Alastair J. Nielson

Preparation of niobium and tantalum organoimido complexes from reactions of the pentahalides with amines: The crystal and molecular structure of bis(t-butylamine)bis(t-butylimido)bis(μ-ethoxy)tetrachloroditantalum

Abstract MCl5 (M = Nb, Ta) reacts with 2 equivalents of Me3SiNHCMe3 to give [M(NCMe3)Cl3(NH2CMe3)] from which [M(NCMe3)Cl3(PMe3)2] is obtained on addition of PMe3. One equivalent of Me3SiNHCMe3 reacts with MCl5 in the presence of 3 equivalents of PMe3 to give [M(NCMe3)Cl3(PMe3)2] and PMe3HCl. MCl5 reacts with excess RNH2 (R = CMe3, CHMe2, CH2Me) to give [M(NR)(NHR)Cl2(NH2R)] and 3 equivalents of RNH3Cl. One equivalent of alcohol replaces the amido ligand in [M(NCMe3)(NHCMe3)Cl2(NH2CMe3)] to give [M(NCMe3)(OR)Cl2(NH2CMe3)]2 (M = Nb, R = OCMe3; M = Ta, R = OEt). The structure of [Ta(NCMe3)(μ-OEt)Cl2(NH2CMe3)]2 was determined by single-crystal X-ray diffraction methods. Crystals are triclinic, space group P 1 with a = 9.900(5), b = 10. 161(17), c = 9.017(6) A and α = 103.91(8), β = 97.77(4), γ = 64.40(7)°. The structure was solved by Patterson and Fourier methods and refined to an R value of 0.062 for 1319 observed data. The TaNimido and TaNamino bond lengths are 1.70(2) A and 2.28(2) A, respectively; the bridging TaO bond lengths are 2.01(2) A and 2.32(2) A, the longer one lying trans to the imido function.

bis-t-Butylimido complexes of tungsten(VI)

Abstract WCl6 reacts with Me3SiNHCMe3 or Me3CNH2 to give [W(NCMe3)(μ-NCMe3) Cl2(NH2CMe3)]2 which contains trans orientated chloro ligands. The reaction does not occur with Me3SiNHR or RNH2 (R = Me2CH-, MeCH2-). An interligand proton transfer between cis-orientated t-butylamido NH groups gives rise to the imido and amine ligands. [W(NCMe3)(μ-NCMe3)Cl2(NH2CMe3)]2 reacts with 4-picoline to give [W(NCMe3)(μ-NCMe3)Cl2(4-pic)]2 and [W(NCMe3)2Cl2(4-pic)2] while the bidentate ligands bipy and tmed give [W(NCMe3)2Cl2(bipy)] and [W(NCMe3)2Cl2(tmed)]. All the complexes retain the trans-chloro orientation. With strong sigma donors, L (L = PMe3, PMePh2, Me3CNC), [W(NCMe3)(μ-NCMe3)Cl2(NH2CMe3)]2 reacts to give the complexes [W(NCMe3)(μ-NCMe3)Cl2(L)]2 which contain cis-chloro ligands. With t-butylamine [W(NCMe3)2 (NHCMe3)2] is formed but less sterically demanding amines (Me2CHNH2, MeCH2NH2) do not react similarly. Reaction of [W(NCMe3)(μ-NCMe3)Cl2(NH2CMe3)]2 with EtOH and Me3CNH2 forms [W(NCMe3)2(OEt)2]x. WOCl4 reacts with Me3SiNHCMe3 or Me3CNH2 to give a complex proposed as [WO(NCMe3)Cl2(NH2CMe3)]x which reacts further with bipy to form [W(NCMe3)2Cl2(bipy)] and various uncharacterized oxo complexes by an oxo-imido exchange. The complexes were characterized by analytical data, IR, 1H and 13C NMR spectroscopy. The position of the t-butyl group quaternary carbon in the 13C NMR spectra differentiates between imido, amido and amine ligands.

