Infrared spectroscopic and density functional theory studies on the CO dissociation by scandium and yttrium dimers

Reactions of laser-ablated scandium and yttrium atoms with dilute carbon monoxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. On the basis of the results of the isotopic substitution, the change of laser power and CO concentration and the comparison with density functional theory (DFT) calculations, the absorption at 1193.4 cm(-1) is assigned to the C-O stretching vibration of the Sc(2)[eta(2)(mu(2)-C,O)] molecule, which has a single bridging CO that is tilted to the side. This CO-activated molecule undergoes ultraviolet-visible photoinduced rearrangement to the CO-dissociated molecule, c-Sc(2)(mu-C)(mu-O). The cyclic c-Sc(2)(mu-C)(mu-O) molecule has a bridging carbon on one side of the Sc(2) unit and a bridging oxygen on the other. The analogous Y(2)[eta(2)(mu(2)-C,O)] molecule has not been observed, but the CO-dissociated c-Y(2)(mu-C)(muO) molecule has been observed in the Y + CO experiments. DFT calculations of the geometry structures, vibrational frequencies, and IR intensities strongly support the assignments. The CO activation mechanism has also been discussed. Our experimental and theoretical results schematically depict an activation process to CO dissociation.     

Infrared-spectroscopic and density-functional-theory investigations of the LaCO, La2[eta2(mu2-C,O)], and c-La2(mu-C)(mu-O) molecules in solid argon

Reactions of laser-ablated lanthanum atoms with CO molecules in solid argon have been studied. The neutral lanthanum monocarbonyl (LaCO), produced upon sample deposition at 7 K, exhibits a C-O stretching frequency of 1772.7 cm(-1); to the best of our knowledge this is the lowest yet observed for a terminal CO in a neutral metal-carbonyl molecule (MCO, M = metal atom), implying anomalously enhanced metal-to-CO back-bonding. The infrared (IR) absorption band at 1145.9 cm(-1) is assigned to the C-O stretching mode of the side-on-bonding CO in the La2[eta2(mu2-C,O)] molecule. This CO-activated molecule undergoes an UV/Vis-photoinduced rearrangement to the CO-dissociated molecule, c-La2(mu-C)(mu-O). Density functional theory (DFT) calculations have been performed on these molecules, the results of which lend strong support to the experimental assignments of the IR spectra. LaCO is predicted to have a quartet ground state, corresponding to a linear geometry. Its formation involves La 6s-->4f promotion, which increases the strength of La-CO bonding by decreasing the sigma repulsion and, remarkably, by increasing the La 5d and 4f-->CO 2pi back-bonding. The observations schematically depict the whole process, starting with the interaction of CO with metal and ending with CO dissociation by the lanthanum dimer.     

Reactions of gadolinium atoms and dimers with CO: formation of gadolinium carbonyls and photoconversion to CO activated molecules

Reactions of gadolinium atoms and dimers with carbon monoxide molecules in solid argon have been studied using matrix isolation infrared absorption spectroscopy. Mononuclear Gd(CO)x (x = 1-3) and dinuclear Gd2(CO)x (x = 1, 2) gadolinium carbonyls formed spontaneously on annealing. The Gd(CO)x complexes are CO terminal-bonded carbonyls, whereas the Gd2CO and Gd2(CO)2 carbonyl complexes were characterized to have asymmetrically bridging and side-on-bonded CO, which are drastically activated with remarkably low C-O stretching frequencies. The cyclic Gd2(mu-C)(mu-O) and Gd3(mu-C)(mu-O) molecules in which the C-O triple bond is completely cleaved were also formed on annealing. The Gd2(CO)2 complex rearranged to the more stable c-Gd2(mu-O)(mu-CCO) isomer, which also has a four-membered ring structure with one CO being completely activated.     

