The Missing Entry in the Agostic–Anagostic Series: Rh(I)–η1-C Interactions in P(CH)P Pincer Complexes

The missing entry, namely, the "C-anagostic" or δ1-C interaction, closing the agostic-anagostic series of metal-CH(aryl) interactions is found in a bis(amidiniophosphine) P(CH)P pincer rhodium complex. The three entries, namely, agostic δ2-(C,H), anagostic (related to hydrogen bonding, thus recoined here as "H-anagostic"), and C-anagostic interactions, are unambiguously characterized by electron localization function (ELF) topological analysis. Other theoretical tools such as noncovalent interaction (NCI) analysis and multicenter electron delocalization indices (MCIs) support the ELF characterization. A δ2-(C,H) agostic interaction is evidenced by a disynaptic V(C,H) or trisynaptic V(M,C,H) ELF basin with a significant quantum topological atoms in molecules (QTAIM) atomic contribution of the metal M and a large covariance (in absolute value) with the metal core basin C(M). The C-anagostic δ1-C interaction is characterized by a disynaptic V(M,C) basin, a weak covariance (in absolute value) of V(C,H) and C(M) populations, and a negligible QTAIM atomic contribution of M to V(C,H). The relevance of these ELF signatures is evidenced in a selected series of related rhodium and osmium complexes The theoretical studies were performed using HPC resources from CALMIP (Grant 2011-2013[0851]) and from GENCI-[CINES/IDRIS] (Grant 2011-2013[085008]). J.P. and M.S. are grateful to the following organizations for financial support: the Ministerio de Ciencia e Innovacion (Projects CTQ2011-23156/BQU and CTQ2011-25086/BQU) and the Generalitat de Catalunya (Projects 2014SGR931, 2009SGR528, and 2009SGR637; AIRE-CTP2012 fellowship for J.P.; 2014 ICREA Academia prize for excellence in research funded by the DIUE for M.S.)