[Me2NN]Co(η6-toluene): OO, NN, and ON Bond Cleavage Provides β-Diketiminato Cobalt μ-Oxo and Imido Complexes

Eta2-organoazide complexes of nickel and their conversion to terminal imido complexes via dinitrogen extrusion

1-Adamantyl- and mesitylazide react with [(dtbpe)Ni]2(eta2-mu-C6H6) to give the eta2 organic azide adducts (dtbpe)Ni(eta2-N3R) (R = Ad, 3a; Mes, 3b) that have been isolated in good yields and crystallographically characterized. These azide adducts are intermediates in the formation of the corresponding terminal imido complexes (dtbpe)NiNR (R = Ad, 4a; Mes, 4b), undergoing intramolecular loss of dinitrogen upon mild thermolysis.

Electronic structure and reactivity of three-coordinate iron complexes

[Reaction: see text]. The identity and oxidation state of the metal in a coordination compound are typically thought to be the most important determinants of its reactivity. However, the coordination number (the number of bonds to the metal) can be equally influential. This Account describes iron complexes with a coordination number of only three, which differ greatly from iron complexes with octahedral (six-coordinate) geometries with respect to their magnetism, electronic structure, preference for ligands, and reactivity. Three-coordinate complexes with a trigonal-planar geometry are accessible using bulky, anionic, bidentate ligands (beta-diketiminates) that steer a monodentate ligand into the plane of their two nitrogen donors. This strategy has led to a variety of three-coordinate iron complexes in which iron is in the +1, +2, and +3 oxidation states. Systematic studies on the electronic structures of these complexes have been useful in interpreting their properties. The iron ions are generally high spin, with singly occupied orbitals available for pi interactions with ligands. Trends in sigma-bonding show that iron(II) complexes favor electronegative ligands (O, N donors) over electropositive ligands (hydride). The combination of electrostatic sigma-bonding and the availability of pi-interactions stabilizes iron(II) fluoride and oxo complexes. The same factors destabilize iron(II) hydride complexes, which are reactive enough to add the hydrogen atom to unsaturated organic molecules and to take part in radical reactions. Iron(I) complexes use strong pi-backbonding to transfer charge from iron into coordinated alkynes and N 2, whereas iron(III) accepts charge from a pi-donating imido ligand. Though the imidoiron(III) complex is stabilized by pi-bonding in the trigonal-planar geometry, addition of pyridine as a fourth donor weakens the pi-bonding, which enables abstraction of H atoms from hydrocarbons. The unusual bonding and reactivity patterns of three-coordinate iron compounds may lead to new catalysts for oxidation and reduction reactions and may be used by nature in transient intermediates of nitrogenase enzymes.

