Ian P. Rothwell

Palladation behaviour of 8-methyl-, 8-ethyl-, and 8-isopropyl-quinolines and some of their 2-substituted derivatives

Abstract 8-Methyl- and 8-ethyl-quinolines give cyclopalladation products with palladium acetate by CH bond cleavage at the 8-substituent, but 8-isopropylquinoline does not. The influence on cyclometallation of introducing 2-substituents (Me, Br, CHO, CHNMe, CH2OH, CO2H) in these quinolines is described. The first three substituents totally prevent cyclopalladation whereas metallation at the 8-substituent proceeds smoothly when the 2-substituent is CHNMe, CH2OH or CO2H. The products are characterised spectroscopically and there is a discussion of the dynamic 1H NMR behaviour of the cis and trans isomers of [Pd(OAc)(CH2C9H6N]2 formed from 8-methylquinoline. Evidence is presented that the cyclopalladation reaction takes place for a three-coordinate palladium(II) intermediate with the reacting hydrocarbon group entering the vacated fourth coordination site.

Solid state structure of the tantalum bis-aryl compounds Ta(OAr-2,6R2)3(C6H5)2 (R = CH3, Pri; OAr-2,6R2 = 2,6-dialkylphenoxide): Observation of a lack of correlation of MOAr distances and MOAr angles for aryloxide derivatives of niobium(V) and tantalum(V)

Abstract Treatment of the tantalum dichloride compounds Ta(OAr-2,6Me2)3Cl2 or Ta(OAr-2,6Pr2i)3Cl2 (OAr-2,6Me2 = 2,6-dimethylphenoxide; OAr-2,6Pr2i = 2,6-diisopropylphenoxide) with phenyl lithium (2 equiv) leads to the formation of the bis-phenyl compounds Ta(OAr-2,6Me2)3(C6H5)2 (1) and Ta(OAr-2,6Pr2i)3(C6H5)2 (2), respectively, in moderate yields. Single crystal X-ray diffraction analyses of both 1 and 2 show them to be isostructural. In both compounds a trigonal bipyramidal environment about the metal centre is evident with trans, axial aryloxide oxygen atoms. Short TaO distances in the range of 1.848(5)-1.881(3) A and almost linear TaOAr angles are present. The central coordination environments in 1 and 2 are strikingly similar to those found for the biscyclometallated compound Ta(OC6H3Ph-C6H4)2(OAr-2,6Ph2). Combining the structural data for 1 and 2 with those of other alkyl, aryloxide compounds of niobium(V) and tantalum(V) shows that the MOAr distances span a narrow range of 1.85-1.95 A, while the corresponding MOOAr angles vary from 135 to 180° with no correlation between the two parameters. Crystal data for TaO3C36H37 (1) at 19°C: a = 19.313(3), b = 11.652(1), c = 15.288(1) A, β = 113.13(1)°, Z = 4, dcalc = 1.446 g cm−3 in space C2/c; for TaO3C48H61 (2) at 21°C: a = 11.955(2), b = 19.585(2), c = 19.337(2) A, β = 103.742(9)°, Z = 4, dcalc = 1.309 g cm−3 in space group P21/n.

Cationic Group 4 metal alkyl compounds containing aryloxide ligation: synthesis, structure, reactivity and polymerization studies

