Reactions of complexes [MoX{q-C,( CF3)2}2(q-C5Hs)] with certain dienes give the paramagnetic complexes [MoX,(q-diene)(q-C,H,)][diene = 1,3-butadiene, X = CI ( l a ) , Br ( l b ) , or I ( l c ) ; diene = isoprene, X = CI (2); diene = trans-l,3-pentadiene, X = CI (3)] characterised by elemental analysis, i.r. spectroscopy, and mass spectrometry. The structure of (1 a), determined from 2 71 6 observed reflections measured at 185 K and refined to R = 0.0367 (R' = 0.0532), shows a molecule of near Cs symmetry. The cyclopentadienyl ligand is distorted from regular q5 bonding by slippage of the Mo atom across the ring by 0.1 2 A towards q3 co-ordination. The 1,3-butadiene adopts a cis-endo configuration with internal C-C bonds shorter by 0.045 A than terminal C-C bonds; the Mo-C bonds are shorter to terminal than to internal C atoms, and the butadiene is tilted away from a parallel geometry to assume a configuration with Mo which approaches a metallacyclopentene unit. Extended-Huckel molecular orbital (EHMO) calculations on complex (1 a) are presented and confirm the stability of the endo conformation relative to the ex0 form (85 k J mol-'). A by-product in the formation of complex ( l a ) is [Mo,(p-CI) (p3-O){p3-0,~:q2:q2-C4(CF3),}(q-C,H,),], (4)' which has been structurally characterised as its 0.5C,H6 solvate by X-ray diffraction. The structure has been refined t o R = 0.0377 (R' = 0.0488) using 4 21 5 data recorded at 185 K. A flattened isosceles triangle of metal atoms, base ca. 2.90 A, base-apex ca. 2.58 A, is face-capped by 0 and (open) edge-bridged by CI. The C,(CF,), unit is symmetrically bonded to the opposite Mo, face to the capping 0 atom, in a 2 0 + 47t bonding mode. EHMO calculations suggest some multiple character for the base-apex Mo-Mo bonds, but little direct bonding between the basal atoms. Complex ( l a ) is interconverted with TI(SR) into [Mo(SR),(q-C,H,)(q-C,H,)][R = C,H,Me-4 (5a) (72%) or C,F5 (5b) (1 5%)], characterised by analysis and spectroscopy. Cyclic voltammetric studies on complexes ( l a ) , (5a), and (5b) establish a reversible reduction process in both tetrahydrofuran and dichloromethane, and also more complex oxidations. The most easily reduced complex is (5b), whereas (5a) is most readily oxidised. Complexes (1) and (5) all show e.s.r. spectra in solution with hyperfine coupling to 9 5 p 9 7 M ~ and to ligand nuclei of 35r37Cl, 7g*e1Br, and diene terminal 'H atoms. E.s.r. spectra of these complexes in frozen 2-methyltetrahydrofuran are also presented. The e.s.r. results are discussed in relation to the electronic structures of the complexes, especially the nature of the singly occupied molecular orbital, as determined by EH M O calculations on complex (1 a). Co-ordinatively unsaturated alkyne complexes of the typeJ and corresponding tungsten(I1) species have been the subjects of a number of studies. It has been established that such complexes undergo substitution reactions at ligand X , ' T ~ to form binuclear complexes with alkyne-bridged metal-metal bonds and are attacked at the co-...
Diacetylenes containing an anhydride function (1) or two s-triazine groups (2) precipitate from organic solvents in large helical or cylindrical forms, respectively, which have been studied by optical and scanning electron microscopy. X-ray diffraction studies on helices of 10,12-tricosadynoic anhydride, {n-C10H21C⋮CC⋮C(CH2)8CO}2O (1), show a lamellar crystalline phase with layer spacing of 42.5 ± 0.5 Å and support a noninterdigitated bilayer structure. The crystal structure of a related amphiphilic diacetylene, n-C10H21C⋮CC⋮C(CH2)8CH2OSO2C6H4Me-4 (3), is also reported and discussed: triclinic, P1̄, a = 5.9730(10) Å, b = 8.0690(10) Å, c = 29.524(3) Å; α = 95.020(10)°, β = 93.260(10)°, γ = 97.480(10)°. The nonamphiphilic, α,ω-difunctionalized diacetylene, 6,6‘-(deca-4,6-diyne-1,10-diyl)di-2,4-diamino-1,3,5-triazine, 2-{4,6-(NH2)2C3N3}(CH2)3C⋮CC⋮C(CH2)3-{C3N3(NH2)2-4,6}-2 (2), forms solid cylindrical particles of mean length ∼0.5 mm, which may derive from helix formation. The origin of macroscopic chirality in the solid-state morphology of the achiral anhydride (1) is discussed.
Reactions of 2-hydroxymethylbenzyl halides with Pd(PPh 3 ) 4 afford complexes Pd(CH 2 C 6 H 4 -2-CH 2 OH-κ 2 C 1R ,O)(PPh 3 )X (X ) Br, 3; X ) Cl, 4) containing bidentate 2-hydroxymethylbenzyl ligands. Further reactions of 3 or 4 with NaH produce the binuclear cyclocondensation product Pd 2 (µ-2-OCH 2 C 6 H 4 CH 2 ) 2 (PPh 3 ) 2 , 7, containing a central planar Pd 2 O 2 unit incorporated into a system of five fused rings. Compound 7 undergoes phosphine substitution to form related binuclear products Pd 2 (µ-2-OCH 2 C 6 H 4 CH 2 ) 2 (PAr 3 ) 2 {Ar ) p-MeC 6 H 4 , 8; p-(MeO)-C 6 H 4 , 9} but is cleaved by more electron-donating phosphines and by diphosphines to give mononuclear alkoxides Pd(OCH 2 C 6 H 4 CH 2 -κ 2 C 1R ,O)(P-P) (P-P ) dppf, 10; dppe, 11). Compounds 3, 4, and 7-9 react readily with carbon monoxide to liberate the lactone 3-isochromanone via carbonyl insertion, and the acyl intermediate PdCl(COCH 2 C 6 H 4 -2-CH 2 -OH)(PPh 3 ), 12b, has been studied spectroscopically. Reactions of 2-halogenobenzenealkanols with Pd(PPh 3 ) 4 afford simple derivatives with monodentate aryl ligands, trans-Pd(C 6 H 4) and the known complex (n ) 1, X ) I, 14), which on reaction with NaH are also converted into binuclear products Pd 2 (µ-2-O(CH 2 ) n C 6 H 4 ) 2 (PPh 3 ) 2 {n ) 1, 19a (previously reported) and n ) 2, 20}; compound Pd 2 (µ-2-OCH 2 C 6 H 4 ) 2 {P(C 6 H 4 -4-OMe) 3 } 2 , 25, is formed from 19a by phosphine exchange, and cleavage of 19a or 20 by diphosphines generates new mononuclear complexes 22-24 containing chelating alkoxide ligands. Carbonylations of these arylpalladium derivatives of 2-hydroxyalkylphenyl halides to form the respective benzolactones, phthalide and 3,4dihydroisocoumarin, have been investigated. Crystal structures of mononuclear compounds 3, 4, 14, and 17, including intermolecular H-bonding interactions to halogen ligands in the solid state, and of binuclear compounds 7, 8, and 25 are reported and discussed. The new complexes are discussed in relation to the mechanism of Pd(0)-catalyzed syntheses of benzolactones from aromatic halo alcohols; in production of 3-isochromanone, the results support a process involving coordination of a hydroxyl group prior to reductive elimination of organic product but with CO insertion into the Pd-C rather than the Pd-O bond.
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