Construction of titanasiloxanes by incorporation of silanols to the metal oxide model [(Ti(eta 5-C5Me5)(mu-O))3(mu3-CR)]: DFT elucidation of the reaction mechanism

A family of novel titanasiloxanes containing the structural unit {[Ti(eta(5)-C(5)Me(5))O](3)} were synthesized by hydron-transfer processes involving reactions with equimolecular amounts of mu(3)-alkylidyne derivatives [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu(3)-CR)] (R=H (1), Me (2)) and monosilanols, R(3)'Si(OH), silanediols, R(2)'Si(OH)(2), and the silanetriol tBuSi(OH)(3). Treatment of 1 and 2 with triorganosilanols (R'=Ph, iPr) in hexane affords the new metallasiloxane derivatives [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu-CHR)(OSiR(3)')] (R=H, R'=Ph (3), iPr (4); R=Me, R'=Ph (5), iPr (6)). Analogous reactions with silanediols, (R'=Ph, iPr), give the cyclic titanasiloxanes [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu-O(2)SiR'(2))(R)] (R=Me, R'=Ph (7), iPr (8); R=Et, R'=Ph (9), iPr (10)). Utilization of tBuSi(OH)(3) with 1 or 2 at room temperature produces the intermediate complexes [{Ti(eta(5)-C(5)Me(5)) (mu-O)}(3)(mu-O(2)Si(OH)tBu)(R)] (R=Me (11), Et(12)). Further heating of solutions of 11 or 12 affords the same compound with an adamantanoid structure, [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu-O(3)SitBu)] (13) and methane or ethane elimination, respectively. The X-ray crystal structures of 3, 4, 6, 8, 10, 12, and 13 have been determined. To gain an insight into the mechanism of these reactions, DFT calculations have been performed on the incorporation of monosilanols to the model complex [{Ti(eta(5)-C(5)H(5))(mu-O)}(3)(mu(3)-CMe)] (2 H). The proposed mechanism consists of three steps: 1) hydron transfer from the silanol to one of the oxygen atoms of the Ti(3)O(3) ring, forming a titanasiloxane; 2) intramolecular hydron migration to the alkylidyne moiety; and 3) a mu-alkylidene ligand rotation to give the final product.     

Interplay of cubic building blocks in (et6-arene)ruthenium-containing tungsten and molybdenum oxides

A series of molybdenum and tungsten organometallic oxides containing [Ru(arene)]2+ units (arene =p-cymene, C6Me6) was obtained by condensation of [[Ru(arene)Cl2]2] with oxomolybdates and oxotungstates in aqueous or nonaqueous solvents. The crystal structures of [[Ru(eta6-C6Me6]]4W4O16], [[Ru(eta6-p-MeC6H4iPr]]4W2O10], [[[Ru-(eta6-p-MeC6H4iPr)]2(mu-OH)3]2][[Ru(eta6-p-MeC6H4iPr)]2W8O28(OH)2[Ru(eta6-p-MeC6H4iPr)(H2O)]2], and [[Ru(eta6-C6Me6)]2M5O18[Ru(eta6-C6Me6)(H2O)]] (M = Mo, W) have been determined. While the windmill-type clusters [[Ru(eta6-arene)]4(MO3)4(mu3-O)4] (M = Mo, W; arene =p-MeC6H4iPr, C6Me6), the face-sharing double cubane-type cluster [[Ru(eta6-p-MeC6H4iPr)]4(WO2)2(mu3-O)4(mu4-O)2], and the dimeric cluster [[Ru(eta6-p-MeC6H4iPr)(WO3)3(mu3-O)3(mu3-OH)Ru(eta6-pMeC6H4iPr)(H2O)]2(mu-WO2)2]2- are based on cubane-like units, [(Ru(eta6-C6Me6)]2M5O18[Ru(eta6-C6Me6)(H2O)]] (M = Mo, W) are more properly described as lacunary Lindqvist-type polyoxoanions supporting three ruthenium centers. Precubane clusters [[Ru(eta6-arene)](MO3)2(mu-O)3(mu3-O)]6- are possible intermediates in the formation of these clusters. The cluster structures are retained in solution, except for [[Ru(eta6-p-MeC6H4iPr)]4Mo4O16], which isomerizes to the triple-cubane form.     

