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

The reaction of secondary phosphines HPR(2) (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(NMe(2))(4) affords octahedral Ti(NMe(2))(2){NC(4)H(2)(4-R')CH(2)P(O)R(2)}(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 HNC(4)H(3)CH(2)P(O)Ph(2) with Y[N(SiHMe(2))(2)](3)(THF)(2) give the homoleptic complex Y[NC(4)H(3)CH(2)P(O)Ph(2)](3); mixed-ligand intermediates Y[N(SiHMe(2))(2)](2)(N-O) and Y[N(SiHMe(2))(2)](N-O)(2) were identifiable but could not be isolated. The bulky ligand HNC(4)H(2)(5-Bu(t))CH(2)P(O)Ph(2) does not react with Ti(NMe(2))(4) but protolyses Zn[N(SiMe(3))(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(SiHMe(2))(2)](3)(THF)(2) affords the mono-amido complex Y{N(SiHMe(2))(2)}{NC(4)H(3)(5-Bu(t))CH(2)P(O)Ph(2)}(2) which shows good activity for the ring-opening polymerisation of cyclic esters.