Mono(dinitrogen) and carbon monoxide adducts of bis(cyclopentadienyl) titanium sandwiches

The silyl-substituted titanocene complex, (eta5-C5Me4SiMe2Ph)2Ti, coordinates dinitrogen upon cooling to -35 degrees C to yield an unprecedented example of a mono(dinitrogen) complex of a substituted bis(cyclopentadienyl) titanium compound, (eta5-C5Me4SiMe2Ph)2Ti(N2). Analogous monocarbonyl derivatives, (eta5-C5Me4R)2Ti(CO) (R = SiMe3, SiMe2Ph, CHMe2), have been prepared by mixing the dicarbonyl compounds with the corresponding sandwiches. Both (eta5-C5Me4SiMe2Ph)2Ti(N2) and (eta5-C5Me4SiMe2Ph)2Ti(CO) have been characterized by X-ray diffraction, and mixed N2-CO titanocene complexes have also been observed by in situ IR spectroscopy.     

Cube-type nitrido complexes containing titanium and zinc/copper

Several azaheterometallocubane complexes containing [MTi3N4] cores have been prepared by the reaction of [{Ti(eta5-C5Me5)(mu-NH)}3(mu3-N)] (1) with zinc(II) and copper(I) derivatives. The treatment of 1 with zinc dichloride in toluene at room temperature produces the adduct [Cl2Zn{(mu3-NH)3Ti3(eta5-C5Me5)3(mu3-N)}] (2). Attempts to crystallize 2 in dichloromethane gave yellow crystals of the ammonia adduct [(H3N)Cl2Zn{(mu3-NH)Ti3(eta5-C5Me5)3(mu-NH)2(mu3-N)}] (3). The analogous reaction of 1 with alkyl, (trimethylsilyl)cyclopentadienyl, or amido zinc complexes [ZnR2] leads to the cube-type derivatives [RZn{(mu3-N)(mu3-NH)2Ti3(eta5-C5Me5)3(mu3-N)}] (R = CH2SiMe3 (5), CH2Ph (6), Me (7), C5H4SiMe3 (8), N(SiMe3)2 (9)) via RH elimination. The amido complex 9 decomposes in the presence of ambient light to generate the alkyl derivative [{Me3Si(H)N(Me)2SiCH2}Zn{(mu3-N)(mu3-NH)2Ti3(eta5-C5Me5)3(mu3-N)}] (10). The chloride complex 2 reacts with lithium cyclopentadienyl or lithium indenyl reagents to give the cyclopentadienyl or indenyl zinc derivatives [RZn{(mu3-N)(mu3-NH)2Ti3(eta5-C5Me5)3(mu3-N)}] (R = C5H5 (11), C9H7 (12)). Treatment of 1 with copper(I) halides in toluene at room temperature leads to the adducts [XCu{(mu3-NH)3Ti3(eta5-C5Me5)3(mu3-N)}] (X = Cl (13), I (14)). Complex 13 reacts with lithium bis(trimethylsilyl)amido in toluene to give the precipitation of [{Cu(mu4-N)(mu3-NH)2Ti3(eta5-C5Me5)3(mu3-N)}2] (15). Complex 15 is prepared in a higher yield through the reaction of 1 with [{CuN(SiMe3)2}4] in toluene at 150 degrees C. The addition of triphenylphosphane to 15 in toluene produces the single-cube compound [(Ph3P)Cu{(mu3-N)(mu3-NH)2Ti3(eta5-C5Me5)3(mu3-N)}] (16). The X-ray crystal structures of 3, 8, 9, and 15 have been determined.     

Alkyl-eta2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl-eta5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)]. NMR studies for all of the new compounds and DFT calculations for the alkene-coordinated metal complexes are compared with those known for related group 4 metal cations.     

Solution structures and dynamic properties of chelated d(0) metal olefin complexes [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))(+) (R = H, Me): Models for the [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(R')(olefin)(+) intermediates in "constrained geometry" catalysts.

