Anirudh Singh

X-ray structure of a derivative of the “simplest metallocene: Cyclopentadienyllithium”, [Li{;η-C5H4(SiMe3)};{;NMe2(CH2)2NMe2};] (i.e., LiCp′(TMEDA))

Abstract Crystalline monomeric tetramethylethylenediamine(trimethylsilylcyclopentadienyl) lithium [LiCp′(TMEDA)] was prepared by addition of an equimolar mixture of n-butyllithium and TMEDA in n-hexane to trimethylsilylcyclopentadienene, and recrystallisation from n-pentane at −30°C. X-ray data show that the lithium atom may be regarded as trigonal planar, with bonds to (a) the two nitrogen atoms (2.142(8) and 2.119(10)A) of the chelating TMEDA and (b) the centroid of the planar η5-cyclopentadienyl ring (1.928A). The Li C bonds range from 2.257(10) to 2.286(10)A(the carbon bearing the SiMe3 substituent), and the cyclopentadienyl C C bonds from 1.38(1) (the two bonds furthest removed fromC SiMe3) to 1.421(8)A.

Use of the bis(trimethylsilyl)cyclopentadienyl ligand for stabilising early (f0–f3) lanthanocene chlorides; X-ray structure of [(Pr{η-[C5H3(SiMe3)2]}2Cl)2] and of isoleptic scandium and ytterbium complexes

Reaction of the appropriate MCl3 and 2Li-[C5H3(SiMe3)2] in tetrahydrofuran affords [M{η-[C5H3-(SiMe3)2]}2Cl)2](M = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu); the X-ray structure of the first early lanthanocene chloride [(Pr{η-[C5H3-(SiMe3)2]}2Cl)2](the Sc and Yb complexes are isostructural) shows the Pr atoms to be in a distorted tetrahedral environment, and important molecular parameters include Pr–Clav.. 2·81, Pr–C(η-)av. 2·76 A, Pr … Pr′ 4·372(1)A, Cl–Pr–Cl′ 78, and Pr–Cl–Pr′ 102 °.

Metallocene(III) tetrahydridoborates of the Group 3A elements and the X-ray structure of [Sc{η-C5H3(SiMe3)2}2(µ-H)2BH2]

Complexes of a range of group 3A metals (Ln) of formula [Ln{η-C5H3(SiMe3)2}2(BH4)(thf)n](thf = tetrahydrofuran, n= 1 or, for Ln = Sc, n= 0) have either a (µ-H)2(for the smaller metals: Ln = Sc, Y, or Yb) or a (µ-H)3(Ln = La, Pr, Nd, or Sm) bridge, and only with the smallest of these (Sc) is the BH4– ligand non-fluxional (11B n.m.r.spectroscopy) at ambient temperature although rapid bridging hydrogen ⇌ terminal hydrogen exchange occurs at 100 °C; the X-ray crystal structure of this title Sc compound shows Sc–H 2.03 (4) and Sc…. B 2.52(3)A and confirms the bidentate mode of BH4– bonding.

Organometallic complexes of the Group 3A and lanthanoid metals containing M(µ-Cl)2Li bridging units; the X-ray structure of [Nd{η-[C5H3(SiMe3)2]}2(µ-Cl)2Li(thf)2](thf = tetrahydrofuran)

The following organometal(III) complexes have been prepared and characterised: (a)[M{η-[C5H3–(SiMe3)2]}2(µ-Cl)2Li(L)2][M = Sc, Y, La, Ce, Pr, Nd, or Yb, and L = tetrahydrofuran (thf): or M = Y or La, and L2= Me2NCH2CH2NMe2(tmeda); or M = Y or Nd, and L2= MeOCH2CH2OMe (dme)], (b)[MCl2 –n(OArMe)n–(µ-Cl)2Li(thf)2](OArMe= OC6H2Bu2t-2,6-Me-4, M = Y, La, Er, or Yb, and n= 1; or M = Y and n= 2), and (c)[ErCl{N(SiMe3)2}(µ-Cl)2Li(thf)2]; the X-ray structure of the title compound shows that both the Nd and Li atoms are in a distorted ttetrahedral environment, and important molecular parameters include Nd–Clav. 2·744, Li–Clav 2·405, Nd … Li 3·63(3)A, Cl–Nd–Cl′ 82·1, and Cl–Li–Cl′97.2(9)°

Metallocene derivatives of early transition elements. Part 4. Synthesis and crystal structures of a series of zirconocene(IV) halides [Zr(η-C5H4SiMe3)2X2](X = Cl or Br) and [Zr{η-C5H3(SiMe3)2-1,3}2X2](XF, Br, or I)

