D. Vaughan Griffiths

Copper(II) nitrite complexes of tripodal ligands derived from 1,1,1-tris(2-pyridyl)methylamine

Copper nitrite complexes of stoichiometric formulae [Cu(NO2)nL] (n=1 or 2), where L is a Schiff base or amide derivative of 1,1,1-tris(2-pyridyl)methylamine, have been prepared and characterized. The crystal structures of the mononuclear Schiff base complex [Cu(NO2)2(tpmbz)] [tpmbz=(C5H4N)3CN=CHC6H5], the nitrite-bridged dinuclear Schiff base complex [{Cu(NO2)(tpmsal)}2]·Et2O [tpmsalH=(C5H4N)3CN=CHC6H4OH-2] and the polymeric amide complex [{Cu(NO2)(tpms)}n]·nH2O [tpmsH=(C5H4N)3CNHC(O)CH2CH2CO2H] are reported. Copper nitrite complexes of new Schiff base and amide ligands derived from 1,1,1-tris(2-pyridyl)methylamine have been prepared and characterized, including three X-ray crystal structures. The complexes have general formulae [Cu(NO2)nL] (n=1 or 2) and the nitrito ligands are coordinated through one or both O atoms.

The synthesis and crystal structures of the amide NS3 macrocycle L1, and the silver complexes [Ag(L1)]n[CF3SO3]n and of [Ag(L2)]2[CF3SO3]2(where L1=9-oxo-1,4,7-trithia-10-azacyclododecane andL2=7-oxo-2,5,11-trithia-8-azatetradecane-12-orthobenzenophane).

he free macrocycle, L 1 was prepared by caesium carbonate promoted ring closure of the free NS 3 dithiol with dibromoethane and crystallised from CDCl 3 . The X-ray structure shows exodentate orientation of the sulfur and nitrogen atoms. Reaction of silver triflate with 1 molar equivalent of L 1 in chloroform⧸methanol affords the homoleptic polynuclear species [ Ag( L 1 )] + n that shows (3+1) thioether coordination to each of the silver centres, with one sulphur donor of each macrocycle bridging between metal centres. The macrocycle is coordinated as a neutral ligand, with ligation occurring only through the sulphur atoms and the amide nitrogen remaining protonated and uncoordinated. Reaction between silver triflate and L 2 affords the dimeric species [ Ag L 2 ] 2 2 with coordination by the three sulphur donor atoms to the silver centre. Tetrahedral coordination is completed by an unexpected Ag–C interaction with the aromatic backbone. In both metal complexes, no interaction is observed between the silver atom and the amide nitrogen.

Solvent-mediated selective single and double ring-opening of N-tosyl-activated aziridines using benzylamine

An efficient methodology has been developed for the synthesis of a series of new diamine 2 and triamine ligands 3 for application in asymmetric catalysis via selective single or double ring-opening of tosylaziridines 1, which are derived from chiral pool amino acids. The selectivity of the ring-opening reaction is readily controlled by the solvent employed. Thus, in acetonitrile formation of secondary amines 2 occurs via a single ring-opening step, whilst in methanol the reactions proceed to give the tertiary amines 3 via the ring-opening of two aziridine molecules.

The synthesis of C2-symmetric 1,4,7-triazacyclononane ligands derived from chiral aziridines

An efficient synthetic route for the synthesis of C2-symmetric derivatives of 1,4,7-triazacyclononanes 14 from chiral pool amino acids has been developed. These investigations have shown that competitive formation of piperazines 7 occurs when inappropriate nitrogen protecting groups are employed. It is apparent that the formation of the piperazines occurs as a result of an intramolecular nucleophilic attack followed by a β-elimination. This appears to only be relevant for the formation of the [9]-N3 ring, as the larger [12]-N4 macrocycle, 11, is formed via a Richman–Atkins cyclisation in the presence of the same benzylic protected nitrogen atom. The single crystal X-ray structures of piperazine 7a and 1,4,7-triazacyclononanes 14a both reveal that weak intermolecular C–H⋯OS interactions occur in the solid state in these systems.

