Quasi-three-coordinate iron and cobalt terphenoxide complexes {Ar(iPr8)OM(µ-O)}2 (Ar(iPr8) = C6H-2,6-(C6H2-2,4,6-(i)Pr3)2-3,5-(i)Pr2; M = Fe or Co) with M(III)2(µ-O)2 core structures and the peroxide dimer of 2-oxepinoxy relevant to benzene oxidation.

The bis(µ-oxo) dimeric complexes {Ar(iPr8)OM(µ-O)}2 (Ar(iPr8) = C6H-2,6-(C6H2-2,4,6-(i)Pr3)2-3,5-(i)Pr2; M = Fe (1), Co (2)) were prepared by oxidation of the M(I) half-sandwich complexes {Ar(iPr8)M(η(6)-arene)} (arene = benzene or toluene). Iron species 1 was prepared by reacting {Ar(iPr8)Fe(η(6)-benzene)} with N2O or O2, and cobalt species 2 was prepared by reacting {Ar(iPr8)Co(η(6)-toluene)} with O2. Both 1 and 2 were characterized by X-ray crystallography, UV-vis spectroscopy, magnetic measurements, and, in the case of 1, Mössbauer spectroscopy. The solid-state structures of both compounds reveal unique M2(µ-O)2 (M = Fe (1), Co(2)) cores with formally three-coordinate metal ions. The Fe···Fe separation in 1 bears a resemblance to that in the Fe2(µ-O)2 diamond core proposed for the methane monooxygenase intermediate Q. The structural differences between 1 and 2 are reflected in rather differing magnetic behavior. Compound 2 is thermally unstable, and its decomposition at room temperature resulted in the oxidation of the Ar(iPr8) ligand via oxygen insertion and addition to the central aryl ring of the terphenyl ligand to produce the 5,5'-peroxy-bis[4,6-(i)Pr2-3,7-bis(2,4,6-(i)Pr3-phenyl)oxepin-2(5H)-one] (3). The structure of the oxidized terphenyl species is closely related to that of a key intermediate proposed for the oxidation of benzene.

New insights into structure and luminescence of Eu(III) and Sm(III) complexes of the 3,4,3-LI(1,2-HOPO) ligand.

We report the preparation and new insight into photophysical properties of luminescent hydroxypyridonate complexes [M(III)L](-) (M = Eu or Sm) of the versatile 3,4,3-LI(1,2-HOPO) ligand (L). We report the crystal structure of this ligand with Eu(III) as well as insights into the coordination behavior and geometry in solution by using magnetic circular dichroism. In addition TD-DFT calculations were used to examine the excited states of the two different chromophores present in the 3,4,3-LI(1,2-HOPO) ligand. We find that the Eu(III) and Sm(III) complexes of this ligand undergo a transformation after in situ preparation to yield complexes with higher quantum yield (QY) over time. It is proposed that the lower QY in the in situ complexes is not only due to water quenching but could also be due to a lower degree of f-orbital overlap (in a kinetic isomer) as indicated by magnetic circular dichroism measurements.

A transition metal Lewis acid/base triad system for cooperative substrate binding.

A frustrated Lewis pair accessory functionality is positioned in the secondary coordination sphere of a terpyridine ligand (Tpy(BN) = 6-morpholino-2,2':6',2″-terpyridine-6″-boronic acid pinacol ester) to promote directed Lewis acid/base interactions. Following metalation with VCl3, the utility of the metal Lewis acid/base triad (LABT) is highlighted with N2H4 as a cooperatively coordinated substrate, affording the first η(2)-[N2H3](-) vanadium complex.

Uranyl sequestration: synthesis and structural characterization of uranyl complexes with a tetradentate methylterephthalamide ligand.

Uranyl complexes of a bis(methylterephthalamide) ligand (LH(4)) have been synthesized and characterized by X-ray crystallography. The structure is an unexpected [Me(4)N](8)[L(UO(2))](4) tetramer, formed via coordination of the two MeTAM units of L to two uranyl moieties. Addition of KOH to the tetramer gave the corresponding monomeric uranyl methoxide species [Me(4)N]K(2)[LUO(2)(OMe)].

