to give [Ru(IMes)(PPh3)2H4] 4, whilst 2 reacts with catecholborane to give [Ru(IMes-Bcat)′(PPh3)2H] 5, in which (IMes-Bcat)′ signifies a borylated NHC ligand that is singly-metallated onto Ru. Treatment of 2 with CO gives the 18-electron dicarbonyl product [Ru(IMes)”(PPh3)(CO)2] 6. Compounds 1–3, 5 and 6 have been structurally characterised

Exceedingly facile Ph−X activation (X=Cl, Br, I) with ruthenium(II) : Arresting kinetics, autocatalysis, and mechanisms

The ICIQ Foundation and The Spanish Government (Grant CTQ2011-25418 and the Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319) are thankfully acknowledged for support of this work. F.M.M. is grateful to the Government of Spain (MICINN) for the FPI Ph.D. Scholarship (BES-2012-054922). S.A.M. and D.M. thank the EPSRC for support through award EP/J010677/1.[(Ph3P)3Ru(L)(H)2] (where L=H2 (1) in the presence of styrene, Ph3P (3), and N2 (4)) cleave the Ph[BOND]X bond (X=Cl, Br, I) at RT to give [(Ph3P)3RuH(X)] (2) and PhH. A combined experimental and DFT study points to [(Ph3P)3Ru(H)2] as the reactive species generated upon spontaneous loss of L from 3 and 4. The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2, originating from the initial PhI activation with 3, is roughly as reactive toward PhI as 3 itself; and 2) the Ph[BOND]I bond cleavage with the just-produced 2 gives rise to [(Ph3P)2RuI2], which quickly comproportionates with the still-present 3 to recover 2. Both the initial and onward activation reactions involve PPh3 dissociation, PhI coordination to Ru through I, rearrangement to a η2-PhI intermediate, and Ph[BOND]I oxidative addition.Publisher PDFPeer reviewe

Heterobimetallic ruthenium–zinc complexes with bulky N-heterocyclic carbenes: syntheses, structures and reactivity

The ruthenium–zinc heterobimetallic complexes, [Ru(IPr)2(CO)ZnMe][BArF4] (7), [Ru(IBiox6)2(CO)(THF) ZnMe][BArF4] (12) and [Ru(IMes)’(PPh3)(CO)ZnMe] (15), have been prepared by reaction of ZnMe2 with the ruthenium N-heterocyclic carbene complexes [Ru(IPr)2(CO)H][BArF4] (1), [Ru(IBiox6)2(CO)(THF)H][BArF4] (11) and [Ru(IMes)(PPh3)(CO)HCl] respectively. 7 shows clean reactivity towards H2, yielding [Ru(IPr)2(CO) (¿2-H2)(H)2ZnMe][BArF4] (8), which undergoes loss of the coordinated dihydrogen ligand upon application of vacuum to form [Ru(IPr)2(CO)(H)2ZnMe][BArF4] (9). In contrast, addition of H2 to 12 gave only a mixture of products. The tetramethyl IBiox complex [Ru(IBioxMe4)2(CO)(THF)H][BArF4] (14) failed to give any isol- able Ru–Zn containing species upon reaction with ZnMe2. The cyclometallated NHC complex [Ru(IMes)’ (PPh3)(CO)ZnMe] (15) added H2 across the Ru–Zn bond both in solution and in the solid-state to afford [Ru(IMes)’(PPh3)(CO)(H)2ZnMe] (17), with retention of the cyclometallati

Alcoholysis of fluoroform

Fluoroform (CHF3) reacts with alkali metal alkoxides MOR (M = Na, K) in the corresponding alcohols ROH (R = Me, Et, i-Pr, t-Bu, and Allyl) at 80-120°C to give orthoformate esters HC(OR)3 in 55-90% yield. Particularly notable is the formation of HC(OBu-t)3 in 75-80% yield (62% isolated yield; X-ray), an exotic organic compound that has been previously synthesized only once (3% yield). Solutions of NaOH in ROH (R = Me, Et, i-Pr and t-Bu) react with CHF3 to give NaF, HCOONa, and orthoformates HC(OR)3. Hydrolysis of fluoroform with MOH (M = Na, K) at 140°C produces largely MF and HCOOM along with small quantities of CO

Total syntheses of pyrroloazocine indole alkaloids : Challenges and reaction discovery

Lapidilectines, grandilodines, lundurines and tenuisines are indole alkaloids, isolated from plants of Kopsia genus. They feature a common indole-fused pyrroloazocine core, whose construction poses a significant synthetic challenge. In this review, we discuss the reported strategies for the total synthesis of this family of alkaloids with a focus on the different methods used for the construction of spiro[cyclohexane-2-indoline] and indole-pyrroloazocine intermediates, introduction of indole-fused cyclopropane as well as other new methodologies uncovered in the course of the total syntheses. In closing, the existing hypothesis of the biosynthetic origin and relationships of the pyrroloazocine indole alkaloids are presented