Diimine supported group 10 hydroxo, oxo, amido, and imido complexes

A series of L(2) = diimine (Bian = bis(3,5-diisopropylphenylimino)acenapthene, Bu(t)(2)bpy = 4,4'-di-tert-butyl-2,2'-bipyridine) supported aqua, hydroxo, oxo, amido, imido, and mixed complexes have been prepared. Deprotonation of [L(2)Pt(mu-OH)](2)(2+) with 1,8-bis(dimethylamino)naphthalene, NaH, or KOH yields [(L(2)Pt)(2)(mu-OH)(mu-O)](+) as purple (Bian) or red (Bu(t)(2)bpy) solids. Excess KOH gives dark blue [(Bian)Pt(mu-O)](2). MeOTf addition to [(Bu(t)(2)bpy)(2)Pt(2)(mu-OH)(mu-O)](+) gives [(Bu(t)(2)bpy)(2)Pt(2)(mu-OH)(mu-OMe)](2+) while [(Bian)Pt(mu-O)](2) yields [(Bian)(2)Pt(2)(mu-OMe)(mu-O)](+). Treatment of [(Bian)Pt(mu-O)](2) with "(Ph(3)P)Au(+)" gives deep purple [(Bian)(2)Pt(2)(mu-O)(mu-OAuPPh(3))](+) while (COD)Pt(OTf)(2) gives a low yield of [(Bian)Pt(3)(mu-OH)(3)(COD)(2)](OTf)(3). Ni(Bu(t)(2)bpy)Cl(2) and [(Ph(3)PAu)(3)(mu-O)](+) in a 3 : 2 ratio yield red [Ni(3)(Bu(t)(2)bpy)(3)(mu-O)(2)](2+). M(Bu(t)(2)bpy)Cl(2) (M = Pd, Pt) and [(Ph(3)PAu)(3)(mu-O)](+) give [M(Bu(t)(2)bpy)(mu-OAuPPh(3))](2)(2+) and [Pd(4)(Bu(t)(2)bpy)(4)(mu-OAuPPh(3))](3+). Addition of ArNH(2) to [M(Bu(t)(2)bpy)(mu-OH)](2)(2+) (M = Pd, Pt) gives [Pt(2)(Bu(t)(2)bpy)(2)(mu-NHAr)(mu-OH)](2+) (Ar = Ph, 4-tol, 4-C(6)H(4)NO(2)) and [M(Bu(t)(2)bpy)(mu-NHAr)](2)(2+) (Ar = Ph, tol). Deprotonation of [Pt(2)(Bu(t)(2)bpy)(2)(mu-NH-tol)(mu-OH)](2+) with 1,8-bis(dimethylamino)naphthalene or NaH gives [Pt(2)(Bu(t)(2)bpy)(2)(mu-NH-tol)(mu-O)](+). Deprotonation of [Pt(Bu(t)(2)bpy)(mu-NH-tol)](2)(2+) with KOBu(t) gives deep green [Pt(Bu(t)(2)bpy)(mu-N-tol)](2). The triflate complexes M(Bu(t)(2)bpy)(OTf)(2) (M = Pd, Pt) are obtained from M(Bu(t)(2)bpy)Cl(2) and AgOTf. Treatment of Pt(Bu(t)(2)bpy)(OTf)(2) with water gives the aqua complex [Pt(Bu(t)(2)bpy)(H(2)O)(2)](OTf)(2).

Vibrational spectroscopy and analysis of pseudo-tetrahedral complexes with metal imido bonds

A number of assignments have been previously posited for the metal-nitrogen stretch (nu(M-NR)), the N-R stretch (nu(MN-R)), and possible ligand deformation modes associated with terminally bound imides. Here we examine mononuclear iron(III) and cobalt(III) imido complexes of the monoanionic tridentate ligand [PhBP3] ([PhBP3] = [PhB(CH2PPh2)3]-) to clarify the vibrational features for these trivalent metal imides. We report the structures of [PhBP3]FeNtBu and [PhBP3]CoNtBu. Pseudo-tetrahedral metal imides of these types exhibit short bond lengths (ca. 1.65 A) and nearly linear angles about the M-N-C linkages, indicative of multiple bond character. Furthermore, these compounds give rise to intense, low-energy visible absorptions. Both the position and the intensity of the optical bands in the [PhBP3]MNR complexes depend on whether the substituent is an alkyl or aryl group. Excitation into the low-energy bands of [PhBP3]FeNtBu gives rise to two Raman features at 1104 and 1233 cm(-1), both of which are sensitive to 15N and 2H labeling. The isotope labeling suggests the 1104 cm(-1) mode has the greatest Fe-N stretching character, while the 1233 cm(-1) mode is affected to a lesser extent by (15)N substitution. The spectra of the deuterium-labeled imides further support this assertion. The data demonstrate that the observed peaks are not simple diatomic stretching modes but are extensively coupled to the vibrations of the ancillary organic group. Therefore, describing these complexes as simple diatomic or even triatomic oscillators is an oversimplification. Analogous studies of the corresponding cobalt(III) complex lead to a similar set of isotopically sensitive resonances at 1103 and 1238 cm(-1), corroborating the assignments made in the iron imides. Very minimal changes in the vibrational frequencies are observed upon replacement of cobalt(III) for iron(III), suggesting similar force constants for the two compounds. This is consistent with the previously proposed electronic structure model in which the added electron resides in a relatively nonbonding orbital. Replacement of the tBu group with a phenyl ring leads to a significantly more complicated resonance Raman spectrum, presumably due to coupling with the vibrations of the phenyl ring. Polarization studies demonstrate that the observed modes have A(1) symmetry. In this case, a clearer resonance enhancement of the signals is observed, supporting a charge transfer designation for the electronic transitions. A series of isotope-labeling experiments has been carried out, and the modes with the greatest metal-nitrogen stretching character have been assigned to peaks at approximately 960 and approximately 1300 cm(-1) in both the iron and cobalt [PhBP3]MNPh complexes. These results are consistent with a multiple M-N bond for these metal imides.

