Leslie D. Field

Rhodium(I) and iridium(I) complexes containing bidentate phosphine-imidazolyl donor ligands as catalysts for the hydroamination and hydrothiolation of alkynes

A series of novel cationic and neutral rhodium and iridium complexes containing bidentate phosphine-imidazolyl donor ligands of the general formulae [M(ImP)(COD)]BPh(4) (M = Rh, ImP = ImP2, 3; ImP1a, 4a; ImP1b, 4b and M = Ir, ImP = ImP2, 5; ImP1a, 6a and ImP1b, 6b), [Ir(ImP)(CO)(2)]BPh(4) (ImP = ImP2, 7; ImP1a, 8a and ImP1b, 8b), [Rh(ImP1b)(CO)(2)]BPh(4) (10b) and [M(ImP)(CO)Cl] (M = Rh, ImP = ImP2, 11; ImP1b,12 and M = Ir, ImP = ImP2, 13; ImP1b, 14 ) where COD = 1,5-cyclooctadiene, ImP2 = 1-methyl-2-[(2-(diphenylphosphino)ethyl]imidazole, 1; ImP1a = 1-methyl-2-[(diphenylphosphino)methyl]imidazole, 2a and ImP1b = 2-[(diisopropylphosphino)methyl]-1-methylimidazole, 2b were successfully synthesised. The solid state structures of 3, 6a, 11 and 12 were determined by single crystal X-ray diffraction analysis. A number of these complexes are effective as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. The cationic complexes are significantly more effective than analogous neutral complexes. The cationic iridium complex 8b , containing the phosphine-imidazolyl ligand with the bulky isopropyl groups on the phosphorus donor, is more efficient than analogous complexes with the phenyl substituents on the phosphorus donor atom, 7 and 8a. The complexes 7-8b are also moderately effective in catalysing the addition of thiophenol to a range of terminal alkynes. In contrast to the hydroamination reaction, placement of the isopropyl group on the phosphorus donor leads to a decrease in the reactivity of the resulting metal complexes as catalysts for the hydrothiolation reaction.

Rhodium(I) and iridium(I) complexes with bidentate N,N and P,N ligands as catalysts for the hydrothiolation of alkynes

Cationic iridium(I), rhodium(I) complexes containing bis(1-methylimidazol-2-yl)methane, bim, [M(bim)(CO)2]BPh4 (M = Ir (1), Rh (2)); bis(pyrazol-1-yl)methane, bpm, [M(bpm)(CO)2]BPh4 (M = Ir (3), Rh (4)) have been shown to be effective in catalysing the regioselective addition of thiophenol to a series of alkynes. Analogous cationic and neutral Ir(I), Rh(I) complexes with the novel mixed P,N-donor bidentate ligand 1-(2-diphenylphosphino)ethylpyrazole, PyP (5), [M(PyP)(COD)]BPh4 (M = Ir (6), Rh (7), COD = 1,5-cyclooctadiene); [Rh(PyP)(COD)]BF4 (8); [Ir(PyP)(CO)2]BPh4 (9); [Rh(PyP)(CO)2]BF4 (10); [M(PyP)(CO)Cl] (M = Ir (11), Rh (12)) have also been synthesised, and characterised by NMR. The solid-state structures of (6), (7), (11) and (12) have been determined by single-crystal X-ray diffraction analysis. The metal complexes (9)–(12) with the mixed P,N-donor ligand, PyP are in most cases more effective in promoting the hydrothiolation of alkynes in comparison with the analogous complexes (1)–(4) with N,N-donor ligands. The iridium complexes were significantly more effective than their rhodium analogues in promoting the hydrothioloation of alkynes. The cationic complexes (9) and (10) are more effective as catalysts for the hydrothiolation of alkynes than their neutral analogues (11) and (12).

Cyclisation of acetylenic carboxylic acids and acetylenic alcohols to oxygen-containing heterocycles using cationic rhodium(I) complexes

Abstract Square planar cationic rhodium(I) dicarbonyl complexes [{Rh((mim) 2 CH 2 )(CO) 2 } + BPh 4 − ] ( 1 ) and [{Rh((mBnzim) 2 CH 2 )(CO) 2 } + BPh 4 − ] ( 2 ) [mim= N -methylimidazol-2-yl, mBnzim= N -methylbenzimidazol-2-yl] are catalysts for the cyclisation of alkynoic acids to lactones. The unsaturated acids, 4-pentynoic acid, 4-hexynoic acid and 5-hexynoic acid were cyclised to γ-methylene-γ-butyrolactone, E -5-ethylidenetetrahydro-2-furanone and 6-methylidenetetrahydo-2-pyrone, respectively. Cyclisation of 4-hexynoic acid proceeds stereoselectively with exclusive formation of the E -isomer of 5-ethylidenetetrahydro-2-furanone. Complexes 1 and 2 also catalyse cyclisation of acetylenic alcohols to oxygen-containing heterocycles.

Base-Mediated Conversion of Hydrazine to Diazene and Dinitrogen at an Iron Center

The treatment of the hydrazine complex cis-[Fe(N(2)H(4))(dmpe)(2)](2+) with base afforded the diazene complex cis-[Fe(N(2)H(2))(dmpe)(2)]. This reaction is reversed by the treatment of the diazene complex with a mild acid, while treatment of the hydrazine complex with a mixture of KOBu(t) and Bu(t)Li afforded the dinitrogen complex [Fe(N(2))(dmpe)(2)].

The first side-on bound metal complex of diazene, HN[double bond]NH.