Ruthenium-catalyzed nucleophilic fluorination of halobenzenes

The first π-coordination-catalyzed nucleophilic fluorination of unactivated aryl halides has been demonstrated. Chlorobenzene reacts with alkali metal fluorides (CsF, KF) in the presence of a Cp∗Ru catalyst at 120-180°C to give fluorobenzene

On the feasibility of nickel-catalyzed trifluoromethylation of aryl halides

A computational screening of 42 bidentate phosphines (PP) has yielded promising candidates for Ph-CF3 reductive elimination from Ni(II) complexes of the type [(PP)Ni(Ph)(CF3)]. The computed barriers and synthetic accessibility considerations have identified two PP ligands, dippf and dcypf (δG± = 22.6 and 23.2 kcal/mol, respectively), for experimental studies with 1-Np (1-naphthyl) in place of Ph. Ligand exchange of [(Ph3P)2Ni(1-Np)Cl] with dippf or dcypf has cleanly produced [(dippf)Ni(1-Np)Cl] and [(dcypf)Ni(1-Np)Cl], the first examples of trans square-planar 1,1′-ferrocenediyl backbone-based diphosphine metal complexes devoid of M⋯Fe dative interactions. Treatment of these chlorides with CF3SiMe3/F-, AgCF3/MeCN or [(Ph3P)3Cu(CF3)] does not furnish isolable or 19F NMR-detectable [(PP)Ni(1-Np)(CF3)] (PP = dippf, dcypf). Other transformations have been observed instead, e.g., ligand exchange with the Ag and Cu complexes, the latter leading to [(dcypf)Cu(CF3)], a rare example of well-defined CF3Cu(I) species. With CF3SiMe3/F-, indirect evidence has been obtained for intermediacy of [(PP)Ni(1-Np)(CF3)] (PP = dippf, dcypf) and instantaneous decomposition via pathways other than C-CF3 reductive elimination. The first Ni(II) complexes with fluoride trans to a non-electron-deficient aryl, [(Cy3P)2Ni(1-Np)F] and [(i-PrXantphos)Ni(1-Np)F], have been prepared and fully characterized. Surprisingly, [(Cy3P)2Ni(1-Np)F] can be produced from [(Cy3P)2Ni(1-Np)Cl] and CsF rather than AgF that is conventionally used for the synthesis of late transition metal fluorides via X/F exchange. While [(Cy3P)2Ni(1-Np)F] is unreactive toward CF3SiMe3, [(i-PrXantphos)Ni(1-Np)F] is readily trifluoromethylated to produce robust [(i-PrXantphos)Ni(1-Np)(CF3)], a rare example of complexes of the type [(PP)Ni(Ar)(CF3)] with PP other than dippe

Planning for woodcarving in the 21st century

This info brief provides information on the positive and negative impacts, challenges and reformulation policy on woodcarving industry. The positive impacts in many developing countries are: to contribute significant income, provide safety net, and it links to tourism and adds considerable value to wood compared to others. The negative impacts are that it depletes raw materials and can affect biodiversity of indigenous forest and impacts negatively on livelihoods of some non-carver households. This brief than identify the challenges to sustain the woodcarving industry and to sustain the resource. Present policies neglect the significant economic and livelihood contributions of forest products other than timber. This brief concludes with recommendations to policy makers in Forestry, Tourism and Development sectors on reformulating the present policy

Well-defined CuC2F5 complexes and pentafluoroethylation of acid chlorides

Four new well-defined CuI complexes bearing a C2F5 ligand have been prepared and fully characterized: [(Ph3P)2CuC2F5] (2), [(bpy)CuC2F5] (3), [(Ph3P)Cu(phen)C2F5] (4), and [(IPr)CuC2F5] (5). X-ray structures of all four have been determined, showing that the C2F5-ligated Cu atom can be di- (5), tri- (2 and 3), and tetracoordinate (4). The mixed phen-PPh3 complex 4 is a highly efficient fluoroalkylating agent for a broad variety of acid chlorides. This high-yielding transformation represents the first general method for the synthesis of RCOC2F5 from the corresponding RCOCl. Four well-defined CuC2F5 complexes have been prepared and fully characterized, with [(phen)Cu(PPh3)C2F5] (phen=1,10-phenanthroline) proving to be a remarkably efficient fluoroalkylating agent for a broad variety of acid chlorides (see scheme). The procedure represents the first general method for the one-step conversion of RCOCl into valuable pentafluoroethyl ketones

Unified Total Synthesis of Pyrroloazocine Indole Alkaloids Sheds Light on Their Biosynthetic Relationship

The total synthesis of seven members of the lapidilectine and grandilodine family of alkaloids has been accomplished in racemic and enantiopure form without protection/deprotection of functional groups. The two key steps, an 8-<i>endo</i>-dig hydroarylation and a 6-<i>exo</i>-trig photoredox cyclization, were catalyzed using gold. A rationale for the formation of the cyclopropane ring of the lundurines is also provided