Synthesis and Structures of Dimeric Iron(III)-Oxo and -Imido Complexes Containing Intramolecular Hydrogen Bonds

Hydrogen bonding networks proximal to metal centers are emerging as a viable means for controlling secondary coordination spheres. This has led to the regulation of reactivity and isolation of complexes with new structural motifs. We have used the tridenate ligand bis[(N'-tert-butylureido)-N-ethyl]-N-methylaminato ([H(2)1](2-)) that contains two hydrogen bond donors to examine the oxidation of the Fe(II)-acetate complex, [Fe(II)H(2)1(η(2)-OAc)](-) with dioxygen, amine N-oxides, and xylyl azide. A complex with Fe(III)-O-Fe(III) core results from the oxidation with dioxygen and amine N-oxides, in which the oxo ligand is involved in hydrogen bonding to the [H(2)1](2-) ligand. A distinctly different hydrogen bonding network was found in Fe(III) dimer isolated from the reaction with the xylyl azide: a rare Fe(III)-N(R)-Fe(III) core was observed that does not have hydrogen bonds to the bridging nitrogen atom. The intramolecular H-bond networks within these dimers appear to adjust to the presence of the bridging species and rearrange to its size and electron density.

Macrocyclic Binucleating β-Diketiminate Ligands and their Lithium, Aluminum, and Zinc Complexes

The incorporation of rigid aromatic linkers into β-diketiminate ligands creates a binucleating scaffold that holds two metals near each other. This paper discloses the synthesis, characterization, and reactivity of mBin(2-), which has a meta-substituted xylylene spacer, and pBin(2-), which has a para-substituted xylylene spacer. Lithium, aluminum, and zinc complexes of each ligand are isolated, and in some cases are characterized by X-ray crystallography. The lithium complexes are coordinated to solvent-derived THF ligands, while the zinc and aluminum complexes have alkyl ligands. Complexes of the mBin(2-) ligand have an anti conformation in which the metals are on opposite sides of the macrocycle, while pBin(2-) complexes prefer a syn conformation. The (1)H NMR spectra of the complexes demonstrate that the conformations rapidly interconvert in the lithium complexes, and less rapidly in the zinc and aluminum complexes.

Transient Terminal Cu−Nitrene Intermediates from Discrete Dicopper Nitrenes

Reaction of the copper(I) beta-diketiminate {[Me3NN]Cu}2(mu-toluene) with the aryl azide N3Ar (Ar = 3,5-Me2C6H3) in toluene results in immediate effervescence and formation of the dicopper nitrene {[Me3NN]Cu}2(mu-NAr) (2) in 77% yield. The X-ray structure of 2 shows nearly symmetric bonding of the nitrene to two Cu centers separated by 2.911(1) A with Cu-N distances of 1.794(5) and 1.808(5) A along with a Cu-N-Cu angle of 107.8(2) degrees . This structure is conceptually related to the dicopper carbenes {[MexNN]Cu}2(mu-CPh2) (x = 2 or 3) (Dai, X.; Warren J. Am. Chem. Soc. 2004, 126, 10085. Badiei, Y. M.; Warren J. Organomet. Chem. 2005, 690, 5989.) which exhibit shorter Cu-Cu distances (2.4635(7) or 2.485(1) A) and acute Cu-C-Cu angles (79.51(14) or 80.1(2) degrees ). Addition of the Cu(I) anilidoimine {[Me2AI]Cu}2 (prepared from CuOtBu and the aniline-imine H[Me2AI] in 77% yield) to a benzene-d6 solution of 2 results in the formation of two new anilidoimine complexes {[Me2AI]Cu(mu- NAr)Cu[Me3NN] (5) and {[Me2AI]Cu}2(mu-NAr) (6) as well as [Me3NN]Cu(benzene) over 3 h. These observations are consistent with the slow dissociation of a [Me3NN]Cu fragment from 2 to generate the transient terminal nitrenes [Me3NN]Cu=NAr and [Me2AI]Cu=NAr quickly trapped by the [Me2AI]Cu fragment to form the new unsymmetrical and symmetrical dicopper nitrenes 5 and 6. Preliminary reactivity studies indicate electrophilic reactivity at the nitrene moiety. Dicopper nitrene 2 reacts with 10 equiv PMe3 and CNtBu to give ArN=PMe3 and ArN=C=NtBu in 94% and 92% yields, respectively, with concomitant formation of [Me3NN]Cu(L) (L = PMe3 and CNtBu). Reaction between 2 and 2 equiv PMe3 allows for observation of the structurally characterized Cu(I) phosphaimide [Me3NN]Cu(ArN=PMe3) (7).