Terphenyl substituted derivatives of manganese(II): distorted geometries and resistance to elimination.

Reaction of {Li(THF)Ar'MnI(2)}(2) (Ar' = C(6)H(3)-2,6-(C(6)H(2)-2,6-(i)Pr(3))(2)) with LiAr', LiC≡CR (R = (t)Bu or Ph), or (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) afforded the diaryl MnAr'(2) (1), the alkynyl salts Ar'Mn(C≡C(t)Bu)(4){Li(THF)}(3) (2) and Ar'Mn(C≡CPh)(3)Li(3)(THF)(Et(2)O)(2)(µ(3)-I) (3), and the manganate salt {Li(THF)}Ar'Mn(µ-I)(C(6)H(2)-2,4,6-(i)Pr(3)) (4), respectively. Complex 4 reacted with one equivalent of (C(6)H(2)-2,4,6-(i)Pr(3))MgBr(THF)(2) to afford the homoleptic dimer {Mn(C(6)H(2)-2,4,6-(i)Pr(3))(µ-C(6)H(2)-2,4,6-(i)Pr(3))}(2) (5), which resulted from the displacement of the bulkier Ar' ligand in preference to the halogen. The reaction of the more crowded {Li(THF)Ar*MnI(2)}(2) (Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)) with Li(t)Bu gave complex Ar*Mn(t)Bu (6). Complex 1 is a rare monomeric homoleptic two-coordinate diaryl Mn(II) complex; while 6 displays no tendency to eliminate ß-hydrogens from the (t)Bu group because of the stabilization supplied by Ar*. Compounds 2 and 3 have cubane frameworks, which are constructed from a manganese, three carbons from three acetylide ligands, three lithiums, each coordinated by a donor, plus either a carbon from a further acetylide ligand (2) or an iodide (3). The Mn(II) atom in 4 has an unusual distorted T-shaped geometry while the dimeric 5 features trigonal planar manganese coordination. The chloride substituted complex Li(2)(THF)(3){Ar'MnCl(2)}(2) (7), which has a structure very similar to that of {Li(THF)Ar'MnI(2)}(2), was also prepared for use as a possible starting material. However, its generally lower solubility rendered it less useful than the iodo salt. Complexes 1-7 were characterized by X-ray crystallography and UV-vis spectroscopy. Magnetic studies of 2-4 and 6 showed that they have 3d(5) high-spin configurations.

Unusual magnetic properties of a two-coordinate heteroleptic linear cobalt(II) complex.

The synthesis and characterization of two-coordinate cobalt(ii) complexes CoAr'(2) (1) and Ar'CoN(SiMe(3))(2) (2) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) are reported. The magnetic data for 2 show that it has an unexpectedly high mu(eff) of 5.65 mu(B) whereas the bent complex 1 has a significantly lower moment.

Synthesis, characterization, and magnetism of divalent aryl transition-metal complexes of the simplest dialkylamide, NMe(2): rare T-shaped coordination at chromium.

