Organometallic Chemistry of a Titanium(IV) meso-Octaethylporphyrinogen Complex: Carrier Properties of Polar Organometallics and Their Behaviour in Insertion Reactions

The reaction of lithium organometallics with the (meso-octaethylporphyrinogenato)titanium complex [(eta(1):eta(1):eta(1):eta(1):-Et(8)N(4))Ti(THF)(2)] (2), which acts as a bifunctional carrier, led to the formation of dimetallic Li-Ti organometallics, where the original LiR unit is present in the ion-separated form. These compounds contain the alkyl or aryl groups bonded to titanium, while the lithium cation remains bonded to the porphyrinogen periphery, [{(eta(1):eta(1):eta(1):eta(1)-Et(8)N(4))Ti-R}{Li(THF)(2)}] (R=Me, 3; R=Ph, 4). The dissolution of 3 in Et(2)O led to the separation of Lif from the porphyrinogen and the formation of [(eta(1):eta(1):eta(1):eta(1)-Et(8)N(4))Ti-Me](-)[Li(Et(2)O)(3)](+) (5). The migratory aptitude of the methyl group has been observed in the reaction of 5 with Bu(t)NC, which leads to the corresponding eta(2)-iminoacyl [{(eta(1):eta(1):eta(1):eta(1)-Et(8)N(4))Ti(eta(2)-C(CH)(3)=NBu(t))}{Li(THF)(2)}] (6). The reaction of 5 with carbon monoxide proceeds via a very reactive eta(2)-acetyl intermediate. The carbenium ion nature of the eta(2)-acyl group favors the attack on one of the pyrrolyl anions, which is homologated to a 4-methylpyridine unit. This reaction requires the complete cleavage of the Cd=O bond, leading to a titanyl complex, which has been recrystallized from pyridine as [{(eta(1):eta(1):eta(1):eta(1)-Et(8)(C4H2N)(3)(4-MeC(5)H(2)N)} T=O ... Li(py)(3)] (8).