Sterically congested tris phenoxide complexes of tantalum(V). The x-ray crystal structures of [TaCl2(2,6-di-t-Butylphenoxide)3] and [Ta2Cl(μ-Cl)2(2,6-di-isopropylphenoxide)5(μ-O)]

Abstract TaCl5 reacts with two equivalents of lithium 2,6-di-t-butylphenoxide in benzene to give [TaCl3(2,6-di-t-butylphenoxide)2] (1) in 70% yield and with three equivalents of the lithium phenoxide in diethyl ether to give [TaCl2(2,6-di-t-butylphenoxide)3] (2) which can also be prepared by reaction of (1) with one equivalent of the lithium phenoxide. Three equivalents of lithium 2,6-di-isopropylphenoxide react with TaCl5 to give [TaCl2(diethylether)(2,6-di-isopropylphenoxide)3] (4) which, on attempted recrystallization in the presence of air, gave [Ta2Cl(μ-Cl)2(2,6-di-isopropylphenoxide)5(μ-O)] (5). Complexes (1), (2), and (4) were characterized by elemental analysis, IR, and 1H and 13C NMR spectra. Coordination of the phenoxide ligand in (2) is accompanied by downfield shifts of the phenyl ring ipso, ortho and para carbon resonances of 9.6, 3.6 and 3.1 ppm respectively, compared with the free ligand. For complex (4) the relative shifts are 5.9, 6.1 and 2.9 ppm. The structures of (2) and (5) have been determined by single-crystal X-ray diffraction methods. Crystals of (2) are monoclinic, space group P21/c with a = 18.902(6) A, b = 10.815(8) A, c = 20.259(4) A and β = 92.62(2)°; crystals of (5) are monoclinic, space group P21/c with a = 11.174(1) A, b = 20.402(4) A, c = 27.143(3) A and β = 94.58(1)°. Both structures were solved by Patterson and Fourier methods and refined to R values of 0.063 for the 1690 observed data for (2) and 0.062 for the 3693 observed data for (5). Complex (2) is monomeric with a square pyramidal coordination geometry about Ta. Observed distances are: TaOaxial 1.83(2) A; TaObasal each 1.90(2) A; TaClbasal each 1.37(1) A. Complex (5) is binuclear with a distorted octahedral geometry about each tantalum atom. The structure consists essentially of TaCl2(2,6-di-isopropylphenoxide)3 and TaCl2(O)(2,6-di-isopropylphenoxide)2 units bridged through the oxygen and Cl atoms. Observed distances are TaObridge 1.69(1) and 2.10(1) A; TaClbridge 2.498(7), 2.396(8), 2.634(7) and 2.781(7) A; TaClterminal 2.309(8) A. The TaOphenoxide distances range from 1.77(2) to 2.19(2) A. In both (2) and (5) the phenyl rings are orientated such as to minimise interactions between the 2- and 6-substituents. In both molecules electron counts are maximized using π-electron density from the terminal ligands.

Organo-imido alkoxides of tungsten(VI). The crystal and molecular structures of [W(NPh)(μ-OMe)(OMe)3]2 and [W(NPh)(OCMe3)3Cl(NH2CMe3)]

