Effect of the Trimethylsilyl Substituent on the Reactivity of Permethyltitanocene

Abstract

The presence of a trimethylsilyl substituent in place of one of the methyl groups of each of the cyclopentadienyl ligands of decamethyltitanocene enhances the thermal stability of the resulting complex, [Ti II {η 5 -C 5 Me 4 (SiMe 3 )} 2 ] (1), and controls the products formed in thermolysis of its methyl derivatives. Titanocene 1 was found to be stable in toluene solution up to 90 °C, while under vacuum at 140 °C it liberated hydrogen to give the asymmetrical doubly tucked-in titanocene [Ti II {η 3 :η 4 -C 5 Me 2 (SiMe 3 )(CH 2 ) 2 }-{η 5 -C 5 Me 4 (SiMe 3 )}] (3). The mono-and dimethyl derivatives of 1, the complexes [Ti III Me{η 5 -C 5 Me 4 -(SiMe 3 )} 2 ] (5) and [Ti IV Me 2 {η 5 -C 5 Me 4 (SiMe 3 )} 2 ] (6), undergo thermolysis at lower temperature than do the corresponding permethyltitanocene derivatives and eliminate hydrogen from their trimethylsilyl group. Thus, the known [Ti III {η 5 :η 1 -C 5 Me 4 (SiMe 2 CH 2 )}{η 5 -C 5 Me 4 (SiMe 3 )}] (4) was obtained from 5, and compound 6 afforded [Ti II {η 6 :η 1 -C 5 Me 3 (CH 2 )(SiMe 2 CH 2 )}{η 5 -C 5 Me 4 (SiMe 3 )}] (7) at only 90 °C, both with liberation of methane. Crystal structures of 3, 5, and 7 were determined. DFT calculations for titanocene 1 revealed that the metal-cyclopentadienyl bonding is accomplished via a three-centerfour-electron orbital interaction. An auxiliary long-range Si-C bond interaction with the Ti center was also established, providing a reason for the enhanced thermal stability of 1. The molecular orbitals participating in the exo methylene-titanium bonds for 3 and 7 are also three-centered and are compatible with the assignment of their activated ligands to η 3 :η 4 -allyldiene and η 6 -fulvene structures, respectively. Qualitatively, the much higher thermal stability of 3 and 7 compared to that of 1 is due to the exploitation of four d orbitals in the bonding molecular orbitals for 3 and 7 versus only two d orbitals for 1.

Ferrocenyl‐Substituted Metallacycles of Titanocenes: Oligocyclopentadienyl Complexes with Promising Properties

“…[19] All four TiÀC distances are typical for single bonds (cf. 2.213 (2) [20] ). The important bond lengths and angles are not significantly different than in [Cp 2 Ti(h 4 -tBuC 4 tBu)].…”

[Cp2TiIII(NCy)2CTiIIICp2]: A Transient Titanocene Carbene Complex?

“…As depicted in Figure 1, the main structural motif of 1 is the planar four-membered N1-N2-C1-Ti2 ring, which is attached to Ti1 by the carbon atom with a Ti1 À C1 distance of 2.199(4) . [6] Also Ti1 is part of the plane (]Ti1-C1-N1-Ti2 = 179.0(6)8) and almost linearly linked to Ti2 through C1 (]Ti1-C1-Ti2 = 175.8 (5) [8] ). The N1-N2-C1-Ti2 ring is slightly distorted, with two short C À N bonds (N1ÀC1 1.325(4), N2ÀC1 1.340(4) ); AEr cov (C-N) = 1.47 and AEr cov (C=N) = 1.27 ; r cov = covalent radius) [9] indicating partial C=N double-bond character, and two slightly elongated Ti À N single bonds (Ti2 À N1 2.154(3), Ti2 À N2 2.144(3) ; cf.…”

“…Interestingly, bridging ligands of the type m-k 2 -k 2 -C 2 (NR) 4 can act as diamide (G, Scheme 4) or diamidinate (H) ligands leading either to five-or four-membered metallacycles. [17] Thermal ellipsoids set at 30 % probability at 173 K. Selected bond lengths [] and angles [8]: Ti1-N1 2.177(2), Ti1-N2 2.189(2), Ti2-N3 2.163(2), Ti2-N4 2.199(2), N1-C1 1.323(3), N2-C1 1.323(3), N3-C24 1.328(3), N4-C24 1.328(3), C1-C24 1.527(3); C1-N1-Ti1 93.0(2), C1-N2-Ti1 92.4(2), N2-C1-N1 113.6(2), N2-C1-C24 124.1(2), N1-C1-C24 122.3(2), N2-C1-Ti1 57.1(1), N1-C1-Ti1 56.6(1), N1-Ti1-N2 60.95(7), N3-Ti2-N4 61.33(7). …”

[Cp2TiIII(NCy)2C‐TiIIICp2]: ein transienter Titanocen‐Carbenkomplex?

“…Unserem Interesse an sterisch gespannten Metallacyclen der 4. Gruppe folgend, [1][2][3] [8] ]. Der N1-N2-C1-Ti2-Ring ist leicht verzerrt und enthält zwei kurze C-N-Bindun- (4) ); AEr cov (C-N) = 1.47 und AEr cov (C= N) = 1.27 ; r cov = Kovalenzradius], [9] die auf einen partiellen C = N-Doppelbindungscharakter schließen lassen, und zwei leicht geweitete Ti-N-Einfachbindungen [d(Ti2-N1) = 2.154(3), d(Ti2-N2) = 2.144(3) ; vgl.…”