To model the Ti-olefin interaction in the putative [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(R')(olefin)(+) intermediates in "constrained geometry" Ti-catalyzed olefin polymerization, chelated alkoxide olefin complexes [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))(+) have been investigated. The reaction of [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]TiMe(2) (1a,b; R = H, Me) with HOCMe(2)CH(2)CH(2)CH=CH(2) yields mixtures of [eta(5)-C(5)R(4)SiMe(2)NH(t)Bu]TiMe(2)(OCMe(2)CH(2)CH(2)CH=CH(2)) (2a,b) and [eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]TiMe(OCMe(2)CH(2)CH(2)CH=CH(2)) (3a,b). The reaction of 2a/3a and 2b/3b mixtures with B(C(6)F(5))(3) yields the chelated olefin complexes [[eta(5): eta(1)-C(5)R(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))][MeB(C(6)F(5))(3)] (4a,b; 71 and 89% NMR yield). The reaction of 2b/3b with [Ph(3)C][B(C(6)F(5))(4)] yields [[eta(5): eta(1)-C(5)Me(4)SiMe(2)N(t)Bu]Ti(OCMe(2)CH(2)CH(2)CH=CH(2))][B(C(6)F(5))(4)] (5b, 88% NMR yield). NMR studies establish that 4a,b and 5b exist as mixtures of diastereomers (isomer ratios: 4a/4a', 62/38; 4b/4b', 75/25; 5b/5b', 75/25), which differ in the enantioface of the olefin that is coordinated. NMR data for these d(0) metal olefin complexes show that the olefin coordinates to Ti in an unsymmetrical fashion primarily through C(term) such that the C=C pi bond is polarized with positive charge buildup on C(int). Dynamic NMR studies show that 4b/4b' undergoes olefin face exchange by a dissociative mechanism which is accompanied by fast inversion of configuration at Ti ("O-shift") in the olefin-dissociated intermediate. The activation parameters for the conversion of 4b to 4b' (i.e., 4b/4b' face exchange) are: DeltaH = 17.2(8) kcal/mol; DeltaS = 8(1) eu. 4a/4a' also undergoes olefin face exchange but with a lower barrier (DeltaH = 12.2(9) kcal/mol; DeltaS = -2(3) eu), for the conversion of 4a to 4a'.     

Ammonolysis of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives

Ammonolyses of mono(pentamethylcyclopentadienyl) titanium(IV) derivatives [Ti(eta5-C5Me5)X3] (X = NMe2, Me, Cl) have been carried out in solution to give polynuclear nitrido complexes. Reaction of the tris(dimethylamido) derivative [Ti(eta5-C5Me5)(NMe2)3] with excess of ammonia at 80-100 degrees C gives the cubane complex [[Ti(eta5-C5Me5)]4(mu3-N)4] (1). Treatment of the trimethyl derivative [Ti(eta5-C5Me5)Me3] with NH3 at room temperature leads to the trinuclear imido-nitrido complex [[Ti(eta/5-CsMes)(mu-NH)]3(mu3-N)] (2) via the intermediate [[Ti(eta5-C5Me5)Me]2(mu-NH)2] (3). The analogous reaction of [Ti(eta5-C5Me5)Me3] with 2,4,6-trimethylaniline (ArNH2) gives the dinuclear imido complex [[Ti(eta5-C5Me5)Me])2(mu-NAr)2] (4) which reacts with ammonia to afford [[Ti(eta5-C5Me5)(NH2)]2(mu-NAr)2] (5). Complex 2 has been used, by treatments with the tris(dimethylamido) derivatives [Ti(eta5-C5H5-nRn)(NMe2)3], as precursor of the cubane nitrido systems [[Ti4(eta5-C5Me5)3(eta5-C5H5-nRn)](mu3-N)4] [R = Me n = 5 (1), R = H n = 0 (6), R = SiMe3 n = 1 (7), R = Me n = 1 (8)] via dimethylamine elimination. Reaction of [Ti(eta5-C5Me5)Cl3] or [Ti(eta5-C5Me5)(NMe2)Cl2] with excess of ammonia at room temperature gives the dinuclear complex [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) where an intramolecular hydrogen bonding and a nonlineal nitrido ligand bridge the "Ti(eta5-C5Me5)Cl(NH3)" and "Ti(eta5-C5Me5)Cl2" moieties. The molecular structures of [[Ti(eta5-C5Me5)Me]2 (mu-NAr)2] (4) and [[Ti2(eta5-C5Me5)2Cl3(NH3)](mu-N)] (9) have been determined by X-ray crystallographic studies. Density functional theory calculations also have been conducted on complex 9 to confirm the existence of an intramolecular N-H...Cl hydrogen bond and to evaluate different aspects of its molecular disposition.     

