Edward G. Robins

Arene–perfluoroarene interactions in crystal engineering 8: structures of 1∶1 complexes of hexafluorobenzene with fused-ring polyaromatic hydrocarbons

A series of 1∶1 complexes of hexafluorobenzene (HFB) with naphthalene, anthracene, phenanthrene, pyrene and triphenylene were prepared and their X-ray crystal structures determined at low temperatures. Each structure contains infinite mixed stacks of alternating nearly-parallel molecules of HFB and arene, which display various ‘slip’ distortions and form different 3-dimensional motifs. The naphthalene, anthracene and pyrene complexes show polymorphism. Crystal packing of HFB complexes is compared with that of corresponding octafluoronaphthalene complexes. Ab initio DFT calculations on the infinite lattices give lattice parameters and ‘slip’ parameters in close agreement with the experimental crystal structures, while showing that intermolecular cohesion is predominantly of electrostatic, rather than van der Waals, origin.

Arene-perfluoroarene interactions in crystal engineering: structural preferences in polyfluorinated tolans

The compounds 4-ROC6F4CCPh (4) where R = Me (a), Et (b), Prn (c), Pri (d), Bun (e), n-C5H11 (f), PhCH2 (g), PhCH2CH2 (h), 4-MeC6H4 (i), 4-EtC6H4 (j) and menthyl (k), have been prepared by reaction of C6F5CCPh (3) with ROH in the presence of KOH, and characterised by NMR (1H, 13C, 19F) and mass spectroscopy. The single-crystal structures of PhCCPh·C6F5CCC6F5 (1∶2), 3 and 4a,c,d,f,g,i have been determined by X-ray diffraction at 120–160 K, and that of 3 also calculated by an ab initio pseudo-potential DFT method. The tolan moiety is nearly planar in each molecule except 4a, which has a Ph/C6F5 dihedral angle of 25.8°. The R group adopts an out-of-plane orientation except in 4f, where the n-pentyl chain is nearly coplanar with the C6F5 group at the cost of severe distortion of the C(ar)–C(ar)–O angles (which differ by 13.5°). The structures of 1∶2, 3 (pseudo-isomorphous with 1∶2), 4a, 4g (disordered) and 4i contain stacks of alternating arene and perfluoroarene moieties; 4c and 4d form discrete centrosymmetric dimers with arene/perfluoroarene overlap, while 4f forms infinite stacks without such overlap. Differential thermal analysis and transmitted polarised light microscopy revealed no liquid-crystalline behaviour of 3 and 4.

Polymer-supported phosphoramidites: Highly efficient and recyclable catalysts for asymmetric hydrogenation of dimethylitaconate and dehydroamino acids and esters

Abstract Several novel phosphoramidites have been prepared by reaction of the primary amines para -vinylaniline, ortho -anisidine, 2-methoxyphenyl(4-vinylbenzyl)amine, 8-aminoquinoline and 3-vinyl-8-aminoquinoline with ( S )-1,1′-bi-2-naphthylchlorophosphite, in the presence of base. Rhodium(I) complexes of these phosphoramidites catalyse the asymmetric hydrogenation of dimethylitaconate and dehydroamino acids and esters giving ee values up to 95%. Soluble non-cross linked polymers of the para -vinylaniline and 3-vinyl-8-aminoquinoline-based phosphoramidites have been prepared by free radical co-polymerisation with styrene in the presence of AIBN as initiator. The corresponding [Rh(COD)] + complexes serve as recyclable catalysts for the asymmetric hydrogenation dimethylitaconate and dehydroamino acids and esters to give ee values up to 80%.

Selectivity for the methoxycarbonylation of ethylene versus COethylene copolymerization with catalysts based on C4-bridged bidentate phosphines and phospholes

Abstract The C 4 -bridged phospholes 11,12-bis(2,3,4,5-tetramethylphospholylmethyl)-9,10-dihydro-9,10-ethano-anthracene ( cis , 4a ; trans , 4b ) and diphosphines 11,12-bis(diphenylphosphinomethyl)-9,10-dihydro-9,10-ethano-anthracene ( cis , 5a ; trans , 5b ) and their corresponding palladium complexes [(PP)PdCl 2 ] ( 6a – d ) have been prepared and characterized. Single-crystal X-ray analyses of 6a – d have been undertaken and they reveal that 4a and b and 5a and b coordinate in a bidentate manner forming seven-membered chelate rings with natural bite angles between 98.62 and 100.30°. The palladium-catalyzed carbonylation of ethylene has been studied using 4a and b and 5a and b . Catalyst mixtures generated from 4a and b , palladium acetate and methanesulfonic acid are selective for the copolymerization of ethylene with carbon monoxide, generating low molecular weight polymers. Surprisingly, the activity of catalyst systems based on cis -( 4a ) is markedly higher than that based on its trans -isomer, 4b . The marked influence of the nature of the four-carbon tether is highlighted by comparative catalyst testing with [{1,4-bis(2,3,4,5-tetramethylphospholyl)butane}Pd(OAc) 2 ], which rapidly decomposes under the conditions used for copolymerization. In contrast, under identical conditions catalyst mixtures formed from 5a and b show a marked dependence of the selectivity on the stereochemistry of the ethano-anthracene tether, the former generating a low molecular weight copolymer while the latter generate mainly methyl propanoate. Interestingly, polyketone generated from catalysts based on bisphosphole 4a has a markedly higher average molecular weight than that formed using its diphenylphosphino counterpart, 5a .

