Mary McPartlin

Mixed alkylamido aluminate as a kinetically controlled base.

The mechanisms by which directed ortho metalation (DoM) and postmetalation processes occur when aromatic compounds are treated with mixed alkylamido aluminate i-Bu3Al(TMP)Li (TMP-aluminate 1; TMP = 2,2,6,6-tetramethylpiperidide) have been investigated by computation and X-ray diffraction. Sequential reaction of ArC(=O)N(i-Pr)2 (Ar = phenyl, 1-naphthyl) with t-BuLi and i-Bu3Al in tetrahydrofuran affords [2-(i-Bu3Al)C(m)H(n)C(=O)N(i-Pr)2]Li x 3 THF (m = 6, n = 4, 7; m = 10, n = 6, 8). These data advance the structural evidence for ortho-aluminated functionalized aromatics and represent model intermediates in DoM chemistry. Both 7 and 8 are found to resist reaction with HTMP, suggesting that ortho-aluminated aromatics are incapable of exhibiting stepwise deprotonative reactivity of the type recently shown to pertain to the related field of ortho zincation chemistry. Density functional theory calculations corroborate this view and reveal the existence of substantial kinetic barriers both to one-step alkyl exchange and to amido-alkyl exchange after an initial amido deprotonation reaction by aluminate bases. Rationalization of this dichotomy comes from an evaluation of the inherent Lewis acidities of the Al and Zn centers. As a representative synthetic application of this high kinetic reactivity of the TMP-aluminate, the highly regioselective deprotonative functionalization of unsymmetrical ketones both under mild conditions and at elevated temperatures is also presented.

Improved syntheses of the hexanuclear clusters [Ru6(CO)18]2–, [HRu6-(CO)18]–, and H2Ru6(CO)18. The X-ray analysis of [HRu6(CO)18]–, a polynuclear carbonyl containing an interstitial hydrogen ligand

The X-ray analyses of two crystalline modifications, (I) and (II), of [N(PPh3)2][HRu6(CO)18] are reported, together with improved synthetic routes to this and the related clusters [Ru6(CO)18]2– and H2Ru6(CO)18. Crystals of (I) are triclinic, space group P1–, with a= 18.083(4), b= 19.101(4), c= 19.238(5)A, α= 117.70(4), β= 78.13(2), γ= 97.05(2)°, and Z= 4. Crystals of (II) are monoclinic, space group P21/n, with a= 33.82(8), b= 52.55(10), c= 9.832(2)A;, β= 92.66(2)°, and Z= 12. Least-squares refinement using diffractometer data (Mo-Kα) has given an R of 0.068 1 for 9 165 reflections for (I) and an R of 0.23 (Ru only) for 1 485 reflections for (II). The unit cell in (I) contains two independent molecules of [HRu6(CO)18]–, cluster (1) which is ordered and cluster (2) which is disordered between two sites (2A) and (2B) that are related by a non-crystallographic two-fold axis. The combined evidence of the X-ray analyses, 1H n.m.r. studies, i.r. [v(CO)] spectra, and variable-temperature 13C n.m.r. is only consistent with the hydrogen ligand lying inside the Ru6 octahedron.

Templating and Selection in the Formation of Macrocycles Containing [{P(μ-NtBu)2}(μ-NH)]n Frameworks: Observation of Halide Ion Coordination

Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported.

Carbide forming and cluster build-up reactions in ruthenium carbonyl cluster chemistry