Synthesis, structural characterization, reactivity, and thermal stability of [eta(5):sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2)

Reaction of [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]TiCl(NMe2) (1) with 1 equiv of PhCH2K, MeMgBr, or Me3SiCH2Li gave corresponding organotitanium alkyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(R)(NMe2) (R = CH2Ph (2), CH2SiMe3 (4), or Me (5)) in good yields. Treatment of 1 with 1 equiv of n-BuLi afforded the decomposition product {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe)(mu:sigma-CH2NMe) (3). Complex 5 slowly decomposed to generate a mixed-valence dinuclear species {[eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti}2(mu-NMe2)(mu:sigma-CH2NMe) (6). Complex 1 reacted with 1 equiv of PhNCO or 2,6-Me2C6H3NC to afford the corresponding monoinsertion product [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-OC(NMe2)NPh] (7) or [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(Cl)[eta(2)-C(NMe2)=N(2,6-Me2C6H3)] (8). Reaction of 4 or 5 with 1 equiv of R'NC gave the titanium eta(2)-iminoacyl complexes [eta:(5)sigma-Me2C(C5H4)(C2B10H10)]Ti(NMe2)[eta(2)-C(R)=N(R')] (R = CH2SiMe3, R' = 2,6-Me2C6H3 (9) or tBu (10); R = Me, R' = 2,6-Me2C6H3 (11) or tBu (12)). The results indicated that the unsaturated molecules inserted into the Ti-N bond only in the absence of the Ti-C(alkyl) bond and that the Ti-C(cage) bond remained intact. All complexes were fully characterized by various spectroscopic techniques and elemental analyses. Molecular structures of 2, 3, 6-8, and 10-12 were further confirmed by single-crystal X-ray analyses.     

Synthesis, characterization and reactivity of new complexes of titanium and zirconium containing a potential tridentate amidinato-cyclopentadienyl ligand

Group 4 metal complexes [M(eta(5)-C(5)Me(4)SiMe(2)-eta(1)-N-2R)(NMe(2))(2)] (R = pyridine, pyrazine, pyrimidine, thiazole, M = Ti; R = pyridine, thiazole; M = Zr) containing the tetramethylcyclopentadienyl-dialkylsilyl bridged amidinato as pendant ligand, were synthesized and characterized by elemental analysis, solution (1)H, (13)C and (15)N NMR spectroscopy and experimental (13)C and (15)N CPMAS in the solid state. The crystal structures of [Ti(eta(5)-C(5)Me(4)SiMe(2)-eta(1)-N-2R)(NMe(2))(2)] (R = pyridine, pyrazine, pyrimidine, thiazole) were determined by single crystal X-ray diffraction studies. All compounds exhibit a distorted tetrahedral geometry, with the ansa-monocyclopentadienyl-amido ligands acting in a bidentate mode. The [M(eta(5)-C(5)Me(4)SiMe(2)-eta(1)-N-2R)(NMe(2))(2)] (R = pyridine, thiazole; M = Zr, Ti) complexes are ethylene polymerization catalysts in the presence of MAO and they are active precursors in regioselective catalytic hydroamination operating with an anti-Markovnikov mechanism.     

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.     

