Investigation of transition metal-imido bonding in M(NBut)2(dpma)

A complete series down group 6 of the formula M(NBu(t))(2)(dpma) has been synthesized, where dpma is N,N-di(pyrrolyl-alpha-methyl)-N-methylamine. A fourth complex, Mo(NAr)(2)(dpma) (4), was also prepared, where Ar is 2,6-diisopropylphenyl. All four of these complexes display geometries in the solid state best described as square pyramidal with one imido ligand occupying the axial position and the other an equatorial site. In all cases, the axial imido ligand has a significantly smaller M-N(imido)-C bond angle with respect to the equatorial multiple-bond substituent. From the (1)H, (13)C, and (14)N NMR spectra, the axial (bent) imido appears to be more electron-rich than the equatorial and linear imido, with the differences becoming less pronounced down the column. The angular deformation energies for the axial imido ligands were studied by DFT in order to discern if and to what extent imido bond angles were important energetically. The electronic energies associated with straightening the axial imido ligand, while holding the remainder of the molecule at the ground-state geometry, for the Cr, Mo, and W derivatives were calculated as 4.5, 2.7, and 2.0 kcal/mol, respectively. A straight-line plot is found for deformation energies versus estimated electronegativity of the group 6 metals in the +6 oxidation state. The study suggests that the electronic differences between metal imido ligands of different angles are quite small; however, the effects may be more pronounced for metal centers with higher electronegativity, e.g. Cr(VI) with electron-withdrawing ligands.     

Application of molybdenum bis(imido) complexes in ethylene dimerisation catalysis

In combination with EtAlCl(2) (Mo : Al = 1 : 15) the imido complexes [MoCl(2)(NR)(NR')(dme)] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (1); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (3); R = R' = Bu(t) (4); dme = 1,2-dimethoxyethane) and [Mo(NHBu(t))(2)(NR)(2)] (R = 2,6-Pr(i)(2)-C(6)H(3) (5); R = Bu(t) (6)) each show moderate TON, activity, and selectivity for the catalytic dimerisation of ethylene, which is influenced by the nature of the imido substituents. In contrast, the productivity of [MoCl(2)(NPh)(2)(dme)] (2) is low and polymerisation is favoured over dimerisation. Catalysis initiated by complexes 1-4 in combination with MeAlCl(2) (Mo : Al = 1 : 15) exhibits a significantly lower productivity. Reaction of complex 5 with EtAlCl(2) (2 equiv.) gives rise to a mixture of products, while addition of MeAlCl(2) affords [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. Treatment of 6 with RAlCl(2) (2 equiv.) (R = Me, Et) yields [Mo({μ-N-Bu(t)}AlCl(2))(2)] (7) in both cases. Imido derivatives 1 and 3 react with Me(3)Al and MeAlCl(2) to form the bimetallic complexes [MoMe(2)(N{R}AlMe(2){μ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (8); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (10)) and [MoMe(2)(N{R}AlCl(2){μ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (9); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (11)), respectively. Exposure of complex 8 to five equivalents of thf or PMe(3) affords the adducts [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)(L)] (L = thf (12); L = PMe(3) (13)), while reaction with NEt(3) (5 equiv.) yields [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. The molecular structures of complexes 5, 9 and 11 have been determined.     

Synthesis and characterization of oxo---imido and alkyl---imido complexes of molybdenum(VI)

Treatment of the complex Mo(Nmes)(O)Cl₂(dme) (mes=2,4,6-trimethylphenyl; dme=1,2-dimethoxyethane) with KTp^Me2, NaCp and bipy gives the corresponding derivatives (Tp^Me2)Mo(Nmes)(O)Cl (1), CpMo(Nmes)(O)Cl (2) and Mo(Nmes)(O)Cl₂(bipy) (3). Other oxo---imido compounds of composition Mo(Nmes)(O)(S₂CNR₂)₂ (R₂=C₄H₄ 4, C₅H₁₀ 5, ⁱPr₂ 6) can be obtained by reacting Mo(Nmes)(O)Cl₂(dme) with the appropriate dithiocarbamate salt. The NMR properties of 4–6 are consistent with the presence of two rapidly equilibrating dithiocarbamate ligands. The reaction of Mo(Nmes)(O)Cl₂(dme) with different Grignard reagents, Mg(R)X, produces the trialkyl imido complexes Mo(Nmes)R₃Cl (R=Me 7, CH₂C(Me)₂Ph 8, CH₂SiMe₃ 9).     

