Acta Chim. Slov. 2003, 50, 199-206. 199 CRYSTAL STRUCTURES OF (^5-C5Me5)TiCl3 AND (^5-C5Me4H)TiCl3 Andrej Pevec Faculty ofChemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, P.O.Box 537, SI-1000 Ljubljana, Slovenia Received 26-09-2002 Abstract Two organotitanium(lV) chloride complexes (^5-C5Me5)TiCl3 (1) and (^5-C5Me4H)TiCl3 (2) have been structurally characterized. These compounds are a key entry for pentamethyl- and tetramethylcyclopentadienyl titanium chemistry. Both complexes adopt the familiar piano-stool geometry. Introduction Cyclopentadienyl ligands have plaved a major role in the development of organometallic chemistrv since the discovery of ferrocene. The studies of compounds with alkylated cyclopentadienyl ligands have been an important area of research for a long period of tirne.1 The alkylated cyclopentadienyl ligands offer several advantages over the unsubstituted ones including increased solubility and crystallizability. Such ligands also significantly effect chemical reactivity of metal complexes. A numerous half-sandwich compounds with the general formula (^5-C5Me5)ML3 (M represents a transition metal and L a monodentate halogen or chalcogen ligand) have been synthesized and characterized. Among those (^5-C5Me5)Re03 deserves special mention because of the versatile chemistry which has been appeared after its discovery.4 The extensive development of the chemistry of half-sandwich rhenium complexes in higher oxidation states exists after that." Moreover, the half-sandwich organotitanium chlorides are among the most common starting materials for the syntheses of titanium organometallic complexes.6 The geometry around the metal atom in those half-sandwich complexes can be described as a three-legged piano-stool configuration. Electron releasing ability of the substituents on the aromatic ring can effects catalytic reactivity of those compounds. The substituted trichloro(cyclopentadienyl)titanium complexes are more efficient catalysts for polymerization reactions than the unsubstituted ones.7 For example, the {rf- A. Pevec: Crystal Structures of (tf-CjMe^TiCli and (rf-CsMe4H)TiCl3 200 Acta Chim. Slov. 2003, 50, 199-206. C5Me5)TiCl3/methylaluminoxane catalytic system has been found to be highly active and syndiospeciflc in the polymerization of styrene. Herein the crystal structures of 0/5-C5Me5)TiCl3 (1) and (//5-C5Me4H)TiCl3 (2), are reported. Although (^5-C5H5)TiCl3,9 (^5-C5H4Me)TiCl310 and (75-C5Me4Et)TiCl3n have been structurally characterized and the synthesis of 1 has been reported already in 1962 to the best of our knowledge the structures of those two compounds have not been determined yet. Results and discussion The asymmetric unit of the complex 1 is depicted in Figure 1 and the complex of 2 in Figure 2. Selected bond lengths and angles for 1 and 2 are given in Table 1 and Table 2, respectively. The Ti-Cl bond distances in 1 range from 2.2423(5) to 2.2491(4) A and those for 2 are from 2.2310(16) to 2.2378(10) A. The distance betvveen titanium and the centre of the ring is 2.021 A and 2.010 A, for 1 and 2 respectively. The Ti-C distances range from 2.3418(15) to 2.3616(15) A for 1 and from 2.299(4) to 2.377(3) A for 2. The C atoms in the cyclopentadienyl ring lie in almost regular plane in both complexes with the similar distances C-C (from 1.419(2) to 1.426(2) A for 1 and from 1.401(4) to 1.423(4) A for 2). The largest deviation from this plane of five C atoms of the cyclopentadienyl ring is 0.0077(9) A for 1 and 0.001(3) A for 2. The average Ti-Cl bond distance in 1 (2.2456 A) is slightly longer than those