47, 49Ti NMR spectra of half-sandwich titanium(IV) complexes

The 47, 49Ti chemical shifts, resonance line half-widths (Deltanu1/2) and energies of the first electronic charge-transfer transitions (lambdamax1.CT) of Cp'TiX3, where Cp' = eta5-C5H5 (Cp), eta5-C5H4Me (MeCp), eta5-C5HMe4 (Me4Cp), eta5-C5Me5 (Me5Cp), eta5-C5H4SiMe3 (SiCp), eta5-C5H4SnMe3 (SnCp) and eta5-C5H4SiMe2Cl (Si'Cp) and X = Cl, Br, I and OBut, half-sandwich complexes are reported. For the compounds studied, a direct linear relationship between delta(49Ti) and lambdamax1.CT was found.     

Dinitrogen activation by titanium sandwich complexes

The activation of dinitrogen by titanium sandwich complexes of the general form (eta5-C5Me4R)2Ti (R = CHMe2, CMe3, SiMe3) has been systematically investigated. Low-temperature, in situ, solution infrared spectroscopy has allowed detection of monomeric bis-dinitrogen complexes of titanium that are isostructural with more familiar dicarbonyl derivatives. One example, (eta5-C5Me4CHMe2)2Ti(N2)2, has also been characterized by X-ray diffraction and reveals weakly activated dinitrogen ligands. From the solution IR data, the relative azophilicity of the titanium sandwich complexes has been established and increases with smaller cyclopentadienyl substituents.     

Titanium "constrained geometry" complexes with pendant arene groups

The synthesis of the proligands C(5)Me(4)HSiMe(2)N(H)R) (R = CMe(2)Ph 1, 2-C(6)H(4)Ph 2) was accomplished via a straightforward salt metathesis reaction of the appropriate lithium amide and ClSiMe(2)(C(5)Me(5)H). Generation of the dilithio salt and reaction with TiCl(3)·(THF)(3) followed by oxidation gave C(5)Me(4)SiMe(2)N(C(6)H(4)Ph)TiCl(2) (3) in low yield. In contrast, deprotonation of 1 and 2 and reaction with (Me(2)N)(2)TiCl(2) afforded C(5)Me(4)(SiMe(2)NR)Ti(NMe(2))(2) (R = CMe(2)Ph 4, 2-C(6)H(4)Ph 5), respectively, in good yields Treatment with MeI gave the analogs C(5)Me(4)(SiMe(2)NR)TiI(2) (R = CMe(2)Ph 6, 2-C(6)H(4)Ph 7). Reduction of 7 with potassium graphite afforded C(5)Me(4)(SiMe(2)NC(6)H(4)Ph)Ti 8. Treatment of 6 and 7 with MeMgBr afforded C(5)Me(4)(SiMe(2)NR)TiMe(2) (R = CMe(2)Ph 9, 2-C(6)H(4)Ph 10). Complexes 9 and 10 in combination with the activator [Ph(3)C][B(C(6)F(5))(4)] catalyzed the polymerization of styrene and ethylene. Copolymerization was also investigated. While the catalyst derived from 10 showed poor activity, compound 9 showed markedly higher activity than 10 and (C(5)Me(4))SiMe(2)(NtBu)]TiMe(2).     

Different C-C coupling reactions of permethyltitanocene and permethylzirconocene with disubstituted 1,3-butadiynes

