Sunlight-induced dehydrogenation rearrangement of the dititanium complex [Ti(η5-C5HMe4)(μ-η1 : η5-C5Me4)]2
Abstract
Sunlight photolysis of the triplet state (S = 1) dititanium compound 1 induced its rearrangement to diamagnetic 2 , which was a molecule containing two hydrogens less. The cage structure of 2 was determined by single crystal X-ray diffraction and was corroborated fully by (1)H and (13)C NMR spectra that identified three simple bridging moieties - a hydrogen atom, a methine carbon and a methylene carbon.
Its extremely short Ti-Ti distance 2.7537(7) Å causes a strong distortion of the bridging fulvalene ligand, which becomes η(5)- bonded to one Ti(IV) and connected by two sigma-bonds from nearest carbon atoms of its other ring to the other Ti(IV) of 2. Other photolytical byproducts in very minor amounts were also isolated, which differed from 2 by the absence of one bridging moiety: compound 4 lacked the methine group and compound 5 had no bridging hydrogen.
In the latter cases, the Ti -Ti distance fell in the range 3.2077(8) - 3.5543(12) Å and the fulvalene ligand was coordinated in the common μ-η(5) : η(5)-mode to both titanium atoms. The octamethylfulvalene ligands in 4 and 5 had their ring planes rotated mutually by about 40 degrees in order to relieve the steric hindrance between their methyl groups.
The thermally robust μ-oxo complex 3 obtained from reacting 2 with water showed a very similar structure.