Reactivity of cyano- and isothiocyanatoborylenes: metal coordination, one-electron oxidation and boron-centred Brønsted basicity

Doubly base-stabilised cyano- and isothiocyanatoborylenes of the form LL′BY (L = CAAC = cyclic alkyl(amino)carbene; L′ = NHC = N-heterocyclic carbene; Y = CN, NCS) coordinate to group 6 carbonyl complexes via the terminal donor of the pseudohalide substituent and undergo facile and fully reversible one-electron oxidation to the corresponding boryl radical cations [LL′BY]˙+. Furthermore, calculations show that the borylenes have very similar proton affinities, both to each other and to NHC superbases. However, while the protonation of LL′B(CN) with PhSH yielding [LL′BH(CN)+][PhS−] is fully reversible, that of LL′B(NCS) is rendered irreversible by a subsequent B-to-CCAAC hydrogen shift and nucleophilic attack of PhS− at boron

Carbenes in Ruthenium Based Olefin Metathesis Catalysts and Stabilization of Low Coordinate Boron Species

Since their discovery, carbenes have been widely used as organocatalysts and as superb ligands for transition metal-based catalysts. They have also, more recently, been shown to stabilize reactive and low-valent main group systems. Catalytic olefin metathesis has proven to be a powerful tool in various chemical fields. Research in this area has received considerable attention specifically with the development of new catalysts. The vast majority of catalysts developed, thus far, have been modifications to the Grubbs catalyst architecture. The research presented herein focuses on the development of a new route for the synthesis of new olefin metathesis catalysts and testing their activity. A new method of preparing ruthenium alkylidene complexes starting with bis-carbene RuHCl species and alkenyl sulfides is developed. This provides a route to bis-mixed carbene ruthenium alkylidene complexes with a hemilabile tridentate carbene and conveniently installs both an alkylidene fragment and a thiolate in one step. The resulting Ru-alkylidene are either inactive or minimally active for the standard metathesis tests. The species generated by the addition of one equivalent of BCl3, however, show improved activity for RCM, ROMP and CM either at room temperature or at slightly elevated temperatures. Halide exchange for these systems results in enhanced metathesis activity for the standard tests where catalytic olefin metathesis was observed at room temperature. Cyclic (alkylamino)carbenes are utilized to stabilize iminoboryl moieties which have only been previously stabilized in the coordination sphere of transition metals. Some of the species are also shown to undergo [2+2] cycloaddition with CO2. CAACs are also used for the synthesis of a boron derivative, which is isoelectronic with singlet carbenes, namely a borylene. This species is shown to react with CO and H2, but in contrast with carbenes, it acts as an electrophile and therefore mimics the behavior of metals.Ph.D

A New Route to Ruthenium Thiolate Alkylidene Complexes

(Im­(OMe)₂)­(SIMes)­(PPh₃)­RuHCl (Im­(OMe)₂ = (C₃H₂(NCH₂CH₂OMe)₂) reacts with aryl vinyl sulfides (PhSCHCH₂ and (C₆F₅)­SCHCHPh) to give the Ru thiolate alkylidene complexes (Im­(OMe)₂)­(SIMes)­(PhS)­RuCl­(CHCH₃) and (Im­(OMe)₂)­(SIMes)­(F₅C₆S)­RuCl­(CHCH₂Ph), which are shown to be effective olefin metathesis catalysts upon activation with BCl₃

Ruthenium and Rhodium Complexes of Thioether-Alkynylborates

The species ((C₆F₅)₂BCH₂SPh)₂ reacts with PhCCLi to give the thioether-alkynylborate (C₆F₅)₂BCH₂SPh­(CCPh)­Li­(THF)₂ (<b>1</b>). Subsequent reaction with (Ph₃P)₃RuHCl, (Ph₃P)₃RhCl, and [(COD)­Rh­(μ-Cl)]₂ gives (C₆F₅)₂BCH₂SPh­(CCPh)­RuH­(PPh₃)₂ (<b>2</b>), (C₆F₅)₂BCH₂SPh­(CCPh)­Rh­(PPh₃)₂ (<b>4</b>), and (C₆F₅)₂BCH₂SPh­(CCPh)­Rh­(COD) (<b>5</b>), respectively, demonstrating a bidentate binding mode via the alkynyl and thioether donors of the borate. Subsequent reactions of <b>2</b> and <b>4</b> with H₂ gave (C₆F₅)₂BCH₂SPh­(CH₂CH₂Ph)­RuH­(PPh₃)₂ (<b>3</b>) and ((C₆F₅)₂BCH₂SPh­(CHCHPh))­Rh­(PPh₃)₂ (<b>6</b>). In the former case, the borate remains bound to the metal via a π-interaction with the thioether-arene ring, while in the latter case, S and alkene binding is observed