Stereochemical consequences of oxygen atom transfer and electron transfer in imido/oxido molybdenum(IV, V, VI) complexes with two unsymmetric bidentate ligands

Two equivalents of the unsymmetrical Schiff base ligand (L(tBu))(-) (4-tert-butyl phenyl(pyrrolato-2-ylmethylene)amine) and MoCl(2)(NtBu)O(dme) (dme = 1,2-dimethoxyethane) gave a single stereoisomer of a mixed imido/oxido Mo(VI) complex 2(tBu). The stereochemistry of 2(tBu) was elucidated using X-ray diffraction, NMR spectroscopy, and DFT calculations. The complex is active in an oxygen atom transfer (OAT) reaction to trimethyl phosphane. The putative intermediate five-coordinate Mo(IV) imido complex coordinates a PMe(3) ligand, giving the six-coordinate imido phosphane Mo(IV) complex 5(tBu). The stereochemistry of 5(tBu) is different from that of 2(tBu) as shown by NMR spectroscopy, DFT calculations, and X-ray diffraction. Single-electron oxidation of 5(tBu) with ferrocenium hexafluorophosphate gave the stable cationic imido phosphane Mo(V) complex [5(tBu)](+) as the PF(6)(-) salt. EPR spectra of [5(tBu)](PF(6)) confirmed the presence of PMe(3) in the coordination sphere. Single-crystal X-ray diffraction analysis of [5(tBu)](PF(6)) revealed that electron transfer occurred under retention of the stereochemical configuration. The rate of OAT, the outcome of the electron transfer reaction, and the stabilities of the imido complexes presented here differ dramatically from those of analogous oxido complexes.     

Regioselective and reversible carbon-nitrogen bond formation: synthesis, structure and reactivity of ureato-bridged complexes [Mo2(NAr)2(mu-X){mu-ArNC(O)NAr}(S2CNR2)2](Ar = Ph, p-tol; X = S, NAr; R = Me, Et, Pr)

Reaction of ArNCO with syn-[MoO(mu-O)(S2CNR2)]2 or syn-[MoO(mu-NAr)(S2CNR2)]2 at 110 degrees C leads to the facile formation of bridging ureato complexes [Mo2(NAr)2(mu-NAr){mu-ArNC(O)NAr}(S2CNR2)2](Ar = Ph, p-tol; R = Me, Et, Pr), formed upon substitution of all oxo ligands and addition of a further equivalent of isocyanate across one of the bridging imido ligands. Related sulfido-bridged complexes [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2] have been prepared from syn-[Mo2O2(mu-O)(mu-S)(S2CNR2)2]. When reactions with syn-[MoO(mu-NAr)(S2CNEt2)]2 were followed by NMR, intermediates were observed, being formulated as [Mo2O(NAr)(mu-NAr){mu-ArNC(O)NAr}(S2CNEt2)2], which at higher temperatures convert to the fully substituted products. A crystallographic study of [Mo2(N-p-tol)2(mu-S){mu-p-tolNC(O)N-p-tol}(S2CNPr2)2] reveals that the bridging ureato ligand is bound asymmetrically to the dimolybdenum centre-molybdenum-nitrogen bonds trans to the terminal imido ligands being significantly elongated with respect to those cis-a result of the trans-influence of the terminal imido ligands. This trans-influence also leads to a trans-effect, whereby the exchange of aryl isocyanates can occur in a regioselective manner. This is followed by NMR studies and confirmed by a crystallographic study of [Mo2(N-p-tol)2(mu-N-p-tol){mu-p-tolNC(O)NPh}(S2CNEt2)2]--the PhNCO occupying the site trans to the terminal imido ligands. Ureato complexes also react with PhNCS, initially forming [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2], resulting from exchange of the bridging imido ligand for sulfur, together with small amounts of [Mo2(NAr)2(mu-S)(mu-S2)(S2CNEt2)2], containing bridging sulfide and disulfide ligands. The ureato complexes [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2] react further with PhNCS to give [Mo2(NAr)2(mu-S)2(S2CNR2)2]n (n = 1, 2), which exist in a dimer-tetramer equilibrium. In order to confirm these results crystallographic studies have been carried out on [Mo2(N-p-tol)2(mu-S)(mu-S2)(S2CNEt2)2] and [Mo2(N-p-tol)2(mu-S)2(S2CNPr2)2]2.     

