The neutron diffraction structure of [C5H4(CH2)3C5H4]TiCl2

Abstract The crystal structure of 1,1′-trimethylene-di-π-cyclopentadienyl titanium dichloride, [C 5 H 4 (CH 2 ) 3 C 5 H 4 ]TiCl 2 , was determined from three-dimensional neutron diffractometry data in order to obtain accurate information for those structural parameters involving hydrogen atoms. Also, we were interested in the effect on the CC bond lengths of shifting electron density from the C atoms and accumulating it in the regions of the π-bonds of the Cp rings. The substance crystallizes as deep red-brown parallelepipeds in the monoclinic space group P2 1 /n with a = 8.490(2), b = 14.209(4), c = 10.185(2) A, and β = 90.43(2)°. The cell volume is 1228.6 A 3 while the measured and calculated densities are 1.566(8) and 1.572 gm-cm −3 , respectively. The molecule consists of a planar TiCl 2 fragment sandwiched equidistantly between two eclipsed rings which are canted such that their normals make an angle of 133.1° and linked by a (CH 2 CH 2 CH 2 ) chain. The entire propyl chain is to one side of the vector bisecting the ClTiCl angle and the ring carbons connected to the terminal CH 2  groups of the propyl chain do not occupy the position of nearest approach between the two rings. The normal to the plane of each of the rings does not coincide with the Ti-(ring centroid) vector, the angle between the two being 0.80° for ring 1 and 0.70° for ring 2. The two TiCl distances are 2.368(8) and 2.365(9) A and the Cl(1)TiCl(2) angle is 93.2(3)°. The average CC distance for rings 1 and 2 are 1.416(7) and 1.402(7) A, respectively. The average Cp CH distance is 1.05(2) and 1.12(2) A for rings 1 and 2. The average CCC and CCH angles are 108.0(5) and 126.0(8)° for ring 1 and 107.9(5)° and 125.6(9)° for ring. 2. The average C(cp)C(H 2 ) distance is 1.494(7) A while the average C(H 2 )C(H 2 ) distance is 1.509(8) A. The average aliphatic CH distance is 1.06(2) A. Finally, the average values of the CCC, CCH, and HCH angles at the aliphatic chain are 115.1(5), 109.9(8), and 105.7(9)°, respectively. The normals to rings 1 and 2 make angles of 23.9 and 22.9° with the normal to the TiCl 2 plane. The Cl atoms 1 and 2 lie 1.703 and 1.736 A, respectively, above and below the plane defined by (ring 1 centroid)-Ti-(ring 2 centroid). The angles between the vectors (ring 1 centroid)-Ti and (ring 2 centroid)-Ti with the normal to the plane defined by the TiCl 2 , fragment are 23.4 and 23.5°, respectively. The perpendicular distances between the ring centroids and the TiCl 2 plane are 1.89 and 1.89 A, respectively, for the rings 1 and 2. Finally, the angles between the TiCl(1) and TiCl(2) vectors with the normal to the (ring 1 centroid)-Ti-(ring 2 centroid) plane are 135.9 and 137.1°. The maximum deviation of any carbon from planarity in rings 1 and 2 is 0.01 and 0.05 A, respectively. The maximum deviation from planarity of any hydrogen from the plane defined by the hydrogens of rings 1 and 2 is 0.03 and 0.02 A. The planes defined by the hydrogens do not coincide with the planes defined by the five carbons of the same Cp ring. There is a slight, very possibly insignificant, but consistent displacement of the ring hydrogens towards the Ti atom in both rings. A measure of this effect can be obtained from the following distances: Ti-(Plane of Carbons, Ring 1) = 2.06 A Ti-(Plane of Hydrogens, Ring 1) = 2.04 Ti-(Plane of Carbons, Ring 2) = 2.06 Ti-(Plane of Hydrogens, Ring 2) = 2.04 For each ring, the difference in pairs of these quantities probably do not exceed two standard deviations and, except for the consistency of the results for the two rings, are doubtful significance. All distances and angles involving heavy atoms are in excellent agreement with the results of an X-ray study reported elsewhere. The CC distances in the rings obtained by neutron diffraction are slightly larger than those obtained in the X-ray study, as expected. The final values of the discrepancy indices for the present study are R 1 = 0.053 and R 2 = 0.048, with an error of fit of 1.04.