Synthesis, characterisation and molecular structure of [Rh(COE)2(acac)] (COE=cyclooctene, η2-C8H14), an important starting material for the preparation of rhodium catalyst precursors

Abstract The compound [Rh(COE) 2 (acac)] ( 1 ) is a catalyst precursor in its own right, and a starting material for the preparation of other catalyst precursors for use in a variety of reactions such as hydroboration, diboration and the addition of arylboronic acids to aldehydes. Although a preparation using Tl(acac) and [Rh(COE) 2 (μ-Cl)] 2 is in the literature, it would appear that it is not widely known and we have received several requests for our synthetic protocol for 1 , which does not use any thallium salts. We present herein a synthesis of 1 from [Rh(COE) 2 (μ-Cl)] 2 and Na(acac), along with its full spectroscopic and structural characterisation. The single crystal X-ray structure of 1 indicates approximate square-planar geometry at Rh, with the two olefinic CC bonds lying perpendicular to the square plane.

Rhodium catalysed diboration of unstrained internal alkenes and a new and general route to zwitterionic [L2Rh(η6-catBcat)] (cat = 1,2-O2C6H4) complexes†

Reactions of [L2Rh(acac)] (L = alkene or phosphine) with B2cat3 yield the zwitterionic complexes [L2Rh(η6-catBcat)] and [(acac)Bcat] cleanly; [(dppm)Rh(η6-catBcat)], the X-ray structure of which is reported, is an excellent catalyst for the diboration of vinylarenes and unstrained internal alkenes cis- and trans-stilbene and trans-β-methylstyrene.

Boron–boron bond oxidative addition to rhodium(I) and iridium(I) centres

The reaction between the diborane(4) compound B2(1,2-O2C6H4)2 and either of the rhodium(I) complexes [RhCl(PPh3)3] or [{Rh(µ-Cl)(PPh3)2}2] afforded the colourless rhodium(III) bis(boryl) species [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Similar reactions have been carried out with the diborane(4) compounds B2(1,2-O2-4-ButC6H3)2, B2(1,2-O2-3,5-But2C6H2)2, B2(1,2-O2-3-MeC6H3)2, B2(1,2-O2-4-MeC6H3)2, B2(1,2-O2-3-MeOC6H3)2, B2(1,2-S2C6H4)2, B2(1,2-S2-4-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 affording analogous rhodium complexes all of which have been characterised spectroscopically. The complexes derived from the reactions with B2(1,2-O2C6H4)2 and B2(1,2-O2-3-MeC6H3)2 have also been characterised by X-ray crystallography, the structures comprising a five-co-ordinate rhodium centre with a square-based-pyramidal geometry in which the apical site is occupied by a boryl group and the phosphines are mutually trans in basal positions. Reactivity studies have also been carried out for [RhCl(PPh3)2{B(1,2-O2C6H4)}2]. Hydrolysis or alcoholysis with catechol afforded [RhH2Cl(PPh3)3] and either B2(1,2-O2C6H4)2(µ-O) or B2(1,2-O2C6H4)3 and addition of the phosphines PMe3, PEt3 and PMe2Ph afforded the new bis(boryl) compounds cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2], [RhCl(PEt3)2{B(1,2-O2C6H4)}2] and cis,mer-[RhCl(PMe2Ph)3{B(1,2-O2C6H4)}2], the PEt3 complex having been characterised by X-ray crystallography and shown to be similar to the PPh3 complex. The iridium analogue [IrCl(PEt3)2{B(1,2-O2C6H4)}2] was also prepared from the reaction between [IrCl(PEt3)3] and B2(1,2-O2C6H4)2 and shown by X-ray crystallography to be isomorphous with the rhodium complex. Reactions between [RhCl(PPh3)2{B(1,2-O2C6H4)}2] and the phosphines PPri3, P(C6H11)3, 1,2-bis(diphenylphosphino)ethane (dppe) and 1,2-bis(dicyclohexylphosphino)ethane (dcpe) are also described although these do not result in new rhodium boryl complexes. The reaction between [{RhCl(dppe)}2] and B2(1,2-O2C6H4)2 afforded a compound tentatively assigned as [Rh(dppe)2{B(1,2-O2C6H4)}] with analogous compounds being formed with the diborane(4) compounds B2(1,2-O2-3-MeC6H3)2 and B2(1,2-O2-4-MeC6H3)2. Finally, the reaction between [Rh(PMe3)4]Cl and the diborane(4) compound B2(1,2-O2C6H4)2 is described which affords cis,mer-[RhCl(PMe3)3{B(1,2-O2C6H4)}2]. Analogous reactions with B2(1,2-O2-3,5-But2C6H2)2, B2(1,2-O2-3-MeC6H3)2 and B2[R,R-1,2-O2CH(CO2Me)CH(CO2Me)]2 afforded similar products.

Reaction between rhodium(iii) bisboryls and diborane(4) compounds: evidence for a ς-bond metathesis process

The rhodium bis(boryl) complex [RhCl(PPh 3 ) 2 {B(cat)} 2 ] (cat = 1,2-O 2 C 6 H 4 ) reacts with the diborane(4) compounds B 2 (O 2 R) 2 {O 2 R = 1,2-O 2 C 6 H 3 Me-4, 1,2-O 2 C 6 H 2 Bu t 2 -3,5 and dimethyl-L-tartrate [OCH(CO 2 Me)CH(CO 2 Me)O]} affording unsymmetrical metal bis(boryls) [RhCl(PPh 3 ) 2 {B(cat)}{B(O 2 R)}] and diborane(4) compounds (cat)B–B(O 2 R), one possible mechanism for which involves ς-bond metathesis.