A series of bis(alkyl) derivatives of titanium and zirconium [(ArO) 2 MR 2 ] (M=Ti, Zr; R=Me, CH 2 Ph; ArO=various 2,6-di-substituted phenoxides) has been synthesized and their reactivity towards the Lewis acid [B(C 6 F 5 ) 3 ] examined. The benzyl compounds generate stable zwitterionic species such as [M(OC 6 HPh 2 -2,6-R 2 -3,5) 2 (CH 2 Ph)][η 6 -C 6 H 5 CH 2 B(C 6 F 5 ) 3 ] (M=Ti, R=H, 12 ; Me, 13 : M=Zr, R=Me, 15 ). Structural studies of 12 and 15 show the boron anion π-bound to the metal center through the original benzyl phenyl ring. In contrast, treatment of the benzyl compound [Zr(OC 6 H 3 Bu t 2 -2,6) 2 (CH 2 Ph) 2 ] with [B(C 6 F 5 ) 3 ] leads to the cyclometallated compound [Zr(OC 6 H 3 Bu t -CMe 2 CH 2 )(OC 6 H 3 Bu t 2 -2,6)][η 6 -C 6 H 5 CH 2 B(C 6 F 5 ) 3 ] 16 which was structurally characterized. In contrast to this behavior the bis(methyl) species react with [B(C 6 F 5 ) 3 ] to produce unstable methyl cationic intermediates which decompose to a mixture of [Ti(OAr) 2 (CH 3 )(C 6 F 5 )] and [CH 3 B(C 6 F 5 ) 2 ]. The titanium zwitterionic benzyl compounds will react with alkynes and α-olefins to produce mono-insertion products such as [Ti(OC 6 H 3 Ph 2 -2,6) 2 {C(CH 3 )C(Ph)CH 2 (η 6 -C 6 H 5 )}][PhCH 2 B(C 6 F 5 ) 3 ] 24 . In these compounds 1,2-insertion of olefins occurs followed by chelation of the original benzyl group to the metal center. Spectroscopic studies show the boron anion is non-coordinated to the metal center. Despite their thermal instability, the methyl cations can be generated in situ in the presence of olefins to produce polymers (ethene and propene) and oligomers (1-hexene). Studies show that the molecular weight of the polymers or oligomers increases systematically with the bulk of the aryloxide ligand. Spectroscopic studies of the polypropylene indicate 1,2-insertion is occurring with β-hydrogen abstraction to produce vinylidene end groups as the termination step.

Aryl imido complexes of the group 4 metals : structural aspects and mechanistic study of formation

Abstract The addition of aniline (PhNH2 ⩾ 2 equivalents) to the organometallic compounds [Ti(OC6H3Pri2-2,6)2(η2-ButNCCH2Ph)(CH2Ph)], [Ti(OC6H3Ph2-2,6)2(C4Et4)] and [Zr(OC6H3But2-2,6)2(CH3)2] in hydrocarbon solvents leads to the formation of the mononuclear bis(phenylamido) derivatives [M(OAr)2(NHPh)2] [M = Ti, OAr = OC6H3Pri2-2,6 (1); M = Ti, OAr = OC6H3Ph2-2,6 (2); M = Zr, OAr = OC6H3But2-2,6 (3)]. Treatment of [Hf(CH2Ph)4] first with PhNH2 (4 equivalents), followed by HOC6H3But2-2,6 (2 equivalents), leads to the related bis(phenylamido) compound 4 (M = Hf; OAr = OC6H3But2-2,6). The two homoleptic aryl amido compounds [M(NHC6H3Pri2-2,6)4] [M = Zr (5); Hf (6)] have also been obtained by addition of 2,6-diisopropylaniline to the tetra-benzyl compounds [M(CH2Ph)4] (M = Zr, Hf). The addition of 4-pyrrolidinopyridine (py′) to all of the aryl amido compounds except 4 leads to elimination of 1 equivalent of aryl amine and the formation of a series of five-coordinate aryl amido derivatives of the general formula [M(OAr)2(NPh)(py′)2] [M = Ti, OAr = OC6H3Pri2-2,6 (7); M = Ti, OAr = OC6H3Ph2-2,6 (8); M = Zr, OAr = OC6H3But2-2,6 (9); and [M(NHAr)2(NAr)(py′)2]; M = Zr, Ar = C6H3Pri2-2,6 (10); M = Hf, Ar = C6H3Pri2-2,6 (11)]. In the case of the hafnium bis(phenylamido) complex 4, addition of 4-pyrrolidinopyridine resulted in the formation of a simple adduct. [Hf(OC6H3But2-2,6)2(NHPh)2(py′)], [4·py′]. (A similar adduct, [4·py′], was detected in the conversion of 3–9.) No elimination of aniline from [4·py′] and formation of a phenylimido derivative were observed. Both 2,2′-bipyridine and 1,10-phenanthroline were found to eliminate aniline from compounds 1–3 to produce insoluble products. Addition of 3,4,7,8-tetramethyl-1,10-phenanthroline to 2, however, yielded a soluble phenylimido derivative (12). The four-coordinate aryl amido compounds 2, 3 and 5 were found to be pseudo-tetrahedral in the solid state, while the five-coordinate aryl imido compounds 7, 9, 10 and 11 are best described as distorted trigonal-bipyramidal with trans-axial pyridine ligands. In the phenanthroline derivative 12 a distorted trigonal-bipyramidal geometry exists about the titanium atom with an aryloxide oxygen atom trans to a phenanthroline nitrogen. The bonding of the aryl imido, aryl amido and pyridine groups is described. A detailed study of the reaction of a series of bis(aryl amido) complexes, [Zr(OAr)2(NHC6H4-4X)2] (3)X (X = H, F, CH3, OMe, Br), with a variety of pyridine ligands was undertaken. The mono-pyridine adduct [3X·py] is rapidly formed, followed by the slow formation of the corresponding aryl imido complex [Zr(OAr)2(NHC6H4-4X)(py)2] [9X] and an equivalent of substituted aniline. Equilibrium constants for the reaction [3Xpy] + py = [9X] + ArNH2 were measured. Formation of the aryl imido ligand was found to be favoured by a more basic pyridine ligand and by electron-withdrawing substituents on the aryl ring of the initial aryl amido group. The rate of attainment of the equilibrium situation from [3] and py was investigated and various pathways for the reaction are considered. X-ray crystal structures were determined for 2, 3, 5, 7, 9, 10, 11 and 12.