Abstract The reinvestigation of an early synthesis of hexaruthenium carbido clusters has lead to the isolation of a number of new clusters which have been fully characterised by spectroscopic and crystallographic techniques. The thermolysis of Ru 3 (CO) 12 in the presence of mesitylene (1,3,5-trimethylbenzene) at moderate temperatures yields two new clusters, [Ru 6 (μ 4 -η 2 -CO) 2 (CO) 13 (η 6 -C 6 H 3 Me 3 )] (I) and [HRu 6 (μ 4 -η 2 -CO)(CO) 13 (μ 2 -η 7 -C 6 H 3 Me 2 CH 2 )] (II), the structures and reactivity of which indicate the origin and mechanism of formation of the carbido-carbon in the hexaruthenium carbido clusters [Ru 6 C(CO) 14 (η 6 -C 6 H 3 Me 3 )] (III) and [Ru 6 C(CO) 17 ] (IV). A further product of the reaction is the decaruthenium carbido cluster dianion [Ru 10 C(CO) 24 ] 2− (V) which has the tetracapped octahedral geometry. The monohydrido-cluster anion [HRu 10 C(CO) 24 ] − (VI) may be synthesised quantitatively from V by protonation. The nature of the hydrido-ligand in VI has been investigated in the solid state by NMR spectroscopy and it has been found to be fluxional, its location being temperature dependent. The decanuclear dianion V has been found to react with mercury salts to yield the 21 metal atom cluster dianion [Ru 18 Hg 3 C 2 (CO) 42 ] 2− (VII) which consists of two tricapped octahedral nonaruthenium “subclusters” fused by a bi-facecapping (Hg 3 ) 2+ unit.

Neutral gadolinium(III) complexes of bulky octadentate dtpa derivatives as potential contrast agents for magnetic resonance imaging

A series of bulky and neutral gadolinium complexes of [bis(R-amide)dtpaH3] (where R = Pri,, Bui,, Bz and phenylethyl, L1--L4)) with potential application as contrast agents for magnetic resonance imaging has been prepared and characterized ; the relaxivity of these complexes is comparable to the contrast agent [Gd(dtpa)(H2OO)]; which is which is currently used in clinics; the X-ray structure analysis of the gadolinium(III) complex of L3 reveals a neutral nine-coordinate complex featuring a water molecule in the tricapped trigonal prismatic metal coordination sphere.

The synthesis of [Ru5C(CO)15] by the carbonylation of [Ru6C(CO)17] and the reactions of the pentanuclear cluster with a variety of small molecules: the X-ray structure analyses of [Ru5C(CO)15], [Ru5C(CO)15(MeCN)], [Ru5C(CO)14(PPh3)], [Ru5C(CO)13(PPh3)2], and [Ru5(µ-H)2C(CO)12{Ph2P(CH2)2PPh2}]

The hexaruthenium cluster [Ru6C(CO)17] reacts with CO at 70 °C and 80 atm to produce [Ru5C(CO)15](1) and [Ru(CO)5]. Complex (1) crystallises in space group P21/c with a= 16.448(3), b= 14.274(2), c= 20.834(4)A, β= 91.36(2)°, and Z= 8. The structure was found to be isomorphous with the analogue [Os5C(CO)15], and was refined to R= 0.051 for 3 256 diffractometer data. The five Ru atoms adopt a square-pyramidal geometry with an exposed carbido-atom lying 0.11 (2)A beneath the basal plane. Reaction of complex (1) with the nitrogen-donor ligand MeCN yields the adduct [Ru5C(CO)15(MeCN)](2) which exhibits a bridged butterfly arrangement of metal atoms with a central carbido-atom. The complex crystallises in space group P21/n with a= 14.116(6), b= 18.167(7), c= 10.276(4)A, β= 95.14(3)°, and Z= 4; the structure was solved by direct methods and difference techniques and refined to R= 0.047 for 1 604 diffractometer data. Reactions of complex (1) with tertiary phosphine ligands PR3[R = Ph (3) or MePh2(4)] or Ph2P(CH2)nPPh2[n= 1 (5) or 2 (6)] produce the substituted complexes [Ru5C(CO)15-m(PR3)m][m= 1 (3a, 4a), 2 (3b, 4b), or 3 (3c, 4c)] or [Ru5C(CO)13{Ph2P(CH2)nPPh2}][n= 1 (5) or 2 (6)]. The structures of these complexes are closely related to that of (1). Complex (3a) crystallises in space group Pn with a= 9.953(2), b= 12.247(2), c= 14.703(3)A, β= 91.23(2)°, and Z= 2, (3b) in space group P21/c with a= 15.923(4), b= 12.494(3), c= 25.210(7)A, β= 93.28(2)°, and Z= 4. Both structures were solved by a combination of direct methods and Fourier techniques and were refined to R= 0.021 for 3 305 reflections (3a) and R= 0.039 for 4 127 reflections (3b), respectively. Hydrogenation of (6) gives the dihydro-complex [Ru5(µ-H)2C(CO)12{Ph2P(CH2)2Ph2}] which crystallises in space group P21 with a= 12.210(4), b= 18.602(6), c= 18.409(6)A, β= 97.63(2)°, and Z= 4. The structure was solved using the same techniques as the other complexes and refined to R= 0.064 for 3 510 diffractometer data. Treatment of complex (1) with halide ions gives the anionic clusters [Ru5C(CO)15X]–(X = F, Cl, Br, or I) whose structures are similar to that of (2). Protonation of these anions gives the monohydrido-clusters [Ru5H(C)(CO)15X]. With Cl2 and Br2 complex (1) undergoes fragmentation to give dimers [Ru2(CO)6X4](X = Cl or Br); in contrast, reaction with I2 gives [Ru5C(CO)15I2].

