Andrew Carvill

Determination of the tacticity of ring‐opened metathesis polymers of norbornene and norbornadiene by 13C NMR spectroscopy of their hydrogenated derivatives

The 125 MHz 13 C nuclear magnetic resonance (NMR) spectra of the hydrogenated derivatives of ring-opened metathesis polymers (ROMP) of bicydo[2.2.1]hept-2-ene (norbornene) and bicydo[2.2.1]hepta-2,5-diene (norbornadiene) prepared using a range of initiators, have been analysed in detail. The signals due to the methylene carbon atoms in the enchained cyclopentyl rings of these polymers show fine structure which is assigned to m and r ring dyads and mm, mr/rm and rr ring triads, enabling the tacticity of the hydrogenated polymer, and thus of the polyolefin precursor, to be determined for high-cis or high-trans polymers. Novel methods for making high-cis polymers are described and solvent-dependent variations in the stereospecificity of the propagation reaction have been observed.

Synthesis and reactions of dimolybdenum(II,II), diruthenium(II,III) and dicopper(II,II) complexes containing unsaturated aliphatic carboxylate bridging ligands: X-ray crystal structure of [Ru2(μ-O2C(CH3)Cz.dbnd&2;CH2)4Cl]

Abstract Metathesis reactions were used to prepare dimolybdenum(II,II), diruthenium (II,III) and dicopper(II,II) tetra-μ-carboxylato complexes containing unsaturated aliphatic carboxylate ligands (O2CR) {R1 = HC:CH2, R2 = (CH3)C:CH2, R3 = H2CHC:CH2, R4 = C7H9, R5 = C8H11}. The X-ray crystal structure of [Ru2(μ-O2C(CH3)C:CH2)4Cl] (9) shows that there are two independent centrosymmetric Ru2L4 dimers in the unit cell, bridged by chlorine atoms to form an infinite polymeric chain. Principal dimensions are RuRu 2.287(1) and 2.290(1) A, RuCl 2.555(2) and 2.572(2) A, RuClRu 118.29(7)°. The terminal ethylene (:CH2) and methyl (CH3) groups of the ligand are mutually disordered. The bicyclo[2.2.1]hept-5-ene-2-carboxylato complexes [Mo2(μ-O2CR4)4] (3), [Ru2(μ-O2CR4)4Cl] (8) and [Cu2(μ-O2CR4)4] · 2H2O (14) were also synthesized by the Diels-Alder [4+21] cycloaddition reaction of cyclopentadiene with the respective propenoato complexes, [Mo2(μ-O2CR1)4] · 0.5H2O (2), [Ru2(μ-O2CR1)4Cl] · 2HO2CR1 (7) and [Cu2(μ-O2CR1)4] · 2H2O (13). The bicyclo[2.2.1]hept-5-ene-2-methyl-2-carboxylato complex, [Ru2(μ-O2CR5)4Cl] (10), was prepared by a similar cycloaddition route from [Ru2(μ-O2CR2)4Cl] (9). No Diels-Alder adducts were formed when cyclopentadiene was reacted with [Mo2(μ-O2CR2)4] · 0.5H2O (4), [Cu2(μ-O2CR2)4] · 2H2O, [Cu2(μ-O2CR3)4] · 2H2O and [Ru2(η-O2CR3)4Cl] (11).

Copolymerization of cycloalkenes as a probe of the propagation steps in olefin metathesis

Abstract A range of ring-opened metathesis copolymers of norbornene and cyclopentene have been prepared and 13 C NMR spectroscopy used to analyse in detail the nature of the homo and heterodyad units. This has provided significant new information on the sensitivity of the [2 + 2] cycloaddition step in metathesis to the steric and electronic factors associated with the [Mt]C and CC moieties involved. Novel very high cis directing catalyst systems, have also been developed for the homopolymerization of norbornene using various ethers with Mo and W-based catalyst systems or chelating dienes and phenylacetylene with RuCl 3 and OsCl 3 systems. The general feature of cis/trans blockiness at high cis content is investigated in much greater detail. A clearer description of the associated relaxation processes of the propagating species emerges from this work. The metathesis polymerization of the matched pair, benzonorbornadiene and 7-oxa-benzonorbornadiene has been investigated using Ru and Os-based initiators. The results illustrate the subtle way whereby the presence of the proximate 7-O-atom may facilitate [2 + 2] cycloadditions. This constitutes a valuable novel method of studying key electronic factors in the mechanism of the metathesis reaction.