Group 6 imido complexes supported by diamido-donor ligands

Reactions of the lithiated diamido-pyridine or diamido-amine ligands Li(2)N(2)N(py) or Li(2)N(2)N(am) with [W(NAr)Cl(4)(THF)] (Ar = Ph or 2,6-C(6)H(3)Me(2); THF = tetrahydrofuran) afforded the corresponding imido-dichloride complexes [W(NAr)(N(2)N(py))Cl(2)] (R = Ph, 1, or 2,6-C(6)H(3)Me(2), 2) or [W(NAr)(N(2)N(am))Cl(2)] (R = Ph, 3, or 2,6-C(6)H(3)Me(2), 4), respectively, where N(2)N(py) = MeC(2-C(5)H(4)N)(CH(2)NSiMe(3))(2) and N(2)N(am) = Me(3)SiN(CH(2)CH(2)NSiMe(3))(2). Subsequent reactions of 1 with MeMgBr or PhMgCl afforded the dimethyl or diphenyl complexes [W(NPh)(N(2)N(py))R(2)] (R = Me, 5, or Ph, 6), respectively, which have both been characterized by single crystal X-ray diffraction. Reactions of Li(2)N(2)N(py) or Li(2)N(2)N(am) with [Mo(NR)(2)Cl(2)(DME)] (R = (t)Bu or Ph; DME = 1,2-dimethoxyethane) afforded the corresponding bis(imido) complexes [Mo(NR)(2)(N(2)N(py))] (R = (t)Bu, 7, or Ph, 8) and [Mo(N(t)Bu)(2)(N(2)N(am))] (9).     

Construction of a novel copper(I) chain polymer of hexanuclear Cu6(2-SC5H4NH)6I6 cores with a new (mu 3-S) mode of bonding of pyridine-2-thione and of an unusual triangular Cu3I3(dppe)3(2-SC5H4NH) cluster

The reactions of copper(I) iodide with pyridine-2-thione (2-SC(5)H(4)NH) in the presence of a series of diphosphane ligands, Ph(2)P[bond]X[bond]Ph(2)P [X = [bond](CH(2))(m)[bond], m = 1(dppm), 2 (dppe), 3 (dppp), 4 (dppb); [bond]CH[double bond]CH[bond] (dppen)], yielded an iodo-bridged hexanuclear Cu(I) linear polymer, [Cu(6)(mu(3)-SC(5)H(4)NH)(4)(mu(2)-SC(5)H(4)NH)(2)(I(4))(mu-I)(2)-](n).2nCH(3)CN (1). A similar reaction with 1,2-bis(diphenylphosphino)ethane (dppe) and 2-SC(5)H(4)NH yielded a triangular cluster, Cu(3)I(3)(dppe)(3)(2-SC(5)H(4)NH), 2. In the chain polymer 1, three Cu(I) iodide and three 2-SC(5)H(4)NH ligands combined via bridging S donor atoms to form a boat-shaped trinuclear Cu(3)S(3)I(3) core, and two such cores combined in an inverse manner via four S-donor atoms (mu(3)-S) to form a centrosymmetric hexanuclear repeat unit, Cu(6)S(6)I(4)(mu-I)(2-), which finally formed the iodo-bridged infinite linear chain polymer 1. Linear chains are separated by the nonbonded acetonitrile molecules. Polymer 1 is the first such example of a linear chain formed by the hexanuclear Cu(6)S(6)I(6) core in copper chemistry as well as in metal-heterocyclic thioamide chemistry. In addition, it has the first mu(3)-S mode of neutral pyridine-2-thione ever reported. In the moiety Cu(3)I(3)(dppe)(3) of 2, two copper(I) centers are bridged by the iodide ligands forming a Cu(mu-I)(2)Cu core, while a third copper(I) center is terminally bonded to another iodide ligand. Polymer 2 is also rare, and the first triangular cluster of Cu(I) with an heterocyclic thioamide.     

