Benjamin G. Harvey

Charge Density Analysis of the (C−C)→Ti Agostic Interactions in a Titanacyclobutane Complex

The experimental electron density study of Ti(C(5)H(4)Me)(2)[(CH(2))(2)CMe(2)] provides direct evidence for the presence of (C-C)-->Ti agostic interactions. In accord with the model of Scherer and McGrady, the C(alpha)-C(beta) bond densities no longer show cylindrical symmetry in the vicinity of the Ti atom and differ markedly from those of the other C-C bonds. At the points along the C(alpha)-C(beta) bond where the deviation is maximal the electron density is elongated toward the metal center. The distortion is supported by parallel theoretical calculations. A calculation on an Mo complex in which the agostic interaction is absent supports the Scherer and McGrady criterion for agostic interactions. Despite the formal d(0) electron configuration for this Ti(IV) species, a significant nonzero population is observed for the d orbitals, the d orbital population is largest for the d(xy) orbital, the lobes of which point toward the two C(alpha) atoms. Of the three different basis sets for the Ti atom used in theoretical calculations with the B3LYP functional, only the 6-311++G** set for Ti agrees well with the experimental charge density distribution in the Ti-(C(alpha)-C(beta))(2) plane.

Zr(C5H5)(6,6-dmch)(PMe3)2, an edge-bridged half-open zirconocene-synthesis, structure, and its reaction with C6H5C2SiMe3

Abstract The synthesis and characterization of an edge-bridged half-open zirconocene, Zr(C5H5)(dmch)(PMe3)2 (dmch=dimethylcyclohexadienyl), are described. As expected, the ZrC bond distances for the dmch ligand are significantly shorter than those for the C5H5 ligand. The compound readily incorporates 2 equiv. of alkyne, with loss of the PMe3 ligands, leading to a zirconacyclopentadiene complex, so that the dmch ligand has remained intact.

Crystal structure of 1,3,5-tri(tert-butyl)benzene-cyclopentadienyl-iron trifluorodimethylsilicate, [Fe(C5H5){C6H3(C4H9)3}][Si(CH3)2F3]

C25H41F3FeSi, orthorhombic, Pna21 (no. 33), a = 14.4031(4) Å, b = 15.5680(5) Å, c = 11.0762(3) Å, V = 2483.6 Å, Z = 4, Rgt(F) = 0.041, wRref(F) = 0.094, T = 150 K. Source of material The compound was prepared by the reaction of Fe(C5H5)[1,3,5C6H3(t-C4H9)3] [1,2] with SF6 in the presence of silicone grease [3].An oily precipitate formed over a period of three days, which slowly deposited pale yellow, diamond-shaped crystals of the compound. Experimental details The hydrogen atoms could be refined successfully isotropically, except those attached to C13, C24, and C25 atoms, which were placed in idealized positions and allowed to ride on their attached carbon atom. Discussion The structure of the cationic portion of the salt is nearly identical to that found in a previous study [3].The Fe—C (C5H5) distances average 2.060(2) Å, while the Fe—C(arene) distances fall into two types, 2.090(3)Å for theFe—C(H) bonds, and 2.120(2)Å for the Fe—C(t-C4H9) bonds.As in the previous structure, the arene ligand’s C–C(t-C4H9)–C angles are contracted relative to the C–C(H)–C angles, 117.5(2)° vs. 122.5(2)°. For the Si(CH3)2F3 anion, theC–Si–C angle of 123.8(2)°, togetherwith theF2–Si–F3 angle of 174.6(1)° and the F1–Si–F(2,3) angles of 86.8(1)° and 88.0(1)°, respectively, are all in accord with the greater expected polar character of the Si—F bonds. The average Si—C bond length is 1.872(3) Å, while the Si—F1 and average Si—F(2,3) bond lengths are 1.648(2) Å and 1.725(4) Å, respectively. Z. Kristallogr. NCS 222 (2007) 337-338 / DOI 10.1524/ncrs.2007.0142 337

Crystal structure of (hydrido)(η3-butenyl)bis(η5-pentamethylcyclopentadienyl) zirconium, Zr(C4H7)[C5(CH3)5]2(H)

Abstract C24H38Zr, triclinic, P1̅ (no. 2), a = 8.6524(3) Å, b = 9.3669(2) Å, c = 14.2269(5) Å, α = 81.977(2)°, β = 88.117(2)°, γ = 72.557(2)°, V = 1089.2 Å3, Z = 2, Rgt(F) = 0.034, wRref(F2) = 0.079, T = 150 K.

Crystal structure of di(n-butyl)bisO(η5-pentamethylcyclopentadienyl)-zirconium, Zr(C4H9)2(C10H15)2

C28H48Zr, orthorhombic, P2\2\2\ (no. 19), a = 17.1538(3) A, b = 17.2598(3) A, c = 17.3568(2) A, V= 5138.8 À, Z = 8, Rgf(F) = 0.028, wRretfF) = 0.063, T = 150 K. Source of material The compound may be synthesized from the reaction of bis(pentamethylcyclopentadienyl)zirconium dichloride with two equivalents of n-butyl lithium in ether at -78 °C. After slow warming to 0 °C, the solution is stirred one hour, the solvent removed in vacuo, and the compound extracted with pentane. The compound undergoes loss of n-butane more slowly than its cyclopentadienyl analogue [1], but must still be kept cold for prolonged periods. The compound was crystallized by cooling a saturated solution in pentane to -60 °C. Experimental details The title compound crystallizes as racemic twin indicated by a Flack x parameter of 0.55(4). Discussion The structural result reveals the presence of two independent molecules in the unit cell. The bonding parameters for the pentamethylcyclopentadienyl ligands are similar, with the average Zr—C distance being 2.580 A. However, one observes a noticeable difference in the Zr-butyl bonding, with the respective Zr—C(21,21 A) andZr—C(25,25A) distances averaging 2.284(1) A and 2.326(1) A. That this is not due to pseudosymmetry is suggested by the unique, nonplanar orientation displayed by one of the butyl groups, for which a C25 A-C26AC27A-C28A torsion angle of 67.2° is found. The differences in the Zr—C bond distances do not appear to be related to any steric effects, but may derive from the electron deficiency in a 16 electron complex, which could lead to partial a-agostic donations from the C-H bonds of C21 and C21A to their respective zirconium centers. Consistent with this suggestion is the fact that the Zr-H separations for their attached hydrogen atoms are ca. 0.14 A shorter than those for their C25 and C25A counterparts. The Zr—C(butyl) bond distances are similar to those in a diphenyl analogue, for which an average Zr—C(phenyl) distance of 2.311(3) A was observed [2]. Table 1. Data collection and handling.

Crystal structure of chlorobis(η5 -pentamethylcyclopentadienyl)- (η3-2-methyl-2-propenyl)zirconium, Zr(C4H7)(C10H15)2Cl

C24H37ClZr, triclinic, PI (no. 2), a = 8.7650(1) A , b = 9.3278(1) A , c = 15.3642(2) A , a = 77.5549(6)°, P = 80.6252(7)°, y = 70.8162(7)°, V = 1152.7 A 3 , Z = 2, RgfiF) = 0.021, wRnffF) = 0.054, 7 = 150 K.