Synthesis, characterisation, crystal structures, reactivity, and electrochemistry of ruthenium-nitrido, ruthenium-cobalt-imido and ruthenapyrrolidone carbonyl clusters containing alkyne ligands

Thermolysis of [Ru3(CO)9(mu3-NOMe)(mu3-eta2-PhC2Ph)] (1) with two equivalents of [Cp*Co(CO)2] in THF afforded four new clusters, brown [Ru5(CO)8(mu-CO)3(eta5-C5Me5)(mu5-N)(mu4-eta2-PhC2Ph)] (2), green [Ru3Co2(CO)7(mu3-CO)(eta5-C5Me5)2(mu3-NH)[mu4-eta8-C6H4-C(H)C(Ph)]] (3), orange [Ru3(CO)7(mu-eta6-C5Me4CH2)[mu-eta3-PhC2(Ph)C(O)N(OMe)]] (4) and pale yellow [Ru2(CO)6[mu-eta3-PhC2(Ph)C(O)N(OMe)]] (5). Cluster 2 is a pentaruthenium mu5-nitrido complex, in which the five metal atoms are arranged in a novel "spiked" square-planar metal skeleton with a quadruply bridging alkyne ligand. The mu5-nitrido N atom exhibits an unusually low frequency chemical shift in its 15N NMR spectrum. Cluster 3 contains a triangular Ru2Co-imido moiety linked to a ruthenium-cobaltocene through the mu4-eta8-C6H4C(H)C(Ph) ligand. Clusters 4 and 5 are both metallapyrrolidone complexes, in which interaction of diphenylacetylene with CO and the NOMe nitrene moiety were observed. In 4, one methyl group of the Cp* ring is activated and interacts with a ruthenium atom. The "distorted" Ru3Co butterfly nitrido complex [Ru3Co(CO)5(eta5-C5Me5)(mu4-N)(mu3-eta2-PhC2Ph)(mu-I)2I] (6) was isolated from the reaction of 1 with [Cp*Co(CO)I2] heated under reflux in THF, in which a Ru-Ru wing edge is missing. Two bridging and one terminal iodides were found to be placed along the two Ru-Ru wing edges and at a hinge Ru atom, respectively. The redox properties of the selected compounds in this study were investigated by using cyclic voltammetry and controlled potential coulometry. 15N magnetic resonance spectroscopy studies were also performed on these clusters.     

2 + 2] cross coupling of benzene and tropylium ligands in reductively activated piano stool complexes of Mn,Cr, and W

We have established cation/anion coupling reactions between the tropylium ligand in [M(eta7-C7H7)(CO)3]+ (M = Cr, W) and the reductively activated eta4-benzene ligand in [Mn(eta4-C6H6)(CO)3]- (3-) to form [M(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3]; [Cr(CO)3(mu2-eta6:eta5-C7H7-C6H6)Mn(CO)3] can be further reduced to [Cr(CO)3(mu2-eta5:eta4-C7H7-C6H6)Mn(CO)3]2-, in which the tropylium and benzene ligands have undergone a [2 + 2] cross coupling reaction.     

Hydrocarbon species mu3-CCH2-, mu3-CCH3 and mu-CHCH3 supported on Ti3O3

Treatment of the mu3-ethylidyne complex [{TiCp*(mu-O)}3(mu3-CMe)](1), (Cp*=eta5-C5Me5) with alkali metal amides leads to the oxoheterometallocubane derivatives [M(mu3-O)3{(TiCp*)3(mu3-CCH2)}] [M = Li (2), Na (3), K (4), Rb (5), Cs (6)] containing the naked carbanion mu3-CCH2-; the addition of triphenylmethanol and tert-butanol to the compounds 2-6 gives rise to the oxoderivatives [{TiCp*(mu-O)}3(mu-CHMe)(OCR3)][R = Me (7), Ph (8)] which show a mu-ethylidene bridge on the surface model Ti3O3.     