Versatility of heterocyclic thioamides in the construction of a trinuclear cluster [Cu3I3(dppe)3 (SC5H4NH)] and Cu(I) linear polymers {Cu6(SC5H4NH)6I6}n x 2nCH3CN and {Cu(I)6 (SC3H6N2)6X6}n (X = Br, I)

Reaction of copper(I) iodide with pyridine-2-thione (2-SC5H4NH) and 1,2-bis(diphenylphosphino)ethane (dppe) in a CH3CN-CHCl3 mixture yielded a triangular cluster, [Cu3I3(mu2-P,P-dppe)3 (eta1-SC5H4NH)], 1. Similar reaction with 2-SC5H4NH and a series of diphosphanes, Ph2P-X-Ph2P {X = -CH2- (dppm), -(CH2)3- (dppp), -(CH2)4- (dppb), -CH=CH- (dppen)}, gave a novel iodo-bridged hexanuclear Cu(I) linear polymer,{Cu6(mu3-SC5H4NH)4 (mu2-SC5H4NH)2 (I4)(mu-I)2-}n x 2nCH3CN, 2. Reactions of copper(I) iodide/copper(I) bromide with 1,3-imidazolidine-2-thione (SC3H6N2) in a CH3CN-CHCl3 mixture yielded hexanuclear Cu(I) linear chain polymers, [{Cu6(mu3-SC3H6N2)2 (mu2-SC3H6N2)4X2 (mu-X)4}n] (X = Br, 4; I, 5). In compound 1, two iodide atoms and one dppe form the dinuclear Cu(mu2-I)2 (mu2-dppe)Cu core, and two dppe ligands bridge this core with the third Cu(I) center coordinated to 2-SC5H4NH via the S atom. The chain polymer 2 has a centrosymmetric hexanuclear central core, Cu6S6I4 (mu-I)2--, formed by dimerization of six-membered trinuclear motifs, Cu3(mu2-SC3H6N2)3I3 via (mu3-S) bonding modes of the thione ligand, and has four terminal and two bridging iodine atoms in trans-orientations. Linear chains are separated by the nonbonded acetonitrile molecules. In 4 and 5, three copper(I) bromide or copper(I) iodide moieties and three SC3H6N2 ligands combined via bridging S donor atoms to form the six-membered trinuclear Cu3(mu2-SC3H6N2)3I3 cores which polymerized via S and X atoms in a side-on fashion to form linear chain polymers, [{Cu6(mu3-SC3H6N2)2 (mu2-SC3H6N2)4X2(mu-X)4}n]. The (mu3-S) modes of bonding of neutral heterocyclic thioamides are first examples, as are trinuclear cluster and linear polymers rare examples in copper chemistry.     

Synthesis, structure, and catalytic oxidation chemistry from the first oxo-imido Schiff base metal complexes

The molybdenum oxo-imido complex, [Mo(O)(NtBu)Cl2(dme)] (1), was obtained from the reaction between [MoO2Cl2(dme)] and [Mo(NtBu)2Cl2(dme)]. Reactions between [Mo(O)(NR)Cl2(dme)] (where R = tBu or 2,6-iPr2C6H3) and the disodium Schiff base compounds Na(2)(3,5-tBu2)2salen, Na(2)(3,5-tBu2)2salpen, and Na(2)(7-Me)2salen afforded the first oxo-imido transition metal Schiff base complexes: [Mo(O)(NtBu)[(3,5-tBu2)2salen]] (2), [Mo(O)(NtBu)[(3,5-tBu2)2salpen]] (3), and [Mo(O)(N-2,6-iPr2C6H3)[(7-Me)2salen]] (4), respectively. The compounds [Mo(NtBu)2[(3,5-tBu2)2salpen]] (5) from [Mo(NtBu)2(NHtBu)2] and [Mo(N-2,6-iPr2C6H3)(2)[(7-Me)2salen]](6) from [Mo(N-2,6-iPr2C6H3)(2)(NHtBu)2] (7) are also reported. Compounds 1-7 were characterized by NMR, IR, and FAB mass spectroscopy while compounds 3, 4, and 5 were additionally characterized by X-ray crystallography. In conjunction with tBuOOH as oxidant, compound 3 is a catalyst for the oxidation of benzyl alcohol to benzaldehyde and cis-cyclooctene and 1-octene to the corresponding epoxides.     

