Novel double substrate insertion versus isocyanate extrusion in reactions of imidotitanium complexes with CO2: critical dependence on imido N-substituents †

Reaction of the cyclopentadienyl–amidinate supported imidotitanium complexes [Ti(η-C5Me5){MeC(NiPr)2}(NR)] (R = tBu 1a or Ar 1b where Ar = 2,6-C6H3Me2) with CO2 proceed via initial cycloaddition reactions, but depending on the imido N-substituent go on to yield products of either isocyanate extrusion or double CO2 insertion, the latter forming [Ti(η-C5Me5){MeC(NiPr)2}{O(CO)N(Ar)(CO)O}] 4; the double CO2 insertion reaction leading to 4 is the first example for any transition metal imide.