Leigh H. Rees

Synthesis and study of new binuclear compounds containing bridging (μ-CN)B(C6F5)3 and (μ-NC)B(C6F5)3 systems

The new compounds [K(18-crown-6)][SCNB(C6F5)3] (1), [K(18-crown-6)][(C6F5)3B(μ-NC)B(C6F5)3] (2), [K(18-crown-6)][NCB(C6F5)3] (3), [Me3Si(μ-NC)B(C6F5)3] (4) and [Hg{(μ-CN)B(C6F5)3}2] (5) have been synthesised. Reaction between [IrCl(PPh3)2(CO)] and one equivalent of 4 gives [Ir{(μ-NC)B(C6F5)3}(PPh3)2CO] (6). Similarly, the reaction between [Fe(η-C5H5)(CO)2Cl] and 4 gives [Fe{(μ-NC)B(C6F5)3}(η-C5H5)(CO)2] (7a). The NMR-scale reaction between [Fe(η-C5H5)(CO)2CN] and B(C6F5)3 gives the isomer [Fe{(μ-CN)B(C6F5)3}(η-C5H5)(CO)2] (7b). In the compounds 3, 4, 6 and 7a the anion [NCB(C6F5)3]− is coordinated to the metal through the nitrogen. Complexes 1, 2 and 7b incorporate a (μ-CN)B unit. The compounds containing the isomeric bridging (μ-CN)B or (μ-NC)B systems have been investigated by 11B{1H} NMR spectroscopy and by DFT calculations. The 11B{1H} NMR spectra enable distinction between the isomers. The single-crystal X-ray structures of 1, 3 and 7a have been determined.

Crystal structures of a series of CoII, CuII and ZnII complexes of 4′-(3,4-dihydroxyphenyl)-2,2′ : 6′,2″-terpyridine and 4′-(3,4-dimethoxyphenyl)-2,2′:6′,2″-terpyridine

Abstract The crystal structures of the bis(terpyridyl)-metal(II) complexes (Co(L 1 ) 2 ][PF 6 ] 2 · 2.5MeCN, [Co (L 2 ) 2 ][PF 6 ] 2 · 3dmf, [Cu(L 2 ) 2 ][PF 6 ] 2 · 2.5MeCN, and [Zn(L 2 ) 2 ][NO 3 ] 2 · 3dmf are reported, where L 1 is 4′-(3,4-dihydroxyphenyl)-2,2′ : 6′,2″-terpyridine and L 2 is 4′-(3,4-dimethoxyphenyl)-2,2′: 6′,2″-terpyridine. The two Co II complexes and the Cu II complex all show elongation along one axis in addition to the normal tetragonal compression imposed by terpyridyl chelates; this is ascribed to the Jahn-Teller effect, in the case of the Co II complexes arising from the presence of a significant proportion of the low-spin state being present at the temperature used for the structural determination (173 K). The Zn II complexes are the first structurally characterised bis(terpyridyl)-Zn II compounds. These do not show the elongation along one axis that was apparent in the Co II and Cu II structures. The relatively small bite angles for the terpyridyl chelates (ca. 150°, compared to ca. 160° for the first three complexes), results in a greater distortion away from regular octahedral geometry, reflecting the absence of stereoelectronic requirements for Zn II compared to Co II and Co II .

Making conjugated connections to porphyrins: a comparison of alkyne, alkene, imine and azo links

A series of porphyrins 5–9 has been prepared, in which an aryl substituent is linked to the porphyrin via azo, imine, alkene and alkyne bridges. The strength of aryl–porphyrin electronic coupling in these systems was evaluated from the red shift and intensification of the Q band absorption and emission spectra, and from the incremental red shift on changing from the phenyl to a 4-nitrophenyl substituent. The azo link provides the strongest electronic communication between the porphyrin and the benzene ring. The crystal structures of azo compounds 5a and 5c show that the porphyrin and benzene rings are almost coplanar, whereas imine 7a and alkene 8a are significantly twisted in the solid state. Imine and alkyne linked porphyrin dimers 18 and 23 were also synthesized; the alkyne-linked dimer is much more conjugated than its imine-linked analogue.

