Synthesis and Reactivity of titanium ‘POCOP’ pincer complexes

The ‘POCOP’ pincer ligand, [2,6-(R2PO)2C6H3], has been attached to titanium in both Ti(III) and Ti(IV) complexes for the first time. Using a lithium-halogen exchange route [2.6-(R2O)2C6H3]Li ([RPOCOP]Li) can be synthesised. Both the iso-propyl and tert-butyl derivatives can be made, but only the latter isolated. These can be reacted with the Ti(III) and Ti(IV) synthons to make [tBuPOCOP]TiCl2 (1), [tBuPOCOP]TiCl3 (2) and {[iPrPOCOP]TiCl2(µ-Cl)}2 (4). In the presence of Ti(IV), THF and [RPOCOP]Li an unprecedented ligand rearrangement occurs. 1 can be derivatised with alkylating agents to make bis-methyl, phenyl and neopentyl complexes. The last of these can activate H2 to make a rare example of a titanium hydride chloride, with the metal pincer fragment staying attached. This opens the door for this archetypical pincer ligand to be used with early transition metals.