Unusual coordination assemblies from platinum(II) thienyl and bithienyl complexes

Dinuclear Pt(2)Br(2)(dppf)(2)(mu-C(8)H(4)S(2)) exchanges with isonicotinic acid to release free bithiophene and gives a molecular square [Pt(4)(dppf)(4)(mu(2)-O(2)CC(5)H(4)N)(4)](4+)4OTf(-) which is an "all-ring" system with four Pt rings disposed at the corners of a larger macrocyclic ring. The related mononuclear complex PtBr(eta(1)(C2)-C(4)H(3)S)(dppf) reacts with AgOTf (OTf = triflate) to give [Pt(2)(dppf)(2)(mu(2),eta(1)(C),eta(1)(S)-C(4)H(3)S)(2)](2+)2OTf(-) with an unusual six-membered ring formed by the fusion of two Pt-thienyl entities at the sulfur sites. All the complexes are structurally characterized by single-crystal X-ray crystallography.     

CO activation on the late lanthanide dimers: matrix infrared spectra of the Ln2[eta2(mu2-C, O)]x (Ln = Tb, Dy, Ho, Er, Lu; x = 1, 2) molecules

Reactions of laser-ablated late lanthanide atoms (Tb, Dy, Ho, Er, Tm, Yb, and Lu) with dilute carbon monoxide molecules in solid argon have been investigated using matrix-isolation infrared spectroscopy. The Ln2[eta2(mu2-C, O)]x (Ln = Tb, Dy, Ho, Er, Lu; x = 1, 2) molecules are observed upon sample annealing, whereas no product is observed for Tm and Yb. The C-O stretching frequencies in these dilanthanide carbonyls range from 1100 to 1300 cm-1, far below the value of free CO in the gas phase (2143.5 cm-1), implying that the C-O bonds are highly activated. Density functional theory calculations have been performed on these products. These Ln2[eta2(mu2-C, O)]x molecules are predicted to have planar structures, which carry asymmetrically bridging CO moieties that are tilted to the side.     

Group 13 organoderivatives supported on a metallic oxide model

The [{TiCp*(micro-O)}3(mu3-CH)] (1) metalloligand, (Cp* = eta5-C5Me5), coordinates in a 1:1 ratio to [AlMe3] or 9-BBN to give [{Me3Al}{(mu3-O)(mu-O)2(TiCp)2(TiCp)3(mu3-CH)}](2) or [{(C8H14)B}(mu-H) {(mu3-O)(mu-O)2(TiCp*)3(mu3-CH)}](4), respectively, partial hydrolysis of 2 leads to the new hydroxo-aluminium derivative [{MeAl} {(mu-OH)(mu3-O)}2{(mu-O)2(TiCp*)3-(mu3-CH)}2](3).     

Reactions of 2,4-hexadiyne-1,6-diol with [H2Os3(CO)9(PR3)] clusters. Cyclization of the diyne and reversible exchange of the phosphine ligands between different positions of the "Os3C3" framework

Reactions between unsaturated [H(2)Os(3)(CO)(9)(PR(3))] clusters (PR(3)= PPh(3), P(4-CF(3)-C(6)H(4))(3), PEt(3)) and 2,4-hexadiyne-1,6-diol have been studied. It was found that the diyne ligand easily reacts with all these complexes to give [HOs(3)(CO)8(PR3)-[mu3, eta1:eta3:eta1)-(CH(3)-C-C=CH-CH=C-O)]] complexes (V, VI and VII, respectively) containing the "Os3C3" pentagonal pyramid cluster framework. This structural pattern is formed through the diyne cyclization, dissociation of a CO ligand and eventual coordination of the cyclized organic moiety to the osmium triangle in the [mu3, eta1:eta3:eta1) manner. In the case of the PEt(3) substituted cluster the second hydride transfer onto the organic fragment occurs to afford the nonhydride [Os(3)(CO)(8)(PR3)[mu3), eta1:eta2:eta1)-(CH(3)-CH-C=CH-CH=C-O)]] cluster, VIII, containing distorted pentagonal pyramid framework with a broken Os-C bond. Heating V, VI of VII and in hexane solutions results in formation of the regioisomers (Va, VIa and VIIa) with the phosphine ligand located at adjacent osmium atoms across the Os-Os bond bridged by the coordinated organic fragment. The most probable mechanism of the isomerization includes reversible phosphine migration between these metal centres. Solid-state structure of V, Va, VI, VIIa and VIII have been established by single crystal X-ray diffraction. A general mechanistic scheme for the diyne ligand cyclization and cluster framework transformations is suggested and discussed.     

