Unprecedented η3-Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)

We present the unprecedented η3-coordination of the 2-phosphaethynthiolate anion in the complex (PN)₂La(SCP) (2) [PN = N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate bridged (PN)₂La(μ-1,3-SCN)₂La(PN)₂ (3) and azide bridged (PN)₂La(μ-1,3-N3)₂La(PN)₂ (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)₂La{SPC(^RCAAC)} (5a,b) (R = Ad, Me). A detailed reaction mechanism for the SCP to SPC isomerization is proposed based on DFT calculations.