Abstract Reaction of phenylimido tungsten tetrachloride with MeOH and t -butylamine gave the dimeric complexes [W(NPh)(μ-OMe)(OMe) 3 ] 2 and [W(NPh)(μ-OMe)(OMe) 2 Cl] 2 . With ethanol [W(NPh)(μ-OEt)(OEt) 2 Cl] 2 was formed whereas iso propyl and neo pentyl alcohols gave the monomeric complexes [W(NPh)(OR) 4 (NH 2 CMe 3 )](R = CHMe 2 , CH 2 CMe 3 ); t -butanol gave [W(NPh)(OCMe 3 )3Cl(NH 2 CMe 3 )] which could not be converted to [W(NPh) (OCMe 3 ) 4 ]. Further reaction of [W(NPh)(μ-OMe)(OMe) 3 ] 2 with o -HOC 6 H 4 CH = NC 6 H 3 Me 2 (salim-H) gave the salicylaldimine complex [W(NPh)(OMC) 3 (salim)]. The products were characterised by analytical data, IR, 1 H NMR, 13 C NMR and mass spectroscopy. The crystal and molecular structures of the title complexes have been determined from single crystal X-ray diffractometer data. Crystals of [W(NPh)(μ-OMe)(OMe) 3 ] 2 are triclinic with a = 8.473(7), b = 10.776(5), c = 7.683(A, α = 102.26(3), β = 102.68(4), γ = 71.13(6)°, space group P 1 Crystals of 3) [W(NPh)(OCMe 3 ) 3 Cl(NH 2 CMe 3 ) are monoclinic with a = 9.341(2), b = 29.608(7), c = 10.257(2) A, β = 106.28(2)°, space group, P 2 1 / c . Both structures were solved by Patterson and Fourier methods and refined to R = 0.075 for the 1022 observed data of [W(NPh) (μ-OMe)(OMe) 3 ] 2 and to R = 0.074. For the 2033 observed data of [W(NPh)(OCMe 3 ) 3 Cl(NH 2 CMe 3 ). The former molecule is shown to be a dimer, the two halves of the molecule being related by a centre of symmetry. Both W atoms adopt a distorted octahedral coordination geometry and they are linked by two methoxy bridges. Trans to one of the bridging donors is the phenyl imido group with a WN bond length of 1.61(4) A; the remaining coordination sites are filled with methoxy groups. The structure of W(NPh)(OCMe 3 ) 3 Cl(NH 2 CMe 3 ) is monomeric with the phenylimido group trans to the NH 2 CMe 3 ligand in a distorted octahedral coordination geometry. Remaining sites are filled with the chloride and 3 OCMe 3 ligands. The WN (imido) bond length is 1.71(2) A, whilst WN(amine) is 2.40(2) A

EVIDENCE FOR HIGH OXIDATION-STATE CHARACTER IN TUNGSTEN ALKYNE COMPLEXES

Abstract Synthetic, spectroscopic and structural analogies to organoimido complexes and theoretical calculations indicate the alkyne complexes [WCl 4 (PhC 2 Ph)] 2 , [WCl 3 (PhC 2 Ph)(P) 2 ] and [WCl 2 (PhC 2 Ph)(P) 3 ] (P= phosphine) have properties similar to d 0 , d 1 and d 2 tungsten complexes.

Organoimido complexes of tungsten and rhenium: Oxo-imido and bis-imido complexes of tungsten(VI), and phenylimido complexes of rhenium(VI) and (V). The X-ray crystal structures of [W(NCMe3)(NPh)Cl2(bipy)] and [Re(NPh)Cl3(NH2CMe3)2]

Abstract Reaction of Me3CNH2 or Me3SiNHCMe3 with WOCl4 gives a mixture containing [W(O)(NCMe3)Cl2(NH2CMe3)]x which on further reaction with 2,2′-bipyridyl (bipy) gives [W(NCMe3)2Cl2(bipy)] and insoluble oxo complexes. Reaction of WOCl4 with p-MeC6H4N(SiMe3)2 and then bipy gives [W(NC6H4Me-p)2Cl2(bipy)] and [W(O)(NC6H4Me-p)Cl2(bipy)]; [W(NPh)Cl4]2 reacts with p-MeC6H4N(SiMe3)2 and then bipy to give [W(NPh)(NC6H4Me-p)Cl2(bipy)]. [W(NCMe3)(μ-NPh)Cl2(NH2CMe3)]2 and bipy give [W(NCMe3)(NPh)Cl2(bipy)] (6). ReOCl4 reacts with PhNCO to give [Re(NPh)Cl4]x which in tetrahydrofuran (THF) or MeCN give the adducts [Re(NPh)Cl4(THF)] and [Re(NPh)Cl4(MeCN)]. [Re(NPh)Cl4]x reacts with Me4NCl to give [Me4N][Re(NPh)Cl5], with PPh3 to give [Re(NPh)Cl3(PPh3)2] and with Me3 SiNHCMe3 gives [Re(NPh)Cl3(NH2CMe3)2] (12). The complexes were characterized by elemental analysis, IR, 1H and 13C NMR spectroscopy. The structures of [W(NCMe3)(NPh)Cl2(bipy)] (6) and [Re(NPh)Cl3(NH2CMe3)2] (12) were determined by single-crystal X-ray diffraction methods. Crystals of (6) are orthorhombic, space group P212121, with a = 8.879(3) A, b = 13.036(3) A, c = 18.837(4) A; crystals of (12) are orthorhombic, space group Pbcn with a = 14.140(1) A, b = 11.806(1), A, c = 11.936(3) A. Both structures were solved by Patterson and Fourier methods and refined to R values of 0.053 for the 2138 observed data for (6) and 0.035 for the 1108 observed data for (12). In complex (6) the tungsten atom is in a distorted octahedral environment comprising cis-t-butylimido and phenylimido groups, trans chlorides and bidentate bipy. The bipy nitrogens lie trans to the imid o functions. Observed distances are: WNphenylimido 1.774(8) A, WNt-butylimido 1.754(10) A, WCl 2.412(3) and 2.390(3) A and WNbipy 2.312(10) A and 2.333(9) A. Interaction between the t-butylimido methyl groups and bipy is relieved by lengthening of one WNbipy bond. In complex (12) the rhenium atom is in a distorted octahedral environment comprising three chloride ligands, two trans-t-butylamine ligands and a phenylimido ligand. Observed distances are: ReNphenylimido 1.709(11) A, ReNt-butylamine 2.187(7) A, and ReCl 2.404(2) and 2.411(5) A. The complex attains an 18-electron count without π-bonding from the chloro ligands.