Synthesis, structures, and solution behavior of di- and trinuclear titanium(IV)--cyclophosphato complexes

The reaction of the cyclotetraphosphate ion (P(4)O(12)(4)(-)) with [CpTiCl(3)] (Cp = eta(5)-C(5)Me(5)) gives [(CpTi)(2)(P(4)O(12))(2)](2)(-) where the P(4)O(12) ligands adopt a saddle conformation, while that with [(CpTiCl)(3)(mu-O)(3)] leads to [(CpTi)(3)(mu-O)(3)(P(4)O(12))](-) containing a crown form P(4)O(12) ligand; both products feature their unique cage structures. On the other hand, the reactions of the cyclotriphosphate ion (P(3)O(9)(3)(-)) with [(CpTiCl(2))(2)(mu-O)] and [(CpTiCl)(3)(mu-O)(3)] afford [(CpTi)(2)(mu-O)(P(3)O(9))(2)](2)(-) and [(CpTi)(3)(mu-O)(3)Cl(P(3)O(9))](-), respectively, and in both cases the P(3)O(9) ligands bridge two titanium centers with an eta(2):eta(1) mode.     

Synthesis and structure of organic-soluble binuclear molecular phosphonates of tantalum,molybdenum, and tungsten

The reaction of (eta 5-C5Me5)TaMe4 with tert-butylphosphonic acid leads to the formation of a mixture of compounds: [[(eta 5-C5Me5)TaMe][t-BuP(O)(OH)][t-BuP(O)(OH)2]]2(t-BuPO3)2 (1) and [[(eta 5-C5Me5)Ta][t-BuP(O)(OH)2]]2(t-BuPO3)2(mu-O)2 (2). Compound 2 was also obtained by recrystallization of 1 from a THF/hexane mixture. Reaction of (eta 5-C5Me5)MCl4 (M = Mo, W) with PhP(O)(OH)2 yields the binuclear phosphonates [[(eta 5-C5Me5)M][PhP(O)(OH)2]]2(PhPO3)2(mu-O)2 (M = Mo (3); M = W (4)). Compounds 2.THF and 3(.)2.5THF were characterized by single-crystal X-ray studies. The tantalum and molybdenum phosphonates 2.THF and 3(.)2.5THF have different structures as compared to those of the previously reported titanophosphonate cages.     

Novel dimetal bridging carbene complexes derived from a terminal carbonyl dimetal compound. Syntheses, structures and reactivities of 7H-indene-coordinated diiron bridging carbene complexes