Dinuclear molybdenum and gadolinium complexes of new ‘back-to-back’ B–B linked bis[tris(pyrazolyl)borate] ligands

Some B–B linked ‘back-to-back’ bis[tris(pyrazolyl)borate] bridging ligands [(Rpz)3B–B(Rpz)3] (where Rpz is 3-R-pyrazolyl) have been prepared: when R=H or Me the ligands have two terdentate compartments, and have been used to prepare a variety of molybdenum complexes; when R=2-pyridyl, the ligand has two B–B linked hexadentate cavities which each bond a lanthanide(III) ion.

Monocyclopentadienyl complexes of niobium, tantalum and tungsten containing heterodifunctional P,O ligandsDedicated to Prof. P. Royo on the occasion of his 65th birthday, with our warmest congratulations.

The reactions of P,O type ligands with the half-sandwich complexes [(η-C5R5)MCl4] (R5 = H5, Me5, iPrH4; M = Nb, Ta, W) have been investigated. Monodentate P-adducts were obtained with the β-amidophosphine Ph2PCH2C(O)NPh2, whereas in the case of the keto ligand Ph2PCH2C(O)Ph a spontaneous HCl elimination occurred to give direct access to the corresponding phosphinoenolate complexes. The crystal structures of [(η-C5H5)NbCl3{PPh2CHC(O)Ph}], [(η-C5H5)TaCl3{PPh2CHC(O)Ph}] and [(η-C5Me5)TaCl3{PPh2CHC(O)Ph}] have been determined. Interestingly, the acetamido derived phosphine Ph2PNHC(O)Me afforded O-adducts, which is an unusual bonding mode for a P,O ligand.

Ruthenium(II) complexes of some new polynucleating ligands incorporating terpyridyl and macrocyclic aza-crown binding sites

A series of five new compounds has been prepared in which terpyridyl fragments are linked to hexadentate aza-crown macrocycles. Reaction of 1-aza-18-crown-6 (1,4,7,10,13-pentaoxa-16-azacyclooctadecane) and 1,10-diaza-18-crown-6 (1,4,10,13-tetraoxa-7,16-diazacyclooctadecane) with 4′-bromo-2,2′:6′,2″-terpyridine afforded macrocycles L1–L3 in which the aza-crown macrocycles are linked directly to the C4′ position of the terpyridyl groups via the macrocyclic N atoms. Compounds L1 and L2 contain a single macrocycle (1-aza-18-crown-6 or 1,10-diaza-18-crown-6 respectively) attached to a terpyridyl group, whereas L3 contains two terpyridyl groups attached to either end of a central 1,10-diaza-18-crown-6-unit. Alternatively, the aza-crown macrocycles reacted with 4′-[(4-bromomethyl)phenyl]terpyridine to give L4 and L5 in which the aza-crown fragments are separated from the terpyridyl fragments by tolyl spacers: L4 contains one macrocycle attached to a terpyridyl core, whereas L5(like L3) contains two terpyridyl binding sites attached to either end of a central 1,10-diaza-18-crown-6 unit. Reaction of these with [Ru(terpy)Cl3] afforded the complexes [Ru(terpy)L1][PF6]2, [Ru(terpy)L2][PF6]2, [{Ru(terpy)}2(µ-L3)][PF6]4, [Ru(terpy)(HL4)][PF6]3 and [{Ru(terpy)}2(µ-H2L5)][PF6]6, the last two having the aliphatic amine groups of the macrocycles protonated. The crystal structure of [(terpy)Ru(L2)Na(BF4)2][PF6]·1.5Me2CO {grown by recrystallising [Ru(terpy)L2][PF6]2 from a medium containing traces of NaBF4} shows that the pendant N2O4-donor macrocyclic group contains a sodium cation co-ordinated by five of the six macrocyclic donor atoms, and two additional monodentate BF4– ligands in axial positions. Significantly, the N atom of the macrocycle which is attached to the terpyridyl fragment is sp2-hybridised with trigonal geometry, which permits the lone pair, in a pz orbital, to conjugate with the π system of the terpyridyl fragment. This macrocylic amine group is therefore a poor base and is not co-ordinated to the sodium cation. The crystal structure of [{Ru(terpy)}2(µ-H2L5)][PF6]6·2MeCN confirms that the central macrocycle is doubly protonated, with the extra protons inside the macrocyclic cavity consistent with an endocyclic disposition of lone pairs. The electrochemical and UV/VIS spectroscopic properties of the complexes were also examined: in the dinuclear complexes there is no electrochemical interaction between the remote metal centres across the saturated bridging group.

