η -Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)*.

We present the η -coordination of the 2-phosphaethynthiolate anion in the complex (PN) La(SCP) (2) [PN=N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate-bridged (PN) La(μ-1,3-SCN) La(PN) (3) and azide-bridged (PN) La(μ-1,3-N ) La(PN) (4) complexes indicates that the [SCP] coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π*-orbital of the [SCP] ligand to the LUMO of complex 2, rendering it the ideal precursor for the first functionalization of the [SCP] anion. Complex 2 was therefore reacted with CAACs which induced a selective rearrangement of the [SCP] ligand to form the first CAAC stabilized group 15-group 16 fulminate-type complexes (PN) La{SPC( CAAC)} (5 a,b, R=Ad, Me). A detailed reaction mechanism for the SCP-to-SPC isomerization is proposed based on DFT calculations.