Synthesis and Reactivity of Ruthenium Hydride Complexes Containing a Tripodal Aminophosphine Ligand

Ru complexes containing a tris­(aminophosphine) ligand (N­(NP)₃) have been prepared and their reactivity examined. The complex [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂(κ²<i>N</i>,<i>P</i>-((CH₂)₂NHP<i>i</i>Pr₂))­RuCl]­[Cl] (<b>1</b>) is transformed to [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂((CH₂)₂NPH<i>i</i>Pr₂))­RuCl]­Cl (<b>2</b>) on standing in solution. Deprotonation of the phosphonium center in <b>2</b> followed by anion exchange generates the Ru hydride complex [(N­((CH₂)₂NHP<i>i</i>Pr₂)­((CH₂)₂NP<i>i</i>Pr₂)­(CH₂CHNHP<i>i</i>Pr₂))­RuH]­[BPh₄] (<b>3</b>), which can bind acetonitrile to give [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂((CH₂)₂NP<i>i</i>Pr₂))­Ru­(CH₃CN)]­[BPh₄] (<b>5</b>). Protonation of <b>3</b> and <b>5</b> with either a 1 M solution of HCl in diethyl ether or NEt₃HCl yields [(N­((CH₂)₂NHPiPr₂)₂((CH₂)₂NPHiPr₂))­RuCl]­[BPh₄] (<b>6</b>). Reaction of <b>3</b> with H₂ gives the Ru hydride complex [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂(κ²<i>N</i>,<i>P</i>((CH₂)₂NHP<i>i</i>Pr₂))­RuH]­[BPh₄] (<b>8</b>), which is deprotonated with KN­(SiMe₃)₂ to give [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂)­((CH₂)₂NP<i>i</i>Pr₂)­RuH] (<b>9</b>). This latter species reacts with H₂ to generate [(N­((CH₂)₂NHP<i>i</i>Pr₂)₃)­Ru­(H)₂] (<b>10</b>). The hydride species <b>3</b> is also shown to react with CO₂, N₂O, phenylacetylene, and 1-pentyne to give [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂((CH₂)₂NP­(CO₂)<i>i</i>Pr₂))­Ru]­[BPh₄] (<b>11</b>), [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂((CH₂)₂NP­(O)<i>i</i>Pr₂))­Ru]­[BPh₄] (<b>12</b>), and [(N­((CH₂)₂NHP<i>i</i>Pr₂)₂((CH₂)₂NP­(R)<i>i</i>Pr₂))­Ru]­[BPh₄] (R = C₈H₆ (<b>13</b>), C₅H₁₀ (<b>14</b>)), in which the substrate is bound to P and the metal center. In contrast, <b>9</b> does not react with N₂O and alkyne but reacts with CO₂ to give CO₂ insertion into the N–P bond, yielding (N­((CH₂)₂NHP<i>i</i>Pr₂)₂((CH₂)₂N­(CO₂)­P<i>i</i>Pr₂)­RuH (<b>15</b>)

Isolation of Au-, Co-η1PCO and Cu-η2PCO complexes, conversion of an Ir-η1PCO complex into a dimetalladiphosphene, and an interaction-free PCO anion

Sodium phosphaethynolate reacts with [MCl(PDI)] (M = Co, Ir; PDI = pyridinediimine) to give metallaphosphaketenes, which in the case of iridium rearranges into a dimetalladiphosphene, via CO migration from phosphorus to the metal. Two different bonding modes of the PCO anion to CAAC-coinage metal complexes [CAAC: cyclic (alkyl)(amino)(carbene)] are reported, one featuring a strong Au–P bond and the other an η2 coordination to copper. The gold complex appears to be mostly unreactive whereas the copper complex readily reacts with various organic substrates. A completely free PCO anion was structurally characterized as the [Cu(La)2]+ (OCP)− salt. It results from the simple displacement of the PCO unit of the cationic (CAAC)Cu(PCO) complex by a second equivalent of CAAC.ISSN:2041-6520ISSN:2041-653