Pentacarbonyl-7H-indenediiron, [Fe2(CO)5(eta3,eta5-C9H8)] (1), reacts with aryllithium, ArLi (Ar = C6H5, p-C6H5C6H4), followed by alkylation with Et3OBF4 to give novel 7H-indene-coordinated diiron bridging alkoxycarbene complexes [Fe2{mu-C(OC2H5)Ar}(CO)4(eta4,eta4-C9H8)] (2, Ar = C6H5; 3, Ar = p-C6H5C6H4). Complexes 2 and 3 react with HBF4.Et2O at low temperature to yield cationic bridging carbyne complexes [Fe2(mu-CAr)(CO)4(eta4,eta4-C9H8)]BF4 (4, Ar = C6H5; 5, Ar = p-C6H5C6H4). Cationic 4 and 5 react with NaBH4 in THF at low temperature to afford diiron bridging arylcarbene complexes [Fe2{mu-C(H)Ar}(CO)4(eta4,eta4-C9H8)] (6, Ar = C6H5; 7, Ar = p-C6H5C6H4). The similar reactions of 4 and 5 with NaSC6H4CH3-p produce the bridging arylthiocarbene complexes [Fe2{mu-C(Ar)SC6H4CH3-p}(CO)4(eta4,eta4-C9H8)] (8, Ar = C6H5; 9, Ar = p-C6H5C6H4). Cationic 4 and 5 can also react with anionic carbonylmetal compounds Na[M(CO)5(CN)] (M = Cr, Mo, W) to give the diiron bridging aryl(pentacarbonylcyanometal)carbene complexes [Fe2{mu-C(Ar)NCM(CO)5}(CO)4(eta4,eta4-C9H8)] (10, Ar = C6H5, M = Cr; 11, Ar = p-C6H5C6H4, M = Cr; 12, Ar = C6H5, M = Mo; 13, Ar = p-C6H5C6H4, M = Mo; 14, Ar = C6H5, M = W; 15, Ar = p-C6H5C6H4, M = W). Interestingly, in CH2Cl2 solution at room temperature complexes 10-15 were transformed into the isomerized 7H-indene-coordinated monoiron complexes [Fe(CO)2(eta5-C9H8)C(Ar)NCM(CO)5] (16, Ar = C6H5, M = Cr; 17, Ar = p-C6H5C6H4, M = Cr; 18, Ar = C6H5, M = Mo; 19, Ar = p-C6H5C6H4, M = Mo; 20, Ar = C6H5, M = W; 21, Ar = p-C6H5C6H4, M = W), while complex 3 was converted into a novel ring addition product [Fe2{C(OC2H5)C6H4C6H5-p-(eta2,eta5-C9H8)}(CO)5] (22) under the same conditions. The structures of complexes 2, 6, 8, 14, 18 and 22 have been established by X-ray diffraction studies.     

Reductive cyclotetramerization of CO to squarate by a U(III) complex: the X-ray crystal structure of [(U (eta-C8H6{SiiPr3-1,4}2)(eta-C5Me4H)]2(mu-eta2: eta2-C4O4)

The U(III) mixed-sandwich compound [U(eta-C5Me4H)(eta-C8H6{SiiPr3-1,4}2)(THF)] 1 may be prepared by sequential reaction of UI3 with K[C5Me4H] in THF followed by K2[C8H6{SiiPr3-1,4}2]. 1 reacts with carbon monoxide at -30 degrees C and 1 bar pressure in toluene solution to afford the crystallographically characterized dimer [(U(eta-C8H6{SiiPr3-1,4}2)(eta-C5Me4H)]2(mu-eta2: eta2-C4O4) 2, which contains a bridging squarate unit derived from reductive cyclotetramerization of CO. DFT computational studies indicate that addition of a 4th molecule of CO to the model deltate complex [U(eta-COT)(eta-Cp)]2(mu-eta1: eta2-C3O3)] to form the squarate complex [U(eta-COT)(eta-Cp)]2(mu-eta2: eta2-C4O4)] is exothermic by 136 kJ mol-1.     

Titanium(IV) and zirconium(IV) sulfato complexes containing the Kläui tripodal ligand: molecular models of sulfated metal oxide surfaces