The chemistry of sterically crowded aryloxide ligands—VII. Synthesis, structure and spectroscopic properties of some group 4 and group 5 metal derivatives of 2,6-diphenylphenoxide

Abstract A series of early transition metal organometallic derivatives containing the ancillary ligand 2,6-diphenylphenoxide (OAr-2,6Ph 2 ) have been synthesized. Compounds of stoichiometry Ti(OAr-2,6Ph 2 ) 2 (R) 2 (R = CH 3 , CH 2 SiMe 3 , CH 2 Ph and Ph) and Ti(OAr-2,6Ph) 3 (R) (R = CH 3 , CH 2 SiMe 3 ) are obtained by treating the corresponding homoleptic alkyl, TiR 4 , with the required amount of phenol, HOAr-2,6Ph 2 . For the Group 5 metals Nb and Ta, the methyl derivatives M(OAr-2,6Ph 2 ) 2 (CH 3 ) 3 and M(OAr-2,6Ph 2 ) 3 (CH 3 ) 2 are obtained via methylation of the corresponding chloro-aryloxides. Besides routine spectroscopic characterization the diphenyl Ti(OAr-2,6Ph 2 ) 2 (Ph) 2 and mono-alkyl Ti(OAr-2,6Ph 2 ) 3 (CH 2 SiMe 3 ) have been structurally characterized by X-ray diffraction techniques. Both molecules contain a pseudo-tetrahedral environment about the titanium atom with short 1.794(3)–1.806(2) A, TiO distances and large, 153–179°, TiOAr angles. The TiC distances appear normal for these types of compounds.