Synthesis of water-soluble and ether-soluble tetra-μ-acetatodiruthenium(II,III) complexes and X-ray crystal structure of [Ru2(μ-O2CC6H5)4(C2H5OH)2][Ru2(μ-O2CC6H5)4(HSO4)2]

[Ru2(μ-O2CCH3)4Cl] reacts readily with aqueous Ag2SO4 (2: 1 molar ratio) to give the sulphate salt [Ru2(μ-O2CCH3)4(H2O)2]2(SO4) (1). Addition of NaBPh4 to an aqueous solution of 1 produces the ether-soluble tetraphenylborate salt [Ru2(μ-O2CCH3)4(H2O)2][BPh4] (2). A methanolic solution of 1 reacts with Ba(C6H5CCCO2)2 · H2O to give the tetraacetatemonophenylpropynoate complex [Ru2(μ-O2CCH3)4(O2CCCC6H5)] · H2O (3). The reaction of an ethanolic suspension of [Ru2(μ-O2CC6H5)4Cl] with Ag2SO4 and H2SO4 (2 : 1 : 1 molar ratio) leads to the tetra-μ-benzoatodiruthenium(II,III) double complex salt [Ru2(μ-O2CC6H5)4(C2H5OH)2][Ru2(μ-O2CC6H5)4(HSO4)2] (4). Complex 4 is also obtained by reacting an ethanolic solution of 1 with an excess of benzoic acid in the presence of H2SO4. The X-ray crystal structure of 4 shows it to consist of [Ru2(μ-O2CC6H5)4(C2H5OH)2]+ and [Ru2(μ-O2CC6H5)4(HSO4)2]− ions, which are linked together by hydrogen bonds into an infinite polymeric chain. The RuRu distances in the cation and anion are very similar [2.265(2) and 2.272(2) A, respectively]. Spectroscopic, magnetic, conductivity and cyclic voltammetry data are given for the complexes.

13C NMR spectra of tactic and atactic hydrogenated ring-opened polymers of enantiomeric and racemic endo,exo-5,6-dimethylnorbornene

Polymers 1 of the title monomer, prepared using well-defined molybdenum carbene complexes as catalysts, have been hydrogenated and the structures of the resultant polymers 2 examined by 13 C NMR spectroscopy. The hydrogenated polymer made from the all-cis isotactic polymer of (+)-monomer showed a single set of 13 C NMR lines as expected for an NX sequence of endo (N) and exo (X) substituents. The hydrogenated polymer made from a cis isotactic polymer of (±)-monomer showed additional fine structure arising from the random incorporation of both enantiomers in the isotactic polymer chain: four equal lines for C-9 (orientational triad sensitivity), two equal lines for C-3, C-4, C-5, and C-1 (dyad sensitivity), but single lines for C-8, C-2, C-7 and C-6 (insensitive to the relative orientation of adjacent repeating units). The hydrogenated polymer made from a trans atactic polymer of (+)-monomer showed fine structure due to the presence of both m and r dyads. That made from a trans atactic polymer of (±)-monomer contains 16 possible triad sequences and gave a more complicated spectrum. A complete assignment was made for the first three polymers and a partial assignment for the fourth. Polymers made using non-carbene catalysts were also examined. Hydrogenation of an all-trans precursor made from (±)-monomer using RuCl 3 as catalyst gave an atactic polymer, confirming previous observations. Hydrogenation of a 61% cis, cis/trans blocky precursor, made from (+)-monomer using OsCl 3 /PhC≡CH as catalyst, gave a syndiotactic-biased stereoblocky polymer, indicating a c/r, t/m correlation in the precursor polymer.

Alternating ring-opening metathesis copolymerization of bicyclo[2.2.1]hept-2-ene and cyclopentene

Almost alternating copolymers of bicyclo[2.2.1]hept-2-ene and cyclopentene have been formed by ring-opening metathesis polymerization using a RuCl3–phenol catalyst system; this highly novel result is attributed to differential steric influences exerted by a hydrogen-bonded solvent cage which encloses the catalyst site.

13C NMR spectra of hydrogenated polymers of exo-5-methyl-, endo-5-methyl-, and 5,5-dimethyl-derivatives of bicyclo[2.2.1]hept-2-ene prepared by ring-opening metathesis polymerization

13C NMR spectra of the three title polymers have been determined for polymers of different tacticities. Assignments to the various possible HH/HT/TT and m/r dyad structures were made. These were facilitated by the use of optically active monomers in the case of 1 and 3. In the precursor polymers the cis double bonds in the HH dyads were less readily hydrogenated than those in the other types of dyad. Methyl substitution parameters are summarized for the hydrogenated polymers and their unsaturated trans precursors.