Herein we describe different C-C coupling reactions of permethyltitanocene and -zirconocene with disubstituted 1,3-butadiynes. The outcomes of these reactions vary depending on the metals and the diyne substituents. The reduction of [Cp2*MCl2] (Cp* = C5Me5; M = Ti, Zr) with Mg in the presence of disubstituted butadiynes RC triple bond C-C triple bond CR' is suitable for the synthesis of different C-C coupling products of the diyne and the permethylmetallocenes, and provides a new method for the generation of functionalized pentamethyl-cyclopentadienyl derivatives. For M = Zr and R = R' = tBu, the reaction gives, by a twofold activation of one pentamethylcyclopentadienyl ligand, the complex [Cp*Zr[-C(=C=CHtBu)-CHtBu-CH2-eta5-C5Me3-CH2-]] (3), containing a fulvene ligand that is coupled to the modified substrate (allenic subunit). When using the analogous permethyltitanocene fragment "Cp2*Ti", the reaction depends strongly on the substituents R and R'. The coupling product of the butadiyne with two methyl groups of one of the pentamethylcyclopentadienyl ring systems, [Cp*Ti[eta5-C5Me3-(CH2-CHR-eta2-C2-CHR'-CH2)]], is obtained with R = R' = tBu (4) and R = tBu, R' = SiMe3 (5). In these complexes one pentamethylcyclopentadienyl ligand is annellated to an eight-membered ring with a C-C triple bond, which is coordinated to the titanium center. A different activation of both pentamethylcyclopentadienyl ligands is observed for R = R' = Me, resulting in the complex [[eta5-C5Me4(CH2)-]Ti[-C(=CHMe)-C(=CHMe)-CH2-eta5-C5Me4]] (6), which displays a fulvene as well as a butadienyl-substituted pentamethylcyclopentadienyl ligand. The influence exerted by the size of the metal is illustrated in the reaction of [Cp2*ZrCl2] with MeC triple bond C-C triple bond CMe. Here the five-membered metallacyclocumulene complex [Cp2*Zr(eta4-1,2,3,4-MeC4Me)] (7) is obtained. The reaction paths found for R = R' = Me are identical to those formerly described for R = R' = Ph.     

Synthesis and structure of boron-bridged constrained geometry complexes of titanium

The boron-bridged constrained geometry titanium complexes [Ti[eta5:eta1-(C5H4)B(NR2)NPh](NMe2)2][R = iPr (3), SiMe3(4)] and [Ti[eta5:eta1-(C9H6)B(NiPr2)NPh](NMe2)2](12) have been prepared in good yields by amine elimination reaction from [Ti(NMe2)4]. Subsequent deamination-chlorination with excess Me3SiCl yielded the corresponding dichloro-complexes (5, 6, 13). Reaction of the analogous ligand precursors (C5H5)B(NiPr2)N(H)R (R = Cy, tBu) with [Ti(NMe2)4] did not result in the expected bridged compounds, but rather in the half-sandwich complexes [Ti[(eta5-C5H4)B(NiPr2)N(H)R](NMe2)3][R = Cy (9), tBu (10)]. All compounds were fully characterised by means of multinuclear NMR spectroscopy. Thorough investigation of substituent effects was achieved by comparative X-ray diffraction studies on complexes 3, 5, 6 and 12.     

Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2): observation of side-on and end-on diazenido complexes in the reduction of N2 to hydrazine

Functionalization of the N2 ligand in the side-on bound dinitrogen complex, [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocene diazenido complexes, [(eta5-C5Me4H)2Zr(C[triple bond]CR)]2(mu2,eta2,eta2-N2H2) (R = nBu, tBu, Ph). Characterization of [(eta5-C5Me4H)2Zr(C[triple bond]CCMe3)]2(mu2,eta2,eta2-N2H2) by X-ray diffraction revealed a side-on bound diazenido ligand in the solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion between eta1,eta1 and eta2,eta2 hapticity of the [N2H2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(eta5-C5Me4H)2ZrX]2(mu2,eta1,eta1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded eta1,eta1 coordination of the [N2H2]2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases pi-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(eta5-C5Me4H)2ZrH]2(mu2,eta2,eta2-N2H2), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting alpha-migration and N2 cleavage up to temperatures of 115 degrees C. Dinitrogen functionalization with [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) was also accomplished by addition of proton donors. Weak Br?nsted acids such as water and ethanol yield hydrazine and (eta5-C5Me4H)2Zr(OH)2 and (eta5-C5Me4H)2Zr(OEt)2, respectively. Treatment of [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) with HNMe2 or H2NNMe2 furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(eta5-C5Me5)2Zr(eta1-N2)]2(mu2,eta1,eta1-N2) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.     