A series of zirconocene(IV) halides, [Zr(η-C5H4SiMe3)2X2][X = Cl (1) or Br (2)] and [Zr{η-C5H3(SiMe3)2-1,3}2X2][X = F (3), Br (4), I (5), or Cl (6)], has been prepared, either by (i) substitutive procedures from ZrCl4[involving the following ligand exchanges: Cl–/C5H4SiMe3–, Cl–/C5H3(SiMe3)2–, Cl–/Br–, Cl–/l–, or Cl–/NMe2– followed by NMe2–/F–], or (ii), for complexes (3), (5), or (6), by oxidative addition to [Zr{η-C5H3(SiMe3)2-1,3}2(CO)2]. The only νasym(ZrX2) vibration to be assigned with confidence is for X = F at 563 cm–1; 1H and 13C n.m.r. data are unexceptional. X-Ray structure determinations of complexes (1)–(5) have been carried out. Their molecular symmetry is close to 2, or crystallographically imposed 2 in (3), with the stereochemistry about the metal centre best described as distorted tetrahedral. The angle X–Zr–X is 93.70(7), 94.2(1), 100.5(3), 100.25(5), and 100.37(4)° for the halides (1)–(5), respectively; and the corresponding centroid–Zr–centroid angles are 129.1, 128.2, 131.4, 131.4, and 131.8°. Metal–halogen distances in (1)[2.505(2) and 2.476(2)A] and (3)[2.212(6]A are significantly longer than in the parent zirconocene(IV) halides [Zr(η-C5H5)2X2](cf. 2.44 A for X = Cl and 1.98 A for X = F) as are [by ca. 0.04 A(average)] the metal–centroid distances in (3)–(5).

Three- and four-co-ordinate, hydrocarbon-soluble-aryloxides of scandium, yttrium, and the lanthanoids; X-ray crystal structure of tris(2,6-di-t-butyl-4-methylphenoxo)scandium

Five new classes of crystalline, hydrocarbon-soluble group 3A metal (M) aryloxides are reported: [M(OAr)3], (1), [M(L)(OAr)3][L = tetrahydrofuran (thf) or P(O)Ph3], [M(OAr)2(µ-OAr)2Na(thf)2], Li[Yb(Cl)(OAr)3], and [{Y(Cl)(OAr)(µ-OAr)}2](Ar = C6H2Me-4-But2-2,6), ranging for (1) from M3+ being the 3d°, 4d°, to the 4fn(n= 0, 1, 2, 3, 9,10, 11, or 13) ion; the title compound (1)(M = Sc) has an approximately trigonal planar ScO3 skeleton (Sc 0.13 A out of the O3 plane) with av. Sc–O 1.869(15)A, av. O–Sc–O 119.5(2)°, and av. Sc–O–C 168.4(5)°

Synthesis and characterisation of stable anionic group 3a dichlorometallocene(III) complexes and the X-ray structure of [AsPh4][Nd{η-C5H3(SiMe3)2}2Cl2]

A new class of group 3a organometallic compounds, containing the dichlorometallocene(III) anion [Ln(cp″)2Cl2]– is reported, obtained most conveniently by Cl– addition to [{Ln(cp″)2Cl}2][cp″=η-C5H3(SiMe3)2]; the X-ray structure of [AsPh4][Nd(cp″)2Cl2] shows Nd–Clav. 2.668(4)A and Cl–Nd–Cl 99.3(1)°.

Hydrocarbon-soluble, crystalline, four-co-ordinate chloro(aryl oxide)s, dialkylamido(aryl oxide)s and di[bis(trimethylsilyl)cyclopentadienyl]s of ThIV and UIV; X-ray crystal structure of diethylamidotris(2,6-di-t-butylphenoxo)uranium(IV)

Two types of reactions [l/X– or Et2/ŌArR exchange; X =η-C5H3(SiMe3)2(cp″), OC6H2But2-2,6-R-4 (OArR), CH2SiMe3, or CH2Ph] gave [Mcp″2Cl2], [Ucp″2R′2](R′= NMe2, CH2SiMe3′ or CH2ph), [Ucp″2(Cl)NMe2], [MCl(OArt-Bu)3], [{MCl2(OArMe)2}n]; (M = Th or U), [U(NEt2)(OArH)3](7), and [U(NEt2)2(OArH)2]; the title compound (7) has tetrahedrally co-ordinated U and trigonal N with U–N 2.162(5) and av. U–O 2.143 (4)A and av. O–U–O 114, av. O–U–N 104, and av. U–O–C 154°.