Ruthenium alkylidenes: a new class of catalysts for Kharasch addition and controlled radical polymerisation of vinyl monomers

Poster (2003, May)

Air-stable and readily available ruthenium benzylidene complexes of the general type (RuCl2 (=CHPh)(L)(L')) (L, L' = P(cC5H9)3, PCy3 and/or a N-heterocyclic carbene) constitute a new class of catalyst ... [more ▼]

Air-stable and readily available ruthenium benzylidene complexes of the general type (RuCl2 (=CHPh)(L)(L')) (L, L' = P(cC5H9)3, PCy3 and/or a N-heterocyclic carbene) constitute a new class of catalyst precursors for atom transfer radical addition (ATRA, also called Kharasch addition) and atom transfer radical polymerisation (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the addition of carbon tetrachloride to methyl methacrylate and styrene in moderate to high yield (Table 1). They also promote the polymerisation of methyl methacrylate and styrene in a controlled way with good to excellent yields (Table 2). The ligands L (P(cC5H9)3, PCy3 and/or a N-heterocyclic carbene) play a particularly important role in determining the rate of the polymerisation. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that: 􀀀 The catalysts decompose quickly under ATRA and ATRP conditions; 􀀀 Polymerisations are mediated by both (RuCl2(=CHPh)(L)(L')) complexes and ruthenium species bereft of the benzylidene moiety. [less ▲]

New ruthenium catalysts bearing N-heterocyclic carbene ligands for ATRP

Poster (2003, May)

Stable nucleophilic N-heterocyclic carbenes (NHCs) are neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are better s- donors and they form ... [more ▼]

Stable nucleophilic N-heterocyclic carbenes (NHCs) are neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are better s- donors and they form stronger bonds to metal centers than most phosphines. Their electronic and steric properties are liable to ample modification simply by varying the substituents on the nitrogen atoms. Therefore, NHCs constitute a promising new class of ligands available for catalyst engineering and fine-tuning. We found that the 18-electron complex RuCl2(p-cymene)(PCy3) was a versatile and efficient promoter for ring-opening metathesis polymerization of both strained and low-strain cyclic olefins when activated by a suitable precursor such as trimethylsilyldiazomethane. This complex was also an excellent catalyst for ATRP (Atom Transfer Radical Polymerization) of MMA and styrene. In this poster, we present preliminary results obtained in olefin metathesis and in radical reactions (ATRP and Kharasch addition) when tricyclohexylphosphine was substituted by an N-heterocylic carbene ligand. [less ▲]

Tuning of ruthenium N-heterocyclic carbene catalysts for ATRP

in Chemical Communications (2003), (13), 1526-1527

Depending on the substituents, R-1 and R-2, ruthenium(II) - p-cymene complexes bearing N-heterocyclic carbene ligands are either efficient catalysts for the well-controlled atom transfer radical ... [more ▼]

Depending on the substituents, R-1 and R-2, ruthenium(II) - p-cymene complexes bearing N-heterocyclic carbene ligands are either efficient catalysts for the well-controlled atom transfer radical polymerisation of methyl methacrylate and styrene, or promote a redox-initiated free-radical process. [less ▲]

Atom Transfer Radical Polymerisation (ATRP) and Kharasch addition mediated by titanium-ruthenium bimetallic systems

Poster (2003)

Numerous studies have been directed towards the synthesis of early-late heterobimetallic complexes. Surprisingly, only few reports have been reported about their catalytic behaviour. However, their ... [more ▼]

Numerous studies have been directed towards the synthesis of early-late heterobimetallic complexes. Surprisingly, only few reports have been reported about their catalytic behaviour. However, their potential in homogeneous catalysis is enormous. Indeed, a co-operative work by the two metal centres in the complex may lead to new catalytic systems with unique reactivity. The Dijon’s team has concentrated their efforts on the synthesis and study of heterobimetallic complexes in which both metal fragments are known for their catalytic activity. Titanocenes are of considerable interest as catalysts for the polymerisation of a-olefins. The catalytic performance of RuCl2(arene) complexes (1) has been demonstrated in different reactions, including olefin metathesis and atom transfer radical polymerisation (ATRP). In attempts to examine such type of catalytic systems, complexation of bent titanocene metallo-ligands by the [RuCl2(p-cymene)]2 dimer is currently investigated. [less ▲]

Atom transfer radical polymerisation (ATRP) and Kharasch addition mediated by titanium-ruthenium bimetallic systems

Poster (2003)

New ruthenium catalysts bearing N-heterocyclic carbene ligands in Kharasch chemistry

Poster (2003)