Studies of π-bonding perturbation in the tungsten-nitrogen multiple bond of isopropylimido tungsten(VI) complexes: The crystal and molecular structures of [W(NCHMe2)Cl4]2·C6H6 and [W(NCHMe2)Cl5][NEt4]

Abstract 13C NMR chemical shift data for the α-carbon (δα) of a variety of tungsten isopropylimido complexes indicate that the extent to which the nitrogen lone pair participates in multiple bonding to tungsten depends on the form of the complex and the ligands involved. The structures of [W(NCHMe2)Cl4]2·C6H6 (1a) and [W(NCHMe2)Cl5][NEt4] (7) which show widely different δα values, have been determined by single-crystal X-ray diffraction methods. Crytals of 1a are triclinic space group P 1 , with a = 6.394(2), b = 8.890(3), c = 11.205(2) A and α = 109.95(2)°, β = 98.91(2)°, γ = 93.96(2)°; crystals of 7 are orthorhombic, space group Pnma, with a = 13.667(5), b = 15.152(2), c = 9.432(2) A. Both structures were solved by Patterson and Fourier methods and refined to an R value of 0.050 for 1325 observed data of 1a and to an R value of 0.050 for the 1157 observed data of 7. Complex 1a is dimeric with a WN bond length of 1.697(12) A and complex 7 is monomeric with a longer WN bond length of 1.763(16) A. Comparison of the WCl bond lengths and correlations with π-bonding to make an 18-electron count, indicates that the WN bond lengths differ in the two complexes as a result of overall π-bonding requirements.

Conversion of a phenylimido complex to a phenylamido complex by the potentially chelating ligand 2,3-dimethyl-2,3-butandiol(pinacol-H2): The crystal and molecular structures of [W2(NHPh)2(μ-pinacol)(pinacol)4] and the reaction side-product [W2(NPh)2(μ-O)(pinacol)2(pinacol-H)2]

Abstract The interaction of 2 equivalents of 2,3-dimethyl-2,3-butandiol (pinacol-H2) with W(NPh)Cl4 in the presence of t-butylamine leads to the complexes W(pinacol)3 (1), and [W2(NHPh)2(μ-pinacol)(pinacol)4] (2). A side-product of the reaction is [W2(NHPh)(μ-O)(pinacol)2(pinacol-H)2] (3). When 3 or more equivalents of diol are used (1) is the sole product. The structures of (2) and (3) have been determined by single-crystal X-ray diffraction methods. Crystals of (2) are monoclinic, space group C2/c with a = 15.086(3), b = 18.370(5), c = 18.428(5) A and β = 106.04(2)°; crystals of (3) are orthorhombic, space group Pbca, with a = 10.571(1), b = 22.449(12), c = 34.142(5) A. Both structures were solved by Patterson and Fourier methods and refined to an R value of 0.059 for the 1023 observed data of (2) and to R = 0.071 for the 1212 observed data of (3). In the amido complex (2) the WN bond length is 2.02(2) A with the longest WO bond length of 2.00(2) A lying trans to it. In the imido complex (3) the WN bond length is 1.75(5) A; the trans WO bond length at 2.30(4) A indicates lone-pair donation by the imido N.