The synthesis and characterization of a series of first-row aryl transition metal derivatives of the simplest dialkylamido ligand NMe(2) are reported. The complexes Cr{Ar'Cr(mu-NMe(2))(2)}(2) (1) and {Ar'M(mu-NMe(2))}(2) (M = Mn (2), Fe (3); Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)) were obtained by reaction of the aryl metal halides {Ar'M(mu-X)}(2) (M = Cr, X = Cl; M = Fe, X = Br) or {Li(THF)Ar'MnI(2)}(2) with LiNMe(2) in a 1:2 ratio. A similar reaction of {Ar(#)Co(mu-I)}(2) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2)) and LiNMe(2) in hexanes gave the unusual complex {Ar(#)Co(mu-I)(eta(1)-CH(2) horizontal lineNCH(3))}(2) (4), in which the NMe(2) ligand is dehydrogenated to afford a complexed imine. Complexes 1-4 were characterized by X-ray crystallography, UV-vis spectroscopy, and magnetic measurements. In the unique trinuclear complex 1, the central chromium(II) ion is bound to four NMe(2) groups in a square planar fashion. The NMe(2) groups also bridge to the two outer chromium(II) ions, which are bound to a terminal Ar' group to yield a rare example of three-coordinate T-shaped geometry at these atoms. In the dimers 2 and 3, each metal center is coordinated to a terminal terphenyl ligand and two bridging NMe(2) groups to give a distorted trigonal planar geometry. In contrast, the reaction of LiNMe(2) with {Ar(#)Co(mu-I)}(2) in a 2:1 ratio did not yield an amido product; instead, the NMe(2) ligand underwent hydrogen elimination. As a result, in the dimeric structure of 4, each cobalt ion is coordinated to a terphenyl ligand, two bridging iodides, and a neutral methylimine ligand, CH(2) horizontal lineNCH(3), to yield a very distorted tetrahedral cobalt(II) coordination environment. The magnetic properties of 1-4 revealed antiferromagnetic exchange coupling between the metal ions with J = -47(1) cm(-1) and J(13) = -25(1) cm(-1) for 1, J = -38(1) cm(-1) for 2, J = -75(3) cm(-1) for 3, and J = -32(4) cm(-1) for 4; the latter compound exhibited an unusually large temperature independent contribution to its molar magnetic susceptibility.

Two-coordinate, homoleptic manganese(II) primary terphenyl amido complexes: the effects of secondary coordination on geometry and Lewis base complexation.

The synthesis and characterization of the mononuclear manganese primary amido complex Mn{N(H)Ar(#)}(2) (), its Lewis base adducts Mn{N(H)Ar(#)}(2)(L) (Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2); L = THF (), and C(5)H(5)N ()), and Mn{N(H)Ar*}(2) () (Ar* = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(i)Pr(3))(2)) are described. Complex was prepared by the reaction of MnCl(2) with two equivalents of LiN(H)Ar(#) in benzene. X-Ray crystallography showed that it had a quasi-two-coordinate strongly bent geometry with Mn-N = 1.979(3) A, N-Mn-N = 138.19(9) degrees and secondary MnC(aryl ring) interactions. In contrast, complex , which was prepared by the same route as , has an almost linear geometry with a wide N-Mn-N angle of 176.1(2) degrees . The complexes and are the first structurally characterized homoleptic primary amido derivatives of manganese. Complex did not react with THF or pyridine, but its THF complex could be formed by the reaction of MnI(2)(THF)(2) with two equivalents of LiN(H)Ar(#). Similarly, complex was prepared either by the direct reaction of MnCl(2) with LiN(H)Ar(#) in hexanes in the presence of pyridine, or by reaction of the THF complex with excess pyridine. Attempts to form Lewis base complexes of by similar routes led to the recovery of unreacted . The results suggested that reaction with Lewis bases is prevented by secondary interactions () or steric effects (). Magnetic studies show that the manganese(ii) ions in have high spin configurations with S = 5/2 and small zero-field splittings, D, of ca.+/-1.5 to +/-3 cm(-1).

Insertion reactions of a two-coordinate iron diaryl with dioxygen and carbon monoxide.

The iron(II) diaryl FeAr'2 (1) (Ar' = C6H3-2,6-(C6H3-2,6-(i)Pr2)2) reacts cleanly with O2 or CO to afford the monomeric, two-coordinate bis(aryloxide) Fe(OAr')2 (2) or the eta2-acyl-carbonyl complex (eta2-Ar'C=O)2Fe(CO)2 (3) via oxygen or CO insertion into the Fe-C bonds; complex 2 has a strictly linear geometry and shows remarkable resistance to O2 oxidation.