Synthesis of cationic rhenium(VII) oxo imido complexes and their tunability towards oxygen atom transfer

A facile method is described for the synthesis of cationic Re(VII) cis oxo imido complexes of the form [Re(O)(NAr)(salpd)+] (salpd = N,N'-propane-1,3-diylbis(salicylideneimine)), 4, [Re(O)(NAr)(saldach)+] (saldach = N,N'-cyclohexane-1,3-diylbis(salicylideneimine)), 5, and [Re(O)(NAr)(hoz)2+] (hoz = 2-(2'-hydroxyphenyl)-2-oxazoline) (Ar = 2,4,6,-(Me)C(6)H(2); 4-(OMe)C(6)H(4); 4-(Me)C(6)H(4); 4-(CF3)C6H4; 4-MeC(6)H(4)SO(2)), 6, from the reaction of oxorhenium(V) [(L)Re(O)(Solv)+] (1-3) and aryl azides under ambient conditions. Unlike previously reported cationic Re(VII) dioxo complexes, these cationic oxo imido complexes can be obtained on a preparative scale, and an X-ray crystal structure of [Re(O)(NMes)(saldach)+], 5a, has been obtained. Despite the multiple stereoisomers that could arise from tetradentate ligation of salen ligands to rhenium, one major isomer is observed and isolated in each instant. The electronic rationalization for stereoselectivity is discussed. Investigation of the mechanism suggests that the reactions of Re(V) with aryl azides proceed through an azido adduct similar to the group 5 complexes of Bergman and Cummins. Treatment of the cationic oxo imido complexes with a reductant (PAr(3), PhSMe, or PhSH) results in oxygen atom transfer (OAT) and the formation of cationic Re(V) imido complexes. [(salpd)Re(NMes)(PPh(3))(+)] (7) and [(hoz)2Re(NAr)(PPh(3))(+)] (Ar = m-OMe phenyl) (9) have been isolated on a preparative scale and fully characterized including an X-ray single-crystal structure of 7. The kinetics of OAT, monitored by stopped-flow spectroscopy, has revealed rate saturation for substrate dependences. The different plateau values for different oxygen acceptors (Y) provide direct support for a previously suggested mechanism in which the reductant forms a prior-equilibrium adduct with the rhenium oxo (ReVII = O<--Y). The second-order rate constants of OAT, which span more than 3 orders of magnitude for a given substrate, are significantly affected by the electronics of the imido ancillary ligand with electron-withdrawing imidos being most effective. However, the rate constant for the most active oxo imido rhenium(VII) is 2 orders of magnitude slower than that observed for the known cationic dioxo Re(VII) [(hoz)2Re(O)(2)(+)].     

Synthesis and molecular and electronic structure of an unusual paramagnetic borohydride complex Mo(NAr)2(PMe3)2(eta2-BH4)

Reaction of Mo(NAr)2Cl2(DME) (Ar=2,6-C6H3iPr2, DME=1,2-dimethoxyethane) with NaBH4 and PMe3 in THF formed the paramagnetic Mo(V) d1 borohydride complex Mo(NAr)2(PMe3)2(eta2-BH4) (1). Compound 1, which was characterized by EPR spectroscopy and X-ray diffraction analysis, provides a rare example both of a paramagnetic bis(imido) group 6 compound and a structurally characterized molybdenum borohydride complex. Density functional theory calculations were used to determine the electronic structure and bonding parameters of 1 and showed that it is best viewed as a 19 valence electron compound (having a primarily metal-based SOMO) in which the BH4- ligand behaves as a sigma-only, 2-electron donor.     

Dioxomolybdenum(VI) and dioxotungsten(VI) complexes supported by an amido ligand

Stepwise addition of one equivalent of n-butyllithium and trimethylsilyl chloride to 2-tert-butylmercaptoaniline affords the new ligand 1-(Me3SiNH)-2-(t-BuS)C6H4 (LH), that reacts with one equivalent of butyllithium to its lithium salt LLi. Dioxodichloromolybdenum [MoO2Cl2] and dioxodichlorotungsten dimethoxyethane [WO2Cl2(dme)] react in tetrahydrofuran solution at low temperature with two equivalents LLi to monomeric dioxomolybdenum(VI) [MoO2L2] (1) and dioxotungsten(VI) complex [WO2L2] (2) employing two bidentate amido thioether ligands. The crystallographic determination of the molecular structures of 1 and 2 show evidence for M...S contacts. The reaction of [MoO2Cl2] with LLi in tetrahydrofuran solution at room temperature leads next to 1 to two compounds where silyl group migration from nitrogen to oxygen atoms occurs forming [Mo(=NL')2(OSiMe)2] (3) and [Mo(=NL')2(OSiMe3)L] (4, L' = N-2-t-BuSC6H4) as determined by NMR spectroscopy. Compound 4 was isolated in low yield and its molecular structure determined by X-ray crystallography. Higher yields of a bisimido complex can be obtained by the direct reaction of one equivalent of LLi with [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H4) forming [Mo(NAr)2LCl] (5).     