Fully polarizable QM/MM calculations: An application to the nonbonded iodine–oxygen interaction in dimethyl-2-iodobenzoylphosphonate

The compound dimethyl‐2‐iodobenzoylphosphonate is unusual in that it forms well‐ordered crystals that clearly show short iodine‐oxygen interactions in which both the iodine and the oxygen are in their normal oxidation states. These interactions were studied using a new hybrid quantum mechanical–molecular mechanical approach that employs a polarizable molecular mechanics component. The electric field at the molecular mechanics atoms was calculated from a distributed multipole expansion of the wave function; this induced dipoles on the molecular mechanics atoms. The electrostatic potential in a spherical shell around the induced dipoles was reproduced through induced charges on the atomic center and those bonded to it using an analytical (rather than numerical) procedure. The new atomic charges (induced charges plus permanent charges) were then able to interact with the quantum mechanical entity and polarize the wave function. The procedure was iterated to convergence. The calculations show that the iodine atom becomes more positive in the crystal environment (modeled by a chain of three molecules of dimethyl‐2‐iodobenzoylphosphonate). Thus, while the cooperative effects of the crystal environment may not be the only feature stabilizing this unusual interaction, they do play a significant role in reducing the otherwise unfavourable iodine–oxygen monopole–monopole interaction.

The reactions of trialkylsilyl-containing phosphites with electrophilic organic compounds

The reactions of silyl-containing phosphites with electrophilic alkynes and various carbonyl compounds have been investigated. The higher nucleophilicity of silyl phosphites, relative to the analogous trialkyl phosphites, and the ease with which transfer of a silyl group occurs from the initially formed quasi-phosphonium intermediates, has a significant impact both on the nature of the products formed and the conditions needed to bring about the reaction.

Binuclear complexes with ligands based on the 2,6-bis(diphenylphosphinomethyl)benzene framework. Syntheses and crystal structures of [Ir2Cl2(µ-CO){2,6-(Ph2PCH2)2C6H3S}2]·2CH2Cl2, [Ni2{2,6-(Ph2PCH2)2C6H4S}2][PF6]2·Et2O·0.5CH2Cl2 and [Rh2Cl2(CO)2{1,3-(Ph2PCH2)2C6H4}2]

The new binucleating phosphinothiolate proligand 2,6-(Ph2PCH2)C6H4SH (L3H) was prepared from bromo-2,6-dimethylbenzene in a 4 step synthesis. Reaction with [IrCl(CO)(PPh3)2] in MeCN gave the carbonyl and thiolate bridged dimer [Ir2Cl2(µ-CO)(L3)2]1. Reaction of [{RhCl(CO)2}2] with half an equivalent of L3H resulted in formation of the dimeric species [Rh2Cl(CO)2(L3)]2 with one bridging thiolate and one bridging chloride. The dimeric species [Ni2(L3)2]2+3 was formed in high yield from reaction of [NiCl2(PPh3)2] with L3H in MeCN. The diphosphine 1,3-(Ph2PCH2)2C6H4 (L4) gave the dimeric species [Rh2Cl2(CO)2(L4)2] 4 with [RhCl(CO)(PPh3)2] with no evidence for metallation at the bridging aryl group. The crystal structures of complexes 1, 3 and 4 are discussed.

Synthesis of technetium-99 nitrido complexes with chelating diphosphine and diimine ligands

The reaction of [TcNCl4]– with bidentate diphosphines P–P gives the cationic complexes [TcNCl(P–P)2]+[A]–[P–P = Ph2PCH2CH2PPh2 or Me2PCH2CH2PMe2(dmpe), A = BPh4 or PF6] in good yield. An analogous complex was prepared with Me2PCH2CH2NMe(CH2)3NMeCH2CH2PMe2 whereas the bulky Pri2PCH2CH2PPRi2(dippe) gave a binuclear complex [Tc2N2Cl4(dippe)2] which on the basis of 31P NMR spectroscopy has bridging chloride groups. An X-ray crystal structure of [TcNCl(dmpe)2][BPh4] revealed a distorted trans-octahedral geometry about technetium with an exceptionally long TcN bond distance of 1.853(6)A. Reaction of [TcNBr4]– with 2,2′-bipyridyl (bipy) in ethanol gives [TcNBr(bipy)2]2[TcBr4]. An X-ray crystal structure revealed a cis-octahedral structure for the nitrido-cation [TcN 1.621(20)A] with the novel tetrahedral tetrabromotechnetate(II) dianion.

