Synthesis, structures and reactivity of 2-phosphorylmethyl-1H-pyrrolato complexes of titanium, yttrium and zinc

Abstract

The reaction of secondary phosphines HPR₂ (R = Ph, Cy) with pyrrole-2-aldehydes gives a new family of 2-phosphorylmethyl-1H-pyrroles as potentially chelating mono-anionic ligands. The reaction with Ti(NMe₂)₄ affords octahedral Ti(NMe₂)₂{NC₄H₂(4-R′)CH₂P(O)R₂}₂ (R′ = H, Bu^t). While the diphenylphosphoryl complexes adopt a configuration with trans-pyrrolato ligands, the dicyclohexyl analogue prefers an all-cis conformation, with profound consequences on metal–ligand bonding. The reaction of sterically undemanding HNC₄H₃CH₂P(O)Ph₂ with Y[N(SiHMe₂)₂]₃(THF)₂ give the homoleptic complex Y[NC₄H₃CH₂P(O)Ph₂]₃; mixed-ligand intermediates Y[N(SiHMe₂)₂]₂(N–O) and Y[N(SiHMe₂)₂](N–O)₂ were identifiable but could not be isolated. The bulky ligand HNC₄H₂(5-Bu^t)CH₂P(O)Ph₂ does not react with Ti(NMe₂)₄ but protolyses Zn[N(SiMe₃)₂]₂ to give a 1 : 2 complex Zn(N–O)₂ as the only isolable product. On the other hand, its reaction with Y[N(SiHMe₂)₂]₃(THF)₂ affords the mono-amido complex Y{N(SiHMe₂)₂}{NC₄H₃(5-Bu^t)CH₂P(O)Ph₂}₂ which shows good activity for the ring-opening polymerisation of cyclic esters.