New ruthenium catalysts bearing N-heterocyclic carbene ligands for ATRP

in e-polymers (2003)

New ruthenium catalysts bearing N-heterocyclic carbene ligands in Kharasch chemistry

Ruthenium alkylidenes: a new class of catalysts for Kharasch addition and controlled radical polymerisation of vinyl monomers

in e-polymers (2003)

Air-stable and readily available ruthenium benzylidene complexes of the general type (RuCl2 (=CHPh)(L)(L')) (L, L' = P(cC5H9)3, PCy3 and/or a N-heterocyclic carbene) constitute a new class of catalyst ... [more ▼]

Air-stable and readily available ruthenium benzylidene complexes of the general type (RuCl2 (=CHPh)(L)(L')) (L, L' = P(cC5H9)3, PCy3 and/or a N-heterocyclic carbene) constitute a new class of catalyst precursors for atom transfer radical addition (ATRA, also called Kharasch addition) and atom transfer radical polymerisation (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the addition of carbon tetrachloride to methyl methacrylate and styrene in moderate to high yield (Table 1). They also promote the polymerisation of methyl methacrylate and styrene in a controlled way with good to excellent yields (Table 2). The ligands L (P(cC5H9)3, PCy3 and/or a N-heterocyclic carbene) play a particularly important role in determining the rate of the polymerisation. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that: 􀀀 The catalysts decompose quickly under ATRA and ATRP conditions; 􀀀 Polymerisations are mediated by both (RuCl2(=CHPh)(L)(L')) complexes and ruthenium species bereft of the benzylidene moiety. [less ▲]

Controlled radical polymerization catalysed by ruthenium complexes: Variations on Ru-Cp#

in Matyjaszewski, K. (Ed.) Advances in Controlled/Living Radical Polymerization / ACS Symposium Series 854 (2003)

A series of isoelectronic ruthenium-based complexes of the general formula [RuX(Cp#)L2] (Cp# = cyclopentadienyl or cyclopentadienyl derivatives) were synthesized, and their relative catalytic activities ... [more ▼]

A series of isoelectronic ruthenium-based complexes of the general formula [RuX(Cp#)L2] (Cp# = cyclopentadienyl or cyclopentadienyl derivatives) were synthesized, and their relative catalytic activities were determined by monitoring the atom transfer radical polymerization of methyl methacrylate, n-butyl acrylate, and styrene. [RuCl(Cp*)(PPh3)2] and [RuCl(Ind)(PPh3)2] were found to be highly efficient catalysts for ATRP, producing polymers with narrow molecular weight distribution (Mw/Mn < 1.2). the following order of increasing efficiency was determined: [RuCl(Cp)(PPh3)2] << [RuCl(ind)(PPh3)2] < [RuCl(Cp*)(PPh3)2]. In sharp contrast, ruthena-carboranes were inefficient for ATRP, demonstrating therefore the prominent role of the Cp# ligand. The effect of the phosphine ligands was also investigated, and additional studies indicated that the release of a phosphine ligand occured prior to the activation of the carbon-halogen bond of both the initiator and polymer growing chain end by the unsaturated ruthenium center. [less ▲]

Controlled Radical Polymerisation catalysed by rutehnium complexes. Variations on Ru-Cp#

in ACS Symposium Series (2002, August)

series of isoelectronic ruthenium-based complexes of the general formula [RuX(Cp#)L2] (Cp# = cyclopentadienyl or cyclopentadienyl derivatives) were synthesized, and their relative catalytic activities ... [more ▼]

series of isoelectronic ruthenium-based complexes of the general formula [RuX(Cp#)L2] (Cp# = cyclopentadienyl or cyclopentadienyl derivatives) were synthesized, and their relative catalytic activities were determined by monitoring the atom transfer radical polymerization of methyl methacrylate, n-butyl acrylate, and styrene. [RuCl(Cp*)(PPh3)2] and [RuCl(Ind)(PPh3)2] were found to be highly efficient catalysts for ATRP, producing polymers with narrow molecular weight distribution (Mw/Mn < 1.2). the following order of increasing efficiency was determined: [RuCl(Cp)(PPh3)2] << [RuCl(ind)(PPh3)2] < [RuCl(Cp*)(PPh3)2]. In sharp contrast, ruthena-carboranes were inefficient for ATRP, demonstrating therefore the prominent role of the Cp# ligand. The effect of the phosphine ligands was also investigated, and additional studies indicated that the release of a phosphine ligand occured prior to the activation of the carbon-halogen bond of both the initiator and polymer growing chain end by the unsaturated ruthenium center. [less ▲]