Cooperative reactivity of early-late heterodinuclear transition metal complexes with polar organic substrates

A comprehensive investigation into the cooperative reactivity of two chemically complementary metal-complex fragments in early-late heterodinuclear complexes has been carried out. Reaction of the partially fluorinated tripodal amidozirconium complexes [HC-(SiMe2NR)3Zr(mu-Cl)2Li(OEt2)2] (R = 2-FC6H4: 2a, 2,3,4-F3C6H4: 2b) with K[CpM(CO)2] (M=Fe, Ru) afforded the stable metal-metal bonded heterodinuclear complexes [HC[SiMe2NR]3-Zr-MCp(CO)2] (3-6). Reaction of the dinuclear complexes with methyl isonitrile as well as the heteroallenes CO2, CS2, RNCO and RNCS led to insertion into the polar metal-metal bond. Two of these complexes, [HC[SiMe2N(2-FC6-H4)]3Zr(S2C)Fe(CO)2Cp] (9a) and [HC-[SiMe2N(2-FC2H4)]3Zr-(SCNPh)Fe(CO)2-Cp] (12), have been structurally characterized by a single crystal X-ray structure analysis, proving the structural situation of the inserted substrate as a bridging ligand between the early and late transition metal centre. The reactivity towards organic carbonyl derivatives proved to be varied. Reaction of the heterobimetallic complexes with benzyl and ethylbenzoate led to the cleavage of the ester generating the respective alkoxozirconium complexes [HC[SiMe2N(2-FC6H4)]3ZrOR] (R = Ph-CH2: 13a, Et: 13b) along with [CpFe-[C(O)Ph](CO)2], whereas the analogous reaction with ethyl formate gave 13b along with [CpFeH(CO)2]; this latter complex results from the instability of the formyliron species initially formed. Aryl aldehydes were found to react with the Zr-M complexes according to a Cannizzaro disproportionation pattern yielding the aroyliron and ruthenium complexes along with the respective benzoxyzirconium species. The transfer of the aldehyde hydrogen atom in the course of the reaction was established in a deuteriation experiment. [HC[SiMe2-N(2-FC6H4)]3Zr-M(CO)2Cp] reacted with lactones to give the ring-opened species containing an alkoxozirconium and an acyliron or acylruthenium fragment; the latter binds to the early transition metal centre through the acyl oxygen atom, as evidenced from the unusuallly low-field shifted 13C NMR resonances of the RC(O)M units. Ketones containing a-CH units react with the Zr-Fe complexes cooperatively to yield the aldol coupling products coordinated to the zirconium complex fragment along with the hydridoiron compound [CpFeH(CO)2], whereas 1,2-diphenylcyclopropenone underwent an oxygen transfer from the keto group to a CO ligand to give a linking CO2 unit and a cyclopropenylidene ligand coordinated to the iron fragment in [HC-[Si(CH3)2N(2,3,4-F3C6H2)]3Zr(mu-O2C)-Fe(CO)[C3Ph2)Cp] (19). The atom transfer was established by 17O and 13C labelling studies. Similar oxygen-transfer processes were observed in the reactions with pyridine N-oxide, dimethylsulfoxide and methylphenylsulfoxide.