Direct formation of λ5-phospholes from trialkyl phosphites and dimethyl acetylenedicarboxylate. Alkoxyphosphonium ylides as reactive intermediates and stable products

Trialkyl phosphites and dimethyl acetylenedicarboxylate react in toluene below –10 °C to form high yields of tetramethyl 1,1,1-trialkoxy-1λ5-phosphole-2,3,4,5-tetracarboxylates (3). These phospholes can either rearrange thermally to stable dialkoxyphosphonium ylides (4) or be converted by addition of hydrogen bromide to give stable tetramethyl 1-alkoxy-1-oxo-1H-1λ5-phosphole-2,3,4,5-tetra-carboxylates (5). The unstable trialkoxy [methoxycarbonyl-(1,2,3-trismethoxycarbonylcyclopropenyl)-methylene]phosphorane precursors of (3) can be formed almost quantitatively by carrying out the reaction in toluene below –50 °C.

Synthesis and characterisation of rhenium dithiocarbamate complexes.Crystal structures of[ReO{O(OH)C6H4}(S2CNEt2)2],[Re{PPh2(C6H4S-2)}2(S2CNEt2)]·Me2CO and[ReO{PPh(C6H4S-2)2}(S2CNEt2)]

The reaction of [Re 2 O 3 (S 2 CNEt 2 ) 4 ] with catechol in acetone yielded the dark orange complex [ReO{O(OH)C 6 H 4 }(S 2 CNEt 2 ) 2 ] 1. The crystal structure shows a distorted-octahedral geometry with the oxo group trans to the monodentate catecholate ligand. The Re–O (catechol) bond length is typical of a Re–O single bond and implies little trans influence of the oxo ligand. Reaction of [Re 2 O 3 (S 2 CNEt 2 ) 4 ] with 1,4-dihydroxybenzene yielded the red-brown dimer [{ReO(S 2 CNEt 2 ) 2 } 2 (C 6 H 4 O 2 -1,4)] 2, in which the dianionic ligand bridges two rhenium centres. With 2-amino-4-methylphenol [ReO(OC 6 H 3 NH 2 -2-Me-4)(S 2 CNEt 2 ) 2 ] 3 was obtained containing the ligand co-ordinated in a monodentate mode. Reaction of [Re 2 O 3 (S 2 CNEt 2 ) 4 ] with dithiolate proligands such as ethane-1,2-dithiol yielded [NEt 2 H 2 ][ReOL 2 ], L = C 2 H 4 S 2 -1,2 4, C 6 H 4 S 2 -1,2 5 or MeC 6 H 3 S 2 -3,4 6, where degradation of the dithiocarbamate ligands to form the diethylammonium counter ion occurs. Reaction of 1 with bidentate phosphines yielded green complexes of the general formula [Re(S 2 CNEt 2 ) 2 L][BPh 4 ], where L = Me 2 PCH 2 CH 2 PMe 2 7 or Ph 2 PCH 2 CH 2 PPh 2 8. These reactions can be contrasted to the inactivity of these phosphine ligands towards [Re 2 O 3 (S 2 CNEt 2 ) 4 ]. The reaction of [Re 2 O 3 (S 2 CNEt 2 ) 4 ] with the bidentate phosphinothiolate proligand PPh 2 (C 6 H 4 SH-2) in acetone at room temperature yielded the red-orange rhenium(III) complex [Re{PPh 2 (C 6 H 4 S-2)} 2 (S 2 CNEt 2 )]·Me 2 CO 9. The crystal structure revealed a distorted-octahedral geometry. The sulfur donors of the phosphinothiolate ligands adopt a cis configuration. Reaction of [Re 2 O 3 (S 2 CNEt 2 ) 4 ] with the tridentate phosphinothiolate proligand PPh(C 6 H 4 SH-2) 2 proceeded at room temperature to yield the red rhenium(V) complex [ReO{PPh(C 6 H 4 S-2) 2 }(S 2 CNEt 2 )] 10. Its crystal structure shows a distorted-octahedral geometry. Reaction of [Re 2 O 3 (S 2 CNEt 2 ) 4 ] with SiMe 3 Cl yielded the new rhenium(V) precursor [ReCl 2 (S 2 CNEt 2 ) 2 ][BPh 4 ] 11 which permits investigation into rhenium dithiocarbamate chemistry without an oxo core.