Axial ligand substitution and photoisomerization reactions in ruthenium(II) trans mixed-chelate complexes containing the ligands 1,2-phenylenebis(dimethylarsine) and 2,2′-bipyridine or 1,10-phenanthroline

Abstract The nitrosyl complex in trans-[RuCl(pdma)(bpy)(NO)][PF6]2 (pdma=1,2-phenylenebis(dimethylarsine), bpy=2,2′-bipyridine) reacts at room temperature with stoichiometric NaN3, followed by an excess of a neutral ligand L1 in 2-butanone under reflux, to afford high yields of the mono-substituted derivatives trans-[RuCl(pdma)(bpy)L1]PF6 (L1=pyridine (py) 1, triphenylphosphine (PPh3) 2, N-methylimidazole (mim) 3, acetonitrile (MeCN) 4, dimethylsulfoxide (dmso) 5 or pyrazine (pyz) 6). The related compound trans-[RuCl(pdma)(phen)(NO)][PF6]2 (phen=1,10-phenanthroline) reacts similarly to yield trans-[RuCl(pdma)(phen)L1]PF6 (L1=py 8, PPh3 9, mim 10 or pyz 11). The pyrazine complexes in 6 and 11 react with MeI at room temperature in acetone to afford trans-[RuCl(pdma)(L–L)(mpyz+)][PF6]2 (mpyz+=N-methylpyrazinium, L–L=bpy 7 or phen 12, respectively). 3 reacts with an excess of a neutral ligand L2 in the presence of stoichiometric AgCF3CO2 in water/acetone under reflux to afford high yields of the di-substituted derivatives trans-[Ru(pdma)(bpy)mim(L2)][PF6]2 (L2=mim 13, py 14 or MeCN 15) and 2 reacts similarly with AgCF3CO2 in water/MeCN to give trans-[RuCl(pdma)(bpy)PPh3(MeCN)][PF6]2 (16). The complexes in 1–16 exhibit intense dπ(RuII)→π*(L–L) and dπ(RuII)→π*(L1/L2) (L1/L2=py, pyz or mpyz+) metal-to-ligand charge-transfer absorption bands in the near-UV–visible region and are mildly photosensitive in solution. Solar irradiation leads to isomerization; for example 3 is converted into cis-[RuCl(pdma)(bpy)mim]PF6 (17) over a period of ca. 100 h exposure to diffuse sunlight in acetone. Single crystal X-ray structures have been determined for 1, 2·DMF, 3, 12·3MeCN, 14·DMF and 17.

DERIVATIVES OF LUMINESCENT METAL-POLYPYRIDYL COMPLEXES WITH PENDANT ADENINE OR THYMINE GROUPS : BUILDING BLOCKS FOR SUPRAMOLECULAR ASSEMBLIES BASED ON HYDROGEN BONDING