Reduction of terphenyl iron(II) or cobalt(II) halides in the presence of trimethylphosphine: an unusual triple dehydrogenation of an alkyl group.

The reduction of {ArFeBr}(2) (Ar = terphenyl) with KC(8) in the presence of excess PMe(3) afforded the Fe(i) complex 3,5-Pr(i)(2)-Ar'Fe(PMe(3)) (1) (Ar'-3,5-Pr(i)(2) = C(6)H-2,6-(C(6)H(3)-2,6-Pr(i)(2))-3,5-Pr(i)(2)), which has a structure very different from the previously reported, linear Cr(i) species 3,5-Pr(i)(2)-Ar*Cr(PMe(3)) (3,5-Pr(i)(2)-Ar* = C(6)H-2,6-(C(6)H(2)-2,4,6-Pr(i)(3))(2)-3,5-Pr(i)(2)) and features a strong Fe-eta(6)-aryl interaction with the flanking aryl ring of the terphenyl ligand. In sharp contrast, the reduction of {ArCoCl}(2) (Ar = 3,5-Pr(i)(2)-Ar' and Ar') afforded the allyl complexes Co(eta(3)-{1-(H(2)C)(2)C-C(6)H(3)-2-(C(6)H(2)-2,4-Pr(i)(2)-5-(C(6)H(3)-2,6-Pr(i)(2)))-3-Pr(i)})(PMe(3))(3) (4) and Co(eta(3)-{1-(H(2)C)(2)C-C(6)H(3)-2-(C(6)H(4)-3-(C(6)H(3)-2,6-Pr(i)(2)))-3-Pr(i)})(PMe(3))(3) (5) formed by an unusual triple dehydrogenation of an isopropyl group. It is proposed that the reduction initially generates an intermediate 3,5-Pr(i)(2)-Ar'Co(PMe(3)), which is similar in structure to , followed by 3,5-Pr(i)(2)-Ar'Co(PMe(3)) decomposition to a cobalt hydride intermediate and dehydrogenation of the isopropyl group via remote C-H activation induced by PMe(3) complexation. Complexes 1, 4, and 5 were characterized by X-ray crystallography. In addition, 1 was studied by NMR and EPR spectroscopy; 4 and 5 were characterized by NMR spectroscopy.

Reactions of Ar'CrCrAr' with N2O or N3(1-Ad): complete cleavage of the Cr-Cr quintuple interaction.

Reaction of Ar'CrCrAr' (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-Pr(i)(2))(2)) with heterocumulene reagents N(2)O or N(3)(1-Ad) resulted in Ar'Cr(micro-O)(2)Cr(O)Ar' or Ar'Cr(micro(2):eta(1),eta(3)-N(3)(1-Ad))CrAr' which have no metal-metal bonding.

N-H and N=C bond formation via germanium(III) diradicaloid intermediates and C-S bond cleavage in reactions of the digermyne Ar'GeGeAr' (Ar' = C6H3-2,6-(C6H3-2,6-Pr(i)2)2) with azides.

Reactions of the digermyne Ar'GeGeAr' (Ar' = C(6)H(3)-2,6(C(6)H(3)-2,6-Pr(i)(2))(2)) (1) with four different azides R'N(3) (R = Me(3)Sn, (n)Bu(3)Sn, PhSCH(2), or 1-adamantanyl) are described. Treatment of 1 with Me(3)SnN(3) or (n)Bu(3)SnN(3) afforded the low-valent germanium (II) parent amido derivative, Ar'Ge(mu(2)-NH(2))(2)GeAr' (3) or the high-valent germanium (IV) parent imido derivative, Ar'((n)Bu(3)Sn)Ge(mu(2)-NH)(2)Ge(Sn(n)Bu(3))Ar' (4), respectively. Addition of AdN(3) (Ad =1-admantanyl) yielded a monoimide bridged species Ar'Ge(mu(2)-NAd)GeAr' (5). The structure of 5 differs from that of the diradicaloid Ar'Ge(mu(2)-NSiMe(3))(2)GeAr' (2), which was previously obtained from the analogous reaction of 1 with Me(3)SiN(3). The reaction of 1 with PhSCH(2)N(3) afforded the germanium ketimide Ar'Ge(SPh)(2)(N=CH(2)) (6) containing the imino -N=CH(2) functional group. These reactions demonstrate a remarkable product dependence on the azide substituent. All compounds were spectroscopically and structurally characterized. Both 3 and 4 feature a four-membered Ge(2)N(2) core. The structure of 5 is stabilized by CH-pi interactions while 6 features a rare example of a pi-pi interaction between an aromatic ring and a non-aromatic double bond (N=C). The mechanism of formation of 3-6 are discussed. It is proposed that 3 and 4 are obtained via diradical imido intermediates followed by H-abstraction from solvents, whereas 6 was formed by the activation of azide group in concert with C-S bond cleavage.