Treatment of titanyl sulfate in about 60 mM sulfuric acid with NaL(OEt) (L(OEt) (-)=[(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)}(3)](-)) afforded the mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(2)(mu-SO(4))] (2). In more concentrated sulfuric acid (>1 M), the same reaction yielded the di-mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(mu-SO(4))(2)] (3). Reaction of 2 with HOTf (OTf=triflate, CF(3)SO(3)) gave the tris(triflato) complex [L(OEt)Ti(OTf)(3)] (4), whereas treatment of 2 with Ag(OTf) in CH(2)Cl(2) afforded the sulfato-capped trinuclear complex [{(L(OEt))(3)Ti(3)(mu-O)(3)}(mu(3)-SO(4)){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a mu-oxo group in the Ti(3)(mu-O)(3) core. Reaction of 2 in H(2)O with Ba(NO(3))(2) afforded the tetranuclear complex (L(OEt))(4)Ti(4)(mu-O)(6) (6). Treatment of 2 with [{Rh(cod)Cl}(2)] (cod=1,5-cyclooctadiene), [Re(CO)(5)Cl], and [Ru(tBu(2)bpy)(PPh(3))(2)Cl(2)] (tBu(2)bpy=4,4'-di-tert-butyl-2,2'-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L(OEt))(2)Ti(2)(O)(2)(SO(4)){Rh(cod)}(2)][OTf](2) (7), [(L(OEt))(2)Ti(O)(2)(SO(4)){Re(CO)(3)}][OTf] (8), and [{(L(OEt))(2)Ti(2)(mu-O)}(mu(3)-SO(4))(mu-O)(2){Ru(PPh(3))(tBu(2)bpy)}][OTf](2) (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 mu(B). Treatment of zirconyl nitrate with NaL(OEt) in 3.5 M sulfuric acid afforded [(L(OEt))(2)Zr(NO(3))][L(OEt)Zr(SO(4))(NO(3))] (10). Reaction of ZrCl(4) in 1.8 M sulfuric acid with NaL(OEt) in the presence Na(2)SO(4) gave the mu-sulfato-bridged complex [L(OEt)Zr(SO(4))(H(2)O)](2)(mu-SO(4)) (11). Treatment of 11 with triflic acid afforded [(L(OEt))(2)Zr][OTf](2) (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L(OEt)Zr(SO(4))(H(2)O)}(3)(mu(3)-SO(4))][OTf] (13). The Zr(IV) triflato complex [L(OEt)Zr(OTf)(3)] (14) was prepared by reaction of L(OEt)ZrF(3) with Me(3)SiOTf. Complexes 4 and 14 can catalyze the Diels-Alder reaction of 1,3-cyclohexadiene with acrolein in good selectivity. Complexes 2-5, 9-11, and 13 have been characterized by X-ray crystallography.     

Molybdenum amido complexes with single Mo-N bonds: synthesis,structure, and reactivity

Reactions of the complex [MoCl(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1) (phen=1,10-phenanthroline) with potassium arylamides were used to synthesize the amido complexes [Mo(N(R)Ar)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (R=H, Ar=Ph, 2 a; R=H, Ar=p-tolyl, 2 b; R=Me, Ar=Ph; 2 c). For 2 b the Mo-N(amido) bond length (2.105(4) A) is consistent with it being a single bond, with which the metal attains an 18-electron configuration. The reaction of 2 b with HOTf affords the amino complex [Mo(eta(3)-C(3)H(4)-Me-2)(NH(2)(p-tol))(CO)(2)(phen)]OTf (3-OTf). Treatment of 3-OTf with nBuLi or KN(SiMe(3))(2) regenerates 2 b. The new amido complexes react with CS(2), arylisothiocyanates and maleic anhydride. A single product corresponding to the formal insertion of the electrophile into the Mo-N(amido) bond is obtained in each case. For maleic anhydride, ring opening accompanied the formation of the insertion product. The reaction of 2 b with maleimide affords [Mo(eta(3)-C(3)H(4)-Me-2)[NC(O)CH=CHC(O)](CO)(2)(phen)] (7), which results from simple acid-base metathesis. The reaction of 2 b with (p-tol)NCO affords [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(eta(2)-MoO(4))] (8), which corresponds to oxidation of one third of the metal atoms to Mo(VI). Complex 8 was also obtained in the reactions of 2 b with CO(2) or the lactide 3,6-dimethyl-1,4-dioxane-2,5-dione. The structures of the compounds 2 b, 3-OTf, [Mo(eta(3)-C(3)H(4)-Me-2)[SC(S)(N(H)Ph)](CO)(2)(phen)] (4), [Mo(eta(3)-C(3)H(4)-Me-2)[SC(N(p-tol))(NH(p-tol))](CO)(2)(phen)] (5 a), and [Mo(eta(3)-C(3)H(4)-Me-2)[OC(O)CH=CHC(O)(NH(p-tol))](CO)(2)(phen)] (6), 7, and 8 (both the free complex and its N,N'-di(p-tolyl)urea adduct) were determined by X-ray diffraction.     