Molybdenum oxo and imido complexes of beta-diketiminate ligands: synthesis and structural aspects

Treatment of [MoO2(eta2-Pz)2] (Pz = 3,5-di-tert-butylpyrazolate) with the diketiminate ligand NacNacH (NacNac = CH[C(Me)NAr]2-, Ar = 2,6-Me2C6H3) at 55 degrees C leads under reduction of the metal to the formation of the dimeric molybdenum(V) compound [{MoO2(NacNac)}2] (1). The compound was characterized by spectroscopic means and by X-ray crystal structure analysis. The dimer consists of a [Mo2O4]2+ core with a short Mo-Mo bond (2.5591(5) A) and one coordinated diketiminate ligand on each metal atom. The reaction of [MoO2(eta2-Pz)2] with NacNacH in benzene at room temperature leads to a mixture of 1 and the monomeric molybdenum(VI) compound [MoO2(NacNac)(eta2-Pz)] (2). From such solutions, yellow crystals of 2 suitable for X-ray structural analysis were obtained revealing the coordination of one bidentate NacNac and one eta2-coordinate Pz ligand. This renders the two oxo groups inequivalent. Further high oxidation state molybdenum compounds containing the NacNac ligand were obtained by the reaction of [Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H3) and [Mo(N-t-Bu)2Cl2(dme)] (dme = dimethoxyethane) with 1 equiv of the potassium salt NacNacK forming [Mo(NAr)2Cl(NacNac)] (3) and [Mo(N-t-Bu)2Cl(NacNac)] (4), respectively, in good yields. The X-ray structure analysis of 3 revealed a penta-coordinate compound where the geometry is best described as trigonal-bipyramidal.     

Dipyrrolyl precursors to bisalkoxide molybdenum olefin metathesis catalysts

Addition of 2 equiv of lithium pyrrolide to Mo(NR)(CHCMe2R')(OTf)2(DME) (OTf = OSO2CF3; R = 2,6-i-Pr2C6H3, 1-adamantyl, or 2,6-Br2-4-MeC6H2; R' = Me or Ph) produces Mo(NR)(CHCMe2R')(NC4H4)2 complexes in good yield. All compounds can be recrystallized readily from toluene or mixtures of pentane and ether and are sensitive to air and moisture. An X-ray structure of a 2,6-diisopropylphenylimido species shows it to be an unsymmetric dimer, {Mo(NAr)(syn-CHCMe2Ph)(eta5-NC4H4)(eta1-NC4H4)}{Mo(NAr)(syn-CHCMe2Ph)(eta1-NC4H4)2}, in which the nitrogen in the eta5-pyrrolyl bound to one Mo behaves as a donor to the other Mo. All complexes are fluxional on the NMR time scale at room temperature, with one symmetric species being observed on the NMR time scale at 50 degrees C in toluene-d8. The dimers react with PMe3 (at Mo) or B(C6F5)3 (at a eta5-NC4H4 nitrogen) to give monomeric products in high yield. They also react rapidly with 2 equiv of monoalcohols (e.g., Me3COH or (CF3)2MeCOH) or 1 equiv of a biphenol or binaphthol to give 2 equiv of pyrrole and bisalkoxide or diolate complexes in approximately 100% yield.     

Synthesis and crystal structure of unprecedented phosphine adducts of d(1)-aryl imido-vanadium(IV) complexes

The reaction of the imido precursor [V(NAr)Cl(2)](n)() (1) (Ar = 2,6-i-Pr(2)C(6)H(3)) with 3 equiv of PMe(2)Ph yields the monomeric complex [V(=NAr)Cl(2)(PMe(2)Ph)(2)] (2). Reacting 1 with 1.5 equiv of dmpe or 1 equiv of dppm affords the dimeric complexes [V(=NAr)Cl(2)(dmpe)](2)(mu-P,P'-dmpe) (3) and [V(=NAr)Cl(2)(dppm)](2) (4), respectively. Complexes 2-4 have been fully characterized by spectroscopic methods, magnetism studies, and X-ray crystallography.     