‘1,3-dimetallabenzene’ derivatives of niobium and tantalum ☆

Abstract The alkylidyne bridged compounds [(cb)2M(μ-CSiMe3)2M(cb)2] (1a M  Nb; 1b, M  Ta; cb = carbazole) react thermally with one equivalent of alkynes EtCCEt and Me3SiCCH to produce new organometallic derivatives 2 and 3, respectively. The molecular structures of 2 and 3 are shown to consist of non-planar six-membered di-metallacycles originating from insertion of an alkyne unit into one of the alkylidyne bridges of 1. Treatment of 1b with 3,5-di-tert-butyl-2,6-diphenylphenol (ArOH) leads to the monophenoxide [(ArO)(cb)Ta(μ-CSiMe3)2Ta(cb)2] 4. Treatment of 4 with Me3SiCCH leads to the corresponding metallacycle [(ArO)(cb)Ta(μ-CSiMe3){μ-C(SiMe3)CHC(SiMe3)}Ta(cb)2] 5. Structural parameters for 2b, 3a, 3b and 5 obtained by X-ray diffraction show delocalization is present with four equivalent MC and two equivalent CC distances. The non-planar structure is best described as a twist of the planar [M(μ-C)M] and [CCC] units within the ring. The non-planar structure of 2a and 2b is maintained in solution as evidenced by diastereotopic methylene protons for the CH2CH3 substituents. At elevated temperatures coalescence to a simple A2B3 pattern is observed. From the coalescence temperatures of 328 K for 2b an activation barrier of 16.1(5) kcal mol−1 can be estimated for the adoption of a planar structure. The insertion of Me3SiCCH produces a 2,4,6-substitution pattern for 3a, 3b and 5 with the 5-H (beta to two metal centers) being downfield shifted to σ 8.43 (3a), 8.64 (3b) and 9.03 ppm (5).

Rare Earth Complexes of Bulky 2,6-Diphenylphenolates Containing Additional, Potentially Buttressing 3,5-Substituents

The rare earth aryloxide complexes, [Yb(OArtBu)3(THF)]·THF, [Sc(OArtBu)3(THF)]·THF, [Yb(OArMe)3(THF)], and [Sm(OArPh)3(THF)2] (OArR = 2,6-diphenyl-3,5-di-R-phenolate), have been prepared by redox transmetallation/ligand exchange between the rare earth metal, bis(pentafluorophenyl)mercury, and HOArR in tetrahydrofuran. This reaction also provided [Yb(OArPh)3(DME)]·3/2THF by incorporation of adventitious 1,2-dimethoxyethane. A similar reaction between Yb metal, diphenylmercury, and HOArMe gave [Yb(OArMe)2(THF)3]. The homoleptic complexes [Yb(OArPh)3] and [Sc(OArH)3] have been prepared by direct reaction of the rare earth element with HOArR in a sealed tube in the presence of mercury at elevated temperatures (200−250 °C) and the latter was converted into [Sc(OArH)3(THF)] by treatment with THF. X-ray crystal structure determinations of [Yb(OArtBu)3(THF)]·THF, [Sc(OArtBu)3(THF)]·THF, and [Yb(OArMe)3(THF)] show the complexes to be monomeric and four coordinate with a trigonal pyramidal stereochemistry. These structures provide clear evidence that groups meta to the phenolate donor can modify the coordination behaviour of the 2,6-diphenylphenolate ligand. In [Yb(OArPh)3(DME)]·3/2THF a distorted square pyramidal stereochemistry is observed. The divalent complex [Yb(OArMe)2(THF)3] exhibits a distorted trigonal bipyramidal arrangement of the oxygen donor atoms with apical THF ligands. The homoleptic scandium 2,6-diphenylphenolate has three oxygen atoms in a triangular array with additional π-η1-Ph···Sc interactions above and below the ScO3 plane [C−Sc−C = 154.2(8)°], providing a new type of binding of this aryloxide ligand.

Group 4 and 5 metal derivatives of 2,2′-methylene-bis(6-phenylphenoxide)