Activation of a CNXylyl ancillary ligand in the reaction of electron-deficient alkynes with a phosphido niobocene complex

The niobium phosphido complex [Nb(eta5-C5H4SiMe3)2-(CNXylyl)(PPh2)] (2) undergoes an unusual cycloaddition reaction with electron-deficient alkynes to give the novel five-membered heteroniobacycles [Nb(eta5-C5H4SiMe3)2(kappaC-C(=N(Xylyl))C(CO2Me)=C(R)PPh2-kappaP)] (R = H 3 and R = Me 4).     

Synthesis and characterisation of aluminium(III) and tin(II) complexes bearing quinoline-based N,N,O-tridentate ligands and their catalysis in the ring-opening polymerisation of ε-caprolactone

The synthesis and catalysis in the ring-opening polymerisation (ROP) of ε-caprolactone (ε-CL) of aluminium(iii) and tin(ii) complexes supported by quinoline-based N,N,O-tridentate ligands are reported. Reaction of 8-{RC(O)CH(2)P(Ph(2)) = N}C(9)H(6)N (R = Bu(t), 2; R = Ph, 3) with AlMe(3) gave [Al(Me(2)){OCR = CHP(Ph(2)) = N(8-C(9)H(6)N)}] (R = Bu(t), 4; R = Ph, 5). Treatment of 2 and 3 with Sn[N(SiMe(3))(2)](2) generated tin(ii) complexes [Sn{OC(R) = CHP(Ph(2)) = N(8-C(9)H(6)N)}{N(SiMe(3))(2)}] (R = Bu(t), 6; R = Ph, 7). A similar reaction of AlMe(3) with 8-{MeC(O)CH(2)C(Me) = N}C(9)H(6)N gave [Al(Me(2)){OC(Me) = CHC(Me) = NC(9)H(6)N}] (9). Compounds 2-9 were characterised by NMR spectroscopy and elemental analysis. The molecular structures of complexes 4, 6 and 9 were determined by single crystal X-ray diffraction techniques. Investigation of catalysis of complexes 4-7 and 9 in the ROP of ε-CL revealed that the aluminium complexes, 4, 5 and 9, are much more active than the tin(ii) complexes. The kinetic studies for the polymerisation of ε-CL catalysed by complexes 4, 5 and 9 in the presence of benzyl alcohol (BnOH) indicated that the polymerisations proceed with the first-order dependence on monomer concentration. The polymerisation was well controlled and gave a polymer with narrow molecular weight distribution.     

A new mode of reactivity for pyridine N-oxide: C-H activation with uranium(IV) and thorium(IV) bis(alkyl) complexes

Uranium(IV) and thorium(IV) bis(alkyl) complexes of the type (C5Me5)2AnR2 (An = U, Th; R = CH3, CH2Ph) activate the sp2 and sp3 hybridized C-H bonds in pyridine N-oxide and lutidine N-oxide to produce the corresponding cyclometalated complexes, (C5Me5)2An(R)[eta2-(O,C)-ONC5H4] and (C5Me5)2An(R)[eta2-(O,C)-ON-2-CH2-5-CH3-C5H3]. These provide rare examples of C-H activation chemistry mediated by actinide metal centers. This chemistry is in contrast to the known oxygen atom transfer reactivity patterns of pyridine N-oxides with oxophilic metal complexes and constitutes a new mode of reactivity for pyridine N-oxides.     