in 2 (2.2344 A). Both distances are shorter than in the unsubstituted compound {rf-C5H5)TiCl3 (2.303 A). The average Ti-C bond distance in 1 (2.356 A) and 2 (2.338 A) is longer than in (//5-C5H5)TiCl3 (2.29 A). The molecule of 2 is more symmetrical than that of 1, since Cl(2), Ti, C(3) and H(l) atoms in 2 lie on a mirror plane. The methyl carbon atoms in the title compounds 1 and 2 are slightly moved out of the ring plane, away from the titanium and its chloride ligands. A view perpendicular to the ring (Figure lb and 2b) provides a plausible rationalization for the different displacements of methyl carbons. The two largest displacements in complex 1 (Figure lb) are for C(7) (0.134(3) A) and C(9) (0.111(3) A) with the shortest methyl carbon - chlorine distances (Table 3). The two medium displacements are for C(6) (0.075(3) A) and C(10) (0.058(3) A), with the A. Pevec: Crystal Structures of (tf-CjMe^TiCli and (rf-CsMe4H)TiCl3 Acta Chim. Slov. 2003, 50, 199-206. 201 (a) (b) Figure 1. Ortep view of the asymmetric unit of 1 with labeling of nonhydrogen atoms (a) and a view along the Ti - (centre of the ring) direction (b). Ellipsoids are at 30% probability level. A. Pevec: Crystal Structures of (tf-CjMe^TiCli and (rf-CsMe4H)TiCl3 202 Acta Chim. Slov. 2003, 50, 199-206. Figure 2. Ortep view of the complex of 2 (a) and a view along the Ti - (centre of the ring) direction (b). Ellipsoids are at 30% probability level. A. Pevec: Crystal Structures of (tf-CjMe^TiCli and (rf-CsMe4H)TiCl3 Acta Chim. Slov. 2003, 50, 199-206. 203 larger methyl carbon - chlorine distances (Table 3). The smallest displacement is for C(8) (0.040(3) A), which is the most remote and thus the less stericaly hindered by chlorine atoms (Table 3). The similar organization of the methyl carbon atoms is in the molecule of 2 (Figure 2b). The two large displacements (0.082(7) A) are for the two symmetrically related methyl carbon atoms C(4) and C(4a) with the shortest distance (3.3111(41)) to the nearest chlorine atoms Cll and Clla. The smaller displacements are for C(5) and C(5a) (0.035(5) A) with the larger distance to the chlorine atoms Cl(l) and Cl(la) (3.5961(42)). Table 1. Selected bond lengths (A) and angles (°) for 1. Ti-Cl(l) 2.2491(4) Ti-C(2) Ti-Cl(2) 2.2423(5) Ti-C(3) Ti-Cl(3) 2.2455(5) Ti-C(4) Ti-C(l) 2.3596(15) Ti-C(5) 2.3529(15) 2.3418(15) 2.3616(15) 2.3578(15) Cl(l)-Ti-C(l) Cl(l)-Ti-C(2) Cl(l)-Ti-C(3) Cl(l)-Ti-C(4) 88.67(4) 119.84(4) 145.56(4) 120.12(4) Cl(l)-Ti-C(5) Cl(2)-Ti-Cl(l) Cl(2)-Ti-Cl(3) Cl(3)-Ti-Cl(l) 88.90(4) 102.695(18) 103.68(2) 103.44(2) Table 2. Selected bond lengths (A) and angles (°) for 2. Ti-Cl(l) 2.2378(10) Ti-C(2) 2.338(3) Ti-Cl(2) 2.2310(16) Ti-C(3) 2.299(4) Ti-C(l) 2.377(3) Cl(l)-Ti-C(l) 86.19(8) Cl(2)-Ti- C(2) 104.76(9) Cl(l)-Ti-C(2) 92.58(9) Cl(2)-Ti-C(3) 86.75(14) Cl(l)-Ti-C(3) 126.39(4) Cl(2)-Ti-Cl(l) 102.63(4) Cl(2)-Ti- C(l) 139.80(9) Cl(l)-Ti-Cl(la) 103.13(6) Table 3. Selected distances (A) between methyl C and Cl atoms in 1. C(6)-C1(1) 3.4306(18) C(8)-C1(3) 3.8669(19) C(7)-C1(3) 3.2380(19) C(9)-C1(2) 3.1818(19) C(8)-C1(2) 3.9007(19) C(10)-C1(1) 3.4297(19) A. Pevec: Crystal Structures of (tf-CjMe^TiCli and (rf-CsMe4H)TiCl3 204 Acta Chim. Slov. 2003, 50, 199-206. Table 4. Details on the crystal structure determination of 1 and 2. 1 Empirical formula Mr Crystal shape, colour Crystal dimensions / mm Radiation Mo Ka / A Crystal system Space group al k bik clk 01° Vik3 Z TIK No. of refl. for celi parameters Dx I g cm"3 ///mm"1 6>Range(°) Data measured, unique Rim R, wR2 [F^laiF2)] R, wR2 (ali data) Goodnes of fit, S Refined parameters (^/