Pseudotetrahedral manganese complexes supported by the anionic tris(phosphino)borate ligand [PhBP(iPr)3]

This paper presents aspects of the coordination chemistry of mono- and divalent manganese complexes supported by the anionic tris(phosphino)borate ligand, [PhBP(i)(Pr)3] (where [PhBP(i)(Pr)3] = [PhB(CH(2)P(i)Pr2)3]-). The Mn(II) halide complexes, [PhBP(i)(Pr)3]MnCl (1) and [PhBP(i)(Pr)3]MnI (2), have been characterized by X-ray diffraction, SQUID magnetometry, and EPR spectroscopy. Compound 2 serves as a precursor to a series of Mn azide, alkyl, and amide species: [PhBP(i)(Pr)3]Mn(N3) (3), [PhBP(i)(Pr)3]Mn(CH2Ph) (4), [PhBP(i)(Pr)3]Mn(Me) (5), [PhBP(i)(Pr)3]Mn(NH(2,6-(i)Pr2-C6H3)) (6), [PhBP(i)(Pr)3]Mn(dbabh) (7), and [PhBP(i)(Pr)3]Mn(1-Ph(isoindolate)) (8). The complexes 2-8 feature a divalent-metal center and are pseudotetrahedral. They collectively represent an uncommon structural motif for low-coordinate, polyphosphine-supported Mn complexes. Two Mn(I) species have also been prepared. These include the Tl-Mn adduct [PhBP(i)(Pr)3]Tl-MnBr(CO)4 (9) and the octahedral complex [PhBP(i)(Pr)3]Mn(CN(t)Bu)3 (10). Some of our initial synthetic efforts to generate [PhBP(i)(Pr)3]MnN(x) species are briefly described, as are DFT studies that probe the electronic viability of these types of multiply bonded target structures.

Characterization of the terminal iron(IV) imides [[PhBP(t)(Bu)2(pz')]Fe(IV)NAd]+

New hybrid bis(phosphine)(pyrazole)borate tripodal ligands ([PhBPtBu2(pz')]-) are reported that support pseudotetrahedral iron in the oxidation states +1, +2, +3, and +4. The higher oxidation states are stabilized by a terminal FeNR linkage. Of particular interest is the generation and thorough characterization of an S = 1 FeIVNR+ imide cation using this new ligand system. The latter species can be observed electrochemically and spectroscopically, and its solid-state crystal structure is reported.

A terminal Ni(III)-imide with diverse reactivity pathways

The synthesis and structure of the beta-diketiminato Ni(I) lutidine adducts [MexNN]Ni(2,4-lutidine) (x = 2 (2); x = 3 (3)) are described which serve as synthons to the "naked" 13-electron [MexNN]Ni fragments in reactions with N3Ad to give Ni-imido complexes. The singly bridged imide {[Me2NN]Ni}2(mu-NAd) (4) possesses short Ni-Ni (2.506(1) A) and Ni-N(imido) distances (1.732(4)-1.752(4) A). Steric modification of the beta-diketiminate ligand to include an additional methyl group in the N-aryl 4-position affords the Ni(III) terminal imide [Me3NN]Ni=NAd (8) isolated in 52% yield. The X-ray structure of terminal imide 8 reveals a contracted Ni-N(imido) bond distance (1.662(2) A) and an only somewhat bent imido linkage (Ni-N-C = 164.5(2) degrees ) consistent with a significant degree of multiple bond character. Frozen glass EPR studies of 5 indicate a rhombic environment in which one of the signals exhibits strong hyperfine coupling (A = 22 G) to the imido 14N (I = 1) nucleus. The terminal imide 5 undergoes complete imido group transfer to CO and CNBut to give AdNCO and AdNCNBut, respectively, as well as with PMe3 to afford AdN=PMe3. Exemplifying the radical character at the imido N atom, 5 adds to cobaltocene and abstracts a H atom from 1,4-cyclohexadiene to give the Ni(II)-amides [Me3NN]Ni-NAd(eta4-C5H5)CoCp (7) and [Me3NN]Ni-NHAd (8).