Synthesis of bis(indenyl)zirconium dihydrides and subsequent rearrangement to eta5,eta3-4,5-dihydroindenediyl ligands: evidence for intermediates during the hydrogenation to tetrahydroindenyl derivatives

Exposure of eta9,eta5-bis(indenyl)zirconium sandwich complexes to 4 atm of H2 resulted in facile oxidative addition to furnish the corresponding zirconocene dihydrides, (eta5-C9H5-1,3-R2)2ZrH2 (R = SiMe3, SiMe2Ph, CHMe2). Continued hydrogenation completed conversion to the tetrahydroindenyl derivatives, (eta5-C9H9-1,3-R2)2ZrH2. Deuterium labeling studies established that dihydrogen (dideuterium) addition to the benzo rings is intramolecular and stereospecific, occurring solely from the endo face of the ligand, proximal to the zirconium. In the absence of dihydrogen, the bis(indenyl)zirconium dihydrides rearranged to new zirconium monohydride complexes containing an unusual eta5,eta3-4,5-dihydroindenediyl ligand, arising from metal-to-benzo ring hydrogen transfer. Mechanistic studies, including a normal, primary kinetic isotope effect measured at 23 degrees C, are consistent with a pathway involving regio- and stereoselective insertion of a benzo C=C bond into a zirconium hydride. The stereochemistry of the insertion reaction, and hence the eta5,eta3-4,5-dihydroindenediyl product, is influenced by the presence of donor ligands and controlled by the preferred conformation of the indenyl rings. Exposure of the zirconium hydrides containing the eta5,eta3-4,5-dihydroindenediyl rings to 1 atm of dihydrogen afforded the tetrahydroindenyl zirconium dihydride complexes, establishing the intermediacy of this unusual coordination environment during benzo ring hydrogenation.     

Titanium imido complexes of cyclooctatetraenyl ligands

Reaction of [Ti(NR)Cl2(py)3] (R=tBu or 2,6-iPr2C6H3) with K(2)[COT] (COT=C8H8) or Li2[COT'] (COT'=1,4-C8H6(SiMe3)2) gave the monomeric complexes [Ti(NR)(eta8-COT)] or [Ti(NR)(eta8-COT')], respectively. The pseudo-two coordinate, "pogo stick" geometry for these complexes is unique in both early transition-metal and cyclooctatetraenyl ligand chemistry. In contrast, reaction of [Ti(N-2,6-Me2C6H3)Cl2(py)3] with K2[COT] gave the mu-imido-bridged dimer [Ti2(mu-N-2,6-Me2C6H3)2(eta8-COT)2]. It appears that as the steric bulk of the imido and C8 ring substituents are decreased, dimerisation becomes more favourable. Aryl imido COT complexes were also prepared by imido ligand exchange reactions between anilines and [Ti(NtBu)(eta(8)-COT)] or [Ti(NtBu)(eta(8)-COT')]. The complexes [Ti(NtBu)(eta(8)-COT)], [Ti(N-2,6-iPr2C6H3)2(eta8-COT)] and [Ti2(mu-N-2,6-Me2C6H3)2(eta8-COT)2] have been crystallographically characterised. The electronic structures of both the monomeric and dimeric complexes have been investigated by using density functional theory (DFT) calculations and gas-phase photoelectron spectroscopy. The most striking aspect of the bonding is that binding to the imido nitrogen atom is primarily through sigma and pi interactions, whereas that to the COT or COT' ring is almost exclusively through delta symmetry orbitals. A DFT-based comparison between the bonding in [Ti(NtBu)(eta8-COT)] and the bonding in the previously reported late transition-metal "pogo stick"complexes [Os(NtBu)(eta6-C6Me6)], [Ir(NtBu)(eta5-C5Me5)] and [Ni(NO)(eta5-C5H5)] has also been undertaken.     