The side-on bound metal complex of diazene cis-[Fe(NH[double bond]NH)(dmpe)(2)] was synthesised by reaction of [Fe(dmpe)(2)Cl(2)] with hydrazine in the presence of potassium graphite and characterised by (15)N NMR spectroscopy and X-ray crystallography.

Catalytic hydrosilylation of acetylenes mediated by phosphine complexes of cobalt(I), rhodium(I), and iridium(I)

Abstract The complexes [Co(PPh 3 ) 3 Cl] ( 1 ), [Co(PPh 3 ) 2 (CO) 2 Cl] ( 2 ), [Co(PMe 3 ) 3 Cl] ( 3 ), [Co(PMe 3 ) 2 (CO) 2 Cl] ( 4 ), [Rh(dppe)(CO)Cl] ( 5 ), [Rh(PPh 2 Me) 2 (CO)Cl] ( 6 ), [Ir(dppe)(CO)Br] ( 7 ), and [Ir(PPh 2 Me) 2 (CO)Cl] ( 8 ) catalyse the hydrosilylation of a range of acetylenes including 1-hexyne, phenylacetylene, and 1-phenyl-1-propyne with triethylsilane. In the case of 1-hexyne and 1-phenyl-1-propyne, only the expected hydrosilylation products were observed; however, when the substrate was phenylacetylene, cyclotrimerisation and dimerisation products were observed in addition to the expected vinylsilanes. No hydrosilation was observed with alkene substrates; however, in the presence of some metal complexes, there was double bond migration and cis / trans -isomerisation probably mediated by the formation of metal hydrides in the reaction mixture.

Iron(0) and ruthenium(0) complexes of dinitrogen

The synthesis of a series of iron and ruthenium complexes with the new ligand PP(i)(3) (1) P(CH(2)CH(2)P(i)Pr(2))(3) is described. The iron(0) and ruthenium(0) dinitrogen complexes Fe(N(2))(PP(i)(3)) (4) and Ru(N(2))(PP(i)(3)) (5) were synthesized by treatment of the iron(II) and ruthenium(II) cationic species [FeCl(PP(i)(3))](+) (2) and [RuCl(PP(i)(3))](+) (3) with potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N(2))H(PP(i)(3))](+) (6) and [Ru(N(2))H(PP(i)(3))](+) (7) were prepared by treatment of 4 and 5, respectively, with 1 equiv of a weak organic acid. Complexes 2.[BPh(4)], 3.[BPh(4)], 4, 5, and 6.[BF(4)] were characterized by X-ray crystallography. The structural characterization of 5 is the first report for a ruthenium(0) dinitrogen complex.

Rhodium complexes containing bidentate imidazolyl ligands : synthesis and structure

The preparation and characterisation of square planar cationic rhodium(I) dicarbonyl complexes {[Rh((mim) 2 CO)(CO) 2 ] + BPh 4 − ] ( 1 ),{[Rh((mim) 2 CH 2 )(CO) 2 ] + BPh 4 − } ( 2 ) and{[Rh((mBnzim) 2 CH 2 )(CO) 2 ] + BPh 4 − } ( 3 ) [mim= N -methylimidazol-2-yl, mBnzim= N -methylbenzimidazol-2-yl] is reported. The carbonyl ligands in 2 and 3 are readily exchanged for triphenylphosphine to form{[Rh((mim) 2 CH 2 )(PPh 3 ) 2 ] + BPh 4 − } ( 7 ) and {[Rh((mBnzim) 2 CH 2 )(PPh 3 ) 2 ] + BPh 4 − } ( 8 ). Complexes 2 and 3 were characterised by multinuclear NMR spectroscopy as well as by X-ray crystallography. Structural characterisation by X-ray analysis confirmed that complexes 2 and 3 are essentially square planar.

Electrochemistry of acetylide complexes of iron

Abstract The synthesis of a symmetrical acetylide-bridged, diiron(II) complex, ClFe(DMPE) 2 (CCC 6 H 4 CC)-(DMPE) 2 FeCl ( 1 ) (DMPE = bis(dimethylphosphine)ethane) is reported. Electrochemistry and EPR spectroscopy are used to examine the redox properties of 1 as well as the mononuclear iron(II) complexes Fe(DMPE) 2 Cl 2 ( 2 ), ClFe(DMPE) 2 (CCPh) ( 3 ), and Fe(DMPE) 2 (CCPh) 2 ( 4 ). Evidence for the corresponding iron(III) and iron(IV) species is provided. The structural rearrangements accompanying redox changes are discussed on the basis of the electrochemical characteristics. The electrochemical behaviour of the bridged diiron species 1 provides evidence that the two metal centres interact electronically.

Mechanochemistry of some hydrocarbons

Abstract Aromatic hydrocarbons (biphenyl, naphthalene, anthracene and phenanthrene) were subjected to ball milling (SPEX® 8000) with approximately ten-fold weight of inorganic materials (alumina or silica). After about 24 h all of the hydrocarbons were converted largely to carbon (graphite), but at intermediate stages disproportionation products (tetralin, phenylcyclohexane, bicyclohexyl, 9,10-dihydroanthracene, 1,2,3,4-tetrahydroanthracene, 1,2,3,4,4a,9,9a,10-octahydroanthracene, 1,2,3,4,5,6,7,8-octahydroanthracene, 9,10-dihydrophenanthrene, 1,2,3,4-tetrahydrophenanthrene, 1,2,3,4,4a,9,9a,10-octahydrophenanthrene, 1,2,3,4,5,6,7,8-octahydrophenanthrene) were also obtained in significant yields.