Imido titanium compounds bearing the 6-dimethylamino-1,4,6-trimethyl-1,4-diazacycloheptane ligand: synthesis, structures, solution dynamics and ethylene polymerisation capability

Reaction of Me(4)DACH (6-dimethylamino-1,4,6-trimethyl-1,4-diazacycloheptane) with Ti(N(t)Bu)Cl(2)(py)(3) or Ti(N(t)Bu)Cl(2)(NHMe(2))(2) gave Ti(N(t)Bu)(Me(4)DACH)Cl(2) (1) which in CD(2)Cl(2) solution exists as a mixture of trans and cis isomers (defined with respect to the imido ligand and the exocyclic NMe(2) donor of Me(4)DACH). Aryl imido analogues of 1 were prepared from Ti(NAr)Cl(2)(NHMe(2))(2) and Me(4)DACH forming Ti(NAr)(Me(4)DACH)Cl(2) (Ar = 2,6-C(6)H(3)Me(2) (2), 2,6-C(6)H(3)(i)Pr(2) (3), 2-C(6)H(4)(t)Bu (4), 2-C(6)H(4)CF(3) (5)) which also exist as isomers in solution. The activation parameters for the interconversion of trans- and cis-3were measured by VT NMR spectroscopy. The solid state structures of trans-1, 3 and and cis-2 have been determined. In the presence of MAO or dried MAO the compounds 1-5 act as moderatley productive ethylene polymerisation catalysts, with a modest productivity gain found on moving from the 1/MAO to 1/dried MAO catalyst system.     

Synthetic, spectroscopic, and structural studies on organoimido molybdenum, tungsten, and rhenium phthalocyanines

Unprecedented imido phthalocyaninato complexes of pentavalent refractory metals [PcM(NR)Cl] (M = Mo, W, Re; R = tBu: 1, 3, 6, Mes: 2, 4, 7 or Ts: 5) have been synthesized by reductive cyclotetramerization of phthalonitrile in the presence of appropriate bis(imido) complexes of Mo, W and Re as templates. While d(1) Mo(V) and W(V) species 1-5 show distinctive EPR spectra corresponding to metal centered radicals with hyperfine coupling of two magnetically non-equivalent nitrogen atoms (4 equatorial and 1 axial N), corresponding d(2) Re(V) compounds 6 and 7 are diamagnetic. [PcMo(NtBu)Cl] 1 crystallizes from 1-chloronaphthalene in the tetragonal space group P4/n. The molecular structure reveals, that the metal center is located above the plane of the equatorial N4 and displaced towards the axial π-donor ligand. Due to the thermodynamic trans effect the Mo-Cl bond trans to the imido group is elongated to about 2.600(2) ?.     

High‐valent Molybdenum Imido Complexes with Tethered Olefins

Against the background of the (propene)Mo(=O)(=NH) and (allyl)Mo(=O)(=NH) surface species suggested as intermediates of the SOHIO process the potential of H₂N–C₆H₄–CH₂– CH=CH–CH₃, ( I ), for the introduction of chelating imido/olefin or imido/allyl ligands at highvalent Mo centres was tested. Reaction of I with Na₂[MoO₄] and trimethylchlorosilane yielded [Cl₂Mo(=N–C₆H₄–CH₂–CH=CH–CH₃)₂(dme)] ( 1 ), containing pendant olefinic arms. All attempts to introduce the olefin into the coordination sphere of the Mo centre failed. The same observation was made with [Cl₂Mo(=O)(=N–C₆H₄–CH₂–CH=CH–CH₃)(dme)] ( 2 ), synthesised via a commutation reaction from 1 and[(dme)Cl₂Mo(=O)₂]. Reaction of three equivalents of I with [CpMoCl_4′] yields [CpCl₂Mo(=N–C₆H₄–CH₂–CH=CH–CH₃)], ( 3 ), again with a pendant olefin arm; the products of experiments aiming at coordinating it to the Mo atom eluded isolation. I thus does not seem suitable for the synthesis of complexes with imido/olefin or imido/allyl ligands. However, products 1 – 3 , (two of which ( 1 , 3 ) were also characterised by single crystal X‐ray diffraction) are nevertheless interesting, e.g., with respect to the grafting of molybdenum complexes on the surfaces of solid supports to obtain heterogeneous oxidation catalysts.     