Bimetallic Anilido-Aldimine Zinc Complexes for Epoxide/CO2 Copolymerization

Acyclic o-phenylene-bridged bis(anilido-aldimine) compounds, o-C(6)H(4){C(6)H(2)R(2)N=CH-C(6)H(4)-(H)N(C(6)H(3)R'(2))}(2) and related 30-membered macrocyclic compounds, o-C(6)H(4){C(6)H(2)R'(2)N=CH-C(6)H(4)-(H)N-C(6)H(2)R(2)}(2) (o-C(6)H(4)) are prepared. Successive additions of Me(2)Zn and SO(2) gas to the bis(anilido-aldimine) compounds afford quantitatively dinuclear mu-methylsulfinato zinc complexes, o-C(6)H(4){(C(6)H(2)R(2)N=CH-C(6)H(4)-N(C(6)H(3)R'(2))-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (R = iPr and R' = iPr, 29; R = Et and R' = Et, 30; R = Me and R'= Me, 31; R = Me and R' = iPr, 32; R = Et and R' = Me, 33; R = Et and R' = iPr, 34; R = iPr and R' = Et, 35) and o-C(6)H(4){C(6)H(2)R'(2)N=CH-C(6)H(4)-N-C(6)H(2)R(2)-kappa(2)-N,N)Zn(mu-OS(O)Me)}(2) (o-C(6)H(4)) (R = Et and R'= Et, 36; R = Me and R' = Me, 37; R = iPr and R' = Me, 38; R = Et and R' = Me, 39; R = Me and R'= iPr, 40). Molecular structures of 34 and 40 are confirmed by X-ray crystallography. Complexes 30-35 show high activity for cyclohexene oxide/CO(2) copolymerization at low [Zn]/[monomer] ratio (1:5600), whereas the complex of mononucleating beta-diketiminate {[(C(6)H(3)Et(2))N=C(Me)CH=C(Me)N(C(6)H(3)Et(2))]Zn(mu-OS(O)Et)}(2) shows negligible activity in the same condition. Activity is sensitive to the N-aryl ortho substituents and the highest activity is observed with 32. Turnover number up to 2980 and molecular weight (M(n)) up to 284 000 are attained with 32 at such a highly diluted condition as [Zn]/[monomer] = 1:17 400. Macrocyclic complexes 36-40 show negligible activity for copolymerization.

Palladium–gold oxo complexes

Treatment of L2PdCl2(L2= 4,4-di-tert-butyl-2,2-bipyridine) with [(L'Au)3(mu3-O)]BF4(L'= PPh3) has yielded cationic oxo complexes with core formulas Pd2Au2O2 and Pd4AuO3 thereby doubling the number of structurally characterized Pd oxo complexes.

Cu(I) β-Diketiminates for Alkene Aziridination: Reversible CuArene Binding and Catalytic Nitrene Transfer from PhINTs

beta-Diketiminato Cu(I)-lutidine complexes [RMeNN]Cu(2,4-lutidine) (R = Me (4a), (i)Pr (4b)) were prepared in high yield from Tl[RMeNN] and [CuBr(2,4-lutidine)(2)](2). Both 4a and 4b reversibly dissociate lutidine base in toluene to give [RMeNN]Cu(toluene) solvento complexes. A related base-free dicopper species [[Me(2)NN]Cu](2) (6) bridged via eta(2)-binding of opposing N-aryl rings could be isolated by the addition of Tl[Me(2)NN] to CuBr. The lutidine precursors serve as precatalysts for the aziridination of alkenes with PhI=NTs. Styrene, beta-methylstyrene, and cyclooctene gave the highest yields (59-96%) with a low olefin to PhI=NTs ratio (3:1) and 5 mol % catalyst loading.