Cationic Bis(Gold) Indenyl Complexes.

Reaction of (P)AuOTf [P=P(t-Bu) ₂ o-biphenyl] with indenyl- or 3-methylindenyl lithium led to isolation of gold η ¹ -indenyl complexes (P)Au(η ¹ -inden-1-yl) (1 a) and (P)Au(η ¹ -3-methylinden-1-yl) (1 b), respectively, in >65 % yield. Whereas complex 1 b is static, complex 1 a undergoes facile, degenerate 1,3-migration of gold about the indenyl ligand (ΔG ^≠ _153K =9.1±1.1 kcal/mol). Treatment of complexes 1 a and 1 b with (P)AuNTf ₂ led to formation of the corresponding cationic bis(gold) indenyl complexes trans-[(P)Au] ₂ (η ¹ ,η ¹ -inden-1,3-yl) (2 a) and trans-[(P)Au] ₂ (η ¹ ,η ² -3-methylinden-1-yl) (2 b), respectively, which were characterized spectroscopically and modeled computationally. Despite the absence of aurophilic stabilization in complexes 2 a and 2 b, the binding affinity of mono(gold) complex 1 a toward exogenous (P)Au ⁺ exceed that of free indene by ~350-fold and similarly the binding affinity of 1 b toward exogenous (P)Au ⁺ exceed that of 3-methylindene by ~50-fold. The energy barrier for protodeauration of bis(gold) indenyl complex 2 a with HOAc was ≥8 kcal/mol higher than for protodeauration of mono(gold) complex 1 a.
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