Abstract Addition of the phenol 2,2′-methylene-bis(6-phenylphenol) [(HOC6H3Ph)2CH2] (1) (1 equiv. per Ti) to hydrocarbon solutions of [TiCl4] or [Ti(OPri)4] leads to dimeric products [Ti{(OC6H3Ph)2CH2}Cl2]2 (2) and [Ti{(OC6H3Ph)2CH2}(μ-OPri)(OPri)]2 (3). Structural studies show 2 (CHCl3 solvate) to consist in the solid state of two tetrahedral titanium centers linked by one end of two di-aryloxide ligands. In contrast, 3 contains five-coordinate titanium atoms linked directly by two bridging isopropoxide ligands. Treatment of [MCl5] (M=Nb, Ta) with 1 equiv. of 1 leads to sparingly soluble trichlorides 4 and 5 which react with pyridine to form soluble adducts [M{(OC6H3Ph)2CH2}Cl3(py)] (M=Nb, 6; M=Ta, 7). Compounds 6 and 7 are isostructural in the solid state (benzene solvates) with a mer arrangement of chloride groups and the pyridine trans to one of the di-aryloxide oxygen atoms. Treatment of 7 with PMe2Ph leads to the products [Ta{(OC6H3Ph)2CH2}Cl3(PMe2Ph)] (8) and [HPMe2Ph][Ta{(OC6H3Ph)2CH2}Cl4] (9). Structurally characterized 9 (benzene solvate) presumably arises via the presence of trace amounts of water during workup. Reaction of 1 with [Ta(NMe2)5] allows isolation of derivatives [Ta{(OC6H3Ph)2CH2}2(NMe2)(HNMe2)] (10) (cis-nitrogen atoms by NMR) and [H2NMe2][Ta{(OC6H3Ph)2CH2}3] (11) depending on the stoichiometry. The anion in 11 was shown by crystallography to contain an octahedral arrangement of oxygen atoms about the tantalum metal center. The crystallographic study of 11 is complicated by a disorder of the cation and partial occupancies for the three types of benzene solvate molecule. The niobium trichloride 4 acts as a catalyst precursor for benzene hydrogenation although with lower activity than reported for monodentate aryloxide precursors. During the catalysis the ortho-phenyl rings of the di-aryloxide ligand are not hydrogenated.

Crystal and molecular structure of [L3(μ2-OAr)3] (OAr = 2,6-diphenyl-3,5-di-tert-butylphenoxide); a cluster containing short LiO distances ☆

Abstract Reaction of 2,6-diphenyl-3,5-di- tert -butylphenol (HOAr) with one equivalent of n -BuLi in toluene generates the hydrocarbon soluble cluster [Li 3 (μ 2 -OAr) 3 ] 1 . The molecular structure of 1 consists of a six-membered ring (crystallographically imposed C 3 axis) of Li and O(aryloxide) atoms with alternating LiO distances of 1.78(a) and 1.840(7) A.

Triosmium clusters with ligands derived from αβ-unsaturated ketones. X-ray crystal structures of [Os3H(CO)10(cis-MeCCHCOMe)] and [Os3H(OH)(CO)9(PMe2Ph)]

The compounds [Os3H2(CO)10] and [Os3(CO)10(MeCN)2] both react with the enones RCHCHCOMe (R = H, Me, or Ph) by metallation at the vinylic C–H groups to give compounds of type [Os3H(CO)10-(RC4H4O)], certain of which were also obtained from [Os3H2(CO)10] and CHCCOMe. Three isomers of [Os3H(CO)10(C4H5O)] were isolated, containing CH2CCOMe and cis- and trans-CHCHCOMe respectively. The most stable isomer, [Os3H(CO)10(cis-CHCHCOMe)], is decarbonylated at 130 °C to give [Os3H(CO)9(cis-CHCHCOMe)] and contains a linear Os3 chain and a terminal hydride replaceable by Cl from CCl4. The substituted compounds [Os3H(CO)10(cis-RCCHCOMe)](R = Me or Ph) have a different structure; crystals of the compound with R = Me are monoclinic, space group C2/c, with a= 17.377(2), b= 14.293(2), c= 16.476(2)A, β= 91.79(3)°, and Z= 8. The structure was solved via the heavy-atom method and refined to R= 0.034 using 2 906 diffractometer data with l 1.5σ(l). The structure is based on that of [Os3(CO)12] with a chelating MeCCHCOMe ligand occupying an axial and an equatorial site. The bridging hydride is not replaced by Cl in CCl4 solution. Unable to obtain good crystals of [Os3H(CO)10(cis-CHCHCOMe)], [Os3H2(CO)9(PMe2Ph)] was treated with CH2CHCOMe in an attempt to obtain a PMe2Ph-substituted derivative but instead [Os3H(OH)(CO)9(PMe2Ph)], was obtained, the crystals of which are monoclinic, space group P21/n, with a= 17.535(2), b= 9.500(1), c= 14.326(2)A, β= 101.86(1)°, and Z= 4. The structure was solved by the heavy-atom method and refined to R= 0.041 using 3 474 diffractometer data with l 1.5σ(l).