Organoimido complexes of tungsten(IV) containing π-acceptor ligands

Abstract Reaction of PhCCPh with [WCl2(NR)(PMe3)3] gives the cis-dichloro-trans- phosphine complexes [WCl2(NR)(PhCCPh)(PMe3)2] [R = Ph (1), R = CHMe2 (3)] in which the π-acceptor acetylene ligand lies cis to the imido function. For 1 v(CC) is at 1760 cm−1 and for 3, 1740 cm−1. Me3SiCCSiMe3 and PhCCPh do not replace phosphine ligands from [WCl2(NPh)(PMe3)3] or [WCl2(NPh)(PMePh2)3]. Reaction of PhCCPh with [WCl2(NPh)(PMe2Ph)3] gives [WCl2(NPh)(PhCCPh)(PMe2Ph)2] (2). Alkyl substituted acetylenes do not react cleanly with [WCl2(NPh)(PMe3)3] but HCCH gives [WCl2(NPh)(HCCH)(PMe3)2] (4). Reaction of PhCCH with [WCl2(NR)(PMe3)3] gives [WCl2(NR)(PhCCH)(PMe3)2] [R = Ph (5), R = CHMe2 (6)]. The phenylacetylene ligand gives rise to asymmetry in 5 and 6 leading to AB system 31P{1H} NMR spectra. Different values of 1J(PW) for the two phosphine ligands in both complexes indicate small differences in WP bonding. The acetylenic protons and carbons in the 1H and 13C{1H} NMR spectra of the phenylacetylene complexes couple differently to the two phosphines. For 5 3J(HP) cis and trans = 5.90 and 17.26 Hz, 2J(C[H]P) cis and trans = 5.29 and 21.99 Hz and 2J(C[Ph]P) cis and trans = 4.88 and 15.63 Hz. The 13C{1H} NMR acetylenic carbon resonance positions in complexes 1, 3, 5 and 6 suggest that an isopropylimido ligand is a better π-donor than a phenylimido ligand, allowing more metal-acetylene π-back donation. Reduction of [WCl3(NPh)(PMe3)2] with Na/Hg amalgam under CO gives [WCl2(NPh)(CO)(PMe3)2] (7) for which v(CO) at 1925 cm−1 indicates considerable π- backbonding.

Alkylimido complexes of titanium(IV)

Abstract TiCl 4 reacts with t-butylamine in benzene to give [Ti(NCMe 3 )Cl 2 (NH 2 CMe 3 ) 2 ] x and t-butylamine hydrochloride. The IR spectrum indicates both c/s and trans metal dichlorides (300; and 308, 208 cm −1 ). In the 13 C NMR spectrum the t-butylimido quaternary carbon resonance occurs at 72.1 ppm. A dimeric structure incorporating symmetric t-butylimido bridges is proposed. TiCl 4 in benzene react under reflux with two equivalents of Me 3 SiNHCMe 3 to give [Ti(NCMe 3 )Cl 2 (NH 2 CMe 3 )] x and with iso-propylamine and ethylamine to give complexes of the form [Ti(NR)Cl 2 (NH 2 R) 2 ] x . Broad bands below 800 cm −1 in the IR spectra suggest polymeric MNM bridges. For [Ti(NCHMe 2 )Cl 2 (NH 2 CHMe 2 )] x the iso-propylimido CH resonance in the 13 C NMR spectrum occurs at 67 ppm. [Ti(NCMe 3 )Cl 2 (NH 2 CMe 3 ) 2 ] 2 reacts with L=bipy or tmed to give [Ti(NCMe 3 )Cl 2 (L)] 2 , and TiCl 4 reacts with two equivalents of Me 3 SiNHCMe 3 in benzene and then tmed to give [Ti(NCMe 3 )Cl 2 (tmed)] 2 . The 13 C NMR spectrum shows the t-butylimido quaternary carbon resonance at 73.5 ppm and the tmed resonances are chemically equivalent. A dimeric μ-NCMe 3 bridging structure is proposed for the complex.