Synthesis and reactivity of calix[4]arene-supported group 4 imido complexes

New mononuclear titanium and zirconium imido complexes [M(NR)(R'(2)calix)] [M=Ti, R'=Me, R=tBu (1), R=2,6-C(6)H(3)Me(2) (2), R=2,6-C(6)H(3)iPr(2) (3), R=2,4,6-C(6)H(2)Me(3) (4); M=Ti, R'=Bz, R=tBu (5), R=2,6-C(6)H(3)Me(2) (6), R=2,6-C(6)H(3)iPr(2) (7); M=Zr, R'=Me, R=2,6-C(6)H(3)iPr(2) (8)] supported by 1,3-diorganyl ether p-tert-butylcalix[4]arenes (R'(2)calix) were prepared in good yield from the readily available complexes [MCl(2)(Me(2)calix)], [Ti(NR)Cl(2)(py)(3)], and [Ti(NR)Cl(2)(NHMe(2))(2)]. The crystallographically characterised complex [Ti(NtBu)(Me(2)calix)] (1) reacts readily with CO(2), CS(2), and p-tolyl-isocyanate to give the isolated complexes [Ti[N(tBu)C(O)O](Me(2)calix)] (10), [[Ti(mu-O)(Me(2)calix)](2)] (11), [[Ti(mu-S)(Me(2)calix)](2)] (12), and [Ti[N(tBu)C(O)N(-4-C(6)H(4)Me)](Me(2)calix)] (13). In the case of CO(2) and CS(2), the addition of the heterocumulene to the Ti-N multiple bond is followed by a cycloreversion reaction to give the dinuclear complexes 11 and 12. The X-ray structure of 13.4(C(7)H(8)) clearly establishes the N,N'-coordination mode of the ureate ligand in this compound. Complex 1 undergoes tert-butyl/arylamine exchange reactions to form 2, 3, [Ti(N-4-C(6)H(4)Me)(Me(2)calix)] (14), [Ti(N-4-C(6)H(4)Fc)(Me(2)calix)] (15) [Fc=Fe(eta(5)-C(5)H(5))(eta(5)-C(5)H(4))], and [[Ti(Me(2)calix)](2)[mu-(N-4-C(6)H(4))(2)CH(2)]] (16). Reaction of 1 with H(2)O, H(2)S and HCl afforded the compounds [[Ti(mu-O)(Me(2)calix)](2)] (11), [[Ti(mu-S)(Me(2)calix)](2)] (12), and [TiCl(2)(Me(2)calix)] in excellent yields. Furthermore, treatment of 1 with two equivalents of phenols results in the formation of [Ti(O-4-C(6)H(4)R)(2)(Me(2)calix)] (R=Me 17 or tBu 18), [Ti(O-2,6-C(6)H(3)Me(2))(2)(Me(2)calix)] (19) and [Ti(mbmp)(Me(2)calix)] (20; H(2)mbmp=2,2'-methylene-bis(4-methyl-6-tert-butylphenol) or CH(2)([CH(3)][C(4)H(9)]C(6)H(2)-OH)(2)). The bis(phenolate) compounds 17 and 18 with para-substituted phenolate ligands undergo elimination and/or rearrangement reactions in the nonpolar solvents pentane or hexane. The metal-containing products of the elimination reactions are dinuclear complexes [[Ti(O-4-C(6)H(4)R)(Mecalix)](2)] [R=Me (23) or tBu (24)] where Mecalix=monomethyl ether of p-tert-butylcalix[4]arene. The products of the rearrangement reaction are [Ti(O-4-C(6)H(4)Me)(2) (paco-Me(2)calix)] (25) and [Ti(O-4-C(6)H(4)tBu)(2)(paco-Me(2)calix)] (26), in which the metallated calix[4]arene ligand is coordinated in a form reminiscent of the partial cone (paco) conformation of calix[4]arene. In these compounds, one of the methoxy groups is located inside the cavity of the calix[4]arene ligand. The complexes 24, 25 and 26 have been crystallographically characterised. Complexes with sterically more demanding phenolate ligands, namely 19 and 20 and the analogous zirconium complexes [Zr(O-4-C(6)H(4)Me)(2)(Me(2)calix)] (21) and [Zr(O-2,6-C(6)H(3)Me(2))(2)(Me(2)calix)] (22) do not rearrange. Density functional calculations for the model complexes [M(OC(6)H(5))(2)(Me(2)calix)] with the calixarene possessing either cone or partial cone conformations are briefly presented.