28 research outputs found
Synthesis and crystallographic studies of novel organotin acenaphthene compounds
Organic frameworks with rigid backbones, such as acenaphthene, are highly suitable for the study of interatomic interactions. The short ânaturalâ peri-distance (2.44 Ă
) and the rigidity of the aromatic system causes considerable steric strain between peri-substituted heteroatoms. As a consequence, substitution at both peri-positions leads to in- and out-of-plane distortions, which often result in buckling of the ring system. In order to relax this geometric strain, weak bonding interactions can also exist between the peri-substituents.
This thesis focuses on the synthesis, structural characterisation and investigation of a range of sterically crowded peri-substituted acenaphthene compounds. This involves the study of the acenaphthene geometry, through X-ray crystallography when different peri-substituents occupy the close 5,6-positions; our main focus is to study weak non-bonded interactions that can occur across the peri-gap, for example weakly attractive three-centre four-electron (3c-4e) type interactions which are known to prevail in such compounds under the appropriate conditions. Repulsion within these systems, resulting from the steric crowding of the peri-space is also investigated, employing changes in bond lengths, bay-region angle splay, displacement of atoms from the mean plane and central acenaphthene torsion angles to help quantify the degree of acenaphthene distortion, which are all conveniently probed by the peri-distance.
To this end we have synthesised a range of novel sterically crowded mixed bromo-tin acenaphthene derivatives (Chapter 3), chalcogen-tin acenaphthene molecules (Chapter 4), phosphorusâtin derivatives (Chapter 5) and a series of homologous tin-tin acenaphthenes (Chapter 6). All the compounds studied in this thesis were characterised by multinuclear NMR spectroscopy and X-ray crystallography in an effort to gain a greater understanding of the deformation that occurs when disparate functionalities are located in close proximity and explore the potential for weak non-covalent intramolecular interactions to occur
Nota del curatore
The authors thank EPSRC and NSERC (Canada) for financial support.Reactions of the dianion [Te(tBuN)P(Îź-NtBu)2P(NtBu)Te]2â with I2 or [Cp*RhCl2]2 unexpectedly produced complexes of the novel spirocyclic Te5 dianion [{tBuN(Te)P(Îź-NtBu)2P(Te)NtBu}2Îź-Te]2â, which is N,Nâ˛-coordinated to two Na+ ions in the disodium derivative and adopts a Te,Teâ˛,Teâ˛â˛-bonding mode in the Cp*Rh complex.PostprintPeer reviewe
A structural, spectroscopic and computational examination of the dative interaction in constrained phosphineâstibines and phosphineâstiboranes
This work was financially supported by the EPSRC and COST actions CM0802 PhoSciNet and CM1302 SIPs.A series of phosphineâstibine and phosphineâstiborane periâsubstituted acenaphthenes containing all permutations of pentavalent groups âSbClnPh4-n (5â9), as well as trivalent groups âSbCl2, âSb(R)Cl, and âSbPh2 (2â4, R = Ph, Mes), were synthesised and fully characterised including single crystal diffraction and multinuclear NMR. In addition, the bonding in these species was studied by DFT computational methods. The PâSb dative interactions in both series range from strongly bonding to non-bonding as the Lewis acidity of the Sb acceptor is decreased. In the pentavalent antimony series, a significant change in the PâSb distance is observed between âSbClPh3 and âSbCl2Ph2 derivatives 6 and 7, consistent with a change from a bonding to a non-bonding interaction in a response to relatively small change in Lewis acidity of the acceptor. In the SbIII series, two geometric forms are observed. The PâSb bond length in the SbCl2 derivative 2 is as expected for a normal (rather than a dative) bond. Rather unexpectedly, the phosphineâstiborane complexes 5â9 represent the first examples of Ď4PâĎ6Sb structural motif.PostprintPeer reviewe
Synthesis and characterization of novel organic heteroatom compounds from reaction of Woollinsâ Reagent with various organic substrates
