Andrew J. Scott

OXIDATIVE ADDITION OF BORON-BORON, BORON-CHLORINE AND BORON-BROMINE BONDS TO PLATINUM(0)

Abstract The synthesis and spectroscopic characterisation of the new diborane(4) compounds B2(1,2-O2C6Cl4)2 and B2(1,2-O2C6Br4)2 are reported together with the diborane(4) bis-amine adduct [B2(calix)(NHMe2)2] (calix=Butcalix[4]arene). B–B bond oxidative addition reactions between the platinum(0) compound [Pt(PPh3)2(η-C2H4)] and the diborane(4) compounds B2(1,2-S2C6H4)2, B2(1,2-O2C6Cl4)2 and B2(1,2-O2C6Br4)2 are also described which result in the platinum(II) bis-boryl complexes cis-[Pt(PPh3)2{B(1,2-S2C6H4)}2], cis-[Pt(PPh3)2{B(1,2-O2C6Cl4)}2] and cis-[Pt(PPh3)2{B(1,2-O2C6Br4)}2] respectively, the former two having been characterised by X-ray crystallography. In addition, the platinum complex [Pt(PPh3)2(η-C2H4)] reacts with XB(1,2-O2C6H4) (X=Cl, Br) affording the mono-boryl complexes trans-[PtX(PPh3)2{B(1,2-O2C6H4)}] as a result of oxidative addition of the B–X bonds to the Pt(0) centre; the chloro derivative has been characterised by X-ray crystallography.

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.

Synthesis, optical properties, crystal structures and phase behaviour of selectively fluorinated 1,4-bis(4′-pyridylethynyl)benzenes, 4-(phenylethynyl)pyridines and 9,10-bis(4′-pyridylethynyl)anthracene, and a Zn(NO3)2 coordination polymer

A series of selectively fluorinated and non-fluorinated rigid rods based on the 4-pyridylethynyl group, namely 1,4-bis(4′-pyridylethynyl)benzene (1a), 1,4-bis(4′-pyridylethynyl)tetrafluorobenzene (1b), 1,4-bis(2′,3′,5′,6′-tetrafluoropyridylethynyl)benzene (1c), 1,4-bis(2′,3′,5′,6′-tetrafluoropyridylethynyl)tetrafluorobenzene (1d), 9,10-bis(4′-pyridylethynyl)anthracene (2), 4-(pentafluorophenylethynyl)pyridine (3a) and 4-(phenylethynyl)tetrafluoropyridine (3b) were prepared in good yields using Pd/Cu-catalysed Sonogashira cross-coupling reactions and/or lithium chemistry involving nucleophilic aromatic substitution. UV-Vis absorption and fluorescence spectra for 1a–d and 2 are reported. The X-ray crystal structures of 1b, 1c, 2, 3a and 3b show a variety of packing motifs, none of which involve arene–perfluoroarene stacking. The phase behaviour of 1a–1c has been studied by differential thermal analysis and transmitted polarised light microscopy. Compound 1b exhibits an ordered phase between 227.6 and 272.5 °C which is either hexatic B or crystal B. A 1 ∶ 1 complex (4) between 1b and Zn(NO3)2 has been prepared; its crystal structure consists of zig-zag polymer chains held together by hydrogen bonds.

Control of single crystal structure and liquid crystal phase behaviour via arene–perfluoroarene interactions†

In contrast to the solid-state structures of the individual compounds, arene-perfluoroarene face-to-face stacking and C–H‥F–C in-plane interactions dominate the solid-state structure of 1∶1 co-crystals of 1,4-bis(phenylethynyl)-tetrafluorobenzene 1b and 1,4-bis(pentafluorophenylethynyl)- benzene 1c, with this supramolecular aggregation leading to the stabilisation of a nematic liquid crystalline phase.

ISOLATION AND STRUCTURAL CHARACTERIZATION OF NOVEL COMPOUNDS CONTAINING B4O2 RINGS

Two compounds containing planar six-membered B4O2 rings have been synthesized and characterized by X-ray crystallography, namely [B4O2(OH)(4)].[NH2Me2][Cl] and [B4O2(dab)(2)] (dab = 1,4-Bu-t-1,4-diazabutadiene), the former compound providing a model for one possible structure of boron monoxide. {BO}(x)

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.

1:1 Adducts of 4-picoline with methylcatecholborane and phenylcatecholborane

In the title compounds, 2-methyl-2-(4-methylpyridine)-1,3,2-benzodioxaborole, C 13 H 14 BNO 2 , and 2-(4-methylpyridine)-2-phenyl-1,3,2-benzodioxaborole, C 18 H 16 BNO 2 , boron has a distorted tetrahedral coordination geometry, the two O-B-C angles being greater and all other angles at boron smaller than the ideal tetrahedral value. Both structures contain two crystallographically independent molecules, and all corresponding geometrical parameters in them are essentially the same, except for minor torsional variations. Bond lengths involving boron are similar to those of related adducts of phenylcatecholborane, and longer than those in the parent compound itself and related compounds with trigonal planar boron.

2,3,5,6-Tetrakis[3,5-bis(trifluoromethyl)phenoxy]-2,5-bis(dimethylamino)2,3,5,6-tetrabora-1,4-dioxane diethyl ether 0.667-solvate.

The title compound, C(36)H(26)B(4)F(24)N(2)O(6).0.667C(4)H(10)O, has centrosymmetric tetraboradioxane molecules, half each of three of these comprising the asymmetric unit together with a molecule of diethyl ether. Disorder affects most of the CF(3) groups and one ethyl group of the solvent molecule. The B(4)O(2) rings are approximately planar and contain two B atoms with trigonal geometry and two with distorted tetrahedral geometry, the B-O bonds for the four-coordinate B atoms being longer than those for the three-coordinate B atoms. N-H...O hydrogen bonds link two of the crystallographically independent molecules together in chains, while the third molecule forms discrete trimolecular clusters with two solvent molecules via N-H...O hydrogen bonds. This is the first crystallographically characterized example of a tetrabora-dioxane molecule containing both four- and three-coordinate B atoms.

Neutral thiolates of antimony(III) and bismuth(III)

A range of bismuth(III) and antimony(III) thiolates, Bi(SR)3(R = C6F5, 4-MeC6H4, 2,6-Me2C6H3 or 3,5-Me2C6H3) and Sb(SR)3(R = 4-MeC6H4 or 3,5-Me2C6H3) has been synthesised and the structures of the two antimony complexes have been determined. Both structures reveal a trigonal-pyramidal antimony centre bonded to three thiolate groups with, for the 4-MeC6H4 complex, additional intermolecular Sb ⋯ S interactions and, for the 3,5-Me2C6H3 complex, intermolecular arene to antimony interactions. The syntheses and structures of the organotransition-metal complexes [Bi(SC6F5){M(CO)3(η-C5H5)}2](M = Mo or W) are also reported in which the bismuth centre is bonded to one SC6F5 group and two M(CO)3(η-C5H5) fragments with no short intermolecular interactions.