Preparation of transition metal complexes of bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (C7H9CO2H) and X-ray crystal structure of [Cu2{(±)-endo-μ-O2CC7H9}4 (CH3OH)2]·2CH3OH

Metathesis reactions were used to prepare a range of dicopper(II), monocopper(I), diruthenium(II, III), dimolybdenum(II,II) and dirhodium(II,II) complexes of either racemic or resolved forms of endo- and exo-bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (C7H9CO2H). The X-ray crystal structure of [Cu2{(±)-endo-μ-O2CC7H9}4(CH3OH)2]·2CH3OH shows the two copper(II) ions bridged by two (+)-endo-bicyclo[2.2.1]hept-5-ene-2-carboxylate anions and two (−)-endo-bicyclo[2.2.1]hept-5-ene-2-carboxylate anions. Methanol molecules occupy the two trans axial sites, and there are also two methanol molecules hydrogen bonded to opposite carboxyl oxygens.

Fluxional behaviour of bis- and tris-(ether phosphine)ruthenium(II) chloro and acetato complexes

The syntheses of bis- and tris-[(2-methoxyethyl)diphenylphosphine]ruthenium(II) complexes with chloro, acetato, and trifluoroacetato ligands are described. The complexes are mer-[RuCl2(P–O)(PO)2], fac-[RuCl(P–O)2(PO)]X (X = Cl, SbF6, or BPh4), fac-[Ru(P–O)3][SbF6]2, [RuCl(P–O)2]SbF6, fac-[Ru(O2CCH3)2(PO)3], fac-[Ru(O2CCH3)(P–O)(PO)2]X (X = O2CCH3 or BPh4), [RuX2(O,P)2](X = O2CCH3 or O2CCF3), [RuCl(O2CCH3)(O,P)2] and mer-[RuH(O2CCH3)(PO)3]; PO represents the ligand which is co-ordinated via phosphorus only (ether function free), P–O ligand which is co-ordinated in the bidentate chelating mode via phosphorus and oxygen, and O,P is used where the mode of co-ordination is not certain. The mechanism of the fluxional behaviour of these complexes in solution has been investigated by the use of temperature-programmed 31P and 13C n.m.r. and by nuclear Overhauser enhancement spectroscopy 31P n.m.r. studies. Fluxional processes occur through exchange between the bidentate (P- and O-bonded) and the monodentate (P-bonded) co-ordination modes of the ether phosphine ligands, as the labile metal–oxygen bonds are broken and reformed. A second type of fluxional process is observed in the six-co-ordinate tris(ether phosphine) complexes due to Berry-type rearrangements of five-co-ordinate intermediates formed upon opening of a metal–oxygen bond. In several of the complexes both types of fluxional process are operating simultaneously. Other complexes show different types of fluxional behaviour in polar and in non-polar solvents, due to ionic dissociation of chloride and acetate ligands in the polar solvents. Some reactions of the complexes are also discussed.

Synthesis, spectroscopic, electrochemical, and magnetic properties of dimolybdenum(II,II), diruthenium-(II,III) and -(II,II) complexes containing bridging aspirinate (2-acetoxybenzoate) ligands

Carboxylate exchange reactions were used to prepare the dimolybdenum(II,II) tetra-aspirinate complex, [MO2(µ-asp)4](1), and the soluble aspirinate/trifluoroacetate, [Mo2(µ-asp)-(µ-O2CCF3)3]·2H2O (2)(asp = aspirinate = 2-acetoxybenzoate). Similar metathesis reactions were used for the synthesis of the diruthenium(II,III) complexes, [Ru2(µ-asp)4Cl](3), [Ru2(µ-asp)2(µ-O2CC6H5)2Cl]·H2O (4), and [Ru2(µ-asp)4(O2CCF3)]·2H2O (5). A methanolic solution of (3) reacts with an aqueous solution of AgNO3at 20 °C to give the Ru25+ nitrate/aspirinate, [Ru2(asp)4(NO3)]·H2O (6). When this reaction is repeated at 70 °C the Ru24+ nitroso/aspirinate, [Ru2(asp)4(NO)]·4H2O (7), is isolated. Complex (7) also formed when a methanolic solution of (6) was either refluxed (70 °C) for 3 h, or allowed to stand (20 °C) for a period of 3–4 weeks. The conversion of (3) and (6) into (7) represents a reduction of both the bimetallic core (Ru25+ to Ru24+) and the nitrate group (NO3–; to NO). Infrared absorption spectra, conductivity, cyclic voltammetry, and magnetic susceptibility data are given.