A series of new selenium-containing heteroatom compounds were synthesized in good yields by the reactions of Woollinsâ reagent with various organic substrates such as cyclohexanamine, N-benzoylbenzamide, benzoic anhydride, 4-fluoro-N-(2-oxo-2-phenylethyl)benzamide, N-benzoylbenzamide, benzoic anhydride, 3-(bromomethyl)benzonitrile, 1,2-diphenylethane-1,2-diol and sodium alcoholate. Three representative X-ray structures are described.PostprintPostprintPeer reviewe
Spirocyclic, macrocyclic and ladder complexes of coinage metals and mercury with dichalcogeno P2N2-supported anions
Financial support from the EPSRC and NSERC (Canada) is acknowledged.Metathetical reactions of alkaliâmetal derivatives of the dianion [tBuN(Se)P(Îź-NtBu)2P(Se)NtBu]2â (2Se2â) with Ag(NHC)Cl, Ag[BF4], AuCl(THT) and HgCl2, as well as the reaction of 2S2â with AuCl(THT) were investigated. The observed products all incorporate the monoprotonated ligands 2SeHâ or 2SHâ in a variety of structural arrangements around the metal centres, including tetrameric and trimeric macrocycles [Ag and Au (E = Se)], a ladder (Au, E = S) and a spirocycle (Hg); the ladder contains both the dianion 2S2â and the monoanion 2SHâ as ligands linking three Au2 units. All complexes have been characterised in the solid state by single crystal X-ray analyses and in solution by multinuclear (1H, 31P and 77Se) NMR spectra.PostprintPeer reviewe
Sterically encumbered tin and phosphorus peri-substituted acenaphthenes
The work in this project was supported by the Engineering and Physical Sciences Research Council (EPSRC), EaStCHEM and the University of St Andrews.A group of sterically encumbered peri-substituted acenaphthenes have been prepared, containing tin moieties at the 5,6-positions in 1 â 3 ([Acenap(SnR3)2], Acenap = acenaphthene-5,6-diyl; R3 = Ph3 ( 1 ), Me3 ( 2 ); [(Acenap)2(SnMe2)2] ( 3 )) and phosphorus functional groups at the proximal peri-positions in 4 and 5 ([Acenap(PR2)(PiPr2)] R2 = Ph2 ( 4 ), Ph(iPr) ( 5 )). Bis(stannane) structures 1 â 3 are dominated by repulsive interactions between the bulky tin groups, leading to peri-distances approaching the sum of van der Waals radii. Conversely, the quasi-linear CPh-P¡¡¡P three-body fragments found in bis(phosphine) 4 suggest the presence of a lp(P)âĎ*(PâC) donorâacceptor 3c-4e type interaction, supported by a notably short intramolecular P¡¡¡P distance and notably large JPP through-space coupling (180 Hz). Severely strained bis(sulfides) 4-S and 5-S , experiencing pronounced in-plane and out-of-plane displacements of the exocyclic peri-bonds, have also been isolated following treatment of 4 and 5 with sulfur. The resulting nonbonded intramolecular P¡¡¡P distances, âź4.05 Ă
and âź12% longer than twice the van der Waals radii of P (3.60 Ă
), are among the largest ever reported peri-separations, independent of the heteroatoms involved, and comparable to the distance found in 1 containing the larger Sn atoms (4.07 Ă
). In addition we report two metal complexes with square planar [( 4 )PtCl2] ( 4-Pt ) and octahedral cis-[( 4 )Mo(CO)4] ( 4-Mo ) geometries. In both complexes the bis(phosphine) backbone is distorted, but notably less so than in bis(sulfide) 4-S . All compounds were fully characterized, and except for bis(phosphine) 5 , crystal structures were determined.PostprintPostprintPeer reviewe
Reactivity profile of a peri-substitution-stabilized phosphanylidene-phosphorane : synthetic, structural, and computational studies
The authors thank the EaStChem, EPSRC, and the COST actions CM0802 PhoSciNet and CM1302 SIPs for financial support.The reactions of peri-substitution-stabilized phosphanylidene-phosphorane 1 with [AuCl(tht)] or [PtCl2(cod)] afford binuclear complexes [((1)(AuCl)2)2] 2 and [((1)(PtCl2))2] 3, in which four electrons of the ligand are used in bonding to two metal atoms in the bridging arrangement. Reactions of 1 with [Mo(CO)4(nbd)] or (RhCl2Cp*)2 afford mononuclear complexes [(1)2Mo(CO)4] 4 and [(1)RhCl2Cp*] 5, in which two electrons of the ligand are used to form terminal complexes. Formation of these complexes disrupts the negative hyperconjugation at the PâP bond to various extents, which is mirrored by variations in their PâP bond distances (2.179(4)â2.246(4) Ă