Spin-state crossover with structural changes in a cobalt(II) organometallic species: low-coordinate, first row, heteroleptic amido transition metal aryls. Synthesis and characterization of Ar'MN(H)Ar# (M = Mn, Fe, Co) (Ar' = C6H3-2,6-(C6H3-2,6-iPr2)2, Ar# = C6H3-2,6-(C6H2-2,4,6-Me3)2).

The synthesis and characterization of the monomeric aryl transition metal amido complexes Ar'MN(H)Ar(#) (Ar' = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2), Ar(#) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-Me(3))(2), M = Mn (1), Fe (2), Co(3a, b)) are reported. The compounds were characterized by X-ray crystallography, electronic and infrared spectroscopy, and magnetic measurements. At about 90 K the complexes 1 and 2 possess quasi-two coordinate geometry with a weak, secondary, M-C interaction involving a flanking aryl ring from an amido group. In contrast, at the same temperature, their cobalt analogue 3a features a strong Co-eta(6)-flanking ring interaction to give an effectively higher coordination geometry. Magnetic studies of 1-3a showed that 1 and 2 have high spin configurations, whereas the cobalt species 3a has a low-spin configuration (S = 1/2). However, 3a undergoes a spin crossover to a high spin (S = 3/2) state 3b near 229 K. An X-ray structural determination above the crossover temperature at 240 K showed that the low temperature structure of 3a had changed to 3b which involves a weak secondary M-C interaction analogous to those in 1 and 2. The complexes 1-3 are very rare examples of heteroleptic quasi-two coordinate open shell transition metal complexes.

Reaction of a sterically encumbered iron(I) aryl/arene with organoazides: formation of an iron(V) bis(imide).

Reaction of 3,5-Pr(i)2Ar*Fe(eta6-C6H6)(3,5-Pr(i)2Ar* = C6H1-2,6-(C6H2)-2,4,6-Pr(i)3)(2)-3,5-Pr(i)2) with (N3C6H3)-2,6-Mes2 (Mes = (C6H2)-2,4,6-Me3) afforded the dimeric iron(II) amido/aryl complex {CH2C6H(2)-2(C6H3)-2-N(H)FeAr*-3,5-Pr(i)2)-3,5-Me2}2 (1) which arises via methyl hydrogen abstraction by nitrogen and dimerization of the radical via C-C bond formation; in contrast, reaction of 3,5-Pr(i)2Ar*Fe(eta6)-C6H6) with N3(1-Ad) (1-Ad = 1-adamantanyl) gave the iron(V) bis(imido) complex 3,5-Pr(i)2Ar*Fe{N(1-Ad)}2 (2).

An arene-stabilized cobalt(I) aryl: reactions with CO and NO.

The half-sandwich cobalt(I) complex (eta (6)-C 7H 8)CoAr*-3,5- ( i )Pr 2 (Ar*-3,5- ( i )Pr 2 = -C 6H-2,6-(C 6H 2-2,4,6- ( i )Pr 3) 2-3,5- ( i )Pr 2) was synthesized by reduction of [3,5- ( i )Pr 2Ar*Co(mu-Cl)] 2 in toluene. It reacts with CO or NO to afford the unusual complexes [3,5- ( i )Pr 2Ar*C(O)Co(CO)] or [3,5- ( i )Pr 2Ar*N(NO)OCo(NO) 2].