Synthesis and structure of a series of new d(1)-Aryl imido-vanadium(IV) complexes stabilized by n-donor ligands

A family of new coordination vanadium(IV) compounds supported by a terminal or bridged aryl imido ligand are reported. Reaction of V(NMe(2))(4) with anilines ArNH(2), where Ar = 2,6-i-Pr(2)-C(6)H(3), 2,6-Me(2)-C(6)H(3), Ph, 2,6-Cl(2)-C(6)H(3), and C(6)F(5), afforded the diamagnetic imido-bridged complexes [V(NAr)(NMe(2))(2)](2) (1a-e). Chlorination of 1a-e with trimethylchlorosilane afforded complexes 2a-e formulated as [V(=NAr)Cl(2)(NHMe(2))(x)()](n)(). One-pot reaction of V(NMe(2))(4) with ArNH(2) in the presence of an excess of trimethylchlorosilane gave the five-coordinate compound [V(=NAr)Cl(2)(NHMe(2))(2)] (3a-e). Reaction of 3a-e with pyridine, bipyridine (bipy), or N,N,N',N'-tetramethylethylenediamine (tmeda) gave respectively the six-coordinate tris- or bis(pyridine) adducts [V(=NAr)Cl(2)(Py)(3)] (4a-e) or [V(=NAr)Cl(2)(Py)(2)(NHMe(2))] (5a), bipyridine complexes [V(=NAr)Cl(2)(bipy)(NHMe(2))] (5a-e) and [V(=NAr)Cl(2)(bipy)(Py)] (9a), and tmeda adduct [V(=NAr)Cl(2)(tmeda)(NHMe(2))] (10a). Moreover, five-coordinate complexes free of NHMe(2) ligands, such as [V(=NAr)Cl(2)(Py)(2)] (5a), [V(=NAr)Cl(2)(bipy)] (8a), and [V(=NAr)Cl(2)(tmeda)] (11a), were directly prepared starting from precursors 2a-e. All compounds were totally characterized by spectroscopic methods (IR, (1)H NMR for diamagnetic complexes, and EPR for paramagnetic complexes), elemental analysis, magnetism, and single-crystal X-ray diffraction studies for 1b, 3a, 3d, 4b, 4d, 7c, 10a, and 11a.     

Dithiolate complexes of manganese and rhenium: X-ray structure and properties of an unusual mixed valence cluster Mn3(CO)6(mu-eta2-SCH2CH2CH2S)3

Treatment of Mn(2)(CO)(10) with 3,4-toluenedithiol and 1,2-ethanedithiol in the presence of Me(3)NO.2H(2)O in CH(2)Cl(2) at room temperature afforded the dinuclear complexes Mn(2)(CO)(6)(mu-eta(4)-SC(6)H(3)(CH(3))S-SC(6)H(3)(CH(3))S) (1), and Mn(2)(CO)(6)(mu-eta(4)-SCH(2)CH(2)S-SCH(2)CH(2)S) (2), respectively. Similar reactions of Re(2)(CO)(10) with 3,4-toluenedithiol, 1,2-benzenedithiol, and 1,2-ethanedithiol yielded the dirhenium complexes Re(2)(CO)(6)(mu-eta(4)-SC(6)H(3)(CH(3))S-SC(6)H(3)(CH(3))S) (3), Re(2)(CO)(6)(mu-eta(4)-SC(6)H(4)S-SC(6)H(4)S) (4), and Re(2)(CO)(6)(SCH(2)CH(2)S-SCH(2)CH(2)S) (5), respectively. In contrast, treatment of Mn(2)(CO)(10) with 1,3-propanedithiol afforded the trimanganese compound Mn(3)(CO)(6)(mu-eta(2)-SCH(2)CH(2)CH(2)S)(3) (6), whereas Re(2)(CO)(10) gave only intractable materials. The molecular structures of 1, 3, and 6 have been determined by single-crystal X-ray diffraction studies. The dimanganese and dirhenium carbonyl compounds 1-5contain a binucleating disulfide ligand, formed by interligand disulfide bond formation between two dithiolate ligands identical in structure to that of the previously reported dimanganese complex Mn(2)(CO)(6)(mu-eta(4)-SC(6)H(4)S-SC(6)H(4)S). Complex 6, on the other hand, forms a unique example of a mixed-valence trimangenese carbonyl compound containing three bridging 1,3-propanedithiolate ligands. The solution properties of 6 have been investigated by UV-vis and EPR spectroscopies as well as electrochemical techniques.