). The PâP bond is ruptured upon formation of Pd diphosphene complex 6, which is likely to proceed through a phosphinidene intermediate. In air, 1 is fully oxidized to phosphonic acid 7. Reactions of 1 with chalcogens under mild conditions generally afford mixtures of products, from which the trithionated 8, dithionated 9, diselenated 10, and monotellurated 11 species were isolated. The bonding in the chalcogeno derivatives is discussed using DFT (B3LYP) and natural bond orbital analysis, which indicate a contribution from dative bonding in 8â10. The buttressing effect of the peri backbone is shown to be an essential factor in the formation of the single pushâdouble-pull bis(borane) 13. This is demonstrated experimentally through a synthesis parallel to that used to make 13, but lacking the backbone, which leads to different products. The PâP bond distances in the reported products, as well as additional species, are correlated with Wiberg bond indices, showing very good agreement for a variety of bonding modes, including the negative hyperconjugation.PostprintPostprintPeer reviewe
Synthesis and structural studies of peri-substituted acenaphthenes with tertiary phosphine and stibine groups
Two mixed peri-substituted phosphine-chlorostibines, Acenap(PiPr2)(SbPhCl) and Acenap(PiPr2)(SbCl2) (Acenap = acenaphthene-5,6-diyl) reacted cleanly with Grignard reagents or nBuLi to give the corresponding tertiary phosphine-stibines Acenap(PiPr2)(SbRRâ) (R, Râ = Me, iPr, nBu, Ph). In addition, the Pt(II) complex of the tertiary phosphine-stibine Acenap(PiPr2)(SbPh2) as well as the Mo(0) complex of Acenap(PiPr2)(SbMePh) were synthesised and characterised. Two of the phosphine-stibines and the two metal complexes were characterised by single-crystal X-ray diffraction. The peri-substituted species act as bidentate ligands through both P and Sb atoms, forming rather short Sb-metal bonds. The tertiary phosphine-stibines display through-space J(CP) couplings between the phosphorus atom and carbon atoms bonded directly to the Sb atom of up to 40 Hz. The sequestration of the P and Sb lone pairs results in much smaller corresponding J(CP) being observed in the metal complexes. QTAIM (Quantum Theory of Atoms in Molecules) and EDA-NOCV (Energy Decomposition Analysis employing Naturalised Orbitals for Chemical Valence) computational techniques were used to provide additional insight into a weak n(P)âĎ*(Sb-C) intramolecular bonding interaction (pnictogen bond) in the phosphine-stibines.Peer reviewe
Speckle-pattern visibility of light transmitted through a multimode optical fiber
We show that the reduction in visibility of the speckle pattern obtained from laser light that has been passed through a step-index light guide can be found from a knowledge of the model dispersion of the guide, and the bandwidth of the laser beam
Strategia graduale integrata in undici fasi: un approccio mimetico al processo di trasferimento nella didattica della traduzione
The work in this project was supported by the Engineering and Physical Sciences Research Council (EPSRC). M.B. wishes to thank EaStCHEM and the University of St Andrews for support.Three related series of periâsubstituted bis(tellurides) bearing naphthalene, acenaphthene and acenaphthylene backbones (Nap/Acenap/Aceyl(TeY)2 (Nap=naphthaleneâ1,8âdiyl N ; Acenap=acenaphtheneâ5,6âdiyl A ; Aceyl=acenaphthyleneâ5,6âdiyl Ay ; Y=Ph 1 ; Fp 2 ; Tol 3 ; Anâp 4 ; Anâo 5 ; Tp 6 ; Mes 7 ; Tip 8 ) have been synthesised and their solidâstate structures determined by Xâray crystallography. Molecular conformations were classified as a function of the two C9âCâTeâC(Y) dihedral angles (θ); in the solid all members adopt AB or CCt configurations, with larger Te(aryl) moieties exclusively imposing the CCt variant. Exceptionally large J(125Te,125Te) spinâspin coupling constants between 3289â3848â
Hz were obtained for compounds substituted by bulky Te(aryl) groups, implying these species are locked in a CCtâtype conformation. In contrast, compounds incorporating smaller Te(aryl) moieties are predicted to be rather dynamic in solution and afford much smaller J values (2050â2676â
Hz), characteristic of greater populations of AB conformers with lower couplings. This conformational dependence of throughâspace coupling is supported by DFT calculations.PostprintPeer reviewe