Univalent transition metal complexes of arenes stabilized by a bulky terphenyl ligand: differences in the stability of Cr(I), Mn(I) or Fe(I) complexes.

Two univalent transition metal complexes, (micro-eta6:eta6-C7H8){MnAr*-3,5-Pri2}2 () and (eta6-C6H6)FeAr*-3,5-Pri2 () (Ar*-3,5-Pri2=C6H-2,6-(C6H(2)-2,4,6-Pri3)(2)-3,5-Pri2), that have eta6 arene coordination were synthesized by reduction of the corresponding metal halides. The complexes are thermally stable in contrast to the corresponding Cri complexes of benzene or toluene which decompose at room temperature.

Substituent effects in formally quintuple-bonded ArCrCrAr compounds (Ar = terphenyl) and related species.

The effects of different terphenyl ligand substituents on the quintuple Cr-Cr bonding in arylchromium(I) dimers stabilized by bulky terphenyl ligands (Ar) were investigated. A series of complexes, ArCrCrAr (1-4; Ar = C6H2-2,6-(C6H3-2,6-iPr2)2-4-X, where X = H, SiMe3, OMe, and F), was synthesized and structurally characterized. Their X-ray crystal structures display similar trans-bent C(ipso)CrCrC(ipso) cores with short Cr-Cr distances that range from 1.8077(7) to 1.8351(4) A. There also weaker Cr-C interactions [2.294(1)-2.322(2) A] involving an C(ipso) of one of the flanking aryl rings. The data show that the changes induced in the Cr-Cr bond length by the different substituents X in the para positions of the central aryl ring of the terphenyl ligand are probably a result of packing rather than electronic effects. This is in agreement with density functional theory (DFT) calculations, which predict that the model compounds (4-XC6H4)CrCr(C6H4-4-X) (X = H, SiMe3, OMe, and F) have similar geometries in the gas phase. Magnetic measurements in the temperature range of 2-300 K revealed temperature-independent paramagnetism in 1-4. UV-visible and NMR spectroscopic data indicated that the metal-metal-bonded solid-state structures of 1-4 are retained in solution. Reduction of (4-F3CAr')CrCl (4-F3CAr' = C6H2-2,6-(C6H3-2,6-iPr2)2-4-CF3) with KC8 gave non-Cr-Cr-bonded fluorine-bridged dimer {(4-F3CAr')Cr(mu-F)(THF)}2 (5) as a result of activation of the CF3 moiety. The monomeric, two-coordinate complexes [(3,5-iPr2Ar*)Cr(L)] (6, L = THF; 7, L = PMe3; 3,5-iPr2Ar* = C6H1-2,6-(C6H-2,4,6-iPr3)2-3,5-iPr2) were obtained with use of the larger 3,5-Pri2-Ar* ligand, which prevents Cr-Cr bond formation. Their structures contain almost linearly coordinated CrI atoms, with high-spin 3d5 configurations. The addition of toluene to a mixture of (3,5-iPr2Ar*)CrCl and KC8 gave the unusual dinuclear benzyl complex [(3,5-iPr2Ar*)Cr(eta3:eta6-CH2Ph)Cr(Ar*-1-H-3,5-iPr2)] (8), in which a C-H bond from a toluene methyl group was activated. The electronic structures of 5-8 have been analyzed with the aid of DFT calculations.

Formation of aluminacyclobutenes via carbon monoxide and isocyanide insertion.

Reaction of LAl[eta2-(CSiMe3)2] (L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3) with carbon monoxide and tert-butyl isocyanide afforded unique AlC3 aluminacyclobutenes via insertion into one of the aluminium-carbon bonds.