Noninnocent DPPBT (2-diphenylphosphino-benzenethiolate) ligand containing both phosphorus and sulfur as the donor atoms was reported to delocalize the electron density in a similar manner to dithiolenes. The electronic nature of the DPPBT-based Re tris(thiolate) complexes was probed using density-functional theory (DFT) and high-level ab initio methods including complete active space self-consistent field (CASSCF), complete active space perturbation theory (CASPT2), Møller-Plesset perturbation theory (MPn, n=2-4), coupled cluster (CCSD and CCSD(T)), quadratic configuration interaction (QCISD and QCISD(T)). Our findings are consistent with the experiment that [Ru(dppbt)3]+, [Re(dppbt)3]+, and [Re(dppbt)3]2+ can add ethylene to form the new C-S bonds, but [Re(dppbt)3]0 cannot. According to the results, the thiyl radicals on the S2 position serve as the intrinsic electron acceptors in the actual alkene addition reactions. The differential reactivity stems from the fact that the neutral species [Re(dppbt)3]0 has a closed shell singlet ground state, which is not a metal-stabilized thiyl radical. By contrast, [Ru(dppbt)3]+, [Re(dppbt)3]+, and [Re(dppbt)3]2+ are in line with the assignment of metal-stabilized thiyl radicals. The cationic species [Ru(dppbt)3]+ that has the same valence count as the neutral species [Re(dppbt)3]0, contains a Ru(III) (S = 1/2) center antiferromagnetically coupled to a thiyl radical S2-pz (S = 1/2). The cationic species [Re(dppbt)3]+ features antiferromagnetic coupling between the Re(III) (S = 1) center and a thiyl radical S2-pz (S = 1/2). The dicationic species [Re(dppbt)3]2+ has a Re(III) center (S = 1) antiferromagnetically coupled to an overall triplet DPPBT ligand (S2-pz (S = 1/2) and S1-py (S = 1/2)). A comparison of the electronic structures between Ru and Re complexes reveals that the Re compounds favor the d4 center, while the Ru compounds disfavor the d4 center. Moreover, DFT results show that a ligand-centered mechanism is preferred for the ethylene addition reactions to these Ru and Re tris(thiolate) complexes.

Understanding the distinctive electronic structure of Re and Ru tris(thiolate) complexes and its role in chemistry

251st National Meeting (2016)

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