Carbon-oxygen bond cleavage with eta9,eta5-bis(indenyl)zirconium sandwich complexes

Treatment of the eta9,eta5-bis(indenyl)zirconium sandwich complex, (eta9-C9H5-1,3-(SiMe3)2)(eta5-C9H5-1,3-(SiMe3)2)Zr, with dialkyl ethers such as diethyl ether, CH3OR (R=Et, nBu, tBu), nBu2O, or iPr2O resulted in facile C-O bond scission furnishing an eta5,eta5-bis(indenyl)zirconium alkoxy hydride complex and free olefin. In cases where ethylene is formed, trapping by the zirconocene sandwich yields a rare example of a crystallographically characterized, base-free eta5,eta5-bis(indenyl)zirconium ethylene complex. Observation of normal, primary kinetic isotope effects in combination with rate studies and the stability of various model compounds support a mechanism involving rate-determining C-H activation to yield an eta5,eta5-bis(indenyl)zirconium alkyl hydride intermediate followed by rapid beta-alkoxide elimination. For isolable eta6,eta5-bis(indenyl)zirconium THF compounds, thermolysis at 85 degrees C also resulted in C-O bond cleavage to yield the corresponding zirconacycle. Both mechanistic and computational studies again support a pathway involving haptotropic rearrangement to eta5,eta5-bis(indenyl)zirconium intermediates that promote rate-determining C-H activation and ultimately C-O bond scission.     

Phosphato, chromato, and perrhenato complexes of titanium(IV) and zirconium(IV) containing Kläui's tripodal ligand

Treatment of titanyl sulfate in dilute sulfuric acid with 1 equiv of NaL(OEt) (L(OEt)(-) = [(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)](3)](-)) in the presence of Na(3)PO(4) and Na(4)P(2)O(7) led to isolation of [(L(OEt)Ti)(3)(mu-O)(3)(mu(3-)PO(4))] (1) and [(L(OEt)Ti)(2)(mu-O)(mu-P(2)O(7))] (2), respectively. The structure of 1 consists of a Ti(3)O(3) core capped by a mu(3)-phosphato group. In 2, the [P(2)O(7)](4-) ligands binds to the two Ti's in a mu:eta(2),eta(2) fashion. Treatment of titanyl sulfate in dilute sulfuric acid with NaL(OEt) and 1.5 equiv of Na(2)Cr(2)O(7) gave [(L(OEt)Ti)(2)(mu-CrO(4))(3)] (3) that contains two L(OEt)Ti(3+) fragments bridged by three mu-CrO(4)(2-)-O,O' ligands. Complex 3 can act as a 6-electron oxidant and oxidize benzyl alcohol to give ca. 3 equiv of benzaldehyde. Treatment of [L(OEt)Ti(OTf)(3)] (OTf(-) = triflate) with [n-Bu(4)N][ReO(4)] afforded [[L(OEt)Ti(ReO(4))(2)](2)(mu-O)] (4). Treatment of [L(OEt)MF(3)] (M = Ti and Zr) with 3 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(3)] (5) and [L(OEt)Zr(ReO(4))(3)(H(2)O)] (6), respectively. Treatment of [L(OEt)MF(3)] with 2 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(2)F] (7) and [[L(OEt)Zr(ReO(4))(2)](2)(mu-F)(2)] (8), respectively, which reacted with Me(3)SiOTf to give [L(OEt)M(ReO(4))(2)(OTf)] (M = Ti (9), Zr (10)). Hydrolysis of [L(OEt)Zr(OTf)(3)] (11) with Na(2)WO(4).xH(2)O and wet CH(2)Cl(2) afforded the hydroxo-bridged complexes [[L(OEt)Zr(H(2)O)](3)(mu-OH)(3)(mu(3)-O)][OTf](4) (12) and [[L(OEt)Zr(H(2)O)(2)](2)(mu-OH)(2)][OTf](4) (13), respectively. The solid-state structures of 1-3, 6, and 11-13 have been established by X-ray crystallography. The L(OEt)Ti(IV) complexes can catalyze oxidation of methyl p-tolyl sulfide with tert-butyl hydroperoxide. The bimetallic Ti/ Re complexes 5 and 9 were found to be more active catalysts for the sulfide oxidation than other Ti(IV) complexes presumably because Re alkylperoxo species are involved as the reactive intermediates.