Synthesis, structural characterization, and reactivity of Cp*Ru(N-phosphinoamidinate) complexes

Abstract

We report herein on the synthesis and spectroscopic/crystallographic characterization of the first isolable, formally 16-electron Cp*Ru( 2 -PϳN) species, which are supported by N-phosphinoamidinate ligands. Despite the stability of such complexes, they have been shown to readily coordinate two-electron (L) donors including carbon monoxide and 2,6-xylylisocyanide, affording crystallographically characterized 18-electron Cp*Ru(L)( 2 -PϳN) adducts. Preliminary reactivity studies confirm that such complexes are capable of extruding hydrogen from ammonia borane.Résumé : Nous décrivons la synthèse et la caractérisation spectroscopique/cristallographique des premières espèces isolables Cp*Ru( 2 -PϳN) formellement à 16 électrons, qui sont supportées par des ligands N-phosphinoamidinate. Malgré leur stabilité, on a montré que ces complexes forment facilement une liaison de coordination avec des donneurs de doublet d'électrons (L), y compris le monoxyde de carbone et le 2,6-xylylisocyanure, pour donner des adduits Cp*Ru(L)( 2 -PϳN) à 18 électrons caractérisés par cristallographie. Les études de réactivité préliminaires confirment que ces complexes sont capables d'extraire l'hydrogène de l'ammonia borane. [Traduit par la Rédaction]

Dynamic π-Bonding of Imidazolyl Substituent in a Formally 16-Electron Cp*Ru(κ2-P,N)+ Catalyst Allows Dramatic Rate Increases in (E)-Selective Monoisomerization of Alkenes

“…For complex 6 , the HOMO–8 is a similar π-type bonding orbital, albeit with the electron density shifted from the C4 carbon toward the phosphorus atom, which contributes 19% toward the bonding orbital as opposed to only 3% for 5 . The π-donation shown from the imidazole provides the metal with the missing two electrons from the formal 16-electron assignment to generate an electronically saturated complex in a similar fashion to the Cp*Ru­(PR 3 )­X (where X = Cl, Br, I, OR, NR) ,,, but differs in that the donation originates from a π-system on the imidazole rather than a lone pair on an anionic X atom. While π-donation is not needed to generate a 16-electron cationic Cp*Ru species, as seen with Cp*Ru­(P–P) + and Cp*Ru­(N–N) + complexes, the competent π-donating ability of imidazole , likely leads to a higher level of stability for complexes 5 and 6 .…”

“…These transformations could be facilitated by the removal of the stabilizing π-donation afforded by the chloride ligand. The closest comparison structurally to 5 is a pair of complexes from Stradiotto, Cp*Ru­( t Bu 2 P–N-amidinate) complexes that contain chelating anionic phosphine-amido ligands (Chart ). To the best of our knowledge, 5 is the first reported example of a fully characterized, cationic Cp*Ru­(P–N) 16-electron complex, and 6 is the first reported 16-electron Cp ⧧ Ru phosphine complex of any kind.…”

(N‐Phosphinoamidinate)cobalt‐Catalyzed Hydroboration: Alkene Isomerization Affords Terminal Selectivity

“…[17] We have also successfully employed this ligand class in the preparation of 16-electron Cp*Ru(Nphosphinoamidinate) complexes. [18] Encouraged by the utility of N-phosphinoamidines/amidinates in these diverse applications, we turned our attention to the identification of first-row transition metal derivatives that could be used to address challenges in alkene hydroboration chemistry. In particular we sought to identify catalysts of this type that are useful in promoting alkene isomerization/hydroboration processes that transform linear internal aliphatic alkenes and related substrates selectively into 1-alkylboronate products-a challenging yet useful reaction class that at the time had only proved feasible with either rhodium or iridium catalysts.…”

“…Notably, whereas such hydrosilylations proceed under mild conditions (0.01–1.0 mol % 1‐Fe ; room temperature), and with broadest substrate scope known for such iron‐catalyzed transformations, the analogous cobalt complex 1‐Co performed poorly in this chemistry 17. We have also successfully employed this ligand class in the preparation of 16‐electron Cp*Ru( N ‐phosphinoamidinate) complexes 18…”

Reactivity of the Dimer [{RuCl(μ-Cl)(η3:η3-C10H16)}2] (C10H16= 2,7-Dimethylocta-2,6-diene-1,8-diyl) toward Guanidines: Access to Ruthenium(IV) and Ruthenium(II) Guanidinate Complexes

“…The rest of the ruthenium guanidinate compounds currently known are paddlewheel-type dinuclear species containing Ru 2 n + ( n = 5, 6) cores, in which the nitrogenated monoanions adopt a bridging coordination ( C in Figure ) . It is worth noting that the catalytic potential of complexes E – I was not explored, a fact that contrasts with the chemistry of related mononuclear ruthenium amidinate systems, which have found several applications in homogeneous catalysis …”