Alkylation of adenine or thymine with 5-bromomethyl-2,2′-bipyridine afforded bipya and bipyt, in which a 2,2′-bipyridyl (bipy) is attached to the N 9 position of adenine or the N 1 position of thymine via a CH 2 spacer. Attachment of the bipy site of bipya to [Ru(bipy) 2 Cl 2 ] or [Ru(dbbipy) 2 Cl 2 ] [dbbipy = 4,4′-bis(tert-butyl)-2,2′ -bipyridine] gave the complexes [Ru(bipy) 2 (bipya)][PF 6 ] 2 and [Ru(dbbipy) 2 (bipya)][PF 6 ] 2 (Ru-Ade) respectively, in which an adenine fragment is pendant from the {Ru(bipy) 3 } 2+ core. Attachment of the bipy site of bipyt to [Os(dbbipy) 2 Cl 2 ] and [Re(CO) 5 Cl] afforded [Os(dbbipy)(bipyt)][PF 6 ] 2 (Os-Thy) and [Re(bipyt)(CO) 3 Cl] (Re-Thy) respectively, in which the {Os(bipy) 3 } 2+ and {Re(bipy)(CO) 3 Cl} cores have pendant thymine groups. Recrystallisation of [Ru(bipy) 2 (bipya)][PF 6 ] 2 from wet MeCN resulted in partial protonation to give [{Ru(bipy) 2 (bipya)}{Ru(bipy) 2 (Hbipya)}][PF 6 ] 5 ·4MeCN in which [Ru(bipy) 2 (bipya)] 2+ and protonated [Ru(bipy) 2 (Hbipya)] 3+ complex cations are associated by a Watson–Crick type hydrogen-bonding interaction between the adenine groups across an inversion centre. Similarly, in [Os(dbbipy) 2 (bipyt)][PF 6 ] 2 ·Me 2 CO there are two [Os(dbbipy) 2 (bipyt)] 2+ complex cations associated via a centrosymmetric thymine–thymine hydrogen-bonding interaction across an inversion centre. In contrast, in [Ru(dbbipy) 2 (bipya)][PF 6 ] 2 ·2MeCN the [Ru(dbbipy) 2 (bipya)] 2+ complex cations are associated via a Hoogsteen-type hydrogen-bonding interaction to give a one-dimensional ‘ribbon-like’ chain of hydrogen bonds. The electrochemical, UV/VIS spectroscopic and luminescence properties of the complexes are very similar to those of the parent unsubstituted complexes, indicating that the adenine or thymine substituents do not perturb the desirable properties of the complex cores. By monitoring the chemical shift of the thymine NH proton, NMR titrations allowed estimation of the association constants of the complementary Ru-Ade/Os-Thy pair in CD 3 CN and CD 2 Cl 2 as 60 and 123 dm 3 mol -1 respectively, and that of the Ru-Ade/Re-Thy pair in CD 3 CN as 17.9 dm 3 mol -1 . At the very low concentrations used for luminescence studies, these association constants are much too low to allow significant formation of hydrogen-bonded associates in mixtures of complementary complexes such as Ru-Ade/Os-Thy and Ru-Ade/Re-Thy. The requirements for observing energy-transfer across hydrogen-bonded bridges in associates of this type are discussed.

An unprecedented coordination mode for hemilabile pendant-arm 1,4,7-triazacyclononanes and the synthesis of cationic organoaluminium complexes

Reaction of AlMe3 or [AlMe3·py] with the pendant arm OH-funtionalised 1,4,7-triazacyclononane proligands, HL1 or HL2, affords the four- and five-coordinate derivatives [Al(L1)Me2] 1 or [Al2(L2)2Me4] 2 in which the pendant alkoxide O-donor and only one macrocycle N-donor is bound to Al; methyl anion abstraction from 1 yields cationic, pentacoordinate [Al(L1)Me]+ in which L1 has a tetradentate coordination mode [L1 = 1-(2-hydroxy-3,5-di-tert-butylbenzyl)-4,7-diisopropyl-1,4,7-triaz cyclononane; L2 = 1-(2-hy- droxy-2-methylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane].

Weakly-coordinating anions stabilise the unprecedented monovalent and divalent η-benzene nickel cations [(η-C5H5)Ni(η-C6H6)Ni(η-C5H5)]2+ and [Ni(η-C6H6)2]2+

Nickelocene in benzene reacts with the Bronsted acid H2O–B(C6F5)3 to give the salt [(η-C5H5)Ni(η-C6H6)Ni( η-C5H5)][B3(μ-O)3(C 6F5)5] which is the first example of a triple-decker nickel sandwich with a bridging η-benzene ligand; the borate anion is also unprecedented; treatment of Ni(η-C5H5)2 with Brookhart’s acid [H(OEt2)2][B(3,5-(CF3)2C6 H3)4] in benzene gives the paramagnetic bis(η-benzene)nickel derivative {[Ni(η-C6H6)2][B(3,5-(CF3 )2C6H3)4]2 ·Ni(η-C5H5)2} in which nickelocene is present as a molecule of crystallisation.