Chemistry of phosphido-bridged dimolybdenum complexes. Part 3. Reinvestigation of the reaction between [Mo2(η-C5H5)2(CO)6] and P2Ph4; X-ray structures of [Mo2(η-C5H5)2(µ-PPh2)2(CO)2], [Mo2(η-C5H5)2(µ-PPh2)2(µ-CO)], and trans-[Mo2(η-C5H5)2(µ-PPh2)2O(CO)]

The thermal reaction of [Mo2(η-C5H5)2(CO)2] with P2Ph2 in toluene gives [Mo2(η-C5H5)2(µ-PPh2)2-(CO)2] in high yield. An X-ray diffraction study shows a Mo–Mo double bond [2.712(2)A] symmetrically bridged by two PPh2 groups, with a planar Mo2P2 core. Under u.v. irradiation, further decarbonylation occurs to give [Mo2(η-C5H5)2(µ-PPh2)2(µ-CO)], in which two PPh2 groups and a carbonyl ligand bridge a Mo–Mo triple bond of length 2.515(2)A. Oxidation of either of these complexes gives cis- and trans-[Mo2(η-C5H5)2(µ-PPh2)2(CO)]; the structure of the trans isomer has been determined by X-ray diffraction. Protonation of [Mo2(η-C5H5)2(µ-PPh2)2(CO)2] occurs across the metal–metal bond to give [Mo2(η-C5H5)2(µ-H)(µ-PPh2)2(CO)2][BF4].

Single-source materials for metal-doped titanium oxide: Syntheses, structures, and properties of a series of heterometallic transition-metal titanium oxo cages

Titanium dioxide (TiO(2)) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)(4) with transition-metal dichlorides (M(II)Cl(2), M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti(4)O(OEt)(15)(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi(4)(μ(4)-O) structural arrangements involving ion pairing of [Ti(4)O(OEt)(15)](-) anion units with MCl(+) fragments. In the case of the reaction of MnCl(2), however, two Mn(II) ions are incorporated into this framework, giving the hexanuclear Mn(2)Ti(4)(μ(4)-O) cage [Ti(4)O(OEt)(15)(Mn(2)Cl(3))] (6) in which the MCl(+) fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl](+) unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)(4) with NiCl(2) gives [Ti(2)(OEt)(9)(NiCl)](2) (7), which has a dimeric Ni(μ-Cl)(2)Ni bridged arrangement arising from the association of [Ti(2)(OEt)(9)](-) ions with NiCl(+) units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials.

Extending the Family of Titanium Heterometallic–oxo–alkoxy Cages

Here we investigate the synthesis of high-nuclearity heterometallic titanium oxo-alkoxy cages using the reactions of metal chlorides with [Ti(OEt)(4)] or the pre-formed homometallic titanium-oxo-alkoxy cage [Ti(7)O(4)(OEt)(20)] (A). The octanuclear Ti(7)Co(II) cage [Ti(7)CoO(5)(OEt)(19)Cl] (1) (whose low-yielding synthesis we reported earlier) can be made in better yield, reproducibly by the reaction of a mixture of heptanuclear [Ti(7)O(4)(OEt)(20)] (A) and [KOEt] with [Co(II)Cl(2)] in toluene. A alone reacts with [Co(II)Cl(2)] and [Fe(II)Cl(2)] to form [Ti(7)Co(II)O(5)(OEt)(18)Cl(2)] (2) and [Ti(7)Fe(II)O(5)(OEt)(18)Cl(2)] (3), respectively. Like 1, compounds 2 and 3 retain the original Ti(7) fragment of A and the II-oxidation state of the transition metal ions (Tm). In contrast, from the reaction of [Ti(OEt)(4)] with [Cr(II)Cl(2)] it is possible to isolate [Ti(3)Cr(V)O(OEt)(14)Cl] (4) in low yield, containing a Ti(3)Cr(V) core in which oxidation of Cr from the II to V oxidation state has occurred. Reaction of [Mo(V)Cl(5)] with [Ti(OEt)](4) in [EtOH] gives the Ti(8)Mo(V)(4) cage [{Ti(4)Mo(2)O(8)(OEt)(10)}(2)] (5). The single-crystal X-ray structures of the new cages 2, 3, 4, and 5 are reported. The results show that the size of the heterometallic cage formed can be influenced by the nuclearity of the precursor. In the case of 5, the presence of homometallic Mo-Mo bonding also appears to be a significant factor in the final structure.